CN100461484C - Phase-change memory storage unit and preparation method thereof - Google Patents

Abstract

The invention relates to a phase-change memory unit and a preparation method thereof, which are characterized in that: a lower electrode layer is covered on the substrate; a heat-insulating material layer is covered on the lower electrode, and holes exist in the heat-insulating material layer; Connected hollow cylindrical heating electrode material structure; the cylindrical heating electrode is covered with a heat insulating material layer, and the insulating material layer contains holes engraved with the cylindrical heating electrode; and there are reversible phase changes in the holes of the cylindrical heating electrode and the holes of the heat insulating material layer Material layer; the phase-change material layer is covered with a heat-insulating material layer, and the heat-insulating material layer contains holes filled with an upper electrode material communicated with the phase-change material. In the present invention, the phase change material is limited in the hollow column of the heating electrode and the hole in the heat insulating material. When the electric pulse operates the storage unit, the phase change material is placed in a high temperature and high pressure environment, and the phase change occurs preferentially, inducing the surrounding The phase change material is further phase changed, so as to realize the low voltage, low power consumption and high speed functions of the phase change memory unit.

Description

Phase-change memory storage unit and preparation method thereof

technical field

The invention relates to a storage unit structure of a phase-change memory and a preparation method thereof, in particular to a hollow column-shaped heating electrode prepared by micro-nano processing technology, and a phase-change material is filled in the hollow column to utilize the electric pulse action The change of temperature and pressure in the lower hollow column induces the phase change of the phase change material, thereby realizing the low voltage, low power consumption and high speed functions of the phase change memory unit. The invention belongs to the technical field of microelectronics.

Background technique

Phase-change memory (C-RAM, Chalcogenide-Random Access Memory) technology is based on Ovshinsky in the late 1960s (Phys. Rev. Lett., 21, 1450-1453, 1968) and early 1970s (Appl. Phys. Lett. , 18,254-257, 1971) proposed that the phase-change thin film can be applied to the idea of phase-change storage media. The characteristic of phase-change alloy, the key material of C-RAM memory, is that when it is given an electric pulse, it can make the material undergo reversible phase transition between amorphous state and polycrystalline state. It exhibits high resistance in the amorphous state and low resistance in the polycrystalline state, and the variation range can reach several orders of magnitude. However, due to the limitation of preparation technology and process, the phase change material can only undergo phase change under a strong electric field, which limits the progress of its practical development. With the development of nano-fabrication technology and process, the size of the effective phase-change region of the phase-change material in the device can be reduced to the nanometer level, the voltage required for the phase change of the material is greatly reduced, the power consumption is reduced, and the performance of the material is also improved. great changes.

C-RAM memory is widely used in the international semiconductor industry due to its advantages of high-speed reading, high erasable times, non-volatility, small component size, low power consumption, low cost, multi-level storage, strong vibration resistance and radiation resistance. The association believes that it is most likely to replace the current flash memory and become the mainstream product of future memory and the first device to become a commercial product.

In the world, only large companies such as Ovonyx, Intel, Samsung, STMicroelectronics, Hitachi, IBM, Toshiba, Philips and Panasonic are conducting research on C-RAM memory, and are currently conducting research and development on technology improvement and manufacturability. At the beginning of 2006, Samsung has produced a 256M C-RAM memory test sample using a 0.12μm process, but the operating current of the device is still relatively high, the power consumption is relatively high, and the stability of the device needs to be further improved. One of the keys to the commercialization of C-RAM memory is the reduction of the operating current of the memory. The main measures currently used are to reduce the contact area between the heating electrode material and the phase change material, and to increase the resistance of the heating electrode material and the phase change material. , Improve device structure design, etc. South Korea's Samsung has adopted a unit structure called "On-axis confined", which confines the phase change material and the heating electrode material in nanoscale holes, which can reduce the area where the phase change occurs, improve thermal efficiency, and enable The amorphization (RESET) current of the device unit is reduced to 0.4mA [Symposium on VLSI Technology Digest of Technical Papers, 2005, 6B-1, 96]. In order to reduce the contact area between the heating electrode and the phase change material, South Korea’s Samsung Company has adopted a ring-shaped heating electrode structure, which can adjust the contact area by controlling the wall thickness of the ring-shaped heating electrode, which can greatly reduce the operating current, but they The ring-shaped heating electrode structure is not hollow, but filled with some kind of insulating material, such a structure cannot make the phase change material confined in the heating electrode [Jpn.J.Appl.Phys., 2006, 45, 3233]. Recently, Kolobov et al. reported that the phase change process of phase change materials is not only related to the temperature effect, but also has a direct relationship with pressure. Their research found that after a certain pressure is applied, even if the phase change material is not heated, it can induce its phase change. Variation [Phys. Rev. Lett., 2006, 97: 035701].

Based on the above principles, the present invention proposes a heat treatment method to introduce phase change materials into the hollow columnar heating electrodes. Due to the microtube effect, the gas in the nanotubes closed at one end is difficult to discharge, and it is phase-change materials. The change material is sealed in the hollow columnar heating electrode, so that the phase change memory storage cell structure obtained in this way has the following advantages: 1) The ring-shaped heating electrode greatly reduces the contact area between the electrode and the phase change material; 2) It is introduced into the hollow columnar The volume of the phase change material in the heating electrode is very small, and the contact area with the heating electrode is also small, so it is easy to undergo a phase change; 3) Under the action of the electric pulse, due to the temperature rise, the volume of the gas in the hollow cylindrical heating electrode expands , compress the phase change material, so that the phase change material is in a high temperature and high pressure environment, and it is very easy to undergo a phase change; 4) After the phase change material in the columnar heating electrode undergoes a phase change, it can further induce the phase change of other phase change materials, thereby Significantly reduces the power consumption required for phase change. The above is the design starting point of the present invention.

Contents of the invention

The object of the present invention is to seek a structure and a preparation method of a storage unit of a phase-change memory that can realize low-voltage, low-power consumption, and high-speed storage. The specific preparation process is as follows:

1) Prepare the lower electrode layer (as shown in Figure 1) on the substrate, using a thin film preparation process, the method is any of sputtering, evaporation, plasma-assisted deposition, chemical vapor deposition and atomic layer deposition A sort of. The substrate is any one of silicon wafer, silicon substrate on insulating layer, glass, GaAs, SiO ₂ , plastic or crystal material; the electrode material is a single metal material, such as W, Pt, Au, Ti, Al, One of the single metal materials in Ag, Cu or Ni, or an alloy material composed of them.

2) Cover the lower electrode with a heat-insulating material layer (as shown in Figure 2), using methods such as sputtering, evaporation, atomic layer deposition, plasma-assisted deposition, chemical vapor deposition, metal-organic thermal decomposition and Any of the laser-assisted deposition methods; the insulating material is one or a mixture of at least two of oxides, nitrides, carbides, and sulfides.

3) Through micro-nano processing technology, holes are prepared in the heat insulating material layer, the diameter of the hole is 10-500nm (as shown in Figure 3), and the micro-nano processing technology used is conventional photolithography technology and focused ion beam etching technology , atomic force microscopy processing technology, electron beam lithography, extreme ultraviolet lithography, nanoimprinting, or any of semiconductor standard processes.

4) Fill the heating electrode material in the hole using chemical vapor deposition (CVD), atomic layer deposition (ALD) or physical vapor deposition (PVD) and other film preparation processes to communicate with the lower electrode, and then perform chemical mechanical polishing (CMP) , remove the excess heating electrode material on the heat insulating material layer to form a hollow cylindrical heating electrode. The inner diameter of the hollow column is controlled by adjusting the CVD, ALD or PVD process time, generally 5-490nm; the heating electrode material is W, TiN, TiON, One of GeWN, GeTiN, TiW, GeN or SiGe (as shown in Figure 4).

5) Cover the thermal insulation material layer on the columnar heating electrode (as shown in Figure 5), the method used is sputtering method, evaporation method, atomic layer deposition method, plasma assisted deposition method, chemical vapor deposition method, metal organic compound thermal decomposition Any one of the method and the laser-assisted deposition method; the insulating material is a mixture of one or at least two of oxides, nitrides, carbides, and sulfides; the thickness of the insulating material layer is 10-300nm.

