JP2773772B2 - Crystal growth equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The present invention relates to a gas source crystal growth apparatus in which the configuration of a gas pipe and a gas supply cell for supplying a source gas to a crystal growth chamber is newly improved. In order to provide a gas source crystal growth apparatus capable of reducing the problem of the residual gas in the crystal growth apparatus affecting crystal growth, a gas source crystal growth apparatus for growing a crystal from a gas source in a low-pressure atmosphere, An airtight crystal growth chamber for accommodating a substrate holder on which a substrate is mounted for growing a crystal on the substrate in a low-pressure atmosphere connected to a first evacuation system; A gas supply cell disposed in the crystal growth chamber for supplying toward the holder, and a first valve for controllably connecting the gas supply cell to a gas source. A gas introduction path connected to the gas supply cell;
In order to controllably connect to the vacuum evacuation system, a second valve is provided and a gas discharge path connected to the gas supply cell is provided.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas source crystal growth apparatus, and more particularly to a gas source crystal growth apparatus in which the configurations of a gas pipe for supplying a source gas to a crystal growth chamber and a gas supply cell are newly improved.

The epitaxial crystal growth method for epitaxially growing a semiconductor film along a crystal substrate is a basic technique of a semiconductor structure, and one of them is a gas source crystal growth method for growing a crystal from a gas source in a low-pressure atmosphere. Recently, gas-source molecular beam epitaxy has been developed as a notable technology.

In this gas source molecular beam epitaxy, a compound gas is introduced into an ultrahigh vacuum crystal growth chamber to form a crystal growth layer.
However, it is difficult to accurately control the composition and thickness of the growth layer by controlling the gas flow. In particular, when forming an interface structure such as a hetero junction structure or a pn junction structure, a steep composition change is required.

[Prior Art] The gas source molecular beam epitaxy uses a gas source instead of a solid source such as a metal in the conventional molecular beam epitaxy (MBE). For example, when growing a gallium arsenide (GaAs) layer or an aluminum gallium arsenide (AlGaAs) layer, triethyl gallium (TEG; Ga (C ₂ H ₅ ) ₃ ), triethyl aluminum (TE
A: An organic metal gas such as Al (C ₂ H ₅ ) ₃ ) is used, and a hydride gas such as arsine (AsH ₃ ) is used as a group V element material.

The gas source molecular beam crystal growth method has advantages over the conventional MBE method in that surface defects can be reduced and a high component velocity can be easily obtained. Further, it is said that the source can be replaced without breaking the clean ultra-high vacuum atmosphere in the growth vessel, which has a great advantage in industrial production.

2 (A), 2 (B) and 2 (C) show a conventional crystal growth apparatus for performing the gas source molecular beam crystal growth. In FIG. 2A showing the entire crystal growth apparatus, reference numerals are used.
51 is a crystal growth chamber, 52 is a substrate (substrate to be grown or wafer), 53 is a substrate holder for supporting the substrate 52, 54 is a heater for heating the substrate, 55 is a molecular beam source cell, 56 is a molecular beam source cell A reference numeral 57 denotes a liquid nitrogen shroud for adsorbing gas, and a reference numeral 58 denotes a gate valve for shutting off the crystal growth chamber 51 from a vacuum exhaust system. As shown, the substrate 52 is held by a substrate holder 53 and heated by a heater 54 to set a predetermined substrate temperature. For example, when the substrate 52 is a GaAs substrate, it is heated to 400 to 700 ° C. Here, a plurality of molecular beam source cells
Are arranged to face each other.

2 (B) and 2 (C) are cross-sectional views of a conventional molecular beam source cell, and FIG. 2 (B) is a low-temperature cell for low-temperature decomposition gas,
(C) is a high-temperature cell for high-temperature decomposition gas.

2 (B) and 2 (C), 61 is a gas introduction pipe, 62 is a heater, 63 is a vacuum flange of the crystal growth chamber 51, 64 is a heat shield around the heater 62, 65 is sintered boron nitride ( PBN) plate.

The molecular beam source cell for low-temperature decomposition gas shown in FIG.
It is used for an organic metal gas such as triethylgallium (TEG) or triethylaluminum (TEA) that is easily decomposed, which is a group III source gas, and the inside of the cell is heated to 50 to 60 ° C. so that gas molecules do not condense. Gas molecules are emitted from the opening of the PBN plate 65 at the outlet.

