Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/352—Working by laser beam, e.g. welding, cutting or boring for surface treatment
  • B23K26/354—Working by laser beam, e.g. welding, cutting or boring for surface treatment by melting
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
  • B23K26/06—Shaping the laser beam, e.g. by masks or multi-focusing
  • B23K26/073—Shaping the laser spot
  • B23K26/0738—Shaping the laser spot into a linear shape
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/08—Devices involving relative movement between laser beam and workpiece
  • B23K26/083—Devices involving movement of the workpiece in at least one axial direction
  • B23K26/0853—Devices involving movement of the workpiece in at least in two axial directions, e.g. in a plane
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/352—Working by laser beam, e.g. welding, cutting or boring for surface treatment
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
  • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
  • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
  • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
  • H01L21/26—Bombardment with radiation
  • H01L21/263—Bombardment with radiation with high-energy radiation
  • H01L21/268—Bombardment with radiation with high-energy radiation using electromagnetic radiation, e.g. laser radiation
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K2101/00—Articles made by soldering, welding or cutting
  • B23K2101/36—Electric or electronic devices
  • B23K2101/40—Semiconductor devices
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K2103/00—Materials to be soldered, welded or cut
  • B23K2103/50—Inorganic material, e.g. metals, not provided for in B23K2103/02 – B23K2103/26
  • B23K2103/56—Inorganic material, e.g. metals, not provided for in B23K2103/02 – B23K2103/26 semiconducting
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
  • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
  • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
  • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
  • H01L21/28—Manufacture of electrodes on semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/268
  • H01L21/28008—Making conductor-insulator-semiconductor electrodes
  • H01L21/28017—Making conductor-insulator-semiconductor electrodes the insulator being formed after the semiconductor body, the semiconductor being silicon
  • H01L21/28026—Making conductor-insulator-semiconductor electrodes the insulator being formed after the semiconductor body, the semiconductor being silicon characterised by the conductor
  • H01L21/28035—Making conductor-insulator-semiconductor electrodes the insulator being formed after the semiconductor body, the semiconductor being silicon characterised by the conductor the final conductor layer next to the insulator being silicon, e.g. polysilicon, with or without impurities
  • H01L21/28044—Making conductor-insulator-semiconductor electrodes the insulator being formed after the semiconductor body, the semiconductor being silicon characterised by the conductor the final conductor layer next to the insulator being silicon, e.g. polysilicon, with or without impurities the conductor comprising at least another non-silicon conductive layer

Definitions

• the invention relates generally to methods and apparatuses for processing a surface of a substrate using a photonic beam. More specifically, the invention relates to methods and apparatuses that carry out such processing in a manner that accounts for and/or rninirnizes reflectivity variations and/or the maximum surface reflectivity of a surface of a substrate relative to the photonic beam.
• the source/drain portions of transistors may be formed by exposing regions of a silicon wafer substrate to accelerated dopants containing boron, phosphorous or arsenic atoms. After implantation, the interstitial dopants are electrically inactive and require activation. Activation may be achieved by heating the entirety or a portion of the substrate to a particular processing temperature for a period of time sufficient for the crystal lattice to incorporate the impurity atoms into its structure.
• Activation may be carried out via flash lamp or laser technology.
• Laser-based technologies are often preferred over conventional heat lamp technologies for annealing because the time scales associated with laser-based technologies are much shorter than those associated with conventional lamps.
• thermal diffusion for laser-based annealing processes plays a lesser role in the diffusion of the impurity atoms through the lattice structure than for convention Rapid Thermal Annealing (RTP) technologies employing conventional lamps (unpolarized flash lamps) to heat the wafer surface.
• RTP Rapid Thermal Annealing
• laser-based thermal processing techniques include laser thermal processing (LTP), laser thermal annealing (LTA), and laser spike annealing (LSA). In some instances, these terms can be used interchangeably.
• LTP laser thermal processing
• LTA laser thermal annealing
• LSA laser spike annealing
• these techniques typically involve forming a laser beam into a long, thin image, which in turn is scanned across a surface to be heated, e.g., an upper surface of a semiconductor wafer.
• a 0.1-mm wide beam may be raster scanned over a semiconductor wafer surface at 100 mm/s to produce a 1 -millisecond dwell time for the heating cycle.
