Method and apparatus for forming deposited film

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a deposited film forming method and a deposited film forming apparatus for continuously forming a deposited film on an elongated substrate by a plasma CVD method.

2. Related Background Art

As a deposited film forming apparatus for continuously forming a deposited film on a surface of a belt-like substrate, there is conventionally known a deposited film forming apparatus using a continuous plasma CVD method which adopts, for example, a roll-to-roll system disclosed by U.S. Pat. No. 4,400,409.

This apparatus is conceived to be capable of continuously forming an element which has a large area and a semiconductor junction by disposing a plurality of glow discharge regions, arranging the glow discharge regions along a path through which a sufficiently long belt-like substrate having a desired width passes, and continuously conveying the above-described substrate in a longitudinal direction while depositing and forming a semiconductor layer with a required conductivity in the glow discharge regions. The roll-to-roll system can therefore be said as a method which is suited for mass production of semiconductor elements having large areas.

In the conventional CVD method, radio frequency (RF) discharge is widely used as glow discharge plasma exciting means for forming a deposited film by decomposing a raw material gas. On the other hand, attentions have recently been paid to a plasma process which uses a microwave.

The microwave which has a frequency higher than that of RF used in the conventional case is capable of enhancing an energy density and is suited for efficient generation and maintenance of plasma.

For example, U.S. Pat. Nos. 4,517,223 and 4,504,518 disclose methods for depositing and forming a thin film on a substrate having a small area in microwave glow discharge plasma at a low pressure, and it is conceived that the microwave is capable of causing discharge at a lower pressure in comparison with RF and prevents polymerization of active species which constitute a cause for degradation of film characteristics, thereby making it possible not only to obtain a deposited film of high quality but also to suppress production of powders such as polysilane in plasma and remarkably enhance a deposition rate.

For mass production of semiconductor junction elements, for example, solar cells, it is necessary and indispensable to enlarge the deposition region by the deposited film forming apparatus by using the continuous plasma CVD method employing the roll-to-roll system.

Deposited films manufactured by apparatuses using the conventional microwave CVD method and RF plasma CVD method have larger ununiformity in a width direction as the deposition rate and the discharge region become larger.

Furthermore, the deposition rate is remarkably changed dependently on a kind of a discharge energy for generating plasma, discharge conditions (for example, discharging electric power and discharging frequency), a flow rate, a flow velocity, a pressure of a raw material gas in a vacuum container and the like, but changes in raw material gas concentration distribution and plasma density distribution are not taken into consideration, thereby posing a problem that a deposited film which has a uniform thickness and uniform quality cannot be formed in a large deposition region.

For example, in the case of pursuing a deposited film having characteristics for a solar cell by the microwave plasma CVD method, it is necessary to lower microwave electric power and enhance an RF bias introduction electric power. However, a deposited film obtained in such conditions has a thickness distribution which is changed depending on a distance from a microwave introduction position, that is, the deposited film is thinned as its portion is farther from the microwave introduction position.

When the plasma CVD method is applied to a deposited film having a large area, it is difficult to obtain a deposited film which has an uniform thickness and an uniform quality over a large area.

As describe above, the apparatus for continuously forming a semiconductor deposited film by the conventional roll-to-roll system poses a problem that the characteristics of a photovoltaic element are liable to be ununiform in a width direction of a substrate when a deposited film is formed by the microwave plasma CVD method which is capable of forming a film at a high speed.

SUMMARY OF THE INVENTION

In view of the above-described problem, an object of the present invention is to provide a deposited film forming method and a deposited film forming apparatus which are capable of forming a photovoltaic element having no ununiform characteristics by depositing semiconductor layers without ununiform thickness and ununiform properties.

In order to accomplish the above-described object, a deposited film forming method according to the present invention is a deposited film forming method for generating plasma in a plurality of successive vacuum containers and continuously forming a deposited film on a belt-like substrate while continuously moving the belt-like substrate in its longitudinal direction, wherein an opening of a discharge container is adjusted with opening adjusting plates having shapes set so as to reduce thickness ununiformity in a width direction of the substrate on the basis of a measurement of a deposition rate distribution.

For the above-described deposited film forming method, when a distance of a discharge space in a conveying direction is represented by x

n

, a distance of the discharge space in a direction perpendicular to the conveying direction is represented by y

n

, a deposition rate at an optional point (x

n

, y

n

) in the discharge space is represented by d(x

n

, y

n

), a deposited film thickness at y=y

n

, X

Pn

≦x

n

≦x

Qn

in the discharge space is represented by δ

n

(x, y

n

), wherein n=3, 4, 5, 6, . . . , and when a substrate conveying rate is represented by v and an ideal thickness of the deposited film is designated by δ,

d

n

(

x, y

n

)=

d

n

(

vt, y

n

)=

a

n

t

2

+b

n

t+c

n

(∵

x=vt

)

(Which is an approximate expression of the deposition rate)

\begin{matrix} δ_{n} (vt, y_{n}) = \int_{Pn}^{Qn} d_{n} (vt, y_{n}) ⅆ t = δ & (1) \end{matrix}

Then, a point A

n

(vP

n

, y

n

) and a point B

n

(vQ

n

, y

n

) which satisfy the formula (1) are obtained.

A quadratic curve passing the point A

n

:

x=F

1

(

y

) (2)

A quadratic curve passing the point Bn:

x=F

2

(

y

) (3)

It is preferable to set both ends of the opening of the discharge container so as to have a curve satisfying the formula (2) and a curve satisfying the formula (3) and limit the deposition region of the belt-like substrate by adjusting the opening of the discharge container. In the present invention, the both ends of the opening mean two portions defining end portions of the opening in the width direction of the substrate.

Furthermore, it is preferable to set a shape of the above-described opening adjusting plate so that the both ends of the opening of the discharge container have an arc passing the above-described point A

n

and an arc passing the above-described point B

n

which are determined from a deposition rate distribution in the width direction of the belt-like substrate and limit the deposition region of the belt-like substrate by adjusting the opening of the discharge container with the opening adjusting plate.

Furthermore, it is preferable to set the shape of the above-described opening adjusting plate within ±10% of a shape of an opening determined from the deposition rate distribution in the width direction of the belt-like substrate.

Furthermore, it is preferable that the above-described deposited film is formed by the microwave plasma CVD method.

Furthermore, it is preferable to set the shape of the opening adjusting plate so that ununiformity of a film thickness distribution of the deposited film is within 10% in the width direction of the belt-like substrate.

Furthermore, it is preferable to adopt the roll-to-roll system in which a belt-like substrate from a roll-like wound substrate are continuously moved through a plurality of discharge containers.

On the other hand, a deposited film forming apparatus according to the present invention is a deposited film forming apparatus for generating plasma in a plurality of successive vacuum containers and continuously forming a deposited film on a belt-like substrate while continuously moving the above-described belt-like substrate in its longitudinal direction, wherein opening adjusting plates having shapes set so as to reduce ununiformity of a film thickness of the deposited film in the width direction of the substrate on the basis of a measurement of a deposition rate distribution are disposed in an opening of discharge container.

For the above-described deposited film forming apparatus according to the present invention, when a distance of a discharge space in a conveying direction is represented by x

n

, a distance of the discharge space in a direction perpendicular to the conveying direction is designated by y

n

, a deposition rate at an optional point (x

n

, y

n

) in the discharge space is denoted by d(x

n

, y

n

), a deposited film thickness at y=y

n

, x

pn

≦x

n

≦x

Qn

in the discharge space is represented by δn(x, y

n

), wherein n=3, 4, 5, 6, and when a substrate conveying rate is represented by v and an ideal deposited film thickness is designated by δ,

d

n

(

x, y

n

)=

d

n

(

vt, y

n

)=

a

n

t

2

+b

n

t+c

n

(∵

x=vt

)

\begin{matrix} δ_{n} (vt, y_{n}) = \int_{Pn}^{Qn} d_{n} (vt, y_{n}) ⅆ t = δ & (1) \end{matrix}

Then, a point A

n

(vP

n

, y

n

) and a point B

n

(vQ

n

, y

n

) which satisfy the formula (1) are obtained.

A quadratic curve passing the point A

n

:

x=F

1

(

y

) (2)

A quadratic curve passing the point B

n

:

x=F

2

(

y

) (3)

It is preferable to set both ends of the opening of the discharge container so as to have a curve satisfying the formula (2) and a curve satisfying the formula (3), respectively, and dispose an opening adjusting plate in the opening of the discharge container to limit the deposition region of the belt-like substrate.