The molecular beam source cell for high-temperature decomposition gas shown in FIG.
For example, it is used for a metal hydride gas such as arsine (AsH ₃ ), which is a group V source gas, and is heated to 800 to 900 ° C. to decompose arsine into As and H ₂ and transfer As to the substrate. Radiate.

In the high-temperature cell, the heater 62 and the PBN plate 65 are densely arranged at the outlet portion, and the openings of the PBN plate 65 are shifted from each other so that the gas collides with the PBN plate 65 heated at a high temperature to decompose the gas. A cracking section 66 is provided. The thermal cracking section 66 is not provided in the low-temperature decomposition gas molecular beam source cell.

These molecular beam source cells are, for example, 1/4 inch in diameter,
It is formed of a quartz tube having a length of about 30 cm, and the distance between the tip of the cell and the wafer 52 is relatively short.

When a GaAs layer or an AlGaAs layer is grown using the gas source molecular beam epitaxial growth apparatus as described above, for example, TEG is used as the Ga source, TEA is used as the Al source, and arsine is used as the As source. About 90
It is released from the high-temperature molecular beam source cell heated to 0 ° C. (FIG. 2 (C)), and the TEG and TEA, which are group III element raw materials, are cooled at a low temperature of about 50-60 ° C. (FIG. 2 (B) )). Since arsine is not decomposed on a GaAs substrate heated to 400 to 700 ° C, it is preliminarily heated and decomposed in a molecular beam source cell to produce single As.
It emits as a molecule or As ₂ molecule.

On the other hand, since TEG and TEA can be thermally decomposed at a low temperature, they are not thermally decomposed in the molecular beam source cell. The cell is heated to such an extent that the source gas does not adhere to the tube wall of the molecular beam source cell (50 to 60 ° C). The gas source is decomposed and deposited on the heated GaAs substrate.

For example, when growing an AlGaAs / GaAs heterostructure, TEA
By opening and closing the gas introduction valve 56 of the molecular beam source cell, the Al composition is turned on and off to switch between the AlGaAs layer and the GaAs layer.

The semiconductor crystal thus formed is used for manufacturing a semiconductor device such as a double hetero (DH) laser or HEMT, or a semiconductor integrated device.

[Problem to be Solved by the Invention] As described above, the gas supply path from the gas source to the gas supply cell in the crystal growth chamber is provided with the valve 56, and shutting off the gas supply closes the valve 56. I was going by that.

However, even when the valve 56 is closed, the source gas remains between the valve 56 and the supply port, and the source gas is released from the cell supply port and reaches the substrate 52.
Although an attempt is made to grow a crystal layer that does not include the blocked components on the substrate 52, the blocked components enter. Even if an attempt is made to form a junction having a steep distribution, only a gradually changing distribution can be obtained.

In addition, when a uniform growth film is required on the substrate in the integrated circuit device, the uniformity of the growth film is reduced.

Attempts have been made to prevent leakage of residual gas by installing a shutter on the supply port of the split source cell.However, there is still the presence of residual gas in the cell, and gas flows through the gap between the shutter and the cell. Released and reach the substrate. Although the amount of outflow of gas per unit time decreases, the time until it disappears increases. Thus, the shutter is not a complete measure. In particular, when a gas such as SiH ₄ or Si ₂ H ₆ is used as a dopant, the residual dopant gas poses a problem.

SUMMARY OF THE INVENTION An object of the present invention is to provide a gas source crystal growth apparatus capable of reducing a problem that a residual gas in a crystal growth apparatus gives to crystal growth when a source gas of a certain component is shut off.

It is another object of the present invention to provide a gas source crystal growing apparatus in which a residual gas in a crystal growing apparatus is automatically discharged when a raw material gas of a certain component is shut off.

With these gas source crystal growth apparatuses, an interface of a hetero junction or a pn junction having a steep distribution is formed.

[Means for Solving the Problems] The above-mentioned object is achieved by a gas source crystal growth apparatus in which a gas discharge path provided with a valve is connected to a gas supply cell in order to connect the gas supply cell to an exhaust system.

In order to automatically discharge the residual gas, a control system for synchronizing and controlling the valve of the gas introduction path and the valve of the gas discharge path may be provided.

