Isolation passageway including annular region

A passageway which includes an annular region, the passageway adapted to isolate the gaseous contents of one of a pair of adjacent, vacuumized environments from the other of the pair while providing for the movement of a substrate therebetween.

FIELD OF THE INVENTION 
This invention relates generally to apparatus adapted to isolate a pair of 
adjacent environments from one another and more particularly to an 
improved isolation passageway operatively interconnecting adjacent 
chambers, at least one chamber of which is adapted to deposit a layer of 
thin film material in such a manner as to substantially eliminate 
contamination of the gaseous atmosphere present in one chamber caused by 
the diffusion of gases from the gaseous atmosphere present in the adjacent 
chamber. 
BACKGROUND OF THE INVENTION 
In its most specific embodiment, this invention relates to apparatus 
specially adapted to produce semiconductor devices on a continuously 
moving substrate by depositing successive layers of thin film 
semiconductor alloy material in each of at least two adjacent 
interconnected deposition chambers. The composition of each layer of said 
thin film material is dependent upon the particular reaction gas 
constituents introduced into each of the deposition chambers. While the 
constituents introduced into the first deposition chamber are carefully 
controlled and isolated from the constituents introduced into the adjacent 
deposition chamber, the apparatus must be constructed so as to provide for 
the continuous passage of said substrate between those chambers. 
Therefore, the deposition chambers are designed to be operatively 
interconnected by a relatively narrow passageway (1) through which the 
substrate may continuously pass and (2) adapted to isolate the reaction 
gas constituents introduced into the first deposition chamber from the 
reaction gas constituents introduced into the adjacent deposition chamber. 
Applicants' assignee has invented and patented "gas gates" such as those 
disclosed in U.S. Pat. Nos. 4,438,724 and 4,450,786, which gas gates were 
operatively designed to prevent dopant gas constituents introduced into a 
first deposition chamber from diffusing into an adjacent second deposition 
chamber, thereby contaminating the layer of intrinsic semiconductor alloy 
material deposited in said second deposition chamber. It is therefore one 
important feature of the present invention to reduce the size of the 
isolation passageway of prior art gas gates so as to correspondingly 
reduce the diffusion of dopant gas constituents present in the dopant 
gaseous environment from contaminating the intrinsic gas constituents 
present in the intrinsic gaseous environment. 
Another and equally important feature of this disclosure will become 
apparent from the description presented in the following paragraphs. It is 
to be noted that the assignee of the subject invention is recognized as 
the world leader in photovoltaic technology. Photovoltaic devices produced 
by said assignee have set world records for photoconversion efficiency and 
long term stablility under operating conditions (the efficiency and 
stability considerations will be discussed in greater detail hereinbelow). 
Additionally, said assignee has developed commercial processes for the 
continuous roll-to-roll manufacture of large area photovoltaic devices. 
Such continuous processing systems are disclosed in the following U.S. 
patents, disclosures of which are incorporated herein by reference: No. 
4,400,409, for A Method Of Making P-Doped Silicon Films And Devices Made 
Therefrom; No. 4,410,588, for Continuous Amorphous Solar Cell Production 
Systems; and No. 4,438,723, for Multiple Chamber Deposition and Isolation 
System And Method. As disclosed in these patents, a web of substrate 
material may be continuously advanced through a succession of operatively 
interconnected, environmentally protected deposition chambers, wherein 
each chamber is dedicated to the deposition of a specific layer of 
semiconductor alloy material onto the web or onto a previously deposited 
layer. In making a photovoltaic device, for instance, of n-i-p type 
configurations, the first chamber is dedicated to the deposition of a 
layer of an n-type semiconductor alloy material, the second chamber is 
dedicated to the deposition of a layer of substantially intrinsic 
amorphous semiconductor alloy material, and the third chamber is dedicated 
to the deposition of a layer of a p-type semiconductor alloy material. The 
layers of semiconductor alloy material thus deposited in the vacuum 
envelope of the deposition apparatus may be utilized to form 
photoresponsive devices, such as, but not limited to, photovoltaic devices 
which include one or more cascaded n-i-p type cells. By making multiple 
passes through the succession of deposition chambers, or by providing an 
additional array of deposition chambers, multiple stacked cells of various 
configurations may be obtained. Note, that as used herein the term "n-i-p 
type" will refer to any sequence of n and p or n, i and p layers of 
semiconductor alloy material operatively disposed and successively 
deposited to form a photoactive region wherein charge carriers are 
generated by the absorbtion of photons from incident radiation. 
The concept of utlizing multiple stacked cells, to enhance photovoltaic 
device efficiency, was described at least as early as 1955 by E. D. 
Jackson in U.S. Pat. No. 2,949,498 issued Aug. 16, 1960. The multiple cell 
structures therein discussed were limited to the utilization of p-n 
junctions formed by single crystalline semiconductor devices. Essentially 
the concept espoused by Jackson was to employ different band gap devices 
to more efficiently collect various portions of the solar spectrum and to 
increase open circuit voltage (Voc). The tandem cell device (by 
definition) has two or more cells with the light directed serially through 
each cell. In the first cell, a large band gap material absorbs only the 
short wavelength light, while in subsequent cells, smaller band gap 
materials absorb the longer wavelengths of light which pass through the 
first cell. By substantially matching the generated currents from each 
cell, the overall open circuit voltage is the sum of the open circuit 
voltage of each cell, while the short circuit current thereof remains 
substantially constant. Such tandem cell structures can be economically 
fabricated in large areas by employing thin film semiconductor alloy 
materials (with or without crystalline inclusions), in accordance with the 
principles of the instant invention. It should be noted that Jackson 
employed crystalline semiconductor materials for the fabrication of his 
stacked cell structure; however, since it is virtually impossible to match 
lattice contents of differing crystalline materials, it is not possible to 
fabricate such crystalline tandem cell structures in a commercially 
feasible manner. In contrast thereto, and as the assignee of the instant 
invention has shown, such tandem cell structures are not only possible, 
but can be economically fabricated over large areas by employing the thin 
film semiconductor alloy materials and the deposition techniques discussed 
and briefly described herein. 
More particularly, the assignee of the instant invention is presently able 
to manufacture stacked large area photovoltaic devices on a commercial 
basis by utilizing the previously referenced, continuous deposition, 
roll-to-roll processor. That processor is characterized by the assignee as 
a 1.5 megawatt capacity machine insofar as its annual output of 
photovoltaic devices is capable of producing 1.5 megawatts of electrical 
power. Said 1.5 megawatt processor, as presently configured, is adapted to 
produce tandem photovoltaic cells which comprise two stacked n-i-p type 
photovoltaic devices disposed optically and electrically in series upon a 
stainless steel web of substrate material. The processor currently 
includes six operatively interconnected, dedicated deposition chambers, 
each deposition chamber adapted to sequentially deposit one of the layers 
of semiconductor alloy material from which the tandem device is 
fabricated. The deposition chambers vary in length depending upon the 
thickness of the particular layer of semiconductor alloy material to be 
deposited therein. 
In order to better understand the manner in which the length of the 
processor is determined, note that the thicknesses of individual layers of 
semiconductor alloy material vary from approximately 100 angstroms for the 
doped layers to approximately 3500 angstroms for the lowermost intrinsic 
layer. Since the processor operates by developing an r.f. plasma which is 
adapted to decompose the process gases and deposit a layer of 
semiconductor alloy material and since the thickness of the deposited 
layer is directly dependent upon the residence time of the web of 
substrate material in the deposition chamber, the approximately 3500 
angstrom thick layer of intrinsic semiconductor alloy material requires a 
deposition chamber of over six feet in length in order to provide an 
annual output of 1.5 megawatts of electrical power. The 1.5 megawatt 
processor also includes additional chambers for (1) the payoff and takeup 
of the web of substrate material, (2) the cleaning of the web of substrate 
material and (3) preventing interdiffusion of the gaseous constituents of 
the adjacent deposition environments, said interdiffusion prevention 
preferably occurring in the form of discrete isolation passageway chambers 
(such as external gas gates). With the addition of all of these chambers, 
the total length of the 1.5 megawatt processor comes to approximately 40 
feet. Accordingly, it must be appreciated that, while this 1.5 megawatt 
processor is the first apparatus capable of commercially fabricating 
photovoltaic devices; it is a complex, elongated piece of machinery. 
The assignee of the instant invention is now designing and constructing a 
new and improved semiconductor processing machine for the production of 
significantly higher annual quantities of photovoltaic energy, i.e., about 
25 megawatts of electrical power. It must be noted that in order to 
produce an annual output of 25 megawatts, the length of the machine must 
be increased so that the length of this 25 megawatt processor will be at 
least an order of magnitude longer than the present 1.5 megawatt machine. 
Since not all of the reasons for this increased length are readily 
apparent, they will be enumerated in the following paragraphs. 
A first reason for the elongation is that the new processor will be 
configured to fabricate tandem photovoltaic devices which comprise at 
least 3 and possibly 4 stacked cells; therefore the processor will require 
9 to 12 dedicated deposition chambers instead of the six dedicated 
deposition chambers required by the present processor. Another factor in 
determining the length of the processor, mentioned previously, is that the 
length of each of the individual deposition chambers is dependent upon the 
thickness of each of the layers of semiconductor alloy material to be 
deposited therein. The thickness of that material is, in turn, dependent 
upon, the rate of deposition of particular mixtures of precursor process 
gases and the speed of the web of substrate material passing through that 
chamber of the processor. Consequently, if the rate of deposition of the 
precursor gas mixture remains constant (and Applicants' assignee finds 
that significantly increasing the rate of deposition of semiconductor 
alloy material tends to deleteriously affect the photovoltaic conversion 
properties of that material), the web speed will also have to be kept 
constant and the deposition chambers in the 25 megawatt processor will 
have to be over sixteen times longer than in the 1.5 megawatt processor in 
order to deposit a sufficient quantity of semiconductor alloy material for 
fabricating photovoltaic devices which would provide an annual output of 
25 megawatts of electrical power. 