6) In the heat insulating material layer, a hole (as shown in Figure 6) that is overlaid with the columnar heating electrode is prepared. The diameter of the hole is 10-2000nm. technology, atomic force microscopy processing technology, electron beam lithography, extreme ultraviolet lithography, nanoimprinting, or any of semiconductor standard processes.

7) Deposit a reversible phase change material in the hole on the columnar heating electrode (as shown in Figure 7), using a thin film preparation process, the preparation method is sputtering method, evaporation method, metal organic chemical vapor deposition method, chemical vapor deposition method and Any one of the atomic layer deposition method; the chalcogenide compound is a compound containing at least one element of the sixth main group; the thickness of the phase change material layer is 10-500nm.

8) Annealing treatment is carried out under the protection of the atmosphere, so that part of the phase change material enters the hollow column of the heating electrode, and the annealing temperature is higher than the glass transition temperature of the phase change material and lower than the melting temperature; the protective gas used is Ar, Any of N ₂ , O ₂ , He or Ne (as shown in FIG. 8 ).

9) Prepare a thermal insulation material on the phase change material layer (as shown in Figure 9), using methods such as sputtering, evaporation, atomic layer deposition, plasma-assisted deposition, chemical vapor deposition, thermal decomposition of metal organics Any one of the method and the laser-assisted deposition method; the insulating material is a mixture of one or at least two of oxides, nitrides, carbides, and sulfides; the thickness of the insulating material layer is 50-500nm.

10) Through micro-nano processing technology, holes are prepared in the heat insulating material layer (as shown in Figure 10). The micro-nano processing technology used is conventional photolithography technology, focused ion beam etching technology, atomic force microscope processing technology, electron beam Any of photolithography, extreme ultraviolet lithography, nanoimprinting, or standard semiconductor processes.

11) Fill the holes with the electrode material so that it communicates with the phase change material (as shown in Figure 11), the methods used are sputtering, evaporation, plasma-assisted deposition, chemical vapor deposition and atomic layer deposition Any one of them; the electrode material is a single metal material, one of the single metal materials in W, Pt, Au, Ti, Al, Ag, Cu or Ni, or a combination of alloy materials.

12) Finally, use micro-nano processing technology to lead out the upper and lower electrodes to form a phase change memory storage unit (as shown in Figure 12). The micro-nano processing technology used is conventional photolithography technology, focused ion beam etching technology, atomic force microscope Any of the processing techniques, e-beam lithography, extreme ultraviolet lithography, nanoimprint, or semiconductor standard processes.

The structural characteristics of the phase change memory storage unit prepared according to the above preparation method are: the substrate is covered with a lower electrode layer; the lower electrode is covered with a layer of heat insulating material, and there are holes in the layer of heat insulating material; The material structure of the hollow columnar heating electrode is communicated; the columnar heating electrode is covered with a layer of heat insulating material, and the layer of heat insulating material contains holes engraved with the columnar heating electrode; and there are reversible Phase-change material; the phase-change material layer is covered with a layer of heat-insulating material, and the layer of heat-insulating material contains holes filled with an upper electrode material communicated with the phase-change material.

The characteristics of the storage unit of the phase-change memory in the present invention are: the phase-change material is introduced into the hollow columnar heating electrode through heat treatment, and due to the microtube effect, the gas in the nanotube with one end closed is difficult to discharge, and it is eliminated by the phase-change material. The change material is sealed in the hollow columnar heating electrode, so that the phase change memory storage cell structure obtained in this way has the following advantages: 1) The ring-shaped heating electrode greatly reduces the contact area between the electrode and the phase change material; 2) It is introduced into the hollow columnar The volume of the phase change material in the heating electrode is very small, and the contact area with the heating electrode is also small, so it is easy to undergo a phase change; 3) Under the action of the electric pulse, due to the temperature rise, the volume of the gas in the hollow cylindrical heating electrode expands , compress the phase change material, so that the phase change material is in a high temperature and high pressure environment, and it is very easy to undergo a phase change; 4) After the phase change material in the columnar heating electrode undergoes a phase change, it can further induce the phase change of other phase change materials, thereby Significantly reduces the power consumption required for phase change.

