METHODS FOR METAL-ORGANIC CHEMICAL VAPOUR DEPOSITION USING SOLUTIONS OF INDIUM-ALKYL COMPOUNDS IN HYDROCARBONS

Abstract

The invention relates to methods for producing an indium-containing layer by metal-organic vapor phase deposition, wherein the indium-containing layer is generated on a substrate in a reaction chamber, wherein the indium is delivered to the process in the form of an indium-containing precursor compound with the formula InR.sub.3, wherein the radicals R, independently of one another, are selected from alkyl radicals with 1 to 6 C atoms, characterized in that the delivery of the indium-containing precursor compound takes place in a solution that contains a solvent and the indium-containing precursor compound dissolved therein, wherein the solvent has at least one hydrocarbon with 1 to 8 carbon atoms.

The invention also relates to a solution consisting of a compound of formula InR.sub.3, wherein R are selected independently of one another from alkyl radicals with 1 to 6 C atoms, and at least one hydrocarbon having 1 to 8 carbon atoms, uses of the solution for producing an indium-containing layer by metal-organic vapor deposition, and devices for executing the method.

Claims

1.-15. (canceled)

16. A method for producing an indium-containing layer by metal-organic vapor phase deposition, wherein the indium-containing layer is generated on a substrate in a reaction chamber, wherein the indium is delivered to the process in the form of an indium-containing precursor compound with the formula InR.sub.3, wherein the radicals R, independently of one another, are selected from alkyl radicals with 1 to 6 C atoms, wherein the indium-containing precursor compound is delivered in a solution that contains a solvent and the indium-containing precursor compound dissolved therein, wherein the solvent has at least one hydrocarbon with 1 to 8 carbon atoms.

17. The method according to claim 16, wherein the metal-organic vapor deposition is a metal-organic vapor epitaxy.

18. The method according to claim 16, wherein the precursor compound is trimethylindium.

19. The method according to claim 16, wherein the solvent has at least one alkane and/or an aromatic.

20. The method according to claim 16, wherein the solvent consists of hydrocarbons with 5 to 8 carbon atoms, wherein the solvent is preferably pentane, hexane, heptane, octane, toluene, benzene, xylene, or a mixture thereof.

21. The method according to claim 16, wherein the share of the precursor compound in the solution is 5 to 60 wt %.

22. The method according to claim 16, wherein the solution is converted into the vapor phase using a direct evaporator before introducing it into the reaction chamber.

23. The method according to claim 22, wherein the direct evaporator has a temperature of 0 C. to 100 C.preferably, between 10 C. and 50 C.and/or a pressure of 50 mbar to 1200 mbar.

24. The method according to claim 22, wherein the solution is converted into the vapor phase before introducing it into the reaction chamber.

25. The method according to claim 24, wherein the direct evaporator has a mixing chamber in which the vapor phase is mixed with the carrier gas.

26. The method according to claim 22, wherein the direct evaporator has a liquid flow rate regulator, a gas flow rate regulator, a mixing chamber, and a mixing valve.

27. The method according to claim 16, wherein at least one additional reactive substance is delivered into the reaction chamber.

28. (canceled)

29. (canceled)

30. (canceled)

Description

[0067] FIG. 1 shows by way of example a device according to the invention for performing the method of the Invention.

