JPH06302524A - Formation of single crystal magnesia spinel film - Google Patents

Abstract

PURPOSE:To provide a method for growing single crystal MgO.Al2O3 films having excellent uniformity and excellent crystallizability with excellent reproducibility. CONSTITUTION:Concerning a formation of a single crystal magnesia spinel (MgO.Al2O3) film on a single crystal semiconductor layer by vapor phase epitaxy, causing magnesium chloride (MgCl2), aluminum chloride (AlCl3), carbon dioxide (CO2), and hydrogen (H2) to react in a reaction tube, the crystal is grown at a reduced pressure, while supplying a gas to the reaction tube 1 sufficiently and exhausting the gas inside the reaction tube 1 forcedly.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a single crystal Si on an insulating layer.
SOI (Silicon on Ins) with a film formed
The present invention relates to a method for forming a single crystal magnesia spinel film used as the insulating layer in the urator structure.

[0002]

2. Description of the Related Art In the SOI structure, element isolation is easy,
Further, since it has features such as reduction of parasitic capacitance and resistance to latch-up, and high integration and high speed of a semiconductor integrated circuit can be achieved, research and development have been actively conducted. Among them, the method of epitaxially growing a single crystal insulating film on a Si substrate and epitaxially growing a single crystal Si film on it is suitable for producing a large-area SOI substrate.

A magnesia spinel film is known as the above-mentioned single crystal insulating film. Since this magnesia spinel film has a good lattice matching with Si and a high-quality SOI substrate is likely to be obtained, Si / MgO ・ Al ₂ O ₃
/ Si structure SOI technology is being developed.

The above magnesia spinel film is, for example,
Japanese Patent Publication No. 60-33304 (H01L 21/8
4) and J. Electrochem. Soc. Vol.
129P. CV as described in 2569 etc.
It can be grown on a Si substrate using the D method.

FIG. 3 is a schematic view of a CVD apparatus for forming a magnesia spinel film. In the figure, 1 is a quartz reaction tube, 2 is a source tube inserted almost to the center of the quartz reaction tube 1, 3 is an Al source, 4 is a MgCl ₂ source, and 5 is S.
i substrate. Reference numerals 6, 7 and 8 are gas inlets. (H ₂ + HCl) gas is supplied from the gas inlet 6, H ₂ gas is supplied from the gas inlet 7, and (CO ₂ + H ₂ ) is supplied from the gas inlet 8.
Gas is supplied respectively. Further, 9, 10, 11 are heaters.

AlCl ₃ source gas produced by the reaction between the above HCl gas and Al source 3, and MgC
The l ₂ source gas is transported onto the Si substrate 5, where the source gas reacts with the CO ₂ gas, and the single crystal magnesia spinel is deposited on the Si substrate 5 as shown in the following chemical reaction formula. The (MgO.Al ₂ O ₃ ) film grows epitaxially.

[0007]

Embedded image MgCl ₂ (g) + 2AlCl ₃ (g) + 4CO ₂ (g) + 4H ₂ → MgO.Al ₂ O ₃ (s) + 4CO (g) + 8HCl (g)

As film forming conditions at this time, the Al source 3, the MgCl ₂ source 4, and the Si substrate 5 are each 650.
° C., 850 ° C., then heated to a 920 ° C., as the flow rate of the (H ₂ + HCl) gas from the gas inlet 6, 15c of HCl
c / min, H ₂ at 2 liters / min, H ₂ gas flow rate from the gas inlet 7 at 3 liters / min,
As the flow rate of (CO ₂ + H ₂₎ gas from the gas inlet 8, the CO ₂ 70 cc / min, the H ₂ 7 liters / m
When set to in, the growth rate of the magnesia spinel film is about 70Å / min.

However, since the magnesia spinel film obtained under the above conditions has three-dimensional nucleus growth, it has fine irregularities on the surface and is not a flat film. Further, since the crystallinity is not sufficient, it is necessary to perform heat treatment after the growth to improve the crystallinity.

FIG. 4 shows a case where the atmosphere in the heat treatment is a dry N ₂ atmosphere and an oxidizing atmosphere (wet N ₂ atmosphere).
₂ or dry O ₂ ) in each case, the degree of improvement in crystallinity is determined by the single crystal MgO.Al ₂ O during growth.
The X-ray diffraction intensity of the _three films (as-grown film) is relatively expressed as "1".

From this figure, it is understood that an oxidizing atmosphere is effective for improving the crystallinity of the single crystal MgO.Al ₂ O ₃ film by heat treatment. It is considered that this is because heat treatment in an oxidizing atmosphere replenishes oxygen deficient in the single-crystal MgO.Al ₂ O ₃ film, and approaches an appropriate stoichiometric composition. This means that when the temperature is lowered to room temperature in a nitrogen atmosphere after film formation, the grown single crystal MgO.Al.
_It can also be inferred from the fact that oxygen is easily released from the ₂ O ₃ film to cause oxygen deficiency.

