CA2105464A1 - Methods for the continuous deposition of semiconductor thin films - Google Patents

Methods for the continuous deposition of semiconductor thin films

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Publication number
CA2105464A1
CA2105464A1 CA002105464A CA2105464A CA2105464A1 CA 2105464 A1 CA2105464 A1 CA 2105464A1 CA 002105464 A CA002105464 A CA 002105464A CA 2105464 A CA2105464 A CA 2105464A CA 2105464 A1 CA2105464 A1 CA 2105464A1
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Canada
Prior art keywords
deposition
electrolyte
semiconductor
substrate
container
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Abandoned
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CA002105464A
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French (fr)
Inventor
Shaolin Shi
Cindy Xing Qiu
Ishiang Shih
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Individual
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Individual
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Priority to CA002105464A priority Critical patent/CA2105464A1/en
Publication of CA2105464A1 publication Critical patent/CA2105464A1/en
Abandoned legal-status Critical Current

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/18—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof
    • H01L31/1876—Particular processes or apparatus for batch treatment of the devices
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/0248—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies
    • H01L31/0256—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies characterised by the material
    • H01L31/0264—Inorganic materials
    • H01L31/032—Inorganic materials including, apart from doping materials or other impurities, only compounds not provided for in groups H01L31/0272 - H01L31/0312
    • H01L31/0322—Inorganic materials including, apart from doping materials or other impurities, only compounds not provided for in groups H01L31/0272 - H01L31/0312 comprising only AIBIIICVI chalcopyrite compounds, e.g. Cu In Se2, Cu Ga Se2, Cu In Ga Se2
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/0248—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies
    • H01L31/036—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies characterised by their crystalline structure or particular orientation of the crystalline planes
    • H01L31/0392—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies characterised by their crystalline structure or particular orientation of the crystalline planes including thin films deposited on metallic or insulating substrates ; characterised by specific substrate materials or substrate features or by the presence of intermediate layers, e.g. barrier layers, on the substrate
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/0248—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies
    • H01L31/036—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies characterised by their crystalline structure or particular orientation of the crystalline planes
    • H01L31/0392—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies characterised by their crystalline structure or particular orientation of the crystalline planes including thin films deposited on metallic or insulating substrates ; characterised by specific substrate materials or substrate features or by the presence of intermediate layers, e.g. barrier layers, on the substrate
    • H01L31/03925—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies characterised by their crystalline structure or particular orientation of the crystalline planes including thin films deposited on metallic or insulating substrates ; characterised by specific substrate materials or substrate features or by the presence of intermediate layers, e.g. barrier layers, on the substrate including AIIBVI compound materials, e.g. CdTe, CdS
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/18—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof
    • H01L31/1828—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof the active layers comprising only AIIBVI compounds, e.g. CdS, ZnS, CdTe
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/18—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof
    • H01L31/186—Particular post-treatment for the devices, e.g. annealing, impurity gettering, short-circuit elimination, recrystallisation
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/541—CuInSe2 material PV cells
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Abstract

METHODS FOR THE CONTINUOUS DEPOSITION
OF SEMICONDUCTOR THIN FILMS
ABSTRACT OF THE DISCLOSURE
The present invention describes methods for the continuous deposition of semiconductor thin films. A flexi-ble, conducting ribbon is partly immersed in an electrolyte containing ions or complexes of the elements to be deposit-ed. A voltage is applied between the ribbon and an anode, which is also immersed in the same electrolyte. The ribbon is fed so that the semiconductor thin film deposition is achieved in a continuous manner. Methods to achieve the desired compositional depth profile and uniform average elemental composition are described. The present methods may be advantageously used for low cost and large area semiconductor device fabrication.

Description

-~ ~1 a~6Ll BACKGRCll3ND OF THE INVENT10N :

1. Field of the Invention The present patent relates to methods to continuous-ly deposit large area thin films of semiconductors such as CuInSe2, CdTe and CdS and to continuously fabricate thin film photovoltaic cells.

:::
~ 2. Description ~f the Prior Art ~ .
The semiconductors CuInSe2, CdTe, CdS and ZnO are ideal materials for the fabrication of photovoltaic cells.
For the photovoltaic cells, thin film form semiconductors must be deposited on large area substrates. Large area thin film deposition using conventional vacuum methods, however, is costly. For large area applications, it is required that the films be prepared using lower cost methods than the vacuum methods currently emplsyed. Low cost thin film ,, ~
deposition methods currently used include screen printing, spray pyrolysis and electrodeposition. Of the three meth-ods, electrodeposition is the most appropriate, because electrodeposition consumes less energy and produces better ~:
films.

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In a pending patent application No. 2,063,679-4 "Methods for the fabrication of CuInSe2 thin films and solar cells" by I. Shih and C.X. Qiu (filed on November 11, 1991), methods for the electrodeposition of semiconduc-tor thin films including CuInSe2 thin films have been disclosed. In the methods described in the aforementioned patent application, a substrate and an anode are immersed in an electrolyte. A voltage is applied between the sub~
strate and the anode to deposit a semiconductor thin film on the substrate. The substrate is removed from the elec-trolyte and a new substrate is used for the sub~equent deposition. Although the methods described allow ons to deposit semiconductor thin films, they are not optimum for large area thin film deposition and cell fabrication. It is thus clear that there is a need to provide an improved electrodeposition method which can produce semiconductor thin films in a continuous manner.

For electronic device application, film composition-al depth profile and average composition must be controlled . For instance, in photovoltaic cells, the compositional depth profile of the absorber material (such as CuInSe2 and CdTe) must be maintained so that the first layar (bottom layer which is adjacent a conducting sub-s,J ~:
;1- strate) of semiconductor deposited is of high conductivity.

!
:i 2~ aa~4 The bottom layer of the deposited semiconductor must be highly conductive to make low resistance ohmic contact with the conducting substrate. The top layer is of relatively low conductivity, so that a good quality heterojunction can form when a window material such as CdS is deposited on the surface. The electrical conductivity of a compound semicon-ductor i6 often determined by the elemental composition.
For instance, high conductivity p-type CuInSe2 can be obtained when the In/Cu in the films is slightly greater than or less than 1. On the other hand, low conductivity p-type or nearly intrinsic CuInSe2 can be obtained when In/Cu is relatively greater than 1.

In the prior art electrodeposition methods for compound semiconductors, the required compositional depth profile for good quality heterojunctions was obtained by controlling the deposition potential (or voltage) during the film deposition. The variation of the potential or voltage during the deposition process limited deposition to stationary substrates. This is because when the substrate is fed into the electrolyte continuously at a given speed, the variation of deposition potential with time will result in a non uniform semiconductor thin film over the film area.

2hOa~61 During the electrodeposition, the ion concentration in the electrolyte decreases with time. If the same elec-trolyte is used for continuous deposition ~or compound semiconductor thin films, the average composition of sam-ples deposited at different times will vary. Therefore, the ion concentration must be kept constant during the entire deposition process i~ film composition is to be maintained. `~

From the above comment, it is clear that there is a need to provide improved deposition methods for compound semiconductor thin film and photovoltaic cell fabrication.

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OBJECTS AND STATEMENT OF THE PRESENT
INVEI ITION

One object of this invention is to provide an im-proved electrodeposition method for the continuous deposi-tion of thin films of semiconductors such as CulnSe2, CdTe and CdS.

Another object of this invention is to present a method to control the compositional depth profile of the deposited compound semiconductor films.

Yet another object of this invention is to provide a method to prepare compound semiconductor thin films with a constant average composition.

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BRIEF DESCRIPTION OF THE DRAWINGS -:

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Fig. 1 is a schematic diagram showing the electrodeposition apparatus for the continuous deposition of CuInSe2, CdTe, CdS, ZnSe and ZnO.

Fig. 2 is a schematic top view of the electrodeposition apparatus for the continuous deposition of semiconductor thin films.

Fig. 3 is a diagram showing an arranqement of the anode ,:
and the substrate to obtain a graded compositional depth profile.

