JP3396395B2 - Amorphous semiconductor thin film manufacturing equipment - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an apparatus for producing an amorphous semiconductor thin film using a glow discharge decomposition method.

[0002]

2. Description of the Related Art In recent years, so-called amorphous semiconductors such as amorphous silicon, amorphous germanium, and amorphous silicon germanium have attracted attention as new semiconductor materials due to the success of impurity control technology, and researches for practical application to devices such as solar energy conversion elements are active. Is being advanced to.

Such an amorphous semiconductor is produced by a glow discharge decomposition method (also called plasma CVD) which is a well-known technique. As a typical example of such conventional production of amorphous semiconductors, Japanese Patent Laid-Open No. 7-
The outline of the method proposed in 99159 will be described below.

FIG. 10 is a schematic view of a conventional diode-type capacitively coupled plasma CVD apparatus. As shown in FIG. 10, a stainless steel mesh electrode 04 is disposed as a mesh heating element between the cathode electrode 02 and the anode electrode 03 in the reaction vessel 01. Here, the distance between the cathode electrode 02 and the mesh electrode 04 is 40 m.
m, the distance between the mesh electrode 04 and the anode electrode 03 is 20 mm, the mesh electrode 04 is not grounded to both the cathode electrode 02 and the anode electrode 03, and is in a floating potential state. Then, it is connected to a heating power source 05 provided outside by a transformer 06, and the amount of current flowing through the mesh electrode 04 is controlled by adjusting the voltage thereof with a sliderac 07. The substrate is fixed on the anode electrode 03 with a stainless jig with good adhesion.

As a preparation before film formation, the wall of the reaction vessel 01, the substrate, and the mesh electrode 04 are sufficiently heated to exhaust the adsorbed impurities as much as possible, and then the temperature is lowered to a predetermined temperature to about 2 × 10 ^-8 Torr. The vacuum is exhausted. This vacuum exhaust is exhausted from a high vacuum exhaust port 08 connected to a turbo molecular pump, and during film formation, the reaction container is exhausted from a pressure adjusting exhaust port 09 connected to a mechanical booster pump and a rotary pump. The inside of 01 is kept at a constant pressure.

Then, pure monosilane gas was introduced into the reaction vessel 01 as a raw material gas, a high frequency voltage of 13.56 MHz was applied between the cathode electrode 02 and the anode electrode 03 from a high frequency power source 010, and a SiH ₄ flow rate: 2 SC was used as a film forming condition.
CM, rf power: 1W / cm ² , pressure: 0.03Torr, substrate temperature: 250
C., mesh temperature: 75 to 400.degree. C., whereby a hydrogenated amorphous silicon film having a film thickness of 1 to 2 .mu.m is formed.

Aluminum (Al) was formed on the hydrogenated amorphous silicon film thus obtained by vacuum deposition.
Coplanar electrodes are formed at intervals of 0.2 mm, and the defect density in the semiconductor in these samples is quantified by the stationary photocurrent method (also referred to as CPM method).

FIG. 11 shows the relationship between the temperature of the mesh electrode 04 on the horizontal axis and the defect density on the vertical axis. The defect density when formed at a normal substrate temperature, that is, 250 ° C. is about 10 ¹⁵ defects / cm ³ , but the mesh electrode 04
When heated to 200 ° C., it is reduced by about an order of magnitude to 10 ¹⁴ pieces / cm ³ .

The mechanism of this high-quality film formation is due to the supply of heat energy to the gas phase. As a result, the temperature rise of the radicals in the gas phase reduces defects by increasing the radical diffusion length in film formation on the substrate surface. As a result, it is believed that the defect density in the film can be reduced. That is, when a mesh heating element is arranged in the reaction container and the mesh heating element is heated during the growth of the reaction to give heat energy to the gas phase, radicals (SiH ₃ , SiH ₂₎ attached to the substrate surface are applied.
As a result, the diffusion state on the surface after they reach the growth surface becomes larger than the diffusion length at the actual substrate temperature due to the higher energy state of the substrate itself. And since the pressure in the reaction vessel is extremely low,
Heat conduction from the mesh heating element to the substrate is of little concern.

[0010]

However, in the conventional technique, although a high quality amorphous silicon film having a defect density of 10 ¹⁴ / cm ³ can be formed, the mesh heating element is used to heat radicals in the gas phase. However, there are the following problems.

The amorphous silicon film adheres to the mesh heating element, and as shown in FIG. 12, for example, the amorphous silicon film 011 adheres to the mesh electrode 04, which is the mesh heating element, and the area of the opening 04a becomes small. There's a problem. Therefore, the radical flow attached to the substrate surface is reduced, and the film formation rate is limited to about 1Å / s or 2Å / s. There is a problem that the amount of the amorphous silicon film deposited on the mesh electrode 04 increases every time the substrate is formed, and the film forming rate changes with time as shown in FIG. This means that, for example, in the application to manufacture of solar cells and thin film transistors for displays, it is necessary to measure the film formation rate in advance for each film formation on a substrate that is subsequently performed, or in the film formation process in the above application. Uncertainty arises in the control of the film thickness of, and the reproducibility and reliability of the performance of manufactured products are significantly reduced. Therefore, there is a fatal problem that it can be used for research on amorphous silicon but cannot be used for industrial applications.

[0012]

An amorphous semiconductor thin film manufacturing apparatus of the present invention for solving the above-mentioned problems is an amorphous semiconductor thin film manufacturing apparatus for forming an amorphous silicon thin film on a substrate arranged in a reaction vessel. A substrate surface heating heater for heating the surface of the substrate is provided between the substrate and a ladder antenna type electrode for generating glow discharge plasma, and the heater for controlling the surface heating temperature has a rod-shaped predetermined distance. It is characterized by being formed by.

In the above-mentioned amorphous semiconductor thin film manufacturing apparatus, the substrate surface heater is grounded via a capacitor.

In the above-mentioned apparatus for producing an amorphous semiconductor thin film, a gas mixing box into which a reaction gas is introduced is arranged in the reaction vessel, and the gas mixing box has an opening on the side facing the substrate, A ladder antenna type electrode is provided so as to cover the opening.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the apparatus for producing an amorphous semiconductor thin film according to the present invention will be described below, but the present invention is not limited to this.

A schematic view of an apparatus for producing an amorphous semiconductor thin film of the present invention is shown in FIGS. Here, FIG. 1 is a sectional view of the plasma CVD apparatus, FIG. 2 is a schematic view of a ladder antenna type electrode used in the plasma CVD apparatus, and FIG. 3 is a schematic view of a substrate surface heating heater. As shown in FIG. 1, a substrate heater body 13 having a heater 12 therein is disposed in the reaction vessel 11, and a substrate 14 provided on the surface of the substrate heater body 13 is directly heated. I am trying to do it.

A substrate surface heater 15 is arranged on the upper surface side of the substrate 14 in the figure, and the surface of the substrate 14 is heated from above the substrate 14. As shown in FIG. 2, the substrate surface heating heater 15 constitutes a heater in the same plane by a single wire rod, and connects the linear heater portion 16a and the U-shaped heater portion 16b to each other. Is formed. The wire heater 1
A power supply 19 for heating the substrate surface is provided at both ends of 6 via power supply lines 17a, 17b and current introduction terminals 18a, 18b.
More power is being supplied.

On the other hand, as shown in FIG. 1, a gas mixing box 20 is arranged on the upper side in the reaction vessel 11, and a reaction gas (SiH ₄ ) 22 is supplied from the outside through a gas introduction pipe 21.
Have been introduced. An opening 20a is formed in the gas mixing box 20 on the side of the gas mixing box 20 that faces the substrate 14, and glow discharge plasma is generated so as to cover (or block) the opening 20a. A ladder antenna type electrode 23 is arranged to turn the supplied reaction gas 22 into glow discharge plasma. As a result, all the reaction gas 22 supplied is changed to the ladder antenna type electrode 2 described above.
It becomes possible to pass through the space between 3 and an efficient reaction becomes possible. As shown in FIG. 3, the ladder antenna type electrode 23 is configured by forming an electrode from two rod-shaped frame members 24 and a ladder-shaped ladder member 25 provided in a direction orthogonal to the frame members 24, At the power supply points 26a and 26b of the electrode 23,
Power supply lines 27a, 27b and current introduction terminals 28a, 2
Electric power is supplied from the high frequency power supply 29 and the impedance matching device 30 via 8b.

The reaction gas introducing pipe 21 is used in combination with a reaction gas supply device and a reaction gas mixing box 20 (not shown) to discharge a reaction gas at an arbitrary flow rate toward the ladder antenna type electrode 23. I am trying. The gas in the reaction container 11 is exhausted to the outside through a vacuum pump (not shown) through the exhaust port 11a.

In the above manufacturing apparatus, a thin film of, for example, amorphous silicon is formed on the surface of the substrate by glow plasma generation of the reaction gas. The temperature of the surface of the substrate depends on the physical properties of the thin film. It is important to monitor and control the substrate temperature with a thermometer, since it is a factor that greatly influences it.

