Abstract:
A method and structure for providing adjustable optical lithography illumination comprises a blade which can be customized to provide a desired light pattern. The adjustable blade can be selectively configured to optimize a light pattern during development of a photolithographic process, then the optimized pattern can be transferred to a diffractive optical element or other light shaping means for production. Descriptions and depictions of specific adjustable blades are provided.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates to the field of semiconductor manufacture and, more particularly, to photolithography equipment useful during the formation of a semiconductor device.  
       BACKGROUND OF THE INVENTION  
       [0002]     During the formation of a semiconductor device many features such as conductors (word lines, digit lines), electrical contacts, and other physical features are commonly formed from, into, and over a semiconductor wafer. A goal of semiconductor device engineers is to form as many of these features in a given area as possible to increase yield percentages and to decrease device size and manufacturing costs.  
         [0003]     All heterogeneous structures on a semiconductor wafer requires lithography. Optical lithography, the lithographic method most used in leading-edge wafer processing, comprises projecting coherent light of a given wavelength from an illumination source (illuminator) through a quartz photomask or reticle having a chrome pattern thereon, and imaging that pattern onto a photoresist-coated wafer. The light chemically alters the photoactive photoresist and allows the exposed photoresist (if positive resist is used) or the unexposed photoresist (if negative resist is used) to be rinsed away using a developer.  
         [0004]     With decreasing feature sizes the limits of optical lithography are continually being tested and lithographic methods and materials are continually being improved through various developments, generally referred to as resolution enhancement techniques (RET&#39;s). RET&#39;s alter various aspects of the lithographic process to optimize the size and shape of a desired feature. For example, the wavelength of light used to expose the photoresist may be decreased, as longer wavelengths cannot resolve the decreasing feature sizes. The wavelength used with lithographic equipment has decreased from 365 nanometers (nm) in the mid-1980&#39;s to the current standard of 193 nm. Another RET includes optical proximity correction, which uses subresolution changes in the chrome pattern on the photomask or reticle to optimize the shape of the light focused on the photoresist. Without optical proximity correction, the chrome pattern is a scaled shape of the pattern which is to be produced. With very small features a scaled shape does not produce the desired pattern due to diffraction effects. However, the chrome photomask features can be modified in a manner that attempts to account for these diffraction effects. U.S. Pat. No. 6,245,468 by Futrell et al., assigned to Micron Technology, Inc. and incorporated herein by reference as if set forth in its entirety, describes an optical proximity correction apparatus and method. A third RET uses unequal photomask thickness of the quartz on which the chrome is formed at selected locations between the chrome to provide a phase-shift photomask. Phase shifting sets up destructive interference between adjacent light waves to enhance the pattern formed on the photoresist.  
         [0005]     Another resolution enhancement technique is off-axis illumination, which improves the resolution of repeating patterns found in semiconductor device manufacture.  FIG. 1  depicts an apparatus comprising off-axis illumination, and depicts an illuminator  10  comprising a laser which provides a coherent light source  12 , a diffractive optical element (DOE)  14 , a zoom axicon  16 , a first reflector  18 , a blade  20 , an optical homogenizer  22 , a second reflector  24 , a vertical photomask  26 , a lens  28 , and a wafer  30  comprising a layer of photoresist (not individually depicted). It should be noted that the simultaneous use of a blade  20  and a DOE  14  as depicted in  FIG. 1  is for illustration purposes only, as the use of one typically excludes the use of the other. A structure similar to the one depicted in  FIG. 1 , as well as the other RET&#39;s previous listed, are described and illustrated in  A Little Light Magic , IEEE Spectrum, September 2003, pp. 34-39.  
