Abstract:
In accordance with the objectives of the invention a new method is provided for the repair of an attenuated phase shifting mask having a contact pattern. The invention etches a single trench in the quartz substrate of the phase shifter mask and removes the impact of a void in the phase shifter material. Alternatively, the invention provides for first conventionally restoring the original dimensions of a contact hole in which a pinhole is present and then etching a single or a double trench in the exposed substrate of the restored contact opening.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a division of U.S. patent application Ser. No. 10/755,500, filed Jan. 12, 2004, now U.S. Pat. No. 7,157,191. 
    
    
     BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The invention relates to the fabrication of integrated circuit devices, and more particularly, to a method of creating an attenuated phase shifting mask by methods of repair thereof, whereby effects of pinholes are removed. 
     (2) Description of the Prior Art 
     During and for the fabrication of semiconductor devices optical projection tools are an integral part of the optical lithography technology that is fundamental to the creation of semiconductor devices and devices features. The optical projection tools conventionally contain an electromagnetic light source, a configuration of lenses and an optical projection mask that contains a replica of the image that is to be created. The image of the mask is, with the interference and the help of the configuration of lenses, projected onto the surface over which the image contained in the mask is to be created. 
     Semiconductor device improvements are traditionally and consistently achieved by sharp reductions in device feature dimensions, resulting in increasing device densities, which imposes on the supporting optical lithography technology the need for a continuing ability to provide images of smaller dimensions while maintaining image resolution. 
     Conventional photolithography masks are limited in this respect due to the increasingly smaller distance between adjacent light projections, which causes increased interference between closely spaced light projections. This has led to the development of phase-shifting masks, where effects of closeness of projecting light rays are cancelled by controlling the relative phase relationship between closely adjacent rays of light. 
     A phase shifting mask is provided with a layer of phase shifter material that is created in a pattern over the substrate of the mask. The patterned layer of phase shifter material causes the light that passes through the layer of phase shifter material to be out-of-phase by 180° with respect to the light that passes through the substrate over which the patterned layer of phase shifter material has been created. This results in a corrective action between the light that passes through the transparent substrate of the phase shifter mask and the light that passes through the layer of phase shifter material, this corrective action allowing further reductions in the images that are created using the phase shifter mask. Optionally, a phase shifter mask may also be provided with a patterned layer of opaque material such as chrome to further enhance the mask application. 
     Phase shifting masks are generally created using methods of photolithography. These methods at times lead to the introduction of fabrication defects in the surfaces of the created mask. For a phase shifter mask to be operational, especially considering the deep-submicron device features that must be created using the phase shifter mask, surface irregularities, such as voids occurring in a layer of phase shifter material, must be prevented or corrected if present. Any surface irregularity that occurs in any of the layers of the phase shifter mask, including the substrate of the phase shifter mask, results in a disruption of the there-through transmitted light and therefore in an interruption of a coherent interaction between the phase controlled light that is transmitted through the phase shifter mask. 
     Cost considerations relating to the creation of phase shifter masks lead to the need for repairing phase shifter masks that show any defects that may negatively affect the desired performance characteristics of the phase shifter mask. The invention addresses this concern and provides a method for the repair of attenuated phase shifter masks with a contact pattern. 
     U.S. Pat. No. 6,159,641 (Baume et al.) shows a method for repairing masks. 
     U.S. Pat. No. 6,016,357 (Neary et al.) discloses a method to repair PSMS. 
     U.S. Pat. No. 6,114,073(Yang) shows a method to repair PSMS. 
     U.S. Pat. No. 5,272,024 (Lin) discloses a structure and method for PSM repair. 
     U.S. Pat. No. 6,361,904 B1 (Chiu) shows a method for repairing the Shifter Layer of an alternating phase shifter mask. 
     SUMMARY OF THE INVENTION 
     A principle objective of the invention is to repair an attenuated phase shifting mask in a cost-effective manner. 
     Another objective of the invention is to repair an attenuated phase shifting mask without impairing operational phase shifting requirements of the mask. 
     Yet another objective of the invention is to repair an attenuated phase shifting mask that is independent of the wavelength for which the mask is designed and used. 
     In accordance with the objectives of the invention a new method is provided for the repair of an attenuated phase shifting mask having a contact pattern. The attenuated phase shifting mask is frequently used for the creation of contact holes or via openings and as such has a surface area of no phase shift and a surface area of 180° phase shift. Conventionally, when a surface defect such as a pinhole occurs in the layer of phase shifter material of an attenuated phase shifter mask, an opaque material is deposited over the pinhole. This opaque material however interrupts the desired and conventional operational characteristics of light transmission of the attenuated phase shifter mask. To avoid such an interruption, the invention etches a single trench in the surface of the quartz substrate of the phase shifter mask and removes the impact of a void in the phase shifter material. Alternatively, the invention provides for first conventionally restoring the original dimensions of a contact hole in which a pinhole is present and then etching a single or a double trench in the exposed substrate of the restored contact opening. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1   a  through  1   c  highlight conventional methods of repairing a pinhole in a layer of phase shifter material. 
         FIGS. 2 through 5  highlight characteristics of phase shifting and light transmission for various combinations of deposition of opaque material and the creation of single and double trenches etched in the surface of the quartz substrate of the attenuated phase shifter mask. 
         FIGS. 6   a  and  6   b  show a normal attenuated phase shifter mask in which no pinhole is present. 
         FIGS. 7   a  and  7   b  show the occurrence of a pinhole in a contact opening. 
         FIGS. 8   a  and  8   b  show the conventional repair of a pinhole by depositing a layer of material around the perimeter of a contact opening in which the pinhole is present. 
         FIGS. 9   a  and  9   b  show a first repair of the invention by providing a single trench etch, in the exposed surface of the substrate (of the attenuated phase shifter mask) of the contact opening in which the pinhole is present. 
         FIGS. 10   a  and  10   b  show a second repair of the invention by providing a double trench etch in the exposed surface of the substrate (of the attenuated phase shifter mask) of the contact opening in which the pinhole is present. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First are highlighted a number of statements of purpose that relate to the invention:
     1. attenuated phase shifter masks are used for the patterning of layers of contact openings   2. conventionally, a commercial repair apparatus is used to deposit an opaque material over a pinhole defect in a layer of phase shifter material; this layer of opaque material however is in the application of a phase shifter mask equal to an opaque layer, such as a layer of chrome, and does therefore not provide a phase shift of 180 degrees to light passing through the attenuate phase shifter mask   3. if the surface of a quartz substrate is etched, the phase shifting function of the attenuated phase shifter mask is maintained around the perimeter of the contact openings, and   4. it is the observed conclusion of the invention that, in order to repair a pinhole defect in a contact area, a single trench etched in the surface of the quartz substrate can be created such that a phase shift of 180 degrees can be provided to light passing through the attenuated phase shifter mask.   

