Hae Do Jeong

The Effect of Mixed Abrasive Slurry on CMP of 6H-SiC Substrate

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.

Effect of Process Parameters on Material Removal Rate in Chemical Mechanical Polishing of 6H-SiC(0001)

2inch 6H-SiC (0001) wafers were sliced from the ingot grown by a conventional physical vapor transport (PVT) method using an abrasive multi-wire saw. While sliced SiC wafers lapped by a slurry with 1~9㎛ diamond particles had a mean height (Ra) value of 40nm, wafers after the final mechanical polishing using the slurry of 0.1㎛ diamond particles exhibited Ra of 4Å. In this study, we focused on investigation into the effect of the slurry type of chemical mechanical polishing (CMP) on the material removal rate of SiC materials and the change in surface roughness by adding abrasives and oxidizer to conventional KOH-based colloidal silica slurry. The nano-sized diamond slurry (average grain size of 25nm) added in KOH-based colloidal silica slurry resulted in a material removal rate (MRR) of 0.07mg/hr and the Ra of 1.811Å. The addition of oxidizer (NaOCl) in the nano-size diamond and KOH based colloidal silica slurry was proven to improve the CMP characteristics for SiC wafer, having a MRR of 0.3mg/hr and Ra of 1.087Å.

Research on CMP Characteristics Attribute to Groove Size

Groove pads are used quite widely in chemical mechanical polishing (CMP), and groove size plays an important role in CMP characteristics. This study focuses on the investigation of the groove size effect using X-Y groove pads which are different with pitch and width. The first experiment shows the size effect on the polishing characteristics including material removal rate (MRR), within wafer non-uniformity (WIWNU) on 4 inch oxide blanket wafers for 60 seconds. The second experiment verifies the reason why MRR and WIWNU are different, by the calculation of slurry duration time (SDT) resulting from the change of friction force. All experimental results indicated that a significant difference of slurry flow attributed to groove width and pitch has an impressive influence on friction force, finally the MRR and WIWNU are affected by the groove size.

Experimental Analysis in Lithium Niobate CMP for Room Temperature Bonding

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.

Structural Effect of PVA Brush Nodule on Particle Removal Efficiency during Brush Scrubber Cleaning

Brush cleaning can trigger both mechanical and chemical reaction to efficiently remove the adsorbed particles on the wafer. However, the removal mechanism of nanosized particles by brush cleaning is far from clear because no direct experimental data, such as the friction and contact force of the interface between brush and wafer surface, are available to back up the theoretical models in the literature. In this paper, we set up a monitoring system to measure the friction force of the interface between brush and wafer surface during brush cleaning to investigate the effect of the brush nodule structure having different nodule heights and nodule gaps on particle removal efficiency. To confirm the mechanical effect of the brush nodule structure, an oxide wafer contaminated with Polystyrene latex (PSL) particles (mean diameter: 300 nm) was cleaned with each PVA brush having different brush nodule structures using de-ionized water (DIW). The silica particle (mean diameter: 22 nm) and chemical solution (NH4OH, 0.1 wt%) were also used to investigate the chemical-aided particle removal. The remaining particles were measured with a Surfscan 6420 (KLA Tencor) and the friction force monitoring was conducted by using a Cleaner812-L (G&P Technology). The results indicated that a higher brush nodule height produced lower friction force, resulting in lower particle removal efficiency. When the nodule gap became smaller, the contact area between brush nodule and wafer surface became larger, resulting in higher particle removal efficiency. However, the experimental results using silica particles and 0.1 wt% of NH4OH showed different trends under each condition. The particle removal mechanism with silica particle and NH4OH was also verified by measuring the zeta potential between the particle and wafer.

Effect of Hydrogen Peroxide and Oxalic Acid on Material Removal in Al CMP

Chemical mechanical polishing achieves surface planarity through combined mechanical and chemical means. The role of the chemical reaction is very important in a metal CMP like aluminum. The slurry used in aluminum CMP typically consists of oxidizers, a chelating agent, corrosion inhibitors, and abrasives. This study investigates the effect of oxalic acid as a chelating agent for aluminum CMP with H2O2. To study the chemical effect of the chelating agent, the two methods of a polishing experiment and an electrochemical analysis were used. Lastly, it was confirmed that the optimum concentration of oxalic acid significantly improved the removal rate and surface roughness of aluminum.

