Micromachining of silicon via ION irradiation with porous silicon formation 5

[...]... used as thin silicon lm solar cells [92, 93], thin silicon transistor [94] or be used for rainbow channeling experiments [ 95] This section discusses early attempts to fabricate thin silicon lms using our methods of micomachining silicon with ion irradiation and PSi formation The schematic for the processes involved in the fabrication of thin silicon lm is shown in Fig 8.11 30 keV oxygen ions were rst... Figure 8.14: Optical image of the 3 .5 m thick silicon grid resting on top of a tweezer 8.4 Summary This chapter provided brief descriptions of preliminary works and experiments but nevertheless shows how versatile this machining technique of silicon using ion irradiation is Three dimensional and free standing silicon structures, thin silicon walls, thin silicon lms as well as silicon based waveguides... as before, with a uence of 5 10 13 /cm2 with 250 keV The sample is then electrochemically anodized in a two-step process 2 anodization in 12% HF with a current density of 100 mA/cm Firstly, for 74 s was performed This creates a layer of PSi which stops at the end of range of the protons This rst layer of PSi is then removed with KOH The second anodization step is then carried out in 2 24% HF with a current... In addition, the large area irradiation facility was successfully constructed during the course of this thesis and was applied to many of the studies presented here The main benet of this machining technique is the ability to selectively form PSi in the lateral and vertical sense by locally introducing defects with irradiation The process of irradiation and electrochemical anodization of silicon has... extent of success Further experimentations and optimization is required before these devices and structures can be fully realized The work described in this chapter forms the basis of several ongoing projects that is being carried out presently Chapter 9 Conclusion The technique and capability of two and three dimensionally micro machining silicon/ PSi using ion irradiation together with PSi formation. .. fabricate arrays of free standing waveguiding structures These structures were relatively easy to achieve with all the prior experience accumulated in machining silicon with ion irradiation The cross sections of the successfully fabricated structures can be seen in Fig 8.9 Figure 8.9: SEM image showing arrays of freestanding irradiated waveguides structures Fig 8.10(a) shows an array of 5. 2 fashion protons... irradiated with 1MeV helium ions (range of $3 .5 m uence of 5 in silicon) This irradiated grid however, has a bigger period of 30m (Fig 8.12(a)), so that both irradiated regions overlaps The second PR layer was then removed and the sample was electrochemically anodized at 60mA/cm2 for $20 mins PSi would form from unirradiated regions (previously covered by square PR), goes pass the end of range and... However, a PR with   83 was used and was shown to be still too steep for the sloping silicon wires to form The same irradiation energies, uences and lines as described in the previous section were irradiated over 8m thick and 5 m wide SU8 PR lines with the silicon wires irradiated at an angle to the PR lines Fig 8.6 shows an SEM image of this sample after the anodization and PSi removal The silicon wires... True three dimensional and free standing silicon structures 121 122 2 Silicon structures with concave proles 3 Multi-leveled PSi structures 4 Multi-leveled silicon structures 5 Silicon structures sloping at an angle from the surface 6 Silicon walls with straight side walls 7 Freestanding PSi structures 8 Freestanding silicon structures The ability to create the many dierent kinds of structures have... to fabricate complex silicon structures and devices The steps involved are simple and direct: 1 Irradiation of the silicon wafers 2 Electrochemical anodization of the irradiated wafers 3 Removal of PSi (or not) by KOH or electropolishing Any pre or post processing are usually simple and depends largely on the requirements of the structures being fabricated To summarize, the kind of structures that were . x0 y2 w2 h3" alt=""