Lens coating/contamination electronic detection

A contamination detection apparatus may include an optical element having an outer surface and an other surface opposing the outer surface, a first capacitor plate located on the outer surface at an outer periphery of the optical element, and a second capacitor plate located on the outer surface at the outer periphery of the optical element. The second capacitor plate is located adjacent the first capacitor plate and separated from the first capacitor by a gap to form a capacitor, whereby a contaminant is electrically detected based on the contaminant entering the gap and varying a capacitance value corresponding to the capacitor.

BACKGROUND

a. Field of the Invention

The present invention generally relates to optical systems, and more particularly to detecting contamination within such optical systems.

b. Background of Invention

Optical metrology and inspection equipment such as, for example, reflectometers may often use high power optical lens/objectives in close proximity to surfaces for measurement and/or inspection purposes. In manufacturing environments these surfaces may often release gases or vapors that can coat the lens/objectives in such a manner that light collected by these lens/objectives is distorted and/or attenuated. The measurement and/or inspection results may thus be distorted as a result of the measurement being influenced by the existing contamination.

BRIEF SUMMARY

According to one or more embodiments, it may therefore, be advantageous, among other things, to electronically detect contaminants (e.g., gases/vapors) that may coat the optical components (e.g., lenses) of equipment (e.g., reflectometer systems, photolithographic systems) in order to determine the authenticity of the measurements or collected data.

According to at least one exemplary embodiment, a contamination detection apparatus may include an optical element having an outer surface and an other surface opposing the outer surface, a first capacitor plate located on the outer surface at an outer periphery of the optical element, and a second capacitor plate located on the outer surface at the outer periphery of the optical element. The second capacitor plate is located adjacent the first capacitor plate and separated from the first capacitor by a gap to form a capacitor, whereby a contaminant is electrically detected based on the contaminant entering the gap and varying a capacitance value corresponding to the capacitor.

According to at least one other exemplary embodiment, a method of determining contamination over an outer surface of a final stage optical element of an optical system is provided. The method may include applying an alternating signal having a predetermined voltage amplitude to a first capacitor plate located on the outer surface at an outer periphery of the optical element, and applying a ground signal to a second capacitor plate located on the outer surface at the outer periphery of the optical element, whereby the second capacitor plate is located adjacent the first capacitor plate and separated from the first capacitor by a gap to form a capacitor. An electrical current value associated with the capacitor is measured based on the applied alternating signal. A capacitive reactance value for the capacitor is then measured based on the measured current value and the applied predetermined voltage amplitude. A contaminant on the outer surface of the optical element is detected based on the calculated capacitive reactance, whereby the capacitive reactance varies based on the contaminant entering the gap.

According to at least one other exemplary embodiment, a computer program product for determining contamination over an outer surface of a final stage optical element of an optical system is provided, whereby the computer program product may include a computer readable storage medium readable by a processing circuit and storing instructions for execution by the processing circuit for performing a method. The method may include measuring an alternating signal having a voltage amplitude that is applied between a first capacitor plate located on the outer surface at an outer periphery of the optical element and a second capacitor plate located on the outer surface at the outer periphery of the optical element. The second capacitor plate is located adjacent the first capacitor plate and separated from the first capacitor by a gap to form a capacitor. An electrical current value associated with the capacitor is measured based on the applied alternating signal. A resistance value is calculated based on the measured current value and the measured voltage amplitude. A contaminant on the outer surface of the optical element is then determined based on the calculated resistance value, whereby the resistance value varies based on the contaminant entering the gap.

DETAILED DESCRIPTION

The following one or more exemplary embodiments describe, among other things, an electronic surface contamination detection apparatus utilized within an optical system for determining measurement errors that may be caused by contaminants coating the one or more optical components of the optical system.

Referring toFIG. 1, an embodiment of an optical system100such as a reflectometer is depicted. The optical system100may include an optical source102, one or more optical elements104such as lenses, mirrors, splitters, etc., a collimating lens106, a first splitter108, a second splitter110, a final stage optical element112such as a focusing lens, a reference signal photodetector114, a surface reflected signal photodetector116, a photodetector focusing lens118, an electrical contamination detection circuit121, and a measurement processing unit120. The above-mentioned components102-120of the optical system100may be housed in a sealed and pressurized enclosure122in order to protect these optical components from debris (e.g., gases) that may impact the measurements.

