JPS5881998A - Anode reaction treatment apparatus - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for uniformly subjecting a semiconductor substrate or a metal substrate to an anodic reaction treatment in an electrolytic solution.

In recent years, this type of equipment has been used particularly in the manufacturing process of semiconductor devices to perform anodic oxidation and anodic polishing on the surface of semiconductor substrates.
It is widely used to form porous silicon on silicon substrates. Therefore, the following explanation will be given using an example in which porous silicon is formed on a silicon substrate, but the apparatus of the present invention is not limited to this, and the apparatus of the present invention is not limited to this. (hereinafter simply referred to as the board)
It can be widely used in anodic reaction treatments.

Conventionally, as an anode reaction treatment apparatus, one having the structure shown in FIG.
(See No. 6). In the figure, 1 is a substrate (silicon substrate),
2 is an upper electrolyte chamber, 6 is a lower electrolyte chamber, 4 is an electrode in the upper electrolyte chamber, 5 is an electrode in the lower electrolyte chamber, 6 is an upper liquid supply port, 7 is a lower liquid supply port, 8 is a Upper drain reservoir, 9 lower drain reservoir, 10 upper drain port, 11 lower drain port, 12
16 is a plurality of lower electrolyte passages provided around the lower electrolyte chamber 3; 14 is a notch in which the substrate 1 is installed; be. Note that the electrolyte circulation device and the like are omitted from illustration.

When forming porous silicon using this device, an electrolyte 15 containing hydrofluoric acid is placed in the upper electrolyte chamber 2, and an appropriate electrolyte 16 (a solution with conductive properties) is placed in the lower electrolyte chamber 6. (it may be the same as the electrolyte 15) from the outside into the upper liquid supply port 6. Injecting electrolyte through the lower liquid supply lower 15. Substrate (silicon substrate) 1 and electrode 4. The electrode 5 is immersed,
Each electrolytic solution is circulated by a pump (not shown) or the like.

For example, when the electrode 5 in the lower electrolyte chamber 6 is used as an anode and the electrode 4 in the upper electrolyte chamber 2 is used as a cathode, a voltage is applied between the two electrodes and a current is passed, the electrodes come into contact with the upper electrolyte 15. Porous silicon is formed from the surface of the substrate 1 toward the inside of the substrate.

According to the structure of this device, the upper liquid supply port 6. Since it is smaller than the diameter of the lower part 3, it is difficult to equalize the pressure of the electrolyte solution 15, 16 sent into the electrolyte solution chambers 2, 6 by a pump or the like within the electrolyte solution chamber. Therefore, the pressure of the electrolyte becomes uneven even within the surface of the substrate, and the porous silicon that is formed becomes thicker in the areas where the electrolyte comes into contact with a strong pressure. There was a problem that the surface was non-uniform.

Furthermore, although the top surface of the substrate 1 that contacts the electrolyte is circular, the bottom surface has a contact area with the lower electrolyte chamber and also contacts the electrolyte in the lower electrolyte passage 16, as shown in FIG. As shown, it has a gear-like shape. As a result, compared to the electrolyte contact area on the top surface of the substrate, the electrolyte contact area on the bottom surface of the substrate becomes larger by the portion corresponding to the teeth in the gear shape. Therefore, as shown in FIG. 6, during the anodic reaction treatment, Of the current flowing into the substrate from the electrolyte contact surface on the bottom surface of the substrate 1, the current flowing from the portion corresponding to the gear-shaped teeth in FIG.
When flowing out, it bends toward the center of the substrate 1. Therefore,
The current density passing around the electrolyte contact surface on the upper surface of the substrate is higher than that at the center of the substrate. In the figure, the same reference numerals as those described above indicate the same or equivalent parts, and arrows indicate the flow of current.

FIG. 4 is a graph showing the relationship between the current density and the rate of formation of porous silicon, and is an example in the case where the concentration of hydrofluoric acid on the side where anodization is performed is 50W1%. As is clear from this graph, the higher the current density, the faster the formation rate of porous silicon becomes. The problem arises that the film becomes thicker.

Furthermore, if the shape and area of the electrodes 4 and 5 are not the same as the electrolyte contact surface of the substrate, the potential distribution between the upper and lower surfaces of the substrate 1 and the interface with the electrolyte will be disturbed. Furthermore, the position of electrode 4.5 is
If there is a large distance between the electrode and the electrolyte, the uniformity of the potential distribution at the interface between the substrate and the electrolyte will be poor in reproducibility due to the flow and pressure of the electrolyte. Such non-uniformity in the potential distribution at the interface between the substrate and the electrolytic solution poses a problem in that the thickness of the formed porous silicon film becomes non-uniform.

The present invention has been made to solve these problems. The first purpose is to insert a perforated plate into the electrolyte circulation path so that the flow of electrolyte comes into contact with the substrate with uniform pressure, allowing uniform anodic reaction treatment. A second purpose is to make the electrolyte contact surfaces on both sides of the substrate face each other, to have the same shape and area, and to equalize the flow of current within the substrate, so that more uniform anodization can be performed. It's about doing. The sixth purpose is to make the electrodes provided in the electrolyte into a mesocye shape, and 1. By making the electrolyte contact surface of the substrate the same shape and area and equalizing the potential in the electrolyte between the substrate and the electrode, we have created a device that performs uniform anodic reaction treatment (manufacturing porous silicon) over the entire surface of the substrate. On offer.

Hereinafter, the present invention will be explained in detail with reference to Examples.

