Gas flow configuration for semiconductor testing

Abstract

One system includes an inspection subsystem configured to direct light onto a region on a sample and generate an output in response to the light from that region on the sample. The system also includes a first gas flow subsystem configured to replace the gas in a first local volume surrounding a region on the sample with a first medium that scatters less light than the gas. In addition, the system includes a second gas flow subsystem configured to replace the gas in a second local volume adjacent to the first local volume with a second medium different from the first medium. The system further includes a computer subsystem configured to detect anomalies on the sample based on the output.

Description

Technical Field

[0001] The present invention generally relates to an inspection system including a gas flow subsystem for reducing non-sample-induced light scattering and foreign matter contamination of a sample being inspected.

Background Art

[0002] The following description and examples are not admitted to be prior art for the reason that they are included in this section.

[0003] Manufacturing semiconductor devices such as logic devices and memory devices typically involves processing a substrate such as a semiconductor wafer using a number of semiconductor manufacturing processes to form various features and multiple levels of the semiconductor device. For example, lithography is a semiconductor manufacturing process that includes transferring a pattern from a reticle to a resist disposed on a semiconductor wafer. Additional examples of semiconductor manufacturing processes include, but are not limited to, chemical mechanical polishing (CMP), etching, deposition, and ion implantation. Multiple semiconductor devices may be fabricated in an array on a single semiconductor wafer and then diced into individual semiconductor devices.

[0004] The inspection process is used at various steps during the semiconductor manufacturing process to detect defects on the wafer and facilitate higher yields and thus higher profits in the manufacturing process. Inspection is always an important part of manufacturing semiconductor devices such as ICs. However, as the dimensions of semiconductor devices shrink, inspection becomes even more important to successfully manufacture acceptable semiconductor devices because smaller defects can cause device failures.

[0005] Particles are killer defects in semiconductor manufacturing. A 10nm particle can destroy or short-circuit circuits in devices with a critical dimension (CD) of 20nm. With the introduction of extreme ultraviolet (EUV) lithography, the scaling of CDs is progressing slowly but steadily. The need to inspect even smaller particles is approaching.

[0006] The currently used method for detecting particles involves measuring scattered light using a dark-field (DF) optical system. A laser beam is shone onto the wafer at an oblique angle. Specular reflection can be ignored, and scattered light is collected through the objective lens. Scattered light includes light from particles, wafer roughness, and air through which the ray passes. To achieve the required signal-to-noise ratio (SNR), surface roughness and air scattering must be suppressed. Air scattering is generally small and was not a problem until the target particles were reduced to less than 10 nm. An effective way to reduce air scattering is to lower the air density by creating a vacuum between the objective lens and the wafer. Some next-generation particle inspection tools are expected to require a vacuum of approximately 10 Torr (approximately 1% atmosphere) from the sample to about 1 mm above the sample.

[0007] To create a vacuum, currently used methods and systems involve constructing a sealed chamber and drawing a vacuum into it. Inspection modules such as chucks, stages, and objective lenses reside within the chamber, or at least partially within it. Examples of currently used methods for creating such a vacuum environment for semiconductor applications are described in Patent Document 1 by Chen et al., published July 16, 1996, and Patent Document 2 by Lombardi et al., published February 21, 2006, which are incorporated herein by reference as if they were fully described.

[0008] The biggest problem with currently used vacuum configurations is the difficulty in maintaining cleanliness. For example, semiconductor yield-related tools that operate in vacuum currently in use are typically orders of magnitude dirtier than the cleanest particle inspection tools currently on the market. Surface inspection tools currently achieve excellent cleanliness by blowing purging air around the wafer to effectively push out any particles that fall onto the wafer. With currently used vacuum configurations, it is impossible to implement air purging because the entire wafer is in a vacuum. Another problem with currently used vacuum configurations is the cost. Vacuum dramatically increases the size of the tools and the cost of the stage, chuck, and objective lens. Throughput is significantly affected because extra time is required to de-vacuum each time a new wafer is loaded. This may not be much of a problem for relatively low-throughput tools such as electron beam inspection equipment and defect review tools, but it can be a major problem for high-throughput tools such as particle inspection tools, where the throughput is typically around 10 to 100 wafers per hour. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] U.S. Patent No. 5,536,330 [Patent Document 2] U.S. Patent No. 7,001,491 [Overview of the project] [Problems that the invention aims to solve]

[0010] Therefore, it is advantageous to develop a system and / or method for inspecting samples that are free from one or more of the above-mentioned drawbacks and have reduced light scattering of particles and foreign matter contamination. [Means for solving the problem]

[0011] The following descriptions of various embodiments should not be construed as limiting the subject matter of the invention in the attached claims.

[0012] One embodiment relates to a system configured to inspect a sample. The system includes an inspection subsystem configured to direct light onto a region on the sample and generate an output in response to the light from that region on the sample. The system also includes a first gas flow subsystem configured to replace the gas in a first local volume surrounding a region on the sample with a first medium that scatters less light than the gas. In addition, the system includes a second gas flow subsystem configured to replace the gas in a second local volume adjacent to the first local volume with a second medium different from the first medium. The system further includes a computer subsystem configured to detect anomalies on the sample based on the output. The system may be further configured as described herein.

[0013] Another embodiment relates to a method for inspecting a sample. This method includes directing light onto a region on the sample and generating an output in response to the light from that region on the sample. The method also includes replacing the gas in a first local volume surrounding the region on the sample with a first medium during the light-directing and generating steps. The first medium scatters less light than the gas. In addition, the method includes replacing the gas in a second local volume located adjacent to the first local region with a second medium during the light-directing and generating steps. The second medium is different from the first medium. The method further includes detecting anomalies on the sample based on the output. The detection is performed by a computer system.

[0014] The steps of the method may be carried out as further described herein. The method may include any other step(s) of any other method(s) described herein. The method may be carried out by any system described herein.

[0015] An additional embodiment relates to a non-temporary computer-readable medium which stores program instructions executable on a computer system for performing a computer implementation method for examining a sample. The computer implementation method includes the steps of the method described above. The computer-readable medium may be further configured as described herein. The steps of the computer implementation method may be performed as further described herein. In addition, a computer implementation method on which program instructions are executable may include any other step(s) of any other method(s) described herein.

[0016] Further objectives and advantages of the present invention will become apparent from reading the detailed description below and from referring to the accompanying drawings. [Brief explanation of the drawing]

[0017] [Figure 1] This is a schematic diagram showing a side view of one embodiment of a system configured to inspect a sample. [Figure 2] This is a schematic diagram showing cross-sectional views of various embodiments of a system configured to inspect a sample and use different media to reduce light scattering and foreign matter contamination during inspection. [Figure 3] This is a schematic diagram showing cross-sectional views of various embodiments of a system configured to inspect samples and use different media to reduce light scattering and foreign matter contamination during inspection. [Figure 4] This is a schematic diagram showing cross-sectional views of various embodiments of a system configured to inspect samples and use different media to reduce light scattering and foreign matter contamination during inspection. [Figure 5] This is a schematic diagram showing cross-sectional views of various embodiments of a system configured to inspect samples and use different media to reduce light scattering and foreign matter contamination during inspection. [Figure 6] This is a schematic diagram showing cross-sectional views of various embodiments of a system configured to inspect samples and use different media to reduce light scattering and foreign matter contamination during inspection. [Figure 7]A block diagram showing an embodiment of a non - transient computer - readable medium storing program instructions executable on a computer system for performing one or more of the computer - implemented methods described herein.

