US20080066864A1 - Etch apparatus - Google Patents
Etch apparatus Download PDFInfo
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- US20080066864A1 US20080066864A1 US11/946,370 US94637007A US2008066864A1 US 20080066864 A1 US20080066864 A1 US 20080066864A1 US 94637007 A US94637007 A US 94637007A US 2008066864 A1 US2008066864 A1 US 2008066864A1
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- Prior art keywords
- etchant
- conduit
- tank
- silicon nitride
- etch
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- HQVNEWCFYHHQES-UHFFFAOYSA-N silicon nitride Chemical compound N12[Si]34N5[Si]62N3[Si]51N64 HQVNEWCFYHHQES-UHFFFAOYSA-N 0.000 claims abstract description 65
- 229910052581 Si3N4 Inorganic materials 0.000 claims abstract description 59
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims abstract description 51
- 230000003134 recirculating effect Effects 0.000 claims abstract description 41
- 239000000377 silicon dioxide Substances 0.000 claims abstract description 24
- 235000012239 silicon dioxide Nutrition 0.000 claims abstract description 23
- 238000005530 etching Methods 0.000 claims abstract description 17
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 15
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 15
- 239000011159 matrix material Substances 0.000 claims abstract description 15
- 238000004090 dissolution Methods 0.000 claims abstract description 14
- 239000011248 coating agent Substances 0.000 claims abstract 2
- 238000000576 coating method Methods 0.000 claims abstract 2
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 claims description 30
- 238000001914 filtration Methods 0.000 claims description 22
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 16
- 229910000147 aluminium phosphate Inorganic materials 0.000 claims description 15
- 239000008367 deionised water Substances 0.000 claims description 13
- 229910021641 deionized water Inorganic materials 0.000 claims description 13
- 238000010438 heat treatment Methods 0.000 claims description 6
- 230000007423 decrease Effects 0.000 claims description 3
- PBZHKWVYRQRZQC-UHFFFAOYSA-N [Si+4].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O Chemical compound [Si+4].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O PBZHKWVYRQRZQC-UHFFFAOYSA-N 0.000 claims 1
- 238000000034 method Methods 0.000 description 58
- 230000008569 process Effects 0.000 description 56
- 235000012431 wafers Nutrition 0.000 description 48
- 239000004065 semiconductor Substances 0.000 description 42
- 239000000126 substance Substances 0.000 description 31
- 239000000463 material Substances 0.000 description 10
- 229910019142 PO4 Inorganic materials 0.000 description 8
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical group [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 7
- 238000010586 diagram Methods 0.000 description 6
- 230000001965 increasing effect Effects 0.000 description 6
- 239000003607 modifier Substances 0.000 description 6
- 239000000243 solution Substances 0.000 description 6
- 229910021420 polycrystalline silicon Chemical group 0.000 description 5
- 238000000151 deposition Methods 0.000 description 4
- 238000004519 manufacturing process Methods 0.000 description 4
- 239000000203 mixture Substances 0.000 description 4
- 229910052710 silicon Inorganic materials 0.000 description 4
- 239000010703 silicon Substances 0.000 description 4
- QGZKDVFQNNGYKY-UHFFFAOYSA-O Ammonium Chemical compound [NH4+] QGZKDVFQNNGYKY-UHFFFAOYSA-O 0.000 description 3
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 3
- 239000002253 acid Substances 0.000 description 3
- 230000002411 adverse Effects 0.000 description 3
- 238000006243 chemical reaction Methods 0.000 description 3
- 150000001875 compounds Chemical class 0.000 description 3
- 238000001816 cooling Methods 0.000 description 3
- 229910052802 copper Inorganic materials 0.000 description 3
- 239000010949 copper Substances 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 238000001704 evaporation Methods 0.000 description 3
- 230000008020 evaporation Effects 0.000 description 3
- 238000011010 flushing procedure Methods 0.000 description 3
- 238000012544 monitoring process Methods 0.000 description 3
- 238000005389 semiconductor device fabrication Methods 0.000 description 3
- XLUBVTJUEUUZMR-UHFFFAOYSA-B silicon(4+);tetraphosphate Chemical compound [Si+4].[Si+4].[Si+4].[O-]P([O-])([O-])=O.[O-]P([O-])([O-])=O.[O-]P([O-])([O-])=O.[O-]P([O-])([O-])=O XLUBVTJUEUUZMR-UHFFFAOYSA-B 0.000 description 3
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 2
- KRHYYFGTRYWZRS-UHFFFAOYSA-N Fluorane Chemical compound F KRHYYFGTRYWZRS-UHFFFAOYSA-N 0.000 description 2
- 238000011109 contamination Methods 0.000 description 2
- 230000003247 decreasing effect Effects 0.000 description 2
- 230000008021 deposition Effects 0.000 description 2
- MNNHAPBLZZVQHP-UHFFFAOYSA-N diammonium hydrogen phosphate Chemical compound [NH4+].[NH4+].OP([O-])([O-])=O MNNHAPBLZZVQHP-UHFFFAOYSA-N 0.000 description 2
- 229910000388 diammonium phosphate Inorganic materials 0.000 description 2
- 230000006872 improvement Effects 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000005192 partition Methods 0.000 description 2
- 239000000843 powder Substances 0.000 description 2
- 125000001339 silanediyl group Chemical group [H][Si]([H])(*)* 0.000 description 2
- 229910021529 ammonia Inorganic materials 0.000 description 1
- 238000013459 approach Methods 0.000 description 1
- 239000007864 aqueous solution Substances 0.000 description 1
- 230000008901 benefit Effects 0.000 description 1
- 150000001768 cations Chemical class 0.000 description 1
- 229910052681 coesite Inorganic materials 0.000 description 1
- 239000000356 contaminant Substances 0.000 description 1
- 229910052906 cristobalite Inorganic materials 0.000 description 1
- 230000002708 enhancing effect Effects 0.000 description 1
- 238000011049 filling Methods 0.000 description 1
- XLYOFNOQVPJJNP-ZSJDYOACSA-N heavy water Substances [2H]O[2H] XLYOFNOQVPJJNP-ZSJDYOACSA-N 0.000 description 1
- 230000002401 inhibitory effect Effects 0.000 description 1
- 238000004255 ion exchange chromatography Methods 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 150000004767 nitrides Chemical class 0.000 description 1
- 230000001376 precipitating effect Effects 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 230000002035 prolonged effect Effects 0.000 description 1
- 238000010791 quenching Methods 0.000 description 1
- 230000002829 reductive effect Effects 0.000 description 1
- 229920006395 saturated elastomer Polymers 0.000 description 1
- 229910052682 stishovite Inorganic materials 0.000 description 1
- 229910052905 tridymite Inorganic materials 0.000 description 1
Images
Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/67—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere
- H01L21/67005—Apparatus not specifically provided for elsewhere
- H01L21/67011—Apparatus for manufacture or treatment
- H01L21/67017—Apparatus for fluid treatment
- H01L21/67063—Apparatus for fluid treatment for etching
- H01L21/67075—Apparatus for fluid treatment for etching for wet etching
- H01L21/67086—Apparatus for fluid treatment for etching for wet etching with the semiconductor substrates being dipped in baths or vessels
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
- H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
- H01L21/30—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26
- H01L21/31—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to form insulating layers thereon, e.g. for masking or by using photolithographic techniques; After treatment of these layers; Selection of materials for these layers
- H01L21/3105—After-treatment
- H01L21/311—Etching the insulating layers by chemical or physical means
- H01L21/31105—Etching inorganic layers
- H01L21/31111—Etching inorganic layers by chemical means
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
- H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
- H01L21/30—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26
- H01L21/31—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to form insulating layers thereon, e.g. for masking or by using photolithographic techniques; After treatment of these layers; Selection of materials for these layers
- H01L21/3205—Deposition of non-insulating-, e.g. conductive- or resistive-, layers on insulating layers; After-treatment of these layers
- H01L21/321—After treatment
- H01L21/3213—Physical or chemical etching of the layers, e.g. to produce a patterned layer from a pre-deposited extensive layer
- H01L21/32133—Physical or chemical etching of the layers, e.g. to produce a patterned layer from a pre-deposited extensive layer by chemical means only
- H01L21/32134—Physical or chemical etching of the layers, e.g. to produce a patterned layer from a pre-deposited extensive layer by chemical means only by liquid etching only
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S134/00—Cleaning and liquid contact with solids
- Y10S134/902—Semiconductor wafer
Definitions
- the present invention relates, in general, to semiconductor device fabrication and, more particularly, to etch processes used in the fabrication of semiconductor devices.
