Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
  • G01N21/1717—Systems in which incident light is modified in accordance with the properties of the material investigated with a modulation of one or more physical properties of the sample during the optical investigation, e.g. electro-reflectance
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
  • H04N25/70—SSIS architectures; Circuits associated therewith
  • H04N25/71—Charge-coupled device [CCD] sensors; Charge-transfer registers specially adapted for CCD sensors
  • H04N25/715—Charge-coupled device [CCD] sensors; Charge-transfer registers specially adapted for CCD sensors using frame interline transfer [FIT]
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B11/00—Measuring arrangements characterised by the use of optical techniques
  • G01B11/30—Measuring arrangements characterised by the use of optical techniques for measuring roughness or irregularity of surfaces
  • G01B11/306—Measuring arrangements characterised by the use of optical techniques for measuring roughness or irregularity of surfaces for measuring evenness
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
  • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
  • G01N21/27—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands using photo-electric detection ; circuits for computing concentration
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/84—Systems specially adapted for particular applications
  • G01N21/88—Investigating the presence of flaws or contamination
  • G01N21/95—Investigating the presence of flaws or contamination characterised by the material or shape of the object to be examined
  • G01N21/956—Inspecting patterns on the surface of objects
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
  • G01N21/1717—Systems in which incident light is modified in accordance with the properties of the material investigated with a modulation of one or more physical properties of the sample during the optical investigation, e.g. electro-reflectance
  • G01N2021/1725—Modulation of properties by light, e.g. photoreflectance
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N2201/00—Features of devices classified in G01N21/00
  • G01N2201/12—Circuits of general importance; Signal processing

Definitions

• the present application relates to line sensors and associated electronic circuits suitable for sensing radiation at visible, UV, deep UV (DUV) , vacuum UV (VUV) , extreme UV (EUV) and X-ray wavelengths, and for sensing electrons or other charged particles, and to methods for operating such line sensors .
• the sensors and circuits are particularly suitable for use in inspection and metrology systems, including those used to inspect and/or measure features on photomasks, reticles, and semiconductor wafers. 1 3 ⁇ 4 ⁇ €! ⁇ 3 ⁇ 4 ⁇ 3 ⁇ 4>3 * " t
• semiconductor inspection and metrology tools are most useful if they can inspect or measure on all, or most, of the different materials and structures used in CMOS manufacturing. Different materials and structures have very different reflectivities from one another. In order to have the flexibility semiconductor inspection and metrology tools may use multiple 'wavelengths and/or
• Selecting which angles to use typically involves switching appropriately shaped and sized apertures into the right location in the optical path according to what is being inspected or measu ed.
• Apertures are mechanical devices that can occupy significant space. Mechanical motion of apertures can take tens or hundreds of milliseconds, thus slowing inspections or measurements that require data to be collected with more than one aperture. Adding or replacing apertures on an existing inspection or metrology system in order to provide new or improved capability can be difficult owing to space constrai ts .
• the present invention is directed to electrically controlling the pixel aperture size in a linear sensor by way of generating a non-monotonic voltage profile that controllably adjusts (reduces or expands) the effective light sensitive region from which photoelectrons are collected for measurement by each pixel.
• Each pixel includes an elongated resistive control gate, and each pixel's maximum light sensitive region is defined by a portion of the semiconductor substrate disposed under
• photoelectrons generated in a first portion of the pixel's light sensitive region that is located on a first side of the central aperture control electrode are driven toward a first end of the resistive control gate, and photoelectrons generated in a second portion of the pixel's light
• each pixel's light sensitive region on a second side of the central aperture control electrode are driven toward the opposite (second) end of the resistive control gate.
• the effective size of each pixel's light sensitive region is thereby controllably adjusted to include only the first portion of the pixel's light sensitive region by way of generating the non ⁇ monotonic voltage profile and subsequently measuring the photoelectron charge collected only from the first end of the resistive control gate.
• a method of inspecting or measuring a sample at high speed is also described. This method includes
• the line sensor incorporates a resistive control gate having a potential gradient generated across its length by way of electrodes, whereby the resis ive control gate generates an electric field that directs photoelectrons in the sensor to one or more accumulation regions.
