Myriad structures for stacking chips, power devices, smart cards, and thin substrates for processors have one thing in common: thin silicon. Wafer thinning will soon be an essential process step for most of the devices fabricated and packaged henceforth. The key driving forces for thinned wafers are improved heat dissipation, three-dimensional stacking, reduced electrical resistance, and substrate flexibility. Handling of thin and ultrathin substrates however is not trivial because of their fragility and tendency to warp and fold. The thinned substrates need to be supported during the backside grinding process and through the subsequent processes such as lithography, deposition, etc. Using temporary adhesives to attach the processed device wafer to a rigid carrier wafer offers an efficient solution. The key requirements for such materials are ease of application, coating uniformity with minimal thickness variation across the wafer, good adhesion to a wide variety of surfaces, thermal stability in processes such as dielectric deposition and metallization, and ease of removal to allow high throughput. An additional requirement for these materials is stability in harsh chemical environments posed by processes such as etching and electroplating. Currently available materials meet only a subset of these requirements. None of them meet the requirement of high-temperature stability combined with ease of removal. We have developed adhesives that meet a wide range of post-thinning operating temperatures. Additionally, the materials are soluble in industry-accepted safe solvents and can be spin-applied to required thicknesses and uniformity. Above all, the coatings can be removed easily without leaving any residue. This paper reports on the development of a wide range of temporary adhesives that can be used in wafer thinning applications while applying both novel and conventional bonding and debonding methods.

wafer stacking technologies offer new possibilities in terms of device architecture and miniaturization [1][2][3]. To stack wafers, reliable throughsilicon vias (TSVs) and interconnections must be processed into ultrathin wafers, and such processing is made possible by new methods for wafer handling. Of the different wafer-level bonding techniques, temporary wafer bonding adhesives can offer a variety of properties sufficient for withstanding the TSV processes: flow properties, mechanical strength, thermal stability, chemical resistance, and easy debonding and cleaning processes. This paper demonstrates that, contrary to tapes and waxes currently used for temporary bonding, a new removable high-temperature adhesive  meets all the requirements named above for reliable TSV processing on 8-inch active wafers. We will first describe formation of TSVs with aspect ratios of 1:1 and 2:1 into thinned wafers. IntroductionTo be successful, 3-D ultrathin wafer stacking technologies require the development of reliable through-die interconnects with varying aspect ratios depending on the application. This type of integration poses forward new challenges in the development of new TSV processes suitable for thin-wafer handling technologies.It has already been demonstrated in a previous publication [4] that a temporary bonding process using new hightemperature adhesives  could provide an innovative and robust solution to produce functional 1:1 aspect ratio TSVs in 70-micron-thick silicon wafers. This first result showed that in addition to presenting sufficient thermal and mechanical properties to withstand all the backside process steps, the high-temperature adhesive enables easy bonding, debonding, and cleaning processes.Although encouraging, these first results obtained on plain silicon wafers were not completely representative of TSV integration in industrial products. Indeed, due to the presence of several metallization and passivation layers, an active CMOS-containing wafer can present a different deformation behavior compared to a plain wafer when heated, which can weaken its adhesion to the temporary layer during the process. Therefore the purpose of this paper is to assess the TSV creation on temporarily bonded complex active wafers.In the first part of this paper, we will assess the full TSV realization on device wafers thinned to 70 microns thanks to a temporary bonding process. The active wafers used were

The fabrication of modern microelectronic silicon devices mechanically challenges these thin silicon substrates during manufacturing operations. Melt and solution polyesterification enabled the synthesis of polyesters containing photoreactive o-nitro benzyl ester units for use as a potential photocleavable adhesive. Melt transesterification provided a solvent-free method for synthesis of 2-nitro-p-xylylene glycol (NXG)-containing polyesters of controlled molecular weights. 1 H NMR spectroscopy confirmed the chemical composition of the photoactive polyesters. Size exclusion chromatography (SEC) determined the number-average molecular weights (M n ) of the polyesters synthesized in the range of 6000 to 12000 g=mol. 1 H NMR spectroscopy confirmed increasing levels of photocleavage of the o-nitro benzyl ester functionality with increasing exposure to broad wavelength UV irradiation, and exposure levels ranged from 0-187 J=cm 2 UVA. Photocleaveage of approximately 90% of the o-nitro benzyl ester (ONB) units within the backbone of the polymer occurred at maximum dosage. Wedge fracture testing revealed approximately a two-fold decrease in fracture energy upon UV irradiation, suggesting that these structural adhesives offer potential for commercial ''flip bonding'' applications.

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Wafer thinning has been effectively used to improve heat dissipation in power devices and to fabricate flexible substrates, small chip packages, and multiple chips in a package. Wafer handling has become an important issue due to the tendency of thinned wafers to warp and fold. Thinned wafers need to be supported during the backgrinding process, lithography, deposition, etc. Temporary wafer bonding using removable adhesives provides a feasible route to wafer thinning. Existing adhesives meet only a partial list of performance requirements. They do not meet the requirements of high-temperature stability combined with ease of removal. This paper reports on the development of a wide range of temporary adhesives to be used in wafer thinning applications that use both novel and conventional bonding and debonding methods. We have developed a series of novel removable high-temperature spin-on adhesives with excellent bonding properties and a wide range of operating temperatures for bonding and/or debonding to achieve a better processing window.