Crystal orientations, polysilicon

Adem of Advanced Micro Devices, Inc. was granted a patent on the use of Raman spectroscopy to monitor the thickness, crystal grain size, and crystal orientation of polysilicon or other films as they are deposited on semiconductor wafers via low-pressure chemical vapor deposition (CVD).89 The spectra are acquired with a non-contact probe through a suitably transparent window in the loading door. A feedback scheme is discussed. When the thickness has achieved the targeted value, the deposition is stopped. If the crystal grain size or orientation is deemed unsuitable, the deposition temperature is adjusted accordingly. 

The structure of the polysilicon depends on the dopants, impurities, deposition temperature, and post-deposition heat annealing. Deposition at less than 575°C produces an amorphous structure deposition higher than 625°C results in a polycrystalline, columnar structure. Heating after deposition induces crystallization and grain growth. Deposition between 600 and 650°C yields a columnar structure having reasonable grain size and (llO)-preferred orientation. 

Polysilicon is an aggregation of pure silicon crystals with random orientation deposited on the top of silicon substrate (see Figure 10.4). Polycrystalline silicon is deposited during... 

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