WO2010140296A1 - 不揮発性記憶素子およびこれを備えた半導体記憶装置 - Google Patents
不揮発性記憶素子およびこれを備えた半導体記憶装置 Download PDFInfo
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- WO2010140296A1 WO2010140296A1 PCT/JP2010/002896 JP2010002896W WO2010140296A1 WO 2010140296 A1 WO2010140296 A1 WO 2010140296A1 JP 2010002896 W JP2010002896 W JP 2010002896W WO 2010140296 A1 WO2010140296 A1 WO 2010140296A1
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- nonvolatile memory
- fuse
- resistance
- electrode
- memory element
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Images
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
- H01L27/02—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components specially adapted for rectifying, oscillating, amplifying or switching and having potential barriers; including integrated passive circuit elements having potential barriers
- H01L27/04—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components specially adapted for rectifying, oscillating, amplifying or switching and having potential barriers; including integrated passive circuit elements having potential barriers the substrate being a semiconductor body
- H01L27/10—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components specially adapted for rectifying, oscillating, amplifying or switching and having potential barriers; including integrated passive circuit elements having potential barriers the substrate being a semiconductor body including a plurality of individual components in a repetitive configuration
- H01L27/101—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components specially adapted for rectifying, oscillating, amplifying or switching and having potential barriers; including integrated passive circuit elements having potential barriers the substrate being a semiconductor body including a plurality of individual components in a repetitive configuration including resistors or capacitors only
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10B—ELECTRONIC MEMORY DEVICES
- H10B63/00—Resistance change memory devices, e.g. resistive RAM [ReRAM] devices
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11C—STATIC STORES
- G11C13/00—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00
- G11C13/0002—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00 using resistive RAM [RRAM] elements
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11C—STATIC STORES
- G11C2213/00—Indexing scheme relating to G11C13/00 for features not covered by this group
- G11C2213/70—Resistive array aspects
- G11C2213/72—Array wherein the access device being a diode
Definitions
- the present invention relates to a nonvolatile memory element and a semiconductor memory device including the same, and in particular, reversibly transitions between a low resistance state and a high resistance state having a higher resistance value than the low resistance state by application of a voltage pulse.
- the present invention relates to a nonvolatile memory element having a variable resistance element and a semiconductor memory device.
- the resistance change element is an element that has a property that the resistance value reversibly changes by an electrical signal, and that can store information corresponding to the resistance value in a nonvolatile manner.
- the resistance change element Unlike a phase change element (PCRAM) in which a resistance value changes due to a change in crystal state due to heat generated by an electrical stimulus, the resistance change element has a resistance directly through an electron transfer, that is, through an exchange of electrons. By changing the redox state of the change material, the resistance value of the element is changed.
- PCRAM phase change element
- a cross-point type semiconductor memory device is known as an example of a large-capacity semiconductor memory device equipped with this variable resistance element.
- a cross-point type ReRAM when reading the resistance value of the resistance change element formed at the intersection where the word line and the bit line intersect three-dimensionally, the memory element in another row or other column
- a diode which is a current control element is inserted in series with the variable resistance element to form a nonvolatile memory element (also referred to as a memory cell) (see, for example, Patent Document 1). ).
- FIG. 13 is a diagram showing a conventional semiconductor memory device equipped with a memory cell composed of a resistance change element and a current control element.
- This figure shows a resistance change element 260 that stores information by a change in electrical resistance due to electrical stress in a cross-point memory cell array having a bit line 210, a word line 220, and a memory cell 280 formed at each intersection thereof.
- a memory cell 280 is formed by serially connecting a two-terminal current control element 270 having a non-linear current-voltage characteristic that allows a current to flow in both directions.
- the bit line 210 serving as the upper wiring is electrically connected to the current control element 270, and the word line 220 serving as the lower wiring is electrically connected to the resistance change element 260.
- the present invention has been made to solve the above-described problem, and even when a defect occurs in a certain nonvolatile memory element, the nonvolatile memory element in the same row or column as the defective nonvolatile memory element is used. It is an object of the present invention to provide a nonvolatile memory element that can effectively prevent writing and reading from being disabled, and a semiconductor memory device including the nonvolatile memory element.
- a nonvolatile memory element includes a current control element having nonlinear current-voltage characteristics, a low resistance state based on an applied voltage pulse, and a resistance higher than the low resistance state.
- a resistance change element that reversibly transitions between a high resistance state having a high value and a fuse, and the current control element, the resistance change element, and the fuse are connected in series, and the fuse is connected to the current control element Alternatively, the variable resistance element is configured to be disconnected when it is practically short-circuited.
- a resistance change element or a current control element constituting a certain nonvolatile memory element when a resistance change element or a current control element constituting a certain nonvolatile memory element is defective and the nonvolatile memory element is substantially short-circuited, a current flowing through the resistance change element is reduced.
- the resistance change element is in a resistance state lower than the low resistance state. Thereby, most of the voltage applied to the nonvolatile memory element is applied to the fuse.
- a voltage applied to the nonvolatile memory element is applied to the fuse, a large current flows through the fuse, and the fuse is disconnected. For this reason, the defective nonvolatile memory element has a resistance value equal to or higher than the high resistance state of the variable resistance element.
- the current control element, the variable resistance element, and the fuse are formed at a three-dimensional intersection of the first wiring and the second wiring that intersect each other to form a cross-point type nonvolatile memory element. Also good.
- a fuse is provided for each cross-point type nonvolatile memory element. Therefore, when a defective nonvolatile memory element is generated, A fuse connected to the non-volatile memory element is cut off and a large current is prevented from flowing through the defective non-volatile memory element, and another non-volatile memory element in the same row or column as the defective non-volatile memory element Since current flows through adjacent rows and columns, the other nonvolatile memory elements can be accessed and normally operated.
- the fuse may have a resistance value smaller than the resistance value in the low resistance state of the nonvolatile memory element before being blown.
