JPS6325498B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for surface treatment of a substrate, such as a semiconductor substrate.

When manufacturing semiconductor devices, it is necessary to thin the semiconductor substrate to a predetermined thickness (usually 100 to 200 [μm]) in the final process of semiconductor element manufacturing in order to reduce thermal resistance and collector parasitic resistance. There is.

When the above-mentioned thickness adjustment of a semiconductor substrate is performed by an etching method, a so-called bubble etching method is often used. The bubble etching method has a very high etching precision due to its excellent stirring effect on the processing solution, and is widely used not only for the above-mentioned thickness adjustment but also for various surface treatment processes of semiconductor substrates.

In the bubble etching method, as shown in FIG. 1, nitrogen (N ₂ ) or carbon dioxide (CO 2 ) is introduced through a large number of small holes 3 opened in a plurality of gas introduction pipes 2 arranged at the bottom of a processing tank ₁ . A holding plate fixed to a support plate 7 with wax or the like and provided at the top of the processing tank 1 is used to stir the processing liquid 6 by sending gas 4 such as into the processing tank 1 and generating bubbles 5. This is a surface treatment method in which a substrate 9 to be processed is held downward by a substrate 8.

The above-mentioned bubble etching method has good etching accuracy, but as semiconductor substrates have become larger in recent years, the processing tank has to be enlarged in order to maintain the same number of substrates processed at one time, which requires a large area and This resulted in the problem of requiring a large amount of processing solution.

In order to eliminate this problem, attempts have been made to, for example, install a basket in which a large number of substrates to be processed are mounted in parallel in a processing tank and perform bubble etching while rotating the basket, but the etching accuracy is limited. It is difficult to say that this is a satisfactory method, as there are problems such as a drop in performance.

An object of the present invention is to provide a method for surface treatment of a substrate using stirring using bubbles, which eliminates the above-mentioned drawbacks and enables mass processing using a small processing tank without reducing etching accuracy. shall be.

The feature of the substrate surface treatment method of the present invention is that the upper surface of a plurality of bubble scattering plates arranged obliquely and substantially parallel to the bubble generation surface provided substantially horizontally at the bottom of the processing tank is coated. The processing substrate is placed on the substrate and bubbles are sent into the processing tank from the bubble generation surface to stir the processing liquid and process the substrate.When the bubbles collide with the floating surface and the bottom surface of the bubble scattering plate. The purpose is to agitate the processing liquid by dispersing and scattering the bubble scattering plate, and to dispose the bubble scattering plate so that the substrate to be processed facing the lower surface thereof is located within the stirring area.

The surface treatment method of the present invention will be explained below with reference to the drawings.

FIG. 2 is a sectional view of a main part showing a state in which a surface treatment of a substrate to be processed is performed using an apparatus that makes the present invention possible.

In the figure, 1 is a processing tank, 2 is a plurality of gas introduction pipes arranged in a plane parallel to the liquid surface (horizontal plane), and a large number of small holes 3 are opened in the upper part of the gas introduction pipe 2. The small holes 3 form a bubble generation surface.
Arrows 4 indicate the direction of introduction of gases such as nitrogen and carbon dioxide, 5 indicates bubbles sent into the processing liquid 6 by introducing the gas 4, 9 indicates the substrate to be processed, and 11 indicates the pyrex. This is a scattering plate made of glass, quartz, Teflon, etc. The scattering plate 11 also serves as a support plate for the substrate 9 to be processed, and supports the substrate 9 to be processed by a method such as fixing with wax.

Further, the scattering plate 11 is supported by a support frame (not shown) or the like so that the scattering plate 11 is 65 to
Tilt at an angle of 75 [degrees] with horizontal spacing of 10 to 20
[mm] above the gas introduction pipe, that is, on the bubble generation surface. Here, the scattering plate 11 is arranged so that the substrate 9 to be processed is above the scattering plate 11.