• a typical maximum temperature during this heating cycle might be about 1350 0 C for silicon wafers.
• LTP may employ either pulsed or continuous radiation from any of a number of sources.
• conventional LTP may use a continuous, high-power, CO 2 laser beam, which is raster scanned over the wafer surface such that all regions of the surface are exposed to at least one pass of the heating beam.
• a continuous radiation source in the form of laser diodes may be used in combination with a continuous scanning system.
• illumination uniformity (both macro- and micro-uniformity) over the useable portion of the laser beam image is a highly desirable trait. This ensures that the corresponding heating of the substrate is correspondingly uniform.
• the energy delivered from the laser should be generally stable over time, e.g., energy per pulse for pulse radiation applications and laser beam power for continuous radiation applications, so all exposed regions are successively heated to a uniform temperature.
• illumination uniformity and stability is generally a desirable characteristic for any laser used for semiconductor annealing applications.
• a photonic beam of appropriate polarization is shaped to form an image on a portion of a silicon wafer surface.
• the image may be generally elongate in shape and scanned over substantially the entire wafer surface. Since uniform wafer surfaces (e.g., bare or unpatterned) exhibit uniform light absorption behavior, a uniform surface will uniformly absorb most of the energy from a beam of proper polarization and at or near the Brewster's angle for the surface (e.g., ⁇ 75° incidence). Consequently, it is a fairly straightforward matter to tailor a beam to heat a uniform substrate surface to a uniform peak temperature simply by selecting an appropriate scan path and rate.
• Wafers with nonuniform surfaces represent a particularly difficult challenge. Items such as devices and conductive pathways on wafer surfaces can hinder uniform light absorption. For example, devices on silicon wafers are often formed from materials other than silicon. Different materials may exhibit different Brewster's angles. Even when substantially the same material are deposited on wafer surfaces, interfaces formed between the deposited and native materials may scatter light or alter reflectivities to light. Thus, regardless whether flash lamp or laser technologies are used, reflectivity differences may cause the energy source to heat different portions of a nonuniform wafer surface differently.
• the invention provides an apparatus for processing a surface of a substrate having a surface normal and a surface pattern.
• the apparatus may, for example, include a radiation source, a stage, a relay, an alignment system, and a controller.
• the radiation source emits a photonic beam.
• the stage supports and moves the substrate relative to the beam.
• the relay directs the photonic beam from the radiation source toward the substrate at an incidence angle relative to the surface normal.
• the alignment system positions the substrate on the stage so the pattern is disposed at an orientation angle relative to the beam.
• the controller is operably coupled to the radiation source, relay, alignment system and/or stage and provides relative scanning movement between the stage and the beam. The controller maintains the orientation angle and incidence angle at values selected to substantially minimize substrate surface reflectivity variations and/or minimize the maximum substrate surface reflectivity during scanning.
• a CO 2 laser may be used to emit a p-polarized beam with respect to the substrate surface.
• the orientation angle may be fixed relative to the substrate surface.
• the incidence angle may be adjustable.
• the incidence angle value may be within about ⁇ 10° of the Brewster's angle.
• the Brewster's angle for a silicon substrate is about 75°.
• the incidence angle value may be within a range of about 65° to about 85° relative to the surface normal.
• the invention provides a method for processing a surface of a substrate as described above.
• the method involves: producing a photonic beam; directing the beam toward the substrate surface at an incidence angle with respect to the surface normal and at an orientation angle relative to the surface pattern; and scanning the beam across the substrate.
• the beam is p-polarized, and the orientation angle is fixed relative to the polarization of the beam.
• the incidence angle may be non-normal to the surface but adjustable with respect the surface normal.
• the beam may be scanned across the substrate while maintaining the orientation angle and incidence angle at values selected to substantially minimize substrate surface reflectivity variations and/or minimize the maximum substrate surface reflectivity during scanning.
• the beam is scanned in a manner so that after scanning, substantially the entire substrate surface has been heated to a uniform peak temperature.
• the peak temperature requirement may differ.
• the peak temperature may be greater than about 1300 0 C for annealing silicon-based material, the peak temperature may be as low as 1200 0 C for substrates that contain a relatively high percentage of germanium.
