JPS6158969B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to molecular beam epitaxy (hereinafter referred to as MBE).
The purpose of the present invention is to provide a growth apparatus that can protect a substrate in a pre-growth stage, which is particularly effective in obtaining a high-quality epitaxial layer.

In the epitaxial growth of compound semiconductors represented by phosphorus-containing - group compounds such as InP or GaP, the substrate surface must be kept clean and flat during the growth stage in order to obtain a high-quality epitaxial growth layer. be.

In order to obtain a clean surface, it is effective to maintain the substrate at high temperature in a high vacuum. However, in the case of phosphorus-containing compounds, when kept at high temperatures in vacuum, phosphorus deviates from the substrate surface, impairing the stoichiometric composition of the surface, and at the same time, the surface structure deteriorates and unevenness occurs. There is. Several techniques have been developed to prevent such thermal deterioration of phosphorus-containing compound substrates.

Specifically, (1) a method to remove the thermally degraded layer before epitaxial growth, (2) a method to place phosphorus-containing Sn or Sb near the substrate, and (3) a method to place a wafer of the same material as the substrate on the substrate surface. Methods such as a method of closely arranging are known.

However, although the above method can be applied to liquid phase epitaxial growth method or vapor phase epitaxial growth method, it is technically difficult to use in MBE, which requires forming a highly pure epitaxial growth layer in a clean vacuum chamber. Not only is this difficult, but it also introduces a source of contamination to the growth layer into the vacuum chamber, making it extremely ineffective.

Furthermore, a method is known in which phosphorus or phosphorus-containing gas is constantly supplied to a phosphorus-containing compound substrate held at a high temperature in an MBE apparatus, and such a method is effective in preventing thermal decomposition of the substrate.

However, even if a supply source for phosphorus or a phosphorus-containing gas is provided in the conventional apparatus, it is not isolated from the branch radiation source to be used for epitaxy, resulting in the following difficulties.

In other words, to prevent thermal decomposition of the substrate by supplying phosphorus, it is necessary to increase the partial pressure of phosphorus on the phosphorus-containing substrate, but since the partial pressure of phosphorus increases with the amount of phosphorus supplied, The higher the temperature, the more phosphorus must be supplied. but,
If the amount of phosphorus supplied is increased, the degree of vacuum in the crystal growth chamber will drop significantly, and phosphorus vapor will accidentally enter the raw material melt in the molecular beam cell for epitaxy, changing the composition of the melt. I was afraid. Therefore, in the conventional apparatus, since the amount of phosphorus supplied is limited, it is difficult to maintain the substrate at a high temperature and sufficiently clean the surface thereof.

In addition, in the conventional apparatus, the molecular beam source to be used for epitaxy is not isolated from the substrate, so it also has the following drawbacks. In other words, when the raw material in the molecular beam cell runs out and the next new raw material is loaded into the cell, with conventional equipment, the entire crystal growth chamber would leak, so the crystal growth chamber must always be kept in a clean vacuum. In addition, since new raw materials are baked out in the crystal growth chamber, impurity gases, oxides, and volatile elements generated by baking out can re-evaporate directly or from the walls of the growth chamber, causing damage to the substrate. There was a risk that it would reach the surface and contaminate it.

In order to eliminate the drawbacks of the conventional apparatus described above, the present invention provides a molecular beam source chamber equipped with a molecular beam cell to be used for epitaxy in a crystal growth chamber and a source of phosphorus to prevent thermal decomposition of the substrate in the pre-growth stage. The chamber is separated into a substrate chamber equipped with This will be explained based on an example.

Figure 1 shows the case of making an InP-InGaAs junction.
1 is a diagram conceptually showing a cross section of an embodiment of an MRE device. 1 is the substrate room, 2 is the molecular beam source room, 3 is InP
a substrate, 4 a heater for heating the substrate, 5 a mass spectrometer,
6 is a gate valve that connects the substrate chamber 1 and the molecular beam source chamber 2; 7, 8, 9, and 10 are molecular beam sources; 7 is a P
8 is for As, 9 is for Ga, and 10 is for In.
71, 81, 91, 101 are respective shutters; 15 is a substrate processing chamber equipped with a substrate transfer mechanism;
16 is a gate valve for connecting the substrate chamber 1 and the processing chamber 15; 11, 12, and 17 are exhaust devices; 13
1 is a vacuum gauge, and 14 is an electron beam diffraction device.

As is clear from FIG. 1, according to the present invention
In the MBE apparatus, a crystal growth chamber A is separated into a substrate chamber 1 and a molecular beam source chamber 2, and the substrate chamber 1 is equipped with a substrate 3, a heater 4 for heating the substrate, and a mass spectrometer 5. It is connected to the molecular beam source chamber 2 via a gate valve 6. The substrate chamber 1 further includes a molecular beam source 7 having a shutter 71, which is a source of the element with the highest saturated vapor pressure, while the molecular beam source chamber 2 has other molecular beam sources 8, 9, 1
0 are provided with shutters 81, 91, and 101, respectively.

