JP4131896B2 - Method for manufacturing nonvolatile semiconductor memory device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a nonvolatile semiconductor memory device, and more particularly to a semiconductor memory cell structure suitable for high density and high integration and a method for manufacturing the same.
[0002]
[Prior art]
A flash memory is well known as a nonvolatile semiconductor memory device that can electrically rewrite data and is suitable for high density and large capacity. In particular, a memory cell having a MOS transistor structure having a stacked gate structure of a charge storage layer and a control gate is widely used.
[0003]
FIG. 15 shows a first conventional example of a memory cell including a shallow trench isolation (STI) structure. FIG. 15A is a plan view, and FIG. It is A 'sectional drawing.
[0004]
An element isolation trench groove 2 is formed in a p-type silicon substrate or p well 1, and an element isolation insulating material, for example, a silicon dioxide material is embedded in the trench groove. A thin tunnel insulating film 4 through which a tunnel current can flow is formed on the entire surface of the element region (channel region) 8 on the element-isolated substrate, and a charge storage layer 5 is formed on the thin insulating film 4. A control gate 7 is formed through the insulating film 6. Further, it can be observed from FIG. 15B that a part 5 a on the lower surface of the charge storage layer 5 protrudes downward along the trench groove 2.
[0005]
FIG. 16 is a cross-sectional view showing a manufacturing process for obtaining the STI cell structure shown in FIG.
[0006]
First, as shown in FIG. 16A, a dummy insulating film 10 is formed on a semiconductor substrate 1 and a mask material 11 such as a photoresist is further deposited, and the mask material 11 in the element isolation region and the dummy insulation are formed by photolithography. The trench 10 is formed by removing the film 10 and the semiconductor substrate 1 by etching so that the side edges thereof are aligned.
[0007]
Next, thermal oxidation is performed using appropriate oxidation conditions to oxidize the trench sidewall surfaces. At this time, the mask material also serves as a mask against oxidation, and the so-called bird's beak formed in the dummy insulating film portion is formed thicker than the oxide film formed in the trench sidewall, Corners are removed and rounded.
[0008]
Subsequently, an element isolation insulating film is deposited on the entire surface of the semiconductor substrate, the element isolation insulating film 3 is filled in the trench groove 2, and the element isolation insulating film is etched back by dry etching or surface polishing by chemical polishing (CMP). 3 is flattened and the upper surface of the mask material 11 is exposed (FIG. 16B).
[0009]
Next, the mask material 11 and the dummy oxide film 10 are removed by dry etching and wet etching by chemical treatment, and then the tunnel insulating film 4 and the charge storage layer 5 are deposited (FIG. 16C).
[0010]
Next, the charge storage layer 7 is cut into a slit shape on the element isolation region by pattern formation by lithography, and subsequently an intergate insulating film 6 and a control gate 7 are deposited, and gate processing is performed by patterning to complete the cell structure. . (FIG. 16 (d)).
[0011]
Next, the reason why a part 5a of the lower surface of the charge storage layer 5 protrudes downward along the trench 2 will be described together with the operation of this memory cell.
[0012]
Data rewriting of a memory cell having such a tunnel oxide film is performed by modulating the amount of charge stored in the charge storage layer 5 by charge transfer between the charge storage layer 5 and the semiconductor substrate 1. In general, at least one of charge injection and charge discharge uses the FN (Fowler-Nordheim) tunneling phenomenon of the tunnel insulating film 4. That is, a high electric field of 10 MV / cm or more is applied between the charge storage layer 5 and the semiconductor substrate 1 to emit electrons from the semiconductor substrate 1 to the charge storage layer 5 or from the charge storage layer 5 to the semiconductor substrate 1. At this time, since the charge storage layer 5 is completely in a floating state, the charge in the charge storage layer 5 does not change unless data is rewritten.
[0013]
In order to apply a high voltage to the charge storage layer 5, it is necessary to capacitively couple the control gate 7 and the charge storage layer 5 by applying a voltage to the control gate 7. However, if the voltage applied to the control gate 7 is high, it is necessary to increase the various breakdown voltages of the transistors constituting the booster circuit, the input / output switch circuit, etc. that generate the applied voltage, which increases the element area. There's a problem.
[0014]
On the other hand, if the capacitance between the charge storage layer 5 and the semiconductor substrate 1 via the tunnel insulating film 4 is C1, and the capacitance between the charge storage layer 5 and the control gate 7 via the inter-gate insulating film 6 is C2, tunnel insulation is achieved. The voltage Vfg applied to the film 4 is expressed by the following equation using the control gate voltage Vcg.
[0015]
Vfg = C2 / (C1 + C2) Vcg
In order to reduce the voltage applied to the control gate 7 from this equation, C2 must be increased, that is, the capacitance between the control gate 7 and the charge storage layer 5 via the intergate insulating film 6 must be increased. It turns out that it is effective. Therefore, it is only necessary to increase the opposing area between the control gate 7 and the charge storage layer 5, and as described above, this requirement is satisfied by making the charge storage layer 5 project from the element region toward the element isolation region. Can do.
[0016]
The memory cell structure shown in the first conventional example has two major problems.
[0017]
The first problem is that it is very difficult to reduce the element isolation width. In order to cut the charge storage layer 5 into a slit shape on the element isolation region, a process finer than the element region and the width of the element isolation region is required. Therefore, the element isolation dimension of the memory cell is determined by the slit process. It will be done. In general, slit processing is performed using lithography technology, but in order to perform slit processing on the element isolation region, even if the slit pattern is misaligned in the lithography process, an alignment margin is provided so that the pattern does not overlap with the lower element region. It is necessary to arrange the pattern including it. Therefore, even if the slit pattern itself can be opened in a pattern thinner than the element isolation width, the element isolation width is widened. In other words, it can be said that it is difficult to reduce the element isolation width in the conventional memory cell structure in which the charge storage layer is slit using a lithography technique.