Even assuming that the presently employed one foot wide web of substrate 
material was to be increased in size to a two foot width, a scaled-up 
version of the present processor which is designed to have a 25 megawatt 
capacity would still total approximately 400 feet in length. Even more 
significantly, note that in a deposition apparatus of this size, the 
cathode utilized for the deposition of the thickest layer of semiconductor 
alloy material, i.e., the bottommost intrinsic layer of semiconductor 
alloy material of the tandem photovoltaic device, would have to be 
approximately 60 feet in length. 
Clearly, a 400 foot long processor which requires the incorporation of a 60 
foot long cathode presents many problems. The physical space required to 
house a machine approximately the length of 11/2 football fields presents 
problems in plant design, location and cost. Additionally, the mechanical 
design and operation of such a large, complex machine creates engineering 
problems related to the maintenance of the required optical, electrical 
and structural characteristics of the deposited semiconductor alloy 
material. The length and weight of the 400 foot span of the web of 
substrate material, which continuously moves through the deposition 
apparatus, makes web handling and steering difficult, which, in turn, 
provides for numerous problems in maintaining substrate tracking, 
alignment and support. Likewise, maintenance of preselected vacuum 
conditions and deposition parameters within the 400 foot long vacuum 
envelope which the web of substrate material must traverse is, at best, 
quite difficult. Similarly, physical maintenance, i.e., disassembly, 
cleaning, etc. of the deposition apparatus becomes a nightmare. 
Even more importantly (because it directly relates to the deposition of 
uniform, high quality semiconductor alloy material), the large areas 
covered by some of the deposition cathodes in such a scaled-up 25 megawatt 
processor creates problems of plasma uniformity and gas utilization within 
the cathode and deposition regions. Of the foregoing, plasma uniformity 
poses the most significant problem. Due to the large area plasma regions 
created by such large area cathodes, nonuniformities in the ionized 
precursor process gas mixtures are likely to arise. More specifically, 
varying compositions of the activated process gas mixture along the length 
of a large area cathode will give rise to irregular and nonhomogeneous 
plasma sub-regions, which irregularities and nonhomogeneties will result 
in the deposition of nonuniform, nonhomogeneous layers of semiconductor 
alloy material. 
It should be abundantly clear from the foregoing discussion that, as the 
1.5 megawatt continuous photovoltaic device production machine is scaled 
up to higher throughput capacities, it becomes an economic necessity to 
substantially reduce the overall length thereof. Such improvements would 
result in a substantial savings of deposition time, floor space, the cost 
of building the machine and the operating cost for the production of 
photovoltaic devices therein. 
The Assignee of the instant application has previously disclosed the 
concept of utilizing a non-horizontally disposed cathode plate in order to 
simultaneously deposit semiconductor alloy material in discrete plasma 
regions developed adjacent both of the opposed faces of that cathode 
plate. This concept is described in U.S. Pat. No. 4,423,701 filed Mar. 29, 
1982 entitled "Glow Discharge Deposition Apparatus Including A 
Non-Horizontally Disposed Cathode", which patent is assigned to the 
assignee of the instant invention. Prior to the disclosure of said patent, 
only one-half (one face) of the potential surface area (two faces) of an 
r.f. powered cathode plate was utilized from which to develop a plasma, 
thereby limiting to one the number of substrates on which layers of thin 
film semiconductor alloy material could be simultaneously deposited. The 
vertical orientation of the cathode plate, as described in said patent 
provided the further advantage that deposition debris which is generated 
during the decomposition of the precursor gaseous mixture could not as 
readily come to rest on the vertically disposed surface of the substrate. 
Therefore, a continuous processor, utilizing such a generally vertically 
disposed cathode plate arrangement, would require less down time for 
dismantling, cleaning and reassembling. Finally, said above-referenced 
patent recognized the possibility of utilizing two webs of substrate 
material for the simultaneous and continuous deposition onto each of the 
webs of successive layers of semiconductor alloy material as said webs 
moved through the discrete plasma regions, developed on both faces of the 
cathode plates in each of the deposition chamber (in a generally linear 
path of travel). 
However, while the deposition apparatus generally disclosed in U.S. Pat. 
No. 4,423,701 described a process of and apparatus for developing a plasma 
region adjacent each of the opposed faces of a generally vertically 
disposed cathode plate in order to continuously and simulataneously 
deposit layers of semiconductor alloy material onto each of two webs of 
substrate material as those webs passed through a plurality of 
interconnected deposition chambers, that process still failed to solve the 
problem of reducing the length of the continuous processor so as to 
provide a commercially viable deposition process capable of depositing 
successive layers of semiconductor alloy material for fabricating triple 
or four (quad) cell tandem photovoltaic devices and having an annual 
capacity of up to 25 megawatts of electrical power. 
Finally, Applicants' assignee, in U.S. Pat. No. 4,601,260 entitled 
"Vertical Semiconductor Processor", was able to substantially reduce the 
length of such a 25 megawatt semiconductor processing apparatus by 
vertically orienting the path of travel of the web of substrate material 
through the deposition chambers thereof. More particularly, that 
application is directed to apparatus for the continuous vapor deposition 
of successive layers of semiconductor alloy material. The apparatus 
includes a plurality of discrete chambers, each chamber of which is 
dedicated to the deposition of a layer of semiconductor alloy material of 
a preselected conductivity type. Pumps are provided for vacuumizing each 
of the chambers and a web of substrate material is continuously advanced 
through each of those chambers for the glow discharge deposition of 
semiconductor alloy material thereonto. The glow discharge structure 
includes (1) a conduit for introducing a precursor mixture of process 
gases, (2) a conduit for exhausting nondeposited gases of the precursor 
mixture and (3) a means for decomposing the precursor mixture in a plasma 
region. As in the earlier generations of continuous processing machines 
referred to hereinabove, an isolation chamber is operatively disposed 
between each of the adjacent discrete deposition chambers for isolating 
the gaseous environments of adjacent chambers from one another while 
providing for the passage of the web of substrate material therebetween. 
The improvement in the apparatus resides in direction of the substrate 
material through at least one of the deposition chambers in a non-linear 
path of travel and the operative disposition of the decomposing means so 
as to develop a plurality of plasma regions in those chambers through 
which the substrate material is non-linearly directed. In the preferred 
embodiment, at least two of the plurality of plasma regions are disposed 
in different non-linear portions of the path of travel through which the 
substrate material is advanced so that the total length of the deposition 
apparatus may be substantially foreshortened. In other words, while the 
web of substrate material must still traverse about 400 feet of real 
estate in order to have the requisite thickness of semiconductor alloy 
material deposited thereupon a high percentage of that real estate is 
traversed in the vertical direction and the aforementioned problems 
regarding machine length are significantly ameliorated. 
In the previously mentioned patent applications, wherein the semiconductor 
deposition systems are primarily concerned with the production of 
photovoltaic cells, isolation between the deposition chambers is 
accomplished either by employing gas gates which pass or "sweep" an inert 
gas, such as argon or hydrogen, about the substrate as it passes 
therethrough; by gas gates which establish unidirectional flow of the 
reaction gas mixture introduced into the intrinsic deposition chamber into 
the dopant deposition chambers; or by magnetic gas gates which result in a 
reduced passageway opening between adjacent deposition chambers, said 
magnetic gates adapted to attract the metallic substrate material moving 
therethrough so as to reduce the size of the passageway opening and 
thereby effect a correspondingly decreased amount of "contaminants" 
diffusing from the dopant deposition chambers into the adjacently disposed 
intrinsic deposition chamber. It should be noted that any of these gas 
gates could also be operably connected between non-deposition chambers, 
as, for example, a chamber in which the transparent conductive oxide layer 
(discussed hereinafter) is added atop the uppermost layer of semiconductor 
alloy material. Since it is clearly undesirable to have gaseous 
constituents from the transparent conductive oxide chamber (or from any 
chamber in which non-semiconductor gaseous precursors are present) diffuse 
into the semiconductor deposition chambers, such prior art gas gates were 
also employed between the transparent conductive oxide chamber and the 
final chamber in which layers of doped semiconductor alloy material were 
deposited. In a like manner, any of these types of gas gates could be 
employed between each and every chamber which is operatively 
interconnected for continuously producing thin film photovoltaic devices. 
While the aforementioned magnetic gas gates proved effective in limiting 
contamination (relative to similarly constructed but non-magnetic gas 
gates) by providing for a passageway opening of reduced size through which 
contaminants could diffuse, the temperature gradients to which the web of 
substrate material is continually subjected (since deposition parameters 
require an elevated temperature of approximately 175.degree.-275.degree. 
C.) tend to warp the web to such a degree that the magnets (which are 
spacedly positioned throughout the length of the gas gate) are unable to 
fully flatten the web into a completely planar configuration. Since the 
web can not be held in a planar configuration, the size of the passageway 
opening must be designed to provide for sufficient tolerance to prevent 
contact of a wall of that opening with the deposition surface of the web. 
The added tolerance means the passageway opening allows for a 
correspondingly greater degree of diffusion between adjacent chambers than 
would be necessary if the web could be made to assume a substantially 
planar configuration while passing therethrough. Further the greater the 
degree of diffusion a passageway permits, the greater the length of the 
passageway must be in order to prevent the diffusing gaseous contaminants 
from one deposition chamber from reaching and entering the adjacent 
deposition chamber. Therefore, the added tolerance necessitated by the 
non-planar configuration of the web results in a longer gas gate 
passageway than would otherwise be necessary and a longer passageway 
results in a lengthier semiconductor processing apparatus. 
It is therefore yet another object of the present invention to provide an 
isolation passageway which is adapted to maintain the web of substrate 
material passing therethrough in a substantially planar attitude (relative 
to the wall of the passageway opening against which it is urged) for 
decreasing the size of the passageway opening and thereby allowing for a 
decrease in the length of the passageway due to a decrease in the 
percentage of contaminants which are permitted entry into that passageway 
opening. 
