More than 150,000 through holes of equal size can be created, which affords smooth and safe debonding whilst the carrier wafer withstands mechanical influences.Īdapter carrier wafers are either surface processed glass or silicon wafers with patterned pocket(s) or silicon wafers permanently bonded to borosilicate glass rings that have been patterned according to the dimensions of the substrate. To be able to distribute the chemistry as fast as possible, extremely small holes with a high density are needed. Such carrier wafers can be produced by combining a blank glass carrier with the latest patterning technologies and tight tolerances. The carrier wafer is perforated to enable the solvent to pass through it and come into contact with the adhesive. Here, the de-bonding is caused by chemicals that dissolve the adhesive after processing (including thinning) of the device wafer ( figure 3). The laser debonding method is mainly used in the fan-out wafer-level packaging and advanced packaging processes. Finally, the carrier wafer needs to be cleaned and can then be re-used several times. After laser exposure, the device wafer can be detached from the carrier wafer. Double-side polished glass or quartz carrier wafers have excellent surface quality and thus meet the requirements of a laser debonding process. ![]() After handling and processing the device wafer using standard semiconductor process tools, the release (debonding) is carried out by way of various techniques, namely chemicals dissolving the adhesive, heat decreasing the viscosity of the adhesive or laser reducing the adhesive force.įor laser debonding processes, highly transparent carrier wafers that transmit the relevant laser wavelength are needed. ![]() The general process flow for temporary bonding is shown in figure 1. In thin wafer handling processes, the device wafer is temporarily bonded to a rigid carrier wafer of high accuracy using a polymer-based adhesive. Furthermore, glass carrier wafers can be cleaned and re-used, thus contributing to cost reduction and environmental protection. Bonding to and de-bonding from glass and quartz carrier wafers can be monitored since they are transparent. Glass and quartz are excellent materials for carrier wafers because of their thermal stability and resistance against acids and other chemicals. High-end carrier wafers made of glass, quartz or silicon can meet the aforementioned requirements. ![]() Furthermore, handling tools sometimes need to be suitable for materials such as GaAs and Si, or even CMOS compatible. Carrier wafers need to have certain properties, such as: mechanical robustness chemical and high-temperature resistance incredibly low tolerances (down to 1 μm thickness variation) and thermal expansion adjusted to the used material, for example, gallium arsenide (GaAs), Indium phosphide (InP), silicon (Si) or silicon carbide (SiC). This means that a thin wafer handling technology with a high degree of flexibility on wafer and substrate sizes is needed. Warping of the wafers during handling and processing causes a high yield loss or can even make it impossible to handle the wafers any more. Producing thin wafers in high quantities puts challenging requirements on handling and processing tools.ĭue to their low thickness, thin wafers are vulnerable to stress and breakage. Those thin and ultra-thin substrates also enable 3D packaging of sensors such as complementary metal-oxide-semiconductor (CMOS) image sensors and others. Smaller package sizes require extremely thin substrates to build up devices. It is mainly consumer applications that are responsible for this trend, but the demand for smaller package sizes is also attributable to technical advantages, for example better electrical performance or improved thermal management. This is because of market demand for smaller devices that afford an increased number of functionalities at reduced cost and for this, smaller package sizes need to be realised. There is ongoing wafer thickness reduction in the MEMS and semiconductor industry. This article details the requirements for carrier wafers as a necessary handling tool for 3D wafer level packaging technologies. ![]() Depending on the temporary bonding and de-bonding techniques, there are different requirements for carrier wafers. By temporarily bonding a device wafer to a carrier wafer, it can be safely handled and processed. Various thin wafer handling systems that require a special handling tool such as a carrier wafer (or support wafer) are already established in the market. MEMS and sensor packaging processes can require the handling and processing of ultra-thin semiconductor wafers. Carsten Wesselkamp, sales manager, and Markus Wagner, marketing manager, Plan Optik
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