Abstract:
A method for repairing an attenuated phase shift mask providing an attenuated phase shift mask comprising an etched opening and at least one underlying light attenuating layer to reveal a quartz substrate the opening including an unetched portion comprising the at least one light attenuating layer; blanket depositing a negative photoresist layer over the at least one light blocking layer to include filling at a portion of the opening; exposing the negative photoresist layer through the quartz substrate and developing the negative photoresist layer to form a negative photoresist layer portion filling a portion of the opening; and carrying out a dry etching process to remove the unetched portion.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention generally relates to methods for forming reticles and photomasks and more particularly to a method for repairing attenuated phase shift masks (PSM) caused by incomplete etching of an attenuating phase shifting layer.  
         BACKGROUND OF THE INVENTION  
         [0002]    In semiconductor device manufacturing, photolithography is typically used to transfer a pattern for forming semiconductor features onto the semiconductor wafer for the formation of multi-layered structures forming integrated circuits. During a photolithographic process, radiant energy having relatively small wavelengths such as ultraviolet light is passed through a mask also referred to as a reticle to expose a radiant energy sensitive material such as photoresist formed on the wafer process surface. The mask includes predetermined circuitry patterns having regions of attenuating and non-attenuating regions where the radiant energy intensity is modulated. For example, Ultraviolet (UV) light passed through the mask onto the photoresist causes chemical reactions in the exposed portion of the photoresist altering it properties. Upon development of the photoresist resist exposed portions are removed in the case of a positive photoresist and non-exposed portions are removed in the case of a negative photoresist.  
           [0003]    As semiconductor device feature sizes have decreased to sizes smaller than the wavelength of light used in photolithographic processes, the diffraction of light at feature pattern edges formed on the reticle cause a loss of resolution in transferring the reticle pattern to the wafer photoresist. To increase the resolution of photolithographic pattern transfer phase shift masks have been developed where the phase of the wavefronts of light passing through alternating portions of the reticle pattern are shifted out of phase with respect to light passing through adjacent portions to produce destructively interfering wavefronts to reduce undesired exposure of the wafer photoresist due to diffraction of light at feature edges of the recticle pattern. As a result, the contrast, and therefore transferable resolution of the reticle pattern is improved.  
           [0004]    There have been several different types of PSM&#39;s developed to improve resolution for different types of reticle patterns. For example, in an attenuated or halftone PSM, the phase shifting function is typically accomplished by adding an extra layer of transmissive material to the mask with predetermined optical properties. Some PSM&#39;s are designed to produce improved resolution while having little improvement in depth of focus, while other PSM&#39;s are designed to have a relatively modest increase in resolution while producing a greater improvement in depth of focus. For example, attenuated PSM&#39;s also referred to as halftone PSM&#39;s are of the latter type of PSM&#39;s.  
           [0005]    Referring to FIG. 1A, for example, in one type of attenuated PSM, a halftone film  12  is formed over a fused silica substrate  10 , also referred to as a quartz substrate. For example, the halftone layer  12  may be formed to transmit a portion of the light producing an accompanying phase shift. Formed overlying the halftone layer is an opaque layer  14  which is not transmissive to light.  
           [0006]    Referring to FIG. 1B, a photoresist layer (not shown) is formed over the chromium containing layer and exposed with an E-beam tool or light source and developed to form a circuitry pattern, for example including lines, pads, and contact holes. The chromium containing layer and the halftone layer are subsequently etched to form a clear light transmissive area, for example opening  16 , revealing the quartz substrate.  
           [0007]    Still referring to FIG. 1B, one problem according to the prior art is that during etching of the halftone layer  12 , for example by a dry etching process, etching residues including halftone layer material, e.g.,  18 , frequently form along the sidewalls of the opening  16  thereby reducing the size of the opening. While a portion of the quartz substrate is frequently exposed at the bottom of the opening, the opening, for example, a contact hole is defective for transferring the contact hole pattern to a process wafer in a photolithographic process. Prior art processes have attempted to repair defectively etched openings by removing the residues in a subsequent process after removing the overlying chromium containing layer. The etching residues remaining with the opening have been removed by selectively dry etching the residues e.g.,  18  surrounding the opening with, for example, a selective area etching tool using a series of masking processes around individually defective contact holes using, for example, XeF gas. However, the selective etching processes of the prior art are typically very time consuming and require expensive selective etching machines to selectively etch portions of the defective reticle pattern areas. Further, time consuming masking processes are required to avoid damage to the quartz substrate during the selective etching process and frequently result in damage to the quartz substrate. Another further problem with prior art processes is the risk of shifting of the contact opening in the several alignment processes required to carry out the selective etching process resulting in deviations from critical dimension. As a result, the critical dimension of the a repaired opening must be verified following the selective etching repair process further adding to the cycle time for a PSM repair process.  