- the fuse has a resistance value of 5 k ⁇ or less.
- the fuse may be made of polysilicon.
- a semiconductor memory device includes a substrate, a plurality of first wirings arranged in parallel to each other on the substrate, and parallel to the main surface of the substrate above the plurality of first wirings.
- a plurality of second wirings formed parallel to each other in a plane and three-dimensionally intersecting with the plurality of first wirings, and a solid of the plurality of first wirings and the plurality of second wirings 2.
- the defective nonvolatile memory element has a resistance value equal to or higher than the high resistance state of the variable resistance element.
- the resistance change element includes a first electrode, a second electrode, and a resistance change layer sandwiched between the first electrode and the second electrode
- the current control element includes a third electrode An electrode, a fourth electrode, an insulator layer or a semiconductor layer sandwiched between the third electrode and the fourth electrode
- the nonvolatile memory element includes the first wiring and the resistance
- Between the first electrode of the change element, between the second electrode of the resistance change element and the third electrode of the current control element, and between the fourth electrode of the current control element and the At least any one of the second wirings may be provided with a contact plug that is electrically connected to each other, and the fuse may be configured as any one of the contact plugs.
- fuse in the claims and the specification means a fuse that is blown when a current of a predetermined current value or more flows.
- the term “when the nonvolatile memory element is substantially short-circuited” in the claims and the specification refers to the resistance value of the low resistance state when the nonvolatile memory element is normal due to electrical breakdown. It means a state having a low resistance value.
- the nonvolatile memory element and the semiconductor memory device of the present invention since the current control element, the resistance change element, and the fuse are connected in series, even if a defective nonvolatile memory element occurs, the defective nonvolatile memory element It is possible to effectively prevent writing and reading from being performed to other nonvolatile memory elements in the same row or column.
- FIG. 1 is a schematic circuit diagram showing a semiconductor memory device according to the first embodiment of the present invention.
- FIG. 2 is a schematic top view showing the semiconductor memory device shown in FIG.
- FIG. 3 is a schematic sectional view showing the semiconductor memory device shown in FIG.
- FIG. 4 is a diagram showing characteristics due to resistance change in the current control element of the present embodiment.
- FIG. 5 is a diagram showing current-voltage characteristics at the time of failure in the nonvolatile memory element of this embodiment and load characteristics in the fuse.
- FIG. 6 is a schematic process diagram showing a method of manufacturing the semiconductor memory device shown in FIG.
- FIG. 7 is a schematic process diagram showing a method of manufacturing the semiconductor memory device shown in FIG.
- FIG. 8 is a schematic process diagram showing a method of manufacturing the semiconductor memory device shown in FIG. FIG.
- FIG. 9 is a schematic process diagram showing a method of manufacturing the semiconductor memory device shown in FIG.
- FIG. 10 is a schematic process diagram showing a method of manufacturing the semiconductor memory device shown in FIG.
- FIG. 11 is a schematic cross-sectional view showing a semiconductor memory device according to the second embodiment of the present invention.
- FIG. 12 is a schematic process diagram showing a method of manufacturing the semiconductor memory device shown in FIG.
- FIG. 13 is a schematic circuit diagram showing a conventional semiconductor memory device.
- FIG. 1 is a schematic circuit diagram showing a nonvolatile semiconductor memory device 10 according to the first embodiment of the present invention.
- FIG. 2 is a schematic plan view showing the configuration of the nonvolatile semiconductor memory device 10 shown in FIG.
- FIG. 3 is a diagram showing a configuration of the nonvolatile semiconductor memory device 10 shown in FIG. 1 in a sectional view, and is a schematic sectional view showing a section taken along the line III-III shown in FIG. is there.
- the semiconductor memory device 10 of this embodiment includes a nonvolatile memory element (nonvolatile memory element) 11 in which a current control element 112, a resistance change element 105, and a fuse 103 are connected in series. Yes. More specifically, one end of the fuse 103 is connected to the first wiring (word line) 101, and one end of the current control element 112 is connected to the second wiring (bit line) 119. In this embodiment, the current control element 112, the resistance change element 105, and the fuse 103 are connected in series between the first wiring 101 and the second wiring 119 in this order. Even if the positions of the variable resistance element 105 and the fuse 103 are switched, the same effect can be obtained.
- the semiconductor memory device 10 includes the substrate 100 and the main surface of the substrate 100 in parallel with each other in the first direction (the horizontal direction in FIGS. 2 and 3). And a plurality of first wirings 101 extending in parallel to each other in a plane parallel to the main surface of the substrate 100 above the plurality of first wirings 101 and the plurality of first wirings 101.
- a plurality of second wirings (bit lines) arranged so as to extend in a second direction (a direction perpendicular to the paper surface in FIG. 3 and a vertical direction in FIG.
- a non-volatile storage element array having elements 11; It is equipped with a.
- the nonvolatile memory element 11 includes a fuse 103, a resistance change element 105, a current control element 112, and a second contact plug 110 that connects the resistance change element 105 and the current control element 112.
- the resistance change element 105 includes a lower electrode (first electrode) 106, an upper electrode (second electrode) 108, and a resistance change layer 107 interposed between the lower electrode 106 and the upper electrode 108. ing.
- the lower electrode 106 and the resistance change layer 107 are in physical contact, and the upper electrode 108 and the resistance change layer 107 are in physical contact.
- the current control element 112 includes a lower electrode (third electrode) 113, an upper electrode (fourth electrode) 115, and an insulator layer or semiconductor layer 114 interposed between the lower electrode 113 and the upper electrode 115. And.
- the lower electrode 113 and the insulator or semiconductor layer 114 are in physical contact, and the upper electrode 115 and the insulator or semiconductor layer 114 are in physical contact.
- a first interlayer insulating layer 102 is formed on the substrate 100 so as to cover the first wiring 101.