Fig. 4 is a schematic diagram of the deposition system with apparatus to add sources of ions to the electrolyte and to circulate the electrolyte during the semiconductor thin film deposition. - -Fig. 5 is a diagram showing the apparatus used to rinse , .;
the substrate after the semiconductor thin film deposition.

Fig. 6 is a schematic diagram showing a unit for the continuous heat treatment of semiconductor thin films.

~;

; -~5~6ll Fig. 7 is a schematic top view of the heat kreatment unit showing the distribution of the gas inlets.

Fig. 8 is a schematic diagram showing the dip coating apparatus for the continuous deposition of CdSe, ZnS, ZnO
, and CdS.

I Fig. 9 is a schematic diagram of the semiconductor dip coating system with apparatus to add sources of ions to the electrolyte and to circulate the electrolyte during the semiconductor thin film deposition.

Fig. 10 is a schematic diagram of a system for the con-tinuous deposition and heat treatment of the first semicon-ductor and the deposition of the second semiconductor.

Fig. 11 is a schematic diagram of a system for the con~
tinuous deposition of the ohmic contact material, the continuous deposition and heat treatment of the first semiconductor, the deposition of the second semiconductor, .:
¦ the deposition of low resistivity window semiconductor and ~
.
~ the deposition of contact grids. ~

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6 il DESCRIPTION OF TIIE PREFERRED E~MBODINIENTS

The preferred system used in this invention for the deposition of semiconductor thin films is illustrated in Fig. 1. An electrolyte ~1) in a glass container (2) is used for the deposition. The electrolyte consists of ions or complexes of Cu, In and Se for CuInSe2 deposition, Cd and Te for CdTe deposition, Cd and S for the CdS deposition, Zn and Se for the ZnSe deposition, and Zn and S for ZnS depo-sition. A small amount of acid such as HN03, HCl, H2S04 or another ion source such as A12C13 is added to the electro-lyte to adjust the pH value and to increase the conductivi-ty of the solution. In plate or rod form, a conducting anode (3), such as Pt or C, is placed in the bottom of the deposition chamber. The anode is connected electrically through a Pt wire (4) to a dc power source (5). A part of the Pt wire (4) is inserted through an electrically insu-lating glass tube ~6~. The top portion of the glass tube " ~ ~
extends above the level (7) of the electrolyte. This glass tube arrangement is important to obtain a well defined ~ --electric line distribution between the anode (3) and the substrate (cathode) (8).
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The other terminal of the power source (5) is con-nected to the ribbon through another wire (9)~ The sub-strate is a flexible ribbon of either Mo, Mo-coated brass, Ni-coated brass or some other metals. The thickness of the ribbon substrate is about 100 micrometers (~m). Thus the ribbon is flexible enough to pass through the deposition system. The ribbon substrate is Eed between two cylindrical rollers (10, 11), which are attached to a support (12) mounted on a top plate (13). One of the rollers (11) is spring loaded (14) so that the ribbon substrate is pressed between the two rollers. The two rollers are composed of metallic material such as Ni-coated copper or brass to achieve low resistance electrical contact. The ribbon is inserted through an opening (15) in the top plate. When the system is activated, the substrate will glide through the electrolyte below and in contact with two glass rollers (16, 17). The rollers are mounted on the bottom of the top plate with two supports (18, 19). The supports are made of electrically insulating and acid resistant material such as ~ i:
glass or Teflon.

The ribbon substrate is then fed through a second ~ ~ opening (20) in the top plate and finally inserted between `~ two other cylindrical rollers (21, 22), which are fixed to ;

a support (23~ mounted on the top plate. One of the rollers 2la~

(22) is spring loaded (24) so that the ribbon substrate is pressed between the two rollers. The other roller (21) is connected through a worm gear (25) to a driving motor (26) powered by an energy source (27). The rotation of the motor is such that the roller (21) turns clockwise. The surfaces of the two cylindrical rollers (21, 22) are either corru-gated or coated with layers of plastic or rubber to in-crease the friction, which is required to feed the ribbon substrate through the unit at a constant speed. The depo-sition chamber (2) is placed on top of an electric heater (28~. The heater is powered by a second energy source (29) with a temperature controller. The temperature of the heater is monitored by a thermocouple (30), which is con-nected to the temperature controller to regulate the output power. The two electrically insulating rollers (16, 17) are arranged so that the rollers are partly or completely immersed in the electrolyte (1).

To initiate the film deposition, the electric power to the heater (28) is turned on. The electrolyte is heated to about 95C. The dc power source (5) connected to the ribbon substrate ~8) and the anode (3), is activated. The voltage is adjusted to a desired value. The power to the driving motor (26) is then switched on so that the roller (21) rotates at a constant speed, clockwise. The ribbon 1'' ~ 11 6 a~ :
substrate (8) is now fed from left to right through the electrolyte at this constant speed. The compound semicon~
ductor thin film is deposited continuously on the sub-strate.

Referring now to Fig. 2 for the top view of the deposition chamber and for the preferred arrangement o~ the anode (3) with respect to the ribbon substrate (83. During the deposition, the ribbon (8), driven by the roller (21), connected to the motor (26), travels from the left to the right side of the chamber at a constant speed of v. The elemental composition of an electrodeposited compound semiconductor thin film is determined by the potential of the cathode with respect to the electrolyte adjacent to it.
To obtain uniform semiconductor thin films (over the sur-face), the anode (3) is placed perpendicular to the direc-;~ .
tion of motion (31) of the ribbon. With the anode so ar-ranged, the ribbon substrate will have the same potential across its width ie. perpendicular to the traveling direc tion of the ribbon, at a given position along its length.
The average chemical composition of the deposited compound ~;
semiconductor over the entire film will be constant. ;

The length, L (32), of the ribbon substrate (8) ~`~
immersed in the electrolyte (1), is slightly greater than the separation between the two rollers (16, 17). The two 12 ~

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rollers are partly or completely submerged in the electro-lyte. When L is fixed, the feed speed of the ribbon sub-strate, v, is governed by the deposition rate, d (~m/minute), and the total thin film thickness, t (~m), required. For instance, for a length L=10 cm and a deposi-tion rate of 0.1 ~m/minute, the feed speed required to deposit a thin film having a thickness t = 1 ~m is v = 1 cm/minute. With this feed spe~d and this length, the total time that any part of the ribbon substrate is immersed in the electrolyte is 10 minutes.

In addition to the uniform average composition required to form electronic devices of uniform performance, composition variation across the depth of the film must be controlled in order to optimized the device performance.
For instance, the semiconductor first deposited (CuInSe2 or CdTe) and adjacent the conducting substrate must have a high carrier concentration (1017 - 1019 cm 3) and low resistivity so that low resistance ohmic contact can ke obtained. On the other hand, the semiconductor last depos-ited must have a relatively low carrier concentration (1015 - 1016 cm 3 ) and high resistivity so that good ~uality junctions can form when a second layer of semiconductor (such as CdS) is deposited on the first one.

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. O '`j ~1 6 ~1 During the electrodeposition of a compound semicon-ductor such as CuInSe2 or CdTe, the chemical composition of the deposited material is determined by the deposition potential or current density. For example in the deposition of CuInSe2, In/Cu increases as the deposition potential is increased. For a p-type CuInSe2 with a relatively large ~ In/Cu, the carrier concentration is small. The carrier ¦ concentration of a film with a relatively small In/Cu is ! large. For CdTe, the material is p-type with a large carri-er concentration when Cd/Te<1. When Cd/Te is close to 1, the material is weak p type with a low carrier concentra-tion. For Cd/Te>1, the material turns n-type. During the electrodeposition of CdTe from the same aqueous electro-lyte, value o~ Cd/Te increases as the deposition potential i~ is increased. Therefore, the required resistivity or con-centrational profile across the depth of the film can be obtained by controlling the deposition potential at differ-ent stages of the film deposition.

