Abstract:
A method and apparatus for performing a dielectric etch, etch mask stripping, and etch chamber clean. A wafer is placed in an etch chamber. A dielectric etch is performed on the wafer using an in situ plasma generated by an in situ plasma device in the etch chamber. The etch mask is stripped using a remote plasma generated in a remote plasma device connected to the etch chamber. The wafer is removed from the etch chamber and either the in situ plasma or the remote plasma may be used to clean the etch chamber. In etch chambers that do not use confinement rings, a heater may be used to heat the etch chamber wall to provide improved cleaning.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to the manufacture of semiconductor devices. More particularly, the present invention relates to improved techniques for dielectric etching and resist stripping.  
           [0002]    In the manufacture of certain types of semiconductor devices, dielectric layers may be etched using a plasma etching system. Such plasma etching systems may be high density plasma systems, such as inductive or ECR systems, or medium density plasma systems, such as a capacitive system. The high density plasma etchers dissociate gases so well that by providing oxygen to the chamber the chamber walls are cleaned. This cleaning may be caused by the heat generated by the plasma, UV radiation generated by the plasma, and a lot of dissociation caused by the plasma.  
           [0003]    Medium density plasma etching systems, such as capacitive plasma systems, may be used for oxide etching. In such medium density plasma etching systems a polymer forming chemistry is typically employed. Such medium density plasma etching systems typically cause polymer deposits to form on the chamber wall. Such systems usually allow the polymer deposits to build on the chamber walls and then are wet cleaned to remove the polymer deposits. The wet cleaning is typically required in medium density plasma systems, since such systems typically do not have sufficient dissociation, and sufficient plasma energy contacting the walls to perform a satisfactory polymer cleaning. When the chamber walls are only partially cleaned and polymer is not satisfactorily removed, sometimes new polymer does not sufficiently stick to the chamber wall possibly creating particles, which could be an added source of contamination. Plasma etching systems that use plasma confinement, such as the device disclosed in U.S. Pat. No. 5,534,751 by Lenz et al., entitled “Plasma Etching Apparatus Utilizing Plasma Confinement”, issued Jul. 9, 1996, generally confine a plasma within a confinement ring that keeps the plasma in a confined area away from the chamber wall. Keeping the plasma in a confined area generally provides a dense enough and hot enough plasma adjacent to the confinement ring to clean the confinement ring.  
           [0004]    It is known to provide CVD devices with remote plasma sources, which are typically used to clean the CVD chamber. Typically such plasma devices use a fluorine chemistry. Such CVD devices are used for vapor deposition.  
           [0005]    It is known to use a remote plasma source in a strip chamber, which typically uses the remotely generated plasma to strip an etch mask.  
           [0006]    In view of the foregoing, it would be desirable in medium density plasma systems, where a plasma of a density that is insufficient to sufficiently clean the chamber wall is generated by the medium density plasma systems, to provide a means for providing a plasma to sufficiently clean the chamber walls.  
         SUMMARY OF THE INVENTION  
         [0007]    The invention relates, in one embodiment, to a medium density dielectric plasma etching system with an additional remote plasma source to provide a cleaning of the plasma system and to possibly allow stripping within the etching system.  
           [0008]    The invention relates, in a second embodiment, to a medium density plasma system with an additional remote plasma source and with a heater for heating the walls of the chamber to allow cleaning of the chamber wall.  
           [0009]    The invention relates, in a third embodiment, to a confined medium density plasma system with an additional remote plasma source to increase the rate of in situ stripping.  
           [0010]    These and other features of the present invention will be described in more detail below in the detailed description of the invention and in conjunction with the following figures. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which:  
         [0012]    [0012]FIG. 1 is a schematic view of an etch chamber.  
         [0013]    [0013]FIG. 2 is a flow chart of the process for using the etch chamber shown in FIG. 1.  
         [0014]    [0014]FIG. 3 is a schematic view of another etch chamber.  