In the above state, if a gas 4 such as nitrogen (N ₂ ) or carbon dioxide (CO ₂ ) is introduced through the gas introduction tube 2 , bubbles 5 are sent out from the small holes 3 into the processing liquid 6 . The bubbles 5 rise in the processing liquid 6, collide with the scattering plate 11 and are dispersed and scattered, and rise in the processing liquid 6 while repeating a zigzag movement due to the buoyancy of the bubbles 5 themselves and the pressure from the bubble generation source. Since the treatment liquid 6 is uniformly stirred by the movement of the bubbles 5, uniform surface treatment is possible even though the substrates 9 to be treated are closely arranged.

Next, using the above method, a diameter of 76 [mm] and a thickness of 400 [μ] were obtained.
An example will be described in which the back side of a silicon substrate of 200 [μm] is etched to adjust the thickness to 200 [μm].

In this embodiment, since 20 silicon substrates 9 are processed at the same time, the size of the processing tank 1 is determined by the length, width,
The depths are 30 [cm], 18 [cm], and 20 [cm], respectively.
Pyrex glass scattering plates measuring 10 [cm] x 10 [cm] were arranged in parallel at intervals of 15 [mm], and the gas introduction pipe 2
Eight small holes 3 were opened in parallel at intervals of 7.5 mm, and a mixed solution of 10 volumes of nitric acid (HNO ₃ ) and 1 volume of hydrofluoric acid (HF) was used as the treatment liquid. ,
Nitrogen gas was used as the introduced gas 4 at a flow rate of about 20 [min], and etching was carried out for about 30 [min].

FIG. 3 shows the etching accuracy of this example.

Figure a shows the thickness distribution of silicon substrates No. 1 to No. 20 before etching, and figure b shows the thickness distribution of each silicon substrate after etching. This shows the maximum and minimum values of the thickness at five locations, the center and four locations around the periphery of each silicon substrate, as indicated by the x marks in Figure c.

As is clear from figures a and b, in this example, the variation in the thickness of the silicon substrate before and after etching hardly changes. This indicates that etching progressed uniformly.

If the above-mentioned etching is carried out using the conventional etching method shown in Figure 1 above, the size of the processing tank will be approximately 40 [cm] x 50 [cm] x 20 [cm].
Requires a processing solution close to 40[].

As described above, according to this embodiment, it is possible to process a large amount of silicon substrates in a small processing tank without reducing the thickness accuracy of the silicon substrate.

The present invention is not limited to the above embodiments, but can be implemented with various modifications.

For example, in the above embodiment, the case where the present invention is applied to etching for adjusting the thickness of a silicon substrate has been described, but it can also be used for various etching processes such as mesa etching in the manufacturing process of mesa type transistors. In short, the present invention is a surface treatment method that can be applied when the reaction depends on the quality of stirring of the liquid, and is therefore effective not only for etching but also for cleaning processes such as water washing.

Furthermore, various types of processing liquid and gas may be selected depending on the type of substrate to be processed and the purpose of processing.

Furthermore, it goes without saying that the structure of the processing apparatus, such as the material and support method of the scattering plate, or the construction method of the bubble generation surface, can be selected as appropriate.

As explained above, according to the substrate processing method of the present invention, a large amount of processing can be performed using a small processing tank without reducing processing accuracy.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a main part showing a conventional bubble etching method, FIG. 2 is a cross-sectional view of a main part showing an embodiment of the surface treatment method of the present invention, and FIG. FIG. DESCRIPTION OF SYMBOLS 1... Processing tank, 2... Gas introduction pipe, 3... Small hole, 4... Introduced gas, 5... Bubble, 6... Processing liquid, 9... Processing target substrate, 11... Scattering plate.

Claims (1)

[Claims] 1. A substrate to be processed is placed on the upper surface of a plurality of bubble scattering plates that are arranged obliquely and substantially parallel to a bubble generation surface provided almost horizontally in a processing tank, and bubbles are emitted from the bubble generation surface. It processes the substrate by stirring the processing liquid by sending it into the processing tank, and the processing liquid is stirred by the floating bubbles and the dispersion and scattering when they collide with the bottom surface of the bubble scattering plate.
A method for surface treatment of a substrate, characterized in that a bubble scattering plate is arranged so that the substrate to be processed facing the lower surface thereof is located within the stirring area.