ZnSe - Wet Etching

ZnSe - Wet Etching

Material Name: ZnSe
Recipe No.: 10329
Primary Chemical Element in Material: Zn
Sample Type: Wafer
Uses: Etching
Etchant Name: None
Etching Method: Wet etching
Etchant (Electrolyte) Composition: The research was carried out using crystal wafers of undoped ZnSe(I) (without thermal annealing), ZnSe(II) (after thermal annealing) and doped ZnSe(Al) and ZnSe(Te) crystals grown by the Bridgman method.

Chemical modification of the II-VI semiconductor compounds surfaces is often carried out using bromine containing mixtures. To obtain more perfect polished surface of ZnSe crystals, bromine containing etching compositions such as Br2 in methanol or ethanol with different bromine content has been used (Table 1).

Mechanical polishing the samples. Polishing: ZnSe(I), ZnSe(II), ZnSe(Al), ZnSe(Te) plates after cutting by our developed method should be performed using abrasive powder with grain sizes M 10, M 5 and M 1, or diamond powders ASM 28/20, ASM 10/7, ASM 5/3, ASM 3/2, ASM 2/1 and ASM 1/0. The polishing mixture is prepared in the form of abrasive powders aqueous suspensions with distilled water. The process should be carried out on a glass grinder, alternately treating the plate with both sides within 1- 5 min by each abrasive (in order to decrease abrasive grit) depending on the thickness of the damaged layer that must be removed. After this, the samples should be thoroughly washed with warm distilled water using the addition of a small amount of detergent, then several times with distilled water and dried in air. The elimination rate of the surface layer was different depending on the nature of these materials and abrasive grit (Table 2). The ZnSe(Al) material elimination rate was 6 µm/min when we made polishing by abrasive diamond powders ASM 28/20, and by powder ASM 5/3 amounts to 4 µm/min. For ZnSe(Te) crystals the surface layer elimination rate with abrasives ASM 28/20 is equal to 18 µm/min and 2 µm/min with diamond powder ASM 5/3.

Chemical-mechanical polising: Elimination of the surface damaged layer should be carried out using the CMP method. To make the CMP process for ZnSe(I), ZnSe(II), ZnSe(Al), ZnSe(Te) samples, we developed polishing solution at a volume ratio of components: 10 H2O2:10 HBr:80 EG characterized by small etching and high polishing ability. We recommend holding the etching mixture for 2 hours in order to achieve the maximum concentration of free bromine, which is formed during interaction of etching components. The CMP process of wafers that are prepared in etching solution with the rate 2 ml/min was carried out for 5 min at T = 298 K using a cambric tissue covered glass polisher, and CMP rate do not exceed 20 µm/min (Table 3).

Inter-cleaning the ZnSe surface after each stage of treatment: After each stage of mechanical treatment carried out surface inter-cleaning of undoped and doped ZnSe single crystals should be made for removing dirt from the surface of plates produced during cutting, grinding and mechanical polishing. At first, to remove the physical or mechanical contamination (dust, abrasive particles, metallic materials and semiconductor crumbs, which are formed during grinding) by rinsing in distilled water with addition of surface-active substances. Removing organic contaminants (grease, glue, residues, suspension, and fingerprint) was conducted by degreasing in organic solvents (ethanol, acetone), after which the crystals should be thoroughly dried in flow of purified air before the following technological operations.
Procedure (Condition): No data
Note: The process of chemical polishing the undoped and doped ZnSe crystals surface with H2O2 – HBr etchants has been studied. The dependence of the samples polishing rate on the concentration of H2O2 in HBr solution has been investigated. Surface states after chemical etching have been established using electron and atomic force microscopies, and it was shown that the surface state is improved after chemical etching. Etchant selection to develop slow polishing compositions for chemicalmechanical polishing the investigated materials has been made. Concentration regions of polishing solutions have been found for various types of ZnSe surface treatment: to remove the damaged layer, to control the etching rate, to obtain samples of a given thickness.
Reference: V.Ì. Tomashyk, et al., Optimization of conditions for treatment of ZnSe crystal surfaces by chemical etching, Semiconductor Physics, Quantum Electronics & Optoelectronics, 2013. V. 16, N 2. pp. 140-145.

Table 1: The etchant compositions for chemical treatment of ZnSe crystals.

Table 2: The elimination rates of ZnSe crystals surface layer during mechanical polishing by free abrasives.

Table 3: The CMP rates of undoped and doped ZnSe crystal surfaces.

Table 4: Surface roughness of undoped and doped ZnSe after chemical treatment in the new bromine emerging etchants.