The invention relates to a continuous vacuum system for processing of substrates, having an inlet air lock and outlet air lock, at least one process chamber and a device for conveying the substrates through the continuous system.
The market demands production systems that meet the requirements of integration into manufacturing lines. This means, among other things, that the efficiency of the production system must be synchronized with the efficiency of the manufacturing line. The production system must first match the throughput of the manufacturing line. Since many different throughputs are customary in manufacturing lines on the market, a system concept, which allows different throughputs, must be available and must be designed so that the compactness of the system is retained for all throughputs and the system cost per unit of throughput remains constant for all throughput variants.
To maximize the throughput of a continuous vacuum system, in addition to the actual process time, the dead time, i.e., the time required for conveyance, opening and closing of the vacuum slide valves, etc., must be minimized. After optimizing these dead times, the throughout may be increased only by increasing the capacity of the substrate carrier.
One problem with the conventional continuous systems is the small and/or limited capacity of the substrate carrier. Despite the large design of a substrate carrier according to the state of the art (approximately 1 to 1.5 m wide and up to 1.8 m long), the capacity for conventional substrates of the size 156×156 mm is actually rather low, amounting to approximately 80 units.
Large-area substrate carriers require a large and therefore expensive vacuum system for processing at a low pressure. The complexity for passing the substrate carriers into and out of the air locks in particular increases with their size, so there is a limit to the throughput achievable at a justifiable expense.
For a throughput of more than 3,000 substrates per hour, continuous systems with flat substrate carriers require a system size that cannot be integrated well into manufacturing lines and also require a disproportionately great complexity in loading and unloading as well as in maintenance.
A large-area substrate carrier also leads to problems in loading because, for some substrates, the distance from receiving the substrate to depositing it on the substrate carrier is very great. Furthermore, for manual loading, the central substrate positions on the substrate carrier are very difficult for the operating personnel to reach during manual loading. The difficulty in loading ultimately results in an increased breakage rate.
For anti-reflective coating of solar cells, flat/planar substrate carriers are generally used in the state of the art; with these carriers, the substrates are arranged in rows and columns in one plane. A typical substrate carrier has a size of 1.0×1.8 m with a thickness of approximately 1 cm. The reactive plasma does not burn directly above or next to the substrates, so there is a loss of plasma-activated reactants on the route between the plasma and substrate.
Continuous systems for anti-reflective coating of solar cells in which planar substrate carriers are likewise used, are also known, whereby the substrates may be arranged in rows and columns in one plane. A typical substrate carrier has a size of 1.2×1.6 m with a thickness of approximately 1 cm.
In the continuous remote plasma systems according to the state of the art, flat substrate carriers are thus run through the system with the substrates arranged in a plane in a two-dimensional manner.
DE 199 62 896 describes a device for manufacturing solar cells according to a combined remote plasma/LPCVD method. This device has an elongated process tube made of quartz glass, which is provided with antechambers at the input and output ends that are large enough to each pass a wafer carrier made of quartz and having a plurality of upright silicon wafers through the air locks. Here, the wafers stand vertically, which allows a definite space-saving effect and/or an increase in productivity of the system. The required process steps (entry through inlet air lock, substrate heating, preplasma, coating, cooling, etc.) then take place one after the other at different positions in the process channel, wherein the quartz wafer carriers are conveyed step by step through the process channel. However, these wafer carriers are comparatively small and are not suitable for operation by the direct plasma technique, which requires a plasma discharge directly above the substrate surface.
Direct plasma CVD systems are provided for processing wafers in electrically conductive wafer carriers in the form of plasma boats, which allow a direct plasma discharge above the wafer surface. The plasma boats are processed in a batch operation, i.e., the process chamber has only a single main opening through which the plasma boats are introduced as well as removed.
Under reduced pressure (usually 0.5 to 5 mbar) and elevated temperature (usually 300-600° C.), the plasma boat is exposed to an atmosphere of reactive gases in the PECVD system (Plasma Enhanced Chemical Vapor Deposition) with the substrates/wafers to be coated and a plasma is generated between the substrate holding plates of the plasma boat by supplying a medium-frequency power. To do so, the plasma boat must be reliably contacted, which would definitely make conveyance in a continuous system difficult. The properties of the layer created can be influenced in a variety of ways by varying the temperature, pressure, frequency, mixing ratio of gases and electric power input. In this direct plasma technique, there is no loss of plasma-activated reactants on the path between the activation site and the deposition site.
The object of the present invention is to create a continuous vacuum system with a compact design and a high throughput for plasma-supported treatment of substrate by a direct plasma technique at a reduced pressure, which ensures simple, rapid and reliable handling of the substrates with a high capacity of the substrate carrier.
This object is achieved according to the invention by the fact that the device for conveying the substrates through the continuous system has at least one plasma boat in which the substrates are arranged on a base plate in a three-dimensional stack in at least one plane at a predetermined distance from one another with intermediate carriers in between, whereby at least the intermediate carriers are made of graphite and can be acted upon by an alternating voltage via electric connecting means.
One characteristic of the invention is that the third dimension is also used for assembling the plasma boats with substrates. In a continuous system, compact three-dimensional substrate carriers are used in which the substrates are arranged side by side and/or one above the other in one or more planes at a slight distance in a horizontal stack arrangement or upright in a vertical arrangement. The substrates are thus processed in the system and/or are run through the system in stacks, which greatly increases capacity.
The substrates may also be arranged in at least two rows side by side on the base plate and/or in any plane whereby the base area of the base plate and/or the intermediate plate is 1 m×0.2 m. Other dimensions may of course also be selected, depending on the local conditions and/or substrate sizes.
In another further embodiment of the invention, the distance provided between the substrates in the stack arrangement is between 3 and 20 mm.
In one variant of the invention, the substrates are fixedly attached on both sides to intermediate plates standing on the base plate in such a way that the two substrates always face one another. The attaching of the substrates may be accomplished here by three mushroom-shaped pins protruding out of the intermediate plate on both sides and arranged in a triangle such that the substrates are secured in space behind the mushroom-shaped pins.
In one special embodiment, at least two plasma boats are arranged side by side and/or one above the other to pass through the continuous oven in one conveyor line. To this end, the base plates are equipped with sliding blocks or, in the interest of low friction, with rollers.
In one special variant, the plasma boat is secured in a conveyor frame consisting of interconnected longitudinal and transverse struts, whereby the longitudinal struts of the conveyor frame are equipped with regular recesses and/or teeth on the underside and engage in the gearwheels for horizontal conveyance of the conveyor frame with the graphite boat mounted therein. In this variant, the conveyor frame, which is subject to a certain wear, may be replaced easily.
The conveyor frame surrounds the graphite boat in a form-fitting manner on the outside in such a way that the graphite boat can be placed on boat supports situated in the corner areas of the conveyor frame.
Finally, the boat supports are designed to be electrically insulated with respect to the conveyor frame.
To form a uniform plasma in the process chambers, in particular near the substrate, in a special embodiment of the invention, every second intermediate plate is passed through and contacted with a predefined point at the base of the plasma boat, forming a first antenna arrangement, and the intermediate plates situated in between are each passed through and contacted at another predefined point at the base of the boat in such a way as to form a second antenna arrangement and are connected via the electric connecting means to feeder lines for alternating voltage to form a plasma between the first and the second antenna arrangements.
The electric connecting means may be embodied in the form of male HF contact plugs, which alternately contact at least the intermediate plates.
The contact plugs are movable by means of an actuator drive into the contact position with the respective contact points at the base of the boat and back again.
Finally, it is possible to provide for the device for conveyance of the substrates to comprise a plurality of conveyor lines running parallel to one another through the continuous system for simultaneous parallel conveyance of multiple plasma boats, such that the conveyor lines extend like a channel through the continuous system.
The substrate carriers are expanded in height to increase the capacity according to the invention, i.e., the third dimension is utilized to increase capacity. The substrate carriers are thus designed so that they are suitable for especially efficient direct plasma PECVD technology in which reactive plasma burns in immediate proximity to the substrates. This system combines the advantages of a batch system with boats with those of a continuous system with flat substrate carriers.
By parallel processing of several compact substrate carriers, the plant size is scalable and the throughput can be adapted to the requirements of the manufacturing line.
By using compact substrate carriers, the throughput achievable in a single system is greater than that in traditional continuous systems.
The system concept allows a modular design both in the direction of material flow as well as transverse thereto. This allows an additional reduction in system and operating costs.
Even for very high throughputs that have not previously been achieved, simple loading and unloading by traditional methods is possible, ensuring a higher throughput with a more compact design so that the cost per unit of throughput remains constant. At the same time a simple loading with less substrate breakage is ensured because all resting positions for the substrates 11 are readily accessible.
The invention will now be explained in greater detail below with reference to one exemplary embodiment. In the respective drawings:
a to h show schematic diagrams of inventive narrow substrate carriers with substrates stacked up in various ways utilizing the third dimension;
The usual continuous systems according to the state of the art for treatment of substrates at a reduced pressure consists according to
The passage of throughput of a substrate carrier through the continuous system according to
The inlet slide valve 20 is opened and the inlet air lock 21 is aerated, the process chamber 23 and the outlet air lock 25 are under a reduced pressure. The substrate carrier 10 is introduced into the inlet air lock 21, then the inlet slide valve 20 is closed and the inlet airlock 21 is evacuated. As soon as the same pressure as in the process chamber 23 has been reached, the second slide valve 22 is opened and the substrate carrier 10 is transferred into the process chamber 23. The second slide valve 22 is closed and the treatment of the substrates 11 may take place.
After conclusion of the treatment, the third slide valve 24 is opened and the substrate carrier 10 is transferred into the outlet air lock 25. Next the third slide valve 24 is closed and the outlet air lock 25 is aerated. Next the outlet slide valve 26 is opened and the substrate carrier 10 may then be removed from the system. The outlet slide valve 26 is closed again and the outlet air lock 25 may be evacuated again.
It is self-evident that such continuous systems according to the state of the art fulfill their assigned purpose only if multiple substrate carriers 10 are within the system at the same time. The sequence of the passage of the substrate carriers 10 through the system is more complex in this case than that described above.
The inventive substrate carrier, also known as a boat, which is represented schematically in
b, 3g show the arrangement of substrates 11 in two planes, whereby the substrates 11 of the upper layer are arranged on an intermediate carrier 32 which is also made of a conductive material, e.g., graphite.
In
The substrates 11 are each arranged across the direction of travel according to
It is self-evident that each substrate 11 must be held securely on the face plate 30 or on the intermediate carrier 32 by means of a suitable holding device, such that the distance between substrates must not be less than a predefined minimum to allow adequate passage of gas.
Furthermore, in all embodiments of
For conveyance, the base plate 30 may be equipped with sliding blocks 31′ (
Due to the three-dimensional stacked arrangement of the substrates 11 on the base plate in one or more levels, a very compact arrangement with a high capacity is created.
The vacuum pumps and reactive gas and/or purging gas supply lines, which are needed for operation of this continuous system, are not shown.
With a usable dimension of the rectangular face plate of 1×0.2 m, for example, and an embodiment of the substrate carrier in 17 levels (
In a two-dimensional plate system according to the state of the art, only six substrates could be accommodated in the same area.
The continuous system according to the invention is designed as a modular unit. The substrate carriers pass through individual stations in it, the functions of which, such as a evacuating, heating, preplasma for surface conditioning, coating, cooling and aerating, may be adapted to meet the demands of the process.
Essentially there is also the possibility of combining the heating chamber 50 with the respective vacuum slide valve 55.1 at the input end and combining the cooling chamber 53 with the respective vacuum slide valve 55.5 at the output end to form a modular group.
The heating chamber 50 is equipped with an integrated lamp field 56 for each conveyor line 54 for rapid heating of the plasma boats equipped with the substrates 11 (
It is also possible to design the entire continuous system as a cold wall reactor with integrated lamps, which ensures very rapid heating. This has the advantage that a longitudinal extending of the heated chambers 50, 51, 52, 53 is omitted.
It is self-evident that each of the chambers of the continuous PECVD system must be connected to a device for generating a vacuum in the form of vacuum pumps. In addition, the cooling chamber 53 may be connected to a purging gas supply line to remove the reaction gases completely before opening the vacuum side valve.
In addition, the chambers for surface conditioning 51 and the downstream coating chamber 52 are connected to supply lines for process gases and purging gases.
The chambers 50, 51, 52, 53 may each be opened for maintenance and cleaning purposes, whereby the seal on the chamber cover may be provided in the form of an O ring rubber seal.
Each process step may be distributed between successive stations if the material flow and cycle times require this.
Because of their compactness, several boats (base plates 30 optionally with intermediate carriers 32) may be processed in parallel.
The chambers 50, 51, 52, 53 are equipped for this with the corresponding number of conveyor lines 54.1, 54.2, 54.3, 54.4 and a respective drive system. This yields the particular feature of the invention whereby the plant throughput can be adapted to the requirements of the line as whole without any problems at all.
The plasma required for coating the substrates 11 is generated between the plates 32 that are located directly opposite one another and the substrates 11. To do so, the plates 32(1-n), which are located directly opposite one another, including the substrates 11 which are placed thereon or attached thereto, are acted upon by an alternating voltage of the opposite polarity, usually in kHz, e.g., at 40 kHz, or in MHz, e.g., at 13.5 MHz or 27 MHz (
If the substrates 11 are arranged on the plasma boat 30 so they are upright, as indicated schematically in
Depending on the composition of the process gas, the plasma may, for example, coat, clean, activate, oxidize, etc. the surface of the substrate 11 facing the plasma.
The supply of alternating voltage to the base plates 30 and the intermediate plates 32, i.e., contacting of the substrate carriers, takes place according to
After the plasma boat has been introduced into the process chamber, e.g., the process chamber for surface conditioning 51 or the coating chamber 52, and correctly positioned there, the stationary plasma boat is contacted electrically.
To do so, two male HF contact plugs 60, 61, for example, which may also be referred to as plasma lances, are inserted upward from beneath, e.g., from front to rear on the plasma boat 30, into corresponding bushings (not shown) in the boat 30 by means of a suitable actuator drive (
The HF contact plugs 60, 61 establish the electric connection between the corresponding plates 32 of the plasma boat 30 and an alternating voltage supply. Under the assumption that one or more process gases are present in sufficient concentration within the process chamber, a plasma develops between the plates after the alternating voltage is turned on. After the process is concluded, the alternating voltage is turned off, the HF contact plugs 60, 61 are retracted and the boat 30 can be conveyed further to the next station.
Details of the conveyor device for the boats 30 in the individual chambers 50, 51, 52, 53 are shown in
The plasma boat 59 is secured in space in a conveyor frame according to
Within the border of the conveyor frame formed by the longitudinal and transverse struts 66, 67 there are boat supports 68, which are electrically insulated, in the corner areas, so that the plasma boat 59 is held securely by its own weight, as shown in
The necessary electric contact elements are shown at the right front end in
In addition, the conveyor frame is provided with coding pins 69 which may be inserted or removed as needed and allow detection of the graphite boat 59 with the help of a binary number by scanning according to a conventional method.
Number | Date | Country | Kind |
---|---|---|---|
10 2007 050 699.8 | Oct 2007 | DE | national |
102008019023.3-45 | Apr 2008 | DE | national |