JPS5826660B2 - Takoushitsu Silicon Noseizouhouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing selectively porous silicon.

When a silicon substrate is immersed in an electrolyte solution, such as an aqueous hydrofluoric acid solution, and anodized, porous silicon is generated on the main surface of the silicon substrate.

Porous silicon has an extremely fast thermal oxidation rate compared to single crystal silicon, and can also be thermally oxidized at low temperatures, making it possible to obtain a thick silicon oxide film through thermal oxidation at low temperatures for a short period of time, making it ideal for IC elements. Attempts are being made to apply this to insulation separation between the two.

At that time, porous silicon must be selectively generated on the main surface of the silicon substrate.

Conventionally, in order to selectively produce porous silicon on a silicon substrate, an electrolyte solution-resistant film, such as a silicon nitride film, was selectively deposited on the main surface of the silicon substrate and anodized.

When porous silicon is selectively produced by such a method, the porous silicon is produced in a manner that extends in the lateral direction as shown in FIG.

1 is a silicon substrate, 2 is a silicon nitride film, 3 is porous silicon, and 4 is a lateral extension of the porous silicon.

According to our experiments, the lateral extent 4 is porous silicon 3
The film thickness reaches 0.7 to 0.9.

In the selective production of porous silicon, the occurrence of lateral spreading hinders the improvement of the degree of integration when porous silicon is applied to ICs, LSIs, and the like.

The present invention provides a method for producing selectively porous silicon without lateral spreading.

Porous silicon is produced with lateral expansion because the current caused by the anodization is concentrated in selective areas from the entire back surface of the silicon substrate.

It can be seen that in order to eliminate the lateral spread of porous silicon, it is sufficient to provide a current path that spreads from the back surface to a selective region.

To provide the current path as described above, the contact area on the backside of the silicon substrate can be made equal to or smaller than the area of selectively porous silicon.

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

FIG. 2 shows a cross section of a substrate in an embodiment of the present invention.

a selectively covers the main surface 11 of the silicon substrate 1 with a silicon nitride film 2, and deposits a metal electrode layer 15 on the back surface 12 of the substrate 1 in a region 14 that is equal to or smaller than the region 13 in which porous silicon is to be formed. After the formation, porous silicon 3 is generated by anodizing.

The figure shows an example in which a conductive wire impurity diffusion layer 16 is provided on the silicon substrate 1 and the metal electrode layer 15 in order to make better contact with the silicon substrate 1 and the metal electrode layer 15 before forming the metal electrode 15 in FIG.

By this method, it was possible to prevent the lateral expansion 4 of the porous silicon 3 from occurring.

FIG. 3 shows another embodiment of the invention.

Porous silicon can be produced by using the silicon substrate itself as an anode electrode, or by bringing the back surface of the silicon substrate into contact with a conductive liquid or an electrolyte solution, i.e., an electrode solution, which the inventors have proposed. There is an indirect electrode method, and this example is a method for producing porous silicon that does not cause lateral spreading using the latter method.

a silicon nitride film 2 is selectively deposited on the main surface 11 of the silicon substrate 1, and a silicon nitride film 2 is deposited on the back surface 12 of the silicon substrate 1 in a region 18 equal to or smaller than the region 13 where porous silicon is to be formed. A porous silicon 3 is produced by selectively depositing a film 17 and using an indirect electrode method.

In the figure, a conductive line impurity diffusion layer 16 is provided in the region 14 to improve contact between the silicon substrate 1 and the electrolyte.

By this method, it was possible to prevent the lateral expansion 4 of the porous silicon 3 from occurring.

In this example, a silicon nitride film was used as a mask for selectively producing porous silicon, but the mask is not limited to this, and any film that is resistant to electrolyte solutions may be used.

Further, in FIG. 3, a silicon nitride film is used as a mask for selectively contacting the back surface of the silicon substrate, but this is not limited either, and any film that is resistant to electrode liquid may be used.

Furthermore, the impurity diffusion layer 16 on the back surface of the silicon substrate for better contact is not limited to the region 14.

As described above, according to the present invention, it is possible to produce selectively porous silicon that does not spread in the lateral direction.

[Brief explanation of the drawing]

FIG. 1 is a structural cross-sectional view of a silicon substrate on which porous silicon is formed by a conventional method, and FIG. 2a is a cross-sectional view of the structure. FIG. 3b is a structural diagram of a silicon substrate in the process of producing porous silicon in one embodiment of the present invention, and FIGS. 3a and 3b are structural diagrams of a silicon substrate in another embodiment. DESCRIPTION OF SYMBOLS 1...Silicon base, 2...Silicon nitride film, 3...Porous silicon, 11...Silicon base main surface, 12...Silicon base Back side, 1
3...Selective porous silicon generation region, 14.
... Contact region, 15 ... Metal electrode layer, 16 ... Impurity diffusion layer, 17 ...
Silicon nitride film, 18... area other than contact.

Claims (1)

[Scope of Claims] 1. A step of forming an insulating film having an opening in a predetermined region in which porous silicon is to be formed on one main surface of a silicon substrate; Correspondingly, the method includes a step of forming an electrode portion having an area smaller than the opening formed in the predetermined region, and a step of forming porous silicon in the predetermined region by anodizing using the electrode portion. A method for producing porous silicon, characterized by: 2. A patent claim characterized in that the electrode portion is made of a wire ring coating that corresponds to a predetermined region in which porous silicon is to be formed and has an opening that is smaller than the opening of the insulating coating formed in the predetermined region. A method for producing porous silicon according to item 1.