Furthermore, it is preferable to set a shape of the above-described opening adjusting plate so that both the ends of the opening of the discharge container have an arc passing the above-described point A

n

and an arc passing the above-described point B

n

which are determined from a deposition rate distribution in the width direction of the belt-like substrate, and dispose an opening adjusting plate in the opening of the discharge container to limit the deposition region of the belt-like substrate.

Furthermore, it is preferable to set the shape of the above-described opening adjusting plate so as to be within ±10% of a shape of an opening adjusting plate determined from the deposition rate distribution in the width direction of the belt-like substrate.

Furthermore, it is preferable that the above-described deposited film is formed by a microwave plasma CVD apparatus.

Furthermore, it is preferable to dispose an opening adjusting plate having such a shape as to limit ununiformity in a film thickness distribution of the above-described deposited film within 10% in the width direction of the belt-like substrate.

Furthermore, it is preferable to configure the deposited film forming apparatus of a roll to roll system type apparatus in which a belt-like substrate from a roll-like wound substrate is continuously moved through a plurality of discharge containers.

The deposited film forming method which uses the plasma CVD method generates a film thickness distribution of a deposited film when a discharge space is expanded so as to enlarge a film forming region. The distribution is largely changed depending on a microwave introducing method and conditions for forming the deposited film. A deposition rate distribution is largely different, for example, between a case where a microwave electric power is introduced in one direction and a case where the microwave electric power is introduced in two directions.

According to the present invention, a deposition rate distribution is measured and a shape of the opening adjusting plate is determined so as to make uniform a deposited film thickness in the width direction of the substrate. By disposing the opening adjusting plate in the opening of the discharge container, it is possible to shield the substrate from the discharge region and limit a deposition region on the belt-like substrate. This method makes it possible to form a deposited film which has a uniform thickness over a large area.

Even when film forming conditions are modified, in order to optimalize deposited film forming conditions, a shape of the opening adjusting plate is determined once again to be able to form a deposited film having a uniform thickness.

Furthermore, the present invention provides a film forming method for generating plasma in a plurality of successive vacuum containers and continuously forming a deposited film on a belt-like substrate while continuously moving the above-described substrate in its longitudinal direction,

wherein both ends of the opening of the discharge container are set so as to have a curve satisfying the following formula (4) and a curve satisfying the following formula (5), respectively, to adjust the opening of the discharge container, thereby limiting a deposition region of the belt-like structure, and

wherein when a distance of a discharge space in a conveying direction is represented by x

n

, a distance of the discharge space in a direction perpendicular to the conveying direction is represented by y

n

, a deposition rate at an optional point (x

n

, y

n

) in the discharge space is represented by d(x

n

, y

n

), a deposited film thickness at y=y

n

, x

Pn

≦x

n

≦x

Qn

in the discharge space is represented by δ

n

(x, y

n

), and n=3, 4, 5, 6, . . . , and when a substrate conveying rate is represented by v and an ideal thickness of the deposited film is represented by,

d

n

(

x, y

n

)=

d

n

(

vt, y

n

)=

a

n

t

2

+b

n

t+c

n

(∵

x=vt

)

\begin{matrix} δ_{n} (vt, y_{n}) = \int_{Pn}^{Qn} d_{n} (vt, y_{n}) ⅆ t = δ & (1) \end{matrix}

\begin{matrix} δ_{n} (vt, y_{n}) = \int_{Pn}^{Qn} d_{n} (vt, y_{n}) ⅆ t = δ & (1) \end{matrix}

a point A

n

(vP

n

, y

n

) and a point B

n

(v

Qn

, y

n

) which satisfy the formula (1) are obtained, and

a quadratic curve passing the point A

n

is x=F

1

(y) . . . (2), and

a quadratic curve passing the point B

n

is x=F

2

(y) . . . (3), and

on the basis of the formulas (2) and (3), the following inequality formulas (4) and (5) are obtained, respectively:

1.1

F

1

(

y

)−0.1

F

2

(

y

)≦

x≦

0.9

F

1

(

y

)+0.1

F

2

(

y

) (4)

0.9

F

2

(

y

)+0.1

F

1

(

y

)≦

x≦

1.1

F

2

(

y

)−0.1

F

1

(

y

) (5).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1

is a conceptional diagram explaining Example 1 of the present invention in which an opening adjusting plate is disposed in an opening of a discharge container so as to make uniform a film thickness distribution in width direction of a belt-like substrate;

FIG. 2

is a schematic diagram showing a roll to roll type plasma CVD apparatus which is used for manufacturing a single cell in the example of the present invention;

FIG. 3

is a diagram showing a location at which ununiformity in a width direction is evaluated in the example of the present invention;

FIG. 4

is a graph showing deposition rates on stationary samples in the example of the present invention;

FIG. 5

is a schematic diagram showing a roll to roll type plasma CVD apparatus which is used for manufacturing triple cells in the example of the present invention;

FIG. 6

is a schematic conceptional diagram of an opening adjusting plate used in Comparative Example 1;

FIG. 7

is a conceptional diagram explaining Example 2 of the present invention in which an opening adjusting plate is disposed in an opening of a discharge container to make uniform a film thickness distribution in a width direction of a belt-like substrate;

FIG. 8

is a graph showing deposition rate distribution on stationary samples in Example 2;

FIG. 9

is a schematic conceptional diagram of an opening adjusting plate in Comparative Example 2;

FIG. 10

is a conceptional diagram explaining Example 3 of the present invention in which an opening adjusting plate is disposed in an opening of a discharge container to make uniform a film thickness distribution in a width direction of a belt-like substrate;

FIG. 11

is a graph showing deposition rate distribution on stationary samples in Example 3 of the present invention; and

FIG. 12

is a schematic conceptional diagram showing an opening adjusting plate in Comparative Example 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the accompanying drawings, description will be made of preferable embodiments of the present invention which do not limit the present invention.

The deposited film forming apparatus according to the present invention is an apparatus for forming a functional deposited film on a surface of a belt-like substrate while continuously conveying the substrate in a longitudinal direction, wherein the belt-like substrate is shielded from a discharge region with an opening adjusting plate provided in an opening of a discharge container, thereby limiting a region for deposition on the substrate.

The deposited film forming apparatus according to the present invention therefore solves a serious problem of the conventional deposited film forming method using the plasm CVD method, thereby making it possible to form a deposited film having a large area, by expanding a discharge space and simultaneously make uniform a thickness and a property of a film deposited on the belt-like substrate.

A deposited film forming apparatus used in the present invention will be described with reference to the accompanying drawings. The apparatus used in the present invention is a conventional roll-to-roll type successive plasma CVD apparatus shown in FIG.

2

.

In

FIG. 2

, the deposited film forming apparatus is configured basically by a belt-like substrate delivery chamber

201

, an n type semiconductor layer vacuum container

202

using a radio frequency plasma CVD method, an i type semiconductor layer vacuum container

203

, an i type semiconductor layer vacuum container

204

, a p type semiconductor layer vacuum container

205

, an i type semiconductor layer vacuum container

206

using a microwave plasma CVD method which contains two discharge containers

207

a

and

207

b

, and a belt-like substrate takeup chamber

208

, the vacuum containers

202

through

206

being connected by a gas gate

209

.

In the apparatus according to the present invention, a belt-like substrate

210

is delivered from a bobbin

211

in the delivery chamber

201

, and moved while passing through the five vacuum containers

202

through

206

which are connected by gas gates

209

until the belt-like substrate

210

is taken up by a bobbin

212

in the takeup chamber

208

. During this period, a deposited film of a semiconductor having a nip structure is formed on a surface of the substrate.

Attached to each of the vacuum containers

202

through

206

are a heater

213

for heating the substrate, a gas introducing pipe

214

which introduces a film forming gas from gas supply means (not shown) into the discharge container, a gas heater

215

which heats the introduced gas, and an exhaust pipe

216

which evacuates a discharge container by exhausting means (not shown). In addition, the exhaust pipes

216

and exhaust adjusting valves

217

are attached also to the delivery chamber

201

and the takeup chamber

208

.

Disposed in discharge regions

218

of the vacuum container

206

which uses the microwave CVD method, are opening adjusting plates

219

which are arranged in openings of discharge containers

207

a

and

207

b

to control a deposited film thickness distribution of the belt-like substrate, applicators

222

which supply a microwave electric power for causing discharge by imparting an energy to the film forming gas in the discharge containers from microwave oscillators

220

through waveguides

221

, and bias bars

223

which apply RF electric power from RF oscillators

227

to plasma so that a deposited film is formed by decomposing the supplied raw material gases.

Disposed at discharge regions

224

of the vacuum containers

202

through

205

which use the RF plasma CVD method are cathodes

225

which apply the RF electric power to the raw material gas to form a deposited film by the RF plasma CVD method.

