JPH0740557B2 - Gas source molecular beam crystal growth equipment - Google Patents

Description

TECHNICAL FIELD The present invention relates to a gas source molecular beam crystal growth apparatus for irradiating a growth substrate surface with a gas containing an organometallic gas to grow crystals.

[Prior Art] In recent years, in the field of III-V group compound semiconductors, a conventional molecular beam crystal growth method using a solid material (hereinafter abbreviated as MBE method)
A gas source MBE method has been developed that solves various shortcomings of (for example, Y. Kawaguchi et.al. Jan. J. Appl. Phys. (Journal of Applied Physics, Japan), 23, L737 (1984)). The features of this MBE method are as follows. That is, (1). Since the raw material can be replenished or exchanged while the growth chamber is kept in vacuum, the quality of the grown crystal is hardly deteriorated due to the replenishment or exchange of the raw material. That is, it is possible to grow crystals with stable quality over a long period of time.

(2). High-purity crystals, which were difficult to obtain by the conventional MBE method, can be grown relatively easily. For example
InP crystal has a carrier concentration of 9.1 × at liquid nitrogen temperature.
It has been reported that an ultrahigh-purity crystal with an electron mobility of 10 ¹³ cm ^-3 and an electron mobility of 105000 cm ² / VS could be grown (Y. Kawaguchi et.a.
l.Inst.Phys.Conf.Ser. (Physics Society Conference Series), 79 ,
79 (1985)).

(3) Selective growth is possible using a dielectric film such as SixNy or SixOy as a mask. In the conventional MBE method, polycrystalline protrusions were formed on the entire surface of the dielectric film, but in the gas source MBE method, no precipitation was observed at all or only granular precipitates were observed.

(4). According to the conventional MBE method, it is possible to grow a multi-element mixed crystal containing two or more kinds of group V elements, which has been difficult to grow, with good controllability.

(5). Since organic metal can be used as a raw material of aluminum, the problem of short life of molecular beam cell of aluminum, which has been a problem in the conventional MBE method, can be solved.

As described above, as a method of controlling the molecular beam intensity in the gas source MBE device which has been reported to date, there is a high precision leak valve (variable leak valve) or a mass flow controller (mass flow controller).

Fig. 4 shows the variable leak valve (hereinafter VL
Gas source M using V) for molecular beam intensity control
1 is a configuration diagram of a BE device, which is a device diagram when an InP crystal is grown. In the figure, the growth chamber 1 is exhausted by an exhaust pump 3 via a gate valve 2. A raw material tank 4 containing, for example, phosphine (PH ₃ ) as an organic compound gas containing a Group V element is connected to the growth chamber 1 through a gas supply pipe 5, and the phosphine is connected by VLV 6 connected to the pipe 5. The amount of introduction is adjusted, and it is jetted onto the heated growth substrate 8 through the thermal decomposition cell 7 heated to about 800 ° C. A cylinder 9 containing, for example, triethylindium (TEIn) as an organometallic gas containing a group III element is connected to the growth chamber 1 through a gas supply pipe 5 and is connected to the pipe 5.
It is ejected onto the growth substrate 8 through the VLV 10 and the molecular beam cell 11.
In addition, 12 is a liquid nitrogen shroud. In this case, the molecular beam intensities of phosphine and triethylindium are individually adjusted by the reading of the ion gate 13, but the accuracy and reproducibility are not so good and are about 5%. On the other hand, in order to grow lattice-matched InxGa ₁ −xAs (x0.53) on an InP substrate, which has been attracting attention as a material for high-speed electronic devices or long-wavelength optical devices in recent years, organic metals containing In and Ga are required. The molecular beam intensities must be controlled with an accuracy of at least about 1% or less with good reproducibility. Therefore, it is difficult to grow a crystal, such as InxGa ₁ -xAs, which requires a strict composition control in a growth system in which the molecular beam intensity is controlled by such VLV6,10.

In addition, a gas source MBE that controls the molecular beam intensity by the above-mentioned mass flow controller (hereinafter abbreviated as MFC)
The device is (WTTsang.J.Appl.Phy. (Journal of Applied Physics),
58, 1415 (1985)). A block diagram of the apparatus is shown in FIG. 5, and the same or corresponding portions as those in the above-mentioned figures are designated by the same reference numerals. In the figure, as a group III source 14a, 14b containing a group III element, an organic metal (TEIn, T
MIn, TEGa, TMGa), V group source 15a, 15b containing V group element
The organic compounds (TEP, TMAs) are used respectively.
The group V sources 15a and 15b are introduced into the growth chamber 1 by directly changing the flow rate through the MFC 16 to grow the group V sources. As in the case of the growth method, H ₂ or Ar is used as a transport gas, and the flow rate is changed through the MFC 16 and introduced into the growth chamber 1 for growth. Reference numeral 17 is a stop valve.