While previously described patent application Ser. No. 718,571 dealt with 
the problem of foreshortening the overall length of a semiconductor 
deposition apparatus while simultaneously increasing the annual electrical 
output of photovoltaic cells produced therein, no attention was paid to 
the existing length of the external isolation passageways deployed between 
every chamber which was adapted to deposit one of the successive layers of 
semiconductor alloy material. This oversight becomes important when 
realizing the fact that, and as pointed out hereinabove, the number of 
discrete layers of semiconductor alloy material which must be deposited in 
said next generation processor will be increased from six in the present 
tandem (two cell) configuration to nine in a triple (3 cell) configuration 
or twelve in a quadruple (4 cell) configuration. For the incorporation of 
each additional layer of semiconductor alloy material, an additional 
isolation passageway will also have to be incorporated in order to achieve 
the requisite degree of isolation between adjacent deposition chambers. 
Accordingly, it can now be appreciated that a reduction in the length of 
the isolation passageways would result in a further and appreciable 
reduction in the total length of the processor. It is therefore another 
object of the present invention to design an isolation passageway which is 
foreshortened over the length of previous gas gates so as to achieve a 
further reduction in the total length of photovoltaic processors which are 
designed to deposit successive layers of semiconductor alloy material. 
One further aspect (of providing isolation through the use of sweep gases) 
must be touched upon in order to fully appreciate the technology involved. 
This aspect deals with the degree of isolation which is necessary in order 
to fabricate a highly efficient photovoltaic device. More particularly, it 
must be realized just how seriously and deleteriously "contaminants" can 
affect the efficiency of the semiconductor device produced in the vacuum 
envelope of the semiconductor processor. For instance, if a gas gate 
passageway is dimensioned to be approximately 0.4 inches high, 16 inches 
wide and 6 inches long with the pressure in a first chamber being 0.6 torr 
and the pressure in an adjacent second chamber being 0.57 torr, a flow 
rate of 500 SCCM of the precursor gaseous constituents passing through the 
gas gate passageway interconnecting those chambers will result in the 
presence of sufficient gaseous precursor constituents to sustain the 
plasma in the deposition chambers as well as to provide a concentration 
ratio of the dopant species from the first deposition chamber to the 
intrinsic species present in the adjacent second deposition chamber of 
about 10.sup.4. This ratio represents a concentration approximately 
sufficient to produce an intrinsic thin film semiconductor alloy material 
in the second deposition chamber of high purity. It must be understood 
that the flow rates, slot dimensions, and chamber pressure stated 
hereinabove represent but one example of parameters which are sufficient 
for the practice of the present invention. Other flow rates, slot 
dimensions and chamber pressures may also be utilized for providing 
effective isolation of the intrinsic semiconductor alloy material 
deposited in one of the chambers from the dopant semiconductor alloy 
material deposited in the adjacent deposition chamber. 
It is further to be noted that Applicants' gas gates, discussed 
hereinabove, are effective in maintaining at least a 10.sup.4 
concentration ratio of the element absent in the intrinsic deposition 
chamber relative to the element present in the dopant deposition chamber 
by establishing a substantially viscous flow of gases through the gas gate 
slot. It must be noted that gases moving within the deposition system of 
the subject application, which system is maintained at a pressure of 
approximately 5.times.10.sup.-1 torr and above, are in the viscous flow 
regime, whereas gases moving through a deposition system which is 
maintained at a pressure of approximately 5.times.10.sup.-2 to 
5.times.10.sup.-3 torr are in a transition flow regime known as the 
Knudsen flow regime, and gases moving through a deposition system which is 
maintained at a pressure of approximately 5.times.10.sup.-3 torr and below 
are in the molecular flow regime. 
In a molecular flow regime, a flow of gases in a first direction cannot 
limit the back diffusion of gases. This is because, at the pressure which 
gives rise to molecular flow, the molecules of the oppositely directed 
process and sweep gases are so widely separated that relatively few 
diffusion limiting collisions can occur therebetween. Applicants' glow 
discharge deposition system, since it operates at approximately 0.5 torr, 
clearly operates in the viscous flow regime. It is in this viscous flow 
regime that, the molecules of oppositely directed process and sweep gases 
realize a sufficient number of intermolecular collisions so as to 
effectively limit back diffusion from one of the pair of chambers to the 
adjacent chamber. 
It should thus be realized that Applicants' improved isolation passageway, 
as described hereinafter, while particularly adapted for use in systems 
operating at below atmospheric pressures, it is effective only in pressure 
regimes which give rise to the viscous flow of gases. It is therefore only 
in these viscous pressure regimes that the isolation passageway of the 
subject invention is operable to limit contamination in the aforedescribed 
10.sup.4 contamination level. 
While the magnetic gas gates disclosed apparatus (namely ceramic magnets 
positioned above the gas gate passageway opening for urging the magnetic 
substrate upwardly) by which the height dimension of the passageway 
opening in the gas gate could be reduced (the reduction in the height 
dimension of the passageway opening correspondingly reducing the diffusion 
of dopant gases for a given flow rate, thereby decreasing the 
contamination of the process gases introduced into and, consequently, the 
layer of semiconductor alloy material deposited in the intrinsic 
deposition chamber), Applicant's assignee has reported in U.S. Pat. No. 
4,450,786 entitled "Grooved Gas Gate", the disclosure of which is 
incorporated by reference, that when the web of substrate material is 
urged by the magnets against the upper wall of the gas gate passageway, 
the passageway is divided by the web of substrate material into a 
relatively wide lower slit and a realtively narrow upper slit. For 
purposes of the instant application the term "upper slit" shall be defined 
as the spacing, however irregular it may be, between the upper surface of 
the substrate and the upper wall of the gas gate passageway. Irregular 
spacing between the web and the upper passageway wall may be present 
because waffling of the web of substrate material cannot be completely 
liminated by the attractive force of the magnets. The process gases, being 
inherently viscous, are unable to travel through the narrow upper slit 
with sufficient velocity to prevent the diffusion of process gases from 
the dopant deposition chamber into the adjacent intrinsic deposition 
chamber. 
More particularly, note that gas may be introduced into the passageway 
opening to "sweep" diffusing contaminants back into the dopant deposition 
chambers. In order to effect this "sweep", it is required that the 
velocity of the inert sweep gases and residual process gases traveling 
through the passageway opening be selected to be sufficiently great to 
substantially prevent the back diffusion of process gases from the dopant 
deposition chamber to the intrinsic chamber. However, and as detailed in 
said '786 patent, due to the fact that the sweep gases employed in the gas 
gates are viscous, which viscosity becomes more pronounced at the elevated 
temperatures required for the glow discharge deposition of thin film 
layers of semiconductor alloy material onto the substrate, the drag on the 
sweep gases along (1) the upper passageway wall and (2) the unlayered 
surface of the substrate, which define the relatively narrow upper slit, 
results in a relatively low velocity flow therethrough. Accordingly, an 
undesirably high amount of dopant process gas is able to diffuse into the 
intrinsic deposition chamber through that narrow upper slit. 
The velocity profile of the sweep gases flowing from the intrinsic 
deposition chamber to the dopant deposition chamber through the relatively 
wide lower passageway slit may be depicted by a generally parabolically 
shaped curve in which the velocity of the sweep gases is greatest at the 
center of the slit and at a minimum along the walls thereof. The velocity 
profile of the sweep gases flowing from the intrinsic deposition chamber 
to the dopant deposition chamber through the relatively narrow upper 
passageway slit may also be depicted by a generally parabolically shaped 
curve, similar to the curve for the wide passageway slit. However, a 
comparison of the two velocity profiles reveals that the velocity of the 
sweep gases flowing through the lower, relatively large passageway slit is 
far greater than the velocity of the sweep gases flowing through the 
upper, relatively narrow passageway slit. Further, since the height 
dimension of the narrow upper slit is permitted to vary with the random 
warping and canoeing of the relatively thin substrate material, the degree 
of contamination due to back diffusion of dopant process gases is able to 
correspondingly fluctuate. 
At this point, and in order to better understand the relationship of the 
counter flow of sweep gas to the diffusion of process gas between adjacent 
deposition environments, it is necessary to discuss the pressure 
differential which is developed between the adjacent deposition chambers 
operatively connected by a gas gate. If one was to plot the number of 
atoms of a gas per second flowing through the narrow passageway opening as 
a function of the size of that opening (assuming a constant pressure 
differential is maintained on both ends of the opening) it would be 
apparent that as the size of the passageway opening is increased, the 
volume of gases flowing therethrough in order to maintain the constant 
pressure differential must correspondingly increase. This represents a 
desirable gas gate characteristic because the greater the velocity of 
sweep gas flowing from the intrinsic deposition chamber to the dopant 
deposition chamber, the more difficult it becomes for dopant gases to 
diffuse against the counter and prevailing flow from the dopant deposition 
chamber to the intrinsic chamber. The functional dependency of back 
diffusion, relative to the size of the gas gate passageway opening is 
represented by the equation (a) (e.sup.-a2 ) where "a" represents the 
passageway opening. That functional dependency, as evidenced by the amount 
of back diffusion, reaches a maximum when "a" is about 200 microns or 
about 10 mils. It is therefore essential that both, the size of the slit 
above, as well as below, the web of substrate material be kept at or above 
the 200 micron level at which gas flow is maximized. Through the 
application of the principles of the subject invention, there is no 
problem in creating a sufficiently large opening below the web of 
substrate material since the substrate material is urged under tension 
against the upper cylindrically-shaped wall of the passageway opening. 