[0068] FIG. 1 shows by way of example and schematically a device for performing the method of the invention. The solution is introduced into the method through an intake 1. In this process, a liquid solution of trimethylindium (10 wt-%) in C5- to C8-alkanes or in C6- to C8-aromatics could be used. The solution is conducted over liquid feed lines 6 into a direct evaporator 2, which has a heating device 8 and a mixing chamber 9. The volume of liquid is controlled and measured using a liquid flow rate regulator 5, which is a component of the direct evaporator or can be connected in front of this. In addition, the metering can be performed using a valve 3. In a direct evaporator 2, the solution is completely converted into the gas phase by setting suitable process parameters, such as temperature and pressure, wherein a temperature of 20 C. to 80 C. is preferably set. The evaporation in this process preferably takes place directly in the mixing chamber, which is an integral part of the direct evaporator. The solution is mixed in the mixing chamber 9 with an inert carrier gas that is introduced through an inlet 11 and gas feed lines 16. The quantity of the carrier gas is controlled with gas flow regulator 12 and valve 13. Preferably, a direct evaporator 2 is used, which has the liquid flow rate regulator 5, the gas flow regulator 12, the mixing chamber 9, and the mixing valve 13 as integral components. The gas phase is introduced from the mixing chamber 9 over gas feed lines 16 into the reaction chamber 4optionally, over suitable additional process steps such as pressure stages. By way of known measures, the reaction and deposition of indium or the incorporation of indium into the mixed crystal on the surface of the heated substrate takes place in the reaction chamber 4. The reaction gas and the carrier gas flow through the reactor and are discharged into the exhaust gas system over gas outlet line 17. Additional reactive substances in the gas phase can be supplied to the reaction chamber over one or more additional gas feed lines 18, so as to produce coatings or mixed crystals from multiple elements.

[0069] The invention solves the its underlying problem. An improved, efficient, and relatively simple method for continuous production of indium-containing layers by metal-organic vapor phase deposition or epitaxy is proposed. Risks in the handling of solid pyrophoric alkyl-indium compounds are avoided or distinctly reduced by avoiding the use of a solution. Consequently, the explosion and ignition hazards are already reduced for the manufacturer of the alkyl-indium compound, who can prepare, store, and transport this directly in solution. Hazards are also avoided in metering, in filling the unit, and in executing the process.

[0070] The use of solutions in low-boiling liquids makes possible a marked increase in the mass flow rate of the indium compound in the gas phase. In contrast, high mass flow rates cannot be achieved in methods of the prior art with bubblers and solid alkyl-indium compounds, even in the form of suspensions, since the saturation of the gas phase with allylindium compounds is thermodynamically limited by the solid aggregation state and the dimensions of the bubbler. The use of solutions also allows for more accurate metering and flexible, rapid adjustment of the solution volume introduced to the process requirements. An additional advantage is that the regular replacement of solid cylinders with residues of pyrophoric alkyl-indium compounds necessary according to the prior art is not required. Therefore, the method can be performed continuously over long time periods. Because of the use of solutions, complete introduction of the starting substances into the process can take place, which is desirable for financial and environmental reasons. An additional advantage is that the solvent does not react and, therefore, can be processed and reused. The method is also financially advantageous, because low-boiling alkanes or aromatics are available in large quantities and are therefore inexpensive.

EXAMPLES

[0071] Deposition Conditions:

[0072] The depositions were carried out in an Aixtron AIX 200-GFR reactor system. Hydrogen (H2) with a flow rate of 6800 mL/min was used as the carrier gas. The depositions were carried out at 50 mbar. The temperature was calibrated based upon a comparison with the melting point of the aluminum-silicon eutectic (melting point 577 C.).

[0073] A solution of trimethylindium in toluene with a concentration of 30 mol % (also referred to as liquid in the following), trimethylgallium (DockChemicals), and trimethylaluminum (EMF) served as group III sources; tert-butylphosphine (DockChemicals) served as group V sources.

[0074] Two different layer types were deposited: [0075] 1) ((Al.sub.0.3Ga.sub.0.7).sub.0.5In.sub.0.5)P double heterostructure with a growth rate of 1.53 m/h. The ratio of group V to group III precursors was 96; the deposition temperature was 685 C. The layer thus deposited was used for the photoluminescence measurements. [0076] 2) ((Al.sub.0.7Ga.sub.0.3).sub.0.5In.sub.0.5)P multilayer structure for SIMS measurements. In this connection, different temperature profiles, as well as group V to group III precursor ratios were examined: V/III=25, 50 and 100, T=625, 655, 670, 685 C. The layer thus deposited was used for SIMS measurements (secondary ion mass spectrometry).

