Source: https://patents.google.com/patent/KR101335383B1/en
Timestamp: 2020-01-25 20:04:08
Document Index: 763675340

Matched Legal Cases: ['Application No. 10', 'Application No. 11', 'Application No. 11', 'Application No. 11', 'application no. 10', 'Application No. 10', 'Application No. 10', 'Application No. 10']

KR101335383B1 - Nonvolatile memory cell comprising a diode and a resistance―switching material - Google Patents
Nonvolatile memory cell comprising a diode and a resistance―switching material Download PDF
KR101335383B1
KR101335383B1 KR1020077027841A KR20077027841A KR101335383B1 KR 101335383 B1 KR101335383 B1 KR 101335383B1 KR 1020077027841 A KR1020077027841 A KR 1020077027841A KR 20077027841 A KR20077027841 A KR 20077027841A KR 101335383 B1 KR101335383 B1 KR 101335383B1
KR1020077027841A
KR20080031668A (en
2005-05-09 Priority to US11/125,939 priority Critical
2005-05-09 Priority to US11/125,939 priority patent/US20060250836A1/en
2006-03-31 Priority to US11/395,995 priority
2008-04-10 Publication of KR20080031668A publication Critical patent/KR20080031668A/en
2013-12-03 Publication of KR101335383B1 publication Critical patent/KR101335383B1/en
In a novel nonvolatile memory cell formed on a substrate, the diode is a reversible resistance-switching material, preferably Ni x O y , Nb x O y , Ti x O y , Hf x O y , Al x O y , Mg x O Metal oxides or nitrides such as y , Co x O y , Cr x O y , V x O y , Zn x O y , Zr x O y , B x N y and Al x N y are composed in pairs. In preferred embodiments, the diode is formed as a vertical filler disposed between the conductors. Multiple memory levels can be stacked to form a monolithic three dimensional memory array. In some embodiments, the diode may use aluminum or copper in the conductors, including germanium or germanium alloys, which may be deposited and crystallized at relatively low temperatures. The memory cells of the present invention can be used as rewritable memory cells or one-time programmable memory cells and can store two or more data states.
NONVOLATILE MEMORY CELL COMPRISING A DIODE AND A RESISTANCE--SWITCHING MATERIAL}
The present invention relates to a rewritable nonvolatile memory array in which each cell comprises a diode and a resistance-switching element connected in series with each other.
Resistance-switching materials are known that can be reversibly switched between high and low resistance states. These two stable resistance states have made the resistance-switching material an attractive material for use in a rewritable nonvolatile memory array. However, it is very difficult to form large, high density cell arrays due to the risk of failure between cells, high leakage current, and numerous manufacturing problems.
Accordingly, there is a need for a large-scale rewritable nonvolatile memory array using resistance-switching elements that can be easily manufactured and reliably programmed.
The invention is defined by the claims and the description set forth in this paragraph is not intended to limit the invention. In general, the present invention provides a nonvolatile memory cell comprising a diode and a resistance-switching material.
A first aspect of the invention is a diode; And a resistance-switching element comprising a layer of resistance-switching metal oxide or nitride compound, the metal oxide or nitride compound comprising only one metal, wherein the diode and resistance-switching element are part of the memory cell. To provide a nonvolatile memory cell.
Another aspect of the invention provides a first plurality of substantially parallel substantially coplanar conductors extending in a first direction; A first plurality of diodes; First plurality of resistance-switching elements; And a second plurality of substantially parallel substantially coplanar conductors extending in a second direction different from said first direction, wherein in each memory cell, one of said first diodes and said first resistor- One of the switching elements is arranged in series, and is formed between one of the first conductors and one of the second conductors; The first plurality of resistance-switching elements include Ni x O y , Nb x O y , Ti x O y , Hf x O y , Al x O y , Mg x O y , Co x O y , Cr x O y A plurality of nonvolatile memory cells are provided, comprising a layer of material selected from the group consisting of V x O y , Zn x O y , Zr x O y , B x N y and Al x N y .
A preferred embodiment of the present invention comprises a) a first memory level formed over a substrate and comprising a first plurality of memory cells, each memory cell of the first memory level being a resistive-switching metal oxide or nitride compound. A resistive-switching element comprising a layer of the metal oxide or nitride having only one metal; And b) at least a second memory level monolithically formed above said first memory level.
Another aspect of the present invention is a method for forming a plurality of nonvolatile memory cells, comprising: forming a first plurality of substantially parallel, substantially coplanar conductors; Forming a first plurality of diodes over the plurality of first conductors; Forming a first plurality of resistance-switching elements; And forming a second plurality of substantially parallel substantially coplanar conductors over the first diodes, wherein the first resistance-switching element comprises Ni x O y , Nb x O y , Ti x O y , Hf x O y , Al x O y , Mg x O y , Co x O y , Cr x O y , V x O y , Zn x O y , Zr x O y , B x N y and Al x N A method of forming a plurality of nonvolatile memory cells, comprising a material selected from the group consisting of y .
Another preferred embodiment of the present invention is a method of forming a monolithic three-dimensional memory array, comprising: a) i) a first step of forming a first plurality of diodes and ii) Ni x O y , Nb x O y , Ti x O y , Hf x O y , Al x O y , Mg x O y , Co x O y , Cr x O y , V x O y , Zn x O y , Zr x O y , B x N y and Al a second step of forming a first plurality of resistance-switching elements comprising a material selected from the group consisting of x N y , wherein a second of each of the first diodes is arranged in series with one of the resistance-switching elements Forming a first memory level on a substrate by a method comprising the step of; And b) monolithically forming at least a second memory level over said first memory level and said substrate.
A related embodiment is a method for forming a monolithic three dimensional memory array, comprising: forming a first plurality of substantially parallel, substantially coplanar conductors formed on a substrate at a first height and extending in a first direction ; Forming a second plurality of substantially parallel, substantially coplanar conductors formed to a second height higher than the first height and extending in a second direction different from the first direction; Ni x O y , Nb x O y , Ti x O y , Hf x O y , Al x O y , Mg x O y , Co x O y , Cr x O y , V x O y , Zn x O y , Forming a first plurality of resistance-switching elements comprising a material selected from the group consisting of Zr x O y , B x N y and Al x N y ; Forming a first plurality of diodes, wherein the first diodes and the first resistive switching elements are disposed above the first height and below the second height; Forming second diodes over the second conductors; And forming third conductors over the second conductors.
Yet another embodiment is a method for forming a nonvolatile memory cell, comprising: forming a first conductor; Forming a second conductor; Forming a resistance-switching element; And forming a diode, wherein the diode and the resistance-switching element are electrically formed in series between the first conductor and the second conductor, and the first and second conductors, the diode and the switching element. A method of forming a monolithic three dimensional memory array, wherein the temperature during formation and crystallization of the diode does not exceed about 500 ° C.
Another preferred embodiment of the invention is a method of forming a monolithic three dimensional memory array, comprising: a) a first memory level comprising a plurality of first memory cells each comprising a) a) a resistance-switching element and b) a diode; Forming over the substrate, wherein the temperature during formation of the first memory level does not exceed about 475 ° C .; And ii) monolithically forming at least a second memory level above the first memory level.
Aspects of the present invention include a diode comprising a semiconductor material that is germanium or a germanium alloy; And a resistance-switching element. A related embodiment includes a first memory level formed over a substrate and comprising a plurality of first memory cells each comprising a diode comprising a) a) a resistance-switching element and b) a semiconductor material that is germanium or a germanium alloy; And ii) at least a second memory level monolithically formed above said first memory level.
Yet another embodiment is a monolithic three dimensional memory array, comprising: i) a first memory level formed over a substrate, the first memory level comprising a plurality of first memory cells, each first memory cell being formed over the substrate; A first lower conductor comprising a layer of aluminum, an aluminum alloy, or copper, a resistance-switching element, and a diode formed over the first lower conductor; And ii) at least a second memory level monolithically formed above said first memory level.
Another aspect of the invention is a method of programming a memory cell of a memory array comprising a resistive-switching layer of a metal oxide or nitride compound comprising exactly one metal, the second programmed resistive state from the first resistive state. Programming the memory cell by changing the resistance-switching layer with; The second programmed resistance state provides a memory cell programming method for storing a data state of the memory cell.
A related aspect of the invention includes a diode comprising a polycrystalline semiconductor material and a resistance-switching layer of a metal oxide or nitride compound comprising exactly one metal, wherein the resistance-switching layer and the diode are electrically arranged in series. A method of programming and sensing memory cells in a memory array, the method comprising: i) applying a first programming pulse to the memory cell, the first programming pulse comprising: a) a first resistor of the resistor-switching layer; Change the state detectably, or b) detectably change the second resistance state of the polycrystalline semiconductor material, or c) detectably change the first resistance state of the resistance-switching layer and Detectably varying a second resistance state of; And ii) reading the memory cell, wherein the first resistive state of the resistive switching layer is used for storing data, and the second resistive state of the polycrystalline semiconductor material is used for storing data, A memory cell programming and sensing method is provided.
1 shows a perspective view showing a possible memory cell with a resistance-switching material inserted between conductors.
Figure 2 shows a perspective view of a rewritable nonvolatile memory cell formed in accordance with the present invention.
FIG. 3 shows a perspective view showing a memory level including cells such as those shown in FIG. 2.
