JPS6127475B2 - - Google Patents

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 apparatus has been widely used, particularly in the manufacturing process of semiconductor devices, to perform anodic oxidation and anodic polishing on the surface of a semiconductor substrate, and to form porous silicon on a silicon substrate. Therefore, the following explanation will be made using the case where porous silicon is formed on a silicon substrate as an example, 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 substrate).

Conventionally, as an anode reaction treatment device, one with the structure shown in Fig. 1 has been proposed (for example,
-Refer to No. 111596). In the figure, 1 is a substrate (silicon substrate), 2 is an upper electrolyte chamber, 3 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 7 is the lower liquid supply port,
8 is the upper drain liquid reservoir, 9 is the lower drain liquid reservoir, 10
11 is a lower drain port, 12 is a plurality of upper electrolyte passages provided around the upper electrolyte chamber 2,
13 is a plurality of lower electrolyte passages provided around the lower electrolyte chamber 3, and 14 is a notch in which the substrate 1 is installed. Note that illustration of an electrolyte circulation device and the like is omitted.

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 3. All you need is electrolyte 15
(may be the same as the above) are fed from the outside through the upper liquid supply port 6 and the lower liquid supply port 7, respectively, and the substrate (silicon substrate) 1, electrodes 4, and electrodes 5 are heated by the electrolytes 15 and 16. It is placed in a state of being immersed, and each electrolytic solution is circulated using a pump (not shown) or the like. For example, when the electrode 5 in the lower electrolyte chamber 3 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 through the substrate 1 in contact with the upper electrolyte 15. Porous silicon is formed from the surface toward the inside of the substrate.

According to the structure of this device, the diameters of the upper liquid supply port 6 and the lower liquid supply port 7 are smaller than the diameters of the upper electrolyte chamber 2 and the lower electrolyte chamber 3. It is difficult to equalize the pressure of the electrolytic solutions 15 and 16 sent into the electrolytic 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 with non-uniformity within the surface.

In addition, 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 13. As shown, it has a gear-like shape. As a result, the area of contact with the electrolyte on the bottom surface of the substrate is larger than the area of contact with the electrolyte on the top surface of the substrate by the portion corresponding to the teeth in the gear shape. Therefore, as shown in Fig. 3, during the anodic reaction treatment, among the current flowing into the substrate from the electrolyte contact surface on the lower surface of the substrate 1, some of the current flows from the portion corresponding to the gear-shaped teeth in Fig. 2. The current curves toward the center of the substrate 1 as it exits the top surface of the substrate 1 to flow into the upper electrolyte 15 . 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 addition, in the figures, the same reference numerals as those mentioned above indicate the same or equivalent parts.
Arrows indicate current flow.

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 50 wt%. 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, if the positions of the electrodes 4 and 5 are far apart from the substrate 1,
The uniformity of the potential distribution at the interface between the substrate and the electrolyte becomes less reproducible due to the flow and pressure of the electrolyte. This non-uniformity of the potential distribution at the interface between the substrate and the electrolyte is caused by
There was a problem in that the thickness of the porous silicon to be formed was 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 contacts the substrate with uniform pressure, allowing uniform anodic reaction treatment. . The second purpose is to make the electrolyte contact surfaces on both sides of the substrate face each other, have the same shape and area, and equalize the flow of current within the substrate, allowing for more uniform anodization. There is a particular thing. The third purpose is to make the electrodes provided in the electrolyte mesh-like, and to make the electrolyte contact surface of the substrate the same shape and area, thereby making the potential in the electrolyte between the substrate and the electrodes uniform. The present invention aims to provide an apparatus that performs a uniform anodic reaction treatment (manufacturing porous silicon) over the entire surface of a substrate.

