Abstract:
A method and apparatus for detecting material accretion and peeling in a system such as a plasma process chamber, including multiple optical sensors which are provided in the chamber above a gas distribution plate or other surface inside the chamber. The optical sensors are connected to a central process controller that is capable of terminating operation of the chamber and may be equipped with an alarm. In the event that the optical sensors detect asymmetries in brightness or light reflection among various portions or regions of the gas distribution plate or other surface, which asymmetries may indicate the formation of a material coating on the plate or dislodging of contaminant particles from the plate, a signal is sent to the process controller, which may be adapted to terminate the plasma process, alert operating personnel, or both.

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to fabrication of semiconductor integrated circuits and more particularly, to an apparatus and method for detecting material accretion and dislodging from a quartz gas distribution plate (GDP) in a plasma process chamber during semiconductor wafer processing. 
     BACKGROUND OF THE INVENTION 
     In the semiconductor production industry, various processing steps are used to fabricate integrated circuits on a semiconductor wafer. These steps include the deposition of layers of different materials including metallization layers, passivation layers and insulation layers on the wafer substrate, as well as photoresist stripping and sidewall passivation polymer layer removal. In modern memory devices, for example, multiple layers of metal conductors are required for providing a multi-layer metal interconnection structure in defining a circuit on the wafer. Chemical vapor deposition (CVD) processes are widely used to form layers of materials on a semiconductor wafer. 
     CVD processes include thermal deposition processes, in which a gas is reacted with the heated surface of a semiconductor wafer substrate, as well as plasma-enhanced CVD processes, in which a gas is subjected to electromagnetic energy in order to transform the gas into a more reactive plasma. Forming a plasma can lower the temperature required to deposit a layer on the wafer substrate, to increase the rate of layer deposition, or both. However, in plasma process chambers used to carry out these various CVD processes, materials such as polymers are coated onto the chamber walls and other interior chamber components and surfaces during the processes. These polymer coatings frequently generate particles which inadvertently become dislodged from the surfaces and contaminate the wafers. 
     In semiconductor production, the quality of the integrated circuits on the semiconductor wafer is directly correlated with the purity of the fabricating processes, which in turn depends upon the cleanliness of the manufacturing environment. Furthermore, technological advances in recent years in the increasing miniaturization of semiconductor circuits necessitate correspondingly stringent control of impurities and contaminants in the plasma process chamber. When the circuits on a wafer are submicron in size, the smallest quantity of contaminants can significantly reduce the yield of the wafers. For instance, the presence of particles during deposition or etching of thin films can cause voids, dislocations, or short-circuits which adversely affect performance and reliability of the devices constructed with the circuits. 
     Particle and film contamination has been significantly reduced in the semiconductor industry by improving the quality of clean rooms, by using automated equipment designed to handle semiconductor substrates, and by improving techniques used to clean the substrate surfaces. However, as deposit of material on the interior surfaces of the processing chamber remains a problem, various techniques for in-situ cleaning of process chambers have been developed in recent years. Cleaning gases such as nitrogen trifluoride, chlorine trifluoride, hexafluoroethane, sulfur hexafluoride and carbon tetrafluoride and mixtures thereof have been used in various cleaning applications. These gases are introduced into a process chamber at a predetermined temperature and pressure for a desirable length of time to clean the surfaces inside a process chamber. However, these cleaning techniques are not always effective in cleaning or dislodging all the film and particle contaminants coated on the chamber walls. The smallest quantity of contaminants remaining in the chamber after such cleaning processes can cause significant problems in subsequent manufacturing cycles. 
     SUMMARY OF THE INVENTION 
     Therefore, it is an object of the present invention to detect the presence of material accretion on interior components of a plasma process chamber during the processing of semiconductors. 
     A further object of the present invention is to detect the dislodging of potential contaminant particles from an interior surface of a plasma process chamber during the processing of semiconductors. 
     Still another object of the present invention is to provide for continuous monitoring of a plasma process chamber during the processing and fabrication of semiconductor integrated circuits in order to prevent or minimize particle contamination of one or multiple semiconductor wafers. 
     Yet another object of the present invention is to provide a mechanism which utilizes differences in brightness, opacity or reflective index of a surface inside a plasma process chamber to reveal material accretion on and/or particle dislodging from the surface for potential wafer substrate contamination. 
     A still further object of the present invention is to prevent or reduce contamination of a semiconductor wafer substrate inside a plasma process chamber by utilizing multiple light sensors which detect differences in brightness or reflective index of a gas distribution plate (GDP) inside the chamber to monitor material accretion on and/or dislodging of potential contaminating particles from the plate. 
