JPH01115896A - Apparatus for growing crystal thin film - Google Patents

Abstract

PURPOSE:To obtain a crystal thin film having a desired thickness in good yield, by irradiating a substrate with laser beams, measuring the intensity of scattered light and enabling the insitu measurement of the thickness from the intensity ratio thereof. CONSTITUTION:For example, a crystal substrate 3, such as GaAs, is placed on a base plate 2 installed at the center in the interior of a molecular-beam (MBE) apparatus 1 for epitaxial crystal growth. The substrate 3 is then irradiated with Ar laser beams, etc., from a laser beam source 4 to take a light scattering spectrum and measure the intensity of scattered light 5 by optical lattice vibration. Molecular beams are subsequently emitted from the respective radiation sources, e.g. Al, Ga and As, to grow different kinds of crystal thin films, e.g. AlGaAs, on the substrate 3. The thin film is then suitably irradiated with laser beams during crystal growth to grow the aimed crystal thin film while determining the thickness of the thin film crystal from the intensity ratio in situ each time the intensity of the scattered light from the substrate 3 is measured through the crystal thin film. Thereby the aimed crystal thin film of different kinds having a desired thickness is obtained.

Description

[Detailed Description of the Invention] [Summary] Regarding a growth device that grows different types of crystal thin films on crystal substrates, the crystal thin film of a desired thickness can be grown by performing crystal growth while measuring the film thickness “in situ”. For the purpose of precise growth, when growing a different type of crystal thin film on a crystal substrate placed in a crystal growth apparatus, the crystal substrate is irradiated with laser light in advance and the intensity of scattered light due to optical lattice vibration is measured. After that, a mechanism is provided for growing the heterogeneous crystal thin film, measuring the scattered light intensity of the crystal substrate through the crystal thin film, and determining the thickness of the heterogeneous thin film crystal on the spot from the scattered light intensity ratio. Configure a crystal thin film growth apparatus.

[Industrial application field]

The present invention relates to a crystal thin film growth apparatus capable of performing crystal growth while determining the composition ratio "on the spot".

Regarding semiconductor integrated circuits such as ICs and LSIs, many devices are formed using a single semiconductor such as silicon (Si) as a substrate, but semiconductor lasers.

High electron mobility transistor (abbreviated as HEMT), light emitting device.

Devices such as passive elements are formed using compound semiconductors.

These devices are constructed by epitaxially growing multiple semiconductor single crystal layers with different conductivity types, compositions, and band gaps, but in order to maintain performance and improve manufacturing yield, For this purpose, each semiconductor layer must have a desired thickness and composition ratio.

To this end, it is desirable to carefully check the thickness and composition throughout the growth process of the semiconductor single crystal layer.

The present invention relates to a crystal thin film growth apparatus that enables "in situ" determination of thickness.

[Conventional technology]

In conventional crystal thin film growth apparatuses, the following two methods are used to grow crystals to a constant film thickness.

(2) The crystal growth rate under certain growth conditions is determined empirically in advance, and the desired film thickness is obtained by precisely controlling the growth time.

(2) A film thickness detector made of a crystal resonator is installed near the crystal substrate, and the film thickness is determined by utilizing the change in the oscillation frequency of the crystal resonator due to the attachment of the crystal forming material.

However, in the case of method (2), it is necessary to perform preliminary growth many times in advance to determine the relationship between growth conditions and growth rate, and therefore precise control of the film thickness is not possible.

Furthermore, when method (2) is used, there is a problem in that the growth rate of the thin film differs to some extent because the crystal substrate and the crystal resonator are separated from each other.

For example, in semiconductor devices, molecular beam epitaxial growth (Molecular Beam Epitaxial Growth) is used.
MBE (axy abbreviation: MBE method) is often used, but the difference in growth rate becomes more noticeable as the distance from the position facing the molecular beam source increases.

For these reasons, it has not been easy to accurately adjust the thickness of a crystal thin film grown on a crystal substrate to obtain a desired film thickness.

However, in order to homogenize the product and improve manufacturing yield, it is necessary to produce a crystal thin film of a desired thickness, and it has been desired to realize a crystal growth apparatus equipped with such a mechanism.

[Problem that the invention seeks to solve]

The technique of epitaxially growing different types of crystal thin films or crystal thin films with different conductivity types and electrical conductivities on crystal substrates is particularly used for the formation of semiconductor devices. It is desirable to obtain a crystal thin film of a desired thickness by "in-situ" measurement, and the challenge is to put into practical use a crystal growth apparatus equipped with such a function.