However, it is further necessary to prevent the back diffusion of dopant 
gases through the narrow opening above the web of substrate material (in 
those instances in which tension on the web is relaxed and dopant gases 
"seep" into the narrow upper slot) by providing a plurality of 
circumferential grooves about the surface of the cylindrical drum of the 
isolation passageway. In this manner, a plurality of spaced, relatively 
high velocity flow channels are provided in the space defined between the 
unlayered surface of the web of substrate material and the upper 
cylindrical wall of the passageway opening. Because the channels are 
relatively deep, the sweep gases and residual process gases are adapted to 
flow therethrough at substantial velocities despite the drag incurred as 
said gases contact the oppositely disposed passageway wall and the 
substrate surface. Although relatively narrow slits still exist between 
adjacent high velocity flow channels established by the elongated grooves, 
it is much more probable for molecules of dopant process gases to enter 
the high velocity channels during their traverse of the passageway opening 
separating the dopant deposition chamber from the intrinsic deposition 
chamber, than to have those molecules remain in the narrow slit between 
the high velocity flow channels for the entire length of that migration. 
In order to further insure that back diffusion is prevented, additional 
sweep gas may be introduced into each of the high velocity flow channels 
at a point intermediate the length of the gas gate passageway opening. 
Because of the velocity which the sweep gas can attain in each of the 
"roomy" flow channels and because of intermolecular collisions which occur 
between the dopant gases and the sweep gas in the viscous flow regime 
present in the isolation passageway, the amount of back diffusion from the 
dopant deposition chamber to the intrinsic deposition chamber is 
substantially reduced and the production of a more efficient photovoltaic 
device may be accomplished. 
These and the many other objects and advantages of the present invention 
will become clear from the drawings, the detailed description of the 
invention and the claims which follow hereinafter. 
BRIEF SUMMARY OF THE INVENTION 
There is disclosed herein an isolation passageway for substantially 
preventing the diffusion of gases from one of a pair of adjacent 
vacuumized environments into the other of said pair of vacuumized 
environments. The first environment differs from the second by the 
presence of at least one elemental contaminant. The improved isolation 
passageway is (1) defined by closely spaced walls, (2) adapted to provide 
for the movement of a substrate therethrough, (3) substantially annular in 
a central cross-sectional region and rectangular in the two regions 
adjacent thereto, said cross-section taken in a plane extending in the 
direction of the path of the substrate and (4) adapted to maintain at 
least a 10.sup.4 ratio of the concentration of the at least one element in 
said first environment as compared to the concentration in said second 
environment. By further urging one surface of the substrate traveling 
through the passageway into contact with one of the passageway walls, an 
isolation passageway of reduced height and length dimensions is provided 
which is adapted to both decrease the diffusion of gases between said 
chambers and decrease the length of the passageway so as to 
correspondingly decrease the length of the deposition machine in which 
said passageway is incorporated. 
The passageway wall which contacts the unlayered surface of the substrate 
is fabricated from a low friction, low thermal conductivity material such 
as borosilicate glass. The substrate may be formed from a magnetically 
attractable material and the substrate may be urged into contact with the 
glass through magnetic attraction. In a preferred embodiment, each of the 
adjacent environments are developed and maintained in a dedicated chamber, 
each chamber adapted to deposit thin film layers of semiconductor alloy 
material. The chambers are vacuumized to a pressure of about 0.25 to 1 
torr. In the most preferred embodiment, the nonlayered surface of the 
substrate is urged into contact with the passageway wall through the use 
of roller means which place said nonlayered substrate surface under 
tension against a passageway wall. 
Also in the most preferred embodiment, (1) the passageway is annular in a 
central cross-sectional region, one boundary of the annular 
cross-sectional configuration of the passageway formed by a cylindrical 
drum, the cross-section taken in a plane extending in the direction of the 
path of the substrate, and (2) the substrate is an elongated web and the 
nonlayered surface of the web is urged against the circumferential surface 
of the drum. A plurality of circumferential grooves are spacedly 
positioned across the entire longitudinal extent of the cylindrical drum 
for accepting and guiding sweep gas into a first series of flow channels 
formed between the grooves and the substrate web. The grooves are adapted 
to sustain a flow of sweep gas at a velocity sufficient to substantially 
prevent the diffusion of process gas from the first to the second chamber 
through said first channels. 
Sweep gas is also introduced into a second flow channel formed between the 
substrate web and the surface of the passageway opposite the surface 
against which said web is urged. The flow of sweep gas through the 
passageway in the second channel is at a velocity sufficient to 
substantially prevent the diffusion of process gas from the first to the 
second chamber. The passageway may further include structure for 
subjecting the surface of the substrate not urged into contact with the 
passageway wall to a plasma as said substrate moves through said 
passageway. The plasma is preferably a hydrogen plasma which is useful in 
capping the surface of the previously deposited layer of semiconductor 
alloy material. The first environment is preferably a first chamber 
adapted for the deposition of a first layer of semiconductor alloy 
material and the second environment is a second chamber adapted for the 
deposition of a second layer of semiconductor alloy material differing in 
conductivity type from the conductivity type of the first layer. Both the 
semiconductor alloy material and the hydrogen plasma may be accomplished 
by either r.f. or microwave energy systems.

DETAILED DESCRIPTION OF THE DRAW-NGS 
I. The Photovoltaic Cell 
Referring now to the drawings and particularly to FIG. 1, a photovoltaic 
cell, formed of a plurality of successive n-i-p layers, each of which is 
formed from, preferably, a thin film semiconductor alloy material as shown 
generally by the reference numeral 10. 
More particularly, FIG. 1 shows a p-i-n type photovoltaic device such as a 
solar cell made up of individual p-i-n type cells 12a, 12b and 12c. Below 
the lowermost cell 12a is a substrate 11 which may be transparent or 
formed from a metallic material such as stainless steel, aluminum, 
tantalum, molybdenum, chrome, or metallic particles embedded within an 
insulator. Although certain applications may require a thin oxide layer 
and/or a series of base contacts prior to the application of the amorphous 
material, for purposes of this application, the term "substrate" shall 
include not only a flexible film, but also any elements added thereto by 
preliminary processing. Also included within the scope of the present 
invention are substrates formed of synthetic polymers, glass or a 
glass-like material on which an electrically conductive electrode is 
applied. 
Each of the cells 12a, 12b and 12c are preferably fabricated with a thin 
film semiconductor body containing at least a silicon alloy. Each of the 
semiconductor bodies includes a p-type conductivity semiconductor layer 
20a, 20b and 20c; a substantially intrinsic semiconductor layer 18a, 18b 
and 18c and an n-type conductivity semiconductor layer 16a, 16b and 16c. 
Note that the intrinsic layer may include traces of n-type or p-type 
dopant material without forfeiting its characteristic neutrality, hence it 
may be referred to herein as a "substantially intrinsic layer". As 
illustrated, cell 12b is an intermediate cell and, as indicated in FIG. 1, 
additional intermediate cells may be stacked atop the illustrated cells 
without departing from the spirit or scope of the present invention. Also, 
although n-i-p photovoltaic cells are illustrated, the methods and 
materials described herein may also be and are preferably utilized to 
produce single or multiple p-i-n cells, accordingly, the term "n-i-p type" 
as used herein is meant to include any aggregation of n, i and p layers 
operatively disposed to provide a photoactive region for generating charge 
carriers in response to the absorption of photon energy. Additionally, the 
disclosed deposition apparatus may be readily adapted to produce p-n 
cells, Schottky barrier cells, as well as other semiconductor or devices 
such as diodes, memory arrays, photoconductive devices and the like. 
It is to be understood that following the deposition of the semiconductor 
alloy layers, a further deposition process may be either performed in a 
separate environment or as a part of a continuous process. In this step, a 
TCO (transparent conductive oxide) layer 22, preferably formed of indium 
tin oxide, is added. An electrode grid 24 may be added to the device where 
the cell is of a sufficiently large area, or if the conductivity of the 
TCO layer 22 is insufficient. The grid 24 is adapted to shorten the 
carrier path and increase the conductive efficiency. 
II. The Multiple Chamber Apparatus 
Turning now to FIG. 2, a generally diagrammatic representation of the 
multi-chambered glow discharge deposition processor for the continuous 
production of tandem or cascade-type photovoltaic cells is illustrated 
generally by the reference numeral 26. Due to the elongated nature of the 
processor 26 (the illustrated processor has a 25 megawatt capacity and is 
about 140 feet in length), it has been necessary to cut away and continue 
the longitudinal extent thereof in a plurality of rows across the sheets 
of drawings. However, and as should be readily apparent, in actual 
construction and operation, the processor 26 is preferably aligned so that 
each of the deposition chambers thereof is arranged in a generally linear 
arrangement. The processor 26 includes a plurality of isolated and 
dedicated deposition chambers. The term "dedicated" as used herein, will 
mean the precursor gaseous mixtures of each adjacent deposition chamber 
are substantially prevented from cross contaminating one another. 
Moreover, each deposition chamber has introduced thereinto a particular 
precursor gaseous mixture of process gases which is protected by an 
external isolation passageway module from (1) contaminating the precursor 
gaseous mixture introduced into adjacent deposition chambers and (2) being 
contaminated by environmental conditions. 
