JPS59145042A - Vapor deposition method - Google Patents

Abstract

PURPOSE:To form a vapor deposition film having desired film characteristics, by holding a substrate to a temp. of 450 deg.C or less in the presence of ionized or activated modifying gas such as hydrogen from a magnetron type gas discharge device. CONSTITUTION:A vacuum pump is connected to a bell jar 1 forming a vacuum tank through an exhaust passage 3 having a butterfly valve 2. A heater 5 for heating a substrate 4 to be vapor deposited arranged in the bell jar 1 to 450 deg.C or less and a DC power source 6 for applying DC negative bias voltage to the substrate 4 are provided. In addition, an evaporation source 7 is arranged so as to be opposed to the substrate 4 and a magnetron type DC ion gun 18 is provided in the bell jar 1 as a gas discharge device so that the gas discharge port thereof is opposed to the substrate 4. By this constitution, for example, an amorphous silicon membrane having hydrogen mixed therein can be formed.

Description

DETAILED DESCRIPTION OF THE INVENTION 1. Industrial Application Field The present invention relates to a vapor deposition method, for example, a vacuum suitable for forming a film of amorphous silicon modified with an element such as hydrogen (hereinafter abbreviated as a-3t). The present invention relates to a vapor deposition method.

2. Conventional technology To form a thin film such as a-3t, glow discharge method, sputtering method, vapor deposition method, etc. can be used, but among these methods, vapor deposition method has a high film formation speed and can also be used for large-area i-films. It is excellent in that it can be formed relatively easily.

On the other hand, thin films such as A-3T are useful in various fields including semiconductor devices, but they are not only made of substances that can be evaporated or sublimated by heating, but also contain other modifying elements in such substances. It is desired to form a thin film having desired characteristics by incorporating it by a vapor deposition method. For example, a-8i, which has recently attracted attention as a solar cell or photoconductive material, has an amorphous structure with irregular atomic arrangement, which inevitably causes unbonded dangling bonds. It is necessary to seal the material by eg, etc., and only then can it become useful as a semiconductor material. Conventionally, such a-3i
Although a satisfactory result has been obtained by a glow discharge method using silane gas, it would be extremely advantageous if an equivalent result could be obtained by a vapor deposition method for the reasons mentioned above.

However, in the vapor deposition method, simply making a supply gas of a modifying element (hereinafter referred to as a modifying gas) exist in the vapor deposition space results in a very small amount of the modifying element being mixed into the deposited film. Forming thin films with these properties is extremely difficult. This is mainly due to the fact that the modifying gas is molecular and stable.

Under these circumstances, it is considered that if the modifying element is ionized or activated and present in the vapor deposition space, the reactivity with the evaporated substance will increase and the modifying element can be effectively mixed into the deposited film.

For example, it has been proposed to introduce an ionized component obtained by discharging a modifying gas in a gas discharge tube using a DC glow discharge into a vacuum chamber. This can be achieved by arranging a means to generate electrical discharge in the vacuum chamber.
Since both the conditions necessary for this discharge and the conditions necessary for vapor deposition must be satisfied at the same time, the setting of conditions is actually limited and it is necessary to avoid not being able to obtain a large degree of freedom. It is something that

The method of mixing a modifying element into a deposited film using such a gas discharge tube is somewhat effective, and has been confirmed in the formation of hydrogen-containing a-3t.

However, as a result of studies conducted by the present inventors, it has been found that when using a gas discharge tube such as the one described above, there are
It has been found that it is not possible to mix modifying elements in a controlled ratio with a large degree of freedom, and in particular, it is not possible to increase the content ratio.

Moreover, the temperature of the substrate on which the deposited film is formed has not been sufficiently studied up to now, and it has been found that depending on the set substrate temperature, only a deposited film with poor characteristics can be obtained.

3. Purpose of the Invention The present inventor has discovered a gas discharge device with significantly higher ion generation efficiency than conventional gas discharge tubes, and has also made rigorous considerations for the first time regarding the substrate temperature, and has determined the electrical conductivity of the deposited film. The optimum temperature range that can significantly improve the properties has been established.

Therefore, an object of the present invention is to provide a vapor deposition method that can increase the amount of modifying elements introduced into a deposited film with good controllability and form a deposited film with desired film characteristics.

4. Structure of the invention, that is, the vapor deposition method according to the present invention deposits silicon, etc. The present invention is characterized in that when the evaporation material from the evaporation source is deposited onto the substrate, the substrate is maintained at a temperature of 450° C. or lower.

5. Examples In the following, the invention will be illustrated in detail with reference to the drawings.

FIG. 1 shows an example of a vapor deposition apparatus.

In this vapor deposition apparatus, a vacuum pump (not shown) is connected to a pelger 1 forming a vacuum chamber via an exhaust path 3 having a butterfly valve 2.

A heater 5 that heats the substrate 4 to be evaporated placed in the Pelger l to 450° C. or less, and a DC power supply 6 that applies a negative DC bias voltage to the substrate 4 (or its rear electrode if it is insulative). will be established. Further, an evaporation source 7 is arranged to face the substrate 4, and a magnetron-type DC ion gun 18, which will be described later as a gas discharger, is provided on the Pelger 1 so that its gas outlet faces the substrate 4. Using the vapor deposition apparatus configured as described above, for example, a thin film of amorphous silicon mixed with hydrogen can be formed in the following manner.

That is, the inside of the Pelger 1 is evacuated to a vacuum state of 10 to 1 Q Torr, the substrate 4 is heated to a temperature of 450° C. or less by the heater 5, and a negative DC voltage of -10 KV or less is applied to the substrate 4 by the DC power source 6. , hydrogen gas 9 as a modifying gas is supplied to the ion gun 18, hydrogen ions or active hydrogen from the ion gun 18 are introduced into the Pelger 1, and the negative DC voltage is applied as a bias to the substrate 4.
The evaporation source 7, which uses silicon as the evaporation source material, is heated by an electron gun heating method (not shown) to evaporate the silicon, thereby forming a thin film of a-3i mixed with hydrogen on the substrate 4. form.

FIG. 2 shows a magnetron type DC ion gun that constitutes the gas discharge tube 18 used above.

This ion gun includes a holder 42, an extraction electrode 43 made of a metal mesh provided on the ion exit 41 side, an anode plate 44 provided to face the extraction electrode 43, and a structure between the extraction electrode 43 and the anode plate 44. It has a cathode plate 40 with a through hole 45 arranged at an interval of about several mm from an anode plate 44, and an electromagnet 46 arranged around the outer periphery of the cathode 40.

A modifying gas introduction pipe 47 is connected near the anode plate 44,
Further, the ion outlet 41 is arranged so as to point toward the substrate @4 from the extraction electrode 43 on the exit side of the ion gun. 48 is a power source (voltage VA) for the anode plate 44, and the applied voltage is 2 KV or less; 50 is a power source for the electromagnet 46, and the magnet (coil) current thereof is O to IA. The extraction electrode 43 is at ground potential in this example, and a cathode power source 49 (
A voltage Vc) is connected, and 0≦VC≦VA. Note that the holder 42 is at the same potential as the cathode 40.

In such an ion gun 18, the modified gas introduction pipe 4
For example, hydrogen gas introduced into the discharge space from 7 is introduced between the anode plate 44 and the cathode plate 40 and is ionized by the discharge, and the ions are magnetically trapped in the space of the through hole 45 by the electromagnet 46. , the vehicle is efficiently accelerated only in the direction of the arrow. Hydrogen ions are extracted from the plasma due to the potential difference with the extraction electrode 43, are introduced into the Pelger 1 through the extraction electrode 43, and are directed toward the substrate 4 by a bias voltage applied to the substrate 4 to be deposited or the electrode behind it. It flies while being attracted efficiently. At the same time, silicon vapor, for example, flies from the evaporation source 7 and collides with the substrate 4, and as a result, a thin film of a-5t mixed with hydrogen is formed on the substrate 4.

As described above, the ions of the modifying gas and the active gas are generated in the magnetron-type DC ion gun or the gas discharger 18 and introduced into the Pelger 1, and the evaporation source material is evaporated in the presence of the modified gas ions and active gas. A thin film mixed with a modifying element can be formed. Moreover, the ion gun 18 is functionally independent from the Pelger 1, and its anode plate 44, cathode plate 40, electromagnet 46, and extraction electrode 43 are
, the magnetic force of the electromagnet 46, the supply amount of the modifying gas, the bias voltage applied to the substrate 4, and the temperature can be individually controlled, and the evaporation rate of the evaporation source 7 can also be controlled. It is possible to control the mixing ratio of modifying elements in a wide range. In particular, the ion gun 18
The Pelger 1 can generate a large amount of ions and active gas even at low power compared to known gas discharge tubes that use simple direct current discharge. The mixing efficiency into the thin film is high, and therefore a thin film having desired properties with a high content of the modifying element can be formed. In the example described above, it is possible to form an a-3t thin film in which hydrogen is mixed at a content rate as high as 30 atom %. In addition, since the modifying element can be mixed with high efficiency in this way, the film forming rate can be further increased without taking advantage of the advantage of the vapor deposition method, which originally provides a high film forming rate. For example, it is also possible to advantageously use a long substrate 4 and move it at a high speed to continuously form a desired thin film on its surface.

However, in the ion gun 18 described above, the extraction electrode 43 is not necessarily necessary, and the cathode 40 and holder 42
may be grounded. Alternatively, the ion gun can be driven with alternating current by applying an alternating current voltage between the cathode and the anode.

Regarding the positional relationship between the ion gun 18 and other members inside the Pelger, the distance between the ion gun 1B and the substrate 4 is the shortest (shorter than the distance to the inner wall surface of the Pelger that is grounded). By doing so, the substrate itself can serve as an ion extraction electrode for an ion gun. Furthermore, since the voltage between the cathode of the ion gun and the substrate can be made sufficiently large by applying a negative voltage to the substrate, ions can be efficiently extracted from the ion gun and delivered to the substrate.

In short, in the ion gun used in this example, even if the above-mentioned extraction electrode 43 is omitted, the substrate can function as an extraction electrode. To do this, move the ground source such as the Pelger wall away from the ion gun as described above.
It is desirable to apply a negative voltage to the substrate.

In addition, when making the deposited film contain a predetermined amount of hydrogen, the known gas discharge tube described above has a small ion (or activated gas) supply capacity, so the rate of Si deposition must be reduced. In the case of the magnetron method, it is possible to form a film with a predetermined hydrogen content even if Si is blown away at high speed. Although it is possible to form a high-resistance film of the required 10 Ω-cm, it is not possible to obtain a film with such performance because known gas discharge tubes cannot supply the required amount of hydrogen at the same speed, and the film must be formed at a much slower rate. In general, just because a thin film has a high hydrogen content does not necessarily mean it has high resistance; the point is that it only needs to contain the required amount of hydrogen.The required hydrogen content varies depending on each film. Although it is different, it is generally considered to be about 10%. Therefore, when the hydrogen supply capacity is small, such as in a known gas discharge tube, the hydrogen content will be less than a few percent at high speeds, and the film quality will be poor.
It becomes impossible to obtain a high resistance film such as 1012 ohms.

In the vapor deposition method using the ion gun 18 described above, the heating temperature (substrate temperature) of the substrate 4 by the heater 5 is set to 450°C.
It has been found that the following settings are essential requirements that can significantly improve the characteristics of the deposited film. This will be explained in detail below.

For example, vapor deposition was actually performed under the following conditions.

