(Second Best Student Paper Award) Blade Test in Atmospheric-Pressure Ar Gas to Characterize Bonded Interface Fabricated Using Atomic Diffusion Bonding
Authors: Iemura Hikaru , Goto Fuki , Uomoto Miyuki , Shimatsu Takehito 
Published: February 2024

Atomic diffusion bonding (ADB) of wafers using thin films is a promising process to achieve room-temperature wafer bonding [1]. For ADB processing, thin oxide [2] and nitride [3] films are useful for bonding, as are thin metal films [1]. For blade testing, a conventional method to examine the surface free energy at the bonded interface γ, the debonding length L is measured after a thin blade is inserted between the bonded wafers. The value of γ is calculated using L values. For a bonded interface such as Si/SiO2 or SiO2/SiO2, stress corrosion caused by oxygen and water gases in air is well-known to affect the L value as does the bonding strength [4]. For this study, a blade test was applied in Ar gas at atmospheric pressure for wafers bonded using ADB processing. Bonded interfaces of two kinds were examined: interfaces bonded using thin metal films and those bonded using oxide films. Using Maszara’s equation for convenience, we assessed the variation of γ values calculated from L values.

Figure 1 presents values of γ for quartz glass wafers bonded using Ti(0.7 nm) film on each side as a function of measurement time t. Two series of data are shown: those measured in Ar and in air. The blade-insertion speed was fixed at 100 μm/s. As t increased, γ measured in air decreased remarkably from the initial value γ0(air) of 3.1 J/m2. The values of γ measured in Ar were higher than those in air. γ in Ar maintained the initial value of γ0(Ar) until t=400 s; it then started decreasing. In fact, γ0(Ar) did not increase concomitantly with increasing blade-insertion speed. Results revealed that the gradual reduction of γ in Ar resulted from oxidation of Ti films with impurities of O2 and H2O in Ar gas. The value obtained without oxidation effects is γ0(Ar).

Figure 2 presents values of γ for quartz glass wafers bonded using oxide thin films as a function of t: (A) using Al2O3(2 nm) films and (B) using ZrO2(0.5 nm) films. In both figures, the values of γ measured in Ar are much higher than those measured in air. Actually, γ in Ar for wafers bonded using Al2O3(2 nm) films maintained the initial value γ0(Ar) until t=150 s; then it started decreasing. This suggests that γ0(Ar) corresponds to the value obtained without the effects of water-stress corrosion. However, γ in Ar for wafers bonded using ZrO2(0.5 nm) films did not maintain the initial value γ0(Ar): γ decreased gradually as t increased, which indicates that the water–stress corrosion effects on the values of γ were not suppressed even in Ar.

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