In such a configuration, the VLV 6,10 described in FIG.
Unlike the case of using, it is possible to adjust the molecular beam intensity with an accuracy within an error of about 1%, and it becomes possible to grow a crystal that requires strict composition control.

[Problems to be solved by the invention]

However, in the gas source molecular beam crystal growth apparatus configured as described above, the organic metal as the group III sources 14a and 14b generally has a low vapor pressure, and a large amount of transport gas is required to obtain a desired gas flow rate. And For example, InxGa ₁ −
In the aforementioned report on the growth of xAs, the group III source 14a,
The flow rates of TEGa + H ₂ (35 ° C) and TMIn + H ₂ (37 ° C) as 14b are 17.5 _SCCM and 8.4 _SCCM , respectively. That is, the flow rates of the organic metals contained therein are slightly 0.25 _SCCM and 0.13 _SCCM , and the remaining most 25.5 _SCCM is the flow rate of H ₂ . In this case, for example, even if an exhaust pump of 1000 l / sec is used, the pressure in the growth chamber 1 is about 3 with only the group III sources 14a and 14b.
If the V group sources 15a and 15b are added in a large amount due to a pressure of × 10 ^-4 Torr, the pressure condition is likely to deviate from the molecular beam region. There was a problem that the pump became large. Further, since the MFC 16 controls the flow rate of the mixed gas of the organic metal and the transport gas, it is said that the vapor pressure fluctuation of the organic metal, that is, the temperature fluctuation of the cylinder 9 accommodating the organic metal changes the composition of the grown crystal. There was a problem.

Therefore, the present invention has been made in view of the above-mentioned conventional problems, and an object thereof is to accurately control the molecular beam intensity of an organic metal, and to eliminate the need for a large exhaust pump. It is to provide a crystal growth apparatus.

[Means for solving problems]

The gas source molecular beam crystal growth apparatus according to the present invention is provided with an organic metal gas supply path connected between a molecular beam cell for irradiating a growth substrate with an organic metal molecular beam and an organic metal gas raw material container, the raw material container side In addition, a mass flow rate control device having a flow rate control valve and a flowmeter side sensor on the molecular beam cell side is provided.

[Action]

In the present invention, since the mass flow rate control device is connected to the metal-organic gas supply path, it is possible to perform highly accurate control for a minute gas flow rate. In addition, since the flow rate of the organic metal itself is controlled, it is not necessary to control the temperature of the container containing the organic metal with high accuracy.

〔Example〕

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

FIG. 1 is a block diagram showing an embodiment of a gas source molecular beam crystal growth apparatus according to the present invention. In this figure, InxGa ₁ -xAs is shown.
FIG. 3 is an apparatus diagram in the case of performing epitaxial growth, in which the same or corresponding parts as those in the above-mentioned figures are designated by the same reference numerals. In the figure, for example, 100% arsine (AsH ₃ ) is contained as a hydride gas containing a group V element in the organic compound gas raw material tank 4, and two organometallic gas cylinders 9a are provided.
In the 9b, for example, TEGa and TMIn are contained as organometallic gases containing group III elements. In the gas supply pipe 5 connecting the organic compound gas raw material tank 4 and the pyrolysis cell 7, a stop valve 17 is connected to the pyrolysis cell 7 side and an MFC 16 is connected to the organic compound gas raw material tank 4 side. There is. In addition, the organometallic gas cylinders 9a, 9
In the gas supply pipe 5 connecting the b and the corresponding molecular beam cells 11a, 11b, respectively, a stop valve 17 is provided on the molecular beam cells 11a, 11b side, and a mass flow controller (hereinafter referred to as a mass flow controller on the organometallic gas cylinders 9a, 9b side). Each of them is abbreviated as MFC) 18. As shown in FIG. 2, the MFC 18 has a flow rate adjusting valve 18b connected near the gas inlet side 18a and a flow rate measuring sensor 18e having a sensor tube 18d inside near the gas outlet side 18c. The conventional MFC16
And these arrangements are the opposite.