The gas gates

209

are disposed so that the vacuum containers are separated and independent, and the belt-like substrate

210

passes through the discharge regions and are continuously conveyed. High quality deposited films which have different compositions and composed of multiple layers can be formed by introducing gate gases from gate gas introducing pipes

226

and preventing the raw material gases in the adjacent vacuum containers from being mixed with each other.

The deposited film forming method according to the present invention is carried out using the deposited film forming apparatus which has the above-described configuration. In other words, the deposited film forming method according to the present invention is a deposited film forming method in which plasma is generated in a plurality of successive vacuum containers and a deposited film is continuously formed on a belt-like substrate while continuously moving the above-described substrate in its longitudinal direction, wherein the opening of the discharge container is adjusted with the opening adjusting plates having shapes set so as to reduce ununiformity in thickness of the deposited film in a width direction of the substrate on the basis of a measurement of a deposition rate distribution.

Specifically, when a distance of a discharge space in the conveying direction is represented by X

n

, a distance of the discharge space in a direction perpendicular to the conveying direction is designated by y

n

, a deposition rate at an optional point (x

n

, y

n

) in the discharge space is denoted by d(x

n

, y

n

), a deposited film thickness at y=y

n

, x

Pn

≦x

n

≦x

Qn

in the discharge space is represented by δ

n

(x, y

n

) wherein n=3, 4, 5, 6, . . . , and when a substrate conveying rate is represented by v and an ideal deposited film thickness is designated by δ,

d

n

(

x, y

n

)=

d

n

(

vt, y

n

)=

a

n

t

2

+b

n

t+c

n

(∵

x=vt

)

\begin{matrix} δ_{n} (vt, y_{n}) = \int_{Pn}^{Qn} d_{n} (vt, y_{n}) ⅆ t = δ & (1) \end{matrix}

are obtained, and a point A

n

(vP

n

, y

n

) and a point B

n

(vQ

n

, y

n

) which satisfy the formula (1) are obtained.

A quadratic curve passing the point A

n

: x=F

1

(y) . . . (2)

A quadratic curve passing the point B

n

: x=F

2

(y) . . . (3)

Both ends of the opening of the discharge container are set so as to have a curve satisfying the formula (2) and a curve satisfying the formula (3), and a deposition region of the belt-like substrate is limited by adjusting the opening of the discharge container.

Furthermore, a shape of the opening adjusting plate is set so that the both ends of the opening of the discharge container have an arc passing the above-described point A

n

and an arc passing the above-described point B

n

which are determined from a deposition rate distribution in the width direction of the belt-like substrate, and the deposition region of the belt-like substrate is limited by adjusting the opening of the discharge container with the opening adjusting plate.

Furthermore, it is preferable that the shape of the opening adjusting plate is set so as to be within 10% of an opening shape determined from the deposition rate distribution in the width direction of the belt-like substrate.

It is preferable to form the deposited film by the plasma CVD method, in particular, the microwave plasma CVD method.

Furthermore, it is preferable to set the shape of the opening adjusting plate so that film thickness ununiformity of the deposited film in the width direction of the belt-like substrate is within 10%.

For continuously forming the deposited film, it is preferable to adopt the roll to toll system capable of continuously moving a belt-like substrate from a roll-like wound substrate through a plurality of discharge containers.

That is, in the present invention, a deposition rate distribution is measured to determine the shape of the opening adjusting plate so as to make uniform a deposited film thickness in the width direction of the substrate. By disposing the opening adjusting plate in the opening of the discharge container, it is possible to shield the substrate from the discharge region and limit a deposition region on the belt-like substrate. This method makes it possible to form a deposited film having an uniform thickness over a large area.

Even when film forming conditions are modified, in order to optimalize conditions for forming the deposited film, a shape of the opening adjusting plate is determined once again, whereby the present invention makes it possible to form a deposited film having an uniform thickness.

When a deposited film is formed over an entire range of the opening of the discharge container without disposing the opening adjusting plate for controlling a deposited film thickness distribution in the opening of the discharge container nor limiting a deposition region, a film deposition rate is widely distributed. This is because a deposition rate tends to be smaller at a location farther from a microwave electric power introducing position, and deposition rates are characteristically distributed depending on microwave electric power introduction methods of deposited film forming apparatuses.

For example, when microwave electric power is introduced using four applicators

101

as shown in

FIG. 1

, deposition rates are distributed at a central position smaller than at both ends. By disposing opening adjusting plates

102

which have shapes shown in FIG.

1

and are matched with such a deposition rate distribution, it is possible to form openings

103

matched with a film thickness distribution in the opening of the discharge container, thereby obtaining a deposited film having an uniform thickness and an uniform quality on a belt-like substrate

104

.

Even when film forming conditions are modified to improve the characteristics of the film, it is possible to form a deposited film having an uniform thickness by modifying the shapes of the opening adjusting plates.

Description will be made below of concrete examples of the deposited film forming method and the deposited film forming apparatus according to the present invention, which do not limit the present invention in any way.

EXAMPLE 1

Using a deposited film forming apparatus shown in

FIG. 2

, the deposited film forming method according to the present invention will be described in a due sequence. In this experiment, a deposition rate distribution of a deposited film having i type layers which was manufactured by the microwave CVD method was checked. The deposited film forming apparatus shown in

FIG. 2

introduces microwave electric power using the four applicators

222

. Manufacturing conditions are shown in Table 1.

TABLE 1

Substrate

SUS430 (Width 350 mm × Length 300 m × Thickness

0.2 mm)

Gate gas

H

2

: 1000 (sccm)

Name of layer

Used gas and

Pressure

Effective

Heating

flow rate

(Pa)

electric

temperature

(sccm)

power (W)

(° C.)

Manufacturing condition for each layer

n type layer

SiH

4

:220

133.3

RF electric

250

PH

3

/H

2

(1.0 Torr)

power: 250

(PH

3

: 2%):

330

H

2

: 3000

i type buffer

SiH

4

:170

134.0

RF electric

270

layer

H

2

:1500

(1.05 Torr)

power: 180

i type layer

SiH

4

:120 × 2

1.3

Microwave

350

GeH

4

:

(0.01 Torr)

electric

100 × 2

power: 200

H

2

: 600 × 2

RF bias

electric

power: 1800

i type buffer

SiH

4

: 170

134.0

RF electric

320

layer

H

2

: 1500

(1.05 Torr)

power: 210

p type layer

SiH

4

: 30

133.3

RF electric

175

BF

3

H

2

(1.0 Torr)

power: 800

(BF

3

: 2%):

380

H

2

: 5000

Transparent

ITO (In

2

O

3

+ SnO

2

) thin film 70 nm

electrode

Collector

Alumimium (Al) thin film 2 μm

electrode

A bobbin

211

around which sufficiently degreased and cleaned stainless steel belt-like substrate (SUS 430, 350 mm wide×300 m long×0.2 mm thick) was wound was set in a vacuum container

201

having a substrate feeding mechanism. The belt-like substrate was passed to a takeup chamber

208

for the belt-like substrate consecutively through gas gates

209

, an n type semiconductor layer vacuum container

202

, an i type semiconductor layer vacuum container

203

, an i type semiconductor layer vacuum chamber

206

, an i type semiconductor layer vacuum container

204

and a p type semiconductor layer vacuum container

205

, and tension was adjusted to a degree at which the substrate is free from slack. A pressure in each of the vacuum containers was reduced to 1.3×10

−4

Pa (1×10

−6

Torr) with an evacuating apparatus (not shown).

First, a deposited film was formed over an entire range of the openings of the discharge containers

207

a

and

207

b

without disposing the opening adjusting plates

219

for adjusting a deposited film thickness distribution in the openings of the discharge containers

207

a

and

207

b

, and a deposition rate distribution was measured.

For heat treatment at a film forming time, 1000 sccm of H

2

was introduced into each gas gate

209

from the gate gas introducing pipe

226

as a gate gas and the belt-like substrate

210

was heated to 300° C. with the substrate heater

213

.

A raw material gas was introduced into each discharge container from the gas introducing pipe

214

. The belt-like substrate was conveyed at a speed of 1270 mm/min, and microwave electric power and RF electric power were applied to the discharge containers from the microwave oscillator

220

and the RF oscillator

227

to cause plasma discharge in the film forming regions, thereby forming an i type amorphous silicon film on the belt-like substrate.