[0018]
The second problem is that it is very difficult to reduce the element region width. In the case of the memory cell structure shown in the conventional example, when the dummy insulating film is peeled off by wet etching, there is a possibility that the trench side end portion is partially exposed. Therefore, as described above, a parasitic MOS capacitor is formed between the charge storage layers at the end portion on the trench side via the tunnel insulating film. When the rounding amount at the end on the trench side of the parasitic MOS capacitor portion is small, a kink characteristic is generated in the subthreshold region in the transistor characteristic of the memory cell, and the cutoff characteristic is remarkably deteriorated. In addition, when data is written by FN tunneling electron injection by applying a high voltage to the control gate, the gate electric field concentrates on the parasitic MOS capacitor and causes dielectric breakdown of the tunnel insulating film.
[0019]
In order to suppress this, it is necessary to further round the trench side end. However, a large amount of rounding oxidation causes the bird's beak described above to be formed at the trench side end. Compared to the formation, it becomes extremely narrow. For this reason, in order to form the element region with a desired width, the width of the pattern must be widened in consideration of the reduction by rounding oxidation. Further, when the amount of bird's beak increases, the variation in the amount of bird's beak increases, and it becomes very difficult to accurately control the fine element dimensions.
[0020]
Thus, the STI memory cell structure shown in the first conventional example has a problem that it is very difficult to reduce the element isolation width and the element region width.
[0021]
FIG. 17 shows the STI structure of the second prior art proposed in Japanese Patent Laid-Open No. 10-017948 as one of the STI cell structures for solving the above-mentioned problems. FIG. 17 (b) is a sectional view taken along the line BB '.
[0022]
An element isolation trench 2 is formed in a p-type silicon substrate or p well 1, and an element isolation insulating material 3, for example, a silicon dioxide material is embedded in the trench. A thin tunnel insulating film 4 through which a tunnel current can flow is formed over the entire channel region on the element-isolated substrate, and a charge storage layer 12 is formed thereon. It coincides with the end of the element isolation region. The element isolation insulating film 3 is in contact with the charge storage layer 12. In order to increase the capacitance between the charge storage layer 12 and the control gate 14, a part of the side surface of the charge storage layer 12 is exposed through the intergate insulating film 13. Facing the control gate 14. The control gate 14 and the charge storage layer 12 are processed in a self-aligned manner in the vertical direction so that the side end portions are aligned, and an n-type diffusion layer 9 is formed between the gates.
[0023]
18 is a cross-sectional view showing a manufacturing process for obtaining the STI cell structure shown in FIG.
[0024]
A conductive material 12 and a mask material 15 to be a charge storage layer are deposited on the semiconductor substrate 1 via the tunnel insulating film 4. The trench groove 2 is formed by etching and removing the mask material 15, the conductive material 12, the tunnel insulating film 4, and the semiconductor substrate 1 in the element isolation region so that the side end portions thereof coincide with each other (FIG. 18A).
[0025]
An element isolation insulating film 3 is deposited after performing thermal oxidation using appropriate oxidation conditions to oxidize the surface of the trench side wall, and then etching back by dry etching or surface polishing by chemical polishing (CMP). The upper surface of the isolation insulating film 3 is planarized and the upper surface of the mask material 15 is exposed. (FIG. 18 (b))
In this state, the element isolation insulating film 3 is further etched back to expose a part of the side surface of the charge storage layer 12, and then the mask material 15 is peeled off. (FIG. 18 (c))
Subsequently, an intergate insulating film 13 and a control gate 14 are deposited, and gate processing by patterning is performed to complete the cell structure. (FIG. 18 (d))
In the STI cell structure shown in the second conventional example, the tunnel insulating film and the charge storage layer are deposited before the trench groove is formed, and then the trench groove is formed and the element isolation insulating film is embedded. Unlike the STI cell structure shown in the first conventional example, it is not necessary to use a dummy insulating film, and the trench side end is not exposed. For this reason, it is suitable for miniaturization of the element region width.
[0026]
Furthermore, since the charge storage layer is completely separated in the element isolation region, it is not necessary to cut the charge storage layer into a slit shape on the element isolation region. For this reason, the element isolation region width can be reduced.
[0027]
[Problems to be solved by the invention]
However, on the other hand, the STI cell structure shown in the second conventional example has a problem that the buried isolation increases when the insulating film for element isolation is embedded in the trench groove, so that the width of the element isolation region cannot be reduced. As described above, in the STI cell structure of the first conventional example, a part of the charge storage layer is projected along the separation element isolation insulating film to increase the area facing the control gate. In the conventional STI cell structure, an area facing the control gate is obtained at a part of the side surface of the charge storage layer. For this reason, it is necessary to increase the thickness of the charge storage layer by an amount necessary for the region facing the control gate.
[0028]
Assume that the element isolation insulating film can be embedded without voids (holes) with an aspect ratio of 2, for example, the trench groove depth is 0.3 μm and the charge storage layer thickness is 0.15 μm. Think. The element isolation width that can be embedded with a mask material thickness of 0.1 μm is 0.275 μm. On the other hand, in the STI cell structure shown in the first conventional example, since the charge storage layer is not sandwiched at the time of embedding, the aspect is low and the element isolation width can be embedded up to 0.2 μm. On the other hand, in the STI cell structure of the second conventional example, the element isolation width is limited not by slit processing of the charge storage layer but by embedding an element isolation insulating film.
[0029]
As described above, in the conventional nonvolatile semiconductor memory device having the STI cell structure, it is difficult to miniaturize the element region width and the element isolation width, and there is a problem that the miniaturization of the memory cell is limited.
[0030]
The present invention has been made in view of the above circumstances, and provides a method for manufacturing a high-density nonvolatile semiconductor memory device that can reduce the element isolation width of the memory cell by reducing the embedding aspect of the element isolation insulating film. The purpose is to do.