The processor 26 is particularly adapted to deposit a high volume of large 
area amorphous triple tandem photovoltaic cells having a generally 
n-i-p-type configuration onto the deposition surface of the web of 
substrate material 11 which is continually fed therethrough. In order to 
deposit the semiconductor alloy material required for producing a tandem 
photovoltaic device of such an n-i-p-type configuration, the processor 26 
includes: a first deposition chamber 28 in which an n-type conductivity 
layer of semiconductor alloy material is deposited onto the deposition 
surface of the web of substrate material 11 as said web passes 
therethrough; a second deposition chamber 30 in which a layer of 
substantially intrinsic semiconductor alloy material is deposited atop the 
layer of n-type semiconductor alloy material on the deposition surface of 
the web of substrate material 11 as the web 11 passes therethrough; a 
third deposition chamber 32 in which a layer of p-type conductivity 
semiconductor alloy material is deposited atop the layer of intrinsic 
semiconductor alloy material on the deposition surface of the web of 
substrate material 11 as the web passes therethrough; a fourth deposition 
chamber 34 in which a second n-type conductivity layer of semiconductor 
alloy material is deposited atop the layer of p-type semiconductor alloy 
material on the deposition surface on the web of substrate material as the 
web 11 passes therethrough; a fifth deposition chamber 36 in which a 
second layer of intrinsic amorphous semiconductor alloy material is 
deposited atop the second layer of p-type semiconductor alloy material on 
the deposition surface on the web of substrate material 11 as the web 11 
passes therethrough; a sixth deposition chamber 38 in which a second layer 
of p-type conductivity semiconductor alloy material is deposited atop the 
second layer of intrinsic semiconductor alloy material on the deposition 
surface of the web of substrate material 11 as the web 11 passes 
therethrough; a seventh deposition chamber 40 in which a third layer of 
n-type conductivity semiconductor alloy material is deposited atop the 
second layer of n-type semiconductor alloy material on the deposition 
surface of the web of substrate material 11 as the web 11 passes 
therethrough; an eighth deposition chamber 42 in which a third layer of 
intrinsic semiconductor alloy material is deposited atop the third layer 
of n-type semiconductor alloy material on the deposition surface of the 
web of substrate material 11 as the web 11 passes therethrough; and a 
ninth deposition chamber 44 in which a third layer of p-type conductivity 
semiconductor alloy material is deposited atop the third layer of 
intrinsic semiconductor alloy material on the deposition surface of the 
web of substrate material 11 as the web 11 passes therethrough. 
It should be apparent that, although nine discrete deposition chambers 
(three triads of the three deposition chambers) have been described, 
additional triad deposition chambers or individual deposition chambers may 
be added to the processor 26 to provide the machine with the capability of 
producing any number of tandem photovoltaic cells having p-i-n-type or 
n-i-p-type or p-n-type or n-p-type configuration. It should further be 
understood that, although, in the preferred embodiment, the substrate is 
formed as a continuous, electrically conductive web of substrate material 
11, the concept of the present invention is equally adapted for depositing 
the successive layers of semiconductor alloy material atop a continuous, 
electrically non-conductive substrate or atop discrete, electrically 
conductive or non-conductive substrate plates which are continuously fed 
through the plurality of deposition chambers thereof. It should also be 
apparent that since the length of the path of travel of the web of 
substrate material 11 through the individual deposition chambers is 
proportional to the thickness of the n-type, or the intrinsic, or the 
p-type layer of semiconductor alloy material to be deposited in any one of 
the given chambers, the length of the path of travel of the web of 
substrate material 11 through an individual deposition chamber must be 
increased (if the speed of the web of substrate material 11 is kept 
constant) in order to deposit a thicker layer thereupon. This can best be 
illustrated with reference to the first triad of deposition chambers in 
which the path of travel of the web 11 through the multiple plasma regions 
developed within the intrinsic deposition chamber 30 can be seen to be 
much longer than the path of travel thereof through the plasma regions 
developed within either of the doped deposition chambers 28 and 32 because 
the intrinsic deposition chamber 30 is adapted for the deposition of a 
3500 angstrom thick layer of intrinsic semiconductor alloy material while 
the doped deposition chambers 28 and 32 are adapted to only deposit layers 
of approximately 100 angstrom thick semiconductor alloy material. 
Still referring to FIG. 2, the processor 26 further includes a plurality of 
external isolation modules 46a-46l for isolating the particular precursor 
gaseous mixture introduced into a particular deposition chamber from the 
mixtures introduced into adjacent chambers, each of said mixtures being 
operative to deposit a particular layer of semiconductor alloy material of 
a preselected conductivity type. The isolation modules 46a-46l are 
preferably disposed externally of the deposition chambers and are adapted 
to permit the web of substrate material 11 to travel between the discrete 
deposition chambers which they interconnect while substantially preventing 
said inter-diffusion of said precursor gaseous mixture from one of a pair 
of adjacent chambers into the other of the pair. External isolation 
modules of this type are fully disclosed in U.S. Pat. No. 4,480,585 
entitled "External Isolation Module", filed June 23, 1983, the disclosure 
of which is incorporated herewith by reference and the assignee of which 
is the same as the assignee of the present invention. Generally, the 
isolation modules 46a-46l are schematically illustrated as including a 
pair of elongated, horizontally-disposed, passageway-forming plates, said 
plates adapted to be spacedly positioned in substantially parallel planes 
for defining the passageway therebetween. The web of substrate material 11 
passing through the passageway divides the passageway into a pair of flow 
channels, i.e., an upper relatively narrow and a lower, relatively wide 
channel. Sweep gas is uniformly introduced into each of the channels to 
prevent the diffusion of the precursor gaseous mixtures between the 
adjacent deposition chambers. 
Positioned on the side of the first deposition chamber 28 opposite the 
second deposition chamber 30, and in operative interconnection therewith, 
is a substrate cleaning chamber 50 in which the web of substrate material 
continuously moving therethrough is subjected to high temperature (on the 
order of 450.degree. C.) so as to bake out contaminants therefrom. A 
substrate cleaning plasma may also be developed within that chamber if it 
is deemed necessary to further rid the web of substrate material 11 of 
contaminants. 
On the side of the cleaning chamber 50 opposite the first deposition 
chamber 30 is the substrate pay-off chamber 52 from which a roll of 
substrate material 11 is supplied, under tension, from a pay-off roll 11a 
to the deposition chambers of the processor 26. As the web 11 is unwound 
from the roll 11a, a sheet of protective interleaf sheeting 9 is wound 
about interleaf take-up roller 52b. Also present in the pay-off chamber 52 
are a pair of idler turning rollers 76a for initially directing the web 11 
in a generally horizontal path of travel through the processor 26. 
Positioned on the side of the ninth deposition chamber 44 opposite the 
eighth deposition chamber 42 is a post deposition take-up chamber 54 in 
which the web of substrate material 11, with the layers of semiconductor 
alloy material deposited thereupon, is wound about a take-up core 11b. As 
the web 11 is wound about the take-up roll 11b, a sheet of protective 
interleaf sheeting 9 from an interleaf pay-off roller 54b is would 
thereabout. Also present in the take-off chamber 54 are a pair of idler 
turning rollers 76 for directing the web 11 from its normally horizontal 
path of travel into winding engagement with the take-up roll 11b. 
The first and last external isolation modules 46a and 46l both include a 
bellows section 56a and 56b, respectively, which bellows are adapted to 
compensate for expansion or contraction which occurs during operation of 
the processor 26. Intermediate at least the third deposition chamber 32 of 
the first triad and the first deposition chamber 34 of the second triad is 
an intermediate web controller chamber 58 in which a spring tensioning 
roller 58a is adapted to cooperate with a pair of turning rollers 58b for 
maintaining the proper tension on the web of substrate material 11. 
Although only one controller chamber 58 is depicted, it should be apparent 
that additional controller chambers may be added at any point along the 
path of travel of the web of substrate material 11 without departing from 
the spirit or scope of the instant invention. It is also to be noted that 
each of the deposition chambers, external isolation modules and pay-off 
and take-up chambers are raised off of the floor and supported by a 
heavy-duty scaffolding generally depicted by the reference numeral 60. By 
raising the processor 26 from the floor, said processor is not as 
responsive to changes in environmental conditions such as heat or cold. 
Referring now to FIG. 4, there is illustrated the interior configuration of 
two of the deposition chambers, such as the deposition chambers 40 and 42 
in which the third layer of n-type semiconductor alloy material and the 
third layer of intrinsic semiconductor alloy material, respectively, are 
to be deposited and through which the web of substrate material 11 is 
adapted to move in a non-linear path of travel. It is to be understood 
that the deposition chambers 40 and 42 are merely intended to be 
representative of any of the deposition chambers of the processor 26 and 
that the third n-type and intrinsic deposition chambers have been selected 
for purposes of illustration only since those deposition chambers require 
the web of substrate material 11 to make only one non-linear pass for the 
deposition thereonto of the third n-type layer and the third intrinsic 
layer of semiconductor alloy material. An explanation of the operation of 
any of the other deposition chambers of the processor 26, such as the 
first intrinsic deposition chamber 30 in which the web of substrate 
material 11 is adapted to make multiple non-linear passes, may be easily 
understood from the explanation of the operation of the deposition chamber 
40 which follows. 
Chambers 40 and 42 are discrete one of the plurality of isolated dedicated 
deposition chambers operatively interconnected by external isolation 
modules, such as 46i. Such an external isolation module is also 
operatively disposed, in the preferred embodiment, between any of the 
chambers of the processor 26 which are not adapted to deposit 
semiconductor alloy material, but which cannot be allowed to contaminate 
the deposition chambers adjacent thereto. Note that the reference numeral 
46i' is employed because the external isolation module depicted in FIG. 4 
is of the type disclosed in detail hereinafter as the novel isolation 
passageway of the instant invention. 
The deposition chambers 40 and 42 include a cathode plate 62 having a 
plurality of apertures formed therethrough so as to perforate same for the 
uniform mixing of process gases introduced into one side of the plate with 
the process gases introduced onto the other side of the cathode plate 62; 
an upper, transversely elongated generally U-shaped cathode shield 68 
which is adapted to restrict the precursor gaseous mixture entering the 
cathode region from a elongated apertured introductory manifold 64 from 
exiting the plasma region; and a lower transversely elongated cathode 
shield 66b which is adapted to prevent the non-deposited precursor gaseous 
mixture from leaving the cathode region after said mixture has passed 
through the plasma region developed between the web 11 and both of the 
faces of the cathode plate 62. The lower cathode shield 66b includes a 
conically-shaped portion which is operatively interconnected with the 
exhaust conduit 66 from which the non-deposited precursor gaseous mixture 
is exhausted from the deposition chamber 40. The lower cathode shield 66b 
further includes a plurality of apertures 66a disposed on both sides of 
the longitudinal extent thereof. Since both the upper cathode shield 68 
and lower cathode shield 66b are elongated members which extend across the 
full transverse extent of the deposition chamber and are coextensive with 
the transverse extent of the web of substrate material 11 and the cathode 
plate 62, the precursor gaseous mixture introduced into the plasma regions 
is substantially confined within those regions. 