However, as-
To obtain an X-ray diffraction intensity more than double that of a grown film, 1
A high temperature of 100 ° C or higher is required. Therefore, for example, it is difficult to use a single crystal MgO.Al ₂ O ₃ film as an interlayer insulating film of a three-dimensional circuit element, considering the adverse effect of the high temperature heat treatment on the lower layer device.

On the other hand, if CO ₂ is simply excessively supplied in order to contain a large amount of oxygen during the growth of the single crystal MgO.Al ₂ O ₃ film, the reaction between CO ₂ and MgCl ₂ occurs preferentially, and the Mg 2 The composition becomes so large that the composition of the grown film cannot be controlled. In addition, excess CO
_{According to 2} , the substrate is oxidized before or even during the growth of the single crystal MgO.Al ₂ O ₃ film, and a film having a desired crystal orientation cannot be obtained.

After growing the single crystal MgO.Al ₂ O ₃ film, it is effective to lower the temperature to room temperature in the atmosphere of CO ₂ and H _{2 at} the same flow rate as during growth. According to this method, A film having an X-ray diffraction intensity of about 2.5 times that of the conventional method is obtained. However, the crystallinity is inferior to the film obtained by the above-mentioned heat treatment after growth.

In order to improve the crystallinity of the single crystal MgO.Al ₂ O ₃ film, it is effective to reduce the growth rate. One of the methods for reducing the growth rate is to dilute the H ₂ carrier gas with an inert gas such as N ₂ to reduce the H ₂ concentration in the carrier gas. This H
₂ The decrease in the growth rate due to the decrease in the concentration is due to H ₂ and C
H ₂ O gas generated by the reaction with O ₂ is MgO.Al.
_This is because it is closely involved in the reaction of forming ₂ O ₃ , and the amount of H ₂ O formed controls the growth rate of MgO.Al ₂ O ₃ .

Here, the H ₂ carrier gas was diluted with N ₂ gas, the H ₂ concentration was 17%, and the growth rate was 18Å / m.
When grown as in, X is about 3.5 times that of the normal method.
A film having a line diffraction intensity is obtained. However, in this method, the regions where good crystals are obtained are limited, and needle-like abnormal growth as shown in FIG. Sex is impaired. This needle-like abnormal growth is caused by H that is an oxidizing species gas.
It is expected that this is due to insufficient supply of ₂ O.

[0017]

Therefore, a single crystal MgO.Al having good reproducibility and uniformity and good crystallinity.
_In order to grow a ₂ O ₃ film, a new growth method that reduces the growth rate while sufficiently supplying an oxidizing species gas is required.

[0018]

In order to solve the above-mentioned problems, the method for forming a single crystal magnesia spinel film according to the present invention is intended to solve the above-mentioned problems, such as magnesium chloride (MgCl ₂ ), aluminum chloride (AlCl ₃ ), carbon dioxide (CO ₂ ). ) And hydrogen (H ₂ ) are reacted in a reaction tube, and a single crystal magnesia spinel (MgO.Al ₂ O ₃ ) film is vapor-phase epitaxially grown on the single crystal semiconductor layer. Is characterized in that the amount of gas supplied into the reaction tube is sufficient, and the crystal is grown under reduced pressure while forcibly exhausting the inside of the reaction tube.

[0019]

If the rate of crystal growth is reduced by simply reducing the amount of gas supplied into the reaction tube, a sufficient amount of oxidizing species gas (H ₂ O) cannot be supplied. However, since the gas amounts of CO ₂ and H ₂ supplied to the reaction tube are sufficient, it is possible to secure the supply of a sufficient amount of oxidizing species gas (H ₂ O) with respect to the source gas. On the other hand, since the crystal growth is performed under reduced pressure while forcibly exhausting the inside of the reaction tube, the migration is favorably performed and the crystal growth rate is lowered with good controllability. Therefore, Mg with good crystallinity
An O.Al ₂ O ₃ film can be formed with good reproducibility and uniformity.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings showing its embodiments. For convenience of explanation, the same members as those in the conventional example are designated by the same reference numerals.

FIG. 1 is a schematic view of a CVD apparatus for carrying out the method for forming a single crystal magnesia spinel film of the present invention. Reference numeral 1 is a quartz reaction tube, and 2 is a source tube extending to almost the center of the quartz reaction tube 1. Two pipe lines 2a and 2b are formed in the source pipe 2, an Al source 3 is placed in the pipe line 2a, and a MgCl ₂ source 4 is placed in the pipe line 2b. A single crystal Si substrate 5 is placed on the susceptor 13 on the terminal side of the source tube 2.

