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°C using a bonding pressure up to 0.1N/cm². Annealing was carried out for times ranging from 30 minutes to 10 hours at temperatures of 1050 °C and 1180 °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_S, R_p), and reverse current (I_S). Strong dependence of R_S and n on bonding temperature and time was observed. At 1180 °C, a series resistance of 3,16Ω 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/mm² (total area 13,5 mm²). These diodes proved to be superior to comparable epitaxial diodes