Vacuum ultraviolet plasma light source and method of controlling the same

Abstract

The present application relates to a vacuum ultraviolet plasma light source and a control method thereof, which can be applied to wafer detection equipment to irradiate a wafer surface. The vacuum ultraviolet plasma light source comprises: a plasma forming cavity; a working gas supply assembly; a pump laser assembly comprising a focusing light path for focusing pump laser into the plasma forming cavity; a vacuum ultraviolet collection cavity; a plume confinement and differential pumping assembly arranged between the plasma forming cavity and the vacuum ultraviolet collection cavity, comprising, in sequence along a direction from the plasma forming cavity to the vacuum ultraviolet collection cavity, a flow limiting structure, a plume confinement cavity and at least one differential pumping cavity, the differential pumping cavity being connected with a pumping assembly; a plasma imaging unit, an imaging field of view of which covers a plasma core in the plasma forming cavity and a plasma plume extending from the plasma core; and a controller for controlling the assemblies connected therewith according to a morphology of the plasma core and the plasma plume.

Description

Technical Field

[0001] This invention relates to the field of light source and light source control technology, and particularly to a vacuum ultraviolet plasma light source and its control method. Background Technology

[0002] Plasma sources generate vacuum ultraviolet light by focusing a pump laser into a working gas to form plasma. During plasma formation, in addition to the formation of a plasma nucleus, an outward-extending plasma plume typically forms. The length, direction, and diffusion of the plasma plume are easily affected by factors such as the working gas flow rate, cavity pressure, pump laser parameters, and gas jet conditions.

[0003] When the plasma plume is too long, deflected, or excessively diffused, the plume and working gas may enter the vacuum ultraviolet collection path, increasing the absorption loss of vacuum ultraviolet light and the gas load of the subsequent vacuum system, thus affecting the stability of vacuum ultraviolet output.

[0004] Existing plasma light sources are typically controlled based on output light intensity, gas flow rate, or cavity pressure. However, abnormal vacuum ultraviolet output can be caused by a variety of factors, such as plasma core misalignment, abnormal plume morphology, insufficient pumping, changes in gas state, or pump laser anomalies. Relying solely on output light intensity makes it difficult to identify the cause of the anomaly and implement targeted control. Furthermore, existing technologies rarely use the morphology of the plasma core and plasma plume as feedback parameters for closed-loop control. Summary of the Invention

[0005] The purpose of this invention is to provide a vacuum ultraviolet plasma source and its control method, which solves the problems of plasma plume diffusion or deflection in existing vacuum ultraviolet plasma sources, which causes working gas and plasma plume to enter the vacuum ultraviolet collection path, increases vacuum ultraviolet absorption loss and subsequent gas load, and makes it difficult to identify the cause of abnormality and implement targeted closed-loop control based solely on output light intensity.

[0006] The first aspect of this invention discloses a vacuum ultraviolet plasma light source, comprising:

[0007] Plasma forming cavity;

[0008] A working gas supply assembly is connected to the plasma forming cavity;

[0009] A pump laser assembly, including a focusing optical path for focusing a pump laser into the plasma forming cavity;

[0010] A vacuum ultraviolet collection chamber is spaced apart from the plasma forming chamber;

[0011] A plume confinement and differential pumping assembly is disposed between the plasma forming cavity and the vacuum ultraviolet collecting cavity, including a flow limiting structure, a plume confinement cavity and at least one differential pumping cavity that are sequentially connected along the direction from the plasma forming cavity to the vacuum ultraviolet collecting cavity, and the differential pumping cavity is connected to a pumping assembly.

[0012] At least one plasma imaging unit, with an imaging field of view covering the plasma core within the plasma forming cavity and the plasma plume extending from the plasma core; and

[0013] A controller, connected to the plasma imaging unit and to at least one of the working gas supply assembly, the pump laser assembly, and the pumping assembly, is used to control the components connected to the controller based on the morphology of the plasma core and plasma plume as characterized by the images acquired by the plasma imaging unit.

[0014] According to a first aspect of the present invention, it further includes a vacuum ultraviolet output monitoring unit and an operating status detection component, wherein the vacuum ultraviolet output monitoring unit is used to detect at least one of vacuum ultraviolet output intensity, the ratio of vacuum ultraviolet output to ultraviolet output, and the position of the emitted light spot, and the operating status detection component is used to detect at least one of cavity pressure, working gas flow rate, and pumping status.

[0015] The controller is also used to determine the abnormality type corresponding to the abnormality of the vacuum ultraviolet output based on the morphology of the plasma core and the plasma plume, the detection results of the vacuum ultraviolet output monitoring unit and the detection results of the operating status detection component, and to determine the component to be controlled based on the abnormality type.

[0016] According to a first aspect of the present invention, the differential pumping chamber includes at least two differential pumping chambers arranged sequentially along the direction from the plasma forming chamber to the vacuum ultraviolet collecting chamber, and each differential pumping chamber is connected to a pumping branch with an adjustable pumping rate, so that the pressure in the plasma forming chamber, the plume confinement chamber, each of the differential pumping chambers and the vacuum ultraviolet collecting chamber decreases sequentially.

[0017] According to a first aspect of the invention, the controller extracts at least two of the following from the image acquired by the plasma imaging unit: plasma core position, plasma core size, plasma plume length, plasma plume opening angle, plasma plume direction, and the brightness ratio of the plasma core to the plasma plume; and controls the component connected to the controller according to the deviation of the extraction result relative to a corresponding preset range.

[0018] According to a first aspect of the invention, the at least one plasma imaging unit includes a first plasma imaging unit and a second plasma imaging unit with different imaging directions, and the controller is used to determine the three-dimensional position of the plasma core and the extension direction of the plasma plume based on the images acquired by the first plasma imaging unit and the second plasma imaging unit.

[0019] The second aspect of the present invention discloses a control method for a vacuum ultraviolet plasma source, applied to the vacuum ultraviolet plasma source of the first aspect of the present invention, the control method comprising:

[0020] Working gas is supplied to the plasma forming cavity, and a pump laser is focused into the plasma forming cavity to form a plasma core and a plasma plume extending from the plasma core;

[0021] The plasma plume is constrained by a flow-limiting structure and a plume-constraining cavity, and evacuated by at least one differential evacuation cavity to reduce the diffusion of the working gas and the plasma plume into the vacuum ultraviolet collection cavity.

[0022] Acquire images with an imaging field of view covering the plasma core and the plasma plume;

[0023] The morphology of the plasma core and the plasma plume is determined based on the image; and

[0024] Based on the morphology of the plasma core and the plasma plume, at least one of the working gas supply component, the pump laser component, and the pumping component is controlled.

[0025] According to a second aspect of the invention, it further includes:

[0026] Detect at least one of the following: vacuum ultraviolet output intensity, the ratio of vacuum ultraviolet output to ultraviolet output, and the position of the emitted light spot; and detect at least one of the following: cavity pressure, working gas flow rate, and evacuation status.

[0027] Based on the morphology of the plasma core and the plasma plume, the detection results of vacuum ultraviolet output, and the detection results of the operating status, the anomaly type corresponding to the vacuum ultraviolet output anomaly is determined; and

[0028] Based on the type of anomaly, the component to be controlled is determined from the working gas supply component, the pump laser component, and the pumping component.

[0029] According to a second aspect of the invention, the evacuation via at least one differential evacuation chamber includes:

[0030] The pumping rates of at least two differential pumping chambers arranged sequentially along the direction from the plasma forming chamber to the vacuum ultraviolet collecting chamber are adjusted respectively, so that the pressure in the plasma forming chamber, the plume confinement chamber, each of the differential pumping chambers and the vacuum ultraviolet collecting chamber decreases sequentially.