Supply hydrogen amount 100-250cc/m1n (e.g. 1
50cc/min) Degree of vacuum in Pelger 2 x 10 to 5 x 10 Torr (e.g. 7 x 10 Torr) Magnetron type DC ion gun anode voltage 0.5 to 2 KV (e.g. 1.7 KV) Coil current 0.4 A or less (e.g. 0.3A) Substrate voltage -2 to -6KV (e.g. -4KV) Silicon deposition rate 30 persons/Sec Deposited film thickness 1 μm Substrate quartz glass substrate Under these conditions, the substrate ion current (due to the adhesion of cations to the substrate A sufficient value of about 40 mA was obtained for the current flowing through the substrate (in the direction in which cations flow).

As a result of vapor deposition under the above conditions, the characteristics of the vapor deposited film (electrical conductivity)
It was found that, as shown in FIG. 3, it depends on the substrate temperature. In other words, when the substrate temperature is around 450°C, Δm (change in electrical conductivity when irradiated with white light) changes rapidly, and below 450'c it is almost uniform and can be maintained at a high value, but at 450'c
If it exceeds this value, the photoresponsiveness will drop sharply and the photoresponsiveness will deteriorate significantly. This means that when the substrate temperature is up to 450'C,
This is believed to be because trivalent silicon hydride (esiH) constituting the deposited film does not undergo hydrogen dissociation and can exist stably. Moreover, in this temperature range, the 5i-1 bond of divalent silicon hydride ()ssH2 is broken in a relatively low temperature range (particularly around 250°C and above), so the deposited film The proportion of the trivalent silicon hydride increases, and it becomes a substantial component of the deposited film.As a result, as shown in the figure, σD (electrical conductivity in the dark) decreases and the dark resistance increases. As a result, the potential holding ability of the photoreceptor film etc. is improved. However, when the substrate temperature exceeds 450"C, the above 3.
The valent silicon hydride 5i-H bonds are also broken, hydrogen atoms are removed, and the number of dangling bonds increases rapidly.As a result, the αD of the deposited film increases and at the same time, the value of slightly less than 60 rapidly decreases, resulting in a significant deterioration of the film properties. do.

From the above facts, maintaining the substrate temperature at 450° C. or lower is an extremely important requirement for film properties, and this was discovered by the present inventor. The lower limit of this substrate temperature range is preferably 150°C;
This is because when the temperature is below .degree. C., voids and defects are likely to occur in the deposited film due to lack of thermal energy, and the mass density thereof tends to become coarse. Further, within this temperature range of 150 to 450°C, a temperature of 250 to 400°C is particularly desirable. That is, 25
Below 0°C, the amount of divalent silicon hydride increases relatively and the amount of hydrogen in the deposited film increases, and as shown in Figure 3, Cip increases, but above 250°C, the above-mentioned For this reason, the amount of divalent silicon hydride decreases, and 3
Hydrogenated silicon comes to mainly constitute the film, and αD is reduced to a sufficient value. Also, the substrate temperature is 400℃
If it exceeds Δ0, the Δ0 value may tend to decrease due to fluctuations in substrate temperature (i.e. fluctuations in heater power supply), etc.
Variations may easily occur in the values.

In addition, in the method of the present invention, when a magnetron-type DC ion gun as shown in FIG. At the same time, the silicon deposition rate, which is determined by the ion supply amount, can be reduced to 30 people/5ec compared to the conventional method (for example, IO people/5ec).
sec.

The above substrate temperature range (450°C or less, especially 250°C to 40°C)
The hydrogen-containing a-St film obtained at 00°C) satisfies both charge retention ability and photosensitivity, and is composed of divalent silicon hydride (;5iH2) and trivalent silicon hydride (;5iH2). “ESjH) is the ratio of each infrared absorption intensity ratio (I
When expressed as I/I2), O≦11/12≦0.
It is desirable that it be 3.