FIG. 1 is a diagram illustrating the principle of the present invention. The crystal growth chamber 1 is an airtight container that houses a substrate holder 3 that supports a substrate 2 and is connected to a first evacuation system 4. A gas supply cell 5 is arranged in the crystal growth chamber 1 so as to face the substrate 2. The gas supply cell 5 is connected to a gas source 7 by a gas introduction path 8 having a first valve 6, and is connected to a second vacuum discharge system 10 by a gas discharge path 11 having a second valve 9. ing. The first evacuation system and the second evacuation system may be the same. Further, the structure between the valves 6, 9 and the gas supply cell 5 may be partially common between the gas introduction path 8 and the gas discharge path 11.

When closing the first valve 6, a control system 12 may be further provided so that the second valve 9 opens synchronously.

[Operation] Conventionally, when the first valve 6 of the gas introduction path 8 is closed, the gas present between the first valve 6 and the outlet of the gas supply cell 5 at that time exits from the outlet of the gas supply cell 5. I had no choice. Outlet of gas supply cell 5 and first evacuation system 4
Since the substrate 2 exists on the path of the gas flow connecting the two, it is difficult to avoid that gas molecules are deposited on the substrate 2. According to the gas source crystal growth apparatus of the present invention, since there is the gas discharge path 11 connecting the gas supply cell 5 to the second evacuation system 10,
If this valve 9 is opened, the gas remaining in the portion of the gas supply cell 5 or the gas introduction path 8 closer to the cell 5 than the first valve 6 can be exhausted to the second evacuation system. For this reason, the discharge of the residual gas becomes faster. Further, gas molecules traveling from the outlet of the gas supply cell 5 toward the substrate 2 can be significantly reduced. In this way, the residual gas reaching the substrate 2 can be reduced quantitatively and temporally,
An interface having a steep distribution can be realized.

Further, the first valve 6 of the gas introduction path 8 and the gas discharge path
By providing a control system that controls the second valve 9 in a synchronized manner, the residual gas can be automatically discharged when the gas supply is cut off.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

3 (A), 3 (B), and 3 (C) show a gas source molecular beam crystal growth apparatus according to one embodiment of the present invention, and FIG. 3 (A) shows the entire main part of the crystal growth apparatus, and FIGS. ) Shows a low-temperature cell and a high-temperature cell used in the apparatus (A).

The crystal growth chamber 1 is formed of an airtight container connected to a vacuum evacuation system by a gate valve 18, and includes therein a substrate holder 3 on which a substrate 2 is mounted and a heater 14 such as a tantalum wire for heating the substrate 2. A liquid nitrogen-cooled shroud that accommodates and absorbs gas molecules to prevent reflection is provided on the inner wall. In the illustrated apparatus, a gas supply cell 5 constituting four molecular beam sources is provided in a crystal growth chamber 1. This number can be increased or decreased as needed. Each gas supply cell 5 has a first
The gas introduction path 8 having the valve 6 and the gas discharge path 11 having the second valve 9 are connected.

FIGS. 3B and 3C show two structures of a gas supply cell and a piping section of the crystal growth apparatus shown in FIG.

A gas discharge pipe 11 provided with a second valve 9 is provided on the gas supply pipe 5 side of the gas introduction pipe 8 from the first valve 6. The gas discharge pipe 11 is evacuated by a dedicated turbo molecular pump. I have. The gas supply cell 5 is a space whose outlet is defined by a sintered boron nitride (PBN) plate 25 having an opening, and is heated by a heater 22 such as a tantalum wire. A heat shield plate 24 is arranged outside the heater 22 to prevent heat from being radiated to the outside. Reference numeral 23 denotes a vacuum flange serving as a wall of the crystal growth chamber 1. In the high-temperature cell shown in FIG. 3 (C), a plurality of PBN plates 25 whose openings are shifted near the outlet are arranged, and a heater 22 in which these PBN plates are densely wound is heated. Gas molecule is PB several times
It will collide with the N plate 25 and head toward the substrate 2. At the time of collision, heat is received from the PBN plate 25, so that gas molecules are decomposed at a high temperature.

In the growth of III-V compound semiconductors, for example, III
An organic metal gas such as TEG or TEA is used as a source gas for the group V element, and arsine,
A hydride such as phosphine is used. In general, the organometallic gas is easily decomposed, so it is supplied in the low-temperature cell shown in FIG. 3 (B). Since the hydride is hardly decomposed, it is heated to a high temperature in the high-temperature cell shown in FIG. To supply.