- a plurality of resistance change elements 105 are arranged on the first interlayer insulating layer 102 so as to be arranged at equal intervals on the first wiring 101 when viewed from the main surface side of the substrate 100 (upward direction in FIG. 3). Is formed.
- the first wiring 101 and the lower electrode 106 of the resistance change element 105 located thereabove are connected by a fuse 103 that functions as a first contact plug formed so as to penetrate the first interlayer insulating layer 102. Yes.
- a second interlayer insulating layer 109 is formed on the first interlayer insulating layer 102 so as to cover the variable resistance element 105.
- a plurality of current control elements 112 are formed at positions overlapping the resistance change element 105 when viewed from the main surface side of the substrate 100.
- the upper electrode 108 of the resistance change element 105 and the lower electrode 113 of the current control element 112 are directly connected to both the resistance change layer 107 of the resistance change element 105 and the semiconductor layer 114 of the current control element 112 by the second contact plug 110. Connected without contact.
- a third interlayer insulating layer 116 is formed on the second interlayer insulating layer 109 so as to cover the current control element 112.
- the second wiring 119 is orthogonal to the first wiring 101 as viewed from the main surface side of the substrate 100 and overlaps the resistance change element 105 and the current control element 112. Is formed.
- the second wiring 119 and the upper electrode 115 of the current control element 112 below the second wiring 119 are connected by a third contact plug 117 formed so as to penetrate the third interlayer insulating layer 116.
- the nonvolatile memory element 11 is provided between the first wiring 101 and the lower electrode 106 of the resistance change element 105, and functions as a first contact plug that conducts each other.
- a second contact plug 110 provided between the upper electrode 108 of the element 105 and the lower electrode 113 of the current control element 112 and conducting to each other, and the upper electrode 115 of the current control element 112 and the second wiring 119
- a third contact plug 117 which is provided between them and is electrically connected to each other.
- the configuration in which the fuse 103 is disposed as the first contact plug is illustrated, but the fuse 103 may be configured as a second or third contact plug, and these The same effect can be obtained also.
- the lead-out wiring 120 extending in the second direction in parallel with the second wiring 119 outside the region where the nonvolatile memory elements 11 are arranged as viewed from the thickness direction. Is formed.
- the first wiring 101 and the lead-out wiring 120 are fourth contact plugs 118 formed so as to penetrate the first interlayer insulating layer 102, the second interlayer insulating layer 109, and the third interlayer insulating layer 116, respectively. Connected by.
- the first wiring 101, the second wiring 119, and the lead-out wiring 120 are made of a conductive material such as aluminum.
- the first interlayer insulating layer 102, the second interlayer insulating layer 109, and the third interlayer insulating layer 116 are configured by an amount of insulating material such as silicon oxide.
- the second contact plug 110, the third contact plug 117, and the fourth contact plug 118 excluding the first contact plug functioning as the fuse 103 are made of a conductive material such as tungsten, for example.
- the fuse 103 is configured to be disconnected when the current control element 112 is substantially short-circuited. More specifically, the fuse 103 is designed not to be blown by the operating current of the nonvolatile memory element 11 but to be blown by a current flowing beyond a predetermined current value.
- the nonvolatile memory element 11 is provided at each of the three-dimensional intersections of the first wiring 101 and the second wiring 119 that intersect each other.
- the semiconductor memory device 10 including the cross-point type nonvolatile memory element array is realized.
- the resistance change layer 107 of the resistance change element 105 in this embodiment includes an oxygen-deficient transition metal oxide (oxygen content [atomic ratio: oxygen atoms in the total number of atoms compared to the stoichiometric oxide] Transition metal oxide) with a small number ratio].
- the resistance change layer 107 is composed of an oxygen-deficient oxide of tantalum (TaO x : 0 ⁇ x ⁇ 2.5) or an oxygen-deficient oxide of hafnium (HfO x : 0 ⁇ x ⁇ 2). Contains transition metal oxides. More preferably, the resistance change layer 107 is composed of only an oxygen-deficient oxide of tantalum or an oxygen-deficient oxide of hafnium.
- a resistance change element using an oxygen-deficient transition metal oxide reversibly changes its resistance value by applying a voltage pulse with a short pulse width of 100 ns or less.
- the standard electrode potential of the material (first material) constituting the lower electrode 106 is V1
- the standard electrode potential of the material (second material) constituting the upper electrode 108 is V2
- the oxygen-deficient transition metal oxide included in the resistance change layer 107 assuming that the standard electrode potential of the transition metal itself (when the oxidation number of the transition metal is zero) is Vt, Vt ⁇ V2 and V1 ⁇ V2 Satisfy the relationship.
- the material of the upper electrode 108 is less likely to be oxidized than the material of the resistance change layer 107.
- the material of the upper electrode 108 is not oxidized and reduced, and the material of the resistance change layer 107 is oxidized and reduced.
- the oxidation state of the resistance change layer 107 in the vicinity of the interface with the upper electrode 108 changes, and a resistance change phenomenon appears.
- the oxidation-reduction reaction at the electrode interface preferentially appears on the upper electrode 108 side. That is, the interface where the resistance change phenomenon appears can be fixed to the upper electrode side.
- the resistance value of the resistance change element 105 is switched by voltage pulses having different polarities.
- a positive voltage positive electrical signal
- current flows from the upper electrode 108 to the lower electrode 106.
- electrons are taken from the variable resistance layer 107 to the electrode on the upper electrode side, so that the material of the variable resistance layer 107 is oxidized and its resistance value increases.
- a negative voltage negative electrical signal
- current flows from the lower electrode 106 to the upper electrode 108.
- electrons are applied from the electrode to the resistance change layer 107 on the upper electrode side, whereby the material of the resistance change layer 107 is reduced and the resistance value thereof decreases.
- tantalum nitride can be used for the lower electrode 106
- platinum can be used for the upper electrode 108, for example.
