Abstract:
A method of detecting surface pressure distribution of a wafer being processed by a CMP (Chemical Mechanical Polishing) process; more specifically, the invention relates to a method of detecting pressure distribution of a wafer surface by employing pressure sensitive films located on various pressure components such as a wafer carrier, a polishing pad, and mechanical arm members of a CMP machine for detecting pressure-related data during different stages of a CMP process. Further, sensed pressure-related data are collected for feedback loop controls of digital image mapping, numeration, simulation, and forecasting, from which more mechanical components of high precision and better circuit layouts on the wafer can then be developed.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method of detecting surface pressure distribution of a wafer being processed by a CMP (Chemical Mechanical Polishing) process; more specifically, the invention relates to a method of detecting pressure distribution on a wafer surface by employing pressure sensitive films located on various pressure components such as a wafer carrier, a polishing pad, and mechanical arm members of a CMP machine for detecting pressure-related data during different stages of a CMP process so that better pressure components can be designed accordingly. 
     2. Description of Related Art 
     In any manufacture of ULSI (Ultra-Large-Scale Integration) devices, a precise and stable CMP (Chemical Mechanical Polishing) process has always been a key in maintaining high production yield. Of all the pressure related components contained in a CMP machine, the electro-static-chuck, the mechanical arm, and wafer clamps on a wafer carrier are the most crucial in directly effecting the yield and finishing quality of the CMP process. Currently, there is no available semiconductor equipment that can provide feedbacks of pressure-related data including image data mapping, numeration, simulation, and forecasting for either manual or automatic surface pressure correction on a wafer. 
     FIG. 1 shows a frontal view depicting relative positions of a wafer carrier  12 , a wafer  10 , and a polishing pad  14  of a conventional CMP device. The wafer carrier  12 , together with a wafer  10 , is to be pushed towards the polishing pad  14  so that exposed surface of the wafer  10  touches the parallel polishing pad surface for a chemical mechanical polishing. The body structure of the wafer carrier is made of steel, and a rubber ring  16  is installed on the working surface of the wafer carrier  12  cushioning a wafer, which is securely held on top of the airtight rubber ring by vacuum pressure during a CMP operation. The vacuum is actuated by evacuating air, with a pump, through a center hole  18  on the wafer carrier  12 . A wafer  10  will then stick to the working surface of the wafer carrier  12  when air is pumped out of the center hole  18 . The polishing pad  14  is made of composite fiber-like materials knit in various patterns depending on application. The knitting patterns can be of grid pattern, concentric circle pattern, or radiating pattern such that different patterns provide different contacting surface pressure distributions during the CMP process. Further, a number of factors also decide the surface pressure distribution of a silicon wafer during the CMP process, and they are: condition of the rubber ring  16 , vacuum efficiency actuated through the center hole  18  of the wafer carrier  12 , and material type of polishing pad  14  (such as type of fiber, coefficient of elasticity, fiber size, and weight ratio, etc). The knitting pattern of said polishing pad  14  is of crucial importance in any chemical mechanical polishing process. Therefore, obtaining a database regarding the distribution of surface pressure through sensors located on various pressure related components of a CMP machine can significantly improve the process in development of new components, problem diagnosis, and controlling and maintaining the overall quality of the CMP process. 
     FIG. 2A and 2B depict simplified frontal views of conventional wafer-manipulating devices such as an electrostatic-chuck or a wafer clamp, so wafers can be conveyed between separate processing chambers securely. For instance, a conventional wafer-manipulating device consists of a mechanical arm with a steel-structured arm members wherein an air opening  24  or a suction cup  24 ′ is adapted as a gripper to pick up and transfer wafers, one by one, to a specified location. Surrounding the wafer will be a plurality of circularly arranged claws  26  or a vacuum-assisted rubber ring  26 ′ to prevent any slipping of the silicon wafer during transferring. As it is with any other conventional vacuum-actuated wafer gripping devices, if the vacuum is too weak, the wafer may loose its grip and fall; if the vacuum is too strong, the wafer may warp or even break. Similarly, if the positioning rubber ring  26  or claws  26  are too loose, then the wafer being transferred may fall or somehow be shifted slightly; the opposite of which will cause the wafer to warp or break. 
     SUMMARY OF THE INVENTION 
     In order to alleviate the aforementioned problems caused by an unevenly distributed surface pressure of a silicon wafer during a CMP process, a method according to preferred embodiment of the present invention is provided to detect surface pressure distribution via pressure sensitive film and obtain image data of surface pressure distribution under different operating conditions for process analysis and correction. Specifically, sensed pressure data are fed to a microprocessor to perform a real-time feedback loop analysis for instant digital image mapping, numeration, simulation, and forecasting, from which more mechanical components of higher precision to be used by the CMP machine can be developed. 
     Accordingly, it is an object of the present invention to provide a pressure detecting method by placing a plurality of pressure sensitive films located on contacting surfaces of various pressure related components such as the wafer carrier, the polishing pad, and the mechanical arm of a CMP machine for pressure-sensing of a wafer surface during different stages of a CMP process. When a silicon wafer, or wafer, is securely held by the wafer carrier, the pressure-sensing films immediately start to collect pressure-related data during different stages of the CMP process, whereby a corresponding digital image of pressure-related data about the wafer is immediately processed by a computer and displayed by a monitor. 
     It is another object of the present invention to provide a data analyzing method for processing pressure distribution data of various pressure related components during a wafer CMP process so that suitable input parameter sets for different operating conditions can be established. The established parameter sets are very helpful in improving production yield and efficiency. 
     Furthermore, pressure distribution data of the pressure related components can be obtained and analyzed at the same time as the pressure distribution data of a wafer are collected. The pressure distribution data on the pressure related components are systematically contrasted and analyzed in order to suitably modify the pressure related components; in addition, it is more convenient to maintain a good working order of the pressure related components with the help of the pressure distribution data set. 
     According, it is necessary for the present invention to provide a method of pressure detection on the surfaces of the wafer and the pressure related components so that sets of input parameters can be generated by feedback loop analysis for system correction and modification and for further improvements on overall wafer CMP process. Specifically, the invention relates to a method of detecting pressure distribution on a wafer surface by employing pressure sensitive films located on various pressure components such as a wafer carrier, a polishing pad, and mechanical arm members of a CMP machine for detecting pressure-related data during different stages of a CMP process. Such method of wafer pressure detection is accomplished by first providing a pressure related component and a wafer, having pressure sensitive films bonded to the pressure components, subjecting the wafer and the pressure related components to various pressure conditions, applying pressures of different intensity to various surfaces of the sub-assembly, and processing and saving pressure image data collected via the pressure sensitive films. In particular, the pressure image data are captured with a scanner or a digital camera, fed into a computer, and various pressure image data are then compared and analyzed by a microprocessor. Further, the microprocessor is to simulate pressure distribution data on the pressure components under different operating conditions, so optimum controlling procedures can be established according to input parameter sets generated by computer feedback loop analysis. The acquired pressure distribution knowledge is advantageous for further development of new mechanical pressure components, modification of input parameters, and diagnosis of any operational abnormalities. 
     The pressure sensitive film according to an embodiment of the present invention comprises a color-forming layer and a color-developing layer of polyester base material bonded together as one sheet. Alternatively, the pressure sensitive film can also be of a single layer polyester film with the color-forming material coated to a surface of the film and the color-developing material coated to the other surface. In both cases, the color-forming layer is composed of a plurality of microcapsules of color-forming material. 
     In addition, the pressure components applied in the embodiment of the present invention refer to, but not limited to, mechanical CMP pressure related components including a wafer carrier, a polishing pad, and mechanical arm members of a CMP machine. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects, features, and advantages of the present invention will become apparent from the following detailed description of the preferred but non-limiting embodiment. The description is made with reference to the accompanying drawings in which: 
     FIG. 1 shows a frontal view depicting relative positions of a wafer carrier  12 , a wafer  10 , and a polishing pad  14  of a conventional CMP device; 
     FIG. 2A depicts a simplified frontal view of a conventional wafer-manipulating device with wafer clamps; 
     FIG. 2B depicts a simplified frontal view of a conventional wafer-manipulating device with an electro-static-chuck; 
     FIG. 3A is a side view of a wafer carrier and polishing pad arrangement of a CMP machine, wherein a detecting method of pressure distribution is applied according to an embodiment of the present invention; 
     FIG. 3B is a side view of another wafer carrier and polishing pad arrangement of a CMP machine, wherein a detecting method of pressure distribution is applied according to an embodiment of the present invention; 
     FIG. 4A depicts a simplified frontal view of a CMP pressure component arrangement; 
     FIG. 4B depicts a simplified frontal view of another CMP pressure component arrangement; 
     FIG. 5A is a cross-sectional view of a type of pressure sensitive film according to an embodiment of the present invention; 
     FIG. 5B is a cross-sectional view of another type of pressure sensitive film according to an embodiment of the present invention; 
     FIG. 6 is a flow chart depicting the overall wafer pressure distribution detecting method of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     It is an object of the present invention to provide a method of pressure detection on the surfaces of the wafer and the pressure related components so that different modes of feedback loop analysis for system correction and modification can be generated for further improvements on the wafer CMP process. 
     Referring to FIG. 3A, a side view of a wafer carrier and a polishing pad belonging to a CMP machine is shown, the components of which are arranged in such a fashion that a method to detect pressure distribution can be directly applied on the surfaces. One of the surface of the wafer  30  to be processed by CMP is in contact with the surface of the wafer carrier  32  in holding position, and both of these two components are to be pushed towards the polishing pad  34  until the other surface of the wafer  30  overlaps and touches the surface of the polishing pad  34 . The body structure of the wafer carrier  32  is made of steel, and a rubber ring  36  is installed on the working surface of the wafer carrier  32  cushioning a wafer  30 , which is securely held on top of the airtight rubber ring by vacuum pressure during a CMP operation. The vacuum is actuated by evacuating air, with a pump, through a center hole  38  on the wafer carrier  32 . A wafer  30  will then stick to the working surface of the wafer carrier  32  when air is pumped out of the center hole  38 . The polishing pad  34  is made of composite fiber-like materials knit in various patterns depending on application. The knitting patterns can be of grid pattern, concentric circle pattern, or radiating pattern such that different knitting pattern provide different contacting surface pressure distribution during the CMP process. For the purpose of detecting and measuring pressure distribution on the surface of the wafer carrier  32  under various operating conditions, pressure sensitive films PSF 1  are bonded to at least a surface of the wafer carrier component for detecting pressure distributions that would significantly effect the composition of the following elements: the rubber ring  36 , vacuum pressure through the center hole  38  of the wafer carrier  32 , material type of the polishing pad  34  (such as type of fiber, coefficient of elasticity, fiber size, and weight ratio etc), knitting pattern of the polishing pad  34  etc. 
     As shown in FIG. 5A, the pressure sensitive film PSF 1  according to the present invention comprises a color-forming layer B 1  and a color-developing layer D 1  of polyester base materials A 1  and C 1 , respectively bonded together as one sheet. Alternatively, as shown in FIG. 5B, the pressure sensitive film PSF 2  can also be of a single layer polyester film A 2  with the color-forming material B 2  coated to a surface of the film and the color-developing material D 2  coated to the other surface. In both cases, the color-forming layer, B 1  or B 2 , is composed of a plurality of microcapsules of color-forming material. When pressure is exerted on the pressure sensitive film PSF 1 , microcapsules of color-forming layer B 1 , B 2  burst and release color-forming pigments. The color-forming then further react with the color-developing layer D 1 , D 2  to produce different intensities of visible colors. In particular, the microcapsules are designed with PSC (Particle Size Control) technology so that different colors or intensities are shown to indicate the variation in pressure force. Consequently, various intensities of the pressure distribution are clearly indicated by the pressure sensitive film PSF 1 , which shows different colors or intensities of colors according to different intensities of pressure force. 
     With the pressure sensitive films PSF 1  bonded to surfaces, the wafer carrier  32  holds the wafer  30  and operates as any other conventional CMP process, and pressure distribution on the wafer carrier  32  under various operating conditions can then be detected and measured from images shown by the pressure sensitive films PSF 1 . 
     FIG. 4A and 4B show simplified frontal views of two different CMP conveyer devices. Similar to the structures shown in FIG. 2A and 2B, a CMP conveyer device such as the mechanical arm consists of steel body structure  42 , with a center air hole  44  or a rubber ring  44 ′, has a plurality of circularly arranged claws  46  or a vacuum-assisted rubber ring  46 ′ serving as a suction pad to prevent any slipping of the silicon wafer  20  during transferring. As shown by FIG. 4A and 4B, a pressure sensitive film PSF 3  is bonded to the surface of the wafer conveyer device in order to detect and measure the pressure distribution on the surface of the conveyer device under various conditions. For example, the vacuum pressure exerted through the center air hole  44  and the gripping force exerted by the claws  46  can be systematically measured and numerated by the use of the pressure sensitive film PSF 3 . 
     Accordingly, a flow chart depicting the entire scheme of detecting and measuring pressure distribution on a pressure component is shown in FIG.  6 . 
     In Step  1 , a pressure related component such as those of a CMP machine (a wafer carrier, a polishing pad, etc) or a wafer conveyer device such as a mechanical arm is provided. 
     Step  2  indicates a pressure related component holding a wafer during a CMP process or simply for conveying. In particular, the wafer holding pressure component is a wafer carrier. 
     Step  3  stresses the requisite of having the pressure sensitive films bonded to specified surfaces of the pressure related components. 
     In Step  4 , said pressure related component, together with a wafer and pressure sensitive films, is subjected to various pressure conditions during CMP operations. For example, different intensities of vacuum pressure are exerted through the center air hole  38  of the wafer carrier  32  during different CMP processes. In response, the pressure sensitive films react by changing colors as soon as pressure force is directly exerted upon them as indicated in Step  5 . 
     Furthermore, Step  6  describes the process of capturing image data appeared on a pressure sensitive film by the use of a scanner or a digital camera after the CMP process is finished. 
     After the image data is captured and input to a computer, a microprocessor takes over to digitize the relevant surface pressure distribution data of a pressure related component as in Step  7 . The digitized pressure distribution data of a pressure related component surface is thus obtained, as indicated in Step  8 , for the next step of simulation and analysis. 
     In Step  9 , the digitized pressure distribution data of the pressure related component is further simulated and analyzed by a microprocessor with fuzzy-contrasting and feedback-loop analysis methods, which provides a basis for future improvement in the CMP process of a silicon wafer whereas the layout of micro-device dies may be re-arranged due to uneven wafer surface pressure distribution. 
     Finally, as shown in step  10 , new pressure related components can be designed, and sets of input parameter guidelines can thus be established. 
     Although the present invention has been explained by the embodiments shown in the drawings described above, it should be understood to the ordinary skilled person in the art that the invention is not limited to the embodiments, but rather that various changes or modifications thereof are possible without departing from the spirit of the invention. Accordingly, the scope of the invention shall be determined only by the appended claims and their equivalents.