JPH0670967B2 - Manufacturing method of zinc sulfide thin film - Google Patents

Description

The present invention relates to a method for producing a zinc sulfide (ZnS) thin film. More specifically, it relates to a method for producing a zinc sulfide thin film using a vapor phase thermal decomposition method (MOCVD method) of an organic metal.

[Conventional technology]

The MOCVD method is capable of producing high-quality compound semiconductor thin films and is highly producible in mass production. Therefore, the MOCVD method is a technology that has received a great deal of attention in the field of materials and devices for obto-electronics. Further, zinc sulfide is a II-VI group compound semiconductor having a large band gap and has been researched for many years as a material for a visible light emitting device, but it has not yet been possible to obtain a good quality bulk crystal or thin film. . This is because the melting point of zinc sulfide is as high as 1850 ° C (under 150 atmospheres), so it is necessary to manufacture it at a high temperature of 800 to 1000 ° C in order to obtain good quality crystals and thin films. For some reason.

(1) Since the manufacturing temperature is high, impurities are mixed into the crystal or the thin film from the manufacturing apparatus and the manufacturing atmosphere.

(2) Since the vapor pressures of the constituent elements zinc (Zn) and sulfur (S) are high, lattice defects are likely to occur due to lack of zinc or sulfur.

However, with the MOCVD method described above, ZnS crystal growth is possible even at a low temperature of 250 to 500 ° C, and the above-mentioned drawbacks 1 and 2 can be expected to be greatly reduced. The MOCVD method enables crystal growth at a low temperature because the organometallic compound used as a raw material is extremely reactive and can easily decompose even at a low temperature to supply zinc (Zn) atoms. Dimethylzinc (DMZ) or diethylzinc (DEZ) is usually used for growth of ZnS thin films by MOCVD.
The organometallic compound of Zn and hydrogen sulfide (H ₂ S) are used. Depending on the pressure in the reaction furnace when growing a thin film,
There are an atmospheric pressure method (J. Crystal Growth 59 (1982) 148-154) and a depressurization method (Jpn. JAP22 (1983) L583-L585). A conventional method of manufacturing a ZnS thin film by the MOCVD method and its principle will be described with reference to the atmospheric pressure MOCVD apparatus schematic diagram shown in FIG.

A rotatable column is provided in the center of a quartz glass reaction tube, and a SiC-coated carbon susceptor and a substrate are placed on it. The substrate is heated from the side of the reaction furnace by a high-frequency heating furnace, an infrared furnace, a resistance heating furnace, or the like. The substrate temperature is monitored by a thermocouple with the tip embedded in a carbon susceptor. The reaction tube is connected to the exhaust system and the exhaust gas treatment system via a valve. DMZ is a Zn Source: (CH _{3) 2} Zn or _{DEZ,: (C 2 H 5} ) 2
Zn is enclosed in a bubbler. Since DMZ and DEZ are liquids, they are bubbled by a carrier gas to be vaporized and then diluted with a carrier gas flowing therethrough, and then introduced into the reaction tube via. On the other hand, H ₂ S, which is the source of S, is enclosed in a cylinder and is introduced into the reaction tube after being diluted by the carrier gas flowing therethrough. Decompression MO
In CVD, a source gas is supplied while maintaining a reduced pressure inside the reaction tube by an exhaust system. The pressure in the reaction tube can be adjusted by the exhaust capacity of the exhaust system and the valve, and is usually several mmTorr to several tens To.
The reaction is carried out in a pressure range quite wide as rr. The valve remains closed as the gas passes through the exhaust system to the waste gas treatment system.

In actual growth, the temperature of the substrate is raised to a predetermined growth temperature while flowing a carrier gas, and then each raw material gas is introduced into the reaction tube to form a ZnS film on the substrate. it can.

The chemical reaction in the MOCVD method using DMZ or DEZ and H ₂ S as raw materials is represented by the following formula.

(CH ₃ ) ₂ Zn + H ₂ S → ZnS + 2CH ₄ − (C ₂ H ₅ ) ₂ Zn + H ₂ S → ZnS + 2C ₂ H ₆ − Reaction formula, is the temperature range used in the MOCVD method 250-500 ℃
In, it progresses extremely quickly. Usually H ₂ S to DMZ
Or, because it is supplied in large excess to DEZ, the reaction is
The rate is controlled by the supply amount of MZ or DEZ, that is, the amount of carrier gas for bubbling DMZ, DEZ and the temperature of DMZ, DEZ at that time. That is, the growth rate of the ZnS film can be controlled by the bubbling amount of the Zn source and the bubbling temperature when the substrate temperature is constant and H ₂ S is supplied in a large excess.

