JP2712367B2 - Method and apparatus for forming thin film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] Regarding the atomic layer epitaxy method and an apparatus applied to it, the purpose of the present invention is to form a high-quality thin film with a small amount of impurities, and to set the kind of raw material gas flowing into a reaction tube to one atom. The thin film forming apparatus is characterized in that the growth is performed by switching every layer and switching the flow direction in the reverse direction every atomic layer with respect to the surface of the substrate to be grown. , A turbo-molecular pump is disposed, a substrate to be grown W and an inert gas inlet Nc opposed to the substrate to be grown are disposed at a center position of the reaction tube, and the center position and the orifice valve are disposed between the center position and the orifice valve. A configuration is adopted in which the raw material gas inlets are arranged on both sides between them.

[Industrial applications]

The present invention relates to a method and an apparatus for forming a thin film, and more particularly, to an atomic layer epitaxy method and an apparatus applied thereto.

In recent years, a method for forming a high-quality semiconductor thin film by an atomic layer epitaxy (ALE) method capable of controlling growth at a monoatomic layer level has been studied, and its future is expected. Also, it is desired that the insulating film has high quality. For example, the insulating layer of the EL panel is required to have a high withstand voltage, no defect, and a long life without any impurities or film defects.

[Conventional technology]

Atomic layer epitaxy is a method in which a plurality of different source gases are alternately switched and introduced onto the surface of a substrate to be grown to grow one atomic layer at a time. In a normal chemical vapor deposition (CVD) method, the source gas is deposited on the substrate to be grown. Atomic layer epitaxy is attracting attention as a method that can form higher quality thin films compared to CVD because the layer is stacked one by one and reacts reliably on the surface of the substrate to be grown. I have. For example, when a GaAs layer is grown by reacting a triethylgallium (Ga (C ₂ H ₅ ) ₃ ) gas with an arsine (AsH ₃ ) gas, ethane (C
₂ H ₆₎ is a method of high-quality film can be obtained without containing such.

FIG. 5 is a cross-sectional view of a conventional thin film forming apparatus to which the atomic layer epitaxy method is applied, wherein 1 is a reaction tube, 2 is a substrate to be grown, 3 is an orifice valve, 4 is a vacuum pump, and 5 is a source gas. Reference numeral A denotes an inlet, reference numeral 6 denotes a source gas B, reference numeral 7 denotes a barrier gas inlet, and reference numerals 5V, 6V, and 7V denote on-off valves thereof. Such a thin film forming apparatus is a method in which the direction of gas flow is constant, and the type of gas flowing on the surface of the substrate to be grown is switched by switching between the barrier gas and the source gases A and B to grow one atomic layer at a time. .

[Problems to be solved by the invention]

However, in the atomic layer epitaxy method using the thin film forming apparatus as described above, the gas inlet is on one side, and the amount and time of the shielding barrier gas flowing between the source gas A and the source gas B are insufficient. In addition, there are parts where the gas tends to stagnate (such as near the wall surface of the reaction chamber or the gas inlet), and the raw material gas reacts on parts other than the surface of the substrate to be grown, and the thin film grows abnormally. Since the abnormally grown thin film is easily peeled, it rides on the gas flow to reach the growth substrate surface,
There is a problem that the impurities are mixed as impurity particles in the thin film formed on the surface of the substrate to be grown and become nuclei of abnormal crystal growth.

The present invention proposes a method and an apparatus for forming a thin film for the purpose of forming a high-quality thin film containing less impurities by solving such problems.

[Means for solving the problem]

The problem is that the type of the source gas flowing into the reaction tube is switched for each atomic layer, and when the type of the source gas is switched, an inert gas is introduced to remove the residual source gas together with the inert gas, In addition, the problem is solved by a method of forming a thin film in which the flow direction is changed in the direction opposite to the surface of the substrate to be grown for each atomic layer to grow.

