Imaging method adopting phase change material to immerse objective lens
Through the imaging method of phase change material immersion objective lens, the problems of contamination, operation complexity and sample damage of liquid immersion objective lens in semiconductor detection are solved, and pollution-free and damage-free efficient imaging is achieved while maintaining high optical resolution.
Patent Information
- Application Number
- CN202510826436.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-06-19
- Publication Date
- 2025-09-12
AI Technical Summary
Liquid immersion objectives have contamination risks, operational complexity, sample damage risks, and measurement interference issues in semiconductor inspection, and cannot meet the stringent requirements of cleanliness, efficiency, and accuracy.
The imaging method uses a phase change material immersion objective lens. Scanning imaging is performed by filling liquid phase change material between the wafer and the objective lens. After completion, the cavity conditions are changed to vaporize it to avoid contamination and damage while maintaining high optical resolution.
It achieves pollution-free, damage-free and efficient imaging, simplifies operation, maintains high optical resolution, and is suitable for semiconductor inspection.
Smart Images
Figure CN120629145A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of objective lens imaging, and in particular to an imaging method using a phase change material immersion objective lens. Background Art
[0002] In semiconductor inspection, although liquid immersion objectives (such as oil or water immersion objectives) can enhance optical resolution by increasing the numerical aperture (NA), they still have the following key limitations in practical applications, which have prevented their widespread adoption.
[0003] 1. Pollution Risk: 1.1 Cleanliness requirements: The semiconductor manufacturing environment must achieve extremely high cleanliness (such as ISO Class 1). Any liquid residue (such as oil or water) may introduce contaminants, causing chip defects or performance degradation.
[0004] 1.2 Material compatibility: Liquids may react with photoresist, metal layers, or other semiconductor materials, affecting device reliability.
[0005] 2. Operational complexity: 2.1 Liquid management: Liquid immersion objectives require precise control of liquid application, uniformity, and cleanliness, which increases process steps and automation difficulty, and reduces detection efficiency.
[0006] 2.2 Maintenance cost: Frequent cleaning of liquid residues will increase equipment maintenance costs and may interfere with the rhythm of high-speed production lines.
[0007] 3. Risk of sample damage: 3.1 Physical contact: Liquid immersion objectives usually need to be in close contact with the sample, which may scratch or damage fragile nanoscale structures (such as FinFET and EUV lithography patterns).
[0008] 3.2 Thermal effects: Liquids may be locally heated by light, affecting the properties of temperature-sensitive materials.
[0009] 4. Measuring interference: Refractive index changes: Liquids may change the effective refractive index of the sample, leading to errors in optical measurements (e.g., critical dimensions, overlay accuracy).
[0010] 5. Advantages of alternative technologies: Dry high-NA optical system: Using air-based high numerical aperture objectives (maximum NA 0.95, minimum magnification 40X), combined with computational imaging technology (such as AI enhancement algorithms), it can meet most detection needs.
[0011] Semiconductor inspection prioritizes non-contact, pollution-free, and highly reliable technologies (such as dry optics and electron beam inspection). However, liquid immersion objectives cannot meet the industry's stringent requirements for cleanliness, efficiency, and precision due to contamination risks, operational complexity, and potential interference issues.
[0012] In order to obtain ultra-high resolution imaging effects of liquid immersion objectives, it is urgent to solve the above-mentioned problems of liquid immersion objectives. Summary of the Invention
[0013] The present invention aims to provide an imaging method using a phase change material immersion objective lens to solve the problems of contamination of the liquid immersion objective lens, complex operation, damage to the sample and interference with measurement.
