JP2003109798A - Discharge device, plasma treatment method and solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide novel antenna structure and power supply method for causing generation of a standing wave to substantially disappear, to provide a discharge device having high plasma evenness, a plasma treatment method of a large-surface substrate and a solar cell having high productivity. SOLUTION: A plurality of U-shaped antenna elements, both ends of which are used as a power supply end and an earth end, respectively, are arranged with equal intervals on a plane in such a manner that the earth end and the power supply end alternate to construct an array antenna, a phase is changed 180 deg. in order from the end of the power supply end to supply AC power of the same frequency at a time, the length of a linear conductor is determined at the frequency of 10 MHz-2 GHz in such a manner that the ratio of a reflected wave measured at the power supply end to a progressive wave measured at the power supply end is 0.1 or lower. When α is regarded as a subtrahend constant, the length La (m) of the linear conductor is controlled to 0.5(1/α)<La<10(1/α).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a discharge device, a plasma processing method, and a solar cell, and more particularly, to a discharge device that uses an array antenna to generate discharge plasma having excellent uniformity, and has excellent productivity and uniformity. A plasma processing method and a solar cell manufactured with excellent productivity.

[0002]

2. Description of the Related Art Solar cells have attracted attention and are expected as a clean energy source, but cost reduction is indispensable for their widespread use. Therefore, high-quality, uniform-thickness silicon-based silicon substrates are used for large-area substrates. A thin film forming apparatus capable of forming a thin film with high throughput is desired. In addition to solar cells, there are demands in various fields for uniform treatment of large areas. For example, in the manufacture of thin film transistors for driving liquid crystal displays, the area of substrates has recently been increased, and it is expected that a production line using glass substrates whose one side length exceeds 1 m will soon come into full-scale operation. . In this manufacturing process, a plasma CVD method or a dry etching method is used. Further, considering the recent heightened interest in environmental issues, it is presumed that the photoresist removal step will need to be dry by plasma ashing (ashing) sooner or later.

Plasma CVD method, dry etching method,
In the plasma processing process such as the plasma ashing method,
A parallel plate type (capacitive coupling type) plasma processing apparatus has been put into practical use. With this type of discharge device,
The substrate to be processed is placed either on the electrode to which a high frequency is applied or on the ground electrode facing the electrode. A large DC potential difference called self-bias is generated near the surface of the high-frequency electrode, which causes high-energy ion bombardment to the substrate placed on the high-frequency electrode, whereas no such action occurs on one ground electrode side. . As a result, the substrate placed on the high frequency electrode and the substrate placed on the ground electrode are differently affected by plasma. Therefore, the same treatment cannot be applied to the substrates on both electrodes.

As described above, the parallel plate type plasma processing apparatus can perform plasma processing on only one surface of one electrode plate. For this reason, when performing simultaneous treatment on two surfaces in the same film forming chamber, it is at best that two high-frequency electrodes are installed in the processing chamber to form two discharge regions and the two-side treatment is performed. There is an idea to increase the number of discharge areas to make it multi-area, but in reality, due to the complexity of the structure and poor maintainability,
It is very difficult to realize due to the problems associated with the adoption of parallel plate electrodes. Furthermore, in this connection, the parallel plate discharge device has another drawback. For example, plasma C
When the film is formed on the glass substrate by the VD method, the material gas introduced into the vacuum chamber is decomposed by the electrons in the plasma, and a thin film is formed not only on the glass substrate but also on the high frequency electrode. That is, of the introduced material gas, an amount of gas substantially equal to the amount of gas used for film formation on the substrate is consumed and wasted for forming the thin film on the electrode. In addition, the thin film on this electrode peels off and contaminates the space,
Need to be removed regularly.

Further, there is a problem in that the uniformity of discharge plasma formed with the increase in size of the substrate is significantly deteriorated, and desired characteristics cannot be obtained. In order to perform highly uniform plasma processing on a substrate to be processed, it is usually necessary to form plasma with a uniform density over the entire surface of the substrate, and various studies have been made for this purpose. However, in the parallel plate type electrode system, when the electrode becomes larger as the substrate becomes larger,
It is not easy to form a uniform-density plasma, and the reason for this is the following problem in principle. That is, when the electrode becomes large, a standing wave is generated on the surface of the electrode, which may cause uneven distribution of plasma.
This becomes more remarkable when a higher frequency such as the VHF band is used. For this reason, for example, 80 MH
In case of high frequency of z, the size of the substrate is 0.3mx0.3m
Is said to be the limit (U. Kroll et al., Mat. Res. S
oc. Symp. Proc. vol 557 (1999) p121-126). Further, in the parallel plate type electrode, in order to form plasma of uniform density, it is necessary to arrange the electrodes while maintaining the distance between the electrodes with high precision over the entire substrate, but this becomes extremely difficult when the size of the substrate increases.

Therefore, the plasma sustaining mechanism is completely different from that of the capacitive coupling type, and the problems such as the accuracy of the distance between the electrodes peculiar to the capacitive coupling type do not occur, and the VHF band of the high quality film is advantageous for high speed film formation. An inductively coupled plasma CVD method capable of generating a high plasma density using a high frequency has been proposed. Specifically, a ladder-shaped electrode is disclosed in
No. 236781) or an electrode such as an electrode in which a conductive wire is bent in a zigzag manner (Japanese Patent No. 2785442), an inductively coupled electrode type plasma CVD apparatus is proposed.

