JPS6351642A - Manufacture of compound semiconductor device - Google Patents

Abstract

PURPOSE:To enable the surface of a semiconductor substrate to be cleaned up by removing an oxide film easily by a method wherein a compound semiconductor substrate with an anode oxide film etc. formed thereon is immersed in an etchant containing phosphoric acid and heated at a temperature exceeding 60 deg.C to be surface- treated and after being picked up, the substrate is immersed in another etchant at room temperature also containing phosphoric acid and then washed up by running water. CONSTITUTION:An etching vessel 11 is filled with a first etchant 12 containing phosphoric acid to be heated at 80-85 deg.C and then an InAsSb substrate 14 held by a holder 13 is immersed in the etchant 12 to etch an anode oxide film 15 on the surface of said structure 14. The InAsSb substrate 14 with the anode oxide film 15 removed is picked up to be immediately held by another holder 23 so that the substrate 14 may be immersed in a second etchant 22 at room temperature containing phosphoric acid in another etching vessel 21 to be cooled down. Later, the InAsSb substrates 14 held by the other holder 33 are washed in an overflow type water cleaning vessel 31 containing water running in the arrow directions. Thus, the surface of InAsSb substrate 14 can be cleaned up not subject to white turbidity at all. Resultantly, the element characteristics of a diode or MIS structure etc. using a compound semiconductor can be improved markedly.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Use) The present invention relates to a method for manufacturing a semiconductor device, and particularly to a method for manufacturing a compound semiconductor device in which surface treatment of a substrate is improved.

(Prior Art) A general device forming process in which a pn junction is formed by ion implantation using a compound semiconductor substrate will be described with reference to FIG. First, an anodic oxide film 2 is formed on the surface of an n-type substrate 1 (
a). Thereafter, a resist mask 3 is formed and, for example, pigeon ions 4 are implanted to form pN 5 (5s, 5t) (b). After this, resist 3 and anodic oxide film 2
The substrate surface is cleaned by removing C), and an anodic oxide film 6 is formed again (D). After this, necessary electrode wiring is formed.

In such a method, phosphoric acid is usually used in the step of removing the anodic oxide film shown in FIG. 4(C).

However, this process of removing the oxide film has the following problems. Generally, in order to remove an oxide film, it is necessary that the etching rate for the oxide film be sufficiently fast and the etching rate for the underlying compound semiconductor substrate be sufficiently slow. The higher the temperature, the higher the etching rate; for example, when removing an anodic oxide film with a thickness of about 5 Qnm,
It takes 3 to 5 minutes using phosphoric acid at 85°C, but it is said that anything longer than that is too fast, and temperatures below 60°C are extremely slow. However, when washing with water after anodic oxidation and etching using phosphoric acid at 80 to 85 degrees Celsius, deposits appear to be formed due to a reaction between phosphoric acid, water, and the compound semiconductor substrate, and the substrate surface deteriorates. becomes cloudy. One way to prevent this cloudiness is to quickly wash the substrate surface with running water, but this requires extremely sophisticated techniques, and this method cannot completely prevent cloudiness. The reason why washing with running water is difficult is because phosphoric acid has a high viscosity.

(Problem to be Solved by the Invention) The cause of the cloudiness described above is that phosphoric acid and water simultaneously exist on the compound semiconductor substrate at high temperatures, and the cloudiness that is generated is due to the hydroxide of the compound semiconductor. I can't think of anything. Once such cloudiness is formed, it is not easy to remove it, and it is almost impossible to remove it while maintaining the flatness of the substrate. Moreover, as shown in Fig. 4, this cloudiness can be avoided by making a diode by inactivating the area around the place where the pn junction is formed by ion implantation, annealing, etc. before this process, or by making a diode later by using MI3. When forming a structure, it becomes a cause of interface states and significantly deteriorates device characteristics.

The present invention was developed in view of the above points, and makes it possible to easily remove an oxide film and expose a clean surface of a semiconductor substrate without requiring any special techniques, thereby improving device characteristics. An object of the present invention is to provide a method for manufacturing a compound semiconductor device.

[Structure of the invention]

(Means and effects for solving the problem) The present invention performs surface treatment by immersing a compound semiconductor substrate on which an anodic oxide film, etc. is formed, in a first etching solution containing phosphoric acid and heated to 60° C. or higher. The method is characterized in that the pulled substrate is immersed in a second etching solution containing phosphoric acid at room temperature and then washed with water.

