Method and apparatus for etching a substrate

[0184]A 2 L beaker containing 500 mL of water is heated at 75° C. 150 ml of 40% KOH solution is added to a 400 mL beaker, which is transferred to the 2 L beaker in order to be heated in water bath. Heating is kept until the temperature of the water in the 2 L beaker reaches 75° C. again.

[0185]The magnetic supporting device of FIG. 15 with the wafer W fixed thereon is then introduced in the 400 mL beaker with the wafer W facing upwards. Then the agitator is turned on at a speed of 150 rpm.

[0186]FIG. 17 is a picture taken with an electronic scanning microscope of the etched face of the wafer W thus obtained by the KOH attack at the end of 89 min (+ / −60 seconds). A surface with homogeneously distributed microstructures M is obtained.

[0187]FIG. 18 (a) to (f) are pictures of microstructures M obtained by KOH attack on different silicon wafers (Si / SiO2).

[0188]In each case, a wafer comprising a homogeneous set of microstructures M is obtained.

[0189]Two substrates each of 1 cm2 having followed UV photolithography are used. The UV photolithography was performed using respective masks with hexagonal networks as illustrated in FIGS. 44(a) and (b). The masks have respective patterns with a base having a diameter of 100 μm and an edge-to-edge distance of 33 μm and a base having a diameter of 75 μm and an edge-to-edge distance of 25 μm.

[0190]As illustrated in FIG. 45, the test substrates T are fixed to respective removable parts 70 of a supporting device as illustrated in FIG. 32.

[0191]Etching is performed with an etching solution of KOH having a concentration of 45% at 70° C., with the magnetic support device turning at a speed of 190 rpm.

[0192]The two test substrates T are respectively etched during 50 and 60 minutes. The results of etching are illustrated on FIGS. 46(a) to (d) and FIGS. 47(a) to (d) respectively.

[0193]Both test substrates show good homogeneity.

[0194]The invention is not limited to the embodiments described abov