[0031]
[Means for Solving the Problems]
According to a first aspect of the invention,
Forming a first gate insulating film on the semiconductor substrate;
Forming a first conductive layer serving as a lowermost layer of a charge storage layer on the first gate insulating film;
Forming a mask material on the first conductive layer;
Etching the mask material, the first conductive layer, the first gate insulating film, and the semiconductor substrate so that the side end positions thereof coincide with each other to form a trench groove;
Oxidizing at least the trench groove sidewall and the first conductive layer sidewall surface;
Depositing an isolation film for element isolation and embedding a trench groove;
Planarizing the element isolation insulating film to expose the upper surface of the mask material;
Peeling the mask material to expose the upper surface of the first conductive layer;
Depositing a second conductive layer as the uppermost layer of a charge storage layer on the entire surface including the upper surface of the first conductive layer and the upper surface of the element isolation insulating film;
Flattening the second conductive layer so that the upper surface thereof is flush with the upper surface of the element isolation insulating film;
Forming a second gate insulating film on the second conductive layer and the element isolation insulating film;
Depositing a control gate material on the second gate insulating film;
Processing the deposited control gate material into a predetermined shape;
Is provided.
[0032]
With this method, the nonvolatile semiconductor memory device can be manufactured stably.
[0033]
According to the method for manufacturing a nonvolatile semiconductor memory device according to the second aspect of the present invention,
Forming a first gate insulating film on the semiconductor substrate;
Forming a first conductive layer serving as a lowermost layer of a charge storage layer on the first gate insulating film;
Forming a mask material on the first conductive layer;
Etching the mask material, the first conductive layer, the first gate insulating film, and the semiconductor substrate so that the side end positions thereof coincide with each other to form a trench groove;
Oxidizing at least the trench groove sidewall and the first conductive layer sidewall surface;
Depositing an isolation film for element isolation and embedding a trench groove;
Planarizing the element isolation insulating film to expose the upper surface of the mask material;
Peeling the mask material to expose the upper surface of the first conductive layer;
Depositing a second conductive layer as the uppermost layer of the charge storage layer on the semiconductor substrate;
Flattening the second conductive layer so that the upper surface thereof is flush with the upper surface of the element isolation insulating film;
Selectively etching the element isolation insulating film so that the upper surface thereof is located between the lower surface and the upper surface of the second conductive layer;
Forming a second gate insulating film on the side wall of the second conductive layer exposed by this etching, the upper surface of the second conductive layer, and the upper surface of the element isolation insulating film;
Depositing a control gate material on the second gate insulating film;
Processing the deposited control gate material into a predetermined shape;
Is provided.
[0034]
Even with this method, the nonvolatile semiconductor memory device can be stably manufactured.
[0035]
According to the method for manufacturing a nonvolatile semiconductor memory device according to the third aspect of the present invention,
Forming a first gate insulating film on the semiconductor substrate;
Forming a first conductive layer serving as a lowermost layer of a charge storage layer on the first gate insulating film;
Forming a mask material on the first conductive layer;
Etching the mask material, the first conductive layer, the first gate insulating film, and the semiconductor substrate so that the side end positions thereof coincide with each other to form a trench groove;
Oxidizing at least the trench groove sidewall and the first conductive layer sidewall surface;
Depositing an isolation film for element isolation and embedding a trench groove;
Planarizing the element isolation insulating film to expose the upper surface of the mask material;
Peeling the mask material to form a recess exposing the upper surface of the first conductive layer;
Increasing the lateral width of the recess by isotropic etching;
Depositing a second conductive layer, which is the uppermost layer of the charge storage layer, on the semiconductor substrate and on the element isolation insulating film and in the recess;
Flattening the second conductive layer so that the upper surface thereof is flush with the element isolation insulating film;
Selectively etching the element isolation insulating film so that the upper surface thereof is located between the lower surface and the upper surface of the second conductive layer;
Forming a second gate insulating film on the side wall of the second conductive layer exposed by this etching, the upper surface of the second conductive layer, and the upper surface of the element isolation insulating film;
Depositing a control gate material on the second gate insulating film;
Processing the deposited control gate material into a predetermined shape;
Is provided.
[0036]
In this method, the uppermost layer of the charge storage layer can be formed sufficiently wider than the lowermost layer.
[0037]
The flattening step of the first and second conductive layers may be performed by dry etching or polishing, whereby the flattening can be achieved stably.
[0038]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, some embodiments of the present invention will be described in detail with reference to the drawings.
[0039]
1A and 1B show a memory cell structure according to a first embodiment of the present invention. FIG. 1A is a plan view and FIG. 1B is a cross-sectional view taken along the line CC ′.
[0040]
An element isolation trench groove 22 is formed in a p-type silicon substrate or p well 21, and an element isolation insulating material, for example, a silicon dioxide material is embedded in the trench groove 22 to form an element isolation insulating film 23. ing.
[0041]
For example, a silicon dioxide film having a thickness of 150 angstroms or less is formed as a thin tunnel insulating film 24 capable of allowing a tunnel current to flow on the entire surface of the channel region 30 on the element-isolated substrate, and the first conductive layer 25 is formed thereon. The side end portion of the first conductive layer 25 is located at the same position as the end portion of the element isolation region.
[0042]
Note that an oxide film 33 is formed on the inner surface of the trench groove 22 and the end surface of the first conductive layer 25 on the element isolation region side. In the subsequent drawings, this oxide film is omitted for simplification. To do.
[0043]
A second conductive layer 26 is formed on the first conductive layer 25 so as to be in contact with the first conductive layer 25, and its side end portion extends slightly outward from the first conductive layer 25. Yes. A charge storage layer 27 is constituted by a laminated structure of the first conductive layer 25 and the second conductive layer 26.
[0044]
The upper surface of the element isolation insulating film 23 coincides with the upper surface of the charge storage layer 27, and a control gate 29 is formed on these upper surfaces via an inter-gate insulating film 28.
[0045]
As shown in FIG. 1A, the control gate 29 and the charge storage layer 27 are processed in a self-aligned manner so that the side edges thereof coincide with the vertical direction, and an n-type diffusion layer 31 is interposed between the gates. Is formed.