As depicted, a focused incident optical signal Ii, as indicated at124, illuminates a surface under test S, whereby a reflected portion (i.e., from surface S) Io, as indicated by129, of the focused incident optical signal Iiis used to determine the reflectivity characteristics of the surface under test S. For example, the surface under test S may include a film, dielectric, or any other layer associated with a device such as a manufactured semiconductor structure. By determining the reflectivity of such surfaces S, the characteristics and/or manufacturing tolerances of the films, dielectrics, or other layers may be determined.

In operation, the optical source102(e.g., arc lamp, incandescent lamp, fluorescent lamp, etc.) generates an optical signal that may have a wavelength anywhere between ultraviolet (UV) and near infrared (IR) wavelengths, depending on system application. The optical signal output from optical source102propagates along path127and is received by the one or more optical elements104such as lenses, mirrors, splitters, etc. As the optical signal traverses through the one or more optical elements104, it is received by collimating lens106. At the collimating lens106, the incident optical signal, as indicated by Ii, is directed towards the beam splitter108(Path A), such that the beam splitter108reflects the collimated incident optical signal Iidown onto the final stage optical element112(Path B), which may, for example, include a focusing lens. Thus, the final stage optical element112generates a focused incident optical signal Iiat the surface under reflectivity test S (Path C).

The surface under test S illuminated by the focused incident optical signal Iimay then, based on its characteristic reflectivity (R), reflect anywhere between approximately all (total reflection) to approximately none (total absorption) of the focused incident optical signal Iiat surface S back towards the final stage optical element112as a reflected optical signal Io(Path C). The final stage optical element112may then collimate the reflected optical signal Iofrom surface S back towards the beam splitter108(Path B). At beam splitter108, the reflected optical signal Iopropagates through the beam splitter108(Path D) and onto beam splitter110. Beam splitter110subsequently directs reflected optical signal Ioonto the photodetector focusing lens118(Path E) for focusing (Path F) onto the active area of the surface reflected signal photodetector116. The surface reflected signal photodetector116then converts the optical intensity of the reflected optical signal Ioto a magnitude value (i.e., voltage or current value) that is determinative of the detected optical intensity (i.e., power). The magnitude value output from the photodetector116is then transmitted to the measurement unit120for processing.

Also at the collimating lens106, a portion of the incident optical signal, as indicated by I′i, is directed towards the beam splitter108(Path 1), such that the beam splitter108also reflects the portion of the incident optical signal I′idown onto the final stage optical element112(Path 2), which may, for example, include a focusing lens. However, the final stage optical element112includes a reflective device130having a known reflective surface that reflects the portion of the incident optical signal I′iback through the final stage optical element112and away from the surface under reflectivity test S (Path 3). Since the reflective surface of the reflective device130is set to provide maximum reflection, the reflective surface may include a high reflectivity material such as aluminum, silver, or gold with known reflectivity. Region125, which includes the final stage optical element112and reflective device130, is further described below with the aid of an expanded view of region125, as depicted inFIG. 1B.

As further shown inFIG. 1A, the portion of the incident optical signal I′ireflected back through the final stage optical element112by reflective device130(Path 3) is then received by the active area of the reference signal photodetector114. The reference signal photodetector114then converts the optical intensity of the portion of the incident optical signal I′ito a magnitude value (i.e., voltage or current value) that is determinative of the detected optical intensity (i.e., power) based on the known reflectivity of reference device130. The magnitude value output from the photodetector114is then transmitted to the measurement unit120for processing. The portion of the incident optical signal I′idetected by reference signal photodetector114acts a reference signal, whereby the ratio between the determined magnitude value corresponding to the reflected optical signal Ioand the determined magnitude value corresponding to the portion of the incident optical signal I′iprovides the reflectivity (R) measure of the surface under test S.

The portion of the incident optical signal I′idetected by reference signal photodetector114may be a predetermined/known percentage (e.g., 10%) of the total optical signal that is output from the optical source102. Therefore, during the calibration of the optical system, this portion (i.e., 10%) of the incident optical signal I′idetected by the reference signal photodetector114may be accordingly weighted (i.e., 90%) to be in proportion with incident optical signal Iithat is applied to surface S. In some implementations, the weighting may be achieved by amplifying the output of photodetector114using known photoreceiver circuitry. In other implementations, the weighting may be achieved by the measurement processing unit120prior to calculating the reflectivity value (R).

