Full Length ArticleDirect bonding of silicon and quartz glass using VUV/O3 activation and a multistep low-temperature annealing process
Graphical abstract
Direct bonding of silicon and quartz glass is realized via VUV/O3 activation. Based on the surface and interface analysis, the bonding mechanism attributed to the gap closure has been proposed.
Introduction
Today, silicon is the most widely used semiconductor material in microelectronics products, and it has been used as a substrate material for large-scale integrated circuits, large-scale integration and other microelectronics devices. Quartz glass is an amorphous material with a compact network structure composed of silica tetrahedron units, and it is often used for image sensors, displays, solar cells and optical waveguides due to its excellent thermal and chemical stability and extremely high light-transmission performance [1]. Therefore, the bonding of silicon- or glass-based materials is important for improving functional device performance or hermetic packages [2], [3]. The coefficient of thermal expansion (CTE) for silicon and quartz is 2.6 × 10−6/K and 0.56 × 10−6/K, respectively, at 25 °C [4], and as the temperature increases, the difference in the CTE values gradually increases. The large difference in the CTE values results in difficulties in bonding these two materials together.
Vacuum ultraviolet (VUV) radiation is a short wavelength (100–200 nm) UV light [5], [6] that can clean surfaces more effectively due to its high energy. Additionally, VUV irradiation has been considered an environmental-friendly dry cleaning method for the removal of surface contaminants without toxic solutions and can be conducted at room temperature and atmospheric pressure without cooling water and a warm-up procedure. The VUV activation method is also an emerging technique for direct wafer bonding [7]. Due to the lack of ion bombardment, VUV activation can clean the surfaces of substrates while causing less damage than plasma [8], [9]. In addition to achieving atomic-level surface cleaning, a hydrophilic surface with an ultrathin hydration layer, beneficial for direct bonding, can also be formed [10]. In this paper, we used VUV/O3-activated direct bonding for the preparation of a heterogeneous combination of silicon and quartz glass substrates. A low-temperature, multistep annealing process is proposed to enhance the bonding strength between the Si and quartz glass, which have a large difference in their CTE values. To determine the conditions for a strong bonding strength, the surfaces and bonding interfaces were characterized to gain insight into the bonding mechanism.
Section snippets
Experimental
P-type, (1 0 0)-oriented, double-polished silicon chips with a size of 10 mm × 10 mm × 400 μm were used in the experiments. The quartz glass chips were 10 × 10 mm2, polished on two sides, and 500-μm thick. Both types of samples were provided by Daheng Optics and Fine Mechanics Co., Ltd, Shanghai, China.
We employed a one-step VUV treatment for the silicon to quartz glass prebonding process. A Xe excimer lamp source (SUS 713, Ushio), which can emit a wavelength of 172 nm with a full width at half
Optimization of the bonding parameters
To obtain the optimum prebonding parameters, the changes in the bonding area ratio as a function of the humidity and irradiation time were examined, and the results are shown in Fig. 1. The bonding area ratio initially increased and then decreased with increasing irradiation time and reached the highest value after 15 min of VUV irradiation. Meanwhile, the largest bonding area was obtained at a humidity of 30 ± 5% after 15 min of irradiation. Therefore, we maintained the humidity and the VUV
Conclusions
We developed a VUV/O3-activated direct bonding method for silicon and quartz glass at a low temperature. This method does not require an ultrahigh vacuum, cleanroom or applied external force during the bonding procedure. After 15 min of VUV irradiation, the silicon and quartz glass surfaces become highly hydrophilic. In addition, some silicon oxide asperities grow on the VUV-irradiated surface. However, the overall surface roughnesses of the Si and quartz glass were very small. In addition,
Acknowledgments
This work was supported by the National Natural Science Foundation of China (Grant No. 51505106) and the China Postdoctoral Science Foundation (Grant No. 2017M610207). The authors also acknowledge support from the Heilongjiang Postdoctoral Foundation (No. LBH-Z16074).
References (26)
- et al.
Low-temperature direct heterogeneous bonding of polyether ether ketone and platinum
Mater. Sci. Eng. C
(2017) - et al.
XPS study on the early stages of oxidation of Si(100) by atomic oxygen
Surf. Sci.
(1989) - et al.
Durable flame retardant finish for silk fabric using boron hybrid silica sol
Appl. Surf. Sci.
(2016) - et al.
Preparation of durable hydrophobic cellulose fabric from water glass and mixed organosilanes
Appl. Surf. Sci.
(2010) - et al.
Hydrophobicity recovery of polydimethylsiloxane after exposure to corona discharges
Polymer
(1998) - et al.
Reactive magnetron sputtering of Si–C–N films with controlled mechanical and optical properties
Diam. Relat. Mater.
(2003) - et al.
Extended-nanofluidics: fundamental technologies, unique liquid properties, and application in chemical and bio analysis methods and devices
Anal. Chem.
(2014) - et al.
Mechanisms for low-temperature direct bonding of Si/Si and quartz/quartz via VUV/O3 activation
RSC Adv.
(2018) - et al.
A high performance micro-pressure sensor based on a double-ended quartz tuning fork and silicon diaphragm in atmospheric packaging
Meas. Sci. Technol.
(2015) - et al.
Room-temperature direct bonding of silicon and quartz glass wafers
Appl. Phys. Lett.
(2017)
Efficient photoresist residue removal with 172 nm excimer radiation
Solid State Phenom.
Effect of VUV lamp on wafer charging by single-wafer wet clean
ECS Trans.
Direct homo/heterogeneous bonding of silicon and glass using vacuum ultraviolet irradiation in air
J. Electrochem. Soc.
Cited by (36)
A fast crack-free bonding method for glass and silicon using laser transmission welding with a defocused beam
2024, Journal of Manufacturing ProcessesCharacterization of plasma-activated, thermally-annealed Si-SiO<inf>2</inf> direct bond strength for vapor HF etching
2023, Sensors and Actuators A: PhysicalPlasma-activated silicon–glass high-strength multistep bonding for low-temperature vacuum packaging
2023, Chemical Engineering JournalInsight into the mechanisms of trichloronitromethane formation by vacuum ultraviolet: QSAR model and FTICR-MS analysis
2023, Journal of Environmental Sciences (China)Irreversible bonding of PDMS-LiNbO<inf>3</inf> heterostructure for microfluidic application by stepwise plasma modification
2022, Surface and Coatings TechnologyCitation Excerpt :Although the nitrogen plasma modification did not produce oxygen free radicals directly, an increase in the content of -OH groups were also observed on the surface modified by nitrogen plasma or dual plasma. We speculated that the nitrogen plasma modification promoted the formation or conversion of -OH groups, which might be due to the water molecules adsorbed on the surface [33], and water molecules reacted with free radicals to generate -OH groups [12,34]. Therefore, the extremely high -OH group content on the surface modified by secondary plasma was the result of combined effect of oxygen plasma in the first step and nitrogen plasma modification in the second step.
Single-crystalline SiC integrated onto Si-based substrates via plasma-activated direct bonding
2020, Ceramics InternationalCitation Excerpt :The Si-O-Si bonds can be broken by plasma to generate active Si-O bonds with higher energy, which could connect free hydroxyl groups in the atmosphere that can form Si-OH groups. However, the proportion of Si-O-Si bonds of N2 or O2 plasma-activated SiO2 substrates exceeded that of Si-O bonds, which is caused by dehydration reactions between more reactive Si-OH bonds after activation [30]. Fig. 6 (b) shows that the Si substrates were covered by dense oxide layers before and after different plasma treatments.