• the beam may be scanned in a manner so that after scanning, substantially the entire substrate surface has been heated to the uniform peak temperature for a period of time that does not exceed about 1 ms.
• the invention provides an apparatus for processing a surface of a substrate, e.g., a substrate having a surface pattern that exhibits directionally and/or orientationally different reflectivities relative to radiation of a selected wavelength and polarization.
• the apparatus includes a radiation source, a relay, a stage, and a controller.
• the radiation source emits a photonic beam of the selected wavelength and polarization.
• the relay directs the photonic beam from the radiation source toward the substrate an incidence angle relative to the substrate surface normal.
• the stage supports the substrate at an orientation angle relative to the beam.
• the controller is operably coupled to the radiation source, relay, and/or stage. In operation, the controller provides relative scanning movement between the stage and the beam while maintaining the orientation angle and incidence angle at values selected to minimize substantially substrate surface reflectivity variations and/or maximum substrate surface reflectivity during scanning.
• the radiation source may be keyed to the substrate.
• the radiation source may emit a photonic beam of a wavelength and polarization selected to generally minimize the reflectivity and/or the reflectivity variation for the substrate and pattern type.
• the substrate may comprise or consist essentially of a semiconductor material such as silicon, germanium, and alloys thereof.
• the substrate surface toward which the beam is directed may include a semiconductor such as silicon, e.g., silicon on insulator.
• the surface pattern may include electrically conductive materials such as metals, e.g., copper, gold, silver, aluminum, etc.
• the surface pattern may be formed from a plurality of electrically conductive structures that tend to be oriented in a specific direction on the substrate.
• the structures may each have a length and width, the lengths define lengthwise axes, and the structures are aligned so their lengthwise axes are parallel to each other.
• the structures have a dominant orientation direction along the lengthwise axes.
• the widths of the structures may be orthogonal to the dominant orientation direction. In such a case, the widths may be much less than the beam wavelength. For example, widths may exceed no more than about 1% to about 5% of the wavelength.
• a method for processing a surface of a substrate as described above, by using a photonic beam of a wavelength and polarization selected to generally minimize the reflectivity and/or the reflectivity variation for the substrate type.
• the method may be carried out so that the substrate surface reflectivity variations do not exceed about 10% to about 20%.
• methods and apparatuses are provided for selecting an optimal orientation and/or incidence angle for processing a surface of a substrate as generally described above with a photonic beam of a selected wavelength and polarization.
• the beam is directed toward the substrate surface at an incidence angle and scanned with respect to the substrate surface.
• the optimal orientation and/or incidence angles may be determined that correspond to a minimum in substrate surface reflectivity variations and/or minimum in the overall or the peak substrate surface reflectivity.
• FIG. 1 schematically depicts a simplified exemplary embodiment of the inventive thermal processing apparatus.
• FIG. 2 shows a graph that plots the reflectivities of a bare silicon wafer surface relative to a patterned wafer surface over a range of incidence angles to a beam of p-polarized radiation.
• FIG. 3 depicts an exemplary patterned silicon wafer having a nonmetallic transistor structure (gate) of low reflectivity.
• FIG. 4 depicts an exemplary patterned silicon wafer having a metal gate structure of a high reflectivity.
• FIG. 5 depicts how electrical current may flow within the metal layer of the structure shown in FIG. 4 in response to a beam's electric field.
• FIG. 6 graphically shows how a longer wire may exhibit a higher reflectivity relative to a shorter wire due to differences in current induction for radiation of a particular wavelength.
• FIGS. 7A and 7B collectively FIG. 7, show a wafer having a plurality of differently shaped structures on its surface that is illuminated by a beam of incident radiation.
• FIG. 7A shows the wafer in top view.
• FIG. 7B shows the wafer in cross-sectional view along dotted line A.
• FIG. 8 shows an exemplary patterned silicon wafer similar to that shown in FIG. 4 with the structure oriented perpendicularly relative to a beam's electric field.
• FIG. 9 graphically depicts a plot of estimated reflectivities of the same silicon surface with metal structure in two different orientations relative to the reflectivity of a bare silicon surface over a range of angles of incidence.
• FIG. 10 depicts an experimental setup that shows how an plurality of elongate surface structures may render the reflectivity of a surface directionally and/or orientationally different relative to a beam of p-polarized radiation.