[0022] 6 and 7, the two conduits 2a of the source tube 2, a gas inlet in 2b, from the gas inlet port 6 (H ₂ + HCl) gas, H ₂ from the gas inlet port 7
Gas is supplied respectively. Further, the gas introduction pipe 8 is
It directly communicates with the quartz reaction tube 1, and a (CO ₂ + H ₂ ) gas is supplied from the gas inlet tube 8.

Further, heaters 9, 10 and 11 are provided around the quartz reaction tube 1. The heater 9 is an Al source 3 and the heater 10 is MgCl 2.
The source 4 and the heater 11 are the single crystal Si substrate 5
Each is heated and maintained at a predetermined temperature.

Reference numeral 14 is an exhaust path communicating with the inside of the quartz reaction tube 1, and a rotary pump 12 is installed in the exhaust path 14. The gas in the quartz reaction tube 1 is forcibly discharged by the rotary pump 12, and the pressure in the quartz reaction tube 1 is reduced.

A method for forming a single crystal magnesia spinel film of the present invention using the CVD apparatus having the above structure will be described below.

First, the heaters 9, 10, 11 described above are used.
By operating each of the
The MgCl source 4 and the single crystal Si substrate 5 are heated and maintained at 0 ° C., 850 ° C. and 920 ° C., respectively. Then, the rotary pump 12 is operated to perform forced evacuation to keep the pressure in the quartz reaction tube 1 at around 50 Torr, and from the gas introduction tube 8, CO ₂ and H ₂ gas are each 70 cc / min, At a flow rate of 7 liters / min, HCl and H ₂ gas from the gas introduction port 6 are 30 cc / min and 2 liters / min, respectively, and further, H ₂ gas is 3 liters / min from the gas introduction port 7. mi
It is supplied into the reaction tube 1 at a flow rate of n.

As a result, AlCl ₃ transported in the pipeline 2a of the source tube 2 and MgC transported in the pipeline 2b.
l ₂ reacts with CO ₂ and H ₂ supplied from the gas introduction pipe 8 to form a single crystal MgO · Al ₂ O on the single crystal Si substrate 5.
_Three films grow epitaxially. The growth rate at this time was about 6 to 10Å / min. That is, the conventional 70Å /
The growth rate was about 1/10 of min. At the time of this reaction, the amount of CO ₂ and H ₂ gas to be supplied into the quartz reaction tube 1 is set to a sufficient amount, so that a sufficient amount of oxidizing species gas (H ₂ O) is supplied to the source gas. it can.

FIG. 2 is a sectional view of a substrate in which a single crystal MgO.Al ₂ O ₃ film is formed on the Si substrate as described above, and the surface of the single crystal MgO.Al ₂ O ₃ film is No needle-like abnormal growth was observed, and a film having a flat surface was obtained on the entire surface of the wafer. In addition, when the crystallinity of the film was examined by an X-ray diffraction method, an X-ray diffraction intensity about four times that of the film obtained by the normal method (growth rate 70 Å / min) was obtained,
It was found that the crystallinity was improved.

[0029]

As described above, according to the present invention, since the growth of the single crystal MgO.Al ₂ O ₃ film on the single crystal semiconductor layer is performed under reduced pressure, it is sufficient to supply the source gas. The growth rate can be reduced while supplying a large amount of oxidizing species gas (H ₂ O), and a single crystal MgO · Al ₂ O ₃ film with excellent crystallinity can be uniformly formed without inducing needle-like abnormal growth. Can be formed. Therefore, higher quality SO using this
It is possible to obtain an I substrate. Furthermore, if the degree of pressure reduction during growth is increased, low temperature growth is also possible, and lowering of the temperature of the wafer process can be promoted.

[Brief description of drawings]

FIG. 1 is a schematic view of a CVD apparatus used in the method for forming a single crystal magnesia spinel film of the present invention.

FIG. 2 is a sectional view of an SOI substrate formed by the method of the present invention.

FIG. 3 is a schematic view of a CVD apparatus used in a conventional method for forming a single crystal magnesia spinel film.

FIG. 4 is a graph showing the atmosphere dependency of the crystallinity improvement of the single crystal MgO.Al ₂ O ₃ film by heat treatment.

FIG. 5 is a cross-sectional view of an SOI substrate formed by a conventional method.

[Explanation of symbols]

1 Quartz Reaction Tube 2 Source Tube 3 Al Source 4 MgCl ₂ Source 5 Si Substrate 12 Rotary Pump

Claims (1)

[Claims] 1. Magnesium chloride (MgCl ₂ ), aluminum chloride (AlCl ₃ ), carbon dioxide (CO ₂ ) and hydrogen (H ₂ ) are reacted in a reaction tube, and a single crystal magnesia spinel ( MgO ・ Al ₂ O ₃ )
A method for forming a single crystal magnesia spinel film for vapor phase epitaxial growth of a film, characterized in that a sufficient amount of gas is supplied into the reaction tube, and the crystal is grown under reduced pressure while forcibly exhausting the reaction tube. Method for forming single crystal magnesia spinel film.