JPS6187339A - Method of etching indium phosphide crystal - Google Patents

Abstract

PURPOSE:To improve the reproductivity of etching speed by determining a capacity mixing ratio of hydrogen peroxide to phosphoric acid to be larger than the specified value when an InP crystal is etched by a mixed solution consisting of phosphoric acid, hydrogen peroxide, and water. CONSTITUTION:When an InP crystal is etched by use of a mixed solution of phosphoric acid, hydrogen peroxide, and water, a capacity mixing ratio of hydrogen peroxide to phosphoric acid is predetermined to be 0.10 or larger. Consequently, the reproductivity of etching speed can be improved easily without deteriorating a surface condition of the InP crystal and requiring any complicated operation. Accordingly, it becomes facile to form the structure which requires accurate control of an etching depth such as the recess structure, etc., e.g. those which are necessary for fabrication of an InP field effect transistor, or the like.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a method for etching indium phosphide,
In particular, the present invention relates to a method for etching indium phosphide in which an object to be etched made of indium phosphide in the form of a bulk crystal or a thin film crystal is etched with excellent controllability without impairing the surface condition of the object.

[Technical background of the invention and its problems]

Indium phosphide (InP) crystal is a gallium arsenide (GaAs) crystal that is currently widely used as a base material for microwave devices. For this reason, it has attracted attention as one of the base materials for high-power microwave devices.

Taking a field-effect transistor as an example of a microwave element made of InP, manufacturing of such an element (such as mesa etching around the electrode or 9-slice etching of the gate electrode part) is required. In the process,
Reproducibility of the etch rate - precise control of the InP thickness using a superior etchant is essential.

Conventionally, bromine/methanol (C) (OH) and a mixture of sulfuric acid/hydrogen peroxide/water have been used as etchants for InP crystals. These conventional mixtures are
We examine its validity from the perspective of an etchant that precisely controls the thickness of P (second order).In etching InP crystals with a bromine/methanol mixture, the etching rate is similar to that of methanol. (The ratio of bromine to trough and C to be added can be changed depending on the ratio, but it is generally as large as several μm/min.

For this reason, it is not suitable for etching away so-called thin film layers such as active layers of field effect transistors, which usually have a film thickness of less than 1 μm, to obtain a desired film thickness.

Although the following sulfuric acid/hydrogen peroxide/water mixture has an etching rate of several thousand i/min, which is lower than that of the bromine/methanol mixture, the reproducibility of the etching rate is poor. It is difficult to precisely control the depth of the recess (C), and this is one of the causes of a significant decrease in the manufacturing yield of field-effect transistors with excellent characteristics. is the current situation.

In addition to the above-mentioned etchants as etchants for InP crystals, recently phosphoric acid-based etchants have been discovered, including phosphorus modified/salt-based etchant/water and phosphorus-based etchant/hydrogen peroxide/water.

One of the characteristics of these phosphoric acid-based etchants is that the etching rate for InP crystals (2) is even lower than that of the sulfur-based etchants (2, approximately 1 oo
Etching rates of oi/min have been obtained. For this reason,
InP i two? It is widely used as an etchant when performing n-dense etching.

However, when etching an InP crystal with the above-mentioned phosphor/salt/water, the flatness of the surface on which the crystal is mounted is likely to be impaired, which may cause problems in device manufacturing. I'L
I was at 2.

On the other hand, as for the phosphorized/decomposed hydrogen water/water mixture, only a mixture having a composition ratio of 38=1:1 is known as an etchant for InP crystals. This etchant does not impair the flatness of the next surface (etching of InP crystals is 61 times), but on the other hand, it has the disadvantage of poor reproducibility of etching speed, To make it practical as an etchant for precision processing of InP (-, there was a desire for a measure to further improve the reproducibility of the etching speed.

[Purpose of the invention]

In view of the above-mentioned conventional [C] pressure point (2), this invention is a method for treating InP crystals with an etchant (
Etch to obtain a flat etch at a rate lower than 2, providing a volumetric mixing ratio that greatly improves the reproducibility of the etch rate.

[Summary of the invention]

In order to improve the above-mentioned conventional problems, the inventor took advantage of the characteristics of phosphoric acid-based etchants and conducted extensive studies to further improve the reproducibility of etching speed, resulting in a marked improvement in the reproducibility of etching speed. It has been discovered that a mixing ratio of 4 ffi exists, and the present invention has been achieved. The method of etching an InP crystal according to the present invention is as follows: 7. When etching the Yoshi crystal with a mixed solution consisting of phosphorus/hydrogen oxide/water, It is characterized by using a mixed liquid with a combined ratio of 6L in each state of 0.10 or more.

[Embodiments of the invention]

An embodiment of the present invention will be described below.

In this example, commercially available linha (85 weight ratio) and hydrogen peroxide solution (35 weight 3; f %) were used, and the volume mixing ratio of phosphorus 3/accumulated peroxide/water was adjusted to the above conventional example. First, the reproducibility of the etching rate when the ratio is approximately the same as <40:1:1 will be illustrated. FIG. 1 shows the variation in etching depth unit i) when an iron (Fe)-doped high-resistance InP single crystal was repeatedly etched using the same etching solution with the above-mentioned mixing ratio. The temperature of the etching solution was fixed at 50' (120 m), the etching time was fixed at 120 seconds, and etching was carried out while stirring the sample. As shown in Fig. 1 above, etching was repeated seven times. However, the etched thickness was up to 200 mm.
It varies from 0λ to a minimum of 16001, and the variation in etched thickness 11V6 is ±1 with respect to the median xsooA.
It reached 1.1%.

Next, the dependence of the fluctuation width of the etched thickness on the volumetric mixing ratio was examined by varying the positive mixing ratio of the hydrogen peroxide solution to the phosphor. The results obtained are shown in FIG. In the example shown in the figure, the volumetric mixing ratio of phosphoric acid and water is fixed at 40=1, and only the volumetric mixing ratio of hydrogen peroxide to phosphoric acid is changed, so that the fluctuation range of the etching rate is extremely small. It was possible to find a range of volumetric mixing ratios of the phosphorus 1/hydrogen peroxide mixture. The etching temperature and time were set at 50°C and 120 seconds, respectively, and the variation in the etched thickness was expressed as the range of variation relative to the median value of the etched thickness obtained by repeating seven etchings. 2 As shown in Figure 1, the range of variation in the etched thickness strongly depends on the volume mixing ratio of the phosphor/filtered hydrogen dihydride water, decreases as the volume mixing ratio increases, and increases above 0.125%. It is almost constant. Therefore,
By setting the volumetric mixing ratio to 0.25 or more, the fluctuation width of the etched depth can be made small and stable. For example, if the volumetric mixing ratio is set to 0.026, When a mixture of 38 phosphorus groups: 1 hydrogen peroxide water: 1 water is used, the above fluctuation range (indicated by the black circle in Figure 2) reaches approximately 12 inches. When the mixing ratio is increased to 0.25 +2, the fluctuation range is within about 5.3 inches (-), which is a significant improvement.

In addition, in this example, the mixing ratio of phosphorus and water was set to 4.
However, this mixing ratio (not limited to 2), the volumetric mixing ratio of hydrogen peroxide to phosphoric acid was 0:1.
By laying the turf above (2), it is possible to easily improve the variation width of the etching depth, that is, the reproducibility of the etching speed, without damaging the surface condition of the InP crystal.

As is clear from the actual example on the paper, InP crystals are etched with a mixture of phosphorus and hydrogen peroxide (at the same time, the mixing ratio of phosphorus and hydrogen peroxide is By simply setting the etchant to 0.25 or more, no complicated operations are required, and compared to the case of using an etchant with a conventionally known volumetric mixing ratio, it is possible to
7. Exacerbating the condition. c<The reproducibility of etching speed can be improved. As mentioned above, the 1 shift of 0.25 indicates the volume mixing ratio when commercially available phosphoric acid (concentration 85%) and hydrogen peroxide solution (brightness 35%) are used. , and the concentration of the hydrogen peroxide component, and based on the following (Equation 1) (2), calculate the net ijl to the net phosphoric acid component C2 [converted to the volumetric mixing ratio of the hydrogen peroxide component] Then, it becomes 0.10.

(Net volume mixing ratio of hydrogen peroxide component to phosphoric acid component (2))... (Formula 1) This invention (-) The lower limit was set at 0.101 for the paper reason (=
It is based on

〔Effect of the invention〕

As stated above, according to this invention, when etching an InP crystal using a mixed solution of phosphoric acid/hydrogen peroxide/water, the volumetric mixing ratio of hydrogen peroxide to phosphoric acid is 0.10. By setting the above (2), it is possible to easily improve the reproducibility of the etching rate without deteriorating the surface condition of the InP crystal and without requiring any complicated operations. It is possible to provide a method for etching InP crystals that facilitates the formation of structures that require precise control of etching depth, such as recessed structures that are commonly known as etching depths.

In the example of the present invention, the etching time was set at 50° C. and 120 seconds, and the sample was etched while stirring. This value can be obtained regardless of the etching time and whether or not the sample is stirred, and is not restricted by these values.

[Brief explanation of the drawing]

Figure 1 shows the etching of a Fe-doped high-resistance InP crystal using a mixture of commercially available phosphoric acid and hydrogen peroxide at a volume ratio of 0.025 and a mixture of phosphoric acid/hydrogen peroxide/water. Figure 2 is a diagram showing the variation of the etched depth for each etching number in the case of the etching process. FIG. 3 is a diagram showing the dependence of the fluctuation width of the etched depth on the capacity and mixing ratio when etched. The black circles in Figure 2 indicate the range of variation in etching depth obtained when using a conventional mixed solution with a composition of 389 phosphoric acid: 1 hydrogen peroxide: 1 water. The numbers in the upper row of the horizontal axis are the volumetric mixing ratio of hydrogen peroxide solution to commercially available phosphorus, and the numbers in parentheses in the lower row are the 6a mixing ratio of net hydrogen peroxide to net rimming powder converted from the volumetric mixing ratio. They are shown respectively. Agent Patent attorney Inoue - Male Figure 1 (θ) 1 Etching fence m →

Claims (1)

[Claims] When etching an indium phosphide crystal with a mixed solution consisting of phosphoric acid/hydrogen peroxide/water, the above-mentioned mixed solution having a volumetric mixing ratio of hydrogen peroxide to phosphoric acid of 0.10 or more is used. Etching method for indium oxide crystal.