         [0015]    [0015]FIG. 4 is a flow chart of the process for using the etch chamber shown in FIG. 3. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0016]    The present invention will now be described in detail with reference to a few preferred embodiments thereof as illustrated in the accompanying drawings.  
         [0017]    In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art, that the present invention may be practiced without some or all of these specific details. In other instances, well-known process steps and/or structures have not been described in detail in order to not unnecessarily obscure the present invention. To facilitate discussion, FIG. 1 depicts a schematic view of an etch chamber  10  of a preferred embodiment of the invention. The etch chamber  10  comprises a chamber wall  12  which is grounded, an electrostatic chuck  14  connected to a radio frequency energy source  16 , an etchant gas distribution system  18  at the top of the etch chamber  10  connected to an etchant gas source  20 , heaters  22  adjacent to and surrounding the chamber wall  12 , and a remote plasma source  24  connected to a stripping gas source  25 . The chamber wall  12  may be of anodized aluminum or a conductive ceramic.  
         [0018]    [0018]FIG. 2 is a flow chart of the operation of the etch chamber used in a preferred embodiment of the invention. A wafer  26  is mounted on the electrostatic chuck  14  within and near the bottom of the etch chamber  10  (step  201 ). The wafer  26  has a dielectric layer  28 , such as an oxide layer of silicon oxide or a nitride layer, where part of the dielectric layer  28  is covered by a resist mask  30  and part of the dielectric layer  28  is not covered by the resist mask  30 .  
         [0019]    Next the etch chamber  10  etches away the part of the dielectric layer  28  that is not covered by the resist mask  30  (step  202 ). This is accomplished by flowing an etchant gas into the etch chamber  10 , so that the pressure in the etch chamber is between 20 and 200 milliTorr. In the preferred embodiment of the invention the etchant gas comprises a fluorocarbon gas with a generic molecular formula of C Y F X  and oxygen. The amount of the etchant gas used is known in the prior art. The etchant gas is provided by the etchant gas source  20  through the etchant gas distribution system  18  at the top of the etch chamber  10 . The radio frequency energy source  16  provides a radio frequency signal to the electrostatic chuck  14 , which creates radio frequency waves between the electrostatic chuck  14  and the grounded chamber wall  12 , which energizes the etchant gas with the electrostatic chuck  14  acting as a cathode and the chamber wall  12  acting as an anode. The energized etchant gas dissociates into ions, which are energized by the radio frequency wave, creating a plasma within the chamber and surrounding the wafer  26 . Since the wafer is within the plasma, the parts of the dielectric layer  28  that are not covered by the resist mask  30  are etched away. Since the chamber wall  12 , electrostatic chuck  14 , energy source  16 , etchant gas distribution system  18 , and etchant gas source  20  form and sustain the plasma around the wafer, these components provide an in situ plasma. As a result of the etching process, a polymer residue  32 , formed from the resist mask  30  and fluorocarbon etchant gas, forms on the chamber wall  12 . When the dielectric layer  28  is sufficiently etched the etching step (step  202 ) is stopped by stopping the generation of the in situ plasma.  
         [0020]    The remote plasma source  24  is shown connected to the chamber wall  12 . The remote plasma source  24  may be placed at another location around the etch chamber  10 . The entry between the remote plasma source  24  and the interior of the chamber  10  must be sufficiently large so that a sufficient number of oxygen radicals created in the remote plasma source  24  are able to pass from the remote plasma source  24  to the interior of the chamber  10  without being lost. The remote plasma source  24  may use either a microwave or an inductive discharge or some other high density dissociative remote source. An example of such a remote source is an ASTRON by ASTeX of Woburn, Mass. Oxygen is provided to the remote plasma source  24  from the stripping gas source  25 . The remote plasma source  24  dissociates the oxygen creating oxygen radicals, which are flowed into the etch chamber  10 , so that the pressure in the chamber is between 100 and 1,000 milliTorr. The oxygen radicals react with the resist mask  30  to strip away the resist mask  30  (step  204 ). In the preferred embodiment, the flow of the etch gas from the etch gas source  20  and power from the radio frequency energy source  16  is discontinued, so that the stripping of the resist mask  30  is accomplished solely by the oxygen radicals. In another embodiment, the in situ plasma may be used in combination with the remote plasma to provide stripping. In another embodiment, for the stripping gas, a hydrogen and nitrogen mixture may be used separately or in combination with oxygen.  