4 shows an I-V curve showing the low resistance vs. high resistance and high resistance vs. low resistance transitions of the omnidirectional resistance-switching material.
FIG. 5A shows an I-V curve showing the low resistance to high resistance transition of the directional resistance-switching material and FIG. 5B shows an I-V curve showing the high resistance to low resistance transition of the directional resistance-switching material.
6 shows a perspective view of a vertically oriented p-i-n diode in some embodiments of the invention.
Figure 7 shows a perspective view of a vertically oriented zener diode in other embodiments of the present invention.
FIG. 8 shows the I-V curve of the p-i-n diode of FIG. 6.
FIG. 9 shows the I-V curve of a zener diode such as the diode of FIG. 7.
10 shows a perspective view of an embodiment of the present invention in which a resistance-switching material is sandwiched between rare metal layers.
FIG. 11A shows a cross-sectional view illustrating an embodiment of the invention in which the resistance-switching material is not patterned and is not etched, and FIG. 11B is a perspective view of a preferred embodiment of the invention in which the resistance-switching material is patterned and etched with the upper conductor. Shows.
Figure 12 shows a graph depicting current versus voltage for four different data states of a memory cell in an embodiment of the invention.
13A-13C illustrate cross-sectional views illustrating stages of formation of memory levels of a monolithic three dimensional memory array formed in accordance with a preferred embodiment of the present invention.
Figure 14 shows a cross-sectional view illustrating a portion of a monolithic three dimensional memory array formed in accordance with a preferred embodiment of the present invention.
Figure 15 illustrates a cross-sectional view illustrating a portion of a monolithic three dimensional memory array formed in accordance with another preferred embodiment of the present invention.
16A-16C illustrate cross-sectional views illustrating stages of formation of memory levels of a monolithic three dimensional memory array formed in accordance with another preferred embodiment of the present invention.
Various materials exhibit reversible resistance-switching properties. These materials include chalcogenides, carbon polymers, perovskites, and any metal oxides and nitrides. In particular, Pagnia and Sotnick in "Bistable Switching in Electroformed Metal-Insulator-Metal Device," Phys. Stat. Sol. As disclosed in (A), 108, 11-65 (1988), there are metal oxides and nitrides comprising only one metal and having reliable resistance switch properties. Such groups include, for example, Ni x O y , Nb x O y , Ti x O y , Hf x O y , Al x O y , Mg x O y , Co x O y , Cr x O y , V x O y , Zn x O y , Zr x O y , B x N y and Al x N y , where x and y are 0 and 1. Examples are stoichiometric compounds NiO, Nb 2 O 5 , TiO 2 , HfO 2 , Al 2 O 3 , MgO, CoO, CrO 2 , VO, ZnO, ZrO, BN, and AlN, but non stoichiometric compounds may also be used. Can be. The layer made of one of these materials may be formed in an initial state, such as a low resistance state. Upon application of sufficient voltage, the material is switched to a stable high resistance state. Such resistance switching is reversible, and the next application of an appropriate current or voltage can be used to return the resistance-switching material to a stable low resistance state. This conversion can be repeated many times. For some materials, the initial state is high resistance rather than low resistance. When this discussion refers to "resistive switching material", "resistive switching metal oxide and nitride", "resistive switching memory element", or similar terms, it should be understood that they mean reversible resistive-switching materials.
Thus, these resistance-switching materials are suitable for use in nonvolatile memory arrays. One resistance state corresponds, for example, to data "0", while the other resistance state corresponds to data "1". Some of these materials may have two or more stable resistance states, and in fact some materials may achieve some of a number of data states.
In order to make memory cells using these materials, the difference in resistance between the high and low resistance states must be large enough to facilitate detection. For example, the resistance of the material in the high resistance state should be at least three times the resistance of the material in the low resistance state. When this discussion refers to "resistance-switching material", "resistance-switching metal oxide or nitride", "resistance-switching memory element" or similar terms, the difference between low and high resistance or low resistance states or high resistance states. Is at least 1/3.
However, there are many obstacles to using these resistance-switching materials in large-scale nonvolatile memory arrays. One possible structure is the formation of a plurality of memory cells shown in FIG. 1, which are cross-pointed between the conductors, for example between the upper conductor 4 and the lower conductor 6. point) resistor-switching memory elements 2 (including one of the resistor-switching materials) disposed in an array. The resistance-switching memory element 2 is programmed by applying a voltage between the upper conductor 4 and the lower conductor 6.
In a large array of cells arranged in a cross-point array, many cells will be addressed by the same top conductor or bottom conductor. When a relatively large voltage or current is required, there is a risk of exposing the cell and the upper or lower conductors to be addressed to sufficient voltage or current causing unwanted resistive switching in half-selected cells. According to the biasing scheme used, excess leakage current flowing through unselected cells may be of interest.
In the present invention, a diode is paired with a resistor-switching material to form a rewritable nonvolatile memory cell that can be formed and programmed into a large, high density array. Using the methods described herein, such arrays can be manufactured and programmed reliably.
Although many embodiments are possible and the choices described are described, a simple version of a memory cell formed in accordance with the present invention is shown in FIG. The cell comprises a conductive material, such as a heavily doped semiconductor material, conductive silicide, or lower conductor 200, preferably comprising a metal such as tungsten, aluminum or copper. On top of this is formed an upper conductor 400, which may be the same material as the lower conductor. The upper and lower conductors of the rail-shape ("rail-shape" in the present invention means a shape that is rectangular in cross section and extends in the longitudinal direction) preferably extend in different directions, for example vertical. The conductors may include a conductive barrier or adhesive layers if desired. Between the upper conductor 400 and the lower conductor 200 is arranged a diode 30 and a resistance-switching element 118 connected in series. Other layers, such as barrier layers, may be included between the conductors 200, 400. The resistance-switching element 118 transitions from a low resistance state to a high resistance state or optionally high resistance upon application of a voltage across the resistance-switching element 118 or when current flows into the resistance-switching element 118. The state is switched from the state to the low resistance state. The transition from low resistance to high resistance is reversible.
Diode 30 acts as a one-way valve that allows current to flow in one direction rather than in several directions. Below the threshold "turn-on" voltage in the forward direction, the diode 30 flows little or no current. By using appropriate biasing schemes, when an individual cell is selected for programming, the diodes of adjacent cells are reversed in turn or on the diode's turn-on voltage when the voltage across the unselected or half selected cells is supplied in the forward direction. As long as it does not exceed the reverse breakdown voltage when supplied, it can be used to electrically insulate the resistive-switching elements of these cells and prevent unintended programming.
Multiple upper and lower conductors can be fabricated with intermediate diodes and resistive switching elements to form a first memory level, some of which are shown in FIG. 3. In preferred embodiments, additional memory levels may be formed to be stacked over this first memory level and may form a high density monolithic three dimensional memory array. The memory array is formed of layers deposited and grown on a substrate, such as a single crystal silicon substrate. A support circuit is advantageously formed in the substrate under the memory array.
An advantageous method for forming a reliably manufacturable high density nonvolatile one-time programmable memory array is disclosed in US Application No. 10 / 326,470 (hereinafter referred to as the '470 application) by Herner et al. Incorporated by reference. Related memory arrays and their uses and fabrication methods are described in US patent application Ser. No. 4, filed Sep. 29, 2004, entitled "Dielectric Antifuse-Free Nonvolatile Memory Cells with High and Low Impedance States." 10 / 955,549 (hereinafter referred to as the '549 application); US Patent Application No. 11 / 015,824, hereafter referred to as the '824 application, filed Dec. 17, 2004, entitled “Non-Volatile Memory Cells Containing Vertical Diodes with Reduced Height”; And US patent application Ser. No. 10 / 954,577 (hereinafter referred to as the '577 application) filed on September 29, 2004, entitled "junction diode comprising variable semiconductor compositions", these applications All are assigned to the assignee of the present invention and incorporated herein by reference. The methods disclosed in these integrated applications will be useful for fabricating a memory array in accordance with the present invention.
Preferred embodiments include several important variations. In general, the properties of the selected resistance-switching material, and the manner in which the memory cells are intended to be used, will determine which embodiments are most advantageous.
Omni-directional vs. directional switching: In general, resistance-switching metal oxides and nitrides have one of two general kinds of switching characteristics. Referring to the IV curve of FIG. 4, some of these materials have a low resistance state in area A on the graph. Current flows with respect to the supplied voltage until the first voltage V 1 is reached. At voltage V 1 , the resistance-switching material transitions to the high resistance state shown in region B and a reduced current flows. At any critical high voltage V 2 , the material switches back to the initial low resistance state and an increased current flows. Arrows indicate state change information. This conversion is repeatable. For these materials, the direction of current flow and voltage bias is not critical and therefore these materials will be referred to as non-directional materials. The voltage V 1 may be referred to as a reset voltage, while the voltage V 2 may be referred to as a set voltage.
On the other hand, other materials of resistance-switching materials act as shown in FIGS. 5A and 5B and will be referred to as directional materials. The directional resistance-switching materials can be formed in the low resistance state shown in region A of FIG. 5A. Current flows with respect to the supplied voltage until the first voltage V 1 , that is, the reset voltage is reached. At voltage V 1 , the directional resistance-switching material transitions to the high resistance state shown in region B of FIG. 5A. However, in order to switch the directional resistance-switching material back to the low resistance state, a reverse voltage must be applied. As shown in FIG. 5B, the directional resistance-switching material is the high resistance of the region B at a negative voltage up to the threshold reverse voltage V 2 , ie the set voltage. At this voltage, the directional resistance-switching material returns to the low resistance state. The arrows indicate the degree of state change (some materials are initially formed in a high resistance state, the switching operation is the same and only one initial state is described for simplicity).