[0007]

DISCLOSURE OF THE INVENTION The present inventors have examined various inductively coupled electrodes including the electrode having the above structure. For example, in the case of a ladder-shaped or zigzag-folded inductively-coupled electrode, if the size of the substrate increases and the size of the electrode increases, it becomes difficult for the current to be uniform, and standing waves are partially generated at unexpected locations. Was confirmed. In conclusion,
It has been found that it is difficult to make the plasma density uniform and it is difficult to deal with a large area substrate in the conventional inductively coupled electrode system.

Therefore, the inventors of the present invention have conducted a basic study on the homogenization of plasma with respect to the inductively coupled electrode, and in the conventional inductively coupled electrode described above, an antenna structure using the standing wave, which is a problem, is reversed. Was developed. This antenna has, for example, a structure in which a power feeding part is provided at one end of a U-shaped antenna and the other end is grounded. The standing wave is erected at a predetermined position (PCT /
JP00 / 06189). Furthermore, by using the antenna of this structure as an element of the array antenna, it becomes possible to generate uniform discharge plasma in a larger area.

However, this film forming method is based on the fact that a standing wave is generated on the antenna.
Therefore, non-uniformity of plasma density occurs due to the presence of standing waves more or less in the direction along the antenna. This non-uniformity can be mitigated by several methods. For example, the uniformity is improved by intermittently supplying the electric power to drive the antenna (Proceedings of the 61st Autumn Meeting of Applied Physics p.841 (September 2000) “VHF-using new type electrode”
Large-area film formation of a-Si: H by PECVD method "). However, these methods could not completely eliminate the nonuniformity due to the influence of standing waves. In addition, since the standing wave is used, it is unavoidable that the plasma density distribution is greatly affected by changes in the geometrical length of the antenna and the excitation frequency.

In view of the above situation, the present invention provides a novel antenna structure and a power supply method for substantially eliminating the generation of standing waves, a discharge device having high plasma uniformity and a plasma of a large area substrate. It is an object to realize a treatment method and a solar cell with high productivity.

[0011]

[Means for Solving the Problems] In order to achieve the above object,
The present inventor has found out that a special effect is exhibited in an antenna array in which a plurality of antenna elements are arranged, while variously examining the method of feeding high frequency power, the electrode structure, the film forming conditions and the like. The present invention has been completed by further studying the uniformization of the film thickness based on such knowledge.

The discharge device of the present invention has the following form. Two first and second linear conductors having the same length are arranged in parallel, and a pair of mutually adjacent ends of the first and second linear conductor ends are mutually disposed. It is electrically coupled. This forms a U-shaped antenna element. One end of the first linear conductor of the antenna element on the uncoupled side serves as a ground end, and one end of the second linear conductor on the uncoupled side serves as a power supply end. AC power can be applied to this power supply end. A plurality of this antenna element, each antenna element on a flat surface in a vacuum, so that the linear conductors of each antenna element are parallel and the ground end and the power supply end are alternately arranged. Arrange them so that they are evenly spaced. The plurality of arranged antenna element functions as an array antenna and forms discharge plasma in a vacuum. The array antennas having such a geometrical shape are simultaneously supplied with AC power of the same frequency. The excitation frequency is 10 MHz to 2 GHz.

If such a mode and excitation method are adopted, a standing wave is generated on the antenna element as described above. This is because the electromagnetic wave starting from the power supply end travels as a traveling wave along the antenna, is reflected at the ground end to become a reflected wave, and a standing wave is generated due to the interference between the traveling wave and the reflected wave. The first problem to be solved by the present invention is to reduce the influence of this standing wave on the plasma uniformity.
In addition, when a plurality of antenna elements are driven, a complicated interaction between the antenna elements occurs, which sometimes makes the electromagnetic field uncontrollable. This is the second problem to be solved by the present invention.

First, in order to solve the second problem,
The present inventor has arrived at the idea that the principle of superposition should be used. This will be explained below. FIG. 5 schematically shows the currents flowing through the array antenna when the phases at the power supply ends of the adjacent antenna elements are the same phase (a) and the opposite phase (b). The antenna element 2 is formed by connecting two linear conductor lines (# 1 and # 2 or # 3 and # 4), one end of which is a power supply end 9 and the other end of which is a ground end 10. is there. In the figure, the direction of the arrow indicates the phase of the current, and it is assumed that the current is flowing in the direction of the arrow at the time of observation, and the upward arrow is positive for convenience. The size of the arrow indicates the size of the current, and it is assumed that a large current flows on the current supply side (the odd-numbered linear conductor portion) at the time of observation.

In the case of in-phase power feeding (FIG. 5A), the line # 2 is sandwiched between the large currents in the line # 1 and the line # 3. Therefore, it is considered that the electric field in the vicinity of the line # 2 is greatly affected by the current flowing on the two adjacent linear conductors. Next, in the case of reverse phase feeding (FIG. 5B), the line #
2 is sandwiched between the large negative current of line # 1 and the large positive current of line # 3. According to the theory of superposition, since the effects of the same magnitude and opposite directions are simultaneously cancelled, the electric field near line # 2 is affected by the current flowing on the linear conductors of the adjacent antennas. It will be difficult. In the above description, the current distribution shape on the antenna element is assumed for the sake of convenience, but if an electrically equivalent antenna element is arranged, the same result will be obtained regardless of the current distribution. . Therefore, when the antenna elements of the same shape are arranged, by inverting the phase between the adjacent elements, it is possible to substantially ignore the influence of not only the adjacent elements but also the return (or forward) current. Therefore, it is considered that the current flowing through the linear conductor behaves similarly to the current on the single line. That is, by supplying the electric power of the opposite phase between the adjacent antenna elements, the interaction between the antenna elements can be practically ignored, and the second problem can be solved.