In addition, as a thin film forming apparatus for performing the same, turbo molecular pumps Va and Vb are arranged on both sides of a cylindrical reaction tube 11 via orifice valves Oa and Ob, respectively, as shown in the embodiment of FIG. A substrate W to be grown and an inert gas inlet Nc opposed to the substrate W to be grown are arranged at a central position of the reaction tube, and
Source gas inlets Na and Nb are arranged on both sides between the center position and the orifice valve.

(Operation)

That is, according to the present invention, the flow direction is switched in the opposite direction to the surface of the substrate to be grown for each atomic layer, and the inert gas is introduced and the residual raw material gas is simultaneously expelled at each switching.

In order to perform this, a thin film forming apparatus is provided in which source gas inlets Na and Nb are provided on both sides of the cylindrical reaction tube 11 and an inert gas inlet Nc is provided at a position opposite to the growth target substrate W at the center position. First, an inert gas was introduced, and the orifice valves Oa, Ob
Is opened to maintain a constant degree of reduced pressure, and then one of the orifice valves Ob is opened to flow the A raw material gas in one direction to form a layer made of the raw material A. Next, an inert gas is introduced again,
The orifice valves Oa and Ob are opened to maintain a constant degree of pressure reduction, and then one of the orifice valves Oa is opened and a B source gas flows in the opposite direction to form an atomic layer of the source B.

In this way, the gas flow direction changes in the opposite direction, so that the gas staying near the wall of the reaction tube or near the gas inlet is easily removed, and the abnormal growth of impurity particles in the thin film described above is eliminated, and the high-quality thin film is removed. Can be formed.

〔Example〕

Hereinafter, embodiments will be described in detail with reference to the drawings.

FIG. 1 is a conceptual diagram of a thin film forming apparatus according to a first embodiment of the present invention, in which 11 is a cylindrical reaction tube, Va and Vb are turbo molecular pumps, Oa and Ob are orifice valves, and W is a valve. Growth substrate, Po is pressure gauge, P is pressure gauge, Nc is inert gas inlet, Na is A source gas inlet, Nb is B source gas inlet, Vc ', Va', Vb '
Are opening / closing valves attached to those inlets. This apparatus has a configuration in which the flow directions of the raw material gas A and the raw material gas B are opposite to each other with respect to the surface of the substrate W to be grown, and the inert gas flows from the center position to both sides and is exhausted. is there.

For example, a case where a GaAs crystal thin film is formed by the thin film forming apparatus shown in FIG. 1 will be described.
(E) is an operation explanatory view of the thin film forming apparatus of FIG. First, 5 × 10 ^-7 Tor using the turbo molecular pumps Va and Vb
After the substrate W was heated to 300 ° C., the opening / closing valve Vc ′ was first opened to flow Ar (argon) gas through the inert gas inlet Nc, and the pressure in the reaction tube 11 was reduced. 10Torr
Is adjusted by the orifice valves Oa and Ob. At this time, fine adjustment is also performed by the orifice valves Oa and Ob so that a pressure difference is not generated on both sides of the reaction tube by the pressure difference gauge Po. FIG. 2 (a) shows the flow state (arrow) of the Ar gas.

Next, the on-off valve Vc 'and the orifice valve Oa are closed,
Opening the opening and closing valve Va 'in a state of opening the orifice valve Ob flows of hydrogen triethyl gallium (H ₂₎ was the carrier gas _{(Ga (C 2 H 5)} 3) gas from the A reactive gas inlet Na. Then, Ga (CH ₃ ) ₃ is adsorbed on the substrate W to be grown.
It decomposes to form a Ga atomic layer. FIG. 2 (b) shows the H ₂
Shows the flow state (arrow) of the Ga (CH ₃ ) ₃ gas using as a carrier gas.

Next, the on-off valve Va 'is closed, and the orifice valves Oa, Ob
Are opened, the open / close valve Vc is opened, Ar gas flows from the inert gas inlet Nc, and the residual H ₂ + Ga (C
H) Exhaust and remove the _three gases. FIG. 2 (c) shows the Ar
This is the gas flow state (arrow). The reason for introducing the inert gas in this manner is that the efficiency of removing the source gas by mixing the inert gas with the residual source gas is improved.