In preferred embodiments, the omnidirectional resistance-switching materials can be paired with a substantially unidirectional diode. One such diode is the pin diode shown in FIG. Preferred pin diodes are formed of a semiconductor material, such as silicon, and are heavily doped bottom regions 12 having a first conductivity type, unintentionally doped intermediate intrinsic regions 14, and opposing first conductivity types. A heavily doped upper region 16 having a two conductivity type. In the pin diode of FIG. 6, the lower region 12 is n-type while the upper region 16 is p-type and the polarity can be reversed if desired. A region of intrinsic semiconductor material, such as region 14, is never completely electrical neutral while inadvertently doped. In many manufacturing processes, the defects of deposited intrinsic silicon cause this material to act as a lightly doped n-type. In some embodiments, it is desirable to lightly dope this region. Upon application of the voltage, this diode is shown by the IV curve of FIG. At very low voltages a small current or no current flows. At the threshold voltage V 3 , the turn-on voltage of the diode, a significant forward current begins to flow in the diode. When a low and medium reverse voltage is supplied to the diode, small current or no current flows as in region D of FIG. 8, and the diode acts as a unidirectional valve.
However, upon application of a very high reverse voltage V 4 , the diode will experience avalanche breakdown and reverse current will begin to flow. These results can destroy diodes even though they are not ideal. Recall that the set and reset voltages of non-directional resistive switching material require only one direction of current. Thus, the pin diode of FIG. 6 can be paired with an omnidirectional resistance-switching material.
However, as described in the IV curves of FIGS. 5A and 5B, the directional resistance-switching materials must be exposed to forward and reverse currents for successful switching. The low to high resistance transition shown in FIG. 5B requires a reverse current (at voltage V 2 ). Reverse current is generally only performed in unidirectional diodes at a reverse breakdown voltage (voltage V 4 in FIG. 8) which is relatively high, for example at least 9 volts.
Thus, the directional resistance-switching materials cannot advantageously be paired with a unidirectional diode. Instead, these materials can be paired with a reversible biomechanical device, ie a device that allows current to flow in either direction. One such device is a Zener diode. A typical zener diode is shown in FIG. It will be appreciated that this diode has a first heavily doped region 12 of the first conductivity type and a second heavily doped region 16 of the opposite conductivity type. The polarity can be reversed. In the zener diode of FIG. 7, no intrinsic region exists, and in some embodiments, an ultrathin intrinsic region may exist. 9 shows the IV curve of a Zener diode. Zener diodes behave like pin diodes under forward bias with turn-on voltage V 3 . However, under reverse voltage bias, once threshold voltage V 4 is reached, the zener diode will allow reverse current to flow. In the Zener diode, the threshold reverse voltage V 4 is substantially lower than the size of the unidirectional diode. This controllable reverse current at an intermediate voltage causes the directional resistance-switching material to switch from a high resistance state to a low resistance state as initially described and shown in FIG. 5B (at voltage V 2 ). Thus, in embodiments of the present invention using directional resistance-switching materials, Zener diodes are preferred (indeed, the distinction between pin diodes and Zener diodes with very small intrinsic regions is easily made by artisans or those skilled in the art).
Non-directional materials do not require current in the forward and reverse directions, but resistance-switching can be achieved in either direction as described. For any circuit arrangement, it may be desirable to pair the zener diode with a non-directional resistance-switching material.
The term junction diode is used herein to refer to a semiconductor device formed of a semiconductor material having a non-ohm conducting property, having two terminal electrodes, one electrode being a p-type and the other electrode being an n-type electrode. Examples include pn diodes and np diodes with p-type semiconductor material and n-type semiconductor material, such as zener diodes, and intrinsic (non-doped) semiconductor material between p-type semiconductor material and n-type semiconductor material. It includes pin diodes inserted into it.
High Current Requirements: In order to reset the resistance-switching material to switch from the high resistance state to the low resistance state in non-directional resistance-switching materials, a relatively high current may be required for any materials. For these materials, it may be desirable for the diode to be germanium or a germanium alloy, which provides a high current at a given voltage compared to silicon.
Rare Metal Contacts and Low Temperature Fabrication: For some of the metal oxides and nitrides mentioned earlier, resistive switching is more likely when the resistive-switching element is sandwiched between rare metal materials, which may be formed of Ir, Pt, Pd or Au, for example. Can be easily achieved. An example of a cell according to the invention in which rare metal contacts are used is shown in FIG. 10. The resistance-switching element 118 is between the rare metal layers 117 and 119.
However, the use of rare metals causes problems. When exposed to high temperatures, rare metals tend to diffuse at high speeds and can damage other parts of the device. For example, in FIG. 10, the rare metal layer 117 is adjacent to the semiconductor diode 30. Wide diffusion of rare metals into the semiconductor material of diodes 30 will impair device performance. When the resistance-switching element is formed between the rare metal metal contacts, it is advantageous to minimize the processing temperatures. The diode can be silicon, germanium or a silicon-germanium alloy. Germanium may crystallize at a lower temperature than silicon, and as the germanium content of the silicon-germanium alloy increases, the crystallization temperature decreases. Diodes formed of germanium or germanium alloys may be desirable when rare metal contacts are used.
Conventional deposition and crystallization temperatures of polycrystalline silicon (polycrystalline silicon in this discussion will be referred to as polysilicon, while polycrystalline germanium will be referred to as polygermanium) are relatively high and are incompatible with any metals with relatively low melting points. Conventionally formed polysilicon diodes. For example, aluminum wires begin to soften and extrude when exposed to temperatures above about 475 ° C. For this reason, it is desirable to use tungsten for conductors in many embodiments of the '470,' 549 and '824 applications because tungsten wiring can withstand high temperatures. However, if germanium or germanium alloys are used, the low deposition and crystallization temperatures of germanium make it possible to use aluminum or copper in the conductors, such as the conductors 200, 400 of FIG. 10. These metals have a low sheet resistance and are therefore generally preferred if the thermal budget allows their use, although tungsten or any other conductive material may be used. The techniques disclosed in US patent application Ser. No. 11 / 125,606, entitled "High Density Non-Volatile Memory Arrays Fabricated at Low Temperature and Including Semiconductor Diodes," may be applicable when low temperature is desired, which application is hereby incorporated by reference. It is incorporated as and relates to low temperature manufacturing.
Conductivity and Insulation: It is described that a diode is included in each memory cell to provide electrical isolation between adjacent cells for programming large arrays. Some resistance-switching materials are deposited in a high resistance state, while others are deposited in a low resistance state. With regard to resistive-switching materials deposited in high resistance states, the transition to low resistance states is generally a local phenomenon. For example, referring to FIG. 11A, a rail-shaped lower conductor 200, a diode 30, and a resistance-switching material layer formed in a high resistance state in which a memory cell (shown in cross section) extends from left to right of a page ( 118), and rail-shaped upper conductor 400 extending outwardly of the page. In this case, layer 118 of resistance-switching material is formed as a blanket layer. As long as the high resistance state of the resistive-switching material layer 118 is high enough, the layer 118 may short the conductor 400 with adjacent conductors or the diode 30 with the adjacent diodes. Will not provide a challenging path unless. When the resistive-switching material layer 118 is exposed to high voltage and transitions to a low resistance-state, only the region of the layer 118 immediately adjacent to the diode is expected to be switched, for example after programming of the layer 118 The formation region will be low resistance and the non-shaded region will maintain high resistance. The shaded areas are resistance-switching elements disposed within the continuous layer 118 of resistance-switching material.
However, according to the read, set and reset voltages, for any resistance-switching materials, the high resistance state of the resistance-switching material may be too challenging for reliable insulation and adjacent when formed in a continuous layer as in FIG. 11A. There will be a tendency to short the conductors and diodes. For other resistance-switching materials, a) leave unpatterned resistance-switching material 118 as in the apparatus of FIG. 11A or b) resistance-switching material 118 with upper or lower conductors as in the apparatus of FIG. 11B. Or c) patterning the resistance-switching material 118 with diode 30 as in the apparatus of FIGS. 2 and 10.
When the memory element is formed of a resistance-switching material formed in a low resistance state, the memory element must be separated from the resistance-switching memory element of adjacent cells to prevent the formation of unwanted conductive paths between adjacent cells.
United States Patent Application No. 11 / 148,530 (hereafter filed on June 8, 2005 and incorporated herein by reference) under the name '549 application and " non-volatile memory cell operating by increasing order in polycrystalline semiconductor material " With respect to polycrystalline semiconductor diodes formed according to the methods described herein in detail, as described in the '530 Application), in some embodiments the polycrystals of the diode are formed in an initial high resistance state and applied with a sufficiently high voltage It can be expected to switch permanently to a low resistance state at time. Thus, referring to the cell of FIG. 2, when such a cell is initially formed, the polysilicon and the reversible resistance-switching element 118 of the diode 30 are formed in a high resistance state.
