JPH0137360B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a chemical etching solution for crystals of -group compounds. Conventional compounds such as InP, GaAs,
Chemical etching solutions are used for surface treatment of crystals such as InGaAs or for device fabrication, and examples of this type of chemical etching solution include a mixture of bromine and methyl alcohol, or a mixture of sulfuric acid, hydrogen peroxide, and water. Commonly used. However, when treating the surface of - group compound crystals with these chemical etching solutions, there are drawbacks such as the appearance of etching pits and the impossibility of achieving a perfect mirror finish due to oxides adhering to the surface. It was hot. In addition, when etching - group compound crystals with these etching solutions, the etching action (etching rate) of these etching solutions has selectivity to the crystal orientation, so the etched cross section (hereinafter simply referred to as etched cross section) Another disadvantage was that the shape differed depending on the crystal orientation. In other words, Figure 1 shows InP/, which is an example of a - group compound crystal.
This figure shows the etch cross-sectional shape when an InGaAsP heterojunction crystal is mesa-etched using a conventional etchant, a mixture of bromine and methyl alcohol. This is the etched cross-sectional shape of the surface. As shown in FIGS. 1a and 1b, there is a clear difference in the etched cross-sectional shapes of the 110 plane and the 110 plane, with the 110 plane having an inverted mesa structure and the 110 plane having a forward mesa structure. Furthermore, when crystals are etched using the bromine-methyl alcohol mixture using photolithographic techniques, there is also the drawback that the resist is immersed in the etching solution. The present invention has been made to solve the above-mentioned drawbacks, and its object is to provide a chemical etching solution for - group compound crystals that provides a mirror-like high-quality etched cross section. Another object of the present invention is to provide a chemical etching solution for - group compound crystals in which the etch cross-sectional shape becomes a normal mesa structure independent of crystal orientation and does not immerse the resist. The chemical etching solution for crystals of - group compounds that achieves the above object of the present invention is composed of an aqueous solution of three components: (a) alkali dichromate, (b) hydrobromic acid, and (c) acetic acid or phosphoric acid. It is characterized by: Although it is not possible to theoretically explain the individual functions of the three components, when a - group compound crystal is etched using the chemical etching solution according to the present invention, it is possible to not only prevent the occurrence of etch pits but also create a mirror-like surface. It has been found that the present invention can be used satisfactorily as an etching solution for mesa etching because the surface treatment becomes possible and the shape of the etched cross section does not depend on the crystal orientation. The chemical etching solution of the present invention is prepared from an aqueous solution of each of the three components described above. For example, the alkali dichromate salt of the component (a) is prepared as an aqueous solution with a concentration of 0.1N to saturated, and the hydrobromic acid of the component (b) is prepared as an aqueous solution with a concentration of 0.1N to saturated. Component (c), acetic acid, is blended as a 17N aqueous solution, and phosphoric acid is blended as a 15N aqueous solution. In the above formulation, the volume ratio of each component is preferably (a):(b):(C) from 0.1 to 10:1:0.1.
100, and outside this range, etching pits will occur and a mirror surface will not be formed. As the alkali dichromate salt, sodium salt or potassium salt is used, and if the concentration of the aqueous solution of the alkali dichromate salt is less than 0.1 normal, etch pits tend to occur. When the mixing ratio of component (b), hydrobromic acid, and component (c), acetic acid or phosphoric acid, is kept constant, and the mixing ratio of component (a), an aqueous dichromate aqueous solution with a constant concentration, is changed, the etching rate increases. varies as shown in the examples below, and this effect can be used to adjust the etching rate. Next, the present invention will be described with reference to Examples, but the present invention is not limited thereto in any way. Examples 1 to 3 In Examples 1 to 3, a chemical etching solution having the composition (as a volume ratio) shown in the table below was used.
InP was etched at room temperature.

[Table] 〃 3 1 1 1
The etching speed was 1 μm/min in Example 1, 4 μm/min in Example 2, and 10 μm/min in Example 3.
No etch pits were generated in any of the examples, and a good mirror-like surface was obtained. As is clear from Examples 1 to 3, one of the characteristics of the etching solution of the present invention is that the etching rate can be changed arbitrarily by changing the mixing ratio of the aqueous dichromate alkali salt solution. Example 4 At room temperature using the etching solution of Example 3.
InP/InGaAsP heterojunction crystal was etched. FIG. 2 shows the etched cross-sectional shape of the bonded crystal. As shown in FIG. 2, the etched cross-sectional shape has no dependence on crystal orientation, and a good normal mesa shape can be obtained. Example 5 Using phosphoric acid instead of acetic acid, 1N potassium dichromate aqueous salt solution: 9N hydrobromic acid: 15N phosphoric acid =
The bonded crystal of Example 4 was etched at room temperature using an etching solution having a composition of 1:4:4 (volume ratio). The etching rate was 4 μm/min, and the etched cross-sectional shape was the same as that for acetic acid shown in FIG. It was also found that when a resist used in general photographic etching was immersed in the etching solution used in the above examples, the resist was not immersed. As is clear from the above explanation, the etching solution of the present invention enables pit-free and mirror surface treatment of - group compound crystals, and the etching rate can also be changed by changing the mixing ratio of the alkali salt of dichromic acid. It has the advantage that it can be easily changed by simply changing the etch, and also has no dependence on the crystal orientation in the cross-sectional shape of the etch, and does not immerse the resist, so it is suitable as an etching solution for mesa etches, and is suitable for manufacturing various semiconductor devices. It holds promise as an etching solution.

[Brief explanation of drawings]

Figure 1 a and b are a conventional etching solution, a mixture of bromine and methyl alcohol, at room temperature.
Figure 2 shows the cross-sectional shape of an etched InP/InGaAsP heterojunction crystal, which is a specific example of the present invention: Potassium dichromate aqueous solution: Hydrobromic acid:
With acetic acid = 1:1:1 chemical etching solution (at room temperature)
FIG. 2 is a schematic diagram showing an etched cross-sectional shape when an InP/InGaAsP heterojunction crystal is etched.

Claims (1)

[Claims] 1 (a) dichromic acid alkali salt, (b) hydrobromic acid and
(c) characterized by consisting of acetic acid or phosphoric acid -
Chemical etching solution for group compound crystals.