Optical systems and methods

Abstract

To provide an improved technique for lifetime improvements for optical elements and lasers.SOLUTION: There is provided a system 100 comprising: CaF2 as an optical component 101; an enclosure 102 surrounding the optical component 103; and a vapor source 103 in fluid communication with the enclosure 102, wherein the vapor source 103 provides vapor to the enclosure 102 with a vapor level that corresponds to CaF2 and are between 5000 ppm and 15000 ppm, wherein the vapor is one of water, methanol, ethylene glycol and ethanol.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present disclosure relates to lifetime improvements for laser and optical systems. [Background technology]

[0002] Advances in the semiconductor manufacturing industry are placing increasing demands on yield management, particularly on metrology and inspection systems. Critical dimensions continue to shrink, yet the industry must reduce the time to achieve high-yield, high-value production. Minimizing the overall time from detecting a yield problem to repairing it determines the return on investment for semiconductor manufacturers.

[0003] Fabricating semiconductor devices, such as logic and memory devices, typically involves processing semiconductor wafers using multiple manufacturing processes to form the various features and multiple levels of the semiconductor devices. For example, lithography is a semiconductor manufacturing process that involves transferring a pattern from a reticle to a photoresist array 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. Complex semiconductor devices may be fabricated in arrays on a single semiconductor wafer that are separated into individual semiconductor devices.

[0004] Inspection processes are used at various stages during semiconductor manufacturing to detect defects on wafers to promote higher yields and therefore higher profits in the manufacturing process. Inspection has always been an important part of manufacturing semiconductor devices, such as integrated circuits (ICs). However, as the dimensions of semiconductor devices decrease, inspection becomes even more important to the successful manufacture of acceptable semiconductor devices because smaller defects can cause the devices to fail. For example, as the dimensions of semiconductor devices decrease, the detection of defects of decreasing size becomes necessary because even relatively small defects can cause unwanted aberrations in the semiconductor device.

[0005] Defect review typically involves re-detecting defects detected by the inspection process; and generating additional information about the defects at higher resolution using either a high magnification optical system or a scanning electron microscope (SEM). Defect review is typically performed at discrete locations on the specimen where defects were detected by inspection. The higher resolution data about the defects generated by defect review is better suited to determining defect attributes, such as profile, topography, or more precise size information.

[0006] Wafer inspection systems typically use illumination sources of deep ultraviolet (DUV) radiation with wavelengths as short as 260 nanometers, with high numerical apertures (NA). Wavelengths of 193 nanometers or even 120 nm may also be used. In some instances, the illumination light may be provided by an arc lamp. For example, electrode-based, relatively high-intensity discharge arc lamps are used in inspection systems. In some other instances, the illumination light is provided by a laser. One approach to achieving the desired short-wavelength emission has been harmonic upconversion of longer-wavelength light sources. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] U.S. Patent Application Publication No. 2014 / 0146838 Summary of the Invention [Problem to be solved by the invention]

[0008] Improved optical and laser lifetimes are necessary to enable next-generation semiconductor manufacturing. Traditionally, vapor-free gases are used to prevent damage to optical components in inspection systems. For water, vapor-free has meant 20 ppm or less water. For other species, vapor-free has meant low ppb levels. The physical and chemical effects of these vapor-free purge gases can limit the lifetime of optical elements, especially under high-intensity conditions.

[0009] Therefore, improved techniques are needed to improve the lifetime of optical elements and lasers. [Means for solving the problem]

[0010] In a first embodiment, a system is provided. The system includes an optical component and an enclosure surrounding the optical component. A vapor source is in fluid communication with the enclosure. The vapor source provides vapor to the enclosure having a vapor level of 500 ppm to 15,000 ppm, the vapor being one of water, methanol, ethylene glycol, or ethanol.

[0011] In one example, the optical component is one of CaF2, MgF2, LiF2, BaF2, SrF2, or BeF2. In another example, the optical component is one of fused silica, quartz, borate, germanium, silicon germanium, rutile, sapphire, silicon, YVO4, SrBO7, or ZnSe. In yet another example, the optical component is one of borosilicate, AMTR, and zinc selenide materials, SrBO7, or YVO4.

[0012] Steam levels may be from 500 ppm to less than 2000 ppm, from 500 ppm to less than 5000 ppm, or from more than 5000 ppm to 15000 ppm. In one example, the steam in these ranges is water, but may also be methanol, ethylene glycol, or ethanol.

[0013] The vapor source may include a bubbler, a permeable membrane, a semi-permeable membrane, a charged mosaic member, or a bipolar membrane. The permeable membrane may include Nafion or polyamide.

[0014] The vapor source may include a gas source that provides nitrogen, helium, carbon monoxide, carbon dioxide, krypton, argon, xenon, hydrogen, oxygen, compressed dry air, or mixtures thereof, where the gas from the gas source is mixed with the vapor.

