COMBINED OCD AND PHOTOREFLECTANCE METHOD AND SYSTEM

A combined OCD and photoreflectance system and method for improving the OCD performance in measurements of optical properties of a target sample. The system comprises (a) either a single channel OCD set-up comprised of a single probe beam configured in a direction normal/oblique to the target sample or a multi-channel OCD set-up having multiple probe beams configured in normal and oblique directions to the target sample for measuring the optical properties of the target sample, (b) at least one laser source for producing at least one laser beam, (c) at least one modulation device to turn the at least one laser beam into at least one alternatingly modulated laser beam, and (d) at least one spectrometer for measuring spectral components of the at least one light beam reflecting off said target sample; wherein the at least one alternatingly modulated laser beam is alternatingly modulating the spectral reflectivity of the target sample,

FIELD OF THE INVENTION

The present invention relates to semiconductor measurement techniques. More specifically, the present invention relates to semiconductor metrology techniques for measurement of device critical dimensions by optical means.

BACKGROUND OF THE INVENTION

OCD (Optical Critical Dimension) is a subset of semiconductor metrology techniques for in-line measurement of device critical dimensions by optical spectroscopic methods (most commonly Spectral Ellipsometry or Spectral Reflectometry).

Since relevant dimensions of semiconductor devices are well below the diffraction limit of UV-Visible light, optical microscopy can't directly measure them. Instead, OCD is a model-based technique which works in the following way:Spectra of the structure to be analyzed are measured (preferably at multiple angles of incidence, polarizations etc.);A parametrized geometric model is built with enough degrees of freedom to closely represent the structure;Theoretical spectra based on that model are calculated using detailed electromagnetic simulation; andThe model parameters are iteratively altered until best match is obtained between the theoretical and measured spectra.

For many years, OCD has been the workhorse of semiconductor fab inline metrology due to advantages thereof over other techniques—it is fast, non-destructive, non-contact and does not require a vacuum or any other special treatment of the sample. It's main weakness, however, lies in its indirect nature—the results can be affected by uncertainties in the model fidelity, calculation errors, optical system parameters, and material optical properties. Some of these concerns can be mitigated by improvements in hardware and software, but some are more fundamental.

The calculation of a theoretical spectrum from model parameters is commonly accomplished through standard electromagnetic modeling engines (such as Rigorous Coupled Wave Analysis). However, the process of interpreting the measured data to deduce the underlying structural parameters is highly challenging its eventual performance (precision, accuracy) is determined by the spectral sensitivity to the dimensional parameters of interest and the correlations between the spectral impact of variations of different parameters. Parameters with weak spectral effect, or parameters for which this effect is highly similar to the changes induced by variations of other parameters, would suffer from poor interpretation performance.

Such issues are increasingly plaguing OCD in direct correlation to the shrinking dimensions and increasing geometric and material complexity encountered in advanced semiconductor technology nodes.

One class of such problems is related to optical contrast—adjacent parts of the structure which are made of different, but optically similar, materials. As an illustration, consider for example a thin film of low Ge concentration Silicon-Germanium over Silicon. The two materials can have very different physical (e.g. electrical) properties while having quite similar optical permittivity. The spectrum will then be weakly sensitive to the film thickness, essentially seeing both materials as the same.

As another very common example, characterization of an ultra-thin film deposited over some complicated structure is needed. It is commonly extremely difficult to separate out the weak spectral sensitivity to this layer, from the (significantly stronger) influences of other dimensional parameters.

It is, therefore, an aim of the present invention to provide a system and method for in-line measurement of device critical dimensions. A system and method suitable to the shrinking dimensions and increasing geometric and material complexity encountered in advanced semiconductor technology nodes.