The gas source molecular beam crystal growth apparatus configured as described above is a molecular beam cell in which each metalorganic gas TEGa, TMIn stored in the metalorganic gas cylinders 9a, 9b corresponds via the MFC 18.
It is supplied to 11a and 11b and is irradiated to the growth substrate 8. In this case, the outlet side 18c of the MFC 18 is in a high vacuum state, and the pressure on the inlet side 18a thereof is substantially equal to the vapor pressure of the organometallic gas. Normally, the flow measurement sensor 18e in the MFC18 is 100-150 ℃
Since it is heated to a certain extent, like the conventional configuration MFC16,
If the flow rate measuring sensor 18e is present in the vicinity of the inlet side 18a, the time during which the organometallic gas that is easily thermally decomposed receives heat becomes long,
For example, the decomposition products such as C ₂ H ₄ and CH ₄ accumulate on the upstream side of MFC 16, so that the molecular beam intensity of the organic metal itself fluctuates, or the metal formed by decomposition decomposes the sensor tube 18d.
It becomes difficult to perform stable operation due to clogging. However, in the MFC 18 shown in FIG. 2, since the inside of the flow rate measuring sensor 18e has a high degree of vacuum, it is possible to measure a minute flow rate, and the time when the organometallic gas receives heat is short, so the effect of thermal decomposition Since there is almost no, it can operate stably over a long period of time. The MFC 16 connected to the hydride gas raw material tank 4 can be of any type. FIG. 3 shows TEGa stored in the above-mentioned two metal-organic gas cylinders 9a and 9b, respectively.
And the ratio of the TMIn flow rate to the sum of the TMIn flow rates obtained
This figure shows the relationship with the composition x of the InxGa ₁ -xAs crystal. In order to epitaxially grow InxGa ₁ -xAs (x = 0.53) with lattice coupling to InP, an organometallic gas containing a group III element is used. It is necessary to control the intensity of the molecular beam of MFC1 within 1%, but as shown in Fig. 3, the MFC1 of TEGa and TMIn
By adjusting the controlled flow rate by 8, it was possible to easily obtain a crystal with a composition ratio of 0.53 with good reproducibility.

Further, according to such a configuration, since the transport gas such as H ₂ or Ar is not used for transporting the organometallic gases TEGa and TMIn in the pipe 5, a relatively small exhaust rate of about 500 l / sec is achieved. Even with a pump, the pressure during growth is about 1x
It was 10 ^-4 Torr, and was mainly a thermal decomposition product of hydrogenated arsine.

In addition, in the above-described examples, the gas source MBE growth of Inx and Ga ₁ -xAs was described, but the present invention is not limited to this, and it is applicable to other crystalline and non-crystalline growth. Needless to say.

〔The invention's effect〕

As described above, according to the present invention, the raw material container side is provided in the organometallic gas supply path connecting between the molecular beam cell for irradiating the crystal growth substrate with the organometallic molecular beam and the organometallic gas raw material container. By combining a mass flow controller with a flow rate control valve and a flow rate measurement sensor on the molecular beam cell side, a minute gas flow rate can be controlled with high precision, so the molecular beam strength of the organometal can be accurately measured. It is possible to control, and since a transport gas for transporting the metal-organic gas raw material is unnecessary, it is possible to perform crystal growth with excellent composition control using a small exhaust pump. Is obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a gas source molecular beam crystal growth apparatus according to the present invention, FIG. 2 is a block diagram showing the mass flow controller of FIG. 1, and FIG. 3 is a source gas flow rate ratio ( TMIn
/ (TMIn + TEGa)] and the composition x of the InxGa ₁ -xAs crystal are shown in FIGS. 4, 5 and 5, which are schematic views showing a conventional gas source molecular beam crystal growth apparatus. 1 ... Growth chamber, 2 ... Gate valve, 3 ... Exhaust pump, 4 ... Hydride gas raw material tank, 5 ... Gas supply pipe, 7 ... Pyrolysis cell, 8 ... Growth substrate, 9a, 9b
…… Organometallic gas raw material tank, 11a, 11b …… Molecular beam cell, 12 …… Liquid nitrogen shell, 14a, 14b …… III group source, 15a, 15b …… V group source, 16 …… MFC, 17 …… Stop valve, 18 …… Mass flow controller (MFC), 18a …… Inlet side, 18b …… Flow adjustment valve, 18c …… Outlet side, 18d
…… Sensor tube, 18e …… Sensor for flow rate measurement.

Claims (1)

[Claims] 1. A gas source molecular beam crystal growth apparatus comprising a growth substrate and a molecular beam cell for irradiating the surface of the growth substrate with a molecular beam of an organometallic gas in an exhausted growth chamber. In the organometallic gas supply path connecting the cell and the organometallic gas raw material container, a mass flow control device having a flow control valve on the organometallic gas raw material container side and a flowmeter side sensor on the molecular beam cell side was provided. A gas source molecular beam crystal growth apparatus characterized by the above.