Defect inspection and photoluminescence measurement system

A system for defect detection and photoluminescence measurement of a sample may include a radiation source configured to target radiation to the sample. The system may also include an optics assembly positioned above the sample to receive a sample radiation. The system may also include a filter module configured to receive the sample radiation collected by the optics assembly. The filter module may separate the sample radiation collected by the optics assembly into a first radiation portion and a second radiation portion. The system may also include a defect detection module configured to receive the first radiation portion from the filter module. The system may further include a photoluminescence measurement module configured to receive the second radiation portion from the filter module. The defect detection module and the photoluminescence measurement module may be configured to receive the respective first radiation portion and the second radiation portion substantially simultaneously.

FIELD

The present disclosure generally relates to the field of inspection systems, and more particularly to a defect inspection and photoluminescence measurement system.

BACKGROUND

Adequately monitoring performance of deposition processes used during electronics production (e.g., high-brightness LED production) is important to ensuring the quality of and consistency of a relatively time-intensive procedure. Various ex-situ processes may be utilized, including photoluminescence (PL) mapping and defect inspection. Under specific excitation conditions, the local photoluminescence spectrum may be indicative of what the emission spectrum will be of an LED from the measured region of a wafer once made into a device. Measured non-uniformity of a PL peak wavelength may be traced to various process conditions, including temperature variations or gradients, which may be utilized to correct undesired process conditions.

Defect inspection may be utilized to detect and monitor various defects in the wafer, including sizes/types of surface imperfections, particles, irregularities in the thickness of epi-layers, and the like, which may hamper the performance of the semiconductor material. Defect inspection may be utilized subsequent to deposition techniques, and therefore the results of a defect inspection may be utilized to detect a defect relatively early in a manufacturing process prior to assembly of a finished product.

Currently, in order to perform both PL mapping and defect detection, two separate platforms are utilized. Such a configuration presents undesired consequences including the costs associated with owning/maintaining two separate platforms, multiple steps of handling a wafer (which increases the risk of contamination to the wafers), difficulty in correlating the separate data from the separate platforms, and the time and costs associated with performing two separate monitoring techniques.

It is therefore desirable to provide a defect inspection and photoluminescence measurement system which addresses the above-mentioned limitations of using two separate platforms, sequentially or otherwise. In addition, it is desirable to provide a defect inspection and photoluminescence measurement system such that the combination of scatter data and PL data taken at the same high resolution may enable a new level of characterization and understanding of certain defect types (e.g. those relevant to the fabrication of high-brightness LEDs).

SUMMARY

A system for defect detection and photoluminescence measurement of a sample may include, but is not limited to, a radiation source configured to target radiation to the sample. The system may also include an optics assembly positioned above the sample to receive a sample radiation. The sample radiation may be radiation which is at least one of reflected by, scattered by, or radiated from the sample, the optics assembly configured to reflect and/or refract the sample radiation. The system may also include a filter module configured to receive the sample radiation reflected or refracted by the optics assembly. The filter module may separate the sample radiation reflected and/or refracted by the optics assembly into a first radiation portion and a second radiation portion. The system may also include a defect detection module configured to receive the first radiation portion from the filter module. The system may further include a photoluminescence measurement module configured to receive the second radiation portion from the filter module. The defect detection module and the photoluminescence measurement module may be configured to receive the respective first radiation portion and the second radiation portion substantially simultaneously.

A method for detecting defects and measuring photoluminescence of a sample may include, but is not limited to irradiating the sample, collecting radiation from the sample, the collected radiation including radiation which is at least one of reflected by, scattered by, or radiated from the sample, filtering the collected radiation between a first radiation portion and a second radiation portion, passing the first radiation portion to a defect detection module, passing the second radiation portion to a photoluminescence measurement module, and analyzing the first radiation portion and the second radiation portion substantially simultaneously.

A method for detecting defects and measuring photoluminescence of a sample may include, but is not limited to irradiating the sample, collecting radiation from the sample, the collected radiation including radiation which is at least one of reflected by, scattered by, or radiated from the sample, filtering the collected radiation between a first radiation portion and a second radiation portion, passing the first radiation portion to a defect detection module, passing the second radiation portion to a photoluminescence measurement module, detecting a scattered defect in at least one of the first radiation portion or the second radiation portion, identifying a site of interest on the sample according to the scattered defect and measuring a spectral photoluminescence of the site of interest.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not necessarily restrictive of the disclosure as claimed. The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the disclosure and together with the general description, serve to explain the principles of the disclosure.

DETAILED DESCRIPTION

Reference will now be made in detail to the presently preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.