After confirming stabilization of a discharge condition, conveyance of the belt-like substrate was stopped and a stationary sample was prepared. Deposition rates of an obtained deposited film were measured with a spectroscope. For evaluating a distribution in the width direction, deposition rates were measured at five points in a central portion (C) and both ends (F, FC, RC and R) as shown in

FIG. 3

by 10 points in a substrate conveying direction, i.e., at 50 points in total. Measured results are shown in Table 2 and FIG.

4

. Points at positions 30 through 110 in Table 2 are located in the discharge container

207

a

, whereas points at positions 250 through 330 in Table 2 are located in the discharge container

207

b

.

TABLE 2

Position (mm)

Position

30

50

70

90

110

250

270

290

310

330

F

71.7

86.6

89.0

81.1

70.0

70.0

81.0

89.2

86.2

72.0

FC

61.0

75.5

77.8

70.9

60.5

60.0

71.5

80.0

74.2

59.3

C

54.4

65.1

67.7

64.9

52.3

53.0

65.9

69.4

64.3

52.4

RC

58.2

73.5

76.3

69.1

58.5

58.0

70.0

78.5

72.0

58.0

R

71.5

85.7

89.0

80.6

68.0

68.0

80.9

88.5

86.0

69.2

As seen from Table 2 and

FIG. 4

, deposition rates of the obtained deposited film were not constant in the substrate width direction and the conveying direction, but a total deposited film thickness exhibited a large distribution in the width direction when the film was deposited while conveying the belt-like substrate

210

.

On the basis of a result of the obtained deposition rate distribution, shapes of the opening adjusting plates were determined for each of left and right discharge containers.

First, shapes of the opening adjusting plates were determined for a discharge space A.

When a distance of the discharge space in the conveying direction was represented by x, a distance of the discharge space in a direction perpendicular to the conveying direction was designated by y, a deposition rate at an optional point (x, y) in the discharge space was denoted by d(x, y), a deposited film thickness at y

1

=175 (mm), x

P1

≦x

1

≦x

Q1

in the discharge space was represented by δ

1

(x, y

1

), a substrate conveying rate v was 1270 (mm/min), an ideal deposited film thickness δ was 300 (Å),

d

1

(

x, y

1

)=

d

1

(

vt, y

1

)=−4.2

t

2

+27

t+

24(∵

x=vt

)

\begin{matrix} δ_{n} (vt, y_{n}) = \int_{Pn}^{Qn} d_{n} (vt, y_{n}) ⅆ t = δ & (1) \end{matrix}

(t, y

1

) satisfying the formula (1) are A

1

(0.28, 175) and B

1

(632, 175)

∵(x, y)=A

1

(6.0, 175), B

1

(134, 175)

When a deposited film thickness at y

2

=35 (mm), x

P2

≦x

2

≦x

Q2

in the discharge space was denoted by δ (x, y

2

), the following was obtained:

d

2

(

x, y

2

)=

d

2

(

vt, y

2

)=−5.0

t

2

+32

t+

37(∵

x=vt

)

\begin{matrix} δ_{2} (vt, y_{2}) = \int_{P2}^{Q2} d_{2} (vt, y_{2}) ⅆ t = δ & {(1)}^{'} \end{matrix}

(t, y

2

) satisfying the formula (1)′ are A

2

(0.85, 35) and B

2

(5.75, 35)

∵(x, y)=A

2

(18, 35), B

2

(122, 35)

When a deposited film thickness at y

3

=315 (mm), x

P3

≦x

3

≦x

Q3

was denoted by δ (x, y

3

), the following was obtained:

d

3

(

x, y

3

)=

d

3

(

vt, y

3

)=−5.2

t

2

+33

t+

35(∵

x=vt

)

\begin{matrix} δ_{3} (vt, y_{3}) = \int_{P3}^{Q3} d_{3} (vt, y_{3}) ⅆ t = δ & {(1)}^{″} \end{matrix}

(t, y

3

) satisfying the formula (1)″ are A

3

(0.78, 315) and B

3

(5.82, 315)

∵(x,y)=A

3

(17, 315), B

3

(123, 315)

A quadratic curve passing the points A

1

, A

2

and A

3

: x=F

1

(y)=5.9×10

−4

y

2

−0.21y+24

A quadratic curve passing the points B

1

, B

2

and B

3

: x=F

2

(y)=−5.9×10

−4

y

2

+0.21y+116

Similarly, shapes of the opening adjusting plates for a discharge space B were determined.

When a deposited film thickness at y

1

=175 (mm), x

P1

≦x

1

≦x

Q1

in the discharge space was denoted by δ

1

(x, y

1

), a substrate conveying rate v was 1270 (mm/min), an ideal deposited film thickness δ was 300 (Å),

d

1

(

x, y

1

)=

d

1

(

vt, y

1

)=−4.7

t

2

+31

t+

19(∵

x=vt

)

\begin{matrix} δ_{n} (vt, y_{n}) = \int_{Pn}^{Qn} d_{n} (vt, y_{n}) ⅆ t = δ & (1) \end{matrix}

(t, y

1

) satisfying the formula (1) are A

1

(0.29, 175) and B

1

(631, 175)

∵(x, y)=A

1

(6.1, 175), B

1

(133.9, 175)

When a deposited film thickness at y

2

=35 (mm), x

P2

≦x

2

≦x

Q2

in the discharge space was denoted by δ (x, y

2

), the following was obtained:

d

2

(

x, y

2

)=

d

2

(

vt, y

2

)=−5.0

t

2

+34

t+

31(∵

x=vt

)

\begin{matrix} δ_{2} (vt, y_{2}) = \int_{P2}^{Q2} d_{2} (vt, y_{2}) ⅆ t = δ & {(1)}^{'} \end{matrix}

(t, y

2

) satisfying the formula (1)′ are A

2

(0.83, 35) and B

2

(5.77, 35)

∵(x, y)=A

2

(17.6, 35), B

2

(122.4, 35)

When a deposited film thickness at y

3

=315 (mm), x

P3

≦x

3

≦x

Q3

in the discharge space was denoted by δ (x, y

3

), the following was obtained:

d

(

x, y

3

)=

d

3

(

vt, y

3

)=−5.6

t

2

+38

t+

25(∵

x=vt

)

\begin{matrix} δ_{3} (vt, y_{3}) = \int_{P3}^{Q3} d_{3} (vt, y_{3}) ⅆ t = δ & {(1)}^{″} \end{matrix}

(t, y

3

) satisfying the formula (1)″ are A

3

(0.77, 315) are B

3

(5.83, 315)

∵(x, y)=A

3

(16.3, 315), B

3

(123.7, 315)

A quadratic curve passing the points A

1

, A

2

and A

3

: x=F

1

(y)=5.9×10

−4

y

2

−0.21y+24

A quadratic curve passing the points B

1

, B

2

and B

3

: x=F

2

=−5.9×10

−4

y

2

+0.21y+116

Using opening adjusting plates

102

having the curved shapes obtained from the above at the opening-side ends, as shown in

FIG. 1

, an nip type single cell was manufactured by controlling a deposited film thickness distribution on the belt-like substrate

104

.

After carrying out steps till gas introduction similarly as in experiment 1, the belt-like substrate was conveyed at a rate of 1270 mm/min, and microwave electric power and RF electric power were applied to the discharge containers from a microwave oscillator

220

and the RF oscillator

227

to cause plasma discharge in the film forming regions, thereby forming the nip type amorphous silicon film on the belt-like substrate.

ITO(In

2

O

3

+SnO

2

) was deposited to a thickness of 70 nm as a transparent electrode on the formed nip type amorphous silicon film by vacuum vapor deposition, and Al was further deposited to a thickness of 2 μm as a collector electrode by vacuum vapor deposition, thereby manufacturing a photovoltaic element. A thickness distribution of an i type layer was evaluated from a C-V characteristic of the obtained photovoltaic element. A thickness distribution of the obtained deposited film is shown in Table 3.

TABLE 3

Position

F

FC

C

RO

R

Ununiformity

Example 1

1.00

0.93

0.92

0.94

0.98

3.1%

Comparative

1.00

0.97

0.94

0.89

0.83

22.1%

Example 1

Example 1 of the present invention indicated that an obtained deposited film thickness was uniform in the width direction and ununiformity of the deposited film thickness was in a range within 10%.

Then, a triple cell was manufactured using a roll to roll type plasma CVD apparatus shown in

FIG. 5

which was capable of forming an nipnipnip type triple cell. Film forming conditions are summarized in Table 4.

TABLE 4

Substrate

SUS430 (Width 350 mm × Length 300 m × Thickness

0.2 mm)

Reflecting

ALuminmium (Al) thin film: 0.2 μm

layer

Reflection

Zinc oxide (ZnO): 1.2 μm

enhancing

layer

Gate gas

H

2

: 1000 (sccm)

Name of layer

Used gas and

Pressure

Efective

Heating

flow rate

(Pa)

electric

temperature

(sccm)

power (W)

(° C.)