To illustrate how this is achieved with the continu-ous deposition method with a constant power source (5), part of the deposition apparatus depicted in Fig. 1 is also shown in Fig. 3. Preparation of CuInSe2 thin films is used as an example for the explanation of the process that follows. The ribbon substrate (8) is being fed from the left to the right into the electrolyte at a constant speed.
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The power source (5) supplies the current flowing between the ribbon (8) and the anode (3). Ions of Cu, In and Se are deposited on the ribbon to form a crystalline CuInSe2 thin film. The thickness of the deposited semiconductor thin film increases as the ribbon travels from the left to right through the electrolyte. In order to obtain the required compositional depth profile, the. anode (3) is located away from the area where the center part of the ribbon extends into the electrolyte (1). This Tneans the distance from the anode to the left-hand part of the ribbon, (33), is greater than the distance between the anode and the right-hand part, (34). Since the ribbon is a good conductor, during the electrodeposition the ribbon substrate represents an equi potential plane. The voltage drop along the path from the anode (3) to ribbon position (33~ will be greater than the drop along the path ~rom the anode (3) to ribbon posi-tion (34). This is due to the finite resistance of the electrolyte. Hence, the deposition potential of ribbon region (33) will be lower than that of ribbon region (34).
The CuInSe2 layer (35) deposited on the left-hand side of the ribbon substrate (36) will have a relatively small In/Cu value, the carrier concentration will be large and the resistivity will be low. Conversely, the deposition potential of ribbon region (34) will be higher than the potential of (33). The surface layer deposited on the 2~ 3~
right-hand side of the ribbon, (37), will have a relatively large In/Cu. In this layer (37), the carrier concentration will be low and the resistivity will be high.

In the actual design, the position of the anode (3) i5 selected so that the deposition potential dif~erence between the two sides of the chamber can give rise to the required profile concentration.

During the electrodeposition of compound semiconduc~
tor thin films, ion concentration decreases with time. In order to obtain thin films of uni~orm average composition, the ion concentration has to be constant. In the present invention, constant concentration is achieved using the improved duo chamber apparatus shown in Fig. 4. Here, in addition to the main deposition chamber (38) containing the electrolyte (39), there is a second container (40) contain-ing electrolyte (41) of the same composition for circula-tion. The second container is made o~ an electrically insulating and acid resistant material like glass. The electrolytes in the two containers are heated to the same temperature by two heaters (42, 43). Th~ two containers are :: ~
connected via a glass or teflon tubing (44, 45). A ~luid pump (46) is installed in the tubing (45) to drive the ;~

~ electrolyte from the container with circulating electrolyte ,~ (40) to the cleposition chamber (38).
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The circulating rate of the electrolyte from the container (40) to the deposition chamber (38) is determined by the ion consumption rate in the deposition chamber (38~.
When the electrolyte is circulated into the deposition chamber (38), the electrolyte level (47) rises. When the electrolyte level (47), in the deposition chamber (3~), reaches the exit level (48) which is connected to tubing (44), the excess electrolyte flows through the tubing (44) back to the container (40). The container (40) is located so that the container electrolyte level (49) is substan-tially below the level of electrolyte (47) in the deposi-tion chamber. This is to maintain the amount of electro-lyte (and thus the level o~ electrolyte) in the deposition chamber. The above described circulation of electrolyte from the container (40) to the deposition chamber (38) may reduce the rate of depletion of ions in the deposition chamber.

~- ~When prolonged el~ctrodeposition of compound semi-conductor thin films is carried out in the above described system, it is not sufficient to maintain constant ion concentration in the deposition chamber (38). To further minimize the decrease of ion concentration, sources of ions must be added to the container (40). A separate receptacle ~(51) containing the sources of ions (50) is used to replen-3:~ 17 21~ 6~
ish the deposition chamber. The amount of the source added is regulated by a flow control valve (52). A microcomputer (53) with an A/D and D/A interface card is used to measure the current supplied by the dc power source (54) and to measure the current flowing between the ribbon substrate (55) and the anode (56) during the deposition. The current is measured every 10 se~onds. The data is stored in the computer. The data is then averaged every minute and the value obtained is used to control the flow rate of the ion sources.

In this manner, the amount of compound semiconductor deposited on ribbon substrate is monitored so that the total amount of ions in the deposition system does not vary appreciably with time. A small amount of acid is also added to the electrolyte (50) to maintain the pH value of the , , ~
electrolyte. The relative amount of ions required for the source electrolyte (50) depends on the composition of the ` `~
deposited films desired. ;;

For proper agitation of the electrolyte, a glass -stirrer (57) is inserted into the electrolyte in the con-tainer (40). The stirrer is allowed to rotate at a constant rate of about 100 rpm. A temperature sensor is also insert- ;
ed into the electrolyte. The output of the temperature sensor is connected to a temperature controller and a power ;~

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supply unit which supplies power to a resistive heater ~43). The heater is used to heat the electrolyte to a specific temperature.

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When the deposition is complete, the substrate (55) with the deposited film emerges from the electrolyte (39) :1 .
j with a small amount of electrolyte adhering to the surface.

If this electrolyte is allowed to dry on the surface, ~- further unwanted semiconductor deposition could occur resulting in poor surface quality and increased interface 'l~: ~:
~ state density. To avoid the uncontrolled deposition, it is ,~ necessary to remove the electrolyte, immediately. The ~ preferred method to remove the remaining electrolyte from a 3 ~ .
film surface is illustrated in Fig. 5. When the ribbon substrate with the deposited film (58) emerges from the electrolyte (59), de-ionized water (60) is sprayed from a nozzle (61) onto the film surface. To prevent the sprayed water from getting into the electrolyte, a cylindrical roller (62) is installed at a position below the nozzle and in contact with the film. This roller is made of acid resistant soft rubber to minimize damage to the film. The used water (63) is trapped by a collector (64). Water leaves the collector via a drain pipe (65).

Electrodeposited compound semiconductor thin films usually require heat treatment to improve the film crystal-2 1 0 ~ ~ 6 4 line and electronic properties. For instance, the crystal-line quality of an electrodeposited CuInSe2 thin film can be significantly improved after a heat treatment in vacuum or Ar at 300-450C for a period of between 10-30 minutes.
The minority carrier lifetime, which affects junction properties, can also be increased by the heat treatment.
Therefore, there is a need to heat-treat the deposited compound semiconductor thin films before final device fabrication. In this invention, the continuous heat treat-. ..
ment is performed in the system shown in Fig. 6.

In Fig. 6, the substrate with the semiconductor thin film (66) is guided by two rollers (67, 68). The rollers (67, 68) rotate at a constant speed in opposite directions so that the thin film is fed into heat treatment chamber (69) at a constant speed of v (cm/minute). At the other end of the system, the thin film is guided by another two rollers (70, 71). The chamber (69) is made of material such as stainless steel, quartz or glass. Two gas inlets (72, 73), on top and underneath, are provided so that gas (such as Ar) can be supplied to the chamber. The injected gas flows along the thin film surface both to the right and to the left and exits from the tapered chamber ends (74, 75).
The purpose of the tapered ends is to minimize flow of air from the environment into the chamber. The treatment cham-1 ' ~ ..
: .

2~ 3~ber is heated by an electric heater (76), with thermocou-ples (77) to monitor and control the temperature. The gases are supplied to the chamber from several inlets (72,73 see Fig. 7) distributed evenly across the chamber.
In this manner, the injected gas flows uniformly through the chamber. Fig. 7 shows a top view of the chamber.

In order to obtain ths desired heat treatment re-sults, the chamber is divided into three zones (78, 79, 80 see Fig. 6). In zone (78) there is a positive temperature gradient so that temperature of the substrate (66) rises gradually as the substrate enters the central zone of the furnace (80). In the central zone (80), the temperature is either constant or graded. In the zone (79), there is a negative temperature gradient so that the temperature of the substrate decreases gradually as it leaves the central zone of the furnace. The lengths of the three zones are determined by the feed speed of the substrate and the required treatment time. For instance, if a substrate with the thin film glides through the system at a rate of 1 cm/minute, the temperature increase rate can be maintained at 50C/minute by adjusting the temperature gradient to 50C/cm in the zone (78~ of the chamber. Similarly, film temperature decrease rats can be maintained at 50Cjminute by adjusting the temperature gradient to 50C/cm in the trail end (79) of ths chamber. In the central zone (80), :: `
~ 21 --' 21~g~

i the temperature is either constant or graded, depending on the film quality requirements. For a length of 10 cm for the zone (80), any part of the sample will be treated for 10 minutes within this zone.