     A conventional method of repairing a pinhole over the surface of a quartz substrate, which is used as the substrate for an attenuated phase shifter mask, is first highlighted using  FIGS. 1   a  through  1   c  for this purpose. 
     The cross section that is shown in  FIG. 1   a  shows a substrate  10 , conventionally comprising quartz, over the surface of which a layer  12  of phase shifter material, such as MoSiON, has been deposited. The layer  12  of MoSiON has been patterned and etched, creating an opening  11  through the layer  12  of MoSiON, exposing the quartz substrate  10 . The phase shifting material  12  provides a 180° phase shift to the light that passes through this layer  12 , the phase of the light that passes through the quartz substrate  10  without passing through the layer  12  of phase shifter material is not affected and therefore has a 0° phase shift. 
     Pinhole  14  in the layer  12  of phase shifter material must be repaired, a repair that conventionally is performed by, as shown in the cross section of  FIG. 1   b , depositing a small amount  16  of opaque material over the pinhole  14 . This method has a number of disadvantages since the opaque material  16  acts as a deposition of chrome and therefore affects the light transmission characteristics of the layer  12  over which the opaque material  16  is deposited. 
     Some of the important parameters of light transmission and phase shifting that are provided by an attenuated phase shifter mask are now highlighted, using parameters that have been highlighted in  FIG. 1   a  for this purpose, as follows:
         for regions  18 , which are the regions of the attenuated phase shifter mask underlying the opening  11  created through the layer  12  of phase shifter material, the light transmission of the light provided by light source  13  is about 100%, the phase shift that is introduced to this light is about 0°, and   for regions  20  and  22 , underlying the patterned and etched layer  12  of phase shifter material, these parameters are: light transmission of about 6%, phase shifting of about 180°.       