[0031] According to a second aspect of the present invention, determining the morphology of the plasma core and the plasma plume based on the image includes:

[0032] Extract at least two of the following from the image: plasma core location, plasma core size, plasma plume length, plasma plume opening angle, plasma plume direction, and the brightness ratio of the plasma core to the plasma plume.

[0033] The control based on the morphology of the plasma core and the plasma plume includes:

[0034] The deviation of each extracted parameter relative to its corresponding preset range is determined, and at least one of the working gas supply component, the pump laser component, and the pumping component is controlled according to the deviation.

[0035] According to a second aspect of the invention, the acquisition of the image includes:

[0036] First and second images covering the plasma core and the plasma plume were acquired from different imaging directions, respectively.

[0037] Determining the morphology of the plasma core and the plasma plume based on the image includes:

[0038] Based on the first image and the second image, the three-dimensional position of the plasma core and the extension direction of the plasma plume are determined.

[0039] The main differences and effects of the embodiments of the present invention compared with the prior art are as follows:

[0040] In this invention, the vacuum ultraviolet plasma source includes: a plasma forming cavity; a working gas supply component connected to the plasma forming cavity; a pump laser component including a focusing optical path for focusing the pump laser into the plasma forming cavity; a vacuum ultraviolet collecting cavity spaced apart from the plasma forming cavity; a plume confinement and differential pumping component disposed between the plasma forming cavity and the vacuum ultraviolet collecting cavity, including a flow limiting structure, a plume confinement cavity, and at least one differential pumping cavity sequentially connected along the direction from the plasma forming cavity to the vacuum ultraviolet collecting cavity, the differential pumping cavity being connected to a pumping component; at least one plasma imaging unit, the imaging field of view covering the plasma core and the plasma plume extending from the plasma core within the plasma forming cavity; and a controller connected to the plasma imaging unit and connected to at least one of the working gas supply component, the pump laser component, and the pumping component, for controlling the component connected to the controller according to the morphology of the plasma core and the plasma plume characterized by the image acquired by the plasma imaging unit. The current-limiting structure and plume confinement cavity limit the extension and diffusion of the plasma plume, while the differential pumping cavity removes the working gas and plasma plume diffusing into the vacuum ultraviolet collection cavity, thereby reducing the gas load on the vacuum ultraviolet collection cavity and minimizing absorption loss of vacuum ultraviolet light. The plasma imaging unit simultaneously acquires images of the plasma core and plasma plume, enabling the controller to adjust the working gas supply component, pump laser component, or pumping component based on changes in their morphology. This suppresses plasma core shift, plume elongation, deflection, and diffusion, improving the stability of plasma morphology and vacuum ultraviolet output.

[0041] In this invention, a control method for a vacuum ultraviolet plasma source is applied to the vacuum ultraviolet plasma source of the first aspect of this invention. The control method includes: supplying a working gas to a plasma forming cavity and focusing a pump laser into the plasma forming cavity to form a plasma core and a plasma plume extending from the plasma core; constraining the plasma plume by a current-limiting structure and a plume-constraining cavity, and evacuating gas through at least one differential pumping cavity to reduce the diffusion of the working gas and plasma plume into the vacuum ultraviolet collecting cavity; acquiring an image covering the plasma core and plasma plume in the imaging field of view; determining the morphology of the plasma core and plasma plume based on the image; and controlling at least one of the working gas supply component, the pump laser component, and the pumping component based on the morphology of the plasma core and plasma plume. By constraining and evacuating the plasma plume and working gas through the current-limiting structure, the plume-constraining cavity, and the differential pumping cavity, their diffusion into the vacuum ultraviolet collecting cavity can be reduced, thereby reducing the absorption loss of vacuum ultraviolet light and the subsequent gas load. By acquiring images of the plasma core and plasma plume, and controlling the working gas supply component, pump laser component, or pumping component according to their morphology, adjustments can be made to address abnormal states such as core offset, excessive plume length, plume deflection, or plume diffusion. This achieves closed-loop control based on plasma morphology and improves the operational stability of the vacuum ultraviolet light source. Attached Figure Description

[0042] Figure 1 A schematic diagram of a vacuum ultraviolet plasma light source according to an embodiment of this application is shown. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of this application clearer, the embodiments of this application will be described in further detail below with reference to the accompanying drawings.

[0044] During operation, the length, direction, and diffusion range of the plasma plume in existing vacuum ultraviolet plasma sources are easily affected by factors such as working gas flow rate, cavity pressure, pump laser power, pump laser focal point position, and the state of the current-limiting structure. When the plasma plume, hot gas, and residual working gas enter the vacuum ultraviolet collection optical path, they may further increase the absorption loss of vacuum ultraviolet radiation and the gas load on subsequent cavities. When only monitoring the vacuum ultraviolet output intensity, it is usually difficult to distinguish whether the output decrease is caused by plasma core shift, plasma plume expansion, insufficient differential pumping, changes in working gas state, changes in pump laser state, or optical component contamination.

[0045] Based on this, this application restricts the diffusion of plasma plume and working gas through a flow-limiting structure, a plume confinement cavity, and a differential pumping cavity. It also acquires images simultaneously covering the plasma core and plasma plume, using the morphology of the plasma core and plume as feedback parameters to control at least one of the following: working gas supply, pump laser, and pumping. Some embodiments further analyze the plasma images in conjunction with vacuum ultraviolet output, cavity pressure, working gas flow rate, and pumping status to identify anomaly types and select the appropriate control target.

[0046] Embodiments of this application disclose a vacuum ultraviolet plasma light source. For example... Figure 1 As shown, the vacuum ultraviolet plasma source includes a plasma forming cavity 11, a working gas supply assembly 12, a pump laser assembly 13, a vacuum ultraviolet collection cavity 14, a plume confinement and differential pumping assembly 15, at least one plasma imaging unit 16, a controller 17, and a pumping assembly 18.

[0047] The working gas supply assembly 12 is connected to the plasma forming chamber 11 and is used to supply the working gas required for plasma formation to the plasma forming chamber 11. The working gas supply assembly 12 may include a working gas source 121 and a gas supply line 122, with the gas supply line 122 connecting the working gas source 121 and the plasma forming chamber 11. The working gas supply assembly 12 may also be provided with a flow regulator or pressure regulator for adjusting the working gas flow rate or pressure, enabling the controller 17 to regulate the working gas flow rate, working gas pressure, or back pressure upstream of the flow limiting structure 151 entering the plasma forming chamber 11.

[0048] The pump laser assembly 13 includes a pump laser 131 and a focusing optical path 132. The focusing optical path 132 receives the pump laser output from the pump laser 131 and focuses the pump laser into a plasma forming cavity 11. The pump laser interacts with the working gas to form and maintain a plasma core 111 within the plasma forming cavity 11. The plasma core 111 generates vacuum ultraviolet radiation and forms a plasma plume 112 extending downstream from the plasma core 111. Adjustable parameters of the pump laser assembly 13 may include at least one of the pump laser power, the pump laser incident position, and the pump laser focal position.

[0049] The vacuum ultraviolet collecting cavity 14 is spaced apart from the plasma forming cavity 11 and is used to receive vacuum ultraviolet radiation emitted by the plasma core 111 and propagating along a predetermined light emission direction. Vacuum ultraviolet collecting optics can be installed in the vacuum ultraviolet collecting cavity 14 to collect the vacuum ultraviolet radiation and guide it to the subsequent illumination optical path.