• a control circuit is configured to apply more negative voltages to one or more centrally located electrodes and more positive voltages to electrodes disposed at end portions of the resistive cont ol gate, thereby generating electric fields that bias (drive) photoelectrons generated in one region of the sensor to an accumulation region while preventing other photoelectrons generated in other regions of the sensor from reaching the accumulation region.
• the method of inspecting can further include setting voltages on the electrodes attached to the
• the voltages may be changed during the inspection or measurement to optimize the light collection process, or may be used to adjust the effective aperture size of each individual pixel during a pre- inspection calibration period to such that all pixels of the sensor have a uniform aperture size.
• a system, for inspecting a sample is also
• This system includes an illumination source, a device configured to perform light detection, optics configured to direct light from the illumination source to the sample and to direct light outputs or reflections from the sample to the device, and a driving circuit.
• the line sensor incorporates a resistive gate with a potential gradient across it that directs photoelectrons in the sensor to an accumulation region.
• the line sensor includes multiple electrodes attached to the resistive gate allowing the potential gradient to be adjusted so as to direct photoelectrons from one region of the sensor to an accumu1ation region whi 1e preventing other photoe1ectrons from reaching the accumulation region.
• the driving circuit sets voltages on one or more of the multiple electrodes in order to control from which regions of the sensor
• photoelectrons are directed to the accumulation region.
• the line sensor may further comprise a semiconductor membrane .
• the semiconductor membrane may include circuit elements formed on a first surface of the semiconductor membrane and a pure boron layer deposited on a second surface of the semiconductor membrane.
• the line sensor may comprise an electron bombarded line sensor.
• the system may include multiple line sensors.
• the line sensor may include an optical knife edge or other mechanical aperture structure, and the electrical aperture adjustment maybe utilized to correct for misaiicrnment of tne
• the knife edge or other mechanical aperture is movable under computer control, so that the computer can select different inspection modes by appropriate
• the sample may be supported by a stage, which moves relative to the optics during the inspection.
• the electrical charges may be read out from the sensor in synchrony with the motion of the stage.
• the exemplary inspection system may include one or more illumination paths that illuminate the sample from different angles of incidence and/or different azimuth angles and/or with different wavelengths and/or
• the exemplary inspection system may include one or more collection paths that collect light reflected or scattered by the sample in different
• Figure 1 illustrates an exemplary inspection or metro1ogy system .
• Figures 2A and 2B illustrates an exemplary inspection system with line illumination and one or more collection channels.
• Figure 3A illustrates an exemplary inspection system with normal and oblique illumination.
• Figure 3B illustrates an exemplary metrology system with multiple measurement subsystems.
• Figure 4 illustrates an exemplary inspection system including a simplified line sensor according to an embodiment of the present invention.
• Figures 5A, 5B, 5C and 5D illustrate exemplary voltage profiles that can be applied to resistive control gates according to alternative embodiments of the present invention .
• Figure 6 is a cross-sectional view showing a pixel of an exemplary line sensor according to another specific embodiment of the present invention.
• Fig, 7 is a cross-sectional view showing a simplified pixel of an exemplary line sensor according to another specific embodiment of the present invention.
• Figure 1 illustrates an exemplary inspection or metrology system 100 configured to inspect or measure a sample 108, such as a wafer, reticle, or photomask.
• Sample 108 is placed on a stage 112 to facilitate movement to different regions of sample 108 underneath the optics.
• Stage 112 may comprise an X-Y stage or an ⁇ .- ⁇ stage. In some embodiments, stage 112 can adjust the height of sample 108 during inspection to maintain focus. In other
• an objective lens 105 can be adjusted to maintain focus.
• An illumination source 102 may comprise one or more lasers and/or a broad-band light source. Illumination source 102 may emit DUV and/or YUV radiation. Optics 103, including an objective lens 105, directs that radiation towards and focuses it. on sample 108. Optics 103 may also comprise mirrors, lenses, polarizers and/or beam splitters
• holographic plate angularly disperses the beam as a function of wavelength to individual detector elements contained in the detector array 66.