         [0021]    To discontinue the stripping step, the flow of the reactants from the remote plasma source  24  is stopped. The wafer  26  is removed from the etch chamber  10  (step  206 ). To clean the polymer residue  32  from the chamber wall  12  the chamber wall heater  22  heats the chamber wall  12 . In a preferred embodiment, the chamber wall is heated to a temperature of 80° to 300° C. In a more preferred embodiment of the invention, the chamber wall is heated to a temperature of 120° C. to 200° C. In a most preferred embodiment of the invention, the chamber wall is heated to a temperature of 150° C. Oxygen is provided to the remote plasma source  24  from the stripping gas source  25 . The remote plasma source  24  dissociates the oxygen creating oxygen radicals, which are flowed into the etch chamber  10 , so that the pressure in the chamber is between 100 and 1,000 milliTorr. The oxygen radicals react with the heated chamber wall  12  to clean the polymer residue  32  from the chamber wall  12  (step  208 ). In another embodiment a hydrogen and nitrogen mixture may be used separately or in combination with oxygen as a plasma source from the remote plasma source. When the chamber wall  12  is sufficiently clean, the plasma from the remote plasma source  24  is stopped and the etch chamber  10  is ready for the next wafer.  
         [0022]    [0022]FIG. 3 is a schematic view of an etch chamber  40  of another preferred embodiment of the invention that uses a confined plasma. The etch chamber  40  comprises a chamber wall  42 , an electrostatic chuck  44  connected to a radio frequency (RF) energy source  46 , an anode  48  that is grounded, an etchant gas source  50 , confinement rings  52  and a remote plasma source  54  connected to a stripping gas source  55 . The electrostatic chuck  44  which acts as a cathode at the bottom of the etch chamber  40  and the anode  48  at the top of the etch chamber  40  are placed close together to confine the plasma region to a small area. The confinement rings  52  surround the sides of the plasma region to further confine the plasma region, keeping the plasma near the center of the etch chamber  40  and away from the chamber wall  42 . The confinement rings  52  may be made of quartz and are formed as ring shaped plates that are spaced apart with narrow gaps between the confinement rings  52 . In this example, three confinement rings  52  are shown, but one or more confinement rings may be used in other embodiments. The narrow gaps between the confinement rings  52  keep the plasma from reaching the chamber wall  42 , since the gaps are so small that most plasma passing within the gap will be extinguished by a collision with a confinement ring  52  before the plasma reaches the chamber wall  42 .  
         [0023]    [0023]FIG. 4 is a flow chart of the operation of the etch chamber used in a preferred embodiment of the invention. A wafer  56  is mounted on the electrostatic chuck  44  within and near the bottom of the etch chamber  40  (step  401 ). The wafer  56  has a dielectric layer  58 , such as an oxide layer of silicon oxide or a nitride layer, where part of the dielectric layer  58  is covered by a resist mask  60  and part of the dielectric layer  58  is not covered by the resist mask  60 .  
