US-20260126733-A1 - SYSTEM AND METHOD FOR SUPPRESSION OF BACKGROUND SIGNAL IN TIME RESOLVED METROLOGY SIGNALS

Abstract

A time resolved reflectance metrology device may detect and image structures in a layer that underlies an at least partially transparent top layer. A pulsed laser beam (pump beam) is used to irradiate the sample to produce transient signals in the underlying layer. The transient signals are detected using a probe beam that reflects from the interface between the top layer and the underlying layer. Light from the probe beam that is reflected from the top surface of the top layer may be eliminated using a confocal lens arrangement before the detector. The confocal lens arrangement, for example, includes a pinhole that is positioned at the image plane for the interface between the top layer and the underlying layer. The structures may be detected and imaged based on the transient signals.

Inventors

• Robin A. Mair
• Matthew Sartin
• Manjusha Mehendale
• George Andrew Antonelli
• Julien Michelon
• Xavier Tridon
• Marco A;ves
• Michael J. Kotelyanskii

Assignees

• ONTO INNOVATION INC.

Dates

Publication Date

20260507

Application Date

20251218

Claims (20)

1. 1 . A metrology device for non-destructive detection of structures in a sample, comprising: a pump arm that irradiates the sample with pump pulses to cause transient perturbations in material in a layer with the structures that underlies a top layer in the sample; a probe arm that irradiates the layer that underlies the top layer of the sample with probe pulses to produce a reflected probe beam that is modulated based on a response of the material to the transient perturbations, wherein the probe pulses penetrate the top layer that is at least partially transparent to wavelengths of light used by the probe arm; a detector that acquires transient signals from the reflected probe beam in response to the transient perturbations that are a function of varying time delay between the pump pulses and the probe pulses; and at least one processor coupled to the detector and is configured to detect at least one structure in the layer that underlies the top layer in the sample based on the transient signals.
2. 2 . The metrology device of claim 1 , wherein the probe pulses reflect from a top surface of the top layer and from an interface between the layer and the top layer, the metrology device further comprising: a confocal lens arrangement before the detector that prevents reflections from the top surface of the top layer from being received by the detector.
3. 3 . The metrology device of claim 2 , wherein the confocal lens arrangement comprises a pinhole or slit positioned in an image plane for an interface between the top layer and the layer with the structures.
4. 4 . The metrology device of claim 1 , wherein the at least one processor is further configured to generate an image of the at least one structure in the sample based on the transient signals.
5. 5 . The metrology device of claim 1 , further comprising an actuator configured to produce relative motion between the sample and the metrology device, wherein the pump arm and the probe arm irradiate the sample at a plurality of locations using the relative motion to scan the sample.
6. 6 . The metrology device of claim 1 , wherein the detector is a lock-in camera with a multi-pixel array that acquires the transient signals from the reflected probe beam at each of a plurality of locations in parallel.
7. 7 . The metrology device of claim 1 , wherein the top layer is a silicon substrate and the wavelengths of light used by the probe arm are infrared, and the layer with the structures that underlies the top layer is opaque to the wavelengths of light used by the probe arm.
8. 8 . The metrology device of claim 1 , wherein the at least one structure is detected based on a comparison of the transient signals at a plurality of locations.
9. 9 . The metrology device of claim 1 , wherein the transient perturbations are non-acoustic transient perturbations and the detector acquires non-acoustic transient signals from the reflected probe beam in response to the non-acoustic transient perturbations.
10. 10 . The metrology device of claim 9 , wherein the non-acoustic transient perturbations are produced by one or more of thermal dissipation, electron-hole recombination, plasma diffusion, symmetry breaking at top and bottom oxide surfaces, and etalon effects.
11. 11 . A method for non-destructive detection of structures in a sample, comprising: irradiating the sample with a pump beam with pump pulses to cause transient perturbations in material in a layer with the structures that underlies a top layer in the sample; irradiating the layer that underlies the top layer of the sample with a probe beam with probe pulses to produce a reflected probe beam that is modulated based on a response of the material to the transient perturbations in the sample, wherein the probe pulses penetrate the top layer that is at least partially transparent to wavelengths of light used in the probe pulses; detecting transient signals from the reflected probe beam in response to the transient perturbations that are a function of varying time delay between the pump pulses and the probe pulses; and detecting at least one structure in the layer that underlies the top layer in the sample based on the transient signals.
12. 12 . The method of claim 11 , wherein the probe pulses reflect from a top surface of the top layer and from an interface between the layer and the top layer, the method further comprising: preventing reflections from the top surface of the top layer from being detected using a confocal lens arrangement.
13. 13 . The method of claim 12 , wherein the confocal lens arrangement comprises a pinhole or slit positioned in an image plane for an interface between the top layer and the layer with the structures.
14. 14 . The method of claim 11 , further comprising generating an image of the at least one structure in the sample based on the transient signals.
15. 15 . The method of claim 11 , further comprising scanning the sample to irradiate the sample at a plurality of locations.
16. 16 . The method of claim 11 , further comprising using a lock-in camera with a multi-pixel array to acquire the transient signals from the reflected probe beam at each of a plurality of locations in parallel.
17. 17 . The method of claim 11 , wherein the top layer is a silicon substrate and the wavelengths of light used in the probe pulses are infrared, and the layer with the structures that underlies the top layer is opaque to the wavelengths of light used in the probe pulses.
18. 18 . The method of claim 11 , wherein detecting the at least one structure comprises comparing the transient signals at a plurality of locations.
19. 19 . The method of claim 11 , wherein the transient perturbations are non-acoustic transient perturbations and non-acoustic transient signals are detected from the reflected probe beam in response to the non-acoustic transient perturbations.
20. 20 . The method of claim 19 , wherein the non-acoustic transient perturbations are produced by one or more of thermal dissipation, electron-hole recombination, plasma diffusion, symmetry breaking at top and bottom oxide surfaces, and etalon effects.

