US-20260126720-A1 - SAMPLE DAMAGE AVOIDANCE IN DEVICES AND METHODS FOR SAMPLE PROCESSING AND SAMPLE REPAIR

Abstract

A method for potential determination pertaining to a sample comprises: positioning a probe above the sample; applying at least a first and a second DC voltage offset each from a first range; applying an AC voltage to the probe for the purpose of inducing a mechanical oscillation of the probe; determining a first induced deflection of the probe for the first DC voltage offset and a second induced deflection of the probe for the second DC voltage offset; and determining a potential outside an interval spanned by the first and second DC voltage offsets at least partly on the basis of the first and second deflections. A method for causing approach by a probe towards a sample comprises: causing approach by the probe towards the sample; repeatedly determining a deflection of the probe during the process of causing approach; and ascertaining an approach termination condition for avoiding sample damage at least partly on the basis of the deflection of the probe or the oscillation frequency thereof.

Inventors

• Rene Kullock
• Hans Hermann Pieper
• Christof Baur
• Robert Heberlein

Assignees

• CARL ZEISS SMT GMBH

Dates

Publication Date

20260507

Application Date

20251105

Priority Date

20241105

Claims (20)

1. 1 . A method for potential determination pertaining to a sample, wherein the method comprises: positioning a probe above the sample; applying at least a first and a second DC voltage offset each from a first range; applying an AC voltage to the probe for the purpose of inducing a mechanical oscillation of the probe; determining a first induced deflection of the probe for the first DC voltage offset and a second induced deflection of the probe for the second DC voltage offset; and determining a potential outside an interval spanned by the first and second DC voltage offsets at least partly on the basis of the first and second deflections.
2. 2 . The method of claim 1 , wherein the deflection comprises an amplitude of the mechanical oscillation and/or a phase of the mechanical oscillation.
3. 3 . The method of claim 1 , wherein the first and second deflections comprise an in-phase component and/or a quadrature component.
4. 4 . The method of claim 1 , wherein determining the first and second deflections comprises a lock-in amplification.
5. 5 . The method of claim 1 , wherein the AC voltage frequency is substantially equal to or a multiple of a resonant frequency of the probe.
6. 6 . The method of claim 1 , wherein the first range extends from −10 V to +10 V.
7. 7 . The method of claim 1 , wherein determining the potential comprises fitting, using a fit function, at least a first data point comprising the first deflection and the first DC voltage offset and a second data point comprising the second deflection and the second DC voltage offset.
8. 8 . The method of claim 7 , wherein determining the potential furthermore comprises extrapolating and/or determining a zero of the fit function.
9. 9 . The method of claim 7 , wherein the fit function comprises a linear function, and preferably a correction of the linear function at least partly on the basis of the resonant frequency, an oscillation quality, and/or a spring constant of the probe.
10. 10 . The method of claim 1 , wherein the positioning is carried out such that the distance between the probe and the sample is 0.001 μm to 1000 μm, preferably 50 μm to 150 μm.
11. 11 . A method for causing approach by a probe towards a sample, wherein the method comprises: causing approach by the probe towards the sample; repeatedly determining a deflection of the probe during the process of causing approach; and ascertaining an approach termination condition for avoiding sample damage at least partly on the basis of the deflection of the probe.
12. 12 . The method of claim 11 , wherein the ascertaining is carried out by use of a real-time device configured to ascertain the approach termination condition in 2 ms or less, preferably 1 ms or less, particularly preferably 0.5 ms or less.
13. 13 . The method of claim 11 , further comprising terminating the process of causing approach by the probe towards the sample at least partly on the basis of ascertaining the approach termination condition.
14. 14 . The method of claim 13 , wherein the terminating is carried out within 2 ms or less, preferably 1 ms or less, particularly preferably 0.5 ms or less, after occurrence of the approach termination condition.
15. 15 . The method of claim 11 , wherein the process of causing approach by the probe is carried out at a speed of 0.1 μm/s or more, preferably 1 μm/s or more, particularly preferably 2 μm/s or more.
16. 16 . The method of claim 11 , wherein the approach termination condition comprises overshooting of a predefined deflection of the probe.
17. 17 . The method of claim 11 , furthermore comprising determining a resonant frequency of the probe during the process of causing approach.
18. 18 . The method of claim 17 , wherein the approach termination condition comprises overshooting of a predefined frequency shift of the resonant frequency.
19. 19 . The method of claim 17 , wherein the approach termination condition comprises undershooting of a predefined minimum frequency by the resonant frequency.
20. 20 . A method for processing a sample, comprising: the steps of the method for potential determination of claim 1 ; and at least partly on the basis of the potential determination, the steps of a second method for causing approach by a probe towards a sample, the second method comprising: causing approach by the probe towards the sample; repeatedly determining a deflection of the probe during the process of causing approach; and ascertaining an approach termination condition for avoiding sample damage at least partly on the basis of the deflection of the probe.

