JP3086014B2 - Method of forming GaAs semiconductor active layer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming an active layer on a GaAs crystal substrate by ion implantation and heat treatment (annealing). A possible method for forming a GaAs semiconductor active layer.

[0002]

2. Description of the Related Art When a field effect transistor (FET) or an integrated circuit is formed by ion implantation into a GaAs crystal substrate, an annealing step is required to electrically activate implanted impurities to form an active layer. Improving the activation rate of implanted impurities (the ratio of carrier concentration to implanted impurity concentration) is an essential step in improving FET characteristics.

At present, the formation of an n-type active layer of a GaAs FET requires:
Si is the most commonly used implantation element. Si
Is a group IV element, it becomes a donor by substituting the lattice position of Ga, a group III element, while it becomes an acceptor, substituting the lattice position of As, a group V element. Therefore, the carrier concentration is the difference between the donor concentration and the acceptor concentration. Here, when the annealing time is fixed, at a relatively low annealing temperature, the crystallinity lost by the ion implantation recovers with the temperature rise, and the Si occupying the Ga lattice position increases. That is, the carrier concentration increases with the annealing temperature. However, on the high temperature side, the amount of Si substituting the As lattice position increases rapidly, so that the carrier concentration decreases. Therefore, in order to obtain a high activation rate, it is necessary to perform heat treatment at an optimum annealing temperature.

Recently, there is a strong demand for high performance GaAs FETs, and in order to meet this demand, it is essential to form an active layer having a high carrier concentration and a small thickness. In order to realize such an active layer, it is necessary to reduce the ion implantation energy (less than 30 keV) and perform the annealing under the condition that a high activation rate can be obtained. This optimum annealing condition strongly depends on the ion implantation condition, and for example, shifts to a lower temperature side or a shorter time side as the implantation energy decreases. That is, the optimum annealing condition for the thick active layer is different from the optimum condition for the thin active layer.

[0005]

Conventionally, as a method of evaluating an active layer for determining an optimum annealing condition, conventionally, generally,
Electrical measurement methods using Hall effect measurement and capacitance-voltage (CV) measurement were used. Although there is a depletion layer region near the surface of the active layer that cannot be evaluated by the above electrical measurement, since the ratio of the surface depletion layer region in a conventional thick active layer is small, it should be sufficiently evaluated by the above measurement method. Was possible. However, in the case of an active layer formed with a low implantation energy of less than 30 keV, since the thickness of the active layer is extremely small, a considerable portion of the active layer is occupied by the surface depletion layer region. However, it is difficult to form a thin active layer with a high carrier concentration because the optimum conditions for annealing cannot be accurately determined. An object of the present invention is to provide a method for forming a GaAs semiconductor active layer capable of realizing a thin active layer with a high carrier concentration by solving the problems of the technology.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for forming an active layer by activating Si ions implanted on a GaAs crystal substrate by annealing to form an active layer. The characteristics of the active layer are evaluated by spectroscopically measuring the luminescence light emitted from
The peak intensity of the emission at a wavelength of 1.3 μm is sufficiently small, and
This can be achieved by performing annealing under the condition that light emission of a wavelength of 0.835 μm hardly appears.

[0007]

First, a method of evaluating an active layer formed by Si ion implantation and annealing will be described. FIG. 2 is a configuration diagram showing a schematic configuration of an optical measuring device used for evaluation. A laser light source 1 irradiates a sample held in a sample chamber 3 with excitation light 2 and emits luminescence light 4 emitted from the sample into a spectroscope 5.
And the intensity is measured by the detector 6. During the measurement, the sample was filled with liquid helium.
Cool to 2K. When the sample to be measured is Si-implanted GaAs, as shown in FIG. 3, four main luminescences are observed in a wavelength range of 0.8 to 2.4 μm. Of these, emission (A) is inter-band emission and emission (B) is emission involving carbon occupying the As lattice position.These two emissions are also observed on a GaAs substrate without ion implantation. Difficult to use for evaluation. On the other hand, emission (C) at 0.835 μm is emission involving Si in which the As lattice position has been substituted, and the stronger the emission, the higher the acceptor concentration. The 1.3 μm emission (D) is emission associated with Ga vacancies, and is reduced by Si occupying the Ga lattice position. That is, it decreases with generation of the donor. Therefore, the carrier concentration, that is, the activation rate can be maximized by performing annealing under the annealing condition in which the emission intensity of 1.3 μm is sufficiently small and emission of 0.835 μm does not yet appear.

[0008]

EXAMPLE FIG. 1 shows the result of examining the relationship between the carrier concentration obtained from the CV measurement and the emission intensity at 1.3 μm and 0.835 μm for a thick active layer sample. Here, the annealing time was constant (0.1 seconds) as the annealing condition.

The following can be seen from the results of FIG. That is, in the low temperature region (925 ° C. or lower), the carrier concentration increases as the emission intensity of 1.3 μm decreases. On the other hand, in the high-temperature region (925 ° C. or higher), the emission intensity at 1.3 μm is sufficiently small, but the carrier concentration decreases as the emission intensity at 0.835 μm increases. From this, it is understood that a high activation rate can be realized by performing annealing at an annealing temperature (925 ° C.) at which the emission intensity of 1.3 μm is sufficiently low and emission of 0.835 μm does not yet appear.

When the annealing temperature is fixed, the optimum annealing time can be obtained from the light emission characteristics in the same manner as described above, and a high activation rate can be obtained by annealing under the conditions.

[0011]

As described above, by forming the GaAs semiconductor active layer forming method according to the present invention,
It has been possible to provide a method for forming an active layer having a high carrier concentration and a small thickness by performing a heat treatment under optimal conditions by solving the problems of the prior art. Applying this method of active layer formation to FET fabrication can also result in significant FET performance improvements.

[Brief description of the drawings]

FIG. 1 is a diagram showing annealing temperature dependence of carrier concentration, 0.835 μm emission intensity, and 1.3 μm emission intensity.

FIG. 2 is a configuration diagram showing a schematic configuration of an optical measurement device used for evaluating an active layer.

FIG. 3 is a typical luminescence spectrum of Si-implanted GaAs measured at a liquid helium temperature (4.2 K).

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Laser light source, 2 ... Excitation light, 3 ... Sample chamber, 4 ... Luminescence light, 5 ... Spectroscope, 6 ... Detector.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-16726 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 21/265

Claims (1)

(57) [Claims] A method for forming an active layer by activating Si ions implanted on a GaAs crystal substrate by heat treatment to form an active layer, wherein the luminescent light emitted from the active layer is dispersed by irradiating light in a predetermined wavelength region. GaAs semiconductor active layer formation characterized by evaluating the characteristics of the active layer by measuring, and performing heat treatment under the condition that the peak intensity of the emission at 1.3 μm is sufficiently small and the emission at 0.835 μm hardly appears. Method.