RELATED APPLICATIONS

This application is related to the following co-pending applications assigned to the same assignee as this applica¬ tion. These applications are incorporated herein by ref¬ erence.

The applications of Rozalie Schachter and Marcello Viscogliosi relating to VACUUM DEPOSITION PROCESSES EMPLOY¬ ING A CONTINUOUS PNICTIDE DELIVERY SYSTEM, Serial No. 581,103, filed February 17, 1984; Mark A. Kuck and Susan W. Gersten relating to CONTINUOUS PNICTIDE SOURCE AND DELIVERY SYSTEM FOR FILM DEPOSITION, PARTICULARLY BY CHEMICAL VAPOR DEPOSITION, Serial No. 581,102, filed February 17, 1984; Mark A. Kuck and Susan W. Gersten relating to METHOD OF PREPARING HIGH PURITY WHITE PHOSPHORUS, Serial No. 581,105, filed February 17, 1984; and, Mark A. Kuck, Susan . Ger¬ sten, John A. Baumann, and Paul M. Raccah relating to HIGH VACUUM DEPOSITION PROCESSES EMPLOYING A CONTINUOUS PNICTIDE DELIVERY SYSTEM, Serial No. 581,104, filed February 17, 1984.

This application is a continuation-in-part of Serial Nos. 581,102, 581,105, and 581,104.

TECHNICAL FIELD

This invention relates to organometallic chemical vapor deposition (OMCVD) ; to the preparation of Ill-rV semiconduc¬ tors and surface layers; to binary, ternary and quaternary III-V semiconductors; and to sources of elemental pnictide gases. The application further relates to the manufacture of electronic semiconductor devices, electro-optical de¬ vices, and thin films.

BACKGROUND ART

All reported commercial organometallic chemical vapor deposition (OMCVD) processes for the preparation of III-V semiconductors involve the use of phosphine or arsine as the pnictide (Group V) _ source. These materials are highly toxic and present difficulties in handling the sources, in the process, and in the residual gases produced that contain the toxic gases.

The preparation of III-V semiconductors via organome¬ tallic chemical vapor deposition (OMCVD) also has been plagued by the reactivity of the indium source — trimethyl indium (TMI) or triethyl indium (TEI) — with the Group V hydrides, PH_ and AsH,. Undesirable polymer formation is especially pronounced in the growth of indium compounds including arsenides, phosphides and antimonides using either TMI or especially TEI. Problems have been reported in growing gallium indium arsenide due to the "parasitic" reactions of TMI with arsine.

These problems may be circumvented by the utilization of the trialkyl phosphine adduct of TMI ( (CH-) -InP(C_H ₅ ) ) . By thus preventing the reaction of the Lewis acid (TMI) with arsine in the vapor phase, good quality GalnAs can be prepared.

Others have reported that they have overcome the problem of growth of Ga In, As alloys ,lattice-matched to InP substrates by using trimethyl arsine (TMAs) in place of arsine (4) . Cooper also has been successful in making quaternary Al Ga In, _ As layers over a wide range of solid compositions on GaAs substrates using TMAs as the arsenic source (5) .

InP can be produced by using the triethyl phosphine

((C ₂ H ₅ ) ₃ P) adduct of trimethyl indium ((CH ₃ ) In)). This volatile adduct is transported to the hot substrate where it reacts with the phosphine to form InP. The dissociated

(C_H_)_P is carried out of the reactor and does not provide a source for the phosphorus which ends up in the InP

epilayer. Hence, the role of the < 2 ^H _ς )3 ^{P is to} prevent reaction of PH., with ^In before it is transported to the hot region near the substrate.

Others have gotten around the problem of the "premature" reaction of R.In with PH_ by the use of a phosphine pyrolysis oven which, operating at 760 ^β C, converts the phosphine to a mixture of P. + H- before injection into the reactor. Hydrogen is used as the carrier gas. The preparation of device-quality homoepitaxial InP layers by this process has been reported. P. in the reactor prevents degradation of the InP surface during thermal treatment.

The problems encountered in using arsine in the preparation of III-V materials containing indium has been demonstrated. One solution is the use of the organo-arsenic compound, trimethyl arsine, as the arsenic source. The major problem with this approach is the fact that there presently is no commercial source of high purity trimethyl arsine.