However, lx is divalent hydrogenation at wave number 2100=':
The infrared absorption intensity of Nocon, I2 is the wave number 2000cm-1
This is the infrared absorption intensity of trivalent silicon hydride. The above It/12 is set to 0 to 0.0 depending on the substrate temperature range.
If the infrared absorption intensity ratio is set within the range of 3 and the film is mainly composed of trivalent silicon hydride (3SiH), the dangling bonds of Si can be sufficiently filled, and hydrogen can be thermally dissociated. Heat resistance can also be improved because of trivalent hydrogenated silicon, which is less likely to cause. It is further desirable that the above-mentioned infrared absorption intensity ratio be 0≦I+/12≦0.1, but this is especially true for the proportion of divalent silicon hydride that tends to cause hydrogen dissociation thermally (at about 250°C). reduce 4
This is because the heat resistance of the photoreceptor can be further improved by overwhelmingly increasing the amount of trivalent silicon hydride that does not undergo hydrogen dissociation even at around 50°C. In this sense, all the bonding species in the a-3 amount consist of trivalent silicon hydride (i.e., the above I
I/12=0) is desirable.

It was confirmed that a certain desirable range exists for the hydrogen content in a-3i in relation to this infrared absorption intensity ratio. That is, its hydrogen content is 3.5 to a-St.
It is preferable to set it as 2Qatom% (percentage of the number of atoms), but
This is because when the amount of hydrogen is less than 3.5 atom%, the dark resistance becomes low and the photoresponse becomes poor because the dangling bonds cannot be compensated for, and when the amount of hydrogen exceeds 20 atom%, the infrared absorption intensity ratio Even if l/I2≦0.3, the photoresponsiveness is good, but the dark resistance is not very high, and 1
Conversely, when 1/12>0.3, the dark resistance is high, but the photoresponsiveness is poor, and the amount of divalent silicon hydride increases, resulting in poor heat resistance, resistance fluctuations during light irradiation, and oxidation when left in the air. This is because instability, such as being easily damaged, may occur.

However, this hydrogen amount is set to 3.5 to 2 Qatom% (more preferably 6 to 1Qatom%) and the above II/
When 12 is 0.3 or less, dark resistance and photoresponsiveness can be both well-balanced and thermally stable a-3t can be obtained. In this case, the above 11/+2>0
．． 3, when the amount of hydrogen approaches 3.5 a tom%, both the dark resistance and the photoresponsiveness are poor, and 2Qato
If it is close to m%, the dark resistance is high but the photoresponse is insufficient.
It is difficult to find a region where dark resistance and photoresponsiveness are well balanced.

Therefore, in the photoreceptor obtained by the present invention, the above L/
While I2 is set to II/I2≦0.3, it is desirable that the hydrogen content in a-3i is also set to 3.5 to 20 atom%.

In the above, the manner in which Si and H in a-3i bond and the amount of bonded H can be determined from the infrared absorption spectrum. In other words, since the stretching mode of 5i-H (i.e. '; 5iH) can be obtained around the wave number 2000 cm, it is possible to determine the binding mode of 5i-H by the wave number position and the HM of the binding by the absorption intensity. can.

Figure 4 shows the infrared absorption intensity ratio (Il/I2) mentioned above.
This is experimental data showing the relationship between the H content of a-3i and its hardness resistance. According to this, 0-≦1/12
In the range of ≦0.3, ρD/ρG (ρD: dark resistance, ρ
G: resistance when irradiated with green light) can be increased, and a
-8i H amount from 3.5 to 20 atom% (especially 6
~10 atom%), both dark resistance and ρD/ρG are sufficient, making it suitable as a base material for a photoreceptor. In addition, the light irradiated here is 200, LjW, 530
It was nm.

In general, a-3i is produced using a known glow discharge device.
When forming a film of :H, due to the nature of the manufacturing process, as shown in Figure 5, increasing the substrate temperature will lower the hydrogen content in the film, and conversely, lowering the substrate temperature will decrease the hydrogen content. There is a tendency to increase. On the other hand, according to the vapor deposition method of the present invention,
The combination of substrate temperature and the use of a magnetron-type gas discharger results in a film with high hydrogen content (5th) even at high substrate temperatures.
In addition, at low substrate temperatures, the hydrogen content can be reduced (region B in FIG. 5).