SUMMΔRY OF THE INVENTION

The present invention provides a system and method for improving the performance of OCD in challenging applications. More specifically, the present invention provides a system and method for in-line measurement of device critical dimensions, a combined OCD and photoreflectance (PR) system and method suitable to the shrinking dimensions and increasing geometric and material complexity encountered. in advanced semiconductor technology nodes. In accordance with some embodiments of the present invention, photoreflectance (PR) spectroscopy offers a unique way to selectively change the sensitivity to different materials and thus highlight some parameters or break correlations between parameters. The reason for this is two-fold:PR response is strongly material dependent. For a given pump wavelength, some materials will experience PR while others will be completely unaffected.The PR spectrum of semiconductors is usually highly localized in frequency, with sharp features located at the band. structure critical point energies. This also can help with decoupling the contributions from different materials.

In accordance with some embodiments of the present invention, there is thus provided a combined OCD and photoreflectance apparatus for improving the OCD performance in measurements of optical properties of a target sample.

The combined OCD and photoreflectance apparatus comprising:(a) either a single channel OCD set-up comprised of a single probe beam configured in a direction normal/oblique to the target sample or a multi-channel OCD set-up having multiple probe beams configured in normal and oblique directions to the target sample for measuring the optical properties of the target sample in said normal direction and/or in said oblique direction;(b) at least one laser source for producing at least one laser beam;(c) at least one modulation device to turn the at least one laser beam into at least one alternatingly modulated laser beam, and thus, to allow said alternatingly modulated laser beam to alternatingly modulate the spectral reflectivity of the target sample, so that, a light beam reflecting off said target sample is alternatingly a “pump on” light beam and a “pump off” light beam; and(d) at least one spectrometer for measuring spectral components of the at least one light beam reflecting off said target sample;wherein said at least one light beam that is reflecting off the target sample is directed into said at least one spectrometer, andwherein said at least one alternatingly modulated laser beam is alternatingly modulating the spectral reflectivity of the target sample.

Furthermore, in accordance with some embodiments of the present invention, the modulating device directly modulating the at least one laser source or in a path of said at least one laser beam to produce at least one modulated laser beam. Furthermore, in accordance with some embodiments of the present invention, the multi-channel OCD set-up is comprised of a first probe beam configured in a direction normal to the target sample and a second probe beam configured in a direction that is oblique to the target sample.

Furthermore, in accordance with some embodiments of the present invention, the single/multiple probe beams) and the laser beam are directed to hit a single spot on said target sample.

Furthermore, in accordance with some embodiments of the present invention, the combined OCD and photoreflectance apparatus further comprises an optical element directing a pre-determined portion of either the single probe beam or at least one of the multiple probe beams onto the target sample.

Furthermore, in accordance with some embodiments of the present invention, the optical element is selected from a beam splitter and a mirror.

Furthermore, in accordance with some embodiments of the present invention, the combined OCD and photoreflectance apparatus further comprising at least one optical member for focusing either the single probe beam or at least one of the multiple probe beams onto the optical element.

Furthermore, in accordance with some embodiments of the present invention, the combined OCD and photoreflectance apparatus further comprising at least one optical member for focusing either the single probe beam or at least one of the multiple probe beams onto the target sample.

Furthermore, in accordance with some embodiments of the present invention, the combined OCD and photoreflectance apparatus further comprising at least one optical member for focusing either the single probe beam or at least one of the multiple probe beams onto the at least one spectrometer.

Furthermore, in accordance with some embodiments of the present invention, the combined OCD and photoreflectance apparatus further comprising a combiner to combine either the single probe beam or at least one of the multiple probe beams pith the at least one alternatingly modulated laser beam into a single beam prior to hitting the target sample.

Furthermore, in accordance with some embodiments of the present invention, the combined OCD and photoreflectance apparatus further comprising a notch filter/polarizer for filtering out the modulated laser beam from a combined beam reflecting off the target sample prior to entering into the spectrometer.

Furthermore, in accordance with some embodiments of the present invention, the combined OCD and photoreflectance apparatus further comprises an optical element directing a pre-determined portion of the combined beam onto the target sample.

Furthermore, in accordance with some embodiments of the present invention, the optical element is selected from a beam splitter and a mirror.