However, during the determination of the reflectivity (R) measure of the surface under test S, there may be a degree of uncertainty leading to a variation in power associated with the measured magnitude of the reflected optical signal Ioand the measured magnitude of the portion of the incident optical signal I′i. For example, due to uncertainties associated with signal loss changes over time (e.g., based on temperature fluctuations, solarization, debris, misalignment etc.) that may be imposed by beam splitters108and/or110, the measured magnitude of the reflected optical signal Ioassociated with surface S may deviate from its actual value.

Similarly, due to uncertainties associated with signal loss changes over time (e.g., based on temperature fluctuations, solarization, debris, misalignment, component aging, etc.) that may be imposed by, for example, beam splitter108, collimating lens106, the one or more optical elements104, and/or optical source102, the measured magnitude of the portion of the incident optical signal I′iserving as an optical reference signal may deviate from its actual value. Since the reflective device130is located at the last stage to reflect back the portion of the incident optical signal I′i(the optical reference signal), it may be advantageous for the reflective device130to provide a reflective surface that is independent of any characteristic changes (e.g., loss) that could apply to the final stage optical element112. Thus, in this case, any deviations in optical power associated with the portion of incident optical signal I′i(the optical reference signal) may be attributed to any one of the components (i.e.,102-108) that are upstream from the final stage optical element112.

As illustrated inFIG. 1B, a cross sectional view of the final stage optical element112depicts the reflective device130being integrated with the final stage optical element112in a manner that mitigates any contamination associated with the reflective device. By removing or reducing such contaminations that can add uncertain variations to the reflectivity R calculation, the reflective device130provides a degree of measurement confidence that identifies any upstream fluctuations in power that results from the optical system components and not the reflectivity device130itself. As depicted, reflective device130is formed on outer surface156of the final stage optical element112, whereby outer surface156faces the surface under test S. The reflective device130is also formed at a region offset X from the optical axis135of the final stage optical element112. By offsetting X the reflective device130relative to the optical axis135, the majority of the lens area, as indicated by Ar, may be devoted to focusing the incident optical signal Iionto surface S. The reflectivity device130includes a reflective surface layer137having top and bottom opposing surfaces140a,140b. The top surface140aof the reflective surface layer137is deposited on outer surface156of the final stage optical element112, such that top surface140ais encapsulated between surfaces156and157, while bottom surface140bof the reflective surface layer137remains exposed to the surface under test S. Since the top surface140ais encapsulated between surfaces156and157, it is shielded from debris and contamination that may result from, for example, the surface under test S. Moreover, outer surface156of the final stage optical element112is enclosed in a sealed and/or pressurized enclosure. In contrast, the bottom surface140bof the reflective surface layer137that is exposed to the surface under test S may become contaminated by gases that may be released from surface S. This, however, does not affect the reflectivity of top surface140a, which as depicted, reflects the portion of the incident optical signal I′ifrom the outer surface156of the final stage optical element112back through opposing surface157of the final stage optical element112. In addition to this determination, an exemplary embodiment of an electronic contamination detection system (i.e.,FIGS. 1B-1D) may be utilized to detect contamination on the outer surface of the final stage optical element112. Thus, in combination with reflectivity device130, the electronic contamination detection system (i.e.,FIGS. 1B-1D) determines the measurement integrity of the optical system across the entire optical path leading to the illuminated surface.

As illustrated inFIG. 1C, the outer surface156plan view of the final stage optical element112depicts capacitor plates155a,155bbeing formed on the outer periphery of the final stage optical element112. The capacitor plates155a,155btherefore create a capacitor for detecting debris or contamination on the outer surface of the optical element. The separation d between the capacitor plates155a,155bmay, for example, be in the range of 0.5-2.0 millimeters (mm). The thickness t1, t2of the capacitor plates155a,155bmay be, for example, 1 mm, while the height h of the capacitor plates155a,155b, as depicted by the A-A′ cross-section view, may be in the region of 2.0 mm. Generally, the height to thickness aspect ratio for the capacitor plates155a,155bshould be no more than two (2) in order to avoid the capacitor plates155a,155bfrom breaking away from outer surface156of the final stage optical element112during, for example, cleaning processes. Larger aspect ratios may, however, be contemplated based on the type of cleaning and adhesion used to couple the capacitor plates155a,155bto the outer periphery of the final stage optical element112.

