Methods and systems for combining ocd with light reflection

Abstract

A system and method of combining OCD and light reflection for improving OCD performance in measurement of optical properties of a target sample. The system comprises: (a) a single-channel OCD setup comprising a single probe beam configured in a normal / oblique direction to the target sample, or a multi-channel OCD setup having multiple probe beams configured in normal and oblique directions to the target sample for measuring optical properties of the target sample, (b) at least one laser source for generating at least one laser beam, (c) at least one modulation device to convert the at least one laser beam into at least one alternating modulated laser beam; and (d) at least one spectrometer for measuring spectral components of the at least one laser beam reflected from the target sample; wherein the at least one alternating modulated laser beam alternately modulates spectral reflectance of the target sample.

Description

TECHNICAL FIELD

[0001] The present invention relates to semiconductor metrology techniques. More specifically, the present invention relates to semiconductor metrology techniques for measuring critical dimensions of devices by optical means. BACKGROUND

[0002] OCD (Optical Critical Dimension) is a subset of semiconductor metrology techniques used to measure critical dimensions of devices on-line by optical spectroscopic methods (most commonly spectroscopic ellipsometry or spectroscopic reflectometry).

[0003] Since the relevant dimensions of semiconductor devices are far below the diffraction limit of UV-visible light, optical microscopy cannot directly measure them. On the contrary, OCD is a model-based technique that works as follows:

[0004] - the spectrum of the structure to be analyzed is measured (preferably at multiple angles of incidence, polarizations, etc.);

[0005] - the parametric geometric model is built with enough degrees of freedom to closely represent the structure;

[0006] - the theoretical spectrum based on this model is calculated using detailed electromagnetic simulations; and

[0007] - the model parameters are iteratively changed until an optimal match between the theoretical and measured spectra is obtained.

[0008] For many years, OCD has been the main tool for on-line metrology in semiconductor fabs, as it has advantages over other techniques - it is fast, non-destructive, non-contact, and does not require vacuum or any other special sample handling. However, its main drawback lies in its indirect nature - the results are affected by the model fidelity, calculation errors, uncertainties in the optical system parameters and material optical properties. Some of these concerns can be mitigated by hardware and software improvements, but some are more fundamental.

[0009] The calculation of the theoretical spectrum from the model parameters is usually done by standard electromagnetic modeling engines (such as rigorous coupled wave analysis), however, the process of interpreting the measured data to infer the underlying structure parameters is very challenging. Its final performance (precision, accuracy) depends on the sensitivity of the spectrum to the parameters of interest and the correlation between the effects of different parameter variations on the spectrum. Parameters with weak spectral effects, or parameters whose spectral effects are highly similar to those caused by variations in other parameters, are poorly explained.

[0010] These problems increasingly plague OCD, directly related to the size reduction, geometry and material complexity increases encountered in advanced semiconductor technology nodes.

[0011] One such class of problems is related to the optical contrast of the structure - adjacent parts made of different but optically similar materials. As an example, consider for instance a low Ge concentration silicon-germanium thin film on silicon, the two materials can have very different physical (e.g. electrical) properties while having very similar optical dielectric constants. Then the spectrum will be weakly sensitive to the film thickness, essentially seeing the two materials as identical.

[0012] As another very common example, there is a need to characterize ultra-thin films deposited on some complex structures. It is often very difficult to separate the weak spectral sensitivity to this layer from the influence of other dimensional parameters (clearly much stronger).

[0013] It is therefore an object of the present invention to provide a system and method for in-line measurement of device critical dimensions. A system and method suitable for the size shrinkage and the increase in geometry and material complexity encountered in advanced semiconductor technology nodes. SUMMARY

[0014] The present invention provides a system and method for improving QCD performance in challenging applications. More specifically, the present invention provides a system and method for in-line measurement of device critical dimensions, a system and method combining QCD and photo-reflectance (PR) suitable for the size shrinkage and the increase in geometry and material complexity encountered in advanced semiconductor technology nodes.

[0015] According to some embodiments of the present invention, photo-reflectance (PR) spectroscopy provides a unique way to selectively change the sensitivity to different materials, thus emphasizing some parameters or breaking the correlation between parameters. There are two aspects to this:

[0016] - The PR response is strongly dependent on the material. For a given pump wavelength, some materials will experience PR while others are completely unaffected.

[0017] - The PR spectrum of a semiconductor is typically highly localized in frequency, with sharp features at the energies of the critical points of the band structure. This also helps to separate the contributions from different materials.

