GB2320129A

GB2320129A - Method of fabricating an aluminium plug using selective chemical vapour deposition

Info

Publication number: GB2320129A
Application number: GB9625172A
Authority: GB
Inventors: Shi-Chung Sun; Hien-Tien Chiu; Ming-Hsing Tsai
Original assignee: United Microelectronics Corp
Current assignee: United Microelectronics Corp
Priority date: 1996-06-24
Filing date: 1996-12-04
Publication date: 1998-06-10
Anticipated expiration: 2016-12-04
Also published as: NL1004841C2; JPH1012737A; DE19702388A1; NL1004841A1; GB9625172D0; FR2750249B1; DE19702388C2; GB2320129B; FR2750249A1

Abstract

An improved method of fabricating an aluminum plug using a selective chemical vapor deposition (CVD) procedure. A semiconductor component is first formed in a substrate having an insulating layer formed over the surface thereof. The insulating layer has a contact opening formed therein that exposes a conductive region of the semiconductor component. Then, a vacuum thermal annealing treatment is performed on the device substrate. Dimethylethylamine alane (DMEAA) is used as a precursor for then depositing an aluminum layer over the surface of the substrate, using a CVD procedure performed at a substrate temperature not exceeding 250 ‹C, for fabricating an aluminum plug in the contact opening. The aluminum plug is selectively deposited over the surface of the exposed conductive region, while relatively not deposited over the surface of the insulating layer.

Description

2320129 i'b]ETIIOI) OF FABRICATING AN ALUMINUM PLUG USING SELECTIVE

CHEMICAL VAPOR DEPOSITION

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates In uenerai to a metallization process for the fabrication of' semiconductor integrated circuits (ICs). In particular, the invention relates to a method of fabricatinu an aluminum plu. for ICs by performing a vacuum thermal annealinu treatment prior to a chemical vapor deposition (CVD) procedure, resulting in improved deposition 1 selectivity.

Description of the Related Art

Sputtering is a technique that is widely used in the fabrication of semiconductor IC devices, for depositing aluminum to form interconnects in the device circuitry. Due to the fact that sputtering is a physical vapor deposition (PVD) procedure, resulting in generally poor step coverage compared to that provided by a CVD procedure, it is not suitable for IC fabrication at the sub-micron level. If sputtening were utilized in sub-micron device fabnicating procedures, undesirable results such as poor uniforrruity In thickness and voids in the deposited aluminum layer would anise. In particular, when recessions, such as holes, in the device substrate are small in cross-section and are deep, metallization may not be effectively achieved down to the bottom of the recessed portion. In such a situation, electrical connection to the underlying conductive region would be incomplete or absent.

In order to provide background for the deschiption of the invention, an alummum deposition layer formed using a conventional sputtening procedure is bniefly examined, with reference to FIG. 1 of the accompanying drawings. Essentially, a substrate 10 is used as the basis for fabrication of semiconductor components for an IC device. For clarity, the entire IC device is not shown: Rather, only a &rtion of the conductive region 12, such as a metal or a metal slilicide layer of the exemplified semiconductor component, is schematically shown in the drawing. An insulating layer 14, such as a thermal silicon dioxide layer, a borophosphosilicate (,]ass (13PSG) layer, or a tetraethoxysi lane (TEOS) W m layer, is formed over the surface of the substrate 10. Photolithography and etching procedures are then utilized to form a contact opening 16 in the Insulating layer 14 exposing, the conductive reolon 12 ofthe semiconductor component being, fabricated A c - sputtering procedure is then conducted to deposit an aluminurn]aver 18 over the insulating laver 14, filline the space inside the contact opening 16 and connect duct inu, to the con lye region 12, thereby forming the interconnect for the fabricated semiconductor component.

However. as the feature size of semiconductor devices is reduced. this conventional metal sputtering procedure for forming the metallization interconnect inevitably becomes less effective. When the dimensions of the contact opening 16 are reduced as a result of device mini aturizati on, the deposited aluminum layer 18 suffers deteriorated step coverage conditions, as well as uneven layer thickness. Voids 15 may even appear in the opening 16. All these factors render the performance characteristics of the device thus fabricated less controllable and often unacceptable. When the space in the contact opening 16 is reduced to a certain level, the sputtered metal may not even reach the bottom of the opening hole at all.