- V1 0.48V (standard electrode potential of tantalum nitride).
- V2 1.18V (standard electrode potential of platinum).
- Vt ⁇ 0.6 V (standard electrode potential of tantalum). Therefore, the relationship of Vt ⁇ V2 and V1 ⁇ V2 is satisfied.
- Vt ⁇ 1.55 V (standard electrode potential of hafnium). In this case, the relationship of Vt ⁇ V2 and V1 ⁇ V2 is satisfied.
- the thickness of the resistance change layer 107 can be set to, for example, 50 nm.
- the resistance value of the resistance change element 105 is switched by voltage pulses having different polarities. Therefore, it is necessary for current to flow through the nonvolatile memory element 11 in any direction, and the bidirectional current control element 112 is applied.
- the current control element 112 is an element having non-linear current-voltage characteristics. When the absolute value of the applied voltage is less than the critical voltage, the resistance value is large (off state), and when the absolute value of the applied voltage is greater than the critical voltage, the resistance value is The element is extremely small (on state).
- the current control element 112 in this embodiment includes, for example, an MSM including a lower electrode 113 made of tungsten, a semiconductor layer 114 made of a silicon nitride film, and an upper electrode 115 made of tantalum nitride. Configured as a diode.
- the thickness of the semiconductor layer 114 can be set to 3 to 20 nm, for example.
- the silicon nitride film can be easily formed so as to have semiconductor characteristics, and the current control element 112 configured as an MSM diode can be manufactured by a simple manufacturing process.
- a nitrogen-deficient silicon nitride film (SiN x : 0 ⁇ x ⁇ 2) can be formed by reactive sputtering in a nitrogen gas atmosphere using a Si target, for example.
- the chamber pressure may be 0.1 Pa to 1 Pa and the Ar / N 2 flow rate may be 18 sccm / 2 sccm at room temperature.
- a current density of 2.5 ⁇ 10 3 A / cm 2 is obtained by applying a voltage of 1.6 V, and 5 ⁇ by applying a voltage of 0.4 V.
- a current density of 10 A / cm 2 is obtained.
- the on / off ratio is 50, which can be sufficiently used as the current control element 112 having non-ohmic properties.
- the current control element 112 may be an MIM diode including an insulator layer 114 between the lower electrode 113 and the upper electrode 115.
- SiO 2 , Si 3 O 4 , Ta 2 O 5 , or the like can be used as the material of the insulator layer 114.
- the MSM diode is advantageous when it is desired to pass a larger current in the on state.
- FIG. 4 is a diagram showing characteristics due to resistance change in the current control element of the present embodiment.
- FIG. 4 (a) is a graph showing a change in resistance value when a voltage pulse is applied, and FIG. 4 (b). Is a graph showing an example of current-voltage characteristics of resistance change.
- a voltage pulse having a voltage value of +5.0 V and a pulse width of 100 nsec is applied to the upper electrode 115 with respect to the lower electrode 106, and the voltage value.
- a voltage pulse of ⁇ 4.0 V and a pulse width of 100 nsec is alternately applied.
- the resistance value of the nonvolatile memory element 11 including the resistance change element 105 at this time is 1E6 (1M) ⁇ when a voltage pulse having a voltage value of +5.0 V is applied as shown in FIG. Degree (high resistance state).
- the resistance value becomes about 80 k ⁇ (low resistance state).
- the operating current at this time is about ⁇ 200 ⁇ A.
- the voltage used for reading these resistance values is 2V.
- the resistance value of the nonvolatile memory element 11 changes by one digit or more between the high resistance state and the low resistance state of the resistance change element 105.
- the point C when a negative voltage is applied to the upper electrode 115 with respect to the lower electrode 106 with respect to the variable resistance element 105 in the high resistance state so that the absolute value of the voltage gradually increases, the point C Thus, the state changes from the high resistance state to the low resistance state (lowering the resistance), and finally becomes the low resistance state at the point D.
- the voltage at point C is about ⁇ 3.3V
- the current is about ⁇ 25 ⁇ A
- the voltage at point D is about ⁇ 4.0V
- the current is ⁇ 170 ⁇ A.
- FIG. 5 is a diagram showing current-voltage characteristics at the time of failure in the nonvolatile memory element of this embodiment and load characteristics in the fuse.
- FIG. 5A is a partially enlarged graph showing the current-voltage characteristics at the time of failure, and
- FIG. 5B is a graph showing the load characteristics of the fuse.
- the current control element 112 When a defect occurs in a certain nonvolatile memory element 11 during the manufacturing process or operation, the current control element 112 is substantially short-circuited. At this time, a voltage of about 4.0 V is applied to the nonvolatile memory element 11 having the current-voltage characteristics of FIG. 4 and a breakdown current BD of about 1500 ⁇ A flows as shown in FIG. It becomes. Thereby, the resistance change element 105 in the defective nonvolatile memory element 11 has a resistance value (for example, about 100 ⁇ ) lower than the resistance value in the low resistance state. Therefore, most of the voltage applied to the defective nonvolatile memory element 11 is applied to the fuse 103.
- the load characteristic of the fuse 103 is such that the smaller the voltage (absolute value) applied in a predetermined voltage range is, the larger the allowable current (absolute value) is. As the voltage (absolute value) increases, the allowable current (absolute value) decreases. That is, the smaller the allowable current (absolute value), the easier the fuse 103 is blown.
- a voltage of about 4.0 V is applied to the fuse 103 in the nonvolatile memory element 11 in which a failure has occurred.
- the current allowed in the fuse 103 is about 100 ⁇ A as shown in FIG.
- the breakdown current BD flowing through the fuse 103 at the time of failure is about 1500 ⁇ A as described above. Therefore, the breakdown current BD flowing through the nonvolatile memory element 11 generates Joule heat exceeding an allowable amount in the fuse 103, and the fuse 103 is blown.