- an etch selectivity is defined as the ratio of the etch rate of one material to the etch rate of another material.
- an aqueous phosphoric acid solution having a concentration of approximately 85 percent heated to a temperature between 165 degrees Celsius (° C.) and 185° C. is routinely used for removing silicon nitride structures from a semiconductor wafer while leaving exposed silicon dioxide structures on the wafer.
- the phosphoric acid solution etches silicon nitride at a rate of approximately 6 nanometers per minute and etches silicon dioxide at a rate of no more than 0.25 nanometers per minute.
- the resulting etch selectivity is at least 24:1.
- the etch selectivity of an etch process depends on the temperature, concentration, and composition of the etchant. Consequently, the etch selectivity usually changes as more wafers are processed in the etchant. For example, the nitride to oxide etch selectivity of the etch process using the phosphoric acid etchant is approximately 24:1 when the etchant is fresh. After processing approximately 1000 wafers having silicon nitride thereon, the etch selectivity increases dramatically to 50:1 or greater. This selectivity variation adversely affects the efficiency, reliability, and yield of the semiconductor device and/or integrated circuit fabrication processes.
- etch process that has a stable etch selectivity and an apparatus for performing the etch process. It is desirable for the etch process to have a high etch selectivity. It would be of further advantage if the etch apparatus can be adapted from existing etch apparatuses.
- a selective etch modifier can be introduced into the etchant.
- the selective etch modifier alters the etch rates of certain materials but has no significant effect on the etch rates of other materials, thereby modifying the etch selectivity of the etch process.
- the etch rate modifier can be either a selective etch intensifier or a selective etch rate suppressor.
- the selective etch intensifier selectively increases the etch rate of certain materials.
- the selective etch rate suppressor selective decreases the etch rate of certain materials.
- a hot phosphoric acid solution is used as the etchant for etching the silicon nitride on a semiconductor wafer.
- a recirculating path is established for the hot phosphoric acid etchant.
- a high surface area structure such as, for example, a carbon matrix filter is coated with silicon nitride.
- the carbon matrix filter is installed in the recirculating path for the etchant. As the etchant in the recirculating path flows through the carbon matrix filter, it dissolves the silicon nitride coated on the carbon matrix filter. The dissolved silicon nitride significantly reduces the etch rate of silicon dioxide on the semiconductor wafer.
- the etch rate of the silicon nitride on the semiconductor wafer is substantially unaffected by the presence of the silicon nitride in the etchant. Therefore, the silicon nitride dissolved in the hot phosphoric acid etchant functions as an etch rate modifier that enhances the etch selectivity of the etch process. More particularly, the dissolved silicon nitride functions as a selective etch rate suppressor that substantially inhibits the etch of silicon dioxide on the semiconductor wafer.
- the concentration of silicon nitride in the etchant can be monitored and adjusted to maintain a stable etch selectivity of the etch process.
- FIG. 1 is a schematic diagram of an etch apparatus in accordance with the present invention.
- FIG. 2 is a flow chart schematically illustrating an etch process in accordance with the present invention
- FIG. 3 is a schematic diagram of another etch apparatus in accordance with the present invention.
- FIG. 4 is a schematic diagram of yet another etch apparatus in accordance with the present invention.
- FIG. 1 is a schematic diagram of an apparatus 10 used in a wet etch process in accordance with the present invention.
- Apparatus 10 is also referred to as a wet etcher or simply an etcher.
- Etcher 10 includes a tank 11 filled with an etchant 12 .
- Tank 11 and etchant 12 form an etchant bath for etching an object, e.g., a semiconductor wafer 15 , submerged in the etchant bath.
- Tank 11 filled with etchant 12 is also referred to as a bath 11 of etchant 12 .
- a heating element 16 such as, for example, a filament is immersed in etchant 12 for adjusting and maintaining the temperature of etchant 12 during the etch process.
- Tank 11 has a drain 18 .
- old and contaminated etchant is periodically removed from tank 11 through drain 18 and tank 11 is then filled with new etchant.
- a spout 19 is connected to a source of deionized water (not shown) and provides tank 11 with deionized water, thereby adjusting the concentration of etchant 12 .
- Etcher 10 also includes a chamber 21 attached to a sidewall 14 of tank 11 . Chamber 21 has an outlet 22 at its bottom.
- a conduit 23 couples outlet 22 of chamber 21 to an inlet 24 of a filtering system 25 .
- Another conduit 27 has a first end connected to an outlet 26 of filtering system 25 and a second end mounted adjacent to tank 11 .
- etchant 12 in tank 11 overflows sidewall 14 into chamber 21 .
- Etchant 12 in chamber 21 is pumped back to tank 11 through conduit 23 , filtering system 25 , and conduit 27 . Therefore, chamber 21 , conduit 23 , filtering system 25 , and conduit 27 form a recirculating path for etchant 12 in tank 11 .
- the second end of conduit 27 serves as an outlet 29 of the recirculating path.
- sidewall 14 is also referred to as an overflow sidewall and chamber 21 is also referred to as an overflow chamber or an overflow compartment.
- Overflow chamber 21 communicates with tank 11 through overflow sidewall 14 .
- etcher 10 includes a substance dissolving system 32 in the recirculating path for etchant 12 .
- substance dissolving system 32 introduces a substance into etchant 12 to modify the characteristics of etchant 12 , thereby achieving a desired result such as, for example, a high etch selectivity, a stable etch selectivity, a contamination free etch process, etc.
- the type and quantity of the substance introduced into etchant 12 depend on the composition of etchant 12 and the desired result.
- Substance dissolving system 32 is installed between the two ends of conduit 27 and includes a split valve 34 , a dissolver 35 , a bypass conduit 37 , and a merge valve 36 .
- Split valve 34 has one inlet and two outlets.
- Merge valve 36 has two inlets and one outlet.
- the inlet of split valve 34 is coupled to the outlet 26 of filtering system 25 via a section of conduit 27 .
- Dissolver 35 has an inlet connected to the first outlet of split valve 34 and an outlet connected the first inlet of merge valve 36 .
- the second outlet of split valve 34 is coupled to the second inlet of merge valve 36 via bypass conduit 37 .
- the outlet of merge valve 36 is coupled to outlet 29 of the recirculating path via another section of conduit 27 .
- Split valve 34 and merge valve 36 control the partition of etchant 12 flowing through dissolver 35 and through bypass conduit 37 .
- dissolver 35 has a high surface area coated with the substance to be introduced into etchant 12 during the etch process.
- dissolver 35 is formed by depositing the substance on a porous structure such as, for example, a carbon matrix filter. When etchant 12 in the recirculating path flows through dissolver 35 , the substance deposited on the porous filter is dissolved in etchant 12 .
- the dissolution rate at which etchant 12 dissolves the substance deposited on the porous filter can be controlled by adjusting the temperature of etchant 12 flowing through the porous filter.
- substance dissolving system 32 includes a temperature controller (not shown), e.g., a heating coil and a cooling coil, for adjusting the temperature of etchant 12 flowing through the porous filter.
- An alternative method for controlling the dissolution rate is changing the surface area of the porous filter exposed to etchant 12 . This can be achieved by partially submerging the porous filter in etchant 12 flowing through substance dissolving system 32 and adjusting the extent to which the porous filter is submerged in etchant 12 .
- the dissolution rate can also be controlled by adjusting the rate at which etchant 12 flows through the porous filter.
- the flow rate of etchant 12 through the porous filter can be controlled by adjusting split valve 34 , merge valve 36 , and a pump (not shown) in the recirculating path.
- etchant 12 adjacent dissolver 35 may be saturated with the substance dissolved from the surface of the porous filter. This may adversely affect the etch process. Therefore, substance dissolving system 32 preferably includes a flushing system (not shown) that can be periodically turned on to flush dissolver 35 .
- FIG. 2 is a flow chart schematically illustrating an etch process 50 in accordance with the present invention.