Next, in order to overcome the first problem, there was a hint in the field of radio wave transmission engineering which is a technical field different from the present invention. That is, an application of the concept of a loaded antenna. The loaded antenna is a communication antenna whose side opposite to the feeding point of the antenna is grounded via a load having an appropriate impedance. With such a configuration, the electromagnetic energy propagating along the antenna is consumed by the load and is not reflected in a wide frequency range. When the concept of the loaded antenna is applied to the antenna of the plasma processing apparatus, it is found that the system studied by the present inventors can obtain the same effect without purposely mounting a load as a circuit element. . It is considered that this is because the plasma surrounding the antenna itself serves as a load as a distributed constant circuit.

The above is summarized as follows. When the phase of the power supplied to the array antenna is changed by 180 °, the linear conductors that make up the array antenna can be regarded as a radio wave propagation guide that exists only in the plasma. It is possible to reduce the deterioration of the plasma density distribution due to the interaction of the. In addition, the interaction between the electromagnetic waves and the plasma is sufficiently large that the generation of standing waves can be suppressed by creating a state in which most of the electromagnetic energy is absorbed in the plasma. Non-uniformity can be reduced. As a result, it becomes possible to form a more uniform plasma over the entire array antenna. The size of the standing wave can be predicted by measuring the traveling wave and the reflected wave at the power supply end of the antenna. If the interaction between the electromagnetic wave and the plasma is sufficiently large, the electric power is absorbed by the plasma, so that the phenomenon can be observed as a reduction of the reflected wave. Therefore, when the geometrical length of the antenna is sufficiently long, or when the discharge pressure is sufficiently high and energy transfer is likely to occur, such a large interaction is observed. It was found that, when the ratio to the ratio was 10% or less, the distribution of the standing waveform was not observed in the plasma density, and the film thickness uniformity was improved. That is, it has been found that the geometrical length of the antenna may be determined by the magnitude of the reflected wave according to the plasma parameter or the like.

The method of determining the length (antenna length) La of the linear conductor by the ratio of the reflected wave to the traveling wave in order to obtain uniform plasma has been described above, but it is preferable from the attenuation constant α of the electromagnetic wave. A simple antenna length La can be determined. That is, 0.5 (1 / α) <La <10 (1
By setting / α), the standing wave can be substantially eliminated and the plasma uniformity can be improved. This will be explained below.

As shown in FIG. 6, a sheath 61 and plasma 63 exist around the antenna 60. Since the plasma 63 exists at a position far away from the antenna 60, when considering the behavior of the electromagnetic wave propagating on the antenna, it is necessary to consider the entire plasma or the entire region of the vacuum chamber where discharge is performed. Looks like. However, the electromagnetic wave cannot propagate in the plasma unless the plasma density is very low or the excitation frequency is very high. This is generally called a cutoff state, and the frequency of the electromagnetic wave is the plasma frequency f _p (= ω _p /
In the case of (2π)) or less, the electric field penetrates into the plasma to some extent, but the electromagnetic wave does not propagate to any place. Therefore, the plasma in a region close to the antenna to some extent should mainly affect its propagation characteristics.

Therefore, a virtual boundary 62 is defined for this region, and the radius d of this boundary 62 is approximated by the so-called skin depth δ. The skin depth δ indicates the distance at which the electric field is attenuated in the plasma and becomes 1 / e times (e is the base of the natural logarithm) when the plane wave electromagnetic wave is perpendicularly incident on the plasma in the cutoff state.
It is well known that cold plasma approximation / linear approximation when collision cannot be ignored is expressed by equation (1) (for example, Michael ALieberman and Allan J. Lichtenb
erg, "Principles of Plasma Discharge and Materials
Processing ", John Wiley & Sons, Inc. 1994 p390). (1) where c is the speed of light, κ _p is the complex relative permittivity of the plasma expressed by equation (2), and ω (= 2πf) is the angular frequency (f is the excitation frequency for driving the antenna). is there. (2) where ν is the collision frequency and ω _p (= 2πf _p ) is the plasma angular frequency. Here, n is the plasma density (m
^-3 ), and f _p (Hz) = 8.98 · n ^0. It is approximated by ⁵ .

When the virtual boundary d (= δ) is determined in this way, the electromagnetic wave propagating along the antenna can be considered as propagating on the coaxial line, so that the attenuation constant α can be easily obtained. Therefore, the inventors considered using the attenuation constant α as a means for determining the antenna length. The attenuation constant α in this case uses an inductance L per unit length of the antenna with respect to the virtual boundary d and a capacitance C per unit length of the antenna, ... (3) ... (4) can be written. However, μ ₀ is the magnetic permeability in vacuum, and ε ₀ is the dielectric constant in vacuum.

Since the above equations (1) to (4) have too many parameters for describing the phenomenon, the inventors have used the equation (4) of the damping constant α within the range where the practicality is not lost. It was decided to make an appropriate assumption so that it would be easy to understand, and to investigate whether the damping constant derived based on that assumption could explain the experimental results well in a wide range. First, in consideration of a realistic antenna diameter, a = 3 mm. 4 mm assuming the plasma parameter expected as the thickness of the sheath
And c = 7 mm. It was confirmed that applying different numerical values to these values, in many cases, does not significantly affect the conclusion as long as the numerical values are practical. Further, the plasma density was assumed to be 2 × 10 ¹⁵ (m ⁻³ ).
The plasma density used in the plasma treatment is from 1 × 10 ¹⁵ (m ⁻³ ) to 1 × 1 unless it is a so-called high density plasma.
It is often in the range of 0 ¹⁶ (m ^-3 ), and does not take a very wide numerical range. Next, the collision frequency ν is calculated by using the discharge pressure p (Pa) as a one-electron approximation. ... (5) In equation (5), the collision cross section of Ar was used to calculate the mean free path λm. The collision cross section varies depending on the type and composition ratio of the gas, but it does not take an extremely different value except in a special case such as a polymer having a large molecular weight. The electron temperature is 10,000.
It was assumed that the value was K, but this too does not change so much in low pressure discharge, but changes by several times at most.

