Method to compensate warping of wafers due to stress in thin-film polymers using a counter-stress layer
Original Publication Date: 2007-Nov-30
Included in the Prior Art Database: 2007-Nov-30
A method is described to alleviate the effects of stress that causes the warping of wafers. This method reduces the warping in a silicon wafer with a polymer thin-film.
Method to compensate warping of wafers due to stress in thin -film polymers using a counter-stress layer
Stress of polymer thin-films (henceforth referred to as the media) can be a major issue. This is because e.g. the cantilevers can be fairly close to the surface of the media. Any large variation in the surface profile is likely to cause the failure of the device. Thus methods to control this stress without greatly affecting the fabrication procedure for the scanning probe system must be developed. Further, in the new designs of the scanner, the flat surface on which the media is deposited is much thinner (25 micrometers) than in previous ones, thus being even more susceptible to warping due to media stress.
This method requires no lithography. This technique can also be extended to other scanning probe storage applications that use media technologies, such as phase change or ferroelectrics. More generally, this concept may be applied in reducing the stress and the warping in MEMS devices.
Spin coating the polymer and curing it (typically at temperatures of 400 C for 1 hour) causes the polymer to be in tensile stress. This causes the wafer to warp as shown in Figure 1. In order to alleviate this stress, metallic films (or other films with stress) can be deposited on the back-side of the wafer. The film stress of this layer must counteract the stress of the polymer by bending the wafer in the opposite direction. An example of such a material is e-beam evaporated platinum (high intrinsic tensile stress). This material wh...