- etch process 50 is a wet etch process using etcher 10 of FIG. 1 for etching silicon nitride structures and/or polycrystalline silicon structures on semiconductor wafer 15 .
- silicon nitride structures are formed on semiconductor wafer 15 .
- a pad layer of silicon dioxide is formed between the silicon nitride structures and the surface of semiconductor wafer 15 to relieve the tension on the wafer surface.
- Other structures such as, for example, polycrystalline silicon structures can also be formed on semiconductor wafer 15 .
- the silicon dioxide layer on semiconductor wafer 15 remains in place after etch process 50 so that it can protect the underlying films or retain a uniform thickness for consistent performance of the semiconductor devices fabricated on semiconductor wafer 15 . Therefore, etch process 50 preferably has a high and stable etch selectivity so that and the etch of the silicon dioxide pad layer on semiconductor wafer 15 is substantially inhibited.
- Etchant 12 for etching silicon nitride and/or polycrystalline silicon on semiconductor wafer 15 is preferably an aqueous solution of phosphoric acid having a concentration of approximately 85 percent and a temperature between approximately 165 degrees Celsius (° C.) and approximately 185° C.
- Silicon nitride is deposited on a high surface area structure such as, for example, a carbon matrix filter, which serves as dissolver 35 in substance dissolving system 32 .
- Etchant 12 dissolves the silicon nitride deposited on the carbon matrix filter as it flows through dissolver 35 .
- the silicon nitride dissolved in etchant 12 alters the composition and modifies the characteristics of etchant 12 .
- the silicon nitride reacts with the phosphoric acid in etchant 12 in a chemical reaction: Si 3 N 4 +7H 3 PO 4 ⁇ 2(NH 4 ) 2 HPO 4 +H2Si(PO 4 ) 2 +HSi 2 (PO 4 ) 3 (1)
- the silicon phosphate acid compounds formed in the reaction are not volatile, so etchant 12 does not lose significant amounts of the silicon phosphate acid compounds through evaporation.
- the silicon phosphate acid compounds are unstable.
- the silicon dioxide formed in etchant 12 suppresses the etch of the silicon dioxide on semiconductor wafer 15 and has no significant effect on the etch rate of silicon nitride and polycrystalline silicon.
- the etch selectivity of etch process 50 is significantly increased. Therefore, the silicon nitride deposited on the carbon matrix filter in substance dissolving system 32 functions as a selective etch rate suppressor during etch process 50 .
- Etch process 50 starts with preparing an etchant bath (step 51 ) by filling tank 11 in etcher 10 with etchant 12 so that etchant 12 overflows sidewall 14 and spills into overflow chamber 21 .
- Heating element 16 in tank 11 maintains etchant 12 at a desired temperature, e.g., approximately 165° C., at which temperature the phosphoric acid solution loses its water component through evaporation.
- Spout 19 continuously adds deionized water into tank 11 to make up the water lost through evaporation, thereby maintaining a substantially constant concentration of etchant 12 .
- a pump pumps etchant 12 in chamber 21 through filtering system 25 and substance dissolving system 32 to establish a recirculating path for etchant 12 (step 52 ).
- the pump also controls the recirculating rate of etchant 12 .
- Filtering system 25 reconditions etchant 12 throughout etch process 50 by filtering out contaminants that may be present in etchant 12 .
- the silicon nitride deposited on the carbon matrix filter is gradually dissolved in etchant 12 and introduced into tank 11 through outlet 29 of the recirculating path (step 53 ).
- the silicon nitride dissolved in etchant 12 changes the characteristics of etchant 12 . More particularly, the silicon nitride functions as a selective etch rate suppressor to enhance the etch selectivity of etchant 12 .
- the introduction of the silicon nitride into etchant 12 continues while semiconductor wafer 15 is submerged in tank 11 of etchant 12 .
- the concentration of the silicon nitride selective etch rate suppressor in etchant 12 determines the etch selectivity of etch process 50 .
- the concentration of the selective etch rate suppressor is sufficiently high to substantially quench or inhibit the etch of silicon dioxide on semiconductor wafer 15 . It should be noted that a very high silicon nitride concentration in etchant 12 may produce too much silicon dioxide in etchant 12 , thereby causing an undesirable effect of silicon dioxide precipitating on semiconductor wafer 15 .
- an equilibrium between the consumption and production of silicon dioxide in etchant 12 is maintained at an appropriate level to achieve an etch selectivity approaching infinity while substantially inhibiting any silicon dioxide deposition on semiconductor wafer 15 .
- a desired equilibrium is achieved when the selective etch rate suppressor concentration in etchant 12 is, by way of example, approximately 0.5 milligram of silicon nitride per milliliter of the phosphoric acid solution. At this concentration, the etch selectivity of etch process 50 approaches infinity to one and there is no significant silicon dioxide precipitation on semiconductor wafer 15 during etch process 50 .
- the concentration of the selective etch rate suppressor in etchant 12 is monitored.
- the concentration of the selective etch rate suppressor is monitored by measuring the etch rates of the silicon nitride structures and the silicon dioxide structures on monitoring wafers (not shown) in etchant 12 .
- the concentration of the selective etch rate suppressor is monitored by measuring the ammonium cation concentration in etchant 12 .
- the ammonium cation concentration in the phosphoric acid solution depends on the dissolved silicon nitride concentration in etchant 12 .
- Methods for measuring the ammonium cation concentration include cation ion chromatography and ammonia selective electrode measurement.
- Adjustments are made to etchant 12 if the monitoring scheme indicates that the concentration of the selective etch rate suppressor therein is not optimal. If the concentration of the selective etch rate suppressor in etchant 12 is too low, the dissolution rate of the silicon nitride deposited on the carbon matrix filter is increased. This can be accomplished by increasing the temperature of etchant 12 flowing through dissolver 35 , increasing the surface area of dissolver 35 in etchant 12 , and/or increasing the flow rate of etchant 12 through dissolve 35 .
- the concentration of the selective etch rate suppressor in etchant 12 is too high, the temperature and/or the flow rate of etchant 12 through dissolver 35 are decreased to reduce the dissolution rate of the silicon nitride deposited on the carbon matrix filter in etchant 12 .
- the dissolution rate can also be reduced by decreasing the surface area of dissolver 35 exposed to etchant 12 flowing through substance dissolving system 32 .
- the temperature of etchant 12 flowing through dissolver 35 is adjusted using a temperature adjusting element or an etchant temperature controller (not shown), e.g., heating coil and a cooling coil, in substance dissolving system 32 .
- the flow rate of etchant 12 through dissolver 35 can be controlled by adjusting the recirculating rate of etchant 12 .
- the flow rate of etchant 12 through dissolver 35 can also be controlled by adjusting split valve 34 and merge valve 36 to alter the ratio of etchant 12 flowing through dissolver 35 with respect to that flowing through bypass conduit 37 .
- Split valve 34 and merge valve 36 are preferably capable of directing all etchant 12 in the recirculating path through dissolver 35 , thereby maximizing the dissolution rate of silicon nitride into etchant 12 .
- split valve 34 and merge valve 36 are also preferably capable of directing all etchant 12 flowing in the recirculating path through bypass conduit 37 , thereby achieving a substantially zero dissolution rate of silicon nitride into etchant 12 .
- the dissolution rate of the silicon nitride deposited on dissolver 35 into etchant 12 can also be adjusted by periodically flushing dissolver 35 with deionized water.
- semiconductor wafer 15 is submerged in etchant 12 in tank 11 (step 56 ).
- semiconductor wafer 15 is mounted on a cassette (not shown).
- the cassette includes a plurality of wafers mounted thereon.
- the wafers mounted on a cassette are referred to as a batch of wafers.
- a batch typically includes between 15 and 20 wafers.
- the wafers in a batch are substantially identical to each other.
- the silicon nitride and/or polycrystalline silicon structures on semiconductor wafer 15 are etched by the hot phosphoric acid. The etch of silicon dioxide on semiconductor wafer 15 is greatly suppressed or substantially inhibited by the selective etch rate suppressor in etchant 12 .
- etch process 50 ends by removing semiconductor wafer 15 from tank 11 of etchant 12 (step 57 ).
