Semiconductor Vacuum Chamber Component — Weld Distortion Control
Eliminating weld distortion and vacuum leak paths in a titanium semiconductor vacuum chamber component through redesigned joint geometry and process sequencing.
Case Facts
| Application | Vacuum chamber sub-assembly |
|---|---|
| Material | Grade 2 Titanium (Commercially Pure) |
| Processes | cnc-machining, welding, turning |
| Equipment | DMG Mori CLX 350, CNC milling center |
| Surface Finish | Ra 0.8 µm |
| Standards | SEMI E67, ISO 2768-m |
| Quantity | 80 units/year |
| Tolerance | ±0.05 mm |
| Lead Time | 10-12 weeks |
Challenge
A titanium vacuum chamber sub-assembly for semiconductor etch equipment required helium leak-tight joints (<1×10⁻⁹ mbar·L/s) after a complex weld sequence. Initial fabrication using standard V-groove welds resulted in 0.3-0.5mm distortion across sealing faces, causing leak rates of 5×10⁻⁷ mbar·L/s. Six of ten prototypes failed helium leak test.
Solution
Redesigned joint geometry from V-groove to U-groove with 30° included angle and 1.5mm root face. Implemented back-purge argon shielding with oxygen monitoring (<50 ppm). Applied balanced welding sequence — stitch welds alternating every 25mm, peening between passes. Final stress relief at 500°C for 2 hours followed by light machining pass on all sealing surfaces.
Result
Weld distortion reduced from 0.5mm to <0.05mm. Helium leak test pass rate improved from 40% to 100%. Sealing face flatness maintained at 0.02mm without post-weld machining. Lead time reduced from 14 to 10 weeks. Annual cost saving of $22,000 on rework and scrap.
Key Metrics
| Metric | Before | After |
|---|---|---|
| Weld Distortion (Before) | 0.5 mm | <0.05 mm |
| Helium Leak Test Pass Rate | 40% | 100% |
| Lead Time | 14 weeks | 10 weeks |
| Annual Savings | - | $22,000 |
Lessons Learned
- U-groove joint geometry provides significantly better distortion control than V-groove for titanium weldments
- Argon back-purge with active oxygen monitoring is essential for weld quality in vacuum applications
- Balanced stitch welding with inter-pass peening controls thermal distortion in thin-section titanium
- A light post-weld machining pass on sealing surfaces guarantees leak-tight performance