JP2000232169A - Nonvolatile semiconductor recorder and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonvolatile semiconductor recorder and a method for manufacturing the recorder by which the number of processes can be reduced. SOLUTION: A nonvolatile semiconductor recorder manufacturing method includes a step for selectively forming buried insulating films 3 which are buried in a semiconductor substrate 30 with their upper parts being protruded from the substrate 30, a step for selectively forming a gate insulating film 4 on the surface of the substrate 30, and a step for forming a silicon film 5 on the whole surface. The method also includes a step for forming an insulating film 6 on the whole surface, a step for forming a silicon film 7 on the whole surface, and a step for flattening the surface until the top faces of the buried insulating films 3 are exposed. In addition, the method also includes a step for respectively forming insulating films 8 and 9 on the surfaces of the silicon films 5 and 7 so that the film 8 may become thicker in thickness than the film 9, a step for flattening the surface so that only the insulating film 9 may be removed completely, and a step for forming a second metallic film for control gate on the whole surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a nonvolatile semiconductor recording device and a method of manufacturing the same, and more particularly, to a nonvolatile semiconductor recording device capable of reducing the number of steps and a method of manufacturing the same.

[0002]

2. Description of the Related Art As a nonvolatile semiconductor recording device, a floating gate electrode formed on a semiconductor substrate via a first gate insulating film, and a second gate insulating film (capacitive insulating film) formed on the floating gate electrode. There is a floating gate type non-volatile semiconductor recording device provided with a control gate electrode which is capacitively joined by a capacitor. The writing and erasing characteristics of information in the floating gate type nonvolatile semiconductor recording device are as follows: the capacitance junction between the channel region of the semiconductor substrate by the first gate insulating film and the floating gate electrode; and the capacitance as the second gate insulating film It is determined by the capacitance division of the capacitance junction between the floating gate electrode and the control gate electrode by the insulating film. In order to perform high-speed operation at a low voltage, it is effective to increase the voltage effectively applied between the floating gate electrode and the channel region. It is necessary to increase the capacitance junction between the two.

For this reason, STI (Shallow Trench Isolation: Shallow) for element isolation is required.
A technique called Trench Isolation has been devised in which the shape of the floating gate electrode is formed in a concave shape using the side wall shape of the buried insulating film to increase the capacitance junction between the floating gate electrode and the control gate electrode.

As a method of manufacturing the first conventional nonvolatile semiconductor memory device, a symposium held in 1998
On-VLSI Technology (Symposium)
onVLSI Technology's Digest of Technical Paper (Digest of Technical Paper)
Technical Paper) 102 and 103
Some are listed on the page. FIG. 6 and FIG.
FIG. 7 is a cross-sectional view showing a method of manufacturing the nonvolatile semiconductor memory device in the order of steps.

First, as shown in FIG. 6A, a tunnel oxide film (first gate insulating film) 104, a first polysilicon film 113 for a floating gate and a stopper are formed on a P-type silicon semiconductor substrate 100. Silicon nitride film 10
2 is deposited.

Next, as shown in FIG. 6B, the silicon nitride film 102 for the stopper, the first polysilicon film 113 for the floating gate, and the first gate insulating film 104 are simultaneously formed by lithography and etching. After the selective removal, the silicon semiconductor substrate 100 is further selectively removed by etching. Then, HDP (High Density Plasma: High Density Plasma) is applied to the entire surface so as to fill the removed portion.
A silicon oxide film is deposited by a CVD method. Next, CM
The surface is flattened by the P technique until the stopper silicon nitride film 102 is exposed, and a buried insulating film 103 is obtained.

After that, as shown in FIG. 6C, the silicon nitride film 102 for stopper is selectively removed, and a second polysilicon film 114 for floating gate is deposited on the entire surface. Then, in order to separate adjacent memory cells, the second polysilicon film 114 is selectively removed by lithography and dry etching so that the upper surface of the buried insulating film 103 is exposed. Thus, the floating gate electrode 105 including the first polysilicon film 113 and the second polysilicon film 114 is formed. Then, a second gate insulating film 106 made of an ONO film (a film in which a silicon oxide film, a silicon nitride film, and a silicon oxide film are stacked) is formed on the entire surface.