Manufacturing condition for each layer

n type layer

SiH

4

: 220

133.3

RF electric

320

PH

3

/H

2

(1.0 Torr)

power: 250

(PH

3

: 2%):

330

H

2

: 1500

i type buffer

SiH

4

: 60

134.0

RF electric

270

layer

H

2

: 900

(1.05 Torr)

power: 180

i type layer

SiH

4

:100 × 2

1.3

Microwave

380

GeH

4

:

(0.01 Torr)

electric

120 × 2

power: 200

H

2

: 600 × 2

RF electric

power: 900

i type buffer

SiH

4

: 170

134.0

RF electric

340

layer

H

2

: 1500

(1.05 Torr)

power: 210

p type layer

SiH

4

: 30

133.3

RF electric

175

BF

3

H

2

(1.0 Torr)

power: 800

(BF

3

: 2%):

800

H

2

: 3000

n type layer

SiH

4

: 220

133.3

RF electric

250

PH

3

/H

2

(1.0 Torr)

power: 250

(PH

3

: 2%):

330

H

2

: 3000

i type buffer

SiH

4

: 60

134.0

RF electric

270

layer

H

2

: 1500

(1.05 Torr)

power: 180

i type layer

SiH

4

:120 × 2

1.3

Microwave

350

GeH

4

:

(0.01 Torr)

electric

100 × 2

power: 200

H

2

: 600 × 2

RF electric

power: 1800

i type buffer

SiH

4

: 170

134.0

RF electric

320

layer

H

2

: 1500

(1.05 Torr)

power: 210

p type layer

SiH

4

: 30

133.3

RF electric

175

BF

3

H

2

(1.0 Torr)

power: 800

(BF

3

: 2%):

800

H

2

: 3000

n type layer

SiH

4

: 100

133.3

RF electric

250

PH

3

/H

2

(1.0 Torr)

power: 250

(PH

3

: 2%):

240

H

2

: 1000

i type

SiH

4

: 100

1.3

RF electric

200

layer (x3)

H

2

: 1000

(0.01 Torr)

power: 220

p type layer

SiH

4

: 30

133.3

RF electric

175

BF

3

H

2

(1.0 Torr)

power: 800

(BF

3

: 2%):

380

H

2

: 5000

Transparent

ITO (In

2

O

3

+ SnO

2

) thin film 70 nm

electrode

Collector

Alumimium (Al) thin film 2 μm

electrode

In place of the above-described stainless steel belt-like substrate, a bobbin

503

wound with a stainless steel belt-like substrate (SUS430)

502

to which an aluminum thin film (0.2 μm) and a ZnO thin film (1.2 μm) were deposited by a sputtering method as a lower electrode was set in a vacuum container

501

having a substrate feeding mechanism, as in the above-described experiment, the belt-like substrate was passed to a takeup chamber

520

for the belt-like substrate through gas gates

504

, an n type semiconductor layer vacuum containers

505

,

506

and

507

, i type semiconductor layer vacuum containers

508

and

509

, second i type semiconductor layer vacuum containers

510

and

511

by the microwave plasma method, i type semiconductor layer vacuum containers

512

,

513

and

514

by RF plasma CVD method, i type semiconductor layer containers

515

and

516

, and p type semiconductor layer vacuum containers

517

,

518

and

519

, and tension was adjusted to a degree at which the substrate is free from slack. Pressures in the vacuum containers

505

to

519

were lowered to 1.3×10

−4

Pa (1×10

−6

Torr) with an exhaust system (not shown).

In order to control a deposited film thickness distribution on the belt-like substrate

502

, opening adjusting plates

102

such as those shown in

FIG. 1

were disposed in openings of the i type semiconductor layer discharge containers

521

and

522

by the microwave plasma method. The deposition regions

103

were limited accordingly.

As a heat treatment at a film forming time, 1000 sccm of H

2

was introduced into each gas gate from the gate gas introducing pipe as gate gas, and the belt-like substrate was heated to 300° C. with the substrate heater.

A raw material gas was introduced into each discharge container from the gas introducing pipe, the belt-like substrate was conveyed at a speed of 1270 mm/min, and electric power was applied to each discharge container from the microwave oscillator and the radio frequency oscillator to cause plasma discharge in film forming regions, thereby forming an nipnipnip type amorphous silicon film on the belt-like substrate.

After feeding one roll amount of the belt-like substrate, supply of all plasma and gases, power supply to all lamp heaters and conveying of the belt-like substrate were stopped. Then, discharge container leaking nitrogen (N

2

) gas was introduced into each discharge container to return the container to atmospheric pressure, and the belt-like substrate was taken out from a takeup bobbin.

On a formed nipnipnip type amorphous silicon film, ITO(In

2

O

3

+SnO

2

) was deposited to a thickness of 70 nm as a transparent electrode by vacuum vapor deposition and Al was further deposited to a thickness of 2 μm as a collector electrode by vacuum vapor deposition, thereby manufacturing a photovoltaic element.

A formed solar cell was evaluated by measuring a spectral sensitivity characteristic, and a photoelectric conversion efficiency η for irradiation with a solar simulator having an AM value of 1.5 and an energy density of 100 mW/cm

2

. In order to evaluate a distribution in the width direction, the spectral sensitivity characteristic and the photoelectric conversion efficiency were measured at five points in a central portion (C) in the width direction of the belt-like substrate and in both ends (F, FC, RC and R). Evaluation results are summarized in Table 5.

TABLE 5

Comparative Example 1

Example 1

Rela-

Rela-

Rela-

Rela-

tive

tive

photo-

tive

photo-

thick-

electric

thick-

electric

ness

Rela-

conver-

ness

Rela-

conver-

of

tive

sion

of

tive

sion

deposited

sensi-

effi-

deposited

sensi-

effi-

Position

film

tivity

ciency

film

tivity

ciency

F

1.00

1.00

1.00

1.00

1.00

1.00

FO

0.93

0.98

0.97

0.81

0.91

0.94

C

0.92

0.98

0.97

0.72

0.78

0.79

RO

0.94

0.98

0.98

0.78

0.89

0.93

R

0.98

0.99

0.99

0.96

0.99

0.99

Ununi-

3.1%

22.1%

formity

Furthermore, a solar cell having a size of 350 mm by 240 mm was manufactured and an efficiency of the whole solar cell was evaluated. Results are shown in Table 6.

TABLE 6

Comparative

Example 1

Example 1

Average photoelectric conversion

10.2%

9.5%

efficiency

(effective area 350 × 240)

As apparent from Table 5 and Table 6, the experiment indicated that the opening adjusting plates suppressed ununiformity of a total deposited film thickness within 10%, thereby suppressing ununiformities of relative sensitivities and photoelectric conversion efficiencies of the solar cells. Furthermore, the experiment indicated that a photoelectric conversion of the whole solar cell could be enhanced by suppressing the ununiformity of the photoelectric conversion efficiency.

Comparative Example 1

In Comparative Example 1, opening adjusting plates

601

shown in

FIG. 6

which had an equal opening length in the width direction were used in contrast to Example 1 wherein the opening adjusting plate

102

shown in

FIG. 1

were used. Other film forming conditions were the same as those in Example 1. In Comparative Example 1, a solar cell was manufactured in the other film forming conditions shown in Table 1 including the microwave electric power.

A film thickness distribution of an obtained deposited film in the width direction provided results shown in Table 3. It was found that ununiformity of the film thickness distribution of the obtained deposited film was larger than 10%.

Similarly as in Example 1, an nipnipnip type amorphous silicon film was formed on a belt-like substrate. On an n type layer, ITO(In

2

O

3

+SnO

2

) was deposited to a thickness of 70 nm as a transparent electrode by vacuum vapor deposition and Al was further deposited to a thickness of 2 μm as a collector electrode by vacuum vapor deposition, thereby manufacturing a photovoltaic element.

A formed solar cell was evaluated by measuring a spectral sensitivity characteristic and a photoelectric conversion efficiency η for irradiation with a solar simulator having an AM value of 1.5 and an energy density of 100 mW/cm

2

.

Evaluation results are summarized in Table 5. Furthermore, a solar cell having a size of 350 mm by 240 mm was manufactured, and an overall efficiency in the width direction of a substrate was evaluated. An evaluation result is shown in Table 6.

Ununiformity of a deposited film thickness was larger than 10% when the opening adjusting plates

601

were used. The ununiformity of the deposited film thickness caused ununiformity of the photoelectric conversion efficiency, thereby resulting in degradation of a photoelectric conversion efficiency of the whole solar cell.