[0018] According to some embodiments of the present invention, there is thus provided a device combining OCD and photo-reflectance for improving OCD performance in the measurement of optical properties of a target sample. The device combining OCD and photo-reflectance comprises:

[0019] (a) a single-channel OCD setup comprising a single probe beam configured in a direction normal / oblique to the target sample, or a multi-channel OCD setup having multiple probe beams configured in a direction normal and oblique to the target sample, for measuring optical properties of the target sample in the normal direction and / or the oblique direction,

[0020] (b) at least one laser source for generating at least one laser beam;

[0021] (c) at least one modulation device to convert the at least one laser beam into at least one alternating modulated laser beam; and thus, to allow the alternating modulated laser beam to alternating modulate the spectral reflectivity of the target sample, so that the light beams reflected from the target sample are alternating "pump on" light beams and "pump off" light beams; and

[0022] (d) at least one spectrometer for measuring the spectral components of the at least one light beam reflected from the target sample; wherein the at least one light beam reflected from the target sample is directed into the at least one spectrometer, and wherein the at least one alternating modulated laser beam alternating modulates the spectral reflectivity of the target sample.

[0023] Further, according to some embodiments of the present application, the modulation device directly modulates the at least one laser source, or generates at least one modulated laser beam in the path of the at least one laser beam.

[0024] Further, according to some embodiments of the present application, the multi-channel OCD setup comprises a first probe light beam configured in a direction perpendicular to the target sample and a second probe light beam configured in a direction inclined to the target sample.

[0025] Further, according to some embodiments of the present application, the single / multi probe light beam and the laser beam are directed to hit a single spot on the target sample,

[0026] Further, according to some embodiments of the present application, the device combining OCD and light reflection further comprises an optical element directing a predetermined portion of at least one of the single probe light beam or the multi probe light beam onto the target sample.

[0027] Further, according to some embodiments of the present application, the optical element is selected from a beam splitter and a mirror.

[0028] Further, according to some embodiments of the present application, the device combining OCD and light reflection further comprises at least one optical means for focusing at least one of the single probe light beam or the multi probe light beam onto the optical element.

[0029] Further, according to some embodiments of the present application, the device combining OCD and light reflection further comprises at least one optical means for focusing at least one of the single probe light beam or the multi probe light beam onto the target sample.

[0030] Further, according to some embodiments of the present application, the OCD and light reflection combined device further comprises at least one optical member for focusing at least one of the single probe beam or the multiple probe beams onto the at least one optical spectrum meter.

[0031] Further, according to some embodiments of the present application, the OCD and light reflection combined device further comprises a combiner for combining at least one of the single probe beam or the multiple probe beams with the at least one alternating modulated laser beam into a single beam before hitting the target sample.

[0032] Further, according to some embodiments of the present application, the OCD and light reflection combined device further comprises a notch filter / polarizer for filtering out the modulated laser beam from the combined beam reflected from the target sample before entering the optical spectrum meter.

[0033] Further, according to some embodiments of the present application, the OCD and light reflection combined device further comprises an optical element for directing a predetermined portion of the combined beam onto the target sample.

[0034] Further, according to some embodiments of the present application, the optical element is selected from a beam splitter and a mirror.

[0035] Further, according to some embodiments of the present application, the OCD and light reflection combined device further comprises at least one optical member for focusing the combined beam onto the optical element.

[0036] Further, according to some embodiments of the present application, the OCD and light reflection combined device further comprises at least one optical member for focusing the combined beam onto the target sample.

[0037] Further, according to some embodiments of the present application, the OCD and light reflection combined device further comprises at least one optical member for focusing the combined beam into the notch filter / polarizer.

[0038] Further, according to some embodiments of the present application, there is provided a system for combining OCD and light reflection for improving OCD performance in optical property measurement of a target sample and for calculating photo-induced changes in optical properties of a target sample. The system for combining OCD and light reflection comprises the above-mentioned OCD and light reflection combined device, wherein the OCD and light reflection combined device converts the "pump-on" beam and the "pump-off" beam into "pump-on" signal and "pump-off" signal and transmits the "pump-on" signal and the "pump-off" signal to a computer for subtracting the "pump-on" signal corresponding to spectrum (R) from the "pump-off" signal corresponding to spectrum (R+AR) to obtain the PR signal AR.