• FIG. 11 shows a plot of the differences in reflectivity versus probability density for a wafer based on experimental results.
• a beam includes a plurality of beams as well as a single beam
• a wavelength includes a range or plurality of wavelengths as well as a single wavelength
• Brewster's angle or “Brewster angle” is used to refer to the angle of incidence between a radiation beam and a surface that corresponds to the minimum or near- minimum reflectivity of the P-polarized component of the beam. Films on the surface of an object, such as a silicon wafer, may prevent it from exhibiting zero reflectivity at any angle. There generally will be an angle of minimum reflectivity for P-polarized radiation. Accordingly, the Brewster's angle as used herein for a specular surface formed from a variety of different films stacked on a substrate can be thought of as having an effective Brewster's angle, which is the incident angle at which the reflectivity of P-polarized radiation is at a minimum. This minimum angle typically coincides with or is near the angle of the Brewster's angle for the substrate material.
• an image in reference to an image or a beam refers to the distribution of the integrated radiation intensity along one or more dimensions.
• an image may have a useful portion and a non-useful portion.
• the useful portion of an image typically has a "uniform" or constant integrated intensity profile over some portion of its length.
• the intensity profile integrated in the scan direction throughout the useful portion of the image may be substantially constant. Accordingly, any point on a substrate surface region that is scanned by a useful portion of an image having a uniform intensity profile will be heated to the same temperature.
• the intensity or intensity profile of the non-useful portion may differ from that of the useful portion.
• the image as a whole may have an overall "non-uniform" intensity profile even though a useful portion by itself may exhibit a uniform intensity profile.
• peak intensity value of an image or a beam refers to the point along the beam length exhibiting the highest integrated intensity across the beam width. Typically, the entirety of the useful portion of an image will exhibit an integrated intensity very close to the peak integrated intensity.
• the term "energy utilization" as in the “energy utilization of an image” refers to the proportion of energy associated with the portion of the image useful for producing a desired effect relative to the total beam energy in the image.
• the "useful portion" of an image may be only that part of the beam that comes within about a percent or two of the maximum or peak beam intensity. In such a case, the "useful portion” exhibits a “substantially uniform” intensity. A small modification to the image profile shape can produce a large change in the "energy utilization.”
• semiconductor is used to refer to any of various solid substances having electrical conductivity greater than insulators and less than good conductors, and that may be used as a base material for computer chips and other electronic devices.
• Semiconductors include elements such as silicon and germanium and compounds such as silicon carbide, aluminum phosphide, gallium arsenide, and indium antimonide.
• semiconductor includes any one or a combination of elemental and compound semiconductors, as well as strained semiconductors, e.g., semiconductors under tension or compression.
• Exemplary indirect bandgap semiconductors suitable for use with the invention include Si, Ge, and SiC.
• Direct bandgap semiconductors suitable for use with the invention include, for example, GaAs, GaN, and InP.
• substantially and “substantially” are used in their ordinary sense and refer to matters that are considerable in importance, value, degree, amount, extent or the like.
• the phrase “substantially Gaussian in shape” refers to a shape that corresponds predominantly to the shape of a Gaussian curve.
• a shape that is “substantially Gaussian” may exhibit some characteristics of a non-Gaussian curve as well, e.g., the curve may also include a non-Gaussian component.
• a "substantially uniform" intensity profile will contain a relatively flat portion where the intensity does not deviate more than a few percent from the profile's peak intensity.
• the intensity deviation is less than about 5%.
• the intensity deviation is no more than about 1% or no more than about 0.8%.
• substrate refers to any material having a surface, which is intended for processing.
• the substrate may be constructed in any of a number of forms, for example, such as a semiconductor wafer containing an array of chips, etc.
• the invention generally provides for apparatuses and methods for thermally processing a substrate surface using a photonic beam, minimizing the reflectivity from the structures on the surface of the substrate, and promoting of surface reflectivity uniformity.
• the apparatuses and methods typically involve thermal processing techniques carried out in a manner that accounts for and/or controls the orientational and/or directional relationship between the photonic beam and the substrate surface.
• the invention may be carried out in a manner that substantially minimize substrate surface reflectivity variations and/or minimize the maximum substrate surface reflectivity during scanning.