• the different detector elements measure the optical intensities of the different wavelengths of light contained in the probe beam
• control circuit 450 applies a first aperture control signal V 30A onto first end electrode 43 OA, a second aperture control signal V430B onto second end electrode 430B, and a third aperture control signal V 431 onto central electrode 431.
• control circuit 450 simul aneously generates and applies aperture control signals V 430 Ai- V 4 3 0 B and V 4 3 1 onto aperture control electrodes 430A, 430B and 431 such that aperture control signals V430 A and V430 B are more positive (i.e., have a more positive voltage level) than aperture control signal V 431 .
• aperture control signals V 430A and ⁇ 430 ⁇ are examples of aperture control signals V 430A and ⁇ 430 ⁇ .
• aperture control signals V 430AI V431 and V 43QB create a non ⁇ monotonic voltage profile E420--1 (depicted by a "V" shaped potential diagram) in resistive control gate 421-1 that generates an electric field that effectively separates associated light sensitive region 4 1 6 20-1 into two portions 415 4 20-iA and 415 4 2o-i3 that are generally disposed opposite sides of the negative peak value of non-monotonic voltage profile E420-1 ⁇
• photoelectrons e.g., photoelectron PI
• photoelectron P2 photoelectron P2
• Electrodes 43 OA, 430B and 431 which contact different locations on each resistive gate in orde to facilitate the generation of potential gradients (electric fields) . More than two such electrical
• connections are required in order to generate non-monotonic voltage profiles in the resistive gate.
• Each readout register 444A is ted to a charge conversion amplifier 446A and buffer 447A that generates an output signal 458.
• Readout registers 44A are controlled by multiple clock signals 454 and 455, which are generated by control circuit 450 along with other control signals (not shown) such as buffer gate and transfer gate control signals. Although a two phase clock generated by clock signals 454 and 455 is shown, readout registers using three and four phase clocks are known in the art. and could be used.
• redirected light output or reflected from sample 401 is directed to sensor 410, also by way of optics 405, and enters sensor 400 through lower (bottom) surface 413.
• optics 405 are configured to direct radiation (light) L from, sample 401 to sensor 410 in the form of a confocal image.
• optics 405 are configured to direct radiation, disposed within, corresponding angle ranges from sample 401 to sensor 410 such that light transmitted from similar structural locations or angles is directed into similar portions of each pixel's light sensitive region.
• optics 405 are configured such that first light portions LI directed, within a first range of angles al from sample 401 to sensor 410 are directed into a first light sensitive portion 415 2 0-IA of associated light sensitive region.
• first light sensitive portion. 415420-iA is closer to first end portion 421-1A. of resistive control gate 421-1 than second light sensitive portion 4152o ⁇ iB and second light sensitive portion 416 20-IB is located closer to second end portion 421- IB than first light sensitive portion 415 4 0 - ⁇
• the radiation (light) L entering each light sensitive portion is absorbed and generates photoelectrons that are collected during an integration period, and then sequentially measured during a subsequent readout period.
• Fig. 4 depicts a first photoelectron PI generated in first light sensitive portion 415420-IA ot light sensitive region 415420-1 in
• buffer/transfer gates 423A-1 controls the transfer of the accumulated photoelectron charge from charge
• sensor 410 includes an optional second readout circuit 440B that is disposed on the second end of pixels 420-1 to 420-4 incl ding
• FIG. 4 illustrates how aperture control electrodes 43 OA 430B and 431 may be used to select
• optics 405 are configured so that control electrodes 43 OA 430B and 431 can be used to select radiation from different locations of sample 401.
• the voltage profile indicated by line 501 in Figure 5A depicts an approximately linear voltage gradient between -5V at location D (which corresponds to the
• central electrodes 525B and 525C at locations B and C may not need to be driven when
• approximately linear voltage gradient 501 is desired.
• the voltage on resistive control gate 521 induces charges in the substrate near the surface of the light sensi ive region just underneath control gate 521, and hence creates a potential gradient (electric field) in the substrate. Since electrons are negatively charged, each photoelectron will rapidly migrate towards the most positive potential in its vicinity. Hence, with an approximately linear gradient like that depicted by line 501 of Figure 5A, the
• this approximately linear potential gradient causes substantially all photoelectrons generated in the light sensitive region of the corresponding pixel to accumulate in a charge accumulation region underneath elec rode 525A, whereby the accumulated charge may be subsequently
• Location C may be driven to an intermediate voltage between --5V and OV such as about -2.5V by way of electrode 525C, or it may be left floating. In this state, the effective pixel aperture size is defined between locations A and B. That is,
• resistive control gate 521 between locations A and B will quickly migrate underneath location A because it is the most positive potential in that region.
