Experimental Investigations Of Ultra-precision Grinding And Polishing Of Soft-brittle Cadmium Zinc Telluride Single Crystals

Cadmium zinc telluride (CZT) single crystals have become the primary material of room temperature nuclear radiation detectors, as well as the best substrate for growing epitaxial mercury cadmium telluride (HgCdTe, MCT) films, and attracted a lot of attention during the last decade. This is attributed to its ultrahigh resolution at room temperature, nitrogen-free for cooling, small volume, portable convenience, etc. Ultraprecision machining of CZT materials plays an important role to the precision and resolution of CZT devices. CZT is a kind of typically soft-brittle material, while traditional machining employed on hard-brittle materials is used to machine CZT wafers presently. This event is easy to induce surface damages after machining, followed by a decrease of property of CZT detectors and grown MCT films, until a final failure on them. Accordingly, ultraprecision machining of CZT wafers is essential to ensure a high quality of dectors and films. Therefore, ultraprecision machining of CZT wafers is preferred as an object of this thesis.Nanoscratch experiments of CZT wafers were performed on a TriboIndenter XP(?) nanoindenter equipped with the in-situ scanning function, to measure nanomachinability of CZT wafers. The results showed that CZT wafer exhibited excellent soft-plastic property at nanoscale level, rather than soft-brittle nature appeared at macroscale level. This issue is beneficial to achieve high quality machined surface of CZT wafers.High resolution environmental scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS), surface profiler, etc. were employed to investigate material removal mechanism of CZT wafers under untraprecision grinding. Abrasive wear, adhensive wear, and fatigue wear were observed during ultraprecision grinding carried out by diamond wheel with various mesh sizes. Abrasive wear prevailed under precision grinding by #3000 and #5000 diamond wheels, resulting a ductile grinding. On the other hand, surface damage mechanisms under wire sawing, precision grinding, and chemical mechanical polishing (CMP) were also addressed. The results show that precision gridning eliminate free abrasives embedding, and abrasive CMP can not completely remove the abrasive embedding.Abrasive embedding induced by traditional machining on CZT wafers was due to its soft and brittle nature. Consequently, abrasive-free CMP was employed to machine CZT wafers. Floss polishing pad was optimized as the suitable one of CZT wafers, according to surface taxtile, hardness and material removal rate of various polishing pad. Five kinds of oxidants with different static corrosion rates were added to abrasive-free CMP slurry respectively, to study the effects of surface removal rate and quality on CZT machined surface. The results showed that H2O2 had the best polishing effect on CZT wafers. Furthermore, when the volume percentage was 1%, best polished surface of CZT wafers was achieved.