Papers by Author: Ho Jun Lee

Abstract: Silicon carbide (SiC) is a wide band gap semiconductor being developed for high temperature, high power, and high frequency device applications. For the manufacturing of SiC to semiconductor substrate, many researchers have studied on the subject of SiC polishing. However, SiC faces many challenges for wafer preparation prior to epitaxial growth due to its high hardness and remarkable chemical inertness. A smooth and defect free substrate surface is important for obtaining good epitaxial layers. Therefore, hybrid process, chemical mechanical polishing (CMP) has been proposed to achieve epi-ready surface. In this paper, the material removal rate (MRR) is investigated to recognize how long the CMP process continues to remove a damaged layer by mechanical polishing using 100 nm sized diamond, and the authors tried to find the dependency of mechanical factors such as pressure, velocity and abrasive concentration using single abrasive slurry (SAS). Especially, the authors tried to get an epi-ready surface with mixed abrasive slurry (MAS). The addition of the 25nm sized diamond in MAS provided strong synergy between mechanical and chemical effects resulting in low subsurface damage. Through experiments with SAS and MAS, it was found that chemical effect (KOH based) was essential and atomic-bit mechanical removal was efficient to remove residual scratches in MAS. This paper concluded that SiC CMP mechanism was quite different from that of relatively soft material to achieve both of high quality surface and MRR.

Abstract: Lithium niobate (LN, LiNbO3) is a kind of artificial crystal with piezoelectricity, pyroelectricity and ferroelectricity, which has been widely used in electron components. The large difference in thermal expansion coefficients between Si and LN causes a serious thermal stress during the thermal-pressure bonding process. Therefore room temperature bonding would be the best candidate to make strong and stress-free interface between Si and LN. However, room temperature bonding requires lower surface roughness (Ra<2nm) and lower defects on the LN wafer surface than those of thermal bonding. Chemical mechanical polishing (CMP) process helps LN to obtain the high quality surface and thin wafer suited in room temperature bonding. The LN wafer was polished using colloidal silica slurry, resulting in high material removal rate (MRR) and fine surface quality under the condition of low pH, high abrasive concentration and low flow rate. The polishing mechanism of LN was discussed by mechanical, chemical and thermal analysis.

Abstract: Chemical mechanical polishing (CMP) has been used as planarization process in the fabrication of semiconductor devices. The CMP process is required to planarize the overburden film in an interconnect process by high relative velocity between head and platen, high pressure of head and chemical effects of an aqueous slurry. But, a variety of defects such as dishing, delamination and metal layer peering are caused by CMP factors such as high pressure, pad bending and strong chemical effect. The electrical energy of the electro-chemical mechanical planarization (ECMP) dissolves copper (Cu) solid into copper ions electrochemically in an aqueous electrolyte. The dissolved copper complex layer or passivation layer is removed by the mechanical abrasions of polishing pad and abrasive. Therefore the ECMP process realizes low pressure processing of soft metals to reduce defects comparing to traditional CMP process. But, if projected metal patterns were removed and not remained on whole wafer surface in final processing stage, Cu layer could not be removed by ECMP process. The two-step process consists of the ECMP and the conventional CMP used in micro patterned Cu wafers. First, the ECMP process removed several tens 'm of bulk copper on Cu patterned wafer within shorter process time than the Cu CMP. Next, residual Cu layer was completely removed by the Cu CMP under low pressure. Total time and process defects are extremely reduced by the two-step process.