Upon first application of the programming voltage, the polysilicon and resistance-switching element 118 of diode 30 will transition to a low resistance state. In general, the switching of diode 30 is permanent while the switching of resistance-switching element 118 is reversible. It is desirable to carry out the initial conversion of polysilicon of the diodes from high resistance to low resistance in factory conditions, ie to effectively "precondition" the diode.
Optionally, US patent application Ser. No. 10 / 954,510, filed on September 29, 2004, entitled “Memory Cells Containing Crystalline Semiconductor Junction Diodes Adjacent to Silicide,” is in a low resistance state as formed. A method of forming a polycrystalline semiconductor diode is described, which application is assigned to the assignee of the present invention and incorporated herein by reference. In preferred embodiments of the '510 application, the semiconductor material of the diode, preferably silicon, is crystallized adjacent to the silicide layer, such as TiSi 2 . The silicide layer provides a crystallization template for silicon when crystallized and thus produces a high crystal diode with few crystal defects. Such techniques can be used in the present invention. If the diode is germanium, the germanium diode is crystallized adjacent to a germanide layer, such as TiGe 2 , which provides a similar crystallization template for germanium. The germanium of such a diode would be a low resistance created without the need for a "programming" step to create a low resistance path through the diode.
One-Time Programmable Memory Cells: Two-State
Diodes paired with a resistor-switching element have been described in embodiments of the invention when used as a rewritable memory cell. These elements can be used in alternative embodiments to form a one-time programmable memory cell.
For some of the resistive-switching binary metal oxides or nitrides that can switch between the nickel oxide or low and high resistance states, the reset switching from the low resistance state to the high resistance state has proved more difficult ( It is to be understood that "nickel oxide" in this discussion may be referred to as stoichiometric NiO or nonstoichiometric compounds). While the actual switching mechanism is not obvious, any voltage must be supplied to the resistance-switching layer so that the resistance-switching layer is switched. If the set state of the material is very low-resistance and the material has high conductivity, it is difficult to establish sufficient voltage for the switching to take place. By using the memory cell of the present invention as a one-time programmable cell, more difficult switching can be prevented. This generally simplifies the programming circuit.
One preferred resistance-switching material, ie nickel oxide, is omnidirectional, meaning that the material switches alone when a positive or negative voltage is applied. In some embodiments, it has been found that the reset of the nickel oxide layer when paired with a diode is easier to achieve with the diode under reverse bias. Extra transistors may be required in the substrate to provide negative voltages to the diodes as reverse bias. These transistors consume substrate space and thus make the device more expensive, and the formation of these transistors can add process complexity. Thus, in embodiments where reverse bias is required for reset, preventing the reset using the cell as a write cell once prevents the difficulty of generating a negative voltage.
In the simplest way of using a memory cell comprising a diode and a resistance-switching layer according to the invention as a one-time programmable memory cell, the cell has two values (programming) corresponding to two separate read currents through the cell. Unprogrammed values and programmed values).
The set voltage will vary depending on the material used for the resistance-switching element, the thickness of the layer, the properties of the material and other factors. Increasing the pulse time may reduce the voltage required to set the material from high resistance to low resistance. The set voltage can vary, for example, from 4 volts to 10 volts.
As mentioned earlier, if the diode is formed of polysilicon, crystallization of polysilicon adjacent to the silicide having a lattice structure in the direction providing a good crystallization template for silicon will result in low defect low resistance polysilicon, Crystallization adjacent to only materials with poor lattice matches, such as titanium nitride, will produce high-defect high-resistance polysilicon. If the diode is formed of higher resistive polysilicon, the application of an appropriate programming voltage to the diode converts the polysilicon into a low resistance state, thus leaving a diode with good rectification.
In addition, in some embodiments, some of the resistance-switching metal oxides or nitrides formed in the initial high resistance state may require a shaped pulse to achieve the first switching from high resistance to low resistance. Such shaped pulses may require higher voltages for low to high resistance or high to low resistance switching. For example, the shaping pulse is about 8.5-9 volts and the next set pulses are 6.5-7 volts.
As described in US Patent Application No. 11 / 287,452 to Herner et al., Filed Nov. 23, 2005, entitled " Reversible Resistance-Switching Metal Oxide or Nitride Layers with Added Metals, " Adding metal to the binary metal oxide or nitride reduces the set and reset voltages and may reduce the amplitude of the shaping pulse or reduce the overall need. Generally, the metal additive is about 0.01 to about 5 percent of the metal atoms in the layer of the metal oxide or nitride compound. Preferred metals used for the metal additives are selected from the group consisting of cobalt, aluminum, gallium, indium, manganese, nickel, niobium, zirconium, titanium, hafnium, tantalum, magnesium, chromium, vanadium, boron, yttrium and ratanium.
Thus, several options are possible with respect to one-time programmable memory cells including binary metal oxide or nitride resistance-switching elements and diodes. The effect of pairing high or low resistance polysilicon and resistance-switching elements should be considered.
If a binary metal oxide or nitride is formed in a high resistance state and the diode is formed of a low defect low resistance polysilicon, the transition of the memory cell to a programmed state, in which a high current flows under the read voltage, sets the binary metal oxide or nitride into the set state. Is achieved by switching. If the diode is formed of innocent high resistance polysilicon, the polysilicon of the diode must withstand a programming voltage that causes the memory cell to behave as if it were programmed to flow a high current under an applied read voltage.
According to the relative voltages necessary to cause the disorder to order conversion of polysilicon and the high resistance to low resistance conversion of binary metal oxide or nitride, the crystallization of polysilicon crystallized adjacent to the low defect polysilicon diode and the appropriate silicide Use may be desirable.
Another alternative is to supply the shaping pulses to the preconditioning step at the factory when large shaping pulses are required for the binary metal oxides or nitrides formed in the high resistance state. The high voltage needed for the shaped pulses can be supplied from outside of the die and thus need not be available at the die. If a reverse bias is required for the reset, the reset pulse can be supplied in an additional preconditioning step, so that when the memory array is ready for the end user, the cells have a reset state and are programmed by a low set voltage after shaping. Can be. In this manner, circuits on the die do not need to provide high voltage shaped pulses or negative voltages, thus simplifying circuit requirements.
In addition, if preconditioning shaping and reset pulses are supplied from the factory, the large voltage required for shaping pulses may be sufficient to switch the defective polysilicon of the diode from high resistance to low resistance. In this case, there are no disadvantages when using an unsiliciated no-defective diode, and the excess process complexity of providing a silicide template layer can be avoided.
Such a memory cell of a memory array, where the memory cell comprises a resistance-switching layer of a metal oxide or nitride compound, a metal oxide or nitride compound comprising exactly one metal, is a second programmed resistor from the first resistance state. Is programmed by a method comprising programming the memory cell by changing the resistance-switching layer to a state, wherein the second programmed resistance state stores the data state of the memory cell. The memory array includes circuitry for programming and reading memory cells, which circuit is suitable for programming memory cells for up to one hour. The memory array is a one-time programmable array.
One-time programmable multistate
In other embodiments, it may be desirable to pair the diode formed of high defect polysilicon with a binary metal oxide or nitride. Two states of the polysilicon constituting the diode, namely the initial high resistance state and the programmed low resistance state, can be used to store data to increase the density of the memory cell.
For example, it is assumed that diodes formed of high defect polysilicon (not crystallized adjacent to appropriate silicides) consist of a pair of nickel oxide layers and these pairs are electrically arranged in series between the upper and lower conductors. Nickel oxide is formed in a high resistance state, which requires a shaped pulse to achieve the first transition from high resistance to low resistance. It is assumed that the diode requires 8 volts of programming voltage to cause the disorder-to-order transition described in the '530 application, which transitions the polysilicon into a high resistance state. Assume that the voltage required by the nickel oxide in relation to the shaping pulse is 10 volts (it will be understood that the voltages given here are merely exemplary, the voltage varies as device characteristics and other factors change).
The formed memory cell has a diode of high resistance polysilicon and high resistance nickel oxide. Table 1 below summarizes the three data states that can be achieved by such memory cells. Table 1 also includes exemplary read currents predicted for each data state at the programming and +2 volt supplied read voltages required to achieve each state.
Data status Polysilicon state Switching layer status programming Read Current at + 2V 00 High resistance reset Non-programming 1 x 10 -10 amps 10 Low resistance reset + 8V 1x10 -8 amps 11 Low resistance set + 11V 1x10 -5 amps
When the non-programming voltage is supplied, the formed memory cell has a first data state, referred to as the "00" state for convenience. An application of +8 volts is sufficient to switch the polysilicon of the diode from high resistance to low resistance but below the voltage required for the shaping pulse, thus keeping the nickel oxide in its initial high resistance state, which is referred to as "10". . Application of +11 volts into the cell in the initial '00' state is sufficient to achieve the disorder to order conversion of polysilicon and set the nickel oxide to a low resistance state. This data state will be referred to as the '11' state.
In other embodiments, atypical pulses or only small shaped pulses may not be required and the set voltage may be less than the voltage required to switch the polysilicon. In this case, attainable data states are summarized in Table 2.
Data status Polysilicon state Switching layer status programming Read Current at + 2V 00 High resistance reset Non-programming 1 x 10 -10 amps 01 High resistance set + 6V 1 x 10 -9 amps 11 Low resistance set + 8V 1x10 -5 amps
As formed, memory cells with polysilicon and nickel oxide high resistance have a '00' state. Application of +6 volts sets nickel oxide but is not sufficient to switch polysilicon and keeps the cell in a '01' state. The application of 8 volts switches polysilicon and nickel oxide and thus maintains low resistance states corresponding to the '11' data state.
