JP3314748B2 - Manufacturing method of nonvolatile semiconductor memory device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a nonvolatile semiconductor Symbol 憶 <br/> device and a manufacturing method thereof, particularly, to a nonvolatile semiconductor Symbol 憶 device and a manufacturing method thereof capable of reducing the number of steps.

[0002]

A floating gate electrode formed via a first gate insulating film on a semiconductor substrate of the Related Art Nonvolatile semiconductor Symbol 憶 device, the floating gate electrode and the second gate insulating film (capacitor insulating film) there is a floating gate type nonvolatile semiconductor Symbol 憶 device and a control gate electrode capacitively joined provided through. Write and erase characteristics of information in the floating gate type nonvolatile semiconductor Symbol 憶 device is a capacitive junction, and the second gate insulating film between the first semiconductor substrate by a gate insulating film of the channel region and the floating gate electrode It is determined by the capacitance division of the capacitance junction between the floating gate electrode and the control gate electrode by the capacitance 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 In this way, it is possible to obtain a floating gate type nonvolatile semiconductor Symbol 憶 device.

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. In this way, it is possible to obtain a floating gate type nonvolatile semiconductor Symbol 憶 instrumentation <br/> location.

[0019]

[SUMMARY OF THE INVENTION However, as described above, in the manufacturing method of the first conventional nonvolatile semiconductor Symbol 憶 device separates the second polysilicon film 114 for a floating gate by lithography Therefore, 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.

Meanwhile, in the manufacturing method of the second conventional nonvolatile semiconductor Symbol 憶 instrumentation <br/> location, the buried insulating film is two layers of the first buried insulating film 205 and the second buried insulating film 206 Since it is configured, there is a drawback that the number of steps is large.

The present invention was made in view of the above problems, and an object thereof is to provide a nonvolatile semiconductor Symbol 憶 device and a manufacturing method thereof capable of reducing the number of steps.

[0022]

[0023]

[0024]

A method of manufacturing a nonvolatile semiconductor memory device according to the present invention comprises the steps of selectively forming a buried insulating film having a lower portion embedded in a semiconductor substrate and an upper portion projecting from the semiconductor substrate. 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 control gate first metal film over the entire surface, exposing an upper surface of the buried insulating film; A second insulating film and 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 so as to be thicker than the third insulating film; a step of flattening the surface so as to completely remove only the third insulating film; And a step of forming the same.

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 nonvolatile memory device according to the present invention, the impurity concentration of the floating gate metal film and the control gate first metal film may be different from each other. It is preferred that The semiconductor may be silicon, and a step of flattening the surface until the upper surface of the buried insulating film is exposed and / or flattening the surface such 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]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the method for fabricating the nonvolatile semiconductor Symbol 憶 device according to an embodiment of the present invention will be specifically described with reference to the accompanying drawings. Figure 1 is a sectional view showing a nonvolatile semiconductor Symbol 憶 device according to an embodiment of the present invention. Also,
2 to 5 are sectional views sequentially showing the steps of producing the nonvolatile semiconductor Symbol 憶 <br/> apparatus according to an embodiment of the present invention.

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)
A floating gate silicon film 5 made of Silicon is formed in a concave shape reflecting 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, explaining the manufacturing method of the nonvolatile semiconductor Symbol 憶 device according to an embodiment of the present invention in 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
Insulating film 9 formed on the exposed surface of the are thinner than the insulating film 8 formed on the exposed surface of the silicon for the floating gate layer 5.

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. In this way, it is possible to obtain a floating gate type nonvolatile semiconductor <br/> Symbol 憶 device.

[0041] In the nonvolatile semiconductor Symbol 憶 device of the present embodiment having such a configuration, as compared with the first conventional nonvolatile semiconductor Symbol 憶 device, the floating gate electrode 1
Since the memory cells are formed in layers, the area of the memory cell does not needlessly increase. Further, as compared with the second conventional nonvolatile semiconductor Symbol 憶 device forms the control gate electrode by forming a metal film (control gate electrode polysilicon layer 10) to the planarized surface Therefore, a control gate electrode having a flat top surface can be obtained.

Further, in the manufacturing method of the nonvolatile semiconductor Symbol 憶 device of the present embodiment, the first conventional nonvolatile semiconductor Symbol
Compared with the memory device manufacturing method, the floating gate film can be separated without using a lithography technique, so that 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 conventional method of manufacturing a second nonvolatile semiconductor Symbol 憶 device, since the buried insulating film is composed of one layer, it is possible to reduce the number of steps.

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]

1 is a cross-sectional view showing a nonvolatile semiconductor Symbol 憶 device according to an embodiment of the present invention.

2 is a cross-sectional view sequentially showing the steps of producing a nonvolatile semiconductor Symbol 憶 device according to an embodiment of the present invention.

3 is a cross-sectional view sequentially showing the steps of producing a nonvolatile semiconductor Symbol 憶 device according to an embodiment of the present invention.

Is a cross-sectional view sequentially showing the steps of producing a nonvolatile semiconductor Symbol 憶 device according to an embodiment of the present invention; FIG.

5 is a cross-sectional view sequentially showing the steps of producing a nonvolatile semiconductor Symbol 憶 device according to an embodiment of the present invention.

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

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 21/8247 H01L 21/762 H01L 27/115 H01L 29/788 H01L 29/792

Claims (6)

(57) [Claims] A step of selectively forming a buried insulating film having a lower portion embedded in the semiconductor substrate and an upper portion projecting 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. 2. A non-volatile method of manufacturing a semiconductor memory device according to claim 1 wherein the floating gate metal film and a control first metal film for the gate is characterized by comprising a semiconductor. 3. The second insulating film and the third insulating film,
The nonvolatile semiconductor memory according to claim 1 or 2, characterized in that each of said oxide film or a nitride film obtained by oxidizing or nitriding by heat treatment of the first metal film for a floating gate metal film and a control gate Device manufacturing method. Wherein any of claims 1 to 3 impurity concentration of the first metal film for the floating gate metal layer and the control gate is characterized by mutually different 1
13. The method for manufacturing a nonvolatile semiconductor memory device according to item 9. Wherein said semiconductor nonvolatile method of manufacturing a semiconductor memory device according to any one of claims 2 to 4, characterized in that a silicon. 6. A step of flattening the surface until the upper surface of the buried insulating film is exposed and / or a step of flattening the surface so that only the third insulating film is completely removed,
The method according to any one of claims 1 to 5 , wherein the method is performed by a P method or an anisotropic etching method.