[0039] Further, according to some embodiments of the present application, there is thus provided a method for measuring and calculating the photo-induced changes in the optical properties of a target sample, of combined OCD and light reflection, the method comprising:

[0040] (a) providing a system of combined OCD and light reflection as described above;

[0041] (b) focusing a single / multiple probe beam and a laser beam alternately modulated onto a spot on the target sample in a direction perpendicular and / or inclined to the spot on the target sample, or focusing a combined beam consisting of a probe beam and a laser beam alternately modulated onto the spot on the target sample;

[0042] (c) hitting the spot on the target sample by one of the single / multiple probe beam and the alternately modulated laser beam or by the combined beam, to alternately modulate the reflectivity of the target sample, thereby causing "pump-on" and "pump-off" beams to alternately reflect from the target sample;

[0043] (d) directing the single / multiple beam or the combined beam comprising the probe beam and the modulated laser beam reflected from the target sample to at least one spectrometer;

[0044] (e) filtering out the modulated laser beam from the combined beam reflected from the target sample before reaching the at least one spectrometer;

[0045] (f) converting the "pump-on" and "pump-off" beams to "pump-on" and "pump-off" signals and transmitting the "pump-on" and "pump-off" signals to a computer; and

[0046] (g) subtracting the "pump-on" signal corresponding to the spectrum (R) from the "pump-off" signal corresponding to the spectrum (R+AR) to obtain the PR signal AR,

[0047] Further, according to some embodiments of the present application, the method of combined OCD and light reflection further comprises synchronizing the at least one spectrometer with the modulation device when using the combined beam. BRIEF DESCRIPTION OF DRAWINGS

[0048] Figure 1 is an example of a PR spectrum of silicon in the range of 320 nm to 400 nm.

[0049] Figure 2 (SROCD device with a normal incidence channel for measuring the optical properties of a target sample.

[0050] Figure 3 A multi-channel OCD device with a normal incidence channel and an oblique incidence channel for measuring optical properties of a target sample is shown.

[0051] Figure 4 A spectroscopy device combining OCD and photo-reflectance (PR) according to some embodiments of the application is shown.

[0052] Figure 5 An optional spectroscopy device combining OCD and photo-reflectance (PR) according to some embodiments of the application is shown.

[0053] Figure 6 A spectroscopy device combining OCD and photo-reflectance (PR) for measuring optical properties of a target sample by 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 to the target sample according to some embodiments of the application is shown.

[0054] Figure 7 A method for measuring optical properties of a target sample via a system combining OCD and photo-reflectance according to some embodiments of the application is shown. DETAILED DESCRIPTION

[0055] Figure 1 is an example of PR spectrum of silicon from 320 nm to 400 nm.

[0056] According to some embodiments of the application, it appears beneficial to make the PR measurement channel work with the standard OCD, measuring the target sample at the same time and location, in order to provide complementary spectral information. These information can be used in several ways:

[0057] - Model-based - incorporate a theoretical model of the PR response in the spectral calculations. Such modeling can take into account various relevant effects, such as thermal reflection, electrical reflection, magnetic reflection, and even take into account excitation and diffusion of charge carriers, band structure and influence of light on the band structure, nonlinear response, etc.

[0058] - In some simple cases, such as thin films, the response at specific wavelengths can be directly related to the film thickness, absorption or refractive index.

[0059] In more complex cases, machine learning algorithms trained on controlled reference data can be used and would benefit from the increase in PR sensitivity.

[0060] The appeal of this approach also comes from the synergy between the two methods. The broadband spectral measurement channel of the OCD tool is well suited as a probe in the PR system. To complete the system, a modulated pump beam needs to be inserted in the optical path and synchronized with the spectral acquisition electronics.

[0061] However, some details need to be considered to make it work. One of the issues is the noise problem. One of the challenges of PR is the relatively small modulation of reflectivity , which requires reflectance measurements at very high signal to noise ratio (SNR) of the order of 10 5-6 . This is especially true in the case of integration with a QCD system, which has a SNR typically of the order of 10 3-4 and requires measurements in less than 1 second to maintain a reasonable throughput. If PR is part of the OCD measurement, it should also meet similar requirements.

[0062] A possible solution to this problem is to use a high brightness light source, such as a supercontinuum laser (SCL) or some type of laser driven plasma source, without completely redesigning the OCD system.

[0063] As a general order of magnitude, to achieve a shot noise limited SNR of 10 5 , it is required that each pixel in the sensor accumulates > 10 10 photoelectrons (i.e. more than 10 3-4 times the light in a similar acquisition time than a typical OCD measurement). To achieve this in 1 s, the product of the frame rate and the full well capacity (FWC) is of the order of 10 10 e - / s.

[0064] The practical values based on current sensors and electronics are frame rates of the order of 10 2-3 FPS and FWC of 10 7-8 e - . This can be achieved with linear array CCDs. Combining this type of acquisition system with a high brightness source such as a SCL can meet the SNR and throughput requirements.