Best Mode for Carrying Out the Invention

[0018] Although the present invention is capable of various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and are described in detail herein. However, the drawings and the detailed description thereof are not intended to limit the present invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present invention as defined by the appended claims.

[0019] Turning now to the drawings, it should be noted that the figures are not drawn to scale. In particular, the scale of some of the elements of the figures is exaggerated greatly to emphasize the characteristics of the elements. Also, note that the figures are not drawn to the same scale. Elements shown in multiple figures that may be similarly configured are denoted using the same reference numerals. Unless otherwise specified herein, any of the elements described and illustrated may include any suitable commercially available elements.

[0020] The embodiments described herein generally relate to systems and methods for inspecting a sample. For example, the embodiments described herein provide a method and a system for using two different media (e.g., applying purge air to create a local vacuum or applying a helium medium) in a particle inspection apparatus. In order to create a next-generation particle inspection tool, the tool needs to have means for reducing air scattering (e.g., through a vacuum or another medium with less light scattering than air) and means for keeping the tool clean (e.g., through purge air). Although these two requirements may seem contradictory, the inventors have created the system architecture described herein that enables both requirements to be met. The embodiments described herein have many advantages and improvements compared to currently available inspection tools. For example, according to an embodiment, a substantially small volume of vacuum can be formed between the sample and the objective lens, eliminating the overhead time of pumping down a large vacuum chamber. According to an embodiment, clean air can also be purged around the sample to keep the sample clean.

[0021] The embodiments described herein may be particularly useful for wafer inspection apparatuses designed for particle inspection, but the embodiments may also be useful for other wafer inspection apparatuses, other types of sample inspection apparatuses, metrology tools, and optical defect review tools, etc.

[0022] In one embodiment, the sample is a wafer. The wafer can include any wafer well-known in semiconductor technology. Some embodiments may be described herein with respect to one wafer or multiple wafers, but the embodiments are not limited to the samples that can be used. For example, the embodiments described herein can be used for samples such as reticles, flat panels, personal computer (PC) boards, and other semiconductor samples.

[0023] A system configured to inspect a sample includes an inspection subsystem configured to direct light onto a region on the sample and generate an output in response to the light from that region on the sample. The inspection subsystem includes at least an illumination subsystem, which includes a light source configured to generate light directed onto a region on the sample, and a detection subsystem, which includes a detector configured to detect light from the sample and generate an output in response to the detected light. One embodiment of such a system is shown in Figure 1.

[0024] As shown in Figure 1, the illumination subsystem includes a light source 100. The illumination subsystem is configured to direct the light generated by the light source onto an area (not shown) on the sample at one or more angles of incidence, the angles of incidence may include one or more oblique angles and / or one or more normal angles. The area may be a relatively large spot, one or more spots, a field, a line, etc. For example, as shown in Figure 1, light from the light source 100 passes through the optical element 102 and then through the lens 104 and is directed onto the sample 106 at an oblique angle of incidence. The angles of incidence may include any suitable angles of incidence, which may be changed depending, for example, on the characteristics of the sample and the process performed on the sample.

[0025] The illumination subsystem may be configured to direct light onto the sample at different angles of incidence and at different times. For example, the inspection subsystem may be configured to modify one or more properties of one or more elements of the illumination subsystem so that, as a result, light can be directed onto the sample at different angles of incidence than those shown in Figure 1. In such an example, the inspection subsystem may be configured to move the light source 100, the optical element 102, and the lens 104 so that light can be directed onto the sample at different angles of incidence.

[0026] In some cases, the inspection subsystem may be configured to direct light onto the sample simultaneously at multiple angles of incidence. For example, the illumination subsystem may include multiple illumination channels, one of which includes a light source 100, an optical element 102, and a lens 104, as shown in Figure 1, and another illumination channel (not shown) may include similar elements that may have different or identical configurations, or may include at least a light source and one or more other components as described further herein where possible. When such light is directed onto the sample simultaneously with other light, one or more properties (e.g., wavelength, polarization, etc.) of the light directed onto the sample at different angles of incidence may differ, and the light produced by illuminating the sample at different angles of incidence may be distinguished from one another by the detector(s).

[0027] In another example, the illumination subsystem may include only one light source (e.g., light source 100 shown in Figure 1), and the light from the light source may be split into different optical paths (e.g., based on wavelength, polarization, etc.) by one or more optical elements (not shown) of the illumination subsystem. Each of the light from the different optical paths may then be directed onto the sample. Multiple illumination channels may be configured to direct light onto the sample simultaneously or at different times (e.g., sequentially illuminating the sample using different illumination channels). In another example, the same illumination channel may be configured to direct light onto the sample at different times using different characteristics. For example, optical element 102 may be configured as a spectral filter, and the characteristics of the spectral filter may be changed in various different ways (e.g., by changing the spectral filter) so that light of different wavelengths can be directed onto the sample at different times. The illumination subsystem may have any other suitable configuration known in the art for directing light having different or the same characteristics onto the sample sequentially or simultaneously at different or the same angle of incidence.

[0028] The light source 100 may include any suitable light source, such as any suitable laser known in the art, configured to produce light at any suitable wavelength(s) known in the art. The laser may be configured to produce monochromatic or nearly monochromatic light. In addition, the laser may be a mode-locked laser. The light source may also include a polychromatic light source, which produces light at multiple discrete wavelengths or wavelength bands.

[0029] Light from the optical element 102 can be focused onto the sample 106 by the lens 104. Although the lens 104 is shown as a single refractive optical element in Figure 1, in practice, the lens 104 may include multiple refractive and / or reflective optical elements, which combine the light from the optical elements to focus on the sample. The illumination subsystem shown in Figure 1 and described herein may include any other suitable optical elements (not shown). Examples of such optical elements include, but are not limited to, polarization components, spectral filters, spatial filters, reflective optical elements, apodizers, beam splitters, and apertures, and may include any such suitable optical elements well known in the art. In addition, the system may be configured to change one or more elements of the illumination subsystem based on the type of illumination used. Furthermore, the illumination subsystem may be configured to direct light to only one area on the sample or to multiple areas on the sample. The domain(s) may have any suitable properties that are well known in the art.

[0030] The inspection subsystem may also include a scanning subsystem configured to scan light over the sample. For example, the inspection subsystem may include a stage (not shown in Figure 1) on which the sample 106 is placed. The scanning subsystem may include any suitable mechanical and / or robotic assembly (including the stage) which may be configured to move the sample so that the light can scan over the sample. In addition or alternatively, the inspection subsystem may be configured so that one or more optical elements of the inspection subsystem perform the scanning of light over the sample. The light can scan over the sample in any suitable manner. The stage may be further configured as described herein.

[0031] The detection subsystem may include one or more detection channels. At least one of the detection channels includes a detector configured to detect light from the sample due to illumination of the sample by the illumination subsystem and to generate an output in response to the detected light. For example, the detection subsystem shown in Figure 1 includes a detection channel formed by an objective lens 112, a tube lens 116, an element 118, and a detector 120. As shown in Figure 1, the detection channel is configured to detect scattered light from the sample. Thus, the detection channel may be configured for dark-field (DF) imaging.

[0032] The detection subsystem may also include multiple detection channels (not shown) that collect and detect light at different collection angles. In some cases, one detection channel is configured to detect specularly reflected light, and other detection channels are configured to detect light that is not specularly reflected from the sample (e.g., scattered light, diffracted light, etc.). However, two or more detection channels may be configured to detect the same type of light (scattered light, etc.) from the sample. Although the objective lens and tube lens are shown in Figure 1 to include a certain number of refractive optical elements having a particular shape, each of the objective lens and tube lens may include one or more refractive optical elements and / or one or more reflective optical elements having any suitable configuration known in the art.