To solve the problem, as shown in FIG. 2, instead of directly depositing the aluminurn layer over the surface of the insulating layer 14 and in the contact opening 16 formed therein, frequently a tungsten plug 17 is first formed inside the contact opening 16 by a selective CVD procedure, followed by aluminum layer deposition over the surface of the insulating layer 14 using a conventional sputtering procedure.

However, fabrication of additional tungsten plugs in contact openings for semiconductor components represents an increase in overall manufacturing costs. Further, the use of a tungsten plug is disadvantageous, as it has an electrical conductivity that is only about one-third that of aluminum. Efforts thus have been devoted toward developing process techniques using CVD procedures for depositing aluminum, that are suitable for semiconductor devices featuring fabnication resolution on the level of 0. 25 pm and less.

When a CV1) procedure is utilized in depositing aluminum layers, trilsobutylaluminum (TIBA) br ditnethylalu[TU'um hydride (DMAH) is typically used as the precursor. TIBA is difficult to use, as it requires a relatively high temperature (about to 170 'C) to vaporize because of its lower vaporization pressure- DMAH, on the other hand, although relatively easier to vaporize because of its inherently higher vaporization pressure, also causes the deposited aluminum layer to have carbon-containinu impurities that reduce the electrical conductivity ofthe deposited aluminum lii,\.ci 1 lils Is because DNIAH has a stronu carbon-alurninum covalent bond in its molecular structure Gladfelterand M G Sininionds of the University of Minnesota proposed a nieiliod for depositing aluminuill using a CVD procedure by utilizing a dimethylettiviaiiiiiie alane (DMEAA) compound as the precursor. As shown in FIG. 3, because 13MEAA has a coordinate covalent bond between the nitrogen and aluminum atoms, featurinu a bonding energy gap that is smaller than the conventional covalent bonds, its vaporization temperature is relatively lower, at about 90 'C. The resulting deposition aluminurn layer would thus have a much lower concentration of impurities. Based on these outstanding 1 results, the present inventor proposed a DMEAA-related semiconductor device fabricatino process in SSDM, p. 634, 1994 as well as in VMIC, p. 362, 1994. The selectivity characteristics with respect to different substrate materials, however, was not investigated in those disclosures.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a method for fabricating an interconnect in a semiconductor IC device that results in a continuous, reliable electrical connection.

The invention provides an improved method of fabricating an aluminum plug in a selective CVI? procedure that includes the following steps. First, a semiconductor component is formed in a substrate having. an insulating layer formed over the surface thereof The insulating layer has a contact opening that exposes a conductive region of the semiconductor component. Then, a vacuum thermal annealing treatment is implemented on the device substrate. Dimethylethylamine alane (DMEAA) is utilized as a precursor for depositing an aluminum layer over the surface of the substrate in a CV1) procedure conducted at a substrate temperature not highr than 250 'C, for fabricating an aluminum plug in the contact opening. The aluminum plug is selectively deposited over the surface of the exposed conductive region 'In the contact opening while relatively not deposited over the surface of the insulating layer.

lo BRIEF DESCRIPTION OF THE DRAWINGS

Other oblects, features, and advantages of the invention will become apparent by way ofthe t'oliowint, detailed description of the preferred but non-linilting, ciiibo(litiierii The description is made with reference to the accompanying drawings in which:

FIG. 1 schematically shows a cross-section of a metallization interconnect fabricated usina a conventional aluminum sputtering- deposition process.' FIG, 2 schematically shows a cross section of -a metallization interconnect pluo fabricated using a conventional selective CVD process for depositing a tungsten g, FIG. 3 shows the molecular structure of precursor 13INfflAA utilized in a fabrication io process in accordance with a preferred embodiment of the invention; FIG. 4 shows the aduminum layer growth rate plotted as a function of the substrate temperature during the process of deposition," FIG. 5 shows the purity of the alurninum layer formed using a CVD procedure, as detemined using an Auger electron spectroscopy process; FIG. 6 shows plots of deposition selectivity for aluminum deposited over different materials at different temperatures using a CVD procedure; FIG. 7 shows a comparison of deposition selectivity, before and after a thermal annealing treatment, for alurninum deposited over different materials at different temperatures using a CVD procedure; and FIG. 8 schernatically shows a cross section of an aluminum plug fabricated in accordance with a preferred embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A preferred method of fabricating alurnlinurn plugs for metallization of semiconductor devices in selective CVD procedures is described with reference to FIG. 8 of the drawings.