Although the capacitor plates155a,155b,155care depicted as elongate and extending circumferentially around the outer periphery of the optical element112, the plates may be any other shape and extend partially around the outer periphery of the optical element112. In some implementations, the capacitor plates155a,155bmay, for example, be located at one or more regions of the outer surface156of the optical element112and be electrically coupled to generate an aggregate capacitance value (i.e., generating parallel capacitors).

Referring to the A-A′ cross-section view, the separation d between the capacitor plates155a,155bis filled by air, whereby the electric constant (∈o) for air is about 8.854×10−12Fm−1. In operation, when no debris or contaminant is covering the outer surface156of the optical element112, air fills the gap gpseparating the capacitor plates155a,155bby d. Thus, the capacitance (C) value is determined by:

Where ∈ois the electric constant, ∈ris the relative static permittivity (for an air dielectric ∈r=1), A is the surface area of each of the capacitor plates155a,155b, and d is the separation between the capacitor plates155a,155b. However, when debris or a contaminant covers the outer surface156of the optical element112, the contaminant fills the gap gpseparating the capacitor plates155a,155bby d. Thus, depending on the material composition of the contaminant (e.g., from photoresist vapors/gases, dust, silicon particles, etc.), the relative static permittivity may vary between, for example, a factor of about 2 to 100. This indicates that the capacitance value may vary between a factor of 2 to 100 when the outer surface156of the optical element112is covered by a contaminant. This change in capacitance (C) may, therefore, create enough sensitivity for an electrical contamination detection system121(FIGS. 1A & 2) to determine the existence of the outer surface156contamination. Furthermore, increasing the surface area of each of the capacitor plates155a,155band reducing the separation between the capacitor plates155a,155bmay also enhance the detection sensitivity by increasing the capacitance. The capacitor plates155a,155bmay be formed from, for example, a silver material. As depicted, the inner capacitor plate155aand the reflectivity device130may be integrated as a result of being formed from the same piece of silver. In some implementations, the optical element112may include a high numeric aperture lens having a diameter of about 20 mm and a working distance in the micrometer (μm) range.

As illustrated inFIG. 1D, a plan view corresponding to the other surface157of the final stage optical element112depicts capacitor plate155cbeing formed on the outer periphery of the final stage optical element112. As depicted, surface157faces the internal optical elements of the system100(FIG. 1A), while outer surface156faces an external device or the surface S under test. The thickness t3of the capacitive plate155cmay be, for example, 1 mm, while the height h of the capacitor plate155c, as depicted by the A-A′ cross-section view, may be in the region of 2.0 mm. Generally, the height to thickness aspect ratio of capacitive plate155cmay be the same as, or similar to, capacitor plate155blocated opposite capacitor plate155con other surface156. As depicted by the A-A′ cross-section view ofFIG. 1D, capacitor plates155band155cform a reference capacitor that may be utilized for evaluating the operation integrity of the electrical contamination detection system121(FIGS. 1A & 2). The operation of the electrical contamination detection system121(FIGS. 1A & 2) in conjunction with the capacitor formed by capacitor plates155aand155b, and the reference capacitor formed by capacitor plates155band155c, is described below with reference toFIGS. 2 and 3. The separation D between the capacitor plates155b,155cmay, for example, be in the range of 1.0-3.0 millimeters (mm). Since the gap gp1between the capacitor plates155b,155cis formed from the body of the optical element112, the relative static permittivity (∈r) may be defined by the material constituting the dielectric optical material forming optical element112. Thus, for a lens optical element112, the relative static permittivity (∈r) may be that of glass (e.g., ∈r=3.7-10). Typically, the capacitance value of the reference capacitor formed by capacitor plate155band155cremains at a fixed value regardless of whether the outer surface156of the optical element becomes covered with a contaminant. However, if a change in the capacitance value of the reference capacitor is detected by the electrical contamination detection system121(FIGS. 1A & 2), it may be indicative of a failure or change in operating conditions corresponding to the electrical contamination detection system121(FIGS. 1A & 2). Therefore, the operational integrity of the electrical contamination detection system121(FIGS. 1A & 2) may also be evaluated.