In any of these embodiments, once the cell is in the '11' state, a fourth data state in which the polysilicon of the diode has a low resistance state and the nickel oxide has a reset state can be achieved by resetting the nickel oxide. Can be. This state will be referred to as the '10' state and is achieved by supplying a negative reset pulse of -4 volts to the cell in the '11' state in embodiments where reverse bias is required for the reset.
In summary, the memory cell just described is the step of i) supplying a first programming pulse to the memory cell, the first programming pulse being a) detectably changing the first resistance state of the resistance-switching layer or b) polycrystalline. A step of detectably changing the second resistance state of the semiconductor material or c) detectably changing the first resistance state of the resistance-switching layer and detectably changing the second resistance state of the polycrystalline semiconductor material, and ii) reading the memory cell, wherein the first resistive state of the resistive switching layer is used to store data and the second resistive state of the polycrystalline semiconductor material is programmed by a method comprising a read step used to store the data. do. The memory cell is suitable for storing either 3 or 4 data states.
The resistance-switching binary oxides or nitrides mentioned herein may achieve two or more stable resistance states. In some embodiments, memory cells in an array formed in accordance with the present invention convert metal oxides or nitrides into three, four or more detectable discrete resistance states such as two or more data states, such as three, four or more. You can save the data state. Detectable individual data states can be reliably detected by sensing and decoding the circuitry of the array. These embodiments may be rewritable or one-time programmable.
For example, the resistance-switching metal oxide or nitride is nickel oxide formed in a high resistance state (it will be understood that some of the materials of other names may be used). Referring to FIG. 12, as formed, the nickel oxide has the lowest resistance state shown by the curve (00).
Nickel oxide can be converted into two or more detectable discrete resistance states. For example, a memory cell similar to the cell shown in FIG. 2 may have four different states, each of which is distinguished by a range of currents flowing under a supplied read voltage, such as about 2 volts.
In this example, a current of about 30 nanoamps or less in the high resistance state flows when 2 volts is applied to the memory cell, which will be referred to as the '00' state. In the '01' state, the current at 2 volts would be about 100 to 300 nanoamps. In the '10' state, at 2 volts the current will be from about 1 microamp to 3 microamps. In the lowest resistance state, the '11' state, at 2 volts the current will be at least 9 microamps. These current ranges and read voltages are supplied for clarity only, and other values may be appropriate depending on the characteristics of the device and the actual materials used.
In this example, the set pulse has a voltage of about 8 to about 10 volts, while the reset voltage is about 3 to 6 volts. In embodiments comprising nickel oxide paired with a p-i-n diode, the reset voltage is supplied to the reverse bias. Depending on the configuration and characteristics of the memory cells and the material used, a reverse bias may not be required to reset the cell.
Referring to FIG. 12, the cell is formed in a '00' state. To program the cell to the 01 state, for example, a set voltage of 8 volts can be supplied. In relation to all set pulses, a current limiter is preferably included in the circuit. After application of the set pulse, the cell is read at 2 volts. If a current of 2 volts has a predicted range for the '01' state between about 100 and about 300 nanoamps, the cell is considered to be programmed. If the current is too small (eg 80 nanoamps), an additional set pulse of a high set voltage is optionally supplied and the cell is read back at 2 volts. The process is repeated until the current through the memory cell is in the correct range at 2 volts.
After the programming pulse is supplied, the current may be above the allowable range for the '01' state, ie the current may be for example 400 nanoamps. In this case there are two options, that is, a reset pulse sufficient to return the nickel oxide to the '00' state can be supplied and then a small set pulse can be supplied as possible, or the reset pulse can be supplied to the nickel oxide layer. Can be supplied to slightly increase the resistance of the current, thus increasing the current to the '01' range. The process is repeated until the current flowing through the memory cell is within the correction range at 2 volts.
Similar methods are taken to transition the memory state to the '10' or '11' state. For example, a set voltage of 9.5 volts may be sufficient to transition the memory cell to the '10' state, while a set voltage of 10 volts may program the memory cell to the '11' data state.
The memory cell is preferably used as a rewritable memory cell. However, it is desirable to save the space of the substrate, omit transistors that can supply reverse bias, and program the cell only under forward bias. If a reverse bias is not needed to reset the cell, this memory array may be rewritable. If reverse bias is required for a reset, such a memory array can be used as a one-time programmable array. In this case setting the cell to a state with a higher current than the desired (low resistance of the nickel oxide layer) for the intended data state is omitted. Low set voltages can be supplied to gradually reduce the resistance of the nickel oxide layer and to raise the current to an acceptable range, which is necessary to increase the desired range because the overshoot cannot be compensated without reverse biasing. prevent.
As in the previous embodiments, advantages or disadvantages should be considered in forming a diode of low defect polysilicon by crystallizing polysilicon adjacent to the appropriate silicide. If high amplitude shaping pulses are required, the voltage of the shaping pulses may be sufficient to convert high defect high resistance polysilicon into low resistance polysilicon, in which case the use of low defect silicide polysilicon does not give an advantage. If no shaping pulse is required or if a small shaping pulse is required, a diode formed of low defect low resistance polysilicon crystallized adjacent to the appropriate silicide may be desirable.
If preconditioning steps such as shaped pulses are to be applied, it may be advantageous to perform these steps at the factory. In this case, no high voltage need be supplied to the die.
First Production Example
Detailed examples will be provided to fabricate a monolithic three dimensional memory array formed in accordance with a preferred embodiment of the present invention. For clarity, many details will be included, including steps, materials, and process conditions. These examples are not limited and the details of these examples may be modified, omitted or increased while the results thereof are within the scope of the present invention.
In general, the '470 application, the' 549 application, the '824 application, and the' 577 application disclose memory arrays comprising memory cells, where each memory cell is a one-time programmable cell. The cell is formed in a high resistance state and permanently transitions to a low resistance state upon application of a programming voltage. In particular, '470,' 549, '824,' 577 and other integrated applications and patents may relate to the formation of a memory according to the present invention. For simplicity, not all of the details of the integrated applications and patents will be included, but the contents of these applications or patents are not intended to be excluded.
Referring to FIG. 13A, memory formation begins at the substrate 100. Such a substrate 100 is known, such as IV-IV compounds, such as amorphous silicon, silicon-germanium or silicon-germanium-carbon, III-V compounds, II-VII compounds, epitaxial layers on substrates or any other semiconductor material. Can be any semiconductor substrate. The substrate can include integrated circuits fabricated therein.
The insulating layer 102 is formed on the substrate 100. Insulating layer 102 may be silicon oxide, silicon nitride, a high dielectric film, a Si—C—O—H film, or any other suitable insulating material.
The first conductors 200 are formed on the substrate 100 and the insulator 102. The adhesive layer 104 may be included between the insulating layer 102 and the conductive layer 106 to assist the adhesion of the conductive layer 106. The preferred material for the adhesive layer 104 is titanium nitride, although other materials may be used, or such layer may be omitted. The adhesive layer 104 may be deposited by any conventional method, such as sputtering.
The thickness of the adhesive layer 104 may be about 20 to about 50 angstroms, preferably about 100 to about 400 angstroms, most preferably about 200 angstroms. It should be noted that in this discussion "thickness" will represent the vertical thickness measured in the direction perpendicular to the substrate 100.
The next layer to be deposited is the conductive layer 106. The conductive layer 106 may comprise any known conductive material, such as a doped semiconductor, a metal, such as tungsten, or a conductive metal silicide, and in a preferred embodiment the conductive layer 106 is aluminum. The thickness of the conductive layer 106 may depend in part on the proper sheet resistance and thus may be any thickness that provides a suitable sheet resistance. In some embodiments, the thickness of the conductive layer 106 may be about 500 to about 3000 angstroms, preferably about 1000 to about 2000 angstroms, more preferably about 1200 angstroms.
Another layer 110 of titanium nitride is deposited on the conductive layer 106. It may have a similar thickness of the thickness of layer 104. The photolithography step will be performed to pattern the aluminum layer 106 and the titanium nitride layer 104. The high reflectivity of aluminum makes it difficult to perform photolithography directly on the aluminum layer. Titanium nitride layer 110 is used as an antireflective coating.
Once all the layers that will form the conductor rails have been deposited, the layers can be patterned and patterned using any suitable masking and etching process to form the substantially parallel, substantially coplanar conductors 200 shown in cross section in FIG. 13A. Will be etched. In one embodiment, the photoresist is deposited and then patterned by photolithography, the layers are etched, and the photoresist is etched with a conventional liquid solution such as "ashing" in an oxygen containing plasma and formulated by EKC. Is removed using standard process techniques such as strips of the remaining polymers formed.
Next, a dielectric material 108 is deposited over the conductor rails 200 and between the conductor rails 200. Dielectric material 108 may be any known insulating material, such as silicon oxide, silicon nitride, or execon oxynitride. In a preferred embodiment, silicon oxide is used as dielectric material 108. Silicon oxide may be deposited using any known process such as chemical vapor deposition (CVD), or high density plasma CVD (HDPCVD), for example.
