Investigating the crystal orientation of SiC CVD using orientation imaging microscopy (OIM) & X-ray diffraction (XRD) by Deepak Ravindra

Transcription

1 Investigating the crystal orientation of SiC CVD using orientation imaging microscopy (OIM) & X-ray diffraction (XRD) by Deepak Ravindra

2 Project Details SiC coating is ~200 microns thick on SiC substrate Coating machined using single point diamond. CVD coating is Beta Polycrystalline Cubic (3C) Phase This project was done as this material was not as brittle as it was claimed to be (DBT ~550nm but max SPDT depth of cut ~1.3µm) 2 methods were examined (OIM and XRD)

3 Orientation Imaging Microscopy (OIM) The SEM beam strikes the crystalline material at 70 o Electrons disperse beneath the sample diffracting crystallographic planes Patterns are imaged using a film/phosphor band Micrographs are obtained from the DAQ and analyzed on the software

4 Orientation Imaging Microscopy (OIM)

5 X-ray Diffraction (XRD)

6 2 ~1.8cm 3 1 ~1.2cm ~1.5cm 5 4 Scan locations Distances are not exact, simply meant to show scans were taken far away from each other Images elongated because originally taken when sample was tilted 70 ; changing height to 292% of original makes images appear roughly as they would flat

7 Scan Area 1 700x SEI image Scanned region Black points= unable to determine orientation Black points= other phase that was excluded or unable to determine orientation All data points CI>0.05 All maps are 112x327 μm area and have step size 1 micron

8 SiC Alpha Scan Area 1 SiC Beta Same data, color and grayscale <112> ~5 from parallel to surface normal

9 Scan Area 2 700x SEI image All data points CI>0.05

10 SiC Alpha Scan Area 2 SiC Beta <112> ~5 from parallel to surface normal

11 Scan Area 3 700x SEI image All data points CI>0.05

12 SiC Alpha Scan Area 3 SiC Beta <112> ~3 from parallel to surface normal

13 Scan Area 4 700x SEI image All data points CI>0.05

14 SiC Alpha Scan Area 4 SiC Beta <112> ~3 from parallel to surface normal

15 Scan Area 5 700x SEI image All data points CI>0.05

16 SiC Alpha Scan Area 5 SiC Beta <112> ~3 from parallel to surface normal

17 Scan Area 1 Scan Area 5 Outer rim is 90 from sample normal SiC X-ray Polefigures (CuKα x-rays) Outer rim is 90 from sample normal

18 Below are the same x-ray polefigures with measuring grids. Each ring is in 15 increments of chi (aka. tilt), rays in 15 increments of phi (aka. azimuth or sample rotation) 002 is equivalent to 001, as is 224 to 112 for practical purposes Sample asymmetry leads to certain positions (chi, phi) of sample to have greater interaction volume with x-ray beam, and so contributing more intensity. X-rays versus X-rays

19 Euler space with (hkl)<uvw> positions of note, common collections of positions are called fibers and labeled with greek letters) These are relevant for rolling of bcc metals Orientation Distribution Function (ODF) from Scan Area 5. Also indicates overall weak texture (2-4x weak, 5-9x moderate, >10x strong) Barely above 1x random along gamma fiber ({111}<uvw>, highlighted by black box and line)

20 Results Summary OIM Observations: Beta phase: Very weak preferred crystal direction <112> ~3-5 from substrate surface normal Majority of area able to be indexed is beta phase, with little alpha phase X-ray Observations of similar un-machined sample: X-ray pole figures are roughly comparable to those made from OIM data; also indicate weak texture though <112> is spread between10-30 from substrate surface normal, with <111> ~10 from substrate surface normal (with a slightly stronger texture) At this point, we will use the results obtained from the XRD as it has stronger texture and also compliments our initial assumption (based on literature review). The <111> crystal direction presumably has a higher fracture toughness making the material lesser brittle and allowing a larger depth of cut.

21 Future Work Obtain 3C SiC Single Crystal Perform cuts in in all directions (360o around the wafer) to determine the preferred cutting direction This test will also tell us the direction that has the maximum DBT threshold limit Since CVD is a very controlled process, we potentially could request the material manufacturers to grow the crystal in the required orientation.