Abstract:
A method is provided for processing and etching a substrate with a patterned photoresist layer on its surface. In one aspect, a method is provided for processing a substrate including illuminating a substrate with ultraviolet light, emitting a fluorescent light from the photoresist layer, measuring the intensity of the emitted fluorescent light and determining the open area percentage value for the patterned substrate. In another aspect, a method is provided for processing a substrate including providing the substrate, measuring the open area percentage value for the substrate, transmitting the open area percentage value to a processor, selecting an etch process for the substrate, transferring the substrate to a processing chamber, and etching the substrate.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     Embodiments of the present invention generally relate to the fabrication of integrated circuits and to the fabrication of photomasks used in the fabrication of integrated circuits.  
         [0003]     2. Description of the Related Art  
         [0004]     Semiconductor device geometries have dramatically decreased in size since such devices were first introduced several decades ago. Since then, integrated circuits have generally followed the two year/half-size rule (often called Moore&#39;s Law), which means that the number of devices on a chip doubles every two years. Today&#39;s fabrication plants are routinely producing devices having 0.15 μm and even 0.13 μm feature sizes, and tomorrow&#39;s plants soon will be producing devices having even smaller geometries.  
         [0005]     The increasing circuit densities have placed additional demands on processes used to fabricate semiconductor devices. For example, as circuit densities increase, the widths of vias, contacts and other features, as well as the dielectric materials between them, decrease to sub-micron dimensions, whereas the thickness of the dielectric layers remains substantially constant, with the result that the aspect ratios for the features, i.e., their height divided by width, increases. Reliable formation of high aspect ratio features is important to the success of sub-micron technology and to the continued effort to increase circuit density and quality of individual substrates.  
         [0006]     High aspect ratio features are conventionally formed by patterning a surface of a substrate to define the dimensions of the features and then etching the substrate to remove material and define the features. To form high aspect ratio features with a desired ratio of height to width, the dimensions of the features are required to be formed within certain parameters, which are typically defined as the critical dimensions of the features. Consequently, reliable formation of high aspect ratio features with desired critical dimensions requires precise patterning and subsequent etching of the substrate.  
         [0007]     Photolithography techniques, as one conventional method of patterning resists for etching processes, use light patterns and photoresist materials deposited on a substrate surface to develop precise patterns on the substrate surface prior to the etching process. Photolithographic reticles, or photomasks, typically include a substrate made of an optically transparent silicon based material, such as quartz (i.e., silicon dioxide, SiO 2 ), having an opaque light-shielding layer of metal, typically chromium, patterned on the surface of the substrate. The patterned metal layer, or photomask layer, define the pattern and correspond to the dimensions of the features to be transferred to the substrate when exposing a photoresist material to a pattern of light through a photolithographic photomask which corresponds to the desired configuration of features. A light source emitting ultraviolet (UV) light, for example, may be used to expose the photoresist to alter the composition of the photoresist. Generally, the exposed photoresist material is removed by a chemical process to expose the underlying substrate material. The exposed underlying substrate material is then etched to form the features in the substrate surface while the retained photoresist material remains as a protective coating for the unexposed underlying substrate material. The exposed underlying material to be etched may be a metal layer or may be a dielectric material.  
         [0008]     As a substrate enters the etching process, an etching process or recipe must be determined for each pattern design. Depending on the material to be etched and the pattern density of the substrate, different etch process with differing compositions may be used to optimize etch performance. Manual determination of the etch process reduces substrate throughput. Previous methods of determining and implementing etch processes have been less than satisfactory.  
         [0009]     Therefore, there remains a need for an improved etch process with higher throughput, which can inspect the substrate and determine the optimal etch process to be utilized.  
       SUMMARY OF THE INVENTION  
       [0010]     The present invention generally provides a method for processing and etching a substrate. In one aspect, a method is provided for processing a substrate including introducing a substrate having a surface comprising a patterned photoresist layer, illuminating the substrate with an ultraviolet light, emitting fluorescent light from the photoresist layer, measuring the intensity of the emitted fluorescent light, and determining an open area percentage value for the substrate from the intensity of the emitted fluorescent light.  
         [0011]     In another aspect, a method is provided for etching a substrate including providing a first substrate having a surface comprising a patterned photoresist layer; measuring an open area percentage value for the first substrate, transmitting the open are percentage value to a processor, selecting an etch process for the open area percentage value from a database coupled to the processor containing a plurality of etch processes, transferring the first substrate to a processing chamber, and etching the first substrate with the selected etch process.  