Referring now toFIG. 1, a schematic illustration of one embodiment of a system100for defect inspection and photoluminescence (PL) measurement of a wafer sample102is shown. The system100may include a radiation source104configured to target radiation to the wafer102. In the embodiment shown inFIG. 1, the radiation source104may generate an oblique input laser beam104a, which may be directed at the sample of interest102(e.g. an epi wafer after MOCVD deposition) under a light collector108of the optics assembly106. The optics assembly106may be a reflective or refractive objective configured to receive wafer radiation, where the wafer radiation may include radiation which is at least one of reflected by, scattered by, or radiated from the wafer102. For example, a portion110of the input laser beam104amay reflect from the top surface of the wafer102, a portion111aof the input laser beam104amay be scattered from the top surface of the wafer102into the light collector108(another scattered portion111bis described below), and a portion111cmay be absorbed and reemitted/radiated (photoluminescence (PL)) by the active structure (e.g. a multi-quantum well (MQW)) or any other fluorescence properties of the sample102under test. The reflected portion110of the radiation may be used to provide information on the reflectivity, slopes, or defects of the sample surface102. The scattered and reemitted/radiated portions (111a,111b, and111c) may be collected by the optics assembly106of system100to provide defect detection, classification, and photoluminescence measurement data.

As shown inFIG. 1, the radiation source104may be configured to target an incident laser beam112, which may be sent at substantially normal incidence to the sample102. For instance, the incident laser beam112may utilize the optical assembly106to direct the incident laser beam112substantially normal to the wafer102. The incident laser beam112may also reflect, scatter, and radiate from the sample102. The scattered portion111bof the incident laser beam112is shown inFIG. 1. In one embodiment, the incident laser beam112has a wavelength longer than a wavelength of the oblique input laser beam104a. For instance, in one particular embodiment, the radiation source104is configured to generate the oblique input laser beam104aat approximately 405 nm and is configured to generate the normally incident laser beam112at approximately 660 nm. It may be appreciated that radiation of other wavelengths may be utilized without departing from the scope of the present disclosure. At least a portion of at least one of the scattered, reflected, or radiated portion of the incident laser beam112may enter the light collector108of the optics assembly106. For example, the scattered portion111bmay be collected by the light collector108of the optics assembly106. As shown inFIG. 1, the scattered portion111bmay be collected substantially simultaneously with the scattered portion111aof the input laser beam104aand with the PL portion111cof the input laser beam104a.

The light collector108ofFIG. 1may be of the finite conjugate type, and thus the collected light111a,111b, and111c(scattered portions of the oblique input laser beam104aand the normally incident laser beam112, as well as photoluminescence from the sample102) may be diverged to a set of optics and detectors that perform the photoluminescence measurement and the scattered light detection at a plurality of laser wavelengths. A finite conjugate type collector may be used so that a pinhole (or field stop) may be placed at the back focal position of the collector. In this case the pinhole would be placed in beam path120just beyond filter116and in beam path128just to the left of filter116. The pinhole or slit serves as a spatial filter to remove scattered light whose origin is not from light which is scattered by the surface102. For instance, stray light from the laser source104or light scattered from the inside or the backside of sample102. The optics assembly106may further be configured to reflect or refract the wafer radiation to a set of optics and detectors, as described below.

The system100may include a filter module114configured to receive the wafer radiation (e.g., the collected light111a,111b, and111c) reflected and/or refracted by the optics assembly106. The filter module114may be configured to separate the wafer radiation into a first radiation portion and a second radiation portion. The filter module114may include a first filter116and a second filter118. In one particular embodiment, the first filter116and the second filter118are dichroic beamsplitters configured to pass light of specified wavelengths while reflecting light other than the specified wavelengths. The wafer radiation collected by the light collector108and reflected and/or refracted may impinge on the first filter116. The first filter116may pass a majority of the portion of light120corresponding to the scattered light from the incident laser beam112to a defect detection module122. For instance, in a particular embodiment, the portion of light120may be approximately 660 nm. The defect detection module122may be configured to receive light scattered from the wafer sample102to detect and monitor various defects in the wafer, including sizes/types of surface imperfections, particles, irregularities in the thickness of epi-layers, and the like, which may hamper the performance of the semiconductor material. In the embodiment shown inFIG. 1, the defect detection module122includes a first light detector124and a second light detector126. In a particular embodiment, the first light detector124and the second light detector126are scattered light detectors, such as photomultiplier tubes. The first filter116may reflect a majority of the portion of light128corresponding to both the scattered light from the oblique input laser beam104aand the photoluminescence from the wafer subsequent to application of the oblique input laser beam104a. For instance, in a particular embodiment, the portion of light128may have a wavelength of less than approximately 650 nm.