• Photoelectrons created in the substrate underneath resistive control gate 521 between locations B and D will quickly migrate to a charge accumulation region located adjacent location D (e.g. , underneath electrode 525D) as it is the most
• the accumulated charge near location A can be read out of the pixel into a readout register, such as register 444A-1 shown in Figure 4.
• the accumulated charge near location D may be discarded by collecting it, for example, with an overflow drain or scupper drain located near location D, or alternatively the charge may be read out of the pixel into a second readout circuit, such as circuit 440B as shown in Figure 4.
• the voltage gradient causes the sensor to collect the signal corresponding to light that hits the sensor between locations A and B, while separating or discarding the signal corresponding to light that hits the sensor between locations B and D, the voltage gradient acts like an aperture or beam divider that, in effect, blocks or separates light that arrives at the sensor between
• Line 505 in Figure 5A illustrates yet another example voltage profile on resistive control gate 521, and shows how pixel aperture size may be adjusted by way of changing the voltages applied to resistive control gate 521.
• location C is held at -5V by way of an associated aperture control signal applied to electrode 525C while locations A and D are held at OV by way of end electrodes 525A and 525D (location B is floating or held at an intermediate voltage) .
• the effective pixel aperture size is between locations A and C. That is, photoelectrons created in the substrate underneath
• resistive control gate 521 between electrodes 525 ⁇ and 525C will quickly migrate to the charge accumulation region underneath electrode 525A because it is the most positive potential in that region.
• Photoelectrons created in the substrate underneath resistive control gate 521 between electrodes 525C and 525D will quickly migrate to the charge accumulation region underneath electrode 525D as it is the most potential in that region of the pixel .
• accumulated charge near location A can be read out of the pixel into a readout register, such as register 444A-1 shown in Figure 4, and the accumulated charge near location D may be discarded or read out into a readout circuit, such as circuit. 440A shown in Figure 4.
• a readout register such as register 444A-1 shown in Figure 4
• the accumulated charge near location D may be discarded or read out into a readout circuit, such as circuit. 440A shown in Figure 4.
• resistive control gate 521 by way of four contact (electrodes) 525A, 525B, 525C and 525D, three contacts could be used (as in the exemplary embodiment of Fig. 4) , or more than four contacts can be used (as in the exemplary embodiment of Fig. 4)
• Three contacts allow the full pixel to be selected and directed to an output, or allow the pixel to be divided into two parts
• Fig. 5B depicts different voltage schemes that may be applied to a resistive control gate 531 by way of five aperture control electrodes (i.e., end electrodes 535A and 535E and three central electrodes 535B, 535C and 535D, all shown in dashed lines for reference) respectively disposed at five different locations (A, B, C, D and E) along the length of resistive control gate 531.
• five aperture control electrodes i.e., end electrodes 535A and 535E and three central electrodes 535B, 535C and 535D, all shown in dashed lines for reference
• Lines 510 and 513 in Figure 5B depict two exemplary non-monotonic voltage profiles applied to resistive control gate 531, which forms part of a corresponding pixel of a line sensor similar to line sensor 410 of Figure 4.
• Line 510 in Figure 5B depicts a voltage profile generated during a first time period and comprising two approximately linear voltage gradients between -5V at location C (central electrode 535C) and 0V at locations A and E (end electrodes 535A and 535E) .
• central electrodes 535B and 535D at locations B and D are floating or otherwise maintained at voltages
• Photoelectrons created in the substrate underneath resistive control gate 531 between locations A and C will quickly migrate to the charge accumulation region near location A (underneath end electrode 535A) because it is the most positive potential in that region. Photoelectrons created in the substrate underneath resistive control gate 531 between locations C and E will quickly migrate underneath location E as it is the most potential in that region of the pixel. At the end of the time period, accumulated charge near location A can be read out of the pixel into a readout register, such as register 444A-1 shown in Figure 4.