Finally, excess dielectric material 108 on top of conductor rails 200 is removed to expose the tops of conductor rails 200 separated by dielectric material 108 and leave a substantially planar surface 109. . The resulting structure is shown in Fig. 13A. Removal of such dielectric overfill to form planar surface 109 may be performed by any known process, such as etching back or chemical mechanical polishing (CMP). For example, the etching bag techniques disclosed in US application no. 10 / 883,417 to Raghuram et al. Filed June 30, 2004 under the name of "non-selective non-patterned etch bag for exposing embedded patterned features" may advantageously be used. This application is hereafter referred to as the '417 application and is incorporated herein by reference.
In preferred embodiments, the bottom conductors 200 deposit a first layer or stack of conductive material; Patterning and etching the first layer or stack of conductive material to form first conductors; It is formed by depositing a dielectric fill between the first conductors.
Optionally, the conductor rails may be formed by a damascene process in which oxides are deposited, trenches are etched in the oxide and then the trenches are filled with conductive material to produce the conductor rails. The formation of the conductors 200 using a copper damascene process is disclosed in US patent application Ser. No. 11 / 125,606, entitled "High Density Non-Volatile Memory Arrays Containing Semiconductor Diodes and Fabricated at Low Temperatures." Copper damascene conductors include at least a barrier layer and a copper layer.
Next, referring to FIG. 13B, vertical pillars will be formed over the finished conductor rails 200 (to save space, the substrate 100 is omitted in FIG. 13B and the following figures and is present therein). Will be assumed). The semiconductor material to be patterned is deposited on the pillars. The semiconductor material may be germanium, silicon, silicon-germanium, silicon-germanium-carbon, or other suitable IV-IV compound, gallium arsenide, indium phosphide, or other suitable III-V compounds, zinc selenide or other II-VII compounds or combinations thereof. Silicon-germanium alloys or pure germanium in any proportion of silicon and germanium, including at least 20, at least 50, at least 80, or at least 90 atomic percent germanium, may be used. This example will describe the use of pure germanium. The term “pure germanium” does not exclude the presence of conductive-enhancing dopants or contaminants commonly found in typical manufacturing environments.
In a preferred embodiment, the semiconductor filler comprises a junction diode, the junction diode comprising a heavily doped bottom region of the first conductivity type and a heavily doped upper region of the second conductivity type. The middle region between the upper and lower regions is an intrinsic or lightly doped region of the first or second conductivity type.
In this example, the heavily doped lower region 112 is a heavily doped n-type germanium. In the most preferred embodiment, heavily doped region 112 is deposited and then doped with an n-type dopant, such as phosphorus, by any conventional method, preferably in situ doping. Such layer is preferably about 200 to about 800 angstroms.
Next, germanium is deposited which forms the remainder of the diode. In some embodiments, the next planarization step removes some germanium and as a result an excess thickness is deposited. If the planarization step is performed using a conventional CMP method, about 800 angstroms of thickness can be lost (this is an average, the amount varies across the wafer, and germanium losses will be small if you follow the methods and slurry used during CMP). Can be). If the planarization step is performed by an etch back method, about 400 angstroms or less of germanium may be removed. Depending on the planarization method to be used and the appropriate final thickness, undoped germanium of about 800 to about 4000, preferably about 1500 to about 2500 angstroms, more preferably about 1800 to about 2200 angstroms, is deposited by any conventional method. If desired, germanium may be lightly doped. Highly doped top region 116 is formed in the following implantation step but is not yet present at this point and is therefore not shown in FIG. 13B.
The just deposited germanium will be panned and etched to form the pillars 300. The pillars 300 should have about the same pitch and about the same width as the conductors 200 below so that each pillar 300 is formed on top of the conductor 200. Some misalignment may be allowed.
The pillars 300 may be formed using any suitable masking and etching process. For example, the photoresist may be deposited, then patterned using standard photolithography techniques, subsequently etched, and then the photoresist may be removed. Optionally, a hard mask of any other material, such as silicon dioxide, may be formed on top of the stack of semiconductor layers having an antireflective coating (BARC) thereon, followed by patterning and etching. Similarly, dielectric antireflective coating (DARC) can be used as a hard mask.
US Application No. 10 / 728,436 by Chen, filed Dec. 5, 2003, entitled “Photomask Features with Internal Nonprinting Window Using Alternating Phase Shifting” or “Chromeless Nonprinting Phase Shifting”. Photolithography techniques disclosed in US Application No. 10 / 815,312 by Chen, filed April 1, 2004, entitled “Photomask Features with Windows” may be used for any photo used in the formation of a memory array according to the present invention. It may advantageously be used to carry out lithographic steps, which application is assigned to the assignee of the present invention and incorporated herein by reference.
Dielectric material 108 is deposited over pillars 300 and between pillars 300 and fills the gaps between pillars 300. Dielectric material 108 may be any known electrically insulating material, such as silicon oxide, silicon nitride, or silicon oxynitride. In a preferred embodiment, silicon dioxide is used as the insulating material. Silicon dioxide can be deposited using any known process such as CVD or HDPCVD.
Next, the dielectric material over the pillars 300 is removed, exposing the tops of the pillars 300 separated by the dielectric material 108, leaving a substantially planar surface. Removal and planarization of such dielectric overfill may be performed by any known process such as CMP or etch back. For example, the etching back techniques disclosed in the '417 application by Raghuram et al. Can be used. This resulting structure is shown in FIG. 13B.
Referring to FIG. 13C, in a preferred embodiment, heavily doped top regions 116 are formed at this point by ion implantation using a p-type dopant, such as boron or BF 2 . The diodes described herein have a lower n-type region and an upper p-region. If desired, the conductivity types can be reversed. Where appropriate, pin diodes with n-regions at the bottom may be used at one memory level, while pin diodes with p-type regions at the bottom may be used at other memory levels.
Diodes disposed in the pillars 300 may comprise depositing a stack of semiconductor layers over the first conductors and the dielectric fill; And patterning and etching the semiconductor layer stack to form the first diodes.
Next, a layer of conductive barrier material such as titanium nitride, metal or any other suitable material 121 is deposited. The thickness of layer 121 may be about 100 to about 400 angstroms, preferably about 200 angstroms. In some embodiments, layer 121 may be omitted. A layer 118 of metal oxide or nitride resistance-switching material is deposited on the barrier layer 121. This layer is preferably about 50 to about 400 angstroms, such as about 100 to about 200 angstroms. Layer 118 may be some of the materials described above, preferably a metal oxide or nitride comprising exactly one metal having resistive switching properties, preferably Ni x O y , Nb x O y , Ti x O y , Hf x O y , Al x O y , Mg x O y , Co x O y , Cr x O y , V x O y , Zn x O y , Zr x O y , B x N y and Al x N y It is formed of a material selected from the group consisting of. For simplicity, this discussion will describe the use of nickel oxide in layer 118. However, it should be understood that some of the other materials described may be used. Nickel oxide has non-directional switching characteristics, and thus is paired with a pin diode even though the zener diode uses the circuit structure shown selectively. As mentioned above, if a directional resistive switching material is selected, a zener diode may be preferred. In a preferred embodiment, such a zener diode has no intrinsic region or an intrinsic region no thicker than about 350 angstroms.
Finally, in preferred embodiments, barrier layer 123 is deposited on nickel oxide layer 118. Layer 123 is preferably titanium nitride, although any other suitable conductive barrier material may be used instead. The purpose of the barrier layer 123 is to allow the planarization step to be performed to be performed on the barrier layer 123 rather than the nickel oxide layer 118. In some embodiments, layer 123 may be omitted.
The layers 123, 118, 121 are patterned and etched to form short pillars ideally directly on top of the pillars 300 formed in the previous pattern and etching step. Some misalignment can occur as shown in FIG. 13C and can be tolerated. The photomask used to pattern the pillars 300 can be reused in this patterning step.
In this example, the layers 123, 118, 121 are patterned with a patterning step different from the germanium layers 112, 114 (and 116 (formed in the next ion implantation step)), which is exposed in the chamber where the semiconductor etching is performed. Having nickel oxide and metal barrier layers may be desirable to prevent possible contaminants and to reduce the etch height, however, in other embodiments, the layers 123, 118, 121, 116, 114, in a single patterning step, It may be desirable to pattern 112. In this case, ion implantation of the heavily doped germanium layer 116 occurs prior to the deposition of the barrier layer 121. Optionally, the heavily doped layer 116 is It may be doped in situ.
In some embodiments, barrier layer 121, nickel oxide layer 118 and barrier layer 123 may be formed before (bottom) diode layers 112, 114, 116 and patterned in the same or separate patterning step. Can be.
Next, a conductive material or stack is deposited to form the top conductors 400. In a preferred embodiment, after titanium nitride barrier layer 120 is deposited, aluminum layer 122 and top titanium nitride barrier layer 124 are deposited. The upper conductors 400 may be patterned and etched as described above. In this example, in each cell, the diode and resistor-switching element (part of nickel oxide layer 118) of (layers 112, 114, 116) are between the upper conductor 400 and the lower conductor 200. Are formed in series. The upper second conductors 400 will extend in a direction different from the first conductors 200, preferably substantially perpendicular to the first conductors 200. The resulting structure shown in FIG. 13C is the bottom or first story of memory cells.
In alternative embodiments, the top conductors may comprise copper and may be formed by the damascene method. A detailed description relating to the manufacture of the top copper conductors of a monolithic three dimensional memory array is disclosed in US patent application Ser. No. 11 / 125,606 entitled "High Density Nonvolatile Memory Array Including Semiconductor Diodes and Fabricated at Low Temperature". have.