         [0006]     During research and development of a production process, simulation software is often used to predict the accuracy of an optical pattern for use with an illumination source on a stepper or scanner. As with circuit simulation, this software closely emulates the actual output which will be produced, but is not an exact representation and some trial and error manipulation of patterns is often necessary. To tune the illumination source pattern, a number of blades having different fixed patterns are used. In operation, each fixed blade is sequentially and manually inserted into the illumination path by a technician or engineer to determine the best illumination pattern for the mask or reticle being used. Changing a blade requires the engineer to first idle the equipment, manually replace the blade, initialize and calibrate the equipment, then return the tool to production. DOE&#39;s may also be used to determine a workable pattern and in fact function better than blades because they do not limit illumination intensity and can be placed into the light path by the equipment itself, however they are very expensive and have a construction lead time of several weeks. In practice, blades are used to determine the best pattern, then a DOE having the correct pattern based on testing using blades is ordered and used in production.  
         [0007]     A method and structure for decreasing the time and expense of selecting a suitable DOE pattern during research and development of a production photolithography process would be desirable.  
       SUMMARY OF THE INVENTION  
       [0008]     The present invention provides a new method and apparatus which, among other advantages, decreases the time and expense required to select a suitable diffused optical element pattern during the research and development of a photolithography process to form a semiconductor device. In accordance with one embodiment of the invention, an adjustable blade mechanism is used which may be adjusted remotely through equipment software. This eliminates the requirement for manual replacement of one blade with another by an engineer or technician.  
         [0009]     Advantages will become apparent to those skilled in the art from the following detailed description read in conjunction with the appended claims and the drawings attached hereto. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  depicts a conventional optical lithography apparatus;  
         [0011]      FIG. 2  depicts a computer controller connected to an adjustable optical lithography blade apparatus;  
         [0012]      FIG. 3  depicts a front view of a first embodiment of an adjustable blade apparatus;  
         [0013]      FIG. 4  is an isometric view of the blade arms and gears for adjusting the arms;  
         [0014]      FIG. 5  is an embodiment of a frame to which the arms of the blade are mounted;  
         [0015]      FIG. 6  is a side view, and  FIG. 7  is a front view, of another embodiment of the blade apparatus having arms which are adjustable using electromagnets;  
         [0016]      FIG. 8  is a front view of a quadrupole blade apparatus;  
         [0017]      FIG. 9  is a front view of an annulus blade apparatus;  
         [0018]      FIG. 10  is an isometric depiction of various components which may be manufactured using devices formed using an embodiment of the present invention; and  
         [0019]      FIG. 11  is a block diagram of an exemplary use of the invention to form part of a transistor array in a memory device. 
     
    
       [0020]     It should be emphasized that the drawings herein may not be to exact scale and are schematic representations. The drawings are not intended to portray the specific parameters, materials, particular uses, or the structural details of the invention, which can be determined by one of skill in the art by examination of the information herein.  
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0021]     A first embodiment of an inventive blade apparatus for use during the formation of a semiconductor device is depicted schematically in  FIG. 2  which depicts a computer  40  which controls an adjustable blade apparatus  42  using settings input by an operator, technician, or engineer.  
         [0022]     It should be noted that while the description specifies the use of this embodiment of the invention as a blade, an inventive embodiment may also be used as a diffused optical element (DOE) and the terms are generally interchangeable as used herein. The term “light mask” also is used herein to denote either a blade or a DOE.  
         [0023]     An exemplary embodiment of a blade apparatus  42  is depicted in  FIG. 3 , with detailed views at  FIGS. 4 and 5 , which comprises: a supporting frame  44 ; two separate overlapping blade arms  46 ,  48  which rotate around a central axis  50 ; and a mechanism  52  which receives an input through a connector  54  attached to a cable  55  from computer  40  for independently controlling each arm  46 ,  48 . The dimensions of the openings through the blade formed by the overlapping arms and the frame are set by the engineer or technician through the use of the controller computer  40 . The two arms  46 ,  48  are attached to the supporting frame  44  at a crossbar  56 . In this embodiment, the supporting frame  44  and crossbar  56  are formed from a single piece of metal and the crossbar  56  is formed at a location which will not obstruct the blade openings formed by the arms  46 ,  48  and frame  44 . The arms may also be formed from metal, for example sheet aluminum or steel, from Mylar® supported by a rigid frame, or from another opaque rigid material or an opaque nonrigid material supported by a rigid frame. To minimize light reflectance, the frame, arms, and other portions of the blade apparatus may be flat black in color.  