First, a substrate 20 is provided as the basis for fabrication of semiconductor components for an IC device. For clarity, only a portion of the conductive region 22, such as a metal or a silicide layer of the exemplified semiconductor component, 'Is schematlically W shown. An insulating layer 24, such as a thermal oxide layer or a borophosphosilicate glass (13PSG) layer, is formed over the surface of the substrate 20. Photolithography and 1 1 1 11 a,, er 2 4 Cleffing procedures are then utilized to forni a contact opening, 26 ri tile 'nsulat'fl_L' exposing, the conductive revion 22 of the semiconductor component beino fabricated Then. a vacutini thermal annealing treatment is performed on the device,, it'er at this stage by heating the wafer to a temperature of about 450 'C for about 30 minutes After-wards, DMEAA is utilized as a precursor for Performing a CVD procedure to deposit an alurninum layer 28. The substrate temperature is controlled to be no higher than 250 'C. in order to achieve excellent deposition selectivity. In other words, under the abo;./edescribed conditions, aluminum can be deposited with high selectivity, only on the conductive region 22 Inside the contact opening 26, not on the surface of the Insulating layer 24. An aluminum plug 28 having a structural configuration such as the one schernatically depicted in FIG. 8 is thus formed. Then, a conventional sputtering procedure can follow to form the interconnects above the insulating layer 24. Because the invention is not directed toward this phase of fabrication, subsequent steps VAill not be elaborated herein.

Thus, because the method of the invention for fabricating aluminum plugs in a selective CVD deposition procedure makes use of DNfflAA as a precursor, more easily controlled fabricating conditions are available for fornuing the aluminum deposition. This is because, as mentioned above, DMEAA has a coordinate covalent bond between the nitrogen and aluminium atoms, featuring a bonding energy gap that is smaller than conventional covalent bonds. That smaller bonding energy gap results in a higher vaporization pressure, so that its vaporization temperature is relatively low, at about 90 'C.

The resulting aluminum plugs have a low level of impurities and feature electrical resistance characteristics comparable to alurninum depositions formed by conventional sputtering procedures.

The vacuum thermal annealing treatment performed before implementing the CVD procedure for depositing the aluminum serves tb greatly improve the deposition selectivity between the insulating layer and the conduction laye r over the surface of the substrate.

Because of this outstanding selectivity, the method of the invention is suitable for fabricating contact plugs such as aluminum plugs, and 'In particular, for integrated circuit device fabricating procedures requiring a high level of 'Integration To demonstrate the 1 SUPC1-10MY OftlIC method of the inventlon, several tests and corresponding -analyse,,; \ cl c conducted, with the followinu, results In the first test, a CVID procedure foi deposltlncl, aILlillinuni was performed. ii.,itIL7 DMEAA as the precursor. The aluminuni layer growth rate plotted as a function ofthe substrate temperature during the deposition process is shown in FIG. 4. The alufflinum was deposited in two CVD procedures, utilizing DMEA.A as a precursor, at respectiVe process ambient pressures of 100 and 200 mTorr. The data collected and presented in FIG, 4 shows that the growth-rate/substrate-temperature relationships at the two selected pressures were basically the same. with the growth rate generally increasing, as the 1 substrate temperature rose. Calculation results show that the surface reaction activation energy is about 0.75 eV, comparable to the bonding energy of aluminum- nitrogen atoms in the molecule. This indicates that the breaking up of the aluminum-nitrogen bond is the key step for selective aluminum deposition using the CVD procedure with DNEA.A as the precursor. DMEAA is more suitable than conventional precursors for this selective alulifflinum deposition because it has a smaller covalent bonding energy.

In another test, an alurninum layer deposited using the above-mentioned CVID procedure was the subject of Auger electron spectroscopy, resulting in the corresponding analysis data shown in FIG. 5. Essentially, FIG. 5 plots data representing the purity of the alunuinum layer formed by the CVD procedures of the invention, as obtained in the Auger electron spectroscopy. The Auger data shows that the deposited aluminum has a very high level of purity, With rare carbon or oxygen impurity atoms barely present in the deposited layer. Analysis of the specimen shows that the layer has a resistance of about 3.0 gfYcm, comparable to that found in layers formed using the conventional sputtering deposition procedures.