     From the cross section that is shown in  FIG. 1   b , it can be seen that these characteristics are disturbed for region  24 , underlying the deposited layer  16 , where for region  24  the light transmission has been reduced while the phase shift is difficult to predict. 
     As a further demonstration of the repair that is conventionally performed to repair a pinhole in the layer of phase shifter material,  FIG. 1   c  shows a cross section wherein the phase shifter material  12  has been symmetrically removed around the perimeter of the contact opening  11 . The removed phase shifter material has been replaced with opaque material  16 ′. The replacement opaque material  16 ′ is known to peel from the surface of the substrate  10  over which it has been deposited. 
     To avoid the above indicated negative effects that are introduced by conventional methods of repairing a pinhole or any other opaque deficiency over the substrate  10  of an attenuated phase shifter mask, the invention provides for etching a single trench into the substrate in areas surrounding the pinhole. 
     Comparisons of light transmission and phase shifting characteristics are first made for a number of configurations of quartz mask and thereover deposited layers of opaque material, using  FIGS. 2 through 6  for this purpose. 
     Referring first to the cross section shown in  FIG. 2 , this represents a normal attenuate phase shifter mask and is used to highlight the relation between phase shift and light transmission for the various surface regions of the conventional attenuated phase shifter mask. 
     Specifically highlighted in the cross section of  FIG. 2  are:
           10 , the transparent substrate of the attenuated phase shifter mask, typically comprising quartz     12 , the patterned and etched layer of phase shifter material, typically comprising MoSiON; other phase shifter materials that can be applied are CrO, ZrSiO 3  or SiON     11 , the opening created through the layer  12  of phase shifter material, exposing substrate  10       18 , the region of the substrate  10  that aligns with opening  11 , ight passes through the attenuated phase shifter mask confined by region  18 , a 0° phase shift is experienced by the light that passes through the attenuated phase shifter mask that is bounded by opening  11     regions  20  and  22 , phase shift about 180°, about 6% of the incident light that strikes the surface of layers  12  passes through these layers.       

     Referring now to the cross section that is shown in  FIG. 3 , there is shown:
           10 , the transparent substrate of the attenuated phase shifter mask, typically comprising quartz     20 , the patterned and etched layer of opaque material     21 , the opening created through the layer  20  of opaque material, exposing substrate  10       22 , the region of the substrate  10  that aligns with opening  21 , 100% light passes through the attenuated phase shifter mask confined by region  22 , a 0° phase shift is experienced by the light that passes through the attenuated phase shifter mask that is bounded by opening  21     regions  24  and  26 , phase shift is difficult to control and predict, no incident light passes through the patterned layer  20 .       

     Referring now to the cross section that is shown in  FIG. 4  which shows a single trench etched in the surface of the quartz substrate, there is shown:
           10 , the transparent substrate of the attenuated phase shifter mask, typically comprising quartz     20 , the patterned and etched layer of opaque material     31 , an opening created through the layer  20  of opaque material, exposing the surface of substrate  10       33 , a single trench etched in the surface of substrate  20     regions  34  and  36 , phase shift is difficult to control and predict, no incident light passes through layers  20     regions  35  and  37 , phase shift is zero, incident light passes 100% through the substrate  10     regions  32 , phase shift 180 degrees, incident light passes 100% through the substrate  10 .       

     Referring now to the cross section that is shown in  FIG. 5 , which represents a double trench etched in the surface of the quartz substrate, there is shown:
           10 , the transparent substrate of the attenuated phase shifter mask, typically comprising quartz     20 , the patterned and etched layer of opaque material     41 , an opening created through the layer  20  of opaque material, exposing substrate  10       43 , two trenches etched in the surface of substrate  20     regions  44  and  46 , phase shift is difficult to control and predict, no incident light passes through the patterned layer  20     regions  45  and  47 , phase shift is 180 degrees, incident light passes 100% through the substrate  10     region  42 , phase shift 180 degrees, incident light passes about 100% through the substrate  10 .       

