JPH0448624A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To suitably control etching of conductive substance and to obtain a semiconductor device having stable transistor characteristics by interposing a thin film becoming an etching stopper at the time of etching and to be removable by heat treating at the time of end of the etching between the substance and a semiconductor substrate. CONSTITUTION:Since a thin film of substance having high etching selectivity to silicon is interposed between a silicon substrate and a polysilicon layer, control of etching of the polysilicon is improved. A field oxide film 2 is formed by normal steps, and an SiO2 film 8 of about several tens-50Angstrom is formed on an active region of the substrate l isolated by the film 2. Then, doped polysilicon 5 is deposited, for example, 3000Angstrom by CVD, and further an SiO2 film 6 is deposited, for example, 5000Angstrom by CVD. The film 6 is removed in an inner base region by etching, and with the remaining film 6 as a mask the polysilicon 5 is removed, for example, by HBr etching gas.

Description

[Detailed Description of the Invention] [Summary] A method for manufacturing semiconductor devices such as bipolar transistors and MOS transistors, in which a film of a conductive material such as polysilicon having etching characteristics similar to those of the semiconductor is formed on a semiconductor substrate such as silicon. The present invention also provides a method for manufacturing a semiconductor device which includes a step of selectively opening a semiconductor substrate by removing a film of the conductive material, and provides a semiconductor device having stable transistor characteristics by appropriately controlling etching of the conductive material. An insulating film forming step of forming an insulating film on a semiconductor substrate with selective openings, a conductive film forming step of forming a conductive film on the insulating film, and a conductive film using the insulating film as an etching stopper. The method includes a processing step of forming a window in the opening by selective processing, and a heat treatment step of eliminating the insulating film under the conductive film by heat treatment after this processing step.

C. Industrial Application Field The present invention relates to a method for manufacturing semiconductor devices such as bipolar transistors and MOS transistors.
More specifically, the present invention relates to a method of manufacturing a semiconductor device having a shallow junction or a fine electrode structure.

In recent years, demands for improved performance in terms of higher speed and higher integration for LF and I have become increasingly strict, and in order to achieve these improvements, it is required to establish microfabrication technology that forms shallow junctions and fine electrodes. There is.

[Prior Art] The conventional technology will be explained below by taking a bipolar transistor as an example.

In recent years, structures having polysilicon base lead electrodes have been frequently used in bipolar transistors. A typical double polysilicon structure is shown in FIG. In the figure, 1 is a silicon substrate, 2 is an isolation insulator that selectively opens the silicon substrate 1, 3 is a base, 3a is an external base, 3b is an internal base, 4 is an emitter, and 5 is a base drawer made of polysilicon. The electrodes 6 are an insulating film on the silicon substrate 1, and 7 is an emitter electrode made of polysilicon deposited in the window of the insulating film 6.

In order to manufacture the structure shown in FIG. 7, polysilicon 5 is deposited on silicon substrate 1, and then the polysilicon 5 in the emitter region is selectively etched down to substrate 1.

[Problems to be Solved by the Invention] However, in this step, it is difficult to obtain a high selectivity because the polysilicon 5 and the single silicon of the substrate 1 have similar etching characteristics. For this reason, when over-etching occurs, as shown in FIG. 8, the silicon substrate 1 is scraped in a groove shape at the stage where the polysilicon 5 is removed, and the external base 3a and the internal base 3b, which are usually about 2000 thick, are connected. There were times when defects occurred. In addition, if the diffusion of the emitter 4 goes deep into the silicon substrate 1 and the base becomes shallow (if
As shown in the figure, leakage between the collector and emitter sometimes occurred by penetrating the base at position 30. On the other hand, if underetching occurs, a thin layer of polysilicon 5' remains within the electrode window as shown in FIG. 10, and leakage between the emitter and the base where the base lead electrode 5 is connected to the emitter 4 may occur.

In particular, as the electrode structure becomes finer and the junction becomes shallower, overetching or underetching tends to occur.
The characteristics of the transistor were unstable, which caused manufacturing problems.