[0015] The system may further include a vapor sensor disposed in fluid communication with the housing. The vapor sensor is one of a carbon monoxide detector, a carbon dioxide detector, a hygrometer, or a hydrogen sensor. The system may also include a processor in electronic communication with the vapor sensor. The processor is configured to adjust the vapor level in the purge gas from the housing based on a reading from the vapor sensor.

[0016] A method is provided in a second embodiment, the method including flowing vapor from a vapor source to an enclosure surrounding an optical component, wherein a vapor level in the purge gas is maintained between 500 ppm and 15,000 ppm, and the vapor is one of water, methanol, ethylene glycol, or ethanol.

[0017] The optical component may be one of CaF2, MgF2, LiF2, BaF2, SrF2, or BeF2.

[0018] The vapor level may be from 500 ppm to less than 2000 ppm, from 500 ppm to less than 5000 ppm, or from greater than 5000 ppm to 15000 ppm.

[0019] The method may further include measuring a vapor level within the enclosure with a vapor sensor disposed within the enclosure. Maintaining the vapor level may be based on readings from the vapor sensor. [Brief explanation of the drawings]

[0020] For a more complete understanding of the nature and subject matter of the present disclosure, reference should be made to the following detailed description taken in conjunction with the accompanying drawings, in which:

[0021] [Figure 1] FIG. 2 illustrates optical components before exposure. [Figure 2] FIG. 10 shows inspection results of optical components after 7 days of exposure without steam. [Figure 3] FIG. 10 shows inspection results of optical components after 68 days of exposure to steam. [Figure 4] FIG. 1 shows the observable difference in surface damage / modification between damaged areas where steam was not present and damaged areas where steam was present. [Figure 5] FIG. 1 is a block diagram of an embodiment of a system according to the present disclosure. [Figure 6] 1 is a flow diagram of an embodiment of a method according to the present disclosure. [Figure 7] FIG. 1 is a diagram illustrating a test system. [Figure 8] FIG. 10 shows that the beam shape is changed, resulting in surface damage and oxidation to the CaF2 optical components. [Figure 9] FIG. 1 shows a partially damaged surface / subsurface. [Figure 10] FIG. 1 is another illustration of CaF2 damage. DETAILED DESCRIPTION OF THE INVENTION

[0022] Although the claimed subject matter is described in terms of particular embodiments, other embodiments, including embodiments that do not provide all of the advantages and features described herein, are also within the scope of this disclosure. Various structural, logical, process step, and electronic changes may be made without departing from the scope of this disclosure. Accordingly, the scope of this disclosure is defined solely by reference to the appended claims.

[0023] The combined vapor gases may contribute to optical element damage in semiconductor inspection tools, semiconductor metrology tools, and other tools having optical components. Selected vapor(s) may further serve as a cooling fluid simply to conduct heat away from the object. In embodiments disclosed herein, the vapor may stop processes that damage the surface of the optical element. Thus, the vapor may prevent damaging physical and chemical effects from occurring. This contrasts with the conventional belief that these vapors contributed to optical element damage.

[0024] Testing has determined that in the presence of strong magnetic fields that damage optics, causing the propagating laser beam to change shape (e.g., perception of damage), or affect another measurable quality of the propagating laser beam, some vapor stopped or reduced the rate of surface and near-surface damage to the optic. In this physical and chemical action, adding vapor to the area surrounding the laser crystal or optic may help stabilize and extend the life of the laser crystal and optic.

[0025] For near-surface damage, the majority of the light-driven energy exchange may occur within approximately the first 50-100 nm of the optical element, which may drive larger material changes that extend at least 1 micron into the surface of the optical element.

[0026] The choice of vapor and its concentration may depend on the material from which the optical elements are made and / or the wavelength and intensity level of the illumination light. For example, MgF2 is water-soluble, so a lower concentration of water may be needed, or alcohol may be used instead of water to avoid water damage to the MgF2 optical components. In another example using water-soluble optical components, the water concentration may be kept low enough to avoid solvation of the optical components and high enough to stop the damage process. Another vapor, such as alcohols, may also be used to prevent damage, and alcohols may be less likely to solvate the optical components. In yet another example, if 193 nm light is used, water may be used instead of alcohol. Alcohols may cause staining on surfaces too quickly at this wavelength. Although alcohols may work well at low intensities, at high intensities, alcohols may not adhere sufficiently to the surface due to localized heating. Therefore, water may be used at high intensities because water has a much greater surface adhesion efficiency.

