Yil Wook Kim

Comparison of deep silicon etching using SF6/C4F8 and SF6/C4F6 plasmas in the Bosch process

Silicon was etched with the Bosch process using C4F8 and C4F6 plasmas in the deposition step to show a feasibility of the use of UFC plasmas in the Bosch process. The use of C4F8 and C4F6 plasmas resulted in different characteristics of fluorocarbon films and radicals, affecting the etch profiles. It was shown that the use of a C4F6 plasma in the deposition step of the Bosch process produced thicker and more strongly bonded fluorocarbon films, compared to a C4F8 plasma. It was because more CF2 radicals and lower F/C ratio fluorocarbon films were generated in C4F6 plasmas than those in C4F8 plasmas, confirmed by OES and XPS measurements. By changing only the duration of the deposition step under the same process conditions, highly anisotropic deep etching of silicon was successfully achieved using both SF6/C4F8 and SF6/C4F6 plasmas in the etching and/deposition steps of the Bosch process.

Material characteristics of electrically tunable zirconium oxide thin films

Material characteristics of zirconium oxide thin films obtained by plasma enhanced chemical vapor deposition on p-type Si (100) substrates were investigated to explain their tunable electrical properties. The films obtained without heating had polycrystalline nanograins that are mostly of a tetragonal phase under oxygen-deficient plasma conditions but transformed into a monoclinic phase with increasing O2 addition in the plasma. Mostly amorphous bulk ZrO2 with a relatively thicker and smoother interfacial layer was obtained from oxygen-rich plasmas, resulting in a decrease in both the overall dielectric constant and the leakage current density. The interfacial layer formed between the bulk ZrO2 and Si substrate was analyzed to be zirconium silicate, which approached SiO2 as its zirconium content decreased with the increasing gas phase O2 content.

Dependence of etch rates of silicon substrates on the use of C4F8 and C4F6 plasmas in the deposition step of the Bosch process

The Bosch process was carried out using SF6∕C4F8 or SF6∕C4F6 plasmas during the etching/deposition steps to examine the etch profiles and etch rates of silicon. The fluorocarbon film deposited in a C4F6 plasma was thicker and more strongly bonded than the film deposited in a C4F8 plasma, which led to a shorter deposition time for the C4F6 plasma. The deposition rate of the fluorocarbon films on the different locations of the silicon substrate in both C4F8 and C4F6 plasmas decreased in the following order: top>bottom>sidewall. However, the normalized deposition rate of the bottom surface with respect to the top surface was higher for the C4F8 plasma (0.92) than for the C4F6 plasma (0.65), indicating that a thicker fluorocarbon film was deposited at the bottom of the pattern in C4F8 plasma under the same process conditions. This resulted in a higher etch rate of the silicon substrate using C4F6 plasma during the deposition step of the Bosch process, even though a fluorocarbon film with a similar thickness h...

Characterization on microstructures of tungsten/barrier metals (TiN,WNx)/silicon multilayer films

Microstructures of W/barrier metals (TiN,WNx)/Si multilayer films followed by heat treatment were precisely investigated by x-ray diffraction and high-resolution transmission electron microscopy. The analysis results showed that in the W/TiN/Si stacked film having the W (110) and (200) preferred orientations, the TiN film itself plays a role as a barrier for the reaction of W and Si, whereas in the case of the WNx barrier having the W (110) one, the amorphous SixNy layer with a thickness of a few nanometers works effectively as a barrier, which was formed during the deposition and denudation process of the WNx film. Furthermore, the nanometer-scaled interfacial reaction in the multilayer films was clearly investigated by x-ray photoelectron spectroscopy coupled with chemical etching and an energy-filtered elemental mapping technique. Based on the results, effects of barrier metals on the W preferred orientation and the interfacial reaction were crystallographically and thermodynamically discussed.

A comparative study on a high aspect ratio contact hole etching in UFC- and PFC-containing plasmas

An etching of a SiO2 contact hole with a diameter of 0.19μm and an aspect ratio of 13, using C4F6/Ar/O2/CH2F2 and c-C4F8/Ar/O2/CH2F2 plasmas, was performed for a feasibility test of the use of unsaturated fluorocarbons (UFCs) as an alternative to perfluorocarbon (PFC) gases for a high aspect ratio contact hole etching. The etch profile of the contact hole obtained in the C4F6/Ar/O2/CH2F2 plasma was shown to have 23% lower degree of bowing than that in the c-C4F8/Ar/O2/CH2F2 plasma. The Kelvin and chain contact resistances of the contact holes etched in the C4F6/Ar/O2/CH2F2 plasma were 10-12% higher than those in the c-C4F8/Ar/O2/CH2F2 plasma, but they were within the device spec. The integration of device with 0.1μm design rule using C4F6/Ar/O2/CH2F2 and c-C4F8/Ar/O2/CH2F2 plasmas during the contact hole etching was also conducted, and it was found that etch profiles, metal coverage, and bottom critical dimensions of the contact in the C4F6/Ar/O2/CH2F2 plasma were nearly identical to those in the c-C4F8/Ar/O2/CH2F2 plasma, suggesting that the use of C4F6 gas as an etchant gas for a high aspect ratio contact hole etching can be a good alternative to PFC gases.

Structural and Morphological Properties of Nitrogen Doped Polysilicon for Advanced Gate Material

Polysilicon (poly-Si) is mainly used as gate material for metal-oxide-semiconductor (MOS) based devices. As the dimensions of the MOS based devices keep shrinking, their performance depends critically on the film properties such as surface morphology and grain size distribution. Especially, it is strongly required that poly-Si gate has a uniform grain size distribution through the entire film stack to keep endurance and reliability of the devices [1]. In this work, improvement of the grain size distribution and morphology of poly-Si was investigated using nitrogen doped poly-Si. Nitrogen doped poly-Si was deposited by low pressure chemical vapor deposition (LPCVD) from silane (SiH4) and ammonia (NH3). The temperature and NH3/SiH4 ratio were varied, and their effects on deposition rate, nitrogen concentration, surface roughness, and grain size were discussed. The deposition rate of nitrogen doped poly-Si decreased with increasing NH3/SiH4 ratio (Figure 1). It was because the pyrolysis of SiH4 was inhibited by the presence of NH3. NH3 reacts with SiH4 to increase H2 concentration in the gas phase [2], resulting in a decrease in the deposition rate. The surface roughness of nitrogen doped poly-Si also decreased with increasing NH3/SiH4 ratio (Figure 2). Therefore, it can be said that the roughness of nitrogen doped poly-Si is related to deposition kinetics rather than to microstructure.