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Low Stress PolySi -Exptl Plan

Experimental plan proposal for characterization of a low stress poly- or amorphous silicon process. Proposed and performed by rik.

Experimental plan

Target: 1000nm, undoped, <50MPa tensile stress, <50A RMS roughness, stable to high thermal budget (1100C)

Timeline: Finish by end of July

Tube: thermcopoly / thermcopoly2
   1. More consistent translation of undoped results to doped
   2. Lower usage in fab [easier to get time]
   3. Backup tool available

Characterization tools:
   1. Thickness -- woolam / nanospec
   2. Stress -- stresstest
   3. Roughness -- afm
   4. Crystallinity -- xrd [need training]
   5. Mechanical properties -- nanoindenter [need to work with Nix's group]

Evaluation Procedure [Pass/Fail tests]:
   Test 1 -- Thickness (lower temperature to improve btw wafer uniformity)
       Deposition must yield thickness uniformity within X% across wafer and Y% between wafers
   Test 2 -- Smoothness (lower temperature to improve)
       Roughness must be < 50A RMS
   Test 3 -- Stress (vary anneal conditions)
       Stress must be tensile and < 50MPa
   Test 4 -- Thermal stability
       Anneal at 1100C in N2 for 1 hour and recheck stress

Parameter split:
   Bottom layer:
       Thermal oxide (1um)
       LSN (500nm) [tylannitride]

   Films to try:
       550C undoped Si [expect amorphous]
       580C undoped Si [expect microcrystalline]
       620C undoped Si [expect poly]

      Annealing conditions
       1100C N2 1hr (tube)
       1100C N2 1min (RTA)
        600C N2 5mins (RTA)

General experimental procedure:
   1. Deposit LSN / Grow oxide
   2. Measure wafer curvature
   3. Deposit silicon
   4. Measure thickness
   5. Measure roughness
   6. Strip backside poly using STS [selectivity]
   7. Anneal to relieve stress
   8. Measure stress
   9. Anneal @ 1100C for 1hr in N2
   10. Measure stress
XRD will be added to the mix as soon as Rishi gets trained on the system in SNL

To do:
1. Work with Maurice to set up a new poly deposition recipe in which temperature may be specified by user 2. Search literature for crystallization theory to check what other anneal conditions work well

1. Lower temperature results in more amorphous films 2. Poly tube may have temperature gradient, which can change a-Si to microcrystalline-Si across the boat. Want to stay away from a-Si / p-Si transition temp.

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