Patent Application
20130015056
The present application relates to technologies for cooling targets in vacuum deposition systems.
Material deposition is widely used in window glass coating, light emitting diode (LED), circuit boards, flat panel display manufacturing, coating on flexible films (such as webs), hard disk coating, industrial surface coating, semiconductor wafer processing, photovoltaic panels, and other applications.
Referring to
The conventional vacuum deposition system has several drawbacks. Some target materials (such as Sn, In) have low melting temperatures or low sublimation temperatures (such as Se, S, etc.), heating induced by sputtering can create unwanted, uncontrolled melting or evaporation of the target materials, which cannot be effectively prevented by conventional cooling methods.
Additionally, a large pressure is needed to force the coolant to cool the target, which increases the pressure differential already exerted on the backing plate by the atmospheric pressure versus the vacuum in the vacuum chamber 110. The pressure difference on the two sides of the assembly of the target 150 and the backing plate 160 causes the target 150 and the backing plate 160 to bend, which often causes the target 150 to crack and delaminate from the backing plate 160.
There is therefore a need to provide a simpler and more effective target cooling, especially for target materials having low melting or sublimation temperatures.
The present invention can overcome aforementioned deficiencies. The present invention can provide faster and more effective cooling to target materials in vacuum deposition systems. As a result, targets can be kept much below room temperature during material deposition, which allows sputtering of Selenium, Indium, and other low melting temperature materials without evaporation caused by sputtering heating.
The presently disclosed systems eliminate the circulating tunnels in the backing plate in some conventional systems, and are thus simpler and of lower cost than some conventional systems.
Furthermore, the presently disclosed systems and methods consume less energy to operate than some conventional systems.
Moreover, the presently disclosed systems can further prevent the target material from cracking and delamination because the invention system does not use forced coolant to cool the target.
In one general aspect, the present invention relates to a vacuum processing system that includes a vacuum chamber that can contain a workpiece therein, a deposition source unit that provides a material to be deposited on the workpiece in vacuum, and a cooling module in thermal contact with the deposition source unit. The cooling module includes one or more holding wells that can contain a cooling liquid. The cooling module can cool the deposition source unit by a loss of latent heat during the evaporation of the cooling liquid.
Implementations of the system may include one or more of the following. The deposition source unit can include a solid target material configured to be sputtered on to the workpiece by physical vapor deposition. The solid target material can include Au, Cu, Ta, Al, Ti, TiW, Ni, NiV, Sn, In, Se, CuGa, CuIn, CuGaSe, CuInSe, InSe, CdTe, CdS, ITO, ZnO, or ZnAlO. The cooling liquid can include water, alcohol, or liquid nitrogen. The vacuum processing system can further include a backing plate in thermal contact with the deposition source unit and the cooling module, wherein the backing plate provides mechanical support to the deposition source unit. The cooling liquid can be water, and the deposition source unit is maintained at below 100° C. The vacuum processing system can further include a fan configured to generate air circulation above the surface of the cooling liquid to accelerate the evaporation of the cooling liquid. The cooling liquid can be water, and the deposition source unit is maintained at between about 30° C. and about 80° C. The cooling module can include a cover configured to enclose the cooling module, wherein the vapor of the cooling liquid is exhausted from the cooling module. The cooling liquid can be water, and the deposition source unit is maintained at between about 5° C. and about 100° C.
In another general aspect, the present invention relates to a method for depositing material in a vacuum environment. The method includes placing a workpiece in a vacuum chamber which contains a deposition source unit a cooling module therein, wherein the cooling module is in thermal contact with the deposition source unit; introducing a cooling liquid in the cooling module; depositing a material from the deposition source unit on to the workpiece in vacuum; and allowing the cooling liquid to evaporate to cool the deposition source unit by the loss of latent heat during the evaporation of the cooling liquid.
Implementations of the system may include one or more of the following. The deposition source unit can include one or more holding wells configured to contain the cooling liquid. The deposition source unit is mechanically supported by a backing plate that is in thermal contact with the deposition source unit and the cooling module. The cooling liquid can be water, and the method further includes keeping the deposition source unit at below 100° C. The method can further include generating air circulation by a fan to above the surface of the cooling liquid to accelerate the evaporation of the cooling liquid. The cooling liquid can be water, and the method further includes keeping the deposition source unit at between about 30° C. and about 80° C. The cooling module can include a cover configured to enclose the cooling module, the method further including exhausting the vapor of the cooling liquid from the cooling module. The cooling liquid can be water, and the method further includes keeping the deposition source unit at between about 5° C. and about 100° C.
The details of one or more embodiments are set forth in the accompanying drawings and in the description below. Other features, objects, and advantages of the invention will become apparent from the description and drawings, and from the claims.
Referring to
The vacuum deposition system 200 can perform physical vapor deposition (PVD) which is a common technique in micro fabrication. The target 250 comprises a material to be sputtered by the magnetron-sputtering source 260 and deposited onto the workpiece 230. The deposition system 200 can also include a magnetron (not shown).
In material deposition, the process chamber 210 is pumped down to a reduced pressure. The workpiece holder 220 can be moved to achieve uniform deposition. The presently disclosed invention can be compatible with other arrangements for the target, the substrate, and transport mechanisms. For example, the target can in general be replaced by a deposition source unit, which can provide deposition materials in PVD, thermal evaporation, thermal sublimation, sputtering, chemical vapor deposition (CVD), and plasma enhanced chemical vapor deposition (PECVD). Details of a suitable deposition system are disclosed in the commonly assigned U.S. patent application Ser. No. 11/847,956, entitled “Substrate processing system having improved substrate transport system”, filed Aug. 30, 2007, the disclosure of which is disclosed herein by reference.
In deposition operation, a lot of heat can be generated by sputtering at the surface of the target 250. The target 250 can be made of solid materials such as Au, Cu, Ta, Al, Ti, TiW, Ni, NiV, Sn, In, Se, CuGa, CuIn, CuGaSe, CuInSe, InSe, CdTe, CdS, ITO, ZnO, or ZnAlO, etc. Some target materials such as In and Sn have low melting or low sublimation temperatures, it is important to keep targets made of these materials cooled at low temperature to prevent unwanted evaporation or sublimation during sputtering deposition. In the vacuum deposition system 200, the target 250 is cooled by the cooling module 270 through the backing plate 260.
The cooling module 270 includes one or more holding wells 272 for containing a cooling liquid 275 such as water, alcohol, liquid nitrogen. The holding wells 272 are positioned outside of the vacuum chamber 210 and facing upwards to receive and hold a cooling liquid 275. Optionally, the holding wells 272 can be separated by ribs 277 that can have holes to allow the cooling liquid 275 to flow between the holding wells 272. For large target sizes, the ribs 277 can provide mechanical strength to prevent the cooling module 270 from bending and buckling under the vacuum pressure and the weight of the deposition material and the cooling liquid 275, which can prevent the target material from cracking and delamination.
The holding wells 272 can be formed in the cooling module 270. Alternatively, the cooling device can have an open bottom such that backing plate 260 forms the bottom of the holding wells 272. The cooling liquid 275 can be in direct contact with the backing plate 260.
The cooling liquid 275 is poured into the holding wells 272 before and/or during material sputtering and deposition. The heat generated by sputtering can boil cooling liquid 275, and can cause the cooling liquid 275 to evaporate. The evaporation of the cooling liquid 275 also creates circulation in the cooling liquid 275 contained in the holding well 272. The latent heat carried away by the evaporated molecules cools the backing plate 260 and the target 250.
Unlike conventional system, the vacuum deposition system 200 does not require active power to circulate the cooling liquid 275 through the cooling module 270. The holding wells 272 are in the ambient environment and easily accessible. When needed, more cooling liquid 275 can be added to the holding well 272 during deposition. Using water as the cooling liquid 272, the target temperature can maintained at below the boiling temperature of 100° C. The elimination of the cooling tunnels also significantly simplifies the making and the cost of the backing plate.
In some embodiments, referring to a vacuum deposition system 300 in
It should be noted that the power consumes to blow air in the vacuum deposition system 300 is much lower than the power needed to actively cool the coolant through a chiller and pump cooling fluid through the backing plate in some conventional systems.
In some embodiments, referring to a vacuum deposition system 400 in
It is understood that the disclosed systems are compatible with many different types of processing operations such as PVD, thermal evaporation, thermal sublimation, sputtering, CVD, PECVD, ion etching, or sputter etching. The disclosed processing systems can include other components such as load lock, transport mechanism for the substrates, etc. without deviating from the spirit of the invention. The deposition materials can be provided by sputtering targets, gas distribution device, and other types of source units without deviating from the spirit of the invention.
