Special Surface Treatment (SST)

Heraeus Quarzglas GmbH & Co. KG

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A typical thin-film application in Semicon-manufacturing: CVD

Material buildup in high temperature and low pressure atmosphere

Stress due to different CTEand (!) temperature dependence of stress in deposited layer

this leads to peeling / particles in the deposited layer, later on to cracks / chipping – worst case cracks distributed into tube

Quartz

Sample Process: DCS + ammonia silicon nitride SiH2Cl2 + 5NH3 Si3N4 + NH4Cl +5HCl + 6H2

whereas the DCS:Ammonia ratio controls layers intrinsic stress (tensile vs. compressive)

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Stress in CVD layers on different quartz surfaces

Firepolished Quartz

Ground/Sandblasted Quartz

SST Quartz

Small Stress Component Vectors

Large Stress Component Vectors

Quartz

Quartz

Roughness != Roughness

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Comparison: machined vs. SST surface

no micro-cracks

Fire-polish closes micro-cracks SST creates necessary roughness.

Fire polished plus SST

SST reduces micro-cracks byfilling with solid crystal.Increase the surface finish.

less micro-cracks

Ground plus SSTGround Surface

Grinding creates sub surface damage (micro-cracks)

many micro-cracks

Tension in CVD layer worsens micro-cracks the lesser micro-cracks the better.SST defines a rough surface without grinding, or sandblasting no micro-cracks

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Machined vs SST surface: post etching @ 500x

mechanicallytreated surface

SST surface

20% HF 30min

20% HF 30min

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