JPH0697079A - Manufacture of amorphous silicon - Google Patents

Abstract

PURPOSE:To reduce a plasma damage in the interface and a defect density in a film, by using a gas containing Si and specifying a substrate temperature and an applied frequency and generating a plasma and depositing an amorphous silicon. CONSTITUTION:A glass substrate 102 is mounted on an anode electrode 101 in a chamber 100, and an exhaust is performed by a drainage pump 109, and a substrate temperature is maintained to 300 to 600 deg.C. An SiH4 gas is introduced into the chamber 100 and is held for 30 minutes. Then, a VHF high frequency with an applied high frequency of 30MHz or higher is applied, and a matching device 104 is regulated and a discharge is started, and the discharge is performed by a necessary time and a film is formed. Accordingly, a silane radical can be stably increased and the film can be formed in a manner that ions by which film characteristics are deteriorated are enclosed in a plasma.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing amorphous silicon. In particular, it relates to a manufacturing method for forming amorphous silicon by using a plasma chemical vapor deposition method.

[0002]

2. Description of the Related Art In recent years, semiconductor devices using amorphous silicon have been actively developed.
In particular, the development of solar cells and photosensitive drums of copying machines that can be manufactured in a large area and at low cost, the development of thin film transistors for liquid crystal displays, and the development of solid-state imaging devices for facsimiles that can be made lightweight and small are active. Conventionally, as a method of depositing an amorphous silicon film used in these semiconductor devices, silane Si is used.
An RF plasma CVD method using H ₄ or disilane Si ₂ H ₆ as a film forming gas, or a reactive sputtering method in which hydrogen gas is mixed with silane and argon gas and a silicon target is sputtered has been used. In the generally popular plasma CVD method, hydrogen gas is mixed with silane or disilane, plasma is generated at a high frequency in the RF band of 13.56 MHz, and the gas is decomposed by the plasma to produce a reactive active species. An amorphous silicon film is deposited on the substrate. However, these films contain 10% or more of hydrogen, which is considered to be the cause of photodegradation, and are greatly damaged by ions in plasma, so that the defect density in the film could not be lowered to about 10 ¹⁵ / cm ³ .
Attempts have been made to reduce hydrogen in this film and suppress photodegradation. For example, a method has been proposed in which hydrogen plasma treatment and film formation are alternately repeated to reduce hydrogen in the film and suppress photodegradation (Spring 1990, Joint Lecture on Applied Physics, 31a-ZD-11, '90. Autumn 28-p-MD-
1). However, this method has a drawback that the device configuration is practically difficult and is not suitable for mass production. On the other hand, the substrate temperature is set to 350 by using the conventional RF high frequency.
It has been attempted to reduce the defect density in the film by keeping the temperature at about ℃ and increasing the film formation speed in this state ('9
2nd Spring Joint Lecture on Applied Physics 30p-ZT-3,
4). However, in this method, since the RF high frequency is used, the pressure is increased and the flow rate ratio is changed in order to increase the film forming speed, which is a very severe condition for the film forming plasma, and abnormal discharge is caused. It is easy to occur, or the reaction in the gas phase is easy to occur, polymer formation occurs, and it is taken into the film in the form of particles, which tends to cause deterioration of the film quality, which causes reproducibility and mass productivity. It is a poor method.

[0003]

According to the present invention, in a manufacturing method for depositing amorphous silicon by using a gas containing Si by a plasma chemical vapor deposition method, a substrate temperature Ts is from 300 ° C to 600 ° C. The temperature is kept constant, the high frequency f applied is VHF high frequency of 30 MHz or higher, plasma is generated, and a film is formed to provide higher quality amorphous silicon as compared with the conventional method. Is.

More preferably, in the present invention, the substrate temperature Ts (° C.) and the applied high frequency f (MHz) are Ts =
It is desirable to apply VHF high frequency to generate plasma so as to satisfy the relationship of kf + a (0.1 ≦ k ≦ 2, a = 300), and higher quality amorphous silicon can be provided.

In the above invention, more preferably,
It is desirable to supply electric power of 10 / f (W / cm ² ) (f: MHz) or less to generate plasma, and hydrogen radical emission intensity [H ^* ] and silane radical emission intensity [S
As i H ^*] ratio of is at ^{[H *] / [Si H} *] ≦ 1, applying a VHF frequency, it is desirable to generate a plasma, to provide a higher quality amorphous silicon be able to.

In the above invention, more preferably,
It is desirable to apply VHF high frequency to generate plasma so that the inter-electrode distance d (cm) satisfies the relationship of f / d <30, and it is possible to provide higher quality amorphous silicon.