- steps 52 , 53 , and 54 described herein above and shown in the flow chart of FIG. 2 continue after semiconductor wafer 15 is removed from tank 11 to maintain etchant 12 in tank 11 in an optimal condition.
- Etcher 10 is ready for receiving the next batch of wafers. If etchant 12 is so contaminated that its continual use may adversely affect the performance, reliability, or yield of the semiconductor devices on semiconductor wafer 15 , it is discharged from etcher 10 through drain 18 at the bottom of tank 11 . Tank 11 is then filled with new and clean etchant 12 .
- Filtering system 25 and dissolver 35 may also need replacement from time to time. Further, the whole apparatus of etcher 10 , which includes tank 11 , chamber 21 , conduits 23 and 27 , filtering system 25 , and substance dissolving system 32 , may need to be cleansed after a prolonged use.
- FIG. 3 is a schematic diagram of another etch apparatus 60 in accordance with the present invention.
- Apparatus 60 is also referred to as a wet etcher or simply an etcher.
- Etcher 60 is structurally similar to etcher 10 shown in FIG. 1 and includes a tank 11 filled with an etchant 12 and a deionized water supply spout 19 .
- Etcher 60 also includes a recirculating path comprised of a chamber 61 , a conduit 23 , a filtering system 25 , and a conduit 27 .
- etcher 60 includes a dissolver 65 in chamber 61 adjacent to outlet 22 .
- dissolver 65 preferably includes a high surface area object coated with the substance to be introduced into etchant 12 .
- dissolver 65 can include a carbon matrix filter with silicon nitride deposited thereon.
- the silicon nitride dissolved in etchant 12 during an etch process functions as a selective etch rate suppressor to substantially inhibit the etch of silicon dioxide on semiconductor wafer 15 .
- dissolution rate of the silicon nitride on dissolver 65 is controlled by adjusting the temperature and the recirculating rate of etchant 12 .
- chamber 61 is attached to a permeable sidewall 64 of tank 11 .
- Etchant 12 in tank 11 flows into chamber 61 either through permeable sidewall 64 or by overflowing permeable sidewall 64 .
- chamber 61 communicates with tank 11 through permeable sidewall 64 .
- Additional differences include the locations of deionized water supply spout 19 and outlet 29 of the recirculating path.
- deionized water supply spout 19 and outlet 29 of the recirculating path are located in chamber 61 . Therefore in etcher 60 , recirculated etchant 12 and deionized water are supplied to tank 11 via chamber 61 and through permeable sidewall 64 between chamber 61 and tank 11 .
- FIG. 4 is a schematic diagram of yet another etch apparatus 70 in accordance with the present invention.
- Apparatus 70 is also referred to as a wet etcher or simply an etcher.
- Etcher 70 is structurally similar to etcher 10 shown in FIG. 1 and includes a tank 11 filled with an etchant 12 and a deionized water supply spout 19 .
- Etcher 70 also includes a recirculating path comprised of a chamber 71 , a conduit 23 , a filtering system 25 , and a conduit 27 .
- etcher 70 includes a substance dissolving system 72 installed between outlet 22 of chamber 71 and inlet 24 of filtering system 25 .
- Substance dissolving system 72 is comprised of a split valve 74 , a dissolver 75 , and a bypass conduit 77 .
- Split valve 74 has one inlet and two outlets. The inlet of split valve 74 is coupled to the outlet 22 of chamber 71 via a section of conduit 23 . An inlet of dissolver 75 is connected to the first outlet of split valve 74 .
- conduit 23 couples an outlet of dissolver 35 to inlet 24 of filtering system 25 .
- Bypass conduit 77 is coupled between the second outlet of split valve 74 and inlet 24 of filtering system 25 .
- Split valve 74 controls the partition of etchant 12 in the recirculating path flowing through dissolver 75 and through bypass conduit 77 .
- dissolver 75 preferably includes a high surface area structure coated with the substance to be introduced into etchant 12 during the etch process.
- dissolver 75 is formed by depositing the substance on a porous filter such as, for example, a carbon matrix filter.
- a porous filter such as, for example, a carbon matrix filter.
- the dissolution rate can be controlled by adjusting the temperature of etchant 12 flowing through dissolver 75 .
- substance dissolving system 72 preferably includes a temperature controller (not shown), e.g., a cooling coil, for adjusting the temperature of etchant 12 flowing through dissolver 75 .
- the dissolution rate can also be controlled by adjusting the rate at which etchant 12 flows through dissolver 75 .
- the flow rate of etchant 12 through dissolver 75 can be controlled by adjusting split valve 74 and/or a pump (not shown) in the recirculating path.
- substance dissolving system 72 preferably includes a flushing system (not shown) that can be periodically turned on to flush etchant 12 near dissolver 75 .
- etcher 70 Another difference between etcher 10 shown in FIG. 1 and etcher 70 is that in etcher 70 , chamber 71 is attached to a permeable sidewall 64 of tank 11 . Etchant 12 in tank 11 flows into chamber 71 either through permeable sidewall 64 or by overflowing permeable sidewall 64 . In other words, chamber 71 communicates with tank 11 through permeable sidewall 64 . Additional differences include the locations of deionized water supply spout 19 and outlet 29 of the recirculating path. In etcher 70 , deionized water supply spout 19 and outlet 29 of the recirculating path are located in chamber 71 . Therefore in etcher 70 , recirculated etchant 12 and deionized water are supplied to tank 11 via chamber 71 and through permeable sidewall 64 between chamber 71 and tank 11 .
- a selective etch rate suppressor is introduced into the etchant bath during the etch process to increase the etch selectivity of the etch process.
- silicon nitride is introduced into the etchant as the selective etch rate suppressor.
- the silicon nitride in the phosphoric acid etchant significantly decreases the etch rate of silicon dioxide on the semiconductor wafer.
- the silicon nitride is introduced into the etchant using a filter coated with the silicon nitride and installed in the recirculating path for the etchant.
- the silicon nitride is dissolved in the etchant while the etchant in the recirculating path flows through the filter.
- the silicon nitride flows back to the etchant bath, the silicon nitride is substantially completely dissolved in the etchant, thereby substantially eliminating the particulate deposition of the silicon nitride on the semiconductor wafer.
- the silicon nitride concentration in the etchant is monitored and maintained at a desirable level by adjusting the temperature and flow rate of the etchant through the filter.
- the etch process of the present invention is efficient and reliable. The increased and stabilized etch selectivity improves the performance, reliability, and yields of semiconductor devices and/or integrated circuits fabricated using the etch process of the present invention.
- the selective etch rate suppressor is not limited to being coated on a porous filter in the recirculating path of the etchant and dissolved in the etchant as the etchant flows through the filter.
- the selective etch rate modifier can be introduced into the etchant in powder form. The powder can be either added directly into the etchant bath, or introduced into the etchant in the recirculating path.
- the application of the present invention is not limited to enhancing the etch selectivity of an etch process. The principle of the present invention is applicable to other processes whose characteristics are improved by introducing a material not required for the process itself.
- This process improvement is not limited to etch selectivity enhancement.
- silicon in a hydrofluoric acid based etch process for etching silicon dioxide on a semiconductor wafer, silicon can be coated on a filter installed in the etchant recirculating path and introduced into the etchant as the etchant flows through the recirculating path.
- the silicon serves to getter copper contamination. More particularly, the silicon removes the copper from the etchant, thereby avoiding the copper being deposited on the exposed silicon on the semiconductor wafer and contaminating the wafer surface.
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Abstract
An etch apparatus. The etch apparatus includes a tank coupled to a recirculating path that includes a dissolver. The dissolver includes a porous carbon matrix filter coated with silicon nitride. An etchant from the tank circulates through the recirculating path and performs a selective etching of a structure in the tank in contact with the etchant. The structure includes silicon nitride on a pad layer that includes silicon dioxide. The selective etching is characterized by the silicon nitride on the pad layer being selectively etched by the etchant relative to an etching by the etchant of the silicon dioxide. The etch apparatus further includes: means for dissolving the silicon nitride coated on the filter into the etchant at a controlled dissolution rate sufficient to cause the selective etching; and means for coating the silicon nitride onto the filter to facilitate the selective etching.
