Silicon to silicon direct bonding-characterization of the interface and manufacture of p-i-n diodes

A silicon direct bonding (SDB) process using a special chamber for cleaning, contacting and prebonding wafers was developed. Yields above 80% on each wafer were achieved. The silicon wafers were contacted immediately after cleaning under cleanroom conditions. Then the contacted wafers were prebonded at 200 degrees C using a bonding pressure up to 0.1N/cm/sup 2/. Annealing was carried out for times ranging from 30 minutes to 10 hours at temperatures of 1050 degrees C and 1180 degrees C. In order to characterize the bonded interface, scanning electron microscopy (SEM), infrared analysis and current voltage (I-V) measurements were conducted. The electrical specification was done by evaluating the I-V characteristics of the p-n junction with respect to the ideality factor (n), series and parallel resistance (R/sub S/, R/sub p/), and reverse current (I/sub S/). Strong dependence of R/sub S/ and n on bonding temperature and time was observed. At 1180 degrees C, a series resistance of 3,16 Omega and an n-factor of 1.07 were achieved. In order to proof the viability of the bonded substrates for application to power devices, p-i-n diodes were fabricated exhibiting breakdown voltages up to 1400 V and forward current densities of 2.5 A/mm/sup 2/ (total area 13,5 mm/sup 2/). These diodes proved to be superior to comparable epitaxial diodes.<
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