In order to form a good quality junction, a second layer of high resistivity semiconductor, such as CdS, must be deposited on either CuIn5e2 or CdTe. The thickness of CdS film required for good quality heterojunctions is between 100 and 500 A. Good quality heterojunctions can be ,~ obtained by dip-coating or electrodepositing the high resistivity CdS on p-type CuInSe2 or CdTe. Conventional ~ dipping of CdS semiconductor involves the preparation of a ¦~ pH adjusted dipping solution containing ions or complexes of Cd and S. The substrate with film is dipped into the solution and CdS deposits. The dipping is usually carried out at a temperature between 45 and 70 C ~or a period of 5 to 30 minutes. After the deposition, the substrate with the deposited thin films is removed from the solution and ; rinsed, to clean the surface. The solution, depleted of the ions or complexes required for the deposition, is discard-ed.

~::
Fig. 8 is an illustration of the preferred unit for continuously coating a thin layer of a high resistivity ~` semiconductor such as CdS on a substrate with a low resis-':

2 ~ 0 3 ~ 6 ~

tivity thin film such as CuInSe2. (The unit used for the thin film CdS deposition is similar to th~ one used for the electrodeposition of CuInSe2.) A dipping solution (81) containing ions and complexes of Cd and 5 is prepared in a glass container (82). A small amount of base such as NH40H
is also added to the electrolyte to adjust the pH value of the solution. The substrate (83) is a ~lexible ribbon of metal such as Mo, Mo-coated brass or Ni-coated brass which has been coated with a layer of semiconductor such as CuInSe2, CdTe, ZnS or ZnO. The thickness of the ribbon substrate is about 100 micrometers ~m). The ribbon, which is thin so that it is flexible enough to be pass through the deposition system is fed between two cylindrical roll-ers (84, 85) which are mounted to a support (86), which is further mounted on a top plate (87). One of the rollers (85) is spring loaded (88) so that the ribbon substrate is pressed between the two rollers. The two rollers are made of metal or plastic materials. The ribbon is inserted through an opening (89) in the top plate.

When the system is activated, the substrate will glide through the electrolyte below (81) and in contact with two glass rollers (90, 91). The rollers are mounted on the bottom of the top plate with two supports (92, ~3). The supports are made of electrically insulating and acid/base 2 ~
resistant material such as glass or Teflon, The ribbon substrate is ~ed through a s~cond opening (94) in the top plate and finally inserted between two other cylindrical rollers (95, 96) fixed to a support (97~. One of the rollers (96) is spring loadecl (98~ so that the ribbon substrate is pressed between the two rollers. The other roller (95) is connected through a worm gear (99) to a driving motor (100), powered by an energy source (101).
The motor (100) turns so that the roller (95) rotates clockwise. The surfaces of the two cylindrical rollers (95, 96) are either corrugated or coated with layers of plastic or rubber to increase the friction, which is required to feed the ribbon substrate through the unit, at a constant speed. The deposition chamber (82) is placed on top of an electric heater (102). The heater is powered by a second energy source. The temperature is controlled by a tempera-ture controller (103). The temperature of the heater is monitored by a thermocouple (104), which is connected to the temperature controller to regulate the output power.
The two electrically insulating rollers (90, 91) are ar-ranged so that the rollers are partly or completely im-mersed in the electrolyte (81).

To initiate the film deposition, the power to the heater (102) is turned on. The electrolyte is heated to about 60C. Polycrystalline CdS starts to deposit on the i ~;,' ~ .

2~ J~4 two surfaces of the ribbon substrate. The power to the driving motor (loo) is now switched on so that the roller (95) rotat~s at a constant speed, clockwise. The ribbon substrate (83) is fed from left to right through the unit and the compound semiconductor thin film is deposited continuously on the substrate.

In the actual design, the distance between the two rollers (90,91) is determined by the ribbon substrate feed rate, v (cm/minute), the deposition rate and the required film thickness. To deposit a film with a thickness of 300 A
with a ribbon feed rate of 1 cm/minute and a deposition rate of 30 A/minute, a distance between the two rollers (90, 91) of about 10 cm, is required. This thickness of CdS
may be sufficient to obtain good heterojunctions with semiconductors such as CuInSe2 and CdTe.

After the ribbon substrate emerges from the electro-lyte, the electrolyte remaining on the substrate surface must be removed. This is accomplished by using the water rinsing apparatus shown in Fig. 5.

During the deposition of compound semiconductor thin films such as CdS, ion concentration decreases with time. This ion concentration decrease cannot be accounted for by the thin ~ilms. The decrease occurs because ions or !~ I

2~5~6~
complexes of Cd and S react in the electrolyte to form CdS
particles and even deposit on the walls of the deposition chamber (82). In order to obtain thin films of uniform composition, ion concentration must be constant. In the present invention, constant ion concentration is achieved by circulating sources of ions in and out of the deposition chamber. The improved duo chamber apparatus with a flow controller shown in Fig. 9 is used. Here, in addition to the main deposition chamber (105) containing the electro-lyte (106), there is a second container (107) containing electrolyte (107-1) of the same composition for circula-tion. The second container is made of an electrically insulating and acid resistant material like glass. The electrolyte in the main deposition chamber (105) is heated to a predetermined temperature by a h~ater (108), while the second container ~107) is cooled by a cooler (109) in order to minimize unwanted reaction between ions and complexes. A
fluid pump (110) is installed in the tubing (111~ to drive the electrolyte from the container for circulating electro-lyte (107) to the deposition chamber (105).

~; ~
The circulating rate of the electrolyte from the container (107) to the deposition chamber (105) is deter-mined by the ion consumption rate in the deposition cham-ber. When the electrolyte is circulated into the deposition ~;~ chamber (105), the electrolyte level (112) rises. When the ` ::

2~ .3~

i level of electrolyte (112) reaches the exit level (113), . the excess electrolyte will begin to flow out of the cham-- ber. A level detector (114) is connected to the container for circulating electrolyte (107). This level detector sends a signal to the PC (115) when the level of electro-J lyte in the container for circulating electrolyte is below a pre-determined level. The PC will then turn on the two valves (116,117) of the two fluid pumps (116, 117~ respec-tively, connected to two other fluid containers (118, 119).
A solution containing ions and complexes of Cd and S (118-1) is stored in one container (118) whereas diluted NH40H
~ (119-1) is stored in the other container (119). The rates 3~ ~ of flow of the two fluid pumps are selected so that the correct proportions of ions for the deposition of good quality CdS will be available. As the level of electrolyte in the container (107~ rises and exceeds a pre-determined value, the level detector (114) will send another signal to the PC to terminate the supply of solutions.

~; The temperature of the two containers (118, 119) is kept at a value substantially below room value but not ~ , below 0C to prevent reaction of ions and complexes and vaporization of NH40H in the containers (118, 119), respec-tively. The purpose of storing the two solutions in two separate containers (118,119) is to minimize the reaction ~:
~: ~ 27 ~:
r,~

¢j~ :
~.~

- 2 10~ 3~
of ions and complexes in the solution, which can readily take place even at room temperature, especially when NH40H
is present. To properly agitate the electrolyte, a glass stirrer (120) is inserted in the container for circulating electrolyte (107). The stirrer is allowed to rotate at a constant rate of about 100 rpm. Circulating the electro-lyte from the container ~107) to the deposition chamber (105) will allow one to maintain an essentially constant ~ ion concentration in the deposition container (105) and i~ will allow continuous deposition of the film on the sub-~ strate (83).

i Fabrication of a photovoltaic cell includes the following steps: [1] deposition of the first semiconductor layer on a conducting substrate, [2] heat treatment of the first semiconductor layer to improve crystalline and elec-tronic quality, [3] deposition of a layer of the second semiconductor to form a heterojunction, [4] deposition of a i metal grid for contacts and [5] deposition of a layer of anti reflective coating. For mass production of large area photovoltaic cells, it is preferable to carry out all the above steps continuously. This is achieved partly using the ~ continuous deposition system depicted in Fig. 10. This 3~ system consists of a unit for the deposition of the first semiconductor layer (121), a heat treatment unit for the heat treatment of the first semiconductor layer (122) and a ~ ,:

... . .