[0046]
FIG. 2 is a cross-sectional view showing a manufacturing process for obtaining the self-aligned STI cell structure shown in FIG.
[0047]
First, a tunnel insulating film 24 is formed on a semiconductor substrate 21, a polysilicon layer doped with impurities as the first conductive layer 25 is formed thereon by a CVD method, and a resist as a mask material 32 is further formed thereon. accumulate. Next, the trench material 22 is formed by etching and removing the mask material 32, the first conductive layer 25, the tunnel insulating film 24, and the semiconductor substrate 21 in the element isolation region so that the side end portions thereof coincide with each other (FIG. 2 ( a)).
[0048]
Subsequently, an oxidation process or a surface modification process is performed to oxidize the sidewalls of the trench grooves 22 and the sidewalls of the first conductive layer 25, and then an element isolation insulating film 23 is deposited over the entire surface and etched by dry etching. The element isolation insulating film 23 is planarized by back polishing or surface polishing by chemical polishing (CMP), and finally the upper surface of the mask material 32 is exposed (FIG. 2B).
[0049]
Next, the mask material 32 is peeled off to expose the upper surface of the first conductive layer 25, and then a second conductive layer 26 made of a polysilicon layer doped with impurities is deposited on the entire surface to form an element isolation insulating film. The second conductive layer 26 is separated by etching back or planar polishing until 23 is exposed (FIG. 2C). These first conductive layer 25 and second conductive layer 26 function as the charge storage layer 27 as described above.
[0050]
Next, an inter-gate insulating film 28 and a control gate are deposited, and gate processing is performed to complete the cell structure. (Fig. 2 (d))
In the structure obtained by such a manufacturing process, the side wall of the first conductive layer 25 is slightly receded by the oxidation process after forming the trench groove, so that the width of the second conductive layer 26 is set to the first conductive layer 25. The structure is slightly wider than the width.
[0051]
Further, when the second conductive layer 26 is deposited, a slight oxide film is formed on the upper surface of the first conductive layer by cleaning the upper surface of the first conductive layer 25 with a chemical treatment. In some cases, an oxide film is sandwiched between the conductive layer 25 and the second conductive layer 26. However, since this oxide film is very thin, there is no problem in electrical conduction, and the first conductive layer and the second conductive layer are kept at the same potential.
[0052]
The memory cell according to the first embodiment has the following characteristics.
[0053]
First, in the STI cell structure shown in the second conventional example described above, there is a problem that the embedding aspect becomes high when the trench groove is embedded with the element isolation insulating film. In contrast, in the present invention, since the charge storage layer has a laminated structure of the first conductive layer and the second conductive layer, the aspect at the time of embedding the element isolation insulating film depends on the thickness of the first conductive layer film and the mask. Determined by the thickness of the material. Therefore, the embedding aspect can be reduced by making the thickness of the first conductive layer thinner than that of the second conductive layer. For example, consider a case where the trench groove depth is 0.3 μm and the charge storage layer thickness is 0.15 μm. If the aspect capable of embedding the element isolation insulating film without voids (holes) is 2, the mask material can be embedded if the thickness of the first conductive layer is 0.05 μm and the thickness of the first conductive layer is 0.1 μm. The device isolation width is 0.225 μm, which can be made finer than the STI cell structure of the second conventional example shown above.
[0054]
Further, by accumulating the second conductive layer 26 on the first conductive layer 25, it becomes possible to adjust to the desired film thickness of the charge storage layer 27 required for gate processing control. It is possible to reduce the resistance of the entire charge storage layer 27 while lowering the impurity concentration of the first conductive layer 25 that forms one gate insulating film interface.
[0055]
Further, in order to increase the capacitance between the charge storage layer 27 and the control gate 29, for example, the upper surface of the charge storage layer 27 may be roughened, but the second conductive layer 26 is sufficiently deposited. As a result, it is possible to perform the surface forming process after element isolation embedding.
[0056]
Further, when impurity doping for the purpose of controlling the threshold voltage of a memory cell, a transistor, or the like is performed on the semiconductor substrate under the gate electrode, ion implantation is performed through the first conductive layer 25 because the first conductive layer 25 is thin. It becomes possible. This makes it possible to perform ion implantation after a high-temperature heat treatment step necessary for forming a gate insulating film such as thermal oxidation, so that the impurity profile in the semiconductor substrate can be precisely controlled.
[0057]
Further, in the memory cell shown in the first embodiment, since the uppermost surface of the charge storage layer 27 is flat over the entire surface of the cell array, the capacity variation due to the variation in the area of the upper surface of the charge storage layer can be suppressed. It is possible to configure a uniform memory cell.
[0058]
FIG. 3 has a configuration similar to that of FIG. 1B, but the side positions of the first conductive layer 25 and the second conductive layer 26 ′ constituting the charge storage layer 27 are the same. An example in which the layer widths match is shown. Such a configuration is a combination of materials and conditions in which the first conductive layer 25 is less likely to recede due to etching when forming the trench groove 23, or a surface modification process other than oxidation that does not cause the first conductive layer to recede. Can be obtained.
[0059]
Such a configuration is a self-aligned structure, and there is no stepped portion. Therefore, parasitic capacitance is not generated, and improvement in characteristics due to smooth charge transfer can be expected.
[0060]
4A and 4B show a cell structure of a nonvolatile semiconductor memory device according to the second embodiment of the present invention. FIG. 4A is a plan view, and FIG. 4B is a DD ′ sectional view. is there.
[0061]
An element isolation trench groove 42 is formed in a p-type silicon substrate or p well 41, and an element isolation insulating material 43, for example, a silicon dioxide material, is embedded in the trench groove 42. A thin tunnel insulating film 44 through which a tunnel current can flow is formed on the entire surface of the channel region on the element-isolated substrate, and a first conductive layer 45 is formed thereon, and this first conductive layer 45 is formed. The position of the side end portion of this is coincident with the end portion of the element isolation region 43.