Description

CLAIM OF PRIORITY This application claims the benefit of and priority to U.S. application Ser. No. 18/986,584, filed Dec. 18, 2024, and entitled “METROLOGY BASED ON TIME RESOLVED NON-ACOUSTIC SIGNALS,” which claims priority to U.S. Provisional Application No. 63/636,334, filed Apr. 19, 2024, and entitled “METROLOGY BASED ON TIME RESOLVED NON-ACOUSTIC SIGNALS,” both of which are assigned to the assignee hereof and are incorporated herein by reference in their entireties. FIELD OF THE DISCLOSURE The subject matter described herein is related generally to microscopy, and more particularly to the use of time resolved reflectivity measurements. BACKGROUND Semiconductor processing for forming integrated circuits requires a series of processing steps. These processing steps include, for example, the deposition and patterning of material layers such as insulating layers, polysilicon layers, and metal layers. For proper operation of such devices, the successful formation, patterning, and alignment of successive layers is sometimes crucial. The packaging of devices, particularly in advanced packaging processes in which multiple devices, including electrical, mechanical, or semiconductor, are aggregated and interconnected, similarly sometimes requires precise processing. For example, in one example of advanced packaging processes, two or more wafers or substrates may be bonded, e.g., attached together using a number of physical and chemical processes. During wafer bonding there is the potential of the presence of voids to be formed between bonded layers. The presence of voids may affect the overall yield. There are various conventional optical techniques that may be used for non-destructive metrology or inspection of devices during processing, e.g., during fabrication or packaging. For example, conventional techniques may use specific wavelengths of light, e.g., ultraviolet (UV), visible, or infrared (IR), to image or otherwise detect one or more structures produced during processing. However, conventional optical techniques are sometimes unsuitable for the measurement or detection of such structures when the structures are under optically opaque layers or are optically transparent to the specific wavelengths of light being employed. Accordingly, improved microscopy techniques are desirable. SUMMARY Opto-acoustic metrology, in general, uses a pump beam and a probe beam with a varying time delay between light pulses in each of the pump and probe beams to detect structures that produce an acoustic response to the pump beam. The light pulses in the pump beam, for example, may produce an acoustic response from structures within the sample and the acoustic response propagates to the surface of the sample, which is detected by the probe beam. The acoustic response, for example, affects the reflectivity of the material in the sample or deflection of the probe beam. Some buried structures, however, do not produce an acoustic response and, accordingly, are not detectable using conventional opto-acoustic metrology. As discussed herein, however, a time resolved reflectance metrology device may detect and image buried structures that do not produce acoustic signals based on time resolved transient signals acquired from non-acoustic transient perturbations produced in response to a pump beam. Buried structures, such as voids or inclusions, that do not produce acoustic signals in response to pump beams are detected and imaged using the time resolved reflectance metrology device, based on the processing of the time resolved transient signals at a plurality of locations. The buried structures, for example, may be present in non-metallic, optically transparent layers that do not produce acoustic signals in response to pump beams. Non-acoustic transient perturbations are produced in response to a pump beam at a plurality of locations due to physical phenomena such as one or more of thermal dissipation, electron-hole recombination, plasma diffusion, symmetry breaking at top and bottom oxide surfaces, etalon effects. Non-acoustic transient signals are detected using a probe beam at the plurality of locations. The pump beam and probe beam have a varying delay to produce time resolved measurements of the transient signals. The buried structures are detected and imaged using a feature analysis (e.g., principal component decomposition, or polynomial fit, or other) for the non-acoustic transient signals at the plurality of locations. The sample may include a thick top layer and the structures may be present in an underlying layer. The wavelengths of light used in the pump and probe beams may be selected such that the top layer is at least partially transparent to the light, while the underlying layer is opaque. Light reflected from the top surface of the top layer may be rejected using a confocal lens arrangement before the detector. In one implementation, a metrology device is configured for non-destructive detection of structures in a sampl