[0033] One or more detection channels may include any suitable detector known in the art, such as photomultiplier tubes (PMTs), charge-coupled devices (CCDs), and time-delay integral (TDI) cameras. Detectors may also include non-imaging detectors or imaging detectors. If the detectors are non-imaging detectors, each detector may be configured to detect certain properties of light, such as intensity, but not necessarily as a function of position in the imaging plane. Thus, the output produced by each detector included in each detection channel may be a signal or data, but not necessarily an image signal or image data. In such cases, a computer subsystem, such as the system's computer subsystem 122, may be configured to generate an image of the sample from the non-imaging output of the detectors. However, in other examples, the detectors may be configured as imaging detectors configured to generate imaging signals or image data. Thus, the system may be configured to produce the outputs and / or images described herein in many ways.

[0034] The inspection subsystem may be configured to generate a sample output, such as an image, in multiple modes. Generally, a “mode” is defined by the values ​​of the parameters of the inspection subsystem used to generate the sample output. Thus, a mode may have different values ​​for at least one parameter of the illumination subsystem and the detection subsystem (other than the position on the sample where the output is generated). For example, different modes may use light of different wavelengths for illumination. Modes may have different illumination wavelengths as further described herein (e.g., by using different light sources, different spectral filters, etc., for different modes). In another example, different modes may use different illumination channels of the illumination subsystem. For example, as described above, the illumination subsystem may include multiple illumination channels. Thus, different illumination channels may be used for different modes. A mode may also be different by one or more acquisition / detection parameters of the detection subsystem, or alternatively, by different parameters. A mode may also be different by any one or more modifiable parameters of the system (e.g., illumination polarization(multiple), angle(multiple), wavelength(multiple), etc.; detection polarization(multiple), angle(multiple), wavelength(multiple), etc.). The inspection subsystem may scan a sample using different modes in the same or different scans, for example, depending on the function of scanning the sample simultaneously using multiple modes.

[0035] Figure 1 is provided herein to illustrate in general terms the configuration of an inspection subsystem that may be included in embodiments of the system described herein. Obviously, the configuration of the inspection subsystem described herein can be modified to optimize the system's performance, as is typically done when designing commercially available systems. In addition, the system described herein can be implemented using existing inspection systems (for example, by adding the functions described herein to an existing optical system), such as the SPx series tools commercially available from KLA Corp., Milpitas, Calif., which are capable of detecting very small particles down to about 10 nm. In some such systems, the methods described herein may be offered as optional features of the system (for example, in addition to other features of the system). Alternatively, the system described herein can be designed "from scratch" to provide a completely new system.

[0036] The system further includes a computer subsystem configured to detect anomalies on a sample based on its output. For example, the system may include a computer subsystem 122, which may be coupled to the detector 120 in any suitable way (e.g., via one or more transmission media, which may include "wired" and / or "wireless" transmission media), so that the computer subsystem can receive outputs, images, etc., generated by the detector during scanning of the sample. The computer subsystem may be configured to detect anomalies on the sample by applying a defect detection method to the output generated by the detector. Detection of anomalies on the sample may be performed using any suitable defect detection method and / or algorithm, in any suitable way known in the art (e.g., applying a defect detection threshold to the output and determining that any output with a value exceeding the threshold corresponds to an anomaly or potential anomaly). The computer subsystem 122 may be configured to perform any other functions further described herein. This computer subsystem may be further configured as described herein.

[0037] As used herein, the term “anomaly” is generally defined as an example of sample characteristics that differ from intent or expectation. Examples of anomalies that can be detected by the embodiments described herein include the presence of particles on the sample (e.g., particle fallout, foreign matter, etc.) and defects (e.g., defects in one or more patterned or unpatterned materials formed on the sample). Generally, the embodiments described herein may be configured to detect various types of anomalies depending on the anomaly in question and the sample characteristics (e.g., type, layer, etc.). In other words, the embodiments described herein are not limited to the types of anomalies that may be configured to detect.

[0038] This computer subsystem (and other computer subsystems described herein) may also be referred to herein as a computer system. Each of the computer subsystems or systems described herein can take various forms, including personal computer systems, image computers, mainframe computer systems, workstations, network appliances, internet appliances, or other devices. Generally, the term “computer system” can be broadly defined to encompass any device having one or more processors that execute instructions from a memory medium. A computer subsystem or system may also include any suitable processors well known in the art, such as parallel processors. In addition, a computer subsystem or system may include a computer platform with high-speed processing and software, either as a standalone or networked tool.

[0039] As described herein, the system is configured as an inspection system. In another embodiment, the system may be configured as a measurement or defect review system. In particular, the embodiment of the system shown in Figure 1 can be modified by one or more parameters to provide different imaging capabilities depending on the application in which it is used. In such an example, the optical subsystem shown in Figure 1 may be configured to have a higher resolution when used for measurement or defect review rather than inspection. In other words, the embodiment of the inspection subsystem shown in Figure 1 illustrates some general and various configurations of the optical subsystem, which can be adjusted in several ways that will be obvious to those skilled in the art to create systems with various imaging capabilities that are generally suitable for different applications.

[0040] The system includes a first gas flow subsystem configured to replace the gas in a first local volume surrounding a region on the sample with a first medium that scatters less light than the gas. The height of the first local volume may be defined by the space between the objective lens of the inspection subsystem (such as objective lens 112 shown in Figure 1) and the top surface of the sample. The first local volume may be located approximately in the center of its region (or more regions) illuminated on the sample, but does not need to be located in the exact center of that region (or more regions). Preferably, the first local volume surrounds a region such that any light from the sample collected by the inspection subsystem travels entirely within the first medium from the sample to the objective lens. Thus, the width of the first local volume may depend on the collection angle (the angle at which light from the sample is collected by the objective lens). The width of the first local volume may also be configured so that light from the illumination subsystem is directed through the first medium to its region (or more regions) on the sample. Therefore, the dimensions of the first local volume may vary depending on the configuration of the inspection subsystem and how close the sample is to the objective lens.

[0041] In one embodiment, the first medium is a vacuum. For example, a vacuum can be created by pumping air from a first local volume through one or more pumping channels. Generally, as shown in Figure 1, the first gas flow subsystem includes a housing block 108 with a plurality of channels 110 formed therein, through which the first gas flow subsystem can replace the gas in the first local volume surrounding the area irradiated onto the sample by the inspection subsystem with a first medium that scatters less light than the gas. The housing block 108 may be separate from the objective lens housing 114 shown in Figure 1, but both these elements, the plurality of channels 110 and the first gas flow subsystem may be further configured as described herein. Embodiments of the system shown in Figure 1 may be further configured as described herein, using additional elements not shown for clarity in Figure 1.

[0042] Figure 2 shows further details of the first gas flow subsystem, configured to create a local vacuum between the objective lens and the sample, as shown in Figure 1. In particular, the first gas flow subsystem may include a number of channels 200, 202, and 204 formed in the housing block 206. The vacuum channels may be perforated in the housing block 206, which may be formed from any suitable material such as stainless steel. The housing block 206 may be a separate assembly attached to the objective lens housing. Thus, the air channels may be machined into a separate assembly attached to the objective lens assembly. The housing block 206 may be coupled to the objective lens housing 208 (e.g., via screws, adhesive, etc.), so that the two housings are adjacent to each other and touch each other as shown by the dashed line between the housings in Figure 2. In this case, the dashed line between the housing block 206 and the objective lens housing 208 can serve as a boundary between the objective lens housing and the air channel housing. However, the housing block 206 and the objective lens housing 208 may be formed from a single material and thus constitute a single element in the system. For example, the air channel may be machined as an integrated part of the objective lens assembly. Generally, the housing block 206 and the objective lens housing 208 may be manufactured in a variety of ways, depending on, for example, the material requirements of the housing, the complexity of manufacturing both from a single material, and the difficulty of joining separate housings to eliminate airflow between them.