[0007]

The present inventors have conducted studies to eliminate the drawbacks of the conventional method for producing an amorphous silicon film and to improve the quality of the film. As a result, a new film formation rate that can be easily improved. I got a way. The new method will be described below. In a manufacturing method of depositing an amorphous silicon film by using a gas containing Si by plasma chemical vapor deposition, a VHF high frequency having an applied high frequency f of 30 MHz or more is applied to generate plasma to form a film. As a result, it was possible to manufacture high-quality amorphous silicon instead of the above-mentioned conventional method.

[0008] Figure 2 Si H ^* radical emission intensity of ^{(414nm) [Si H *]} , shows the application high frequency f dependency of hydrogen radicals H ^* emission intensity [H ^*]. FIG. 3 shows the dependence of the deposition rate R on the applied high frequency f. The condition at this time is Si
The H ₄ flow rate is 10 sccm, the pressure is 0.5 Torr, and the applied high frequency power is 10 mW / cm ² .

As shown in FIG. 2, when the applied high frequency f is increased,
From around f = 30 MHz, Si H ^* radicals and hydrogen radicals in the plasma start to increase accordingly. However, it can be seen that it has a maximum value around f = 80 MHz to 100 MHz, and tends to decrease thereafter.
Since the decomposition rate of silane gas or hydrogen gas depends on the electron density ne in the plasma, Si H ^* radicals and H ^* radicals generated by the decomposition also depend on the electron density ne. Therefore, it is considered that the electron density ne in the plasma has a dependency on the applied high frequency f, and the emission intensity of the radicals accordingly has a dependency as shown in FIG.

As shown in FIG. 3, the deposition rate R also starts to increase from around f = 30 MHz as the applied high frequency f increases, and reaches a maximum around f = 80 MHz to around 100 MHz. Therefore, preferably 30 MHz to 100 MHz
The effect of the present invention can be sufficiently exerted in the frequency band of. Generally, the film formation rate in silane gas is proportional to [Si H ^* ], and the tendency in FIG. 3 seems to depend on the tendency of [Si H ^* ] in FIG. It is considered that by increasing the applied frequency, the amount of silane radicals that contribute to film formation increases, which in turn increases the film formation rate.

In FIG. 4, the applied high frequency f is 13.56 MH.
The applied high-frequency power Pw dependence of the emission intensity [SiH ^* ] of the Si H ^* radical and the emission intensity [H ^* ] of the hydrogen radical at z, 50 MHz, and 100 MHz is shown. Increasing the high frequency power applied from FIG ^{4, [SiH *], [} H *] also has both increased, [Si H ^*] compared to, greater dependence towards [H ^*].

[0012] Generally, there are some conditions for forming amorphous silicon. First, the relationship of [H ^* ] / R ≦ a (a is a constant) must be established between [H ^* ] in plasma and the film formation rate R. This means that if a certain amount of hydrogen covering the film-forming surface is present, microcrystallization will occur. In the plasma using silane gas, the film formation rate R is proportional to [Si H ^* ], so this condition is [H
^* ] / [Si H ^* ] ≦ a ′ can also be rewritten. Under the actual conditions of the invention, this value was a '= 1. By increasing the applied high frequency, the gas decomposition efficiency can be increased, the film formation speed can be increased, and the film formation time can be shortened. Focusing on the point P where [H ^* ] / [Si H ^* ] = 1 in FIG. 4, the point P moves to the upper left of the figure as the applied high frequency f is increased. Applied power P at point P
w and the applied high frequency f are approximately Pw = 10 / f (Pw:
W / cm ² , f: MHz). Not only the point P, but also the point satisfying [H ^* ] / [Si H ^* ] = a ′ shows the same change. That is, in order to realize the [H ^* ] / [Si H ^* ] ratio below a certain fixed ratio at a certain applied high frequency f, there is an upper limit of the applied high frequency power. In order to increase the deposition rate at the conventional 13.56 MHz, increasing the applied high frequency power causes [H ^* ] / [Si H ^* ]
It is as described above that the value becomes large, the condition becomes such that microcrystallization easily occurs, and the film quality is deteriorated. The present invention is very effective in suppressing this ratio to be low and increasing the film formation rate.

When this is obtained under various conditions, FIG.
The upper limit is the curve of Pw = 10 / f as shown in
It has been found that the shaded area in the figure is a realizable area of the present invention. The ability to form a good quality film at a lower applied high-frequency power was particularly effective when the apparatus was enlarged and film formation was performed in a large area. In other words, despite the large size of the device, the high frequency power supply can be downsized,
It was possible to reduce the device cost. Also, even if it affects the characteristics of the film, if it can be created in a region where the applied power is small, the total energy of the ions in the plasma will decrease, so the damage caused by the ions incident on the film surface should be reduced. It is possible to produce a film having good film characteristics. Further, as described below, in order to improve the film formation rate, it is not necessary to use a high applied high frequency power region where discharge becomes unstable and abnormal discharge occurs as in the case of using RF high frequency discharge. In addition, the film formation rate could be stably and reproducibly improved. Next, this situation will be described in detail.

FIG. 6 shows that the applied high frequency f is 13.56 MH.
The applied high-frequency power Pw dependence of the film formation rate for z, 50 MHz, and 100 MHz is shown. The conditions at this time are SiH ₄
The flow rate is 10 sccm and the pressure is 0.5 Torr. A in the figure
Is 13.56 MHz, b in the figure is 50 MHz, c in the figure is 1
This is the case of 00 MHz. In each case, it can be seen that the deposition rate increases almost in proportion to the applied high frequency power.

Generally, the method used to increase the film formation speed is to increase the applied high frequency power. When the conventional frequency of 13.56 MHz is used, as can be seen from FIG. 6A, the applied high frequency power of about 30 mW / cm ² or more is required to realize the film forming rate of 20 Å / sec or more. However, the shaded area in the figure is in the state where the power is excessively supplied to the plasma, the discharge becomes unstable, abnormal discharge is likely to occur, and the production of polysilane in the gas phase increases, resulting in deterioration of the film quality. The area becomes 30 Å / s as above by using RF high frequency.
When an electric power of 30 mW / cm ² or more was applied to obtain a film formation rate of ec, a discharge unstable region of a shaded area in the figure was entered, and a film with good reproducibility and stability could not be obtained. However, as shown in b and c in the figure, as the applied high frequency was increased, the film forming rate could be easily improved with a lower applied high frequency power without any concern about abnormal discharge or generation of polysilane.

FIG. 7 shows the pressure dependence of the film formation rate. The conditions at this time are Si H ₄ flow rate of 10 sccm and applied power of 10
It is mW / cm ² . In the figure, a is 13.56 MHz, b is 50 MHz, and c is 100 MHz.
When the conventional frequency of 13.56 MHz is used, for example, a pressure of several Torr is required to realize a film forming rate of 30 Å / sec. However, when entering the shaded area in the figure, that is, the area exceeding approximately 1 Torr, the gas phase reaction is likely to occur and the production of polysilane, etc. in the gas phase becomes vigorous, and these reach the film formation surface and reach the film formation surface. It is often taken into the film or deposited on the chamber wall, and film peeling occurs, and this is taken into the film being formed, which often causes deterioration of the film quality. When a film is formed at a pressure of several Torr in order to obtain a film forming rate of 30 Å / sec as described above, the film enters the gas phase reaction region, and the film should be formed stably and with good reproducibility in this region. I couldn't. However, in the figure b,
As shown in FIG. 6C, as the applied high frequency was increased, it was possible to easily improve the film formation rate with a lower applied high frequency power without any concern about abnormal discharge or generation of polysilane.

From the viewpoint of reducing the damage of ions, attention will be paid to the movement of ions in plasma. Generally, the ions in the high frequency plasma oscillate in the plasma according to the oscillating electric field due to the high frequency in the plasma.
This situation can be expressed by the following equation. Here, A is the amplitude of oscillation of the ions.

A = V / ω V: maximum speed in one cycle of high frequency ω: angular frequency of high frequency: f = 2πω The film forming apparatus under consideration is a parallel plate type apparatus, and the distance between the electrodes is d. . Then, if the condition of d> A is satisfied, the ions in the plasma will move back and forth in the plasma without reaching the substrate. Such a state is generally called a state of being trapped or trapped in plasma. As is clear from this relational expression, by increasing the applied high frequency, it is possible to create a trapped state of ions regardless of the size of the device. By doing so, the amount of ions incident on the substrate could be reduced. The present invention intends to positively utilize such a state. By reducing the amount and energy of incident ions, it was possible to reduce defects due to these.

This is illustrated in FIG. A mass spectrometer was installed at the substrate position, and the distribution of the incident energy and the incident amount of the ions that jumped in here was determined. This data was obtained for argon gas to facilitate analysis. The reaction gas of the present invention shows essentially the same tendency. Conventional applied high frequency f = 13.56M
Under the condition of Hz and f = 80 MHz according to the present invention, the incident energy and the incident amount of the ions incident on the substrate are different. Obviously, under the condition of f = 80 MHz, the average incident energy becomes lower and the incident amount decreases.

Next, the influence of the distance between the electrodes when using the parallel plate type plasma chemical vapor deposition apparatus was investigated. FIG. 9 shows the dependence of the film thickness distribution on the applied high frequency. As shown in the figure, when the frequency is large for a certain inter-electrode distance d, the distribution becomes large. This poses a serious problem for increasing the area. Therefore, the inventors of the present invention tried to improve various film forming parameters, and found that the distance between electrodes had an influence on the film thickness distribution, and the distribution was reduced by increasing the distance between electrodes. I found that. Under the condition that the film thickness distribution T (%) in the substrate under various conditions is within 10%, the relation is obtained, and d = 2c
It was found that when m is larger than m, the distribution is remarkably large, and when d is larger than 3 cm, if d / f <30 is satisfied, a generally good distribution can be obtained. In FIG. 10, the applied high frequency is 8
As 0 MHz, the relationship between the interelectrode distance and the defect level density in the film under various conditions is shown. It can be seen that the defect density gradually decreases when the inter-electrode distance exceeds 4 cm, but begins to increase when the inter-electrode distance becomes smaller than 4 cm. It can be seen that when the applied frequency is 80 MHz, the distance between the electrodes is preferably 4 cm or more. Therefore, in the examples of the present invention, the distance between the electrodes was fixed at 4 cm for the study.