EXAMPLE 2

In Example 2, an i type layer was formed by using an applicator

701

and introducing microwave electric power as shown in

FIG. 7

, in contrast to Example 1 wherein the i type layer was formed by using the four applicators

222

and introducing the microwave electric power as shown in FIG.

2

. The i type layer was manufactured by setting film forming conditions as shown in Table 1. In

FIG. 7

, reference numeral

702

denotes an opening adjusting plate, reference numeral

703

denotes a deposition region and reference numeral

704

denotes a belt-like substrate.

After passing the belt-like substrate (SUS 430) through vacuum containers and lowering their pressures to 1.3×10

−4

Pa (1×10

−6

Torr) with an exhaust system (not shown) in the procedures described in Example 1, an i type amorphous silicon film was formed on the substrate by causing discharge. A deposited film was formed over an entire range of openings of discharge containers

207

a

and

207

b

without disposing the opening adjusting plates

219

for controlling a deposited film thickness distribution in the openings of the discharge containers

207

a

and

207

b

. After confirming stabilization of a discharge condition, a stationary sample was prepared by stopping conveyance of the substrate.

In order to evaluate the distribution in the width direction, deposition rates were measured with a spectroscope at 3 points in a central portion (C) and in both ends (F and R) as shown in

FIG. 3

by at 7 points in the conveying direction of the substrate, i.e., at 21 points in total. Results of a deposition rates of an obtained deposited film are shown in Table 7 and FIG.

8

.

TABLE 7

Position (mm)

Position

5

45

85

125

165

205

245

F

38.0

60.4

76.4

92.1

100.7

90.1

61.9

C

43.5

60.5

73.6

88.8

97.2

87.2

61.4

R

38.0

52.9

63.4

73.4

82.6

75.2

53.4

As understood from Table 7 and

FIG. 8

, deposition rates of the obtained deposited film were not constant in the width direction of the substrate and the conveying direction, but a total deposited film thickness exhibited a large distribution on the width direction when the film was deposited while conveying the belt-like substrate

210

.

On the basis of a measurement of a deposition rate distribution, shapes of opening adjusting plates were determined.

When a distance of a discharge space in the conveying direction is represented by x, a distance of the discharge space in a direction perpendicular to the conveying direction is designated by y, a deposition rates at an optional point (x, y) in the discharge space is denoted by d(x, y), a deposited film thickness at y

1

=60 (mm), x

P1

≦x

1

≦x

Q1

in the discharge space is represented by δ

1

(x, y

1

), a substrate conveying rate v is 1270 (mm/min), an ideal deposited film thickness δ is 700 (Å),

d

1

(

x, y

1

)=

d

1

(

vt, y

1

)=−1.2

t

2

+16

t+

35(∵

x=vt

)

\begin{matrix} δ_{n} (vt, y_{n}) = \int_{Pn}^{Qn} d_{n} (vt, y_{n}) ⅆ t = δ & (1) \end{matrix}

and points (t, y

1

) satisfying the formula (1) are A

1

(2.8, 60) and B

1

(90, 60)

∵(x, y)=A

1

(59, 60), B

1

(191, 60)

When a deposited film thickness at y

2

=20 (mm), x

P2

≦x

2

≦x

Q2

in the discharge space is represented by δ (x, Y

2

), the following was obtained:

d

2

(

x, y

2

)=

d

2

(

vt, y

2

)=−1.3

t

2

+19

t+

29(∵

x=vt

)

\begin{matrix} δ_{2} (vt, y_{2}) = \int_{P2}^{Q2} d_{2} (vt, y_{2}) ⅆ t = δ & {(1)}^{'} \end{matrix}

and points (t, y

2

) satisfying the formula (1)′ are A

2

(0.91, 35) and B

2

(10.89, 35)

∵(x, y)=A

2

(19, 20), B

2

(231, 20)

When a deposited film thickness at y

3

=100 (mm), x

P3

≦x

3

≦x

Q3

in the discharge space is denoted by δ (x, y

3

), the following was obtained:

d

3

(

x, y

3

)=

d

3

(

vt, y

3

)=−5.2

t

2

+33

t+

35(∵

x=vt

)

\begin{matrix} δ_{3} (vt, y_{3}) = \int_{P3}^{Q3} d_{3} (vt, y_{3}) ⅆ t = δ & {(1)}^{″} \end{matrix}

points (t, y

3

) satisfying and the formula (1)″ are A

3

(0.35, 100) and B

3

(11.45, 100)

∵(x, y)=A

3

(17, 100), B

3

(123, 100)

a quadratic curve passing the points Al, A2 and A

3

: x=F

1

(y)=2.6×10

−2

y

2

−5.2y−94

and a quadratic curve passing the points B

1

, B

2

and B

3

: x=F

2

(y)=−5.9×10

−4

y

2

+6.0y+107

Shapes of opening adjusting plates were determined from the obtained curves, and an nip type single cell was manufactured while controlling a deposited film thickness distribution on the belt-like substrate

704

using the opening adjusting plates

702

which had distributions in the width direction of the deposition region

703

as shown in FIG.

7

. Steps till gas introduction were carried out similarly as in the experiment 1, the belt-like substrate

704

was conveyed at a speed of 1270 mm/min, and microwave electric power and RF electric power were applied to the discharge container from the microwave oscillator

220

and the RF oscillator

227

to cause plasma discharge in a film forming region, thereby forming an nip type amorphous silicon film on the belt-like substrate.

On the formed nip type amorphous silicon film, ITO (In

2

O

3

+SnO

2

) was deposited to a thickness of 70 nm as a transparent electrode by vacuum vapor deposition and Al was further deposited to a thickness of 2 μm as a collector electrode by vacuum vapor deposition, thereby manufacturing a photovoltaic element. A film thickness distribution of an i layer was evaluated from a C-V characteristic of the obtained photovoltaic element. The film thickness distribution of the obtained deposited film is shown in Table 8.

TABLE 8

Position

F

C

R

Ununiformity

Example 2

1.00

0.97

0.96

3.1%

Comparative

1.00

0.94

0.82

19.8%

Example 2

It was found in Example 2 that an obtained deposited film thickness was uniform in the width direction and ununiformity of the deposited film thickness was within 10%.

Then, a triple cell was manufactured using a roll to roll type plasma CVD apparatus which was capable of forming an nipnipnip type triple cell such as that shown in FIG.

5

. Film forming conditions are shown in Table 4.

A bobbin

503

wound with a belt-like substrate (SUS430)

502

on which an aluminum thin film (0.2 μm) and a ZnO thin film (1.2 μm) were deposited by a sputtering method as a lower electrode was set, in place of the stainless steel belt-like substrate (SUS430), in a vacuum container

501

having a substrate feeding mechanism, the belt-like substrate was passed to a belt-like substrate takeup chamber

520

through gas gates

504

, n type semiconductor layer vacuum containers

505

,

506

and

507

, i type semiconductor layer vacuum containers

508

and

509

, i type semiconductor layer vacuum containers

510

and

511

by the microwave plasma method, i type semiconductor layer vacuum containers

512

,

513

and

514

by the RF plasma CVD method, i type semiconductor layer vacuum containers

515

and

516

, and p type semiconductor layer vacuum containers

517

,

518

and

519

, and a tension was adjusted to a degree at which the substrate was free from slack as in the above-described experiment. The internal pressures of the vacuum containers

505

through

519

were lowered to 1.3×10

−4

Pa (1×10

−6

Torr) with an exhaust system (not shown).

Opening adjusting plates

102

such as those shown in

FIG. 1

were disposed in openings of i type semiconductor layer discharge containers

521

and

522

by the microwave plasma method to control a deposited film thickness distribution on the belt-like substrate

502

. A deposition region

103

was limited accordingly.

As a heat treatment at a film forming time, 1000 sccm of H

2

was introduced into each gas gate from a gate gas introducing pipe as a gate gas and the belt-like substrate was heated to 300° C. with a substrate heater.

A raw material gas was introduced into each discharge container from the gas introducing pipe, the belt-like substrate was conveyed at a speed of 1270 mm/min, and electric power was applied to each discharge container from a microwave oscillator and a radio frequency oscillator to cause plasma discharge in a film forming region, thereby forming an nipnipnip type amorphous silicon film on the belt-like substrate.

After feeding one roll amount of the belt-like substrate, all plasma, supply of all gases, power supply to all lamp heaters and conveyance of the substrate were stopped. Then, discharge container leaking nitrogen (N

2

) gas was introduced into the discharge containers to return the discharge containers to atmospheric pressure and the belt-like substrate was taken from a takeup bobbin.