- the blown fuse 103 enters the surrounding interlayer insulating layer 102 and maintains the insulating state.
- the defective nonvolatile memory element 11 maintains a resistance value (for example, 1E7 (10 M) ⁇ or more) higher than the high resistance state of the variable resistance element 105.
- the current is prevented from flowing through the defective nonvolatile memory element 11, and the defective nonvolatile memory element is defective. Since current flows to other nonvolatile memory elements 11 in the same row or the same column as the elements 11 via adjacent rows and columns, the other nonvolatile memory elements 11 can be accessed and normally operated. Therefore, even when a failure occurs in a certain nonvolatile memory element 11, it is effective that writing and reading cannot be performed on another nonvolatile memory element 11 in the same row or the same column as the defective nonvolatile memory element 11. Can be prevented.
- the oxygen-deficient transition metal oxide used as the resistance change layer 107 of the resistance change element 105 in this embodiment has a resistance value by applying a voltage pulse having a short pulse width of 100 nsec or less. Changes reversibly. That is, only by applying a voltage pulse having a very short pulse width, a current sufficient for normal operation of the nonvolatile memory element 11 can be passed through the nonvolatile memory element 11. This means that the amount of current per unit area flowing through the fuse 103 by the current control element 112 is large.
- the defective nonvolatile memory element 11 is automatically disabled when the fuse 103 is blown, so that either the semiconductor memory device is manufactured or the semiconductor memory device is used. In this case, the operation of another nonvolatile memory element 11 in the same row or the same column can be ensured against the occurrence of a defect in the nonvolatile memory element 11.
- the fuse 103 is designed not to be blown by the operating current of the nonvolatile memory element 11 but to be blown when a current of a predetermined current value or more flows.
- the ease with which the fuse 103 is blown can be predicted by an average failure time MTBF (Mean-Time-Between-Failure) expressed by the following equation.
- MTBF KJ ⁇ n exp (qE a / kT)
- K is a constant
- J is a current density
- n is generally a value of 1.0 to 5.0
- E a is an activation energy
- k is a Boltzmann constant
- T is an absolute temperature.
- a higher current density J means a shorter MTBF. Therefore, as the current density J increases, the fuse 103 is easily blown.
- the MTBF becomes shorter as the temperature becomes higher. Therefore, the fuse 103 is easily blown as the temperature increases.
- the temperature of the fuse 103 is mainly determined by thermal energy transferred by Joule heat generated by current.
- the amount of heat is the product of the square of the current value and the resistance value of the fuse 103.
- the heating of the fuse 103 may be decelerated due to heat generation, and the resistance change of the fuse 103 may be hindered. Therefore, it is necessary to supply a current that generates heat instantaneously to the fuse 103 and to keep the heat in the fuse for a short time required to complete the resistance change of the fuse 103.
- a heat conducting material such as metal takes heat away.
- a heat insulating material such as an insulator can release heat energy from the fuse relatively gently. Therefore, a design in which the fuse is covered with an insulating layer and separated from the metal wiring is preferable.
- the fuse 103 can be stably operated by configuring the fuse 103 as the first contact plug covered with the interlayer insulating layer 102. Note that since the fuse 103 is covered with the interlayer insulating layer 102 and connected to the upper and lower metal wirings 101 and 106, the fuse 103 preferably has a length of 500 nm or more.
- the specific characteristics of the fuse 103 vary depending on the surrounding structure.
- the specific configuration of the fuse 103 can be appropriately selected based on the above so that desired characteristics can be obtained in relation to the variable resistance element and other components.
- the contact plug (first contact plug) functioning as the fuse 103 may have a smaller cross-sectional area than the other contact plugs (second and third contact plugs 110 and 117).
- the second and third contact plugs 110 and 117 have a circular cross section with a diameter of 240 nm
- the fuse 103 which is the first contact plug has a rectangular cross section with a side of 70 nm.
- the configuration is preferably used.
- the fuse 103 does not melt when the resistance change element 105 reversibly transitions between the high resistance state and the low resistance state, and the nonvolatile memory element 11 becomes the resistance change element. It is only necessary to have a resistance value that generates Joule heat so that the fuse 103 is blown when the resistance value becomes higher than the resistance value in the high resistance state.
- the fuse 103 preferably has a resistance value R (F) smaller than the resistance value R (LR) in the low resistance state of the variable resistance element 105.
- the resistance variable element 105 and the current control element 112 are connected in series with the resistor having the above resistance value, the current that flows when the resistance change element 105 is reduced in resistance is limited. Can be effectively prevented.
- the resistance change element 105 transitions from the high resistance state to the low resistance state, when a voltage pulse having a short pulse width of 100 nsec or less as described above is applied, the resistance change element 105 is connected in series to the resistance change element 105 and has a nonlinear current ⁇ There is a possibility that a current larger than a desired current value flows due to an instantaneous increase in current due to the current control element 112 having voltage characteristics. If a current larger than the desired current value flows through the resistance change element 105, the resistance value is lower than the desired low resistance state, and the current flowing through the resistance change element 105 may not stop even after the voltage pulse is applied. Therefore, the voltage pulse applied to the resistance change element 105 needs to be instantaneously lowered.
- the fuse 103 functions as a series resistor for performing current control when the resistance change element 105 is reduced in resistance, so that it is not necessary to separately provide a series resistor, thereby increasing the manufacturing cost. Therefore, the normal operation of the nonvolatile memory element 11 can be stably achieved.
- the sum of the value R (D) preferably satisfies R (LR) ⁇ R (F) + R (D) ⁇ R (HR).
- the fuse 103 preferably has a resistance value of 5 k ⁇ or less.
