Optimising SiCr Deposition for High-Yield Bipolar-CMOS-DMOS Manufacturing with Picosecond Ultrasonics

Why It Matters

SiCr film uniformity directly impacts resistor stability and TCR, which are critical for analog precision in automotive, medical and consumer electronics. Reliable, in‑line metrology therefore safeguards BCD device performance and reduces costly yield losses.

Key Takeaways

• Picosecond ultrasonic metrology measures SiCr thickness with sub‑angstrom repeatability.
• Process gas flow changes affect SiCr reflectivity, indicating film roughness.
• Uniform SiCr films reduce resistance drift, boosting BCD device yield.
• Dual‑metric monitoring enables early detection of deposition excursions.
• 0.5 Å (1σ) repeatability meets automotive reliability standards.

Pulse Analysis

Bipolar‑CMOS‑DMOS (BCD) technology underpins power‑intensive functions in cars, smartphones, medical imaging and emerging EV infrastructure. By merging bipolar, CMOS and DMOS transistors on a single die, BCD delivers high current handling, low‑power digital logic and robust high‑voltage switching. The Achilles’ heel of this integration is the silicon‑chromium (SiCr) resistive layer, whose thickness and micro‑structure dictate temperature‑coefficient resistance (TCR) and long‑term reliability. Traditional metrology often requires destructive sampling, limiting real‑time feedback and risking yield loss in high‑volume fabs.

Picosecond ultrasonic (PULSE™) technology solves these challenges with a laser‑based pump‑probe approach that generates and detects acoustic echoes from the SiCr surface. By measuring echo transit times and applying a calibrated speed of sound (≈69.7 Å/ps for the studied process), the system delivers thickness readings with sub‑angstrom precision and repeatability better than 0.5 Å (1σ). Validation against cross‑section TEM confirms accuracy, while the non‑contact nature preserves wafer integrity for downstream processing. The platform also captures reflectivity data, offering a simultaneous view of film density and surface roughness—key indicators of gas‑flow‑induced micro‑structural changes.

The dual‑metric capability translates into tangible business benefits. Early detection of deposition excursions allows process engineers to adjust sputtering gas flows before resistor drift compromises analog performance, directly protecting automotive safety systems and medical devices that demand strict reliability. Consistent SiCr uniformity improves BCD yield, reduces scrap, and shortens cycle time, delivering cost savings that scale across the automotive, consumer‑electronics and healthcare supply chains. As the industry pushes toward higher integration and stricter reliability standards, picosecond ultrasonic metrology is poised to become a cornerstone of advanced semiconductor process control.