         [0012]     In yet another aspect, a method is provided for etching a substrate including introducing a first substrate having a surface comprising a patterned photoresist layer, illuminating the substrate with an ultraviolet light, emitting a fluorescent light from the photoresist layer, measuring the intensity of the emitted fluorescent light, transmitting the open area percentage value to a processor, determining an open area percentage value for the first substrate from the intensity of the emitted fluorescent light, selecting an etch process for the open area percentage value from a database coupled to the processor containing a plurality of etch processes, and etching the substrate with the selected etch process. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.  
         [0014]      FIG. 1  is a schematic view of a system for use with the processes described herein;  
         [0015]      FIG. 2  is a schematic view of a front end metrology device for use with the processes described herein; and  
         [0016]      FIG. 3  is a flow chart illustrating one embodiment of a sequence for processing a substrate. 
     
    
     DETAILED DESCRIPTION  
       [0017]     The present invention is described with reference to processing and etching a substrate, for example, to improve etch performance and substrate throughput. The determination of the open area percentage value for a substrate allows an optimized etch process to be selected. The open area percentage value for a substrate with a patterned photoresist layer covering a portion of its surface is the ratio of the exposed surface area of the substrate to the entire surface area of the substrate, where the exposed portion of the substrate is to be etched.  
         [0000]     Apparatus  
         [0018]     Suitable reactors that may be adapted for use with the teachings disclosed herein include, for example, the Decoupled Plasma Source (DPS™) II reactor, or the Tetra I and Tetra II Photomask etch systems, all of which are available from Applied Materials, Inc. of Santa Clara, Calif. The DPS™ II reactor may also be used as a processing module of a Centura™ integrated semiconductor wafer processing system, also available from Applied Materials, Inc.  
         [0019]      FIG. 1  is depicts a schematic diagram of one embodiment of an etch system  100 . The particular components of the etch system  100  shown herein are provided for illustrative purposes and should not be used to limit the scope of the invention.  
         [0020]     The system  100  generally includes an etch mainframe or etch platform  110 , a front end staging area  120 , a front-end metrology device  130 , a processor  140  that performs the analysis disclosed herein electronically, a computer software-implemented database system  150 , known as a manufacturing execution system (MES) conventionally used for storage of process information; and a post etch metrology device  160 .  
         [0021]     A substrate is introduced into the system  100  through the front end staging area  120 , a loading area, which is generally known as a factory interface or mini environment. As shown in  FIG. 1 , the front end staging area  120  is coupled to a transfer chamber  107  of the etch platform  110  by one or more loadlock chambers  104 . The front-end staging area  120  includes one or more cassette holders  113 , a robot  111 , for transferring a substrate to the loadlock chambers  104 .  
         [0022]     The front end staging area may further include a front-end metrology device  130  and/or a post etch metrology device  160 . The front-end metrology device  130  inspects the substrate prior to etching to determine the open area percentage value for the substrate. Additionally, the front-end metrology device  130  may inspect the substrate by processes described herein after it has been etched and or cleaned to ensure all of the photoresist has been removed. The metrology device  130  may alternatively be a stand-alone device.  
         [0023]     Referring to a schematic view of one embodiment of a front-end metrology device  130 ,  FIG. 2  depicts. The front end metrology device  200  generally includes a stage  205 , a light source  210  and sensing equipment  230 . The front-end metrology device  130 , as described herein may rapidly process and/or inspect a substrate  220  having a surface that includes a patterned photoresist layer and determine the open area percentage value for the substrate  220 . While the substrate  220  shown in  FIG. 2  is square-shaped (rectangular of equal length sides), such as used in photolithographic reticle manufacturing, the invention contemplates that substrates of various sizes and various shapes, such as circular substrate for chip manufacturing and rectangular shapes having different side lengths, such as used in some liquid crystal displays, may be used with the invention herein. The embodiment of the front-end metrology device  130  shown herein is provided for illustrative purposes and the description should not be construed or interpreted to limit the scope of the invention.  
         [0024]     The light source  210  generates an initial light beam  215  directed onto the substrate  220  that is mounted on a stage  205 . The light source  210  emits light with an ultraviolet light wavelength. The ultraviolet light wavelength may vary in length. The ultraviolet light wavelength is of a wavelength that is typically inert to reaction with the photoresist layer. Photoresist materials are designed to be sensitive to wavelengths of a desired ultraviolet light to have precise reactions to form regions of modified resist material that are etched to produce feature definitions of a desired critical dimension in the photoresist material.  