As described above, by using the VHF high frequency plasma, it is possible to easily, stably, and reproducibly improve the film forming rate as compared with the case of using the conventional RF high frequency plasma. A good quality film with little damage and a small film thickness distribution could be obtained.

Although the above description has been made in the case where only the silane gas is used, the same effect can be realized in a system diluted with a diluent gas such as hydrogen. However, since a high film forming rate can be realized at a low pressure, it is not necessary to dilute with hydrogen and adjust the pressure as in the conventional case, and the film can be easily formed with 100% silane.

The inventors of the present invention have been able to realize a high-quality, high-speed deposited film by the method using the above-mentioned VHF high-frequency plasma, but as a result of further study, they have found a method capable of realizing further improvement. This will be described below. The influence of the substrate temperature on this film forming method was examined. Conventionally, there is a certain optimum value for the substrate temperature at the time of film formation, and it is said that the optimum value in a method using a normal RF high frequency is 200 ° C to 250 ° C. Regarding this situation, the results obtained by our experimental system as the substrate temperature dependence of the defect density in the film are shown in FIG.
Shown in. In the figure, a is a case where a film is formed using a conventional RF high frequency of 13.56 MHz. The defect density in the film was the lowest near 250 ° C., and at this time, other film characteristic photoconductivity and the like also showed the best values. Here we see how increasing the applied frequency affects the defect density in the film and how the substrate temperature affects it. In the figure, b is data at 50 MHz and c is data at 100 MHz. It was found that by increasing the frequency, the substrate temperature Topt at which the defect density in the film becomes the minimum increases. Further, it can be seen that the minimum value of the defect density is decreasing. When the substrate temperature exceeds Topt, the defect density increases again. Although only the data at three points in the figure, when the frequency dependence is examined in detail, the substrate temperature dependence of the defect density was 13.56 MHz at 30 MHz or less. Therefore, for the first time in the VHF high frequency band of 30 MHz or more,
Such substrate temperature dependence was observed. At frequencies below 30 MHz, no improvement in film quality was observed due to the above mechanism.

The substrate temperature dependence of the minimum defect density Nsmin (point P in FIG. 11) was determined under various conditions while applying a frequency of 30 MHz or higher, and this is shown in FIG.
Below 300 ° C., the defect density does not decrease from the value obtained by normal RF discharge, but decreases from around 300 ° C. In the experiment conducted this time, the defect density in the film at a temperature higher than 300 ° C. was 10 ¹⁴ to 10 ¹⁵ defects / cm ³ and could be reduced from the conventional one digit to two digits. Also 550 ° C
The defect density starts to rise from around this point, and increases sharply above 600 ° C. X sample at 600 ℃
When observed by line diffraction, a crystal peak was observed, so that the crystallization temperature of amorphous silicon was 550 ° C to 600 ° C.
It is said that the temperature is 0 ° C., and it is explained that this rapid increase in defects is due to an increase in defects at crystal grain boundaries due to crystallization.

The mechanism of the effect that the density of defects in the film can be reduced by using a frequency of 30 MHz or higher and the substrate temperature of 300 ° C. or higher cannot be clearly determined at present, but it is roughly It can be inferred as follows.

In general, when the substrate temperature is 300 ° C. to 250 ° C. or less, the film growth surface is covered with hydrogen, and the film growth is determined by the interaction between the surface hydrogen and the silane radicals Si H ₃ ^* reaching the surface. That is, as shown in the following reaction formula Silane radicals draw hydrogen from the surface and bond there. At this time, it is considered that the hydrogen which has not been extracted is taken into the film as it is and forms hydrogen in the film. When the temperature exceeds 350 ° C., almost all hydrogen on the surface is desorbed and dangling bonds are formed on the surface. At this time, as shown in the following reaction formula, The dangling bond on the surface and the silane radical are directly bonded. Further, hydrogen attached to the radicals is released at the same time, and a new dangling bond is formed on the outermost surface. When the temperature further rises, the supply of silane radicals cannot catch up with the generation of dangling bonds due to hydrogen desorption in the conventional method using RF high-frequency discharge, and unterminated dangling bonds are taken into the film as they are. . This tendency becomes more pronounced as the temperature rises further, as shown in FIG.
If the temperature is 00 ° C. or higher, the defect density in the film becomes very large, and the deterioration of the film quality cannot be denied. Thus, it was difficult to improve the film quality at 300 ° C. or higher in the film formation by the ordinary RF high frequency discharge.