[Problems to be solved by the invention]

In the above-mentioned conventional MOCVD method, the reaction formula, easily progresses even at room temperature due to the reactivity of DMZ and DEZ. That is, DMZ and DEZ react with H ₂ S immediately to form ZnS. ZnS produced in the gas phase
Are deposited as agglomerates on the growth substrate as if it were snowing. In general, in order to grow a good quality crystal or thin film, it is necessary to set up a situation in which constituent atoms that reach the growth surface move on the surface and settle in the most energetically stable position. Is said. However, since the above-mentioned ZnS agglomerates are simply deposited on the growth surface, they have a significant adverse effect when trying to produce a good quality thin film. In order to prevent the formation of ZnS agglomerates due to the reaction of DMZ, DEZ and H ₂ S in the vapor phase, mixing of DMZ, DEZ and H ₂ S in the vicinity of the growth substrate is effective to some extent. Can be improved. In order to achieve the above-mentioned purpose, the gas introduction pipe shown in Fig. 1 functions to spatially separate DMZ, DEZ and H ₂ S so that they are not mixed near the substrate. A method of reducing the pressure inside the reaction tube is also under study. This is because by reducing the pressure, the linear velocity of the raw material gas flowing in the reaction tube is made larger than that at normal pressure, so that the air flow is kept in a laminar flow state and the gas is mixed only after reaching the substrate. There is. The above-mentioned measures taken to prevent the formation of ZnS agglomerates in the gas phase are basically to control the flow of the raw material gas so that the raw material gas is mixed near the substrate. . However, this policy is in a direction contradictory to the uniform mixing of the raw material gases, which is required when a thin film having uniform thickness and electrical characteristics is to be formed on a substrate of a certain size. Mass production and large substrate processing capability, which are major features, cannot be used. Moreover, suppressing the mixing of the raw material gases is a matter of degree, and ZnS generated in the gas phase is
The adverse effect of agglomerates on the growth film remains a problem even if the above-mentioned measures are taken. (J. Crystol Growth59
(1982) 148-154, Jpn. JAP (1983) L583-L585) [Means for Solving the Problem] A method for producing a zinc sulfide thin film according to the present invention is to use dialkyl zinc as a zinc source and hydrogen sulfide as a sulfur source. In the method for producing a zinc sulfide thin film on a substrate by the vapor phase pyrolysis method, a dialkylzinc in the vapor phase and a general formula RSR '(R and R'are alkyl groups) are used. It is characterized in that the adduct of both vapor phase is formed by mixing with the thio ether in vapor phase, and the adduct is used as the zinc source.

Further, when forming the adduct, an amount of the thio.
It is characterized by supplying ether.

Further, the dialkyl zinc and the thioether are mixed to form the adduct, the adduct is mixed with the hydrogen sulfide, and then the mixture is introduced onto the substrate. .

[Action]

The reason for the high reactivity of dialkylzinc and hydrogen sulfide is that the dialkylzinc and hydrogen sulfide adducts formed by the acid-base reaction resulting from the action of dialkylzinc as a Lewis acid and hydrogen sulfide as a Lewis base. Group-
The bond of zinc and the bond of sulfur-hydrogen are activated along with the formation of the adduct, and the bond is easily broken.
This is because -R is released. The S—H bond of hydrogen sulfide is accompanied by the formation of an adduct with dialkylzinc, It is considered that the S-H bond in the adduct is more easily broken than the S-H bond of hydrogen sulfide by causing such polarization. Therefore, it is expected that the stability of the adduct can be increased by introducing a substituent that reduces polarization in the S—H bond, that is, an alkyl group having an electron donating property, and prevents ZnS formation in the gas phase. It becomes possible. Furthermore, when hydrogen sulfide and thioether are compared, thioether having an electron-donating alkyl group has a stronger basicity as a Lewis base than hydrogen sulfide, so the formation constant of the adduct with dialkylzinc is also The use of thioether is larger than that of using hydrogen sulfide. Therefore, even if the adduct of dialkylzinc and thioether is allowed to coexist with hydrogen sulfide, the substitution reaction should be difficult to occur. The adduct of dialkylzinc and thioether is formed by mixing them, and then the adduct and H ₂ S are uniformly mixed and supplied to the heating zone, where ZnS is generated by decomposition of the adduct itself. Alternatively, the addition product is dissociated into dialkylzinc and thioether by heating, and the production of ZnS by the reaction of dialkylzinc and hydrogen sulfide is utilized again in the present invention. ZnS in the gas phase
This is the reason why the generation of can be suppressed.