Description
- This application is a continuation application claiming priority to Ser. No. 10/760,896, filed Jan. 20, 2004; which is a divisional application of U.S. Pat. No. 6,699,400, issued Mar. 2, 2004.
- The present invention relates, in general, to semiconductor device fabrication and, more particularly, to etch processes used in the fabrication of semiconductor devices.
- The fabrication of semiconductor devices and/or integrated circuits often requires removing certain materials from a semiconductor wafer while leaving other materials on the wafer. This can be accomplished in a selective etch process that uses an etchant having different etch rates with respect to different materials. To characterize the selective etch process, an etch selectivity is defined as the ratio of the etch rate of one material to the etch rate of another material. For example, an aqueous phosphoric acid solution having a concentration of approximately 85 percent heated to a temperature between 165 degrees Celsius (° C.) and 185° C. is routinely used for removing silicon nitride structures from a semiconductor wafer while leaving exposed silicon dioxide structures on the wafer. At the temperature of 165° C., the phosphoric acid solution etches silicon nitride at a rate of approximately 6 nanometers per minute and etches silicon dioxide at a rate of no more than 0.25 nanometers per minute. The resulting etch selectivity is at least 24:1.
- The etch selectivity of an etch process depends on the temperature, concentration, and composition of the etchant. Consequently, the etch selectivity usually changes as more wafers are processed in the etchant. For example, the nitride to oxide etch selectivity of the etch process using the phosphoric acid etchant is approximately 24:1 when the etchant is fresh. After processing approximately 1000 wafers having silicon nitride thereon, the etch selectivity increases dramatically to 50:1 or greater. This selectivity variation adversely affects the efficiency, reliability, and yield of the semiconductor device and/or integrated circuit fabrication processes.
- Accordingly, it would be advantageous to have an etch process that has a stable etch selectivity and an apparatus for performing the etch process. It is desirable for the etch process to have a high etch selectivity. It would be of further advantage if the etch apparatus can be adapted from existing etch apparatuses.
- A general object of the present invention is to provide an efficient and reliable etch process and an apparatus for performing the etch process. It is a further object of the present invention for the etch process to be capable of producing semiconductor devices and/or integrated circuits having high performance, high reliability, and high yield. Another object of the present invention is to implement the etch process with modifications to existing etch apparatuses.
- These and other objects of the present invention are achieved by adjusting and controlling the composition of the etchant during the etch process. For example, a selective etch modifier can be introduced into the etchant. The selective etch modifier alters the etch rates of certain materials but has no significant effect on the etch rates of other materials, thereby modifying the etch selectivity of the etch process. By monitoring and controlling the concentration of the etch rate modifier in the etchant, a stable etch selectivity is maintained during the etch process. The etch rate modifier can be either a selective etch intensifier or a selective etch rate suppressor. The selective etch intensifier selectively increases the etch rate of certain materials. On the other hand, the selective etch rate suppressor selective decreases the etch rate of certain materials.
- In a preferred embodiment of the present invention, a hot phosphoric acid solution is used as the etchant for etching the silicon nitride on a semiconductor wafer. A recirculating path is established for the hot phosphoric acid etchant. A high surface area structure such as, for example, a carbon matrix filter is coated with silicon nitride. The carbon matrix filter is installed in the recirculating path for the etchant. As the etchant in the recirculating path flows through the carbon matrix filter, it dissolves the silicon nitride coated on the carbon matrix filter. The dissolved silicon nitride significantly reduces the etch rate of silicon dioxide on the semiconductor wafer. The etch rate of the silicon nitride on the semiconductor wafer is substantially unaffected by the presence of the silicon nitride in the etchant. Therefore, the silicon nitride dissolved in the hot phosphoric acid etchant functions as an etch rate modifier that enhances the etch selectivity of the etch process. More particularly, the dissolved silicon nitride functions as a selective etch rate suppressor that substantially inhibits the etch of silicon dioxide on the semiconductor wafer. The concentration of silicon nitride in the etchant can be monitored and adjusted to maintain a stable etch selectivity of the etch process.
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FIG. 1 is a schematic diagram of an etch apparatus in accordance with the present invention; -
FIG. 2 is a flow chart schematically illustrating an etch process in accordance with the present invention; -
FIG. 3 is a schematic diagram of another etch apparatus in accordance with the present invention; and -
FIG. 4 is a schematic diagram of yet another etch apparatus in accordance with the present invention. - Preferred embodiments of the present invention are described herein with reference to the figures. It should be noted that the figures are not necessarily drawn to scale. It should also be noted that elements having similar functions are labeled using the same reference numerals in the figures.
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FIG. 1 is a schematic diagram of anapparatus 10 used in a wet etch process in accordance with the present invention.Apparatus 10 is also referred to as a wet etcher or simply an etcher.Etcher 10 includes atank 11 filled with an etchant 12.Tank 11 and etchant 12 form an etchant bath for etching an object, e.g., asemiconductor wafer 15, submerged in the etchant bath.Tank 11 filled withetchant 12 is also referred to as abath 11 ofetchant 12. Aheating element 16 such as, for example, a filament is immersed in etchant 12 for adjusting and maintaining the temperature ofetchant 12 during the etch process.Tank 11 has adrain 18. In a semiconductor device fabrication process, old and contaminated etchant is periodically removed fromtank 11 throughdrain 18 andtank 11 is then filled with new etchant. Aspout 19 is connected to a source of deionized water (not shown) and providestank 11 with deionized water, thereby adjusting the concentration ofetchant 12.Etcher 10 also includes achamber 21 attached to asidewall 14 oftank 11.Chamber 21 has anoutlet 22 at its bottom. Aconduit 23couples outlet 22 ofchamber 21 to aninlet 24 of afiltering system 25. Anotherconduit 27 has a first end connected to anoutlet 26 offiltering system 25 and a second end mounted adjacent totank 11. During an etch process, etchant 12 intank 11 overflowssidewall 14 intochamber 21. Etchant 12 inchamber 21 is pumped back totank 11 throughconduit 23,filtering system 25, andconduit 27. Therefore,chamber 21,conduit 23,filtering system 25, andconduit 27 form a recirculating path foretchant 12 intank 11. The second end ofconduit 27 serves as anoutlet 29 of the recirculating path. Becauseetchant 12 intank 11reaches chamber 21 by overflowingsidewall 14,sidewall 14 is also referred to as an overflow sidewall andchamber 21 is also referred to as an overflow chamber or an overflow compartment.Overflow chamber 21 communicates withtank 11 throughoverflow sidewall 14. - In addition,
etcher 10 includes asubstance dissolving system 32 in the recirculating path foretchant 12. During an etch process,substance dissolving system 32 introduces a substance intoetchant 12 to modify the characteristics ofetchant 12, thereby achieving a desired result such as, for example, a high etch selectivity, a stable etch selectivity, a contamination free etch process, etc. The type and quantity of the substance introduced intoetchant 12 depend on the composition ofetchant 12 and the desired result.Substance dissolving system 32 is installed between the two ends ofconduit 27 and includes asplit valve 34, adissolver 35, abypass conduit 37, and amerge valve 36.Split valve 34 has one inlet and two outlets. Mergevalve 36 has two inlets and one outlet. The inlet ofsplit valve 34 is coupled to theoutlet 26 offiltering system 25 via a section ofconduit 27.Dissolver 35 has an inlet connected to the first outlet ofsplit valve 34 and an outlet connected the first inlet ofmerge valve 36. The second outlet ofsplit valve 34 is coupled to the second inlet ofmerge valve 36 viabypass conduit 37. The outlet ofmerge valve 36 is coupled tooutlet 29 of the recirculating path via another section ofconduit 27.Split valve 34 and mergevalve 36 control the partition ofetchant 12 flowing throughdissolver 35 and throughbypass conduit 37. - Preferably,
dissolver 35 has a high surface area coated with the substance to be introduced intoetchant 12 during the etch process. In a preferred embodiment,dissolver 35 is formed by depositing the substance on a porous structure such as, for example, a carbon matrix filter. Whenetchant 12 in the recirculating path flows throughdissolver 35, the substance deposited on the porous filter is dissolved inetchant 12. - The dissolution rate at which