Description

CROSS-REFERENCE TO RELATED APPLICATION The present application claims priority to German patent application 10 2024 132 213.6, filed on Nov. 5, 2024, which is hereby incorporated by reference in its entirety. TECHNICAL FIELD The present invention relates to methods for potential determination pertaining to a sample, methods for causing approach by a probe towards a sample, methods for processing a sample, and also corresponding devices and computer programs. BACKGROUND As a result of constantly increasing integration density in microelectronics, there is a need for substrates, for example, lithographic masks, mask blanks or wafers, to have ever better surfaces. For example, lithographic masks are intended to image ever smaller structural elements into a photoresist layer of a wafer. This is likewise true of templates that are used in nanoimprint lithography. In order to meet these requirements, the exposure wavelength is being shifted to ever shorter wavelengths. The trend is towards ever shorter wavelengths that extend into the extreme ultraviolet (EUV) wavelength range (10 nm to 15 nm) and towards corresponding EUV masks. It is frequently the case that defects occur in the production of masks because of the ever decreasing dimensions of the structural elements. Since production is associated with high costs, defective photomasks, photolithographic masks, and likewise the templates used in nanoimprint lithography are repaired whenever possible. In the repair of photomasks, parts of an absorber pattern that exist at positions on the mask that are not envisaged by the design may be removed. In addition, absorbing material may be deposited at positions on the mask that are free of absorbing material even though the mask design envisages absorbing pattern elements. Both types of repair processes can create debris fragments or particles that can settle at opaque, transparent or reflective sites on photomasks and cause imaging aberrations in lithographic exposure that are visible on a structured wafer. A further problem is particles from the environment that settle on the surface of a mask or another substrate or on components of a photolithographic exposure system. Moreover, the handling of a mask during the process for production thereof and/or operation thereof can create particles that can settle on the mask. There are two further difficulties in the case of photolithographic exposure systems that work with electromagnetic radiation in the EUV wavelength range. For EUV masks, there is currently no satisfactory protection (for instance a pellicle) for the surface thereof that bears structure elements. As a result, EUV masks are particularly prone to the settling of particles on this structured surface. Secondly, an EUV radiation source typically uses tin plasma for producing the EUV radiation. Particles from the hot plasma can be deposited on components of an EUV exposure system, especially on the optical components or elements thereof, including the EUV mask, and can impair the function thereof. The decreasing structural dimensions of photolithographic masks are increasing the difficulty of cleaning processes. Moreover, as a result of the decreasing exposure wavelength, increasingly smaller foreign particles or dirt particles adhering on the surface of the mask or of an optical element of the exposure system are becoming visible on a wafer in an exposure process. In view of ever smaller structures, tailored solutions are becoming increasingly important for processing and cleaning of masks and—more generally—substrates. In particular, it may be necessary to eliminate various defects on the same substrate with an acceptable level of cost and inconvenience. The processing of surfaces, especially the moving of particles and the lifting and/or removal of individual particles from a surface, is typically a difficult and time-consuming process. External constraints can limit the tools and treatment options available. Moreover, it can be costly and inconvenient to completely remove a particle adhering on a surface of a substrate from the substrate. Typically, processing a sample necessitates causing approach by a probe towards the sample, although this is not always possible without problems, for the following reasons: During processes for loading the sample into a vacuum, e.g., evacuating and measuring processes may cause the sample to become electrostatically charged. In the course, too, of viewing samples (e.g., photomasks) in a scanning electron microscope (SEM), the sample may likewise be charged by the introduced electrons of the primary beam and also by the secondary electrons (SE). The charging behavior may be dependent here primarily on the SE yield (SEY). Samples having large conductive structures which are not or cannot be electrically contacted are critical in both cases. These include, e.g., so-called “chrome on glass blanks” for particle monitoring tests and EUV masks. EUV masks, as high-end mask types