Furthermore, in accordance with some embodiments of the present invention, the combined OCD and photoreflectance apparatus further comprising at least one optical member for focusing the combined beam onto the optical element.

Furthermore, in accordance with some embodiments of the present invention, the combined OCD and photoreflectance apparatus further comprising at least one optical member for focusing the combined beam onto the target sample.

Furthermore, in accordance with some embodiments of the present invention, the combined OCD and photoreflectance apparatus further comprising at least one optical member for focusing the combined beam into the notch filter/polarizer.

Furthermore, in accordance with some embodiments of the present invention, there is thus provided a combined OCD and photoreflectance system for improving the OCD performance in measurements of optical properties of a target sample and for calculating light-induced change in optical properties of a target sample. The combined OCD and photoreflectance system comprising the above-described combined OCD and photoreflectance apparatus wherein the combined OCD and photoreflectance apparatus converting said “pump on” light beam and said “pump off” light beam to a “pump on” signal and a “pump off” signal and transferring said “pump on” signal and said “pump off” signal to a computer for subtracting the “pump on” signal corresponding to a spectrum (R) from the “pump off” signal corresponding spectrum (R+ΔR) to get a PR signal ΔR.

Furthermore, in accordance with some embodiments of the present invention, there is thus provided a combined OCD and photoreflectance method for measuring and calculating light-induced change in optical properties of a target sample. The method comprising:(a) providing the above-described combined OCD and photoreflectance system;(b) either focusing a single/multiple probe beam(s) in a direction normal and/or oblique to a spot on a target sample and a laser beam that is alternatingly modulated onto said spot on the target sample or focusing a combined beam comprised of a probe beam and a laser beam that is alternatingly modulated to a spot on said target sample;(c) hitting said spot on the target sample either via said single/multiple probe beam(s) and said laser beam that is alternatingly modulated or via said combined beam to alternatingly modulate the reflectivity of the target sample, thus, to have “pump-on” light beam and “pump off” light beam alternatingly reflecting off the target. sample;(d) directing either a single/multiple light beam(s) or a combined beam comprised of a probe beam and a modulated laser beam reflecting off the target sample to at least one spectrometer;(e) filtering out the modulated laser beam from the combined beam reflecting off the target sample prior to reaching the at least one spectrometer;(f) converting the “pump on” light beam and the “pump off” light beam into a “pump on” signal and a “pump off signal and transferring the “pump on” signal and the “pump off signal to a computer; and(g) subtracting the “pump on” signal corresponding to a spectrum(R) from the “pump off” signal corresponding to a spectrum (R+ΔR) to get a PR signal ΔR.

Furthermore, in accordance with some embodiments of the present invention, the combined OCD and photoreflectance method further comprising synchronizing the at least one spectrometer with a modulation device when using said combined beam.

DETAILED DESCRIPTION OF THE FIGURES

FIG.1is an Example of PR spectrum of Silicon from 320 nm to 400 nm.

In accordance with some embodiments of the present invention, it would seem beneficial to have a PR measurement channel working in conjunction with standard OCD, measuring the target sample at the same time and location so as to provide complementary spectral information. This information can be used in several ways:Model-based—by including a theoretical model of the PR response into the spectrum calculation. Such modeling can include account for the multiple related effects, such as thermos-reflectance, electro-reflectance, magneto-reflectance, and even such considerations as charge carrier excitation and diffusion, band structure and photo-effects on the band structure, nonlinear responses etc.In certain simple cases like thin films, the response at specific wavelengths can be directly correlated to film thickness, absorption or refractive index.

In more complicated cases, Machine Learning algorithms trained on controlled reference data can be employed, and would benefit from the increased sensitivities of PR.

The appeal of this approach also comes from the synergy between the two methods. The broadband spectroscopic measurement channel of an OCD tool is suited to serve as the probe in a PR system. To complete the system, a modulated pump beam needs to be inserted into the optical path and synchronized to the spectral acquisition electronics.

