JPS5917530B2 - Manufacturing method of semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION 5 The present invention relates to a method for diffusing impurity atoms into a semiconductor substrate.

Conventionally, the following method has been mainly used to diffuse impurity atoms into a silicon substrate.

Using a liquid diffusion source such as Ξ boron bromide BBr3, boron oxide B2O3 is first deposited on a heated silicon substrate.
deposit. Next, B2O3 is removed using a hydrofluoric acid aqueous solution, and the impurity atoms B are diffused into the silicon substrate by a so-called drive-in process in a high-temperature heat treatment furnace. In the above diffusion method, an impurity diffusion layer can be selectively formed only in desired regions by first forming a protective film such as a silicon oxide film to an appropriate thickness in regions where diffusion is not performed. can do.

According to the conventional diffusion method described above, a deposition furnace for depositing impurity atoms onto the silicon substrate and a drive-in furnace for diffusing the impurity atoms into the silicon substrate are required.

In addition, the impurity concentration in the diffusion layer depends on the deposition conditions, i.e., the carrier gas flow rate, the temperature of the silicon substrate surface, the number of charged silicon substrates, and the impurity that is the diffusion source.
5 It has been extremely difficult to control the impurity concentration because it varies depending on the temperature of the liquid and other factors. Furthermore, when performing selective diffusion, there are drawbacks such as the need for a diffusion prevention mask, such as a silicon oxide film, outside the desired area, and when forming multiple impurity diffusion layers, the same method must be repeated multiple times. I had to repeat it. The present invention provides a method for diffusing impurity atoms without the above-mentioned drawbacks, including a step of forming diporous silicon on the main surface of a semiconductor substrate by anodizing, and dipping the substrate in a solution to form diporous silicon. a step of cleaning the substrate containing the impurity; a step of heat-treating the substrate to diffuse the impurity contained in the porous silicon into the substrate; and a step of completely removing the porous silicon. It is composed of a process including a process of changing the quality into a fine object. Therefore, only one heat treatment furnace is required as a diffusion furnace, and since the impurity concentration in the diffusion layer depends on the formation conditions and film thickness of the porous silicon layer, if the formation conditions of the porous silicon layer are constant, the impurity concentration will be the same as in the porous silicon layer. It is determined by the thickness of the silicon layer, and it is better to control the impurity concentration.
Furthermore, a low concentration diffusion layer, which has been difficult to form using conventional methods, can be formed by reducing the thickness of the porous silicon layer. Furthermore, a mask for preventing diffusion is not required during selective diffusion according to the method of the present invention. Furthermore, it is also possible to simultaneously form a plurality of impurity diffusion layers by one heat treatment. Generally, when a certain amount of impurity Q is applied to the surface of a semiconductor substrate,
When this is diffused into the semiconductor, the impurity concentration N in the depth direction is expressed as follows.

From the above equation, it can be seen that the impurity concentration N is proportional to the impurity amount Q.

The amount Q of impurities contained in the porous silicon layer is expressed as follows, assuming that the thickness of the porous silicon layer is D and the conditions for forming the porous silicon layer are constant.

Therefore, the impurity concentration N in the semiconductor substrate is proportional to the thickness D of the porous silicon layer. Therefore, in order to form a diffusion layer with a low impurity concentration, the thickness D of the porous silicon layer can be made small. I understand that. The present invention will be described in detail below with reference to the drawings.

FIG. 1 shows a method according to one embodiment of the invention. (a) First, a silicon nitride film 13 is deposited on the main surface of a P-type silicon substrate 11 except for a desired region 12 where a diffusion layer is to be formed. 0)) Next, a porous silicon layer 14 is selectively formed in desired areas 12.

The porous silicon layer 14 is formed by anodization in an electrolytic solution, for example, an aqueous hydrofluoric acid solution. If impurity atoms are included in the hydrofluoric acid aqueous solution at this time, the impurity atoms will be included in the formed porous silicon layer 14.
In this example, an anodic treatment was carried out by containing phosphoric acid H3PO4 containing phosphorus as an N-type impurity in a hydrofluoric acid aqueous solution. After forming the porous silicon layer 14, the silicon nitride film 13 is removed while the power is turned off and the substrate 11 remains immersed in the hydrofluoric acid aqueous solution. (c) After thoroughly cleaning the substrate 11, the substrate 11 is placed in a 1000°C heat treatment furnace, and the inside of the substrate 11 is filled with N-type impurity diffusion layer 15.
form. In this case, when heat treatment is performed in an oxygen or water vapor atmosphere, the porous silicon layer 14 becomes a silicon oxide film. In the above examples, a solution containing impurity atoms was added to a hydrofluoric acid aqueous solution and then subjected to anodization. Alternatively, the substrate may be immersed in a solution containing impurity atoms after forming the porous silicon.