It is to be noted at this point that the precursor gaseous mixture 
introduced through the apertured introductory manifold 64 is adapted to 
assume a generally vertical path of travel as depicted by arrow A, said 
path of travel being generally parallel to the path of movement of the web 
of substrate material through the plasma region. A plurality of banks of 
substrate heaters 72a, including heat reflecting shields 72, are 
operatively disposed on either side of the web of substrate material 11 so 
as to maintain the temperature thereof at the preselected deposition 
temperature. A plurality of elongated ceramic magnets 74 are also 
operatively disposed along the path of travel of the web of substrate 
material 11 so as to urge said web of substrate material 11 into a 
generally planar configuration as said web moves through the plasma region 
and has semiconductor alloy material deposited thereupon. A power source 
70 which, in the preferred embodiment is a source of r.f. electromagnetic 
energy, is operatively coupled to the cathode plate 62 for generating an 
electromagnetic field between both faces of that cathode plate 62 and the 
conductive web of substrate material 11 passing therepast. In this manner, 
the precursor gaseous mixture flowing through the space developed between 
both faces of the cathode plate 62 and the web of substrate material 11 is 
subjected to an electromagnetic field and decomposed into a highly 
energetic plasma from which a preselected layer of semiconductor alloy 
material is continuously deposited upon the moving web of substrate 
material 11. 
It should therefore be apparent that the web of substrate material 11 is 
adpated to enter the deposition chambers 40 and 42 and move about a first 
turning roller 76a which rotatably engages a support 76. After passing 
about the first roller 76a, said web 11 assumes a generally vertical and 
upwardly directed path of travel past the plasma region created on the 
left-hand side of the cathode plate 62 so that semiconductor alloy 
material from the plasma region can be continuously deposited thereupon. 
At the upper end of the deposition chambers 40 and 42, a second turning 
roller 76b, also rotatably engaging a support 76, changes the direction of 
movement of the web of substrate material 11 from a vertical and upward 
direction to a downward and vertical direction through the plasma region 
developed on the right-hand face of the cathode plate 62 so that 
semiconductor alloy material from said right-hand region is continuously 
deposited thereupon. Finally, a third turning roller 76c, which is in 
rotatable engagement with support 76, is adapted to change the direction 
of travel of the web of substrate material 11 from its downward and 
generally vertical direction to the exit orientation it must assume as it 
departs from the deposition chambers 40 and 42. Note that the 
circumferential periphery of the second turning roller 76b is in 
surface-to-surface contact with the deposition surface of the web of 
substrate material 11. However, the central portion of said roller 76b is 
recessed so that only the longitudinal edges of the web 11 are in contact 
with the circumferential periphery of the roller 76b and the semiconductor 
alloy material deposited thereupon is not scratched or otherewise marred 
by frictional contact with the roller (the longitudinal edges of the web 
11 are subject to the deposition thereonto of poorer quality semiconductor 
alloy material than is deposited onto the central portion due to "edge 
effects" and the edges are therefore removed from the photovoltaic devices 
prior to modularization thereof). 
III. The Circular Isolation Passageway 
From the foregoing description of the multichamber processor, it can be 
seen that by utilizing the non-linear path of travel principles of 
Applicants' assignee's previously filed application, the total length of 
the processor 26 has been substantially foreshortened. The result is the 
more efficient, more economical manufacture of photovoltaic devices. 
However, as should also be apparent from the foregoing description of the 
processor, as well as a perusal of FIG. 2, the gas gates 46a-46b for a 
substantial proportional of the total length of that processor. 
Accordingly, the operative disposition of the improved, non-linear 
isolation passageway of the present invention, when taken in combination 
with the nonlinearity of the aforedescribed processor, will not only serve 
to still further shorten the overall length thereof, but will also further 
improve the degree of isolation between adjacent environments. 
It must be borne in mind, before proceeding with a detailed description of 
the improved isolation passageway of the subject invention, that the 
primary purpose of such a passageway remains the prevention of diffusion 
of dopant contaminants from the dopant depositon chamber into the 
intrinsic deposition chamber operatively connected thereto. To this end, 
all of the "tricks" previously described in the aforementioned patent 
applications of Applicants' assignee are also available for use with the 
subject isolation passageway. For instance, the p dopant deposition 
chamber and n dopant deposition chambers may be maintained at lower 
internal pressure than the intrinsic deposition chamber by providing each 
deposition chamber with automatic throttle valves, pumps and manometers. 
In this manner the pressure within the dopant deposition chambers may be 
maintained at, for instance, approximately 0.55 Torr and the pressure 
within the intrinsic deposition chamber may be maintained at for example, 
approximately 0.6 Torr. Hence a pressure differential is established and 
maintained between the dopant deposition chambers and the intrinsic 
deposition chamber to provide for substantially unidirectional gas flow of 
non-contaminating intrinsic gases through the isolation passageway. 
Turning now to FIG. 3, the isolation passageway of the instant invention is 
illustrated generally by the reference numeral 100. It is to be noted that 
the isolation passageway 100 is formed with an inner, generally elongated, 
cylindrically-shaped drum 102. The length of the drum 102 is dependent 
upon the width of the web of substrate material 11 which is adapted to 
pass therethrough between one of the deposition chambers such as the 
n.sub.3 deposition chamber 40 and the intrinsic deposition chamber 42, 
i.e., the length of the drum 102 must be at least equal to the width of 
the web 11. The isolation passageway 100 further includes a top plate 101 
which has a pair of elongated slots 104a and 104b spacedly formed 
therethrough, the length of the slots approximating the width of the web 
of substrate material 11 which is adapted to pass therethrough. More 
particularly, the web of substrate material 11 enters the isolation 
passageway 100 through the introductory slot 104a and exits the passageway 
100 through exit slot 104b. The top plate 101 is generally planar in 
configuration and, in the preferred embodiment, is adapted to be secured 
to the undersurface of each of the adjacent deposition chambers 40 and 42. 
Because of the manner in which it may be secured in overlapping 
relationship below the adjacent deposition chambers, the isolation 
passageway 100 is further adapted to foreshorten the total length of the 
processor 26. Note that as best seen in FIG. 4, the passageway 100 is 
generally annular in a central region and generally rectangular in the 
regions adjacent to the central region. 
It is further to be noticed, and as best illustrated in FIG. 4, that the 
web of substrate material 11 may be brought into the deposition chambers 
or may exit from the deposition chamber at an angle with respect to the 
turning rollers 76a and 76c because of the tangential manner in which the 
web of substrate material 11 is wrapped about a portion of the 
circumference of both the turning rollers 76a and 76c and the circularly 
shaped drum 102. It is to be noted herewith that total length of the 
passageway opening 100 which a molecule of contaminating reaction gas must 
pass in order to traverse the distance from one of the adjacent deposition 
chambers to the other of the chambers is the same as the distance through 
the passageway which must be traversed in the planar FIG. 2 embodiment of 
the gas gates, however, that distance is now formed so as to be at least 
partially circular so that while the total linear distance is identical to 
molecules of gaseous contaminants, the horizontal length of the gas gate 
is greatly shortened, there correspondingly shortening the total overall 
length of the semiconductor deposition processor 26. 
Returning now to the stuctural configuration of the circular isolation 
passageway 100, the planar top plate 101 is secured by a radially 
outermost, circumferentially extending enclosure panel 106, the radial 
difference between said panel 106 and the drum 102 serving to define the 
dimension of the lowermost substrate-contacting passageway opening 105. 
More particularly, the panel 106 includes a generally circularly shaped 
lower portion 106a which is joined by side portions 106b to the top plate 
101. The generally circular bottom portion 106a has a radius greater than 
the radius of the cylindrical drum 102, but is concentrically formed 
therewith. In a like manner, a top circumferential portion defines an 
upper non-substrate contacting passageway 107. 
The web of substrate material is held tightly against the bottom peripheral 
surface of the cylindrical drum 102 by tension developed by the turning 
rollers 76a and 76c operatively disposed in the bottom part of each of the 
deposition chambers 40 and 42, respectively. Since the isolation 
passageway 100 interconnects these two adjacent deposition chambers, 
contaminating reaction gases may pass between the deposition chambers 
through either (1) the upper non-substrate contacting passageway 107 
defined between the upper circumferential portion 108 of the plate 101 and 
the upper circumferential surface of the drum 102 or (2) the lowermost 
substrate-contacting passageway 105 defined between the inner 
circumferential surface 106a of the encapsulating plate 106 and the lower 
circumferential surface of the drum 102. Since the likelihood of 
contamination exists, some mechanism is necessary in order to prevent 
diffusion of contaminating molecules of reaction gases between the 
adjacent, operatively interconnected deposition chambers. One such 
solution has been mentioned hereinabove and resides in the ability to 
maintain the dopant deposition chambers at a different partial pressure 
than the partial pressure present in the intrinsic deposition chamber. In 
this manner, it is possible to limit the flow of gaseous reactants through 
the gas gate passageway to the intrinsic gaseous reactants introduced into 
the intrinsic deposition chambers. These intrinsic deposition gases are 
moved through the passageway at a sufficient velocity to collide with any 
diffusing dopant gas molecules and thereby prevent the diffusion of the 
dopant molecules into the intrinsic deposition chamber. 