[0014] An imaging method using a phase change material immersion objective lens in this solution includes the following steps: Step 1: Place the wafer into the imaging chamber, directly below the objective lens, and pressurize the imaging chamber to a preset pressure; Also includes: Step 2: Pumping protective gas into the imaging chamber and heating the imaging chamber to a set temperature that can liquefy the phase change material in the gas. At the same time, a set amount of liquefied liquid phase change material is filled between the wafer and the objective lens through the sample feeding pipeline; Step 3: The imaging chamber maintains the set temperature, the wafer is translated to complete the scanning imaging of the wafer, and the liquid phase change material is replenished according to the set replenishment amount to keep the space between the objective lens and the wafer full; Step 4: extracting the protective gas and the phase change material that changes into gas under preset conditions.
[0015] The beneficial effects of this program are: During the wafer scanning and imaging process, the space between the objective lens and the wafer in the imaging chamber is filled with liquid phase change material. After the scanning and imaging is completed, the phase change material is directly changed from liquid to vapor by changing the conditions in the imaging chamber. The first-stage phase change material on the wafer will not cause wafer contamination or damage. In addition, the operation is simpler by extracting the protective gas and the gasified phase change material at the same time. The space between the objective lens and the wafer is filled with liquid phase change material, while maintaining very good optical resolution.
[0016] Furthermore, the method further includes step 5, adding air into the imaging chamber to normal pressure, and taking out the wafer.
[0017] The beneficial effect is that after the protective gas and the gas of the phase change material are extracted, the protective gas and the gas of the phase change material will not flow into the external environment, and the added air can facilitate the removal of the wafer.
[0018] Furthermore, in step 3, the preset condition is set according to the required refractive index of the liquid phase change material.
[0019] The beneficial effect is that the preset conditions are set according to the refractive index corresponding to the phase change material, so that better optical performance can be maintained.
[0020] Furthermore, in step 3, within a preset time period after the wafer scanning imaging is completed, the pressure and temperature in the imaging chamber are reduced to below a critical value corresponding to the set refractive index to vaporize the phase change material.
[0021] The beneficial effect is that vaporization is performed as soon as possible after wafer scanning and imaging is completed, which can improve processing compactness and ensure that the phase change material is completely vaporized to be discharged.
[0022] Furthermore, in step 2, the set amount is set according to the size of the wafer, and the set replenishment amount is set according to the size of the wafer at 10-15 times the set amount per second.
[0023] The beneficial effect is that during the wafer scanning process, the amount of liquid phase change material added will not affect the scanning imaging of the wafer, and at the same time can ensure that it is quickly vaporized and discharged from the imaging cavity after the wafer scanning imaging is completed.
[0024] Furthermore, the preset conditions are set based on the phase change material not reacting with the wafer material, and the preset conditions are a temperature range of 50-100° C., a pressure range of 40-100 atm, and a short wavelength.
[0025] The beneficial effect is that the preset conditions do not produce chemical reactions with the wafer, which can prevent the wafer from being damaged.
[0026] Furthermore, the preset pressure is set to be greater than the critical pressure value corresponding to the set refractive index, and the preset pressure is set to 50 atm. The set temperature is set to be greater than the critical temperature value corresponding to the set refractive index, and the set temperature is 60°C.
[0027] The beneficial effect is that the preset pressure and the preset temperature are set to be greater than the critical value corresponding to the set refractive index, which can increase the refractive index of the phase change material while ensuring the set refractive index.
[0028] Furthermore, the phase change material includes sulfur hexafluoride or a mixture of sulfur hexafluoride and fluoride.
[0029] The beneficial effect is that sulfur hexafluoride, as a phase change material, can not only maintain optical resolution well, but also does not produce chemical reaction with the wafer. BRIEF DESCRIPTION OF THE DRAWINGS
[0030] Figure 1The figure is a flow chart of an embodiment of an imaging method using a phase change material immersion objective lens according to the present invention. DETAILED DESCRIPTION
[0031] The following is further detailed description through specific implementation methods.
[0032] The reference numerals in the accompanying drawings of the specification include: .