Further, the hydrofluoric acid aqueous solution may be replaced by other electrolytes such as hydrochloric acid. Another method is to eliminate air bubbles generated during anodization! In order to remove impurity atoms, a gas containing impurity atoms, such as a mixed gas of phosphine PH3 and nitrogen, may be bubbled into the electrolyte. When such post-anodization is performed, porous silicon containing phosphorus as impurity atoms is formed as in the previous embodiment. Thereafter, a 1N type impurity diffusion layer is formed by performing the same steps as in the previous embodiment. In this method, phosphine was used as a bubble in the electrolyte, but diborane B2H6 or boron trichloride B was used for boron diffusion.
CI3 or the like may also be used. Or boron tribromide BB
Nitrogen gas that bubbles in a liquid such as r3 may also be used. Further, although heat treatment was performed in the above embodiments, this heat treatment is not necessarily necessary, and porous silicon containing impurities can be used as it is as a low resistance layer.

Here, in this embodiment, since impurities are contained in the diporous silicon by chemical adsorption, it is possible to perform sufficient cleaning and prevent contamination of the electric furnace and the like. FIG. 2 shows a double diffusion method according to another embodiment of the present invention, and (a) is a diagram in which an N-type impurity diffusion layer 15 is formed by the method shown in FIG.

In this case, the diffusion heat treatment was performed in an N2 gas atmosphere.
Next, the substrate 11 was immersed in a boron king bromide BBr3 solution, cleaned, and then placed in a heat treatment furnace at 1000° C. to form a P-type impurity diffusion layer 16 as shown in FIG. In the above embodiment, the entire porous silicon layer 14 contains boron tribromide BBr3, but it is also possible to contain a solution containing impurities only in a predetermined region of the porous silicon layer 14.

In this case, an oxidation-resistant mask such as a silicon nitride film is applied only to the desired areas, and the porous silicon layer other than the desired areas is made into a silicon oxide film, and then the substrate is immersed in a solution containing impurities. good. Another method of double diffusion is to use a solution containing two types of impurity atoms with different diffusion coefficients, such as a mixed solution of phosphorous oxychloride and methyl borate, to spread the silicon substrate on which a porous silicon layer is formed using the above mixture. It is also possible to form P-type and N-type impurity diffusion layers at the same time through I heat treatment after immersion in a liquid.

Further, by using a solution containing three or more types of impurity atoms, it is also possible to simultaneously form an antinominal number of impurity diffusion layers in one heat treatment. Furthermore, as another method for double diffusion, a gas containing two types of impurity atoms with different diffusion coefficients, such as a mixed gas of phosphine PH3 and diborane B2H6 diluted with nitrogen, may be bubbled simultaneously or separately into the electrolyte. .

It is also possible to simultaneously form a plurality of impurity diffusion layers using a gas containing three or more types of impurity atoms. When the heat treatment in the above examples is performed in an oxidizing atmosphere,
Porous silicon is preferable because it forms a silicon oxide film that is a stable protective film for semiconductor devices.

Furthermore, semiconductor elements such as transistors and thyristors can also be formed by combining the methods of the above embodiments or by repeating them multiple times. As described above, the impurity atom diffusion method according to the present invention requires only one heat treatment furnace.

Furthermore, since the impurity concentration can be controlled by the thickness of the porous silicon layer, it is possible to easily form a diffusion layer with good controllability and a low impurity concentration. Furthermore, in the impurity atom diffusion method according to the present invention, the number of silicon substrates to be charged is arbitrary. Further according to the invention,
A mask to prevent wax is not required when selectively diffusing impurity atoms. Further, according to the present invention, a plurality of impurity diffusion layers are
It is also possible to form them simultaneously through two heat treatments. As described above, the impurity diffusion method according to the present invention is useful for manufacturing semiconductor devices.

[Brief explanation of the drawing]

FIGS. 1A, b, CL and 2A, 2B are process cross-sectional views of a method for diffusing impurities into a semiconductor substrate according to each embodiment of the present invention. 11... Silicon substrate, 13... Silicon nitride film, 14
...Porous silicon, 15...N-type diffusion layer, 16...
・P-type diffusion layer.

Claims (1)

[Claims] 1. A step of forming porous silicon on the main surface of a semiconductor substrate by anodizing, a step of immersing the substrate in a solution containing impurities to make the porous silicon contain the impurities, and The method includes the following steps: cleaning the substrate, heat-treating the substrate to diffuse at least a portion of the impurity contained in the porous silicon into the substrate, and transforming the porous silicon into an insulator. A method for manufacturing a semiconductor device. 2. Claim 1, characterized in that a semiconductor substrate is anodized in the electrolytic solution using an electrolytic solution containing impurities, and the impurity is made to be contained in the porous silicon while forming porous silicon. A method for manufacturing a semiconductor device according to paragraph 1. 3. A patent claim characterized in that a semiconductor substrate is anodized in the electrolytic solution while gas containing impurities is flowing out, and the impurity is made to be contained in the porous silicon while forming porous silicon. A method for manufacturing a semiconductor device according to item 1. 4. The method of manufacturing a semiconductor device according to claim 1, wherein the porous silicon contains at least two types of impurities. 5. The method of manufacturing a semiconductor device according to claim 1, wherein the heat treatment is performed in an oxidizing atmosphere to diffuse impurities into the semiconductor substrate and simultaneously change the porous silicon into a silicon oxide film.