Further, the substrate chamber 1 and the molecular beam source chamber 2 are equipped with exhaust devices 11 and 12, respectively. moreover,
Inside the substrate chamber 1 are a vacuum gauge 13 and an electron beam diffraction device 1.
4 are provided.

Such a substrate chamber 1 is connected to a substrate processing chamber 15 via a gate valve 16, and like the substrate chamber 1 and molecular beam source chamber 2, the substrate processing chamber 15 is equipped with an exhaust device 17. .

Next, we will explain how to operate this device.

Finally, the approximately 0.5 mm thick InP substrate 3 that has been mirror-finished with a mixture of methanol and bromine is placed in the substrate processing chamber 15.
and evacuated using the exhaust device 16. After reaching a sufficiently clean vacuum, open the gate valve 16,
The InP substrate 3 is transferred by a substrate transfer mechanism (not shown).
is placed at a predetermined position within the substrate chamber 1. Immediately close the gate valve 16.

Next, with the gate valve 6 closed, the shutter 71 is opened and the InP substrate 3 is heated with the substrate heater 4 while supplying phosphorus from the phosphorus molecular beam source 7.
Heated to 600℃. The dissociation pressure of InP at 600°C is approximately 10 ^-4 Torr, so to prevent thermal decomposition of InP, the vacuum gauge 13 is adjusted so that the partial pressure of phosphorus on the InP substrate 3 exceeds the above value. The temperature of the phosphorus molecular beam cell was adjusted while monitoring the pressure using
When converting the phosphorus supply rate from the pressure, it is approximately 10 ²⁰ pieces/
It was ^cm2・s.

After the above operations were completed, the InP surface structure was examined using the electron beam diffraction device 14, and it was confirmed that the surface was clean. Furthermore, when InP was taken out into the air and examined under an optical microscope, the surface was flat and no signs of thermal deterioration were observed. During this time, the gate valve 6 is closed, and the molecular beam source chamber 2 is maintained in a clean vacuum by the exhaust device 12. Therefore, phosphorus vapor is introduced into the molecular beam sources 8, 9, and 10 without contaminating arsenic, gallium, or indium. In the end, without decomposing InP,
For the first time, it has become possible to clean substrates at 600°C, which was considered difficult with MBE.

Next, film growth on the InP substrate will be explained.
After performing the above substrate surface treatment, reduce the substrate temperature.
The temperature was lowered to 500°C, the shutter 71 was closed, the supply of phosphorus was stopped, and the gate valve 6 was immediately opened and the shutter 81 was opened to evaporate arsenic from the arsenic molecular beam source 8. Next, shutters 91 and 1
01 is also opened, gallium and indium are simultaneously evaporated from the gallium and indium molecular beam sources 9 and 10 that have been baked out, and while the beam intensities of each are monitored by the mass spectrometer 5, the intensity ratio is kept constant. I adjusted it so that Molecular beam intensity ratio I during growth
_As / (I _Ga + I _lo ) is about 5, and the growth rate is about 1 μ.
m/h. Epitaxial layer thickness is approximately 4μ
m, the shutters 81, 91, 1
01 was closed to stop growth. Thus, the I _o0.53 G _a0.47 A _s layer with lattice matching with InP is formed on the InP substrate 3.
was able to grow on top of.

After the growth, the fabricated InP-InGaAs wafer was taken out, cleaved, and the bonded cross section was observed.
The substrate surface, which had been carefully pretreated, remained intact and had excellent flatness.

As explained above, the molecular beam epitaxial growth apparatus of the present invention includes a vacuum chamber equipped with a phosphorus source for protecting a compound semiconductor substrate, a vacuum chamber equipped with a molecular beam source used for epitaxy, and a gate valve. Since the phosphorus is isolated by bakeout can be performed without contaminating the substrate, and furthermore, a clean and flat substrate surface can be prepared before epitaxial growth, resulting in a high-quality epitaxial layer. There is an advantage. Although the case of a phosphorus-containing substrate has been described above, it is clear that similar effects can be expected if this apparatus is used also in the case of an arsenic-containing substrate. Further, the gist of the present invention is not changed in any way even if a gas containing these is used instead of phosphorus or arsenic.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a molecular beam epitaxial growth apparatus according to an embodiment of the present invention. 1...Substrate room, 2...Molecular beam source room, 3...InP
Substrate, 4... Heater for heating the substrate, 5... Mass spectrometer, 6... Gate valve, 7, 8, 9, 10...
Molecular beam source, 71, 81, 91, 101... Shutter, 11, 12, 17... Exhaust device, 13...
Vacuum gauge, 14...Electron beam diffraction device, 15...Substrate processing chamber, 16...Gate valve, A...Crystal growth chamber.

Claims (1)

[Claims] 1 In a split line epitaxial growth apparatus used for molecular beam epitaxial growth on compound semiconductor substrates, a crystal growth chamber for forming an epitaxial growth layer is installed, a molecular beam source chamber equipped with a molecular beam source, and a substrate. Each chamber is equipped with an exhaust system, and the molecular beam source chamber and the substrate chamber are connected by a gate valve. A molecular beam epitaxial growth apparatus characterized by having only a high-element molecular beam source in a substrate chamber.