The second valve 9 of the gas discharge pipe 11 synchronizes the opening and closing of the first valve 6 of the gas introduction pipe 8, and when the second valve 9 is open, the first valve 6 is automatically closed, When the second valve 9 is closed, a synchronous control system may be provided so that the first valve 6 is automatically opened.

Using such a gas supply cell, for example, GaAs / AlGaAs using arsine (AsH ₃ ), triethylgallium (TEG), and triethylaluminum (TEA) as source gases
When forming a hetero junction, these gases are introduced into the gas supply cell 5 via the gas introduction pipe 8 and the first valve 6. The high-temperature cell shown in FIG. 3 (C) is used for arsine, and the low-temperature cell shown in FIG. 3 (B) is used for TEG and TEA. When molecular beams are supplied from the three gas supply cells and the growth of the GaAs layer is started, the valve 6 of the gas introduction pipe of the TEA gas supply cell is closed, and the valve 9 of the gas discharge pipe is opened at the same time. The TEA gas remaining in the TEA gas supply cell is exhausted through the gas exhaust pipe 11.

A specific example of growing an AlGaAs layer on a GaAs substrate by introducing arsine, TEG, and TEA using the gas source molecular beam crystal growth apparatus shown in FIGS. 3 (A), (B) and (C) will be described. .
The substrate temperature is 600 ° C. After growing the AlGaAs layer by about 0.5 μm, the valve 6 of the gas inlet tube of the molecular beam source cell for TEA is closed and the valve 9 of the gas outlet tube is opened at the same time to terminate the growth of the AlGaAs layer. To start. The GaAs layer grows about 0.1 μm. Thus, the steepness of the interface of the grown AlGaAs / GaAs heterostructure can be examined by a depth profile of the Al element by sputter auger (AES). Al grown using only the on-off valve 6 of the conventional gas introduction pipe and controlling the components in the same manner.
Compared with the GaAs / GaAs heterostructure, in the crystal formed by the above-described growth process, the steepness of the Al element in the depth direction is about 5 °, which is about half that of the conventional one. It turns out that it is effective for forming a steep heterocrystal growth layer.

Although the above is described in the embodiment in which the molecular beam of the group III element is closed, a sharp doping profile can be obtained by using a molecular beam source cell for a gas for a dopant such as disilane (Si ₂ H ₆ ). Needless to say, it is possible to grow a crystal. In the case of disilane, the high temperature cell shown in FIG. 3 (C) is used.

FIGS. 4A and 4B show another embodiment of the present invention.
In FIG. 4 (A), the gas from the gas source 7 is controlled at a constant flow rate by the mass flow meter 32 and supplied to the gas introduction path 8. A first opening / closing valve 6 is arranged between the mass flow meter 32 and the gas supply cell 5 in the crystal growth chamber 1 to control the gas flow on and off. When the first on-off valve 6 is closed, the second on-off valve 9 and the third on-off valve
34 is opened. The second opening / closing valve 9 is provided in a first gas discharge passage 11 connected to a gas introduction passage between the first opening / closing valve 6 and the gas supply cell 5. By closing the first opening / closing valve 6 and opening the second opening / closing valve 9, the residual gas in the gas supply cell 5 can be evacuated via the first gas discharge path 11.

Further, the third opening / closing valve 34 is provided in the second gas discharge path 36. The second gas discharge path 36 is connected to the gas introduction path 8 between the first opening / closing valve 6 and the mass flow meter 32, and the other end is connected to an exhaust system. When the first opening / closing valve 6 closes, the third opening / closing valve 34 is opened to bypass the gas flow from the mass flow meter 32.

These three on-off valves 6, 9, and 34 are synchronously controlled by a synchronous control system 38. That is, the gas flow supplied from the mass flow meter 32 is
Sent to one of the gas discharge paths 36 of the crystal growth apparatus 1
The gas supply cell 5 is supplied with a source gas from a gas introduction path 8 or is exhausted through a first gas discharge path 11.

