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Ch77-I044963.fm Page 383 Tuesday, August 1, 2006 9:45 PM
1, 2006
Tuesday, August
Page 383
9:45 PM
Ch77-I044963.fm
383
383
(a) Oxidize (e) Remove oxide
Displacement
(b) Lithograph (f) Deposit Parylene of square
. Photoresist „ Parylene

Table3 Parameters for evaluating jagged groove
(c) Etch oxide (g) Mold and etch hack PLA
No. DiaiiKler of circlefum] Displacement of square[(.un]
1 70 1.5
2 70 2.0
3 70 2.5
(d) Etch silicon (h) Release 4 70 3.0
5 90 2.5
6 90 3.0
7 90 3.5
Figure 2: Fabrication process of micro-needle 8 90 4.0
9 90 4.5
Anisotropic Wet Etching
The jagged groove of the micro needle is fabricated by anisotropic wet etching of silicon (100) surface.
Tn order to produce desired jagged shape, optimal value of radius of circles and their distance are
investigated. Figure 3 shows the schematic view of the mask pattern. Table 3 shows the parameters
for evaluating jagged groove. If the displacement of circles in Fig.3 is too close, before pyramidal
holes would be made, they are connected to each other and desired jagged shape cannot be formed as
shown in Fig. 4. On the other hand, the displacement of circles is too apart, the pyramidal holes are not
connected easily, which consumes large process time. According to these phenomena, uniform
connection of pyramidal holes is not obtained by using only KOH solution as shown in Fig. 5.
Therefore, a new process of etching silicon groove is developed. First KOH solution is used for
pyramidal part, since etching is stopped accurately on (111) surface, second TMAH solution is used for
connecting part, since TMAH etching forms more isotropic shape compared with KOH etching. The
result of etched groove using both KOH and TMAH solutions is shown in Fig. 6.

Connected part
Not connected
part

(a) 60min etching by (b) 90min etching by
KOH solution KOH solution Figure 5: Jagged groove when etched
only by KOH solution
Figure 4: Etched groove when squares are too close

Figure 6: Jagged groove of silicon cavity for
micro needle which is etched by both
KOH and TMAH solutions