Abstract:
A method and apparatus for improving etch uniformity in reticle etching by eliminating local effects at the edge of the reticle is disclosed. The present invention relates to a reticle frame which surrounds the reticle. The reticle frames are patterned with a pattern profile similar to that of the reticle to prevent edge uniformities of the reticle by allowing uniform plasma etching of the entire reticle surface. The reticle frames may also be used to move the reticle in and out of etch chambers without damaging them.

Description:
This application is a divisional of application, Ser. No. 09/354,303 filed Jul. 16, 1999 now U.S. Pat. No. 6,280,646, the entirety of which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to the field of photolithography used in fabricating semiconductor devices and, more particularly to a method and apparatus for improving etch uniformity in reticle etching by eliminating local etching effects at the edge of the reticle. 
     DESCRIPTION OF THE RELATED ART 
     In the manufacture of semiconductor wafers, photolithography is used to pattern various layers on a wafer. A layer of resist is deposited on the wafer and exposed using an exposure tool and a template such as a mask or reticle. During the exposure process a form of radiant energy, such as ultraviolet light, is directed through the reticle to selectively expose the resist in a desired pattern. The resist is then developed to remove either the exposed portions, for a positive resist, or the unexposed portions, for a negative resist, thereby forming a resist mask on the wafer. The resist mask can then be used to protect underlying areas of the wafer during subsequent fabrication processes, such as deposition, etching, or ion implantation processes. 
     An integral component of the photolithographic process is the reticle. The reticle includes the pattern corresponding to features (e.g., transistors or polygates) at a layer of the integrated circuit (IC) design. The reticle may be a transparent glass plate coated with a patterned light blocking material such as, for example, chromium. This type of reticle is typically referred to as a binary mask since light is completely blocked by the light blocking material and fully transmitted through the transparent glass portions. 
     Another type of reticle is the attenuated phase shift mask (PSM). Attenuated PSMs utilize partially transmissive regions instead of the light blocking regions used in binary masks. The partially transmissive regions typically pass (i.e., do not block) about three to eight percent of the light they receive. Moreover, the partially transmissive regions are designed so that the light that they do pass is shifted by 180 degrees in comparison to the light passing through the transparent (e.g., transmissive) regions. 
     During the fabrication of reticles, the reticle is often affected by edge effects in the etching chamber. Reference is made to FIGS. 1-3. FIG. 1 shows a plasma etching system  10  including a radio frequency (“RF”) source power supply  11 , a coil  12 , a chamber  13 , a dielectric plate  9 , a multi-frequency bias power supply  15 , and a decoupling capacitor  16 . The chamber  13  is connected to a ground potential  17 . Reticle  18  is mounted onto electrode  14  which applies a bias voltage or bottom power. Electrode  14  may be an electrostatic-chuck or susceptor for holding the reticle  18  during the etching process. Modulated-bias plasma  19  is generated in chamber  13  from source material  20 . Source material may be provided to chamber  13  via one or more feed tubes  52 . Reticle has a chrome layer  21  formed thereon and a patterned photoresist layer  22  formed over chrome layer  21 . Reticle  18  is reacted with plasma  19  to etch a portion of a surface of chrome layer  21  according to the patterned photoresist  22  to impart the pattern onto the reticle  18 . As can be seen from FIGS. 1-3, the reticle  18  is positioned directly over electrode  14 . As the plasma bombards the reticle, it etches the reticle on an upper surface as well as at the edges of the reticle  18 . FIG. 2 shows a top view of the etched reticle and FIG. 3 shows a cross section of the reticle as shown in FIG.  2 . The reticle suffers from edge effects in the etching of the reticle. These edge effects are caused by the existence of the edge of the reticle and the nonuniformity in the reticle formed due to nonuniformity of chemical loading and electrical power at the edge of the reticle. The edge effects may be manifest as a different print quality at the edge of the reticle. Thus, if an integrated circuit pattern extends to the edge of the reticle it will be adversely affected by these edge effects. 
     There is a need to eliminate edge effects in the reticle to prevent edge anomalies from being transferred onto an integrated circuit or onto a mask used in fabrication of an integrated circuit. This is especially true as feature sizes continue to dramatically decrease, and as the number of features within the IC design continues to increase, it requires reticles which can use a greater portion of the surface for transferring a pattern to an integrated circuit. Accordingly, there is a need and desire for a method and apparatus for eliminating edge effects from the high density etchers in the formation of reticles. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method and apparatus for improving etch uniformity in reticle etching by eliminating local effects at the edge of the reticle. Specifically, the invention relates to a reticle carrier which surrounds the reticle and is subjected to a plasma etch along with the reticle to reduce edge non-uniformities. The reticle carrier may also be used to move reticles in and out of etch chambers without damaging or contaminating them. To help reduce edge non-uniformities, the reticle carriers are formed of materials similar to that of the reticle and are patterned with a pattern profile similar to that of the reticle. 