Then, the inflow opening and closing valve Vc 'and in a state of opening the orifice valve Oa closes the orifice valve Ob, the opening and closing valve Vb' hydrogen open the arsine (AsH ₃₎ gas that is a carrier gas from the B reaction gas inlet Nb I do. Then, AsH ₃ is adsorbed and decomposed on the growth target substrate W to form an As atomic layer. Second
FIG. 4D shows the flow state (arrow) of the AsH ₃ gas using H ₂ as a carrier gas.

Next, the on-off valve Vb 'is closed, and the orifice valves Oa, Ob
Are opened, the open / close valve Vc 'is opened, Ar gas flows in from the inert gas inlet Nc, and the residual H ₂ + AsH ₃ together with the Ar gas.
The gas is exhausted and removed. FIG. 2 (e) is a flow state (arrow) diagram of the Ar gas.

The above operation was repeated 500 times to form GaAs consisting of 500 molecular layers.
Grow a crystalline thin film. In the GaAs crystal thin film thus formed, no impurity particles and abnormal growth were observed in the thin film.

Next, FIG. 3 shows a conceptual diagram of a thin film forming apparatus according to a second embodiment of the present invention. In FIG. 3, the same parts as those in FIG. Trap, Sa
Is an A source gas source container, Sb is a B source gas source container, and Ha and Hb are carrier gas inlets. That is, in addition to the features of the configuration described with reference to FIG. 1, the present apparatus does not have an opening / closing valve at the A source gas inlet Na and the B source gas inlet Nb, and the A source gas source container S
a, B This is an example of an apparatus for flowing / stopping a reaction gas into a reaction tube by flowing / stopping a carrier gas into / from a source gas source container Sb. Such devices are useful for forming a thin film using a strong reaction gas corrosive, for example, Al ₂ O
₃ (alumina) cannot achieve a sufficient dielectric strength by the conventional CVD method, and for that reason, an atomic layer epitaxy method is used. However, it is used for forming such an Al ₂ O ₃ thin film. The adsorption traps Ta and Tb are portions for trapping floating impurities in the reaction tube, and are provided particularly when a thin film is formed by violently reacting.

To describe the case of forming a Yotsute Al ₂ O ₃ thin film in the thin film forming apparatus shown in FIG. 3, and the fourth diagram (a) ~ (e) shows a view for explaining an operation of the third view of a thin film forming apparatus . First, A source gas source container Sa is AlCl ₃ (aluminum chloride)
And heated to 70 to 80 ° C., water is stored in the B source gas source container Sb at 10 to 20 ° C., and 5 × 10 ⁻⁴ Torr by turbo molecular pumps Va and Vb. The substrate W to be grown is heated to 300 ° C. First, open the on-off valve Vc '
r Gas flows in from the inert gas inlet Nc, and is adjusted by the orifice valves Oa and Ob so that the pressure in the reaction tube 11 becomes 10 Torr. The orifice valves Oa and ob are finely adjusted so as not to cause bleeding.
FIG. 4 (a) shows the flow state (arrow) of the Ar gas.

Next, the on-off valve Vc 'and the orifice valve Oa are closed,
With the orifice valve Ob open, Ar gas flows into the A source gas source container Sa from the carrier gas inlet Ha, and sublimates AlCl ₃ gas using Ar gas as the carrier gas to the A reaction gas inlet Na.
From the reaction tube. At the same time, Ar gas flows into the A source gas source container Sb from the carrier gas inlet Hb, and steam using the Ar gas as the carrier gas flows from the B reaction gas inlet Nb into the rear pipe. However, since the water vapor is exhausted without passing over the growth substrate W, only the AlCl ₃ molecules are adsorbed on the growth substrate W. Further, only one molecular layer is adsorbed, and the others are removed by passing over the substrate. FIG. 4B shows the flow state (arrow) of the gas.

Next, the inflow of the Ar gas into the carrier gas inlets Ha and Hb was stopped (the main stopper not shown was closed), and the orifice valves Oa and O
opened both b, Ar gas was supplied from the inert gas inlet Nc by opening the opening and closing valve Vc ', residual AlCl ₃ with Ar gas
And the water vapor is exhausted and removed. FIG. 4 (c) shows the flow state (arrow) of the Ar gas.