Here, as shown in FIG. 1, the substrate heater body 13 is provided with the heater 1 disposed inside thereof.
2 and the cooling pipe 31, and a first thermometer (for example, thermocouple type thermometer) 3 installed in advance inside the heater body 3
When used in combination with 2, the substrate 14 described later
The temperature of can be set to any value. Further, the temperature of the surface of the substrate 14 is set to the second temperature which is previously set on the surface of the substrate.
Is measured by a thermometer (for example, thermocouple type thermometer) 33.

As the power source for heating the substrate surface, a DC power source, a commercial frequency power source (50 Hz, 60 Hz) and a half wave,
A power supply having a built-in full-wave rectifier can be used as appropriate.

Further, since the substrate surface heating heater 15 generates a high frequency (for example, 13.56 MHz) voltage induced by the electric field and magnetic field generated by the ladder antenna type electrode 23 (induction noise), it is high. For grounding a frequency (eg 13.56 MHz) voltage, a high frequency removal capacitor (eg 13.56 MHz, 600 p
F) Remove induced noise via 34.

Next, an example of manufacturing a high quality amorphous silicon film using the apparatus shown in FIG. 1 will be described.

First, the basic characteristics of the substrate heater body 13 and the substrate surface heater 15 were confirmed using the apparatus shown in FIG. SiH ₄ was supplied into the reaction vessel at a flow rate of 80 SCCM, and the pressure was adjusted to 50 mTorr with a pressure gauge (not shown). The temperature of the substrate surface heater 15 measured under these conditions (not shown, for example, an ultrafine (15 μm diameter) thermocouple is attached to the heater surface for measurement) and the substrate surface temperature (second
The output of the thermometer 33 is shown in FIG.

In the basic characteristic confirmation test, the substrate was taken in and out ten times under each condition in order to simulate the actual film formation. In FIG. 4, the variation of the measured value (I mark) is the second thermometer 33.
The substrate 14 provided with the
The variation of the result of measuring 0 times is shown. However, the temperature of the substrate heater body 13 was 120 ° C.

Further, under the above conditions, the temperature of the substrate surface heating heater 15 was set to room temperature, and the relationship between the temperature of the heater and the temperature of the substrate heating surface when only the substrate heating heater body 13 was used for heating was grasped. The result is shown in FIG.

In FIG. 5, variations in measured values (I mark)
Indicates the variation in the results of measuring the substrate 14 provided with the second thermometer 33 in and out of the reaction container 11 ten times. It should be noted that in FIGS. 4 and 5, the variation greatly differs depending on whether the substrate surface heater 15 is used or not.
As shown in FIG. 6, when the substrate surface heater 15 is used (temperature Tw), since the surface side (Ts) of the substrate 14 is higher than the temperature of the substrate back side, the substrate 14 and the substrate heater body 13 come into contact with each other. While the influence of the situation is small, on the other hand, when the substrate surface heater 15 is not used, the substrate 14 receives heat only from the surface (Th) side of the substrate heater body 13 as shown by the dotted line in FIG. Therefore, it is considered that the contact situation has a great influence.

Next, the plasma potential distribution was measured by the probe method (also referred to as Langmuir probe method) with and without the heater for heating the substrate surface. The result is shown in FIG. 7.
As shown in FIG. 7, when the substrate surface heating heater 15 is used for heating, the plasma potential between the surface of the substrate 14 and the substrate surface heating heater 15 is between the heater 15 and the ladder antenna type electrode 23. It is about 1/4 smaller than the plasma potential. That is, the plasma in the vicinity of the surface of the substrate 14 is weak, indicating that SiH ₄ is not decomposed or dissociated by glow discharge plasma.

This phenomenon is caused by high quality amorphous silicon.
It is extremely important for the production of membranes. That is, in FIG.
The effect that the plasma is shielded by the substrate surface heater 15
Due to the presence of the fruit, it is possible to reach the surface of the substrate 14
Zical is a long-life SiH ₃Radicals are dominant and short
Lifetime SiH₂Radicals on the way, for example SiH ₂+ H
₂→ SiH_FourAnd so on. Therefore, in this state
Is SiH₃Radical-based high-quality film, that is, low
A film having a defect density can be formed. Note that the substrate surface temperature
High and low reached SiH₃Radical diffusion on the substrate surface
High accuracy control of the temperature because it is related to the length of the distance
Is an even more important factor. Based on the above findings,
An amorphous silicon film is manufactured as shown below.
It was

<Typical film forming conditions> SiH ₄ flow rate: 80 SCCM Pressure: 50 mTorr RF power: 50 W Substrate surface temperature: 140 to 220 ° C. Substrate heating heater wire interval: 1 to 20 mm Substrate: Corning 7059 glass <Deposition method > A 1.1 mm thick glass substrate is ultrasonically washed with a neutral detergent, washed with pure water and dried, and then with acetone and then with ethanol. The glass substrate is set on the substrate heater of the apparatus shown in FIG. The reaction vessel is evacuated and the degree of vacuum is maintained up to about 2 × 10 ⁻⁸ Torr. Next, while keeping the substrate heater and the substrate surface heater at a predetermined temperature, the vacuum evacuation is continued and the impurities in the reaction vessel are removed by baking. The cleanliness inside the reaction container is monitored by a mass spectrometer (not shown), and after reaching a predetermined cleanliness, SiH ₄ gas is supplied through the reaction gas introducing pipe 21. SiH ₄ gas flow rate 80 SCCM, pressure 50 mTo
RF set to rr and supplied to the ladder antenna type electrode
Power is 50W, and substrate surface temperature is 140 ° C to 220 ° C.
℃ and substrate surface heating heater wire interval 1mm to 20m
An amorphous silicon film having a thickness of 1 μm was manufactured. In order to measure the defect density of the manufactured amorphous silicon film, aluminum (Al) coplanar electrodes were formed on the film by a vacuum deposition method at intervals of 0.2 mm.
Then, the defect density of the amorphous silicon film was measured by the steady photocurrent method (CPM method).

The results are shown in FIG. As shown in FIG. 8, the substrate surface heating heater 15 and the substrate heating heater 13
By using the combination of
The substrate surface heater 1 is maintained at 0 ° C. to 200 ° C.
By utilizing the plasma shielding effect of No. 5, a high-quality amorphous silicon film having a defect density of 10 ¹⁴ defects / cm ³ was obtained. Also, the wire rod spacing of the wire rod heater 16 of the heater 15 for heating the substrate surface is set to 1 mm to 20 mm, and the film deposition time dependency, that is, a film thickness equivalent to depositing a film having a film thickness of 3000 Å about 100 times: about 30 μm Was formed into a film, and the change in the film formation rate was measured. However, the wire 16 of the heater had a diameter of 0.2 mm. The result is shown in FIG.

From FIG. 9, it was found that if the wire interval of the heater is 3 mm or more, there is almost no dependency of the film formation rate on the film formation time. That is, in FIG. 9, the initial film formation rate is (R ₀ ), the film formation rate at the time of forming a film thickness of 30 μm, which corresponds to the film formation of about 3000 Å film about 100 times, is R ₁₀₀ , The reduction rate of the film formation rate is [1- (R ₁₀₀ / R
₀ )] and the reduction rate is illustrated. Figure 9
According to the above, if the wire interval of the heater is 3 mm or more,
It was found that there was almost no blockage due to the amorphous silicon film attached to the heater.

It should be noted that, when the wire diameter of the wire rod of the heater for heating the substrate surface is set to about 1 mm, the results are similar to those shown in FIGS. 8 and 9. Furthermore, as a result of using 30 MHz in addition to 13.56 MHz as the frequency of the high frequency power source, the plasma potential distribution in FIG. 7 tended to decrease the plasma voltage. That is, the film quality tended to be higher.

[0035]

As described above in conjunction with the embodiments, the present invention is applied to a substrate heating temperature in an apparatus for manufacturing an amorphous semiconductor thin film for forming an amorphous silicon thin film on a substrate arranged in a reaction vessel. Since the heater for controlling the temperature is formed of a rod-shaped wire rod, the temperature of the surface of the substrate can be accurately controlled by using the wire rod heater made of the rod-shaped wire rod, and the film thickness can be easily controlled in the film forming process. Become.

Since a capacitor is added as a means for short-circuiting the induced voltage of the high frequency component to the ground, it is not affected by the electric field generated by the ladder antenna type electrode of the plasma source,
The substrate surface heating heater is prevented from becoming the second electrode without inducing a noise voltage.

Reaction gas (eg SiH ₄ ) with high frequency power
Is converted into plasma and various types of radicals such as SiH ₃ and SiH ₂ are generated, and the radicals are diffused to the surface of the substrate to form an amorphous silicon-based thin film. It was shielded by a heater for heating the substrate surface provided on the side to prevent the above plasma from being generated near the substrate surface. This effect is that only the SiH ₃ radical having the longest life, that is, the longest diffusion length, can reach the substrate surface predominantly among the various radicals described above, and a high quality thin film can be formed.

In the present invention, by using a ladder antenna type electrode with a small pressure loss due to reaction gas supply as an electrode,
The reaction gas supply control can be performed accurately, and it is difficult to control due to the pressure loss of the reaction gas as in the case of using a pair of parallel plate electrodes called a cathode and an anode as a conventional plasma generation source. Was prevented.

Further, according to the present invention, in the above-mentioned apparatus for producing an amorphous semiconductor thin film, a box-shaped gas mixing box into which a reaction gas is introduced is arranged in the reaction vessel, and the substrate of the gas mixing box is placed on the surface. Since the ladder antenna type electrode is provided so as to cover the opening and the opening is provided on the side where all the reaction gas is supplied, the reaction gas is supplied between the ladder antenna type electrodes and the efficiency is improved. Reaction becomes possible.

[Brief description of drawings]

FIG. 1 is a schematic view of an apparatus for producing an amorphous semiconductor thin film of the present invention.

FIG. 2 is a schematic view of a substrate surface heater of the present invention.

FIG. 3 is a schematic view of a ladder antenna type electrode of the present invention.

FIG. 4 is a diagram showing the relationship between the temperature of the substrate surface heater and the temperature of the substrate surface.

FIG. 5 is a relationship diagram between the temperature of the substrate heater body and the temperature of the substrate surface.

FIG. 6 is a diagram showing a temperature state at each position of substrate heating.

FIG. 7 is a diagram showing a state depending on the plasma potential and the presence or absence of heating of the substrate surface.

FIG. 8 is a diagram showing a relationship between a substrate surface temperature and a defect density.

FIG. 9 is a diagram showing the relationship between the distance between the wire rods of the heater for heating the substrate surface and the reduction rate of the film formation rate.

FIG. 10 is a schematic view of a conventional plasma CVD apparatus.

FIG. 11 is a diagram showing the relationship between the mesh electrode temperature and the defect density of a conventional plasma CVD apparatus.

FIG. 12 is a diagram showing a state in which an amorphous silicon film is attached to a mesh electrode.

FIG. 13 is a diagram showing the relationship between the number of film formations and the film formation rate using a conventional plasma CVD apparatus.

[Explanation of symbols]

01 Reaction container 02 Cathode electrode 03 Anode electrode 04 Mesh electrode 05 Heating power supply 06 Transformer 07 Slide vacuum 08 High vacuum exhaust port 09 Pressure adjustment exhaust port 11 Reaction container 12 Heating heater 13 Substrate heating heater main body 14 Substrate 15 Substrate surface heating heater 16 Wire material heaters 17a, 17b Power supply wires 18a, 18b Current introduction terminal 19 Substrate surface heating power supply 20 Gas mixing box 20 Opening 21 Gas introduction pipe 22 Reactive gas (SiH ₄ ) 23 Ladder antenna type electrode 24 Frame material 25 Ladder member 26a , 26b Power supply points 27a, 27b Power supply lines 28a, 28b Current introducing terminal 29 High frequency power source 30 Impedance matching device 31 Cooling pipe 32 First thermometer 33 Second thermometer 34 High frequency noise removing capacitor

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tatsushi Aoi 5-717-1 Fukahori-cho, Nagasaki-shi, Nagasaki Mitsubishi Heavy Industries, Ltd. Nagasaki Research Institute (72) Inventor Akemi Takano 5-chome, Fukahori-cho, Nagasaki-shi, Nagasaki Prefecture 717-1 Mitsubishi Heavy Industries, Ltd. Nagasaki Laboratory (56) Reference JP-A-5-70958 (JP, A) JP-A-7-99159 (JP, A) JP-A-8-253864 (JP, A) ( 58) Fields investigated (Int.Cl. ⁷ , DB name) H01L 21/205

Claims (3)

(57) [Claims] 1. An apparatus for producing an amorphous semiconductor thin film for forming an amorphous silicon thin film on a substrate arranged in a reaction vessel, wherein the substrate is provided between the substrate and a ladder antenna type electrode for generating glow discharge plasma. An apparatus for producing an amorphous semiconductor thin film, comprising: a substrate surface heating heater for heating the surface of the substrate, wherein the heater for controlling the surface heating temperature is formed of wire rods having a predetermined interval. 2. The apparatus for producing an amorphous semiconductor thin film according to claim 1, wherein the substrate surface heating heater is grounded through a capacitor. 3. The apparatus for producing an amorphous semiconductor thin film according to claim 1, wherein a gas mixing box into which a reaction gas is introduced is arranged in the reaction container, and the gas mixing box is provided on the side facing the substrate. An apparatus for manufacturing an amorphous semiconductor thin film, which has an opening, and a ladder antenna type electrode is provided so as to cover the opening.