:--' 2~

unit for the continuous deposition o~ the second semicon~
ductor layer (123).

Pictorials of the unit for the deposition of the first semiconductor layer (121) are to be found in Figs. 1, 2, 3, 4 and 5. The unit for the continuous heat treatment of the first deposited semiconductor layer his been pre-sented in Fig. 6. The deposition system for the second semiconductor layer could be one similar to the system used to deposit the first semiconductor layer (121) or it could be the one described in Figs. 8 and 9. The exit for the deposition system (121) is aligned with the entrance of the heat treatment unit (122). The deposition unit for the .
first semiconductor layer (121) and the heat treatment unit (122) are connected by a channel (124). The exit for the heat treatment unit (122) is also aligned with the entrance of the deposition unit for the second semiconductor layer (123). The heat treatment unit (122) and the deposition unit for the second semiconductor layer (123) are connected by a channel (125). It is worthwhile to mention that gas such as Ar will be supplied from the inlet (126) of the heat treatment unit (122) to provide an atmosphere appro-priate for obtaining a good quality semiconductor layer.

The conducting ribbon substrate (127) is preferably wound around a roller (128). A cross-sectional view of a 29 ' 2 ~
, section of the ribbon substrate is indicated by (129). To start the deposition, the electrolyte required for the deposition of the first semiconductor is prepared and poured into the deposition chamber and into the container for circulation of electrolyte in the deposition unit (121). Gas such as Ar is allowed to flow from the inlets into the heat treatment unit (122). The chemical solutions required for the deposition of the second semiconductor are prepared and poured into the containers for the deposition unit (123). The power supplies of the two deposition units (121, 123) and of the heat treatment unit (122) are turned on. When the temperatures in these three units reach'preset values, the ribbon substrate is fed into the deposition unit (121). The substrate passes through the channel (124) connecting the deposition unit (121) and the heat treat,-ment unit (122). The ribbon then passes through another channel (125) to the second deposition unit (123). The substrate emerges from the exit of the second deposition unit (123) and is fastened to the second roller (130). The roller (130) rotates clockwise at a rate equal to the rate of the driving motors in the deposition units so that the ~. ~ ,. .
ribbon :travels through the system at a constant rate. ,':

''` To obtain good quality thin films, the microprocès~
sors for the two deposition unlts and the heat treatment ' ' ;:

~ .

2 ~ 6 ;^~

unit are activated so that the electrolyte in the first deposition unit (121) circulates between the deposition chamber and container for circulation of the electrolyte.
The solution in the second deposition unit is also circu-lated or replenished in order to maintain constant ion or complex concentration. The cross sectional views of the ribbon substrate a~ter different stages (129,131,132~ give some idea of the function of each of the units in the system. The ribbon substrate (129) could be an Mo sheet, Mo-coated Al, Ni-coated Al, Mo-coated brass, Ni-coated brass or some other suitable conducting material. A~ter the ribbon substrate has passed through the first deposition unit (121), a layer of the first semiconductor (131) will have been coated on the surface. How thick the layer will be will depend on the deposition rate, the ribbon feed speed and the length of the ribbon substrate immersed in the electrolyte. After the ribbon has passed through the heat treatment unit (122), the crystalline and electronic properties of the film will have improved.

After the ribbon substrate has passed through the second deposition unit (123), a layer of the second semi-conductor (132) will have been deposited on the first semiconductor layer (131). The thickness of the s~cond semiconductor layer will also depend on the deposition rate, the ribhon substrate feed rate and the length of thei , ~ ' ' ! 31 ~' ~93~6~

ribbon immersed in the solution of the second deposition unit. The ribbon substrate is then wound around the second roller (130). To prevent scratching of the deposited film, a thin layer of soft fiber material (such as soft lintless tissue) (133) is wound around the roller. The substrate with the deposited films is now ready for subsequent elec-tronic device fabrication processes. These processes in-clude the deposition of a low resistance window layer, the deposition of metal grids for counter electrodes and the ~¦

deposition of anti-reflective coating.
' .' ,~ To reduce photovoltaic cell production cost, it is advantageous to incorporate a ribbon substrate preparation unit into the fabrication system. It is also advantageous to incorporate a deposition unit for the continuous deposi-~: .
tion of the low resistivity window layer and to incorporate a unit that deposits metal ~rids on top of the low resis-tivity window layer for counter electrodes.

`~ The continuous fabrication of photovoltaic cells is , : :
~ achieved using the system depicted in Fig. 11. This system j~ consists of a unit for the preparation of ribbon substrate (134), a unit for the deposition of the first semiconductor layer ~135), a heat treatment unit for the heat treatment of the first semiconductor thin film (136), a unit for the 3~ continuous deposition of the second semiconductor layer :~

2 ~ 6 ~

(137), a unit for the deposition of low resistivity window semiconductor (138) and a unit for the deposition of the grid contacts (139). The unit (134) for the continuous deposition of ohmic contact layer is similar to the one described in Figs. 1, 2, 3, 4, and 5. The ohmic contact layer could be a metal selectecl from a group of Ni, Mo or Cu. The unit for the continuous deposition of the first semiconductor (135) has been described in Figs. 1, 2, 3 ,4 and 5. Details of the unit for the deposition of the second semiconductor layer have been shown in Figs. 8 and 9. The unit for the continuous heat treatment of the ~irst semi-conductor layer deposited has been presented in Fig. 6. The deposition system for the third semiconductor layer could be similar to the one for the first semiconductor layer (135) or it could be the one depicted in Fig. 9. The exit of the unit for the preparation of ribbon substrate (134) is aligned with the entrance o~ the first semiconductor deposition unit (135). The two units are connected by a channel (140). The exit of the deposition unit (135) is aligned with the entrance of the heat treatment unit (136).
The two units (135, 136) are connected by a channel (141).
The exit of the heat treatment unit (136) is also aligned w,ith the entrance of the second semiconductor deposition unit (137). The two units (136, 137) are connected by a channel (142). The exit of the second semiconductor depo-r-. ~1 ~3~ fi L~
., , sition unit (137) is aligned with the entrance of the low resistivity window semiconductor deposition unit (138). The two units (137, 138) are connected by a channel (143).
Finally, the exit of the low resistivity window deposition unit (138) is aligned with the entrance of the deposition unit for the contacts (139). The two units (138, 139) are connected by a channel (144). It is worthwhile to mention again that gas such as Ar will be supplied to the inlets (145) of the heat treatment unit (136) to provide an appro-priate atmosphere for obtaining good quality semiconductor.

~':
The conducting ribbon substrate (146) is woundaround a roller (147), preferably. A cross-section of the ribbon substrate is indicated by (148). To start the depo-sition, the alectrolyte required for the deposition of the ohmic contact layer of the ribbon substrate is prepared and poured into the container of the deposition unit (134). The electrolyte required for the first semiconductor deposition is prepared and poured into the deposition chamber and the container for circulating the electrolyte in the deposition unit (135)o Gas such as Ar is allowed to flow from the inlet~ into the heat treatment unit (136). The chemical solutions required for the second semiconductor deposition is prepared and poured into the deposition unit containers (137). The electrolyte required ~or the low resistivity '~

-- 2~ ~5~6'1 window layer deposition is also prepared and poured into the deposition chamber and container ~'or circulation of electrolyte in unit (138). Finally, the electrolyte for the grid contact deposition is prepared and poured into the depo6ition chamber and container for circulation of elec-trolyte ~139).