[0043] As further shown in Figure 2, the multiple channels are configured such that air 210 can be drawn through the channels from the sample 212 and from the volume 214 between the objective lens 216 and the sample, thereby creating a vacuum between the objective lens and the sample. For example, each of the multiple channels may be coupled to a vacuum pump (not shown in Figure 2) that draws air through the channels in this manner. The vacuum pump may be any suitable vacuum pump known in the art and may be selected based on information regarding the volume between the sample and the objective lens, the required or desired vacuum level, the channel configuration, etc. The first gas flow subsystem may include any other suitable elements (not shown) that are typically included in a vacuum system, such as valves, exhaust elements, controllers, etc. The vacuum created in the local volume between the objective lens and the wafer may be about 10 Torr or any other suitable value, depending on the requirements of the inspection system that includes the first gas flow subsystem.

[0044] The objective lens 216 may be further configured as described herein, and the optical elements of the objective lens 216 shown in Figure 2 may be only one of the multiple optical elements of the objective lens shown in Figure 1. For example, the optical elements of the objective lens 216 shown in Figure 2 may be the element of the objective lens 112 shown in Figure 1 that is closest to the sample. Alternatively, the objective lens 216 may consist of only one optical element as shown in Figure 2. As further described herein, light 218 scattered from the area irradiated onto the sample may be collected by the objective lens and directed to one or more other elements of the inspection subsystem. The vertical line 220 indicates the optical axis of the collection / detection subsystem of the inspection subsystem.

[0045] In additional embodiments, the first gas flow subsystem includes multiple channels for replacing gas with a first medium, and the first gas flow subsystem is configured to provide the first medium with different characteristic values ​​adjacent to two or more of the multiple channels. In such an embodiment, the first medium is vacuum and the characteristic is pressure. Thus, the first gas flow subsystem may be configured to create multiple stages of vacuum using multiple stages of pumping. Figure 3 shows the results of a numerical simulation performed for one embodiment of multistage vacuum achievable by the embodiments described herein. This figure shows the simulation estimate of the capabilities of the embodiments described herein. In this figure, the first gas flow subsystem has three stages of pumping. The first stage reduces the air pressure by 90%, from 101 kPa at position 300 at the end of the housing block 302 to approximately 10 kPa at position 304 adjacent to the inlet of channel 306 of the first gas flow subsystem. In the second stage, the air pressure is reduced from approximately 10 kPa at position 304 to approximately 1.3 kPa at position 308, which is close to the inlet of channel 310 of the first gas flow subsystem. In the third stage, it is reduced by 56%, from approximately 1.3 kPa at position 308 to approximately 0.6 kPa at position 312, which is close to the inlet of channel 314 of the gas flow subsystem. The third stage may be less efficient than the first two stages because the air is already considerably thinner as it approaches the center due to the first two stages.

[0046] The pressure values ​​described above are merely non-limiting examples of the possible vacuum levels in the embodiments described herein. Vacuum pressure is adjustable based on the use case (e.g., the amount of air scattering reduction required, which may vary depending, for example, on the haze level of the wafer). In addition, the term “vacuum” as used herein is not necessarily intended to mean a perfect or complete vacuum, as can be seen from the vacuum pressure values ​​described above. Instead, the term “vacuum” as used herein is generally defined as a medium having a pressure below atmospheric pressure, and any of the vacuum pressures described herein may be selected by the user when configuring the first gas flow subsystem. The term “vacuum” as defined herein is created by intentionally drawing one or more gases out of a volume, but not by intentionally replacing one or more gases with one or more other gases. For example, intentionally replacing one or more gases in a volume with one or more other gases (the same or different as the original one or more gases) whose pressure in the volume is unintentionally lower (or designed to be lower) than the original one or more gases would not be considered, as used herein, to have created a vacuum in the volume. The portion of the first gas flow subsystem shown in Figure 3 may be further configured as described herein and may be coupled to an inspection subsystem (not shown in Figure 3) as further described herein.

[0047] Accordingly, one novel and important feature of the embodiments described herein is that they are configured, or may be configured, for multiple stages of pumping to create a vacuum. Three stages of pumping are shown in Figure 2 by three different channels in the housing block, and three vacuum levels are shown in Figure 3 at different pressures, although different stages of pumping and vacuum may be used. For example, the embodiments described herein may be configured for one or more stages of pumping and different levels of vacuum. In some cases, the first gas flow subsystem may consist of as many vacuum channels as deemed practical, and fewer than all vacuum channels may be used if fewer stages of vacuum are required. For example, which channel is used to create a vacuum may be controlled by a vacuum pump attached to each channel. In one such case, the first gas flow subsystem configured for three stages of vacuum may also be used for two stages of vacuum by simply not operating the vacuum pump(s) connected to one of the three stages of the channel.

[0048] In the vacuum embodiments described herein, the sample may be held by a vacuum chuck with a higher vacuum at the bottom than at the top, so that the sample is not lifted from the chuck and does not come into contact with the housing block and / or objective lens housing by the first medium. For example, the chuck 222 shown in Figure 2 may be a vacuum chuck. The chuck may also be a vacuum chuck or an air / vacuum composite chuck. The system may also be configured to actively control the vacuum pressure of the vacuum chuck according to the vacuum level above the sample. Chuck 222 may, alternatively, be an electrostatic chuck including any such chuck suitable for use in a vacuum environment. Thus, the chuck may be configured to hold the sample by electrostatic force. The particle problem associated with electrostatic chucks may be acceptable because, as further described herein, an air purge can be performed to surround the chuck and prevent external particles from entering. The chuck may be coupled to a scanning subsystem and configured to scan light over the sample in any suitable manner, as further described herein. In addition, the chuck may be an R-θ stage configured for rotational and linear motion.

[0049] In another embodiment, the first local volume includes a gap 236 between the housing block 206 and the sample. For example, the housing block of the local vacuum subsystem may be positioned substantially close to the sample, for example, with a gap of about 50 μm to 1 mm from the sample, without contact with the sample. As further described herein, a vacuum may be created by pumping air out of the gap through one or more pumping channels. Due to such a small gap, a pressure gradient is formed as air flows from the outside towards the center of the objective lens. This also creates a vacuum in the volume 214 below the objective lens.

[0050] In some embodiments, the refractive index of the first medium at one or more wavelengths of light directed to and from the region is lower than that of dry air at one or more wavelengths. As described above, the first gas flow subsystem is configured to replace the gas placed in close proximity to the region on the sample with the first medium, which scatters less light than the gas, thereby improving the sensitivity of the system. More specifically, in some embodiments, the first gas flow subsystem is configured to suppress atmospheric Rayleigh light scattering interference in a light scattering-based surface inspection system by replacing the ordinary air present near the region on the sample with a light propagation medium that has a lower Rayleigh scattering cross-section than ordinary air.