In preferred embodiments, this first story of memory cells comprises: a first plurality of substantially parallel substantially coplanar conductors extending in a first direction; A first plurality of reversible resistance-switching elements; And a plurality of non-volatile memory cells comprising a second plurality of substantially parallel, substantially coplanar conductors extending in a second direction different from the first direction, one of the first diodes in each memory cell and Some of the first reversible resistance-switching elements are arranged in series and disposed between one of the first conductors and one of the second conductors, and the first plurality of reversible resistance-switching elements are Ni x O y , Nb. x O y , Ti x O y , Hf x O y , Al x O y , Mg x O y , Co x O y , Cr x O y , V x O y , Zn x O y , Zr x O y , B material selected from the group consisting of x N y and Al x N y . The first conductors are formed at a first height, the second conductors are formed at a second height, and the second height is higher than the first height.
Additional memory levels may be formed above this first memory level. In some embodiments, the conductors can be shared between memory levels, ie, upper conductor 400 is used as the lower conductor of the next memory level. In other embodiments, an interlevel dielectric is formed over the first memory level of FIG. 13C, the surface of the dielectric is planarized, and the construction of the second memory level begins with a planarized interlevel dielectric without shared conductors. . If the upper conductors 400 are not shared between memory levels, CMP need not be performed for these conductors. In this case, if appropriate, the titanium nitride barrier layer 124 may be replaced with a layer of DARC.
The deposited germanium is either undoped or doped with n-type dopants and will generally be amorphous when deposited at relatively low temperatures. After all of the memory levels have been configured, the final relatively low temperature annealing, eg, performed at about 350 to about 470 ° C., may be performed to crystallize germanium diodes, in which the resulting diodes will be formed of polygerium. Large batches of wafers, eg, more than 100 wafers, can be annealed simultaneously to maintain sufficient manufacturing throughput.
Vertical interconnects between memory levels and between circuits of the substrate are formed as tungsten flags, which can be formed by any conventional method.
Photomasks are used during photolithography to pattern each layer. Any layers are repeated at each memory level, and the photomasks used to form these layers can be reused. For example, the photomask defining the pillars 300 of FIG. 13C may be reused for each memory level. Each photomask includes reference marks used to assign them appropriately. When the photomask is reused, the reference marks formed in the second or subsequent use may interfere with the same reference marks formed during the preferential use of the same photomark. US patent application Ser. No. 11 / 097,496, filed Mar. 31, 2005, entitled " Marking of Aligned Marks and Repeated Overlays to Enable Reuse of Photomasks in Vertical Structures, " A method of preventing interference during the formation of the same monolithic three dimensional memory array is disclosed, which application is incorporated herein by reference.
Many variations on the steps and structures described herein may be devised. A few variations will be described in order to more fully describe the invention, and all variations that fall within the scope of the invention need not be described completely so that those skilled in the art can make and use the widest range of variations possible.
Second Manufacturing Example: Rare Metal Contacts on Diode
10 illustrates an embodiment in which a resistive switching material 118 is inserted between the rare metal layers 117, 119. Preferred rare metals are Pt, Pd, Ir and Au. Layers 117 and 119 may be formed of the same rare metal or other metals.
When a resistive switching material is inserted between the noble metal layers, the noble metal layers must be patterned and etched so as not to provide an unwanted conductive path between adjacent diodes or conductors.
The memory level comprising cells such as the cells of FIG. 10 is shown in cross section in FIG. 14. In a preferred method for forming this structure, the bottom conductors 200 are formed as described above. Highly doped germanium layer 112 and undoped germanium layer 114 are deposited as described above. In one preferred embodiment, ion implantation of the heavily doped top layer 116 may be performed on a blanket germanium layer before the pillars are patterned and etched. Next, the resistive-switching material 118 and the rare metal layer 119 are deposited after the rare metal 117 is deposited. The rare metal layers 117, 119 may be about 200 to about 500 angstroms, preferably about 200 angstroms.
The pillars are patterned and etched at this point so that the layers 117, 118, 119 are included in the filler and electrically insulated from each other. Depending on the etchant selected, it may be desirable to perform a first etching step that only etches the layers 119, 118, 117 and then etch the rest of the filler using these layers as a hard mask.
Optionally, the layers 112, 114, 116 can be patterned and etched, the gaps in these layer yarns are filled and the tops of the pillars are exposed through planarization. Deposition of layers 117, 118, 119 may be followed with etching and individual patterns of these layers.
The gaps are filled and the CMP or etch back steps are performed as described above to create a substantially planar surface. The top conductors 400 are then formed on this planar surface as described above and include a titanium nitride layer 120, an aluminum layer 122 and a titanium nitride layer 124. Optionally, the top rare metal layer 119 may be etched with the top conductors 400 after it is deposited and patterned.
Alternatively, the heavily doped layer 116 may be doped by in situ doping rather than ion implantation.
Third Manufacturing Example: Rare Metal Contacts Under Diode
In the alternative embodiment shown in FIG. 15, resistance-switching elements 118 interposed between the rare metal layers 117, 119 are formed below the diode rather than over the diode.
In order to form this structure, the lower conductors 200 are formed as described above. Layers 117, 118, 119 are deposited on the planarized surface 109 of the conductors 200 separated by the gap fill. A germanium stack is deposited that includes a heavily doped layer 112 and an undoped layer 114. Layers 114, 112, 119, 118, optionally 117, are patterned and etched as described above to form pillars 300. After gap fill and planarization, the heavily doped top region 116 is formed by ion implantation. Top conductors 400 deposit conductive layers, such as titanium nitride layer 120, aluminum layer 122, and titanium nitride layer 124, and patterning and etching to form conductors 400. Is formed as in the above-described embodiment.
As in other embodiments, where appropriate, layers 117, 118, 119 can be patterned and etched away from layers 110, 112, 114, 116 rather than etching all of these layers in a single pattern step. have.
In the preferred embodiments just described, formed a) Ni x O y , Nb x O y , Ti x O y , Hf x O y , Al x O y , Mg x O y , Co x O y , Cr a first element comprising a reversible resistance-switching element each comprising a material selected from the group consisting of x O y , V x O y , Zn x O y , Zr x O y , B x N y and Al x N y A monolithic three dimensional memory array comprising a plurality of memory cells and comprising a first memory level formed over a substrate and b) at least a second memory level monolithically formed over the first memory level.
Many other alternative embodiments may be devised. For example, in some embodiments the rare metal layers 117, 119 may be omitted. In this case, the resistance-switching material 118 can be patterned into the bottom conductors 200 together with the pillars 300 and remain as a continuous layer above or below the diodes.
The advantages of the embodiments just described are that germanium is used in the diode to form a first conductor, a second conductor, a reversible resistance-switching element, and a diode to form a nonvolatile memory cell. , The diode and the reversible resistance-switching element are electrically arranged in series between the first conductor and the second conductor, and the temperature exceeds about 500 ° C. during the formation of the first and second conductors, the diode and the switching element and the crystallization of the diode. I never do that. Depending on the deposition and crystallization conditions used (long crystallization annealing can be performed at low temperatures), the temperature may not exceed about 350 ° C. In alternative embodiments, the deposition and crystallization temperatures of the semiconductor material may be arranged such that the maximum temperature does not exceed 475, 425, 400 or 375 ° C.
Fourth Manufacturing Example: Silicide Diode
It may be desirable to form diodes of silicon, especially polysilicon, crystallized adjacent to the silicide, which may provide an advantageous crystallization template such as titanium silicide or cobalt silicide to form a relatively low defect, low resistance polysilicon.
Referring to FIG. 16A, the lower conductors 200 may be formed as described above. Polysilicon generally requires a crystallization temperature that is incompatible with copper and aluminum, so that a material that can tolerate high temperatures, such as tungsten, may be the preferred conductive material 106 for the bottom conductors 200.
In a preferred embodiment, an adhesive layer 104 is first deposited followed by a tungsten layer 106 which is patterned and etched to form substantially parallel conductors 200. A dielectric fill 108 is deposited over the conductors 200 and between the conductors 200, and then the planarization step by CMP removes the overfill to expose the conductors 200 and the substantially planar surface. Leave dielectric 108.
Next, a thin film barrier layer 110 of titanium nitride is deposited on the planar surface. Next, a semiconductor material forming a diode is deposited. In this embodiment, the semiconductor material is preferably silicon or silicon-rich silicon-germanium alloy. Highly doped n-type region 112 is first deposited and then preferably doped by in situ doping. Such layer may be about 100 to about 1000 angstroms, preferably about 200 angstroms.
Intrinsic silicon is then deposited to a thickness of about 800 to about 3300 angstroms. The heavily doped p-type region 116 at the top of the silicon stack is doped, preferably for ion implantation of p-type dopants such as boron or BF 2 , leaving the intermediate region 114 as an undoped region. Is doped. In an alternate embodiment, heavily doped p-type region 116 is doped with in-situ doping.
A thin film layer 125 of titanium of about 50 to about 200 angstroms is deposited. After the optional barrier layer 121 is deposited, a nickel oxide layer 118 (some other resistive-switching metal oxide or nitride may be used instead) and an upper barrier layer 123, which may optionally be titanium nitride, is deposited. do. Layer 118 of nickel oxide may include an additive metal described in the '452 application, which may be used to reduce the switching voltage or current and to reduce or eliminate the need for shaped pulses.