Description of drawings

Figure 1 Preparation of the lower electrode layer on the substrate

Figure 2 Covering the lower electrode with a layer of insulating material

Figure 3 Holes are made in the insulating material layer

Figure 4 Fill the heating electrode material in the hole, and remove the excess heating electrode material on the surface of the insulating material layer to form a hollow columnar heating electrode

Figure 5 The cylindrical heating electrode is covered with a layer of heat insulating material

Figure 6: In the heat insulating material layer, the holes that are overlaid with the columnar heating electrodes are prepared

Figure 7 Depositing a reversible phase change material in the hole on the columnar heating electrode

Figure 8 Annealing treatment under the protection of the atmosphere, so that part of the phase change material enters the hollow column of the heating electrode

Figure 9 prepares thermal insulation material on the phase change material layer

Figure 10 Holes are made in the insulating material layer

Figure 11 Filling the holes with electrode material

Figure 12 leads out the upper and lower electrodes to form a phase change memory storage unit

Detailed ways

Example 1:

A specific preparation process of a phase change memory storage unit is as follows:

1) A layer of Al lower electrode layer is prepared by DC magnetron sputtering method on the silicon substrate covered with SiO ₂ , the SiO ₂ of the silicon substrate is prepared by thermal oxidation method, and the thickness of the SiO ₂ material is 1000nm. The process parameters for preparing the Al electrode are: the background pressure is 2×10 ^-4 Pa, the Ar gas pressure is 0.2Pa during sputtering, the sputtering power is 200W, the substrate temperature is 25°C, and the film thickness is 400nm. (figure 1)

2) SiO ₂ thermal insulating material layer is prepared on the Al electrode, the process used is chemical vapor deposition method, and the film thickness is 500nm. (figure 2)

3) Holes are prepared in the SiO ₂ heat insulating material layer by using a 0.18 μm standard process, and the diameter of the holes is 260 nm. (image 3)

4) Use chemical vapor deposition technology to fill the heating electrode material W in the hole so that it communicates with the lower electrode Al, and then perform chemical mechanical polishing to remove excess W on the surface of the _SiO2 heat insulating material layer to form a hollow columnar heating electrode. The inner diameter of the hollow column is 160nm. (Figure 4)

5) Cover the SiO ₂ heat insulating material layer on the columnar heating electrode, the method adopted is chemical vapor deposition method, and the thickness of the film is 100nm. (Figure 5)

6) A 0.18 μm standard process is used to prepare a hole in the SiO ₂ heat insulating material layer that is overlaid with the columnar heating electrode. The hole is coaxial with the columnar heating electrode, and the diameter of the hole is 500 nm. (Figure 6)

7) Deposit Ge ₂ Sb ₂ Te ₅ phase change material in the hole, the method used is DC magnetron sputtering method, the process parameters are: the background pressure is 3×10 ^-4 Pa, and the Ar gas pressure is 0.15 during sputtering Pa, the sputtering power is 300W, the substrate temperature is 25°C, and the film thickness is 400nm. (Figure 7)

8) Annealing treatment is carried out under the protection of Ar gas, so that part of the phase change material enters the hollow column of the heating electrode, the annealing temperature is 550° C., and the annealing time is 10 minutes. (Figure 8)

9) SiO ₂ thermal insulation material was prepared on the Ge ₂ Sb ₂ Te ₅ phase change material layer, the method used was sputtering, and the process parameters were: the background pressure was 2×10 ^-4 Pa, and the Ar gas pressure during sputtering was 0.2Pa, the sputtering power is 200W, the substrate temperature is 25°C, and the film thickness is 500nm. (Figure 9)

