JPS6312388B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a semiconductor device, and in particular, to improve reliability such as memory retention characteristics in a double silicon gate field effect type non-volatile semiconductor device. The present invention relates to a method of manufacturing a semiconductor device in which a self-alignment process with a drain is improved.

Conventionally, in manufacturing nonvolatile semiconductor devices,
A self-alignment method between a polysilicon double-layer gate, source, and drain is commonly used. That is, FIG. 1 shows the state at each step of manufacturing a double silicon gate field effect type nonvolatile semiconductor device by the conventional method. In the conventional method, first, a gate oxide film 2,
After sequentially forming a polysilicon film 3 as a first gate, an interlayer oxide film 4, and a polysilicon film 5 as a second gate, a resist mask 6 is formed on the second polysilicon film 2, and the device is removed. The structure is as shown in FIG. 1a. Next, the second polysilicon film 5 is patterned by dry etching using normal CF ₄ gas, the interlayer oxide film 4 below it is patterned by wet etching using a hydrofluoric acid etching solution, and then the bottom side thereof is patterned by wet etching using a hydrofluoric acid-based etching solution. first polysilicon film 3 of
is patterned by dry etching using CF ₄ gas, and then the gate oxide film 2 underneath is patterned again by wet etching using a hydrofluoric acid-based etching solution to form the double gate portion 13 as shown in FIG. 1b. form a structure. Then, the resist mask 6 is removed, and a source portion 7 and a drain portion 8 are formed on the substrate 1 by ion implantation or phosphorous diffusion. Thereafter, an oxide film 9 is formed on the source portion 7 and the drain portion 8, and this element is further covered with a phosphorus glass film 10. In this way, a semiconductor device having the structure shown in FIG. 1c is formed.

However, such a conventional method has reliability problems different from the usual self-alignment method of a single-layer polysilicon film gate and source/drain used in the manufacture of dynamic RAM, static RAM, etc., for example. That is, in a nonvolatile semiconductor device, two layers of polysilicon films 3 and 5 are required as gates, and the first layer of polysilicon film 3 is characterized by storing and retaining charges. The interlayer insulating film 4 between the polysilicon film 3 and the second layer polysilicon film 3 and 5 is qualitatively extremely important, but in the conventional method, each film 2, 3, 4, and 5 is sequentially patterned using different etching methods. , the structure of the completed double gate part 13 is the first one.
As shown in FIG. d, the pattern edges of the interlayer oxide film 4 are set back inward from the pattern edges of the polysilicon films 3 and 5. As a result, both polysilicon films 3,
5 is slightly covered with the oxide film 9 in the subsequent process, but the phosphorus glass film 10 invades between the two films 3 and 5, which deteriorates the insulation properties between the double gates 3 and 5. This degrades the charge retention characteristics of the first polysilicon film 3 and deteriorates the quality of the device.

This invention has been made in view of the above-mentioned conventional problems, and includes a method for manufacturing a field-effect nonvolatile semiconductor device with a double silicon gate structure.
After patterning the double gate structure and the source,
Before forming the drain, an oxide film is formed to improve the pattern shape of the double gate portion consisting of the first and second polysilicon films and the interlayer oxide film, thereby improving reliability such as memory retention characteristics. It is an object of the present invention to provide a method for manufacturing a semiconductor device that can be used in various ways.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 shows the state at each step of manufacturing a double silicon gate field effect type nonvolatile semiconductor device according to an embodiment of the present invention. In this manufacturing method, first, each film 2, 3, 4, 5 is formed on a silicon substrate 1.
form. That is, a gate oxide film 2 with a thickness of 600 Å was formed on a silicon substrate 1 by a thermal oxidation method, and a film was formed on this gate oxide film 2 using thermal decomposition of silane (SiH ₄ ) and phosphin (PH ₃ ) at 630°C. A first polysilicon film 3 having a thickness of 3500 Å is formed by low pressure CVD. Then, an interlayer oxide film 4 with a thickness of 800 Å is formed on this first polysilicon film 3 by a thermal oxidation method, and a second polysilicon film with a thickness of 4000 Å is formed on this interlayer oxide film 4 by the above-mentioned low pressure CVD method. form 5.