    
    
     Additional advantages of the present invention will be apparent from the detailed description and drawings, which illustrate preferred embodiments of the invention. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other advantages and features of the invention will become more apparent from the detailed description of the preferred embodiments of the invention given below with reference to the accompanying drawings in which: 
     FIG. 1 is a schematic view of a conventional plasma etching system. 
     FIG. 2 is a top view of a conventional reticle placed on a chuck. 
     FIG. 3 is a view taken along the line III—III of FIG.  2 . 
     FIG. 4 is a top view of a reticle placed on the reticle carrier according to the present invention. 
     FIG. 5 is a view of the reticle carrier of the present invention taken along the line V—V of FIG.  4 . 
     FIG. 6A is a cross sectional view of the reticle and carrier according to a second embodiment of the present invention. 
     FIG. 6B is a cross sectional view of the reticle and carrier according to a third embodiment of the present invention. 
     FIG. 7 is a schematic view of a reticle plasma etching system using a reticle carrier according to the present invention. 
     FIG. 8 shows a reticle undergoing an intermediate stage of processing according to the present invention. 
     FIG. 9 a reticle undergoing a processing according to the present invention at a point subsequent to that shown in FIG.  8 . 
     FIG. 10 a reticle undergoing a processing according to the present invention at a point subsequent to that shown in FIG.  9 . 
     FIG. 11 a reticle undergoing a processing according to the present invention at a point subsequent to that shown in FIG.  10 . 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     In the following detailed description, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized, and that structural, logical and electrical changes may be made without departing from the spirit and scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, as the scope of the present invention is defined by the appended claims. 
     Reference is now made to FIG.  4 . This figure shows a top view of the reticle  118  and frame  123  surrounding reticle  118  according to the present invention. While the reticle  118  is depicted as square in shape and the frame  123  is depicted as being circular in shape, it should be understood that these components could be any desired shape. For example, both the reticle  118  and the frame  123  may be rectangular in shape. The reticle  118  may be formed of any suitable material for example, silica glass, fused quartz glass, borosilicate glass or another material transparent to various types of radiation commonly used in semiconductor lithographic operations. Preferably the reticle is formed of quartz. Further, the reticle may be any reticle including a light blocking reticle, a phase shifting reticle, an attenuated phase shifting reticle, a hard phase shift reticle or a multi-layered phase shifting reticles. 
     Reticle  118  has formed thereon patterned light blocking or partially light transmissive regions  121  formed on the surface of the reticle  118  depending upon whether the reticle is a binary reticle or a phase shifting reticle. The light blocking regions  121  can be a homogeneous metal layer, such as chrome, gold, or the like. Alternatively, the light blocking regions  121  may be a composite material of different metals, such as chrome and gold, or chrome and another metal, or the like. In yet another alternative, partially light transmissive regions  121  can be formed of any attenuating material employed in a phase shifting mask, such as, for example, molybdenum silicide. 
     The reticle  118  is placed on frame  123 . Frame  123  is formed of a material similar to that of reticle  118  such that the reticle  118  and frame  123  have similar chemical and electrical properties in the plasma etcher. Accordingly, it is preferable that the frame  123  be formed of silica glass, fused quartz glass, borosilicate glass or another material transparent to various types of radiation commonly used in semiconductor lithographic operations. Preferably the frame  123  is formed of quartz. 
     The frame  123  is also patterned with a light blocking or partially light transmissive region similar to that of reticle  118 . Thus, frame  123  has formed thereon patterned light blocking or partially light transmissive regions  124  formed on the surface of the frame  123  depending upon whether the reticle  118  is a binary reticle or a phase shifting reticle. The light blocking regions  124  can be a homogeneous metal layer, such as chrome, gold, or the like. Alternatively, the light blocking regions  124  may be a composite material of different metals, such as chrome and gold, or chrome and another metal, or the like. In yet another alternative, partially light transmissive regions  124  can be formed of an attenuating material employed in a phase shifting mask, such as, for example, molybdenum silicide. 
     The light blocking or partially light transmissive region  124  formed on frame  123  may be formed during the formation of light blocking or partially light transmissive region  121  on reticle  118 , or at a time prior to or subsequent to the patterning of the reticle  118 . This is discussed in more detail below in reference to the method for forming the reticle  118  with reference to FIGS. 8-9. 