- the fuse 103 in the present embodiment is made of, for example, polysilicon having a rectangular cross section with a side of 70 nm, a length of 500 nm, and a resistivity of 0.03 ⁇ ⁇ cm. Further, the fuse 103 is not blown by current and voltage while the resistance change element 105 reversibly transits between a high resistance state and a low resistance state, and a voltage of about 5 V when the nonvolatile memory element 11 is defective. And has a resistance value such that it is blown by a current of about 1500 ⁇ A.
- the fuse 103 is made of polysilicon. Thereby, the fuse 103 can be formed inexpensively and easily. In addition, since the resistance value of the fuse 103 can be easily changed by changing the amount of impurities doped into polysilicon, the fuse 103 having an optimum resistance value can be formed in accordance with the specifications and the like. Polysilicon may be silicided by combining with a metal. That is, as the material of the fuse 103, for example, SiNi, SiCo, SiCu, or the like may be applied.
- FIG. 6A is a diagram showing a process of forming the first wiring on the substrate
- FIGS. 6B to 8H are fuses that are the first interlayer insulating layer and the first contact plug.
- 8 (i) is a diagram showing a step of forming a resistance change element
- FIG. 9 (j) is a diagram of forming a second interlayer insulating layer and a second contact plug.
- FIG. 9K is a diagram illustrating a process of forming a current control element
- FIG. 9L is a diagram illustrating a third interlayer insulating layer, a third contact plug, and a third contact plug.
- 10 (m) is a diagram illustrating a process of forming a fourth contact plug
- FIG. 10 (n) is a process of forming a second wiring and a lead-out wiring.
- FIG. 6A is a diagram showing a process of forming the first wiring on the substrate
- FIGS. 6B to 8H are fuses that are the first interlayer
- a first wiring 101 is formed on a substrate 100 on which a transistor, a lower layer wiring, and the like are formed using a desired mask.
- the first wiring 101 is covered.
- the first interlayer insulating layer 102 is formed on the entire surface of the substrate 100, and then a contact hole (opening) that penetrates the first interlayer insulating layer 102 and reaches the first wiring 101 is formed.
- a fuse 103 which is a first contact plug is formed by embedding a filler containing polysilicon as a main component in the contact hole.
- the fuse 103 made of polysilicon first, in the step shown in FIG. 6B, the first polysilicon layer 103a is formed on the first interlayer insulating layer 102. To do. Next, a photoresist film is formed on the first polysilicon layer 103a and patterned to form an etching mask 104. Next, in the process shown in FIG. 6C, the first polysilicon layer 103a is etched using the etching mask 104, a contact hole is opened in the first polysilicon layer 103a, and the first interlayer insulating layer 102 is formed. To expose. Further, in the step shown in FIG.
- a second polysilicon layer 103b is formed on the entire surface of the main surface of the substrate 100 including the first polysilicon layer 103a and the inside of the contact hole.
- the second polysilicon layer 103b is etched to form a sidewall 103c made of polysilicon on the side wall of the contact hole.
- a contact hole penetrating the first interlayer insulating layer 102 is opened by using the sidewall 103c and the first polysilicon layer 103a as a mask to form the first wiring 101. Expose. Subsequently, in the step shown in FIG.
- a third polysilicon layer is formed on the entire surface on the main surface side of the substrate 100 including the sidewalls 103c and the first polysilicon layer 103a while filling the contact holes with polysilicon. 103d is formed. Further, in the step shown in FIG. 8H, the third polysilicon layer 103d, the sidewall 103c, and the first polysilicon layer 103a are etched back by using Cl 2 gas, thereby the first interlayer insulating layer. A fuse 103 made of polysilicon that penetrates 102 and is connected to the first wiring 101 is formed in the contact hole.
- a conductive layer made of a noble metal is sequentially formed. Thereafter, these three layers are patterned with a predetermined mask created by photolithography, whereby the lower electrode 106, the resistance change layer 107, and the upper portion of the resistance change element 105 are positioned on the upper end surface of the fuse 103.
- An electrode 108 is formed.
- the oxygen-deficient tantalum oxide can be formed, for example, by so-called reactive sputtering, in which a target composed of tantalum is sputtered in an argon and oxygen gas atmosphere.
- a second interlayer insulating layer 109 is formed on the entire surface of the first interlayer insulating layer 102 so as to cover the variable resistance element 105. Thereafter, a contact hole that penetrates through the second interlayer insulating layer 109 and reaches the upper electrode 108 of the resistance change element 105 is formed. After that, a second contact plug 110 is formed by filling the contact hole with a filler mainly composed of tungsten.
- a conductive layer made of tungsten, a semiconductor layer made of silicon nitride, and tantalum nitride on the second interlayer insulating layer 109 are sequentially formed. Thereafter, these three layers are patterned with a predetermined mask created by photolithography, whereby the lower electrode 113 of the current control element 112 and the semiconductor layer are positioned on the upper end surface of the third contact plug 110. 114 and the upper electrode 115 are formed.
- a third interlayer insulating layer 116 is formed on the entire surface of the second interlayer insulating layer 109 so as to cover the current control element 112. Thereafter, a contact hole (opening) is formed so as to penetrate the third interlayer insulating layer 116 and reach the upper electrode 115 of the current control element 112. Thereafter, a third contact plug 117 is formed by filling a contact hole with a filler mainly composed of tungsten.
- a contact hole (opening) that reaches the first wiring 101 through the third interlayer insulating layer 116, the second interlayer insulating layer 109, and the first interlayer insulating layer 102. ).
- a fourth contact plug 118 is formed by filling a contact hole with a filler mainly composed of tungsten.
- the second wiring 119 is formed on the third interlayer insulating layer 116 so as to cover the upper end surface of the third contact plug 117 by photolithography and patterning. Then, the lead-out wiring 120 is formed so as to cover the upper end surface of the fourth contact plug 118.
- the resistance change type semiconductor memory device 10 that stably changes the resistance can be easily realized by the manufacturing method described above.