On the formed nipnipnip type amorphous silicon film, ITO(In

2

O

3

+SnO

2

) was deposited to a thickness of 70 nm as a transparent electrode by vacuum vapor deposition and Al was further deposited to a thickness of 2 μm as a collector electrode by vacuum vapor deposition, thereby manufacturing a photovoltaic element.

A formed solar cell was evaluated by measuring a spectral sensitivity characteristic and a photoelectric conversion efficiency η for irradiation with a solar simulator having an AM value of 1.5 and an energy density of 100 W/cm

2

.

In order to evaluate the distribution in the width direction, the spectral sensitivity characteristic and the photoelectric conversion efficiency were measured at three points of a central portion (C) in the width direction and both ends (F and R) of the belt-like substrate. Evaluation results are shown in Table 9.

TABLE 9

Comparative Example 2

Example 2

Rela-

Rela-

Rela-

Rela-

tive

tive

photo-

tive

photo-

thick-

electric

thick-

electric

ness

Rela-

conver-

ness

Rela-

conver-

of

tive

sion

of

tive

sion

deposited

sensi-

effi-

deposited

sensi-

effi-

Position

film

tivity

ciency

film

tivity

ciency

F

1.00

1.00

1.00

1.00

1.00

1.00

C

0.97

0.98

0.98

0.94

0.94

0.95

R

0.96

0.97

0.99

0.83

0.82

0.81

Ununi-

3.1%

22.1%

formity

Furthermore, a solar cell having a size of 350 mm×240 mm was manufactured and an efficiency of the whole solar cell was evaluated. An evaluation result is shown in Table 10.

TABLE 10

Comparative

Example 2

Example 2

Average photoelectric conversion

10.2%

9.1%

efficiency

(effective area 350 × 240)

As apparent from Table 9 and Table 10, it has been found that the opening adjusting plates suppressed ununiformity of a total deposited film thickness within 5%, thereby suppressing a relative sensitivity and a photoelectric conversion efficiency of a solar cell. Furthermore, the suppression of ununiformity of the photoelectric conversion efficiency makes it possible to enhance a photoelectric conversion efficiency of the whole solar cell.

Comparative Example 2

Opening adjusting plates

901

which had an equal opening length in the width direction shown in

FIG. 9

were used in Comparative Example 2, in contrast to Example 2 in which the opening adjusting plates

702

shown in

FIG. 7

were used. Other film forming conditions were the same as those in Example 2. In Comparative Example 2, a photovoltaic element was manufactured by setting microwave electric power and other film forming conditions as shown in Table 1. In

FIG. 9

, reference numeral

902

denotes an applicator, reference numeral

903

denotes a deposition region and reference numeral

904

denotes a belt-like substrate.

A thickness distribution in a width direction of an obtained deposited film is shown in Table 8. It was found that the thickness distribution of the obtained deposited film was larger than 10%.

Similarly as in Example 2, an nipnipnip type amorphous silicon film was formed on the belt-like substrate. On an n type layer, ITO(In

2

O

3

+SnO

2

) was deposited to a thickness of 70 nm as a transparent electrode by vacuum vapor deposition and Al was further deposited to a thickness of 2 μm as a collector electrode by vacuum vapor deposition, thereby manufacturing a photovoltaic element.

A formed solar cell was evaluated by measuring a spectral sensitivity characteristic and a photoelectric conversion efficiency η for irradiation with a solar simulator having an AM value of 1.5 and an energy density of 100 mW/cm

2

.

Evaluation results are summarized in Table 9. Furthermore, a solar cell having a size of 350 mm×240 mm was manufactured and an efficiency in the width direction of the whole solar cell was evaluated. An evaluation result is shown in Table 10.

When the opening adjusting plates

901

were used, ununiformity of the deposited film thickness was larger than 10%. The ununiformity of the deposited film thickness caused ununiformity of a photoelectric conversion efficiency, thereby resulting in degradation of the solar cell as a whole.

EXAMPLE 3

In Example 3, an i type layer was formed by using two applicators

1001

and introducing microwave electric power as shown in

FIG. 10

, in contrast to Example 1 where the i type layer was formed by using the four applicators and introducing the microwave electric power as shown in FIG.

2

. The i type layer was formed by setting film forming conditions as shown in Table 1. In

FIG. 10

, reference numeral

1002

denotes opening adjusting plates, reference numeral

1003

denotes a deposition region and reference numeral

1004

denotes a belt-like substrate.

A stainless steel substrate (SUS430) was passed through vacuum containers in the sequence described with reference to Example 1, their pressures were lowered to 1.3×10

−4

Pa (1×10

−6

Torr) with an exhaust system (not shown) and discharge was caused, thereby forming an i type amorphous silicon film on the belt-like substrate. A deposited film was formed in an entire range of openings of discharge containers

207

a

and

207

b

without disposing the opening adjusting plates

219

for controlling a deposited film thickness distribution in the discharge containers. After confirming stabilization of a discharge condition, a stationary sample was prepared by stopping conveyance of the substrate.

In order to evaluate a distribution in the width direction, deposition rates were measured at three points in a central portion (C) and both ends (F and R) by five points in a substrate conveying direction, i.e., at 15 points in total as shown in FIG.

3

. Results of deposition rates of the obtained deposited film are shown in Table 11 and FIG.

11

.

TABLE 11

Position (mm)

Position

20

68

117

166

214

F

47.7

68.7

82.7

75.2

53.8

C

48.7

61.2

69.8

64.6

50.1

R

56.3

75.2

85.6

79.0

55.8

As seen from Table 11 and

FIG. 11

, the deposition rates of the obtained deposited film were not constant in the width direction and the conveying direction of the substrate, and a total deposited film thickness was largely distributed when the film was deposited while conveying the belt-like substrate

210

.

On the basis of the measurement of the deposition rate distribution, shapes of the opening adjusting plates were determined.

When a distance of a discharge space in the conveying direction was represented by x, a distance of the discharge space in a direction perpendicular to the conveying direction was designated by y, a deposition rate at an optional point (x, y) was denoted by d(x, y), a deposited film thickness at y

1

=175 (mm), x

P1

≦x

1

≦x

Q1

was represented by δ

1

(x, y

1

), a substrate conveying speed v is 1270 (mm/min), an ideal deposited film thickness δ was 600 (Å),

d

1

(

x, y

1

)=

d

1

(

vt, y

1

)=−0.93

t

2

+10.5

t+

38.9(∵

x=vt

)

\begin{matrix} δ_{n} (vt, y_{n}) = \int_{Pn}^{Qn} d_{n} (vt, y_{n}) ⅆ t = δ & (1) \end{matrix}

points (t, y

1

) satisfying the formula (1) are A

1

(0.43, 175) and B

1

(10.87, 175)

∵(x, y)=A

1

(9, 175), B

1

(231, 175)

When a deposited film thickness at y

2

=35 mm, x

P2

≦x

2

≦x

Q2

in the discharge space is represented by δ (x, y

2

), the following was obtained:

d

2

(x, y

2

)=d

2

(

vt, y

2

)=−1.45

t

2

+16.9

t+

32.1(∵

x=vt

)

\begin{matrix} δ_{2} (vt, y_{2}) = \int_{P2}^{Q2} d_{2} (vt, y_{2}) ⅆ t = δ & {(1)}^{'} \end{matrix}

and points (t, y

2

) satisfying the formula (1)′ are A

2

(0.80, 35) are B

2

(10.5, 35)

∵(x, y)=A

2

(17, 35), B

2

(223, 35)

When a deposited film thickness at y

3

=315 (mm), x

P3

≦x

3

≦x

Q3

in the discharge space is designated by δ(x, y

3

), the following was obtained:

d

3

(

x, y

3

)=

d

3

(

vt, y

3

)=−5.2

t

2

+33

t+

35(∵

x=vt

)

\begin{matrix} δ_{3} (vt, y_{3}) = \int_{P3}^{Q3} d_{3} (vt, y_{3}) ⅆ t = δ & {(1)}^{″} \end{matrix}

points (t, y

3

) satisfying the formula (1)″ are A

3

(1.05, 315) and B

3

(10.25, 315)

∵(x, y)=A

3

(23, 315), B

3

(217, 315)

a quadratic curve passing the points A

1

, A

2

and A

3

: x=F

1

(y)=5.6×10

−4

y

2

−0.17y+22

and a quadratic curve passing the points B

1

, B

2

and B

3

: x=F

2

(y)=−5.6×10

−4

y

2

+0.17y+218

Shapes of the opening adjusting plates were determined from the obtained curves, and an nip type single cell was manufactured while controlling a deposited film thickness distribution on the belt-like substrate

1004

using the opening adjusting plates

1002

which had distributions in a width direction of the deposition region

1003

as shown in FIG.

