CMP 후세정에서 콜로이달 실리카 입자의 부착 및 제거 메커니즘 = Adhesion and removal mechanism of colloidal silica particle in post-cmp cleaning

다국어 초록 (Multilingual Abstract)

Chemical Mechanical Polishing (CMP) has emerged as a critical technology for achieving global and local planarization in advanced integrated circuit manufacturing. The CMP has been continuously improved to enable multilevel ULSI device fabrication. As device features continue shrinking, post-CMP cleaning technique to remove the submicron particles becomes more and more important. Particulate matter on a semiconductor wafer can cause circuit defects and thus yield loss in the final product. RCA cleaning in a wet station is a typical wet chemical cleaning method based on the etching mechanism. However, RCA cleaning causes critical environmental issues resulting from a huge amount of chemical and DIW waste. Therefore, Physical cleaning can solve the issues introduced in conventional chemical cleaning, and brush scrubbing is one of the most effective physical cleaning methods. The brush asperities engulf the wafer surface contaminations in direct contact while brush rotates. However, if the removal force does not overcome the adhesion force between the wafer surface and the particle, the particle will still remain on the wafer surface as a contamination. While the high cleaning force condition can generate the defects such as scratch and collapse of pattern. Therefore, the post-CMP cleaning requires understanding of particle adhesion for efficiently removal of particle and prevention of pattern and surface.
In this research, AFM equipment was calibrated to measure the removal force of the colloidal silica particles, which is used as the abrasive particle during CMP process. AFM is a useful tool, not only imaging surfaces but also for the quantification of interfacial force both in the normal force and lateral force. It can be measured adhesion force between particle and substrate surface using calibration factor of AFM. The adhesion force between two surfaces depends of both the material properties and the condition of the surfaces such as chemical bonding, interfacial reactions, condensation and diffusive mixing. The adhesion force of colloidal silica particle were classified into the contact area and contact energy was obtained by the AFM lateral friction force and the theoretical analysis of Van der Waals interaction, capillary force and electrostatic force.
From the results, the adhesion force between silicon surface and silica particle of 100nm was increased as a function of contact area. If the presence of an external force such as CMP pressure, the particle was penetrated the substrate surface by CMP pressure and particle and substrate surface had higher contact area than dipping due to down force. If external force does not exist, the Van der Waals interaction is a dominant force in the adhesion of particle. A poor roughness of the substrate surface results in an increase of the contact area. This can be proved through AFM friction experiment, the adhesion force increased from about 44nN to 60nN according to roughness of surface. The average removal forces were measured to be about 41nN, 45nN, 60nN and 70nN for 10%, 20%, 50% and 90% in relative humidity, respectively. This indicates that the control of capillary force is very important for effective cleaning. In the high humidity condition of more than 70%, the meniscus is formed in the contact area and additional normal force occurred by meniscus area.The particle size affects Van der Waals force and deformation of particle due to the passage of time affects the contact area. After 720 hours of time later, the force to remove particles is needed more than 300nN.The results of AFM test have a similar tendency with mathematical calculated adhesion force by Van der Waals interaction. Also, the adhesion force between particle and substrate is increased in proportion to the contact area.
To confirm the effect of contact energy on the adhesion force, the surface treatment was carried out using NH4OH and BOE solution. The Cleaning efficiency of MH(more hydrophilic) surface is reduced than LH (less hydrophilic) surface. However, removal force by AFM lateral friction test does not seem noticeable difference according to substrate surface energy of wettability. When the colloidal silica particles are attached with different materials, Van der Waals force and electrostatic force change by Hamaker constant and surface potential. The particles on the Cu substrate formed zeta potential of opposite polarity; particle deposit amount was increased due to attractive interactions between the particles and Cu surface. In addition, the increase of slurry pH results in a reduction in adsorption of particles due to repulsive interaction. However, adhesion force by AFM test was measured almost the same value of 50nN. The electrostatic force due to the change of zeta potential doesn’t have a significant impact after dry of particles. As time goes by, the removal of particle becomes more difficult. A covalent bond proceeds in the contact area between particle and substrate due to the supply of oxygen of atmosphere and formation of native oxide. Therefore, high energy of 110kcal requires breaking the siloxane bonding between particle and substrate; it matches well with the AFM lateral friction force over 300nN. The electrostatic force affects the adsorption amount, Van der Waals force and capillary force play a dominant role in the adhesion force and it can be explained by the theory of DMT model.
From this research by AFM, it was possible to find a maximum removal force for efficient cleaning. Also, the physical cleaning condition by AFM test should be optimized for high cleaning efficiency, keeping a defect-free surface.