         [0024]    Next the etch chamber  40  etches away the part of the dielectric layer  58  that is not covered by the resist mask  60  (step  402 ). This is accomplished by flowing an etchant gas into the etch chamber  40 , so that the pressure in the etch chamber is between 20 and 200 milliTorr. In the preferred embodiment of the invention, the etchant gas comprises a fluorocarbon gas with a generic molecular formula of C Y F X  and oxygen. The amount of the etchant gas used is known in the prior art. The etchant gas is provided by the etchant gas source  50  connected to the etch chamber  40 . The radio frequency energy source  46  provides a radio frequency signal to the electrostatic chuck  44 , which creates radio frequency waves between the electrostatic chuck  44  and the grounded anode  48 , which energizes the etchant gas. The energized etchant gas dissociates into ions, which are energized by the radio frequency wave, creating a plasma within the chamber and surrounding the wafer  56 . Since the wafer is within the plasma, the parts of the dielectric layer  58  that are not covered by the resist mask  60  are etched away. Since the electrostatic chuck  44 , energy source  46 , anode  48 , and etchant gas source  50  form and sustain the plasma around the wafer, these components provide an in situ plasma. As a result of the etching process, a polymer residue  62 , formed from the resist mask  60  and fluorocarbon etchant gas, forms on the confinement rings  52 . When the dielectric layer  58  is sufficiently etched, the etching step (step  402 ) is stopped by stopping the generation of the in situ plasma.  
         [0025]    The remote plasma source  54  is shown connected to the etch chamber wall  40  through the anode  48 . The entry between the remote plasma source  54  and the interior of the chamber  40  must be sufficiently large so that a sufficient number of oxygen radicals created in the remote plasma source  54  are able to pass from the remote plasma source  54  to the interior of the chamber  40  without being lost. The remote plasma source  54  may use either a microwave or an inductive discharge or some other high density dissociative remote source. An example of such a remote source is an ASTRON by ASTeX of Woburn, Massachusetts. Oxygen is provided to the remote plasma source  54  from the stripping gas source  55 . The remote plasma source  54  dissociates the oxygen creating oxygen radicals, which are flowed into the etch chamber  40 , so that the pressure in the chamber is between 100 and 1,000 milliTorr. The oxygen radicals react with the resist mask  60  to strip away the resist mask  60  (step  404 ). In the preferred embodiment, the flow of the etch gas from the etch gas source  50  and power from the radio frequency energy source  46  is continued, so that the stripping of the resist mask  60  is accomplished by the oxygen radicals from the remote plasma source  54  and in situ plasma. In another embodiment, a hydrogen and nitrogen mixture may be used separately or in combination with oxygen as a plasma source from the remote plasma source. To discontinue the stripping step, the flow of the reactants from the remote plasma source  54  and the in situ plasma are stopped.  
         [0026]    The wafer  56  is removed from the etch chamber  40  (step  406 ). To clean the polymer residue  62  from the confinement rings  52 , an oxygen or nitrogen/hydrogen etchant gas is flowed into the etch chamber  40  so that the pressure in the chamber is between 100 and 1,000 milliTorr. The amount of the etchant gas used is known in the prior art. The radio frequency energy source  46  provides a radio frequency signal to the electrostatic chuck  44 , which creates radio frequency waves between the electrostatic chuck  44  and the grounded anode  48 , which energizes the etchant gas. The energized etchant gas dissociates into ions, which are energized by the radio frequency wave, creating a plasma within the chamber and surrounding the wafer  56 . Since the in situ plasma is confined to a small region by the electrostatic chuck  44 , the anode  48 , and the confinement rings  52 , the in situ plasma is dense and energetic enough to clean the polymer residue  62  from the confinement rings  52 . When the confinement rings  52  are sufficiently clean, the in situ plasma is stopped and the etch chamber  40  is ready for the next wafer.  
         [0027]    In another embodiment, the in situ plasma and the remote plasma are both used for cleaning either in an etch chamber without a confined plasma or an etch chamber with a confined plasma.  
         [0028]    While this invention has been described in terms of several preferred embodiments, there are alterations, permutations, and equivalents, which fall within the scope of this invention. It should also be noted that there are many alternative ways of implementing the methods and apparatuses of the present invention. It is therefore intended that the following appended claims be interpreted as including all such alterations, permutations, and equivalents as fall within the true spirit and scope of the present invention.