         [0024]      FIG. 4  depicts a detailed view of the exemplary embodiment of  FIG. 3 . In this embodiment, each blade arm  46 ,  48  is rotated by a separate gear  60 ,  62 , with both gears being controlled by the computer  40 , for example using one electric motor housed in mechanism  52  which controls both gears  60 ,  62  or with a separate motor for each gear, with each motor being controlled by computer  40 . Each gear  60 ,  62  and the edge of each arm  46 ,  48  comprises a plurality of intermeshing teeth or other frictional rotation means, which, for simplicity, are not depicted. The teeth of the gear mesh with teeth on the edge of the arm, and the gears are rotated to rotate the arm around the pivot point. While  FIG. 4  depicts gears which are laterally spaced as well as vertically spaced, providing the gears such that they are vertically centered with respect to crossbar  56  of  FIG. 3  and which have points of rotation centered around a single axis would allow for maximum adjustability of arms  46 ,  48 .  
         [0025]     Each gear  60 ,  62  can rotate both clockwise and counterclockwise, but will generally rotate in opposite directions in matched rotation so that each opening in the blade is centered along a vertical axis  64 . In other words, the center of the top and bottom openings, regardless of the angles of the openings, are centered along the vertical axis  64 . In this embodiment, the vertical axis  64  is perpendicular to crossbar  56  so that the openings through the blade are not obstructed by crossbar  56 .  
         [0026]     It may be desirable with some uses of the blade to have off-axis openings, in which case the two gears  60 ,  62  may rotate in the same direction (both clockwise or counterclockwise) or at unmatched rotational distances to allow an opening having an adjustable axis of rotation (i.e. an axis which can be rotated around the pivot point while maintaining an opening having unchanged dimensions). The maximum angle of the openings is determined by the arcs of each blade arm, the dimensions and configuration of each arm, the placement of the gears  60 ,  62 , and the percent of the arc of each arm which allows rotation by the gear.  
         [0027]     In use, the blade (which includes the frame  44  and the arms  46 ,  48 ) is inserted into place within the optical lithography equipment as is typically done with conventional blades. If the blade has not been previously connected to the controller computer  40 , connection is made, typically with a USB, serial, or parallel cable  55  and connector  54  through which signals pass from the computer  40  through the cable  55  to the gears  60 ,  62  or to other apparatus adapted to rotate the arms housed with mechanism  52 . Mechanism  52  will typically only receive signals from the computer  40  to rotate the arms, although in some uses of the invention mechanism  52  may comprise circuitry which returns information to the computer (for example to ensure that the arms of the blade have reached their desired position) or to directly control the movement of the arms (for example to move the blade through a series of positions based on instructions from the computer). Next, any required initial calibration is performed and the light path provided through the blade by the arms are set to a desired size and axis angle and testing is performed by controlling the rotational position of each arm through the use of the controller  40 . The openings of the blade are changed to increase or decrease the area of the openings, to change the rotational axis of the openings, or both, until the openings are optimized. Thus the present invention requires only an initial calibration, then any number of blade settings can be tested without requiring removal of the blade from the photolithographic equipment.  
         [0028]      FIG. 6  is a side view, and  FIG. 7  is a front view, of a second embodiment of the invention. In this embodiment, one edge of each arm  46 ,  48  comprises one or more laterally separated magnets, and the arms are rotated to a desired setting using first 70 and second  72  electromagnets. In this exemplary embodiment, arm  46  comprises one or more magnets along the right side and is controlled by electromagnet  70 , and arm  48  comprises one or more magnets along the left side and is controlled by electromagnet  72 . Two electromagnets are depicted for simplicity, however it may be possible to control the two arms with a single electromagnet, or more than two electromagnets. This embodiment allows control using only electronic means (an electromagnet) rather than the electromechanical means (one or more electric motors and gears) of the first embodiment. Further, this embodiment allows for a larger opening through the blade as the adjustment of the arms does not rely on a gear to mesh with a toothed arc of each arm.  