목차 (Table of Contents)

• 1.서론 1
• 1.1 연구 배경 1
• 1.2 CMP와 Post-CMP Cleaning 6
• 1.2.1 화학 기계적 연마 6
• 1.2.2 화학 기계적 연마 후 세정 9
• 1.3 연구 목적 15
• 1.4 논문의 구성 18
• 2.이론적 배경 21
• 2.1 콜로이달 실리카 입자 21
• 2.1.1 콜로이드 21
• 2.1.2 콜로이달 실리카 22
• 2.1.3 CMP 슬러리 내의 콜로이달 실리카 25
• 2.2 접촉 역학 29
• 2.2.1 Hertz 이론 29
• 2.2.2 JKR 이론 32
• 2.2.3 DMT 이론 35
• 2.3 콜로이달 실리카 입자의 부착 및 제거 39
• 2.3.1 반데르 발스 힘 40
• 2.3.2 모세관 응력 44
• 2.3.3 정전기력 48
• 2.3.4 입자의 제거 모델 54
• 3.실험 장치의 구성 62
• 3.1 AFM 마찰력 측정 62
• 3.1.1 AFM의 원리 63
• 3.1.2 수평 방향으로의 스캔 66
• 3.1.3 마찰력 측정을 위한 교정 계수 68
• 3.1.4 교정 계수를 이용한 표면 마찰력 측정 73
• 3.1.5 힘-거리 곡선 80
• 3.2 입자 배열을 통한 신뢰성 84
• 3.2.1 모세관 현상을 이용한 입자 배열 84
• 3.2.2 AFM 을 이용한 입자 제거 89
• 3.3 PVA 브러쉬 세정 장치 및 입자 제거 효율 91
• 4.접촉 면적에 따른 입자의 부착 및 제거 98
• 4.1 CMP 공정에 의한 영향 98
• 4.1.1 실험 조건 및 방법 99
• 4.1.2 CMP 공정에 의한 입자 침투 101
• 4.1.3 CMP 압력의 영향 108
• 4.2 표면 형상의 영향 114
• 4.3 상대 습도의 영향 121
• 4.3.1 상대 습도에 따른 모세관 응력의 변화 121
• 4.3.2 힘-거리 곡선을 이용한 모세관 응력 123
• 4.3.3 AFM 마찰 신호 분석 126
• 4.4 입자의 변형과 크기의 영향 130
• 4.4.1 입자의 크기와 변형과의 관계 130
• 4.4.2 입자 크기에 따른 영향 133
• 4.4.3 입자 변형에 따른 영향 137
• 4.5 요약 141
• 5.접촉 에너지에 따른 입자 부착 및 제거 144
• 5.1 표면 에너지의 영향 144
• 5.1.1 표면 에너지와 접촉각의 관계 145
• 5.1.2 표면 에너지와 입자 부착력 147
• 5.2 기판 재료의 영향 152
• 5.3 pH의 영향 159
• 5.3.1 pH와 입자 분산의 관계 159
• 5.3.2 pH와 입자 부착력 163
• 5.4 시간에 따른 영향 168
• 5.5 요약 175
• 6.결론 178
• References 183
• Abstract 191