         [0025]     Preferred ultraviolet light wavelengths for measurement by the process herein are the ultraviolet light wavelengths that the photoresist is insensitive to chemical reaction. For example, photoresist may be sensitive to ultraviolet light having wavelengths of about 250 nanometers or less, for example, 248 nanometers, 193 nanometers, and 157 nanometers, and suitable ultraviolet light wavelengths for emission for the process described herein are about 300 nanometers or greater, such as between about 300 nanometers and about 525 nanometers. Ultraviolet light wavelengths ranging from 300 nanometers to 525 nanometers may be emitted by a high energy or high intensity source, such as a xenon, mercury, or other filtered arc lamps, or a HeCd or Ar-ion laser. The invention contemplates that different ranges of ultraviolet light may be used to provide an inert ultraviolet light wavelength to photoresist having different wavelength sensitivities, such as photoresists having sensitivities of 365 nanometers or 430 nanometers.  
         [0026]     Suitable ultraviolet light wavelengths are provided at sufficient intensity to produce a corresponding fluorescent light intensity between about 0.1% and about 1% of the ultraviolet light intensity. For example, the ultraviolet light may be provided at an intensity of at least 1 milliwatt per square centimeter, such as between about 1 milliwatt per square centimeter and about 100 milliwatts per square centimeter to produce a measurable fluorescent light intensity. The invention further contemplates that the sensitivity of detectors may be adjusted or provided that would allow fluorescent light intensity measurements beyond the described intensity between about 0.1% and about 1% of the ultraviolet light intensity.  
         [0027]     Once generated, the initial light beam  215  may pass through an excitation filter  212  prior to illuminating the substrate  220 . When the beam passes through the excitation filter  212 , wavelengths of light that will not cause the photoresist layer to emit fluorescent light may be removed. The initial light beam  215  may be reflected off of the dichromatic mirror (not shown) to direct the light beam onto the substrate  220 . Further, the initial light beam  215  may optionally pass through a beam expander (not shown) so that the entire surface of the substrate may be illuminated at one time.  
         [0028]     A secondary light beam  225  of fluorescent light is emitted from the photoresist layer on the substrate. The secondary light beam  225  of fluorescent light has a longer wavelength than the light beam  225 . Prior to being measured by the sensing equipment  230 , the secondary light beam  225  may pass through a suppression filter  235  to absorb undesired emitted light. The sensing equipment  230  senses the secondary light beam  225  with a light intensity sensor, such as a silicon diode sensor, as an electronic intensity signal. This signal is converted into a numerical value, such as a digital or analog value, that can be transmitted to the processor  240  for analysis. Additionally, other lens and filters (not shown) may be incorporated into the above described device for enhancing, filtering, directing, and otherwise improving performance of the light beam.  
         [0029]     Referring back to  FIG. 1 , the post etch metrology device  160  may be any inspection apparatus, film thickness, or critical dimension (CD) metrology apparatus, including a phase angle measurement apparatus and/or a fluorescent light detector apparatus. The fluorescent light detector may be the same as used for the front end metrology device  130 . One example of an inspection apparatus is the Excite™ inspection apparatus available from Applied Materials, Inc., of Santa Clara, Calif.  
         [0030]     Alternatively, the post etch metrology device may be a stand-alone device. While the post etch metrology device is shown coupled to the load lock chambers  104 , the device may be incorporated into other areas of the system  100  with high-speed data collection and analysis capabilities. An exemplary example of a stand alone device is the VeraSEM 3D from Applied Materials, Inc., of Santa Clara, Calif.  
         [0031]     The etch platform  110  includes a transfer chamber  107  and one or more processing chambers, or etching chambers  102 . Alternatively, a post-etch cleaning chamber (not shown) may also be included in the etch platform  110 . A robot  105  disposed in the transfer chamber  107  transfers a substrate  222  between the load lock chambers  104 , processing chambers  102 , and any other processing chambers disposed on the platform  110 , such as the mentioned post-etch cleaning chamber.  
