CdTe Thin Film - Wet Etching

CdTe Thin Film - Wet Etching

Material Name: CdTe
Recipe No.: 10311
Primary Chemical Element in Material: Cd
Sample Type: Thin film
Uses: Etching
Etchant Name: None
Etching Method: Wet etching
Etchant (Electrolyte) Composition: All measurements were carried out on 5 mm CdTe films deposited on ITO/7059 glass substrates. NP etch solutions were prepared with concentrated acids, 70% HNO3 and 85% H3PO4. A series of NP etch solutions, 1:70:29 by vol. HNO3:H3PO4:H2O (NP1), 1:99:0 by vol. HNO3:H3PO4:H2O (NP2) and 0.5:99.5:0 by vol. HNO3:H3PO4:H2O (NP3), were used. NP etch solutions are stable during storage for many months. BM etches containing 0.01 – 0.1%, Br2 were used for CdTe etching. Br2 solutions can expire within less than a day due to reaction of Br2 with the solvent and vapor loss. Therefore, Br2 solutions were always prepared immediately prior to use. During NP and BM etching, samples were completely immersed in the etch solution for the required time. Upon removal, films were immediately washed with distilled water and dried with an Ar(g) flow. Samples were then immediately transferred for measurement. All measurements were begun within 2-3 minutes of etching.
Devices were processed using 5 mm CdTe/2000 Å CdS/ITO/glass structures. The CdTe was deposited by vapor transport technique. All substrates received a post-deposition hightemperature anneal and CdCl2 treatment. Contacts were completed by depositing 6% w/w Cu/graphite paste and annealed at 200°C in Ar(g) for 30 min.
Procedure (Condition): No data
Note: CdTe etching was investigated using variable angle spectroscopic ellipsometry and glancing angle x-ray diffraction. Treatment with HNO3:H3PO4 (NP) based etches was shown to form amorphous-Te surface films which spontaneously crystallize following etching. Br2/methanol (BM) etching forms very thin amorphous-Te films. NP-etched surfaces are stable in ambient air for ~1 hr before beginning to oxidize, while BM etched films oxidize immediately following treatment. CdTe grain boundary etching by NP was minimized using more acidic etches. Device analysis suggests that a higher Te content produces more stable back contacts by attenuating Cu diffusion. Mechanistic details of NP etching are discussed.
Reference: K. D. Dobson, P. D. Paulson, B. E. McCandless and R. W. Birkmire, The Dynamics of Cadmium Telluride Etching, Mat. Res. Soc. Symp. Proc. Vol. 763 2003 Materials Research Society, pp. B3.1.2 - B3.1.11.