[0062]
A second conductive layer 46 is formed on the first conductive layer 45 so as to be in contact with the first conductive layer 45, and its side end portion extends slightly outward from the first conductive layer 45. Yes. A charge storage layer 47 is constituted by a laminated structure of the first conductive layer 45 and the second conductive layer 46.
[0063]
Further, the upper surface of the element isolation insulating film 43 is positioned slightly higher than the lower surface of the second conductive layer 46, and the upper surface and the side wall of the second conductive layer 46 are higher than the element isolation insulating film position. An intergate insulating film 48 is formed on a part of the element isolation insulating film 43, and a control gate 49 is formed thereon. As shown in FIG. 4A, the control gate 49 and the charge storage layer 47 are processed in a self-aligning manner so that the side edges thereof are aligned in the vertical direction, and an n-type diffusion layer 51 is formed between the gates. Has been.
[0064]
FIG. 5 is a cross-sectional view for explaining a manufacturing process for obtaining the STI cell structure shown in FIG.
[0065]
A tunnel insulating film 44 is formed on the semiconductor substrate 41, and a first conductive layer 45 and a mask material 52 are deposited thereon. After that, the trench material 42 is formed by removing the mask material 52, the first conductive layer 45, the tunnel insulating film 44, and the semiconductor substrate 41 in the element isolation region so that the side edges thereof are aligned.
[0066]
Subsequently, an oxidation process or a surface modification process is performed to oxidize the sidewalls of the trench groove 42 and the sidewalls of the first conductive layer 45, and then an element isolation insulating film 43 is deposited and etched back by dry etching or The element isolation insulating film 43 is planarized by surface polishing by chemical polishing (CMP), and finally the upper surface of the mask material 52 is exposed (FIG. 5A).
[0067]
Next, the mask material is peeled off, and then a second conductive layer 46 is deposited (FIG. 5B).
[0068]
Subsequently, the second conductive layer 46 is separated by etching back or planar polishing until the element isolation insulating film 43 is exposed (FIG. 5C).
[0069]
Further, only the element isolation insulating film 43 is etched so that the upper surface reaches an appropriate position within the thickness of the second conductive layer 46, for example, 1/3 or 1/4 of the thickness from the lower surface. Etching is continued until an inter-gate insulating film 48 and a control gate 49 are deposited, and gate processing is performed to complete the cell structure (FIG. 5D).
[0070]
The capacitance can be increased as the upper surface position of the element isolation insulating film 43 is located on the lower side of the second conductive layer 46. However, the inter-gate insulating film located on the lower side can be stably formed. Since it will not be possible, the position should be determined taking these into account.
[0071]
In such a memory cell according to the second embodiment, in order to increase the capacitance between the charge storage layer 47 and the control gate 49, a part of the side surface of the second conductive layer 46 is exposed to face the control gate 49. Yes. Therefore, the coupling capacitance can be made larger than that of the memory cell shown in the first embodiment. The step amount between the upper surface of the second conductive layer 46 and the upper surface of the element isolation insulating film 48 is such that the facing area can be obtained so that the capacitance between the charge storage layer 47 and the control gate 49 is adjusted to a desired value. It is possible to set the level difference and to make the level difference uniform in the cell array. Note that the thickness of the second conductive layer 46 is preferably larger than the thickness of the first conductive layer 45 in order to easily expose a part of the side wall.
[0072]
FIG. 6 shows a case where the widths of the first conductive layer 45 and the second conductive layer 46 are the same as in FIG. 3, and the structure is suitable for manufacturing by self-alignment.
[0073]
FIG. 7 shows a cell structure of a nonvolatile semiconductor memory device according to the third embodiment of the present invention. FIG. 7 (a) is a plan view thereof, and FIG. 7 (b) is a sectional view taken along line EE ′ thereof. It is.
[0074]
This configuration is similar to that of the second embodiment, and the corresponding components are those obtained by adding 20 to the reference numbers in the second embodiment shown in FIG. 4, that is, the 60s and 70s. The difference between the second embodiment and the third embodiment is that the width of the second conductive layer 66 corresponding to the second conductive layer 46 in the second embodiment is the same as that of the first conductive layer 65. It is a point that is wider than the width. 7A and 7B clearly show that the width of the second conductive layer is widened.
[0075]
FIG. 8 is a cross-sectional view showing a manufacturing process for obtaining the cell structure shown in FIG.
[0076]
A tunnel insulating film 64 is formed on the semiconductor substrate 61, and a first conductive layer 65 and a mask material 72 are deposited thereon. In this state, the trench 72 is formed by removing the mask material 72, the first conductive layer 65, the tunnel insulating film 64, and the semiconductor substrate 61 in the element isolation region so that the side edges thereof are aligned. Subsequently, an oxidation process or a surface modification process is performed to oxidize the sidewalls of the trench groove 62 and the sidewalls of the first conductive layer 65, and then an element isolation insulating film 63 is deposited and etched back by dry etching or The element isolation insulating film is planarized by surface polishing by chemical polishing (CMP), and finally the upper surface of the mask material 72 is exposed (FIG. 8A).
[0077]
After the mask material 72 is peeled off, the element isolation insulating film is etched laterally by a desired amount by isotropic etching such as wet etching. As a result, a portion where no element isolation insulating film wider than the width of the first conductive layer 65 is formed is formed (FIG. 8B).
[0078]
Next, the second conductive layer 66 is deposited on the entire surface of the semiconductor substrate, and the second conductive layer is separated by etching back or planar polishing until the element isolation insulating film 63 is exposed. (FIG. 8 (c)).
[0079]
Subsequently, the element isolation insulating film 63 is additionally etched back, the element isolation insulating film 63 is retracted to the lower side of the second conductive layer 66, and the upper side of the second conductive layer 66 is exposed.
[0080]
In this state, an inter-gate insulating film 68 and a control gate 69 are deposited, and gate processing is performed to complete the cell structure (FIG. 8D).