[0051] Thus, it is preferable that the first medium has a refractive index at the operating wavelength(s) of the inspection subsystem that is lower than the refractive index of dry air at the operating wavelength(s) of the inspection subsystem. For example, the inspection subsystem may operate at ultraviolet (UV) wavelengths. Therefore, in one embodiment, it is preferable that the first medium has a refractive index at UV wavelengths that is lower than the refractive index of dry air at UV wavelengths. In one preferred embodiment, the first medium is the gas with the lowest known Rayleigh cross-section for UV wavelengths (e.g., wavelengths up to about 200 nm).

[0052] In one embodiment, the first medium is essentially helium (He). For example, the purpose of the vacuum in the embodiments described herein is to effectively reduce non-anomalous light scattering detected by the system in the presence of clean dry air. Therefore, other mediums can be used instead of the vacuum if they can reduce light scattering to the same extent as the vacuum (or substantially the same extent depending on the application, such as when the cost of vacuum implementation is unacceptable or vacuum implementation is impractical). In one such acceptable alternative, the vacuum can be replaced by a helium purge. Helium is effective in reducing air scattering as well as a vacuum. In particular, helium molecules are smaller than air molecules, so helium scatters less light than air, just as it does in a vacuum. The first gas flow subsystem may be configured to deliver helium directly under the objective lens. The helium pressure can push air out of the gap between the housing block and the sample. One advantage of helium purging is that the pressure required to smooth the flow is low. In addition, using helium instead of a vacuum to reduce light scattering by air may be preferred because it is easier to implement.

[0053] As an alternative to elemental helium, the first medium may consist essentially of neon (Ne). The term “essentially consisting of” as used herein refers to a medium containing one of the aforementioned gases in combination with other gases present in amounts that do not substantially affect the fundamental properties of light scattering induced by the first medium. For example, a first medium consisting essentially of elemental helium or neon may contain a small amount of dry air that does not substantially affect the fundamental properties of light scattering induced by the medium. Further information regarding how helium and neon may reduce light scattering in inspection systems and thereby increase the sensitivity of the system is contained in U.S. Patent No. 7,372,559 by Haller et al., published May 13, 2008, which is incorporated herein by reference as if it were fully described herein. The embodiments described herein may be further configured as described herein.

[0054] Figure 4 shows one embodiment of helium purging. In particular, the first gas flow subsystem may include a channel 400 formed in a housing block 402. The housing block 402 may be coupled to an objective lens housing 404 as further described herein, so that the two housings are adjacent and in contact as shown by the dashed line between the housings in Figure 4. Thus, the helium channel may be machined in a separate assembly attached to the objective lens assembly. However, the housing block 402 and the objective lens housing 404 may be formed from a single material and therefore may be a single element in the system. The housing block 402 and the objective lens housing 404 may be further configured as described herein. Although a certain number of helium flow channels are shown in Figure 4, the first gas flow subsystem may include any suitable number of channels in any suitable configuration as described herein.

[0055] As in the embodiment shown in Figure 2, instead of drawing air from the sample 406, the channel 400 is configured such that helium 408 replaces the air or gas in the volume 410 between the objective lens 412 and the sample, thereby forming a reduced scattering medium within the volume. For example, each channel may be coupled to a helium source (not shown) and one or more other elements that thus push helium through the channel. The helium source and any other elements (not shown) included in such a first gas flow subsystem may include any suitable sources and elements known in the art and may be selected based on information regarding the volume between the sample and the objective lens, the required or desired level of helium pressure, the configuration of the channel, etc. The first gas flow subsystem may include any other suitable elements (not shown) that are commonly included in gas flow subsystems, such as valves, exhaust elements, and controllers.

[0056] The objective lens 412 may be further configured as described herein, and the optical elements of the objective lens 412 shown in Figure 4 may be only one of the multiple optical elements of the objective lens shown in Figure 1. Alternatively, the objective lens 412 may include only one optical element as shown in Figure 4. As further described herein, light 414 scattered from the sample may be collected by the objective lens and directed to one or more other elements (not shown in Figure 4) of the inspection subsystem. The vertical line 416 indicates the optical axis of the collection / detection subsystem of the inspection subsystem. This embodiment may also include a chuck 418, which may be configured according to any of the embodiments described herein.

[0057] The system also includes a second gas flow subsystem, which is configured to replace the gas in a second local volume adjacent to a first local volume with a second medium different from the first medium. For example, as shown in Figure 2, the second gas flow subsystem schematically represented by channel 224 can guide a second medium 226 to a second local volume adjacent to a first local volume, thereby replacing any gas in that second local volume with the second medium. In another example, as shown in Figure 4, the second gas flow subsystem schematically represented by channel 420 can guide a second medium 422 to a second local volume adjacent to a first local volume, thereby replacing any gas in that second local volume with the second medium. As shown in these figures, the second gas flow subsystem is configured so that the second medium is near the objective lens and the objective lens housing and rains down around them. The objective lens and sample may be placed in a closed scanning chamber (not shown). A second medium may be introduced into the chamber from above and exhausted from below (not shown). In some cases, the second medium may generate a positive pressure, e.g., a pressure about 10 to 100 Pascals higher than the ambient pressure, within the chamber outside the first local volume. Thus, one novel and important feature of the embodiments described herein is that they are configured to generate a reduced scattering medium (e.g., a local vacuum) inside between the sample and the objective lens while purging the objective lens / sample from the outside. In this way, the embodiments described herein can reduce scattering while keeping the sample clean by using a purging medium outside a different medium (e.g., a local vacuum). The inventors are unaware of any other architecture that can generate a vacuum while keeping the sample clean.

[0058] In one embodiment, the second medium is essentially clean dry air (CDA). Thus, the embodiments described herein may be configured for local vacuum air purging. Alternatively, the embodiments described herein may be configured for air purging with helium purging. In either case, the system may use different first and second mediums. In particular, helium may be used for both the first and second mediums, but helium is not required for the second medium, which would unnecessarily increase the cost of the system compared to using CDA as the second medium. Therefore, the preferred combination of mediums for the embodiments described herein is either vacuum or helium, used in combination with CDA.

[0059] In another embodiment, the second gas flow subsystem is configured to prevent the second medium from guiding light into and out of a region. In some embodiments, the second gas flow subsystem is configured to use the second medium to keep foreign matter away from the sample. For example, the purpose of the second gas flow subsystem and the second medium is independent of the imaging performance of the inspection subsystem. In particular, unlike the first gas flow subsystem and the first medium, which are intended to improve the sensitivity of the inspection subsystem by reducing light scattering from non-anomalous sources, the second gas flow subsystem and the second medium are used primarily (perhaps only) to keep the sample clean. In other words, it is preferable that the second gas flow subsystem and the second medium be configured to reduce any dropping onto particles or other foreign matter that may accumulate on the sample during the inspection process. This foreign matter may come from any possible source, such as foreign matter in the cleanroom or foreign matter from the inspection subsystem. The second gas flow subsystem and the second medium may be configured to have gas flow characteristics, such as gas flow rate and gas pressure, to encourage foreign matter to move away from the sample and into the exhaust subsystem (not shown) which is either contained within or coupled to the second gas flow subsystem. Therefore, there is no reason to configure the second gas flow subsystem to direct the second medium into either the path of light directed to the sample and / or the path of light returned from the sample. In addition, if the second medium is a medium such as CDA, directing the medium into the path of light within the inspection subsystem may actually adversely affect the performance of the system.