By making the above assumptions, (1 ')-
Equation (4 ') can be derived. ... (1 ') ... (2 ') ... (3 ') ... (4 ')

The damping constant α is calculated, and the reciprocal of the damping constant is taken. The unit of the reciprocal of the attenuation constant is meters. Physically, it means that the electromagnetic wave starting from the power supply point of the coaxial cylinder attenuates by 1 / e times when it reaches the position of 1 / α. There is. Therefore, the length L of the straight part of the array antenna is
It can be considered appropriate to give a value near a reciprocal of the damping constant as a. That is, if it is much shorter than the reciprocal of the attenuation constant, the electromagnetic wave is not attenuated so much by the ground end of the antenna element, so a reflected wave occurs at the ground end
It is expected that standing waves will be formed. On the other hand, if a straight line portion that is much longer than the reciprocal of the attenuation constant is provided, it becomes impossible to generate discharge over the entire length of the antenna, and discharge plasma is exclusively formed near the power supply point. Therefore, when the excitation frequency was changed, numerical values 0.5 times and 10 times the reciprocal of the damping constant were tentatively calculated as discharge pressure dependence. As a part of this calculation result, FIGS. 7 to 9 show the relationship between the pressure and La for the excitation frequencies of 10 MHz, 85 MHz and 400 MHz. As will be described later in the section of Examples, the inventors have confirmed that the optimum value of the length of the straight line portion exists in the region sandwiched by the two curves shown in FIGS. In other words, it was concluded that the linear portion length La should be selected as follows: 0.5 (1 / α) <linear portion length La <10 (1 / α) (6). In the derivation of the equations so far, the plasma density was set to 2 × 10 ¹⁵ (m ⁻³ ).
Therefore, theoretically, the frequency at which the cutoff state occurs is 4
It becomes 00 MHz.

As described above, the straight line length La can be predicted only by the two parameters of the discharge frequency and the discharge pressure, but the equations (1 ') to (4') are experimentally determined. In order to match the result, it is a formula that was obtained by prioritizing convenience and practicality of use, and was obtained by limiting the range of use for the purpose of discharge device or plasma treatment.

Although two methods for determining the length of the straight portion of the antenna have been described above, it is desirable to make the diameter of the antenna smaller than 10 mm in either case. By selecting a straight part with a thin diameter like this, even if the antenna has the same geometric length,
The plasma can be easily formed over the entire length. In other words, the choice of small diameter has the effect of shortening the electrical length of the antenna. It is speculated that this is because the diameter of the antenna is related to the strength of the interaction between the electromagnetic wave and the plasma. This is because, for example, when the diameter of the straight part increases, the energy transfer (OAPopov ann
d VA Godyak, J. Appl. Phys. 57, 53 (1985).), and the ratio of capacitive coupling increases as electrical coupling between the antenna and plasma. As described above, although the selection of the antenna diameter affects the selection of the length of the straight line portion of the antenna, the degree is not so large, and the optimum length of the straight line portion of the antenna is still expressed by the formula (6) even if the antenna diameter is reduced. It is within the range required from. As described above, it is advantageous that the antenna diameter is thin to some extent from the viewpoint of increasing the area, but if it is too thin, the shape stability is lost. Considering the manufacturing and maintenance of the antenna, it is not appropriate to select the thinness that easily causes plastic deformation during handling. Furthermore, considering the power loss and heat generation due to the current flowing on the antenna, the diameter of the straight part is 1 mm.
It is desirable to select the above.

Although it has been described that the diameter of the straight line portion is related to the radio wave propagation on the antenna, it can be considered to positively utilize this. That is, in the case of the antenna element having the same diameter over the entire length of the straight line portion, the plasma density may be increased or decreased due to the attenuation of the electromagnetic wave. In addition, in some cases, it is desired to increase the plasma density only in the vicinity of the substrate to be treated. Furthermore, it is also conceivable that the plasma may become non-uniform due to specific design conditions in the vacuum chamber. As a method of coping with this, the inventors have found that the plasma density can be controlled by changing the diameter along the length of the straight portion. In this case, the thickness of the straight part is 1
It has been found that this effect becomes more pronounced by making the area thinner than 0 mm.

Further, as described above, the propagation constant of the electromagnetic wave propagating along the antenna is dominated by the sheath around the antenna and the plasma. Here, if the linear portion is covered with a ceramic such as alumina or a dielectric such as plastic such as Teflon (registered trademark), electromagnetic waves propagate in a space formed by the dielectric around the antenna, the sheath, and the plasma. Become. by this,
Even if the geometric lengths of the straight portions are the same, a uniform plasma can be formed in a wider range. This effect is
Effective even if the diameter of the straight part is set to 10 mm or less,
It was also effective when the diameter of the straight part was changed.