     In accordance with these and other objects and advantages, the present invention comprises multiple optical sensors which are provided in the top portion of a plasma process chamber above a gas distribution plate of the chamber and are connected to a central process controller that is capable of terminating operation of the chamber and may be equipped with an alarm. In the event that the optical sensors detect relative disparities or asymmetries in brightness or light reflective index among various portions or regions of the gas distribution plate, which disparities or asymmetries may indicate the formation of a material accretion or coating on the plate or dislodging of contaminant particles from the plate, a signal is sent to the process controller, which may be adapted to terminate the plasma process, alert operating personnel, or both. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
     FIG. 1 illustrates interior components of a conventional plasma process chamber; 
     FIG. 2 illustrates a plasma process chamber according to the present invention, which plasma process chamber is provided with an apparatus for early detection of material accretion and peeling; 
     FIG. 3 is a bottom perspective view of the lid and gas distribution plate components of the plasma process chamber illustrated in FIG. 2; and 
     FIG. 4 is an enlarged sectional view, taken along section line  4  in FIG. 2, more particularly illustrating an illustrative structure for mounting each optical sensor in the lid of the plasma process chamber according to the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     When used herein, the term optical sensor shall be understood to mean any device which is capable of detecting light radiation or reflection from a surface. When used herein, the term process controller shall be understood to mean any device capable of calculating light reflective indices and determining differences in light radiation or light reflective indices responsive to differential data input from multiple optical sensors, and/or comparing light radiation or reflective index data input with a standard value and modulating the operation of a system accordingly. When used herein, the term alarm shall be understood to mean any device capable of indicating a condition by audio alarm, video alarm, or both, responsive to data input. 
     The present invention has particularly beneficial utility in application to monitoring polymer or other material coating, accretion or buildup on a gas distribution plate (GDP) in a plasma process chamber. However, the invention is not so limited in application, and while references may be made to such gas distribution plate and plasma process chamber, the invention may be more generally applicable to detecting coating buildup and/or fragmentation and dislodgment on other interior surfaces of a plasma process chamber or other closed system. 
     A conventional plasma process chamber is generally indicated schematically by reference numeral  10  in FIG.  1 . The plasma process chamber  10 , also known in the art as a plasma etch reactor, includes a housing  12  which is typically constructed of a nonmagnetic material such as aluminum and defines a chamber interior  13 . A clamp lid assembly  15  including a lid  16  is removably attached to the housing  12  for selectively sealing the chamber interior  13 . A wafer platform  14  is provided in the bottom portion of the chamber interior  13  for supporting a semiconductor wafer  20 , which wafer platform  14  further acts as a cathode. A quartz gas inlet nozzle  18 , or “showerhead”, also known in the art as a gas distribution plate (GDP), is mounted in the chamber interior  13 , directly above the wafer platform  14 . Reaction gases introduced through a gas inlet  22  flow into the chamber interior  13  through multiple openings  21  in the gas distribution plate  18 . 
     During operation of the conventional plasma process chamber  10 , the semiconductor wafer  20  is heated in the chamber interior  13  and is selectively cooled by a cooling gas (not illustrated) as the wafer  20  transfers heat to the water-cooled wafer platform  14 . Precursor reaction gases flowing into the chamber interior  13  through the openings  21  in the gas distribution plate  18  are typically reacted with the heated substrate semiconductor wafer  20 . Alternatively, the reaction gases may be subjected to electromagnetic energy to form a reactive plasma which is capable of reacting with the semiconductor wafer  20  at lower temperatures. As the gases or plasma reacts with the wafer  20 , various films or layers such as metallization layers, passivation layers, insulation layers, etc., depending upon the chemical composition of the reaction gases or plasma, are deposited on the wafer  20  for the fabrication of integrated circuits on the wafer  20 . An exhaust gas outlet  28 , which is normally connected to a vacuum pump (not illustrated), is used to evacuate the gases or plasma from the chamber interior  13 . 
     One of the problems inherent in such chemical vapor or plasma deposition processes is that layer or film deposition is not limited to the wafer  20 , but polymer or other material coatings may be deposited on other surfaces in the chamber interior  13 . Particularly problematic in this regard is the accretion of films or coatings on the gas distribution plate  18 , which films or coatings are a significant source of particulate contaminants that frequently become dislodged from the gas distribution plate  18  as a result of mechanical and thermal stresses. The dislodged particulate contaminants tend to fall from the gas distribution plate  18  and contaminate the underlying wafer  20 , and these impurities significantly compromise the functional integrity of the integrated circuits formed on the wafer  20 . 