〔Example〕

Hereinafter, the outline of the MOCVD apparatus used in the present invention will be described first, and then the content of the present invention will be described with reference to specific examples.

FIG. 2 shows a schematic diagram of the MOCVD apparatus used in the present invention.

A rotatable column is provided in the center of a quartz glass reaction tube, and a Sic-coated carbon susceptor and a substrate are placed on it. The substrate is heated from the side of the reaction furnace by a high-frequency heating furnace, an infrared furnace, a resistance heating furnace, or the like. The substrate temperature is monitored by a thermocouple with the tip embedded in the carbon susceptor. The reaction tube is connected to the exhaust system and the waste gas treatment system via a valve. The Zn source, dialkyl zinc, is enclosed in a bubbler. The carrier gas is bubbled while the bubbler is maintained at an appropriate temperature to vaporize the dialkylzinc, and the dialkylzinc is diluted with the carrier gas flowing through the carrier gas and then introduced into the reaction tube. The thioether is enclosed in a bubbler, vaporized by the bubbling of carrier gas, diluted with the carrier gas flowing through the thioether, and then merges. An adduct is formed at the confluence.
H ₂ S, which is the S source, is enclosed in a cylinder, diluted with the carrier gas flowing through the dilution line, and then merges with to mix with the already formed adduct.

In the above gas mixing step, the formation of the adduct is promptly promoted by making the supply amount of thioether excessive with respect to the dialkylzinc, and further, the equilibrium of the adduct formation reaction is moved toward the formation of the adduct. become. To further complete the formation of the adduct, lengthen the inlet tube between the dialkylzinc and the thioether and then the H ₂ S, or directly into the reaction tube without merging H ₂ S with. It may be introduced and the adduct and H ₂ S may be mixed in the reaction tube.

Although the vertical reactor is shown in FIG. 2, the basic structure is the same also in the horizontal reactor. However, instead of the rotation mechanism of the substrate, the uniformity of the film obtained by tilting the Sic-coated carbon susceptor and the substrate at an appropriate angle with respect to the gas flow can be ensured.

[Example 1] Gallium arsenide (GaAs) gallium arsenide (GaP) sliced and mirror-polished on a (100) plane and a plane having a deviation of 5 ° or 2 ° from the (100) plane to the (110) plane Etching is performed on the single crystal substrate of 1) after ultrasonic cleaning with trichloroethylene, acetone, and methanol. The etching conditions are as follows.

GaAs substrate H ₂ SO ₄ : H ₂ O ₂ : H ₂ O = 3: 1: 1 (volume ratio) 2 min at room temperature GaP substrate HCl: HNO ₃ = 3: 1 (volume ratio) 30 sec at room temperature Using pure water The etching was stopped, the product was washed with pure water and methanol, and then stored in Daiflon. The substrate is taken out of the diflon immediately before the reaction tube is set, and the diflon is dried and removed by dry nitrogen blowing. After the substrate is set, the inside of the reaction furnace is evacuated to about 10 ⁻⁵ Torr to remove the gas remaining in the system, and a carrier gas is introduced to return the system to normal pressure. The temperature rise is started while flowing the Argus. An infrared heating furnace was used for heating. As carrier gas, He with a purity of 99.9999% or H ₂ passed through a purifier was used. After the substrate temperature reaches the specified temperature and stabilizes, supply of raw material gas is started and ZnS
Perform film growth. The zinc source was diethyl zinc having a purity of 99.9999%, and the thioether was commercially available diethyl sulfur. The conditions are as follows. Substrate temperature 450 ℃ Distance from material inlet to substrate 20cm Diethyl zinc bubbling amount 100ml / min (2.3 × 10 ^-5 mol / min) at 0 ° C Diethyl sulfur bubbling amount 120ml / min (1.2 × 10 ^-4 mol) at 0 ° C / min) 2% H ₂ S diluted with He
100 ml / min (9.0 × 10 ⁻⁵ mol / min) total gas flow rate including carrier gas 4.5 l / min Growth time 90 min After growing for a predetermined time, supply of raw material is stopped and cooled. Flow He at 1-2 l / min during cooling. To prevent thermal etching of the substrate surface, 50% to 6% of H ₂ S diluted with 2% He is used.
It may be cooled while flowing about 0 ml / min. When the substrate returns to room temperature, the reaction furnace is evacuated to remove hydrogen sulfide remaining in the system. After returning the system to atmospheric pressure, the substrate is taken out. The thickness of the ZnS film obtained at this time was about 1 μm, and the growth rate was about 0.7 μm / hr.