The dielectric preferably has a thickness that varies in the longitudinal direction of the electrode. In particular, in order to suppress the phenomenon that the plasma density increases due to the effect of undamped electromagnetic waves near the power supply part, cover the electrode part near the power supply part with a thick dielectric and thin the other parts, and In order to increase the plasma density in the vicinity, it is preferable to reduce the dielectric thickness in this vicinity. Further, it is desirable that the thickness be gradually changed in the longitudinal direction of the straight line portion. As a result, abrupt changes in the characteristic impedance at the ends of the dielectric can be suppressed, and plasma with a more uniform density can be formed. Alternatively, the electrodes may be coated in a spiral shape along the longitudinal direction of the electrodes. As a result, the plasma density at the end of the dielectric is flattened, and the plasma density along the electrodes is made more uniform.

According to the array antenna of the present invention, a slab-shaped discharge plasma can be formed so as to sandwich the array antenna, and by placing two substrates to be processed so as to sandwich the antenna, Equivalent plasma treatment is possible on the substrate. This doubles the processing capacity and doubles the use efficiency of the material gas.

Further, in the conventional parallel plate type processing apparatus,
The limit is to provide at most two discharge areas in the vacuum chamber. On the other hand, in the present invention, the structure of the array antenna is simple and the weight is light, so that the disassembly and reassembly are easy. Further, since the power supply end is on the side surface, it becomes easy to create a plurality of discharge regions in the vacuum chamber. This improves productivity. The productivity is further improved by disposing two substrates on both sides of the array antenna so as to sandwich the antenna, and disposing a plurality of this combination in the same vacuum chamber.

On the other hand, in the plasma processing method of the present invention, two first and second linear conductors having the same length are arranged in parallel, and the first and second linear conductor end portions are adjacent to each other. Electrically couple a pair of matching ends, one end of the first straight conductor on the uncoupled side is the ground end, and one end of the second straight conductor on the uncoupled side is the AC power source. A plurality of antenna elements that can be applied as power supply ends, and the linear conductors of each antenna element are parallel to each other, and the grounding end and the power supply end are alternated on the first plane in vacuum. In a plasma processing method in which array antennas are arranged at equal intervals and alternating-current power is supplied to the array antennas to form discharge plasma in a vacuum, the phase is sequentially changed by 180 ° from the beginning of the power feeding end. Power the same frequency all at once, The frequency and 10MHz～2GHz, the ratio of the reflected wave to the traveling wave that is measured by the power supply end, characterized by using an array antenna that defines the length of linear conductors so that 0.1 or less.

Alternatively, the phase of the power supply terminal is sequentially changed by 180 ° in sequence from the beginning to supply power of the same frequency all at once, and the frequency f (Hz) is 10 MHz to 400 M.
Hz and the dielectric constant κ _{p of} plasma is calculated by using the frequency and the discharge pressure p (Pa). And the skin depth δ of the electromagnetic field that penetrates the plasma.
(M) The damping constant α (1 / m) calculated by Therefore, an array antenna in which the length La (m) of the linear conductor is 0.5 (1 / α) <La <10 (1 / α) is used.

On the other hand, the solar cell of the present invention is characterized in that a thin film containing silicon is formed by the plasma CVD method of the present invention and the thin film is used as a semiconductor layer.

In the present invention, the substrate includes not only insulators such as glass, so-called substrates and wafers such as semiconductors and metals, but also film-like (including roll-like ones) and block-like ones. Is the meaning. Further, the discharge device of the present invention can be used not only for the substrate treatment described above, but also for decomposition and synthesis of raw materials such as exhaust gas treatment and polymerization of organic substances.

[0036]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing a configuration example of an array antenna used in the discharge device of the present invention. As shown in the figure, in the discharge device, a plurality of U-shaped bent antenna elements 2 are arranged facing a substrate 11 in a vacuum chamber 1 having a gas introduction port 5 and an exhaust port 6, and one end of each of them is arranged. The power supply end 9 is connected to the high frequency power source 7 via the coaxial cable 8, and the ground end 10 at the other end is connected to the wall of the vacuum chamber 1 for grounding. Here, the length between the power supply end 9 and the grounding portion 10 and the folded portion 4 (that is, the length La of the linear conductor) has a ratio of the reflected wave at the power supply end to the traveling wave of 0.1 or less. Or the equation (6) is satisfied. The surface of the antenna is covered with a dielectric 3 such as Teflon (registered trademark).

The antenna element 2 preferably has a U-shaped linear conductor made of SUS, Al or the like, but may have a rectangular shape such as a "U" shape. Further, it may not be integrally formed, and may have a structure in which, for example, two linear conductors are connected and fixed by a metal plate or the like. The linear conductors need not necessarily be made of the same material, but may be made of different materials connected to each other.

The dielectric 3 may be formed so as to cover the entire surface of the linear conductor, but may cover only a part of the surface of the conductor. In either case, the film thickness uniformity can be improved, and the dielectric formation position and its shape are determined according to the pattern of the plasma density distribution (or film thickness distribution). For example, as shown in FIG. 2A, it may be formed only on the linear portion on the power supply end side. This suppresses an increase in the plasma density on the power feeding unit side, and the plasma density is averaged over the entire antenna. Furthermore, by providing a dielectric coating on a part of the antenna only in a place where the plasma density is likely to be high, it becomes possible to further improve the uniformity along the longitudinal direction of the antenna. Here, depending on the thickness of the dielectric to be coated, the plasma density may increase at the end of the dielectric. In this case, as shown in FIG. 2B, it is preferable that the cross section at the end of the dielectric is tapered and the thickness of the dielectric is gradually reduced toward the end of the dielectric. . This suppresses the appearance of a plasma density peak at the portion corresponding to the dielectric end portion. Alternatively, as shown in FIG. 2C, the dielectric may be spirally coated along the longitudinal direction of the antenna, and this method also averages the plasma density at the ends of the dielectric. The thickness and the dielectric constant (material) of the dielectric are appropriately selected according to the plasma density distribution to be improved, but for Teflon (registered trademark), about 0.1 mm or more is preferably used. The dielectric may be any material such as an organic material such as Teflon (registered trademark), an inorganic material such as alumina or quartz, as long as it is stable to plasma and heat. A material having a large high frequency loss is not preferable.

