Patent Application
20120055916
Semiconductor processing is used to fabricate an enormous variety of semiconductor devices and systems. Some substrate processing techniques involve placing the substrate, such as a semiconductor wafer, on a substrate platform and processing the substrate. These processes can include chemical processes, plasma induced processes, etching, processes, and deposition processes. Typically, these processes are temperature dependent and heating and cooling of the semiconductor substrate during processing is utilized. In order to increase wafer/substrate throughput, heating and/or cooling of substrates and processing equipment in a short time period is desirable. Therefore, there is a need in the art for improved methods and systems related to thermal treatment of substrates.
Embodiments of the present invention provide for a rapid temperature change (RTC) capability that is used to reduce or increase the temperature of the substrate heating apparatus (e.g., a bake plate) from a first set point to a second set point in a short time period. In an exemplary embodiment, a temperature change of ±50° C. in less than one minute is achieved. The RTC capability described herein results in many benefits, including higher system throughput.
According to an embodiment of the present invention, a rapid temperature change (RTC) system is provided. The RTC system includes a bake plate assembly including a heat spreader; a heater substrate coupled to the heat spreader; and a heater layer coupled to the heater substrate. The RTC system also includes a passive chill structure positioned adjacent the bake plate assembly. The passive chill structure is moveable to make physical contact with the heater layer. The passive chill structure includes a chill plate and a thermal pad coupled to the chill plate. The RTC system further includes an active chill structure positioned adjacent the passive chill structure. The passive chill structure is moveable to make physical contact with the active chill structure.
Numerous benefits are provided by embodiments of the present invention. These include uniform thermal contact between a passive plate and the heater, a low mechanical impact on the heater, resulting in a reduced impact on the flatness of the heater. Additionally, benefits include fast thermal contact between the passive plate and the active cooling plate, low sensitivity to PCW water temperature, reduced or no adverse effect on process thermal uniformity, reduced or no pulling on RTD or power lead wires, and easy assembly and removal of the bake plate. The inventors anticipate that thermal systems incorporating the designs discussed herein will provide more than five years of working life for the bake plate and RTC assembly.
These and other embodiments of the invention along with many of its advantages and features are described in more detail in conjunction with the text below and attached figures.
The bake plate assembly 205 includes a vacuum pad 220 (e.g., a thermal pad) attached to a heat spreader 222 by vacuum. In an embodiment, the vacuum pad 220 is patterned to provide for proximity pins on the upper surface of the vacuum pad. Although multiple vacuum sources are used to provide vacuum assist to multiple portions of the system, not all of the illustrated vacuum sources are required by embodiments of the present invention. Accordingly, one or more of the illustrated vacuum systems can be utilized alone or in combination. As an example, vacuum assist can be used for the RTC vacuum assist 230 (thermal pad to passive RTC chill plate) only. As another example, the RTC vacuum assist can be used in combination with vacuum to hold and flatten the thermal pad and/or the substrate vacuum assist. As yet another example, these vacuum assists can be combined with the bake plate heater vacuum assist 232, also referred to as a bake plate vacuum assist. One of ordinary skill in the art would recognize many variations, modifications, and alternatives.
The heat spreader 222 provides for high thermal conductivity between the vacuum pad 220 and the heater layer 224, which can be a seven zone heater plus a booster heater. The heat spreader 222 can be made of any suitable material characterized by good thermal conductivity, for example, aluminum, copper, or the like. Additional description related to multi-zone bake plates is provided in commonly assigned U.S. Pat. No. 7,427,728, the disclosure of which is hereby incorporated by reference for all purposes. Thus, embodiments of the present invention provide a multi-zone (e.g., 6 or 7 zone) heater with a booster layer. A heater substrate layer 226 is disposed between the heat spreader 222 and the heater layer 224. The heater substrate layer 226 provides mechanical support for the system. As an example, aluminum is a good material in relation to heat transfer, but is characterized by poor material strength. On the other hand, alumina is characterized by high strength, but poor thermal conductivity. Embodiments of the present invention utilize the good characteristics of both materials to provide a high thermal conductivity heat spreader 222 and a high strength heater substrate 226 to provide a thin mechanical support. As an example, the high strength layer can be alumina or silicon carbide.
The number of zones used in embodiments of the present invention is typically seven zones, but embodiments of the present invention are not limited to this number. As an example, a seven-zone heater can include four peripheral zones, a central zone, and two zones consisting of two halves of an annulus surrounding the central zone. In another embodiment, two concentric annular zones surround the central zone. One of ordinary skill in the art would recognize many variations, modifications, and alternatives.
Preferably, the thickness of the heater substrate 226 is decreased in order to provide a more rapid temperature change despite poor thermal conductivity. At the same time, the strength of the heater substrate should be sufficient to provide mechanical rigidity. Typically, the vacuum pad 220 is made from Kapton or other suitable material. Typically, the initial thickness of the vacuum pad is about 100 μm, with proximity pins formed in the upper surface using a masking and etching technique.
Typically, the thickness of the heat spreader 222 will be in the range of 4 mm-10 mm, for example, 6 mm. Typically, the thickness of the heater substrate 226 will be in the range of 3 mm-4 mm. The bake plate assembly 205 will have a total thickness of 10 mm in some embodiments.
As semiconductor processing operations are characterized by increasing tolerance requirements, the time needed to reach the new set point is decreasing. In order to heat the bake plate to the set point, limitations are associated with the power provided by the zones of a multi-zone bake plate. In order to control small fluctuations in the heater zones, fine control of the heater zones is desirable, which runs counter to provision of fine control. In order to provide for rapid increases in bake plate temperature, embodiments of the present invention provide a booster layer that can provide a temperature increase for all heater zones. The booster layer is integrated into the heater layer and provides for concurrent heating of all heater zones. Thus, the booster provides rapid heating of the entire bake plate while fine tuning of the various zones with fine zone control.
Referring to
Additional description related to engageable thermal masses is provided in commonly assigned U.S. Pat. No. 7,274,005, the disclosure of which is hereby incorporated by reference in its entirety.
In order to increase the thermal conductivity between system elements and to increase the planarity of the surfaces in thermal contact, including the substrate 204, elements of the bake plate assembly 205, and the passive RTC plate 240, vacuum assist is provided at several levels of the system. A bake plate heater vacuum assist 232 is provided to provide for a continuous vacuum between the heater spreader 222 and the heater substrate 224. The vacuum provides for an improvement in planarity of the bake plate elements and increased planarity and/or thermal conductivity between the bake plate assembly and the passive RTC plate. As a result of the increase in planarity and/or compliance, the temperature spread between the various zones is decreased in comparison to the differences illustrated in
The bake plate assembly 205 also includes a substrate vacuum port 234 to provide for vacuum chucking of the substrate 201 to the vacuum pad 220. In an embodiment, the substrate vacuum port 234 is operated at about 7 kPa. Operation at about 7 kPa provides benefits, including ensuring long life of the vacuum (e.g., Kapton) pad. Additionally, a pad vacuum port 236 provides vacuum to adhere the vacuum pad 220 to the heat spreader 222. In an embodiment, the pad vacuum port 236 is operated at about 14 kPa. Other vacuum pressures are utilized in other embodiments.
An additional vacuum assist is provided (the RTC vacuum assist 230) to provide for increased planarity and/or thermal conductivity between the thermal pad and the passive RTC plate. In
The passive RTC plate 240 is also moveable to contact the active RTC chill plate 242, which is water cooled in the illustrated embodiment, with the chilled water (CW) supply 244 and CW return 246 illustrated. Although not illustrated in
During operation, when the substrate 201 is being heated, the passive chill plate 240 is in thermal contact with the active chill plate 242. In the illustrated embodiment, the passive chill plate is in physical contact with the active chill plate. In order to decrease the set point from a high temperature to a low temperature, the passive chill plate is moved vertically (using, for example, the passive RTC plate air cylinder 248) to engage with the back of the bake plate assembly 205. As discussed above, variations in the flatness of the heater layer 224 and the passive chill plate 240 are compensated for by the compliant thermal pad 210. The electrodes and the lamination associated with the heater layer contribute to these flatness variations that are compensated with by the thermal pad. The compressibility of the thermal pad is typically limited as a result of properties of the material. To increase the softness of the materials, the density of the fine particles inside the pad (e.g., graphite) have to be decreased, reducing the thermal conductivity. Thus, a balance is struck between high thermal conductivity and high compliance.
Embodiments of the present invention differ from conventional approaches in which vacuum is used to change the shape of the thermal pad to conform to the fixed shape of the bake plate. As described throughout the present specification, vacuum assist is used to change the shape of the vacuum pad in contact with the bake plate. Vacuum is used to change the surface profile of the thermal pad 210 coupled to the passive chill plate 240. Typically, vacuum is used to change the shape of an object (e.g., a substrate) that is separate from the chuck having the vacuum. Here, instead of applying the vacuum on a chuck in order the change the shape of something that is separate from the chuck, the vacuum is applied to the passive chill plate in order to change the shape of the thermal pad. The passive chill plate has through holes and the vacuum channels 212 are positioned in light of the position of the various through holes.
In forming the vacuum channels 212 in the thermal pad 210, there are two competing design constraints: a large enough thickness of the thermal pad material to maintain a vacuum in the channel and a small enough thickness to maintain good thermal conductivity for the pad. The inventors have determined that by improving the contact area, the temperature non-uniformity was reduced due to cooling from 12° C. to less than 2° C. and the cooling time reduced by 45%. Typically implementing a temperature change from 140° C. to 90° C. change takes about 150 seconds (100 s cooling/50 s stabilization). Utilizing embodiments of the present invention, only 50 seconds vs. 93 seconds to achieve a temperature drop of 50° C. (i.e., 45% improvement). Additionally, the stabilization time is expected to be reduced by about 70%.
In summary, several vacuum assists are utilized with the bake plate assembly 205 as illustrated in
It is also understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application and scope of the appended claims.
This application claims priority to U.S. Provisional Patent Application No. 61/309,286, filed on Mar. 1, 2010, entitled “Method and System for Thermal Treatment of Substrates,” the disclosure of which is hereby incorporated by reference in its entirety for all purposes.
| Number | Date | Country | |
|---|---|---|---|
| 61309286 | Mar 2010 | US |