In view of the above points, the present invention forms a film of a conductive material such as polysilicon having etching characteristics similar to that of the semiconductor on a semiconductor substrate such as silicon, and selectively etches the semiconductor substrate by removing the film of the conductive material. An object of the present invention is to provide a semiconductor device having stable transistor characteristics by properly controlling etching of a conductive material in a method of manufacturing a semiconductor device including a step of forming an opening.

(Means for Solving the Problem) The above problem can be solved by sandwiching a thin film between the conductive material and the semiconductor substrate, which acts as an etching stopper during etching and can be removed by heat treatment after etching.

That is, the first aspect of the present invention is an insulating film forming step of forming an insulating film on a semiconductor substrate with selective openings, a conductive film forming step of forming a conductive film on the insulating film, and an etching stopper for the insulating film. A processing step of selectively processing the conductive film to form a window in the opening, and a heat treatment step of eliminating the insulating film under the conductive film by heat treatment after this processing step. do.

The second aspect of the present invention is a method in which an etching stopper is used throughout the window forming process, and when the conductive film is completely removed and the window is formed in the processing process, the insulating film remains within the window. This method is characterized by removing this remaining conductive film.

In the final stage of the third window forming step of the present invention, the etching stopper is not used, and when the conductive film is completely removed in the processing step, the insulating film is removed within the window, and the semiconductor substrate is further removed through the window. It is characterized by removing 1000 Å or less within the area.

A fourth aspect of the present invention relates to a method in which the insulating film is left in a part of the semiconductor substrate and used as an element, and is used as an etching stopper in another part, and then disappears. A plurality of insulating films having different thicknesses and/or film types are formed at different locations on the same semiconductor substrate, and only a portion of the plurality of films is eliminated by the heat treatment.

Hereinafter, first to third aspects of the present invention will be explained.

The following will mainly explain a specific example in which silicon constitutes a semiconductor substrate and polysilicon constitutes a conductive film.

FIG. 1 is a drawing explaining the present invention in detail, in which an isolation insulator 2 selectively opens a silicon substrate 1, an insulating film 8 is formed in the opening, and then polysilicon 5 and An insulating film 6 is formed on the entire surface of the silicon substrate, and then the insulating film 6 is patterned, and using this pattern as a mask, the polysilicon 5 is selectively processed to form a window inside the opening of the isolation insulator 2. It is shown that. In this processing step, the insulating film 8 is used as an etching stopper. The insulating film 8 is made of oxide, nitride, etc., and has a high etching selectivity with respect to the polysilicon 5, so that the etching controllability of the polysilicon 5 is improved. That is, the insulating film 8a exposed within the window prevents the silicon substrate 1 from being over-etched. After such selective processing of polysilicon, heat treatment is performed to eliminate insulating film 8b under polysilicon 5. For example, the insulating film 8b has several tens of Si 0
2, the insulating film 8b disappears by performing a short heat treatment at a temperature of 1000 to 1200°C.

The polysilicon 5 may be manufactured by either CVD or sputtering, and the present invention can be practiced even if amorphous silicon is used. Further, a conductive material such as a high melting point metal or a high melting point metal silicide can be similarly used in place of the polysilicon 5.

The insulating film 8 must have a thickness that is at least the minimum thickness that acts as an etching stopper, and must have a thickness that is not more than the maximum thickness that can be eliminated by heat treatment. This film thickness is determined by the film formation method (sputtering, CVD, etc.), etching selectivity, degree of overetching, and the like.

The etching selectivity ratio may be less than 1 (etching rate of SiOg) + 1 OOO (etching rate of polysilicon), but in reality it is preferably about 1:20 to 1:100. For example, if the selection ratio is 1:50, 3,000 polysilicon layers 5 are completely etched, and an additional 1,000 polysilicon layers are etched.
When over-etching people, the number of etching holes for S i O2 is 1°00X (1150) = 20 people.