[0077] Photoluminescence Measurements:

[0078] The layers was examined for their photoluminescence by means of stimulation with an Nd-YAG laser. Two samples, which are used at the firm NAsP as a reference, served as a comparison. Their photo properties serve as upper or lower limits and are used for qualifying the samples. The measurement configuration is shown in FIG. 2.

[0079] Impurities and crystalline defects in the layers can be identified in photoluminescence spectra: The broader the photopeak (FWHM in Table 1) or the lower the radiated photo intensity (i.e., integrated intensity in Table 1), the worse the quality of the layer examined.

[0080] FIG. 3 shows photoluminescence spectra of the sample obtained using liquid In (27030, thick solid black line, above), of a comparison sample with pure trimethylindium as a comparative example (27026, thin solid black line), and of the two reference samples (Ref 1 and Ref 2, with dot-dashed or dotted lines).

[0081] As can be seen from FIG. 3 and Table 1, the layer which was deposited from liquid In lies, in terms of its properties, between (integrated intensity) or close to the two reference values (FWHM or half-width) and is therefore suitable for use as a precursor for indium-containing layers.

TABLE-US-00001 TABLE 1 Evaluation of the photoluminescence measurement of the AlGalnP-DH structures 27026 27030 Ref 1 Ref 2 Integrated 2.98 * 10.sup.4 8.68 * 10.sup.4 4.91 * 10.sup.3 1.69 * 10.sup.4 Intensity [a.u.] .sub.Peak [eV] 1.987 1.992 2.061 1.992 FWHM [eV] 0.0571 0.0643 0.0383 0.0603

[0082] SIMS Measurements:

[0083] Secondary ion mass spectrometry provides information as to which and how many Impurities are present in a sample.

[0084] The layers for the SIMS measurements (layer 2) were produced by means of depositions being effected on a substrate, with, for one, the deposition temperature for the depositions being gradually increased and, for another, the ratios of the concentrations of the group V- to group III sources being varied.

[0085] This means that a layer structure with 9 layers was deposited, each differing in their deposition temperature and the ratios of the group V to group III sources.

[0086] These ratios are shown as the bottom row of figures in the diagram in FIG. 4 (values of 100, 50, 100, 50, 25, 100, 50, 25, 100); the deposition temperatures are shown in the row of figures above.

[0087] For example, it can be seen that the progression of the black curve on the right-hand side has a high plateau, which is formed at deposition temperatures of 625 C., independently of the ratio of group V to group III sources.

[0088] With the aid of the oxygen/carbon integration rate, the person skilled in the art can, depending upon the group V/group III source ratios and the deposition temperatures, make statements concerning the purity of the layers and, therefore, the precursors used.

[0089] FIG. 4 shows the SIMS measurement of a sample obtained by using liquid In as an indium source. The conditions for layer deposition are provided above.

[0090] The oxygen content (solid line) and carbon content (dotted line) are shown in the SIMS spectrum. The layers examined were effected at varying temperatures (top row of figures in C.) and with varying group V to group III ratios (bottom row of figures). Surprisingly, no conspicuous integration of carbon or oxygen into the layers could be observed by means of SIMS measurements. The increased carbon integration at 655 C. and a ratio of 25 can be attributed to an insufficient disintegration of the group III precursors, an observation which is often made for depositions with trimethylindium. The increased oxygen integration in the temperature range of 625 C. can be attributed to oxygen impurities which were introduced from the group V precursors.

REFERENCE SYMBOLS

[0091] 1 Solution inlet [0092] 2 Direct evaporator [0093] 3 Valve [0094] 4 Reaction chamber [0095] 5 Liquid flow rate regulator [0096] 6 Liquid feed lines [0097] 8 Heating apparatus [0098] 9 Mixing chamber [0099] 11 Carrier gas feed [0100] 12 Gas flow rate regulator [0101] 13 Valve [0102] 16, 18 Gas inlet lines [0103] 17 Gas outlet line