A third test for alurninum deposition selectivity for the method of the invention was conducted. For this test, aluffilnurn was deposited over the surface of a conduction layer, as well as on Insulating layers of a variety of different materials at different process temperatures. FIG. 6 shows the aluminum deposition selectivity recorded for this test. As shown in the drawing, aluminum particles were measured as they were deposited over the surface of four insulating layers composed of different materials, including. thermal oxide (Th-OX), tetraethoxysi lane (TEOS), borophosphosilicate glass (BPSG), and oxide formed by a plasma-enhanced CVD procedure (PEOX) Basically, the deposition sciecil\11\ deteriorated as the deposition temperature increased. In other words, aluiiil'lillill parlicles were easily deposited over the surfaces of both the conduction and insulatin-go layers hl,-,ii process temperatures, while, when the process temperature was maintained at a lower level, the same insulatino lavers cathered considerably fewer aluminum par-ticles than did the conduction layer.

A fourth test was conducted wherein an additional vacuum thermal annealint; treatment was performed, the remainder of the test proceeded according to the third test procedure described above. The vacuum thermal annealing treatment procedure was conducted at a temperature of about 450 'C and was sustained for about 30 minutes. The test results are plotted in FIG. 7, which shows the aluminum deposition selectivity improvement, before and after the vacuum thermal annealing treatment, as the aluminum is deposited over different materials using the CVD procedure. As clearly shown in the plot, aluminum deposition selectivity (deposition over the conduction layer rather than the insulating layer) improved for the CVD procedure when a vacuum thermal annealing treatment was performed first. In particular, the selectivity was shown to be best for the Th-OX insulating layer, followed by the BMG layer, and then by the PEOX layer. This selectivity ranking could have been based on the fact that PEOX is a material that absorbs more water molecules than does Th-OX. There would therefore be fewer -OH bonds in the Th-OX material than in the PEOX. When the vacuum thermal annealing treatment is performed pn"or to deposition, water is removed. Therefore, while aluminum particles deposit smoothly over the surface of the conduction layers, fewer aluminum particles are deposited over the surface of PEOX insulating layers, and even fewer on the Th-OX layers.

The invention has been described by way of example and in terms of a preferred embodiment, but the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cdver various molfications and similar arrangements. The appended claims, therefore, should be accorded the broadest interpretation so as to encompass all such modifications and similar structures.

Claims

What is clainied is:

1 1 1 -1 i 6 7 8 9 1 () 11 12 1 2 1 1 2 1 2 1 2 3 4 A niethod of fabricating an alumInuni plug, usIng a selective chelilical vapor deposition procedure comprising the steps of forming a senuiconductor component In a substrate having an insulating layer formed over the surface thereof, the insulating layer having formed therein a contact opening exposing a conductive region of the semiconductor component, performing a vacuum thermal annealing treatment on the substrate- and depositing an aluminum layer over the surface of the substrate in a chemical vapor deposition procedure utilizing dimethylethylamine alane as a precursor and performed at a substrate temperature not higher than 250 'C, for fabricating an aluminum plug in the contact opening and in contact with the conductive region, the aluminum plug being selectively deposited over the surface of the exposed conductive region while not being deposited over the surface of the insulafing layer.

2. The method of claim 1, wherein the vacuum thermal annealing treatment is performed at a temperature of about 450 'C and is sustained for about 30 minutes.

3. The method of claim 1, wherein the insulating layer is a thermal oxide layer.

4 The method of claim 1, wherein the insulating layer is a borophosphosilicate glass layer.

5. The method of claim 1, wherein the insulating layer is a plasma enhanced chemical vapor deposited oxide layer.

1

6. A method of fabdicating an aluminum plug, comprising the steps of forming a contact opening in an insulating layer over a substrate to expose a conductive region in the substrate; performing a vacuum thermal annealing treatment on the substrate., and performing a chemical vapor deposition procedure at a substrate temperature not exceeding 250 'C using dimethylethylamine alane as a precursor, to deposit an aluminum]aver on the exposed conductive region in the contact opening 1 2 7- The method of claim 6, wherein the vacuum thermal annealing treatment is performed at a temperature of about 450 'C and is sustained for about 30 minutes.

1 8. The method of claim 6, wherein the insulating layer is a thermal oxide layer.

1 9. The method of claim 6, wherein the insulating layer is a borophosphosilicate glass layer.

2 1 2 10. The method of claim 6, wherein the insulating layer is a plasma enhanced cherruical vapor deposited oxide layer.