A change in capacitance value may generate a corresponding change in capacitive reactance given by:

Whereby capacitance C is replaced by the capacitance formula of Equation 1 and f is the frequency of the signal received by the capacitor C. Accordingly, the electrical contamination detection system121depicted inFIG. 2uses the changes in capacitive reactance value (Xc), which follows any changes in capacitance C, to determine the existence of a contaminant over the outer surface156(FIG. 1C) of the optical element112. Referring to Equation 2, as previously described, depending on the material composition of the contaminant (e.g., from photoresist vapors/gases, dust, silicon particles, etc.), the relative static permittivity (∈r) may vary between, for example, a factor of about 2 to 100. This indicates that the capacitance C and, therefore, the capacitive reactance Xcmay vary between a factor of 2 to 100.

Referring toFIG. 2, one exemplary embodiment of the electrical contamination detection system121may include a signal generation source such as a signal generator202, an electrical current measurement device such as a current meter204, switch SW1, and switch SW2. For example, the ground terminal206of the signal generator202may be electrically coupled to capacitor plate155bof the contamination detection capacitor (CCD)220formed by capacitor plates155aand155b(also seeFIG. 1C). Terminal208of the signal generator202may be electrically coupled to input terminal210of the current meter204. Output terminal212of the current meter204couples to capacitor plate155a(also seeFIG. 1C) of the contamination detection Capacitor (CCD)220via switch SW1. The output terminal212of the current meter204also couples to capacitor plate155cof the reference capacitor (CR)225formed by capacitor plates155band155c(also seeFIG. 1D) via switch SW2.

In a test operation mode, switch SW2may be periodically closed while SW1is opened. In this switch configuration, the signal generator202generates an alternating signal having a predetermined frequency (e.g., 1 MHz) and voltage value (e.g., 5V). As the alternating signal is applied to the reference capacitor (CR)225, the current meter204measures the current value (Ir) drawn by the reference capacitor (CR)225based on its capacitive reactance. Under a normal failure-free operation, the current value remains constant at the different measurement periods based on the reference capacitor (CR)225having a constant capacitance value. However, if this current value (Ir) varies as a result of a change in capacitance value for the reference capacitor (CR)225, it may be an indication of a circuit failure.

Alternatively, in a contamination detection mode of operation, switch SW2remains open while SW1is closed for continuous monitoring. In this switch configuration, the signal generator202generates an alternating signal having a predetermined frequency (e.g., 1 MHz) and voltage value (e.g., 5V). As the alternating signal is applied to the contamination detection capacitor (CCD)220, the current meter204measures the current value (Ic) drawn by the contamination detection capacitor (CCD)220based on its capacitive reactance.

Under a normal contamination-free operation, the current value (Ic) is measured to be at a first value based on the contamination detection capacitor (CCD)220having a capacitance and, therefore, a capacitive reactance that is based on a relative static permittivity (∈r) of about one (1). As previously described, when there is little to no contamination, the gap gp(FIG. 1C) between capacitor plates155aand155bmay be almost entirely filled with air, which includes a relative static permittivity (∈r) of about one (1).

However, when there is contamination covering the outer surface156(FIG. 1C) of the contamination detection capacitor (CCD)220, the gap gp(FIG. 1C) between capacitor plates155aand155bmay almost entirely be filled with the contaminant, which includes a relative static permittivity (∈r) ranging from, for example, 2-100. Thus, the capacitance (C) and, therefore, the capacitive reactance (Xc) may change by a factor of about 2-100 based on the variation in the relative static permittivity (∈r). This change in the capacitance (C) and, therefore, the capacitive reactance (Xc) changes the current value (Ic) measured by the current meter204, which may be indicative of a contaminant covering the outer surface156(FIG. 1C) of the contamination detection capacitor (CCD)220. Referring to Equation 2, as the capacitance (C) and, therefore, the capacitive reactance (Xc) is magnified by a factor of about 2-100, the capacitive reactance (Xc) is accordingly reduced by a factor of about 2-100. This in turn may cause the current value (Ic) to increase by about 2-100 times, which will be measured by the current meter204.

