Apparatus and method for evaluating a wafer of semiconductor material
First Claim
1. An apparatus for evaluating a wafer, said apparatus comprising:
- a first source of a first beam of photons having a first intensity modulated at a frequency sufficiently low to avoid creation of a wave of charge carriers in a region of said wafer when said first beam is incident on said region;
a second source of a second beam of photons, said photons in said second beam having energy sufficiently lower than said energy of said photons in said first beam to avoid creation of more than a negligible number of charge carriers in said region when said second beam is incident on said region; and
a photosensitive element located in a path of a portion of said second beam, said portion being modulated at said frequency after reflection by said region, said photosensitive element generating a first signal indicative of a first concentration of said charge carriers created in said region by incidence of said first beam.
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Abstract
An apparatus and method uses diffusive modulation (without generating a wave of carriers) for measuring a material property (such as any one or more of: mobility, doping, and lifetime) that is used in evaluating a semiconductor wafer. The measurements are carried out in a small area, for use on wafers having patterns for integrated circuit dice. The measurements are based on measurement of reflectance, for example as a function of carrier concentration. In one implementation, the semiconductor wafer is illuminated with two beams, one with photon energy above the bandgap energy of the semiconductor, and another with photon energy near or below the bandgap. The diameters of the two beams relative to one another are varied to extract additional information about the semiconductor material, for use in measuring, e.g. lifetime.
140 Citations
63 Claims
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1. An apparatus for evaluating a wafer, said apparatus comprising:
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a first source of a first beam of photons having a first intensity modulated at a frequency sufficiently low to avoid creation of a wave of charge carriers in a region of said wafer when said first beam is incident on said region; a second source of a second beam of photons, said photons in said second beam having energy sufficiently lower than said energy of said photons in said first beam to avoid creation of more than a negligible number of charge carriers in said region when said second beam is incident on said region; and a photosensitive element located in a path of a portion of said second beam, said portion being modulated at said frequency after reflection by said region, said photosensitive element generating a first signal indicative of a first concentration of said charge carriers created in said region by incidence of said first beam. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29)
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30. An apparatus for generating an electrical signal indicative of a property of a region in a wafer, said wafer including a semiconductor material at said region, said apparatus comprising:
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an oscillator oscillating at a frequency lower than 1000 KHz during operation; a first source of a first beam, said first source being coupled to said oscillator to generate said first beam at an intensity modulated at said frequency, said first beam containing a plurality of first photons having energy greater than the bandgap energy of said semiconductor material thereby to create a plurality of charge carriers when incident on said region, the number of said plurality of charge carriers being modulated at said frequency without the creation of a wave; a second source of a second beam, said second beam containing a plurality of second photons having energy lower than said bandgap energy; a partially transmissive mirror located in the path of each of said first beam and said second beam, said partially transmissive mirror being positioned to reflect one of said first beam and said second beam along a path coincident with the path of the other of said first beam and said second beam thereby to create a combined beam; a beam splitter positioned in said coincident path; a sensor capable of sensing said second photons, said sensor being coupled to said beam splitter to receive a group of second photons reflected by said region; a lock-in amplifier coupled to said oscillator and to said sensor, said lock-in amplifier having an output line; wherein said lock-in amplifier generates on said output line a signal indicative of an average number of said second photons modulated at said frequency and reflected by said region. - View Dependent Claims (31, 32, 33)
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34. An apparatus for measuring a property of a wafer, said wafer including a semiconductor material, said apparatus comprising:
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an oscillator capable oscillating at a frequency smaller than 1000 KHz; a first source of a first beam, said first source being coupled to said oscillator to generate said first beam at an intensity modulated at said frequency, said first beam containing a plurality of first photons having energy greater than the bandgap energy of said semiconductor material thereby to create a plurality of charge carriers when incident on a region of the semiconductor material, the number of said plurality of charge carriers being modulated at said frequency; a second source of a second beam, said second beam containing a plurality of second photons having energy lower than said bandgap energy, said second beam being polarized; a partially transmissive mirror located in the path of each of said first beam and said second beam, said partially transmissive mirror being positioned to reflect one of said first beam and said second beam along a path coincident with the path of the other of said first beam and said second beam; a polarizing beam splitter located in the path of reflection of said second beam from said wafer; a first sensor coupled to said polarizing beam splitter to receive a first portion of electromagnetic radiation from said polarizing beam splitter; and a second sensor coupled to said polarizing beam splitter to receive a second portion of electromagnetic radiation from said polarizing beam splitter; wherein said first portion and said second portion are respectively the sum and difference components of interference of; a portion of said second beam prior to said reflection by said wafer; and another portion of said second beam subsequent to said reflection by said wafer. - View Dependent Claims (35, 36)
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37. A method for evaluating a wafer, said method comprising:
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creating a plurality of charge carriers in a region of said wafer, the number of said charge carriers being modulated at a frequency that is sufficiently low to avoid creation of a wave of said charge carriers; focusing on said region a first beam of first photons having energy lower than bandgap energy of a semiconductor material in said region; and measuring a first intensity of a portion of said first beam modulated at said frequency after reflection by said region. - View Dependent Claims (38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52)
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53. A method for evaluating a wafer, said method comprising:
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focusing on a region of said wafer a first beam of first photons having energy lower than the bandgap energy of a semiconductor material in said region, said first beam being polarized; focusing on said region a second beam of second photons having energy greater than said bandgap energy, said second beam having an intensity modulated at a predetermined frequency, said second beam creating a plurality of charge carriers when incident on said region, said predetermined frequency being sufficiently small to avoid the creation of a wave of said charge carriers; reflecting said first beam at said predetermined frequency by using said charge carriers; interfering a reflected portion of said first beam with an unreflected portion of said first beam to obtain a sum component and a difference component; measuring a difference between a first magnitude of said sum component and a second magnitude of said difference component. - View Dependent Claims (54, 55, 56, 57, 58, 59)
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60. A method for evaluating a wafer, said method comprising:
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creating a plurality of charge carriers in a region of said wafer, the number of said charge carriers being modulated at a frequency that is sufficiently low to avoid creation of a wave of said charge carriers; focusing on said region a probe beam of photons having energy lower than bandgap energy of a semiconductor material in said region; measuring a first intensity of a portion of said probe beam modulated at said frequency after reflection by said region; changing the concentration of said charge carriers at a surface of said wafer; measuring, after said changing, a second intensity of a portion of said beam modulated at said frequency after reflection by said region; determining a value of an attribute of a function that relates, at least approximately, said first intensity and said second intensity to the corresponding values of said concentration before and after said changing; and interpolating said attribute with respect to a plurality of attributes of corresponding functions of semiconductor materials having known values of a property thereby to determine the value of said property in said region. - View Dependent Claims (61, 62, 63)
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Specification