[0008] Next, as shown in FIG.
Polycide is deposited to form a control gate electrode 110.

Next, the control gate electrode 110, the second gate insulating film 106, and the floating gate electrode 105 are selectively etched by a photolithography technique and dry etching until the first insulating film 104 is exposed in a stripe shape. Then, a control gate electrode pattern corresponding to the word line is obtained. Further, arsenic ions are implanted using the control gate electrode pattern as a mask, and a source diffusion layer and a drain diffusion layer (not shown) are formed in the silicon semiconductor substrate 100.
To form Thus, a floating gate type nonvolatile semiconductor recording device can be obtained.

As a second conventional method for manufacturing a nonvolatile semiconductor memory device, there is one disclosed in Japanese Patent Application Laid-Open No. 3-64972. 8 to 10 are sectional views showing a method of manufacturing a second conventional nonvolatile semiconductor memory device in the order of steps.

First, as shown in FIG. 8A, an insulating film 202 is formed on a semiconductor substrate 201 made of silicon, and an etching stopper film 203 is formed thereon.

Next, as shown in FIG. 8B, a photoresist film 204 is formed on the entire surface, and a predetermined region of the etching stopper film 20 is formed by using a known photolithography technique.
3. The insulating film 202 and a part of the semiconductor substrate 201 are sequentially removed by etching to form a groove.

After that, as shown in FIG. 8C, a first buried insulating film 205 is formed on the entire surface, and a second buried insulating film 206 is formed on the entire surface.

Next, as shown in FIG. 9A, the entire surface of the second buried insulating film 206 is changed to the first buried insulating film 205.
Then, only the first embedded insulating film 205 is selectively removed by etching until the surface of the etching stopper film 203 is exposed.

Next, as shown in FIG. 9B, after removing the etching stopper film 203 and the insulating film 202, a gate oxide film 207 is formed.

Thereafter, as shown in FIG. 9C, a first polycrystalline silicon film 208 is formed on the entire surface, and a photoresist 209 is formed on the entire surface to planarize the surface.

Next, as shown in FIG. 10A, etch back is performed until the entire surface of the second buried insulating film 206 is exposed, and the first polycrystalline silicon film 208 is replaced with the second buried insulating film. Separated at 206.

Thereafter, as shown in FIG. 10B, after removing the photoresist 209, another insulating film 210 is formed on the first polycrystalline silicon film 208, and a second polycrystalline silicon film is formed on the entire surface. A crystalline silicon film 211 is formed. Thus, a floating gate type nonvolatile semiconductor recording device can be obtained.

[0019]

However, as described above, in the first conventional method for manufacturing a nonvolatile semiconductor recording device, the second polysilicon film 114 for the floating gate is separated by the lithography technique. And the margin of misalignment is narrow. Further, since this lithography step is required, the number of steps increases. Further, since the floating gate electrode is formed by laminating two polysilicon films, and the adjacent memory cells are separated by lithography, the processing of the first polysilicon film 113 for the floating gate is performed. The size is larger than the processing size of the second polysilicon film 114, and there is a problem that the area of the memory cell increases.

On the other hand, in the second conventional method of manufacturing a nonvolatile semiconductor recording device, the buried insulating film is composed of two layers, the first buried insulating film 205 and the second buried insulating film 206. There is a disadvantage that the number of steps is large.

The present invention has been made in view of the above problems, and has as its object to provide a nonvolatile semiconductor recording device capable of reducing the number of steps and a method of manufacturing the same.