Barrier layer 123, nickel oxide layer 118, and barrier layer 121 are patterned and etched to form short pillars. The layer 118 of nickel oxide may be sputter etched, or preferably US patent application number 11 by Raghuram et al., Filed June 11, 2005, entitled “Method for Plasma Etching Transition Metals and Compounds thereof”. Which may be etched using the chemical process disclosed in / 179,423, which is incorporated herein by reference. The structure at this time is shown in Fig. 16A.
Referring to FIG. 16B, while using the etched layers 121, 118, 123 as a hard mask during the etching of the titanium layer 125, the etching is performed at a heavily doped p-type region 116, intrinsic region 114. ), Heavily doped n-type region 112, and barrier layer 110 forming pillars 300. Dielectric material 108 is disposed over and between pillars 300 to fill the gaps between pillars 300. The planarization step, for example by CMP, removes the overfill of dielectric 108 and selectively barrier layer 123 (or if barrier layer) on top of pillars 300 separated by pillar 108. If 123 is omitted, nickel oxide layer 118 is exposed. Fig. 16B shows the structure at this time.
Referring to FIG. 16C, the top conductors 400 are preferably formed, for example, with an adhesive layer 120 of titanium nitride and a conductive layer 130 of tungsten, as in previous embodiments.
The annealing step causes the titanium layer 125 to work with the silicon region 116 forming titanium silicide. The next high temperature anneal crystallizes the silicon in the silicon regions 116, 114, 112 to form a diode of relatively low defect, low resistance polysilicon.
Many variations are possible when forming such memory cells. For example, if appropriate, the nickel oxide layer 118 and any barrier layers associated with it may be patterned and etched into individual steps rather than the same patterning step to form a diode.
Fifth Manufacturing Example: Non-Silicide Diode
In one-time programmable embodiments that use the resistive state of the polysilicon of the diode to store the data state, forming an uncrystallized polysilicon diode adjacent to the silicide that promotes the formation of low defect polysilicon. It should be noted that this may be desirable.
In this case, the bottom conductors 200 are formed as described above. The pillars 300 are formed as described in the previous silicide embodiment except that the titanium layer 125 is omitted in the embodiment that reacts with the silicon of the diode to form the titanium silicide. Nickel oxide layer 118 and any barrier layers associated with it are preferably first patterned and etched, which is used as a hard mask to etch silicon regions 116, 114, 112 and barrier layer 110. Optionally, the diode layers 116, 114, 112 may be patterned and etched first, with gaps on these diode layers filled with a dielectric, the tops of the diodes exposed to a planarization step, and then a nickel oxide layer 118 and associated barrier layers are deposited and then patterned and etched in separate steps.
As in all embodiments, a first story of memory cells has been formed. The additional memory levels can preferably be stacked above the first memory level to form a monolithic three dimensional memory array formed over the semiconductor substrate.
One-time programmable monolithic three dimensional memory arrays are described in US Pat. No. 6,034,882 to Johnson et al. Entitled "Vertically Stacked Field Programmable Non-Volatile Memory and Methods for Making the Same; US Patent No. 6,420,215 to Knall et al. Entitled "Three-Dimensional Memory Arrays and Methods for Making the Same; And US Patent Application No. 10 to Vyvoda et al., Filed June 27, 2002, entitled " Electrically Insulated Pillars of Active Devices, " and assigned to the assignee of the present invention and incorporated herein by reference. / 185,507.
A monolithic three dimensional memory array is an array in which multiple memory levels are formed on a single substrate, such as a wafer, without intermediate substrates. Layers that form one memory level are deposited or grown directly on top of an existing level or layers of levels. In contrast, stacked memories were constructed by forming memory levels on individual substrates and alternately adhering the memory levels to each other, as in US Pat. No. 5,915,167 by Leedy entitled "Three-dimensional Structure Memory". Substrates can be stripped or removed from memory levels prior to bonding, but when memory levels are initially formed over individual substrates, these memories are not true monolithic three dimensional memory arrays.
A monolithic three dimensional memory array formed over a substrate includes at least a first memory level formed at a first height above the substrate, and a second memory level formed at a second height different from the first height. Three, four, eight or any number of memory levels can be formed on the substrate in such a multilevel array.
Although the manufacturing method is described herein in detail, any other method of forming the same structures can be used and the results thereof are within the scope of the present invention.
The foregoing detailed description has described only some of the many forms that the invention can take. For this reason, this detailed description has been described by way of example and not of limitation. It is intended that the scope of the invention only be limited by the following claims, which include all equivalents.
In a nonvolatile memory cell,
A reversible resistance-switching element connected in series with the diode, the reversible resistance-switching element comprising a layer of reversible resistance-switching metal nitride compound, wherein the reversible resistance-switching metal nitride compound is only one metal The resistance-switching element comprising;
The diode and the reversible resistance-switching element are part of the memory cell,
And the reversible resistance-switching element is adjacent to a metal selected from the group consisting of Pt, Pd, Ir, and Au.
The nonvolatile memory cell of claim 1, wherein the metal nitride compound is selected from the group consisting of B x N y and Al x N y , wherein x and y have a range between 0 and 1.
The nonvolatile memory cell of claim 1, wherein the diode and the reversible resistance-switching element are disposed between a first conductor and a second conductor.
5. The nonvolatile memory cell of claim 4 wherein the second conductor is formed over the first conductor and the diode and the reversible resistance-switching element are disposed vertically between the first conductor and the second conductor.
6. The nonvolatile memory cell of claim 5 wherein the diode is formed over the reversible resistance-switching element.
6. The nonvolatile memory cell of claim 5 wherein the reversible resistance-switching element is formed over the diode.
6. The nonvolatile memory cell of claim 5 further comprising a pillar, wherein the diode is formed in the pillar and is oriented vertically.
The nonvolatile memory cell of claim 8, wherein the first conductor and the second conductor have a rail-shape.
10. The non- volatile memory cell of claim 9, wherein the first conductor extends in a first direction, and the second conductor extends in a second direction different from the first direction.
The nonvolatile memory cell of claim 10 wherein the reversible resistance-switching element is disposed in the filler.
12. The nonvolatile memory cell of claim 10 wherein the reversible resistance-switching element has a rail-shape, disposed between the second conductor and the diode, and extending in the second direction.
The nonvolatile memory cell of claim 10, wherein the reversible resistance-switching element has a rail shape and is disposed between the first conductor and the diode and extends in the first direction.
9. The nonvolatile memory cell of claim 8 wherein the first conductor and the second conductor comprise aluminum.
9. The nonvolatile memory cell of claim 8 wherein the first conductor or the second conductor comprises tungsten.
The nonvolatile memory cell of claim 1 wherein the diode is a semiconductor junction diode.
18. The nonvolatile memory cell of claim 17 wherein the silicon, the germanium, or the alloy of silicon or the germanium is polycrystalline.
18. The semiconductor junction diode of claim 17 wherein the semiconductor junction diode is vertically oriented and has a heavily doped bottom region having a first conductivity type, an intermediate region doped with intrinsic or low concentration, and a heavily doped upper region having a second conductivity type. A nonvolatile memory cell comprising a region.
18. The nonvolatile memory cell of claim 17 wherein the semiconductor junction diode is a zener diode.
22. The nonvolatile memory cell of claim 21 wherein the zener diode is vertically oriented and includes a heavily doped bottom region having a first conductivity type and a heavily doped upper region having a second conductivity type.
2. The nonvolatile memory cell of claim 1 wherein the memory cell is part of a first memory level.
24. The nonvolatile memory cell of claim 23 wherein the first memory level is formed over a single crystal silicon substrate.
24. The nonvolatile memory cell of claim 23 wherein at least a second memory level is monolithically formed above the first memory level in a monolithic three dimensional memory array.
The nonvolatile memory cell of claim 1, wherein the layer of reversible resistance-switching metal nitride compound may have one of a number of resistance states.
29. The nonvolatile memory cell of claim 28 wherein the layer of reversible resistance-switching metal nitride compound transitions from a high resistance state to a low resistance state upon application of a set pulse to the reversible resistance-switching element.
29. The nonvolatile memory cell of claim 28 wherein the layer of reversible resistance-switching metal nitride compound transitions from a low resistance state to a high resistance state upon application of a reset pulse to the reversible resistance-switching element.
2. The nonvolatile memory cell of claim 1 wherein the memory cell is rewritable.
33. The nonvolatile memory cell of claim 32 wherein the layer of reversible resistance-switching metal nitride compound transitions from a high resistance state to a low resistance state upon application of a set pulse to the reversible resistance-switching element.
33. The nonvolatile memory cell of claim 32 wherein the layer of reversible resistance-switching metal nitride compound transitions from a low resistance state to a high resistance state upon application of a reset pulse to the reversible resistance-switching element.
The nonvolatile memory cell of claim 1, wherein the layer of reversible resistance-switching metal nitride compound comprises a metal additive, wherein the metal additive is 0.01 to 5 percent of the metal atoms in the layer of metal nitride compound.
36. The method of claim 35, wherein the metal additive is selected from the group consisting of cobalt, aluminum, gallium, indium, manganese, nickel, niobium, zirconium, titanium, hafnium, tantalum, magnesium, chromium, vanadium, boron, yttrium, and lanthanum. Nonvolatile Memory Cells.
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