.
The power supplies of the fivs deposition units (134, 135, 137, 138, 139) and the heat treatment unit (136) are turned on. When the temperatures in the six units reach the preset values, the ribbon substrate is fed into the deposition unit (134), through the channel (140) into the deposition unit (135). The ribbon is then fed into heat treatm~nt unit (136) and through another channel (142) to the third deposition unit (137). The ribbon substrate is fed in a similar way through the deposition unit for the window layer (138) and the grid contacts (139). The sub-strate emerges from the grid contact deposition unit (139) exit and is fastened to the second roller (154). The roller (154) rotates clockwise at a rate equal to the rate of the driving motors in the deposition units so that the ribbon travels through the system at a constant rate. To obtain 3 ~ :.
.!'; ~ good quality thin films, the microprocessors for the five ;
deposition units and the heat treatment unit are activated ~ ~ ~ so that the electrolytes in the deposition units (134, 135, ij~ 137, 138, 139) circulate between the deposition chamber and ii,, ':

7~
":

o ~

2 ~ a ~ L~

the container for circulation of electrolyte. As the sub-strate passes through each step of the procedure, the cross sections of the ribbon substrate resemble 149-153. The ribbon substrate ~148) could be a brass sheet, an Al sheet or a sheet of some other low cost conducting material.

After the ribbon substrate has passed through the first deposition unit (134), a layer of metal such as Ni or Mo (149), which can make low resistance contact to the first semiconductor is deposited. After the ribbon has passed through the deposition unit (135), a layer of the first semiconductor (150) is coated on the surface. The thickness of the layex is determined by the deposition rate, the ribbon feed speed, and the length of the ribbon substrate immersed in the electrolyte. After the ribbon has passed through the heat treatment unit (136~, the crystal-line and electronic properties are improved. After the ribbon substrate has passed through the third deposition j~
unit (137), a layer of the second semiconductor ~lS1) is deposited on the first semiconductor layer (150). The thickness of the second semiconductor layer is determined by the deposition rate, the ribbon substrate feed rate and the length the ribbon immersed in the solution of the third deposition unit.

~; 36 `1 i::

21~ 6~

A~ter the ribbon has passed through the fourth deposition unit (138), a layer o~ low resistivity window material (152) is coated over the high resistivity CdSo Finally, a~ter the ribbon substrate has passed through the fifth deposition unit (139), a layer of grid contacts (153) is deposited. The ribbon substrate with deposited layers is wound around the second roller (154). In order to minimize back sur~ace scratching by the roller, a thin layer of soft ; fiber material (such a~ soft lintless tissue), (155), is wound around the roller. The substrate with the deposited films is now ready for the final processes to form photo~
voltaic cell arrays. The final processes include applying ~;~ anti reflection layers, separation of cells, attaching ~; contacts, mounting on a support and ~orming protecting '~ structure.

!~ Before the grid contacts can be deposited, most of the window layer surface, (152), must be covered with a layer of photoresist. The whole window layer surface need ~ not be covered, since only a part of the window layer j~ surface will be covered by the ohmic contact material, which is opaque. The main part of the window layer should ~j~ not be covered so that photons in the incident light can ~ penetrate the window layer and reach the semiconductors. An !j on-line patterning unit (156), based on the conventional ~ 37 --` 2 ~ 6 ~

photolithography process used in microelectronic indus-tries, is used to deposit the photoresist.

The patterning equipment includes a photoresist spray unit, a photoresist ba}cing unit, an ultraviolet exposure unit and a photoresist developing unit. The spray unit is to spray a layer of photoresist (thickness about 2 micrometers) over the window layer surface. The baking unit is to harden the sprayed photoresist (typical temperature required about 80C). The ultraviolet exposure unit is to expose the sprayed photoresist selectively under ultravio-:
let light (typical exposure time about 20 seconds). The developing unit is to develop the exposed photoresist and to expose the window regions where grid contacts (153~ are to be deposited.

To obtain well defined patterns on the window sur-face, the apparatus required to accomplish the ultraviolet exposure should move at the same speed as the ribbon sub-i ~
~ strate. During the operation, a photomask, containing the 1:'~:`:
required grid patterns, is held against the desired part ofthe thin film substrates. The ultraviolet light source is then turned on to expose the photoresist. After a given period of time, the light is turned off. During the proc-ess, the photomask, the substrate holder and the ultravio-let light source, all move at the same speed and in the `~

..-, i: ~

2 ~ ~ ~3 ~

same direction as ths ribbon substrate. After the exposure, the photomask, the sample holder and the ultraviolet light source are returned to their original positions. The ribbon substrate with the exposed photoresist is then ~ed into a developing unit which contains photoresist developing solution. Once the development is finished, the ribbon substrate is rinsed and dried. The ribbon substrate with the semiconductor thin films and the patterned photoresist is now ready to be fed into the grid contact deposition unit (139) to deposit the grid contacts.
~
- In the following some examples for the continuous deposition and continuous heat treatment of semiconductor thin films are given, which are illustrative of the em-ployed techniques, but non limitative as far as the variety of the processes and products is concerned.
~ ' . '' :: .
~ ~ Example 1 Continuous deposition of CuInSe2 films . ~
One example of the continuous deposition of the ternary semiconductor CuInSe2 using the method described in this patent is given below. An electrolyte (total volume 12 liters) containing ions and complexes of Cu, In and Se is prepared. The electrolyte contains sources of ions with the following concentrations in de-ionized water: 10 3-10 2 M

2 ~ 4 CuC12, 10 3-10 2 M In2(SO4)3, 10 3-10 2 M SeO2. The pH
value of the electrolyte is adjusted by adding 5xlO 2-5xlO 1 M HNO3. After a thorough mixing, part of the electrolyte is poured into a glass deposition chamber with a diameter of 15 cm, a height of 12 cm and a capacity of about 2.1 liters. ~he other part of the electrolyte is poured into the container for circulation with a capacity of about 20 liters. Another electrolyte for replenishing is also prepared with the following concentrations (volume 10 liters): 1.95xlO 2 M CuC12, 1.025xlO 2 M In2(SO4~3, 4xlO 2 M SeO2 and 0.1 M HNO3. The atomic ratio of Cu, In and Se in the electrolyte is determined according to the required atomic ratio in the deposited CuInSe2 films. The electro-lyte is poured into a receptacle with an ~lectronically controlled valve. A Mo sheet substrate with a thickness of 100 ~m, a width of 3 cm and 400 cm long is inserted through the driving mechanism into the electrolyte in the deposi-tion container. The length of the substrate immersed in the electrolyte is 10 cm. A Pt anodP in a form of wire is located on the bottom of the deposition chamber with the long axis of the Pt anode perpendicular to the direction of feeding of the substrate. The position of the Pt anode is 4 I ~ ~
, cm away fr,om the projection of the center of the substrate immersed in the electrolyte. ~i , 2lo~fi~
Electric power to the heaters for the deposition container and the container for circulation is turned on.
, When the temperatures of the electrolytes in the two con-tainers reach 95C, the dc power source connecting to the Pt anode and the Mo sheet substrate is turned on and the i voltage adjusted to about 2.4 volts. Ions of Cu, In and Se ;~ start to deposit on the Mo sheet substrate to form a poly-I crystalline CuInSe2 thin film with a deposition rate of about 0.12 ~m/minute. The other power source to the driving motor is turned on so that the Mo sheet substrate is driven through the electrolyte at a speed of 1 cm/minute. The motor connected to the stirrer in the container for circu-lation is turned on and the rotating speed adjusted to 100 rpm for stirring. The fluid pump which circulates the electrolyte from the container for circulation to the deposition container is also turned on and the flow rate is adjusted to about 200 CC/minute. The microprocessor which controls the rate of flow of the replenishing electrolyte from the receptacle and senses the current flowing through the Pt anode and Mo sheet substrate is activated. The amount of charges flowing from the anode to cathode is calculated once a minute. The calculated charge amount is used by the microprocessor to control the electronic valve to regulate the rate of flow of the electrolyte from recep-tacle to the container for circulation. The average flow 21 Oa~64 rate from the receptacle to the container for circulation is about 0.7 CCtminute under the above deposition condi-tions. After the deposition, the Mo sheet substrate with the CuInSe2 emerges from the electrolyte. The surface is rinsed immediately by spraying de-ionized water. The total time to deposit the CuInSe2 film on the Mo sheet substrate with a length of 400 cm is about 6 hours. The deposited CuInSe2 film has a thickness of 1.2 ~m with a (112) pre-ferred plane from X-ray diffraction analysis. This plane will produce minimum interface state density when (001) oriented ~CdS) is deposited on it to form a heterojunction.
The film shows p-type conduction with an average composi- -~
tion (from electron probe microanalysis) of: Cu 24.0 at.~, In 24.5 at.%, Se 50.5 at.%. Ratio of In/Cu for the last deposited layer ~top layer) is 1.1 and is 1.0 for the first deposited layer (bottom layer) from secondary ion mass spectroscopy.

Example 2 Continuous heat treatment of CuInSe2 films ~ ~ -:

~.
Electrodeposited compound semiconductor thin films ~-usually require heat treatment to improve the film crystal~
line and electronic properties. The Mo sheet substrate with -~
the deposited CuInSe2 thin film (thickness about 1.2 ~m~ is i ''''.;

~- 210a46Ll inserted through the rollers into a heat treatment furnace.
The Mo sheet substrate has a thickness of 100 ~m, a width - -of 3 cm and 400 cm long. The regulator for Ar gas is turned on and the flow rate is adjusted to 300 CCtminute.
At least 10 minutes is allowed in order to minimize residu al gases in the heat treatment chamber. After this, power source of the furnace is turned on so that the central zone (length 10 cm) reaches 380C. The temp~rature gradients in the two outer zones are 40/cm (zone length 9 cm). After the temperature is stabilized, the motor for ~eeding the substrate is turned on. The Mo sheet substrate is fed through the furnace at a rate of 1 cm/minute. The effective treatment time of the CuInSe2 film is about 18 minutes. ~-After the heat treatment, the intensity of X-ray diffrac ~-~ tion peaks (for example (112) peak) increases to about 4 - -¦`~ times before the treatment. The conduction type is p-type j with a carrier concentration of about 1016 cm 3.

~ ~; Example 3 Continuous dip coating of CdS films ~ ~

An electrolyte (total volume 6 liters~ containing ~:
ions and complexes of Cd and S is prepared. ~he electrolyte contains sources of ions with the following concentrations in de-ionized water: 2xlO 3 M CdC12, 2xlO 2 M NH4Cl, 2xlO 2 ~i, 21 ~3 ~

M NH2CSNH2. The pH value of the electrolyte is adjusted by adding 150 CC NH40H. After a thorough mixing, part of the electrolyte is poured into a glass deposition chamber with a diameter of 15 cm, a height of 6 cm and a capacity of about 1 liters. The other part of the electrolyte is poured into the container for circulation with a capacity of about 10 liters. Another two solutions (solutions A and B) fo~
replenishing are also prepared with the following concen-trations: solution A (20 litters) - 2xlO 3 M CdCl2, 2xlO 2 M NH4Cl, 2xlO 2 M NH2CSNH2, solution B (1 litter) - 500 CC
NH40H in 500 CC de-ionized water. The solution A is poured into the first receptacle with an electronically controlled valve and the solution B is poured into the second recepta-cle also with another electronically controlled valve. A Mo sheet substrate with a layer of heat treated CuInSe2 film (thickness 1.2 ~m) is inserted through the driving mecha-nism into the electrolyte in the deposition container. The Mo sheet substrate has a thickness of 100 ~m, a width of 3 cm and 400 cm long The length of the substrate immersing in the electrolyte is 10 cm.

Electric power to the heater for the deposition container and for the cooler to the container for circula-tion is turned on. When the temperatures of the electrolyte in the deposition container reaches 70C, ions of Cd and S

I

2 1 0 5 ~
start to deposit on the CuInSe2 surface to form a thin layer of CdS. The deposition rate is about 30 A/minute. The temperature of the electrolyte in the container for circu-lation is controlled to about 10C to avoid unwanted reaction of the ions. The other power source to the driving motor is turned so that the Mo sheet substrate with the CuInSe2 film is fed through the electrolyte at a speed of 1 cm/minute. The motor connected to the stirrer in the container for circulation is turned on and the rotating speed adjusted to 100 rpm for stirring. The fluid pump which circulates the electrolyte from the container for circulation to the deposition container is also turned on and the electrolyte flow rate is adjusted to about 50 CC/minute. The microprocessor senses the level of the solution in the container for circulation and turned on the electronic valves in the two receptacles for solutions A
and B. The rate of flow for the solution A is 400 CC/minute and is 12.5 CC/minute for the solution B. When the solution level in the container for circulation exceeds a predeter-mined value, the microprocessor senses the rise of the level and turned off both of the electronic valves.

,~ .
After the deposition, the Mo sheet substrate with the CuIn5e2 and the dip coated CdS emerges from the elec-- trolyte. The surface is rinsed immediately by spraying de-ionized water. The total time to deposit the CdS film on 2~5~

the Mo sheet substrate with a length o~ 400 cm is about 6 hours. The deposited CdS film has a thickness of 300 A with an electrical resistivity of about 105 ohm-cm.

1: ` .:,.
~; ';.

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Claims (41)

1. A method for the continuous electrodeposition of semi-conductor thin films on a substrate comprising:

(A) introducing an electrolyte containing ion sources for the deposition of said semiconductor in the deposition container, (B) introducing an electrolyte containing ions sources for the deposition of said semiconductor in the container for circulation of electrolyte, (C) inserting an anode in the electrolyte contained in said deposition container and adjusting position of said anode, (D) inserting part of the said substrate in the electrolyte contained in the said deposition container, (E) controlling temperature of said electrolyte in said deposition container and temperature of said electro-lyte in said container for circulation of electrolyte, (F) feeding said substrate at a constant speed in one direction through the electrolyte in the said deposi-tion container, (G) circulating an electrical current between said anode and said substrate to deposit a layer of said semi-conductor on said substrate.
2. A continuous semiconductor thin film deposition method as in Claim 1, wherein concentration of said electrolyte is regulated according to average composition of said semicon-ductor required to form an electronic device.
3. A continuous semiconductor thin film deposition method as in Claim 1, wherein part of said anode is shielded in an electrically insulating and acid resistant material. Long axis of said anode is perpendicular to said direction of feeding of said substrate, said long axis of anode is parallel to a substrate section perpendicular to said direction.
4. A continuous semiconductor thin film deposition method as in Claim 1, wherein at least part of the said substrate immersed in said electrolyte is parallel to level of said electrolyte.
5. A continuous semiconductor thin film deposition method as in Claim 1, wherein positive terminal of said electrical source is connected to said anode and negative terminal is connected to said substrate to form a closed electrical loop.
6. A continuous semiconductor thin film deposition method as in Claim 1, further comprising a step of disseminating electrolyte between said deposition container and said container for circulation of electrolyte at a constant rate. Said rate of circulation is selected so that concen-tration of said electrolyte in deposition container is essentially constant during deposition of said semiconduc-tor film.
7. A continuous semiconductor thin film deposition method as in Claims 1 and 6, further comprising a step of stirring electrolyte in said deposition container to obtain uniform ion distribution.
8. A continuous semiconductor thin film deposition method as in Claims 1 and 6, further comprising a step of stirring electrolyte in said container for circulation of electro-lyte to obtain uniform ion distribution.
9. A continuous semiconductor thin film deposition method as in Claims 1 and 6, further comprising a step of adding sources of ions at a rate to said container for circulation of electrolyte to replenish ions in said electrolyte. Said rate of adding source of ions is determined by the consump-tion rate of ions in said electrolyte. Said consumption rate of ions is selected from flowing rate of charges from said anode to said substrate.
10. A continuous semiconductor thin film deposition method as in Claims 1 and 6, wherein position of said anode is selected so that deposition potential in one end of said substrate immersed in said electrolyte is different from the other end. Said deposition potential results in a first deposited material with one composition and a last deposit-ed material with another composition.
11. A continuous semiconductor thin film deposition method as in Claims 1 and 6, further comprising a step of rinsing surface of said semiconductor emerging from said electrolyte to minimize uncontrolled deposition.
12. A continuous semiconductor thin film deposition method as in Claim 1, further comprising a step of adding dopant.
Said resistivity of said semiconductor is controlled by regulating amount of said dopant introduced in said semi-conductor.
13. A continuous semiconductor thin film deposition method as in Claim 1, wherein said semiconductor is selected from a group of CuInSe2, CuInTe2, CdTe, CdS, ZnSe, ZnS and ZnO.
14. A continuous semiconductor thin film deposition method as in Claims 1 and 6, wherein said feeding speed (cm/minute) of substrate is equal to the length (cm) of said part of substrate immersed in said electrolyte times deposition rate (µm/minute) of said semiconductor and divided by total thickness (µm) required for said semicon-ductor thin film.
15. A continuous semiconductor thin film deposition method as in Claim 1, wherein said substrate is flexible and at least a part of it is electrically conducting so that said substrate can pass through said chamber for the deposition of said semiconductor.
16. A method for the continuous dip coating of thin films of a semiconductor on a substrate comprising:

(A) introducing an electrolyte containing ion sources for the dip coating of said semiconductor in the deposition container, (B) introducing an electrolyte containing ion sources for the dissemination from said container for circulation of electrolyte to the said deposition contain-er, (C) inserting part of the said substrate in the electrolyte contained in the said deposition container, (D) controlling temperature of said electrolyte in said deposition container and temperature of said electro-lyte in said container for circulation of electrolyte, (E) feeding said substrate at a constant speed in one direction through the electrolyte in the said deposi-tion container,
17. A continuous semiconductor thin film dip coating method as in Claim 16, wherein concentration of said elec-trolyte used depends on the average composition of said semiconductor required to form an electronic device.
18. A continuous semiconductor thin film dip coating method as in Claim 16, wherein at least part of the said substrate immersed in said electrolyte is parallel to level of said electrolyte.
19. A continuous semiconductor thin film dip coating method as in Claim 16, further comprising a step of dissem-inating electrolyte between said deposition container and said container for circulation of electrolyte at a constant rate. Said rate of circulation is selected so that concen-tration of said electrolyte in the deposition container is essentially constant during the deposition of said semicon-ductor film.
20. A continuous semiconductor thin film dip coating method as in Claims 16 and 19, further comprising a step of stirring electrolyte in said deposition container to obtain uniform ion distribution.
21. A continuous semiconductor thin film dip coating method as in Claims 16 and 19, further comprising a step of stirring electrolyte in said container for circulation of electrolyte to obtain uniform ion distribution.
22. A continuous semiconductor thin film dip coating method as in Claims 16 and 19, further comprising a step of adding sources of ions at a rate to said second container to replenish ions in said electrolyte. Said rate of adding source of ions is determined by the consumption rate of ions in said electrolyte. Said consumption rate of ions is determined from rate of formation of said semiconductor in said deposition system.
23. A continuous semiconductor thin film dip coating method as in Claims 16 and 19, further comprising a step of rinsing surface of said semiconductor emerging from said electrolyte to minimize uncontrolled deposition.
24. A continuous semiconductor thin film dip coating method as in Claim 16, further comprising a step of adding dopant. Said resistivity of said semiconductor is con-trolled by regulating amount of said dopant introduced in said semiconductor.
25. A continuous semiconductor thin film dip coating method as in Claim 16, wherein said semiconductor is se-lected from a group of CdS, Znse, ZnS and ZnO.
26. A continuous semiconductor thin film dip coating method as in Claims 16 and 19, wherein said feed speed (cm/minute) of substrate is equal to the length (cm) of said part of substrate immersed in said electrolyte times deposition rate (µm/minute) of said semiconductor and divided by total thickness (µm) required for said semicon-ductor thin film.
27. A continuous semiconductor thin film dipping method as in Claim 16, wherein said substrate is flexible so that it can pass through said chamber for the deposition of said semiconductor.
28. A method for the continuous fabrication of an elec-tronic device comprising, [A] depositing continuously from a first electrolyte in a first deposition container, a first semiconductor film on a substrate, part of said substrate forms the first contact for said electronic device, [B] heat-treating continuously said first semiconductor film in a controlled environment, [C] depositing continuously from a second electrolyte in a second deposition container, a second semiconductor thin film on said first semiconductor film, [D] depositing continuously from a third electrolyte in a third deposition container, a third semiconductor thin film on said second semiconductor thin film.
29. A method for the continuous fabrication of electronic devices according to Claim 28, wherein an anode is inserted in electrolyte of said first deposition container. An electrical source is connected between said substrate and said anode, forming a complete electrical loop for the deposition of said first semiconductor film.
30. A method for the continuous fabrication of electronic devices according to Claim 28, further comprising a step of inserting an anode in electrolyte of said second semicon-ductor deposition container. An electrical source is con-nected between said substrate and said anode, forming a complete electrical loop for the deposition of said second semiconductor film.
31. A method for the continuous fabrication of electronic devices according to Claim 28, further comprising a step of inserting an anode in electrolyte of said deposition container. An electrical source is connected between said substrate and said anode, forming a complete electrical loop for the deposition of said semiconductor film window.
32. A method for the continuous fabrication of electronic devices according to Claim 28, further comprising a step of applying a photoresist layer and patterning said photore-sist layer into a grid pattern.
33. A method according to Claims 28 and 32, further com-prising a step of depositing continuously a metal grid in said photoresist grid pattern, said metal grid forming a second contact to said device. Said photoresist defining said grid pattern is removed after deposition of said metal grid.
34. A method according to Claim 28, wherein at least part of said first semiconductor is p-type. Composition of said first semiconductor is controlled by regulating composition in said first electrolyte and deposition potential.
35. A method according to Claim 28, wherein said second semiconductor is of high resistivity. Composition of said second semiconductor is controlled by regulating composi-tion of said second electrolyte and deposition temperature.
36. A method according to Claim 28, wherein said third semiconductor (the window) is n-type with low resistivity.
Composition of said third semiconductor is controlled by regulating composition of said third electrolyte and deposition potential.
37. A method according to Claim 28, wherein said first semiconductor is selected from a group of CuInSe2, CdTe, CuInTe2 and CuInS2.
38. A method according to Claim 28, wherein said second semiconductor is selected from a group of CdS, CdSe, ZnO, ZnS and ZnSe.
39. A method according to Claim 28, wherein said third semiconductor is selected from a group of CdS, CdSe, ZnS, ZnSe and ZnO.
40. A method according to Claim 28, wherein resistivity of the part of the said first semiconductor adjacent said substrate is substantially smaller than the resistivity of the part of the said first semiconductor adjacent said second semiconductor.
41. A method according to Claim 28, further comprising a step of adding ion sources of dopant to the electrolyte in said third deposition container to reduce resistivity of said third semiconductor thin film. Said ion sources con-tain ions selected from a group of Al, Ga and In.
CA002105464A 1993-09-02 1993-09-02 Methods for the continuous deposition of semiconductor thin films Abandoned CA2105464A1 (en)

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2001057932A1 (en) * 2000-02-07 2001-08-09 Cis Solartechnik Gmbh Flexible metal substrate for cis solar cells, and method for producing the same
CN104520409A (en) * 2012-02-29 2015-04-15 康宁股份有限公司 Laminated glass sheet depth profile determination
US10295330B2 (en) 2014-06-04 2019-05-21 Corning Incorporated Method and system for measuring thickness of glass article

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2001057932A1 (en) * 2000-02-07 2001-08-09 Cis Solartechnik Gmbh Flexible metal substrate for cis solar cells, and method for producing the same
CN104520409A (en) * 2012-02-29 2015-04-15 康宁股份有限公司 Laminated glass sheet depth profile determination
CN104520409B (en) * 2012-02-29 2017-03-22 康宁股份有限公司 Laminated glass sheet depth profile determination
US10295330B2 (en) 2014-06-04 2019-05-21 Corning Incorporated Method and system for measuring thickness of glass article

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