FLUORINE ASSISTED STRIPPING AND RESIDUE REMOVAL IN SAPPHIRE DOWNSTREAM PLASMA ASHER

Abstract: A method for removing material from a substrate. A plasma is generated in a plasma generating and discharge device including a sapphire plasma tube (40). At least one fluorine-containing compound is introduced into the plasma. A forming gas is introduced into the plasma. The plasma is directed toward the material to be removed from the substrate (88).

Description: FLUORINE ASSISTED STRIPPING AND RESIDUE REMOVAL IN SAPPHIRE DOWNSTREAM PLASMA ASHER Field of the Invention The invention relates to a method and apparatus for removing materials from a substrate. In particular, the present invention relates to removing materials from substrates m semiconductor manufacturing processes. Background of the Invention Several steps in the manufacture of semiconductor devices require the removal of photoresist (PR) and otner materials from substrates. The "removal" of PR is synonymous with "ash," "burn," "strip," and "clean." One example of a substance that may be removed is a residue that may remain on a silicon wafer after an etching step is completed. Such residue is frequently composed of a polymeric material that may be present in the form of "veils" and is caused by over etching during etch processes . One way to remove PR and other materials such as those described above is by directing a plasma stream at the substrate with the attached substance. In some cases, the substance is removed from the substrate by the "afterglow" of the plasma rather than the plasma itself. One gas that may be used in generating the plasma to strip the substrates is oxygen In order to increase the effectiveness and/or efficiency of processes for removing materials from a substrate, a source of fluorine may be added to the oxygen. A problem inherent in utilizing a fluorine-containing substance is degradation of the plasma generatmg/discnarge device by the fluorine. For example, plasma generating and discharge devices typically include a tube through whicn the plasma flows. Microwave or radio- frequency energy is introduced into the tube to excite the gas and form the plasma Typically, the tube is made of quartz It was observed that fluorine was particularly destructive to the quartz tubes. Therefore, quartz tubes were replaced by sapphire tubes in order to overcome the corrosive effects of fluorine . Although the sapphire plasma discharge tube included m the plasma generating and discharge devices overcame tne significant degradation of the quartz tubes, ash rates of photoresist utilizing the sapphire tube were markedly lower than ash rates observed when utilizing the quartz tubes. One reason for the decreased efficiency of ash by an oxygen plasma generated with a plasma generating and discharge device that includes a sapphire tube is that oxygen atoms m the plasma may be lost at the surface of the sapphire to a much greater degree than at the surface of the quartz Summary of the Invention The present invention was developed through efforts to overcome the above -described as well as other problems. Accordingly, one obiect of the present invention is to provide a method and apparatus that reduces the recombination/loss rate of oxygen atoms on the surface of a sapphire tube in a plasma generating and discharge device and, hence, increases the effectiveness/efficiency of standard ashing processes. An additional obiect of the present invention is to provide a method and apparatus for removing materials from a substrate utilizing an oxygen plasma with at least one added fluorine -containing compound while maintaining minimal oxide loss . A further object of the present invention is to provide a method and apparatus for removing material from a substrate utilizing forming gas. A still further object of the present invention is to increase the effectiveness of residue removal from a substrate. In accordance with these and other obηects and advantages, aspects of the present invention provide a method for removing material from a substrate . According to the method, a plasma is generated in a plasma generating and discharge device including a sapphire plasma tube. At least one fluorine-containing compound is introduced into the plasma. A forming gas is introduced into the plasma. The plasma is directed toward the material to be removed from the substrate . Other aspects of the present invention provide a device for removing material from a substrate. The device includes a plasma generating and discharge device including a sapphire plasma tube. The device also includes a source of at least one gas for introducing the at least one gas into the plasma generating and discharge device for forming a plasma. At least one source of at least one fluorine-containing compound is provided for introducing at least one fluorine-containing compound into the plasma generating and discharge device. At least one source of at least one forming gas is also provided for introducing the at least one forming gas into the plasma. The device also includes apparatus for directing the plasma toward the material to be removed from the substrate. Still other objects and advantages of the present invention will become readily apparent by those skilled in the art from the following detailed description, wherein it is shown and described only the preferred embodiments of the invention, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature and not as restrictive . Brief Description of the Drawings Figures 1-3 represent graphs that demonstrate various resist removal rates given different flow rates of oxygen- containing compound (s) and fluorine-containing compoun (s) and power levels, without any additional source of heat, according to various embodiments of processes according to the present invention; Figure 4 represents a table illustrating ash rates and oxide loss rates for various embodiments of processes according to the present invention; Figure 5 represents a table illustrating oxide loss rates achieved when applying various