Influences of Polyurethane Nozzle Shape on Mixing Efficiency

For reaction injection molding (RIM) polyurethane was mixed in the mixing head by impingement mixing, injected into the mold, and cured quickly, as soon as the mold is filled. The shape of the nozzle in the mixing head is critical to improve the quality of polyurethane. To achieve homogeneous mixing, an intensive turbulence energy in the mixing nozzle is essential. In this study, a mixing nozzle for RIM was designed, and mixing efficiency was investigated based on experiment. Experiments were conducted with different combinations of nozzle tips and exit diameter to measure the mixing efficiency by measuring jet force and investigating mixing image with high speed camera. Jet force increased gradually and reaches steady state conditions. The jet force depended on shape of nozzle tip and outlet sizes. These results suggest that optimized nozzle configurations are necessary for high efficiency mixing with RIM.

Analysis of Acoustic Emission Signal Sensitivity to Variations in Thin-film Material Properties During CMP Process

CMP 공정중 웨이퍼 표면에 발생하는 결함 중에는 스크래치(Scratch), 스틱 슬립(Stick Slip) 등과 같은 결함들이 있다. 이러한 웨이퍼 표면 결함들은 슬러리(Slurry), Key Words: CMP(화학 기계 연마), Acoustic Emission Sensor(음향 방출 센서), Monitoring System(감시 시스템) Oxide Wafer(산화막 웨이퍼), Cu Wafer(구리막 웨이퍼) 초록: 본 연구에서는 화학 기계 연마(CMP) 공정 중 발생하는 다양한 영역대의 신호를 분석하기 위하여 음향 방출 센서(AE)를 이용하였다. 특히 음향 방출 센서는 공정 중 발생하는 기계적 소음을 전기적 신호로 변환하기 용이하며, 특히 고주파 영역대의 신호를 감지하기에 용이하다. 그래서 본 연구에서는 CMP 장비에 음향 방출 센서를 부착하여 CMP 공정 중 발생하는 신호를 동시에 획득하였다. 본 음향 방출 모니터링 시스템은 CMP 공정 조건 변화 및 패드, 슬러리, 웨이퍼와 같은 소모재의 변화에 따른 신호분석을 하기 위해 제작 되었다. 본 연구에서는 산화막 웨이퍼와 구리막 웨이퍼에 본 시스템을 적용하였다. 음향 방출 센서로 획득한 신호로 Raw 신호 분석, 주파수 분석, 진폭 분석을 통해서 CMP 공정 중 발생하는 현상을 분석하였다. 최종적으로 다양한 대역폭의 신호를 음향 방출 센서로 획득하여 CMP 공정 모니터링이 가능함을 확인하고자 하였다. Abstract: In this study, an acoustic emission (AE) sensor was used for measuring the abrasive and molecular-scale phenomena in chemical mechanical polishing (CMP). An AE sensor is a transducer that converts a mechanical wave into an electrical signal, and is capable of acquiring high-level frequencies from materials. Therefore, an AE sensor was installed in the CMP equipment and the signals were measured simultaneously during the polishing process. In this study, an AE monitoring system was developed for investigating the sensitivity of the AE signal to (a) the variations in the material properties of the pad, slurry, and wafer and (b) the change in conditions during the CMP process. This system was adapted to Oxide and Cu CMP processes. AE signal parameters including AE raw frequency, FFT , and amplitude were analyzed for understanding the abrasive and molecular-level phenomena in the CMP process. Finally, we verified that AE sensors with different bandwidths could function in complementary ways during CMP process monitoring.

Modeling and Analysis of Material Removal Characteristics in Silicon Wafer Double Side Polishing

As advancing technologies increase the demand for yield and planarity in integrated circuits, wafers have become larger and their specifications more stringent. Flatness, thickness variation and nanotopography have emerged as important concerns in the wafering process. Double side polishing has been adopted as a solution to these problems. This paper focuses on the material removal characteristics and wafer profile variation during Si double side polishing. A polishing experiment to investigate Si removal characteristics according to process parameters was carried out in a single head rotary polisher equipped with a monitoring system for friction force. It was found that the material removal rate is related to friction energy rate, and the polishing state was transited and divided into three conditions according to pressure. On the basis of the experimental results, the wafer profile variation in double side polishing was modelled and simulated according to pressure. The friction energy was calculated to find the material removal amount across the wafer. With the conversion of calculated friction energy to the material removal amount, wafer profile variation was simulated. As a result, the wafer profile variation and its range were increased with a pressure increase, and originated from the position near the wafer edge.

The Effect of PVA Brush Scrubbing on Post CMP Cleaning Process for Damascene Cu Interconnection

Cu (copper) has been widely used for interconnection structure in integrated circuits because of its properties such as a low resistivity and high resistance to electromigration when compared with aluminum [1, 2]. Damascene process for the interconnection structure utilizes 2-steps CMP (chemical mechanical polishing). After 2-steps CMP process, many abrasive particles leave on the wafer surface, which should be removed in post-Cu CMP cleaning process. Cleaning efficiency affects directly on the subsequent process and device yield [3]. Therefore, cleaning of abrasive particles is the critical issue in semiconductor manufacturing.