The current meter204measurements, and the predetermined frequency and voltage settings of the signal generator202are coupled to the measurement processing unit120(FIG. 1A) by the electrical contamination detection circuit121via communications link123(FIG. 1A). The communications link123may include either a wired or wireless link employing any suitable communication protocol and data communications format.

In alternative embodiments, an electrical contamination detection circuit may include any exemplary electrical circuit or device capable of generating electrical output changes as a function of variations in capacitance. For example, an integrator circuit (not shown) employing an operational amplifier may be used to determine capacitance changes as a function of output rise time or fall time governed by the RC-time-constant of the integrator. Accordingly, the RC-time-constant may be measured and analyzed within measurement processing unit120(FIG. 1A) by sampling and digitizing the integrator output. Moreover, in some embodiments, the electrical contamination detection circuit121(FIG. 1A) may be included, and thus, integrated within the measurement processing unit120(FIG. 1A).

FIG. 3is a flow chart300for an electronic contamination detection process corresponding to the outer surface of the final stage optical element112within the optical system ofFIG. 1A, according to one embodiment. The process of flow chart300may be described with the aid ofFIGS. 1A-1DandFIG. 2. Moreover, the process of flow chart300may be implemented as an executable program within measurement processing unit120(FIG. 1A). The process of flow chart300may, therefore, also be defined as electronic contamination detection process (ECDP) program300.

Referring toFIG. 3, at302, the measurement processing unit120receives the voltage (V) and frequency values (f) of a known alternating voltage (e.g., sinusoidal waveform) having a predetermined frequency that is applied to the contamination detection capacitor220(CCD). In some implementations, the measurement processing unit120may set the voltage (V) and frequency values (f) of the known alternating voltage generated by the signal generator202, which is then applied to the contamination detection capacitor220(CCD). In such an implementation, the measurement processing unit120(FIG. 1A) may control the signal generator202via a control bus interface (not shown).

At304, the measurement processing unit120receives a measured current value (Ic) from the current meter204of the electrical contamination detection circuit121. At306, based on the received measured current value (Ic) and the received voltage (V) value of the applied alternating signal from signal generator202, the capacitive reactance Xcof the contamination detection capacitor220(CCD) is determined. At308, a reference capacitive reactance Xrcfor the contamination detection capacitor220(CCD) is retrieved based on measuring the capacitive reactance of the contamination detection capacitor220(CCD) when the optical element112is contaminant free.

At310, the capacitive reactance Xcof the contamination detection capacitor220(CCD) is compared against the reference capacitive reactance Xrcof the contamination detection capacitor220(CCD) using the relationship of Equation (2). If the reference capacitive reactance Xrcvalue exceeds the measured capacitive reactance Xcvalue by a predetermined amount (e.g., Xrc>Xc, or Xrc>Xc+predetermined value), this may be indicative of the outer surface of the156of the optical element112being covered by a contaminant material. As indicated by Equation (2), with increased contamination covering the outer surface156of the optical element112, the capacitive reactance Xcvalue reduces based on the relative static permittivity (∈r) increasing. Following this comparison (310), if it is determined that the reference capacitive reactance Xrcvalue exceeds the measured capacitive reactance Xcvalue, at312the integrity of the electrical contamination detection circuit121is checked by monitoring the capacitive reactance value of the reference capacitor (CR)225. This integrity may be evaluated by ensuring that the capacitive reactance value of the reference capacitor (CR)225has remained substantially constant and the same as the capacitive reactance value obtained for the reference capacitor (CR)225during the error-free operation of the electrical contamination detection circuit121.

If at312it is determined that the capacitive reactance value of the reference capacitor (CR)225has changed, the operational integrity of the electrical contamination detection circuit121may need to be evaluated (314). However, if at312it is determined that the capacitive reactance value of the reference capacitor (CR)225has not changed, at316a cleaning process for the optical element112may be initiated.

However, if at310it is determined that the reference capacitive reactance Xrcvalue does not exceed the measured capacitive reactance Xcvalue by a predetermined amount (i.e., Xrcand Xcare approximately the same), this may be indicative of the outer surface of the156of the optical element112being contaminant-free. Thus, the process returns to302and the contamination monitoring process continues.