• apparatuses and methods for selecting an optimal substrate orientation and/or beam incidence angle for processing a surface of a substrate e.g., one of a group of similar substrates, with a photonic beam of a selected wavelength and polarization.
• the substrate surface exhibits different reflectivities depending on the orientational or directional relationship between itself and the beam. Variations in reflectivities may be associated with patterns on the substrate surface.
• FIG. 1 is a schematic diagram of a simplified exemplary embodiment of a thermal processing apparatus 10 that may be used to anneal and/or otherwise thermally process one or more selected surface regions of a substrate according to the present invention.
• LTP system 10 includes a movable substrate stage 20 having an upper surface 22 that supports a semiconductor substrate 30 having an upper surface P and a surface normal, N, thereto.
• Substrate stage 20 is operably coupled to controller 50.
• Substrate stage 20 is adapted to move in the X-Y plane under the operation of controller 50 so the substrate can be scanned relative to the image generated from radiation provided by radiation source 110.
• the stage 20 may also controUably rotate substrate 30 about an axis Z which extends orthogonally relative to the X-Y plane. As a result, the stage 20 may controUably fix or alter the orientation of substrate 30 in the X-Y plane.
• the stage may include different components to carry out different functions.
• an alignment system may be provided to position the substrate on the stage at a variable orientation angle relative to the surface normal.
• the stage may independently control the substrate movement while the alignment system controls the substrate orientation.
• the radiation source 110 is operably coupled to controller 50, and a relay 120 that serves to relay radiation generated by the radiation source toward the substrate to form an image on its surface.
• radiation source 110 is a CO 2 laser that emits radiation at a wavelength A ⁇ ⁇ 10.6 ⁇ m (heating wavelength) in the form of beam 112,
• the radiation suitable for use with the invention may include LED or laser diode radiation as well, e.g., radiation having a wavelength of about 0.8 ⁇ m.
• a plurality of radiation sources may be employed. As shown, the laser 110 generates an input beam 112 that is received by a relay 120 that is adapted to convert the input beam to an output beam that forms an image on the substrate.
• the intensity profile of the beam is manipulated so a portion of the image intensity is rendered uniform about its peak intensity for even heating and high energy utilization.
• the relay 120 may transform the input beam 112 into output beam 140.
• the relay may be constructed in a manner to provide for desired coherent beam shaping so the output beam exhibits a uniform intensity profile over a substantial portion thereof.
• the relay 120 and the radiation source 110 in combination may stabilize, the directionality, intensity profile, and phase profile of the output beam to produce a consistently reliable laser annealing system.
• Beam 140 travels along optical axis A, which makes an angle ⁇ with a substrate surface normal N.
• optical axis A which makes an angle ⁇ with a substrate surface normal N.
• it is not desirable to image a laser beam on a substrate at normal incidence because any reflected light may cause instabilities when it returns to the laser cavity.
• Another reason for providing optical axis A at an incidence angle ⁇ other than at normal incidence is that efficiently coupling of beam 140 into the substrate 30 may best be accomplished by judicious choice of incidence angle and polarization direction, e.g., making the incidence angle equal to the Brewster's angle for the substrate and using p-polarized radiation.
• the stage may be adapted to scan the substrate through the beam position while preserving or altering the incidence angle.
• the stage may be adapted to control, fix or vary the orientation angle of the substrate relative to the beam. The selection of the incidence and/or orientation angle is discussed below.
• Image 150 is an elongate image, such as a line image, having its lengthwise boundaries indicated at 152, and located within a plane containing the incident beam axis and the surface normal. Accordingly, the incidence angle of the beam ( ⁇ ) relative to the substrate surface may be measured in this plane.
• the controller may be programmed to provide relative movement between the stage and the beam.
• the image may be scanned across the substrate surface to heat at least a portion of the substrate surface.
• Such scanning may be carried out in a manner effective to achieve a desired temperature within a predetermined dwell time, D. Scanning may typically be performed in a direction that is orthogonal to the lengthwise axis of the image although this is not a firm requirement. Non-orthogonal and non-parallel scanning may be carried out as well.
• a means may also be included to provide feedback of the uniformity in maximum temperature achieved.
• Various temperature measuring means and methods may be used with the invention.