It has been found that the amount of silane radicals in the vapor phase is increased by using the VHF high frequency discharge, as shown in FIG. It seems that the amount of Si H ₃ ^* that reaches is naturally increasing, and it is possible to easily supply sufficient radicals to terminate the dangling bonds on the surface.

Further, generally, at the substrate temperature Ts, the surface diffusion coefficient D of particles on the film growth surface is expressed by the following equation.

D = νa0 exp (-Ea / kTs) a0: Distance between binding sites ν: Vibrational frequency at the site Ea: Activation energy required to jump from one site to the next In this case, the bonding site is considered to be a dangling bond on the surface. FIG. 13 shows a schematic diagram of substrate temperature dependence of D that is generally considered. It increases monotonically up to 300 ° C, but begins to decrease at temperatures above 300 ° C, 350
It seems that the temperature will start to increase again around ℃. It is considered that the hydrogen covering the surface affects Ea and becomes smaller than the state in which the dangling bond is exposed. Moreover, when hydrogen is present on the surface, the number of exposed dangling bonds does not change with temperature and is considered to be constant. However, as the temperature exceeds 300 ° C. and hydrogen on the surface is desorbed, the number of dangling bonds on the surface begins to increase, and the distance between sites, that is, the distance between dangling bonds decreases. Moreover, the exposed dangling bond has a large bonding force, and the activation energy is larger than that in the case where hydrogen is covered. Therefore, it seems that D starts to decrease at around 300 ° C., and starts to increase at around 350 ° C. at which hydrogen is completely desorbed, with new activation energy and inter-site distance.

In the present invention, the region C in FIG. 13 is utilized, the substrate temperature is kept at 300 ° C. or higher, the surface hydrogen is desorbed, the dangling bonds are exposed, and then a large amount of radicals are generated. It is considered that the gas is supplied and, as a result, it efficiently encounters defects on the film-forming surface and terminates the defects, and that the effect was exhibited at 300 ° C. or higher. It is considered that if the temperature is further increased and the supply amount is further increased, the diffusion coefficient is increased, radicals reaching the surface are rapidly diffused, and the dangling bonds are terminated more efficiently. From the above consideration, the substrate temperature Topt at which the defect density in the film becomes the minimum when the frequency found in FIGS.
It can also explain the phenomenon of rising. Therefore, this phenomenon was formulated and the optimum conditions for improving the film quality were obtained. The relationship between the substrate temperature Topt (° C.) that minimizes the defect density and the applied frequency f (MHz) was tested under various conditions. As a result, a constant relationship between the optimal substrate temperature and the optimal frequency Topt = kf +
It was found that there was a (0.1 ≦ k ≦ 2, a = 300). This is shown in FIG. The stitch portion in the figure is the range occupied by the above relational expression.

In order to bring out the effect of the present invention, it is necessary to remove hydrogen from the surface, that is, a substrate temperature of 300 ° C. or higher, preferably a substrate temperature of 350 ° C. at which surface hydrogen is completely desorbed. By doing so, it is possible that the defects that were conventionally not incorporated into the film can be terminated, and the final defect density in the film can be reduced.

At 600 ° C. or higher, crystallization of the film starts as described above and defects in the film increase, so that the substrate temperature range of the present invention is 300 ° C. ≦ Ts ≦ 600.
C., preferably 350.degree. C..ltoreq.Ts.ltoreq.550.degree.
As for the frequency, as shown in FIG. 2, 30 MHz at which radicals in the gas phase start to increase is required. This condition is shown by the shaded area in FIG.

Further, an advantage of the present invention is that hydrogen in the film can be easily reduced at the same time as the above-mentioned action. Figure 15
Shows the substrate temperature dependence of the hydrogen concentration in the film. Conventionally, the hydrogen concentration in the film depends on the substrate temperature and can be reduced by raising the substrate temperature. However, in this method, the conventional R
F As long as the high frequency discharge is used, if the temperature is raised to 250 ° C or higher, surface hydrogen begins to be desorbed, and as a result, hydrogen taken into the film decreases, but the supply amount of radicals that should terminate the dangling bond generated at the same time is insufficient. Start, Figure 11a
As shown in, the defect density in the film increases, and the photoconductivity also decreases accordingly, so that it is not possible to obtain the characteristics that can be used in a device utilizing light. Therefore it was not possible to raise the temperature any further. However, as described above, according to the method of the present invention, it is possible to increase the substrate temperature while further reducing the defect density in the film without increasing the defect density in the film, so that the initial defect density in the film is reduced and further incorporated into the film. The amount of hydrogen generated could be reduced. As a result, weak bonds, which are said to be caused by hydrogen in the film, were reduced, and the weak bonds were also reduced, so that photodegradation of photocurrent could be suppressed.