DISCLOSURE OF THE INVENTION

We have overcome the problems involved with the use of highly toxic arsine and phosphine and the problems involved in obtaining high purity pnictide compounds such as trimethyl arsine or the requirement of the use of adducts of organoindium compounds. We use pnictide bubblers as the sources of elemental pnictide (group V) gases in a carrier gas together with organometallic sources of group III compounds in carrier gas such as N_ or Ar ^~ . The group III and group V gases are suppled to a conventional chemical vapor deposition reactor together with hydrogen gas where they react to form III-V semiconductors. Alternatively, hydrogen may be used as the carrier gas. Preferable such an all hydrogen atmosphere would provide monoatomic hydrogen at the reaction surface.

OBJECTS OF THE INVENTION

It is therefore an object of the invention to provide III-V semiconductor materials.

Another object of the invention is to eliminate the use of arsine and phosphine in the production of such materials.

A further object of the invention is to eliminate the use of pnictide compounds in the production of such materials.

Other objects of .the invention will in part be obvious and will in part appear elsewhere in this application.

The invention accordingly comprises an apparatus and method and products produced thereby comprising the features of construction, selection of elements, and arrangement of parts; and the several steps and the relation of one or more of such steps with respect to each of the others; and features, and properties of the products which will be exemplified in the apparatus, method and productd herein¬ after described. The scope of the invention is indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and objects of the invention reference should be made to the following detailed description in connection with the accompanying drawings in which:

Figure 1 is a schematic diagram of apparatus employing the method according to the invention; and

Figure 2 is a schematic cross section of a semiconduc¬ tor layer on a substrate produced according to the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Apparatus according to the invention for chemical vapor deposition is shown in Figure 1. It comprises a reactor vessel, generally indicated at 4, an elemental pnictide bubbler source generally indicated at 6, and an organome¬ tallic group III bubbler source generally indicated at 8.

The reactor 4 is conventional as is the organometallic group III source 8. The pnictide (group V) source 6 is constructed in accordance with the above-identified co- pending applications Serial Nos. 581,102, 581,104, and 581,105.

The conventional chemical vapor deposition reactor vessel 4 may be formed of inert material such as Quartz and comprises a long tube 10 and a cap 12 sealed thereto. Cap 12 supports a rod 14 having a substrate holder 16 at the end thereof. The substrate holder 16 and the substrate therein (not shown), are heated by the RF heater coil 18. A thermocouple (not ^" shown) monitors the temperature of the substrate within the substrate holder 16. The reactor vessel 4 is provided with a exhaust tube schematically indicated at 20.

The organometallic source 8 is conventional and com¬ prises a vessel 22 for containing the organometallic ma¬ terial such as trimethyl gallium or trimethyl indium which are in liquid or solid form. The vessel 2 _^ 2 is surrounded by a constant temperature bath 24. Carrier gas is supplied on line 26 through metering valve 28 and bubbles through the appropriate trimethyl group III compound in the vessel 22. The resulting gaseous trimethyl compound is carried by the carrier stream through metering valve 30 and line 32 to the reactor 4. Additional carrier gas dilutant is supplied on line 34 through shutoff valve 36 to line 32. Hydrogen .gas is supplied on line 38 through shutoff valve 40 to line 32 unless hydrogen is used as the carrier gas. Flows to the lines 26, 34, and 38 and thus the total flow in line 32 are controlled by metering valves (not shown) upstream of the shutoff valves. Pnictide. gas (e.g. P. or As.) is supplied

to reactor 4 from the pnictide source 6 constructed in accordance with the above-identified co-pending patent applications. It comprises a vessel 44 surrounded by a constant temperature bath or furnace 46 for liquid white phosphorus or granular arsenic, depending upon the product desired. White phosphorus prepared in accordance with the above-identified Serial No. 581,105 is preferred. Carrier gas is bubbled through the pnictide in the vessel 44 and is supplied on line 48 through shutoff valve 50; the exiting pnictide and carrier gases being carried on line 52 to the reactor 4. Additional dilutant carrier gas is supplied on line 54 through shutoff valve 56. Flows to the lines 48 and 54 and thus the total flow in line 52 are controlled by metering valves (not shown) upstream of the shutoff valves.

We call both sources 6 and 8 bubblers in that the carrier gas, e.g. nitrogen, argon or hydrogen, is bubbled through the appropriate liquid or granular solid in order to produce the reaction gases mixed. with the carrier gas. In both cases the bubblers are provided with a bypass valve 60 and 62 so that gas flows can be established prior to the initiation of the "bubbling" process.

For example, we have demonstrated the chemistry of the process which produces growth of GaAs on a GaAs substrate or glass

Ga(CH ₃ ) (g) + 1/4 As ₄ (g) [N ₂ /H ₂ ]GaAs (s) + waste gases.

