Integration of a temporary carrier in a TSV process flow

Abstract

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

How to select adhesive materials for temporary bonding and de-bonding of 200mm and 300mm thin-wafer handling for 3D IC integration?

“…For all the other processes conducted in atmosphere, even for solder reflow at high temperature (240 o C), the tolerance of adhesives is found to be much wider and thus hardly affects the test results. The adhesives can be made from various polymers, and its thermal stability is a very important consideration in selecting, especially after high temperature processing [6,8]. Some adhesive has been reported to be able to withstand up to 280 o C in PECVD [6], but others like adhesive A have not.…”

Ultrathin Wafer Pre-Assembly and Assembly Process Technologies: A Review

“…The commonly reported adhesive failure modes after exposure to high temperatures are: complete delamination of the thinned wafer from the carrier; localized delamination of the thinned wafer in the form of gas pockets; 63,64 and flower-shaped delamination defects. 69 These defects occur during high temperature and high vacuum processing indicating that the pressure of the volatile decomposition products is enhanced by the high vacuum. Therefore, high temperature characterization of temporary adhesives for thermal decomposition and outgassing using methods such as thermogravimetric analysis (TGA) will be helpful in selecting the proper type of adhesive for a specific process temperature budget.…”

“…[63][64][65]69 The thermal stability of temporary adhesives is dependent upon its ability to resist decomposition and outgassing during exposure to high process temperatures. The commonly reported adhesive failure modes after exposure to high temperatures are: complete delamination of the thinned wafer from the carrier; localized delamination of the thinned wafer in the form of gas pockets; 63,64 and flower-shaped delamination defects.…”

3D integration technology for set-top box application

“…This scheme implies TSV process in the interposer, as well as small pitch back-side connection for the report on the plastic board. All of those processes are done on thin wafers (via last approach), using a temporary carrier [2] [3]. Concerning the face to face stacking of components, copper pillar technology has been chosen for its possibility of low pitch [4].…”

“…In order to achieve TSV into the bottom wafer, a temporary bonded carrier has been used [2] [3]. The device wafers are coated with a spin-on adhesive (Brewer Science HT 10.10 product) on the active surface where the technology is embedded.…”