However, in view of the high degree of purity which must be maintained 
between the adjacent deposition chambers, it may be necessary to still 
further limit the diffusion of contaminating gas molecules. In view of 
this concern toward the maintenance of ultra-high purity deposition 
environments, it becomes necessary to further inhibit gas diffusion by 
providing for a sweep of an inert gas into either or both (1) the upper 
non-substrate contacting passageway 107 and/or (2) the lowermost 
substrate-contacting passageway 105 developed in the circular isolation 
passageway 102 of the subject invention. This can be best seen in FIG. 7 
wherein sweep gas is introduced into both the upper and lower isolation 
passageways. More specifically, a source of sweep gas 110 is provided to 
introduce sweep gas through an introductory conduit 112 into the upper, 
generally circular passageway 107 which separates two adjacent deposition 
chambers (such as 40 and 42 of FIG. 4). Similarly, a source of sweep gas 
114 is adapted to supply an inert gas such as hydrogen or argon into the 
lowermost circular passageway 105 through an introductory conduit 116. It 
is to be noted that the lowermost passageway 105 is defined to exist 
between the coated surface of the web of substrate material 11 and the 
generally circularly-shaped lower portion 106a of the encapsulating plate 
106. 
As illustrated in FIG. 7A, the sweep gas source 114 and introductory 
conduit 116 which are adapted to introduce the inert gas into the lower 
passageway 105 are shown in phantom outline. This is because of the 
presence in that figure of a hydrogen plasma developing chamber generally 
117, which may be included as another preferred embodiment of the 
isolation passageway 100 of the subject invention. The hydrogen plasma 
chamber 117 is formed by a generally bulbous shaped extension 119 of the 
lower circumferentially extending portion 106a of the encapsulating plate 
106, the extension including a hydrogen gas introductory duct 118 and a 
spent gas exit duct 120. A cathode plate 122 (curved in the FIG. 7A 
embodiment) is operatively disposed in proximate relationship to the 
correspondingly configured and layered surface of the web of substrate 
material 11, as that web passes through the lowermost isolation passageway 
105. The cathode plate 122 is preferably shaped in a generally circular 
configuration so as to be at all points equidistant from the contiguous 
surface of the web of substrate material 11 which has assumed the contour 
of the cylindrical drum 102 against which it is tightly pressed. The 
cathode plate 122 is connected to a source of electromagnetic energy 124, 
such as alternating current microwave energy or radio energy frequencies. 
It is to be appreciated that if microwave energy is to be used, instead of 
employing a cathode plate for decomposing the hydrogen gas and thereby 
depositing a hydrogenated cap atop the amorphous silicon layered surface 
of the web of substrate material 11 passing therepast, a microwave antenna 
could be employed. Also, although alternating current represents the 
preferred embodiment of electromagnetic energy, a DC power source could 
also be employed to decompose the hydrogen gas. As is well known to those 
skilled in the art, the distance from the cathode plate 122 to the 
substrate 11 must be greater than the dark space distance for the 
particular operating conditions employed if a plasma is to be generated 
and sustained therein. 
A cathode shield 126 divides the bulbous compartment 119 into two portions 
so that the introduced hydrogen gas from source 128 must, of necessity, 
flow around the bottom edge of the cathode plate 122 into the lowermost 
passageway 105. It is in this passageway 105 that said hydrogen gas is 
decomposed and the decomposed species are deposited upon the exposed 
surface of the web of substrate material 11 before leaving the passageway 
105 through the exit duct 120. The incorporation of the bulbous extension 
117 into the passageway assembly 100 serves two functions. In the first 
place, said extension 117 is specifically adapted to provide for the 
hydrogen capping of the previously deposited layer of semiconductor alloy 
material, a cap which has been shown important to achieve the highest 
possible photovoltaic conversion efficiencies from the solar cells 
fabricated in the processor 26. The second function which the hydrogen 
plasma developed in the bulbous extension 117 serves is to prevent any 
further diffusion of process gases from one of the deposition chambers 
into the adjacent deposition chamber. This diffusion prevention mechanism 
occurs because contaminating gases flowing past the cathode 120 must be 
decomposed and deposited upon the web of substrate material 11 along with 
the hydrogenated species. It is for this reason that the FIG. 7A sweep gas 
source 114 and conduit 116 are illustrated in phantom, i.e., because the 
sweep gas is not an essential element of diffusion prevention if the lower 
passageway 105 is equipped with hydrogen plasma capabilities. It is also 
to be noted that the reason the bulbous extension 117 has not been 
illustrated in the FIG. 4 embodiment or in the FIG. 2 embodiment of the 
processor 26 is because of space limitations only. The use of a hydrogen 
plasma is considered an important feature and when employed to cap at 
least the layer of intrinsic semiconductor alloy material (after the web 
of substrate material 11 exits from the intrinsic deposition chamber), 
said plasma represents the best mode of operation of the processor. 
Turning now to FIG. 5, a cross sectional view of the inner cylindrical drum 
102 of the isolation passageway 100 of the instant invention is employed 
so as to best illustrate the grooved circumferential surface thereof. More 
particularly, the cylindrical drum 102 includes a circumferential surface 
120 against a portion of which the web of substrate material 11 is 
continuously urged into contact. The length of the circumferential surface 
120 must be at least as wide as the width of the web of substrate material 
11 passing thereagainst so that the entire width of the web 11 contacts a 
grooved portion of that circumferential surface 120. Although not shown, a 
drive system may be employed to provide for the rotation of the 
cylindrically shaped drum 102 so that rotation of the drum 102 can be used 
to provide tension on the web of substrate material 11 intermediate of the 
web drive assemblies which were heretofore present only adjacent the 
pay-off and take-up chambers of the processor 26. Because of the tight 
tension which may now be placed on the web of substrate material 11, 
warpage and canoeing of the web 11 (which, although reduced in prior art 
gas gates of Applicants' design, was still present therein) is almost 
totally eliminated thereby enabling the total height of the passageway 
opening 105 to be reduced thereby decreasing the possible diffusion of 
gases from one of the dopant deposition chambers to the adjacent intrinsic 
deposition chamber. Through the use of the concepts espoused by the 
present invention, the height of the isolation passageway opening has been 
decreased in such a manner that a corresponding decrease in back 
diffusion, by a factor of approximately two orders of magnitude, has been 
achieved. 
As best seen in FIG. 6 the inner surface 106a of the encapsulating wall 106 
of the isolation passageway 100 forms the bottom surface of the lowermost 
passageway opening 105 connecting deposition chambers 40 and 42. It is 
between this surface 106a and the layered surface of the web of substrate 
material 11 that a minimum tolerance must be maintained so as to provide 
for the passage of the web 11 therethrough while, at the same time, 
preventing any rubbing or scraping of the deposited layers of 
semiconductor alloy material thereagainst. As previously explained, 
despite the relatively small size of the opening 105, sweep gas from the 
source 114 must be introduced into the lower opening 105 through nozzle 
116 so as to inhibit the back diffusion of process gases from a dopant 
deposition chamber into the adjacent and operatively interconnected 
intrinsic deposition chamber. However, the relatively narrow upper slit 
defined between the cylindrical drum 102 and the unlayered surface of the 
web of substrate material 11 may be sufficiently narrow that the viscous 
sweep gases are unable to attain sufficient velocity to prevent back 
diffusion of dopant gases from the dopant chambers into the intrinsic 
deposition chamber. 
In order for the inherently viscous inert gases to be swept through the 
relatively narrow upper passageway formed between the web of substrate 
material 11 and the outer surface of the elongated drum 102 with 
sufficient velocity to substantially prevent the back diffusion of process 
gases from the dopant chambers into the intrinsic chamber, the outer 
circumferential portion of the drum 102 is formed with a plurality of 
circumferentially extending generally parallel grooves, some of which are 
illustrated and represented by the number 103. The grooves 103 extend 
about the entire circumferential extent of the drum 102 so as to be able 
to operatively communicate at one end with a dopant deposition chamber and 
at the other end with the adjacent intrinsic deposition chamber. It is in 
this manner that sweep gases may be passed through the flow channels 
defined by the grooves 103 to prevent diffusion of gaseous contaminants 
between said adjacent chambers. Each of the substantially parallel grooves 
103 is defined by opposed side walls 103a and an innermost wall 103b. The 
unlayered surface of the web of substrate material 11 is urged against the 
upper surface 120 of the elongated cylindrical drum 102. The side walls 
103a extend downwardly approximately 1/8 inch and are separated by the 
innnermost wall 103b which is about 1/4 inch wide, thereby providing a 
plurality of 1/8 inch high and 1/4 inch wide flow channels between the web 
11 and the upper surface 120 of the drum 102, thereby interconnecting 
adjacent deposition chambers. Because of the increased size of the flow 
channels as compared to the size of the passageway which would otherwise 
exist between the unlayered surface of the web of substrate material 11 
and the exposed surface 120 of the elongated drum 102, the velocity of 
gases swept therethrough is substantially increased to a value which is 
effective in minimizing the back diffusion of process gases. 
It should be appreciated that the molecules of gases flowing through the 
upper passageway opening 105 may either travel through the flow channels 
defined by the grooves 103 or through the relatively narrow space which 
exists between adjacent grooves 103. In either event the inert gases which 
is caused to flow through the grooves 103 are able to attain sufficient 
velocity to substantially prevent back diffusion of process gases. This is 
true despite the fact that the inert gases flowing through the relatively 
narrow space between adjacent grooves are not able to attain sufficient 
velocity to prevent diffusion. However, due to the length of the path 
which the dopant process gases must traverse in order to back diffuse into 
the intrinsic deposition chamber, the probability is remote that said 
gases will be able to complete the journey to the intrinsic deposition 
chamber without entering the high velocity flow channel grooves 103. Once 
the gas molecules enter the high velocity grooves 103, those dopant 
process gases will move with the swift and counter-directed flow of the 
sweep gases and be returned to the dopant chamber. In this manner, 
contamination of the intrinsic chamber caused by dopant process gases 
diffusing through the upper, relatively narrow passageway opening 105 may 
be substantially reduced. 