To produce crystalline GaAs on GaAs^ liquid trimethyl gallium and powdered solid arsenic are used as sources in the "bubbler" delivery system. N_ is used as the carrier gas through both the arsenic and trimethyl gallium (TMG) bubblers. Additional N_ gas is added downstream of both bubblers to assist in the flow of materials to the reactors and dilute them prior to mixing. The two reactant streams are separately plumbed into the reactor wherein mixing occurs. H- is added to the TMG flow, again, downstream of the bubbler but prior to entrance to the reactor. The total flow is used to fix the velocities of gases through the reactor.

The TMG line is essentially at ambient temperature. The bubbler is immersed in a bath which is thermostatically controlled. The flow through the bubbler and its tempera¬ ture fix the flux of TMG. In contrast, the arsenic line is heated as indicated by hatching at 64 to prevent condensa¬ tion of the As. gas species generated in the arsenic bub¬ bler. The latter is supported in a furnace. The tempera¬ ture of the furnace, the flow of carrier gas through the bubbler, and the geometry of the bubbler are used to fix the flux of As.. The pressure in the reactor 4 is maintained in the conventional range for OMCVD of about one atmosphere.

The total flow has been varied between 1.7 and 2.9 liters/min.; the hydrogen flow has been 14 to 22% of the total; the flow through the As bubbler has been varied from 90 to 160 ml/min., while the temperature of the As bubbler has been held between 410° and 435°C. The As feed line has been held within 50°C of the bubbler temperature. Nitrogen flows through the TMG bubbler have varied from 1.0 to 1.5 ml/min. , while the bubbler bath temperature has varied from -20 to -5°C. Substrate temperatures have been varied from 500° to 1000°C. The specific parameters for a typical run are:

T _sub =900°C, flow _TMG =1.5 ml/min.,

^Tem P _T MG T 7 ¹⁹ ° ^C '

Flow As-bubbler = 160 ml/min..

Temp As = 430°C,

Total flow = 2841 ml/min.,

H ₂ % = 20%

In preparing" indium phosphide, trimethyl indium would be utilized in the organometallic source 8 and phosphorus in the phosphorus source 6. Again,, hydrogen would be added to the organometallic gas stream.

Other known organo etallics may be used in these processes such as the triethyls I (C_H_) or GafC-H _^ )...

Figure 2 shows a product of the process of the invention in cross section comprising a substrate 70 on which is deposited a semiconductor layer 72 by the process of the invention.

We have successfully grown films of gallium arsenide on gallium arsenide substrates and films of gallium arsenide on Corning 7059 glass. This may be used as solar cells for example. Other III-V semiconductor layers such as indium phosphide could be grown on appropriate substrates, such as indium phosphide or glass. Other binary, ternary, and quaternary III-V layers could be grown by employing the appropriate elemental pnictide (group V) , e.g. phosphorus and arsenic, and group III organometallic compounds contain¬ ing gallium, indium, and aluminum, in the bubblers 6 and 8 of Figure 1. If more than one group V element is required, then two group V bubblers, constructed as bubbler 6 in Figure 1, would be utilized. If two or more group III components were desired in a layer, then two or more organo¬ metallic group III bubblers, constructed as bubbler 8 in Figure 1, would be utilized.

We also contemplate that group III halide might be employed in the group III bubbler 8, such as indium mono- chloride or gallium trichloride.

In another alternative embodiment of the invention we contemplate utilizing hydrogen as the carrier gas in the group V bubbler 6, and in the group III bubbler 8 when organometallic sources are employed.

In another alternative embodiment of the invention hydrogen would be used exclusively as the carrier gas so that the reaction in the reactor 4 is carried out in an exclusive hydrogen atmosphere. Preferably, at least some of the hydrogen would be monoatomic hydrogen obtained through cracking by means of a plasma discharge, heated filament, laser illumination or the like.

The reactor 4 may be provided with coaxial inlets such as disclosed in Figure 50 of U.S. Patent No. 4,508,931 for the group III compound gases and the elemental group V gases to facilitate proper mixing before being presented to the deposition surface.

The thickness of the films produced depend upon the time that the reaction is carried ^" out. We have produced

films up to 2 microns in thickness. Much thicker films could be made by lengthening the reaction time.

It will thus be seen that the objects set forth above among those made apparent from the preceding description are efficiently attained and since certain changes may be made in the above articles and in carrying out the above methods and the product set forth without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawing shall _' be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described and all state¬ ments of the scope of the invention which as a matter of language might be said to fall therebetween.

Particularly it is to be understood that in the claims ingredients or compounds recited in the singular are in¬ tended to include compatible mixtures of such ingredients wherever the sense permits.

Having described our invention what we claim as new and desire to secure by Letters Patent is: