Etch depth

Reactor type Chip micro reactor with multiple vertical injections in a main channel Micro-channels etch 146 pm 38 pm mask width etch depth... 

The majority of micromechanical devices require 3D machining of the bulk silicon material with etching depths of up to wafer thickness. Generally, three basic etching process types can be distinguished ... 

Srinivasan etal.,64 in a phenomenological development, split the etch rate into thermal and photochemical components and used zeroth-order kinetics to calculate the thermal contribution to the etch rate. An averaged time-independent temperature that is proportional to the incident fluence was used to determine the kinetic rate constant. The photochemical component of the etch rate was modeled using, as previously discussed, a Beer s law relationship. The etch depth per pulse is expressed, according to this model, in the form... 

Deviations between the actual ablation rates and those predicted using Eq. (2) occur at higher fluences. 64 65 Hence, a different rate equation is required to determine the relationship between amax and fluence. According to a rate model proposed by Sauerbrey and Pettit,46 the etch depth per pulse is given by... 

Masking is required for many micromechanical applications. While Si3N4 is only suitable for a small etching depth because of its significant etch rate in HF, noble metals like gold are sufficient mask materials. In contrast to alkaline etchants, organic materials like certain resists or even some adhesive tapes are well suited to protect the silicon surface in isotropic etchants. 

Figure 10. Calculated variation with cladding thickness of the birefringence in a SOI ridge waveguide, for different Si02 cladding film stress values. The model waveguide is formed in a 2.2 [j,m thick Si layer and has a typical trapezoidal wet etched ridge profile, with a base width of 3.8 pm, a top width of 1.1 pm, and an etch depth or 1.47 pm.

Figure 11. Comparison of calculated and measured birefringence for different Si02 cladding thicknesses for a trapezoidal waveguide formed in a 2 im thick Si layer as shown in the inset. The ridge base width is 3.8 p,m, the top width is 1.1 pm, and the etch depth is 1.47 pm.

Figure 18. Experimental procedure (a) and stylus thickness measurement (b) for determining etch depth.

In the selection of etch mask for deep glass etching, thick SU-8 is a choice, but SU-8 cannot be used in a HF bath (48%) because SU-8 does not adhere well to Si02 [123]. However, with a polycrystalline amorphous Si seed layer SU-8 adheres very well. For instance, with a 1.5-pm-thick polished poly silicon, a 50-pm-thick SU-8 can be deposited as the etch mask, leading to a maximum etch depth of 320 pm. Usually photoresist (2 pm thick) is only useful for shallow etch, less than 50 pm [123]. 

Polished or unpolished polysilicon (by low-pressure CVD at 620°C) is another etch mask option. Utilizing 2.5-pm-thick unpolished polysilicon, a maximum etch depth of 160 pm was reached using a HF/H20/HN03 (6 40 100) solution. Further etching causes large pits (1.5-2.2 mm dia.) to form on the glass. With polished poly silicon (1.5 pm thick), etch depth up to 250 pm can be achieved. When amorphous Si is used as the etch mask, a maximum etch depth of 170 pm can be reached [123]. 

Etch Conditions Etch Depth Wet HF Etch References... 

Infrared detection of toluene can be achieved on a microchip. The chip substrate, which should be IR-transparent, has been fabricated from CaF2. The microchannels were etched on CaF2 using a saturated Fe(NH4)(S04)2 solution at room temperature for 24 h. The etched depths were -18 im or - 8 im, when the etchant was stirred or unstirred, respectively. Bonding was achieved using photoresist as an adhesive layer and with heating (135°C, 30 min) [743,744],... 

Figure 2.10 Different forms, simple comer compensation and design elements. The edge length a depends on the etching depth D accordingto the empirical formula the complete compensation reached with o= D.

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