[0022]

According to the present invention, there is provided a nonvolatile semiconductor recording device comprising: a buried insulating film selectively formed so that a lower portion is embedded in a semiconductor substrate and an upper portion protrudes from the semiconductor substrate; A gate insulating film formed on the surface of the semiconductor substrate; a floating gate electrode formed in a concave shape in a region defined by a side surface of the buried insulating film and the surface of the gate insulating film; A first part of the capacitive insulating film formed on the inner surface, a second part of the capacitive insulating film formed on the upper end of the floating gate electrode, and an upper surface buried in the recess and having a height of the upper surface of the buried insulating film Control gate electrode substantially equal in height to the buried insulating film, the capacitor insulating film first portion, the capacitor insulating film second portion, and the control gate electrode. A second portion control gate electrode formed on the gate electrode the first part, and having a.

Further, the first part of the floating gate electrode and the first part of the control gate electrode may be composed of a semiconductor layer. Further, the control gate electrode can be formed so as to be formed in a direction orthogonal to the direction of the concave groove of the first portion of the capacitive insulating film.

According to the method of manufacturing a nonvolatile semiconductor recording device of the present invention, a step of selectively forming a buried insulating film having a lower portion embedded in a semiconductor substrate and an upper portion protruding from the semiconductor substrate; Selectively forming a first gate insulating film, forming a floating gate metal film over the entire surface, forming a first insulating film over the entire surface, and forming a control gate first metal film. Forming the entire surface; planarizing the surface until the upper surface of the buried insulating film is exposed; and forming a second insulating film on the surfaces of the floating gate metal film and the control gate first metal film, respectively. A step of forming the film and the third insulating film so that the second insulating film is thicker than the third insulating film; and a step of completely removing only the third insulating film. Wherein the step of flattening and forming a second metal film for a control gate over the entire surface, to have a.

Further, the metal film for the floating gate and the first metal film for the control gate can be made of a semiconductor. Further, the second insulating film and the third
The insulating film may be an oxide film or a nitride film obtained by oxidizing or nitriding the floating gate metal film and the control gate first metal film by heat treatment, respectively.

Further, in the method of manufacturing a semiconductor device according to the present invention, it is preferable that the floating gate metal film and the control gate first metal film have different impurity concentrations. The semiconductor may be silicon, and a step of flattening the surface where the upper surface of the buried insulating film is exposed and / or flattening the surface so that only the third insulating film is completely removed. This step may be performed by a CMP method or an anisotropic etching method.

In the present invention, a first portion of the capacitor insulating film and a second portion of the capacitor insulating film constitute a capacitor insulating film, and the first portion of the control gate electrode and the second portion of the control gate electrode.
A control gate electrode is formed from the portion. And
Since the floating gate electrode is formed in one layer, the area of the memory cell does not increase unnecessarily as compared with the conventional first semiconductor device. In addition, since the base of the second part of the control gate electrode is substantially flat,
The second part of the control gate electrode is formed with its upper surface flat. Therefore, a control gate electrode having a flat upper surface can be obtained as compared with the conventional second semiconductor device.

In the method of the present invention, the first
Compared to the method of manufacturing the nonvolatile semiconductor memory device of the first embodiment, the first process is performed by the flattening process without using the lithography technology.
Since the capacitor insulating film composed of the first insulating film and the second insulating film can be formed and the floating gate metal film can be separated, the margin of misalignment is wide. Further, the lithography step is not required, and the number of steps can be reduced. Further, as compared with the second conventional method for manufacturing a nonvolatile semiconductor memory device, the number of steps can be reduced because the buried insulating film is composed of one layer.

Also, for example, the floating gate metal film and the control gate first metal film are both silicon films, and the floating gate metal film has a higher impurity concentration than the control gate first metal film. If the second insulating film formed by the heat treatment is compared with the third insulating film with respect to the film thickness, the second insulating film is thicker. Thus, the thickness of the second insulating film can be easily made larger than the thickness of the third insulating film.

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for manufacturing a nonvolatile semiconductor recording device according to an embodiment of the present invention will be specifically described below with reference to the accompanying drawings. FIG. 1 is a sectional view showing a nonvolatile semiconductor recording device according to an embodiment of the present invention. Also,
2 to 5 are sectional views showing a method for manufacturing a nonvolatile semiconductor recording device according to an embodiment of the present invention in the order of steps.