• a detector array might be used to take a snap-shot of the emitted radiation distribution over the surface or multiple snap-shots might be used to derive a map of the maximum temperature as a function of the position across the length of the beam image.
• a means for measuring the intensity profile of the beam on the substrate may be used as well.
• a real-time temperature measurement system may be employed that can sense the maximum temperature with a spatial resolution preferably comparable to the thermal diffusion distance and with a time constant less than or preferably comparable to the dwell time of the scanned beam.
• a temperature measurement system may be used that samples the emitted radiation 20,000 times a second at 256 points spread evenly over a 20 mm line-image length.
• 8, 16, 32, 64, 128, 256, 512, or more distinct temperature measurements may be made at a rate of 100, 1000, 10,000, 50,000 line scans per second.
• An exemplary temperature measurement system is described in U.S. Patent Application Publication No.
• FIG. 2 shows a graph that plots the reflectivities to a beam of p-polarized radiation from a CO 2 laser over a range of incidence angles for: (1) a bare (unpatterned) silicon wafer surface (solid line); and a metal surface (dashed line).
• the Brewster's angle for bare silicon surface is about 75° but the Brewster's angle for the metal surface is closer to about 87°. It is also evident that the minimum reflectivity for the metal surface is higher than that for the bare wafer. It is further evident that the metal surface at most incidence angles is more reflective than the bare wafer surface. Such discrepancies in reflectivity can be explained in view of the structures associated with patterned wafer surfaces.
• a hypothetical gate-like structure for a semiconductor device is illustrated in FIG. 3, where the gate is comprised mostly of semiconductor and dielectric matter whose optical properties are similar to those of bulk silicon.
• Patterned silicon wafers 30 may contain a large number of these transistor structures such as gates 200 that contain a silicon dioxide layer 202, a silicon layer 204, and a silicon nitride layer 206. Such structures are somewhat typical of devices seen in the modern day semiconductor industry, however this invention is not limited to the applications within the semiconductor industry.
• a laser beam 140 may be directed to such a structure. Because the optical properties (absorption and reflection) of the structures in the gate-like regions are similar to those of bulk silicon, their absorption and reflection characteristics are similar, and it is possible to achieve relatively uniform temperatures on the structures.
• FIG. 4 depicts a hypothetical metal gate structure that might be found in memory structures or in advanced logic (“high-k, metal gate”) structures.
• the gate 300 includes a high-K material layer 302, a silicon layer 304, a metal layer 306, and a silicon nitride layer 308. Other layers and materials can be used. Additional layers can be added or subtracted.
• electrical surface currents are produced within the metal. Given an appropriate beam wavelength, as shown in FIG. 5, electrical current may flow within the metal layer in response to the electric field of the beam. Naturally, the electrical current flows in a direction consistent with the polarization of the beam (as indicated by double headed arrow I). The reflectivity of the layer to the beam generally varies proportionally with electrical current flow.
• metals or other conductive materials in a wafer surface structure may be thought of as a wire dipole antenna having an "antenna length".
• a sine wave representing the amplitude of a polarized electric field from a p-polarized incident beam
• the longer wire has an antenna length of approximately one-half of the wavelength of the sine wave.
• This wire has a large positive induced voltage at position A, but has nearly zero voltage at position B.
• the large voltage difference creates an alternating current in the wire (illustrated as the double ended arrow) which ultimately reflects the electric field.
• the induced voltage difference at the ends of the shorter wire is much smaller due to its shorter antenna length.
• the induced current and reflectivity of the shorter wire are both lower than that of the longer wire.
• a wafer 30 may have a plurality of differently shaped structures, indicated at 300A and 300B, on it upper surface P.
• structure 300A has a circular shape with a diameter of D
• structure 300B has a rectangular shape with a width of D and a length of 10OD.
• both structures 300A and 300B are similar to the structure 300 shown in FIG. 4.
• two p-polarized radiation sources IOOA and 11OB are provided that illuminate the wafer surface from directions that run parallel to axes X and Y, respectively.
• p-polarized radiation from source IOOA strikes structures 300A and 300B, both structures exhibits the same effective antenna length D.
• the effective antenna length for structure 300B is about 100 times as long as the effective antenna length for structure 300A.