[0065] Another issue in PR spectroscopy is the contamination of the probe beam by the brighter pump beam, either directly or through stray light. In this case, a key parameter of the OCD tool design is the number of angles of incidence (AOI), which can be of two main types:

[0066] - Normal incidence channel: usually present in integrated metrology tools that need to have a small footprint. A single objective provides both illumination and collection.

[0067] - Multi-channel (normal and oblique incidence channels): Typically found in standalone metrology tools. Separate objectives are used for oblique illumination and collection of the reflected beam.

[0068] Depending on the system design, there are several ways to achieve the focusing of the pump and probe beams on the target sample:

[0069] - Non-collinearity: The most straightforward way to separate the pump and probe beams is to use different AOI, separating them geometrically in the detector plane, as shown in Figure 4 This requires matching the focal points and lines of sight of the two beams.

[0070] - In multi-channel tools, this can be achieved by using one channel (normal or oblique) as the pump beam and the other as the probe beam.

[0071] Alternatively, the pump light can be inserted obliquely from outside the objective in a normal-only design. However, this requires more substantial modifications to the system to accommodate.

[0072] Another option is to use a normal channel with a large-NA objective and illuminate only the central part of the entrance pupil with the probe beam and the outer ring with the pump beam, enabling easy separation in the collection channel by using a suitable aperture.

[0073] - Collinearity: Combining the pump and probe into a collinear beam has some advantages, such as eliminating the need for focusing and foresight alignment of two channels, as shown in Figure 5 and Figure 6 However, this requires separating them in other ways, such as:

[0074] • Polarization: The pump and probe beams can be orthogonally polarized, so that the polarization in the collection channel will prevent the pump beam from reaching the detector.

[0075] • Spectrally: If the pump WL is far enough from the region of interest in the probe spectrum, it can be separated by a dispersive element in or before the spectrometer, or if the pump wavelength is outside the measured spectral range, it will not be directly probed.

[0076] • Temporally: The probe beam itself can be modulated at a different frequency, so the PR signal is recovered by the LID at the frequencies of the pump and probe modulations, while suppressing the pump itself and other artifacts related to it, such as photoluminescence.

[0077] The pump beam can be selected or controlled in several ways to change the performance:

[0078] - Wavelength: Different wavelengths will affect the material differently, depending on its band structure and occupancy level, thus selectively enhancing sensitivity to different materials in the structure.

[0079] - Intensity: PR is usually nonlinear, as the generated charge carriers affect the band structure, which in turn changes the absorption of more photons. By varying the intensity of the pump beam, one can probe these nonlinearities, providing information about, for example, charge carrier lifetime, charge trapping, and defects.

[0080] - Polarization: Changing the pump polarization can change the absorption profile of the pump beam, highlighting different parts of the structure.

[0081] - Repetition rate and illumination spot: Since charge carriers are mobile, they diffuse out of the pump spot in a manner that depends on their lifetime, mean free path, effective mass, etc. Changing the temporal and spatial mode of the pump illumination will affect the PR response in a manner that depends on these physical parameters. In addition, when the repetition frequency is comparable to the lifetime of the excited charge carriers, the PR signal becomes strongly dependent on the specific repetition frequency.

[0082] Of course, proper selection of the "probe" path characteristics (wavelength range, degree of polarization, AOI, etc.) will determine the metrology benefits of this approach - parameter sensitivity, correlation, and overall performance.

[0083] Figure 2 The prior art shows an SROCD device 200 having a normal incidence channel for measuring optical properties of a target sample.

[0084] According to some embodiments of the present application, the OCD device 200 is configured for measuring optical properties of a target sample 208 by a probe beam 204 configured in a direction normal to the target sample 208.

[0085] The OCD device 200 comprises a probe source 202 for generating the probe beam 204, and a spectrometer 206 for measuring spectral components of the beam reflected from the target sample 208. The OCD device 200 further comprises optical elements 210, such as beam splitters, mirrors, etc., and a plurality of lenses, e.g., lens 212, lens 214, and lens 216.

[0086] The optical elements 210 direct the probe beam 204 onto the target sample 208, and direct the beam reflected from the target sample 208 to the spectrometer 206.

[0087] According to some embodiments of the present application, lens 212 focuses probe beam 204 onto optical element 210, lens 214 is a single objective lens, lens 216 focuses the light beam exiting optical element 210 into spectrometer 206 while simultaneously acting as an illumination and collection lens when it focuses the light beam exiting optical element 210 onto target sample 208 and focuses the light beam reflected from target sample 208 onto optical element 210.

