Film forming method

Details Film forming method Film forming method

1999-06-22

2002-01-15

Beck, Shrive (Department: 1762)

Coating processes

Coating by vapor, gas, or smoke

C427S058000, C427S074000, C427S255500, C427S255700, C438S047000, C438S061000, C438S062000, C118S715000, C118S718000

Reexamination Certificate

active

06338872

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a film forming apparatus and method for forming functional deposited films for photovoltaic elements or various kinds of sensors. More particularly, the invention relates to an improved film forming apparatus and method in which the maintenance time for continuous film formation such as a roll-to-roll film formation is shortened to enhance the working efficiency of the apparatus.
2. Related Background Art
A variety of semiconductor devices or electronic devices including photovoltaic elements or various kinds of sensors are provided with one or more functional deposited films on a substrate. In a manufacturing process of such devices, it is desired to form the deposited films as having certain level of characteristics continuously and efficiently to mass produce the products of superior characteristics.
For example, in a photovoltaic element such as a solar cell of the structure in which a plurality of semiconductor layers (i-layer, n-layer, p-layer) are laminated, various examinations for the stable film forming process have been made to enhance its function.
In recent years, a power generation system with a solar battery using the sunlight has drawn attention as a clean power generation system which can cope with increased demands for electric power in the future, without causing environmental destruction, since it does not bring about problems of radioactive pollution or global warming, uses a less maldistributed energy source, and further can accomplish a relatively high efficiency of power generation without needing complex and large installations. Various activities of research and development have been made for practical use of such a battery.
To establish the power generation system using the solar battery as meeting the demands for electric power, it is fundamentally required that the solar battery has a high enough photoelectric conversion efficiency, stable characteristics, and is capable of mass production.
In this respect, a solar battery which can be fabricated, using a source gas such as silane, in a gaseous body, which is easily available, by depositing a semiconductor film of e.g. amorphous silicon (hereinafter abbreviated as “a-Si”) on a relatively inexpensive substrate made of glass or metal, has been noted, such a battery is suited for mass production, with the possibility of lower production costs, as compared with the solar battery fabricated using a single crystal silicon. Various proposals have been made for the constitution of basic layers and the manufacturing methods thereof.
Although a-Si deposited film is formed on a band-like substrate by chemical vapor deposition (CVD) which typically occurs from the gas phase under reduced pressures, or sputtering, a plasma CVD method making use of glow discharge plasma is widely utilized because the characteristics of the deposited film are superior, and can be mass produced.
Recently, a plasma process making use of microwave has been also noted. The microwave, which is short in frequency band, can have a higher energy density than when using RF, and thus is suited for generating and sustaining plasma efficiently.
For example, in U.S. Pat. Nos. 4,517,223 and 4,504,518, a method of depositing a thin film on a substrate of small area within microwave glow discharge plasma under low pressures has been disclosed. With this method, since the film formation can be made via a process under low pressures, high quality deposited films can be produced by preventing polymerization of active species which may cause degraded film characteristics. In forming an Si film, the film forming speed can be remarkably increased, while generation of polymers such as polysilane in plasma is suppressed.
However, in microwave plasma, though much higher film forming speed may be typically expected, microwave applicator means making use of a microwave generator, an isolator, a waveguide, and an arsela ceramics window is needed to introduce microwave into a film forming chamber, resulting in higher costs than the conventional RF methods. Accordingly, for example, in the formation of a-Si film in manufacturing the a-Si solar cell, the microwave is used for fabrication of a photovoltaic layer (i-type a-Si layer) having large film thickness for which high throughput is required, while the RF method is used for making other layers, i.e., n-type a-Si layer and p-type a-Si layer. A so-called hybrid method has thus been proposed.
On the other hand, from the viewpoint of a film formation process, and in consideration of mass production of final devices, a continuous plasma CVD system which adopts a roll-to-roll (Roll to Roll) type substrate which is wound like a roll has been disclosed in U.S. Pat. No. 4,400,409.
With this apparatus, a plurality of glow discharge regions are provided, a flexible substrate having a desired width and a sufficient length is laid along a path extending through the glow discharge regions, through which the substrate is passed successively. A semiconductor layer of the required conduction type is deposited in the glow discharge regions, while the substrate is conveyed continuously in a longitudinal direction, to allow for the continuous formation of elements having semiconductor junctions.
Note that in U.S. Pat. No. 4,400,409, a gas gate was used to prevent dopant gas for use in forming each semiconductor layer from diffusing and mixing into other glow discharge regions. Specifically, the glow discharge regions are separated from one another by a slit-like separation passage, and the separation passage is provided with means for forming the flow of scavenging gas such as Ar or H
2
. In this respect, it can be said that the roll-to-roll type is suitable for mass production of semiconductor devices in which various functional films are laminated.
In addition, a continuous plasma CVD system of roll-to-roll type for forming a large area a-Si deposited film was disclosed in U.S. Pat. No. 4,485,125.
For a plasma process using microwave, a deposited film forming method and apparatus of roll-to-roll type using a microwave plasma CVD system was disclosed, for example, in Japanese Laid-Open Patent Application No. 3-30419.
A typical plasma CVD system of roll-to-roll type will be described below with reference to the drawings.
FIG. 1
is a cross-sectional view showing the constitution of the plasma CVD system of roll-to-roll type, and
FIG. 2
is a cross-sectional view showing the constitution of a vacuum vessel (chamber) and a film forming chamber which are contained in the apparatus. In
FIG. 1
,
500
to
504
are vacuum vessels (chambers),
505
to
507
are film forming chambers,
508
to
510
are discharge electrodes,
511
to
513
are glow discharge spaces,
514
to
516
are rf oscillators,
517
to
519
are substrate heaters,
520
to
522
are gas heaters,
523
to
525
are source gas inlet ports,
526
is a magnet roller,
527
to
530
are gas gates,
531
to
533
are exhaust pumps,
534
to
535
are pressure gauges,
537
to
540
are gate gas inlet ports,
541
is a delivery bobbin,
542
is a winding bobbin, and
543
to
545
are gas gate exhaust ports.
FIG. 2
is a cross-sectional view of the apparatus (one vacuum vessel) as seen from the side. The prismatic vacuum vessels
500
to
504
are arranged on a straight line as viewed from the upper face, or like a catenary as viewed from the lateral side. The substrate for forming the film thereon is a band-like substrate
100
having a desired width and a sufficient length.
Provided inside the vacuum vessels
501
to
503
are film forming chambers
505
to
507
, respectively, in which desired semiconductor layers are formed on the band-like substrate
100
within the glow discharge spaces
511
to
513
which are enclosed by the band-like substrate
100
, the discharge electrodes
508
to
510
, and the film forming chambers
505
to
507
.
In
FIG. 1
, a vacuum vessel
500
at the left end as shown contains the delivery bobbin
541
for the band-like substrate
100
, and a

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