JPH02194625A - Diffusion method - Google Patents

Abstract

PURPOSE:To accelerate diffusion of impurities in a semiconductor or self- diffusion of crystal constituting atoms by heat-treating a semiconductor crystal at the same as the projection of an electron beam or after the projection of the electron beam. CONSTITUTION:In a single quantum well structure, the following layers are laminated on a P-type GaAs substrate 1: a GaAs buffer layer 2; an AlAs layer 3; a GaAs quantum well layer 4; an AlAs layer 5; and a GaAs cap layer 6. An electron beam is projected on the single quantum well structure. Thereafter, heat treatment is performed. Thus, the GaAs quantum well part of a part 7 which the electron beam is projected is transformed into a mixed crystal. The quantum well structure at a part to which the electron beam is not projected remains intactly. Therefore, diffusion of impurities in a semiconductor or self- diffusion of crystal constituting atoms is accelerated.

Description

[Detailed description of the invention] [Industrial application field]

In the fabrication of semiconductor devices, diffusion of impurity atoms or self-diffusion of crystal constituent atoms is an important process. The present invention relates to a diffusion method thereof.

[Conventional technology]

Conventional methods for diffusing impurities into semiconductors include supplying impurities from a vapor state, such as with Zn, or depositing impurities on the semiconductor surface with low vapor pressure, such as Si, followed by heat treatment. is common. In addition, an ion implantation method in which impurity atoms are ionized and directly implanted into a semiconductor is also widely used. [Problems to be Solved by the Invention] In recent years, with the development of focused ion beam technology, the beam diameter has been narrowed down to several thousand angstroms or less, making it possible to locally implant impurities. It is well known that the incorporation of impurities promotes self-diffusion or interdiffusion at heterointerfaces. By finely implanting impurities using a focused ion beam method or the like, the superlattice structure fabricated by the epitaxial method is further partially and selectively promoted to interdiffusion only in the impurity implanted areas, causing mixed crystal formation in the superlattice. However, there are also many attempts to construct a superlattice structure in the layer direction as well. but,
When creating such a multidimensional superlattice, it is extremely difficult to narrow down the beam diameter to about a few dozen ion beams.
Furthermore, the damage to the semiconductor crystal caused by ion implantation is considerable and recovery is not easy. (Means for Solving the Problems J) The present invention involves subjecting a semiconductor crystal to electron beam irradiation and heat treatment in order to promote the diffusion of impurity atoms in a semiconductor or the self-diffusion of crystal constituent atoms. This is a diffusion method that is performed simultaneously with or after the electron beam irradiation.The atomic diffusion mechanism in semiconductors is dominated by point defects in the semiconductor.In general, vacancies are the most important among them. The promotion of superlattice structure mixed crystal formation by ion implantation is also thought to be due to the creation of vacancies by the implantation of atoms.6 In the present invention, electron beams are used to form vacancies. The focusing of electron beams is relatively easier than that of ions, and it is expected that the damage to semiconductor crystals caused by electron beam irradiation will be less than that of ions.In addition, it is difficult for impurities to get mixed in. Even in such cases, there is no need to worry because electrons are used.The inventor proposed that the mechanism for promoting superlattice structure mixed crystal formation by impurities is that the constituent atoms of the crystal diffuse through the crystal while replacing the impurity atoms that enter the lattice points. In other words, an impurity that enters a lattice point of a crystal is more likely to jump out than an atom that should originally be at that lattice point, and the constituent atoms of the crystal diffuse through that lattice point, promoting diffusion. In this way, if a vacancy is formed by electron beam irradiation, and if an impurity or an antisite defect in the case of a compound semiconductor is actively formed in the vacancy based on the above-mentioned diffusion mechanism, that part will be locally And the diffusion is finely promoted.Dose: 10'4 to 10"am-", acceleration energy: 3
This diffusion method can be suitably implemented in the range of about 0 to +000 keV. [Example] Example ■ As shown in FIG.
0 nm, AlAs layer 3 15 nm, GaAs quantum well layer 4 8 nm, AlAs layer 5 15 nm and G
A single quantum well structure was formed by stacking 10 nm of aAs cap layers 6 (none of which was doped). To this, 5
Electrons accelerated to 00 keV (dose amount I x 10”
cm-") in a width of 1 μm, and then heat-treated at 850°C for 1 hour in an As atmosphere. When the cross section of this sample was observed with a transmission electron microscope, it was found that the area 7 exposed to the electron beam was
Although the GaAs quantum well part of 1 was mixed crystal, the quantum well structure of the other part remained unchanged. It goes without saying that this diffusion method is also effective for other semiconductor or compound semiconductor materials. Example 11. Undoped G on the semi-insulating GaAs substrate 11
A sample in which aAs was deposited to a thickness of 3 μm by MBE (12) was exposed to 500 keV and a dose of I × 10” cm.
” (14), and then a lonm of Si was deposited on the surface by sputtering (13), 85
Heat treatment was performed at 0° C. for 0.5.1 and 2 hours, respectively. When the diffusion surface was measured using a secondary ion mass spectrometer, the diffusion depth in the electron beam irradiated area was approximately three times that in the non-irradiated area. FIG. 3 shows the relationship between the Si diffusion depth and the heat treatment time in the electron beam irradiated area and non-irradiated area. Example III In a single quantum structure similar to Example I, AIAsM was doped with 1×10 cm of Si as an impurity. This sample was irradiated with an electron beam at 500 keV and at a dose of
After irradiation with I.times.10"cm", heat treatment was performed at 850.degree. C. for 1 hour in a He atmosphere. When the cross section was observed using a transmission electron microscope (TEM), it was found that the GaAs single quantum well portion in the electron beam irradiated portion had become a mixed crystal, but the other portions remained as they were. This results in
It was found that electron irradiation also causes mixed crystallization of the superlattice structure due to impurities. Effects of the invention 1. Impurity or self-diffusion is promoted. 2. Damage to semiconductor crystals caused by electron beam irradiation is smaller than that caused by ion implantation. 3. No atoms other than crystal constituent atoms are mixed into the crystal. 4. The diameter of the electron beam can be made smaller than the diameter of the ion beam, making it possible to perform microfabrication by several dozen people.

[Brief explanation of the drawing]

Figure 1 shows the mixed crystal formation of a GaAs/AlAs single quantum well structure by electron irradiation, and Figure 2 shows St in the electron irradiation area.
FIG. 3 is a cross-sectional view of a sample in which Sj is diffused, and is a diagram showing the relationship between Sj diffusion depth and heat treatment time in the electron beam irradiated part and non-irradiated part in Example If. 1...P-type GaAs substrate 2...GaAs buffer layer 3.5...AlAs layer 4...GaAs single quantum well layer 6...
GaAs gap layer 7...Electron beam irradiation part mixed crystal layer II...Semi-insulating GaAs substrate 12...
-GaASli 13...Si deposited layer 14...Electron beam irradiation area

Claims (1)

[Claims] In order to promote the diffusion of impurity atoms in the semiconductor or the self-diffusion of crystal constituent atoms, a semiconductor crystal is subjected to electron beam irradiation and heat treatment, and the heat treatment is performed at the same time as or after the electron beam irradiation. A diffusion method characterized by: