The present invention relates to the field of semiconductor processing, and more in particular to an apparatus configured to floatingly support and process a train of substantially rectangular wafers.
During semiconductor device fabrication semiconductor substrates or wafers may be subjected to a variety different treatments such as, for example, deposition and annealing. An apparatus for performing these treatments may be configured to process the substrates in continuous succession, which may offer improved throughput rates relative to alternative batch systems. Accordingly, said apparatus may feature a linear track or path along which the substrates may be transported while being processed.
To simplify the design of such an apparatus, and to reduce the need for periodic maintenance, substrates may preferably be transported along the track by means of a ‘contactless’ method, i.e. a method that does not employ mechanical components that physically contact the substrates to propel them in a desired direction. One such method may involve the use of two gas bearings, an upper and a lower one, between which substrates may be floatingly accommodated while being transported and processed. A problem with substrates thus supported is that they may become destabilized by the gas flows necessary to maintain the gas bearings. Consequently, the substrates may start to stray from their predetermined trajectory towards the edges of the gas bearings, and/or undergo angular displacements. In this regard it is relevant that some processing apparatus, such as for example spatial atomic layer deposition apparatus, may be particularly suited to process rectangular substrates. Due to their constant width (seen along their length) rectangular substrates may make better use of the processing capacity of the apparatus than for example circular wafers. Rectangular substrates, however, do not possess circular symmetry. Along narrow tracks bounded by lateral walls, which themselves may be favorable for reasons of economic gas flow management, the lack of circular symmetry may cause destabilized substrates to collide with and get stuck between said walls. Generally, substrate-wall contacts are best prevented as they are bound to lead to fracture of the respective, typically fragile substrate and/or congestion of the track. A lateral stabilization mechanism capable of correcting positional aberrations, such as in particular angular deviations, within an operational double gas bearing is therefore desired.
It is an object of the present invention to provide for an apparatus having such a lateral stabilization system.
According to one aspect of the invention, a substrate processing apparatus is provided. The apparatus may comprise a process tunnel, including a lower tunnel wall, an upper tunnel wall, and two lateral tunnel walls. Together the tunnel walls may bound a process tunnel space that extends in a transport direction of the process tunnel, and that is configured to accommodate at least one substantially planar substrate that is oriented parallel to the upper and lower tunnel walls. The apparatus may further comprise a plurality of gas injection channels, provided in both the lower and the upper tunnel wall. The gas injection channels in the lower tunnel wall may be configured to provide a lower gas bearing, while the gas injection channels in the upper tunnel wall may be configured to provide an upper gas bearing. Said gas bearings may be configured to floatingly support and accommodate the substrate between them. Each of the lateral tunnel walls may also comprise a plurality of gas exhaust channels, wherein said gas exhaust channels may be spaced apart in the transport direction.
The apparatus according to the present invention may be employed to facilitate a variety of semiconductor treatments. In one embodiment, for example, the apparatus may be set up as a spatial atomic layer deposition apparatus featuring at least one depositing gas bearing, which bearing may comprise a number of spatially separated reactive materials or precursors. To this end, gas injection channels in at least one of the lower wall and the upper wall may, viewed in the transport direction, be successively connected to a first precursor gas source, a purge gas source, a second precursor gas source and a purge gas source, so as to create a process tunnel segment that—in use—comprises successive zones including a first precursor gas, a purge gas, a second precursor gas and a purge gas, respectively. In another embodiment, the apparatus may be set up as an annealing station. For this purpose, the gas flows of the gas bearings may be heated to a suitable annealing temperature, at least over a portion of a track along which a substrate may be transported. In yet another embodiment, the apparatus may merely provide for a safe transport environment for substrates.
These and other features and advantages of the invention will be more fully understood from the following detailed description of certain embodiments of the invention, taken together with the accompanying drawings, which are meant to illustrate and not to limit the invention.
The construction of the apparatus according to the present invention will be described below in general terms. In doing so, reference will be made to the exemplary embodiment shown in
The disclosed apparatus 100 according to the present invention may include a process tunnel 102 through which a substrate 140, e.g. a silicon wafer, preferably as part of a train of substrates, may be conveyed in a linear manner. That is, the substrate 140 may be inserted into the process tunnel 102 at an entrance thereof to be uni-directionally conveyed to an exit. Alternatively, the process tunnel 102 may have a dead end and the substrate 140 may undergo a bi-directional motion from an entrance of the process tunnel, towards the dead end, and back to the entrance. Such an alternative bi-directional system may be preferred if an apparatus with a relatively small footprint is desired. Although the process tunnel 102 itself may be rectilinear, such need not necessarily be the case.
The process tunnel 102 may include four walls: an upper wall 130, a lower wall 120, and two lateral or side walls 108. The upper wall 130 and the lower wall 120 may be oriented horizontally, mutually parallel and be spaced apart slightly, e.g. 0.5-1 mm, such that a substantially flat or planar substrate 140, having a thickness of for example 0.1-0.3 mm and oriented parallel to the upper and lower walls 130, 120, may be accommodated in between without touching them. The lateral walls 108, which may be oriented substantially vertically and mutually parallel, may interconnect the upper wall 130 and the lower wall 120 at their lateral sides. The lateral walls 108 may be spaced apart by a distance somewhat larger than a width of a substrate 140 to be processed, e.g. its width plus 0.5-3 mm. Accordingly, the walls 108, 120, 130 of the process tunnel 102 may define and bound an elongate process tunnel space 104 having a relatively small volume per unit of tunnel length, and capable of accommodating one or more substrates 140 that are successively arranged in the longitudinal direction of the tunnel.
Both the upper tunnel wall 130 and the lower tunnel wall 120 may be provided with a plurality of gas injection channels 132, 122. The gas injection channels 132, 122 in either wall 130, 120 may be arranged as desired as long as at least a number of them is dispersed across the length of the tunnel 102. Gas injection channels 132, 122 may, for example, be disposed on the corners of an imaginary rectangular grid, e.g. a 25 mm×25 mm grid, such that gas injection channels are regularly distributed over an entire inner surface of a respective wall, both in the longitudinal and transverse direction thereof.
The gas injection channels 132, 122 may be connected to gas sources, preferably such that gas injection channels in the same tunnel wall 120, 130 and at the same longitudinal position thereof are connected to a gas source of a same gas or gas mixture. For ALD-purposes, the gas injection channels 122, 132 in at least one of the lower wall 120 and the upper wall 130 may, viewed in the transport direction T, be successively connected to a first precursor gas source, a purge gas source, a second precursor gas source and a purge gas source, so as to create a process tunnel segment 114 that—in use—will comprise successive (tunnel-wide) gas zones including a first precursor gas, a purge gas, a second precursor gas and a purge gas, respectively. It in understood that one such a tunnel segment 114 corresponds to a single ALD-cycle. Accordingly, multiple tunnel segments 114 may be disposed in succession in the transport direction T to enable the deposition of a film of a desired thickness. Different segments 114 within a process tunnel 102 may, but need not, comprise the same combination of precursors. Differently composed segments 114 may for example be employed to enable the deposition of mixed films.
Whether opposing gas injection channels 122, 132, which share a same longitudinal position of the process tunnel but are situated in opposite tunnel walls 120, 130, are connected to gas sources of the same gas composition may depend on the desired configuration of the apparatus 100. In case double-sided deposition is desired, i.e. ALD treatment of both the upper surface 140b and lower surface 140a of a substrate 140 travelling through the process tunnel 102, opposing gas injection channels 122, 132 may be connected to the same gas source. Alternatively, in case only single-sided deposition is desired, i.e. ALD treatment of merely one of the upper surface 140b and lower surface 140a of a substrate 140 to be processed, gas injection channels 122, 132 in the tunnel wall 120, 130 facing the substrate surface to be treated may be alternatingly connected to a reactive and an inert gas source, while gas injection channels in the other tunnel wall may all be connected to an inert gas source.
In the exemplary embodiment of
Each of the lateral walls 108 of the process tunnel 102 may, along its entire length or a portion thereof, be provided with a plurality of gas exhaust channels 110. The gas exhaust channels 110 may be spaced apart—preferably equidistantly—in the longitudinal direction of the process tunnel. The distance between two neighboring or successive gas exhaust channels 110 in a same lateral wall 108 may be related to a length of the substrates 140 to be processed. In this text, the ‘length’ of a rectangular substrate 140 is to be construed as the dimension of the substrate generally extending in the longitudinal direction of the process tunnel 120. For reasons to be clarified below, a lateral wall portion the length of a substrate 140 may preferably always comprise between approximately 5 and 20, and more preferably between 8 and 15, exhaust channels 110. The center-to-center distance between two successive gas exhaust channels 110 may be in the range of approximately 10-30 mm. The longitudinal distance between edges of two neighboring gas exhaust channels 10 may preferably be at least about 75% of said center-to-center distance, which is to say that the gas exhaust channels are relatively ‘short’ compared to their center-to-center separation distance. The gas exhaust channels 110 may have any suitable shape or size. The exhaust channels 110 in a said lateral wall 108 may further be identical to each other, but need not be. In one embodiment of the apparatus 100, for example, all gas exhaust channels 110 may have a rectangular cross-section having a cross-sectional area of about 1×0.5 mm2. The 1 mm may correspond to the dimension in the longitudinal direction of the process tunnel 102, whereas the 0.5 mm may correspond to the dimension in the height direction of the process tunnel 102. In other embodiments the exhaust channels 110 may, of course, have different shapes and sizes.
The gas exhaust channels 110 may be connected to and discharge into gas exhaust conduits 112 provided on the outside of the process tunnel 102. In case the apparatus 100 is set up to perform ALD, the exhaust gases may contain quantities of unreacted precursors. Accordingly, it may be undesirable to connect gas exhaust channels 110 associated with mutually different reactive gas zones to the same gas exhaust conduit 112 (which may unintentionally lead to chemical vapor deposition). Different gas exhaust conduits 112 may thus be provided for different precursors.
The general operation of the apparatus 100 may be described as follows. In use, both the gas injection channels 132, 122 in the upper wall 130 and the lower wall 120 inject gas into the process tunnel space 104. Each gas injection channel 122, 132 may inject the gas provided by the gas source to which it is connected. As the apparatus 100 is capable of operating at both atmospheric and non-atmospheric pressures, gas injection may take place at any suitable pressure. However, to render vacuum pumps superfluous, and to prevent any contaminating gas flows from the process tunnel environment into the tunnel space 104 (especially at the substrate entrance and exit sections), the tunnel space may preferably be kept at a pressure slightly above atmospheric pressure. Accordingly, gas injection may take place at a pressure a little above atmospheric pressure, e.g. at an overpressure on the order of 1.103 Pa. In case a lower pressure is maintained in the gas exhaust conduits 112, for example atmospheric pressure, the gas injected into the tunnel space 104 will naturally flow sideways, transverse to the longitudinal direction of the process tunnel and towards the gas exhaust channels 110 in the side walls 108 that provide access to the exhaust conduits 112.
In case a substrate 140 is present between the upper and lower walls 130, 120, the gas(es) injected into the tunnel space 104 by the gas injection channels 132, 122 in the upper wall 130 may flow sideways between the upper wall and a top surface 140b of the substrate. These lateral gas flows across a top surface 140b of the substrate 140 effectively provide for an upper fluid bearing 134. Likewise, the gas(es) injected into the tunnel space 104 by the gas injection channels 122 in the lower wall 120 will flow sideways between the lower wall and a lower surface 140a of the substrate 140. These lateral gas flows across a bottom surface 140a of the substrate 140 effectively provide for a lower fluid bearing 124. The lower and upper fluid bearings 124, 134 may together encompass and floatingly support the substrate 140.
To deposit a film onto a substrate 140, the substrate may be moved through the process tunnel 102 in the transport direction T. Movement of the substrate 140 may be effected in any suitable way, both by contact and non-contact methods. Non-contact methods are preferred, among other reasons because wearable mechanical parts for driving substrates may typically complicate the design of apparatus and increase the need for maintenance. Contactless methods of propelling a substrate 140 may include propulsion by directed gas streams effected through gas injection channels 122, 132 that are placed at an angle relative to the transport direction T such that the injected gas streams have a tangential component in the transport direction; propulsion by electric forces and/or magnetic forces; propulsion by gravity (which may be effected by inclining the entire process tunnel 120 with respect to the horizontal), and any other suitable method.
Whatever method of driving the substrate 140 is chosen, care must be taken to ensure a suitable substrate transport velocity is effected. In the ALD-apparatus of
As the substrate 140 moves through the process tunnel 102 of
Now that the general operation of the apparatus according to the present invention has been discussed, attention is invited to the lateral stabilization mechanism incorporated into the design thereof.
The lateral stabilization mechanism serves to correct two kinds of motional/positional aberration that may be picked up by substrates 140 travelling through the process tunnel 102: translational and rotational aberrations. A translational aberration concerns the undesired sideways movement of an entire substrate 140 towards one of the lateral walls 108 of the process tunnel 102, and away from the other; see the left drawing in
A problem with these aberrations is that they may lead to contact between a moving substrate 140 and a static side wall 108. Due to the impact of a collision, a substrate 140 may fracture. The fracture may result in debris that may come into contact with subsequent substrates and is likely to cause a pile-up of substrates and congestion of the process tunnel. A rectangular substrate 140 has the additional problem, resulting from its lack of circular symmetry, that rotation may change its effective width. Consequently, a rotationally destabilized rectangular substrate may get stuck or jammed in between the two side walls 108 of the process tunnel 102. Again, a pile-up of substrates crashing into each other may be the result. In either case, the apparatus 100 would have to be shut down for maintenance to allow the process tunnel 102 to be cleared out. Obviously, the fractured substrates, the downtime of the apparatus and the man-hours spent on maintenance represent economical losses that are best prevented by averting any contact between substrates 140 and tunnel walls 108.
To correct both translational and rotational aberrations, a lateral stabilization mechanism may provide for correctional forces in accordance with the arrows drawn in
As mentioned, the process tunnel 102 may preferably be slightly wider than a substrate 140. As a result, a (narrow) longitudinal gas channel 106 may be present on either lateral side of a centered substrate 140, in between a lateral edge of the substrate and the respective side wall 108 of the process tunnel 102. A longitudinal gas channel 106 may have a good conductance in the longitudinal direction of the process tunnel 102, and may be said to collect the gases that flow sideways across the substrate surfaces 140a, 140b before distributing them to the longitudinally spaced apart gas exhaust channels 110 in the respective adjacent side wall 108. The gas exhaust channels 110 in the lateral walls of the tunnel 102 may serve as flow restrictions, inhibiting the free flow of gas from the process tunnel space 104 into the exhaust conduits 112. Accordingly, pressure may build up between adjacent gas exhaust channels 110, while relatively low pressures may occur at or near the gas exhaust channels.
Now, when a substrate 140 destabilizes and moves towards a side wall 108 of the tunnel 102—either entirely due to translation or partially due to rotation—it may ‘invade’ the longitudinal gas channel 106 originally present along that side wall. The width of longitudinal gas channel 106 may thereby be locally diminished, which in turn may locally obstruct the exhaust of gases from the tunnel space 104 to the gas conduits 112. Consequently, pressures may be built up between successive exhaust channels 110, which pressures may be greatest at the points where the longitudinal gas channel 106 is pinched off most. As the buildup of pressure occurs alongside the longitudinal edge of the substrate, said edge experiences a (distributed) correctional force. Indeed, the correctional force may be largest at the positions of closest approach.
In the case of the translational aberration shown in
The pressure distributions that may develop when a longitudinal gas channel 106 is pinched off by a substrate 140 may, besides on the local width of the gas channel, depend on a number of other parameters, among which the center-to-center distance between successive gas exhaust channels 110. Both situations shown in
In the situation of
In the situation of
Individually,
The left-side pressure distributions shown in
The ability of the opposing side walls 108 to provide for a restoring force couple depends on the number of gas exhaust channels 110 distributed along the length of substrate 140. Too few gas exhaust channels 110, and the pressure distribution is not fine enough to effect a gentle restoring force couple at every longitudinal position along the processing track. Too many exhaust channels 110, and there is an insufficient development of high-pressure bumps between them. As before, experiments have revealed that a gas exhaust channel density, i.e. the number of gas exhaust channels 110 in a lateral wall 108 present along the length of a longitudinal substrate edge, in the range 5-20 is workable, while an exhaust gas channel density in the range 8-15 is preferred.
As a general measure to enhance the lateral stabilisation of a substrate, and more in particular to increase the magnitude of any correctional forces acting on the substrate, the substrate processing apparatus 100 described above with reference to in particular
The positioning gas injection channels 123, 133 may be connected to gas sources of an inert positioning gas, such as for example nitrogen, and preferably be controllable independently of the gas injection channels 122, 132. I.e. the gas injection rate of the positioning gas injection channels 123, 133 may preferably be controllable independently of the gas injection rate of the gas injection channels 122, 132. Alternatively, the gas injection rate of the positioning gas injection channels 123, 133 may be fixed relative to the gas injection rate of the gas injection channels 122, 132, which in itself may be controllable. In the case of such a fixed relation between the injection rates, the gas injection rate of the positioning gas injection channels 123, 133 may preferably be configured to be larger than the gas injection rate of the gas injection channels 122, 132. In case at least some of the gas injection channels 122, 132 are configured to inject an inert process gas that may also be used as a positioning gas (e.g. in the case of (purge) gas injection channels 122, 132 in an ALD configuration), a fixed relation between the flow rates of those gas injection channels 122, 132 and the positioning gas injections channels 123, 133 may be effected in an economical fashion, for example by connecting the respective groups of channels to a single (main) inert gas supply conduit by means of conduits having different diameters that reflect the desired injection flow rate ratio.
Although illustrative embodiments of the present invention have been described above, in part with reference to the accompanying drawings, it is to be understood that the invention is not limited to these embodiments. Variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, it is noted that particular features, structures, or characteristics of one or more embodiments may be combined in any suitable manner to form new, not explicitly described embodiments.
Number | Date | Country | Kind |
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2003836 | Nov 2009 | NL | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/NL2010/050772 | 11/19/2010 | WO | 00 | 8/3/2012 |