V whose frequency f (MHz) is 30 MHz or more
By using a high frequency in the HF band, the silane radicals could be increased more stably than in the case of the conventional RF band, and the film formation rate film could be improved stably and with good reproducibility. Furthermore, since the film is formed in such a manner that the ions that deteriorate the characteristics of the film are confined in the plasma, the damage due to the ions can be suppressed and the plasma damage at the interface can be reduced, so that a stable and high-quality film can be provided. Further, the substrate temperature Ts (° C.) during film formation is a high temperature of 300 ° C. to 600 ° C., preferably Ts = kf + a (0.1 ≦ k ≦ 2, a = 3.
By holding so as to satisfy the relationship of (00), it is possible to suppress the hydrogen concentration in the film to be low, and at the same time, it is possible to reduce the defect density in the film, the photoconductivity is large, and the photodegradation characteristic is greatly It was possible to make an improved high-quality film.

[0035]

Embodiments of the present invention will now be described in detail with reference to the drawings. [Embodiment 1] FIG. 1 shows a manufacturing apparatus used in this embodiment.
As a basic structure, conventional parallel plate type plasma CVD
It is similar to the device.

In the figure, 100 is a vacuum chamber,
101 is an anode electrode, 102 is a substrate, and 103 is a cathode electrode. The anode electrode 101 is grounded at 106. Reference numeral 104 is a matching box, and 105 is a high frequency power source. 107 is a gate valve, 108 is a turbo molecular pump, and 109 is a rotary pump. 110,118
Is a silane gas line valve, 111 and 119 are hydrogen gas line valves, 112 and 120 are phosphine gas line valves, 113 and 121 are ammonia gas line valves, and 114, 115, 116 and 117 are mass flow meters. In addition, if attention is paid to the way of applying the VHF high frequency and the handling, not only the parallel plate type as in the present embodiment but also the internal electrode type, the external electrode, such as the carousel type used in the manufacture of the photosensitive drum, is used. The present invention can be applied regardless of the method, capacitive coupling type or inductive coupling type.

Based on the above experimental facts and consideration, amorphous silicon containing no impurities was prepared by the manufacturing method of the present invention, and a single film was evaluated. FIG. 21A shows the device configuration. In FIG. 21A, 161 is a substrate, 162 is an intrinsic amorphous silicon layer, 163 is an n ⁺ type microcrystalline silicon layer, and 164 is an aluminum electrode.

[0038] Such a device manufacturing method, first, a glass substrate 102 mounted on the anode electrode in the chamber 100 was evacuated by the exhaust pump 109, 10 ^-6 T
orr. The substrate temperature was changed from 250 ° C to 400 ° C. Si H ₄ gas was caused to flow at 10 sccm, the chamber internal pressure was set to 0.5 Torr, and the chamber was maintained for 30 minutes.
After that, high-frequency power was applied and the matching device was adjusted to start discharge, and discharge was performed for a required time to form a film.

Samples were prepared by changing the applied high frequency from f = 13.56 MHz to f = 150 MHz. The high frequency power at this time was 10 mW / cm ² .

Aluminum comb electrodes were vapor-deposited on this film, and the dark conductivity and activation energy were measured at room temperature (25 ° C.).

FIG. 16 shows the applied high frequency dependence of the photoconductivity of the film. At this time, the substrate temperature is selected such that the defect density in the film is minimized at that frequency. As the frequency increases, the initial defect level decreases and the photoconductivity increases accordingly.

It is considered that the ions in the plasma are in a trapped state as the applied high frequency is increased, and the number of ions incident on the substrate and the energy thereof are reduced as described in FIG. FIG. 17 shows the change over time of the photocurrent (normalized by the initial photocurrent. Ip is the photocurrent,
Ip ⁰ is the initial photocurrent. ). a is the conventional 13.56
Films formed at MHz, b, c, and d are films formed by increasing the frequency and the substrate temperature in this order. It can be seen that the deterioration characteristics are improved by increasing the frequency and the substrate temperature. Improvement of film quality is 30 MH
It was found at frequencies above z, and it was found that more frequencies were needed to achieve the effect of the mechanism of the present invention. Since the hydrogen concentration in the film is reduced by increasing the substrate temperature, it is considered that weak bonds due to hydrogen are reduced and the generation of defects due to light is suppressed. By realizing the high-concentration radical plasma as described above with reference to FIG. 11, it is possible to suppress the generation of defects due to heat even at this temperature and to realize a sufficiently low defect density from the initial stage. [Embodiment 2] Next, a second embodiment in which the amorphous silicon film according to the present invention is used for the i layer of a thin film transistor will be described. Figure 2
1 (b) shows the device configuration. In FIG. 21B, 171 is a substrate, 172 is a gate electrode, 173 is an amorphous silicon nitride layer, 174 is an intrinsic amorphous silicon layer, 175 is an n ⁺ -type microcrystalline silicon layer, and 176 is an aluminum electrode. is there.