           [0008]    Thus, there is a need in the semiconductor manufacturing art for a more reliable and cost effective method for repairing etching defects in the reticle patterning process to form attenuated phase shift masks.  
           [0009]    It is therefore an object of the invention to provide a more reliable and cost effective method for repairing etching defects in the reticle patterning process to form attenuated phase shift masks while overcoming other shortcomings and deficiencies of the prior art.  
         SUMMARY OF THE INVENTION  
         [0010]    To achieve the foregoing and other objects, and in accordance with the purposes of the present invention, as embodied and broadly described herein, the present invention provides a method for repairing an attenuated phase shift mask.  
           [0011]    In a first embodiment, the method includes providing an attenuated phase shift mask comprising an etched opening extending through a thickness of at least one light blocking layer and at least one underlying light attenuating layer to reveal a quartz substrate the opening including an unetched portion comprising the at least one light attenuating layer; blanket depositing a negative photoresist layer over the at least one light blocking layer to include filling at least a portion of the opening; exposing the negative photoresist layer through the quartz substrate and developing the negative photoresist layer to form a negative photoresist layer portion filling at least a portion of the opening; and carrying out a dry etching process to remove the unetched portion.  
           [0012]    These and other embodiments, aspects and features of the invention will be better understood from a detailed description of the preferred embodiments of the invention which are further described below in conjunction with the accompanying Figures.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1A is a cross sectional view of an attenuated PSM at a stage in production according a prior art process.  
         [0014]    [0014]FIG. 1B is a cross sectional view of an attenuated PSM at a stage in production according a prior art process.  
         [0015]    [0015]FIGS. 2A through 2E are cross sectional views of an attenuated PSM at stages in production according to an embodiment of the present invention.  
         [0016]    [0016]FIG. 3 is a process flow diagram including several embodiments of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]    In a first embodiment of the invention, a light transmitting substrate, preferably quartz is provided having at least one light attenuating layer formed over the light transmitting substrate and at least one light blocking layer formed over the at least one light attenuating layer. A photolithographic patterning process is carried out to form a circuitry feature pattern followed by etching through a thickness of the at least one light blocking layer followed by etching through a thickness of the at least one light attenuating layer to form a feature opening revealing the light transmitting substrate. A negative photoresist is then applied to fill the at least a portion of the feature opening, preferably all of the feature opening, and the negative photoresist layer exposed to a light activating source through a reverse side of the light transmitting substrate. The negative photoresist is developed to leave a photoresist plug covering the exposed substrate and filling a portion of the feature opening and a second etching process is carried out to remove a remaining portion of the light attenuating layer remaining within the feature opening.  
         [0018]    In exemplary implementation, referring to FIG. 2A is shown a cross sectional side view of a portion of an attenuated phase shifting mask (PSM), for example a portion of a reticle for carrying out a photolithographic patterning process in a semiconductor wafer microelectronic circuit fabrication process. Shown is a substrate  22 , for example fused silica, also referred to as quartz. Formed overlying the quartz substrate  22  is formed a light attenuating layer  24 , for example formed of a material and sufficient thickness to pass from about 4% to about 40% of incident light together with a phase shift of the transmitted light of about 180 degrees. For example the light attenuating layer  24  is preferably, but not exclusively, formed of at least one layer of MoSi, MoSi x N y  and MoSi x O y N 2  having a thickness of from about 500 Angstroms to about 1500 Angstroms, depending on the optical properties of the material and the thickness required to retard the phase of transmitted light about 180 degrees. Formed overlying the light attenuating layer  24  is a light blocking layer  26  substantially opaque (non-transmitting) to incident light, for example, ultraviolet light. Preferably, the light blocking layer  26  is a chromium containing layer, for example formed of at least one layer of Cr, CrO x N y , and CrN x , having a thickness less than about 1000 Angstroms.  
         [0019]    Referring to FIG. 2B, a conventional photolithographic patterning process is used to pattern a photoresist layer (not shown) formed over the light blocking layer  26 , for example using an E-beam or light exposure process followed by a development process to form an etching pattern for etching feature openings. For example a first etching process is carried out to etch through a thickness of the light blocking layer  26 , for example using a wet or more preferably, a dry etching process. For example a dry etching chemistry for etching through a chromium containing light blocking layer preferably includes a chlorine and oxygen containing chemistry. Following etching through a thickness of the light blocking layer  26  the photoresist layer (not shown) is removed by a wet or dry etching process, preferably a dry etching process and a second etching process, preferably a dry etching process, for example using a dry etching chemistry including SF 6  for a MoSiON containing layer may. The second dry etching process is carried out to etch through a thickness of the light attenuating layer  24  to form opening  28  extending through the light blocking layer  26  and through the light attenuating layer  24  to reveal the quartz substrate  22 .  