[0050] A plume confinement and differential pumping assembly 15 is disposed between the plasma forming chamber 11 and the vacuum ultraviolet collecting chamber 14. The plume confinement and differential pumping assembly 15 includes a flow-limiting structure 151, a plume confinement chamber 152, and at least one differential pumping chamber, sequentially connected along the direction from the plasma forming chamber 11 to the vacuum ultraviolet collecting chamber 14. The flow-limiting structure 151, which may be formed by a nozzle, is used to limit the flow rate of working gas from the plasma forming chamber 11 to the plume confinement chamber 152 and to confine the initial extension range of the plasma plume 112. The plume confinement chamber 152 is disposed along a predetermined extension direction of the plasma plume 112 and is used to limit the directional and lateral diffusion range of the plasma plume 112.

[0051] The differential pumping chamber is connected to the pumping assembly 18. The pumping assembly 18 pumps air from the differential pumping chamber, creating a pressure difference between the plume confinement chamber 152, the differential pumping chamber, and the vacuum ultraviolet collection chamber 14. Vacuum ultraviolet radiation can enter the vacuum ultraviolet collection chamber 14 through the flow-limiting structure 151, the plume confinement chamber 152, and the light-transmitting area of ​​the differential pumping chamber, while most of the working gas, hot gas, and plasma plume 112 are limited by the airflow and pressure gradient formed by the flow-limiting structure 151, the plume confinement chamber 152, and the differential pumping.

[0052] The plasma imaging unit 16 can be positioned laterally to the plasma forming cavity 11, and its imaging field of view simultaneously covers the plasma core 111 and the plasma plume 112 extending from the plasma core 111. The plasma imaging unit 16 can acquire plasma images continuously or at predetermined intervals. During image acquisition, the exposure time, imaging gain, and optical filtering conditions can be fixed to allow for comparison of images acquired at different times. The plasma imaging unit 16 can also perform exposure normalization on the images when camera parameters change.

[0053] The controller 17 is connected to the plasma imaging unit 16 and is controlled by at least one of the working gas supply assembly 12, the pump laser assembly 13, and the pumping assembly 18. The controller 17 receives images acquired by the plasma imaging unit 16, identifies the plasma core 111 and the plasma plume 112 from the images, and determines parameters characterizing the morphology of the plasma core 111 and the plasma plume 112. The controller 17 controls at least one of the working gas supply assembly 12, the pump laser assembly 13, and the pumping assembly 18 based on the determined morphological parameters.

[0054] For example, when the length of the plasma plume 112 exceeds a corresponding preset range, or when the plasma plume 112 extends into the vacuum ultraviolet collection path, the controller 17 can increase the pumping rate of the pumping assembly 18, or decrease the working gas flow rate supplied by the working gas supply assembly 12. When the plasma core 111 deviates from a preset position, the controller 17 can adjust the focal position or incident position of the pump laser assembly 13, and can also adjust the working gas pressure. When the opening angle of the plasma plume 112 increases or its direction deflects, the controller 17 can adjust the pumping rate, the working gas flow rate, the back pressure upstream of the flow-limiting structure 151, or the cavity pressure.

[0055] When the controller 17 performs automatic adjustment, it can set adjustment limits, adjustment intervals, control hysteresis, and recovery confirmation conditions. For pump laser power or focal position with a fast response, a shorter observation time can be used; for working gas flow rate, cavity pressure, evacuation valve opening, or vacuum pump speed with a slow response, a corresponding stabilization time can be waited after each adjustment. The controller 17 can prioritize changing one main control variable within a control cycle, and after judging the adjustment effect of the main control variable, decide whether to adjust other control variables to reduce closed-loop oscillations caused by simultaneous changes in multiple control variables.

[0056] Therefore, the flow-limiting structure 151, the plume confinement cavity 152, and the differential pumping cavity can spatially restrict the diffusion of the working gas and plasma plume 112 into the vacuum ultraviolet collection cavity 14. The plasma imaging unit 16 and the controller 17 can use the morphology of the plasma core 111 and the plasma plume 112 as feedback quantities for control. Compared with control based solely on the vacuum ultraviolet output intensity, this embodiment can more directly reflect the spatial state of the plasma, which is beneficial for stabilizing the position and size of the plasma core 111, limiting the length and diffusion range of the plasma plume 112, and reducing the absorption loss of vacuum ultraviolet radiation in the working gas and residual gas.

[0057] The vacuum ultraviolet plasma light source according to the embodiments of this application further includes a vacuum ultraviolet output monitoring unit 19 and an operating status detection component 20.

[0058] The vacuum ultraviolet output monitoring unit 19 can be disposed in the vacuum ultraviolet collection cavity 14 or in the subsequent optical path of the vacuum ultraviolet collection cavity 14, and is used to detect at least one of the following: vacuum ultraviolet output intensity, the ratio of vacuum ultraviolet output to ultraviolet output, and the position of the emitted light spot. The ratio of vacuum ultraviolet output to ultraviolet output can be obtained by detection channels with different response bands. The position of the emitted light spot can be used to characterize the positional deviation of the vacuum ultraviolet radiation relative to the predetermined collection optical path.

[0059] The operational status detection component 20 is used to detect at least one of the following: chamber pressure, working gas flow rate, and pumping status. The chamber pressure may include the pressure of at least one of the plasma formation chamber 11, the plume confinement chamber 152, the differential pumping chambers, and the vacuum ultraviolet collection chamber 14. The pumping status may be characterized by the opening degree of the pumping valve, the vacuum pump speed, the pressure of the pumping branch, or the operational status of the pumping assembly 18. The operational status detection component 20 is connected to the detected chamber, the gas supply line 122, or the pumping assembly 18 via corresponding detection terminals and sends the detection signals to the controller 17.

[0060] The controller 17 determines the type of abnormality corresponding to the abnormality of the vacuum ultraviolet output based on the morphology of the plasma core 111 and the plasma plume 112, the detection results of the vacuum ultraviolet output monitoring unit 19 and the detection results of the operating status detection component 20, and determines the component to be controlled based on the type of abnormality.

[0061] For example, when the morphology of the plasma core 111 and plasma plume 112 remains relatively stable, but the vacuum ultraviolet output intensity decreases, the controller 17 can determine that the anomaly is more likely related to residual gas absorption, window contamination, or collection optics contamination in the vacuum ultraviolet transmission path, rather than directly increasing the pump laser power. In this case, the controller 17 can increase the differential pumping capability, perform purging or self-cleaning operations, or output a maintenance prompt.

[0062] When the image brightness and vacuum ultraviolet output intensity of the plasma core 111 decrease synchronously, the controller 17 can determine that the anomaly may be related to pump laser focus shift, insufficient pump laser energy coupling, unsuitable working gas density, or plasma extinguishing. The controller 17 can first check the position of the plasma core 111 and adjust the pump laser focus position, and if necessary, slightly adjust the pump laser power, working gas flow rate, or working gas pressure.

[0063] When the image brightness of the plasma core 111 increases or remains essentially unchanged, while the vacuum ultraviolet output intensity decreases and the plasma plume 112 becomes longer, the controller 17 can determine that the absorption or reabsorption of vacuum ultraviolet radiation has increased. At this time, the differential pumping rate can be increased or the working gas flow rate and the back pressure upstream of the flow-limiting structure 151 can be reduced to cause the plasma plume 112 to contract.

