Chih-Chen Cho

Preparation Of Low-Density Xerogels At Ambient Pressure For Low K Dielectrics

Low density silica xerogels have many properties which suggest their use as a low dielectric constant material. Recent process improvements to control capillary pressure and strength by employing aging and pore chemistry modification, such that shrinkage is minimal during ambient pressure drying, have eliminated the need for supercritical drying. Although xerogels offer advantages for intermetal dielectric (IMD) applications because of their low dielectric constant (

Visible photoluminescence from porous Si formed by annealing and chemically etching amorphous Si

We have studied the visible photoluminescence (PL) and microstructure of amorphous Si (a‐Si) after annealing and etching. The a‐Si layers were grown on (100)Si substrates and partially crystallized by annealing between 550–1150 °C. Porous Si layers (PSLs) were then produced by etching in HF‐HNO3. While no visible PL was observed from unannealed and etched a‐Si, visible PL was detected after annealing and etching. The observation of visible PL after etching coincided with the observation of Si microcrystallites in the annealed layer. The results suggest that an initial crystalline structure is important for fabricating luminescent PSLs.

Low dielectric-constant insulators for electronics applications

Abstract The decreasing device geometry and the increasing use of portable electronics have escalated the need to reduce the capacitance of electronic devices so that higher speed, less crosstalk and lower power consumption can be achieved. High porosity SiO2 (silica xerogel) and Teflon® AF are two examples that show the challenges in introducing new intermetal dielectrics into VLSI interconnect structures. Teflon® AF and crack-free silica xerogel films have been grown by spin-coating and show dielectric constants of 1.9 and 1.14–1.56 (at optical frequency), respectively. The growth processes and the film characteristics are discussed.

Photoluminescence from submicron CaF2: Nd films grown epitaxially on Si(111) and Al(111)/Si(111)

Nd3+ doped CaF2 films have been grown epitaxially on Si(111) and Al(111)/Si(111) using CaF2 and NdF3 evaporation. Photoluminescence spectra from these samples show high intensity and narrow emission linewidth even when the thickness of the CaF2:Nd films is reduced to 0.2 μm. The 10 457 A emission line is not quenched until the Nd concentration exceeds 3.8 wt.%. Moreover, while similar spectra are observed, the photoluminescence intensity from the CaF2:Nd films grown on Al/Si(111) is significantly higher than from the CaF2:Nd on Si(111).

Effects of a predeposited boron layer during the epitaxial growth of Ge on CaF2

Using a thin predeposited B layer prior to the epitaxial growth of Ge on CaF2, we have obtained significantly improved Ge crystalline quality and surface morphology for Ge/CaF2/Si(111) and Ge/CaF2/Si(100) structures. Although B acts as a surfactant in suppressing island formation, it does not migrate to the growth front during Ge growth, which was widely observed in the surfactant‐assisted epitaxial growth of Ge on Si. The B predeposit also prevents Ca from migrating to the Ge surface, and promotes A‐type epitaxy of Ge(111) when Si(111) substrates are used.