[0027] As an example, adding steam to the environment around an optical component significantly extends the life of an optical component that typically lasts only 5-10 days before being damaged beyond its specifications. Figure 1 shows the optical component before exposure to photons. Figure 2 shows inspection of the optical component after 7 days of exposure without steam. A 10 nm bump has formed in the center of the optical component. This adversely affects the operation and / or lifespan of the optical component. Figure 3 shows inspection of the optical component after 68 days of exposure with steam. The optical component in Figure 3 does not exhibit the damage seen in Figure 2. The optical component in Figure 3 has a surface roughness of approximately 0.1 nm. In the example of Figure 3, steam concentrations ranging from 800 ppm to 2200 ppm were used. Thus, exposing the optical component to steam causes approximately 100 times less surface damage in 10 times the time for this example.

[0028] Steam can affect many damage mechanisms, including reducing surface temperature, inhibiting damaging surface chemistry (e.g., oxidation), or influencing another driver for the observed physical change. These mechanisms are merely examples, and there may be other mechanisms that improve optical component lifetime in the presence of steam.

[0029] Figure 4 shows the observable difference in surface damage / modification between damaged areas where steam was not present and damaged areas where steam was present: areas with steam exhibit no discernible damage for periods 10 times longer than areas without steam.

[0030] 5 is a block diagram of an embodiment of a system 100. Optical components 101 are disposed within a housing 102. The housing 102 encloses the optical components 101.

[0031] Optical component 101 may be one of borosilicate, AMTR (Newport), zinc selenide material, silicon germanium, sapphire, MgF2, LiF2, CaF2, BaF2, SrF2, SrB4O7 (SBO), or BeF2. Optical component 101 may also be one of any grade and type of fused silica, quartz, borate (e.g., barium borate (BBO)), germanium, rutile, sapphire, silicon, YVO4, or ZnSe. Other materials are possible.

[0032] The optical component 101 may be used for high fluence operation. Light of 193 nm, 213 nm, 248 nm, 265 nm, 266 nm, or 2 μm may be incident on the optical component 101. Broadband light from a light bulb or open plasma source may also be used. Other wavelengths may be present that contain more ionizing x-rays.

[0033] Vapor source 103 is in fluid communication with enclosure 102. Vapor source 103 slows or stops optical element or crystal damage by providing vapor to enclosure 102 having levels ranging from ppb to high ppm levels (e.g., tens of thousands). For example, vapor levels may range from 500 ppm to 15,000 ppm, including all values ​​in the range therebetween in 1.0 ppm increments.

[0034] In one example, the vapor level is from 500 ppm to less than 2000 ppm. In yet another example, the vapor level is about 2000 ppm. In yet another example, the vapor level is about 5000 ppm. The concentration of vapor in the environment may suppress physical and / or chemical processes that cause optical element damage. For example, the effects of high electric fields caused by intense laser beams may be mitigated. The rate of damage to optical elements may be reduced by at least 100 times through the use of the correct vapor / material combination in the optical environment as disclosed herein. For example, levels of 5000 ppm or greater may be acceptable for CaF2 but not for MgF2.

[0035] The vapor may be added to the environment in gas form. For example, the vapor source 103 may include a bubbler. Liquid vaporization may add a desired vapor concentration to the gas purge. The bubbler may produce a consistent amount of vapor within the environment.

[0036] The vapor source 103 may be a pressurized gas cylinder.

[0037] Vapor source 103 may also use a permeable membrane, which may comprise Nafion, polyamide, or another permeable material. The permeable membrane, which may be a tube, diaphragm, or wall adjacent to the environment, preferentially draws the target vapor from an adjacent vapor-rich reservoir into the controlled optical environment.

[0038] Nafion is an example of a permeable membrane. Nafion allows polar molecules to pass from vapor-rich air to a vapor-poor purge gas stream. The vapor concentration in the purge gas may be measured and controlled to produce a specified concentration in the optical environment.

[0039] The membrane may also be high density polyethylene (HDPE) or a nylon copolymer of polyolefin. The membrane may also be acetal, acrylonitrile, or functionalized polyvinyl chloride (PVC).

[0040] The vapor source 103 may also use a semi-permeable membrane, a charged mosaic membrane, or a bipolar membrane.

[0041] In one example, the vapor source 103 includes a gas source 104. The gas source 104 may provide one or more of nitrogen, helium, carbon monoxide, carbon dioxide, krypton, argon, xenon, hydrogen, oxygen, compressed dry air, or a mixture of these gases mixed with steam.

[0042] The vapor sensor 105 may be disposed in fluid communication with the housing 102. The vapor sensor 105 may be disposed within the housing 102 or along a vapor supply path to the housing 102. The vapor sensor 105 may be, for example, a hydrogen sensor, a hygrometer, a carbon monoxide detector, or a carbon dioxide detector. The processor 106 may be in electronic communication with the vapor sensor 105. The processor 106 may adjust the vapor level within the housing based on readings from the vapor sensor 105.

[0043] The system embodiments disclosed herein may be implemented in any laser system or plasma-based light source system.

[0044] 6 is a flow diagram for an embodiment of method 200. A vapor-rich gas flows at 201 from a vapor source to an enclosure that surrounds optical components. The optical components may be one of CaF2, MgF2, LiF2, BaF2, SrF2, BeF2, or another material. The environment around the optical components within the enclosure may include at least one of nitrogen, helium, carbon monoxide, carbon dioxide, krypton, argon, xenon, hydrogen, oxygen, or compressed dry air, or a mixture of these gases.

[0045] At 202, the vapor level in the gas is maintained from ppb levels to approximately the concentrated concentration of vapor under the atmospheric conditions of the use case (e.g., pressure, temperature, vapor concentration, and gas mixture in the vapor), e.g., 500 ppm to 15,000 ppm vapor. In one example, the vapor level is 500 ppm to less than 2,000 ppm vapor. In another example, the vapor level is greater than 5,000 ppm to 15,000 ppm. For example, a vapor level of greater than 5,000 ppm to 15,000 ppm may provide improved results for CaF2 optical components, and a vapor level of 500 ppm to less than 2,000 ppm may provide improved results for MgF2.

[0046] In one particular embodiment, the steam level is from greater than 6000 ppm to 15000 ppm, from greater than 7000 ppm to 15000 ppm, from greater than 8000 ppm to 15000 ppm, from greater than 9000 ppm to 15000 ppm, from greater than 10000 ppm to 15000 ppm, from greater than 11000 ppm to 15000 ppm, from greater than 12000 ppm to 15000 ppm, from greater than 13000 ppm to 15000 ppm, or from greater than 14000 ppm to 15000 ppm.

[0047] The vapor level may be added to or maintained in the gas using a bubbler or permeable membrane.

[0048] In one example, the vapor level within the enclosure is measured using a vapor sensor disposed within the enclosure, and the vapor level within the enclosure may be adjusted based on readings from the vapor sensor.

[0049] Figure 7 is a block diagram for testing using the test system. Clean dry air (CDA) and N2 flow through separate needle valves to a purifier. The CDA and N2 may be adjusted to 30 psi. After the purifier, the CDA and N2 flow to a bubbler and then to sensors, which may include an O2 meter and a steam sensor. The resulting gas may be used as input and mixed with steam.

[0050] FIG. 8 shows that the beam shape has changed, resulting in surface damage and oxidation to the CaF2 optical components.

[0051] Figure 9 shows the partially damaged surface / subsurface.

[0052] Another illustration of CaF2 damage is shown in Figure 10. As shown in Figure 10, the damage can result in beam shape changes.

[0053] Many polar molecules may be used as vapors to suppress optical element damage, for example, water, methanol, ethylene glycol, or ethanol.

[0054] Although the present disclosure has been described with respect to one or more particular embodiments, it will be understood that other embodiments of the present disclosure may be made without departing from the scope of the present disclosure. Accordingly, the present disclosure is intended to be limited only by the appended claims and their reasonable interpretation.

Claims

1. 1. A system comprising: an optical component onto which laser light having a wavelength of 193 nm is incident; a housing enclosing the optical components; and a steam source in fluid communication with the enclosure, the steam source providing steam to the enclosure having a steam level of from 5000 ppm to 15000 ppm, the steam containing water and no alcohol; A system comprising:

2. The system of claim 1 , wherein the vapor source comprises a bubbler.

3. The system of claim 1 , wherein the vapor source comprises a permeable membrane, the permeable membrane comprising a polyamide.

4. The system of claim 1 , wherein the vapor source comprises a semi-permeable membrane.

5. The system of claim 1 , wherein the vapor source comprises a charged mosaic membrane or a bipolar membrane.

6. 10. The system of claim 1, wherein the vapor source comprises a gas source providing nitrogen, helium, carbon monoxide, carbon dioxide, krypton, argon, xenon, hydrogen, oxygen, compressed dry air, or mixtures thereof, and wherein the gas from the gas source is mixed with the vapor.

7. The system of claim 1 , further comprising a sensor disposed in fluid communication with the housing, the sensor being one of a carbon monoxide detector, a carbon dioxide detector, a hygrometer, or a hydrogen sensor.

8. 8. The system of claim 7, further comprising a processor in electronic communication with the sensor, the processor configured to adjust the vapor level in the purge gas from the enclosure based on a reading from the sensor.

9. 1. A method comprising: Flowing vapor from a vapor source to an enclosure surrounding optical components onto which laser light having a wavelength of 193 nm is incident; maintaining a vapor level in the purge gas between 5000 ppm and 15000 ppm, said vapor containing water and no alcohol; A method comprising:

10. The method of claim 9 further comprising measuring the vapor level within the enclosure with a sensor disposed within the enclosure.

11. The method of claim 10 , wherein the maintaining step is based on readings from the sensor.

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