As shown in FIG. 1, a P-type silicon semiconductor substrate 30 has a lower portion embedded in the silicon semiconductor substrate 30 and an upper portion formed with a buried insulating film 3 projecting from the silicon semiconductor substrate 30. A first gate insulating film (tunnel oxide film) 4 made of a silicon oxide film
Are formed. Furthermore, DOPOS (doped amorphous silicon: DOped amOrphous)
The floating gate silicon film 5 made of Silicon is formed in a concave shape reflecting the shape of the surface of the first gate insulating film 4 and the side wall of the buried insulating film 3, and an ONO film is formed on the inner surface of the concave portion. An insulating film 6 is formed. Further, a control gate silicon film 7 is formed so as to be buried in the recess. On the upper end of the silicon film 5 for the floating gate, an insulating film 8 made of SiO ₂ is formed. The upper surface heights of the buried insulating film 3, the insulating film 8, the insulating film 6, and the control gate silicon film 7 are substantially equal. The control gate polysilicon film 10 is formed thereon. That is, the floating gate polysilicon film 5 is used as a floating gate electrode, the insulating films 6 and 8 are used as second gate insulating films (capacitive insulating films), and the control gate silicon film 7 and the control gate polysilicon film 10 are used as control gate electrodes. Floating electrode type nonvolatile semiconductor memory device.

Next, a method for manufacturing a nonvolatile semiconductor recording device according to an embodiment of the present invention will be described in the order of steps. First, FIG.
As shown in (a), a pad silicon oxide film 1 made of SiO ₂ and having a thickness of 300 ° and a stopper silicon nitride film 2 made of Si ₃ N ₄ and having a thickness of 5000 ° are sequentially deposited on the surface of a silicon semiconductor substrate 30. Then, after the stopper silicon nitride film 2 and the pad silicon oxide film 1 are simultaneously removed in the form of stripes by the lithography technique and the dry etching technique, the silicon semiconductor substrate 30 is selectively removed by etching so that the depth becomes 5000 °. Then, a concave portion is formed.

Next, as shown in FIG. 2B, the resist used in the previous step is peeled off, and a silicon oxide film is deposited on the entire surface by HDP / CVD so as to fill the recess. Then, planarization is performed by the CMP technique until the silicon nitride film for stopper 2 is exposed. Thereby, the buried insulating film 3 is obtained.

Thereafter, as shown in FIG. 2C, the silicon nitride film for stopper 2 and the pad silicon oxide film 1 are selectively removed, and a first silicon oxide film having a thickness of 80 ° is formed by a thermal oxidation method. A gate insulating film (tunnel gate oxide film) 4 is formed.

Next, as shown in FIG. 3A, a floating gate silicon film 5 made of DOPOS having a thickness of 1500 ° and an insulating film 6 made of an ONO film are formed on the surface of the first gate insulating film 4 and the buried insulating film. The film 3 is formed in a stripe shape reflecting the shape of the side wall. This allows
A recess covered with the insulating film 6 is formed. Then, a control gate silicon film 7 made of DOPOS is deposited on the entire surface so as to fill the recess. The impurity concentration of the control gate silicon film 7 is lower than that of the floating gate silicon film 5.

Next, as shown in FIG. 3B, the surface of the buried insulating film 3 is flattened by a CMP method until the upper surface of the buried insulating film 3 is exposed. The floating gate silicon film 5 is formed.

Thereafter, as shown in FIG. 3C, a thermal oxidation process is performed to oxidize the exposed surface of the silicon film 5 for the floating gate and the exposed surface of the silicon film 7 for the control gate. Insulating film 8 and 9
To form Since the impurity concentration of the control gate silicon film 7 is lower than the impurity concentration of the floating gate silicon film 5, the control gate silicon film 7
Is formed thinner than the insulating film 9 formed on the exposed surface of the silicon film 5 for the floating gate.