     Reference is now made to FIG.  5 . This figure is a cross sectional view along line V—V as shown in FIG.  4 . As can be seen from the figure, the reticle  118  is supported at a bottom layer of reticle  118  by L-shaped sections of frame  123 . While frame  123  is shown as having L-shaped sections near the bottom of the frame  123 , it should be understood that any suitable support may be used to support reticle  118  within frame  123 . For example, the frame may have angled support pieces or round nubs formed at the bottom of the frame to support reticle  118 . In addition, frame is designed such that the upper surface of reticle  118  and frame  123  are essentially coplanar. 
     An alternative embodiment of the present invention is shown with reference to FIGS. 6A and 6B. Reference is first made to FIG.  6 A. This figure shows a reticle  138  having a portion of the bottom of the reticle  138  cut away in a square cross section so as to engage protruding portions  135  of frame  133 . Reference is now made to FIG. 6B where reticle  148  having a portion of the bottom of the reticle  148  cut away in a triangular cross section so as to engage complimentary triangular protruding portions  145  of frame  143 . As can be seen from FIGS. 6A and 6B, the upper and lower surfaces of the reticles  138 ,  148  are coplanar with the upper and lower surfaces of frames  133 ,  143 . The presence of portions of frame  123 ,  133 ,  143  directly adjacent to the edges of reticle  118 ,  138 ,  148  provides a more uniform etching surface on both sides of the reticle, which, in turn, allows even chemical loading and electrical power across both the reticle  118 , 138 ,  148  and frame  123 ,  133 ,  143  using a conventional plasma etching apparatus similar to that depicted in FIG.  1 . 
     Reference is made to FIG. 7 which shows a plasma etching system  110  including a radio frequency (“RF”) source power supply  111 , a coil  112 , a chamber  113 , a dielectric plate  109 , a multi-frequency bias power supply  115 , and a decoupling capacitor  116 . The chamber  113  is connected to a ground potential  117 . Reticle  118  is mounted on a frame  123  and then mounted onto an electrode  114  which applies a bias voltage or bottom power. Electrode  114  is formed such that electrode  114  contacts both frame  123  and reticle  118 . The electrode  114  may have a raised column structure to efficiently contact both the frame  123  and electrode  118  as illustrated in FIG.  7 . 
     Modulated-bias plasma  119  is generated in chamber  113  from source material  120 . Source material  120 , such as, for example, HBr, O 2 , Ar, Cl, fluorocarbon containing gases and the like, may be provided to chamber  113  via one or more feed tubes  152 . Reticle  118  has a light blocking or partially light transmissive region, such as a chrome layer,  121  formed thereon and a patterned photoresist layer  125  formed over chrome layer  121 . Frame  123  has a light blocking or partially light transmissive region, such as a chrome layer,  124  formed thereon and a patterned photoresist layer  122  formed over chrome layer  124  in the manner described above. Reticle  118  and patterned frame  123  are reacted with plasma  119  to etch a portion of a surface of chrome layer  121 ,  124  according to the patterned photoresist  125 ,  122  to impart the pattern onto the reticle  118  and frame  123 . Reticle  118  and frame  123  are then removed from the chamber  113 , reticle  118  is removed from frame  123  and the remaining photoresist layers  125  are removed from the reticle  118 . 
     As can be seen from FIG. 7, the reticle  118  is positioned within frame  123  and both frame  123  and reticle  118  are in direct contact with electrode  114 . As the plasma bombards and etches the reticle  118 , it also bombards and etches the frame  123 , thus reducing the edge effect at the upper surface of reticle  118  caused by nonuniformity in chemical loading and electrical power at the edge of reticle  118 . Thus, a greater surface area of the reticle can be used to transfer a pattern onto an integrated circuit. Additionally, by eliminating edge effects, the present invention allows the use of the perimeter of the surface of the reticle which are currently not patterned. The present invention therefore would provide an increase of greater than about 150 mm 2  of reticle surface area to transfer patterns to an integrated circuit device. 