As a method of alternately supplying antiphase high frequencies to a plurality of antenna elements, a coaxial cable equivalent to a length of half a wavelength is provided at the power supply end every other antenna element. Just add more. Further, a phase shifter may be provided in the high frequency power source to supply the high frequencies shifted by half wavelength every other one.

As shown in FIG. 3, the discharge device of the present invention has a structure in which array antennas in which a plurality of antenna elements 2 are arranged in the width of the substrate to be processed are further arranged in a plurality of layers with a predetermined gap. It is preferable to have a multi-region structure in which the substrate 11 to be processed is arranged on both sides of each layer. With such a configuration, plasma processing can be performed simultaneously on a large number of substrates (six in the illustrated example), and the throughput can be significantly increased. Moreover, since the distance between the array antenna and the base can be shortened to about 30 to 60 mm, it is possible to realize a discharge device having an excellent throughput ratio with respect to the device installation area.

[0041]

EXAMPLES Next, the present invention will be described more specifically with reference to examples. The following experiment was conducted using the plasma processing apparatus having the configuration schematically shown in FIG. At this time, the length of the straight line portion was three kinds of 0.5 m, 1.0 m, and 1.6 m, and the reflected power was measured at an excitation frequency of 50 MHz and a discharge pressure of 10 Pa, and the plasma density distribution was visually observed. . As a result, discharge could not be generated at 0.5 m. At 1.0 m, discharge plasma was generated, but the reflection was large and exceeded 10% of the traveling wave.
Attention was paid to the plasma at this time, and it was observed that the density became dense near the center of the straight line part and became thinner toward the end part. On the other hand, with a 1.6 m antenna,
The reflected power became very small, and the density of the plasma could hardly be observed. Next, the discharge pressure was set to 20 Pa and the same observation was performed. As a result, discharge was generated even with an antenna of 0.5 m, but the reflected wave was largely over 10%. Regarding the plasma density distribution at this time, a phenomenon was observed in which the plasma density at the antenna coupling portion (around the U-shaped bend) increased and the emission intensity from the plasma decreased toward the power supply end and the ground end. . At this pressure (20 Pa), the reflected power was small and the uniformity of the plasma density was good for the antennas of 1.0 and 1.6 m.

From the above, it is possible to suppress the reflected wave to a small level by selecting the straight part of the antenna having an appropriate length or more, and at the same time, to prevent the nonuniformity of the plasma which is considered to be caused by the standing wave. It turned out that the occurrence can be suppressed. As a result of trying similar experiments under various discharge conditions,
It is possible to maintain good plasma uniformity by selecting the length of the straight line portion to a value that keeps the ratio of the reflected wave to the traveling wave to 10% or less. However, it was also found that the reflected wave does not rise again.

Based on the above results, the excitation frequency 85 MH
A plasma CVD apparatus having an array antenna with z and a straight portion having a length of 1.6 m was prototyped, and quantitative observation was performed with this apparatus. The straight portion of the antenna was covered with Teflon (registered trademark) having a thickness of 1 mm. The gas used for the discharge is SiH ₄
/ H ₂ = 0.2 mixed gas. Initially, electric power was supplied to the respective antenna elements in the same phase, but as shown in FIG. 4, the film thickness distribution was very bad. Next, an experiment was conducted by changing the film forming pressure while shifting the phase of each antenna element by 180 °, and as shown in the figure, the film thickness uniformity at a discharge pressure of 2 to 3 Pa was It became good. The reflected wave at this time was 3% or less of the traveling wave. It should be noted that due to the restriction on the pumping speed of the device, experiments at a pressure lower than this were not possible. Further, when the discharge frequency was lowered, the reflected wave increased and the film thickness distribution became uneven. That is, it was confirmed that even if the geometric length of the straight line portion of the antenna is the same, reducing the discharge frequency has the same effect as shortening the electrical length of the straight line portion. .

Next, the same experiment was carried out using an array antenna having a straight portion having a length of 1.6 m in a discharge pressure range of 0.1 to 1000 Pa, and the relationship with the graphs of FIGS. First, the excitation frequency for driving the antenna is 10 MHz
Consider the case where According to FIG. 7, it is suggested that a linear portion length of several tens to tens of thousands of meters is required in the low pressure region, otherwise, non-uniformity of plasma and increase of reflected wave will occur due to generation of standing wave. . That is, it was expected that the geometrical straight line length of 1.6 m would be too short. In an actual experiment, discharge could not be started at a pressure of 100 Pa or less. When the pressure was raised, electric discharge occurred, but the reflected wave was large in almost all pressure regions and was almost in the state of total reflection.