etchant 12 dissolves the substance deposited on the porous filter can be controlled by adjusting the temperature ofetchant 12 flowing through the porous filter. Preferably,substance dissolving system 32 includes a temperature controller (not shown), e.g., a heating coil and a cooling coil, for adjusting the temperature ofetchant 12 flowing through the porous filter. An alternative method for controlling the dissolution rate is changing the surface area of the porous filter exposed toetchant 12. This can be achieved by partially submerging the porous filter inetchant 12 flowing throughsubstance dissolving system 32 and adjusting the extent to which the porous filter is submerged inetchant 12. The dissolution rate can also be controlled by adjusting the rate at which etchant 12 flows through the porous filter. The flow rate ofetchant 12 through the porous filter can be controlled by adjustingsplit valve 34, mergevalve 36, and a pump (not shown) in the recirculating path. Further,etchant 12adjacent dissolver 35 may be saturated with the substance dissolved from the surface of the porous filter. This may adversely affect the etch process. Therefore,substance dissolving system 32 preferably includes a flushing system (not shown) that can be periodically turned on to flushdissolver 35. -
FIG. 2 is a flow chart schematically illustrating anetch process 50 in accordance with the present invention. By way of example,etch process 50 is a wet etchprocess using etcher 10 ofFIG. 1 for etching silicon nitride structures and/or polycrystalline silicon structures onsemiconductor wafer 15. In a semiconductor device fabrication process, silicon nitride structures are formed onsemiconductor wafer 15. Typically, a pad layer of silicon dioxide is formed between the silicon nitride structures and the surface ofsemiconductor wafer 15 to relieve the tension on the wafer surface. Other structures such as, for example, polycrystalline silicon structures can also be formed onsemiconductor wafer 15. Preferably, the silicon dioxide layer onsemiconductor wafer 15 remains in place afteretch process 50 so that it can protect the underlying films or retain a uniform thickness for consistent performance of the semiconductor devices fabricated onsemiconductor wafer 15. Therefore,etch process 50 preferably has a high and stable etch selectivity so that and the etch of the silicon dioxide pad layer onsemiconductor wafer 15 is substantially inhibited. -
Etchant 12 for etching silicon nitride and/or polycrystalline silicon onsemiconductor wafer 15 is preferably an aqueous solution of phosphoric acid having a concentration of approximately 85 percent and a temperature between approximately 165 degrees Celsius (° C.) and approximately 185° C. Silicon nitride is deposited on a high surface area structure such as, for example, a carbon matrix filter, which serves asdissolver 35 insubstance dissolving system 32.Etchant 12 dissolves the silicon nitride deposited on the carbon matrix filter as it flows throughdissolver 35. Intank 11, the silicon nitride dissolved inetchant 12 alters the composition and modifies the characteristics ofetchant 12. More particularly, the silicon nitride reacts with the phosphoric acid inetchant 12 in a chemical reaction:
Si3N4+7H3PO4→2(NH4)2HPO4+H2Si(PO4)2+HSi2(PO4)3 (1)
The silicon phosphate acid compounds formed in the reaction are not volatile, soetchant 12 does not lose significant amounts of the silicon phosphate acid compounds through evaporation. However, the silicon phosphate acid compounds are unstable. They react with the water inetchant 12 as described in the following equations:
H2Si(PO4)2+2H2O→2H3PO4+SiO2 (2)
HSi2(PO4)3+4H2O→3H3PO4+2SiO2 (3)
Therefore, the series of chemical reactions described by equations (1), (2), and (3) can be described by the following equation:
Si3N4+2H3PO4+6H2O→2(NH4)2HPO4+3SiO2 (4) - The silicon dioxide formed in
etchant 12 suppresses the etch of the silicon dioxide onsemiconductor wafer 15 and has no significant effect on the etch rate of silicon nitride and polycrystalline silicon. The etch selectivity ofetch process 50 is significantly increased. Therefore, the silicon nitride deposited on the carbon matrix filter insubstance dissolving system 32 functions as a selective etch rate suppressor duringetch process 50. -
Etch process 50 starts with preparing an etchant bath (step 51) by fillingtank 11 inetcher 10 withetchant 12 so thatetchant 12overflows sidewall 14 and spills intooverflow chamber 21.Heating element 16 intank 11 maintainsetchant 12 at a desired temperature, e.g., approximately 165° C., at which temperature the phosphoric acid solution loses its water component through evaporation.Spout 19 continuously adds deionized water intotank 11 to make up the water lost through evaporation, thereby maintaining a substantially constant concentration ofetchant 12. - A pump (not shown) pumps
etchant 12 inchamber 21 throughfiltering system 25 andsubstance dissolving system 32 to establish a recirculating path for etchant 12 (step 52). The pump also controls the recirculating rate ofetchant 12.Filtering system 25 reconditionsetchant 12 throughoutetch process 50 by filtering out contaminants that may be present inetchant 12. - When
etchant 12 flows throughdissolver 35 insubstance dissolving system 32, the silicon nitride deposited on the carbon matrix filter is gradually dissolved inetchant 12 and introduced intotank 11 throughoutlet 29 of the recirculating path (step 53). The silicon nitride dissolved inetchant 12 changes the characteristics ofetchant 12. More particularly, the silicon nitride functions as a selective etch rate suppressor to enhance the etch selectivity ofetchant 12. - The introduction of the silicon nitride into
etchant 12 continues whilesemiconductor wafer 15 is submerged intank 11 ofetchant 12. The concentration of the silicon nitride selective etch rate suppressor inetchant 12 determines the etch selectivity ofetch process 50. Preferably, the concentration of the selective etch rate suppressor is sufficiently high to substantially quench or inhibit the etch of silicon dioxide onsemiconductor wafer 15. It should be noted that a very high silicon nitride concentration inetchant 12 may produce too much silicon dioxide inetchant 12, thereby causing an undesirable effect of silicon dioxide precipitating onsemiconductor wafer 15. Preferably, an equilibrium between the consumption and production of silicon dioxide inetchant 12 is maintained at an appropriate level to achieve an etch selectivity approaching infinity while substantially inhibiting any silicon dioxide deposition onsemiconductor wafer 15. A desired equilibrium is achieved when the selective etch rate suppressor concentration inetchant 12 is, by way of example, approximately 0.5 milligram of silicon nitride per milliliter of the phosphoric acid solution. At this concentration, the etch selectivity ofetch process 50 approaches infinity to one and there is no significant silicon dioxide precipitation onsemiconductor wafer 15 duringetch process 50. - The concentration of the selective etch rate suppressor in etchant 12 (step 54) is monitored. In one embodiment, the concentration of the selective etch rate suppressor is monitored by measuring the etch rates of the silicon nitride structures and the silicon dioxide structures on monitoring wafers (not shown) in
etchant 12. In another embodiment, the concentration of the selective etch rate suppressor is monitored by measuring the ammonium cation concentration inetchant 12. As described in equations (1) and (4) above, the ammonium cation concentration in the phosphoric acid solution depends on the dissolved silicon nitride concentration inetchant 12. Methods for measuring the ammonium cation concentration include cation ion chromatography and ammonia selective electrode measurement. - Adjustments are made to etchant 12 if the monitoring scheme indicates that the concentration of the selective etch rate suppressor therein is not optimal. If the concentration of the selective etch rate suppressor in
etchant 12 is too low, the dissolution rate of the silicon nitride deposited on the carbon matrix filter is increased. This can be accomplished by increasing the temperature ofetchant 12 flowing throughdissolver 35, increasing the surface area ofdissolver 35 inetchant 12, and/or increasing the flow rate ofetchant 12 through dissolve 35. If the concentration of the selective etch rate suppressor inetchant 12 is too high, the temperature and/or the flow rate ofetchant 12 throughdissolver 35 are decreased to reduce the dissolution rate of the silicon nitride deposited on the carbon matrix filter inetchant 12. The dissolution rate can also be reduced by decreasing the surface area ofdissolver 35 exposed toetchant 12 flowing throughsubstance dissolving system 32. The temperature ofetchant 12 flowing throughdissolver 35 is adjusted using a temperature adjusting element or an etchant temperature controller (not shown), e.g., heating coil and a cooling coil, insubstance dissolving system 32. The flow rate ofetchant 12 throughdissolver 35 can be controlled by adjusting the recirculating rate ofetchant 12. The flow rate ofetchant 12 throughdissolver 35 can also be controlled by adjustingsplit valve 34 and mergevalve 36 to alter the ratio ofetchant 12 flowing throughdissolver 35 with respect to that flowing throughbypass conduit 37.Split valve 34 and mergevalve 36 are preferably capable of directing alletchant 12 in the recirculating path throughdissolver 35, thereby maximizing the dissolution rate of silicon nitride intoetchant 12. Likewise, splitvalve 34 and mergevalve 36 are also preferably capable of directing alletchant 12 flowing in the recirculating path throughbypass conduit 37, thereby achieving a substantially zero dissolution rate of silicon nitride intoetchant 12. The dissolution rate of the silicon nitride deposited ondissolver 35 intoetchant 12 can also be adjusted by periodically flushingdissolver 35 with deionized water. - After an appropriate silicon nitride concentration in