         [0032]     A processor  140  is coupled to the system  100  and includes or is coupled to a database that contains a plurality of etch processes which may be used to etch the substrate. Processor  140  can be a controller including a central processing unit (CPU), support circuits and memory. The CPU is generally one or more processors, microprocessors, or micro-controllers that operate in accordance with instructions that are stored in memory. Support circuits are coupled to the CPU for supporting the processor in a conventional manner. Support circuits include cache, power supplies, clock circuits, input/output circuitry and subsystems, and can include input devices used with the controller, such as keyboards, trackballs, a mouse, and display devices, such as computer monitors, printers, and plotters. Such controllers are commonly known as personal computers; however, the present invention is not limited to personal computers and can be implemented on workstations, minicomputers, mainframes, and supercomputers. Memory comprises random access memory, read only memory, removable memory, disk drives, or combinations thereof. The memory stores various types of software including equipment control software and design intent parameters.  
         [0033]     The controller  140 , when executing equipment control software, sends a control message to various processing equipment within the system of  FIG. 1 . The processor  140  can be in communication with a computer software-implemented database system  150  known as the “manufacturing execution system” (MES), as well as additional processing equipment, such as a second processing system  155 , including an additional etch platform  110 . The computer software-implemented database system  150  stores and transmits substrate processing information and may additionally be in communication with the second processing equipment  155 .  
         [0034]     A process, for example an etching process described below, is generally stored in the memory  145 , typically as a software routine. The software routine may also be stored and/or executed by a second CPU that is remotely located from the hardware being controlled by the CPU.  
         [0035]     The processes described herein may be implemented as a computer program-product for use with a computer system or computer based controller. The programs defining the functions of the preferred embodiment can be provided to a computer via a variety of signal-bearing media and/or computer readable media, which include but are not limited to, (i) information permanently stored on non-writable storage media (for example, read-only memory devices within a computer such as read only CD-ROM disks readable by a CD-ROM or DVD drive; (ii) alterable information stored on a writable storage media (for example, floppy disks within diskette drive or hard-disk drive); or (iii) information conveyed to a computer by communications medium, such as through a computer or telephone network, including wireless communication. Such signal-bearing media, when carrying computer-readable instructions that direct the functions of the invention, represent alternative embodiments of the present invention. It may also be noted that portions of the product program may be developed and implemented independently, but when combined together are embodiments of the present invention.  
         [0000]     Processing of a Substrate  
         [0036]      FIG. 3  depicts a flow chart of one embodiment of a process sequence  300 , which may use the devices of  FIGS. 1 and 2 . The flow chart is provided for illustrative purposes and should not be construed or interpreted as limiting the scope of the invention.  
         [0037]     A substrate  220 , such as a photolithographic reticle, having a patterned photoresist layer disposed thereon is introduced to the system  100  at step  310 , specifically to the front-end metrology device  130  of  FIG. 1 . The front-end metrology device  130  acknowledges a substrate identifier for the substrate to be stored by the computer software-implemented database system  150  at step  315 . This substrate identifier can be attached to other substrates within the same batch with the same pattern density as the first substrate for future or parallel processing, eliminating the need to inspect every substrate within the batch.  
         [0038]     When the substrate  220  is placed in the front-end metrology device  130 , it is illuminated with the initial light beam  215  that is generated by the light source  210  at step  320 . The initial light beam  215  must be of sufficient intensity and wavelength so as to cause the photoresist layer upon the substrate  220  to emit a secondary light beam  225  of fluorescent light at step  325 . The primary light beam may optionally be filtered, reflected or expanded prior to hitting the substrate  220 .  
         [0039]     The front end metrology device  130  may operate by either a rapid inspection process or a rastering process. In a rapid inspection process the light source  210  illuminates the entire surface of substrate  220  with an exposure of light less than about 1 second in duration, preferably less than about 0.1 second in duration. The light beam generated may be passed through a beam expander so that the entire substrate may be illuminated at one time. In a rastering process, the light source  210  illuminates the substrate  220  by scanning small portions of the substrate  220 . The intensity of the emitted fluorescent light is calculated from the summation of the individual intensity values measured for each small portion of the substrate.  
         [0040]     The fluorescent light emitted from the photoresist layer ranges between about 550 nanometers and about 850 nanometers, such as between about 600 nanometers and about 800 nanometers with an intensity of at least 1 microwatt per square centimeter, such as between about 1 microwatt per square centimeter and about 10 milliwatts per square centimeter, for example, between about 50 microwatts per square centimeter and about 100 microwatts per square centimeter. The secondary light beam  225  may be filtered to reduce or eliminate any wavelengths of light that were not emitted from the photoresist layer to produce a filtered light beam that is substantially free of undesired wavelengths. The sensing equipment  230  measures the intensity of the filtered light beam. From the intensity of the filtered light beam, the open area percentage value for the substrate  220  can be determined by the processor  140  at step  330 .  