The portion of light128may impinge on second filter118, as shown inFIG. 1. The second filter118may reflect a majority of the portion of light130corresponding to the scattered light from the oblique input laser beam104a, which may be sent to second light detector126. For instance, in a particular embodiment, the portion of light130may be approximately less than 410 nm. The second filter118may pass the portion of light132originating from photoluminescence by the wafer sample102. For instance, in a particular embodiment, the portion of light132may be between approximately 650 nm and 415 nm. Thus, where the filter module114includes the first filter116and the second filter118, the filter module may be configured to separate the wafer radiation (e.g.,111a,111b, and111c) into a first radiation portion comprised of light portions120and130and a second radiation portion comprised of light portion132. The first radiation portion (e.g., light portions120and130) may be received by the defect detection portion122, as described above, and the second radiation portion (e.g., light portion132) may be received by a photoluminescence module134, as described below. It may be appreciated that the first radiation portion and the second radiation portion may comprise differing portions of light depending on the type and amount of filters utilized in the filter module114. For example, the first radiation portion and the second radiation portion may each include a single light portion or may include multiple light portions.

The portion of light132may pass to the photoluminescence measurement module134of the system100. The photoluminescence measurement module134may detect and monitor a local photoluminescence spectrum from the sample102, which may be indicative of what the emission spectrum will be of an LED from the measured region of the wafer102once made into a device, such as shown inFIG. 2, which provides a PL spectrum at one location of a green LED wafer.

The photoluminescence measurement module134may include a third light detector such as a photomultiplier, an avalanche photo-diode (APD), or another type of photo-diode, depending on the light level from the photo-luminescence and the required sensitivity. In a particular embodiment, the photoluminescence measurement module134includes a spectrometer, that may be fiber-coupled or not, configured to provide photoluminescence mapping at a rate sufficient to provide a color map of the photoluminescence (e.g., full spectral measurement of the photoluminescence), such as the example shown inFIG. 3, which provides a PL map for a peak wavelength from a blue LED wafer. A fiber-coupled ultra-fast spectrometer may enable a single pass measurement of the wafer sample102at a defect detection throughput of between approximately 15 to 25 wafers per hour for approximately four-inch wafers. This sampling rate may be slower than the sampling rate performed by the defect detection module122. By utilizing photoluminescence mapping at this rate, wavelength variations and intensity variations may be obtained for the wafer sample102, including resolution of the chromatic content of the portion of light132.

As described above, the photoluminescence measurement module134may include a simple non-spectrometric light detector, such as a relatively fast photodiode to permit relatively high speed sampling. In this embodiment, an integrated photoluminescence may be obtained, which may correlate to a local internal quantum efficiency of a multiple quantum well (MQW) of the wafer sample102. Thus, with the relatively high speed sampling, a high resolution luminosity map of the wafer sample102may be measured. The sampling rate may be similar to the sampling rate performed by the defect detection module122, thereby allowing the photoluminescence measurement module134to sample as fast as the defect detection module122. By co-sampling with the defect detection module122and the photoluminescence measurement module134, the system100may permit viewing photoluminescence measurements simultaneously with defect detection measurements and at a substantially similar resolution. The data obtained by both modules may be used to correlate data directly between the observed data. For instance, scattered data may be obtained by the defect detection module122and the correlating data from the photoluminescence measurement module134(obtained substantially simultaneously with the scattered data) may be utilized to indicate that a pit in the wafer sample102disrupted the output of an MQW of the wafer sample102. For instance, as shown inFIGS. 4A and 4B, photoluminescence and defect detection (respectively) may be separately measured to correlate respective abnormalities to adjust variables of the production process of the wafer (e.g., gas flow, temperature, and the like), but such separate measurements may be inefficient and may not correlate the photoluminescence measurements with the defect detection measurements. System100may operate to measure substantially simultaneously photoluminescence and defect detection, such as shown inFIG. 4C, which may correlate the photoluminescence measurements with the defect detection measurements for more focused adjustment of the production process of the wafer.

Referring now toFIG. 5, a schematic illustration of another embodiment of the system100for simultaneous defect inspection and photoluminescence (PL) measurement is shown. In this embodiment, system may be configured substantially similarly to the embodiment shown inFIG. 1, however the photoluminescence measurement module134may include a beamsplitter136, a first photo-detector138, and a second photo-detector140. As shown inFIG. 5, the portion of light132is split by the beamsplitter136into a first portion of light142and a second portion of light144. The beamsplitter136may be a standard beamsplitter (e.g., broadband dielectric) so as to split the light (e.g., symmetrically or asymmetrically), rather than filter the light according to wavelength. The first portion of light142may be directed to the first photo-detector138, which may be a photo-multiplier type of photo-detector configured for fast sampling rates and for obtaining an integrated photoluminescence measurement. The second portion of light144may be directed to the second photo-detector140, which may be a spectrometer type of photo-detector configured for slower sampling rates and for obtaining full spectral measurements of the photoluminescence. In a particular embodiment, the second photo-detector140includes a fiber-coupler which interfaces with the second portion of light144.