[0064] When the plasma core 111 shifts and the position of the emitted laser spot changes, the controller 17 can prioritize adjusting the pump laser focus position or the pump laser incident position. When the plasma plume 112 deflects and there is an asymmetry in the pressure or pumping state of each differential pumping chamber, the controller 17 can determine that the abnormality may be related to the state of the flow limiting structure 151 or uneven pumping, and adjust the pumping rate of the corresponding pumping branch.

[0065] It should be noted that the image brightness of the plasma core 111 is used to characterize the plasma morphology and energy coupling state, and a linear relationship between it and the vacuum ultraviolet output intensity is not required. Image brightness and vacuum ultraviolet output intensity may also be affected by factors such as spectral self-absorption, local electron density, gas temperature, residual gas absorption, optical component contamination, and imaging response characteristics. Therefore, the controller 17 can use the image parameters in conjunction with vacuum ultraviolet output, pressure, flow rate, and pumping status, rather than using image brightness to replace the detection results of the vacuum ultraviolet output monitoring unit 19.

[0066] In one embodiment, the controller 17 can sequentially perform illumination confirmation, stable baseline acquisition, normal operation, anomaly correction, and protection processing. After the plasma is illuminated and the pressure and flow rate are basically stable, the controller 17 acquires images and detection data within a predetermined time to form a stable baseline for parameters such as plasma core position, core size, core brightness, plume length, plume opening angle, and vacuum ultraviolet output. During normal operation, the controller 17 uses the deviation of each parameter from the stable baseline as the basis for judgment. When the deviation continuously exceeds the warning threshold, the controller 17 enters the anomaly correction state; when the deviation reaches the protection threshold, or fails to recover after multiple consecutive adjustments, the controller 17 can reduce or turn off the pump laser 131, increase the pumping rate, close the output shutter, or output a maintenance prompt.

[0067] By jointly analyzing plasma images, vacuum ultraviolet output, and operating status, this embodiment can determine the causes of abnormal vacuum ultraviolet output and select the working gas supply component 12, pump laser component 13, or pumping component 18 as the control object according to the cause of the abnormality, thereby reducing the situation where repeated adjustments using a single control quantity cannot eliminate the abnormality.

[0068] According to an embodiment of this application, the vacuum ultraviolet plasma light source includes at least two differential pumping chambers arranged sequentially along the direction from the plasma forming chamber 11 to the vacuum ultraviolet collecting chamber 14. Figure 1 In the embodiment shown, at least two differential suction chambers include a first differential suction chamber 153 and a second differential suction chamber 154.

[0069] The first differential pumping chamber 153 is disposed between the plume confinement chamber 152 and the second differential pumping chamber 154, and the second differential pumping chamber 154 is disposed between the first differential pumping chamber 153 and the vacuum ultraviolet collection chamber 14. The pumping assembly 18 includes a first pumping branch 181 and a second pumping branch 182. The first pumping branch 181 is connected to the first differential pumping chamber 153, and the second pumping branch 182 is connected to the second differential pumping chamber 154. The pumping rates of the first pumping branch 181 and the second pumping branch 182 are adjustable, for example, by adjusting the opening of the pumping valve or the speed of the vacuum pump to adjust the pumping rate of the corresponding differential pumping chamber.

[0070] During the operation of the light source, by adjusting the first extraction branch 181 and the second extraction branch 182 respectively, the pressure in the plasma forming cavity 11, the plume confinement cavity 152, the first differential extraction cavity 153, the second differential extraction cavity 154, and the vacuum ultraviolet collection cavity 14 can be sequentially reduced along the direction of vacuum ultraviolet radiation propagation, that is, satisfying:

[0071] The pressure in plasma forming chamber 11 > the pressure in plume confinement chamber 152 > the pressure in first differential pumping chamber 153 > the pressure in second differential pumping chamber 154 > the pressure in vacuum ultraviolet collection chamber 14.

[0072] The first differential pumping chamber 153 is mainly used to remove the working gas flowing out of the plume confinement chamber 152 and limit the plasma plume 112 from continuing to extend. The second differential pumping chamber 154 further reduces the gas load entering the vacuum ultraviolet collection chamber 14. The controller 17 can adjust the first pumping branch 181 and the second pumping branch 182 according to the length, opening angle, and direction of the plasma plume 112, as well as the pressure of the first differential pumping chamber 153 and the second differential pumping chamber 154.

[0073] For example, when the plasma plume 112 becomes longer or extends into the differential pumping channel and the vacuum ultraviolet collection path, the pumping rate of the first pumping branch 181 can be increased preferentially. If the pressure in the vacuum ultraviolet collection chamber 14 is still too high after adjusting the first pumping branch 181, the pumping rate of the second pumping branch 182 can be further increased. If the plasma plume 112 still does not return to the preset range after increasing the pumping rate, the controller 17 can reduce the working gas flow rate or the back pressure upstream of the flow-limiting structure 151.

[0074] In one example, controller 17 uses the plume length L0 during stable operation as a baseline. When the increase in the current plume length Lp relative to L0 reaches a warning condition and persists for a predetermined time, controller 17 can gradually increase the opening of the suction valve of the first suction branch 181; if the plume length Lp has not recovered after the predetermined observation time, the opening of the suction valve of the second suction branch 182 is further increased. The above adjustment range and observation time can be preset according to the cavity volume, suction capacity, and type of working gas.

[0075] By setting at least two differential pumping chambers for pumping gas, a multi-stage pressure gradient can be formed between the plasma forming chamber 11 and the vacuum ultraviolet collecting chamber 14. Compared with setting only a single pumping chamber, the multi-stage differential pumping structure is beneficial to gradually reduce the gas load without excessively disturbing the plasma core 111, and to reduce the entry of plasma plume 112, hot gas and residual working gas into the vacuum ultraviolet collecting chamber 14.

[0076] According to the vacuum ultraviolet plasma light source of this application embodiment, the controller 17 extracts at least two of the following from the image acquired by the plasma imaging unit 16: plasma core position, plasma core size, plasma plume length, plasma plume opening angle, plasma plume direction, and the brightness ratio of the plasma core to the plasma plume. The controller 17 then controls the components connected to the controller 17 based on the deviation of the extraction results relative to a corresponding preset range.

[0077] Before extracting morphological parameters, the controller 17 can preprocess the image acquired by the plasma imaging unit 16. Preprocessing may include at least one of dark field subtraction, flat field correction, exposure normalization, region of interest (ROI) cropping, and temporal denoising. The dark field image can be acquired when the pump laser 131 is not lit, and is used to subtract dark current, fixed pattern noise, and background stray light. The ROI may at least cover the outlet of the current-limiting structure 151, the plasma core 111, the plasma plume 112, and the region adjacent to the vacuum ultraviolet collection path.

[0078] The controller 17 can use one or more methods selected from threshold segmentation, edge recognition, contour fitting, skeleton extraction, principal axis fitting, and machine learning classification to obtain the plasma core region and the plasma plume region. The plasma core region can be defined as a relatively compact and bright connected region located near a preset illumination area. The plasma plume region can be defined as a region connected to the plasma core region or the outlet region of the flow-limiting structure 151, with a lower brightness than the plasma core region, and extending along a predetermined airflow direction.

[0079] In one example, controller 17 determines the core region segmentation threshold Tc based on the image background mean Ib, background noise σb, and grayscale statistics within the region of interest. The core region segmentation threshold Tc can be expressed as:

[0080] Tc=max(Ib+kc·σb, ηc·I95),

[0081] Where I95 is the 95th percentile value of gray level in the region of interest, and kc and ηc are preset coefficients. For example, kc can be 8 to 15, and ηc can be 0.45 to 0.65. The controller 17 selects a connected region close to the preset illumination position from the connected regions where the gray level is higher than the core region segmentation threshold Tc as the plasma core region.

[0082] The controller 17 can calculate the gray-weighted centroid of the plasma core 111 based on the position and gray level of each pixel within the plasma core region, and use this gray-weighted centroid as the position of the plasma core. The controller 17 can also obtain the core area Ac based on the pixel area of ​​the plasma core region, calculate the equivalent diameter Dc based on the core area Ac, and sum the pixel gray levels within the plasma core region to obtain the core brightness Bc. The plasma core size can be characterized by at least one of the core area Ac, equivalent diameter Dc, major axis dimension, minor axis dimension, or aspect ratio.

[0083] Plasma plumes can be segmented using a plume segmentation threshold Tp that is lower than the core region segmentation threshold Tc. For example, the plume segmentation threshold Tp can be expressed as:

[0084] Tp=max(Ib+kp·σb, ηp·I95),

[0085] Wherein, kp can be 3 to 6, and ηp can be 0.08 to 0.18. Controller 17 can exclude pixels that have been identified as plasma core regions, and based on the connectivity between the plume region and the plasma core region or the outlet region of the flow-limiting structure 151, exclude random noise, reflected light spots, and non-plume luminescent regions.

[0086] The controller 17 can perform contour fitting, skeleton extraction, or principal axis fitting on the plasma plume region to obtain the centerline or principal axis of the plasma plume 112. The length of the plasma plume can be characterized by the distance from the outlet of the plasma core 111 or the flow-limiting structure 151 to the end of the plume region along the centerline or principal axis; the opening angle of the plasma plume can be characterized by the angle formed by the two sides of the plume region relative to the plume principal axis; the direction of the plasma plume can be characterized by the direction angle of the plume principal axis relative to a preset direction. The brightness ratio of the plasma core to the plasma plume can be characterized by the ratio of the cumulative brightness of the core region to the cumulative brightness of the plume region.

[0087] Furthermore, the controller 17 can also extract at least one of the following: plasma plume width, plume center offset, core brightness fluctuation, plume length fluctuation, and protection optical path intrusion index. The protection optical path intrusion index characterizes the degree of overlap between the plasma plume region and a preset protected vacuum ultraviolet collection path region, and can be determined by the ratio of the overlapping pixel area of ​​the plume region and the protected vacuum ultraviolet collection path region to the pixel area of ​​the protected region. Here, the plasma plume region can characterize not only the visible plasma afterglow but also the risk range of working gas, hot gas, or contaminant particles entering the subsequent collection optical path.

[0088] The controller 17 can continuously acquire images for a predetermined time after the light source is lit and stabilized, and establish a stable baseline based on the acquired images. The stable baseline may include the core position baseline, core size baseline, core brightness baseline, plume length baseline, plume opening angle baseline, plume direction baseline, and vacuum ultraviolet output baseline. The corresponding preset range can be set based on the relative deviation of the stable baseline, rather than using a fixed absolute threshold applicable to all working gases, flow-limiting structures, and working pressures.

[0089] To reduce the impact of plasma scintillation on the control results, the controller 17 can perform median processing or weighted averaging on multiple consecutive frames of images, and can also calculate short-time window averages and long-time window averages separately. The short-time window average is used for closed-loop operation and minor anomaly correction, while the long-time window average and its rate of change are used to identify slow changes such as window contamination, reduced pumping capacity, or changes in the state of the flow-limiting structure 151. If a single frame parameter exceeds the preset range, it can be recorded; adjustment is only performed when the parameter exceeds the preset range for multiple consecutive control cycles or for a predetermined duration.

[0090] When the plume length, plume opening angle, or protective optical path intrusion index exceeds the corresponding preset range, the controller 17 can preferentially adjust the pumping component 18 or the working gas supply component 12 to improve the differential pumping capability or reduce the gas load. When the plasma core position deviates from the corresponding preset range, the controller 17 can preferentially adjust the focal position or incident position of the pump laser component 13. When the plasma core brightness decreases and the vacuum ultraviolet output decreases synchronously, the power of the pump laser 131 can be slightly increased after confirming that there are no abnormalities in the core position and plume length that are unsuitable for increasing the power.

[0091] By simultaneously extracting at least two morphological parameters, control decisions can be avoided based solely on a single image brightness or a single plume length. For example, combining core position and plume direction can distinguish between pump laser focus shift and airflow deflection, while combining core brightness, plume length, and vacuum ultraviolet output can distinguish between insufficient energy coupling and increased plume absorption, thereby improving the targeting and stability of closed-loop control.

[0092] According to the vacuum ultraviolet plasma light source of the present application embodiment, at least one plasma imaging unit 16 includes a first plasma imaging unit 161 and a second plasma imaging unit 162 with different imaging directions.

[0093] The first plasma imaging unit 161 and the second plasma imaging unit 162 acquire images covering the plasma core 111 and the plasma plume 112 from different directions. The two imaging directions can form a predetermined angle, for example, they can be approximately perpendicular to each other. The first plasma imaging unit 161 and the second plasma imaging unit 162 can use a unified time reference for image acquisition, so that the controller 17 can match images at the same operating time or adjacent operating times.

[0094] Before determining the three-dimensional position, the correspondence between the pixel coordinate system of the first plasma imaging unit 161 and the second plasma imaging unit 162 and the light source mechanical coordinate system can be established respectively. The controller 17 extracts the projection position of the plasma core 111 and the projection direction of the plasma plume 112 from the images acquired by the first plasma imaging unit 161 and the second plasma imaging unit 162 respectively, and determines the three-dimensional position of the plasma core 111 and the spatial extension direction of the plasma plume 112 by combining the geometric relationship between the two imaging directions.

[0095] In one example, when the plasma core 111 determined by both imaging directions is offset relative to a preset position, the controller 17 adjusts the focal position of the pump laser assembly 13 according to the synthesized three-dimensional offset direction. When the plume deflection is more significant in one imaging direction, while the plume direction remains basically unchanged in the other imaging direction, the controller 17 can determine that the plasma plume 112 is mainly deflected in the plane corresponding to the previous imaging direction, and accordingly determine the pumping branch or other control quantities that need to be adjusted.

[0096] When the spatial extension direction of the plasma plume 112 deviates from the predetermined vacuum ultraviolet light direction, and the vacuum ultraviolet output monitoring unit 19 detects a corresponding shift in the position of the emitted light spot, the controller 17 can adjust the working gas pressure, the pumping rate of the pumping component 18, or the focal position of the pump laser component 13 to restore the plasma core 111 and the plasma plume 112 to the corresponding preset range.

[0097] The core position, plume length, and plume opening angle obtained from a single imaging direction are typically projection parameters within the corresponding imaging plane. By setting up a first plasma imaging unit 161 and a second plasma imaging unit 162, the possibility that the plasma core 111 or plasma plume 112 may be offset along the single camera's line of sight and thus difficult to identify can be reduced, which helps to improve the accuracy of determining the spatial position and plume extension direction.

[0098] Embodiments of this application also disclose a control method for a vacuum ultraviolet plasma source. This control method can be applied to the aforementioned vacuum ultraviolet plasma source.

[0099] The controller 17 controls the working gas supply assembly 12 to supply working gas to the plasma forming cavity 11 through the gas supply pipeline 122, and controls the pump laser 131 to output pump laser. The focusing optical path 132 focuses the pump laser into the plasma forming cavity 11, so that the working gas forms a plasma core 111, and forms a plasma plume 112 extending downstream from the plasma core 111.

