具高度差之晶圆在化学机械研磨中之研磨机制与研磨参数研究
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¨ã°ª«×®t¤§´¹¶ê¦b¤Æ¾Ç¾÷±ñ¬ã¿i¤¤¤§¬ã¿i¾÷¨î»P¬ã¿i°Ñ¼Æ¬ã¨s -p¹º½s¸¹¡G NSC89-E-002-022 °õ¦æ´Á¶¡¡G¤K¤Q¤K¦~¤K¤ë¤@¤é¦Ü¤K¤Q¤E¦~¤C¤ë¤T¤Q¤@¤é ¥D«ù¤H ¡G³¯¹F¤¯ ¡A°ê¥ß¥xÆW¤j¾Ç±Ð±Â -pµe°Ñ»P¤H-û ¡G§õ§B¾± ¡B±i¥@©÷ ¡BªL§»µÏ ºK-n ¥»¬ã¨s-pµe¦®¦b«Ø¥ß¤Æ¾Ç¾÷±ñ¬ã¿i¤§´¹¶ê¬ã¿i ¼Ò«¬ ¡A ¨ä¤¤±N¦Ò¼{´¹¶êªí-±°ª«×®t¹ï¬ã¿iªºÃö«Y ¡F ¨Ã¬ã¨s¬ã¿i°Ñ¼ÆªºÅܤƹï©ó¬ã¿i¯S©Ê¤§¼vÅT ¡C ¤å¤¤©Ò«Ø¥ß¤§¤Æ¾Ç¾÷±ñ¬ã¿i¼Ò«¬ ¡A ±NµJÂI©ñ¦b¬ã ¿iªº¾÷±ñ®ÄÀ³¤W ¡C -º¥ý«Ø¥ß¤@-ӤƾǾ÷±ñ¬ã¿i¤§¬ã ¿i¼Ò«¬ ¡A¦Ò¼{´¹¤ùªí-±°ª«×®t¸g¥Ñ¬ã¿i¦Ó´î¤Ö ¡A¶i ¦Ó´£¥X¤@-Ó»P®É¶¡¬ÛÃöªº¬ã¿i³t²v¤½¦¡ ¡C ¦b¬ã¿i¹B °Êªº¬ã¨s¤W ¡A«Ø¥ß¤F¤@-Ó¶}°j¸ô¾Þ§@¾¹ªº¼Ò«¬ ¡C¥Ñ ¦¹µ¥®Ä¼Ò«¬¡A¶i¦Ó¨D±o¬ã¿i³t²vªºªí¥Ü¦¡ ¡F¨Ã±N¬ã ¿i³t²vªí²{¬°¤Æ¾Ç¾÷±ñ¬ã¿i¾÷¤§´X¦ó¥~«¬ ¡B Âà³t¤ñ ¤Î¬ã¿i¹ÔÂà³tªº¨ç¼Æ ¡C¦¹¥~ ¡A°t¦X¹êÅ窺¸ê®Æ¡A¥H ¨ú±o¥²-nªº¬ã¿i°Ñ¼Æ ¡A«Ø¥ß§¹¾ãªº¬ã¿i¼Ò«¬ ¡C §Q¥Î¬ã¿i¼Ò«¬¡A¥i¥H¨D±o¬ã¿i®É¶¡¡B¬ã¿i«p«×¤Î ¥-©Z¤Æ®Ä²vªºªí¥Ü¦¡¡C¨ä¤¤ ¡A¬ã¿i®É¶¡ ¡B¬ã¿i«p«× ¤Î¥-©Z¤Æ®Ä²v ¡A ¯à°÷Åã¥Ü¤Æ¾Ç¾÷±ñ¬ã¿i¦b§½³¡ÂIªº ¬ã¿i¦æ¬° ¡C¥t¤@¤è-± ¡A¥þ-±¥-©Z¤Æªº§¡¤Ã©Ê©M¬ã¿i °Ñ¼Æ¶¡ªºÃö«Y ¡A¤]¯à°÷¨D±o¡C³Ì«á±N´£¥X³o¨Ç¬ã¿i °Ñ¼ÆÅܤƪº®ÄªG ¡A¥H¤Î©Ò³y¦¨ªº¼vÅT ¡A»¡©ú¬ã¿i°Ñ ¼Æ½Õ¾ãªº¤è¦V ¡C¥»-pµeªºµ²ªG ¡A¯à´£¨Ñ¤@-Ó¦³®Äªº ¹w´ú©M§ïµ½¤Æ¾Ç¾÷±ñ¬ã¿i»sµ{¡C ABSTRACT A polishing model of chemical mechanical polishing (CMP) is established with consideration of the effects of pattern density. This paper focuses on mechanical polishing behaviors and isolates the roles of chemical effects when patterns exist. A three-link manipulator, which is in equilibrium with the polishing motion of CMP, is adopted to study the kinematics of CMP. Timedependent removal rate formulas are presented by considering the decrement of pattern step height. The necessary parameters wear coefficient and loading density coefficient, are obtained by fitting to experimental data and the complete model is presented. Based on the pattern planarization model, the polishing time, the polished thickness and the planarization efficiency of a point of interest on the wafer during chemical-mechanical process are expressed as function of polishing parameters. The influences as well as the variation of the polishing time, polished thickness and the planarization efficiency across the wafer are also presented. The polished thickness uniformity and the planarization uniformity are also presented. The effects of the polishing parameters on the process are discussed and the predicted trends in adjusting these polishing parameters are illus1 trated. 1. Introduction Chemical mechanical polishing (CMP) is one of the most effective planarization technologies for achieving smaller feature size and multilevel interconnections for the integrated circuit (IC) industry. CMP is used for planing interlevel dielectrics (ILDs) and metal films in general and can be extended to many planarization techniques in device fabrication. Because of its ability to meet the increasingly stringent lithographic requirements of device manufacture on silicon wafer, CMP is receiving increasing attention in the fabrication of ULSI/VLSI chips. The polishing mechanism, process control and basic understanding of CMP remain essentially on thLeabharlann Baidu experiential level. There is a variety of physical and chemical effects that are involved in the CMP process and analysis from various science and engineering fields are needed. It is assumed that the polishing mechanism is a function of both chemical effects and mechanical effects. Chemical effects are achieved by applying the slurry to the wafer and changing the chemical properties of the wafer. Chemical reactions between slurries and the wafer surface change the solubility and mechanical properties of the wafer surface. The mechanical process is affected by the down force, the rotational speeds of the pad and the wafer, the density and viscosity of the slurry, and the material and the surface microstructures of pad and carrier film. Most previous research has focused on planarization behavior in polishing blanket wafer. The Preston equation, an experiential equation for glass polishing, summarized the mechanical removal rate and hence provided a way for process control. Cook (1990) reviewed the mechanics and chemical polish for glass polishing and proposed a micro-cutting mechanism to simulate the breaking of chemical bonds. Runels and Eyman (1994) analyzed the fluid film between wafer and pad. Based on statistical method and elastic theory, Liu et al. (1996) showed that the removal rate is dependent on the elastic modulus of the slurry particle and polished film. Tseng (1997) modified the Preston equation and showed the removal rate is proportional to the terms P5/6 and V1/2. However, the polishing of blanket wafer and patterned wafer is different. The element configuration on the wafer affects the results of CMP planarization and can behave in a different way.
In this model, the polishing motion is also studied based on the principle of kinematic inversion. Experimental results conduce to necessary parameters and the verification of the CMP model. This semi-experimental model allows quantitative evaluation of a given CMP process and provides a basis for process optimization to meet specific technological requirements for planarization. 2. Polishing Model A schematic diagram of the CMP is shown in Fig. 1. The wafer is mounted upside down on the wafer carrier and rotated above a pad sitting on a table. The slurry that flows between the wafer and the pad dissolves and removes the wafer layer. Figure 2(a) shows a schematic crosssection of wafer surface. There are elements constructed on the wafer surface with different features and the pad is deflected by the down force. An initial step height, h0, between the upper and lower feature surfaces is shown in Fig. 2(b). The polished thicknesses on upper and lower feature surfaces are denoted as δU and δL. For the upper feature surface area, AU, and the lower feature surface area, AL, we have: (1) A = A U + AL where, A is the total wafer area. The pattern density, D, can be defined as A (2) D= U A In the following, polishing behavior with the existence of patterns is considered with the following assumptions A1. The material removal is anisotropic downward and has no effect on the sidewall of the profiles, i.e. (3) PUA U + PL A L = PA where PU and PL are the pressures on the upper and lower feature surfaces, and P is the total pressure. A2. The pressures on the upper and lower surfaces are directly proportional to the step height, h, i.e. (4) PU − PL = αh where the loading density coefficient, α, indicates the stiffness of the polishing pad. A3. The polishing mechanism of every point on the wafer follows the linear wear equation (Rigney, 1965) KLS (5) W= H where W is the wear volume, K is the wear coefficient, L is the down force of the pad onto the wafer, S is the polishing path of the polished point and H is the hardness of the polished material. From Eqs. (2), (3) and (4), PU and PL can be written as
In this model, the polishing motion is also studied based on the principle of kinematic inversion. Experimental results conduce to necessary parameters and the verification of the CMP model. This semi-experimental model allows quantitative evaluation of a given CMP process and provides a basis for process optimization to meet specific technological requirements for planarization. 2. Polishing Model A schematic diagram of the CMP is shown in Fig. 1. The wafer is mounted upside down on the wafer carrier and rotated above a pad sitting on a table. The slurry that flows between the wafer and the pad dissolves and removes the wafer layer. Figure 2(a) shows a schematic crosssection of wafer surface. There are elements constructed on the wafer surface with different features and the pad is deflected by the down force. An initial step height, h0, between the upper and lower feature surfaces is shown in Fig. 2(b). The polished thicknesses on upper and lower feature surfaces are denoted as δU and δL. For the upper feature surface area, AU, and the lower feature surface area, AL, we have: (1) A = A U + AL where, A is the total wafer area. The pattern density, D, can be defined as A (2) D= U A In the following, polishing behavior with the existence of patterns is considered with the following assumptions A1. The material removal is anisotropic downward and has no effect on the sidewall of the profiles, i.e. (3) PUA U + PL A L = PA where PU and PL are the pressures on the upper and lower feature surfaces, and P is the total pressure. A2. The pressures on the upper and lower surfaces are directly proportional to the step height, h, i.e. (4) PU − PL = αh where the loading density coefficient, α, indicates the stiffness of the polishing pad. A3. The polishing mechanism of every point on the wafer follows the linear wear equation (Rigney, 1965) KLS (5) W= H where W is the wear volume, K is the wear coefficient, L is the down force of the pad onto the wafer, S is the polishing path of the polished point and H is the hardness of the polished material. From Eqs. (2), (3) and (4), PU and PL can be written as