Solid Film Growth Apparatus

FIG. 1 is a sectional view of one example of the compound semiconductor growth apparatus of the present invention.

FIG. 2 is a sectional view of a conventional MBE apparatus.

FIG. 3 is a sectional view of a conventional MO-MBE apparatus.

In the solid film growth apparatus of the present invention as shown in FIG. 1, introduction and interception of raw material gas are carried out by opening and closing operations of switching devices 10. Gas introduction chambers 9 can be evacuated by evacuation facilities 16 during growth of the compound semiconductor and at least during the time the switching devices are being closed. When switching devices 10 are closed, raw material gases are completely intercepted and not introduced into growth chamber 1. In this case, the entire raw material gases flowing into gas introduction chambers 9 are evacuated by evacuation facilities 16. When switching devices 10 are opened, raw material gas molecules go straight in growth chamber 1 and reach substrate 3. In this case, since gas introduction chambers 9 are evacuated by evacuation facilities 16 at least until just before opening of the switching devices, flow of residual gas in gases introduction chambers 9 into growth chamber 1 when switching devices 10 are opened can be ignored. Thus, the introduction of the raw material gases into the growth chamber and interception of the gas can be performed under much better controllability as compared with the conventional MO-MBE method and it becomes possible to form a solid film, e.g., a compound semiconductor heterojunction, having an extremely abrupt interface similar to that obtained by the conventional MBE method. Furthermore, since gas is employed as a raw material, the process for replenishment of raw material as in the MBE method is not necessary and the growth method of the present invention is also superior in mass-productivity and reproducibility. Any devices can be employed as switching devices 10 as far as they can intercept raw material gases and usually, a device called a gate valve or the like is used. It is necessary that gas introduction chambers 9 can be evacuated at least during switching devices 10 being closed, but it may be evacuated throughout the growth of the compound semiconductor.

In one example of the present invention, formation of an AlGaAs/GaAs/AlGaAs heterojunction will be explained with reference to FIG. 1. However, the invention is also applicable to growth of any solid film, e.g., an elemental, e.g., silicon semiconductor film, a metal film or an insulative film.

As raw material gases, AsH.sub.3, trimethyl gallium (TMG) and triethyl aluminum (TEA) are respectively introduced into gas introduction chambers 9 from raw material gas introduction pipings 13. In this case, all switching devices are opened. AsH.sub.3 is cracked by cracking cells 15. Temperature of substrate 3 is about 560.degree. C. Under this condition, AlGaAs grows on substrate 3 At this point, when switching device 10 of the gas introduction chamber which introduces TEA is closed, GaAs begins to grow on the substrate. When the switching device 10 is again opened, AlGaAs grows on substrate 3 to obtain the desired AlGaAs/GaAs/AlGaAs junction.

In the above procedure, when the flow rate Q of TMA is 5.times.10.sup.-3 .multidot.Torr.multidot.sec.sup.-1 and evacuation speed S of evacuation facility 16 at ultimate pressure of 1.times.10.sup.-8 Torr or less is 500.multidot.sec.sup.-1, degree of vacuum p in gas introduction chamber 9 under the condition of the TMA switching device being closed is sufficiently high, i.e.,

Therefore, when switching device 10 is opened again, introduction of residual gas in gas introduction chamber 9 into growth chamber 1 has substantially no effect on the growth. It has been confirmed by a photoluminescence method that abruptness of the thus obtained AlGaAs/GaAs interface and GaAs/AlGaAs interface are of about two monolayers.

In this example, the evacuation facility for the growth chamber and that for the gas introduction chamber are separately provided, but these may be common to both chambers as stated before.

As mentioned previously, the present invention can also be used to grow other solid films. For example, a silicon semiconductor film can be grown according to the present invention using, e.g., SiH.sub.4 as a gas source. A gas source Si MBE apparatus is disclosed in H. Hirayama et al, "Gas source silicon molecular beam epitaxy using silane," in Applied Physics Letters. Vol. 51, No. 26, 28 Dec. 1987, pages 2213-2215, the contents of which are incorporated herein by reference. In this apparatus, a subchamber is used to control the flow rate of the SiH.sub.4 gas source by changing the subchamber pressure.

A gas source in combination with a solid source may also be used. For example, a GaAs film can be grown according to the present invention using a gas source such as AsH.sub.3 in combination with a source of Ga in a solid state. Similarly, an InP film can be grown according to the present invention using a gas source such as PH.sub.3 in combination with an In source in a solid state. Use of such gas sources in combination with a source in a solid state is disclosed in M. B. Panish, "Molecular Beam Epitaxy of GaAs and InP with Gas Sources for As and P," in Journal of the Electrochemical Society: Solid State Science and Technology, Dec. 1980, pages 2709-2733, the contents of which are incorporated herein by reference.

According to the present invention, interception and introduction of raw material gases into the growth chamber can be performed with high controllability and hence, abrupt interfaces such as a compound semiconductor heterojunction having abruptness comparable to that formed by the compound semiconductor growth method using solid sources, namely, so-called MBE method can be obtained. Besides, since gaseous raw materials are used, the process for replenishment of raw materials as required in the MBE method is unnecessary in the present invention and thus, the present method is also superior in mass-productivity and reproducibility.