[0100] The working gas and plasma plume 112 enter the plume confinement cavity 152 via the flow-limiting structure 151. The flow-limiting structure 151 restricts the gas flow rate, and the plume confinement cavity 152 restricts the direction and lateral diffusion range of the plasma plume 112. The pumping assembly 18 pumps gas through at least one differential pumping cavity, creating a pressure gradient between the plume confinement cavity 152, the differential pumping cavity, and the vacuum ultraviolet collection cavity 14 to reduce the diffusion of the working gas and plasma plume 112 into the vacuum ultraviolet collection cavity 14.

[0101] The plasma imaging unit 16 acquires images covering the plasma core 111 and plasma plume 112 within its imaging field of view, and sends the images to the controller 17. The controller 17 processes the images, identifies the plasma core 111 and plasma plume 112, and determines the plasma morphology based on at least one of the following: plasma core location, plasma core size, plasma plume length, plasma plume opening angle, plasma plume direction, and the brightness relationship between the core and plume.

[0102] The controller 17 compares the determined plasma configuration with a corresponding preset range and controls at least one of the working gas supply assembly 12, the pump laser assembly 13, and the pumping assembly 18 based on the comparison result. For example, it increases the pumping rate or decreases the working gas flow rate when the plasma plume 112 is too long, adjusts the pump laser focus position when the plasma core 111 is deflected, and adjusts the pumping rate of the corresponding differential pumping branch when the plasma plume 112 is deflected.

[0103] This embodiment continuously or periodically acquires the spatial morphology of the plasma core 111 and plasma plume 112 during the operation of the vacuum ultraviolet plasma source, and uses this spatial morphology as a control feedback quantity, enabling direct feedback control of plasma state changes. Simultaneously, by limiting the flow and using differential pumping to reduce the entry of working gas and plasma plume 112 into the vacuum ultraviolet collection cavity 14, it is beneficial to balance plasma operation stability and vacuum ultraviolet transmission efficiency.

[0104] According to the control method of the vacuum ultraviolet plasma source in the embodiments of this application, at least one of the vacuum ultraviolet output intensity, the ratio of vacuum ultraviolet output to ultraviolet output, and the position of the emitted light spot is detected by the vacuum ultraviolet output monitoring unit 19, and at least one of the cavity pressure, working gas flow rate, and pumping status is detected by the operating status detection component 20.

[0105] The controller 17 can acquire plasma images, vacuum ultraviolet output detection results, and operating status detection results synchronously or in a manner with a defined time correspondence. Based on the morphology of the plasma core 111 and plasma plume 112, the vacuum ultraviolet output detection results, and the operating status detection results, the controller 17 determines the anomaly type corresponding to the vacuum ultraviolet output anomaly.

[0106] When the vacuum ultraviolet output decreases but the morphology of the plasma core 111 and plasma plume 112 does not deteriorate synchronously, the anomaly can be identified as increased absorption along the vacuum ultraviolet transmission path or optical contamination. When the vacuum ultraviolet output decreases and the brightness of the plasma core 111 decreases synchronously, the anomaly can be identified as insufficient energy coupling, focus shift, abnormal gas state, or plasma extinguishing. When the vacuum ultraviolet output decreases, the brightness of the plasma core 111 does not decrease, but the plasma plume 112 lengthens, the anomaly can be identified as plume expansion or increased gas absorption. When the emitted laser spot shifts synchronously with the plasma core 111, the anomaly can be identified as an abnormal pump laser focus or plasma core position.

[0107] Based on the type of anomaly, the controller 17 determines the component to be controlled from the working gas supply component 12, the pump laser component 13, and the pumping component 18. For plume expansion or increased gas absorption, the pumping component 18 is adjusted first, or the working gas load is reduced; for abnormal plasma core position, the focal position of the pump laser component 13 is adjusted first; for insufficient energy coupling, the pump laser power is adjusted after confirming that the plume has not expanded excessively; for contamination of the vacuum ultraviolet transmission path, a maintenance prompt can be output or corresponding purging and protection operations can be performed.

[0108] Once the detection result recovers to the corresponding preset range, the controller 17 can maintain the current control parameters and exit the abnormal correction state after the recovery conditions are met for several consecutive control cycles. When the detection result reaches the protection condition or continuous adjustment fails to produce improvement, the controller 17 can perform at least one of the following actions: reducing the pump laser power, turning off the pump laser 131, increasing the pumping rate, turning off the output shutter, pausing the operation of downstream equipment, or outputting a maintenance prompt.

[0109] Therefore, this embodiment can distinguish the cause of the abnormality based on the corresponding change relationship between multiple detection quantities, and select the control object corresponding to the cause of the abnormality, thereby avoiding directly increasing the pump laser power based solely on the decrease in vacuum ultraviolet output, which would reduce the possibility of further expansion of the plume or further increase in the subsequent gas load.

[0110] According to the control method of the vacuum ultraviolet plasma source according to the embodiments of this application, gas is pumped through at least one differential pumping chamber, including adjusting the pumping rate of at least two differential pumping chambers arranged sequentially along the direction from plasma forming chamber 11 to vacuum ultraviolet collecting chamber 14.

[0111] In the embodiment with a first differential pumping chamber 153 and a second differential pumping chamber 154, the controller 17 controls the first pumping branch 181 and the second pumping branch 182 respectively. The first pumping branch 181 pumps air from the first differential pumping chamber 153, and the second pumping branch 182 pumps air from the second differential pumping chamber 154, thereby sequentially reducing the pressure in the plasma forming chamber 11, the plume confinement chamber 152, the first differential pumping chamber 153, the second differential pumping chamber 154, and the vacuum ultraviolet collection chamber 14.

[0112] The controller 17 can determine the target pumping rates of the first pumping branch 181 and the second pumping branch 182 based on the pressure deviation of each cavity and the shape of the plasma plume 112. When the plasma plume 112 mainly expands near the plume confinement cavity 152 or the first differential pumping cavity 153, the pumping rate of the first pumping branch 181 can be increased preferentially; when the pressure of the second differential pumping cavity 154 or the vacuum ultraviolet collection cavity 14 increases, while the plasma core 111 is basically stable, the pumping rate of the second pumping branch 182 can be increased.

[0113] During the adjustment of the pumping rate, the controller 17 can limit the adjustment range of a single pumping operation and wait for the pressure and plume parameters to reach a relatively stable state after each adjustment. If increasing the pumping rate of the first pumping branch 181 or the second pumping branch 182 causes a significant change in the position or size of the plasma core 111, the controller 17 can reduce the corresponding adjustment range or restore the previous pumping setting.

[0114] This embodiment controls the pumping rate of different differential pumping chambers separately, which can be adjusted in stages according to the changes in gas load at different positions. This reduces the disturbance of the plasma core 111 caused by the changes in pumping while limiting the plasma plume 112 and reducing the pressure of the vacuum ultraviolet collection chamber 14.

[0115] According to the control method of the vacuum ultraviolet plasma source according to the embodiments of this application, the morphology of the plasma core 111 and the plasma plume 112 is determined based on the image, including preprocessing the image to obtain the plasma core region and the plasma plume region respectively, and extracting at least two of the following from the image: plasma core position, plasma core size, plasma plume length, plasma plume opening angle, plasma plume direction, and the brightness ratio of the plasma core and the plasma plume.

[0116] Preprocessing may include at least one of dark field subtraction, flattening correction, exposure normalization, region of interest clipping, and temporal denoising. Controller 17 can use different segmentation thresholds to identify the relatively compact and bright plasma core region, as well as the smaller, larger plasma plume region that extends along the airflow direction. Controller 17 can also exclude noise regions that are not connected to the plasma core 111 or the outlet of the flow-limiting structure 151 based on connectivity.

[0117] The controller 17 determines the deviation of each extracted parameter relative to a corresponding preset range. The corresponding preset range can be determined based on a stable baseline acquired during stable operation of the light source, and may include a normal range, a warning range, and a protection range. The controller 17 can also determine whether to perform control based on the duration and trend of the deviation, so as to avoid unnecessary adjustments caused by single-frame flicker.

[0118] When the extracted parameters are within the warning range, the controller 17 can adjust a main control variable with a small adjustment range and reacquire the image parameters after a predetermined observation time. When the parameters return to the normal range and maintain the predetermined control cycle, recovery is confirmed; when the parameters continue to deviate or enter the protection range, the controller 17 performs further adjustment or protection actions.

[0119] For example, when the plasma plume length or plume opening angle increases relative to the stable baseline, the pumping rate of the first pumping branch 181 can be increased, the pumping rate of the second pumping branch 182 can be increased, and the working gas flow rate can be decreased sequentially. When the plasma core position shifts relative to the stable baseline, the pump laser focus position can be adjusted according to the shift direction. When the brightness ratio of the plasma core to the plasma plume decreases and the plume length increases, the pumping assembly 18 or the working gas supply assembly 12 can be prioritized for control, rather than prioritizing increasing the pump laser power.

[0120] By using the deviations, durations and trends of multiple image parameters relative to a stable baseline for control, this embodiment can reduce malfunctions caused by plasma flicker and select appropriate control quantities based on the different abnormal behaviors of the plasma core 111 and the plasma plume 112.

[0121] According to the control method of the vacuum ultraviolet plasma source in the embodiments of this application, the first plasma imaging unit 161 and the second plasma imaging unit 162 respectively acquire a first image and a second image covering the plasma core 111 and the plasma plume 112 from different imaging directions.

[0122] The controller 17 extracts the first projection position of the plasma core 111 in the first imaging plane and the first projection direction of the plasma plume 112 from the first image, and extracts the second projection position of the plasma core 111 in the second imaging plane and the second projection direction of the plasma plume 112 from the second image. Based on the calibration parameters of the two imaging units and the geometric relationship between the two imaging directions, the controller 17 determines the three-dimensional position of the plasma core 111 and the spatial extension direction of the plasma plume 112.

[0123] When the determined three-dimensional position deviates from the preset three-dimensional position, the controller 17 adjusts the pump laser assembly 13 according to the direction of deviation. When the spatial extension direction of the plasma plume 112 deflects, the controller 17 adjusts the first extraction branch 181, the second extraction branch 182, the working gas flow rate, or the working gas pressure according to the direction of deflection.

[0124] By acquiring plasma images from different directions, this embodiment can identify plasma core shifts and plasma plume deflections that are not easily observed along a single imaging direction, thereby improving the reliability of closed-loop control of the plasma spatial state.

[0125] Application Examples

[0126] The aforementioned vacuum ultraviolet plasma light source can be applied to wafer bright field inspection equipment. The vacuum ultraviolet radiation generated by the plasma core 111 enters the vacuum ultraviolet collection cavity 14 through the plume confinement and differential pumping assembly 15, and is collected by the vacuum ultraviolet collection optics before entering the illumination optical path of the wafer bright field inspection equipment to irradiate the wafer surface.

[0127] When controller 17 determines that the vacuum ultraviolet output has decreased, the plasma plume 112 is too long, the plasma core 111 is misaligned, or the pressure in the vacuum ultraviolet collection chamber 14 is abnormal, it can send status information to the main controller of the wafer bright-field inspection equipment. The wafer bright-field inspection equipment can then perform alarms, pause inspection, recalibrate, or switch inspection parameters based on the status information. This reduces the impact of abnormal light source status on the wafer inspection results.

[0128] In summary, this application establishes spatial constraints and a pressure gradient for the working gas and plasma plume 112 by setting a flow-limiting structure 151, a plume confinement cavity 152, and at least one differential pumping cavity between the plasma forming cavity 11 and the vacuum ultraviolet collecting cavity 14. The plasma imaging unit 16 simultaneously monitors the plasma core 111 and the plasma plume 112, and controls at least one of the working gas supply component 12, the pump laser component 13, and the pumping component 18 based on their morphology. Furthermore, joint diagnosis can be performed using the vacuum ultraviolet output monitoring unit 19 and the operating status detection component 20. This structure and control method are beneficial for stabilizing the plasma core 111 and the plasma plume 112, reducing the diffusion of the working gas into the vacuum ultraviolet collecting cavity 14, reducing vacuum ultraviolet absorption loss, and improving the targeting of vacuum ultraviolet output anomaly identification and closed-loop control.

[0129] It is understood that the specific embodiments described herein are merely for illustrative purposes and not for limiting the scope of this application. Furthermore, for ease of description, the accompanying drawings show only the parts relevant to this application, and not all of the structures or processes. It should be noted that similar reference numerals and letters in the drawings denote similar items throughout this application.

[0130] It should be understood that although the terms "first," "second," etc., may be used herein to describe various features, these features should not be limited by these terms. The use of these terms is merely for distinction and should not be construed as indicating or implying relative importance. For example, without departing from the scope of the exemplary embodiments, a first feature may be referred to as a second feature, and similarly, a second feature may be referred to as a first feature.

[0131] In the description of this application, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set up," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this embodiment based on the specific circumstances.

[0132] The illustrative embodiments of this application include, but are not limited to, vacuum ultraviolet plasma light sources and their control methods.

[0133] Various aspects of the illustrative embodiments will be described using terminology commonly employed by those skilled in the art to convey the essence of their work to others skilled in the art. However, it will be apparent to those skilled in the art that some alternative embodiments will be practiced using the features partially described. Specific figures and configurations are set forth for purposes of explanation in order to provide a more thorough understanding of the illustrative embodiments. However, it will be apparent to those skilled in the art that alternative embodiments may be practiced without specific details. In some other instances, well-known features have been omitted or simplified herein to avoid obscuring the illustrative embodiments of this application.

[0134] Furthermore, the various operations will be described as multiple separate operations in a manner most conducive to understanding the illustrative embodiments; however, the order of description should not be construed as implying that these operations must depend on the order of description, and many of these operations may be performed in parallel, concurrently, or simultaneously. Moreover, the order of the operations may also be rearranged. The process may be terminated when the described operations are completed, but may also include additional steps not included in the figures. The process may correspond to a method, function, procedure, subroutine, subroutine, etc.

[0135] References to "an embodiment," "embodiment," "illustrative embodiment," etc., in this application indicate that the described embodiment may include specific features, structures, or properties; however, each embodiment may or may not necessarily include specific features, structures, or properties. Furthermore, these phrases are not necessarily directed at the same embodiment. Moreover, when specific features are described in conjunction with specific embodiments, the knowledge of those skilled in the art can influence the combination of these features with other embodiments, whether or not those embodiments are explicitly described.

[0136] Unless the context otherwise specifies, the terms “comprising,” “having,” and “including” are synonyms. The phrase “A and / or B” means “(A), (B), or (A and B).”

[0137] In the accompanying drawings, some structural or methodological features may be shown in a specific arrangement and / or order. However, it should be understood that such a specific arrangement and / or order is not necessary. Rather, in some embodiments, these features may be illustrated in a manner and / or order different from that shown in the illustrative drawings. Furthermore, the inclusion of structural or methodological features in a particular drawing does not mean that all embodiments need to include such features; in some embodiments, these features may be omitted or may be combined with other features.

[0138] In some cases, the disclosed embodiments may be implemented in hardware, firmware, software, or any combination thereof. The disclosed embodiments may also be implemented as instructions or programs carried or stored on one or more transient or non-transient machine-readable (e.g., computer-readable) storage media, which may be read and executed by one or more processors, etc. When the instructions or program are run by a machine, the machine may perform the various methods described above. For example, the instructions may be distributed via a network or other computer-readable media. Therefore, machine-readable media may include, but are not limited to, any mechanism for storing or transmitting information in a machine-readable (e.g., computer-readable) form, such as floppy disks, optical disks, optical disc read-only memories (CD-ROMs), magneto-optical disks, read-only memories (ROMs), random access memories (RAMs), erasable programmable read-only memories (EPROMs), electronically erasable programmable read-only memories (EEPROMs), magnetic cards or optical cards, or flash memory or tangible machine-readable storage for transmitting network information via electrical, optical, acoustic, or other forms of signals (e.g., carrier waves, infrared signals, digital signals, etc.). Therefore, machine-readable media includes any form of machine-readable medium suitable for storing or transmitting electronic instructions or machine-readable (e.g., computer-readable) information.

[0139] The embodiments of this application have been described in detail above with reference to the accompanying drawings. However, the use of the technical solutions of this application is not limited to the various applications mentioned in the embodiments of this application. Various structures and modifications can be easily implemented with reference to the technical solutions of this application to achieve the various beneficial effects mentioned herein. Within the scope of knowledge possessed by those skilled in the art, all changes made without departing from the spirit of this application should be considered within the scope of this patent application.

Claims

1. A vacuum ultraviolet plasma light source, characterized in that, include: Plasma forming cavity; A working gas supply assembly is connected to the plasma forming cavity; A pump laser assembly, including a focusing optical path for focusing a pump laser into the plasma forming cavity; A vacuum ultraviolet collection chamber is spaced apart from the plasma forming chamber; A plume confinement and differential pumping assembly is disposed between the plasma forming cavity and the vacuum ultraviolet collecting cavity, including a flow limiting structure, a plume confinement cavity and at least one differential pumping cavity that are sequentially connected along the direction from the plasma forming cavity to the vacuum ultraviolet collecting cavity, and the differential pumping cavity is connected to a pumping assembly. At least one plasma imaging unit, with an imaging field of view covering the plasma core within the plasma forming cavity and the plasma plume extending from the plasma core; as well as A controller, connected to the plasma imaging unit and to at least one of the working gas supply assembly, the pump laser assembly, and the pumping assembly, is used to control the components connected to the controller based on the morphology of the plasma core and plasma plume as characterized by the images acquired by the plasma imaging unit.

2. The vacuum ultraviolet plasma light source according to claim 1, characterized in that, It also includes a vacuum ultraviolet output monitoring unit and an operating status detection component. The vacuum ultraviolet output monitoring unit is used to detect at least one of the following: vacuum ultraviolet output intensity, the ratio of vacuum ultraviolet output to ultraviolet output, and the position of the emitted light spot. The operating status detection component is used to detect at least one of the following: cavity pressure, working gas flow rate, and pumping status. The controller is also used to determine the abnormality type corresponding to the abnormality of the vacuum ultraviolet output based on the morphology of the plasma core and the plasma plume, the detection results of the vacuum ultraviolet output monitoring unit and the detection results of the operating status detection component, and to determine the component to be controlled based on the abnormality type.

3. The vacuum ultraviolet plasma light source according to claim 1, characterized in that, The differential pumping chamber includes at least two differential pumping chambers arranged sequentially along the direction from the plasma forming chamber to the vacuum ultraviolet collecting chamber. Each differential pumping chamber is connected to a pumping branch with an adjustable pumping rate, so that the pressure in the plasma forming chamber, the plume confinement chamber, each differential pumping chamber and the vacuum ultraviolet collecting chamber decreases sequentially.

4. The vacuum ultraviolet plasma light source according to claim 1, characterized in that, The controller extracts at least two of the following from the image acquired by the plasma imaging unit: plasma core position, plasma core size, plasma plume length, plasma plume opening angle, plasma plume direction, and the brightness ratio of the plasma core to the plasma plume. Based on the deviation of the extraction results relative to a corresponding preset range, the controller controls the components connected to the controller.

5. The vacuum ultraviolet plasma light source according to claim 1, characterized in that, The at least one plasma imaging unit includes a first plasma imaging unit and a second plasma imaging unit with different imaging directions. The controller is used to determine the three-dimensional position of the plasma core and the extension direction of the plasma plume based on the images acquired by the first plasma imaging unit and the second plasma imaging unit.

6. A method for controlling a vacuum ultraviolet plasma source, characterized in that, The control method, applied to a vacuum ultraviolet plasma source according to any one of claims 1-5, comprises: Working gas is supplied to the plasma forming cavity, and a pump laser is focused into the plasma forming cavity to form a plasma core and a plasma plume extending from the plasma core; The plasma plume is constrained by a flow-limiting structure and a plume-constraining cavity, and evacuated by at least one differential evacuation cavity to reduce the diffusion of the working gas and the plasma plume into the vacuum ultraviolet collection cavity. Acquire images with an imaging field of view covering the plasma core and the plasma plume; The morphology of the plasma core and the plasma plume is determined based on the image; and Based on the morphology of the plasma core and the plasma plume, at least one of the working gas supply component, the pump laser component, and the pumping component is controlled.

7. The control method according to claim 6, characterized in that, Also includes: Detect at least one of the following: vacuum ultraviolet output intensity, the ratio of vacuum ultraviolet output to ultraviolet output, and the position of the emitted light spot; and detect at least one of the following: cavity pressure, working gas flow rate, and evacuation status. Based on the morphology of the plasma core and the plasma plume, the detection results of vacuum ultraviolet output, and the detection results of the operating status, the abnormality type corresponding to the abnormal vacuum ultraviolet output is determined. as well as Based on the type of anomaly, the component to be controlled is determined from the working gas supply component, the pump laser component, and the pumping component.

8. The control method according to claim 6, characterized in that, The evacuation through at least one differential evacuation chamber includes: The pumping rates of at least two differential pumping chambers arranged sequentially along the direction from the plasma forming chamber to the vacuum ultraviolet collecting chamber are adjusted respectively, so that the pressure in the plasma forming chamber, the plume confinement chamber, each of the differential pumping chambers and the vacuum ultraviolet collecting chamber decreases sequentially.

9. The control method according to claim 6, characterized in that, Determining the morphology of the plasma core and the plasma plume based on the image includes: Extract at least two of the following from the image: plasma core location, plasma core size, plasma plume length, plasma plume opening angle, plasma plume direction, and the brightness ratio of the plasma core to the plasma plume. The control based on the morphology of the plasma core and the plasma plume includes: The deviation of each extracted parameter relative to its corresponding preset range is determined, and at least one of the working gas supply component, the pump laser component, and the pumping component is controlled according to the deviation.

10. The control method according to claim 6, characterized in that, The acquisition of the image includes: First and second images covering the plasma core and the plasma plume were acquired from different imaging directions, respectively. Determining the morphology of the plasma core and the plasma plume based on the image includes: Based on the first image and the second image, the three-dimensional position of the plasma core and the extension direction of the plasma plume are determined.

Images