Illustration of Bosch Process

The cartoon shows a deep reactive ion etch by Bosch process which consists of pulsed or time-multiplexed etching steps. Two modes are cyclically alternating using respectively two gases: one for plasma etching and the other for sidewall passivation. To adjust the duty cycle, the via-hole size and shape can be adjusted, making it straight with almost vertical sidewalls. In reality, however, the via-hole is slightly tapered.