JPH01281721A - Method for preventing contamination of compound semiconductor wafer - Google Patents

Abstract

PURPOSE:To enable an improved active layer to be formed with superb productivity by performing ion implantation, annealing under steam pressure of semiconductor constituting elements, and then eliminating a protection film immediately before device process after forming the protection film to a wafer whose surface is cleaned. CONSTITUTION:Ion is implanted into a chemical compound semiconductor wafer whose surface is cleaned and then annealing is performed under steam pressure of semiconductor constituting elements to allow an active layer to be formed. At this time, a protection film of 50Angstrom -1000Angstrom in thickness is formed on a wafer before and after ion implantation or after annealing and the protection film is eliminated immediately before device process. Thus, it prevents distortion or cracks from being generated, and constituting elements from being dissociated and enables ion implantation and annealing process to be performed while protecting the wafer against contamination.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for preventing contamination of a wafer in the process of forming an active layer on a compound semiconductor.

(Prior Art) Generally, when ions are implanted into a compound semiconductor wafer, annealing is performed to recover damage caused by the implantation and to activate the implanted atoms.

Contamination of the wafer during this active layer formation process is: (1) contamination due to impurities mixed in from the vacuum pump during ion implantation, (2) contamination due to impurities in the atmospheric gas during annealing, and (2) contamination from the bin sets and trays used for attaching and detaching the wafer. Contamination, ■Storage until device processing after annealing J'JI I
Contamination from trays, etc. and deterioration of the wafer surface are expected during fjl. Among these, contamination during high temperature annealing is a problem.

Conventionally, there has been a method of ion implantation and annealing without using a protective film as described in JP-A-54-104770, and a method of ion implantation and annealing without using a protective film as described in JP-A-52-47675. A method is known in which a protective film is formed before annealing to prevent dissociation. The latter method uses, for example, 5ift or Si as a protective film for GaAs semiconductors.
When N4 is used, the stoichiometric composition of GaAs changes due to the semiconductor components dissociating and diffusing into the protective film during high-temperature annealing. This is intended to prevent compositional changes.

(Problems to be Solved by the Invention) As mentioned above, when using a protective film such as S s Ot * S 13 Na, composition changes cannot be sufficiently prevented, so a relatively thick protective film of 1000 Å to 3000 Å is usually used. A method has been used to suppress compositional changes by using

However, the thicker the protective film (the difference in expansion rate between the wafer and the protective film) can cause large distortions in the wafer, leading to cracks and sometimes peeling of the protective film, resulting in poor implantation on the wafer surface. There was a problem in that an abnormal distribution of elements and impurities was formed.

The present invention solves the above-mentioned problems, prevents distortion and cracks from occurring, prevents dissociation of constituent elements, and prevents contamination of the wafer 1 by enabling ion implantation and annealing while protecting the wafer from contamination. It is intended to provide a method.

(Means for Solving the Problems) The present invention is directed to a step of forming an active layer by implanting ions into a compound semiconductor wafer whose surface has been cleaned and annealing it under the vapor pressure of semiconductor constituent elements. , before and after ion implantation or after annealing, a film thickness of 50 Å is applied to the above wafer.
~1000 protective film formation and device process B
, a wafer contamination prevention method characterized in that the protective film is removed before the wafer contamination is removed.

Note that the protective film can be formed not only on the surface of the wafer into which ions are implanted but also on the side and back surfaces of the wafer to more completely prevent contamination. The material of the protective film is 5iOt+Si,
Conventional materials such as lN4+ Att'3 can be used.

(Operation) FIG. 1 is a flow diagram of the method for preventing wafer contamination of the present invention. There are the following three methods depending on when the protective film is formed. The steps of organic cleaning and pre-etching of mirror-treated compound semiconductor wafers are common. The first method is to form a protective film immediately after pre-etching, then perform ion implantation and annealing. The protective film plays a role in preventing contamination and deterioration by maintaining it until just before device processing. The second method is to form a protective film immediately after ion implantation, and if ion implantation through the protective film is not appropriate, ion implantation is performed directly onto the wafer surface. The protective film serves to prevent annealing and subsequent contamination. The third method is to form a protective film after ion implantation and annealing, which serves to prevent contamination and deterioration during storage until device processing.

The contamination prevention protective film according to the present invention is as thin as sQ Å~1000, so even if there is a difference in expansion coefficient between the wafer and the protective film, the wafer will not be significantly distorted and the protective film will not crack. There is nothing you can do. Furthermore, since the annealing is performed under the vapor pressure of the semiconductor constituent elements, the release of high dissociation pressure elements from the Ueno film is also prevented. Note that the above-mentioned thin protective film is also convenient for uniform ion implantation.

(Example) Two pieces of GaA cut from the same rod at close positions
s wafer, 150 KeV, 2X10' snow e1
After that, one sheet was coated with a protective film of 500 5isN4 on the surface, and the second sheet was intentionally annealed in a contaminated furnace without a protective film.
The figure shows the D obtained from c-v measurements of annealed wafers.
The characteristics are shown in a graph.

LSS theory is the distribution of implanted ions determined by the ion implantation conditions (implantation voltage, implantation amount, implanted element), and this
The presence or absence of contamination and the quality of activation are determined by comparing the SS theoretical curve and the actual carrier concentration distribution curve. As is clear from the figure, wafers annealed without a protective film are not sufficiently activated and are susceptible to contamination, whereas wafers annealed after forming a protective film are well activated and are effective in preventing contamination. It turns out that there is.

(Effects of the Invention) By employing the above configuration, the present invention can effectively prevent contamination or deterioration during ion implantation, annealing, and the subsequent storage period in the step of forming an active layer in a compound semiconductor, resulting in a good This made it possible to form a high-quality active layer with good activation and high mobility with good reproducibility.

[Brief explanation of the drawing]

FIG. 1 is a flow diagram of the pollution prevention method of the present invention, and the second
The figure shows a carrier concentration profile of an active layer formed on a GaAs wafer in an example.

Claims (3)

[Claims] (1) In a method for preventing wafer contamination in the process of forming an active layer on a compound semiconductor, a protective film with a thickness of 50 Å to 1000 Å is formed on a wafer whose surface has been cleaned, and then ions are implanted to reduce the vapor pressure of the semiconductor constituent elements. 1. A method for preventing contamination of a wafer, the method comprising: annealing under a wafer and removing the protective film immediately before device processing. (2) In a method for preventing contamination of a wafer in the process of forming an active layer on a compound semiconductor, after implanting ions into a wafer whose surface has been cleaned, a protective film with a thickness of 50 Å to 1000 Å is formed, and then semiconductor constituent elements A method for preventing contamination of a wafer, the method comprising: annealing under a vapor pressure of (3) In a method for preventing contamination of a wafer in the process of forming an active layer on a compound semiconductor, ions are implanted into a wafer whose surface has been cleaned, and after annealing under the vapor pressure of the semiconductor constituent elements, the film thickness is 50 Å to 100 Å. 1. A method for preventing contamination of a wafer, the method comprising: forming a protective film, and removing the protective film immediately before device processing.