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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
   Logic:
   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]

   Thicknesses:
       1000nm
      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

Thoughts:
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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