On the other hand, if the SiO□ film formed by acid-based chemical treatment is less than several tens of angstroms, it can be eliminated by short-time heat treatment at 1°OO to 1200°C. Therefore, when a 20-layer Si0g film is used as an etching stopper, 5iO7 is removed from inside the window when the window is formed in polysilicon, and the amount of etching of the silicon substrate can be made zero. However, in reality, it is difficult to reduce the etching amount of the silicon substrate to zero, but in order to embody the second aspect of the present invention and protect the silicon substrate, a SiO
Let's say there are 5 people. Then, some Si remaining after window formation
The silicon substrate can be protected by the O2 film. It is necessary to remove this SiOz film, but since a window has already been formed in the polysilicon film, etching is performed for 5 ins taking into consideration the etching selectivity between silicon and 5fOa. There are many etching agents such as HF that have a high etching selectivity for SiO□, so the remaining Si can be removed without over-etching the silicon substrate.
O□ can be removed. In the above example, if the third aspect of the present invention is embodied and the film thickness of Sing is 30, the silicon substrate will be etched by about 1000 people at the end of the polysilicon etching process, which requires a total of 4000 people.

Defects on the surface of the silicon substrate can be removed by shallow overetching of 1000 Å or less, and the drawbacks of overetching described with reference to FIG. 9 do not appear.

It is desirable that the heat treatment be performed for as short a time as possible in order to form a shallow bond. The heat treatment time is preferably 10 seconds or more and 1 minute or less, particularly 30 seconds or less. Also, 10
S
The iO□ film may be destroyed, and then a diffusion heat treatment may be performed at, for example, 850° C. for 30 minutes to diffuse oxygen from the surface of the destroyed film. Note that it is also effective to use a reducing substance such as hydrogen as an auxiliary means to eliminate SiOx.

Next, the second aspect of the present invention will be explained with reference to FIGS. 3 and 4. The same reference numerals in FIGS. 3 and 4 as in FIG. 1 have the same meaning. Therefore, 88 in the left half of Figure 2
8b means an SiO2 film which functions as an etching stopper during processing of polysilicon 5a, and 8b means an SiO□ film which disappears by heat treatment after processing (see FIG. 3). On the other hand, 8c is a 5in2 film made of the same material as 8a and 8b, but has a thickness greater than that which disappears by heat treatment, so it remains even after processing polysilicon 5 and heat treatment (see FIG. 3). Polysilicon 5 after heat treatment
After oxidizing the surface to form Sing films 10a, b, and c, the exposed 5in2 film 8 is removed using the 5tOa film as a mask.
Remove d and 8e. When processed in this way, the window 12 is made into an emitter window, and the removed portions of the 5iO=films 8d and 8e are made into source/drain electrode windows, resulting in a bipolar MO
8 mixed elements can be manufactured.

[Function] In the method according to claim 1, since a thin film of a substance having a high etching selectivity to silicon is sandwiched between the silicon substrate and the polysilicon layer, the controllability of polysilicon etching is improved. Since the above-mentioned thin film can be removed by heat treatment after etching, the contact between the silicon substrate and polysilicon is not adversely affected. Furthermore, since an insulating film serving as an etching stopper is formed over the entire opening of the silicon substrate, alignment for forming the insulating film is not required, and an increase in element size to provide a margin for alignment can be avoided.

The method according to claims 2 to 4 is a configuration in which the above-mentioned effect of claim 1 is adapted to a specific process or device, and the method according to claim 2 is adapted to prevent over-etching of a silicon substrate. The method according to claim 3 is effective for removing defects on the surface of a silicon substrate, and the method according to claim 4 is effective for manufacturing heterogeneous devices. Similarly, the method according to claim 5 is a method devised to complete the diffusion of the external base in the heat treatment step for eliminating the insulating film, and can shorten the steps.

Hereinafter, the present invention will be explained in more detail with reference to a method for manufacturing a self-aligned bipolar transistor using polysilicon as a base lead electrode.

[Example] A field oxide film 2 (Fig. 4) is made by a normal process,
On the active region of the silicon substrate 1 separated by the field oxide film 2, about 10 to 50 F-Oa films 8 are formed.

After that, the B-doped polysilicon 5 is heated to, for example, 3000 C.
The SiO□ film 6 is deposited by VD, and then the SiO
Deposited by CVD on 0 people.