10) Etch holes in the _SiO2 heat insulating material by ultraviolet exposure and reactive ion etching. The diameter of the holes is 1000nm. The specific process parameters of ultraviolet exposure are: photoresist is 6809, coating speed is 4000r/min, The coating time is 30s, the pre-baking is on a baking plate, the temperature is 100°C, the pre-baking time is 3min, the UV exposure power is 4mW, the exposure time is 12s, and the development is using tetramethylammonium hydroxide, and the development time is 5s; The specific process parameters of etching are: the etching background pressure is 1.3×10 ^-3 Pa, the etching gas is a mixed gas of CHF ₃ and Ar, the flow rates are 25 and 25 sccm respectively, the etching pressure is 4 Pa, and the substrate temperature is 15°C, the etching power is 250W, and the etching rate is 38.5nm/s. (Figure 10)

11) Fill the holes with electrode material W to communicate with the Ge ₂ Sb ₂ Te ₅ phase change material. The method used is DC magnetron sputtering, and the process parameters are: the background pressure is 2×10 ^-4 Pa, During sputtering, the Ar gas pressure is 0.2Pa, the sputtering power is 200W, the substrate temperature is 25°C, and the film thickness is 600nm. (Figure 11)

12) Finally, the W electrode is etched and drawn out by ultraviolet exposure and reactive ion etching, and the lower electrode Al is drawn out to form a phase change memory storage unit. The width of the electrode is 1000nm. The specific process parameters of ultraviolet exposure are: photolithography The glue is 6809, the glue coating speed is 4000r/min, the glue coating time is 30s, the pre-baking is using a baking plate, the temperature is 100°C, the pre-baking time is 3min, the UV exposure power is 4mW, the exposure time is 12s, and the development is using a tetramethyl ammonium hydroxide, and the development time is 5s; the specific process parameters of reactive ion etching are: the etching background pressure is 1.3×10 ^-3 Pa, the etching gas is a mixed gas of CF ₄ and O ₂ , and the flow rates are 20 and 2sccm, the etching pressure is 10Pa, the substrate temperature is 15°C, the etching power is 200W, and the etching rate is 32nm/s. (Figure 12)

In this embodiment, the phase change material is limited in the hollow column of the heating electrode and the hole in the heat insulating material through micro-nano processing technology and annealing treatment, so that when the electric pulse operates the storage unit, due to the temperature rise, the hollow column The thermal expansion of the volume of the gas and the phase change material is limited by the surrounding conditions, so that the phase change material in the electrode hollow column is in a high pressure and high temperature environment, and the phase change can occur preferentially, thereby inducing the further phase change of the surrounding phase change material. In the case of optimizing and controlling the operating window, the nanoscale high-speed reversible phase change process of the phase change material around the electrode hollow column is realized, thereby realizing the low voltage, low power consumption, and high speed functions of the phase change memory unit.

Example 2

The W columnar electrode in Embodiment 1 is changed to TiN, and the rest is similar to Embodiment 1.

Example 3

Change the Ge ₂ Sb ₂ Te ₅ phase change film in Embodiment 1 and Embodiment 2 into Si ₂ Sb ₂ Te ₅ phase change film, and the rest are similar to Embodiment 1 and Embodiment 2.

Example 4

Change the inner diameter of the columnar electrodes in Embodiment 1, Embodiment 2 and Embodiment 3 to 50 nm, and the rest are similar to Embodiment 1, Embodiment 2 and Embodiment 3.

Example 5

The SiO that is used for perforation in embodiment 1, embodiment 2, embodiment 3 and embodiment 4 changes the heat insulating film into Si ₃ N ₄ film, all _the other are the same as embodiment 1, embodiment 2, embodiment 3 and embodiment 4 similar.

Claims (10)

1. a phase-change memory storage unit is characterized in that: be coated with lower electrode layer on substrate; On lower electrode layer, be coated with insulation material layer, have hole in the insulation material layer; Comprise the open column shape heating electrode material that communicates with bottom electrode in the hole; Be coated with insulation material layer on the open column shape heating electrode, comprise hole in the insulation material layer with open column shape heating electrode alignment; And in open column shape heating electrode hole, contain the reversible transition material layer with the insulation material layer hole; On phase-change material layers, be coated with insulation material layer, in insulation material layer, comprise hole, and filled the upper electrode material that communicates with phase-change material within it.

