Copper sulphate will bring out n-diffusion areas of pn junctions when illuminated (: how strong?). Chemistry is something like:

Cu+2 + 2 e- =====⇒ Cu

Si + 4 HF + 2 CuSO4 =====⇒ SiF4 + 2 Cu + 2 H2SO4

At higher temperatures, HF etch takes over, so it needs to be done cold. In particular, do not use a hot light source such as a bare halogen lamp. If it goes through a microscope it should be fine as the thermal part should be heavily attenuated / distorted by the time it reaches the sample.

Good at showing where doping changes. Strong etch rate dependence on illumination. Room temp: mostly etches highly doped areas, especially p+ with max conc 1018 atoms / cm3 Increased illumination favors weaker doping.

• 20-50 seconds
• 50 mL H2O
• 5 g H5IO6 (periodic acid)
• 5 mg KI
• 2 mL 48 % HF
• Must be added in given order

3 mL KMnO4

97 mL 48 % HF

5.5 um / min on <111> @ 23C

Brings out n doped areas. Use 1:10 diluted Secco etchant. : H2O

• 20 mL acetic acid
• 1 mL 40% HF
• 3 mL 65% HNO3
• 1-3 seconds

• 12 mL 65 % HNO3 (works without nitric if just exposed to air?)
• 200 mL 48% HF
• 5-10 seconds

• http://www.tf.uni-kiel.de/matwis/amat/def_en/kap_6/advanced/t6_1_2.html