Next, as shown in FIG. 4A, the insulating films 8 and 9 are removed by etching until the surface of the control gate silicon film 7 is exposed. At this time, since the insulating film 9 is thinner than the insulating film 8, the insulating film 9 formed on the surface of the control gate silicon film 7 is completely removed, but the insulating film 9 formed on the surface of the floating gate silicon film 5 is removed. The film 8 remains.

Next, as shown in FIG. 4B, a control gate polysilicon film 10 is formed on the entire surface. Then, the polysilicon film 10, the silicon film 7, the insulating film 6, and the silicon film are exposed by the photolithography technique and the dry etching until the first gate insulating film 4 is exposed in a pattern orthogonal to the stripe-shaped floating gate silicon film 5. 5 is selectively removed by etching to obtain a control gate electrode pattern corresponding to a word line.

Thereafter, as shown in FIG. 5 (FIG. 5 is a cross-sectional view cut in a direction orthogonal to the drawing before FIG. 4), arsenic ions are implanted using the control gate electrode pattern as a mask, and silicon is implanted. The source diffusion layer 11 and the drain diffusion layer 12 are formed on the semiconductor substrate 30. Thus, a floating gate type nonvolatile semiconductor recording device can be obtained.

In the nonvolatile semiconductor recording device of the present embodiment thus configured, the floating gate electrode is one in comparison with the first conventional nonvolatile semiconductor recording device.
Since the memory cells are formed in layers, the area of the memory cell does not needlessly increase. Further, as compared with the conventional second nonvolatile semiconductor recording device, a control film is formed by forming a metal film (polysilicon film 10 for control gate electrode) on the surface subjected to the planarization process. Thus, a control gate electrode having a flat top surface can be obtained.

In the method of manufacturing a nonvolatile semiconductor recording device according to the present embodiment, a film for a floating gate can be formed without using a lithography technique as compared with the first conventional method of manufacturing a nonvolatile semiconductor recording device. Can be separated, so the misalignment margin is wide.
Further, the lithography step is not required, and the number of steps can be reduced. Further, as compared with the second conventional method of manufacturing a nonvolatile semiconductor recording device, the number of steps can be reduced since the buried insulating film is composed of one layer.

In this embodiment, a silicon film is used as a semiconductor film, and a silicon oxide film or an ONO film is used as an insulating film. However, the present invention is not limited to this. Or another insulating film such as a nitride film.

[0044]

As described in detail above, according to the present invention,
The control gate electrode can be obtained in which the area of the memory cell is not unnecessarily increased as compared with the conventional first semiconductor device and the upper surface is flatter as compared with the conventional second semiconductor device. According to the method of the present invention, the floating gate metal film can be separated without using a lithography technique, as compared with the first conventional method for manufacturing a nonvolatile semiconductor memory device. The margin is wide. Further, the lithography step is not required, and the number of steps can be reduced. Further, as compared with the second conventional method for manufacturing a nonvolatile semiconductor memory device, the number of steps can be reduced because the buried insulating film is composed of one layer.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a nonvolatile semiconductor recording device according to an embodiment of the present invention.

FIG. 2 is a sectional view illustrating a method of manufacturing a nonvolatile semiconductor recording device according to an embodiment of the present invention in the order of steps.

FIG. 3 is a sectional view illustrating a method of manufacturing a nonvolatile semiconductor recording device according to an embodiment of the present invention in the order of steps.

FIG. 4 is a cross-sectional view illustrating a method for manufacturing the nonvolatile semiconductor recording device according to the embodiment of the present invention in the order of steps.

FIG. 5 is a sectional view illustrating a method for manufacturing the nonvolatile semiconductor recording device according to the embodiment of the present invention in the order of steps.

FIG. 6 is a cross-sectional view illustrating a method of manufacturing the first conventional nonvolatile semiconductor memory device in the order of steps;

FIG. 7 is a sectional view illustrating a method of manufacturing the first conventional nonvolatile semiconductor memory device in the order of steps;

FIG. 8 is a cross-sectional view illustrating a method of manufacturing the second conventional nonvolatile semiconductor memory device in the order of steps.

FIG. 9 is a cross-sectional view showing a method of manufacturing the second conventional nonvolatile semiconductor memory device in the order of steps.