[0060] The first gas flow subsystem may also be configured to effectively prevent the second medium from being placed within the first local volume surrounding the irradiation area on the sample. For example, if the first medium is in a vacuum, and any of the second mediums enters the first local volume, that second medium will also be removed by the first gas flow subsystem when generating and / or maintaining the vacuum. If the first medium is essentially helium, the first gas flow subsystem may be configured such that the properties of helium, e.g., flow rate, pressure, etc., are such that the helium effectively pushes the second medium out of the first local volume. Thus, the embodiments described herein can be easily configured so that the second medium does not interfere with the performance of the inspection subsystem.

[0061] In further embodiments, the first and second gas flow subsystems do not alter the gas outside the second local volume. For example, other than creating, controlling, and maintaining the first and second media in the first and second local volumes, respectively, the first and second gas flow subsystems are not configured to alter the surrounding gas or other gases in the rest of the tool. One reason for this is the design purpose of the gas flow subsystems, namely, to create, control, and maintain the first and second media in relatively specific local volumes within the inspection subsystem. Any areas inside or around the rest of the inspection subsystem, such as areas outside the second local volume, and possibly areas within the housing of the inspection subsystem, are substantially unaffected by the first and second gas flow subsystems. Those areas outside the second local volume may be able to maintain the ambient conditions in which the entire inspection subsystem is situated. These configurations are possible because the first and second gas flow subsystems are intended to replace gas within relatively small local volumes, and there are specific reasons for this. Therefore, the first and second gas flow subsystems can be far less expensive than other systems configured to control the entire inspection subsystem and the entire environment in which the sample is placed.

[0062] In additional embodiments, the entire inspection subsystem is not placed in a vacuum. For example, one novel and important feature of the embodiments described herein is that the vacuum is created only in a local volume of the inspection tool, i.e., only in the relatively small volume between the objective lens and the sample. Because the vacuum is created in such a small volume, the entire sample and inspection subsystem do not need to be placed in a vacuum. This overcomes many of the shortcomings of currently used inspection systems. For example, regarding reduced throughput, in the embodiments described herein, for example, there is no need to create a vacuum after the sample has been moved to the inspection tool, and regarding increased costs, in the embodiments described herein, for example, there is no need for a vacuum housing large enough to enclose the sample plus all the optical hardware of the tool, leaving room for the sample to move within the housing. For example, the embodiments described herein are configured to create a vacuum sufficient to reduce air scattering detected by the inspection subsystem, and thus it is possible to maintain a distance between the objective lens and the sample that allows for the movement and / or rotation of the sample, while increasing the sensitivity of the inspection subsystem.

[0063] In one embodiment, the first and second gas flow subsystems are configured to simultaneously replace the gas in the first and second local volumes, respectively. For example, it may be possible to turn off one of the gas flow subsystems so that they can be used separately when such a configuration is desirable. Furthermore, as described above, both gas flow subsystems can be used simultaneously with no physical barrier between the different media and the first and second local volumes directly adjacent to each other, because (1) the first gas flow subsystem may be configured to keep the second medium away from the first local area, and (2) if the first medium is essentially helium, the performance of the second gas flow subsystem and the second medium will not be hindered even if some of the helium moves into the second local area. Thus, the embodiments described herein can achieve excellent performance by using different media and different gas flow subsystems, while minimizing costs by tailoring the media and gas flow subsystems to specific functions within specific volumes of the inspection subsystem.

[0064] In another embodiment, the first and second gas flow subsystems are configured to control the first and second media during the light shining process and the generation process, respectively. For example, at the start of an inspection process performed on a sample, the first and second gas flow subsystems may replace the gas in the first and second local volumes, respectively. Generally, in the embodiments described herein, the properties of the first and second media in the first and second local volumes should not change substantially during the inspection process. Therefore, the parameters of the first and second gas flow subsystems may be set at the start of the process and not readjusted until the inspection is completed.

[0065] However, the first and second gas flow subsystems may include any sensors or other devices for monitoring one or more characteristics of the first and second media within the first and second local volumes, respectively, during the inspection process. The first and / or second gas flow subsystems and / or the system control subsystem (not shown) may change one or more parameters of the first and / or second gas flow subsystems based on any output in response to the monitored one or more characteristics. Thus, the first and second gas flow subsystems may be configured to have different values ​​for at least one parameter of the gas flow subsystem, for example, the flow rate, during the inspection process. In such an example, if the thickness of the sample changes significantly across the sample, the distance between the objective lens and the sample may change as the inspection subsystem scans the sample. In such a case, it may be desirable to change the settings of one or more vacuum pumps of the first gas flow subsystem during scanning. This would ensure that the vacuum pressure within the first local volume remains substantially the same throughout the entire scan of the sample, regardless of the change in sample thickness.

[0066] In one embodiment, the system includes a chuck configured to support a sample during the illuminating and generating processes, the chuck including a recess in which the sample is positioned during the illuminating and generating processes, the recess configured such that the upper surface of the sample is flush with the upper surface of the chuck outside the recess, while the sample is positioned within the recess. For example, as shown in Figure 2, a sample 212 may be positioned on the chuck 222 during inspection, the chuck having a recess 228, and the sample is positioned such that the upper surface 230 of the sample is substantially flush with the upper surface 232 of the chuck outside the recess. Thus, the diameter of the chuck is larger than the diameter of the sample. The central recess accommodates the sample. The depth of the recess approximates the thickness of a typical sample, such as a wafer, so that the upper surface of the sample is flush with the chuck. Different types of samples may have slightly different thicknesses, but such variations are small with respect to the gap between the housing block and the sample, and the distance between the objective lens and the sample. Vacuum performance can be maintained. The flush design allows the vacuum to be maintained even when scanning the edges of the sample.

[0067] Figure 5 shows in more detail the possible chuck configurations of the embodiments described herein. As previously stated, the chuck may extend beyond the sample, and the upper surface of the portion of the chuck that extends beyond the sample is preferably flush with the upper surface of the sample. In particular, to maintain vacuum when the objective lens 500 approaches the edge of the sample, the extension wing 502 may be contained in the chuck assembly from the mount of the chuck and spindle element 504, and this element may rotate about axis 506. The upper surface of the wing 502 is preferably flush with the upper surface of the sample 508, as shown in Figure 5. In this way, a relatively small gap between the housing block and the sample, and / or between the housing block and the upper surface of the wing, can be maintained over the entire diameter (and area) of the sample.

[0068] Maintaining such a small gap across the entire sample between the housing block and the sample and / or chuck eliminates the need to place the entire inspection subsystem and the sample in a vacuum, and facilitates the creation and maintenance of a vacuum between the objective lens and the sample, as further described herein. In particular, the extension wings can help maintain a vacuum seal between the sample and the objective lens, even when scanning near the edges of the sample. Thus, the vacuum can be maintained throughout the entire inspection process performed on the sample, even when the inspection process scans the edges of the sample, near the edges of the sample, or even beyond the edges of the sample. The thickness may vary slightly depending on the type of sample, but this variation should be small compared to the height of the gap, for example, about 0.5 mm. In this way, the different parts of the chuck assembly can be fixedly mounted to each other without the need for adjustment, as further described herein.

[0069] Figure 5 shows the objective lens 500 as a simplified version of the housing 510, which collectively includes the objective lens housing and the vacuum channel 512 formed therein, but the housing is shown so only so that it can be shown in relation to improved details of the chuck assembly. The inspection subsystem and first and second gas flow subsystems included in the embodiment of the system with the chuck assembly shown in Figure 5 may be further configured as described herein. In addition, the extension wings included in the chuck assembly may surround the entire sample, and are shown in Figure 5 on only one side of the sample for simplification. Furthermore, although the chuck and spindle are shown as a single element in Figure 5, the chuck and spindle may be separate elements coupled in any suitable manner known in the art. The chuck assembly shown in Figure 5 may be further configured as described herein and may be part of a scanning subsystem configured as described herein.

[0070] The chuck may also include two different parts (not shown) whose heights may be adjustable relative to each other, so that the top surface of a sample with a different thickness is flush with the top surface of the part that is not beneath the sample. The system may be configured to control the different parts of the chuck based on prior information about the sample, e.g., the expected thickness of the sample, or the thickness of the sample measured with another tool. The system may also be configured to control the different parts of the chuck based on some visual feedback generated by the system itself regarding the position of the top surface of the sample relative to the top surface of the chuck that is outside the sample. For example, while aligning the sample to the inspection tool, or during a phase of the process performed before the inspection scan, the system may illuminate areas of the sample near and beyond the edges of the sample and detect the light reflected from those areas. The reflected light image may be used to determine whether the top surface of the sample and the chuck outside the sample are flush, and / or whether the depth of the recess needs to be adjusted so that the two surfaces can be flush. Such a function may be similar to an autofocus function performed to focus on the sample before scanning, but in this case, instead of the chuck moving as a single unit, at least one part of the chuck moves relative to the other parts, and the height of the top surface of the sample is positioned relative to the height of the top surface of the chuck outside the sample, rather than the optical hardware.

[0071] Some embodiments of the system include an air bearing positioned outside the first local volume and configured to prevent the first and second gas flow subsystems from contacting the sample. For example, the air bearing may be used in the outer ring of the housing block as a safety guard and, optionally, to reduce the air gap. Thus, the air bearing can prevent the vacuum housing block from contacting the sample. The outlet of the air bearing may be an array of relatively small holes located outside the outermost vacuum stage. The air bearing may include any suitable commercially available vacuum pre-pressurized air bearing known in the art. While the air bearing is optional, it can provide significant advantages to the embodiments described herein. For example, in the absence of an air bearing, a relatively large gap, e.g., several hundred microns, is required between the housing block and the sample, which can prevent the housing block from colliding with the sample. With an air bearing, this gap can be reduced to tens of microns.

[0072] Figure 6 shows one possible implementation configuration including an air bearing. As with other embodiments described herein, the first gas flow subsystem may include a housing block 600. Multiple channels 602 are formed in the housing block and connected to a vacuum pump 604, which together can draw air from a first local volume 606 between the housing block (and an objective lens located therein (not shown in Figure 6)) and the sample 608. The air bearing may include a channel 610 formed in the housing block and located outside any of the channels included in the first gas flow subsystem (e.g., outside any vacuum channel or helium purge channel). The channel may be coupled to a pressurized air source 612 and any other suitable gas flow elements (not shown) as further described herein.

[0073] The air bearing may be configured to allow pressurized air to flow from a source through a channel and out through an outlet of a channel formed in the housing block. In this way, the pressurized air 614 can be pushed into the gap between the outer end of the housing block and the sample, thereby reducing the possibility that the housing block may come into contact with the sample for any reason, such as the vacuum generated by the first gas flow medium.

[0074] This pressurized air is preferably different from any CDA used in the second gas flow subsystem. For example, the pressurized air in the air bearing is used to maintain a proper gap between the housing block and the sample, particularly near the ends of the housing block, while the CDA used as the second medium is used to reduce foreign matter contamination on the sample. Therefore, the pressurized air and the CDA may differ in properties such as pressure, airflow direction, and composition.

[0075] In some embodiments, the first gas flow subsystem includes a housing block through which gas replaces a first medium, and the inspection subsystem is configured to direct light into a region through one or more passages formed through the housing block. For example, the housing block and any of the first and second gas flow subsystems formed therein and / or coupled thereto (including any pump outlets, gas flow channels, channel inlets, etc.) may be configured so that light can be directed to and collected from the sample, regardless of which configuration is selected. In one such example, the pump outlet of a channel formed in the housing block for the first gas flow subsystem may be solid in a certain azimuthal region and perforated to allow illumination to pass through and a reflected beam to emerge. For example, in the embodiment shown in Figure 1, light from a light source 100 is shown directed to a sample through a housing block 108, and the housing block 108 may include a passage (not shown) configured to allow light to pass through. The passage may be an open channel with a window near the sample end of the channel, so that the channel does not affect the first medium formed in the first local volume. Apart from being sealed in some way at the sample end of the passage, the passage may be formed within the housing block in any of the same manner as described herein with respect to the channel of the first gas flow subsystem.

[0076] In another embodiment, the system includes a window element, which is positioned between the objective lens of the inspection subsystem and the sample, and is configured to transmit light from the region without altering the light. For example, a hemispherical dome window may be used with stronger glass such as sapphire, independently of the lens housing. Examples of such window elements are shown in the hemispherical dome windows 234 and 424 in Figures 2 and 4, respectively. As shown in these figures, the hemispherical dome window is positioned between the objective lens and the sample, and the first medium replaces any gas within the dome window and between the dome window and the sample. An advantage of using an additional dome window is that it reduces the stress on the optical element by using stronger glass. The additional dome window may have two conformal and concentric surfaces with the sample surface as the center of curvature to minimize optical aberrations.

[0077] The computer subsystem may be configured to generate sample results, which may include any of the information described herein, such as any defect and / or particle information, or a map of defect and / or particle information for the entire sample. Anomaly results may include, but are not limited to, information regarding the classification of defects and / or particles, such as the location of the anomaly, detection score, class label or ID, or any such appropriate information known in the art. Sample results may be generated by the computer subsystem in any appropriate manner.

[0078] All embodiments described herein may be configured to store the results of one or more steps of the embodiments on a computer-readable storage medium. The results may include any of the results described herein and may be stored in any manner well known in the art. The results of a sample may have any suitable format or type, such as a standard file type. The storage medium may include any storage medium described herein or any other suitable storage medium well known in the art. After the results are stored, the results may be accessed on the storage medium, used by any embodiment of the method or system described herein, formatted for display to a user, and used by another software module, method, or system, etc., to perform one or more functions on a sample or another sample of the same type.

[0079] Such functionality includes, but is not limited to, modifying processes such as manufacturing processes or steps performed on or to be performed on a sample, in a feedback or feedforward manner. For example, a computer subsystem may be configured to determine one or more changes to processes performed on and / or to processes to be performed on a sample based on anomalies. Changes to processes may include any appropriate changes to one or more parameters of the process. The computer subsystem preferably determines these changes so that, for example, anomalies on the sample can be compensated for in another process performed on the sample, so that anomalies on the sample can be corrected or eliminated in another process performed on the sample, so that anomalies can be mitigated or prevented in other samples on which the modified process is performed. The computer subsystem may determine such changes in any appropriate method known in the art.

[0080] These changes may then be transmitted to a semiconductor manufacturing system (not shown) or a storage medium (not shown) accessible to both the computer subsystem and the semiconductor manufacturing system. The semiconductor manufacturing system may or may not be part of the embodiments of the system described herein. For example, the inspection subsystem and / or computer subsystem described herein may be coupled to the semiconductor manufacturing system via one or more common elements such as a housing, power supply, sample processing device, or mechanism. The semiconductor manufacturing system may include any semiconductor manufacturing system well known in the art, such as lithography tools, etching tools, chemical mechanical polishing (CMP) tools, and deposition tools.