• the accumulated charge near location E may be discarded by collecting it, for example, with an overflow drain or scupper drain located near location E, or alternatively the charge may be read out of the pixel into a second readout circuit, such as circuit 440B as shown in Figure 4.
• a second readout circuit such as circuit 440B as shown in Figure 4.
• Line 513 in Figure 5B depicts a second voltage profile generated during a second time period (e.g. , subsequent to or before the first time period) and
• resistive gate 531 between locations A and B will quickly migrate underneath location A because it is the most positive potential in that region.
• Photoelectrons created in the substrate underneath resistive control gate 531 between locations D and E will quickly migrate underneath location. E as it is the most potential, in that region of the pixel .
• accumulated charge near location A can be read out of the pixel into a readout register, such as register 444A-1 shown in Figure .
• the accumulated charge near location E may be read out of the pixel into a. second readout circuit, such as circuit 440B as shown in Figure 4.
• the accumulated charge near location C can be subsequently read out of the pixel, for example, by first changing the voltage profile on. resistive control, gate 531 (e.g., to a. profile such, as 501 shown in Figure 5A or 510 shown in Figure 5B) such that the charge accumulated at location C is driven to one or both end locations A and/or E. Once the charge has been moved to one or both, sides of the pixel, it can. be
• the senor may be configured to simultaneously collect three image data values, even though the sensor has only two readout
• FIG. 5C depicts different voltage schemes that may be applied to a resistive control gate 541, which forms part of a corresponding pixel of a line sensor similar to line sensor 410 of Figure 4, by way of five aperture contro1 e1ectrodes ( i.e., end e1ectrodes 545A and 545E and three ce ral electrodes 545B, 5 5C and 545D) respectively disposed at five different locations (A, B, C, D and E) along the length of resistive control gate 541.
• central electrodes 545B, 545C and 545D are offset in the direction, of location.
• central electrodes 545B, 545C and 545D corresponding alternative relatively negative voltages (e.g., -5V) to central electrodes 545B, 545C and 545D, thereby generating a relatively small aperture size (i.e., between locations A and B) , a medium aperture size (i.e., between locations A and C) , and a relatively large aperture size (i.e., between locations A and D) ,
• Fig. 5C can be used to finely adjust the effective aperture size of all pixels of a sensor in order to optimize the light collection, or may be used to ad ust the effective aperture size of each individual pixel during a calibration period to such that all pixels of the sensor have a uniform aperture si ze ,
• Fig. 51 depicts different voltage schemes that may be applied to a resistive control gate 551, which forms part of a corresponding pixel of a line sensor similar to line sensor 410 of Figure 4, by way of five aperture control electrodes (i.e., end electrodes 555A and 555E and three central electrodes 555B, 555C and 555D) respectively disposed at five different locations (A, B, C, D and E) along the length of resistive control gate 551.
• central electrodes 555B and 555D are disposed closer to central electrode 555C (central location C) to facilitate further incremental fine adjustments to the effective aperture of each pixel by way of generating fringing fields .
• a resistive control gate 551 which forms part of a corresponding pixel of a line sensor similar to line sensor 410 of Figure 4, by way of five aperture control electrodes (i.e., end electrodes 555A and 555E and three central electrodes 555B, 555C and 555D) respectively disposed at five different locations (A, B,
• an intermediate adjustment voltage (e.g., -2.5V) is applied to central electrode 555B, thereby producing a voltage profile depicted by line 518 that causes resistive gate elect ode 521 to generate a corresponding asymmetric electric field shifted toward location E.
• an intermediate adjustment voltage (e.g., -2.5V) is applied to central electrode 555D, thereby producing a voltage profile depicted by line 519 that causes resistive gate electrode 521 to generate a corresponding asymmetric electric field shifted toward location A.
• the approach depicted in Fig. 5D can be used to continuously adjust the pixel edge location during operation by way of changing the adjustment voltages applied to central electrodes 555B and 555D.
• Figures 5A to 5D shows voltages gradients between -5V and 0V, this is merely an example of voltage ranges that can be useful. For example, voltage gradients between about -6V and -IV or about -4V and +1V would have a substantially similar effect as gradients between -5V and OV and could be used instead.