FIG. 10 is a sectional view illustrating a method of manufacturing the second conventional nonvolatile semiconductor memory device in the order of steps.

[Explanation of symbols]

 1; pad silicon oxide film 2, 102; stopper silicon nitride film 3, 103; buried insulating film 4, 104; first gate insulating film 5; floating gate silicon film 6, 8, 9, 202; insulating film 7 Control gate silicon film 10; control gate polysilicon film 11; source diffusion layer 12; drain diffusion layers 30, 100; silicon semiconductor substrate 105; floating gate electrode 106; second gate insulating film 110; First polysilicon film for floating gate 114; second polysilicon film for floating gate 201; semiconductor substrate 203; etching stopper film 205; first buried insulating film 206; second buried insulating film 207; Film 208; first polycrystalline silicon 209; photoresist 210; other insulating film 211; the second polycrystalline silicon film

Continued on the front page F term (reference) 5F001 AA02 AA25 AA31 AA43 AB08 AD60 AE50 AG02 AG07 AG21 AG22 5F032 AA35 AA44 AA77 CA17 CA21 DA04 DA23 DA33 5F083 EP13 EP23 EP27 EP55 GA09 GA28 GA30 JA33 JA35 JA39 JA53 PR40 PR40

Claims (9)

[Claims] A buried insulating film selectively formed so that a lower portion is embedded in the semiconductor substrate and an upper portion protrudes from the semiconductor substrate; a gate insulating film formed on a surface of the semiconductor substrate; A floating gate electrode formed in a concave shape in a region defined by a side surface of the insulating film and a surface of the gate insulating film; a first portion of a capacitive insulating film formed on an inner surface of the concave portion of the floating gate electrode; A second portion of a capacitive insulating film formed on an upper end of the floating gate electrode; a first portion of a control gate electrode embedded in the concave portion and having a height of an upper surface substantially equal to a height of an upper surface of the buried insulating film; A control gate electrode formed on the buried insulating film, the capacitor insulating film first part, the capacitor insulating film second part, and the control gate electrode first part. 2. A nonvolatile semiconductor recording device comprising: 2. The nonvolatile semiconductor recording device according to claim 1, wherein the first part of the floating gate electrode and the first part of the control gate electrode are semiconductor layers. 3. The non-volatile semiconductor recording device according to claim 1, wherein the control gate electrode is formed in a direction orthogonal to a direction of a concave groove of the first portion of the capacitive insulating film. 4. A step of selectively forming a buried insulating film having a lower portion embedded in a semiconductor substrate and an upper portion protruding from the semiconductor substrate, and selectively forming a first gate insulating film on a surface of the semiconductor substrate. Forming a floating gate metal film over the entire surface; forming a first insulating film over the entire surface;
Forming a metal film on the entire surface, flattening the surface until the upper surface of the buried insulating film is exposed, and forming a first metal film on the surface of the floating gate metal film and the first metal film for the control gate respectively. Forming the second insulating film and the third insulating film so that the second insulating film is thicker than the third insulating film; and completely removing only the third insulating film. A process of flattening the surface and a step of forming a second metal film for a control gate over the entire surface. 5. The method according to claim 4, wherein the floating gate metal film and the control gate first metal film are made of a semiconductor. 6. The second insulating film and the third insulating film,
6. The non-volatile semiconductor recording device according to claim 4, wherein the floating metal film and the control gate first metal film are oxidized or nitrided by heat treatment, respectively. Device manufacturing method. 7. The floating gate metal film and the control gate first metal film have different impurity concentrations from each other.
13. The method for manufacturing a nonvolatile semiconductor recording device according to item 13. 8. The method for manufacturing a nonvolatile semiconductor recording device according to claim 5, wherein said semiconductor is silicon. 9. The step of flattening the surface where the upper surface of the buried insulating film is exposed and / or the step of flattening the surface so that only the third insulating film is completely removed is performed by CM.
9. The method according to claim 4, wherein the method is performed by a P method or an anisotropic etching method.