The escalating cost for next generation lithography (NGL) tools is driven in part by the need for complex sources and optics. The cost for a single NGL tool could exceed $50M in the next few years, a prohibitive number for many companies. As a result, several researchers are looking at low cost alternative methods for printing sub-100 nm features. In the mid-1990’s, several research groups started investigating different methods for imprinting small features. Many of these methods, although very effective at printing small features across an entire wafer, are limited in their ability to do precise overlay. In 1999, Colburn et al. [Proc. SPIE 379 (1999)] discovered that imprinting could be done at low pressures and at room temperatures by using low viscosity UV curable monomers. The technology is typically referred to as step and flash imprint lithography. The use of a quartz template enabled the photocuring process to occur and also opened up the potential for optical alignment of the wafer and template. This article traces the development of nanoimprint lithography and addresses the issues that must be solved if this type of technology is to be applied to high-density silicon integrated circuitry.

Current voltage curves and the effective dissolution valence have been determined for GaP electrodes in 3N NaOH solution. At electrode potentials of a few volts the current density for p-type (NA ~ 4(10)17-cm-3) is a factor of 10 4 greater than for n-type (ND ~ 4 (10)17 cm-3) electrodes. This difference allows selective removal of p material from p-n structures. Application of this selective etching to the fabrication of mesa structures for GaP light emitting diodes, and to junction delineation, is discussed. At large current densities, 6 charges are transferred per dissolved GaP molecule in distinction to the 3 transferred charges found previously in alkaline solution at low (< 2mA cm -~) current densities.As III-V compound semiconductor device technology is advanced, it becomes desirable to apply some of the electrochemical processing and evaluation techniques which have proven useful for silicon and germanium (1-3) to those materials. The present paper discusses anodic dissolution and selective etching of gallium phosphide.In comparison to germanium and silicon, the electrochemistry of the III-V compounds has not been widely studied. The occurrence and nature of surface films (4, 5) and the morphology of the etched surface (5, 6) have been determined for InSb. Several authors have discussed the electrochemistry (7-12) and Nuese and Gannon have described selective etching (13) of GaAs. Memming (14, 15) has studied GaP, but not at the rather large anodic current densities desired for etching and shaping operations.Experimental Current density-potential relations were determined in the apparatus of Fig. 1. The electrolyte was 3N aqueous NaOH maintained at 20~ although the exact temperature is not critical. Measurements were made in the dark and potentials are relative to the saturated calomel reference electrode. The samples were of (111) orientation, and both the Ga (111) and P-(lil) faces were studied. The faces were distinguished by their chemical etching characteristics in C12 saturated methanol. This and equivalent techniques are ultimately traceable to x-ray evidence. N-type samples were Se doped and p-type samples were Zn doped to a level of about 4(10) 17 cm -8 and were cut from LEC (Liquid Encapsulated Czochralski) pulled ingots. Ohmic contacts on p-type (n-type) were prepared by evaporating and alloying gold containing 1% Be (2% Si). Surfaces were chemically or mechanically polished, as applicable, before use as electrodes. The number of electronic charges passing through the external circuit per dissolved atom was determined by integrating the current for a certain time and measuring the weight loss with a microbalance.

Infrared spectra of NH4Cl, ND4Cl, NH4Br, and ND4Br have been recorded at numerous temperatures between 21 and 300°K using thin sublimed films, single-crystal sections, and pressed disks. At 21°K each spectrum contains a large number of sharp intense bands which can be assigned to combinations involving the internal vibrational modes of the ammonium ion, the librational (torsional oscillation) mode, and various lattice modes. Observation of the first and second librational overtone makes it possible to discuss the potential barrier hindering the rotation of the ammonium ion. Barrier heights of 1860 cm−1 (5.32 kcal mole−1) for NH4Cl and ND4Cl and 1520 cm−1 (4.35 kcal mole−1) for NH4Br and ND4Br were calculated from the Gutowsky–Pake–Bersohn model, but the experimental frequencies show that the libration is more anharmonic than this model would predict. The temperature dependence of an anomalous component of the ν4 bending fundamental was studied in detail. The intensity of this component can be directly correlated with the breakdown of translation symmetry due to disorder in the ammonium ion orientations. In addition, this feature of the spectrum indicates that there is appreciable distortion in the ordered cubic phase of NH4Br and ND4Br prior to the first-order transition into the ordered tetragonal phase.

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The escalating cost for Next Generation Lithography (NGL) tools is driven in part by the need for complex sources and optics. The cost for a single NGL tool could exceed $50M in the next few years, a prohibitive number for many companies. As a result, several researchers are looking at low cost alternative methods for printing sub-100 nm features. In the mid-1990s, several research groups started investigating different methods for imprinting small features. Many of these methods, although very effective at printing small features across an entire wafer, are limited in their ability to do precise overlay. In 1 999, Willson and Sreenivasan discovered that imprinting could be done at low pressures and at room temperatures by using low viscosity UV curable monomers. The technology is typically referred to as Step and Flash Imprint Lithography (5-FIL). The use of a quartz template enabled the photocuring process to occur and also opened up the potential for optical alignment of the wafer and template. This paper traces the development of nanoimprint lithography and addresses the issues that must be solved if this type of technology is to be applied to high-density silicon integrated circuitry.