etchant 12 is achieved,semiconductor wafer 15 is submerged inetchant 12 in tank 11 (step 56). Usually,semiconductor wafer 15 is mounted on a cassette (not shown). The cassette includes a plurality of wafers mounted thereon. The wafers mounted on a cassette are referred to as a batch of wafers. By way of example, a batch typically includes between 15 and 20 wafers. Preferably, the wafers in a batch are substantially identical to each other. Intank 11, the silicon nitride and/or polycrystalline silicon structures onsemiconductor wafer 15 are etched by the hot phosphoric acid. The etch of silicon dioxide onsemiconductor wafer 15 is greatly suppressed or substantially inhibited by the selective etch rate suppressor inetchant 12. - When a desired etch result is achieved,
etch process 50 ends by removingsemiconductor wafer 15 fromtank 11 of etchant 12 (step 57). Preferably, steps 52, 53, and 54 described herein above and shown in the flow chart ofFIG. 2 continue aftersemiconductor wafer 15 is removed fromtank 11 to maintainetchant 12 intank 11 in an optimal condition.Etcher 10 is ready for receiving the next batch of wafers. Ifetchant 12 is so contaminated that its continual use may adversely affect the performance, reliability, or yield of the semiconductor devices onsemiconductor wafer 15, it is discharged frometcher 10 throughdrain 18 at the bottom oftank 11.Tank 11 is then filled with new andclean etchant 12.Filtering system 25 anddissolver 35 may also need replacement from time to time. Further, the whole apparatus ofetcher 10, which includestank 11,chamber 21,conduits filtering system 25, andsubstance dissolving system 32, may need to be cleansed after a prolonged use. -
FIG. 3 is a schematic diagram of anotheretch apparatus 60 in accordance with the present invention.Apparatus 60 is also referred to as a wet etcher or simply an etcher.Etcher 60 is structurally similar toetcher 10 shown inFIG. 1 and includes atank 11 filled with anetchant 12 and a deionizedwater supply spout 19.Etcher 60 also includes a recirculating path comprised of achamber 61, aconduit 23, afiltering system 25, and aconduit 27. - A difference between
etcher 10 ofFIG. 1 andetcher 60 is thatsubstance dissolving system 32 installed betweenfiltering system 25 andoutlet 29 of the recirculating path ofetcher 10 is absent inetcher 60. Instead,etcher 60 includes adissolver 65 inchamber 61 adjacent tooutlet 22. Likedissolver 35 inetcher 10,dissolver 65 preferably includes a high surface area object coated with the substance to be introduced intoetchant 12. For example, whenetcher 60 is used for etching silicon nitride onsemiconductor wafer 15,dissolver 65 can include a carbon matrix filter with silicon nitride deposited thereon. The silicon nitride dissolved inetchant 12 during an etch process functions as a selective etch rate suppressor to substantially inhibit the etch of silicon dioxide onsemiconductor wafer 15. In an etchprocess using etcher 60, dissolution rate of the silicon nitride ondissolver 65 is controlled by adjusting the temperature and the recirculating rate ofetchant 12. - Another difference between
etcher 10 shown inFIG. 1 andetcher 60 is that inetcher 60,chamber 61 is attached to apermeable sidewall 64 oftank 11.Etchant 12 intank 11 flows intochamber 61 either throughpermeable sidewall 64 or by overflowingpermeable sidewall 64. In other words,chamber 61 communicates withtank 11 throughpermeable sidewall 64. Additional differences include the locations of deionizedwater supply spout 19 andoutlet 29 of the recirculating path. Inetcher 60, deionizedwater supply spout 19 andoutlet 29 of the recirculating path are located inchamber 61. Therefore inetcher 60, recirculatedetchant 12 and deionized water are supplied totank 11 viachamber 61 and throughpermeable sidewall 64 betweenchamber 61 andtank 11. -
FIG. 4 is a schematic diagram of yet anotheretch apparatus 70 in accordance with the present invention.Apparatus 70 is also referred to as a wet etcher or simply an etcher.Etcher 70 is structurally similar toetcher 10 shown inFIG. 1 and includes atank 11 filled with anetchant 12 and a deionizedwater supply spout 19.Etcher 70 also includes a recirculating path comprised of achamber 71, aconduit 23, afiltering system 25, and aconduit 27. - A difference between
etcher 10 ofFIG. 1 andetcher 70 is thatsubstance dissolving system 32 installed betweenfiltering system 25 andoutlet 29 of the recirculating path ofetcher 10 is absent inetcher 70. Instead,etcher 70 includes asubstance dissolving system 72 installed betweenoutlet 22 ofchamber 71 andinlet 24 offiltering system 25.Substance dissolving system 72 is comprised of asplit valve 74, adissolver 75, and a bypass conduit 77.Split valve 74 has one inlet and two outlets. The inlet ofsplit valve 74 is coupled to theoutlet 22 ofchamber 71 via a section ofconduit 23. An inlet ofdissolver 75 is connected to the first outlet ofsplit valve 74. Another section ofconduit 23 couples an outlet ofdissolver 35 toinlet 24 offiltering system 25. Bypass conduit 77 is coupled between the second outlet ofsplit valve 74 andinlet 24 offiltering system 25.Split valve 74 controls the partition ofetchant 12 in the recirculating path flowing throughdissolver 75 and through bypass conduit 77. - Like
dissolver 35 inetcher 10,dissolver 75 preferably includes a high surface area structure coated with the substance to be introduced intoetchant 12 during the etch process. In a preferred embodiment,dissolver 75 is formed by depositing the substance on a porous filter such as, for example, a carbon matrix filter. Whenetchant 12 in the recirculating path flows throughdissolver 75, the substance deposited on the porous filter is dissolved inetchant 12. - The dissolution rate can be controlled by adjusting the temperature of
etchant 12 flowing throughdissolver 75. Likesubstance dissolving system 32 inetcher 10,substance dissolving system 72 preferably includes a temperature controller (not shown), e.g., a cooling coil, for adjusting the temperature ofetchant 12 flowing throughdissolver 75. The dissolution rate can also be controlled by adjusting the rate at which etchant 12 flows throughdissolver 75. The flow rate ofetchant 12 throughdissolver 75 can be controlled by adjustingsplit valve 74 and/or a pump (not shown) in the recirculating path. Further,substance dissolving system 72 preferably includes a flushing system (not shown) that can be periodically turned on to flushetchant 12 neardissolver 75. - Another difference between
etcher 10 shown inFIG. 1 andetcher 70 is that inetcher 70,chamber 71 is attached to apermeable sidewall 64 oftank 11.Etchant 12 intank 11 flows intochamber 71 either throughpermeable sidewall 64 or by overflowingpermeable sidewall 64. In other words,chamber 71 communicates withtank 11 throughpermeable sidewall 64. Additional differences include the locations of deionizedwater supply spout 19 andoutlet 29 of the recirculating path. Inetcher 70, deionizedwater supply spout 19 andoutlet 29 of the recirculating path are located inchamber 71. Therefore inetcher 70, recirculatedetchant 12 and deionized water are supplied totank 11 viachamber 71 and throughpermeable sidewall 64 betweenchamber 71 andtank 11. - By now it should be appreciated that an etch process and an apparatus for performing the etch process have been provided. In accordance with the present invention, a selective etch rate suppressor is introduced into the etchant bath during the etch process to increase the etch selectivity of the etch process. For example, in an etch process using hot phosphoric acid etchant to etch silicon nitride on a semiconductor wafer, silicon nitride is introduced into the etchant as the selective etch rate suppressor. The silicon nitride in the phosphoric acid etchant significantly decreases the etch rate of silicon dioxide on the semiconductor wafer. Preferably, the silicon nitride is introduced into the etchant using a filter coated with the silicon nitride and installed in the recirculating path for the etchant. The silicon nitride is dissolved in the etchant while the etchant in the recirculating path flows through the filter. When the etchant flows back to the etchant bath, the silicon nitride is substantially completely dissolved in the etchant, thereby substantially eliminating the particulate deposition of the silicon nitride on the semiconductor wafer. The silicon nitride concentration in the etchant is monitored and maintained at a desirable level by adjusting the temperature and flow rate of the etchant through the filter. The etch process of the present invention is efficient and reliable. The increased and stabilized etch selectivity improves the performance, reliability, and yields of semiconductor devices and/or integrated circuits fabricated using the etch process of the present invention.
