Etching ratio

Schematic polarisation curves for phases a and 0 showing the selection of optimum dilTerential etch ratio conditions...

Electrodes 2, an insulating layer 3 and an HgCdTe layer 4 are formed on a substrate 1. A mask 5 is provided and the structure is dry etched. The etching ratio of the mask to HgCdTe is selected so as to form an uniform layer 6 of type converted HgCdTe. 

The requirement for use of these membranes as templates is to have high track etch ratios. For PC, track etch ratios above ten thousand have been observed. At the other extreme, addition of solvents, such as methanol, ethanol or propanol can dramatically decrease the track etch ratio, down to 2 to 4 in the case of PET. Although they accelerate the etching process, polymers like PMMA are generally etched with an acidic medium leading to very low etch track ratios 1-10. In a recent study on the polymer polyallyl diglycol carbonate (PADC) [9] it was found that etch-rate values of the PADC increase nearly fourfold if the polymer is irradiated with 100 Mrad dose of electrons at 2 MeV prior to the heavy ion irradiation. The etch tracks were created by 140 MeV Si ions. 

Strictly speaking, the dry-process compatibility for a resist is very process dependent, and must be measured for the specific process involved. A general idea of compatibility, however, can be obtained by doing a CF4/O2 plasma etch test vs Si02 and/or PMMA references, and this test has been adopted as a quick screen test for dry-process compatibility for new resists. The relative etch ratios vs these references usually, but not always, remain constant when the process requiring resist masking is changed (e.g., PE to RIE), thus, what is measured is resist compositionally-dependent. 

Block copolymers can be employed as templates to direct the deposition of inorganic nanostructures. Parket al. [82] used an Os04-stained microphase-separated thin film of poly(styrene-foZock-butadiene) that produced holes upon RIE in silicon nitride substrates. The etch ratio between the two phases, stained butadiene and styrene, was only about 1 2. MoUer et aL discussed the use of poly(styrene-fc/ock-2-vinylpyridine), to prepare masks for nanolithography by loading the PVP domains with gold particles [83] or by selective growth of Ti on top of the PS domains [84]. 

The second approach demonstrated the ability to switch the durability of the PB block under RIE conditions. In the inverse process, the reactive double bonds in PB can be stained with a heavy metal vapor of osmium tetroxide, dramatically increasing the polymer s CF4/O2 etch resistance relative to the PS matrix ( 2 1 etch ratio of PS osmium-stained PB). This enabled the creation of silicon nanopillars, which foresaw later industrial applications of BCs, as described below. 

Etching rate of the unmodified glass (nm min ) Etching rate of the modified glass (pm min ) Etching ratio... 

Etching rate (mg cm min ) Etching ratio relative to the FS21 glass areas... 

If 15 or 20% HF solutions were used the etching rate of the glassy areas were also very high, resulting in a bad etching ratio. 

The best etching ratio between partially crystallised and glassy areas was found when HF solutions with concentrations between 5 and 10% were used. The etching ratio was not remarkably different when HF solutions in this concentration range were used. 

Fig. 9.26. Etching ratio Q as function of the etching time te and the relative energy density Ds [190]...

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