[0081]
In the memory cell according to the third embodiment, after the mask material 72 is peeled off, the element isolation insulating film is etched in the lateral direction by a desired amount so that the second conductive layer is the first conductive layer, that is, the element. A structure that is wider than the width is realized. Therefore, the memory cell shown in the third embodiment can increase the capacitance between the charge storage layer and the control gate as compared with the memory cell shown in the first embodiment and the memory cell shown in the second embodiment.
[0082]
Note that the step of additionally etching back the element isolation insulating film 63 after planarizing the second conductive layer 66 to expose a part of the side surface of the charge storage layer 67 is performed by the capacitance between the control gate 69 and the charge storage layer 67. This is not necessary when the capacitance between the control gate 69 and the charge storage layer 67 can be sufficiently large with the facing area of only the upper surface of the charge storage layer 67.
[0083]
FIG. 9 shows a nonvolatile semiconductor memory device according to the fourth embodiment of the present invention. FIG. 9A is a plan view, and FIG. 9B is a sectional view taken along line FF ′.
[0084]
Since the cross-sectional view shown in FIG. 9B is exactly the same as the cross-sectional view shown in FIG. 4B, the same components are denoted by the same reference numerals and detailed description thereof is omitted.
[0085]
In this embodiment, the case where the cell array configuration has a NAND configuration is shown as an example. That is, in this embodiment, 16 NAND cells connected in series are connected to the bit line and the source line via the selection transistor 53. The select transistor is composed of the same material, the same film thickness and the same stacked structure as the cell. A gate electrode called a charge storage layer in a memory cell has a floating structure in a select transistor as well, and the charge storage layer is not electrically connected between transistors between adjacent bit lines. The selection transistor has no difference in appearance. However, the gate length may be different between the memory cell and the select transistor as necessary. In the selection transistor, a predetermined voltage is applied to the charge storage layer by capacitive coupling between the charge storage layer and the control gate, so that a normal transistor operation is performed by applying a voltage to the control gate. Therefore, when the memory cell and the select transistor have the same gate structure, unnecessary processing steps can be omitted in the cell array, and the memory cell can be manufactured with the minimum number of steps.
[0086]
In addition, in the AND type and DINOR type other than the NAND configuration, the array configuration forms a unit by connecting a plurality of memory cells in series or in parallel, and a selection transistor that is a switching transistor is connected to the bit line or the source line. This embodiment can be applied similarly.
[0087]
FIG. 14 is an element cross-sectional view showing the relationship between the distance between the end portions on the element isolation region side, the uppermost interlayer distance and the lowermost interlayer distance of the charge storage layer in each of the above-described embodiments.
[0088]
As described above, since the width of the uppermost layer of the charge storage layer is formed wider than the width of the lowermost layer, the distance between the adjacent end portions on the element isolation region is X1, and among the adjacent charge storage layers When the distance between the lowermost layer side ends is Y and the distance between the uppermost layer side ends is X2,
Y>X1> X2 or Y> X1 = X2
It can be seen that
[0089]
FIG. 10 shows a nonvolatile semiconductor memory device according to another fifth embodiment of the present invention. 10A is a plan view of the low-voltage transistor, FIG. 10B is a cross-sectional view thereof along GG ′, FIG. 10C is a plan view of the high-voltage transistor, and FIG. 'A cross-sectional view is shown.
[0090]
These are fabricated in the same element, and the planar configuration is the same. However, when the cross-sectional structure is seen, both have a laminated gate structure, and the lower gate of the two-layer configuration similar to the charge storage layer. (83, 87 for low voltage and 83, 97 for high voltage) and an upper gate 88 formed of the same conductive material as the control gate. Of these, the thickness of the upper layer of the lower gates is thicker in the low voltage transistor than in the high breakdown voltage transistor. The low voltage transistor has a thin gate oxide film 82, whereas the high voltage transistor has a thick gate oxide film 92.
[0091]
This is based on the following reason. Generally, a transistor having a desired gate insulating film thickness is used for a sense amplifier, a booster circuit, and an input / output switch circuit for driving a memory cell, and a low voltage capable of high-speed operation in the sense amplifier. A gate insulating film equivalent to or thinner than a tunnel insulating film of a memory cell is used for a transistor. On the other hand, a thicker gate insulating film than a tunnel insulating film is used for a high-voltage transistor capable of high-voltage operation in a thickening circuit or input / output switch circuit that drives a high voltage for data rewriting of a memory cell. .
[0092]
11 and 12 are cross-sectional views showing the steps of manufacturing the memory cell transistor of the nonvolatile semiconductor memory device shown in FIG. In these figures, the left side shows the manufacturing process of the low voltage transistor, and the right side shows the manufacturing process of the high voltage transistor.
[0093]
First, a low voltage transistor will be described.
[0094]
A plurality of gate insulating films are formed with a desired film thickness on the semiconductor substrate 81. For example, a thermal oxide film of 100A, for example, is formed as a tunnel insulating film 82 for a memory cell, or an thermal oxide film of 80A, for example, is formed as a thin gate insulating film for NMOS and PMOS for sense amplifier operation (FIG. 11A). For example, a 200 A thermal oxide film 92 (FIG. 11D) is formed as a thick gate insulating film for a high breakdown voltage transistor for boost circuit operation, and a first conductive layer 83 and a mask material 84 are further formed. .
[0095]
The trench groove 85 is formed by removing the mask material in the element isolation region, the first conductive layer, the tunnel insulating film having a plurality of thicknesses, the gate insulating film, and the semiconductor substrate so that the side ends thereof are aligned (FIG. 11). (B) (e)).
[0096]
After oxidizing the sidewalls of the trench groove 85 and the first conductive layer 83, an element isolation insulating film 86 is deposited, and the element isolation insulating film 86 is etched back by dry etching or surface polishing by chemical polishing (CMP). And finally the upper surface of the mask material 84 is exposed (FIGS. 11C and 11F). At this time, the height after the etch-back is the same even though the thickness of the gate insulating film is different. Therefore, in the low voltage transistor and the high breakdown voltage transistor, the thickness of the remaining mask material is 84 ′ and 84 ″. Is different.