     From the above a number of relevant observations can be made. 
     Relating to the single trench etch as shown in the cross section of  FIG. 4 , the following applies:
         the etched area  33  is centered within the area of the contact pattern, which is represented by opening  31  created through the layer  20  of opaque material   the etched width of the etched single trench  33  approaches the critical diameter of the contact area, exposed through the opening  31     the etching of the quartz substrate is limited to a one-time etch per contact area   the width of the etched trench exceeds the combined width of the double trenches, which are shown in the cross section of  FIG. 5     compared to the etching of the double trenches ( 43 , shown in the cross section of  FIG. 5 ), the etching of the single trench ( 33 , shown in the cross section of  FIG. 4 ) is easy to control in etch width and etch location, and   relative to the deposited material  20  in combination with the double trench etch, the single trench etch can be expected to provided a larger repair window.       

     Relating to the double trench etch as shown in the cross section of  FIG. 5 , the following applies:
         the etched area  43  is at the edge of the contact pattern, which is represented by opening  41  created through the layer  20  of opaque material   the etched width 45/47 of the etched single trench  43  is smaller than the critical diameter of the contact area, exposed through the opening  41 , a suitable combined etch width 45/47 must be experimentally determined   the etch of the double trenches  43  must be located around the perimeter of the contact pattern  41     the width (45+47, shown in the cross section of  FIG. 5 ) of the etched double trenches  43  is less than the width ( 32 , shown in the cross section of  FIG. 4 ) of the single trench  33     compared to the etching of the single trench  33 , the etching of the double trenches  43  is difficult to control in etch width and etch location, and   the etch of double trenches  43  requires four steps of etch from which follows that the creation of the double trenches  43  is a process that is more difficult to control.       

     The single trench etch is therefore the preferred method of repairing a pinhole defect in the layer of phase shifter material as has been highlighted in the cross section of  FIG. 4 . That is the defect is assumed to be present in the region that is bounded by the opening  31  over the surface of the quartz substrate, the etch therefore removes the phase shifter material from this surface region and further etches into the surface of substrate  10 , as has been highlighted in the cross section of  FIG. 4  with the trench  33  etched into the surface of substrate  10 . The phase relationships and light passing capabilities are, with the etch of trench  33 , modified as follows: 
     The phase shift of 180° is achieved by selecting the depth of the created trench  33  such that, for a given incident light wavelength, an appropriate amount of quartz is removed. The light passing through the remaining layer of quartz underlying the created trenches can be provided with a phase shift of 180° in this manner. 
     For instance, for an incident light wavelength of 248 nm, the thickness of the quartz underlying the created trench must be about 238.5 nm. For an incident light wavelength of 193 nm, the thickness of the quartz underlying the created trench must be about 172.3 nm. 
     The following can be concluded:
         for proper operation of a phase shifter mask, capabilities of light transmission and phase shifting must be controlled   in conventionally repairing a pinhole or a void in the phase shifter material of a phase shifter mask, the pinhole is covered with an opaque material; where previously this region of the phase shifter material has about 6% light transmission and 180 degree phase shift, the repaired region has 6% light transmission and unknown degree phase shift   by removing the phase shifter material that contains the pinhole or void and by in addition etching into the surface of the quartz substrate, the effectiveness of the phase shifter material is not altered since, see  FIG. 4  for the single trench etch, the required characteristics of 100% light transmission and 0 degrees phase shift are maintained for surface areas  35  and  37  while the etch for single trench  33 , surface area  32 , the light transmission characteristics through this surface are to still 100% light transmission but now having, as determined by the depth of the trench  33 , a 180 degree phase shift.       