The reference photograph shows the electron diffraction (RHEED) pattern of the ZnS film formed on the GaP substrate.

As shown in the reference photo, a clear diffraction spot appears, indicating that the ZnS film on the GaP substrate is a single crystal film. The X-ray locking curve is shown in FIG. The half-width of the locking curve is 1.0 degree, which indicates that the obtained ZnS single crystal film is a good quality film.

A similar electron diffraction pattern, X, was also obtained from the ZnS film on the GaAs substrate.
A line diffraction curve and an X-ray locking curve are obtained, and a high-quality single crystal film is grown like the GaAs substrate.
When the surface structure of the obtained single crystal film was observed with a scanning electron microscope, wrinkle-like irregularities having a width of about 1000Å were observed. On the surface of the ZnS single crystal obtained by the conventional method, irregularities having a period of several 1000Å to 1 μm were observed. (J. Crystal Growth59 (1982) 148-154., Jp
nJAP22 (1983) L583-L585) It can be seen that the ZnS film obtained according to the present invention has improved surface flatness.

[Example 2] Transparent quartz, which is an amorphous material, was sliced, mirror-polished, and then used as a substrate to form a ZnS film. After cleaning the brush with a weak alkaline cleaning solution, ultrasonic cleaning in pure water, alcohol, and diflon was sequentially performed on the quartz substrate according to the process and growth conditions shown in [Example 1], to form a ZnS film. It has grown. The ZnS film obtained by 90 min of growth had a thickness of about 7,000 Å and a growth rate of 0.5 μm / hr. The reason that the growth rate is lower than that of GaAs and GaP substrates is considered to be due to the use of an infrared furnace as a heating source. In other words, since the infrared absorption coefficient of transparent quartz is small, the actual temperature of the substrate surface will not change even if the temperature set by the thermocouple monitor is the same.
This is probably because it is lower than that of GaAs and GaP substrates.
The electron diffraction pattern of the obtained ZnS film showed concentric circles with shades, indicating that it was a polycrystalline film.
FIG. 4 shows an X-ray diffraction curve. It can be seen that the ZnS thin film on transparent quartz is a polycrystalline film with a remarkable orientation on the (111) plane. In the X-ray diffraction curve of the polycrystalline ZnS film obtained by the conventional method, when the film thickness is similar, (111)
Peak intensity was weaker than that of the ZnS film produced by the production method according to the present invention, and diffraction peaks from higher surfaces such as (311) (220) (200) (331) were also observed. With the manufacturing method according to the present invention, it is possible to manufacture a ZnS film having better orientation than the conventional method.

In the example, the example in which diethylzinc and diethylsulfur are mixed in a gas phase to form an adduct, the ZnS thin film manufacturing method according to the present invention is not limited to this example, and dialkylzinc may be dimethylzinc. Can be used. As the thioether used for forming the adduct, dimethylsulfur methyl, ethylsulfur, dipropylsulfur, etc. can also be used. Even when a dialkylzinc and a thioether other than those shown in the examples are used, they can be used under the same conditions based on the same principle as the case shown in the examples.

The substrate used for growth is Si, glass, transparent electrodes such as ITO on transparent quartz, Ta ₂ O ₅ , SiO ₂ , Si ₃ N ₄ , Al ₂ O ₃ , Sm.
Those having an insulating film such as ₂ O ₃ formed thereon can also be used in the same process as in the embodiment.

〔The invention's effect〕

As is clear from the examples, in the ZnS film manufacturing method according to the present invention, the adduct formed by the reaction of dialkylzinc and thioether and the inlet and the substrate for introducing H ₂ S are 20c.
A good quality ZnS film can be manufactured even though they are separated by m. This is because ZnS is produced by the reaction of dialkylzinc and H ₂ S in the gas phase from the mixing position of the adduct and H ₂ S to the inside of the downstream introduction tube, and from the introduction port to the heating region near the substrate. The thioether and dialkylzinc are highly suppressed by forming an adduct, which is nothing more than this. By the way, if dialkyl zinc alone is supplied as a Zn source without supplying thioether, it can be observed that ZnS agglomerates flow like smoke, immediately reacting at the confluence point with H ₂ S. Most of the ZnS generated at this time adheres to the inner wall of the introduction tube and the inner wall of the reaction tube as white powder, and the growth rate on the substrate is significantly reduced.The ZnS film obtained is a ZnS agglomerate formed in the vapor phase. As a result, the low quality film with poor crystallinity and orientation was obtained.