[0097]
After the mask material is peeled off, a second conductive layer is deposited on the semiconductor substrate, and the second conductive layer is etched back or planarly polished until the element isolation insulating film is exposed to separate the second conductive layer. To do. Also at this time, the thickness of the second conductive layer is different as indicated by 87 for the low-voltage transistor and 97 for the high-voltage transistor (FIGS. 12A and 12D). The stacked structure of the first conductive layer and the second conductive layer described above forms a charge storage layer or a first gate electrode.
[0098]
Next, the element isolation insulating film 85 is additionally etched back to expose part of the side surfaces of the charge storage layers (83, 87, 97) and the first gate electrodes (82, 92) (FIG. 12B). (E)).
[0099]
Next, as an inter-gate insulating film, for example, an ONO film is formed on the semiconductor substrate, and then at least a part of the ONO film in the peripheral circuit part excluding the memory cell part is peeled off, and then the control gate 88 is deposited. Note that the control gate is formed as a second gate electrode 88 in the transistor, and since the inter-gate insulating film is removed, the first gate electrode and the second gate electrode are electrically connected to have the same potential. . The cell structure and the transistor structure are completed by performing gate processing so that the side ends of the stacked structure in the memory cell portion and the transistor are aligned (FIGS. 12C and 12F).
In the nonvolatile semiconductor memory device shown in the fifth embodiment, since the gate material constituting the memory cell and the gate of the transistor is the same, it is easy to realize cost reduction and high yield. Further, since the process of exposing a part of the side surface of the charge storage layer is performed on the entire surface of the chip, a lithography process is not required, and cost reduction can be expected. However, the exposed height is higher in the transistor than in the memory cell because an additional step of peeling the inter-gate insulating film is added. Therefore, the thickness of the second conductive layer may be larger than that required for the memory cell. This may affect the process yield when processing the gate structure of the memory cells arranged at high density.
[0100]
When it is necessary to reduce the film thickness of the second conductive layer, a lithography process is added to perform an etch back process for exposing a part of the side surface of the charge storage layer only to the memory cell portion. In this case, the exposed height of the charge storage layer and the first gate electrode is higher in the memory cell even when the inter-gate insulating film is peeled off. It is possible to control by the film thickness of the second conductive layer required in the memory cell portion.
[0101]
FIG. 13 shows a structure in which the upper layer and the lower layer of the first gate electrode have the same end face position by selecting appropriate conditions in the fifth embodiment.
[0102]
Although various embodiments have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made.
[0103]
For example, in the embodiment, the electrode serving as the charge storage layer or the like has a two-layer structure, but it may have a multilayer structure of three or more layers. In that case, the uppermost layer is the upper layer in the embodiment, the lowermost layer is What is necessary is just to have the structure and function similar to the lower layer in a form.
[0104]
In the embodiment, a silicon dioxide layer is used as the tunnel insulating film which is the first gate insulating film. However, the silicon nitride layer, the silicon oxynitride layer, or an arbitrary laminated film thereof is used. May be.
[0105]
In addition, although the silicon oxide film is used as the insulating film between the charge storage layer and the control gate in the embodiment, it may be a nitride film, an oxynitride film, or a stacked film of an oxide film and a nitride film.
[0106]
Furthermore, although the polysilicon layer doped with impurities is used as the control gate in the embodiment, the amorphous silicon layer, the refractory metal material layer such as tungsten, the low resistance metal layer such as aluminum, and the metal such as tungsten silicide (WSi). A salicide film formed by causing a chemical reaction with silicon by laminating a silicide and a silicon material, depositing a metal such as titanium on the silicon material, and performing thermal annealing can be appropriately used.
[0107]
Further, as the insulating film for element isolation, doped oxide films such as PSG and BPSG containing impurities such as phosphorus and boron in addition to the silicon dioxide excellent in high aspect embedding characteristics described in the embodiment. Alternatively, a laminated structure of these can be used.
[0108]
Further, various capacitors other than the peripheral circuits, resistance elements, and the like can be variously modified and implemented as necessary without departing from the gist of the present invention.
[0109]
【The invention's effect】
According to the present invention, in a nonvolatile semiconductor memory device including a memory cell having a self-aligned STI structure in which a charge storage layer is formed in a self-aligning manner with an element isolation region, that is, a trench groove, the charge storage layer includes at least two layers. As the structure, the first conductive layer is thinned to reduce the embedding aspect of the element isolation insulating film, and the second conductive layer has a film thickness necessary for setting the capacitance between the control gates to a desired value. It is possible to provide a low-cost, high-density, large-capacity nonvolatile semiconductor memory device having excellent processing controllability and excellent data rewriting characteristics.
[0110]
The second conductive layer is formed by a planarization process using an element isolation insulating film as a stopper, and a charge storage layer required in a conventional nonvolatile semiconductor memory device is cut into a slit shape on the element isolation region. Therefore, the process can be reduced by omitting lithography for the purpose.
[Brief description of the drawings]
1A and 1B are a plan view and a cross-sectional view of a nonvolatile semiconductor memory device according to a first embodiment of the invention.
FIG. 2 is a cross-sectional view for each process showing a manufacturing process for obtaining the configuration of FIG. 1;
FIG. 3 is a cross-sectional view showing a special case of the configuration shown in FIG.
4A and 4B are a plan view and a cross-sectional view of a nonvolatile semiconductor memory device according to a second embodiment of the invention.
5 is a cross sectional view for each process showing a manufacturing process for obtaining the configuration of FIG. 4; FIG.
6 is a cross-sectional view showing a special case of the configuration shown in FIG.
7A and 7B are a plan view and a cross-sectional view of a nonvolatile semiconductor memory device according to a third embodiment of the invention.
8 is a cross-sectional view showing a manufacturing process for obtaining the configuration shown in FIG. 1; FIG.