Next, the on-off valve Vc 'and the orifice valve Ob are closed,
With the orifice valve Oa opened, Ar gas flows into the A source gas source container Sb from the carrier gas inlet Hb, and water vapor using Ar gas as the carrier gas flows into the reaction tube from the B reaction gas inlet Nb, At the same time, Ar gas flows from the carrier gas inlet Ha into the A source gas source container Sa, and AlCl ₃ gas using Ar gas as the carrier gas flows from the A reaction gas inlet Na into the reaction tube. Then, only water molecules are adsorbed on the growth target substrate W, and react with the already adsorbed AlCl ₃ to form an Al ₂ O ₃ molecular layer. FIG. 4D shows the gas flow state (arrow). At this time, AlCl ₃ is not adsorbed because it does not pass over the substrate W to be grown.

Next, the on-off valve Vb 'is closed, and the orifice valves Oa, Ob
Are opened, the open / close valve Vc 'is opened, Ar gas flows in from the inert gas inlet Nc, and the remaining water vapor and AlCl ₃ gas together with the Ar gas are exhausted and removed. FIG. 4 (e) is a flow state (arrow) diagram of the Ar gas.

In the above operation, the orifice valve is adjusted so that the pressure in the reaction tube does not fluctuate from 10 Torr.
Repeat 3,000 times to grow a 2000mm alumina polycrystalline thin film. The alumina thin film formed in this manner has no abnormal growth near the surface of the substrate to be grown because there is no stagnation of the reaction gas. Therefore, no impurity particles and abnormal growth are observed in the thin film, and there is no defect and high withstand voltage. An alumina thin film is obtained.

Such an alumina thin film can be used as an insulating layer of an EL panel to improve the quality of the EL panel, such as extending its life.

〔The invention's effect〕

As is clear from the above description of the embodiment, according to the method and apparatus for forming a thin film according to the present invention, a high-quality crystalline thin film and polycrystalline thin film can be obtained without including an abnormally grown film in the thin film. This is very useful for improving the performance of semiconductor devices and other electronic devices.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of a thin film forming apparatus according to a first embodiment of the present invention, FIGS. 2 (a) to 2 (e) are explanatory diagrams of the operation of the thin film forming apparatus of FIG. 1, and FIG. FIGS. 4 (a) to 4 (e) are conceptual diagrams of a thin film forming apparatus according to the second embodiment, FIGS. 4 (a) to 4 (e) are explanatory diagrams of the operation of the thin film forming apparatus of FIG. 3, and FIG. . In the figure, 11 is a reaction tube, Va and Vb are turbo molecular pumps, Oa and Ob are orifice valves, W is a substrate to be grown, Po is a pressure differential gauge, P is a pressure gauge, Nc is an inert gas inlet, and Na is A source gas inlet, Nb is B source gas inlet, Vc ', Va', Vb 'are open / close valves, Ta and Tb are adsorption traps, Sa is A source gas source container, Sb is B source gas source container, Ha , Hb indicates the carrier gas inlet.

Claims (3)

(57) [Claims] The type of source gas flowing into the reaction tube (11) is switched for each atomic layer, and when the type of source gas is switched, an inert gas is introduced to remove the residual source gas. And a growth method wherein the flow direction is changed for each atomic layer in a direction opposite to the surface of the substrate to be grown (W). 2. A thin film forming method according to claim 1, wherein the flow of said source gas into and out of said reaction tube is performed by the flow of a carrier gas into and out of said source gas source. . 3. Turbo molecular pumps (Va, Vb) are disposed on both sides of a reaction tube (11) via orifice valves (Oa, Ob), and a substrate to be grown (W) is located at a center position of the reaction tube. An inert gas inlet (Nc) facing the substrate to be grown (W) is arranged, and source gas inlets (Na, Nb) are arranged on both sides between the center position and the orifice valve. An apparatus for forming a thin film, comprising: