JPS5817264B2 - Germanium etching method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a germanium etching method suitable for mirror etching germanium wafers.

Germanium has recently been studied as a material for long-wavelength light detectors, and various etching solutions have been developed to mirror-etch its surface.

That is, in order to etch germanium wafers, nitric acid (HNOa), hydrofluoric acid (HF), and acetic acid (CH3) are usually used.
An etching solution containing COOH), bromine (Br2), etc. was used.

For example, CP4A is HNO3:HF:CH3CO0H
=5:3:3, CF2 is HNO3:HF:C
H3CO0H:Br2=5:3:3:0.
66.

CPD2 is HNO3:HF:Br2 = i5:
The composition was 15:0.02.

However, since all of the above conventional etching solutions contain hydrofluoric acid, they cannot be used with quartz beakers, and in order to obtain a smooth etched surface, the etching temperature must be raised, and there is a risk of damaging the skin of the user. Workability was poor due to the presence of cracks.

Furthermore, etching solutions containing bromine have the disadvantage that the bromine easily decomposes and escapes, resulting in a gradual decrease in the etching rate.

Furthermore, conventional etching solutions have various drawbacks, such as the relatively high etching speed, making it difficult to control the etching state, resulting in poor etching conditions, and the production of semiconductor devices with large dark currents.

In view of the above-mentioned conventional drawbacks, an object of the present invention is to provide a germanium wafer etching method that improves workability, makes it easy to control the etching state, provides a good etching state, and reduces dark current. shall be.

According to the present invention, phosphoric acid (H3PO4) and hydrogen peroxide (H
The present invention provides an etching method for etching germanium wafers by using an etching solution having a composition of 2O2).

Examples of the present invention will be described in detail below.

Using phosphoric acid, which is a commercially available high-purity reagent, and commercially available hydrogen peroxide with a concentration of 31, H3PO4:H20□=1
An etching solution having a composition of 3 was prepared, and a germanium wafer to be mirror-etched was immersed in this etching solution.

The wafer can be handled in a quartz holder (basket), and when selective etching is performed, a mask such as an oxide film or resist is formed on the wafer.

Furthermore, three types of wafers were used: 111-sided, 110-sided, and 100-sided.

When etching is finished, dilute with a large amount of water and then immerse in hydrogen peroxide solution for a few seconds.

After this, it is diluted again with a large amount of water, washed, and etching is completed.

FIG. 1 shows the etching rate (μmin) versus the temperature of the etching solution.

The characteristic feature here is that the 100-sided surface can be etched in the same way as other surfaces, and conventional hydrofluoric acid and nitric acid-based etching solutions cannot or cannot etch the 190-sided surface. Even so, the surface became cloudy and a mirror surface could not be obtained.

It is clear that the etching solution according to the present invention can be used in a wide temperature range from room temperature to 60° C., and no bubbles are generated on the surface of the germanium wafer during etching, and no uneven etching occurs.

The etching solution of the present invention can have various composition ratios.

FIG. 2 shows the etching rate (μm 7 min) for the volume ratio H2O2/)I20□+H3PO4.

Note that the concentrations of H2O2 and H3PO4 are the same as above.

From this result, a practical volume ratio is 40% to 95%, most preferably 50 to 90%.

As shown in FIGS. 1 and 2, a 111-sided germanium wafer has a speed of about 0.15 μm/min at a temperature of 15°C.
It can be seen that the etching is performed at an etching rate in which the volume ratio is in the range of 50 to 90.

Further, as shown in FIG. 1, the etching rate increases as the etching temperature increases, but since the etching rate is slow, the etching depth can be easily controlled.

The table below shows a comparison of experimental results regarding the effects of the etching solution having the above composition and a conventional etching solution.

The dark current in the table above was measured using a diode manufactured as follows.

The P-Ge wafer was fully diffused with arsenic to a depth of 0.3 μm, and then the diode diameters were 300 μm and 100 μm.
The dark current is measured by applying a probe to the mesa-etched diode so that there are two types of m, and the condition is that the current value when a voltage of 1/2 of the breakdown voltage is applied is It is for comparison.

The etching solution according to the present invention has a slower etching speed than conventional ones, provides a good etching condition and provides a smooth etched surface, and reduces dark current when used in the production of mesa-type photodiodes. I can do it.

Another feature is that there is no seepage during etching.

Furthermore, since this etching solution does not contain hydrofluoric acid,
Etching can be performed using a silicon oxide film (Si02 Oki resist (OMR)) as a mask, quartz bead force can also be used, and hydrofluoric acid does not irritate the skin, so workability can be improved.

As explained above, according to the present invention, workability is improved by using etching consisting of phosphoric acid and hydrogen peroxide.
In addition, it is possible to obtain a good etching condition, reduce dark current, and have the advantage that no bubbles appear during germanium etching, and there is no etching unevenness or seepage. It is effective when applied to mirror etching for removal, etc., and is also expected to be effective when applied to similar surface treatments.

[Brief explanation of the drawing]

Fig. 1 shows the relationship between temperature and etching rate when germanium wafers with various crystal planes are etched using the etching solution according to the present invention, and Fig. 2 shows the relationship between etching speed when etching the etching solution composition of the present invention. FIG. 3 is a diagram showing changes in etching speed.

Claims (1)

[Claims] 1. A germanium etching method characterized by etching a germanium wafer with an etching solution consisting of phosphoric acid and hydrogen peroxide.