However, some details need to be considered for this to work. One such is the question of noise. One of the challenges of PR is the small relative modulation of the reflectance (ΔR/R˜10−4−10−5) which requires reflectometry measurement at very high signal-to-noise ratios (SNRs) of the order of18105−6. This is especially true in the context. of integration with OCD systems which usually have SNR on the order of ˜103−4and are required to measure at less than ˜1 second to maintain reasonable throughput. If PR is to be part of the OCD measurement, it also should conform to similar requirements.

A possible way to address this problem without completely redesigning the OCD system is to use a high brightness source such as a supercontinuum laser (SCL) or some types of laser-driven plasma sources.

As an illustration of typical numbers, achieving a shot noise limited SNR of 105requires each pixel in the sensor to accumulate>1010photoelectrons (i.e., ˜103−4times more light than a typical OCD measurement, at a similar acquisition time). To achieve this in a span of 1 s, the product of frame rate to full well capacity (FWC) is ˜1010e−/s.

Practical values based on current sensor and electronics technology are frame rates of ˜102−3PPS and FWC of ˜107−8e−, which are achievable with linear array CCDs. By combining this sort of acquisition system with a high brightness source such as a SCL, the SNR and throughput requirements can be met.

Another issue in PR spectroscopy is contamination of the probe beam by the much brighter pump beam, either directly or through stray light. In this context, a key parameter of OCD tool design is the number of angles of incidence (AOIs), which mostly come in two flavors:Normal Incidence channel: usually found in integrated metrology tools that need to have a small footprint. Single objective lens serves both illumination and collection.Multichannel (Normal and Oblique Incidence channels): usually found in stand-alone metrology tools. Separate objectives are used for the oblique illumination and collection of the reflected beam.

Bringing the pump and probe beam together on the target sample can be implemented in several ways depending on the system design:Noncolinear: The most straightforward way to separate the pump and probe beams is by using different AOIs, geometrically separating them at the detector plane as illustrated below inFIG.4. This requires focus and boresight matching of the two beams.In multichannel tools, this can be achieved by using one of the channels (normal or oblique) for the pump and the other for the probe beams. Alternatively, the pump light can be inserted obliquely from outside the objective in a normal-only design. This however requires a more substantial modification of the system to accommodate.Another option is to use a normal channel with large-NA objective, and illuminate only the central part of the entrance pupil by the probe beam and the outer ring by the pump, allowing them to be easily separated in the collection channel by using suitable apertures.Colinear: Combining the pump and probe into a co-linear beam as illustrated. inFIGS.5&6below has some advantages, such as removing the need for focus and boresight alignment of the two channels. This however requires that they be separated in some other way, such as:Polarization: The pump and probe beams can be orthogonally polarized such that a polarized in the collection channel will block the pump beam from reaching the detector.Spectrally: If the pump WL is sufficiently far from the region of interest in the probe spectrum, it can be separated by a dispersive element in the spectrometer or before it, or if the pump wavelength resides outside the measured spectral range it would not be directly detected.Temporally: The probe beam can itself be modulated at a different frequency, so that the PR signal is recovered by LID at the sum frequency of the pump and probe modulation while rejecting both the pump itself and other artifacts associated with such as Photoluminescence.

The pump beam can be chosen or controlled so as to alter performance, in several ways:Wavelength: different wavelengths will affect materials differently according to their band structure and occupancy levels, allowing selective enhancement of sensitivity to different materials in the structure.Intensity: PR is generally non-linear, since the generated charge carriers affect the band structure which in turn changes the absorption of more photons. By changing the pump beam intensity, these non-linear properties can be probed, providing information on (e.g.) charge carrier lifetime, charge traps and defects.Polarization: Changing pump polarization can change the absorption profile of the pump beam, highlighting different parts of the structure.Repetition rate and illumination spot: Since charge carriers are mobile, they diffuse away from the pump spot in a way governed by their lifetime, mean free path, effective mass etc. Changing the temporal and spatial pattern of the pump illumination will affect the PR response in a way that can be linked to these physical parameters. In addition, as soon as the repetition rate becomes comparable with the excited charge carriers' lifetime, the PR signal can strongly depend on the specific repetition rate.

Of course, a proper choice of the ‘probe’ path properties (wavelength range, polarizations, AOI etc.) would dictate the metrological benefit of this scheme—the parameter sensitivities, correlations and overall performance.

FIG.2(PRIOR ART) illustrates an SR OCD apparatus200having a normal incidence channel for measuring optical properties of a target sample. In accordance with some embodiments of the present invention, the OCD apparatus200is used for measuring optical properties of a target sample208via a probe beam204configured in a direction normal to the target sample208. The OCD apparatus200comprises a probe source202for producing a probe beam204, and a spectrometer206for measuring the spectral components of a beam reflected from a target sample208. The OCD apparatus200further comprises an optical element210such as a beam splitter, a mirror and the like and multiple lenses, e.g., lens212, lens214and lens216.

The optical element210directing the probe beam204onto the target sample208and directing the beam reflecting off the target sample208to the spectrometer206.

In accordance with some embodiments of the present invention, lens212focuses the probe beam204to the optical element210, lens214is a single objective lens serving both illumination and collection as it focuses the beam exiting the optical element210to the target sample208and the beam reflecting off the target sample208to the optical element210, and lens216focuses the beam exiting the optical element210to the spectrometer206.

Thus, while in operation, the probe source202generates a continuous probe beam204which is focused via lens212onto optical element210. Optical element210directs a pre-determined portion of the probe beam204onto the target sample208via lens214, the beam reflecting off the target sample208is focused via lens214onto the optical element210and the beam exiting the optical element210, is focused via the lens216into the spectrometer206.

Thus, while in operation, the probe source202generates a continuous probe beam204which is focused via lens212onto optical element210. Optical element210directs a pre-determined portion of the probe beam204onto the target sample208, and the beam reflecting off the target sample208is focused onto the optical element210via the lens214and into the spectrometer206via lens216.

FIG.3(PRIOR ART) illustrates a multichannel OCD apparatus300having a normal and oblique incidence channels for measuring optical properties of a sample.

In accordance with some embodiments of the present invention, the multichannel OCD apparatus300comprises a first probe beam302configured in a direction normal to the target sample330and a second probe beam306configured at an oblique angle of incidence onto the target sample330for measuring optical properties of a sample via a combined OCD and photoreflectance system in accordance with some embodiments of the present invention.

In accordance with some embodiments of the present invention, separate objectives are used for the oblique illumination and collection of the reflected beam.

The OCD apparatus300further comprises a first spectrometer310and a second spectrometer312for measuring the spectral components of beams reflected from the target sample330, an optical element314such as a beam splitter, a mirror and the like and multiple focusing members such as lens316, lens318, lens320, lens322, lens324, lens326and lens328.

As seen in the figure, the optical element314directing the probe beam304in a direction normal to the target sample330and directing the beam reflecting off the target sample330to the first spectrometer310, and lens316focuses the probe beam304to the optical element314, lens320focuses the beam exiting the optical element314to the first spectrometer310, and lens318is a single objective lens serving both illumination and collection as it focuses the beam exiting the optical element314to the target sample330and the beam reflecting off the target sample313to the optical element314.

The second probe source306produces a second probe beam308which is directed at an oblique angle of incidence onto the target sample330. The second probe beam308is focused onto the target sample330via lenses322and324, and the beam reflected from the sample330is focused via lenses326and328onto the second spectrometer312.

Thus, while in operation, the first probe source302and the second probe source306generate continuous probe beams304and308continuously. Probe beam304is focused via lens316onto optical element314. Optical element314directs a pre-determined portion of the probe beam304in a direction normal to the target sample330, and the beam reflecting off the target sample330is focused onto the optical element314via the lens318and into the first spectrometer210via lens320.

The second probe beam308is directed at an oblique angle of incidence onto the target sample330. The second probe beam308is focused. onto the target sample330via lenses322and324, and the beam reflected from the target sample330is focused via lenses326and328onto the second spectrometer312.

As the spectral reflectivity of a material is closely related to electronic properties such as band structure, density of states, free carries etc., modulation spectroscopy (MS) is uniquely sensitive to these properties more than any other optical spectroscopy method. This can be of high value when electrical testing of semiconductor devices needs to be done at the early stages of their fabrication process, where conventional E-testing s impossible.

The following figures illustrate combined OCD and photoreflectance (PR) systems suitable to the shrinking dimensions and increasing geometric and material complexity encountered in advanced semiconductor technology nodes in accordance with some embodiments of the present invention.

FIG.4illustrates a combined OCD and Photoreflectance (PR) spectroscopy apparatus400in accordance with some embodiments of the present invention.

The OCD set up comprises a probe source402for producing a probe beam404, and a spectrometer406for measuring the spectral components of a beam reflecting off a target sample407. The OCD set up further comprises an optical element408such as a beam splitter, a mirror and the like and focusing members such as lens410, lens412and lens414for focusing the probe beam404to the optical element408, for focusing the beam exiting the optical element408to the target sample407, and the beam reflecting off the target sample407to the spectrometer406respectively. Lens412is a single objective lens serving both illumination and collection as it focuses the beam exiting the optical element408to the target sample407and the beam reflecting off the target sample407to the optical element408.

In accordance with some embodiments of the present invention, the Photoreflectance (PR) spectroscopy set up comprises a pump laser418, a modulator420in the path of the laser beam422and at least one optical member such as lens424and lens426for focusing the modulated laser beam428onto the target sample407.

In accordance with some embodiments of the present invention, the laser beam422is modulated in order to alternatingly modulate the reflectivity of the sample407and thus to have a “pump on” light beam and a “pump off” light beam reflecting off the sample407.

In accordance with some embodiments of the present invention, the laser beam422may be attenuated electronically or via appropriate attenuation optical filters, e.g., mechanically shiftable into/out optical path of pump beam and/or based on electro-optical means, etc.

While in operation, the probe source402generates a continuous probe beam404which is focused via lens410onto optical element408. Optical element408directs a pre-determined portion of the probe beam404onto the target sample407, and the beam reflecting off the target sample407is focused onto the optical element408via the lens412and into the spectrometer406via lens414.

In accordance with some embodiments of the present invention, the modulator420alternatingly directs the pump beam422to the target sample407, and thus, alternatingly modulates the reflectivity of the target sample407.

Thus, in accordance with some embodiments of the present invention, there are two modes in measurements, one while the modulated laser beam428is reaching the target sample407and another while the modulated laser beam428is shuttered out.

While the laser beam422is reaching the target sample407, the light beam reflecting off the target sample407is a “pump-on” beam, and when the laser beam422is shuttered out, the light beam reflecting off the target sample407is a “pump-off” beam.

Thus, such combined OCD and Photoreflectance (PR) spectroscopy apparatus400allows measuring alternatingly (a) the spectral reflectivity of the target sample407, and (b) the modulated reflectivity of the target sample407, e.g., the change in spectrum rather than the spectrum itself as a response to that perturbation.

FIG.5illustrates an alternative combined OCD and Photoreflectance (PR) spectroscopy apparatus500in accordance with some embodiments of the present invention.

The alternative combined OCD and Photoreflectance (PR) spectroscopy apparatus500is more compact compared to the apparatus illustrated and described inFIG.4, and therefore, may be suitable for use in spaces limited in size, for instance in semiconductor manufacturing equipment such as coating devices and the like.

In accordance with some embodiments of the present invention, the alternative combined OCD and Photoreflectance (PR) spectroscopy apparatus500is comprised of a probe source502for producing a probe beam504, and a spectrometer506for measuring the spectral components of a beam reflected from a target sample507. The alternative combined OCD and Photoreflectance (PR) spectroscopy apparatus500further comprises a pump laser508, a modulator510in the path of the laser beam512, a combiner514, a notch filter/polarizer516and electronics518.

In accordance with some embodiments of the present invention, the laser beam512is modulated in order to alternatingly modulate the reflectivity of the target sample507and thus to have a “pump on” light beam and a “pump off” light beam reflecting off the target sample507.

The alternative combined OCD and Photoreflectance (PR) spectroscopy system500further comprises an optical element520directing a pre-determined portion of the combined beam522onto the target sample507, and multiple optical members such as lens524, lens526and lens528for focusing the combined. beam onto the optical element520, onto the target sample507and into the notch filter/polarizer516respectively.

In contrast to the OCD and Photoreflectance (PR) spectroscopy system400ofFIG.4which uses two separate beams, a probe beam and a pump laser beam, directed to hit a single spot on the target sample, here, the probe beam504and the pump laser beam512are combined into a single beam that is alternatingly modulated.

The pump laser beam512is modulated via modulator510and the modulated laser beam513is combined via combiner514with the probe beam504to produce an alternatingly modulated combined beam522.

The alternatingly modulated combined beam522is focused via lens524onto optical element520which directs a pre-determined portion of the alternatingly modulated combined beam522in a direction normal to the target sample507.

In accordance with some embodiments of the present invention, the beam reflecting off the target sample507is focused via lens526onto the optical element520, and the beam505exiting the optical element520is focused via lens528onto notch filter/polarizer516prior to entering into the spectrometer506.

Notch filter/polarizer516is used for filtering out the modulated laser beam513from the combined beam reflecting off the target sample507in order to avoid damage to the spectrometer506.

In accordance with some embodiments of the present invention, electronics518is used. for synchronizing the modulator510and the spectrometer506.

FIG.6illustrates a combined OCD set-up and Photoreflectance (PR) spectroscopy apparatus600for measuring optical properties of a target sample via a first probe beam configured in a direction normal to the target sample and a second probe beam configured at an oblique angle of incidence onto the target sample in accordance with some embodiments of the present invention.

The combined OCD set-up and Photoreflectance (PR) spectroscopy apparatus600is comprised of the combined OCD set-up and Photoreflectance (PR) spectroscopy500ofFIG.5and an additional OCD set-up with a probe beam configured at an oblique angle of incidence onto the target sample.

The combined OCD and Photoreflectance (PR) spectroscopy apparatus600is compact and may be suitable for use in spaces of limited in size, for instance in semiconductor manufacturing equipment such as coating devices and the like.

In accordance with some embodiments of the present invention, the combined OCD and Photoreflectance (PR) spectroscopy apparatus600is comprised of a first probe source602for producing a first probe beam604, and a first spectrometer606for measuring the spectral components of a beam reflecting off a target sample607.

The combined OCD and Photoreflectance (PR) spectroscopy apparatus600further comprises a pump laser608, a modulator610in the path of the laser beam612, a combiner614for combining the first probe beam604with the modulated laser beam613into a combined beam622, electronics618, and a notch filter/polarizer619.

In accordance with some embodiments of the present invention, the laser beam612is modulated in order to alternatingly modulate the reflectivity of the target sample607and thus to have a “pump on” light beam and a “pump off” light beam reflecting off the target sample607.

In accordance with some embodiments of the present invention, electronics618is used for synchronizing the modulator610and the spectrometer606.

The combined OCD and Photoreflectance (PR) spectroscopy apparatus600further comprises an optical element620directing a pre-determined portion of the combined beam622onto the target sample607, and multiple optical members such as lens624, lens626and lens628for focusing the combined beam onto the optical element620, onto the target sample607and into the notch filter/polarizer respectively619prior to entering into the first spectrometer606.

As in the OCD and Photoreflectance (PR) spectroscopy apparatus500ofFIG.5, the probe beam604and the modulated laser beam613are combined into a single, combined beam622that is alternatingly modulated.

The alternatingly modulated combined beam622is focused via lens624onto optical element620which directs a pre-determined portion of the alternatingly modulated combined beam622in a direction normal to the target sample607.

In accordance with some embodiments of the present invention, the beam reflecting off the target sample607is focused via lens626onto the optical element620, and the beam605exiting the optical element620is focused via lens628onto notch filter/polarizer619prior to entering into the spectrometer606.

The Notch filter/polarizer619is used for filtering out the modulated laser beam613from beam605in order to avoid damage to the spectrometer606.

In accordance with some embodiments of the present invention, the second probe source630produces a second probe beam632directed at an oblique angle of incidence onto the target sample607. The second probe beam632is focused onto the target sample607via lenses634and636, and the beam reflecting off the target sample607is focused via lenses638and640onto the second spectrometer642.

Thus, while in operation, the first probe source602and the second probe source630generate continuous probe beams604and632continuously. Probe beam604and a modulated laser beam613are combined into a combined beam622that is alternatingly modulated. The combined beam622is focused via lens624onto an optical element620which directs a pre-determined portion of the combined beam622in a direction normal to the target sample607, and the beam603reflecting off the target sample607is focused onto the optical element620via the lens626.

The beam605exiting the optical element620is focused onto the notch filter/polarizer619via lens628prior to entering into the spectrometer606.

In accordance with some embodiments of the present invention, the beam603reflecting off said target sample607is carrying some modulation due to the spectral reflectivity of the target sample607that is alternatingly modulated.

In accordance with some embodiments of the present invention, the second probe beam632is directed at an oblique angle of incidence onto the target sample607. The second probe beam632is focused onto the target sample607via lenses634and636, and the beam reflecting off the target sample607is focused via lenses638and640onto the second spectrometer642.

In accordance with some embodiments of the present invention, a photoreflectance (PR) spectroscopy system may comprise one of the photoreflectance (PR) spectroscopy apparatus400, the photoreflectance (PR) spectroscopy apparatus500and the photoreflectance (PR) spectroscopy apparatus600and a computer.

The photoreflectance (PR) spectroscopy apparatus400,500,600converts the “pump on” light beam and the “pump off” light beam to a “pump on” signal and a “pump off” signal and transfers the “pump on” signal and the “pump off” signal to a computer where the “pump on” signal corresponding to a spectrum (R) is subtracted from the “pump off” signal corresponding spectrum. (R+ΔR) to get a PR signal ΔR.

FIG.7illustrates a method700for measuring optical properties of a target sample via a combined OCD and photoreflectance system in accordance with some embodiments of the present invention.

The method700comprising the following steps:

Step702: providing one of the above-described combined OCD and photoreflectance systems ofFIGS.4-6;

Step704: focusing a single/multiple probe beam(s)404,632in a direction normal and/or oblique to a spot on a target sample407,507,607and a laser beam428that is alternatingly modulated onto said spot on the target sample407,507,607.

Alternatively, focusing a combined beam522,622comprised of a probe beam504,604and a laser beam513,613that is alternatingly modulated to a spot on said target sample407,507,607;

Step706: hitting a single spot on the target sample407,507,607via single/multiple probe beam(s)404,632and alternatingly hitting that single spot on the target sample407,507,607via the laser beam to alternatingly modulate the reflectivity of that spot on the target sample407,507,607.

Alternatively, synchronizing the spectrometer506,606with the modulator510,610and hitting the target sample507,607continuously via a combined beam522,622comprised of a modulated laser beam513,613and a probe beam504,604;

Step708: directing the single/multiple light beam(s) (corresponding to the single/multiple probe beam(s)) reflecting off the target sample407,507,607to at least one spectrometer406,506,606,642;

Step710: in case a combined beam522,622comprised of a probe beam504,604and a modulated laser beam513,613is used, filtering out the modulated laser beam513,613from the beam reflecting off the target sample507,607prior to reaching the spectrometer506,606;

Step712: converting the “pump on” light beam and the “pump off” light beam into a “pump on” signal and a “pump off signal and transferring the “pump on” signal and the “pump off signal to a computer; and

Step714: subtracting the “pump on” signal corresponding to a spectrum (R) from the “pump off” signal corresponding to a spectrum (R+ΔR) to get a PR signal ΔR.