     Referring next to FIGS. 2-4, a plasma process chamber according to the present invention is generally indicated by reference numeral  1  in FIG.  2 . The lid  16  of the plasma process chamber  1  is fitted with multiple optical sensors  2  that are capable of monitoring the brightness or light reflection of the underlying gas distribution plate  18 . As illustrated in FIG. 3, the multiple sensors  2  are typically distributed spatially in the lid  16  in such a manner that four sensors  2  are circumscribed by an imaginary outer circle  32  (illustrated in phantom) and four additional sensors  2  are circumscribed by an imaginary inner circle  33  (illustrated in phantom). However, it is understood that any desired number of the sensors  2  may be arranged in any desired pattern in the lid  16  sufficient to monitor selected areas or all areas of the underlying gas distribution plate  18 . 
     Discrepancies or asymmetries in the relative brightness or opacity of the inner regions of the gas distribution plate  18  with respect to that of the outer or peripheral regions of the gas distribution plate  18  indicate the buildup of a material coating or accretion on one or more regions of the plate  18  exclusive of the other regions of the plate  18 . Additionally, a sudden increase in the brightness or light reflective index of one region with respect to the relative opacity of the other regions of the disc may indicate dislodging of a potentially contaminating portion or portions of the coating from the plate  18 . This data is sent through sensor wiring  9  to a conventional process controller  30 , which is connected to the control system of the plasma process chamber  1 . The process controller  30  is programmed according to the knowledge of those skilled in the art to calculate light reflective indices using the incoming data input from the respective optical sensors  2 ; and detect any differences in light reflective indices among the multiple optical sensors  2  which may reflect the differences in brightness or opacity between those areas of the gas distribution plate  18 . In the event that there are significant differences (about 10% or more) between the reflective indices calculated using the data input from the respective optical sensors  2 , the process controller  30  terminates operation of the control system to prevent initial or further contamination of the semiconductor wafer  20 . Alternatively, the process controller  30  may be programmed to compare the brightness or opacity of the gas distribution plate  2  with a known standard for the brightness or opacity of the gas distribution plate  2 , in which case the process controller  30  terminates operation of the control system when the light reflective index or brightness of the gas distribution plate  2  deviates from the control value by at least about 1, and typically, about 10%. 
     As further illustrated in FIG. 2, in another embodiment, the optical sensors  2  can be wired to an alarm  31 , which can be an audio alarm, a visual alarm, or both, according to the knowledge of those skilled in the art. The discrepancy or asymmetry in brightness between the various regions of the gas distribution plate  18  or sudden change in the light reflective index between the areas of the plate  18  or with respect to a standard value is thus relayed to the alarm  31 , which alerts to operating personnel audibly or visually, of a material coating buildup or accretion on or dislodging of a contaminant portion of the material coating from the gas distribution plate  18 . In that event, operating personnel have sufficient warning to manually terminate operation of the plasma process chamber  1  before initial or additional particulate contamination to the wafer  20  occurs. The contaminated gas distribution plate  20  can then be cleaned to prevent further contamination of wafers  20  in the chamber interior  13 . In still another embodiment, the alarm  31  may be incorporated in the circuitry of the process controller  30  according to the knowledge of those skilled in the art, such that operation of the plasma process chamber  1  is terminated while the alarm  31  alerts operating personnel to the presence of material accretion on or dislodging from the gas distribution plate  18 . 
     FIG. 4 illustrates a representative structure for mounting each optical sensor  2  in the lid  16  of the plasma process chamber  1 . Each sensor  2  is contained in a sensor cavity  4  provided in a sensor retainer disc  3 , and each sensor retainer disc  3  is seated in a sensor opening  19  in the lid  16  and rests on a retainer disc shoulder  24  of the lid  16 . Fasteners  8  typically extend through registering openings (not illustrated) provided in the sensor retainer disc  3  and retainer disc shoulder  24 , respectively, to secure each sensor retainer disc  3  in the corresponding sensor opening  19 . A quartz sensor lens  6  and an o-ring  7  are interposed between the bottom surface of the sensor retainer disc  3  and an annular flange  17  in the lid  16 , and the sensor lens  6  closes the bottom of the sensor cavity  4 . Sensor wiring  9 , which extends from the optical sensor  2  and is connected to the process controller  30 , passes through a wiring opening  5  provided in the upper portion of the sensor retainer disc  3 . While the foregoing describes a representative structure for mounting each sensor  2  in the lid  16 , it will be appreciated by those skilled in the art that other mounting structures are possible without departing from the spirit and scope of the invention. 
     While the preferred embodiments of the invention have been described above, it will be recognized and understood that various modifications can be made in the invention and the appended claims are intended to cover all such modifications which may fall within the spirit and scope of the invention.