CMOS compatible thin wafer processing using temporary mechanical wafer, adhesive and laser release of thin chips/wafers for 3D integration

Abstract

This paper reports a thin wafer handling technology that is compatible to CMOS processing conditions to enable 3D integration and assembly with high throughput at low cost. Using pulsed ultraviolet (UV) radiation from excimer lasers, device wafers as thin as 50µm can be released from the temporary mechanical handler wafer in less than 1min. Bonding, adhesive, debonding and post debond clean processes were demonstrated. CMOS circuit test vehicles were shown to be compatible with this temporary bonding and debonding processes.

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

“…4(b) shows crack-free and chipping-free after glue cleaning although a little wavy of the tape surface. Compared to the reported de-bonding example, which is 200mm wafer in around 70μm thick de-bonded by laser ablation technology [5], this study demonstrates an effective de-bonding method without high-cost glass handler wafers, and will be further evaluated for 300mm thin wafers in this paper. …”

Demonstration of a novel low cost single material temporary bond solution for high topography substrates based on a mechanical wafer debonding and innovative adhesive removal

“… Mechanical sliding of the wafer after melt of a thermoplastic material [4].  Laser release methods by degrading the adhesive layer itself or by employing light sensitive release layers [5]. Such method necessary implies the use of glass as carrier substrate.…”

Advanced wafer bonding and laser debonding

“…Based on previous experience using a 308 nm laser and UV-absorbing materials on glass handlers [2] it is known that debonding by UV ablation begins at a minimum threshold fluence controlled primarily by the absorption and thickness of the material being ablated. As mentioned above, the material must adhere well both to the glass handler and the bonding adhesive, it must be thermally stable up to at least the maximum bonding temperature, it must be highly absorbing at 355 nm, and for ease of inspection of the bonded interface throughout 3D wafer processing, it should be as transparent as possible at optical wavelengths.…”

“…Since the goal is to transmit as much laser radiation as possible through the glass to the ablation layer, the results show that 266 nm is a poor choice. We have previously reported good debonding of glass coated with a polyimide-based adhesive using the 308 nm wavelength from a XeCl excimer laser [2]. In that work, a portion of the adhesive itself served as the ablation layer, and a relatively high-power line beam (~50 mm wide) was scanned across the wafer using a moving stage.…”

“…Room-temperature debonding techniques, which include laser-assisted debonding as well as mechanical peeling [1] appear to be gaining wider acceptance than other methods due to their compatibility with standard dicing tape frame mounting and materials. Ultraviolet (UV) laser ablation using an excimer source in combination with an x-y scanning stage has previously been demonstrated to effectively debond wafers that have been bonded using polyimide-based adhesives [2]. At the same time, a number of mechanical debonding approaches have arisen that rely on controlled peeling of a handler from a thinned wafer, for example by engineering the handler to have a central lowadhesion zone, or by the application of a special release layer to the wafer before bonding [3].…”