• a voltage difference of about. 5V is a convenient value for a pixel that is about ⁇ long, a smaller voltage difference could be used, particularly if the pixel were shorter than about lOOum.
• the voltage difference could be larger than 5V.
• a larger voltage difference could be particularly useful if the pixel is longer than about
• FIG. 6 illustrates an exemplary line sensor 600 in cross-section according to another specific embodiment of the present invention.
• Sensor 600 is fabricated in a semiconductor membrane 601 (e.g., a layer of lightly p- doped epitaxial silicon) that was grown on a silicon wafer
• the dopant concentration in epitaxial silicon 601 is preferably about 2x10 iJ atoms cm J or less.
• a pure boron layer 602 of a few nm thickness is deposited on the bottom (illuminated) surface of epitaxial silicon 601 to prevent oxidation and make sensor 600 resilient against damage from exposure to DUV radiation and charged particles. Since DUV light is particularly useful for inspection and measurements of small features on semiconductor wafers, sensors with multi-year lifetimes under continuous exposure to DUV radiation are particularly useful in semiconductor inspection and metrology systems.
• pure boron layer 602 is particularly useful for inspection and measurements of small features on semiconductor wafers.
• Such an embodiment may be useful where the average DUV power density incident on sensor 600 is low enough that sensor degradation is minimal, such as a DUV power density less about 20 ⁇ 3 ⁇ 4 citf ⁇ (in general shorter wavelength light is more damaging, so systems using very- short wavelengths and lower power densities might benefit from the pure boron layer 602, whereas another system using longer wavelengths and a higher power density might have acceptable sensor lifetime without the boron layer 602) .
• a DUV power density less about 20 ⁇ 3 ⁇ 4 citf ⁇ in general shorter wavelength light is more damaging, so systems using very- short wavelengths and lower power densities might benefit from the pure boron layer 602, whereas another system using longer wavelengths and a higher power density might have acceptable sensor lifetime without the boron layer 602) .
• some boron diffuses into the silicon forming a highly p-doped layer of silicon 603 just a few nm thick adjacent to the pure boron layer 602. In one
• the highly p-doped silicon layer 603 creates a built-in electric field that drives any photoelectrons created near the back surface of the silicon away from that bottom surface.
• This built-in field is very important because most DUV radiation is absorbed within 10 to 15 nm of the silicon surface. If any of those photoelectrons reach the surface, there is a high probability that they will recombine and be lost thus reducing the quantum efficiency (QE) of sensor 600.
• QE quantum efficiency
• an anti-reflection coating 680 is formed over lower surface 613 (e.g., deposited onto boron coating 602, or directly onto lower surface 613 of epitaxial silicon 601 in embodiments where pure boron coating 602 is not present) . Because both boron and silicon have high absorption coefficients for DUV light, they reflect light strongly. The QE of sensor 600 can be significantly improved by using an anti-reflection layer 680.
• Anti-reflection coating 680 may comprise one or more layers of dielectric materials such as silicon
• the anti- reflection coating 680 including, in addition to those just listed, hafnium, dioxide and silicon nitride.
• Charged particle sensors typically do not require an anti-reflection coating.
• layer 680 may be omitted, or may comprise a thin conductive coating, such as a few-run thick layer of a refractory metal.
• a dielectric layer 608 is deposited or grown on the top su face of the epitaxial silicon 601.
• Dielect ic layer 608 may comprise a silicon dioxide layer, or it may comprise two or three layers such as silicon nitride on silicon dioxide or silicon dioxide on silicon nitride on silicon dioxide. Typically the thickness of dielectric layer 608 is in the range of about 50nm to about 200nm.
• a layer of n-type silicon 604 is created under the front surface as a buried channel to collect photoelectrons.
• gate electrodes such as 630, 635 and 640 are deposited and pat erned on top of dielectric layer 608.
• the gate electrodes are typically made of polysilicon or aluminum, but other conductive materials including other metals and semi-metallic compounds (such as TiN) may be used. Electrical connections such as 631, 636 and 641 may be made to the gate electrodes.
