Non-wear shutter apparatus for a vapor deposition apparatus

An apparatus and associated method for vapor deposition of a sublimated source material as a thin film on a photovoltaic (PV) module substrate includes a deposition head wherein a source material is sublimated. A distribution manifold is provided with a plurality of passages defined therethrough for passage of the sublimated source material to the substrate. A shutter plate is disposed above the distribution manifold and includes a plurality of passages therethrough that align with the passages in the distribution manifold in a first position of the shutter plate. The shutter plate is movable to a second position wherein the shutter plate blocks the passages in the distribution manifold to flow of sublimated material therethrough. A lifting mechanism is configured between the shutter plate and the distribution manifold to lift and move the shutter plate between the first and second positions without sliding the shutter plate on the distribution manifold.

FIELD OF THE INVENTION

The subject matter disclosed herein relates generally to the field of thin film deposition processes wherein a thin film layer, such as a semiconductor material layer, is deposited on a substrate. More particularly, the subject matter is related to a shutter apparatus that selectively passes sublimated source material in a vapor deposition apparatus.

BACKGROUND OF THE INVENTION

Thin film photovoltaic (PV) modules (also referred to as “solar panels”) are gaining wide acceptance and interest in the industry, particularly modules based on cadmium telluride (CdTe) paired with cadmium sulfide (CdS) as the photo-reactive components. Solar energy systems using CdTe photovoltaic (PV) modules are generally recognized as the most cost efficient of the commercially available systems in terms of cost per watt of power generated. However, the advantages of CdTe not withstanding, sustainable commercial exploitation and acceptance of solar power as a supplemental or primary source of industrial or residential power depends on the ability to produce efficient PV modules on a large scale and in a cost effective manner.

Certain factors greatly affect the efficiency of CdTe PV modules in terms of cost and power generation capacity. For example, CdTe is relatively expensive and, thus, efficient utilization (i.e., minimal waste) of the material is a primary cost factor. In addition, the energy conversion efficiency of the module is a factor of certain characteristics of the deposited CdTe film layer. Non-uniformity or defects in the film layer can significantly decrease the output of the module, thereby adding to the cost per unit of power. Also, the ability to process relatively large substrates on an economically sensible commercial scale is a crucial consideration.

CSS (Close Space Sublimation) is a known commercial vapor deposition process for production of CdTe modules. Reference is made, for example, to U.S. Pat. Nos. 6,444,043 and 6,423,565. Within the vapor deposition chamber in a CSS system, the substrate is brought to an opposed position at a relatively small distance (i.e., about 2-3 mm) opposite to a CdTe source. The CdTe material sublimes and deposits onto the surface of the substrate. In the CSS system of U.S. Pat. No. 6,444,043 cited above, the CdTe material is in granular form and is held in a heated receptacle within the vapor deposition chamber. The sublimated material moves through holes in a cover placed over the receptacle and deposits onto the stationary glass surface, which is held at the smallest possible distance (1-2 mm) above the cover frame. The cover is heated to a temperature greater than the receptacle.

While there are advantages to the CSS process, the related system is inherently a batch process wherein the glass substrate is indexed into a vapor deposition chamber, held in the chamber for a finite period of time in which the film layer is formed, and subsequently indexed out of the chamber. The system is more suited for batch processing of relatively small surface area substrates. The process must be periodically interrupted in order to replenish the CdTe source, which is detrimental to a large scale production process. In addition, the deposition process cannot readily be stopped and restarted in a controlled manner, resulting in significant non-utilization (i.e., waste) of the CdTe material during the indexing of the substrates into and out of the chamber, and during any steps needed to position the substrate within the chamber.

Accordingly, there exists an ongoing need in the industry for an improved vapor deposition apparatus and process for the economic large scale production of PV modules that reduces film defects and waste of the source material.

BRIEF DESCRIPTION OF THE INVENTION

In accordance with an embodiment of the invention, an apparatus is provided for vapor deposition of a sublimated source material, such as CdTe, as a thin film on a photovoltaic (PV) module substrate. Although the invention is not limited to any particular film thickness, a “thin” film layer is generally recognized in the art as less than 10 microns (μm). The apparatus includes a deposition head wherein a source material is sublimated. A distribution manifold is provided with a plurality of passages defined therethrough for passage of the sublimated source material to an underlying substrate. A shutter plate is disposed above the distribution manifold and includes a plurality of passages therethrough that align with the passages in the distribution manifold in a first position of the shutter plate. The shutter plate is movable to a second position wherein the shutter plate blocks the passages in the distribution manifold to flow of sublimated material therethrough. A lifting mechanism is configured between the shutter plate and the distribution manifold to lift and move the shutter plate between the first and second positions without sliding the shutter plate on the distribution manifold. Any manner of lifting profile may be used, including for example an arc-like path or any other non-coplanar profile.

The lifting mechanism may take on various configurations. In a particular embodiment, the lifting mechanism includes a plurality of ramps spaced along longitudinal sides of the distribution manifold, and a corresponding number of rollers spaced along longitudinal sides of the shutter plate. The rollers may be housed in recesses in the sides of the shutter plate so as not to extend radially to a bottom surface of the shutter plate. The ramps may have a lift profile such that when the rollers are located at a first side of the ramps, the shutter plate is at the first position and lies flat against the distribution manifold. When the rollers are located at a second opposite side of the ramps, the shutter plate is in the second position and lies flat against the distribution manifold. The rollers may be recessed such that they are not in contact with the distribution manifold in the first and second positions of the shutter plate.

An actuation mechanism may be connected to the shutter plate to move the shutter plate over the ramps between the first and second positions. This actuation mechanism can vary widely within the scope and spirit of the invention. In a particular embodiment, the actuation mechanism includes a driven rotatable rod and a linkage that connects the rod to the shutter plate to convert rotational motion of the rod to linear pushing or pulling motion imparted to the shutter plate. The linkage may include a drive member fixed to the rod, and an arm pivotally engaged with the drive member, for example by a pin engaged in an elongated slot. The slot may have a length such that the rollers are driven up the ramps by rotation of the rod and roll at least partially down the ramps by gravity without rotation of said rod. The slot length may further be defined such that the pin moves a limited extent within the slot when the rollers are off of the ramps in the first and second positions of the shutter plate.

In still another aspect, the invention encompasses a process for vapor deposition of a sublimated source material, such as CdTe, as a thin film on a photovoltaic (PV) module substrate. The process includes supplying source material to a deposition head and heating the source material with a heat source to sublimate the source material. The sublimated source material is directed downwardly within the deposition head through a distribution manifold and onto an upper surface of the substrates. Passages in the distribution manifold are temporarily blocked to passage of the sublimated source material through the distribution member by moving a blocking member, which may be a shutter plate, to a position on the distribution member to block passages defined through the distribution member without sliding the blocking member on the distribution member.

In a particular method embodiment, the blocking member is lifted and moved to the blocking position. This may be done, for example, by driving the blocking member up and over ramps between a first position on one side of the ramps wherein the passages in the distribution member are unblocked and a second position on the opposite side of the ramps wherein the passages in the distribution member are blocked.

These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description and appended claims, or may be obvious from the description or claims, or may be learned through practice of the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1illustrates an embodiment of a system10that may incorporate a vapor deposition apparatus100(FIGS. 2 and 3) in accordance with embodiments of the invention configured for deposition of a thin film layer on a photovoltaic (PV) module substrate14(referred to hereafter as a “substrate”). The thin film may be, for example, a film layer of cadmium telluride (CdTe). As mentioned, it is generally recognized in the art that a “thin” film layer on a PV module substrate is generally less than about 10 microns (μm). It should be appreciated that the present vapor deposition apparatus100is not limited to use in the system10illustrated inFIG. 1, but may be incorporated into any suitable processing line configured for vapor deposition of a thin film layer onto a PV module substrate14.

For reference and an understanding of an environment in which the vapor deposition apparatus100incorporating a shutter plate and distribution manifold in accordance with the present invention may be used, the system10ofFIG. 1is described below, followed by a detailed description of the apparatus100.

Referring toFIG. 1, the exemplary system10includes a vacuum chamber12defined by a plurality of interconnected modules. Any combination of rough and fine vacuum pumps40may be configured with the modules to draw and maintain a vacuum within the chamber12. The vacuum chamber12includes a plurality of heater modules16that define a pre-heat section of the vacuum chamber through which the substrates14are conveyed and heated to a desired temperature before being conveyed into the vapor deposition apparatus100. Each of the modules16may include a plurality of independently controlled heaters18, with the heaters defining a plurality of different heat zones. A particular heat zone may include more than one heater18.

The vacuum chamber12also includes a plurality of interconnected cool-down modules20downstream of the vapor deposition apparatus100. The cool-down modules20define a cool-down section within the vacuum chamber12through which the substrates14having the thin film of sublimated source material deposited thereon are conveyed and cooled at a controlled cool-down rate prior to the substrates14being removed from the system10. Each of the modules20may include a forced cooling system wherein a cooling medium, such as chilled water, refrigerant, gas, or other medium, is pumped through cooling coils (not illustrated) configured with the modules20.

In the illustrated embodiment of system10, at least one post-heat module22is located immediately downstream of the vapor deposition apparatus100and upstream of the cool-down modules20in a conveyance direction of the substrates. The post-heat module22maintains a controlled heating profile of the substrate14until the entire substrate is moved out of the vapor deposition apparatus100to prevent damage to the substrate, such as warping or breaking caused by uncontrolled or drastic thermal stresses.

As diagrammatically illustrated inFIG. 1, a feed device24is configured with the vapor deposition apparatus100to supply source material, such as granular CdTe. The feed device24may take on various configurations within the scope and spirit of the invention, and functions to supply the source material without interrupting the continuous vapor deposition process within the apparatus100or conveyance of the substrates14through the apparatus100.

Still referring toFIG. 1, the individual substrates14are initially placed onto a load conveyor26, and are subsequently moved into an entry vacuum lock station that includes a load module28and a buffer module30. A “rough” (i.e., initial) vacuum pump32is configured with the load module28to drawn an initial vacuum, and a “fine” (i.e., final) vacuum pump38is configured with the buffer module30to increase the vacuum in the buffer module30to essentially the vacuum pressure within the vacuum chamber12. Valves34(e.g., gate-type slit valves or rotary-type flapper valves) are operably disposed between the load conveyor26and the load module28, between the load module28and the buffer module30, and between the buffer module30and the vacuum chamber12. These valves34are sequentially actuated by a motor or other type of actuating mechanism36in order to introduce the substrates14into the vacuum chamber12in a step-wise manner without affecting the vacuum within the chamber12. In operation of the system10, an operational vacuum is maintained in the vacuum chamber12by way of any combination of rough and/or fine vacuum pumps40.

An exit vacuum lock station is configured downstream of the last cool-down module20, and operates essentially in reverse of the entry vacuum lock station described above. For example, the exit vacuum lock station may include an exit buffer module42and a downstream exit lock module44. Sequentially operated valves34are disposed between the buffer module42and the last one of the cool-down modules20, between the buffer module42and the exit lock module44, and between the exit lock module44and an exit conveyor46. A fine vacuum pump38is configured with the exit buffer module42, and a rough vacuum pump32is configured with the exit lock module44. The pumps32,38and valves34are sequentially operated to move the substrates14out of the vacuum chamber12in a step-wise fashion without loss of vacuum condition within the vacuum chamber12.

System10also includes a conveyor system configured to move the substrates14into, through, and out of the vacuum chamber12. In the illustrated embodiment, this conveyor system includes a plurality of individually controlled conveyors48, with each of the various modules including a respective one of the conveyors48. It should be appreciated that the type or configuration of the conveyors48may vary. In the illustrated embodiment, the conveyors48are roller conveyors having rotatably driven rollers that are controlled so as to achieve a desired conveyance rate of the substrates14through the respective module and the system10overall.

As described, each of the various modules and respective conveyors in the system10are independently controlled to perform a particular function. For such control, each of the individual modules may have an associated independent controller50configured therewith to control the individual functions of the respective module. The plurality of controllers50may, in turn, be in communication with a central system controller52, as diagrammatically illustrated inFIG. 1. The central system controller52can monitor and control (via the independent controllers50) the functions of any one of the modules so as to achieve an overall desired heat-up rate, deposition rate, cool-down rate, conveyance rate, and so forth, in processing of the substrates14through the system10.

Referring toFIG. 1, for independent control of the individual respective conveyors48, each of the modules may include any manner of active or passive sensors54that detects the presence of the substrates14as they are conveyed through the module. The sensors54are in communication with the respective module controller50, which is in turn in communication with the central controller52. In this manner, the individual respective conveyor48may be controlled to ensure that a proper spacing between the substrates14is maintained and that the substrates14are conveyed at the desired conveyance rate through the vacuum chamber12.

FIGS. 2 and 3relate to a particular embodiment of the vapor deposition apparatus100that includes a deposition head110defining an interior space in which a receptacle116is configured for receipt of a granular source material (not shown), which may be supplied by a feed device or system24(FIG. 1) to a distributor144disposed in an opening in a top wall114of the deposition head110. The distributor144includes a plurality of discharge ports146that are configured to evenly distribute the granular source material into the receptacle116. The receptacle116has an open top and may include any configuration of internal ribs120or other structural elements.

In the illustrated embodiment, at least one thermocouple122is operationally disposed through the top wall114of the deposition head110to monitor temperature within the deposition head110adjacent to or in the receptacle116.

The deposition head110also includes longitudinal end walls112and side walls (FIGS. 2 and 3) and the receptacle116has a shape and configuration such that the transversely extending end walls118of the receptacle116are spaced from the end walls112of the head chamber110. The longitudinally extending side walls of the receptacle116lie adjacent to and in close proximation to the side walls of the deposition head110so that very little clearance exists between the respective side walls. With this configuration, sublimated source material will primarily flow out of the open top of the receptacle116and downwardly over the transverse end walls118as leading and trailing curtains of vapor119over, as depicted by the flow lines inFIGS. 2 and 3. The curtains of vapor119are “transversely” oriented in that they extend across the transverse dimension of the deposition head110, which is generally perpendicular to the conveyance direction of the substrates through the system.

A heated distribution manifold124is disposed below the receptacle116. This distribution manifold124may take on various configurations within the scope and spirit of the invention, and may serve to indirectly heat the receptacle116, as well as to distribute the sublimated source material that flows from the receptacle116. In the illustrated embodiment, the heated distribution manifold124has a clam-shell configuration that includes an upper shell member130and a lower shell member132. Each of the shell members130,132includes recesses therein that define cavities134when the shell members are mated together as depicted inFIGS. 2 and 3. Heater elements128are disposed within the cavities134and serve to heat the distribution manifold124to a degree sufficient for indirectly heating the source material within the receptacle116to cause sublimation of the source material. The heat generated by the distribution manifold124is also sufficient to prevent the sublimated source material from plating out onto components of the head chamber110.

Still referring toFIGS. 2 and 3, the heated distribution manifold124includes a plurality of passages126defined therethrough. These passages have a shape and configuration so as to uniformly distribute the sublimated source material towards an underlying substrate through a distribution plate152disposed below the distribution manifold124.

A debris shield150may be disposed between the receptacle116and the distribution manifold124. This shield150includes holes defined therethrough (which may be larger or smaller than the size of the holes of the distribution plate152) and primarily serves to retain any granular or particulate source material from passing through and potentially interfering with operation of the movable components of the shutter plate136.

Referring toFIGS. 2 and 3, apparatus100may include longitudinal seals155and transversely extending seals154at each longitudinal end of the head chamber110. In the illustrated embodiment, the seals154define an entry slot and an exit slot at the longitudinal ends of the head chamber110and are disposed at a distance above the upper surface of the substrates that is less than the distance between the surface of the substrates14and the distribution plate152and help to maintain the sublimated source material in the deposition area above the substrates.

Referring toFIGS. 2 and 3, the illustrated embodiment includes a movable shutter plate136disposed above the distribution manifold124. This shutter plate136includes a plurality of passages138defined therethrough that align with the passages126in the distribution manifold124in a first operational position of the shutter plate136as depicted inFIG. 3wherein the sublimated source material is free to flow through the shutter plate136and through the passages126in the distribution manifold124for subsequent distribution through the plate152. Referring toFIG. 2, the shutter plate136is movable to a second operational position relative to the upper surface of the distribution manifold124wherein the passages138in the shutter plate136are misaligned with the passages126in the distribution manifold124. In this configuration, the sublimated source material is blocked from passing through the distribution manifold124, and is essentially contained within the interior volume of the head chamber110.

The movable shutter plate136is particularly beneficial in that the sublimated source material can be quickly and easily contained within the head chamber110and prevented from passing through to the deposition area above the conveying unit. This may be desired, for example, during start up of the system10while the concentration of vapors within the head chamber builds to a sufficient degree to start the deposition process. Likewise, during shutdown of the system, it may be desired to maintain the sublimated source material within the head chamber110to prevent the material from condensing on the conveyor or other components of the apparatus100.

Referring toFIGS. 4 through 11, a lifting mechanism200is provided for moving the shutter plate136between its operational positions wherein it covers (blocks) and uncovers (unblocks) the passages126in the distribution manifold124without sliding the shutter plate136along the upper surface216of the manifold124. It is desired to prevent sliding movement between the shutter plate136and manifold124for various reasons. For example, sliding movement between the components can result in frictional wear, as well as the generation of particulates that could fall through the passages126in the distribution manifold124and result in defects in the film layer formed on the underlying substrates. In addition, sliding relative motion between the shutter plate136and upper surface216of the distribution manifold124may also result in binding or sticking between the components, and thus a loss of control over the shutter plate136. In addition, for various reasons, it may be desired that the shutter plate136and distribution manifold124are provided with a protective outer layer, such as graphite with a silicon carbide coating. Sliding frictional movement between the components will eventually wear away this coating and result in loss of protection of the coating.

Referring again toFIGS. 4 through 11, the lifting mechanism200is configured between the shutter plate136and the upper surface216of the distribution manifold124to lift and move the shutter plate136between its first and second operational positions in an arc-like path without causing sliding relative movement of the components against each other.

The lifting mechanism200may take on various configurations. In the illustrated embodiment, the lifting mechanism200includes a plurality of ramps204that are spaced along opposite longitudinal sides210of the distribution manifold124, as particularly illustrated inFIGS. 4 and 5. Each of the ramps204includes a first ramp side206and an oppositely inclined second ramp side208.

A corresponding number of rollers212are provided along the longitudinal sides214of the shutter plate136. The rollers212may be rotationally supported within recesses218defined in the longitudinal sides214, as particularly illustrated inFIGS. 5 through 11. The rollers212are disposed within the recesses218at a height so that the rollers204do not contact the upper surface216of the distribution manifold124on either side of the ramp204. In other words, when the shutter plate136is in either of its operational positions, the bottom surface234of the shutter plate136rests (by gravity) on the upper surface216of the underlying distribution manifold124without the rollers212being in contact with the distribution manifold.

The ramps204have a lift profile such that when the rollers212are located at the first side206of the ramp, the shutter plate136is at the first operational position and lies flat against the distribution manifold. In this position, however, the rollers212are in contact against the first side206of the ramp such that linear motion imparted to the shutter plate136causes the rollers212to immediately roll up the first side206of the ramps204. When the rollers212are located at the opposite side208of the ramps204(as depicted inFIG. 11), the shutter plate136is in its second operational position and again lies flat against the upper surface216of the distribution manifold124.

An actuation mechanism140is connected to the shutter plate136to move the shutter plate over the ramps204between the first operational position (depicted inFIG. 6) and the second operational position (depicted inFIG. 11). The actuation mechanism140may vary widely within the scope and spirit of the invention. In the illustrated embodiment, the actuation mechanism140includes a driven rotatable rod142and a linkage143that connects the rod142to the shutter plate136. The linkage143serves to convert rotational motion of the rod142to linear pushing or pulling motion (depending on the rotational direction of the rod142) imparted to the shutter plate136.

It should be appreciated that the linkage143may include any manner of operationally connected elements. In the depicted embodiment, the linkage143includes a drive member224that is fixed to the rod142. An arm226is pivotally engaged with the drive member224, for example by a pin228that extends into an elongated slot230defined in the arm226, as particularly illustrated inFIGS. 6 through 11. The opposite end of the arm226is connected to the shutter plate136.

Referring toFIG. 6, the slot230defined in the arm226may have an elongated longitudinal length such that, in the first operational position of the shutter plate136depicted inFIG. 6and the second operational position of the shutter plate136depicted inFIG. 11, the pin228floats within the slot230without engaging either end of the slot230. With this configuration, an initial degree of rotation of the rod142and drive member224is needed to engage the pin228against the end of the slot230before motion is imparted to the shutter plate136, as depicted inFIG. 7.

FIG. 8depicts further rotation of the rod142and drive member224after the pin228has engaged the slot230, which causes linear motion to be imparted to the shutter plate136. This motion causes the rollers212to ride up the first side206of the ramps204until the rollers212reach the peak of the ramps204as depicted inFIG. 8. At this position, the shutter plate136is lifted above the upper surface216of the distribution manifold by an amount220corresponding to the height of the ramps204. Referring toFIG. 9, slight further rotation of the rod142causes the rollers212to roll down the second side208of the ramps204by the force of gravity, which results in the arm226shifting relative to the pin228until the pin228engages against the opposite side of the slot230, as depicted inFIGS. 9 and 10.

Further rotation of the rod142and drive member224as depicted inFIGS. 10 and 11drives the pin228into the free-floating position within the slot230as depicted inFIG. 11without further movement of the rollers212relative to the ramp204.

FIG. 11depicts the configuration wherein the shutter plate136is at its second operational position with the rollers212at the second side208of the ramps204. The rollers212are engaged on the ramp without touching the upper surface216of the distribution manifold124and are in position for a reverse sequence of the steps depicted inFIGS. 6 through 11to move the shutter plate136back to its first operational position.

It should thus be appreciated from the sequence of events depicted inFIGS. 6 through 11that the shutter plate136is lifted up off of the upper surface216of the distribution manifold, moved in an arc-like path in this lifted position from the first operational position to the second operational position, and then lowered back down onto the upper surface216of the distribution manifold without any relative sliding motion between the components. The slot230in the arm226provides several degrees of rotational tolerance of the rod142at both operational positions of the shutter plate136. Thus, rotational control of the rod142and linkage143can accommodate for the reality that the rod142may not stop in the exact same rotational position for each operating sequence of the shutter plate136.

As mentioned, the present invention also encompasses various method embodiments for vapor deposition of a sublimated source material as a thin film on a substrate. The process includes supplying source material to a deposition head110and heating the source material with a heat source to sublimate the source material. The sublimated source material is then directed downwardly within the deposition head110through a distribution manifold124and onto an upper surface of a substrate conveyed under the distribution manifold124. Passages126in the distribution manifold are temporarily blocked to passage of the sublimated source material through the distribution manifold124by lifting and moving a blocking member, which may be, for example, a shutter plate136as discussed above. The blocking member is lifted and moved relative to the distribution manifold124, for example in an arc-like path, to block the passages126in the manifold without sliding the blocking member along the distribution manifold124.

In a particular embodiment, the method for lifting and moving the blocking member includes driving the blocking member up and over ramps204on the distribution manifold124between a first operational position on one side of the ramps204and a second operational position on the opposite side of the ramps204wherein the passages126in the distribution manifold are blocked.