Laser Debonding for 2.5D, 3D and Emerging Advanced Packaging Solutions

Abstract

In recent years temporary bonding has evolved to a widely used process technology as it is an enabling process for many products relyinnovel solutions are typically assessed on two key criteria which are a broad process window and cost effectiveness. Thus in this paper these criteria will be discussed in more detail for the case of UV laser debonding with respect to wafer level packaging. By temporary bonding the thin or to be thinned device wafer is bonded to a carrier wafer by an adhesive interlayer to provide sufficient mechanical support which is crucial for many downstream processes. In the past several different technologies have been studied and implemented. A major differentiation factor between the offered solutions is the debonding method, including separation processes at room or elevated temperatures. Nowadays a particular focus is on UV laser debonding as it offers several advantages, as the debonding process can be performed at room temperature with fast process times and force free separation. Furthermore crosslinking adhesive materials with high temperature stability can be used. This can be achieved due to the high intensity UV light provided by an excimer laser system which is absorbed by the polymer close to the carrier surface and breaks the chemical bonds. The low debonding temperature in combination with high temperature stability of the adhesives leads to a broad process window for the temporary bonded stack. In addition transparent adhesive materials can be used in combination with the glass carrier to support better visibility of alignment marks within the bond interface. However, for industrial requirement besides the technical advantages the most critical parameters are ease of implementation, throughput and costs. In this paper we will review integration principles for advanced packaging as well as new devices that utilize temporary bonding. Special focus will also be put on upcoming demands for future device concepts. A short discussion will discuss temporary bonding methods and materials, benefits and drawbacks of each one. In the following laser debonding will be discussed as a focus topic for next generation packaging process technology. Laser debonding is already being applied in volume for couple of technologies, focussing on different wavelengths. We will focus on a newly developed technology, using UV solid state laser technology. Here, we will discuss all relevant process parameter, critical process steps along with reliability of different laser debonding material systems.