A pre-wafer-bonding remote-plasma treatment is presented as a route to hydrophilic elevated temperature wafer bonding. This particular remote plasma technique was used as a non-etching surface activation technique. We report a post anneal surface energy of 2,250 mJ/m 2 using remote plasma activation which is higher than other reported results. Furthermore, the trend in increasing surface energy with increased with plasma exposure time showed no tail-off. The surface damage present in other plasma techniques is avoided and as a consequence exposure times could be extended. An increase in pre-bonding remote plasma treatment times resulted in increased surface energy, this held true for; initial pre-anneal bonding where van der Waals forces hold the wafers together, for ambient covalent bonding, and, for elevated temperature covalent bonding. It also held true for homo and heterowafer bonding. Increased surface energy was evident over a variety of bonding and annealing conditions. Surface energies or more descriptively, bonding energies result are reported for Si to Si and Si to quartz bonding and compared with various other pre-bonding treatments. Attention is focused on results obtained by varying different plasma parameters; exposure time, gas species, etc., and their effect on the surface energy of bonded pair. For silicon to quartz, we report an annealing temperature of 200°C without de-bonding, which is an extension of 50°C over previously reported values. Pre-and post plasma surface roughness measurements were made using an atomic force microscope while bond interface was characterized using scanning acoustic microscopy.
Remote plasma activation is presented here as a surface technique allowing hydrophilic wafer bonding at elevated temperatures. Prebonding remote plasma treatment resulted in a marked improvement over other techniques, increasing bonding energy for both the initial van der Waals bond and the final covalent bond. Increased bonding energy is reported over a variety of bonding and annealing conditions. Bond energies of 2.4 J/m 2 were attained for Si-Si pairs annealed at 275°C. Increased bonding energy enabled elevated-temperature ͑180°C͒ Si-quartz bonding. Results focus on plasma parameter variations of exposure time and gas species and the effect on surface energy.Wafer bonding is the preferred method used in producing siliconon-insulator ͑SOI͒ substrates for the semiconductor industry. Much work 1,2 is currently focused on combining SOI technology with strained Si. Strained SOI ͑SSOI͒ combines numerous SOI advantages, such as reduced parasitics and absence of latch-up along with the enhanced performance of strained Si. This allows us to use larger devices that exhibit deep submicrometer attributes such as higher speeds and lower power dissipation. Larger devices can be fabricated using standard SOI techniques; they are also highly reliable and have a high yield. SSOI would allow 130 nm node reliability and fabrication ease to be combined with the speeds expected from a 32 nm node. High channel mobility and isolation can be obtained with a strained silicon layer on top of an insulator or a quartz substrate. The work presented here is part of a larger research program of elevated temperature silicon-quartz bonding to produce strained silicon on quartz ͑SSOQ͒. 3,4 We are working to produce a silicon layer which is strained within its elastic, damage-free region. Our research is attempting to use elevated temperature silicon-quartz bonding to produce low-strain-level SOI. We have extensively reported 5-7 the benefits of low-level strain.Plasma activation is commonly used in wafer bonding to attain high bonding energy at low bonding and annealing temperatures. 8,9 Conventional plasma sources produce both ionized and reactive neutral species in the same chamber; remote plasma sources deliver only reactive species to the process chamber. 10, 11 We observed remote plasma pretreatment to be increasingly beneficial at longer exposure times. We report a remote plasma surface activation technique which enables higher bonding energy at elevated temperatures, for both silicon-silicon bonding as well as silicon quartz bonding, extending the practical bonding temperature range in hydrophilic wafer bonding. The plasma is generated remotely, away from the surfaces, avoiding sputtering and surface damage.Silicon-silicon wafer bonding was investigated first. Siliconsilicon wafer bonding is not hampered by debonding ͑wafer pair separation͒ due to coefficient of thermal expansion ͑CTE͒ mismatch and so this was the easiest way to monitor the hydrophilic bonding process. A range of experimental variables were determined prior to attemptin...
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