Next, the case of an excitation frequency of 85 MHz will be considered. In this case, according to the graph of FIG. 8, 1.6m
The length of the straight line part is 0.5 in the pressure range of 1 to 100 Pa.
Located between (1 / α) and 10 (1 / α), the reflected power is small and it is expected that the discharge will spread over the entire length of the antenna. The actual experimental results were as follows. Discharge did not occur at 0.1 to 0.6 Pa, but discharge plasma was generated in a pressure region higher than that. Particularly in the vicinity of 2 to 3 Pa, the reflected wave was small, and the uniformity of the plasma was good by visual confirmation. 10 to several 10
The plasma density was low at the tip of the antenna near Pa, which is considered to be because the electrical antenna length was too long. In the pressure range where discharge could not occur,
It is speculated that the spark conditions could not be satisfied with the applied power because the collision frequency was small.

The case where the excitation frequency is 400 MHz will be described. According to the graph of FIG. 9, at a pressure of about 10 Pa, the length of the linear portion of the antenna is 10 (1 / α).
It is expected that the plasma density at the tip of the antenna will decrease and the reflected wave will decrease. As a result of the experiment, such a phenomenon was observed in the discharge pressure region near 10 Pa, but in the high discharge pressure region,
The plasma uniformity was good, and the reflection was small. From the above, in any case, by selecting the antenna length within the range of 0.5 (1 / α) <the length of the straight line portion La <10 (1 / α), the reflected wave becomes small, It was found that good plasma uniformity was obtained.

As can be seen from the above description, in principle, the attenuation constant is determined by the type of gas, the thickness of the antenna, the dielectric constant / thickness of the dielectric material attached around the antenna, and the plasma density (excitation power). And so on. However, the optimum antenna length does not change extremely by changing these parameters, and it is confirmed that the optimum value of the straight line length exists in the upper range within the parameter range tested by the inventors. Was done.

Substrates were mounted on both sides of the array antenna using the method of the present invention to fabricate an a-Si solar cell as a prototype. As a result, a battery having the same characteristics as the parallel plate discharge device was obtained, and the solar cell characteristics on the substrates placed on both sides of the array antenna were almost the same.

[0049]

According to the present invention, a discharge device having high productivity can be obtained, and the plasma processing method with high productivity is realized by the present invention. Further, by applying the present invention as a plasma CVD apparatus for manufacturing a solar cell,
It will greatly contribute to the realization of low-cost solar cells.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing a configuration example of a discharge device of the present invention.

FIG. 2 is a schematic diagram showing a configuration example of an antenna element.

FIG. 3 is a schematic cross-sectional view showing a discharge device capable of simultaneously processing a plurality of substrates.

FIG. 4 is a graph showing a relationship between a power feeding method and a film thickness distribution.

FIG. 5 is a schematic diagram illustrating an interaction between antenna elements.

FIG. 6 is a schematic view showing a state around the antenna.

FIG. 7 is a graph showing the relationship between antenna length and pressure at an excitation frequency of 10 MHz.

FIG. 8 is a graph showing the relationship between antenna length and pressure at an excitation frequency of 85 MHz.

FIG. 9 is a graph showing the relationship between antenna length and pressure at an excitation frequency of 400 MHz.

[Explanation of symbols]

1 vacuum chamber, 2 antenna elements, 3 dielectric, 4 Folded part, 5 gas inlet, 6 exhaust port, 7 high frequency power supply, 8 coaxial cable, 9 power supply end, 10 ground edge, 11 bases, 12 substrate holder, 60 antennas, 61 sheath, 62 virtual boundaries, 63 Plasma.

Continued front page    (72) Inventor Norikazu Ito             5-8 Yotsuya, Fuchu-shi, Tokyo Anel             Within BA Co., Ltd. (72) Inventor, Yoshi Watanabe             5-8 Yotsuya, Fuchu-shi, Tokyo Anel             Within BA Co., Ltd. F-term (reference) 5F045 AA08 AB04 BB01 BB08 CA13                       CB01 DP01 EH02 EH11                 5F051 CA16 CA23 CA40

Claims (16)