embodiments of processes according to the present invention; Figures 6 - 9 represent graphs demonstrating the different ash rates achieved utilizing a plasma generating and discharge device with a sapphire plasma tube with and without utilizing CF 4 and utilizing an oxygen plasma with at least one nitrogen- containing compound ana at least one hydrogen-containing compound added as well according to various embodiments of processes of the present invention, Figures 10-19 represent photomicrographic evidence of the results of embodiments of processes according to the present invention according to Example 3 ; Figure 20 represents a graph illustrating the advantage of the increased ash rate according to the present invention of adding a trickle of at least one fluorine-containmg compound, in this case, CF 4 , according to an embodiment of the present invention; Figure 21 represents a graph illustrating ash rate as a function of temperature utilizing another embodiment of the present invention; Figure 22 represents a graph illustrating oxide loss as a function of temperature for one embodiment of a process according to the present invention, Figure 23 represents a graph illustrating etch rate as a function of flow of CF4 , utilized as a fluorine-containmg compound, for one embodiment of a process according to the present invention; Figure 24 represents a cross -sectional view of a typical via structure; Figure 25a represents a photomicrograph illustrating a post-etch via prior to treatment with a process according to the present invention; Figure 25b represents a photomicrograph illustrating a via after treatment with a process according to the present invention; Figure 26a represents a photomicrograph illustrating a via after treatment with a process according to the present invention similar to the process described in Example 4, illustrating undercutting; Figure 26b represents a photomicrograph illustrating a via after treatment with a process according to the present invention similar to the process described in Example 4, wherein the process time was shortened to eliminate the undercutting seen in Figure 26a; Figure 27a represents a photomicrograph illustrating a via after treatment with a process of the present invention described in Example 5, illustrating residue remaining in the via; Figure 27b represents a photomicrograph illustrating a via after treatment with a process of the present invention described in Example 5, wnerem residue in the via has been removed with a deionized water rinse; Figure 28a represents a photomicrograph illustrating pos -poly residues after treatment with a process according to the present invention described in Example 6 ; Figure 28b represents a photomicrograph illustrating residue- free samples after treatment with a process according to the present invention described in Example 6 after a deionized water rinse; Figure 29a represents a photomicrograph illustrating post-poly residues after treatment with a process according to the present invention described m Example 7, Figure 29b represents a photomicrograph illustrating residue- free samples after treatment with a process according to the present invention described m Example 7 after rinsing with deionized water; Figure 30a represents a photomicrograph illustrating post-poly residues after treatment with a process according to the present invention described in Example 8; Figure 30b represents a photomicrograph illustrating residue- free samples after treatment with a process according to the present invention described in Example 8 after rinsing witn deionized water, Figure 31 represents a electric field intensity distribution in the rectangular TM 110 mode, which provides azimuthal and axial uniformity; Figure 32 represents a microwave structure that may be utilized for carrying out processes according to the present invention; and Figure 33 and Figure 34 illustrate a more complete device that may be utilized for carrying out processes according to the present invention Detailed Description of the Invention As discussed above, the present invention provides an enhanced process for removing photoresist and other materials from a substrate. It has been unexpectedly discovered tnat a combination of techniques may be utilized to increase the efficiency and effectiveness of ash and residue removal. The present invention in part was developed after an investigation of the "memory effect" in which ash rates continued to be enhanced after the cessation of flow of fluorme-containing compound (s) into the plasma. The memory effect may be a result of residual fluorine, fluorine seasoning of, or remaining in and/or on, all surfaces exposed to it, including chamber walls and the plasma tube of a plasma generating and discharge device. This residual fluorine will provide the effects of fluorine addition to the plasma without actual fluorine being added to the plasma for one or more additional wafers being processed after the addition of fluorine has ceased. The techniques included in the method of the present invention include generating an oxygen plasma m a plasma generating and discharge device that includes a sapphire plasma discharge tube, adding at least one source of fluorine to the oxygen plasma, and introducing a source of forming gas to the oxygen plasma. By utilizing a combination of these techniques, it has been unexpectedly discovered that ash rates may be increased significantly while maintaining plasma tube integrity. Additionally, the techniques of the present invention have been demonstrated to remove residues post via etch, oxide etch, poly, nitride, implant, and other levels, while not causing additional plasma damage. According to the process of the present invention, a plasma generating and discharge device such as in U.S. Patent Application Serial No. 07/626,451 may be utilized to generate plasma. Alternatively, any other plasma generator capable of generating oxygen plasma for use in applications such as removing materials from a substrate by ashing may be utilized. Examples of commercially available plasma generating and discharge devices that could be utilized to carry out the method of the present invention include the FUSION ENHANCED STRIP ASHER and FUSION GEMINI ENHANCED STRIP ASHER, both available from Fusion Semiconductor Systems Other examples of plasma generating and discharge devices that may be utilized according to the present invention generate a plasma utilizing radio frequency (RF) energy According to the process of the present invention, an oxygen plasma is generated in the plasma generating and discharge device while source (s) of fluorine-containing compound(s), nitrogen-containing compound(s), and hydrogen- containing compound (s) are added to the gas inlet of the plasma generating and discharge device It has been found that the introduction of this combination into the plasma generating and discharge device with the sapphire plasma tube unexpectedly results in a significantly increased rate of removal of certain materials from a suostrate The unexpected result achievable according to the present invention of vastly improved rate of removal of material from a substrate while not degrading the container by utilizing a sapphire plasma tube was not known. As discussed above, it was known that utilizing a sapphire plasma tube markedly decreased ashing rates. Therefore, although the advantages of utilizing oxygen- containing compound{s), fluorine-containing compound(s), and nitrogen-containing compound (s) or gases that include oxygen, fluorine, and nitrogen may have been known, it was not known to utilize this combination of materials m a sapphire plasma tube . According to the present invention, at least one oxygen- contaming compound may be introduced into the plasma generator as molecular oxygen, atomic oxygen, ozone, or other oxygen-contaming compound such as N 2 0, N0 2 , NO, C0 2 , or CO. The at least one oxygen-conta ing compound may be introduced nto the plasma generating and discharge device at a rate of from about 200 standard cubic centimeters per minute (seem) to about 4000 seem. Alternatively, the at least one oxygen- contaming compound may be introduced into the plasma generating and discharge device at a rate of at least about 200 seem. Similarly, the at least one oxygen-contaming compound may be introduced into the plasma generating and discharge device at a rate of up to about 4000 seem. Preferably, the at least one oxygen-conta mg compound in the form of 0 2 is introduced at a rate of from about 1500 seem to about 2000 seem. If another gas were used, the flow rate would be adjusted to provide an equivalent amount of oxygen to the system. The flow rate of the at least one oxygen-contammg compound preferably generates a pressure in the plasma tube of from about 0.5 torr to about 10 torr. More preferably, the pressure in the process chamber is about 1.5 torr. Lower flow rates could be used if a lower pressure were desired. For example, some plasma generating and discharge devices utilizing RF energy to generate a plasma may employ lower pressures in the plasma tube. However, any flow rates and pressure could be used if the gases of the method were utilized in a sapphire plasma tube. At least one source of fluorine may be added to the at least one oxygen-containing compound in a variety of forms. For example, suitable fluorine-containing compounds include CF 4 , C : F, , CHF 3 , CFH 3 , C,H 2 F 4 , C 2 H 4 F 2 , CH 2 F : , CH,CF, , C 3 F 8 , SF,, and NF 3 . The amount of fluorine-containing compound (s) added to the oxygen-containing compound (s) may vary. For example, according to one process of the present invention, the fluorine containing compound (s) is added up to about ten percent of the amount of oxygen in a plasma to be generated by the plasma generator. In absolute terms, the amount of fluorine-containing compound (s) added is up to about 200 seem. Forming gas may be added to the oxygen-containing compound (s) and plasma in the plasma generating and discharge device. The forming gas typically is a mixture of at least one nitrogen-containing compound and at least one hydrogen- containing compound in the form of N 2 and H 2 . The forming gas may include up to about 10% H 2 . The forming gas may be added to the plasma generating and discharge device in an amount up to about 2000 seem. The nitrogen-contammg compound (s) and hydrogen- containing compound (s) of the forming gas may be provided by sources of nitrogen and hydrogen other than N 2 and H 2 added to the plasma. In one example, N0 2 is used as an oxygen source. The nitrogen of the forming gas could be provided by the N m the N0 2 . Similarly, the hydrogen of the forming gas could be provided by CHF 3 used as a fluorine source. Processes according to the present invention may include a plurality of steps. In each step, one or more of tne materials listed above may be included in the plasma generated in the plasma generating and discharge device. Other process parameters that may be controlled m the operation of the plasma generating and discharge device include the power provided to the plasma generating and discharge device and the temperature of the substrate. The temperature of the substrate may be varied from to from about 20°C to about 350°C for different processes. According to the present invention, the pressure maintained in the plasma generating and discharge device is from about a few millitorr to about 10 torr. Additionally, the power supplied to a microwave plasma generating and discharge device may vary from about 500 watts to about 2000 watts. Plasma generators using RF to generate plasma may operate at lower power levels. In either case, the power supplied to the plasma generating and discharge device should be sufficient to result in the enhanced removal of material from the substrate, while not causing damage or other unwanted effects to the substrate. In fact, the oxygen-containing compound(s), nitrogen- containing compound (s) , hydrogen-containing compound (s), and fluorine-containing compound (s) may be added