High-Performance Temporary Adhesives for Wafer Bonding Applications

Abstract

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.

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

“…Temporary wafer bonding and debonding have emerged as critical enabling processes for ultrathin wafer thinning. 6,7,[63][64][65][66][67][68]70 This approach involves temporarily bonding a rigid and flat support carrier to the wafer before backgrinding. The carrier could be made of silicon, ceramic, or glass.…”

Photoactive Polyesters Containingo-Nitro Benzyl Ester Functionality for Photodeactivatable Adhesion

“…There remains a sustained trend towards smaller and more advanced electronic components [1][2][3][4][5] in the microelectronics industry, which demands advancement of manufacturing techniques. Devices manufactured from mechanically brittle substrates, such as silicon wafers, often require advanced fabrication techniques such as ''flip bonding'' in order to prevent product damage and subsequent waste.…”

“…Devices manufactured from mechanically brittle substrates, such as silicon wafers, often require advanced fabrication techniques such as ''flip bonding'' in order to prevent product damage and subsequent waste. This is due in part to the rigorous grinding and etching that occurs during manufacturing processes [2]. Thus, adhesion of the device wafer to a supporting substrate with hot melt adhesives typically provides sufficient mechanical reinforcement to ensure device survival through the grinding and lithographic processes [1][2][3][4][5].…”

“…It is desirable that this room-temperature debondable adhesive also operate without chemical debonding agents, such as acid-or base-cleavable polymers or solvents. Chemical debonding agents for product removal are impractical due to lengthy time requirements for adhesive penetration and solvation [1,2]. However, an adhesive that contains a photocleavable unit within the backbone of the polymer in combination with a transparent support substrate may quickly decrease the adhesive properties without significant heating [1][2][3].…”

Temporary wafer bonding and debonding by an electrochemically active polymer adhesive for 3D integration

“…Two methods are predominantly applied in temporary wafer bonding and releasing of thin wafers in semiconductor industry. In the first method, an adhesively bonded wafer stack is heated to an elevated temperature during which the adhesive softens and becomes liquid [3,4]. The device wafer is then released by sliding it off from the carrier wafer.…”