         [0020]    According to the present invention, it has been found that the second dry etching process to etch the light attenuating layer, especially where a fluorine containing etching chemistry is used to etch molybdenum and silicon containing materials, for example MoSiON, results in dry etching residues along the light attenuating layer portion of the opening  28  sidewalls e.g.,  20 A. Referring to FIG. 2C, according to an embodiment of the present invention, following the second dry etching process to form opening  28 , a negative photoresist layer  32 A is blanket deposited, for example by spin coating the negative photoresist over the light blocking layer to include filling the opening  28 .  
         [0021]    Preferably, the negative photoresist is activated by I-line light sources, but negative photoresists activated by DUV light sources may also be suitably used.  
         [0022]    Still referring to FIG. 2C, the negative photoresist layer  32 A is exposed to a light activating source through the quartz substrate, that is, the exposing light source is incident on the side opposite the quartz substrate having the light attenuating layer as indicated by directional arrows e.g.,  33  indicating the direction of the exposing light. In operation, the etching residues along the opening  16  sidewalls e.g.,  20 A attenuate the light to an extent that the negative photoresist layer portions adjacent and overlying the light attenuating layer portions are not adequately exposed to the activating light thereby rendering the non-exposed portions (i.e., not sufficiently exposed) of the negative photoresist soluble in a negative photoresist developer. Simultaneously, the exposed portion of the negative photoresist layer  32 A, forming a plug in the opening  28  extending above the revealed portion of the quartz substrate is exposed to the activating light source rendering that portion insoluble in the negative photoresist developer.  
         [0023]    Referring to FIG. 2D, following photoresist development of photoresist layer  32 A according to conventional processes, negative photoresist plug portion  32 B is formed over the exposed portion of the quarts substrate. In the case sidewall residues are not present within an opening, for example other openings forming part of the circuitry pattern where such other openings have already been adequately etched as shown in FIG. 2E, the negative photoresist portion will fill the opening thereby protecting the quartz substrate during a subsequent etching process.  
         [0024]    Referring to FIG. 2E, following exposure and development of the negative photoresist layer  32 A to form negative photoresist layer portion (plug)  32 B, a third etching process, preferably a dry etching process, for example using a dry etching chemistry, preferably including a fluorine containing etching chemistry, including for example, SF 6  and XeF, is carried out to etch away remaining portions of the attenuating blocking layer  24  within opening  28 , for example residues remaining from the second dry etching process, such as MOSiON containing etching residues remaining along opening sidewalls e.g.,  20 A. Following the third etching process, the remaining negative photoresist layer portion  32 B is removed according to a conventional wet or dry etching process to leave a cleared opening  28 . During the third etching process, the quartz substrate is advantageously protected from etching damage by the negative photoresist plug portion  32 B. Furthermore, the light blocking layer  26  acts a hard etching mask during the third etching process, thereby retaining the critical dimensions of the opening  28 . In other words, the third etching process is preferably selective to the light attenuating layer with respect to the light blocking layer and the negative photoresist plug portion  32 B. Conventional processes are subsequently carried out to complete the formation of the attenuated PSM, for example removing all or a portion of the light blocking layer.  
         [0025]    Referring to FIG. 3 is a process flow diagram including several embodiments of the present invention. In process  301 , a quartz substrate having a first light attenuating layer and a second light blocking layer overlying the first attenuating layer is provided. In process  303 , an photolithographic patterning and first etching process is carried out etch through a thickness of the light blocking layer followed by a second etching process to etch through a thickness of the light attenuating layer to form an opening revealing the quartz substrate. In process  305 , a negative photoresist layer is blanket deposited over the light blocking layer to include filling at least a portion of the opening. In process  307 , the negative photoresist layer is exposed through the reverse side of the quartz substrate and developed to form a negative photoresist protective plug filling at least a portion of the opening. In process  309 , a third etching process is carried out to remove a remaining portion of the light attenuating layer remaining within the opening to clear the opening followed by removal of the remaining negative photoresist plug. In process  311 , the attenuated PSM formation process is completed.  
         [0026]    The preferred embodiments, aspects, and features of the invention having been described, it will be apparent to those skilled in the art that numerous variations, modifications, and substitutions may be made without departing from the spirit of the invention as disclosed and further claimed below.