JPH1092747A - Manufacture of amorphous gaas thin film and manufacture of amorphous gaas tft - Google Patents

Abstract

PROBLEM TO BE SOLVED: To grow an amorphous GaAs thin film of a desirable composition for characteristics of a device. SOLUTION: A bell jar 6 is mounted on a plate 4 to form a vacuum vessel, in which a temperature controlling cylinder 16 is mounted on the plate 4. A board 8 for vapor deposition source provided with a vapor deposition source heater is set up in one opening part of the temperature controlling cylinder 16, and a substrate holding jig 10 provided with a substrate heater is set up in the other opening part, and a glass substrate 12 whose surface is mirror- polished is attached to the jig. A heater 18 for cylinder is wound on the outer surface of the temperature controlling cylinder 16, which is provided with a thermocouple 20 in addition. The temperature of the temperature controlling cylinder 16 is measured by the thermocouple 20, and the heater 18 for cylinder is so controlled as to keep temperature constant by a temperature controller. An evaporated vapor-depositing material is made to pass through the temperature controlling cylinder 16 so as to be vapor-deposited on the glass substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an amorphous GaAs thin film and a method for manufacturing an amorphous GaAs TFT, and more particularly, to a method for manufacturing a liquid crystal display device and a solar cell.

[0002]

2. Description of the Related Art Conventionally, as a method of growing an amorphous GaAs thin film, a method of growing without particularly controlling the composition ratio of Ga and As, and a method of growing Ga and As by using a flash method.
And a method of separately preparing a source for Ga and a source for As and controlling the composition ratio of Ga and As using a large-scale apparatus.

FIG. 17 is a configuration diagram of a vacuum deposition apparatus used in a conventional method for growing an amorphous GaAs thin film.
A bell jar 6 is installed on a plate 4 of a vapor deposition table to form a vacuum chamber. An exhaust port for exhausting the inside of the vacuum chamber is provided at the center of the plate 4 and connected to a vacuum exhaust system (not shown). In the vacuum chamber, a deposition source board 8 having a deposition source heating heater and on which a deposition material to be deposited is placed.
And a substrate holding jig 10 having a substrate heating heater at a position opposed to the substrate holding jig 10, and between the evaporation source board 8 and the substrate holding jig 10, evaporating particles evaporated from the evaporation source board 8 to the substrate. Shutter 1 for controlling evaporation by opening and closing
4 are arranged.

Using this vacuum deposition apparatus, the glass substrate 14 attached to the substrate holding jig 10 is energized to a substrate heating heater to heat the glass substrate 14 to a predetermined temperature while evacuating by a vacuum evacuation system. The source heater is energized to heat the deposition material to a predetermined temperature and evaporate from the deposition source board 8, and the shutter 14 is opened and closed to control the deposition of the deposition material on the glass substrate 12 and to control the deposition on the glass substrate 12. Is a normal deposition method. At this time, the current supplied to the substrate heating heater and the evaporation source heating heater, the type of the evaporation source board 8, and the like are determined according to the material to be evaporated.

[0005]

When a material having a single composition, such as Au or Al, is deposited using such a vacuum deposition apparatus, a normal deposition method is used, focusing on the deposition rate. Vapor deposition may be performed, and a thin film having a desired thickness can be obtained. However, when the evaporation material is a sublimation type material composed of a plurality of elements, such as GaAs in which the vapor pressures of these elements are significantly different, the composition of the elements of the evaporation material is significantly different from the composition of the elements of the evaporation material in a normal evaporation method. Film is deposited.

Further, depending on the device manufactured using the thin film, there is a case where it is desired to use a thin film having a composition consciously changed from the composition of the deposition material. In such a case, it is an important issue in a device manufacturing process to manufacture a film having a composition required by the device by a simple and reliable method. However, such a thing is impossible with a normal vapor deposition method.

Accordingly, an object of the present invention is to provide an amorphous GaAs thin film manufacturing method capable of growing an amorphous GaAs thin film having a composition necessary for device characteristics by a simple method, and an amorphous GaAs thin film.
An object of the present invention is to provide a method for manufacturing an amorphous GaAs TFT using an aAs thin film.