- FIG. 11 is a schematic cross-sectional view showing a semiconductor memory device 20 according to the second embodiment of the present invention.
- the semiconductor memory device 20 in the present embodiment is different from the semiconductor memory device 10 in the first embodiment in that the fuse 103B is positioned between the resistance change element 105 and the current control element 112. That is, the fuse 103B in the present embodiment functions as the second contact plug in the first embodiment. Further, in the semiconductor memory device 20 in the present embodiment, the first contact plug in the first embodiment is not present, and the lower electrode 106 of the resistance change element 105 is directly connected to the first wiring 101. Yes.
- the lower electrode 106 of the resistance change element 105 is formed on the first wiring 101.
- the variable resistance layer 107 and the upper electrode 108 of the variable resistance element 105 and the fuse 103B are formed in an opening (memory cell hole) formed in the interlayer insulating layer 102B.
- the number of masks can be reduced, and the manufacturing process itself can also be reduced.
- Other configurations of the present embodiment are the same as those of the first embodiment. Therefore, in the second embodiment, the same reference numerals and names are assigned to the same components as those in the first embodiment, and the description thereof is omitted.
- FIG. 12 is a schematic process diagram showing a manufacturing method of the semiconductor memory device shown in FIG.
- the first wiring 101 and the lower electrode 106 of the resistance change element 105 are formed on a substrate 100 on which transistors, lower layer wirings, and the like are formed using a predetermined mask. Then, a lower interlayer insulating layer 102B made of a silicon oxide film is formed on the entire surface so as to cover the lower electrode 106. Thereafter, an opening (memory cell hole) that penetrates the lower interlayer insulating layer 102B and is connected to the lower electrode 106 is formed.
- tantalum oxide of the resistance change layer 107 is formed in the memory cell hole.
- a tantalum target is formed by sputtering in a argon and oxygen gas atmosphere, so-called reactive sputtering.
- the film is formed by sputtering until the tantalum oxide is completely filled in the memory cell hole.
- unnecessary tantalum oxide on the lower interlayer insulating layer 102B is removed by CMP, and the resistance change layer 107 is formed only in the memory cell hole.
- hafnium oxide as the resistance change layer 107, it can be formed by performing reactive sputtering in which a hafnium target is similarly sputtered in an atmosphere of argon and oxygen gas. Further, etch back is performed under the condition that the resistance change layer 107 formed in the memory cell hole is selectively etched as compared with the lower interlayer insulating layer 102B.
- the resistance change layer 107 made of tantalum oxide having a thickness of about 50 nm is formed in the memory cell hole, and a recess is formed in the memory cell hole. The depth of the recess is about 600 nm.
- tantalum nitride is formed on the entire surface covering the concave portion of the memory cell hole, and etching is performed under the condition that the tantalum nitride formed in the memory cell hole is selectively etched as compared with the lower interlayer insulating layer 102B. Do the back.
- an upper electrode 108 made of tantalum nitride of about 50 nm is formed in the memory cell hole, and a recess is formed again in the memory cell hole. The depth of the recess at this time is about 500 nm.
- the recesses of the memory cell holes are filled with polysilicon to form the fuse 103B.
- the current control element 112, the contact plug 117 and the second wiring 119 are formed as in the first embodiment.