[0088] Thus, when in operation, probe source 202 generates a continuous probe beam 204 which is focused via lens 212 onto optical element 210. Optical element 210 directs a predetermined portion of probe beam 204 via lens 214 to target sample 208, the light beam reflected from target sample 208 is focused via lens 214 onto optical element 210 and the light beam exiting optical element 210 is focused via lens 216 into spectrometer 206.

[0089] Thus, when in operation, probe source 202 generates a continuous probe beam 204 which is focused via lens 212 onto optical element 210. Optical element 210 directs a predetermined portion of probe beam 204 to target sample 208 and the light beam reflected from target sample 208 is focused via lens 214 onto optical element 210 and via lens 216 into spectrometer 206.

[0090] Figure 3 (Background Art) shows a multi-channel OCD device 300 having a normal incidence channel and an oblique incidence channel for measuring optical properties of a sample.

[0091] According to some embodiments of the present application, multi-channel OCD device 300 includes a first probe beam 302 configured in a direction normal to target sample 330 and a second probe beam 306 configured at an oblique incidence angle on target sample 330 for measuring optical properties of the sample by a combined OCD and light reflection system according to some embodiments of the present application.

[0092] According to some embodiments of the present application, separate objective lenses are used for oblique illumination and collection of the reflected light beam.

[0093] OCD device 300 further includes first and second spectrometers 310 and 312 for measuring spectral components of the light beam reflected from target sample 330, optical elements 314 such as beam splitters, mirrors and the like and a plurality of focusing means such as lenses 316, 318, 320, 322, 324, 326 and 328.

[0094] As shown, the optical element 314 directs the probe beam 304 in a direction normal to the target sample 330 and directs the light beam reflected from the target sample 330 to the first spectrometer 310, the lens 316 focuses the probe beam 304 to the optical element 314, the lens 320 focuses the light beam exiting the optical element 314 to the first spectrometer 310, and the lens 318 is a single objective that simultaneously functions as an illumination and collection when it focuses the light beam exiting the optical element 314 to the target sample 330 and focuses the light beam reflected from the target sample 330 to the optical element 314.

[0095] The second probe source 306 generates a second probe beam 308 that is directed at an oblique angle of incidence onto the target sample 330. The second probe beam 308 is focused onto the target sample 330 via lenses 322 and 324, and the light beam reflected from the sample 330 is focused onto the second spectrometer 312 via lenses 326 and 328.

[0096] Thus, when in operation, the first probe source 302 and the second probe source 306 continuously generate the continuous probe beams 304 and 308. The probe beam 304 is focused onto the optical element 314 via the lens 316. The optical element 314 directs a predetermined portion of the probe beam 304 in a direction normal to the target sample 330, and the light beam reflected from the target sample 330 is focused onto the optical element 314 via the lens 318 and into the first spectrometer 210 via the lens 320.

[0097] The second probe beam 308 is directed at an oblique angle of incidence onto the target sample 330. The second probe beam 308 is focused onto the target sample 330 via lenses 322 and 324, and the light beam reflected from the sample 330 is focused onto the second spectrometer 312 via lenses 326 and 328.

[0098] Since the spectral reflectivity of a material is closely related to electronic properties such as band structure, state density, free carriers, etc., modulation spectroscopy (MS) is more sensitive to these properties than other optical spectroscopy methods. This can be of high value when electrical testing of semiconductor devices needs to be performed at early stages of their manufacturing process, for which conventional electrical testing is not feasible.

[0099] The following figure shows a combined OCD and photo reflectance (PR) system suitable for the size reduction and the increase of geometrical and material complexity encountered in advanced semiconductor technology nodes, according to some embodiments of the application.

[0100] Figure 4 A spectroscopy apparatus 400 for combined OCD and photo reflectance (PR) according to some embodiments of the application is shown.

[0101] The OCD setup includes a probe source 402 for generating a probe beam 404 and a spectrometer 406 for measuring spectral components of the light beam reflected from the target sample 407. The OCD setup also includes optical elements 408, such as beam splitters, mirrors, etc., and focusing means, such as a lens 410, a lens 412, and a lens 414, for focusing the probe beam 404 to the optical elements 408, for focusing the light beam leaving the optical elements 408 to the target sample 407, and for focusing the light beam reflected from the target sample 407 to the spectrometer 406, respectively. The lens 412 is a single objective that both illuminates and collects when it focuses the light beam leaving the optical elements 408 to the target sample 407 and focuses the light beam reflected from the target sample 407 to the optical elements 408.

[0102] According to some embodiments of the present application, the photo-reflectance (PR) spectroscopy setup includes a pump laser 418, a modulator 420 in the path of the laser beam 422, and at least one optical means, such as a lens 424 and a lens 426, for focusing the modulated laser beam 428 to the target sample 407.

[0103] According to some embodiments of the present application, the laser beam 422 is modulated so as to alternately modulate the reflectivity of the sample 407, thereby having "pump-on" and "pump-off" light beams reflected from the sample 407.

[0104] According to some embodiments of the present application, the laser beam 422 can be attenuated electronically or via appropriate attenuating optical filters, e.g., mechanically removable into / from the optical path of the pump beam and / or based on electro-optical devices, etc.

[0105] When in operation, the probe source 402 generates a continuous probe beam 404, which is focused via the lens 410 to the optical elements 408. The optical elements 408 direct a predetermined portion of the probe beam 404 to the target sample 407, and the light beam reflected from the target sample 407 is focused via the lens 412 to the optical elements 408 and via the lens 414 to the spectrometer 406.

[0106] According to some embodiments of the present application, the modulator 420 alternately directs the pump beam 422 to the target sample 407 and thus alternately modulates the reflectivity of the target sample 407.

[0107] Thus, according to some embodiments of the present application, there are two modes in the measurement, one when the modulated laser beam 428 reaches the target sample 407 and the other when the modulated laser beam 428 is off.

[0108] When the laser beam 422 reaches the target sample 407, the light beam reflected from the target sample 407 is a "pump-on" light beam, and when the laser beam 422 is turned off, the light beam reflected from the target sample 407 is a "pump-off" light beam.

[0109] Thus, this combined OCD and photo-reflectance (PR) spectroscopy apparatus 400 allows to alternately measure (a) the spectral reflectance of the target sample 407, and (b) the modulated reflectance of the target sample 407, e.g., as a change in the spectrum in response to the perturbation, rather than the spectrum itself.

[0110] Figure 5 An alternative combined OCD and photo-reflectance (PR) spectroscopy apparatus 500 according to some embodiments of the present application is shown.

[0111] In comparison to the apparatus shown and described in Figure 4 The alternative combined OCD and photo-reflectance (PR) spectroscopy apparatus 500 is more compact than the apparatus shown and described in

[0112] According to some embodiments of the present application, the alternative combined OCD and photo-reflectance (PR) spectroscopy apparatus 500 comprises a probe source 502 for generating a probe light beam 504, and a spectrometer 506 for measuring the spectral components of the light beam reflected from a target sample 507. The alternative combined OCD and photo-reflectance (PR) spectroscopy apparatus 500 further comprises a pump laser 508, a modulator 510 in the laser light beam path 512, a combiner 514, a notch filter / polarizer 516, and electronics 518.

[0113] According to some embodiments of the present application, the laser light beam 512 is modulated so as to alternately modulate the reflectance of the target sample 507, thereby having "pump-on" and "pump-off" light beams reflected from the target sample 507.

[0114] The alternative combined OCD and photo-reflectance (PR) spectroscopy system 500 further comprises an optical element 520 for directing a predetermined portion of the combined light beam 522 onto the target sample 507, and a plurality of optical members such as a lens 524, a lens 526, and a lens 528 for focusing the combined light beam onto the optical element 520, onto the target sample 507, and into the notch filter / polarizer 516, respectively.

[0115] In comparison to the apparatus shown and described in Figure 4The system 400 of OCD and photo reflectance (PR) spectroscopy differs from the system 400 of FIG. 1 in that it uses two separate beams, a probe beam and a pump laser beam, that are directed to hit a single spot on the target sample, where the probe beam 504 and the pump laser beam 512 are combined into an alternating modulated single beam.

[0116] The pump laser beam 512 is modulated via the modulator 510, and the modulated laser beam 513 is combined with the probe beam 504 via the combiner 514 to produce an alternating modulated combined beam 522.

[0117] The alternating modulated combined beam 522 is focused via the lens 524 onto the optical element 520, which directs a predetermined portion of the alternating modulated combined beam 522 in a direction perpendicular to the target sample 507.

[0118] According to some embodiments of the present application, the beam reflected from the target sample 507 is focused via the lens 526 onto the optical element 520, and the beam 505 exiting the optical element 520 is focused via the lens 528 onto the notch filter / polarizer 516 before entering the spectrometer 506.

[0119] The notch filter / polarizer 516 is used to filter out the modulated laser beam 513 from the combined beam reflected from the target sample 507 to avoid damage to the spectrometer 506.

[0120] According to some embodiments of the present application, the electronics 518 are used to synchronize the modulator 510 and the spectrometer 506.

[0121] Figure 6 A combined OCD setup and photo reflectance (PR) spectroscopy apparatus 600 is shown for measuring optical properties of a target sample by a first probe beam configured at a normal to the target sample and a second probe beam configured at an oblique angle of incidence to the target sample, according to some embodiments of the present application.

[0122] The combined OCD setup and photo reflectance (PR) spectroscopy apparatus 600 comprises Figure 5 The combined OCD setup and photo reflectance (PR) spectroscopy 500 and the additional OCD setup having a probe beam configured to hit the target sample at an oblique angle of incidence.

[0123] The combined OCD and photo reflectance (PR) spectroscopy apparatus 600 is compact and can be suitable for use in a limited size space, such as in semiconductor manufacturing equipment, such as a coating apparatus.

[0124] According to some embodiments of the application, the spectroscopy device 600 combining OCD and photo reflectance (PR) includes a first probe source 602 for generating a first probe beam 604 and a first spectrometer 606 for measuring spectral components of the light beam reflected from the target sample 607.

[0125] The spectroscopy device 600 combining OCD and photo reflectance (PR) further includes a pump laser 608, a modulator 610 in the path of the laser beam 612, a combiner 614 for combining the first probe beam 604 with the modulated laser beam 613 into a combined beam 622, electronics 618 and a notch filter / polarizer 619.

[0126] According to some embodiments of the application, the laser beam 612 is modulated so as to alternately modulate the reflectivity of the target sample 607, thereby having "pump-on" and "pump-off" beams reflected from the target sample 607.

[0127] According to some embodiments of the application, the electronics 618 are used for synchronizing the modulator 610 and the spectrometer 606.

[0128] The spectroscopy device 600 combining OCD and photo reflectance (PR) further includes an optical element 620 for directing a predetermined portion of the combined beam 622 onto the target sample 607, and a plurality of optical members such as a lens 624, a lens 626 and a lens 628 for focusing the combined beam separately onto the optical element 620, onto the target sample 607 and into the notch filter / polarizer 619 before entering the first spectrometer 606. As in the spectroscopy device 500 of OCD and photo reflectance (PR) of Figure 5 In the spectroscopy device 500 of OCD and photo reflectance (PR), the probe beam 604 and the modulated laser beam 613 are combined into a single combined beam 622 which is alternately modulated.

[0129] The alternately modulated combined beam 622 is focused via the lens 624 onto the optical element 620 which directs a predetermined portion of the alternately modulated combined beam 622 perpendicular to the direction of the target sample 607.

[0130] According to some embodiments of the application, the light beam reflected from the target sample 607 is focused via the lens 626 onto the optical element 620, and the light beam 605 exiting the optical element 620 before entering the spectrometer 606 is focused via the lens 628 onto the notch filter / polarizer 619.

[0131] The notch filter / polarizer 619 is used for filtering out the modulated laser beam 613 from the light beam 605 to avoid damage to the spectrometer 606.

[0132] According to some embodiments of the application, the second probe source 630 generates a second probe beam 632 directed at an oblique angle of incidence onto the target sample 607. The second probe beam 632 is focused onto the target sample 607 via lenses 634 and 636, and the light beam reflected from the target sample 607 is focused onto the second spectrometer 642 via lenses 638 and 640.

[0133] Accordingly, when in operation, the first probe source 602 and the second probe source 630 continuously generate the continuous probe beams 604 and 632. The probe beam 604 and the modulated laser beam 613 are combined into the alternating modulated combined beam 622. The combined beam 622 is focused onto the optical element 620 via lens 624, which directs a predetermined portion of the combined beam 622 perpendicular to the direction of the target sample 607, and the light beam 603 reflected from the target sample 607 is focused onto the optical element 620 via lens 626.

[0134] The light beam 605 exiting the optical element 620 is focused onto the notch filter / polarizer 619 via lens 628 before entering the spectrometer 606.

[0135] According to some embodiments of the application, the light beam 603 reflected from the target sample 607 carries some modulation due to the alternating modulation of the spectral reflectivity of the target sample 607.

[0136] According to some embodiments of the application, the second probe beam 632 is directed at an oblique angle of incidence onto the target sample 607. The second probe beam 632 is focused onto the target sample 607 via lenses 634 and 636, and the light beam reflected from the target sample 607 is focused onto the second spectrometer 642 via lenses 638 and 640.

[0137] According to some embodiments of the application, the photo-reflectance (PR) spectroscopy system can include a computer and one of the photo-reflectance (PR) spectroscopy device 400, the photo-reflectance (PR) spectroscopy device 500, and the photo-reflectance (PR) spectroscopy device 600.

[0138] The photo-reflectance (PR) spectroscopy devices 400, 500, 600 convert the "pump-on" beam and the "pump-off" beam into a "pump-on" signal and a "pump-off" signal, and transmit the "pump-on" signal and the "pump-off" signal to the computer, in which the "pump-on" signal corresponding to the spectrum (R) is subtracted from the "pump-off" signal corresponding to the spectrum (R+△R) to obtain the PR signal △R.

[0139] Figure 7 A method 700 for measuring optical properties of a target sample via a combined OCD and photo-reflectance system according to some embodiments of the application is shown.

[0140] The method 700 comprises the following steps:

[0141] Step 702: providing one of the systems of the above Figures 4 to 6 combination of OCD and light reflection;

[0142] Step 704: focusing the single / multiple probe beams 404, 632 and the laser beams 428 that are alternately modulated onto the spots on the target sample 407, 507, 607 in the direction perpendicular and / or inclined to the spots on the target sample 407, 507, 607.

[0143] Or, focusing the combined beams 522, 622 composed of the probe beams 504, 604 and the laser beams 513, 613 that are alternately modulated onto the spots on the target sample 407, 507, 607;

[0144] Step 706: hitting a single spot on the target sample 407, 507, 607 by the single / multiple probe beams 404, 632, and hitting the single spot on the target sample 407, 507, 607 by the laser beams alternately to modulate the reflectivity of the spot on the target sample 407, 507, 607.

[0145] Or, synchronizing the spectrometer 506, 606 with the modulator 510, 610 by the combined beams 522, 622 composed of the modulated laser beams 513, 613 and the probe beams 504, 604, and continuously hitting the target sample 507, 607;

[0146] Step 708: directing the single / multiple beams reflected from the target sample 407, 507, 607 (corresponding to the single / multiple probe beams) to at least one spectrometer 406, 506, 606, 642;

[0147] Step 710: in the case of using the combined beams 522, 622 composed of the probe beams 504, 604 and the modulated laser beams 513, 613, filtering out the modulated laser beams 513, 613 from the beams reflected from the target sample 507, 607 before reaching the spectrometer 506, 606;

[0148] Step 712: converting the “pump-on” beams and the “pump-off” beams into “pump-on” signals and “pump-off” signals, and transmitting the “pump-on” signals and the “pump-off” signals to the computer; and

[0149] Step 714: Subtract the "pump on" signal corresponding to the spectrum (R) from the "pump off" signal corresponding to the spectrum (R+△R) to obtain the PR signal, AR.

Claims

1. A method of combining OCD and light reflection for measuring and calculating photo-induced changes in optical properties of a target sample, the method of combining OCD and light reflection comprising: (a) providing a system of combining OCD and light reflection; (b) focusing a single / multiple probe beam and a laser beam modulated alternately onto a spot on the target sample in a direction perpendicular and / or tilted to the spot on the target sample or focusing a combined beam consisting of a probe beam and the laser beam modulated alternately onto the spot on the target sample by the probe beam / the multiple probe beam and the laser beam modulated alternately or by the combined beam; (c) hitting the spot on the target sample by the single / multiple probe beam and the laser beam modulated alternately or by the combined beam to modulate reflectivity of the target sample alternately, so that "pump on" and "pump off" beams are alternately reflected from the target sample; (d) directing the single / multiple beam or the combined beam comprising a probe beam and a modulated laser beam reflected from the target sample to at least one spectrometer; (e) filtering out the modulated laser beam from the combined beam reflected from the target sample before reaching the at least one spectrometer; (f) converting the "pump on" and "pump off" beams into "pump on" and "pump off" signals and transmitting the "pump on" and "pump off" signals to a computer; and (g) subtracting the "pump on" signal corresponding to spectrum R from the "pump off" signal corresponding to spectrum R+AR to obtain a PR signal AR.

2. The method of combining OCD and light reflection according to claim 1, further comprising synchronizing the at least one spectrometer with a modulation device when using the combined beam.

3. An apparatus of combining OCD and light reflection, the apparatus for performing the method of combining OCD and light reflection according to any one of claims 1-2.

4. A system of combining OCD and light reflection, the system for improving OCD performance in measurement of optical properties of a target sample and for calculating photo-induced changes in the optical properties of the target sample, the system of combining OCD and light reflection comprising a computer and the apparatus of combining OCD and light reflection recited in claim 3.

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