2. by the described phase-change memory storage unit of claim 1, it is characterized in that:

1) diameter of hole is 10-500nm in the described insulation material layer that covers on the bottom electrode;

2) internal diameter of the described open column shape heating electrode that communicates with bottom electrode is 5-490nm;

3) thickness of the described insulation material layer that covers on the open column shape heating electrode is 10-300nm;

4) described is 10-2000nm with the hole diameter of open column shape heating electrode alignment on the insulation material layer that covers on the open column shape heating electrode;

5) thickness of sediment phase change material layer is 10-500nm in the hole on described open column shape heating electrode;

6) the heat-insulating material layer thickness that covers on described phase-change material layers is 50-500nm.

3. prepare the method for phase-change memory storage unit as claimed in claim 1 or 2, it is characterized in that:

1) on substrate, prepares lower electrode layer;

2) on lower electrode layer, cover insulation material layer;

3) by the micro-nano process technology, in insulation material layer, prepare hole;

4) in hole, utilize chemical vapour deposition (CVD), ald or physical gas-phase deposite method to fill heating electrode material, make it to communicate, carry out chemico-mechanical polishing then, form the open column shape heating electrode with bottom electrode;

5) on the open column shape heating electrode, cover insulation material layer;

6) in insulation material layer, prepare hole with open column shape heating electrode alignment;

7) deposition reversible transition material layer in the hole on the open column shape heating electrode;

8) under atmosphere protection, carry out annealing in process, the partial phase change material is entered in the open tubular column of open column shape heating electrode, in the scope that annealing temperature is in the glass transformation temperature that is higher than phase-change material, be lower than fusion temperature;

9) on phase-change material layers, prepare insulation material layer again;

10) by the micro-nano process technology, in insulation material layer, prepare hole;

11) in hole, fill upper electrode material, make it to communicate, to form top electrode with phase-change material;

12) utilize the micro-nano process technology that upper and lower electrode is drawn at last, form memory cell.

4. by the preparation method of the described phase-change memory storage unit of claim 3, it is characterized in that described substrate is silicon, glass, GaAs, the SiO on silicon chip, the insulating barrier ₂Or in the plastics any one.

5. press the preparation method of the described phase-change memory storage unit of claim 3, it is characterized in that preparing described electrode material and be adopt thin film preparation process, its method be in sputtering method, evaporation, plasma ion assisted deposition method, chemical vapour deposition technique and the atomic layer deposition method any one; Described electrode material is a kind of in the monometallic material among W, Pt, Au, Ti, Al, Ag, Cu or the Ni, or its alloy material that is combined into.

6. by the preparation method of the described phase-change memory storage unit of claim 3, it is characterized in that method that the preparation of described insulation material layer is adopted be in sputtering method, evaporation, atomic layer deposition method, plasma ion assisted deposition method, chemical vapour deposition technique, metallo-organic decomposition process and the laser assistant depositing method any one; Described insulating material is the mixture of a kind of or at least two kinds of formations in oxide, nitride, carbide, the sulfide.

7. press the preparation method of the described phase-change memory storage unit of claim 3, the preparation that it is characterized in that described filling heating electrode material is to adopt thin film preparation process, is specially in chemical vapour deposition technique, atomic layer deposition method and the physical vaporous deposition any one; Described heating electrode material is a kind of among W, TiN, TiON, GeWN, GeTiN, TiW, GeN or the SiGe.

8. press the preparation method of the described phase-change memory storage unit of claim 3, it is characterized in that preparing described phase-change material and be and adopt thin film preparation process, in sputtering method, evaporation, Metalorganic Chemical Vapor Deposition, chemical vapour deposition technique and the atomic layer deposition method any one.

9. by the preparation method of the described phase-change memory storage unit of claim 3, it is characterized in that preparing micro-nano process technology that described hole adopts in conventional photoetching technique, focused-ion-beam lithography technology, atomic force microscope process technology, electron beam lithography method, extreme ultraviolet photolithographic method, nano impression method or the semiconductor standard processes any.

10. by the preparation method of the described phase-change memory storage unit of claim 3, it is characterized in that carrying out annealing in process under atmosphere protection, the partial phase change material is carried out in the open tubular column of heating electrode, employed protective gas is Ar, N ₂, O ₂, among He or the Ne any.

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