     This latter alteration of the contact region, bounded by opening  31 , does not detract from the functionality of the contact surface. The exposure (of 100% light transmission) remains in effect over the entire contact area while the light transmitted through region  32  of the quartz substrate has a not detrimental phase shift of 180 degrees. 
     The contact region will continue to be exposed (in light intensity) as desired, the fact that the light within the area of exposure now has a phase shift of zero degrees and a phase shift of 180 degrees there-within does not affect the exposure of the contact area. It would, if beneficially applied, further minimize negative effects of light interference within the exposed contact area. 
     For further clarification and extension of the invention,  FIGS. 6   a  through  10   b  are presented. 
     Shown in  FIG. 6   a  is a cross section of a substrate  10  of an attenuated phase shifter mask over which a patterned layer  50  of shifter material has been created. Openings  51  created through the layer  50  of phase shifter material are normal contact openings for pattern exposure by incident light  56 .  FIG. 6   b  shows a top view corresponding to the cross section of  FIG. 6   a , the cross section shown in  FIG. 6   a  has been taken along the line  6   a - 6   a ′ shown in  FIG. 6   b . It is clear that the  FIGS. 6   a  and  6   b  relate to a normal pattern, that is a pattern in which no pinhole defect is present. 
     Shown in  FIG. 7   a  is a cross section of a substrate  10  of a attenuated phase shifter mask over which a patterned layer  52  of shifter material has been created. Opening  51  created through the layer  52  of phase shifter material is a normal contact opening for pattern exposure by incident light  56 . Opening  53  created through the layer  52  of phase shifter material is a contact opening in which a pinhole is present, as is obvious from the deformed and considerably larger diameter of opening  53  when compared with the cross section of opening  51 .  FIG. 7   b  shows a top view corresponding to the cross section of  FIG. 7   a , the cross section shown in  FIG. 7   a  has been taken along the line  7   a - 7   a ′ shown in  FIG. 7   b.    
     Referring now to  FIGS. 8   a  and  8   b , therein is shown how a pinhole is conventionally repaired by deposition of an opaque material  54  around the perimeter of opening  53 , restoring the cross section of opening  53  to a cross section  53 ′, which is equal to a cross section of the normal contact opening  51 . 
     As has previously been pointed out, the repaired contact opening  53 ′ has, after the highlighted repair has been completed by the addition of layer  54 , lost the phase shifting function while at the same time the depth of focus and the process window of the opening  53 ′ is smaller than the normal contact opening  51 . 
       FIG. 8   b  shows a top view corresponding to the cross section of  FIG. 8   a , the cross section shown in  FIG. 8   a  has been taken along the line  8   a - 8   a ′ shown in  FIG. 8   b.    
     Referring now to  FIGS. 9   a  and  9   b , there is shown how, in the structure that has previously been discussed using  FIGS. 8   a  and  8   b , a single trench  58  has been etched into the surface of substrate  10  where the substrate  10  is exposed in opening  53 ′, creating the opening  60  which comprises the single trench etch  58 . For this method of repairing the pinhole  53 , as shown in  FIGS. 9   a  and  9   b , the results are that the contact created by the repaired opening  60  provides the required phase shifting function while the depth of focus and the process window of the opening  60  are the same as the normal contact opening  51 . 
       FIG. 9   b  shows a top view corresponding to the cross section of  FIG. 9   a , the cross section shown in  FIG. 9   a  has been taken along the line  9   a - 9   a ′ shown in  FIG. 9   b.    
     The etch of double trenches is shown in  FIGS. 10   a  and  10   b , where in the structure that has been discussed using  FIGS. 8   a  and  8   b , the double trenches  62  have been etched into substrate  10  where this substrate is exposed in opening  53 ′, creating the opening  60 ′, which comprises the double trench etch  62 . The area highlighted as area  64  is the area of the substrate  10  that is surrounded by the double trenches  62 . 
     For this method of repairing the pinhole  53 , as shown in  FIGS. 10   a  and  10   b , the results are that the contact created by the repaired opening  60 ′ provides the required phase shifting function while the depth of focus and the process window of the opening  60 ′ is the same as the normal contact opening  51 . 
       FIG. 10   b  shows a top view corresponding to the cross section of  FIG. 10   a , the cross section shown in  FIG. 10   a  has been taken along the line  10   a - 10   a ′ shown in  FIG. 10   b.    
     The cross sections and top views that are shown in  FIGS. 6   a  through  10   b  highlight:
         a normal attenuated phase shifter mask in which no pinhole is present,  FIGS. 6   a  and  6   b      the occurrence of a pinhole in a contact opening,  FIGS. 7   a  and  7   b      the conventional repair of a pinhole,  FIGS. 8   a  and  8   b , by depositing a layer of material around the perimeter of a contact opening in which the pinhole is present   providing a single trench etch,  FIGS. 9   a  and  9   b , in the exposed surface of the substrate (of the attenuated phase shifter mask) of the contact opening in which the pinhole is present   providing a double trench etch,  FIGS. 10   a  and  10   b , in the exposed surface of the substrate (of the attenuated phase shifter mask) of the contact opening in which the pinhole is present.       

     Although the invention has been described and illustrated with reference to specific illustrative embodiments thereof, it is not intended that the invention be limited to those illustrative embodiments. Those skilled in the art will recognize that variations and modifications can be made without departing from the spirit of the invention. It is therefore intended to include within the invention all such variations and modifications which fall within the scope of the appended claims and equivalents thereof.