In the method of manufacturing such a device, first, a 1000 liter film of aluminum was formed on a glass substrate by a vacuum deposition method, and patterning was performed to form a gate electrode.

Next, the glass substrate 101 is placed in the chamber 1.
Exhaust pump 10 mounted on the anode electrode in 00
It was evacuated to 10 ^-6 Torr by 8, 109. The substrate temperature was set at 350 ° C., SiH ₄ gas was flowed at 3 sccm, H ₂ gas was flowed at 150 sccm, and nitrogen gas was flowed for 60 s.
ccm flow, chamber internal pressure is 0.2 Torr,
It was kept for 30 minutes and waited for the substrate temperature to stabilize.
After that, high-frequency power was applied and the matching device was adjusted to start discharge, and discharge was performed for a required time to form a film. The frequency at this time was f = 13.56 MHz. The high frequency power was set to 30 mW / cm ² . After the discharge was completed, the gas was exhausted and a high vacuum was drawn up to 10 ⁻⁶ Torr.

Next, with the substrate temperature kept at 350 ° C., S
iH ₄ gas was caused to flow at 10 sccm, and the chamber internal pressure was adjusted to 0.
The pressure was set to 5 Torr and held for 5 minutes, and waited until the substrate temperature stabilized. After that, the high frequency of 80MHz is 10
A film was formed by applying a power of mW / cm ² and adjusting a matching unit to start discharge, and then discharging for a required time. Partial discharge was performed to form 5000 Å intrinsic amorphous silicon. Then, the gas was evacuated and a high vacuum was drawn up to 10 ⁻⁶ Torr. Similarly, change the frequency from 30MHz to 100
A sample in which the i layer was changed by shaking to MHz was prepared.

Next, the substrate temperature is set to 250 ° C. and the Si
H ₄ gas was flowed at 3 sccm, phosphine gas diluted to 100 ppm with H ₂ gas was flowed at 150 sccm, the chamber internal pressure was set to 0.5 Torr, and the temperature was maintained for 30 minutes to wait until the substrate temperature became stable. After that, a normal high frequency of 13.56 MHz was applied at a power of 30 mW / cm ² , and the matching device was adjusted to start discharge, and discharge was performed for a required time to form a film. Discharge for 30 minutes and 1500Å
Of n ⁺ type amorphous silicon was deposited. Then, the gas was evacuated and a high vacuum was drawn up to 10 ⁻⁶ Torr.

Next, this substrate is taken out from the film forming apparatus,
Aluminum was formed into a film with a thickness of 1 μm by a vacuum deposition method. After that, this aluminum was patterned to form source and drain electrodes.

Finally, using this electrode as a mask, the n ⁺ type amorphous silicon was removed by etching.

The characteristics of a thin film transistor formed at f = 100 MHz, which is a typical thin film transistor thus formed, is shown in FIG. It shows sufficiently good characteristics. In the figure, (b) is conventional data.

FIG. 19 shows the Vg dependence of the threshold voltage Vth shift when the ON state is maintained for 100 hours. In the figure, (a) is data of a conventional device. Conventionally, the shift was made to the positive side with time, but according to the present embodiment, this shift is considerably improved. Generally this Vth
Two types of factors are considered for the shift. In the region A in the figure, the weak bond in the i layer near the nitride film is broken during operation, the level density distribution in the gap changes, and Vth shift occurs. ing. The area B in the figure is a carrier during ON operation,
In this case, since it is an N-channel operation, electrons enter the insulating film and are trapped in the trap level in the film, and fixed charges are formed there. According to the manufacturing method of the present invention, hydrogen in the film can be suppressed to a low level, the weak bond in the i layer resulting from this can be reduced, and as a result, the bond is less likely to break, and the Vth shift in the A region can be reduced. We were able to. Further, the ion damage to the nitride film during the formation of the i layer was reduced, the defects in the nitride film were reduced, and the Vth shift in the B region was also reduced. The dependence of the Vth shift on the applied high frequency is shown in FIG. It can be seen that the above effect appears from around f = 30 MHz. In the present example, since the i layer can be formed at the same temperature after the nitride film, the waiting time for achieving temperature stability during this period could be significantly reduced. Further, it has been conventionally pointed out that when the film forming temperature is largely deviated between the nitride film and the i-layer as in the conventional case, the difference in thermal stress when returning to room temperature deteriorates the interface property between the nitride film and the i-layer. By using the present invention, it was possible to reduce the difference in thermal stress and improve the interface characteristics.