9A and 9B are a plan view and a cross-sectional view of a nonvolatile semiconductor memory device according to a fourth embodiment of the invention.
FIGS. 10A and 10B are a plan view and a cross-sectional view showing a configuration of a low voltage transistor and a high voltage transistor used in a nonvolatile semiconductor memory device according to a fifth embodiment of the present invention. FIGS.
11 is a cross-sectional view by process showing the first half of the manufacturing process of the transistor shown in FIG. 10; FIG.
12 is a sectional view by process showing the latter half of the manufacturing process of the transistor shown in FIG. 10; FIG.
13 is a cross-sectional view showing a special case of the configuration shown in FIG.
FIG. 14 is an element cross-sectional view illustrating general characteristics of a nonvolatile semiconductor memory device according to the present invention.
15A and 15B are a plan view and a cross-sectional view showing a configuration of a nonvolatile semiconductor memory device according to a first conventional example.
16 is a cross-sectional view showing a manufacturing process for obtaining the configuration shown in FIG. 15; FIG.
17A and 17B are a plan view and a cross-sectional view showing a configuration of a nonvolatile semiconductor memory device according to a second conventional example.
18 is a cross-sectional view showing a manufacturing process for obtaining the configuration shown in FIG. 17; FIG.
[Explanation of symbols]
21, 41, 61, 81 Substrate or well
22, 42, 62, 85 Trench grooves
23, 43, 63, 86 Element isolation insulating film
24, 44, 64, 82 Tunnel insulating film
25, 45, 65, 83 First conductive film
26, 46, 66, 87, 97 Second conductive film
27, 47, 67 Charge storage layer
28, 48, 68 Inter-gate insulating film
29, 49, 69, 88 Control gate
30, 50, 70 element area
31, 51, 71 n-type diffusion layer
32 Mask material
53 Select transistor gate

Claims (4)

Forming a first gate insulating film on the semiconductor substrate;
Forming a first conductive layer serving as a lowermost layer of a charge storage layer on the first gate insulating film;
Forming a mask material on the first conductive layer;
Etching the mask material, the first conductive layer, the first gate insulating film, and the semiconductor substrate so that the side end positions thereof coincide with each other to form a trench groove;
Oxidizing at least the trench groove sidewall and the first conductive layer sidewall surface;
Depositing an isolation film for element isolation and embedding a trench groove;
Planarizing the element isolation insulating film to expose the upper surface of the mask material;
Peeling the mask material to expose the upper surface of the first conductive layer;
Depositing a second conductive layer as the uppermost layer of a charge storage layer on the entire surface including the upper surface of the first conductive layer and the upper surface of the element isolation insulating film;
Flattening the second conductive layer so that the upper surface thereof is flush with the upper surface of the element isolation insulating film;
Forming a second gate insulating film on the second conductive layer and the element isolation insulating film;
Depositing a control gate material on the second gate insulating film;
Processing the deposited control gate material into a predetermined shape;
A method for manufacturing a nonvolatile semiconductor memory device comprising: Forming a first gate insulating film on the semiconductor substrate;
Forming a first conductive layer serving as a lowermost layer of a charge storage layer on the first gate insulating film;
Forming a mask material on the first conductive layer;
Etching the mask material, the first conductive layer, the first gate insulating film, and the semiconductor substrate so that the side end positions thereof coincide with each other to form a trench groove;
Oxidizing at least the trench groove sidewall and the first conductive layer sidewall surface;
Depositing an isolation film for element isolation and embedding a trench groove;
Planarizing the element isolation insulating film to expose the upper surface of the mask material;
Peeling the mask material to expose the upper surface of the first conductive layer;
Depositing a second conductive layer as the uppermost layer of the charge storage layer on the entire surface including the upper surface of the first conductive layer and the upper surface of the element isolation insulating film on a semiconductor substrate;
Flattening the second conductive layer so that the upper surface thereof is flush with the upper surface of the element isolation insulating film;
Selectively etching the element isolation insulating film so that the upper surface thereof is located between the lower surface and the upper surface of the second conductive layer;
Forming a second gate insulating film on the side wall of the second conductive layer exposed by this etching, the upper surface of the second conductive layer, and the upper surface of the element isolation insulating film;
Depositing a control gate material on the second gate insulating film;
Processing the deposited control gate material into a predetermined shape;
A method for manufacturing a nonvolatile semiconductor memory device comprising: Forming a first gate insulating film on the semiconductor substrate;
Forming a first conductive layer serving as a lowermost layer of a charge storage layer on the first gate insulating film;
Forming a mask material on the first conductive layer;
Etching the mask material, the first conductive layer, the first gate insulating film, and the semiconductor substrate so that the side end positions thereof coincide with each other to form a trench groove;
Oxidizing at least the trench groove sidewall and the first conductive layer sidewall surface;
Depositing an isolation film for element isolation and embedding a trench groove;
Planarizing the element isolation insulating film to expose the upper surface of the mask material;
Peeling the mask material to form a recess exposing the upper surface of the first conductive layer;
Increasing the lateral width of the recess by isotropic etching;
Depositing a second conductive layer, which is the uppermost layer of the charge storage layer, on the semiconductor substrate and on the element isolation insulating film and in the recess;
Flattening the second conductive layer so that the upper surface thereof is flush with the element isolation insulating film;
Selectively etching the element isolation insulating film so that the upper surface thereof is located between the lower surface and the upper surface of the second conductive layer;
Forming a second gate insulating film on the side wall of the second conductive layer exposed by this etching, the upper surface of the second conductive layer, and the upper surface of the element isolation insulating film;
Depositing a control gate material on the second gate insulating film;
Processing the deposited control gate material into a predetermined shape;
A method for manufacturing a nonvolatile semiconductor memory device comprising:   4. The method of manufacturing a nonvolatile semiconductor memory device according to claim 1, wherein the planarizing step of the second conductive layer is performed by dry etching or polishing.

Images