[0033] Example An imaging method using a phase change material immersion objective lens, such as Figure 1 As shown, the following steps are included: Step 1: Place the wafer into the imaging chamber, directly below the objective lens, and pressurize the imaging chamber to a preset pressure. The preset pressure is set to be greater than the critical pressure value corresponding to the set refractive index. For example, the critical pressure value for a refractive index of 1.6 is 37.6 atm, and the preset pressure is set to 50 atm. The imaging chamber is equipped with a control system for pressurization and temperature control, and adopts the existing pressurization and temperature control system, which will not be repeated here. The specific structure and materials of the imaging chamber are set according to the actual cost requirements and the imaging requirements of the wafer.
[0034] Step 2: Pump protective gas into the imaging chamber and heat the imaging chamber to a set temperature at which the phase change material of the gas can be liquefied. The protective gas in the imaging chamber is pumped in through the corresponding pipeline, and the set temperature is set to be greater than the critical temperature value corresponding to the set refractive index. For example, the critical temperature value corresponding to the set refractive index of 1.6 is 45.5°C, and the set temperature is 60°C. At the same time, a set amount of liquefied liquid phase change material is filled between the wafer and the objective lens through the sample feeding pipeline. The set amount is set according to the size of the wafer. For example, the set amount corresponding to a 12-inch wafer is 10-20 microliters.
[0035] In step 3, the imaging chamber maintains the set temperature, the wafer is translated to complete the scanning imaging of the wafer, and the liquid phase change material is synchronously replenished according to the set replenishment amount to keep the space between the objective lens and the wafer filled. The translation of the wafer is performed by the existing translation mechanism preset in the imaging chamber. The set replenishment amount is set according to the size of the wafer at 10-15 times the set amount per second. For example, the set replenishment amount of a 12-inch wafer is 100 microliters / second to ensure that the phase change material is always filled between the wafer and the objective lens under the condition of high-speed movement of the wafer.
[0036] After wafer scanning and imaging is complete, the pressure and temperature in the imaging chamber are reduced to below the critical pressure and temperature values corresponding to the set refractive index within a preset time period to vaporize the phase change material. This preset time period is set based on the amount of phase change material used during the actual wafer size scanning and imaging, for example, 3 seconds.
[0037] Step 4: Extract the protective gas and the phase change material that has become a gas under preset conditions. The preset conditions are set based on the desired refractive index of the liquid phase change material. The preset conditions are set so that the phase change material does not react with the wafer material. The preset conditions are a temperature range of 50-100°C (above the critical temperature), a pressure range of 40-100 atm (above the critical pressure), and a short wavelength (such as ultraviolet light).
[0038] Step 5: Add air into the imaging chamber to normal pressure and remove the wafer.
[0039] Phase change materials include sulfur hexafluoride and a mixture of sulfur hexafluoride and fluoride.
[0040] When the phase change material is sulfur hexafluoride and the refractive index is 1.3, the refractive index increases significantly when sulfur hexafluoride is in liquid or high-pressure gas state; for liquid sulfur hexafluoride, at standard atmospheric pressure, the boiling point of sulfur hexafluoride is -63.8°C, and the refractive index of liquid sulfur hexafluoride is usually high, close to 1.3 (for example, at visible light wavelength). The temperature requirement is about -50°C to -60°C (to maintain liquid state), the pressure is normal pressure or slightly higher than normal pressure (to avoid vaporization), and the wavelength is 589 nm (sodium D line).
[0041] Achieving a refractive index of 1.6 requires an extremely high molecular density, which can only be achieved in a supercritical state or a special mixed system. In supercritical sulfur hexafluoride, when it is in a supercritical state (a critical temperature of 45.55°C and a critical pressure of 37.6 atm), the density of sulfur hexafluoride approaches that of a liquid, and the refractive index can be significantly increased. The required temperature is 50–100°C (above the critical temperature), the pressure is 40–100 atm (above the critical pressure), and the wavelength is short (such as ultraviolet light).