[0051]

As described in detail above, according to the present invention, by using a high frequency wave in the VHF band having a frequency f (MHz) of 30 MHz or more, the frequency can be more stable than that in the conventional RF band. Since the number of silane radicals can be increased and the ions that deteriorate the characteristics of the film are confined in the plasma, the damage caused by the ions can be suppressed and the plasma damage at the interface can be reduced. In addition to the advantages of VHF high-frequency plasma, such as the provision of a film of, the substrate temperature Ts (° C.) during film formation is high at 300 ° C. to 600 ° C., preferably Ts = kf + a.
By maintaining the relationship of (0.1 ≦ k ≦ 2, a = 300), the hydrogen concentration in the film can be suppressed low, and at the same time, the defect density in the film can be reduced. A high-quality film having high photoconductivity and significantly improved photodegradation characteristics could be produced.

[Brief description of drawings]

FIG. 1 is a diagram showing an apparatus for realizing a manufacturing method according to the present invention.

FIG. 2 shows the emission intensity [Si H ^* ] of Si H ^* radicals,
It is a figure which shows the applied high frequency f dependence of the light emission intensity [H ^* ] of a hydrogen radical.

FIG. 3 is a diagram showing an applied high frequency f dependency of a film formation rate R.

FIG. 4 shows the emission intensity [Si H ^* ] of SiH ^* radicals,
Applied high-frequency power Pw of emission intensity [H ^* ] of hydrogen radicals
It is a figure which shows dependence.

FIG. 5 is a diagram showing a relationship between an applied high frequency power Pw and an applied high frequency f.

FIG. 6 is a diagram showing the applied high frequency power Pw dependence of the film formation rate.

FIG. 7 is a diagram showing a pressure Pr dependence of a film formation rate.

FIG. 8 is a diagram showing incident energy and distribution of ions incident on a substrate.

FIG. 9 is a diagram showing a relationship between an applied high frequency f and a film thickness distribution.

FIG. 10 is a diagram showing the relationship between the distance between electrodes and the defect density in the film.

FIG. 11 is a diagram showing the substrate temperature dependence of the defect density in the film.

FIG. 12 is a diagram showing the substrate temperature dependence of the minimum defect density.

FIG. 13 is a diagram showing the substrate temperature dependence of the surface diffusion coefficient.

FIG. 14 is a diagram showing the relationship between substrate temperature and applied frequency.

FIG. 15 is a diagram showing the substrate temperature dependence of the hydrogen concentration in the film.

FIG. 16 is a diagram showing an applied high frequency f dependence of photoconductivity.

FIG. 17 is a diagram showing changes in photoconductivity over time.

FIG. 18 is a diagram showing characteristics of the thin film transistor of this example.

FIG. 19 is a diagram showing Vg dependence of Vth shift during ON operation.

FIG. 20 is a diagram showing an applied high frequency F dependence of Vth shift.

21A is a diagram showing a configuration of a coplanar sensor, and FIG. 21B is a diagram showing a configuration of a thin film transistor.

[Explanation of symbols]

100 Vacuum chamber 101 Anode electrode 102 Substrate 103 Cathode electrode 104 Matching device 105 High frequency power supply 106 Grounding 107 Gate valve 108 Turbo molecular pump 109 Rotary pump 110, 118 Silane gas line valve 111, 119 Hydrogen gas line valve 112, 120 Phosphine gas line valve 113 , 121 Ammonia gas line valve 114, 115, 116, 117 Mass flow meter 161 Substrate 162 Intrinsic amorphous silicon layer 163 n ⁺ type microcrystalline silicon layer 164 Aluminum electrode 171 Substrate 172 Gate electrode 173 Amorphous silicon nitride layer 174 in Trinsic amorphous silicon layer 175 n ⁺ type microcrystalline silicon layer 176 Aluminum electrode

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Hidemasa Mizutani 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (5)

[Claims] 1. In a manufacturing method for depositing amorphous silicon by using a gas containing Si by plasma chemical vapor deposition, the substrate temperature Ts is maintained at a temperature from 300 ° C. to 600 ° C. V with frequency f of 30MHz or more
A method for producing amorphous silicon, characterized in that HF high frequency is applied to generate plasma. 2. The method for producing amorphous silicon according to claim 1, wherein the substrate temperature Ts (° C.) and the applied high frequency f (M
Hz is Ts = kf + a (0.1 ≦ k ≦ 2, a = 30)
A method for producing amorphous silicon, characterized in that a VHF high frequency is applied so as to satisfy the relationship of 0) and plasma is generated. 3. The method for producing amorphous silicon according to claim 1, wherein the VHF high frequency f is 10 / f (W / cm).
² ) A method for producing amorphous silicon, characterized in that plasma is generated by supplying electric power at (f: MHz) or less. 4. The method for producing amorphous silicon according to claim 1, wherein the ratio of the emission intensity [H ^* ] of hydrogen radicals to the emission intensity [Si H ^* ] of silane radicals is [H ^* ] /
A method for producing amorphous silicon, characterized in that [Si H ^* ] ≦ 1. 5. The method for producing amorphous silicon according to claim 1, wherein the inter-electrode distance d (cm) satisfies the relationship of f / d <30.