[0008]

SUMMARY OF THE INVENTION The present invention relates to an amorphous G
The method of manufacturing an aGaAs thin film is a method of manufacturing an amorphous GaAs thin film in which an evaporation material is evaporated from a deposition source board and evaporated on a substrate to form an amorphous GaAs thin film. A hollow guide member for guiding the evaporated deposition material onto the substrate is provided between the evaporation source board and the substrate, and the temperature of the hollow guide member is maintained in a range of 180 ° C or more and 300 ° C or less, and the temperature of the evaporation source board is maintained. Is heated to about 1000 ° C. within about 10 seconds after the start of vapor deposition, the temperature of the substrate is kept at 205 ° C. or less, and the vapor deposition material that has vaporized from the vapor deposition source board and passed through the hollow guide member is vapor-deposited on the substrate. I do.

Since the temperature of the vapor deposition material is rapidly increased by controlling the temperature profile of the vapor deposition source board as described above, Ga and As having greatly different vapor pressures are separated when evaporating from the vapor deposition source board. Can be prevented. Further, since the hollow guide member is provided in the passage connecting the substrate and the evaporation source board, most of the evaporation material evaporated from the evaporation source board can be introduced into the hollow guide member, and the introduced evaporation material can be transferred to the substrate surface. In the vicinity of Further, the temperature of the hollow guide member is controlled, and the hollow guide member is provided in the passage between the evaporation source board and the substrate. Therefore, when the evaporated particles evaporated from the evaporation source board collide with the inner wall of the hollow guide member, Since the inner wall of the hollow guide member serves as a reflecting plate, the temperature of the hollow guide member becomes substantially the same as the temperature of the hollow guide member due to the collision of the vapor composed of the evaporated particles before reaching the vicinity of the substrate surface. Therefore, by applying the adhesion coefficient, the vapor pressure of each element inside the hollow guide member can be controlled. That is, Ga, A reaching the vicinity of the substrate surface
The composition of s can be controlled.

In the method of manufacturing an amorphous GaAs thin film according to the present invention, the substrate is a mirror-polished glass substrate, and the substrate has a CaF ₂ of 100 nm or more and 300 nm or less.
A film may be formed.

By forming the CaF ₂ film in this way, the adhesion and adhesion of the deposited film to the substrate can be improved.

In the method of manufacturing an amorphous GaAs thin film according to the present invention, the composition ratio of As to Ga is As / Ga of 1.1.
The amorphous GaAs thin film described above may be formed.

As described above, the composition ratio of As to Ga is As.
If / Ga can be 1.1 or more, the deposited GaAs thin film can have a high specific resistance.

The method for producing an amorphous GaAs thin film according to the present invention has a specific resistance of 10 ⁹ Ω · cm or more and an electron mobility of 0.17 cm ² / V · sec or more and 0.45 cm ^2.
An amorphous GaAs thin film of not more than / V · sec may be formed.

If the specific resistance can be increased to 10 ⁹ Ω · cm or more, a semi-insulating amorphous aAs thin film can be formed.
If the electron mobility is 0.17 cm ² / V · sec or more and 0.45 cm ² / V · sec or less, it can be used for a thin film for manufacturing a device.

According to the method of manufacturing an amorphous GaAs TFT according to the present invention, a gate electrode is formed on one surface of an amorphous GaAs channel layer with a gate insulating film interposed therebetween.
In a method for manufacturing an amorphous GaAs TFT in which a source electrode and a drain electrode are formed in contact with a source electrode and a drain electrode on the other surface of an As channel layer on a substrate, an evaporation material evaporated from a heated evaporation source board is removed. The substrate is placed in the opening in the hollow guide member leading to the substrate, the temperature of the hollow guide member is maintained at a temperature in the range of 180 ° C. or more and 300 ° C. or less, and the temperature of the evaporation source board is set to about 10 seconds after the start of evaporation. Within 1000 ° C., the temperature of the substrate is maintained at 205 ° C. or lower, and the amorphous GaAs channel layer passes the vaporized material evaporated from the vapor deposition source board through the hollow guide member to form a film on the substrate. Formed by evaporation.

Since the amorphous GaAs channel layer is formed as described above, the composition of Ga and As can be controlled, so that an amorphous GaAs TFT having various device characteristics can be formed.

In the method of manufacturing an amorphous GaAs TFT according to the present invention, the substrate is a mirror-polished glass substrate,
In addition, 100 nm or more and 300 nm or less of Ca
An F ₂ film may be formed.

By forming the CaF ₂ film in this way, a TFT can be formed using a deposited film such as an amorphous GaAs thin film having good adhesion and adhesion to a substrate.

According to the method of manufacturing an amorphous GaAs TFT according to the present invention, the gate insulating film is formed to have a thickness of 100 nm to 300 nm.
The MgF ₂ film having the following thickness may be used.

As described above, the gate insulating film has a thickness of 100 n.
When the thickness of the MgF ₂ film is not less than m and not more than 300 nm, the operating characteristics of the thin film transistor can be obtained by using the amorphous GaAs thin film, and the voltage for controlling the TFT with the gate electrode through the insulating film is used. The size can be set to a preferable size.

In the method for manufacturing an amorphous GaAs TFT according to the present invention, the amorphous GaAs channel layer may have a composition ratio of As to Ga to Ga of As / Ga of 1.1 or more.

As described above, when the composition ratio of As to Ga in the amorphous GaAs thin film is made to be not less than 1.1, a TFT can be formed on the GaAs thin film having a high specific resistance.

In the method of manufacturing an amorphous GaAs TFT according to the present invention, the gate electrode, the source electrode and the drain electrode are formed of AuGe, and the amorphous GaAs channel layer has a specific resistance of 10 ⁹ Ω · cm or more. And an electron mobility of at least 0.17 cm ² / V · sec and at least 0.45 cm ² /
V · sec or less.

If the electrodes are formed of AuGe,
Ohmic contact with GaAs can be easily obtained. If the amorphous GaAs thin film has a specific resistance of 10 ⁹ Ω · cm, the device can be easily separated because it is a semi-insulating film, and the ON-OFF characteristics of the TFT current can be increased. Electron mobility is 0.17 cm ² / V · sec
When the thickness is 0.45 cm ² / V · sec or less, it can be used for a thin film for manufacturing a TFT.

[0026]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

(First Embodiment) FIG. 1 shows a vacuum deposition apparatus 1 used in the method for producing an amorphous GaAs thin film of the present invention.
FIG. A bell jar 6 is placed on the plate 4 of the vapor deposition table to form a vacuum chamber. An exhaust port for exhausting the inside of the vacuum layer is provided at the center of the plate 4, and the exhaust port is connected to a vacuum exhaust system (not shown). In the vacuum chamber, a metal temperature control cylinder 16 is provided as a hollow guide member.
It is installed above. An evaporation source board 8 having an evaporation source heating heater is installed near one opening on the exhaust port side of the temperature control cylinder 16. Materials are loaded. A substrate holding jig 10 having a substrate heating heater is provided near the other opening at a position facing the deposition source board 8.
Is installed, and the mirror-polished glass substrate 12 is attached with the mirror-polished surface facing the opening of the temperature control cylinder 16. In the temperature control cylinder 16 between the evaporation source board 8 and the substrate holding jig 10, a shutter 14 for controlling the passage of the evaporated particles evaporated from the evaporation source board 8 is arranged. Evaporation source board 8
Is preferably made of Mo, W, Ti or the like. However, the material is not limited to this as long as it is a high-melting-point material that can be obtained with high purity and does not affect the characteristics of the GaAs film.

A cylindrical heater 18 is wound around the outer surface of the temperature control cylinder 16 as temperature control means, and a thermocouple 20 is provided as temperature measurement means.
The temperature of the temperature control cylinder 16 is measured by a thermocouple 20, and the temperature is controlled so that the temperature of the cylinder heater 18 is kept constant by a temperature controller (not shown). The temperature control cylinder 16 is preferably formed of Ti having a thickness of 0.5 mm. In order to keep the temperature of the temperature control cylinder 16 constant, a material having good thermal conductivity is preferable. However, the material is not limited to this as long as it is a high-melting-point material from which a high purity can be obtained and does not affect the characteristics of the GaAs film. The cylindrical heater 18 is preferably a shield type heater. The shape of the temperature-controlled hollow guide member is preferably a cylinder. It is not limited to this as long as it acts as a reflector for the deposited particles and can control the composition of Ga and As reaching the substrate surface by applying the adhesion coefficient of Ga and As.

Next, using this vacuum deposition apparatus, the amorphous G
A method for manufacturing an aAs thin film will be described. The evaporation source board 8 is filled with GaAs as an evaporation material, and the mirror-polished glass substrate 12 is attached to the substrate holding jig 10. The substrate heating heater is set so that the substrate 12 can be maintained at a temperature of approximately 190 ° C. When the temperature of the evaporation source board 8 is rapidly increased and the shutter 14 is opened simultaneously with the start of the temperature rise, the evaporated particles evaporated from the evaporation source board 8 are deposited on the substrate 12. Further, it is preferable that a CaF ₂ film is deposited on the glass substrate in advance. This is because when the CaF ₂ film is formed, the adhesion and adhesion of the deposited film to the glass substrate can be improved.

In the present embodiment, vapor deposition was performed on the glass substrate 12 under the following conditions. The temperature of the glass substrate 12 is
The control was performed in the range of 190 ° C. ± 15 ° C. The reason why the substrate temperature is controlled is that when the substrate temperature is high, the substrate becomes a polycrystalline thin film instead of an amorphous thin film. The temperature of the substrate 12 was measured directly above the substrate using a thermocouple.

The temperature of the evaporation source board 8 is controlled by, for example,
Preferably, this is performed as shown in FIG. FIG. 2 shows a temperature profile of the deposition source board 8. In about 10 seconds from the start of the temperature rise, the temperature is raised at a stretch to a temperature near 1000 ° C. Then, at about 1000 ° C for 10 seconds
After that, the temperature is lowered for about 10 sec. More specifically, from about 500 ° C. to 1
Raise the temperature to around 000 ° C in about 10 seconds,
It is held for about 10 seconds in the vicinity, and then lowered to about 300 ° C. in about 10 seconds. The reason why the temperature is rapidly increased in this manner is to prevent the vapor deposition material from evaporating from the vapor deposition source board 8 from separating as much as possible because the vapor pressures of Ga and As are greatly different. In order to keep GaAs from separating, 1
A heating rate of about 000 ° C. was sufficient.
When the evaporation material evaporates from the evaporation source board 8, G
If the separation of a and As is prevented, the temperature profile is not limited to the temperature profile shown in FIG. The temperature of the evaporation source board 8 was measured directly below the board using a thermocouple.

As described above, the temperature of the vapor deposition source board 8 is rapidly increased to prevent separation of Ga and As when the vapor deposition material evaporates from the vapor deposition source board 8.
The composition ratio of Ga and As when evaporating can be controlled. Also,
Temperature control cylinder 16 between evaporation source board 8 and substrate 12
The particles evaporated from the evaporation source board 8 can be guided to the surface of the substrate 12 by the temperature control cylinder 16. Since the particles evaporated from the evaporation source board 8 are almost introduced into the temperature control cylinder 16, the vapor pressure of the evaporated particles is controlled by the temperature control cylinder 16. Further, the vaporized particles collide with the inner wall of the temperature control cylinder 16 during a period from the vapor deposition source board 8 to the surface of the substrate 12, so that the temperature of the vapor composed of the vaporized particles is substantially the same as the temperature of the temperature control cylinder 16. Become. That is, the substrate 1
The surface of 2 comes into contact with steam whose temperature and vapor pressure are controlled. Furthermore, since the adhesion coefficient is applied by controlling the temperature of the temperature control cylinder 16, the composition of Ga and As reaching the substrate surface can be controlled by using a material having a large adhesion coefficient.

Under such conditions, the temperature control cylinder 1
The characteristics of the thin film were examined by changing the temperature of No. 6. FIG. 3 is a characteristic diagram showing the relationship between the temperature of the temperature control cylinder 16 and the specific resistance of the thin film. The temperature of the temperature control cylinder 16 is about 180 ° C
A thin film having a high specific resistance of 10 ⁷ Ω · cm or more is obtained in the range of not less than about 300 ° C. and the temperature of the temperature control cylinder 16 is about 1 ° C.
A thin film having a high specific resistance of 10 ⁹ Ω · cm or more was obtained in the range of 80 ° C. or more and about 280 ° C. or less.

FIG. 4 is a characteristic diagram showing the relationship between the temperature of the temperature control cylinder 16 and the composition ratio As / Ga of As to Ga in the thin film. According to FIG. 4, in order to obtain a thin film having a high specific resistance of 10 ⁷ Ω · cm or more, a composition ratio of As / Ga
≧ 1.1 is preferred.

FIG. 5 is a characteristic diagram showing the relationship between the substrate temperature and the electron mobility of the amorphous GaAs thin film. From the behavior of the electron mobility of the thin film, the thin film obtained by vapor deposition became amorphous on the low temperature side and became polycrystalline on the high temperature side with a substrate temperature of 205 ° C. From the measurement results, the electron mobility of the amorphous GaAs thin film was 0.17 cm ² / V · sec or more and 0.1 μm / V · sec.
The range was 45 cm ² / V · sec. The electron mobility of the polycrystalline GaAs thin film is 125 cm ² / V · se
c and 180 cm ² / V · sec or less. In addition,
From the result of the intensity profile of the electron beam diffraction, the crystal size was 75 Å. From the results of the X-ray diffraction image analysis, the plane spacing and the diffraction intensity of the crystal film were identical to those of GaAs.

The GaAs thin film thus obtained is coated with A
After forming uGe electrodes and connecting them to an ammeter, the GaAs thin film was irradiated with light. As a result, it was confirmed that a good amorphous GaAs thin film was obtained because the ammeter greatly fluctuated.

The obtained amorphous GaAs thin film is an N-type semiconductor due to stoichiometric deviation.

Further, X-ray analysis was performed to specify the structure of the obtained GaAs thin film in detail. The result is shown in FIG.
And FIG. FIG. 6 is a characteristic diagram of an interference function of X-ray diffraction of a GaAs thin film. FIG. 7 is a characteristic diagram of a radial distribution function (RDF) obtained by performing a radial distribution analysis from the interference function of FIG. 6, and a horizontal axis indicates a distance in the radial direction. The short-range order showing the bond peak in the radial distribution curve is GaAs.
This shows that the structure of the s thin film is the structure of the GaAs tetrahedral molecule shown in FIG. According to FIG. 8, there is an As atom at each vertex of a tetrahedron having a side of 4 Å, and Ga
Exists at the center thereof, and the interatomic distance of Ga-As is 2.4.
4 Å. As described above, it was confirmed that the film was an amorphous GaAs thin film also in structure.

(Second Embodiment) Next, a method of manufacturing a thin film transistor (TFT) using an amorphous GaAs thin film grown in the first embodiment will be described. FIG.
Is a plan view of a TFT manufactured by the method of manufacturing an amorphous GaAs TFT according to the present embodiment, and FIG.
It is a line sectional view. In FIG. 9, the source electrode and the drain electrode are not visible from the uppermost layer, but are shown by broken lines so that the relative positional relationship with the gate electrode becomes clear.

According to FIG. 9, the structure of the TFT is such that the source electrode 45 and the drain electrode 46 are opposed to each other with an interval of the channel length L of the TFT. The width becomes the channel width W of the TFT. The gate electrode 53 is provided with an overlapping portion in a region between the source electrode 45 and the drain electrode 46 facing each other. The width of gate electrode 53 is longer than channel length L by the amount of overlap with source electrode 45 and drain electrode 46. As shown in FIG.
3 is that the source electrode 45 and the drain electrode 46 are Mg
Insulated by the F ₂ thin film. And the gate electrode 5
3, the gate insulating film MgF
₂ The conductivity of the GaAs layer below the thin film is modulated.

Hereinafter, a method of manufacturing the TFT shown in FIGS. 9 and 10 will be described step by step with reference to FIG.

Using a mirror-polished glass substrate 40 (FIG. 11A), a CaF ₂ film 42 is deposited on the substrate 40 by a vapor deposition method to have a thickness of 100 nm to 200 nm (FIG. 11B).
Next, an AuGe film 44 serving as a source electrode and a drain electrode is deposited to a thickness of 100 nm on the CaF ₂ film 42 by Arroy's resistance heating evaporation method (FIG. 11C). After that, the AuGe film 44 is patterned using the photolithography technique to form the source electrode 45 and the drain electrode 46. Next, an amorphous GaAs thin film 48 is deposited to a thickness of 200 nm on the CaF ₂ film 42, the source electrode 45, and the drain electrode 46 by the method described in the first embodiment (FIG. 11D). After that, the amorphous GaAs layer 48
An MgF ₂ film 50 serving as a gate insulating film is deposited to a thickness of 100 nm by Arroy's resistance heating evaporation method. continue,
An AuGe film 52 serving as a gate electrode is deposited to a thickness of 100 nm by the resistance heating evaporation method of Arrowy (FIG. 11E). Then, the AuGe film 52 is patterned using a photolithography technique to form a gate electrode 53 (FIG. 1).
0, FIG. 11 (f)).

Thus, the amorphous Ga film is formed on the CaF ₂ film 42 formed on the mirror-polished glass substrate 40.
An amorphous GaAs TFT using an As thin film as a channel layer is obtained. That is, the Au formed on the CaF ₂ film 42
Ge source electrode 45 and drain electrode 46
And an amorphous GaAs channel layer 48 formed on the CaF ₂ film 42, the source electrode 45 and the drain electrode 46.
And Mg formed on the amorphous GaAs channel layer 48.
An amorphous GaAs TFT having a gate insulating film 50 made of an F ₂ film and an AuGe gate electrode 53 formed on the gate insulating film 50 in a channel region between the source electrode 45 and the drain electrode 46 can be manufactured (FIG. 10, FIG. 11
(F)).

When an MgF ₂ film is used as a gate insulating film, an operating characteristic as a thin film transistor can be obtained by using an amorphous GaAs thin film.

As described above, according to this embodiment, a TFT can be manufactured using an amorphous GaAs thin film having a composition suitable for device characteristics. For example, by controlling the composition of Ga and As, amorphous Ga having a specific resistance of 10 ⁹ Ω · cm
A TFT can be manufactured using an As thin film.

(Third Embodiment) A method of manufacturing a TFT having a structure different from that of the second embodiment, which uses the amorphous GaAs thin film grown in the first embodiment, will be described. I do. FIG. 12 shows the amorphous GaAs of the present embodiment.
FIG. 13 is a plan view of the TFT manufactured by the sTFT manufacturing method, and FIG. 13 is a cross-sectional view taken along the line BB ′. In FIG. 12, the gate electrode is not visible from the uppermost layer, but is shown by a broken line so that the relative positional relationship between the source electrode and the drain electrode becomes clear.

According to the structure of the TFT, according to FIG. 12, the source electrode 71 and the drain electrode 72 are arranged opposite to each other with a distance of the channel length L of the TFT, and the electrode of the portion where the source electrode 71 and the drain electrode 72 face each other. The width becomes the channel width W of the TFT. The gate electrode 53 is a source electrode 71
And the drain electrode 72 are provided with an overlapping portion in a region between them facing each other. The width of gate electrode 65 is longer than channel length L by the amount of overlap with source electrode 71 and drain electrode 72. As shown in FIG. 13, the gate electrode 65 is different from the source electrode 71 and the drain electrode 72 by M
Insulated by the gF ₂ thin film. Then, the voltage applied to the gate electrode 65 causes the gate insulating film Mg
F ₂ the conductivity of the GaAs layer on the thin film is subjected to modulation.

Hereinafter, a method of manufacturing the amorphous GaAs TFT shown in FIGS. 12 and 13 will be described step by step.

Using a mirror-polished glass substrate 60 (FIG. 14A), a CaF ₂ film 62 is deposited on the substrate 60 by an evaporation method from 100 nm to 200 nm (FIG. 14B).
Next, an AuGe film 64 serving as a gate electrode is deposited on the CaF ₂ film 62 to a thickness of 100 nm by the resistance heating evaporation method of Arrowy (FIG. 14C). Thereafter, the AuGe film 64 is patterned using the photolithography technique to form the gate electrode 65 (FIG. 14D). Next, Aro
MgF ₂ which becomes a gate insulating film by resistance heating evaporation method of y
A film 66 is deposited to a thickness of 100 nm. Thereafter, GaAs is formed on the MgF ₂ film 66 by the method described in the first embodiment.
A 200 nm thin film 68 is deposited. Subsequently, the AuGe film 70 serving as a source electrode and a drain electrode is
Is deposited to a thickness of 100 nm on the GaAs thin film 68 by the resistance heating evaporation method shown in FIG. Next, the source electrode 71 and the drain electrode 72 are formed by patterning the AuGe film 70 using the photolithography technique (FIG. 14).
(F), FIG. 13).

In this manner, amorphous Ga is formed on the CaF ₂ film 62 formed on the mirror-polished glass substrate 60.
An amorphous GaAs TFT using an As thin film as a channel layer is obtained. That is, the Au formed on the CaF ₂ film 62
A gate electrode 65 made of Ge, a CaF ₂ film 62, a gate insulating film 66 made of an MgF ₂ film formed on the gate electrode 65, and an amorphous G film formed on the gate insulating film 66.
An amorphous GaAs TFT having an aAs channel layer 68 and an AuGe source electrode 45 and a drain electrode 46 formed on both sides of the channel portion of the amorphous GaAs channel layer 68 on the gate electrode 65 can be manufactured. (FIGS. 13 and 14 (f)).

As described above, according to this embodiment, a TFT can be manufactured using an amorphous GaAs thin film having a composition suitable for device characteristics. For example, by controlling the composition of Ga and As, amorphous Ga having a specific resistance of 10 ⁷ Ω · cm
A TFT can be manufactured using an As thin film.

FIG. 15 shows the drain current characteristics of the amorphous GaAs TFT described in the second and third embodiments. The drain current characteristics of FIG.
The measurement was performed using an equivalent connection circuit for the TFT 80 shown in FIG. In FIG. 16, a positive voltage is applied to the drain electrode 88 with respect to the source electrode 87 by the voltage source 82, and a positive and negative voltage (gate voltage) is applied to the gate electrode 89 with respect to the source electrode 87 by the voltage source 84. ing. Also,
An ammeter 86 is arranged between the drain electrode 88 and the voltage source 82 to measure the drain current. In FIG. 15, the vertical axis indicates the drain current, and the horizontal axis indicates the gate voltage applied to the gate electrode. According to the result of FIG. 16, a normally-off type TFT having a large ON-OFF current ratio was obtained. At this time, the channel length L = 10 μm and the channel width W = 25 μ
m TFTs were measured. In FIG. 16, the drain current is normalized by the drain reverse current Ir.

Since the amorphous GaAs TFT described in the second and third embodiments uses a high-resistivity GaAs thin film, a plurality of TFTs are formed on the same substrate. In addition, it is not necessary to electrically isolate each TFT. This simplifies the manufacturing process and makes the substrate surface flat. However, one TFT may be formed in an island-shaped or mesa-shaped region by etching a GaAs thin film formed by vapor deposition. By doing so, each TFT can be separated. Further, if a plurality of TFTs are formed in an island-shaped or mesa-shaped region, a group of TFTs for circuit operation can be integrated.

[0054]

As described in detail above, according to the method for manufacturing an amorphous GaAs thin film of the present invention, an amorphous GaAs thin film having a composition suitable for the device characteristics can be grown by a simple method.

Then, a TFT having a large ON-OFF current ratio can be manufactured using this amorphous GaAs thin film.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a vacuum vapor deposition apparatus used for vapor deposition of an amorphous GaAs thin film of the present invention.

FIG. 2 is a temperature profile of a deposition source board.

FIG. 3 is a characteristic diagram of a specific resistance of a film deposited by the method for producing an amorphous GaAs thin film of the present invention.

FIG. 4 is a characteristic diagram of the composition ratio of Ga and As of a film deposited by the method for producing an amorphous GaAs thin film of the present invention.

FIG. 5 is a characteristic diagram showing the relationship between the electron mobility of a film deposited by the method for producing an amorphous GaAs thin film of the present invention and the substrate temperature.

FIG. 6 is a characteristic diagram of an X-ray interference function of a film deposited by the method for producing an amorphous GaAs thin film of the present invention.

FIG. 7 is a characteristic diagram of an X-ray radial distribution function curve of a film deposited by the method for producing an amorphous GaAs thin film of the present invention.

FIG. 8 is a structural diagram showing a structure of amorphous GaAs estimated from an X-ray radial distribution function curve of a film deposited by the method of manufacturing an amorphous GaAs thin film of the present invention.

FIG. 9 is a plan view of an amorphous GaAs TFT.

FIG. 10 is a sectional view taken along line A-A ′ of FIG. 9;

FIGS. 11A to 11F are process cross-sectional views of a method for manufacturing an amorphous GaAs TFT according to the present invention.

FIG. 12 is a plan view of an amorphous GaAs TFT.

FIG. 13 is a sectional view taken along line BB ′ of FIG. 12;

FIGS. 14A to 14F are process cross-sectional views of another method of manufacturing an amorphous GaAs TFT according to the present invention.

FIG. 15 is a drain current characteristic diagram of a TFT obtained by the method of manufacturing an amorphous GaAs TFT according to the present invention.