- the nonvolatile memory element and the semiconductor memory device of the present invention are capable of high-speed operation and have stable rewriting characteristics, and are used in various electronic devices such as digital home appliances, memory cards, portable telephones, and personal computers. It is useful as a nonvolatile memory element and a semiconductor memory device to be used.
- Non-volatile memory element (memory cell) DESCRIPTION OF SYMBOLS 100 Board
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Abstract
Description
[概略構成]
図1は、本発明の第1の実施の形態における不揮発性半導体記憶装置10を示す概略回路図である。図2は、図1に示す不揮発性半導体記憶装置10の平面視における構成を示す概略平面図である。さらに、図3は、図1に示す不揮発性半導体記憶装置10の断面視における構成を示す図であって、図2に示すIII-III線に沿って切断したときの断面を示す概略断面図である。
本実施形態における抵抗変化素子105の抵抗変化層107は、酸素不足型の遷移金属酸化物(化学量論的な酸化物と比較して酸素の含有量[原子比:総原子数に占める酸素原子数の割合]が少ない遷移金属酸化物)を含む。好ましくは、抵抗変化層107は、タンタルの酸素不足型酸化物(TaOx:0<x<2.5)またはハフニウムの酸素不足型酸化物(HfOx:0<x<2)で構成される遷移金属酸化物を含む。より好ましくは、抵抗変化層107は、タンタルの酸素不足型酸化物またはハフニウムの酸素不足型酸化物のみで構成される。これらの抵抗変化層は、可逆的に安定した抵抗値の切り換え特性を示す。
本実施の形態においては、前述のように、極性の異なる電圧パルスで抵抗変化素子105の抵抗値を切り換える。したがって、不揮発性記憶素子11にはいずれの方向にも電流が流れる必要があり、双方向の電流制御素子112が適用される。電流制御素子112は、非線形の電流-電圧特性を有する素子であり、印加電圧の絶対値が臨界電圧未満では抵抗値が大きく(オフ状態)、印加電圧の絶対値が臨界電圧以上では抵抗値が極端に小さくなる(オン状態)素子である。
以下では、抵抗変化層107としてタンタルの酸素不足型酸化物(膜厚:約30nm)を用いた抵抗変化素子105と半導体層114として窒素不足型窒化シリコンを用いた電流制御素子112を直列接続したときの特性について説明する。図4は本実施の形態の電流制御素子における抵抗変化による特性を示す図であって、図4(a)は電圧パルスを印加した場合における抵抗値の変化を示したグラフ、図4(b)は抵抗変化の電流-電圧特性の一例を示したグラフである。
図5は、本実施の形態の不揮発性記憶素子における不良時の電流-電圧特性およびヒューズにおける負荷特性を示す図である。図5(a)は、故障時の電流-電圧特性を示すグラフを部分的に拡大したものであり、図5(b)は、ヒューズの負荷特性を示すグラフである。
ヒューズ103は、前述の通り、不揮発性記憶素子11の動作電流で溶断されず、所定の電流値以上の電流が流れることによって溶断されるように設計されている。ヒューズ103の溶断され易さは、以下の式によって示される平均故障時間MTBF(Mean-Time-Between-Failure)によって予測することができる。
ただし、Kは定数、Jは電流密度、nは一般に1.0~5.0の値、Eaは活性化エネルギー、kはボルツマン定数、Tは絶対温度である。この式に示されるように、電流密度Jがより高くなるということは、MTBFがより短くなることを意味する。よって、電流密度Jが高くなるほど、ヒューズ103は溶断し易くなる。
図6~図10は、本実施の形態における半導体記憶装置の製造方法を示す工程図である。図6(a)は基板上に第1の配線を形成する工程を示す図であり、図6(b)~図8(h)は第1の層間絶縁層と第1のコンタクトプラグであるヒューズを形成する工程を示す図であり、図8(i)は抵抗変化素子を形成する工程を示す図であり、図9(j)は第2の層間絶縁層と第2のコンタクトプラグを形成する工程を示す図であり、図9(k)は電流制御素子を形成する工程を示す図であり、図9(l)は第3の層間絶縁層と第3のコンタクトプラグと第3のコンタクトプラグとを形成する工程を示す図であり、図10(m)は第4のコンタクトプラグを形成する工程を示す図であり、図10(n)は第2の配線と引き出し配線とを形成する工程を示す図である。
図11は、本発明の第2の実施の形態における半導体記憶装置20を示す概略断面図である。本実施の形態における半導体記憶装置20が第1の実施の形態の半導体記憶装置10と異なる点は、ヒューズ103Bが抵抗変化素子105と電流制御素子112との間に位置していることである。すなわち、本実施の形態におけるヒューズ103Bは、第1の実施の形態における第2のコンタクトプラグとして機能する。さらに、本実施の形態における半導体記憶装置20は、上記第1の実施の形態における第1のコンタクトプラグが存在せず、抵抗変化素子105の下部電極106が第1の配線101に直接接続されている。
11 不揮発性記憶素子(メモリセル)
100 基板
101 第1の配線
102 第1の層間絶縁層
102B 下部層間絶縁層
103 ヒューズ(第1のコンタクトプラグ)
103B ヒューズ(第2のコンタクトプラグ)
103a 第1ポリシリコン層
103b 第2ポリシリコン層
103c サイドウォール
103d 第3ポリシリコン層
104 フォトレジストエッチングマスク
105 抵抗変化素子
106 抵抗変化素子の下部電極(第1の電極)
107 抵抗変化層
108 抵抗変化素子の上部電極(第2の電極)
109 第2の層間絶縁層
110 第2のコンタクトプラグ
112 電流制御素子
113 電流制御素子の下部電極(第3の電極)
114 半導体層
115 電流制御素子の上部電極(第4の電極)
116 第3の層間絶縁層
116B 上部層間絶縁層
117 第3のコンタクトプラグ
118 第4のコンタクトプラグ
119 第2の配線
120 引き出し配線
Claims (7)
- 非線形の電流-電圧特性を有する電流制御素子と、印加される電圧パルスに基づいて低抵抗状態と当該低抵抗状態より抵抗値が高い高抵抗状態との間を可逆的に遷移する抵抗変化素子と、ヒューズとを備え、前記電流制御素子、前記抵抗変化素子及び前記ヒューズが直列接続され、前記ヒューズは、前記電流制御素子が実質的に短絡状態となったときに断絶するよう構成されている、不揮発性記憶素子。
- 前記電流制御素子、前記抵抗変化素子および前記ヒューズは、互いに交差する第1の配線と第2の配線との立体交差部に互いに直列に接続されて形成されることにより、クロスポイント型の不揮発性記憶素子を構成する、請求項1に記載の不揮発性記憶素子。
- 前記ヒューズは、前記抵抗変化素子の低抵抗状態における抵抗値より小さい抵抗値を有している、請求項1に記載の不揮発性記憶素子。
- 前記ヒューズは、5kΩ以下の抵抗値を有している、請求項3に記載の不揮発性記憶素子。
- 前記ヒューズは、ポリシリコンで構成されている、請求項1に記載の不揮発性記憶素子。
- 基板と、
前記基板上に互いに平行に配設された複数の第1の配線と、前記複数の第1の配線の上方に前記基板の主面に平行な面内において互いに平行に且つ前記複数の第1の配線に立体交差するように形成された複数の第2の配線と、前記複数の第1の配線と前記複数の第2の配線との立体交差部のそれぞれに対応して前記第1の配線と前記第2の配線とを接続するように設けられた複数の、請求項1に記載された不揮発性記憶素子を有する不揮発性記憶素子アレイと、
を備えた、半導体記憶装置。 - 前記抵抗変化素子は、第1の電極と、第2の電極と、前記第1の電極と前記第2の電極とに挟まれた抵抗変化層とを備え、
前記電流制御素子は、第3の電極と、第4の電極と、前記第3の電極と前記第4の電極とに挟まれた絶縁体層または半導体層とを備え、
前記不揮発性記憶素子は、前記第1の配線と前記抵抗変化素子の前記第1の電極との間、前記抵抗変化素子の前記第2の電極と前記電流制御素子の前記第3の電極との間、および前記電流制御素子の前記第4の電極と前記第2の配線との間の少なくともいずれか1つに、互いを導通するコンタクトプラグを備えており、
前記ヒューズは、前記コンタクトプラグのうち、いずれか1つのコンタクトプラグとして構成されている、請求項6に記載の半導体記憶装置。
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