This SiO□ film 6 is removed by etching in the internal base region, and the remaining 5iOa film 6 is used as a mask to remove the polysilicon 5 using, for example, HBr-based etching gas. The selectivity ratio of this etching gas is approximately 1 (SiO□):5
0 (polysilicon), the SiO2 film 8 remains during the removal of the polysilicon 5 and acts as an etching stopper, and the remaining SiO□ film at the time of completion of etching is
Remove using chemicals.

Subsequently, as shown in FIG. 5, approximately 200 F Si Ox films 9 were formed within the window by thermal oxidation.

Thereafter, ions were implanted through the Stow film 9 to implant impurities for forming the internal base 4 (see FIG. 6). Next, high-temperature, short-time heat treatment is performed at 1000 to 1200° C. for 1 minute or less to diffuse the external base 3a from the polysilicon 5, and at the same time diffuse the SiO2 film 8 below the polysilicon 5.
B was balled up (disappeared). Furthermore, a polysilicon layer 7, which will become an emitter electrode, was formed by CVD.

[Effects of the Invention] As described above, according to the present invention, the controllability of etching in the contact window forming portion can be improved, contributing to stabilization of device characteristics and improvement in yield.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the principle of the present invention, Fig. 2 is an explanatory diagram of the inventive method using insulating films of different thicknesses, Fig. 3 is a diagram showing the structure after the etching stopper is removed, Fig. 4 are the etching stopper, polysilicon, and the eyebrow insulating film.
, FIG. 5 is a diagram showing a structure in which the structure of FIG. 4 is opened, FIG. 6 is a diagram showing the main parts of a bipolar transistor, and FIG. 7 is a diagram showing a conventional Figure 8 shows the main parts of a double polysilicon bipolar transistor. Figure 8 is an illustration of how overetching occurs in the conventional method for manufacturing double polysilicon bipolar transistors. Figure 9 shows the conventional method for manufacturing double polysilicon bipolar transistors. FIG. 10 is an explanatory diagram of the occurrence of leakage between the emitter and the base in the conventional manufacturing method of a double polysilicon Ibora transistor. 1-Silicon substrate, 2-Isolation insulator, 3-
base, 3a - external base, 3b - internal base, 4 - emitter, 5 is a base extraction electrode made of polysilicon, 6
-Insulating film, 7-Emitter electrode, 8-Insulating film to serve as etching stopper Month 9 Chitose 1st 4th PA Final process figure 5 Figure '4 Hirami's sunset Purpuri S1 Okaku 1 Sumire Figure 7 Ohsho'□Eshi Figure 8 Co1. // 7ri Emi, 7ta mater 9th diagram Quemi... 7ta hepa-humanri 10th diagram

Claims (1)

[Claims] 1. An insulating film forming step of forming an insulating film on a semiconductor substrate with selective openings, a conductive film forming step of forming a conductive film on the insulating film, and using the insulating film as an etching stopper. The present invention is characterized by comprising a processing step of forming a window in the opening by selectively processing the conductive film, and a heat treatment step of disappearing the insulating film under the conductive film by heat treatment after this processing step. A method for manufacturing a semiconductor device. 2. In the processing step, when the conductive film is completely removed and the window is formed, the insulating film remains within the window, and the remaining conductive film is then removed. 1. The method for manufacturing a semiconductor device according to 1. 3. In the processing step, when the conductive film is completely removed, the insulating film is removed within the window, and the method further includes an etching step of removing 1000 Å or less of the semiconductor substrate within the window. 2. The method of manufacturing a semiconductor device according to claim 1. 4. The insulating film is formed in different locations on the same semiconductor substrate as a plurality of films having at least one of different film thicknesses and film types, and only a part of the plurality of films is eliminated by the heat treatment. Any one of claims 1 to 3
A method for manufacturing a semiconductor device according to section 1. 5. The method of manufacturing a semiconductor device according to any one of claims 1 to 4, wherein an external base of a bipolar transistor is diffused in the heat treatment step.