FIG. 6 is a cross-sectional view of a main part structure showing an example of the configuration of the anode reaction treatment apparatus of the present invention. In the figure, 1718 is a perforated plate having a large number of holes (for example, 2 mm in diameter and 5 mm apart). An example thereof is shown in FIG. Electrolytes 15 and 16 are fed into electrolyte chambers 2 and 6 through liquid supply ports 6 and 7, respectively, and come into contact with porous plates 17 and 18 due to the pressure exerted by the pump. The pressure of the electrolyte 15, 16 is distributed to the surroundings by the perforated plate and is made uniform within the electrolyte chamber. Therefore, after passing through the perforated plates 17 and 18, the electrolytes 15 and 16 come into contact with the entire surface of the substrate 1 under uniform pressure, and are then discharged from the electrolyte chambers 2 and 3.

By spraying the electrolyte onto the substrate, air bubbles generated by the chemical reaction and adhering to the substrate surface are removed, but by inserting the perforated plates 17 and 18, the electrolyte is sprayed with uniform pressure over the entire surface of the substrate. Therefore, it is possible to completely remove all bubbles on the substrate surface. Unless a chemical current flows through the portion where the bubbles are attached, the formation of porous silicon will stop at that portion, and the uniformity of the porous silicon film within the substrate surface will deteriorate. However, by inserting the perforated plate, all the air bubbles within the plane of the substrate can be removed, which improves the uniformity.

The shape and area of the electrolyte contacting surface on the upper surface of the substrate 1 and the electrolyte solution contacting surface on the lower surface of the substrate 1 are the same, and the electrolyte contacting surfaces of the substrate 1 are made to face each other.

In Fig. 8, the diameter of the upper electrolyte contact surface is 65 mm,
The diameter of the bottom electrolyte contact surface is (a) 60 mm, (b)
The film thickness distribution of the porous silicon film formed when the thickness was 65 mm and (c) 73 mm is shown. The conditions for forming the porous silicon film are the same in all cases, and the concentration of hydrofluoric acid on the side where anodization is performed is s and o wt %.

Current density 5mA/cm2. The chemical formation time was 40 minutes.

As can be seen from this figure, the uniformity is best when the electrolyte-contact areas on the top and bottom surfaces are the same (b).

Further, the electrodes 4 and 5 are formed into a net shape, for example, with an interval of 3 to 5 mm, so as not to obstruct the flow of the electrolytic solution 15.16.
The shape and area of the substrate 1 are made to be the same as the electrolyte contact surface of the substrate 1. Further, the electrodes 4 and 5 are positioned approximately 14 mm from the substrate 1, and the substrate 1 and the electrodes 4 and 5 are parallel to each other. Figure 9 is a diagram showing these effects.
a) When the electrode is installed at a distance of 14 mm from the substrate,
(b) shows the film thickness distribution of porous silicon when the electrode is placed at a distance of 25 mm from the substrate. The conditions for forming the porous silicon film are the same as those shown in FIG. As is clear from the figure, (b) has worse uniformity and poorer reproducibility than (a).

Note that the same effect can be obtained even if the positional relationship between the porous plate and the electrode is reversed.

As explained above, according to the anodic reaction treatment apparatus of the present invention, porous silicon with excellent uniformity and reproducibility can be formed over the entire surface of the substrate. Furthermore, as mentioned above, the apparatus of the present invention can also be used for anodic oxidation, anodic polishing, etc., and similar effects can be expected.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view showing the configuration of the main parts of a conventional anodic reaction treatment device, Figure 2 is an illustration of the electrolyte contact state on the bottom surface of the substrate, and Figure 6 is an explanation of the flow of current during anodic reaction treatment in the conventional device. Figures 4 and 4 are graphs showing the relationship between current density and the formation rate of porous silicon, Figures 5, 8 (a) to (C), and 9 (a) and (b) are graphs showing the relationship between the current density and the formation rate of porous silicon. FIG. 6 is a cross-sectional view of the main structure of the anodic reaction treatment apparatus of the present invention, and FIG. 7 is a plan view of a porous plate. 1... Substrate (substrate to be processed) 2... Upper electrolyte chamber 3... Lower electrolyte chamber 4.
5...Electrode 6...Upper liquid supply lower...Lower liquid supply port 8...Upper drain liquid reservoir 9...Lower drain liquid reservoir 1 Leaf...Upper' drain port 11...Lower Drain port 12... Upper electrolyte passage 13... Lower electrolyte passage 14... Notch 15.16... Electrolyte
17.18 ... Perforated plate patent applicant Nippon Telegraph and Telephone Public Corporation Patent attorney Junnosuke Nakamura 1-1 Title 1'2 Figure 1P3 Figure 1 Figure 7 17 axis → Pass s*5o'w! X f*Shuu Return Tar/C-Nabesaki Dou 40 Threat IP9 Diagram

Claims (1)

[Scope of Claims] (1) In an anode reaction treatment apparatus having an electrolyte chamber divided by the substrate to be processed and a means for circulating an electrode and an electrolyte in each of the divided electrolyte chambers, An anode reaction processing apparatus, characterized in that the liquid circulation path is provided with means for bringing the flow of the electrolyte sent into the electrolyte chamber into contact with the entire surface of the substrate to be processed with uniform pressure. (2) The anodic reaction treatment apparatus according to claim 1, wherein the front and back surfaces of the substrate to be processed are opposed to each other and are in contact with an electrolyte. (5) The anodic reaction treatment apparatus according to claim 1, wherein the electrode provided in the electrolyte chamber is parallel to the electrolyte contact surface of the substrate to be processed.