While the grooves 103, when taken in combination with the introduction of 
sweep gas adjacent the intrinsic deposition chamber side of the isolation 
passageway 100 serves to substantially reduce diffusion problems, it has 
been determined that the introduction of additional sweep gas directly 
into each of the grooves 103 approximate th midway point between the 
adjacent deposition chambers seems to provide an additional reduction in 
the back diffusion of contaminating process gases. The inert sweep gas 
introduction system, which will be described in the following paragraph, 
has been found to offer excellent results in increasing the rate of flow 
of sweep gas through the relatively narrow upper passageway opening 105, 
consequently reducing diffusion. 
More particularly, argon, hydrogen or another substantially inert gas is 
adapted to flow into a sweep gas supply manifold, generally 122, via feed 
line 124 from a sweep gas source 126. The inert gas is then fed from the 
manifold 122, at a flow rate of at least 50 SCCM through each of the feed 
conduits 128 directly into each of the flow channel grooves 103. Since the 
sweep gas is introduced into the grooves 103 at a pressure of about 1.0 
Torr, the pressure at both of the deposition chambers are sensed to be 
substantially identical (actually a higher pressure is maintained in the 
intrinsic deposition chamber to obtain a substantially unidirectional flow 
of process gases toward the dopant deposition chamber) and the inert gas 
flows in substantially equal volumes per unit time toward both of the 
adjacent chambers. 
However, it should be noted that the length of the passageway must be 
increased when such an intermediate sweep gas introduction mechanism is 
employed. This is because it is desirable that the total length which the 
process gases must travel in order to be substantially prevented from any 
back diffusing is about 8 inches (from the point of inert ga 
introduction). Should the dopant process gases reach the intermediate 
introduction point, the dopant gases would likely be caught in the flow of 
the incoming sweep gas and swept therealong toward the intrinsic 
deposition chamber. The only significant restriction as to the 
intermediate sweep gas introduction system is that the cross sectional 
area of the feed conduits 128 should be small relative to the size of the 
groove into which they supply the inert sweep gas. This is because the web 
of substrate material 11 may occasionally not be maintained in a perfectly 
planar configuration and the dimension of the upper passageway opening is 
likely to vary with the linearity of the web. Therefore, in order to 
introduce substantially equal volumes of gas per unit time into each of 
the grooves 103, despite fluctuating groove capacities and corresponding 
pressures (due to fluctuating web linearity) it is necessary that the 
cross-sectional area of the feed conduits 128 be small relative to the 
size of the flow channels formed by the grooves 103. 
Referring now to FIG. 7B, a partial cross-sectional view of FIG. 7A is 
illustrated. FIG. 7B shows the operative position of a hydrogen capping 
assembly relative to yet another preferred embodiment of the isolation 
passageway 100 of the instant invention, said assembly including a pair of 
spaced rotary drums 102a and 102a. The FIG. 7B embodiment is to be 
utilized in cases wherein it is necessary to achieve the highest degree of 
isolation between adjacent passageways and particularly in those instances 
wherein it is not desired to allow for any chance of contaminants from one 
of the pair of adjacent deposition chambers to be deposited in the 
hydrogen capping plasma. More particularly, a sweep gas 114 and an 
introductory conduit 116 are adapted to introduce an inert gas into the 
lower passageway 105a. In this embodiment, the dopant deposition chamber 
is disposed on the right hand side so that the web of substrate material 
11 is entering thereinto. Therefore the sweep gas source 114 is adapted to 
prevent the dopant constituents from entering the hydrogen plasma assembly 
in which it would be deposited along with the hydrogen to cap the 
deposited layer of semiconductor alloy material which is of an intrinsic 
nature. The hydrogen plasma assembly 117 is formed by a generally bulbous 
shaped extension 119 of the lower circumferentially extending portion 106a 
of the encapsulating plate 106, the extension including a hydrogen gas 
introductory duct 118 and a spent gas exit duct 120. A cathode plate 122 
is operatively disposed in proximate relationship to the correspondingly 
configured and layered surface of the web of substrate material 11 as that 
web passes through the space between contiguous cylindrically shaped drums 
102a and 102b. The cathode plate 122 is connected to a source of 
electromagnetic energy 124 such as alternating current microwave energy or 
radio energy frequencies. Again, a microwave antenna may be employed if 
the microwave energies are used and the systems from the cathode plate 122 
to the web of substrate material 11 must be greater than the dark space 
distance for the particular operating conditions employed if a plasma is 
to be generated and sustained. 
A cathode shield 126 divides the bulbous compartment 119 into two portions 
so that the introduced hydrogen gas from the source 128 must, of 
necessity, flow around the bottom edge of the cathode plate 122 into the 
lowermost passageway 105. It is in this passageway 105 that the hydrogen 
gas is decomposed and the decomposed species are deposited upon the 
exposed surface of the web of substrate material 11 before leaving the 
passageway 105 to the exit duct 120. Unlike the embodiment illustrated in 
FIG. 7A, the sweep gas source 114 and the conduit 116 are illustrated in 
solid lines because the sweep gas is an essential element of the diffusion 
prevention even though the passageway 105 is equipped with hydrogen plasma 
capabilities. It is further to be noted that sweep gas from the source 110 
and the conduit 112 enter into the upper passageway 107 and prevent 
gaseous contaminants from diffusing into the adjacent upper passageways 
107a and 107b of the rollers 102a and 102b, respectively. It should 
therefore be apparent that the FIG. 7B embodiment provides the most 
contaminant free embodiment of the isolation passageway 100 of the subject 
invention. 
It should therefore be understood, and as best seen in FIG. 6, the 
isolation passageway 100 of the instant invention, will, in a preferred 
embodiment, include three sources of sweep gas introduced into each 
discrete one of the passageway openings. More particularly, the first 
source of sweep gas 114 is adapted to introduce an inert gas via nozzle 
116 between the enclosure wall 106a and the layered surface of the web of 
substrate material 11; the second sweep gas introductory source 110 is 
adapted to introduce sweep gas via nozzle 112 into the passageway opening 
107 which exists at the upper portion of the cylindrical drum 102, i.e., 
the portion about which the web of substrate material 11 is not in 
contact; and the third source of sweep gas 122 which is adapted to 
introduce sweep gas via nozzle 124 (shown in FIG. 5), manifold 122 and 
conduits 128 into the flow channels 103 (shown in FIG. 5) so as to prevent 
diffusion between the unlayered surface of the web of substrate material 
11 and the surface 120 of the elongated cylindrically shaped drum 102. 
Therefore, from the illustration of FIG. 6, it can be seen that sweep gas 
is preferably introduced into three areas of the isolation passageway 
assembly 100 so as to substantially prevent the diffusion of process gases 
between adjacent deposition environments. Of course, in the embodiment of 
the subject invention wherein a hydrogen plasma is employed, one of the 
sweep gas flows may be eliminated. Specifically, sweep gases are 
introduced at the upper, generally circularly shaped portion of the 
passageway 107 which is defined between the upper encapsulating wall 109 
and the upper surface of the cylindrically shaped drum 102 from sweep gas 
introductory tank 110 via introductory nozzle 112. Similarly, sweep gas is 
introduced from sweep gas manifold 114 via nozzle 116 into that portion of 
the isolation passageway which is defined between the layered surface of 
the web of substrate material 11 and the cylindrically shaped lower wall 
106a of the encapsulating wall 106. Finally, sweep gas is introduced from 
a manifold 122 via nozzle 128 into the grooves 103 so as to move through 
the flow channels within each of the grooves 103 so as to prevent 
diffusion in the passageway formed between the web of substrate material 
11 and the surface of the drum 120. While the three distinct sources of 
sweep gas represent a preferred embodiment of the instant invention, note 
that the use of this plurality of sources is dependent upon the degree of 
isolation between adjacent environments which is required. It is only 
necessary to provide all three of the sources of sweep gas if an ultrapure 
environment is required; however, for environments wherein the minimum 
10.sup.4 ratio of contamination is acceptable, a lesser number of these 
sources may suffice. 
Finally, it is still essential that a leak-tight seal be provided between 
the environment and the edge portions of the isolation passageway assembly 
100. To that end, specially designed end plates 130, see FIG. 8, have been 
developed for use with said isolation passageway. Each of the end seals 
130 is generally annularly shaped with a substantially E-shaped cross 
sectional configuration. Note that in the interest of simplicity, the 
various sweep gas manifolds as well as the grooved nature of the elongated 
cylindrically shaped drum 102 have not been illustrated in FIG. 8. The 
sole purpose of this figure is to depict the leak-proof nature of the end 
seals 130. To this end, the radially outermost bite portion 130a of the 
E-shaped outer end seal 130 is adapted to receive thereinto the 
encapsulating wall 106, while the radially innermost bite portion 130b of 
the E-shaped seal 130 is adapted to receive thereinto a peripheral edge of 
the elongated cylindrically shaped drum 102. Both the radially innermost 
wall of the innermost bite shaped portion 130b and the radially outermost 
portion of the outermost bite 130a are indented to receive a pair of 
spaced O-rings 132. Pumps 134 are operatively disposed and adapted to 
evacuate any diffusing gases from the space between each of the pair of 
O-rings 132 in both the upper and lower bite portions of the E-shaped 
seals so as to prevent the introduction of contaminants from the 
atmosphere into the vacuumized isolation passageway 100. 
It should thus be apparent, based upon the foregoing description, that the 
isolation passageway of the subject invention has not only improved the 
diffusion barrier of prior gas gates, but has accomplished that 
improvement while foreshortening the overall length of the deposition 
apparatus. Therefore, benefits are derived from the subject invention in 
terms of improved photovoltaic devices, lower capital expenditures and 
reduced operational difficulties. 
It should be understood that the present invention is not limited to the 
precise structure of the illustrated embodiment. It is intended that the 
foregoing description of the presently preferred embodiments be regarded 
as an illustration rather than as a limitation of the present invention. 
It is the claims which follow, including all equivalents, which are 
intended to define the scope of this invention.