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, 1
Reference numerals 7 and 18 are perforated plates having a large number of holes (for example, 2 mm in diameter and 5 mm apart). An example is shown in FIG. Electrolytes 15 and 16 are supplied to liquid supply ports 6 and 7, respectively.
The electrolyte is sent to the electrolyte chambers 2 and 3 through the porous plate 1 due to the pressure pushed out by the pump.
Contact 7,18. The pressure of the electrolytes 15 and 16 is dispersed to the surroundings by the porous plates and is made uniform within the electrolyte chamber. Therefore, the electrolytes 15 and 16 are connected to the porous plate 1.
After passing through the electrolyte chambers 2 and 18, the electrolyte contacts the entire surface of the substrate 1 with uniform pressure, and is then discharged from the electrolyte chambers 2 and 3.

By spraying the electrolytic solution onto the substrate, air bubbles generated by the chemical reaction and attached to the substrate surface are removed. By inserting the perforated plates 17 and 18, the electrolytic solution is sprayed with uniform pressure over the entire surface of the substrate. is sprayed, making it possible to completely remove all air bubbles from the substrate surface. Since a chemical current does not flow through the portion where the bubbles are attached, the formation of porous silicon stops in that portion, and the uniformity of the porous silicon film within the substrate surface deteriorates. However, by inserting the perforated plate, all the air bubbles within the substrate surface can be removed, resulting in improved uniformity.

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

In Figure 8, the diameter of the upper electrolyte contact surface is 65 mm, and the diameter of the lower electrolyte contact surface is a60 mm and b65.
The film thickness distribution of the porous silicon film formed when mm and c are 70 mm is shown. The conditions for forming the porous silicon film were the same in all cases, including a hydrofluoric acid concentration of 50 wt%, a current density of 5 mA/cm ² , and a formation time of 40 minutes.

As can be seen from this figure, the electrolyte contact areas on the top and bottom surfaces are the same. The uniformity is the best in case b.

Further, the electrodes 4 and 5 have a net shape, for example, with an interval of 3 to 5 mm, so as not to obstruct the flow of the electrolyte solutions 15 and 16, and the shape and area of the electrodes 4 and 5 are made the same as the surface of the substrate 1 in contact with the electrolyte solution. Furthermore, the positions of the electrodes 4 and 5 are approximately 14 mm from the substrate 1, and
and electrodes 4 and 5 are parallel to each other.

Figure 9 shows these effects; Figure a shows the film thickness distribution of porous silicon when the electrode is installed at a distance of 14 mm from the substrate, and Figure b shows the film thickness distribution of porous silicon when the electrode is installed at a distance of 25 mm from the substrate. This is what is shown. The conditions for forming the porous silicon film are the same as those shown in FIG. As is clear from the figure, b has poorer uniformity and 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. Note that, as described 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 the drawing]

Fig. 1 is a cross-sectional view showing the configuration of main parts of the anodic reaction treatment apparatus of the present invention, Fig. 2 is an explanatory diagram of the electrolyte contact state on the bottom surface of the substrate, and Fig. 3 is a diagram showing the current flow during anode reaction treatment in the conventional apparatus. An explanatory diagram, FIG. 4 is a graph showing the relationship between current density and the formation rate of porous silicon, and FIGS. 5, 8 a to 8 c, and 9 a and b show the formed porous silicon film. FIG. 6 is a cross-sectional view of the main structure of the anode reaction treatment apparatus of the present invention, and FIG. 7 is a plan view of the perforated plate. 1... Board, 2... Upper electrolyte chamber, 3... Lower electrolyte chamber, 4, 5... Electrode, 6... Upper liquid supply port,
7... Lower liquid supply port, 8... Upper drain liquid reservoir, 9...
...Lower drain reservoir, 10...Upper drain port, 11...
...Lower drain port, 12...Upper electrolyte passage, 13...
...Lower electrolyte passage, 14...Notch, 15,1
6... Electrolyte, 17, 18... Porous plate.

Claims (1)

[Claims] 1 An electrolyte chamber divided by the substrate to be processed,
An anode reaction treatment apparatus having a means for circulating an electrode and an electrolyte in each of the divided electrolyte chambers, characterized in that porous plates are provided on both sides of the substrate in the electrolyte circulation path. Device.