FIG. 16 is an equivalent connection circuit diagram for measuring a drain current of the amorphous GaAs TFT of the present invention.

FIG. 17 is a configuration diagram of a conventional vacuum vapor deposition apparatus used for vapor deposition of an amorphous GaAs thin film.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Vacuum vapor deposition apparatus, 4 ... Plate, 6 ... Bell jar, 8 ...
Deposition source board, 10: substrate holding jig, 12: glass substrate, 14: shutter, 16: temperature control cylinder, 18
... cylindrical heater, 20 ... thermocouple, 40, 60 ... glass substrate, 42, 62 ... CaF ₂ film, 44,52,64,70
... AuGe film, 45, 71 ... Source electrode, 46, 72 ...
Drain electrode, 48, 68... Amorphous GaAs film, 50,
66: MgF ₂ film, 53, 65: gate electrode, 80: T
FT

Claims (9)

[Claims] 1. A method for producing an amorphous GaAs thin film, wherein an evaporation material is evaporated from a deposition source board to form an amorphous GaAs thin film on a substrate. A hollow guide member for guiding the deposited material onto the substrate is provided between the deposition source board and the substrate, and the temperature of the hollow guide member is maintained in a range of 180 ° C. or more and 300 ° C. or less. Maintain the temperature of the source board for about 10 seconds after the start of evaporation.
Within about 1000 ° C., the temperature of the substrate is kept at 205 ° C. or less, and the evaporation material evaporated from the evaporation source board and passed through the hollow guide member is evaporated on the substrate. A method for producing an amorphous GaAs thin film. 2. The substrate is a mirror-polished glass substrate, and has a thickness of 100 nm or more and 300 nm on the substrate.
The method for producing an amorphous GaAs thin film according to claim 1, wherein the following CaF ₂ film is formed. 3. The method for producing an amorphous GaAs thin film according to claim 1, wherein an amorphous GaAs thin film having an As / Ga composition ratio of As / Ga of 1.1 or more is formed. 4. A specific resistance of at least 10 ⁹ Ω · cm and an electron mobility of at least 0.17 cm ² / V · sec.
^{2. The} amorphous Ga according to claim 1, wherein an amorphous GaAs thin film having a thickness of 5 cm ² / V · sec or less is formed.
Method for producing As thin film. 5. A gate electrode is formed on one surface of the amorphous GaAs channel layer with a gate insulating film interposed therebetween, and a source electrode and a drain electrode are formed on the other surface of the amorphous GaAs channel layer. In a method of manufacturing an amorphous GaAs TFT for manufacturing an amorphous GaAs TFT on a substrate, the substrate is placed in an opening in a hollow guide member for guiding a vapor deposition material evaporated from a heated vapor deposition source board onto the substrate. Holding the temperature of the hollow guide member in the range of 180 ° C. or more and 300 ° C. or less, and keeping the temperature of the evaporation source board at about 10 seconds after the start of evaporation.
Within about 1000 ° C., the temperature of the substrate is kept at 205 ° C. or less, and the amorphous GaAs channel layer transfers the deposition material evaporated from the deposition source board through the hollow guide member. A method for manufacturing an amorphous GaAs TFT, wherein the amorphous GaAs TFT is formed by passing through and evaporating on the substrate. 6. The substrate is a mirror-polished glass substrate, and the substrate surface has a thickness of 100 nm or more and 300 nm or more.
6. The method for manufacturing an amorphous GaAs TFT according to claim 5, wherein a CaF ₂ film of m or less is formed. 7. The semiconductor device according to claim 1, wherein the gate insulating film has a thickness of 100 nm or more.
6. The method for manufacturing an amorphous GaAs TFT according to claim 5, wherein the MgF ₂ film has a thickness of 00 nm or less. 8. The method according to claim 1, wherein the amorphous GaAs channel layer is formed of Ga.
6. The amorphous GaAs TFT according to claim 5, wherein a composition ratio of As to Ga is not less than 1.1.
Manufacturing method. 9. The gate electrode, the source electrode, and the drain electrode are formed of AuGe, and the amorphous GaAs channel layer has a specific resistance of 10 ⁹ Ω ·
cm or more and an electron mobility of 0.17 cm ² / V
6. The amorphous GaAs TFT according to claim 5, wherein the thickness is not less than 0.45 cm ² / V · sec.
Manufacturing method.