Next, the films 3, 4, and 5 thus formed are sequentially patterned into a predetermined pattern shape as shown in FIG. 2a. That is, first, a resist mask 6 is formed on the second polysilicon film 5, and this second
The polysilicon film 5 is patterned by dry etching using CF ₄ gas plasma, and then the interlayer oxide film 4 underneath is patterned by wet etching using a hydrofluoric acid-based aqueous solution at a ratio of 6:1. Then, after patterning the first polysilicon film 3 under the interlayer oxide film 4 by the dry etching described above, the resist mask 6 is removed by oxygen plasma.

Then, the element with resist mask 6 removed is 1100
Oxidation is carried out by placing it in a dry oxygen atmosphere of 2% HCl at ℃ for 20 minutes. As a result, a first oxide film 11 with a thickness of approximately 1000 Å is formed on the second polysilicon film 5 and the exposed end of the first polysilicon film 3, and the first oxide film 11 is The recess 12 between the silicon films 3 and 5 is almost filled with this oxide film 11, and the pattern shape of the double gate part 13 is improved, but the gate oxide film 3 on the substrate 1 only increases in thickness to about 700 Å. .

After that, 160 KeV was applied to substrate 1, and the number of ions was 4×10 ¹⁵
cm ^-2 arsenic ion implantation (see Figure 2b),
It is placed in a nitrogen atmosphere at 1050° C. for 2 hours and treated in nitrogen to form a source portion 7 and a drain portion 8 on the substrate 1. Finally, by a method similar to the conventional method, the source section 7, the drain section 8, and the first oxide film 11 are coated on the substrate 1, and the second oxide film 9 and the phosphorus glass film 10 are formed. In this way, a semiconductor device having the structure shown in FIG. 2c can be manufactured.

In the manufacturing method of this embodiment as described above, after patterning the second polysilicon film 5, interlayer oxide film 4, and first polysilicon film 3, an oxide film 11 is formed to form a double gate. Since the pattern shape of the portion 13 has been improved, the phosphor glass film 10 has the shape shown in FIG. 2d, and hardly penetrates between the first and second polysilicon films 3 and 5. This has been confirmed by observing the cross-sectional shape using a scanning electron microscope (SEM). Therefore, the withstand voltage of the interlayer insulating film 4 between the first and second polysilicon films 3 and 5 increases from 65V of the conventional product to 85V,
As a result, reliability such as charge retention characteristics was greatly improved, and good results were shown when applied to 32K-bit nonvolatile memory.

Note that the present invention is not limited to the above-mentioned embodiments; for example, the gate oxide film 2 may be etched during patterning of a double gate, or may be etched after thermal oxidation to improve the pattern shape. You can also do this.

As described above, according to the method for manufacturing a semiconductor device according to the present invention, in the method for manufacturing a field effect type non-volatile semiconductor device with a double silicon gate structure, after patterning the double gate structure and before forming the source and drain, , an oxide film is formed from the first and second polysilicon films and the interlayer oxide film to improve the pattern shape of the double gate part.
This has the effect of greatly improving reliability such as memory retention characteristics.

[Brief explanation of the drawing]

1A to 1D are sectional views at each step of manufacturing a semiconductor device according to a conventional method, and FIGS. 2A to 2D are sectional views at each step of manufacturing a semiconductor device according to an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Silicon substrate, 2... Gate oxide film, 3... First polysilicon film, 4... Interlayer oxide film, 5... Second
polysilicon film, 7... source part, 8... drain part, 9... second oxide film, 10... phosphorus glass film, 1
1...First oxide film, 13...Double gate part. In the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A method for manufacturing a field-effect nonvolatile semiconductor device with a double silicon gate structure, in which a gate oxide film, a first polysilicon film, an interlayer oxide film, and a second polysilicon film are formed on a silicon substrate. a step of forming the second polysilicon film, the interlayer oxide film, and the first polysilicon film into a predetermined pattern shape; A step of forming an oxide film covering the side surfaces of the interlayer oxide film to improve the pattern shape of the gate portion, a step of forming a source portion and a drain portion on the silicon substrate, and a step of forming the double layer on the silicon substrate. 1. A method of manufacturing a semiconductor device, comprising the step of forming a second oxide film and a phosphorous glass film to cover a gate portion, a source portion, and a drain portion.