Atomic diffusion bonding using oxide underlayers for optical applications

Abstract

Atomic diffusion bonding of quartz glass wafers using thin Ti films, with SiO 2 underlayers on wafer surfaces, provides 100% light transmittance at the bonded interface along with strong bonding energy, after post-bonded low-temperature annealing. Cross-section images obtained using transmission electron microscopy show that the bonded interface after annealing at 350 °C consists of amorphous structure including nanocrystalline grains. Structural analysis using electron energy loss spectroscopy shows that post-bonded annealing enhances oxidation of Ti with oxygen dissociated from SiO 2 underlayers, and that Ti oxides form close to TiO 2 or Ti 4 O 7 . This oxidation provides 100% light transmittance with high bonding strength attributable to the annealing. Moreover, we applied this technique for bonding glass and sapphire wafers using SiO 2 -Nb 2 O 5 underlayers, demonstrating that 100% light transmittance and control of refractive index matching are achieved simultaneously at the

Atomic diffusion bonding with oxide underlayers using Al and amorphous Si films for high optical density applications

“…These results indicate that the HfO 2 layer is formed by oxygen dissociated from the SiO 2 underlayer by annealing after bonding, which is true also when using Ti films. 20) Using Al films, the light transmittance of 100% was achieved at annealing temperatures of 300 °C for interfaces bonded with δ less than 0.5 nm. Figure 6 portrays STEM cross-section images of bonded interfaces using Al films with δ = 0.5 nm after annealing at 400 °C: (A) a bright field (BF) image and (B) a high-angle annular dark field (HAADF) image.…”

“…Results indicate that, even with a 1 nm thick Ti film on each side for bonding, the bonded interface changed to TiO 2 or Ti 4 O 7 -like Ti oxide after post-bonded annealing at 300 °C. 20) In fact, 100% light transmittance and surface free energy of the bonded interface of more than 2 J m −2 were achieved. [19][20][21] Herein, 100% light transmittance indicates that the loss of optical power at the bonded interface is less than the detection limit.…”

“…20) In fact, 100% light transmittance and surface free energy of the bonded interface of more than 2 J m −2 were achieved. [19][20][21] Herein, 100% light transmittance indicates that the loss of optical power at the bonded interface is less than the detection limit. The IAD method, a widely used technique for formulating optical thin films, 22) can be used for bonding interfaces with optical thin films such as dielectric multilayers.…”

Room Temperature Wafer Bonding of Glass Using Aluminum Oxide Intermediate Layer

“…Besides SAB, atomic diffusion bonding (ADB) was also applied for room temperature bondings. [26][27][28] In this approach, the bonding surfaces are covered with deposited metals such as Al and Ti, followed by a subsequent contact in an ultra high vacuum of the order of 10 −7 Pa pressure, resulting in bonding at room temperature. In addition, the optical transparency at the bonding interface was achieved using ADB with less than 1 nm thick intermediate layer or oxidized intermediate layer by annealing at around 300 °C.…”

“…In addition, the optical transparency at the bonding interface was achieved using ADB with less than 1 nm thick intermediate layer or oxidized intermediate layer by annealing at around 300 °C. [27,28] In contrast to these metal or Si intermediate layers, aluminum oxide (AlO) has been focused as an intermediate material for bonding. AlO is widely utilized for optical devices such as waveguides due to its high mechanical toughness, high water corrosion resistance, and excellent optical characteristics of low absorbance and refraction index uniformity for 400-1000 nm wave length.…”