That is, the method of the present invention has a function of forcibly introducing hydrogen into the film or suppressing the amount of hydrogen introduced.

In addition, as modifying gases that can be used in the above example,
Any gas may be used as long as it provides ions and activated products of elements that can be mixed into the substance formed by vapor deposition by the evaporation source, and gases consisting of a single element such as halogens such as I2.02, N2, and F2'J may be used. In addition to gases, compound gases can also be used. For example, N I5.5iHq, PH5
, B2H6, A s I5, and hydrocarbons such as CHn, freon, etc. In this case, for example, if part of the hydrogen gas is replaced with hydrocarbon gas, a thin film of amorphous silicon carbide mixed with hydrogen can be obtained.

Further, as the evaporation source material contained in the evaporation source 7, all materials that can be generally deposited, such as Si and Ge, can be used. The number of evaporation sources 7 may be plural. In the case of forming an a-3i thin film as described above, co-evaporation can also be performed using an evaporation source of an element of group Ⅰ or group V of the periodic table. For example, a thin film of p-type or n-type amorphous silicon can be obtained.

The thin film formed by the apparatus of this example has a-3i: H, a-3i: F, .
a-3i:H:F, a-3iC:H, a-3iC:
F, a-8iC:H:F, etc. are obtained. In this case, if germanium is used instead of silicon as the evaporation source, corresponding hydrogenated and/or fluorinated amorphous germanium etc. similar to the above can be obtained.

The heating method of the evaporation source 7 is electron gun heating, resistance heating,
Any method such as induction heating may be used.

It is also preferable to have a structure that can prevent coarse particles from flying away.

Although the present invention has been illustrated above, the above-mentioned example can be further modified based on the technical idea of the present invention.

For example, the structure of the gas discharger such as the above-mentioned magnetron-type DC ion gun can be modified in various ways, and its position within the Pelger is not limited to the above-mentioned example. In order to attract the modifying gas ions toward the substrate, in addition to applying the bias voltage described above, a magnetic field may be formed near the substrate by an induction coil or the like.

When a magnetic field is generated, the ion particles are accelerated by the ion gun and are effectively deflected toward the substrate.

6. Effects of the Invention As described above, in the present invention, since the vapor deposition is carried out while maintaining the temperature of the substrate to be vaporized at 450° C. or lower, a vapor deposited film having the desired resistance value or electrical conductivity can be reliably obtained. . Furthermore, since a magnetron type gas discharger is used, the ion generation efficiency can be increased with low power, and ions can be introduced into the membrane with easy control.

[Brief explanation of the drawing]

The drawings are for explaining the present invention; Fig. 1 is a schematic cross-sectional view of the vapor deposition method, Fig. 2 is a cross-sectional view of a magnetron-type DC ion gun, and Fig. 3 is a diagram showing the substrate temperature and electrical conduction of the vapor-deposited film. Figure 4 is a graph showing the relationship between the hydrogen content of the a-3T film and the hydrogen content of the a-3T film. --- Heater 6 --- Bias voltage 7 --- Evaporation source 9 --- One modification gas 18 --- Magnetron type DC ion gun 40 ---
-Cathode 43---One extraction electrode 44---One anode 46---An electromagnet.

Claims (1)

[Claims] 1. When evaporating material from an evaporation source onto a substrate in the presence of an ionized or activated modification gas from a magnetron-type gas discharger, A vapor deposition method characterized by maintaining the temperature at 450°C or less. 2. The method according to claim 1, wherein the temperature of the substrate to be deposited is maintained at 250 to 400'C. 3.1 Claim 1 or 2 characterized by a magnetron type DC ion gun as the magnetron type gas discharger
The method described in section. 4. The ionized modification gas from the gas discharger is attracted onto the substrate to be deposited by applying a bias voltage to the substrate to be deposited, according to any one of claims 1 to 3. The method described.