[Claims] 1. A pair of first and second linear conductors having the same length are arranged in parallel, and a pair of adjacent ones of the first and second linear conductor ends are electrically connected. Antenna with the first linear conductor not connected to the ground end and the second linear conductor first end not connected to the power supply end capable of applying AC power. A plurality of elements, the linear conductors of the respective antenna elements are parallel, and the ground end and the power supply end alternate,
In a discharge device that forms array antennas by arranging them at equal intervals on a first plane in a vacuum and supplies AC power to the array antennas to form discharge plasma in a vacuum, in order from the power supply end The first feature is to supply alternating-current power of the same frequency all at once by changing the phase by 180 °, and the second feature is to set the frequency to 10 MHz to 2 GHz, which is measured at the power supply end. A third feature of the discharge device is that the length of the linear conductor is determined so that the ratio of the reflected wave to the traveling wave is 0.1 or less. 2. A pair of first and second linear conductors having the same length are arranged in parallel, and a pair of adjacent ones of the first and second linear conductor ends are electrically connected. Antenna with the first linear conductor not connected to the ground end and the second linear conductor first end not connected to the power supply end capable of applying AC power. A plurality of elements, the linear conductors of the respective antenna elements are parallel, and the ground end and the power supply end alternate,
In a discharge device that forms array antennas by arranging them at equal intervals on a first plane in a vacuum, and supplying AC power to the array antenna to form discharge plasma in a vacuum, in order from the power supply end The first feature is that AC power of the same frequency is supplied all at once by changing the phase by 180 °, and the frequency f (Hz) is 10 MHz to 400 MHz.
The second characteristic is that the frequency is set to MHz, and the dielectric constant κ _{p of the} plasma is calculated by using the frequency f and the discharge pressure p (Pa). And the skin depth δ of the electromagnetic field that penetrates the plasma.
(M) The damping constant α (1 / m) calculated when According to the third aspect, the discharge device is characterized in that the length La (m) of the linear conductor is set to 0.5 (1 / α) <La <10 (1 / α). 3. The discharge device according to claim 1, wherein the linear conductor has a diameter of 10 mm or less. 4. The discharge device according to claim 3, wherein the diameter of the linear conductor is 1 mm or more. 5. The discharge device according to claim 1, wherein a diameter of the linear conductor is changed in a length direction. 6. The discharge device according to claim 5, wherein at least a part of the diameter of the linear conductor is 10 mm or less. 7. The discharge device according to claim 1, wherein a part or the whole of the surface of the linear conductor is covered with a dielectric. 8. The discharge device according to claim 7, wherein the thickness of the dielectric is changed in the lengthwise direction of the linear conductor. 9. The discharge device according to claim 8, wherein an end portion of the dielectric has a tapered cross-sectional shape. 10. The dielectric is coated in a spiral shape along the longitudinal direction of a linear conductor.
Discharge device according to any one of 11. A substrate is arranged on each of second and third planes sandwiching the first plane on which the array antenna is arranged, and the substrates are arranged on the second and third planes by the discharge plasma. The electric discharge device according to claim 1, wherein the substrate is processed simultaneously. 12. The discharge device according to claim 11, wherein a plurality of the array antennas are arranged in one vacuum chamber. 13. A pair of first and second linear conductors having the same length are arranged in parallel, and one set of adjacent ones of the first and second linear conductor ends is electrically connected. Antenna with the first linear conductor not connected to the ground end and the second linear conductor first end not connected to the power supply end capable of applying AC power. A plurality of elements, the linear conductors of the respective antenna elements are parallel, and the ground end and the power supply end alternate,
In a plasma processing method of forming array antennas by arranging them at equal intervals on a first plane in a vacuum, and supplying alternating current power to the array antennas to form discharge plasma in a vacuum, The phases are sequentially changed by 180 °, AC power of the same frequency is fed all at once, the frequency is set to 10 MHz to 2 GHz, and the ratio of the reflected wave to the traveling wave measured at the power supply end is 0.1 or less. A plasma processing method characterized in that an array antenna in which a length of a linear conductor is defined is used for the. 14. Two linear conductors having the same length are arranged in parallel, and a pair of adjacent ones of the first and second linear conductor end portions is electrically connected. Antenna with the first linear conductor not connected to the ground end and the second linear conductor first end not connected to the power supply end capable of applying AC power. A plurality of elements, the linear conductors of the respective antenna elements are parallel, and the ground end and the power supply end alternate,
In a plasma processing method of forming array antennas by arranging them at equal intervals on a first plane in a vacuum, and supplying alternating current power to the array antennas to form discharge plasma in a vacuum, By sequentially changing the phase by 180 ° and supplying AC power of the same frequency all at once, the frequency f
(Hz) is 10 MHz to 400 MHz, and the dielectric constant κ _{p of} plasma is calculated by using the frequency f and the discharge pressure p (Pa). And the skin depth δ of the electromagnetic field that penetrates the plasma.
(M) The damping constant α (1 / m) calculated by Then, the plasma processing method is characterized by using an array antenna in which the length La (m) of the linear conductor is 0.5 (1 / α) <La <10 (1 / α). 15. A pair of first and second linear conductors having the same length are arranged in parallel, and a pair of adjacent ones of the first and second linear conductor ends are electrically connected. Antenna with the first linear conductor not connected to the ground end and the second linear conductor first end not connected to the power supply end capable of applying AC power. A plurality of elements, the linear conductors of the respective antenna elements are parallel, and the ground end and the power supply end alternate,
A plasma CV using an electric discharge plasma generated in a vacuum by forming an array antenna by arranging the array antenna at equal intervals on a first plane in a vacuum and supplying alternating current power to the array antenna.
A thin film containing silicon is formed by the D method, and in a solar cell using this thin film as a semiconductor layer, the phase is sequentially changed by 180 ° from the beginning of the power feeding end, and AC power of the same frequency is fed all at once. , The frequency is 1
The solar cell is characterized in that the length of the linear conductor is set to 0 MHz to 2 GHz and the ratio of the reflected wave to the traveling wave measured at the power supply end is 0.1 or less. 16. A pair of first and second linear conductors having the same length are arranged in parallel, and a pair of adjacent ones of the first and second linear conductor ends are electrically connected. Antenna with the first linear conductor not connected to the ground end and the second linear conductor first end not connected to the power supply end capable of applying AC power. A plurality of elements, the linear conductors of the respective antenna elements are parallel, and the ground end and the power supply end alternate,
A plasma CV using an electric discharge plasma generated in a vacuum by forming an array antenna by arranging the array antenna at equal intervals on a first plane in a vacuum and supplying alternating current power to the array antenna.
A thin film containing silicon is formed by the D method, and in a solar cell using this thin film as a semiconductor layer, the phase is sequentially changed by 180 ° from the beginning of the power feeding end, and AC power of the same frequency is fed all at once. , The frequency f
(Hz) is 10 MHz to 400 MHz, and the dielectric constant κ _{p of} plasma is calculated by using the frequency and the discharge pressure p (Pa). And the skin depth δ of the electromagnetic field that penetrates the plasma.
(M) The damping constant α (1 / m) calculated by Thus, the length La (m) of the linear conductor is set to 0.5 (1 / α) <La <10 (1 / α).