In some implementations, using the capacitive reactance relationship (i.e., see Equation 2), the relative static permittivity (∈r) and, thus, the type of contaminant may be determined. Specifically, since the capacitive reactance Xcis measured, using the known values of f, d, and A, the ∈rvalue may be calculated.

According to another embodiment, the process of flow chart300may determine the existence of outer surface contaminant coatings using resistance value calculations in place of capacitive reactance. For example, the known or measured alternating voltage V value (i.e., amplitude) and the measured current I value may be used, based on the V/R relation, to determine a resistance value (306). Thus, for example, step310may determine whether a retrieved (308) predetermined reference resistance value (RR) exceeds the determined resistance value (R) based on driving the contamination detection capacitor (CCD) with an alternating signal.

FIG. 4shows a block diagram of the components of a data processing system800,900, such as measurement processing unit120(FIG. 1A) in accordance with an illustrative embodiment of the present invention. It should be appreciated thatFIG. 4provides only an illustration of one implementation and does not imply any limitations with regard to the environments in which different embodiments may be implemented. Many modifications to the depicted environments may be made based on design and implementation requirements.

Measurement processing unit120(FIG. 1A) may include respective sets of internal components800a, b, cand external components900a, b, cillustrated inFIG. 4. Each of the sets of internal components800a, b, cincludes one or more processors820, one or more computer-readable RAMs822and one or more computer-readable ROMs824on one or more buses826, and one or more operating systems828and one or more computer-readable tangible storage devices830. The one or more operating systems828and programs such as the ECDP program300corresponding to measurement processing unit120(FIG. 1A) is stored on one or more computer-readable tangible storage devices830for execution by one or more processors820via one or more RAMs822(which typically include cache memory). In the embodiment illustrated inFIG. 4, each of the computer-readable tangible storage devices830is a magnetic disk storage device of an internal hard drive. Alternatively, each of the computer-readable tangible storage devices830is a semiconductor storage device such as ROM824, EPROM, flash memory or any other computer-readable tangible storage device that can store a computer program and digital information.

Each set of internal components800a, b, calso includes a R/W drive or interface832to read from and write to one or more portable computer-readable tangible storage devices936such as a CD-ROM, DVD, memory stick, magnetic tape, magnetic disk, optical disk or semiconductor storage device. The optical system processing program300(FIG. 3) associated with measurement processing unit120(FIG. 1A) can be stored on one or more of the respective portable computer-readable tangible storage devices936, read via the respective R/W drive or interface832and loaded into the respective hard drive830.

Each set of internal components800a, b, cmay also include network adapters (or switch port cards) or interfaces836such as a TCP/IP adapter cards, wireless wi-fi interface cards, or 3G or 4G wireless interface cards or other wired or wireless communication links. Optical system processing program300(FIG. 3), in measurement processing unit120(FIG. 1A), can be downloaded to measurement processing unit120(FIG. 1A) from an external computer (e.g., server) via a network (for example, the Internet, a local area network or other, wide area network) and respective network adapters or interfaces836. From the network adapters (or switch port adaptors) or interfaces836, the optical system processing program300(FIG. 3) associated with measurement processing unit120(FIG. 1A) is loaded into the respective hard drive830. The network may comprise copper wires, optical fibers, wireless transmission, routers, firewalls, switches, gateway computers and/or edge servers.

Each of the sets of external components900a, b, ccan include a computer display monitor920, a keyboard930, and a computer mouse934. External components900a, b, ccan also include touch screens, virtual keyboards, touch pads, pointing devices, and other human interface devices. Each of the sets of internal components800a, b, calso includes device drivers840to interface to computer display monitor920, keyboard930and computer mouse934. The device drivers840, R/W drive or interface832and network adapter or interface836comprise hardware and software (stored in storage device830and/or ROM824).

Aspects of the present invention have been described with respect to block diagrams and/or flowchart illustrations of methods, apparatus (system), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer instructions. These computer instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks.

The aforementioned programs can be written in any combination of one or more programming languages, including low-level, high-level, object-oriented or non object-oriented languages, such as Java, Smalltalk, C, and C++. The program code may execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer, or entirely on a remote computer or server. In the latter scenario, the remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet service provider). Alternatively, the functions of the aforementioned programs can be implemented in whole or in part by computer circuits and other hardware (not shown).