         [0029]      FIG. 8  depicts a blade apparatus for a quadrupole element comprising two sets of arms, with two vertically-oriented arms  80 ,  82  and two horizontally-oriented arms  84 ,  86 . Arms  80 ,  82 ,  84 , and  86  are each controlled by electromagnets  88 ,  90 ,  92 , and  94  respectively.  
         [0030]      FIG. 9  depicts a blade apparatus for an annulus comprising an iris shutter  100  and a circular electromagnet  102  for adjusting the size of the aperture  104  in the shutter. In this embodiment, the shutter  100  is manufactured from rigid, opaque sheet metal such as steel or aluminum, and is preferably flat black in color.  
         [0031]     Other variations of the adjustable blade are possible. For example, a radial frame may be in which the blade is part of the frame itself in which discrete plates can rotate relative to each other to determine the axis and size of the opening through the blade. Further, mechanisms other than the gear assembly and the electromagnet described herein can be used to adjust the arms of the blade. Also, arrangements other than the dipole element, quadrupole element, and annulus discussed can be manufactured. Two or more blade types, such as an adjustable quadrupole element and an adjustable annulus, may be used together to provide additional patterns.  
         [0032]     Automatic setting of the blade will decrease the time the equipment must remain idle, decrease engineering and technician time, and therefore reduce manufacturing costs.  
         [0033]     The blade may be used in at least two different methods of optimizing a pattern for a diffractive optical element. In the first use, the blade is configured to a first position by forming at least one light path through the blade. A coherent light source is then patterned by the light path through the blade, which then provides a first exposure of an optical pattern. Based on the results from the first exposure, the arms of the blade are adjusted to alter the light path through the blade, then the light path is patterned by the blade to provide a second exposure of the optical pattern. This process of exposure, measurement, blade adjustment, and exposure is continued until the opening in the blade is optimized, wherein a sufficient DOE is then ordered or manufactured. In the second use, prior to using the blade a number of possible openings through the blade are predetermined. The possible openings may be programmed into the controller computer or they can be manually set prior to each measurement. In either case, the blade is adjusted to the first setting, the coherent light source is patterned by the blade, the first exposure is performed using the patterned light source, then the blade is adjusted to the second setting and the second exposure is performed. This process of exposure, blade adjustment, exposure is performed until all predetermined blade positions are used to expose the pattern. The results are then analyzed to determine the desired DOE pattern, which is then ordered or manufactured.  
         [0034]     As depicted in  FIG. 10 , a semiconductor device  110  formed in accordance with the invention may be attached along with other devices such as a microprocessor  112  to a printed circuit board  114 , for example to a computer motherboard or as a part of a memory module used in a personal computer, a minicomputer, or a mainframe  116 .  FIG. 16  may also represent use of device  110  in other electronic devices comprising a housing  116 , for example devices comprising a microprocessor  112 , related to telecommunications, the automobile industry, semiconductor test and manufacturing equipment, consumer electronics, or virtually any piece of consumer or industrial electronic equipment.  
         [0035]     The process and structure described herein can be used to manufacture a number of different semiconductor structures. In a semiconductor memory device, these structures may comprise a capacitor such as a container capacitor or a pedestal capacitor.  FIG. 11 , for example, is a simplified block diagram of a memory device  110  such as a dynamic random access memory having a memory array with container capacitors which may be formed using an embodiment of the present invention. The general operation of such a device is known to one skilled in the art.  FIG. 11  depicts a processor  112  coupled to a memory device  110 , and further depicts the following basic sections of a memory integrated circuit: control circuitry  120 ; row  122  and column  124  address buffers; row  126  and column  128  decoders; sense amplifiers  130 ; memory array  132 ; and data input/output  134 .  
         [0036]     While this invention has been described with reference to illustrative embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the illustrative embodiments, as well as additional embodiments of the invention, will be apparent to persons skilled in the art upon reference to this description. It is therefore contemplated that the appended claims will cover any such modifications or embodiments as fall within the true scope of the invention.