[Means for solving problems]

The above problem arises when growing a different type of crystal thin film on a crystal substrate placed in a crystal growth apparatus. A crystal thin film growth apparatus equipped with a mechanism for growing a heterogeneous crystal thin film, measuring the scattered light intensity of the crystal substrate through the crystal thin film, and determining the thickness of the heterogeneous thin film crystal on the spot from the scattered light intensity ratio. It can be solved by using

[Effect]

In the crystal thin film growth apparatus according to the present invention, before growing a crystal thin film, a crystal substrate is irradiated with a laser beam, a light scattering spectrum due to optical lattice vibration is measured, and the intensity of Stokes scattered light is determined, and then a heterogeneous crystal thin film is grown. At this stage, the intensity of the Stokes scattered light due to the optical lattice vibration of the crystal substrate is measured again, and the thickness of the heterogeneous crystal thin film is determined from the attenuation rate.

For example, when growing an A I GaAs crystal thin film on a GaAs crystal substrate, the vertical optical lattice vibration intensity of the GaAs crystal substrate before crystal growth is I G-A-(0) and A j! of thickness d! The vertical optical lattice vibration intensity of the GaAs crystal substrate after growing the GaAs crystal thin film is I c
-a-(d), I G-A-(d) − Icatt(0) x (1-exp (-2c
x ALGaAs d) ),
A E As the GaAs crystal thin film grows, the GaAs
The optical lattice vibration intensity of the crystal substrate is attenuated.

Here, αA10mA1 is the absorption coefficient of the GaAs crystal for the excitation laser beam, and the table shows the absorption coefficient for other semiconductor materials as well.

Table Therefore, by measuring the values of Ia-A-(0) and IGmA-(a), the thickness of the A I GaAs crystal thin film can be determined.

〔Example〕

Figure 1 is a partial configuration diagram of a molecular beam epitaxial apparatus (abbreviated as an MBE apparatus) that is equipped with a function to measure the thickness of a crystal thin film grown on a crystal substrate "in situ", and performs molecular beam epitaxy (MBE). Molecular beam sources are omitted.

Here, a GaAs crystal substrate 3 is installed on a base 2 installed in the center of the MBB device 1, and molecular beams are emitted from Al, Ga, and As radiation sources (not shown) to produce GaAs. The structure is such that an A I GaAs crystal thin film is formed on a crystal substrate 3 .

First, prior to crystal growth, the GaAs crystal substrate 3 is irradiated with an Ar laser from the laser light source 4 to obtain a light scattering spectrum due to optical lattice vibration, and from this, the vertical optical lattice vibration intensity of the GaAs crystal F , , A, (0) seek.

The method is to MBE the scattered light 5 from the GaAs crystal substrate 3.
Through the window of the device 1, the light is focused by a lens 6 onto the end of an optical fiber 7 and guided through this to a multichannel detector 8.

Next, the data processing device 9 determines the vertical optical grating vibration intensity 1 cmA-(0) from the light scattering spectrum due to the optical grating vibration shown by the multi-channel detector 8.

The reason why we chose Ar laser as laser light source 4 is G.
This is to obtain scattered light on the surface of the aAs crystal substrate 3, and for this purpose it is necessary to have a lattice energy larger than the band width of the forbidden band of the crystal. It is appropriate to use an Ar laser.

Next, when epitaxial growth is performed, laser light is irradiated at appropriate times and the multi-channel detector 8 is placed in the same manner as before.
From the light scattering spectrum detected, the vertical optical lattice vibration intensity IG, □(d) of the GaAs crystal substrate 3 is determined, and from this the thickness of the A I GaAs crystal thin film is calculated by the data processing device 9.

Figure 2 shows AlG film formed on a GaAs crystal substrate by the MBE method.
This shows the spectrum of scattered light obtained during the epitaxial growth process of aAs.
Although the vertical optical lattice vibration intensity with As appears, AI
As epitaxial growth of GaAs progresses, GaAs
The intensity of A It GaAs decreases, while the intensity of A It GaAs increases.

〔Effect of the invention〕

By implementing the present invention, it becomes possible to measure the thickness of a crystal film during growth "in situ", thereby making it possible to obtain a crystal thin film having a desired thickness.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a film thickness measurement system of a crystal thin film growth apparatus according to the present invention, and FIG. 2 is a scattered light spectrum obtained during the crystal growth process. In the figure, 1 is an MBE device, 3 is a GaAs substrate, 4 is a laser light source, 5 is a scattered light, 8 is a multi-channel detector, and 9 is a data processing device.

Claims (1)

[Claims] When growing a heterogeneous crystal thin film on a crystal substrate placed in a crystal growth apparatus, the crystal substrate is irradiated with a laser beam in advance and the scattered light intensity due to optical lattice vibration is measured, and then the heterogeneous crystal thin film is grown. A crystal thin film growth apparatus comprising a mechanism for performing growth, measuring the intensity of scattered light of the crystal substrate through the crystal thin film, and determining the thickness of a different type of thin film crystal on the spot from the scattered light intensity ratio. .