Alternatively, the beamsplitter136may be a fiber-coupler which includes a bifurcation to separate the portion of light132to each of the first photo-detector138and the second photo-detector140.

Accordingly, the system100ofFIG. 5may enable substantially simultaneous defect detection, integrated photoluminescence measurement, and full spectral photoluminescence measurement on a single platform, with a single optical head. Additionally, the system100may enable the direct correlation of photoluminescence measurement (e.g., integrated and spectral measurements) with defect detection measurement. Such a configuration avoids the undesired consequences of two separate measurement platforms, including the costs associated with owning/maintaining two separate platforms, multiple steps of handling a wafer (which increases the risk of contamination to the wafers), difficulty in correlating the separate data from the separate platforms, and the time and costs associated with performing two separate monitoring techniques.

Referring now toFIG. 6, a flow chart of a method200for detecting defects and measuring photoluminescence of a sample is shown. The method200may include irradiating the sample210. For instance, the sample may be irradiated with oblique input laser beam104aand/or normally incident laser beam112from radiation source104. The method200may include collecting radiation from the sample, the collected radiation including radiation which is at least one of reflected by, scattered by, or radiated from the wafer220. The radiation from the sample may be collected by the optics assembly106. The method200may include filtering the collected radiation between a first radiation portion and a second radiation portion230. The collected radiation may be filtered by the filter module114. The method200may include passing the first radiation portion to a defect detection module240. For instance, the first radiation portion may be at least one of the portion of light120or the portion of light130passed to the defect detection module122. In one particular embodiment, the first radiation portion includes both scattered light portions120and130filtered by the filter module114. The method200may include passing the second radiation portion to a photoluminescence measurement module250. For instance, the second radiation portion may include the portion of light132passed to the photoluminescence measurement module134from the filter module114. The method200may include analyzing the first radiation portion and the second radiation portion substantially simultaneously260. For instance, since the system100may utilize a single optical head for the defect detection module122and the photoluminescence measurement module134, the first radiation portion and the second radiation portion may be analyzed substantially simultaneously, enabling correlation of the PL measurements and the defect detection.

Referring now toFIG. 7, a flow chart of a method300for detecting defects and measuring photoluminescence of a sample is shown. The method300may include irradiating the sample310. For instance, the sample may be irradiated with oblique input laser beam104aand/or normally incident laser beam112from radiation source104. The method300may include collecting radiation from the sample, the collected radiation including radiation which is at least one of reflected by, scattered by, or radiated from the wafer320. The radiation from the sample may be collected by the optics assembly106. The method300may include filtering the collected radiation between a first radiation portion and a second radiation portion330. The collected radiation may be filtered by the filter module114. The method300may include passing the first radiation portion to a defect detection module340. For instance, the first radiation portion may be at least one of the portion of light120or the portion of light130passed to the defect detection module122. In one particular embodiment, the first radiation portion includes both scattered light portions120and130filtered by the filter module114. The method300may include passing the second radiation portion to a photoluminescence measurement module350. For instance, the second radiation portion may include the portion of light132passed to the photoluminescence measurement module134from the filter module114. The method300may include detecting a scatter defect in at least one of the first radiation portion or the second radiation portion360. The scatter defect may be detected by at least one of the defect detection module122or the photoluminescence measurement module134(e.g., when the photoluminescence measurement module134includes a photo-multiplier type of photo-detector configured for fast sampling rates and for obtaining an integrated photoluminescence measurement). The method300may include identifying a site of interest on the sample according to the scatter defect370. For instance, defects in the sample may be identified by performing a relatively fast scan rate of a sample, and location data of the defect on the sample may be saved in a computer memory. The method300may include measuring a spectral photoluminescence of the site of interest380. For instance, the photoluminescence measurement module134may include a spectrometer to measure spectral photoluminescence of the sample at the site of interest with a relatively slower scan rate. However, since the site of interest is determined according to a relatively fast scan rate procedure, only the sites of interest (as opposed to the entire sample) may be subjected to the relatively slower scan rate of a spectrometer-based PL measurement, thereby increasingly the overall efficiency of the wafer analysis.