Advanced Packaging and Manufacturing Technology Based on Adhesion Engineering

Packaging for MEMS (microelectromechanical systems) is attracting increased interest because it is being recognized as an essential technique for successful commercialization of MEMS product. Similar to integrated circuit (IC) packaging in microelectronics, packaging of MEMS bears the highest cost within the whole manufacturing processes.

As explained in the previous section, transfer packaging is one of interesting MEMS packaging technologies because it doesn’t have process compatibility issues with main MEMS process. Thus, the different transfer techniques will be thoroughly explained in the following

This chapter will describe polymer cap transfer packaging techniques based on Si carrier substrate with anti-adhesion coating to achieve post-it-like debonding. The anti-adhesion coating, principally implemented by SAM (Self-Aligned Monolayer), is different from the thin-film coating explained in the previous section as it depends on chemical chains attached to Si substrate.

Thin film packaging caps are generally fabricated through sacrificial etch via access holes after deposition of the material over MEMS devices as depicted in Chap. 1. Access hole sacrificial etching would be a barrier for the thin film encapsulation to realize high throughput packaging technology. As demonstrated in previous section, polymers caps in tensile stress exhibit downward deflection making the housing cavities volume reduced from the designed one. Moreover, the polymer materials used for the packaging have relatively high tensile stress resulting in high wafer bow which is a barrier to achieve high yield transfer packaging. As a solution for the existing issues, buckling of thin film is interesting as it makes naturally out-of-plane deflection due to applied compressive stress. The buckling of thin film is typically considered as a major cause of failure creating delamination or crack etc. However, such a suspended buckled film would be useful for MEMS packaging. Difficulty exists in making buckled thin film as packaging cover. As the developed transfer packaging uses hydrophobicity for the transfer of the packaging cap, film in compressive stress can’t be grown directly on the surface. Therefore, buckling of thin film on compliant substrate is adopted to use the buckled film as a packaging cap. It is known that thin elastic film attached to thick compliant substrate can lead to buckling instability as the compliant substrate is subjected to compressive stress.

As already demonstrated previously, the critical step of the transfer packaging is debonding of the temporary carrier substrate. Mechanical modeling is one of solution for such critical step to understand the exact mechanism governing the failure mode of the transfer packaging. Therefore, this chapter will explain the way how to establish an appropriate FEM model to simulate the debonding process occurring in the interface between Si carrier wafer and transferred cap. The modeling will be useful to comprehend the behavior of the transferred cap in terms of deformation and stress during the debonding process.

Interface energy control technique of transfer cap packaging can be useful for other applications which require a temporary carrier or support to implement suspended structure or flexible substrate etc. This chapter describes a few examples of fabrication methods and devices which utilize the interface energy control technique.