Effect of Au Film Thickness and Surface Roughness on Room-Temperature Wafer Bonding and Wafer-Scale Vacuum Sealing by Au-Au Surface Activated Bonding.

Michitaka Yamamoto,Hideki Takagi,Tadatomo Suga,Seiichi Takamatsu,Takashi Matsumae,Eiji Higurashi,Toshihiro Itoh,Yuichi Kurashima

doi:10.3390/mi11050454

Abstract

Au-Au surface activated bonding (SAB) using ultrathin Au films is effective for room-temperature pressureless wafer bonding. This paper reports the effect of the film thickness (15–500 nm) and surface roughness (0.3–1.6 nm) on room-temperature pressureless wafer bonding and sealing. The root-mean-square surface roughness and grain size of sputtered Au thin films on Si and glass wafers increased with the film thickness. The bonded area was more than 85% of the total wafer area when the film thickness was 100 nm or less and decreased as the thickness increased. Room-temperature wafer-scale vacuum sealing was achieved when Au thin films with a thickness of 50 nm or less were used. These results suggest that Au-Au SAB using ultrathin Au films is useful in achieving room-temperature wafer-level hermetic and vacuum packaging of microelectromechanical systems and optoelectronic devices.

Highlights

Sealing techniques are essential to protect the sensitive elements of microelectromechanical systems (MEMS) and optoelectronic devices from the environment [1,2,3]
This paper reports on the use of Au thin films with different film thicknesses in room-temperature pressureless wafer bonding and vacuum sealing processes
We investigate the effect of film thickness and surface roughness on wafer bonding and vacuum sealing quality

Summary

Introduction

Sealing techniques are essential to protect the sensitive elements of microelectromechanical systems (MEMS) and optoelectronic devices from the environment [1,2,3]. An effective way to achieve sealing is to bond cap wafers to device wafers. Many types of bonding techniques such as anodic bonding [4], thermocompression bonding [5,6,7], solder bonding [8,9], and eutectic bonding [10] have been used as sealing techniques. These techniques require high bonding temperature, which causes problems such as thermally induced mechanical stress due to thermal expansion mismatch. Research on bonding using Au intermediate layers has been increasing [11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35], because Au has several highly desirable properties such as high resistance to oxidation and corrosion

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Results

Conclusion