Such a valve group 6, 9, 34 can be constituted by a four-way valve as shown in FIG. 4 (B). In FIG. 4 (B), A, B, C, and D indicate four ports, and 41, 42,
43 indicates a bellows valve. Port A is connected to the gas supply cell side, port B is connected to the gas source side, and ports C and D are connected to the exhaust system. When the valves 41 and 42 are closed, no bellows appear on the surface facing the crystal growth chamber 1 where the vacuum becomes extremely high.

Such a four-way valve may be controlled by electromagnetic force or fluid force such as air.

FIGS. 5A and 5B show a four-way valve driven by an air cylinder valve, where FIG. 5A is a plan view and FIG.
The cross section along the line VB-VB 'is shown.

In FIG. 5 (A), A, B, C, and D are four ports constituting four ports, and the air cylinder valves 44, 45, 46
Is a drive source for operating three valves with air.

In the sectional view of FIG. 5B, the air cylinder valve 44,
45 and 46 receive the air flow shown by the arrows and move their drive cylinders 47, 48 and 49, and these drive cylinders 47 and
The bellows valves 41, 42, 43 are operated by 48, 49. Branches A ′ and B ′ are inlets of a flow path toward ports A and B. By synchronously controlling the three air flows, the four-way valve shown in FIGS. 5A and 5B can be synchronously controlled.

Although the present invention has been described with reference to the embodiments, the embodiments are not limited in any way. It will be apparent to those skilled in the art that various changes, modifications, combinations, and the like can be made within the scope of the present invention.

[Effects of the Invention] As described above, according to the present invention, since the gas supply cell can be directly evacuated, the residual gas in the gas supply cell or the like can be quickly discharged, and the composition of the source gas supplied onto the substrate can be reduced. Can be changed quickly.

When the valves are controlled synchronously, the automatically shut off gas can be discharged.

An interface structure such as a hetero junction or a pn junction having a steep profile can be realized by quickly switching the source gas composition.

[Brief description of the drawings]

FIG. 1 is a view for explaining the principle of the present invention, FIGS. 2 (A), (B) and (C) show a conventional gas source molecular beam crystal growing apparatus, wherein (A) is an overall sectional view,
(B) and (C) are cross-sectional views of a gas supply cell portion for a low temperature and a high temperature, and FIGS. 3 (A), (B) and (C) show gas source molecular beam crystal growth according to one embodiment of the present invention. (A) is an overall cross-sectional view, (B) and (C) are cross-sectional views of a low-temperature and high-temperature gas supply cell section, and FIGS. 4 (A) and (B) show other examples of the present invention. Example of the,
(A) is a block diagram of a main part, (B) is a diagram showing a valve system, and FIGS. 5 (A) and (B) are embodiments of the present invention shown in FIGS. 4 (A) and (B). (A) is a plan view and (B) is a sectional view. In the figure, 1 ... crystal growth chamber 2 ... substrate 3 ... substrate holder 4 ... first evacuation system 5 ... gas supply cell 6 ... first valve 7 ... gas source 8 ... gas introduction Path 9 Second valve 10 Second vacuum exhaust system 11 Gas exhaust path 12 Synchronous control system 14 Heater 17 Shroud 18 Gate valve 22 Heater 23 Flange 24: heat shield plate 25: PBN plate 34: third valve 36: second gas discharge passage 41, 42, 43 ... bellows valve 44, 45, 46 ... air cylinder valve A, B, C, D ... ports 47, 48, 49 ... driving cylinder 51 ... crystal growth chamber 52 ... substrate 53 ... substrate holder 54 ... heater 55 ... molecular beam source cell 56 ... valve 57 ... shroud 58 … Gate valve 61… Gas inlet tube 62… Heater 63… Vacuum flange 64… Heat shield plate 65… PBN plate 66… Thermal cracking part

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) C30B 25/00-25/22 H01L 21/205 C30B 28/00-35/00

Claims (2)

(57) [Claims] 1. A crystal growth chamber connected to a first evacuation system, a gas supply cell opening into the crystal growth chamber, a gas introduction path connected to the gas supply cell and communicating with a gas source. A gas discharge passage branched from the gas introduction passage and communicating with a second evacuation system; and a first gas supply passage provided on the gas introduction passage upstream of a branch point between the gas introduction passage and the gas discharge passage. And a second valve provided in the gas discharge path, wherein the first valve and the second valve are synchronously controlled. 2. The crystal growth apparatus according to claim 1, wherein the second valve is opened simultaneously with the closing of the first valve.