     The method for fabricating a reticle according to the present invention will now be described with reference to FIGS. 8-11. Reference is first made to FIG. 8. A light blocking or partially light transmissive layer  121  is deposited over a reticle substrate  118  which may be formed of silica glass, fused quartz glass, borosilicate glass or another material transparent to various types of radiation commonly used in semiconductor lithographic operations, by any conventional method. Light blocking or partially light transmissive layer  121  is then deposited which may be any suitable material such as a homogeneous metal layer, such as chrome, gold, or the like or a composite material of different metals, such as chrome and gold, or chrome and another metal, or the like. Light blocking or partially light transmissive layer  121  may also be an attenuating material employed in a phase shifting mask such as a molybdenum silicide. A pattern transfer layer  125  is then deposited over light blocking or partially light transmissive layer  121 . Pattern transfer layer  125  may be any material used to transfer a pattern to a subsequent layer and will depend upon the radiation characteristics of the equipment used to form the lithographic reticle  118 . For example, where an electron beam direct write system is used, pattern transfer layer  125  will be formed of an electron beam sensitive photoresist. Alternatively, where an optical system is used to generate radiation of a particular wavelength, pattern transfer layer  125  will be a conventional photoresist material sensitive to the particular wavelength. It should be understood that those skilled in the art will recognize that many different combinations of materials can be used to form the layers shown in FIG.  8 . 
     Reference is made to FIG.  9 . After preparing reticle substrate  118  with light blocking or partially light transmissive layer  121  and pattern transfer layer  125 , pattern transfer layer  125  is exposed to radiation by a scanning electron beam or laser. Radiation emerging from a radiation source is imaged onto pattern transfer layer  125 . The imaging process results in the transfer of a pattern present in a reticle generating data base to pattern transfer layer  125 . 
     The pattern transfer layer  125  is written with an electron beam direct write system and the pattern transfer layer is developed to arrive at the structure illustrated in FIG.  9 . The present invention contemplates the use of many different types of pattern transfer layer  123  depending upon the particular lithographic system to be used in the fabrication of semiconductor devices, this includes deep-ultraviolet (deep UV), x-ray, and standard i-line and g-line lithographic systems. While the transfer of pattern will typically use an electron beam direct write system, it is also possible to perform pattern transfer using an optical imaging process using radiation having a wavelength ranging from the deep-UV to about 200 nanometers to optical wavelengths up to about 440 nanometers. 
     The lithographic pattern may includes a large number of patterned metal features overlying reticle substrate  118 . The exact arrangement of the lithographic pattern will depend upon the particular masking level for which lithographic reticle  118  is to be used. For example, where lithographic reticle  118  is to be used to form interconnect traces in a semiconductor device, the lithographic pattern will include a series of lead traces having the necessary geometric arrangement to form metal interconnects in a semiconductor device. In other applications, reticle  118  can be used to form, for example, gate electrodes in a semiconductor device, or via openings in an interlevel dielectric layer, and the like. 
     It should be understood that those skilled in the art will recognize the reticles can be of two general types, either brightfield or darkfield. In a brightfield reticle patterned features to be transferred are opaque features on a clear background. The process of the invention is intended to function with either type of reticle. In the case of a darkfield reticle, the lithographic pattern will appear as openings in a sheet of opaque material overlying reticle substrate  118 . 
     Reference is now made to FIG.  10 . Reticle  118  having a light blocking or partially light transmissive region  121  overlying reticle substrate  118  and a pattern transfer layer  125  overlying light blocking or partially light transmissive region  121  is placed on reticle frame  123 . Reticle frame  123  is independently deposited with a light blocking or partially light transmissive layer  124  and patterned with a pattern transfer layer  122 . Because the frame  123  will ultimately be discarded, it is not essential that the frame be patterned with the precision of the electron beam writing system as used for reticle  118 . In fact, the frame  123  may be patterned with crude lithography of about 2 to 3 times the design geometry rule of reticle  118 . While the frame  123  should be patterned with approximately the same pattern density as reticle  118 , frame  123  does not need to be patterned with the same precision as reticle  118 . This allows efficient use of the writing system. While the present invention has been described by patterning the frame  123  and reticle  118  separately, it should be understood that reticle  118  and frame  123  may also be patterned in the same step. The reticle  118  and frame  123  are then placed onto an electrode  114  in a high-density plasma etcher, as depicted in FIG.  10 . 
     Reference is now made to FIG.  11 . After preparing reticle substrate  118  with light blocking or partially light transmissive region  121  and pattern transfer layer  125  and preparing frame  123  with light blocking or partially light transmissive region  124  and pattern transfer layer  122 , the light blocking or partially light transmissive regions  121 ,  124  are removed from the reticle  118  and frame  123  in a high-density plasma etcher. Since the reticle  118  and frame  123  are both formed of materials that are electrically and chemically similar and have similar pattern density, edge effects in the plasma etcher are reduced or eliminated. Thus, the reticle can be formed such that a greater surface of the reticle may be patterned. 
     While the invention has been described in detail in connection with the preferred embodiments known at the time, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.