10

. Steps till gas introduction were carried out similarly as in the experiment 1, the belt-like substrate

1004

was conveyed at a speed of 1270 mm/min, and microwave electric power and RF electric power were applied to discharge containers from the microwave oscillator

220

and the RF oscillator

227

to cause plasma discharge, thereby forming a nip type amorphous silicon film on the belt-like substrate.

On the formed nip type silicon film, ITO (In

2

O

3

+SnO

2

) was deposited to a thickness of 70 nm as a transparent electrode by vacuum vapor deposition and Al was further deposited to a thickness of 2 μm as a collector electrode by vacuum vapor deposition, thereby manufacturing a photovoltaic element. The thickness distribution of an i type layer was evaluated from C-V characteristics of the obtained photovoltaic element. A thickness distribution of a deposited film is shown in Table 12.

TABLE 12

Position

F

C

R

Ununiformity

Example 3

1.00

0.96

0.98

3.1%

Comparative

1.00

0.80

1.00

21 .8%

Example 3

It was found that the obtained deposited film thickness was uniform in the width direction and the ununiformity was suppressed within 10%.

Then, a triple cell was manufactured using the roll to roll type plasma CVD apparatus shown in

FIG. 5

which was capable of forming a nipnipnip type triple cell. Film forming conditions are shown in Table 4.

In place of the stainless steel belt-like substrate (SUS430), a bobbin

503

wound with a stainless steel belt-like substrate (SUS430)

502

on which an aluminum thin film (0.2 μm) and a ZnO thin film (1.2 μm) were formed by the sputtering method as a lower electrode was set in a vacuum container

501

having a substrate feeding mechanism, the belt-like substrate was passed to the belt-like substrate takeup chamber

520

through the gas gates

504

, the n type semiconductor layer vacuum containers

505

,

506

and

507

, the i type semiconductor layer vacuum containers

508

and

509

, the i type semiconductor layer containers

510

and

511

by the microwave plasma method, the i type semiconductor layer vacuum chambers

512

,

513

and

514

by the RF plasma method, the i type semiconductor layer vacuum containers

515

and

516

, and the p type semiconductor layer vacuum containers

517

,

518

and

519

similarly as in the above-described experiment, and a tension was adjusted to a degree at which the belt-like substrate was free from slack. Pressure in each of the vacuum containers was lowered to 1.3×10

−4

Pa (1×10

−6

Torr) with an exhaust system (not shown).

The opening adjusting plates

102

were disposed in the openings of the i type semiconductor layer discharge containers

521

and

522

using the microwave plasma method as shown in

FIG. 1

in order to control a deposited film thickness distribution on the belt-like substrate

502

. A deposition region

103

was limited accordingly.

As a heat treatment at a film forming time, 1000 sccm of H

2

was introduced into each gas gate from the gate gas introducing pipe and the belt-like substrate was heated to 300° C. with the substrate heater.

A raw material gas was introduced into each discharge container from the gas introducing pipe, the belt-like substrate was conveyed at a speed of 1270 mm/min and electric power was applied to each discharge container from the microwave oscillator and the radio frequency oscillator to cause plasma discharge in a film forming region, thereby forming a nipnipnip type amorphous silicon film on the belt-like substrate.

After conveying one roll amount of the belt-like substrate, all plasma, supply of all gases, power supply to all lamp heaters and conveyance of the substrate were stopped. Then, a discharge container leaking nitrogen (N

2

) gas was introduced into the discharge containers to return the containers at atmospheric pressure, and the belt-like substrate was taken from the takeup bobbin.

On the formed nipnipnip type amorphous silicon film, ITO (In

2

O

3

+SnO

2

) was deposited to a thickness of 70 nm as a transparent electrode by vacuum vapor deposition and Al was further deposited as a collector electrode to a thickness of 2 μm by vacuum vapor deposition, thereby manufacturing a photovoltaic element.

The formed solar cell was evaluated by measuring a spectral sensitivity characteristic and a photoelectric conversion efficiency η for irradiation with a solar simulator having an AM value of 1.5 and an energy density of 100 mW/cm

2

. In order to evaluate a distribution in the width direction, the spectral sensitivity characteristic and the photoelectric conversion efficiency were measured at three points of a central portion (C) and both ends (F and R). Measured results are summarized in Table 13.

TABLE 13

Example 3

Comparative Example 3

Relative

Relative

Relative

Relative

thick-

photo-

thickness

photo-

ness of

Relative

electric

of

Relative

electric

Posi-

deposi-

sensi-

conversion

deposited

sensi-

conversion

tion

ted film

tivity

efficiency

film

tivity

efficiency

F

1.00

1.00

1.00

1.00

1.00

1.00

C

0.96

0.96

0.98

0.76

0.81

0.87

R

0.98

0.99

0.99

0.99

0.99

1.01

Ununi-

4.1%

22.1%

formity

Furthermore, a solar cell having a size of 350 mm×240 mm was manufactured and an efficiency of the whole solar cell was evaluated. An evaluation result is shown in Table 14.

TABLE 14

Comparative

Example 3

Example 3

Average photoelectric conversion

10.2%

9.2%

efficiency

(effective area 350 × 240)

As apparent from Table 13 and Table 14, it was found that the opening adjusting plates suppressed ununiformity of the deposited film thickness within 10%, thereby suppressing ununiformities of the relative sensitivity and the photoelectric conversion efficiency. Furthermore, it was found that a photoelectric conversion efficiency of the whole solar cell could be enhanced by suppressing the ununiformity of the photoelectric conversion efficiency.

Comparative Example 3

In Comparative Example 3, opening adjusting plates 1201 which had an equal opening length in the width direction shown in

FIG. 12

were used in contract to the opening adjusting plate

1002

shown in

FIG. 10

which were used in Example 3. Other film forming conditions were the same as those in Example 3. In Comparative Example 3, a photovoltaic element was manufactured using the microwave electric power and other film forming conditions shown in Table 1. In

FIG. 12

, reference numeral

1202

denotes an applicator, reference numeral

1203

denotes a deposition region and reference numeral

1204

denotes a belt-like substrate.

The obtained deposited film had a film thickness distribution in the width direction which is shown in Table 12. It was found that ununiformity of the film thickness distribution of the obtained deposited film was larger than 10%.

Similarly as in Example 3, a nipnipnip type amorphous silicon film was formed on the belt-like substrate. On an n type layer, ITO (In

2

O

3

+SnO

2

) was deposited to a thickness of 70 nm as a transparent electrode by vacuum vapor deposition and Al was further deposited to a thickness of 2 μm as a collector electrode by vacuum vapor deposition, thereby manufacturing a photovoltaic element.

The formed solar cell was evaluated by measuring a spectral sensitivity characteristic and a photoelectric conversion efficiency η for irradiation with a solar simulator having an AM value of 1.5 and an energy density of 100 mW/cm

2

. Evaluation results are shown in Table 13.

Furthermore, a solar cell having a size of 350 mm×240 mm was manufactured for evaluating an efficiency of the whole solar cell in the width direction. A result is shown in Table 14.

Ununiformity of a deposited film thickness was larger than 10% when the above-described opening adjusting plates

1201

were used. The ununiformity of the deposited film caused ununiformity of the photoelectric conversion efficiency, thereby resulting in decrease of the photoelectric conversion efficiency of the whole solar cell.

As described above, the deposited film forming method and the deposited film forming apparatus according to the present invention are configured to dispose the opening adjusting plates in the openings of the discharge containers so as to partially shield the belt-like substrate from the discharge region, thereby making it possible to improve a film thickness distribution of the deposited film in the width direction and make uniform various characteristics of the deposited film. As a result, the deposited film forming method and the deposited film forming apparatus according to the present invention make it possible to provide a photovoltaic element having a large area with high uniformity and excellent characteristics as well as devices which use the photovoltaic element.

Number	Name	Date	Kind
4400409	Izu et al.	Aug 1983	A
4504518	Ovshinsky et al.	Mar 1985	A
4517223	Ovshinsky et al.	May 1985	A
5720826	Hayashi et al.	Feb 1998	A
6025039	Yajima	Feb 2000	A
6096389	Kanai	Aug 2000	A
6350489	Moriyama et al.	Feb 2002	B1

Method and apparatus for forming deposited film

Information

Patent Number

Date Filed

Date Issued

Inventors

Original Assignees

Examiners

Agents

CPC

US Classifications

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US

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Term Extension

Abstract

Description

Claims

Priority Claims (1)

US Referenced Citations (7)