[0042] When a mixture of sulfur hexafluoride and fluoride is used to achieve a high refractive index, sulfur hexafluoride is mixed with other high-refractive-index materials (such as fluorinated liquids) to achieve a synergistic effect of 1.6. Liquid mixtures (such as sulfur hexafluoride and perfluoropolyether) can coexist in a gas-liquid state under high pressure.
[0043] That is, the refractive index must reach 1.3, and the liquid sulfur hexafluoride must be in a low-temperature, normal-pressure environment or in a high-pressure gaseous state (tens of atm). The refractive index must reach 1.6, and the supercritical sulfur hexafluoride must be in a high-temperature, high-pressure environment or mixed with other high-refractive-index materials.
[0044] Compared with the prior art, in this embodiment, during the scanning and imaging process of the wafer, the space between the objective lens and the wafer in the imaging chamber is filled with liquid phase change material. After the scanning and imaging is completed, the phase change material is directly changed from liquid to vapor by changing the conditions in the imaging chamber. The phase change material gas is extracted while the protective gas is removed, which will not cause wafer contamination or damage to the wafer. Moreover, by extracting the protective gas and the phase change material that has become gas at the same time, the operation is simpler. The space between the objective lens and the wafer is filled with liquid phase change material, and the optical resolution of the imaging operation is maintained very well.
[0045] The above is only an embodiment of the present invention, and the common knowledge such as the specific structure and characteristics of the scheme is not described in detail here. It should be pointed out that for those skilled in the art, without departing from the structure of the present invention, several variations and improvements can be made, which should also be regarded as the scope of protection of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.
Claims
1. An imaging method using a phase change material immersion objective lens, comprising the following steps: Step 1: Place the wafer into the imaging chamber, directly below the objective lens, and pressurize the imaging chamber to a preset pressure; It is characterized by further comprising: Step 2: Pumping protective gas into the imaging chamber and heating the imaging chamber to a set temperature that can liquefy the phase change material in the gas, while simultaneously filling a set amount of liquefied liquid phase change material between the wafer and the objective lens through a sample feeding pipeline; Step 3: The imaging chamber maintains the set temperature, the wafer is translated to complete the scanning imaging of the wafer, and the liquid phase change material is replenished according to the set replenishment amount to keep the space between the objective lens and the wafer full; Step 4: extracting the protective gas and the phase change material that changes into gas under preset conditions.
2. The imaging method using a phase change material immersion objective lens according to claim 1, characterized in that: The method further includes step 5 of adding air into the imaging chamber to normal pressure and taking out the wafer.
3. The imaging method using a phase change material immersion objective lens according to claim 1, characterized in that: In step 3, the preset condition is set according to the required refractive index of the liquid phase change material.
4. The imaging method using a phase change material immersion objective lens according to claim 1, characterized in that: In step 3, within a preset time period after the wafer scanning imaging is completed, the pressure and temperature in the imaging chamber are reduced to below a critical value corresponding to the set refractive index to vaporize the phase change material.
5. The imaging method using a phase change material immersion objective lens according to claim 1, characterized in that: In step 2, the set amount is set according to the size of the wafer, and the set replenishment amount is set according to the size of the wafer at 10-15 times the set amount per second.
6. The imaging method using a phase change material immersion objective lens according to any one of claims 1 to 5, characterized in that: The preset conditions are set based on the phase change material not reacting with the wafer material. The preset conditions are a temperature range of 50-100° C., a pressure range of 40-100 atm, and a short wavelength.
7. The imaging method using a phase change material immersion objective lens according to claim 6, characterized in that: The preset pressure is set to be greater than the critical pressure value corresponding to the set refractive index, and the preset pressure is set to 50 atm. The set temperature is set to be greater than the critical temperature value corresponding to the set refractive index, and the set temperature is 60°C.
8. The imaging method using a phase change material immersion objective lens according to any one of claims 1 to 5, characterized in that: The phase change material includes sulfur hexafluoride or a mixture of sulfur hexafluoride and fluoride.