[0081] Each embodiment described herein may be combined into a single embodiment unless otherwise specified herein. The embodiments described herein are based on McAninch's U.S. Patent No. 6,813,026, published November 2, 2004; Fielden et al.'s U.S. Patent No. 7,359,052, published April 15, 2008; Wang et al.'s U.S. Patent No. 7,420,681, published September 2, 2008; Fielden et al.'s U.S. Patent No. 7,564,552, published July 21, 2009; and Fielden et al.'s U.S. Patent No. 7,564,552, published November 4, 2009. The invention may also be constructed as described in U.S. Patent No. 7,623,239, U.S. Patent No. 7,755,764 by Kwak et al., issued on 13 July 2010, U.S. Patent No. 7,764,376 by Fielden et al., issued on 27 July 2010, and U.S. Patent No. 11,315,816 by Pressburger et al., issued on 26 April 2022, all of which are incorporated by reference as if they were fully described herein.

[0082] Another embodiment relates to a method for inspecting a sample. This method includes directing light onto a region on the sample and generating an output in response to the light from the sample, which may be performed by an inspection subsystem as shown in Figure 1. This method also includes replacing the gas in a first local volume surrounding the region on the sample with a first medium during the light directing and generating steps, which may be performed by a first gas flow subsystem as shown in Figures 2 and 4. The first medium scatters less light than the gas. In addition, this method includes replacing the gas in a second local volume located adjacent to the first local volume with a second medium during the light directing and generating steps, which may be performed by a second gas flow subsystem as shown in Figures 2 and 4. The second medium is different from the first medium. This method further includes detecting anomalies on the sample based on the output. Detection is performed by a computer system, such as the computer subsystem 122 shown in Figure 1.

[0083] Each step of the method may be performed as further described herein. The method may also include any other step(s) that may be performed by the system(s) described herein. The steps of the method may be performed by the system(s) described herein and may be configured according to any embodiment described herein.

[0084] Additional embodiments relate to a non-temporary computer-readable medium storing program instructions executable on a computer system for performing a computer implementation method for inspecting a sample. One such embodiment is shown in Figure 7. In particular, as shown in Figure 7, the non-temporary computer-readable medium 700 includes program instructions 702 executable on a computer system 704. The computer implementation method may include any step(s) of any(s) of any(s) methods described herein.

[0085] Program instructions 702 implementing a method such as those described herein may be stored on a computer-readable medium 700. The computer-readable medium may be a storage medium such as a magnetic or optical disk, a magnetic tape, or any other suitable non-temporary computer-readable medium known in the art.

[0086] Program instructions can be implemented in any of the following ways, including, in particular, procedure-based techniques, component-based techniques, and / or object-oriented techniques. For example, these program instructions may be implemented using ActiveX controls, C++ objects, JavaBeans, Microsoft Foundation Classes ("MFC"), SSE (Streaming SIMD Extensions), or other techniques or methodologies as needed.

[0087] The computer system 704 may be configured according to any of the embodiments described herein.

[0088] Further modifications and alternative embodiments of various aspects of the present invention will be apparent to those skilled in the art in consideration of this description. For example, methods and systems for inspecting samples are provided. Therefore, this description should be interpreted as merely illustrative and is intended to teach those skilled in the art a general way of carrying out the present invention. It should be understood that the forms of the present invention shown and described herein should be taken as preferred embodiments at present. Elements and materials may be replaced with those illustrated and described herein, parts and processes may be reversed, and certain features of the present invention may be used independently, all of which will be apparent to those skilled in the art in consideration of this description of the present invention. Modifications may be made in elements described herein without departing from the spirit and scope of the present invention as set forth in the following claims.

Claims

1. A system configured to inspect a sample, An inspection subsystem configured to direct light onto a region on the sample and generate an output in response to the light from that region on the sample, A first gas flow subsystem, configured to replace the gas in a first local volume surrounding the region on the sample with a first medium that causes less light scattering than the gas, A second gas flow subsystem, configured to replace the gas in a second local volume adjacent to the first local volume with a second medium different from the first medium, and A computer subsystem configured to detect abnormalities on the sample based on the output, A system equipped with these features.

2. The system according to claim 1, wherein the first medium is essentially helium.

3. The system according to claim 1, wherein the first medium is a vacuum.

4. The system according to claim 1, wherein the first gas flow subsystem includes a plurality of channels for replacing the gas with a first medium, and the first gas flow subsystem is further configured to provide the first medium with different characteristic values ​​adjacent to two or more of the plurality of channels.

5. The system according to claim 4, wherein the first medium is a vacuum and the characteristic is pressure.

6. The system according to claim 1, wherein the refractive index of the first medium at one or more wavelengths of light directed to the region and the light from the region is lower than the refractive index of dry air at one or more wavelengths.

7. The system according to claim 1, wherein the height of the first local volume is defined by the distance between the objective lens of the inspection subsystem and the sample.

8. The system according to claim 1, wherein the second medium is essentially clean dry air.

9. The system according to claim 1, wherein the second gas flow subsystem is further configured not to guide the second medium into the light path directed to the region and the light path from the region.

10. The system according to claim 1, wherein the second gas flow subsystem is further configured to use the second medium to move foreign matter away from the sample.

11. The system according to claim 1, wherein the first and second gas flow subsystems do not alter the gas outside the second local volume.

12. The system according to claim 1, wherein the entire inspection subsystem is not placed in a vacuum.

13. The system according to claim 1, wherein the first and second gas flow subsystems are further configured to simultaneously replace the gas in the first and second local volumes, respectively.

14. The system according to claim 1, wherein the first and second gas flow subsystems are further configured to control the first and second media during the light directing step and the generation step, respectively.

15. The system according to claim 1, further comprising a chuck configured to support the sample during the process of directing light and the process of generating, wherein the chuck includes a recess in which the sample is positioned during the process of directing light and the process of generating, and the recess is configured such that the upper surface of the sample is flush with the upper surface of the chuck outside the recess, while the sample is positioned within the recess.

16. The system according to claim 1, further comprising an air bearing positioned outside the first local volume and configured to prevent the first and second gas flow subsystems from coming into contact with the sample.

17. The system according to claim 1, wherein the first gas flow subsystem includes a housing block through which the gas is replaced with a first medium, and the inspection subsystem is further configured to direct the light to the area through one or more passages formed through the housing block.

18. The system according to claim 1, further comprising a window element, which is positioned between the objective lens of the inspection subsystem and the sample and is configured to transmit light into and from the region without altering the light.

19. A non-temporary computer-readable medium that stores program instructions executable on a computer system for performing a computer implementation method for inspecting a sample, and the computer implementation method is To direct light onto a region on a sample and generate an output that responds to the light from the region on the sample, Replacing the gas in a first local volume surrounding the region on the sample with a first medium during the process of directing light and the process of generating, wherein the first medium causes less light scattering than the gas. Replacing the gas in a second local volume, which is positioned adjacent to the first local volume, with a second medium during the process of directing light and the process of generating, wherein the second medium is different from the first medium, and To detect abnormalities on the sample based on the output, Non-temporary computer-readable media, including [specific examples of such media].

20. A method for detecting a sample, To direct light onto a region on a sample and generate an output that responds to the light from the region on the sample, Replacing the gas in a first local volume surrounding the region on the sample with a first medium during the process of directing light and the process of generating, wherein the first medium causes less light scattering than the gas. Replacing the gas in a second local volume, which is positioned adjacent to the first local volume, with a second medium during the process of directing light and the process of generating, wherein the second medium is different from the first medium, and The detection of an abnormality on the sample is performed based on the output, and the detection is performed by a computer system. Methods that include...

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