         [0041]     The open area percentage value is determined by comparing the measured intensity of the filtered light to a calibration curve. A calibration curve is initially determined for the substrates to be processed, and may be done for every batch of substrates processed. The calibration curve may be a pre-determined set of values stored in a database from prior processing of similar substrates.  
         [0042]     The calibration curve measurement utilizes the same process as described above, except that it uses substrates with known open area percentage values. A substrate with no photoresist upon its surface (open area percentage=100%) and a substrate surface completely covered in photoresist (open area percentage=0%) are respectively measured. Additionally, the calibration is not limited to the use of these two percentages of photoresist coverage. Substrates with other known open area percentages, for example, open area percentages of 30% and 60%, 25%, 50%, and 75% or 20%, 40%, 60% and 80% may be used in the calibration. Furthermore, the intensity of light emitted from a photoresist may vary or remain consistent with the thickness of the photoresist layer and the open are percentage. The calibration curve may be adapted to reflect the changing light intensities for varying photoresist thicknesses having the same and different open area percentage. For example, a photoresist layer of 3000 nanometers in thickness with an open area percentage of 50% will emit a fluorescent beam of about the same intensity as a layer of 6000 nanometers with an open area percentage of 25%.  
         [0043]     The calibration curve determined by the processor  140  may be analog or digital. Once the calibration is complete, the measured intensity of emitted fluorescent light from substrate  220  is applied to the calibration to produce a value of the pattern density or open area percentage value for the substrate  220 , which is transmitted to processor  140  at step  335 .  
         [0044]     Processor  140  also contains a database of etch processes. The plurality of etch processes contained within the database are pre-established to correspond to particular range of open area percentages. The calculated open area percentage for substrate  220  is transmitted to an advanced process control algorithm within the processor  140  to select the optimized etch process to be used in processing the substrate  220  at step  340 . Any suitable dielectric etch process for substrate, such as etching to form feature definitions in dielectric materials for damascene application as well as metal etching processes, such as photomask etching for use in photolithographic reticles, that use patterned photoresist materials may be used by this invention. The invention also contemplates application of processes herein to other resist materials, such as e-beam resists, that are capable of emitting fluorescent light, whether from ultra-violet light or other light source, for measurement in the device described herein.  
         [0045]     The substrate parameters, including the open area percentage value for the substrate  220 , the optimal etch process, and the substrate identifier, are transmitted to the processor  140  to be sent to memory device  145  and to the computer software-implemented database system  150  for storage of the information at step  345 . In essence, the substrate parameters are supplied to the controller to facilitate creation of substrates that inform the processing apparatus of what they are actually making such that they may efficiently optimize the product. These parameters may be supplied to other processing equipment to facilitate an increase in substrate throughput.  
         [0046]     If the front-end metrology device is incorporated in the front-end staging area, a robot  111  then transfers the substrate  220  into a loadlock chamber  104 . If the front-end metrology device  130  is a stand-alone apparatus, the substrate  220  then is moved to the front-end staging area  120  prior to being transferred into a loadlock chamber  104  by robot  111 . At step  355 , a robot  105  moves the substrate  220  from the loadlock chamber  104  into a processing chamber  102 . In the processing chamber  102 , the substrate  200  may be etched with the selected etch process at step  355 . After etching, the substrate  220  may be transferred to the endpoint metrology device  160  for post-etch inspection. Alternatively, it may be first transferred to a post-etch cleaning chamber  103  for removal of any remaining photoresist layer at step  360  and then transferred to the endpoint metrology device  160 . The endpoint metrology device  160  may measure the etched substrate&#39;s critical dimension bias or sidewall angle or detect if there is any photoresist remaining on the substrate  220  at step  365 . Alternatively, the front-end metrology device  130  may be used to inspect the etched substrate for any remaining photoresist by illuminating the etched substrate with an ultraviolet light and detecting whether the substrate  220  fluoresces, which would indicate the presence of remaining photoresist.  
         [0047]     While the methods, as described herein, are described with reference to photolithography, they can also be useful for related processes such as the formation of dual damascenes, thin film transistors, and shallow trench isolation structures.  
         [0048]     While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.