JPS60227416A - Annealing method of semiconductor substrate - Google Patents

Abstract

PURPOSE:To realize capless annealing for a GaAs substrate without applying an As pressure to an annealing atmosphere, by a method wherein a GaAs substrate in which ions are implanted is subjected to heat treatment in an atmosphere containing NH3 gas. CONSTITUTION:<29>Si ions are implanted in an undoped GaAs substrate of surface azimuth (100) at a room temperature and in a dose amount of 5X10<12>/cm<2> by using an energy of 100keV. Next, the GaAs substrate in which the ions are implanted is put in an atmosphere of a 100% pure NH3 gas or N2 and pure NH3 gases in the volume ratio of 5:1 and subjected to heat treatment for about 15min at the temperature of 800 deg.C. According to this method, the generation of a heat pit due to the vaporization of As or the formation of a nitride is not perceived on the surface of the GaAs substrate, and an annealed substrate of sheet carrier concentration 3.13X10<12>/cm<2> and sheet mobility 3,620cm<2>/V.Sec can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of annealing a gallium arsenide (hereinafter referred to as GaAs) substrate into which ions have been implanted.

[Prior art and its problems]

In recent years, GaAs has been used for the purpose of speeding up semiconductor integrated circuits.
GaAs integrated circuits using semiconductors as active layers are being actively developed. Field effect transistors are generally used as basic elements of GaAs integrated circuits, and ion implantation is used as a method for forming the active layer of such elements from the viewpoints of uniformity, controllability, and mass production. In the ion implantation method, a heat treatment step is required after ion implantation to recover crystal defects introduced during implantation and to electrically activate implanted impurities.
Heat treatment for several tens of minutes is usually performed at a temperature of 700 to 900° C. at which aAs undergoes thermal decomposition. G during such heat treatment
Currently, two methods are used to suppress the thermal decomposition of aAs. One is the so-called cage annealing method, in which the GaAa surface is covered with a protective film and heat-treated, and the other is Kasahara et al.
pl, Phys, 50.

As described in P., 541 (1979), this is the so-called Charabres annealing method in which As pressure is applied in the annealing atmosphere. The former method attempts to physically prevent the evaporation of As from the GaAa surface by using a protective film attached to the surface, and has the advantage of being the simplest method for preventing thermal decomposition. On the other hand, from the viewpoint of manufacturing integrated circuits, this method has the disadvantage that it requires an extra process of forming and removing a protective film, which complicates the manufacturing process.

It is also known that the characteristics of the ion-implanted layer are affected by the properties of the protective film used. For example, when silicon dioxide (SIO□) is used as the protective film, during the heat treatment process, Ga, a constituent element of GaAs, is 5I
GaAs stoichiometry (IJ) by external diffusion in O2
However, when silicon nitride (5t3N4) is used as a protective film, there is a large gap between GaAs, Si, and N4. Thermal stress occurs at the interface due to the difference in thermal expansion coefficients, which causes abnormal diffusion of implanted impurities and Cr atoms added to the GaA* crystal, which has the disadvantage of deteriorating the uniformity and controllability of the implanted impurity distribution. was. On the other hand, in the latter method, the capless annealing method, the protective film/G
It has the advantage of simplifying the manufacturing process of integrated circuits because various problems that occur at the aAs interface can be avoided, and there is no need for a process for forming or removing a protective film. As a source of As, it is usually necessary to use a large amount of arsine (AsH3), which is a highly poisonous gas, and from the standpoint of mass production, there are currently major safety issues.

[Purpose of the invention]

The purpose of the present invention is to eliminate the above-mentioned safety defects in capless annealing, and to
Capless production of GaAs substrates without applying pressure
The objective is to provide a method for realizing annealing.

[Structure of the invention]

The present invention is a method of annealing a semiconductor substrate, which is characterized by performing ion implantation in an atmosphere containing at least ammonia gas and subjecting the GaA substrate to heat treatment.

〔Example〕

The present invention will be explained below using experimental facts and examples. The substrate used was LEC (Lig) with plane orientation (100).
uid Ineapaulat+al Czoahra
Lakl ) method Si ions were added to an undoped GaAs substrate at room temperature at a dose of 5 x 101.
2 cm −2 was injected. As an example of the present invention, a sample implanted with these ions is subjected to heat treatment at 800°C for 15 minutes in an atmosphere of 100 cm of pure ammonia gas, or a mixed gas of nitrogen and pure ammonia (volume ratio 5:l). We conducted an experiment. Under the above annealing conditions, the GILA after annealing
No thermal pits or surface nitrides were observed on the surface of No. 11 due to evaporation of As. The reason why reaction products and thermal decomposition of Aa do not occur on the surface during annealing at 800°C in a pure ammonia or nitrogen/ammonia mixed gas atmosphere is currently unknown. It is expected that the generated nitrogen (N), which is a group V element, has the effect of suppressing the evaporation of As, which is also a group V element.

〔Effect of the invention〕

As a result of Hall measurement on a sample annealed in a pure ammonia gas atmosphere, the sheet carrier concentration was 3.13X.
1012 am-2, sheet mobility 3620 cm2/V,
esc was obtained, and the air in an ammonia gas atmosphere was obtained.

It has been confirmed that the rus annealing provides comparable characteristics compared to conventional capless annealing, +f annealing, and capless annealing that applies As pressure.

As explained above, the annealing method according to the present invention can significantly shorten the manufacturing process compared to the conventional cap annealing method, and has the advantages of the capless annealing method using As pressure application. Similar effects can be expected by using an annealing atmosphere gas which is extremely safe compared to AsHs gas.

Claims (1)

[Claims] (1) A method for annealing a semiconductor substrate, which comprises subjecting a gallium arsenide substrate into which ions have been implanted to heat treatment in an atmosphere containing at least ammonia gas.