• Figure 6 depicts gates electrodes such as 630, 635 and 640 only on the left side of resistive gate 620, similar structures may also be present on the right side of resistive gate 620 in order to allow readout from both sides of the pixel as illustrated by readout, circuits 4 OA and 440B in Figure 4.
• the gate electrodes overlap one another, as shown, for example, at 632 in order to minimize and control fringe electric fields near the edges of the electrodes.
• the gate electrodes are separated by a dielectric material (not shown) .
• Resistive gate 620 preferably comprising undoped or lightly doped poly-crystalline silicon (poly-silicon) , overlays the light-sensitive pixel. Multiple electrical connections are made to different locations on the
• resistive gate These connections (or contacts) are shown schematically by 621A, 621B, 621C and 621D. Although four electrical connections are shown, three, four or more may be used depending on how many different light collecting modes are needed.
• voltage gradients are created in resistive gate 620 by applying different voltages to the different contacts 621A, 62 IB, 621C, 62 ID connected to it. Different locations along the length of the resistive gate are at different voltages as a result of the different voltages applied to the contacts as
• the potential at the surface of the epitaxial silicon 601 varies with location according to the voltage at the corresponding location on resistive gate 620. This varying potential creates an electric field in the epitaxial layer 601 that controls where the photoelectrons collect. Because the epitaxial layer 601 is lightly doped, they are few free carriers and the electric fields from charges near the surface will extend throughout all, or almost all, of the epitaxial layer 601.
• contact 621A is more positive than contact 62 ID and contacts 62 IB and 621C are at
• buffer gate 630 If buffer gate 630 is held at a more negative voltage than 621A, electrons will not move underneath buffer gate 630.
• the voltage on buffer gate 630 can be raised by, for example, applying a voltage to contact 631 that is more positive than the voltage applied to contact 621A. Raising the potential on transfer gate 635 by applying an
• appropriate voltage to contact 636 can move electrons from under buffer gate 630 to under transfer gate 635.
• the potential on buffer gate 630 may be lowered at the same time as, or slightly later than, the potential on transfer gate 635 is raised to block direct transfer of electrons from the pixel under transfer gate 635.
• registers such as 640, may be included as needed.
• the electrons are transferred to a floating diffusion region (not shown) , which in turn is connected to an output amplifier.
• Fig. 7 is a simplified cross' ⁇ section showing a pixel of a linear sensor 700 including a wedge-shaped optical knife edge (mechanical aperture structure) 760 disposed on or over a backside surface of substrate 701 such that a portion of light reflected or otherwise directed to sensor 700 from a sample is blocked by optical knife edge 760.
• a wedge-shaped optical knife edge mechanical aperture structure
• resistive control gate 721 is formed on a dielectric layer 708 over a frontside surface of substrate 701, and multipl aperture control electrodes 725A to 725E are disposed on a upper surface of resistive control gate 721.
• optical knife edge 760 is implemented using a slit aperture filter as taught in co-owned and co-pending U.S. Patent Application Serial No. 14/691,966, filed April 21, 2015 and entitled CONFOCAL LINE INSPECTION OPTICAL SYSTEM, which is incorporated herein by reference in its entirety.
• a control circuit (not shown.) of system 700 is configured to

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• Spectroscopy & Molecular Physics (AREA)
• Investigating Materials By The Use Of Optical Means Adapted For Particular Applications (AREA)
• Testing Or Measuring Of Semiconductors Or The Like (AREA)
• Investigating Or Analysing Materials By Optical Means (AREA)
• Solid State Image Pick-Up Elements (AREA)
• Transforming Light Signals Into Electric Signals (AREA)
• Length Measuring Devices By Optical Means (AREA)

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• 2016
  • 2016-05-12 US US15/153,543 patent/US9860466B2/en active Active
  • 2016-05-13 KR KR1020177035444A patent/KR102284002B1/ko active Active
  • 2016-05-13 CN CN201680025778.5A patent/CN107548554B/zh active Active
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• 2017
  • 2017-10-24 IL IL255230A patent/IL255230B/en active IP Right Grant
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• 2020
  • 2020-03-25 JP JP2020054037A patent/JP6789428B2/ja active Active

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