in amounts sufficient to result in the enhanced removal of selected material from the substrate, while not causing damage cr other unwanted effects to the substrate or the apparatus. According to one example, a process according to the present invention for removing PR may include a first step of generating a temperature of about 270°C and a pressure of about 1.5 torr in the plasma generating and discharge device while supplying about 2000 watts of power. About 2000 seem of oxygen, about 300 seem of N 2 /H 2 , and about 5 seem of CF. are supplied to the plasma generating and discharge device. This temperature, pressure, power, and gas supply are maintained for the minimum time necessary for the plasma generating and discharge device to reach 270°C. In a second step, these conditions are held substantially constant for about 60 seconds. According to an example of a process according to the present invention for removing residue, the above two steps are first carried out. Then, a third step is carried out m which the power level is decreased, the forming gas is eliminated, and about 5% CF 4 is added to the plasma generating and discharge device. The addition of at least one fluorine-containing material to the oxygen plasma may result in generation of more oxygen atoms m the plasma and minimize the recombination of oxygen atoms on the tube/chamber surface. Fluorine may also cause hydrogen abstraction from the surface cf the resist being removed thereby leaving the resist more prone to attack by oxygen atoms, effectively lowering the activation energy required to remove the resist. At least one hydrogen-containmg compound may be added to the oxygen-contammg compound (s), fluorine-containing compound(s), and nitrogen-containing compound(s) to provide a cleaner residue removal as well as to lower activation energy. Furthermore, nitrogen present in the mixture may enhance production of oxygen atoms. The present invention also permits low temperature residue removal. Below are described numerous examples of process according to the present invention and investigations that led up to the present invention. The examples are means to be illustrative in nature and not exhaustive. Figures 1-3 represent graphs that demonstrate various resist removal rates given different oxygen-contam g compound (s) and fluorme-contammg compound (s) flow rates and power levels, without any external heat source to the substrate that material is being removed from. Figures 4 and 5 represent a table illustrating ash rates and oxide loss rates for various processes according to the present invention. Figures 6-9 represent graphs demonstrating the different ash rates achieved utilizing a plasma generating and discharge device with a sapphire plasma tube with and without utilizing CF., and utilizing an oxygen plasma with nitrogen-contammg compound (s) and hydrogen-containing compound (s) added as well. The processes utilized to produce the results illustrated m Figure 6 included three process steps The first step included a minimum time of about 15 seconds necessary to bring the plasma generating and discharge device up to a temperature of 270°C, at a pressure of 1.5 torr, and supplying the amounts of the gases specified on the horizontal axis of the graph The second and third steps included the same process parameters, but were carried out for thirteen seconds. The plasma was turned on during the third step, supplying about 1500 watts of power to the plasma generating and discharge device. No oxide loss was detected. The results shown in Figure 7 were achieved utilizing the same three steps as the processes shown in Figure 6. However, the amounts of oxygen-contammg compound (s) and forming gas supplied were about 1700 seem and about 300 seem, respectively. Figure 7 shows tne results for processes tnat included 5 seem CF or did not include CF 4 at all. The results shown in Figure 8 were achieved utilizing the same three steps as the processes shown in Figure 6. However, the amounts of oxygen-contammg compound (s) and forming gas supplied were about 2000 seem and about 300 seem, respectively, to compensate for a larger substrate being treaced. Figure 8 shows the results for processes that included 5 seem CF 4 or did not include CF 4 at all. The results shown in Figure 9 were achieved utilizing the same three steps as the processes shown m Figure 6 and demonstrates the repeatability of the results over a plurality of substrates. However, the amounts of oxygen-contammg compound(s), forming gas, and CF 4 supplied were about 2000 seem, about 300 seem, and about 5 seem, respectively. Figure 20 illustrates the advantage of the increased ash rate according to the present invention of adding a trickle of at least one fluorine-containing gas, in this case, CF 4 , especially at lower temperatures. Figure 21 illustrates temperature variation of ash rate while utilizing a 5 seem trickle of CF 4 . Figure 22 illustrates a characterization of oxide loss for a process that includes two treatment steps during which different process parameters were utilized. In the first step, the plasma generating and discharge device was turned on for a time sufficient for the device to reach a temperature of about 140 °C. No power is provided to the plasma generating and discharge device. At least one fluorine-containing compound in the form of CF 4 is provided to the plasma generating and discharge device at a flow rate of about 300 seem. At least one oxygen-contaming compound in the form of 0 2 is provided to the plasma generating and discharge device at a flow rate of about 1700 seem. The pressure with the plasma generating and discharge device is about 1.5 torr. According to the second step m the process whose results are shown in Figure 22, the plasma generating and discharge device was turned on for about 20 seconds. About 1500 watts of power is provided to the plasma generating and discharge device. At least one fluorme-contammg compound in the form of CF 4 is provided to the plasma generating and discharge device at a