- While specific embodiments of the present invention have been shown and described, further modifications and improvements will occur to those skilled in the art. For example, the selective etch rate suppressor is not limited to being coated on a porous filter in the recirculating path of the etchant and dissolved in the etchant as the etchant flows through the filter. The selective etch rate modifier can be introduced into the etchant in powder form. The powder can be either added directly into the etchant bath, or introduced into the etchant in the recirculating path. Further, the application of the present invention is not limited to enhancing the etch selectivity of an etch process. The principle of the present invention is applicable to other processes whose characteristics are improved by introducing a material not required for the process itself. This process improvement is not limited to etch selectivity enhancement. For example, in a hydrofluoric acid based etch process for etching silicon dioxide on a semiconductor wafer, silicon can be coated on a filter installed in the etchant recirculating path and introduced into the etchant as the etchant flows through the recirculating path. The silicon serves to getter copper contamination. More particularly, the silicon removes the copper from the etchant, thereby avoiding the copper being deposited on the exposed silicon on the semiconductor wafer and contaminating the wafer surface.
Claims (12)
1. An etch apparatus, comprising:
an etching tank comprising an etchant, said etchant configured to perform a selective etching of a structure in the tank in contact with the etchant, wherein the structure comprises silicon nitride on a pad layer comprising silicon dioxide, wherein said selective etching is characterized by the silicon nitride on the pad layer being selectively etched by the etchant relative to an etching by the etchant of the silicon dioxide of the pad layer;
a recirculating path coupled to the tank, wherein the recirculating path comprises a dissolver, wherein the dissolver comprises a porous carbon matrix filter coated with silicon nitride, and wherein the recirculating path is configured to receive the etchant from the tank and to circulate the etchant from the tank through the recirculating path, including through the dissolver, and back into the tank;
means for dissolving the silicon nitride coated on the filter into the etchant at a controlled dissolution rate sufficient to cause the selective etching to decrease an etch rate of the silicon dioxide of the pad layer in the etchant in a controlled manner such that an etch rate of silicon nitride of the silicon nitride structure is substantially unchanged; and
means for coating the silicon nitride onto the filter to configure the coated silicon nitrate to facilitate said selective etching.
2. The etch apparatus of claim 1 , wherein the silicon nitride coated on the filter has a different spatial distribution on the filter than would silicon nitride coated on the filter by being precipitated from the etchant onto the filter while the etchant is passing through the filter.
3. The etch apparatus of claim 1 , wherein the tank comprises a heating element for heating and adjusting a temperature of the etchant, and wherein the heater is immersed in the etchant.
4. The etch apparatus of claim 1 , further comprising an etchant temperature controller adjacent said dissolver, said etchant temperature controller adjusting a temperature of the etchant flowing through said dissolver.
5. The etch apparatus of claim 1 , wherein the etchant comprises a phosphoric acid solution;
6. The etch apparatus of claim 1 , wherein the recirculating path further comprises a chamber in contact with the tank, a filtering system, a first conduit, and a second conduit comprising the dissolver,
wherein the chamber is in direct mechanical contact with the tank,
wherein a first end of the first conduit is connected to an outlet of the chamber,
wherein an inlet of the filtering system is connected to a second end of the first conduit, wherein an outlet of the filtering system is connected to a first end of the second conduit,
wherein a second end of the second conduit is connected to the tank or the chamber,
wherein the recirculating path is configured to receive the etchant from the tank into the chamber and to flow the etchant from the chamber through the first conduit, the filtering system, the second conduit, and back into the tank.
7. The etch apparatus of claim 6 , further comprising a spout for providing deionized water to the tank to adjust the concentration of the etchant in the tank, wherein the spout is directly connected to the chamber.
8. The etch apparatus of claim 6 , wherein a permeable sidewall is disposed between the tank and the chamber, and wherein the etchant flows from the tank to the chamber by flowing through the permeable sidewall and/or by overflowing the permeable sidewall.
9. The etch apparatus of claim 8 , wherein the etchant flows from the tank to the chamber by flowing through the permeable sidewall.
10. The etch apparatus of claim 8 , wherein the etchant flows from the tank to the chamber by overflowing the permeable sidewall.
11. The etch apparatus of claim 6 , wherein the second end of the second conduit is connected to the chamber, and wherein the etch apparatus further includes:
a split valve within the first conduit; and
a bypass conduit external to the first conduit, wherein a first end of the bypass conduit is connected to the split valve and a second end of the bypass conduit is connected to a merge location in the first conduit, wherein the dissolver is disposed within the first conduit between the split valve and the merge location, wherein the split valve is configured to split the etchant flowing into the split valve from the first end of the first conduit into a first etchant component flowing through the filter and a second etchant component flowing through the bypass conduit, and wherein the second etchant component merges with the first etchant at the merge location into a merged etchant flowing into the second end of the first conduit and into the inlet of the filtering system.
12. The etch apparatus of claim 6 , wherein the etch apparatus further includes:
a split valve within the second conduit;
a merge valve within the second conduit, wherein the dissolver is disposed within the second conduit between the split valve and the merge valve, wherein the merge valve is closer to the second end of the second conduit than is the split valve, and wherein the second end of the second conduit is connected to the tank; and
a bypass conduit connecting the split valve to the merge valve, wherein the bypass conduit is external to the second conduit, wherein the split valve is configured to split the etchant flowing into the split valve from the first end of the second conduit into a first etchant component flowing through the filter and a second etchant component flowing through the bypass conduit, and wherein the merge valve is configured to merge the first etchant component flowing through the filter and the second etchant component flowing through the bypass conduit into a merged etchant flowing into the second end of the second conduit and into the tank.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
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US11/946,370 US20080066864A1 (en) | 1999-06-04 | 2007-11-28 | Etch apparatus |
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US09/326,514 US6699400B1 (en) | 1999-06-04 | 1999-06-04 | Etch process and apparatus therefor |
US10/760,896 US7332054B2 (en) | 1999-06-04 | 2004-01-20 | Etch apparatus |
US11/946,370 US20080066864A1 (en) | 1999-06-04 | 2007-11-28 | Etch apparatus |
Related Parent Applications (1)
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US10/760,896 Continuation US7332054B2 (en) | 1999-06-04 | 2004-01-20 | Etch apparatus |
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US20080066864A1 true US20080066864A1 (en) | 2008-03-20 |
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US09/326,514 Expired - Lifetime US6699400B1 (en) | 1999-06-04 | 1999-06-04 | Etch process and apparatus therefor |
US10/760,896 Expired - Lifetime US7332054B2 (en) | 1999-06-04 | 2004-01-20 | Etch apparatus |
US11/946,370 Abandoned US20080066864A1 (en) | 1999-06-04 | 2007-11-28 | Etch apparatus |
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US09/326,514 Expired - Lifetime US6699400B1 (en) | 1999-06-04 | 1999-06-04 | Etch process and apparatus therefor |
US10/760,896 Expired - Lifetime US7332054B2 (en) | 1999-06-04 | 2004-01-20 | Etch apparatus |
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Also Published As
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US6699400B1 (en) | 2004-03-02 |
US20040144750A1 (en) | 2004-07-29 |
US7332054B2 (en) | 2008-02-19 |
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