1st. As the second etching solution, phosphoric acid (HsPO
4) Hydrogen peroxide solution (H!0.+H,0), hydrofluoric acid (H
F) etc., but since the second etching liquid is used to cool the surface-treated compound semiconductor substrate rather than washing it with water, it is not necessary that the two have the same composition. For that purpose, it is desirable that the etching rate of the second etching solution be extremely slow, and that the replacement of the first etching solution with the second etching solution should be carried out in a short period of time so that the entire surface of the clean compound semiconductor board can be etched. desirable for producing Washing is performed with running water, but since phosphoric acid has a high viscosity, it is desirable to wash it for a sufficient time of 10 minutes or more. In addition, even pure water usually contains dissolved oxygen, and a natural oxide film is formed when washed for a long time. Therefore, in order to remove the natural oxidation group, for example, 3% citric fi + H,
It is preferable to add an etching step for 3 to 5 minutes with an O□ (1:1) solution. Washing with water after etching with this solution is as follows:
Since the viscosity of the solution is low, 1 to 2 minutes is sufficient. In addition, the etching rate of a (111) B compound semiconductor substrate using this solution is, for example, 20 to 3 Qnr when In = ssb.
It is slow at n/min and does not easily cause surface irregularities.

(Example) The present invention will be described in detail below. In the step shown in FIG. 4('b), the present invention was applied to the step of removing the anodic oxide film after implanting Mg ions at a dose of 5.times.10"7 cm" and annealing at 350'O. First of all, as shown in the first cause, etching! ! 11 is filled with a first etching solution 12 containing phosphoric acid heated to 80 to 85°C, and the holder 1 is
The InAsSb substrate 14 supported by the substrate 3 was immersed in the etching process, and the anodic oxide film 15 on the surface was etched. 16 is a heater with a temperature controller. In from which the anodic oxide film 15 has been removed
The AsSb substrate 14 was pulled up, immediately supported in a holder as shown in FIG. 2, and immersed in a second etching solution B containing phosphoric acid in another etching tank 21 at room temperature for cooling. Thereafter, as shown in FIG. 3, this InAsSb substrate 14 was supported in a holder and placed in an overflow type running water cleaning tank 31 in which water stamens flow as shown by the arrows, and was washed with water.

According to this embodiment, a clean I
The surface of the nAs S b substrate could be exposed. When we measured the diode characteristics of this body using the process shown in Figure 4(d), we found that the ROA value (product of zero bias resistance value x 02 area) was sufficiently high to be over 3 x 10゜Ω1m''. It was big.

Note that the present invention is not limited to the removal of an anodic oxide film of an InAsSb substrate, but can be similarly applied to the removal of a decayed film by high-pressure steam oxidation. In addition, the InAsSb substrate (
100) side, (111) B side, (211)
Non-invention is valid regardless of whether side B or the like is used.

〔Effect of the invention〕

According to the present invention, it is possible to remove the anodic oxide film, etc. on the surface of a compound semiconductor substrate to provide a clean surface without clouding, and therefore the characteristics of devices such as diodes and MI8 structures using compound semiconductors are significantly improved. Ru.

[Brief explanation of the drawing]

FIG. 3 is a diagram for explaining a compound semiconductor anodic oxide film removal process according to an embodiment of the present invention, and FIG. 4 is a diagram for explaining a conventional method. DESCRIPTION OF SYMBOLS 11... Etching tank, 12... First etching liquid, 13... Holder, 14... InAsSb substrate, 15... Anodized film, 16... Heater with temperature controller, 21...・Etching tank, n...Second etching jig liquid, n...Holder, 31
・-・Overflow type running water cleaning tank, 32...Water,
Ah... holder. Agent Patent Attorney Noriyuki Chika Yudo Kikuo Takehana Figures 1 and 2

Claims (3)

[Claims] (1) After surface treatment of a compound semiconductor substrate by immersing it in a first etching solution containing phosphoric acid heated to 60°C or higher, and then immersing the pulled-up substrate in a second etching solution containing phosphoric acid at room temperature. . A method for manufacturing a compound semiconductor device, comprising the steps of washing with water. (2) The method for manufacturing a compound semiconductor device according to claim 1, wherein the surface treatment of the compound semiconductor substrate is the removal of an anodic oxide film. (3) The method for manufacturing a compound semiconductor device according to claim 1, further comprising the step of removing a natural oxide film on the surface of the compound semiconductor substrate after the water washing.