flow rate of about 90 seem. At least one oxygen- containing compound in the form of 0 2 is provided to the plasma generating and discharge device at a flow rate of about 2210 seem. The pressure within the plasma generating and discharge device is about 1.5 torr. Figure 23 illustrates a characterization of nitride etch for a process that includes two treatment steps during which different process parameters were utilized. In the first step, the plasma generating and discharge device was turned on for a time sufficient for the device to reach a temperature of about 140°C. No power is provided to the plasma generating and discharge device. At least one f uorme-contammg compound in the form of CF„ is provided to the plasma generating and discharge device at a flow rate of about 300 seem. At least one oxygen-contammg compound in the form of 0 2 is provided to the plasma generating and discharge device at a flow rate of about 1700 seem. The pressure within the plasma generating and discharge device is about 1.5 torr. According to the second step in the process whose results are shown in Figure 23, the plasma generating and discharge device was turned on for aoout 60 seconds. The temperature within the plasma generating and discnarge device was about 170°C. About 1500 watts of power was provided to the plasma generating and discharge device. At least one fluorme- contammg compound in the form of CF 4 is provided to the plasma generating and discharge device at a flow rate of about 300 seem. At least one oxygen-contammg compound m the form of 0 2 is provided to the plasma generating and discharge device at a flow rate of about 1700 seem. The pressure within the plasma generating and discharge device is about 1.5 torr. According to one example of a plasma generating and discharge device including a sapphire plasma tube that may be utilized in carrying out processes according to the present invention, microwave excitation electric field is utilized that is substantially uniform in the azimuthal and axial directions of the tube. Such a field will cause substantially equal heating of the tube in the azimuthal and longitudinal directions, thus obviating cracking. The resultant azimuthal and longitudinal uniformity may be provided by modes including the rectangular TM 110 mode or the cylindrical TM 010 mode, or possibly by a combination of other modes, the resultant of which is the desired uniformity. In order to create the conditions necessary to excite and support the rectangular TM 110 or cylindrical TM 010 modes, such that it is the dominant driven mode, it is necessary to use a relatively short microwave cavity. This would ordinarily dictate using a correspondingly short plasma tube. However, a problem caused by using a short plasma tube may be that the longitudinal temperature gradient is too great at the ends of the tube where there is a transition from inside the cavity, where there is a field, to outside the cavity where there is no field, thus causing cracking. To solve this problem, a relatively long microwave structure is provided, which is divided into lengthwise sections by partitions. The plasma tube is fed through a hole in each partition, and thus runs the length of the microwave structure, while each of the lengthwise sections is separately fed with microwave energy. Each section thus appears to the incoming microwave energy to be a separate cavity of relatively short length, thus promoting the formation of the correct mode, while the plasma tube is relatively long, thus obviating any problems with cracking. Microwave energy may be provided having an electric field which is substantially uniform in the azimuthal and axial directions of the tube. Such an electric field will heat the tube substantially uniformly in the azimuthal and axial directions of the tube, which will prevent or minimize the formation of temperature stresses due to unequal heating. As used herein, the term "azimuthal direction" applies to tubes having both circular and non-circular cross - sections , and means the direction which follows the periphery of the tube m a plane which is perpendicular to the axial direction. The rectangular TM 110 and circular TM 010 modes both provide substantial azimuthal and axial uniformity for a tube of circular cross-section. In Figure 31, the idealized electric field intensity distribution 20 for such modes are depicted (shown in rectangular cavity 22) . The intensity distribution may be viewed as concentric cylinders having azimuthal and axial uniformity with the strength increasing towards the center. There is negligible variation in field strength over the relatively small radial dimension of the tube. A relatively short cavity favors the formation of modes having azimuthal and axial uniformity, which suggests the use of a correspondingly short plasma tube. In a practical system, process etch rates are related to microwave input power. When an input power that attains an acceptable etch rate is used with a short plasma tube, the power density is such that an unaeceptably large thermal gradient exists at the ends of the tube, which may cause cracking. This problem is solved by using a microwave enclosure which is partitioned into lengthwise sections . Referring to Figure 32, microwave enclosure 42 is a rectangular box which is partitioned into lengthwise sections by partitions 44, 45, and 46 having plasma tube 40 passing therethrough. While four sections are shown in the embodiment which is illustrated, fewer or more sections may be used. Each partition has an opening through which the plasma tube passes. Each section is separately fed with microwave energy. Thus, each section appears to be a relatively short cavity to the incoming microwave energy, promoting the formation of modes having azimuthal and axial uniformity, and preventing the formation of modes such as the TE 101 , TE 102 , etc., which do not. However, the total length of the plasma tube is relatively long, thus ensuring that the power density m the tube is such that the temperature gradient at the tube ends is within acceptable limits. Outer tube 41 surrounds the plasma tube inside the cavity. The outer tube is slightly separated from the plasma tube, and air under positive pressure is fed between the two tubes to provide effective cooling of the plasma tube. Tube 41 would typically be made of quartz. The openings in the partitions 44, 45, and 46 through which the concentric tubes are fed are made larger than the exterior dimension of the plasma tube. There is microwave leakage through such openings which causes a plasma to be excited in the part of the tube that is surrounded by the partition. Such leakage helps reduce thermal gradients in the plasma tube between regions surrounded by partitions and regions that are not. If an outer tube is not used (cooling provided in some other manner) , the openings m the partitions are sized so that there is a space between the plasma tube and the partition to provide such microwave leakage. In the embodiment shown m Figure 32, there is a space between the outer tube and the partition. Figure 32 also shows an iris plate 50 which covers the open side of the microwave structure, and is effective to feed microwave energy into the adjacent sections. Plate 50 is a flat metallic plate having irises 52, 54, 56 and 58, through which the microwave energy is fed. The invention is applicable to devices where either the plasma or the afterglow from the plasma is used to remove material. Microwave traps 43 and 45 are provided at the ends to prevent microwave leakage. Such traps may be of the type disclosed in U.S. Patent No. 5,498,308, which is incorporated herein by reference. Air seals/directional feeders 47 and 49 are provided for admitting cooling air and feeding it to the space between the concentric tubes. Air seal/directional feeder 51 is shown at the outlet end, and a fourth such unit is present, but is not seen. Figure 33 shows a more complete device as assembled. Magnetron 60 provides microwave power, which is fed through coupler 62 to a waveguide supplying a TE 10 mode, having mutually perpendicular sections 64 and 66. The length of waveguide section 66 is adjustable with moveable plunger 82. The bottom plate of waveguide section 66 in Figure 33 is iris plate 50, which couples microwave energy into partitioned microwave structure 42, through which the plasma tube extends; thus, a plasma is excited in the gas flowing through the plasma tube. Referring again to Figure 33, it is seen that end cap 70 abuts microwave trap 43, and fitting 72 having a central orifice for admitting gas to the plasma tube extends into the end cap. The plasma tube is supported at this end by 0 ring 71 in the end cap. The outer tube 41 is supported at its ends by abutment against microwave traps 43 and 45. Spacer 78 is present to provide the proper spacing in relation to the process chamber. The other end of the plasma tube is located in end member 80, and has an orifice 86 for emitting gas into the process chamber. The process chamber 84 includes retractable wafer support pins 90 and 91, which support wafer 88, to be processed. Chuck 92 is for providing the correct heating to the wafer during processing. One or more baffle plates may be present above the wafer to promote even distribution of the gas. Referring to Figure 33, an exterior view of the device is shown. The reference numerals in Figure 34 correspond to those which are in the other Figures. In the preferred embodiment, microwave enclosure 42 is dimensioned to support the rectangular TM 110 mode and the enclosure 42 may have a square cross section. The dimensions of the cross sections are such that the TM 110 mode is resonant . The length of each section is less than λ g /2 where λ g is the guide length within the cavity of the TE 104 mode. In an actual embodiment which was built, the magnetron frequency was 2443 MHz, the microwave enclosure was 3.475 - 3.5 inches on each side, and the length of each of four sections was 2.875 inches. A sapphire tube having an ID of about .900" and an OD of about 1.000" was used, and a gas of 85% 0 2 , 5% He, 10% NF 3 was flowed through the tube for removing residue of polymeric materials in the form of veils which are caused by over etching. The power density was about 36 watts/in 3 . As discussed above, the example of a plasma generating and discharge device including a sapphire plasma tube described herein finds a particular use with plasma tubes which are made of a material which is inclined to crack when heated unequally. One example of such materials are those having a linear thermal expansion coefficient greater than 7 x 10 "7 /K° at operating temperature. However, the example of a plasma generating and discharge device including a sapphire plasma tube may also be used with other plasma tubes made of other material, for example those made of quartz, as the uniform field will tend to keep the plasma off the tube wall and may provide improved lifetime of the quartz. A quartz tube may be used with at least one fluorine- containing gas by coating the inside of the tube with a fluorine resistant coating such as A1 2 0 3 , CaF 2 , fluorosilicade glasses A1N, or other fluorine resistant coating. Example 1 Example 1, on the following page, describes the treatment of photoresist on nitride to be stripped using a process according to the present invention. The Example includes four different processes described in four tables, labeled 1-4. Each process includes three process steps. Demonstration of nitride level srrip 1. Time(seej I Temp.(deg. C) 1 Press, (torr; Poweri warts) | Q : fsccm) ;H,(sc mj j CF MEs I 270 I 1.5 2000 I 2000 300 60 270 1.5 2000 2000 300 20 270 1.5 2000 2000 300 MIN: minimum αme needed to reach said temperature (18 sec) Time(sec ) [ Tesιp.(deg. C) | Press, (ton) | Po erfwaπs) | Q : sccm) | ? K 2 (sccaι [ r Λ MEN ' 175 1.5 1500 2000 300 60 175 1.5 1500 2000 300 20 OFF 1250 < ! 8: 1 1: MEN * : 7sec 3. Tian ses) 1 Temp.( 9 C) | Press, (torr) | Powcnwaπs) | Q-(sc;m) \ N,H-fscqn) CF 4 MEN 175 1.5 ~~ 2000 2000 30 ■" 0 " - "■" 1 3 60 175 1.5 2000 2000 300 i s 20 OFF 1.5 1250 2185 115 Time ' sec | Tenιp.(° Q [ Press, (torr) | Po ert ' waits) | Q : (sccm) | N 2 K ; (scan) CF, MEN * 175 1.5 2000 2000 300 60 175 1.5 2000 2000 300 20 175 1.5 1500 2000 300 Example 2 Example 2 describes a plurality of different processes performed utilizing a plurality of different process steps, to optimize residue removal while preventing undercuts and minimizing oxide loss. A 50 seem MFC ir.sαlled Wafer Oxide loss (A) 1 1 33 32 A 50 seem MFC insτailed Process 3) 4% CF4 Wafer number "" A 50 seem MFC installed Example 3 Example 3 includes five processes carried out on a Fusion Gemini Enhanced Strip tool Example 3 shows effective ash processes for via, poly, oxide, and nitride process levels Gemini Enhanced Strip processes were demonstrated for these process levels that effectively eliminate a wet strip step and may require, if necessary, only dry ash followed by a deionized water (DI) rinse. A Gemini Enhanced Strip (GES) process was developeα for the ion implant process level that removes all photoresist and implant residue using only the dry ash followed by about a five minute DI rinse. No photoresist poppers were seen on the sample or in the chamber. Descum recipes were demonstrated that removed about 530 A. It may be possible to fine tune the process recipes to even further improve the results. However, the process would basically remain the same as described herein. The processes may also be shortened to improve total wafer throughput Figures 10-19 show photomicrographic evidence of the results of the processes according to Example 3. r x . e. I 5. 4. ζ. Exampl e 4 Example 4 includes another process combination according to the present invention for removing material from a substrate. Figure 26a and Figure 26b illustrate vias that have been treated with a process including parameters substantially similar to those of Example 4. Figure 24 illustrates a cross- sectional view of a typical via structure similar to the vias shown in Figure 26a and Figure 2βb and treated according to the present invention Figure 26a illustrates undercut of the TiN layer m the substrate. Figure 26b illustrates a via that by reducing the treatment time by about 15 seconds from that shown in Example 4, the undercutting may be eliminated Figure 25a illustrates a via prior to treatment with the process of Example 4. As can be seen in Figure 25a, debris remains in the via. On the other hand, Figure 25b represents vias after treatment with a process according to Example 4 followed by a deionized water rinse Example 5 Example 5 includes another process combination according to the present invention for removing material from a substrate. According to Example 5, oxide loss can be reduced by utilizing hydrogen in the forming gas to scavenge fluorine radicals while utilizing relatively high flows of CF 4 . Example 5 provides one example of such a process . Figure 27a illustrates a via after treatment with a process according to Example 5. As shown in Figure 27a, residue may remain in the via after processing with the present invention. However, as illustrated by Figure 27b, the residue may be water-removable since Figure 27b shows a via after a deionized water rinse . No undercutting is seen in the vias shown in Figure 27a or Figure 27b. > ' C ^.' Oxide loss can also be reduced by using the hydrogen in forming gas to scavenge the F radicals while using high CF., flows. Recipe V5 is an example. Example 6 Example 6 includes another combination of process steps according to the present invention for removing material from a substrate. According to Example 6, about 9% CF 4 may be added to the plasma during step 3. Figure 28a illustrates a substrate of post poly residues after treatment with a process according to the present invention. Figure 28b illustrates residue removal after treatment with the process of Example 6 and a deionized water rinse . 8" Gas Flows Step 3 - 9% CF4 Concentration • Minimum time to reach required temperature Example 7 Example 7 includes another combination of process steps according to the present invention for removing material from a substrate. According to Example 7, about 7.5% CF 4 may be added to the plasma during step 3. Figure 29a illustrates a substrate of post poly residues after treatment with a process according to the present invention. Figure 29b illustrates residue removal after treatment with the process of Example 7 and a deionized water rinse . Minimum time to reach required temperature Example 8 Example 8 includes another combination of process steps according to the present invention for removing material from a substrate. According to Example 8, about 3.75% CF 4 may be added to the plasma during step 3. Figure 30a illustrates a substrate of post poly residues after treatment with a process according to the present invention. Figure 30b illustrates residue removal after treatment with the process of Example 8 and a deionized water rinse . Minimum time to reach required temperature The foregoing description of the invention illustrates and describes the present invention. Additionally, the disclosure shows and describes only the preferred embodiments of the invention, but as aforementioned, it is to be understood that the invention is capable of use in various other combinations, modifications, and environments and is capable of changes or modifications within the scope of the inventive concept as expressed herein, commensurate with the above teachings, and/or the skill or knowledge of the relevant art. The embodiments described hereinabove are further intended to explain best modes known of practicing the invention and to enable others skilled in the art to utilize the invention in such, or other, embodiments and with the various modifications required by the particular applications or uses of the invention. Accordingly, the description is not intended to limit the invention to the form disclosed herein. Also, it is intended that the appended claims be construed to include alternative embodiments.

Claims: Claims : We claim: 1. A method for removing material from a substrate, said method comprising the steps of: generating a plasma in a plasma generating and discharge device including a sapphire plasma tube; introducing at least one fluorine-containing compound into said plasma; introducing a forming gas into said plasma and directing said plasma toward the material to be removed from the substrate . 2. The method according to claim 1, wherein the forming gas includes at least one nitrogen-containing compound and at least one hydrogen-containing compound. 3. The method according to claim 2, wherein the at least one nitrogen-containing compound includes at least one member selected from the group consisting of N 2 and N0 2 and the at least one hydrogen-containing compound includes at least one member selected from the group consisting of H 2 and CHF 3 . 4. The method according to claim 2, wherein the forming gas includes about 10% hydrogen and is introduced into the plasma at a rate of up to about 2000 seem. 5. The method according to claim 1, wherein said plasma is an oxygen plasma. 6. The method according to claim 5, wherein at least one oxygen-containing compound to form said plasma is provided by introducing at least one oxygen-containing compound selected from the group consisting of molecular oxygen, atomic oxygen, ozone, and oxygen-containing compounds. 7. The method according to claim 6, wherein said at least one oxygen-containing compound includes at least one compound selected from the group consisting of N 2 0, N0 2 , NO, C0 2 , or CO. 8. The method according to claim 1, wherein said plasma is an oxygen plasma and the step of generating said plasma includes the steps of generating a temperature of about 270°C in the plasma generating and discharge device, generating a pressure of about 1.5 torr in the plasma generating and discharge device, supplying from about 500 watts to about 2000 watts of power to the plasma generating and discharge device, introducing about 2000 seem of at least one oxygen-containing gas into the plasma generating and discharge device, wherein about 300 seem of forming gas are introduced into the plasma generating and discharge device, and wherein about 5 seem of at least one fluorine-containing gas are introduced into the plasma generating and discharge device. 9. The method according to claim 1, wherein said plasma generating and discharge device utilizes microwave frequency electromagnetic radiation to generate said plasma. 10. The method according to claim 6, wherein said at least one oxygen-contammg compound, said forming gas, and said at least one fluorine-containing compound are introduced into said plasma generating and discharge device simultaneously. 11 The method according to claim 6, wherein said at least one oxygen-contammg compound is introduced into said plasma generating and discharge device at a rate of from about 200 seem to about 4000 seem. 12. The method according to claim 6, wherein said at least one oxygen-contaming compound is introduced into said plasma generating and discharge device at a rate of from about 1500 seem to about 2000 seem. 13. The method according to claim 6, wherein said at least one oxygen-containing compound is introduced into said plasma generating and discharge device at a rate sufficient to generate a pressure of from about 0.75 torr to about 10 torr in the plasma generating and discharge device. 14. The method according to claim 1, wherein said at least one fluonne-contaming compound includes at least one member selected from the group consisting of CF„ , C 2 F 6 , CHF 3 , CFH 3 C 2 H 2 F 4 , C 2 H 4 F 2 , CH 2 F 2 , CH 3 CF 3 , C 3 F 8 , SF 6 , and NF 3 . 15. The method according to claim 6, wherein the amount of said at least one fluorine-containing compound introduced into the plasma generating and discharge device is up to about one-tenth the amount of the at least one oxygen containing compound introduced into the plasma generating and discharge device . 16. The method according to claim 6, wherein the amount of said at least one fluorine-containing compound introduced into the plasma generating and discharge device is up to about 200 seem. 17. The method according to claim 1, wherein the substrate is heated to a temperature of from about 20 °C to about 350°C. 18. The method according to claim 1, wherein said plasma generating and discharge device is supplied with power from about 500 watts to about 2000 watts. 19. The method according to claim 1, wherein said plasma generating and discharge device is supplied with a level of power sufficient to result in removal of material from the substrate without causing unwanted effects to the substrate. 20. The method according to claim 1, further comprising the steps of: operating the plasma generating and discharge device at multiple temperatures, multiple power levels for multiple periods of time, multiple pressures, and multiple levels of said at least one fluorine-containmg compound and said forming gas . 21. A device for removing material from a substrate, comprising: a plasma generating and discharge device including a sapphire plasma tube; a source of at least one gas for introducing the at least one gas into the plasma generating and discharge device for forming a plasma; at least one source of at least one fluorine-containing compound for introducing at least one fluorme-contammg compound into said plasma generating and discharge device; a source of at least one forming gas for introducing the at least one forming gas into said plasma, and means for directing said plasma toward the material to be removed from the substrate.

Inventors: HUFFMAN MARIA, NOBLE THOMAS, SAKTHIVEL PALANIKUMARAN, ZIMMERMAN TERESA, HUFFMAN, MARIA, NOBLE, THOMAS, SAKTHIVEL, PALANIKUMARAN, ZIMMERMAN, TERESA
Applicants: FUSION SYSTEMS CORP, HUFFMAN MARIA, NOBLE THOMAS, SAKTHIVEL PALANIKUMARAN, ZIMMERMAN TERESA, FUSION SYSTEMS CORPORATION, HUFFMAN, MARIA, NOBLE, THOMAS, SAKTHIVEL, PALANIKUMARAN, ZIMMERMAN, TERESA
Application year: 1997
Main classification: H05H1
IPC codes: C23F4, H01J37, H01L21, H05H1