• the antenna length for structure 300A is generally independent of its orientation angle relative to the illuminating radiation, whereas the antenna length for structure 300B can vary over a range of D to IOOD depending on the structure's orientation angle.
• the difference in reflectivity and absorptivity
• the orientation of a metal structure relative to the incident electric field
• the angle of incidence As shown in FIG. 8, this may be done, for example, by rotating a substrate having structures similar to those shown in FIG. 4 so the orientation of the metal structure has its long axis perpendicular to the polarization vector of the incident electric field. That is, the lengths of the structures are substantially perpendicular to the plane of polarization of the incident laser beam.
• FIG. 9 graphically depicts a plot of estimated reflectivities of the same surface with metal structure in two different orientations as well as a plot of the reflectivity from bulk silicon over a range of angles of incidence. These plots assume p-polarized incident radiation.
• the reflectivity of the structure relative to radiation having an electric field vector in the plane of the long dimension of the metal structure is much higher than the reflectivity of the structure relative to radiation having an electric field vector is perpendicular to the long dimension.
• the reflectivity difference between the silicon and metal structure can be greater than 50% for one orientation, whereas in the reflectivity difference can be less than 10% in the proper orientation. Also notably, it is possible to match the reflectivity of the two regions exactly when the incidence angle is greater than about 75 °, e.g., approximately 82° or larger.
• FIG. 10 shows the setup for an experiment that demonstrated how a plurality of elongate surface structures renders the reflectivity of a surface directionally and/or orientationally different relative to a beam of p-polarized radiation.
• the experimental setup employed a metal structure similar to that of a metal-gate DRAM structure.
• the metal structures were formed from a ⁇ 50 nm-thick metal layer on a silicon wafer surface. A ⁇ 100 nm-thick layer of polysilicon was deposited above the metal layer.
• the metal structures were each approximately 100 nm in width by 1000 nm in length, with a repeat distance of approximately 300 nm.
• FIG. 11 shows a plot of the reflectivity versus probability density for the wafer was generated that indicated that the reflectivity difference for the wafer may be further reduced by increasing the incidence angle to 82°.
• the experiment generally shows that it is possible to equalize the reflectivity between silicon areas and metal structures of patterned wafer to equalize the amount of heating in the various structures.
• Such equalization may involve directing a photonic beam with an appropriate polarization to an appropriately oriented wafer at an appropriate incidence angle.
• the illumination source has a wavelength much longer than the minimum structure dimension.
• the wavelength-to-minimum-structure-dimension ratio may be greater than 100: 1.
• the incidence angle required to effect such equalization may be greater than the Brewster angle for the substrate to match the reflectivity between the two regions.
• the invention also includes methods and apparatuses for selecting an optimal orientation and/or incidence angle for processing a surface of a substrate as described above with a photonic beam as described above.
• the methods and apparatuses involve directing the photonic beam toward the substrate surface at an incidence angle, scanning the photonic beam with respect to the substrate surface, and measuring radiation reflected from the substrate as a result. By rotating the substrate about the normal and/or changing the incidence angle while the beam illuminates the substrate, one may find the optimal orientation and/or incidence angles that correspond to a minimum in substrate surface reflectivity variations and/or maximum substrate surface reflectivity.
• the selection methods and apparatuses typically employ a beam power level less than that required to process the surface.
• the angle(s) may be programmed into an apparatus for processing the substrate surface. Such an apparatus may then be used at a beam power level required to process the surface of the substrate.
• the apparatus may also be used to process identical or similar substrate with identical or similar surface patterns and or reflectivities.
• high-power CO 2 lasers e.g., having a power of at least 250 W, 1000 W, or 3500 W or higher, may be used to generate an image, which, in turn, is scanned across a surface of a substrate to effect rapid thermal processing, e.g., melt or non- melt processing, of the substrate surface.
• Such power levels may provide exposure energy doses of about 30 J/cm 2 or more over a l ms dwell time. Longer dwells require higher energies.
• the wavelength of the CO 2 laser, ⁇ is 10.6 ⁇ m in the infrared region, which is large relative to the typical dimensions of wafer features, and may therefore be uniformly absorbed as the beam scans across a patterned silicon wafer with the result that each point on the wafer is raised to very nearly the same maximum temperature.

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