When an adduct was formed by reacting dialkylzinc and thioether in the gas phase, ZnS formation was not observed in the gas phase from the confluence of the adduct and H ₂ S to the heating region near the substrate. The amount of ZnS adhering to the inner wall of the introducing tube and the inner wall of the reaction tube was very small even after repeated growth for a long time. The formation of the adduct of dialkylzinc and thioether
It is shown that the reaction inhibiting effect of dialkylzinc and H ₂ S is extremely effective.

Further, by forming the adduct, the adduct and H ₂ S are combined and mixed,
It is now possible to supply from a single inlet. This has made it possible to process large substrates in large quantities as compared with conventional methods. In other words, by mixing in the introduction tube, uniformity of mixing can be ensured, and by increasing the distance from the introduction port to the substrate, one batch of a substrate having a size and number corresponding to the shape and inner diameter of the reaction tube can be obtained. Can be processed by. In the conventional method, since dialkylzinc and H ₂ S were mixed near the substrate, there was a limit to forming a uniform growth film on a large substrate. In the ZnS thin film manufacturing method according to the present invention, MOCVD
The mass productivity of can be fully utilized.

When a ZnS thin film is manufactured by the MOCVD method, a stable adduct is formed by mixing Zn source dialkylzinc and thioether in the gas phase, thereby heating dialkylzinc and H ₂ S in the vicinity of the substrate. It became possible to suppress the gas phase reaction before reaching the region, and consequently, it became possible to uniformly form a good quality ZnS thin film on a large substrate.

The ZnS thin film is used as an electroluminescent light emitting layer by doping a polycrystalline emission center such as Mn, and a single crystal film as an active layer of a MIS light emitting diode by doping Al, I (iodine). . Due to the above effects of the present invention, the characteristics of these devices can be improved and the cost can be reduced. Furthermore, we are convinced that the ZnS thin film manufacturing method according to the present invention will be an extremely important technique in the formation of a pn junction by ZnS and the development of a current injection type light emitting diode and a laser.

[Brief description of drawings]

FIG. 1 is a diagram showing an outline of a MOCVD apparatus used in a conventional ZnS thin film manufacturing method. ...... Quartz glass reaction tube ...... Rotary support,
...... Sic coated carbon susceptor,
...... Substrate, ...... High frequency heating, infrared, resistance heating, etc.
Bubbler containing dialkylzinc, ... Valve, ...
… Carrier gas line for dilution ………… Zn source introduction pipe ………… Cylinder containing H ₂ S ………… Carrier gas line for dilution ………… H ₂ S introduction line FIG. 2 is a ZnS thin film production according to the present invention. MOCVD used in the method
The figure which shows the outline of an apparatus. ...... Quartz glass reaction tube ...... Rotary support,
...... Sic coated carbon susceptor,
...... Substrate, ...... High frequency heating, infrared, resistance heating, etc.
Bubbler containing dialkylzinc, ... Carrier gas line for dilution, ... Raw material gas introduction pipe, Bubbler containing thioether, ... Cylinder containing H ₂ S,
, ... Diluting carrier gas line, ... Valve Fig. 3 shows X-ray locking curves of the ZnS film formed on the GaP substrate by the ZnS thin film manufacturing method according to the present invention. FIG. 4 shows an X-ray diffraction curve of a ZnS film formed on a quartz substrate by the thin film manufacturing method according to the present invention.

Claims (3)

[Claims] 1. A method for producing a zinc sulfide thin film which forms a zinc sulfide thin film on a substrate by a vapor phase pyrolysis method using dialkylzinc as a zinc source and hydrogen sulfide as a sulfur source. By mixing with a gas phase thioether represented by the general formula RSR '(R and R'are alkyl groups), both gas phase adducts are formed. A method for producing a zinc sulfide thin film, which is used as: 2. The method according to claim 1, wherein an amount of the thioether equal to or in excess of the amount of the dialkylzinc is supplied in forming the adduct. A method for producing the zinc sulfide thin film described. 3. The dialkylzinc and the thioether are mixed to form the adduct, the adduct is mixed with the hydrogen sulfide, and then the mixture is introduced onto the substrate. The method for producing a zinc sulfide thin film according to claim 1, which is characterized by the above-mentioned.