Fluorescence mode for workpiece inspection

Abstract

A light beam is directed onto a workpiece containing a low-k dielectric material to induce fluorescence emission from the material. The workpiece is then imaged during the fluorescence emission. For imaging, an optical filter can be used that is located in the imaging path of the light beam and selects at least one wavelength from 300 nm to 900 nm.

Description

Technical Field

[0001] Cross - Reference to Related Applications This application claims priority based on U.S. Provisional Patent Application No. 63 / 453526, filed on March 21, 2023, and incorporated herein by reference in its entirety.

[0002] The present disclosure relates to the inspection of workpieces, and more particularly to semiconductor inspection.

Background Art

[0003] As the semiconductor manufacturing industry develops, the demand for yield management, particularly for metrology and inspection systems, is increasing. Critical dimensions are continuing to shrink, and there is still a need in the industry to shorten the time to achieve high - yield and high - value - added production. By reducing the total time from detecting a yield problem to correcting it, the return on investment for semiconductor manufacturers increases.

[0004] When manufacturing semiconductor devices such as logic devices and memory devices, semiconductor wafers are typically processed using a number of manufacturing processes to form various features and multiple layers of those semiconductor devices. For example, in a semiconductor manufacturing process such as lithography, a pattern is transferred from a reticle to a photoresist arranged 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. An array of multiple semiconductor devices can be created on a single semiconductor wafer and then separated into individual semiconductor devices.

[0005] Inspection processes are used in various stages of semiconductor manufacturing, and by detecting defects on wafers, they can improve yield and, consequently, profitability in the manufacturing process. Inspection has always been a crucial part of semiconductor device manufacturing, such as integrated circuits (ICs). However, as semiconductor devices shrink in size, even small defects can cause device malfunctions, making inspection more important than ever for the successful manufacture of acceptable semiconductor devices. For example, as semiconductor devices shrink, even relatively small defects can cause unwanted errors in the semiconductor device, thus necessitating the detection of even smaller defects.

[0006] On the other hand, as design rules are reduced, semiconductor manufacturing processes will operate closer to the limits of their performance capabilities. In addition, as design rules are reduced, even smaller defects can affect the electrical parameters of the device, leading to the need for more sensitive inspection. Smaller defects mean weaker defect signals, which in turn leads to more candidates on the noise floor being flagged as defects. Controlling the number of defects on a workpiece will be difficult. Semiconductor manufacturers are seeking ways to determine whether or not predicted defects are present, and therefore whether or not process parameters are under control. By determining which defects affect the electrical parameters and yield of the device, it will be possible to focus process control techniques on those defects while largely ignoring others. Furthermore, with smaller design rules, process-induced malfunctions tend to be systematic, in some cases. That is, process-induced malfunctions tend to cause malfunctions in certain design patterns that are often repeated many times within the design. Eliminating spatially systematic electrical defects can affect yield.

[0007] Current optical defect detection systems for IC devices rely on the reflection and scattering of light. As shown in Figure 1, process noise appears at each stage of the manufacturing process. Although shown as rectangles in Figure 1, IC features can be irregular and rough. In logic devices, low-k dielectric materials are used as interlayer dielectrics (ILDs) for MEOL (middle end of the line) and BEOL (back end of the line). Because low-k dielectrics are optically transparent, the light used for inspection travels across the layers and interacts with both the intended pattern structure and process noise. As a result, the signal emitted from the wafer and received by the detector includes the intended pattern, process noise, and light reflected from defects. As the size of the defects decreases, the inspection is overwhelmed by the cumulative light reflected from various noise sources within the stack, limiting the sensitivity of defect detection.

[0008] Techniques have been used to enhance the signal-to-noise ratio (SNR) of defects. Wavelength, illumination angle, polarization, and focus offset have been used to reduce the contribution of process noise signals and increase the intensity of defect signals. Design information has been used to isolate wafer regions based on noise contribution so that quieter regions exhibit higher sensitivity. Filter optimization and algorithmic parameter tuning have been used to maximize the differentiation of defects and wafer noise. Different optical modes have been used to allow process noise to be discriminated from defects and noise to be filtered out with higher sensitivity.

[0009] Current SNR enhancement and noise suppression techniques tend to work well when defects have characteristics that allow them to be distinguished from wafer noise through optical mode selection, design area identification, or image morphology. However, using these noise suppression techniques when defect size is small is challenging. When defect intensity is close to or below wafer noise levels, discriminating defects from wafer noise using optical mode optimization is unlikely to work well. As defect size decreases, signals from process noise in any region become equal to, and often even stronger than, the defect. Using design care areas and focusing on detecting defects in the quietest regions also becomes ineffective. As the noise source signal overwhelms the defect signal, algorithm tuning becomes difficult because defect information is lost in images immersed in wafer noise. Inspection using a combination of data from multiple optical modes also faces challenges when the defect signal is wafer noise or weaker, due to insufficient optical information to select an optical mode that can discriminate the defect from wafer noise. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] U.S. Patent Application Publication No. 2005 / 0037615 [Patent Document 2] U.S. Patent Application Publication No. 2005 / 0282300 [Overview of the project] [Problems that the invention aims to solve]

[0011] Thus, when the defect signal is equal to or lower than the process noise, current technology is insufficient. New optical methods are needed to generate additional signals to reinforce the defect signal. [Means for solving the problem]

[0012] A method is provided in the first embodiment. In this method, a workpiece is placed on a stage in an optical inspection system. The workpiece is said to contain a low-k dielectric material. A light beam is generated with a wavelength of 190 nm to 900 nm. By directing this light beam onto the workpiece, fluorescence emission is induced from the low-k dielectric material. The workpiece is imaged during fluorescence emission. An optical filter is used in the imaging path of the light beam for this imaging. The optical filter selects at least one wavelength from 300 nm to 900 nm.

[0013] The workpiece can be a semiconductor wafer. In one example, the low-k dielectric material is a dielectric oxide.

[0014] This method may include using a processor to quantify the k-value of a low-k dielectric material based on the spectral shape and / or intensity level of the fluorescence emission.

[0015] This method may also include using a processor to determine the uniformity of the k-value of the low-k dielectric material.

[0016] This method may include using a processor to inspect low-k dielectric materials for defects. In one example, the workpiece further contains metal, and all signals used for inspection originate from the low-k dielectric material. The metal does not emit fluorescence during the aforementioned orientation.

[0017] This method may also include tuning the wavelength between a first value of 190 nm to 700 nm and a second value of 300 nm to 900 nm using the optical filter.

[0018] In the second embodiment, a system is provided. This system includes a light source configured to generate an optical beam at wavelengths from 190 nm to 900 nm, a stage configured to hold a workpiece on the path of the optical beam, a tunable optical filter on the path of the optical beam, a detector that receives the optical beam reflected from the workpiece, and a processor that communicates electronically with the detector. The workpiece shall contain a low-k dielectric material. The optical beam causes fluorescence emission from the low-k dielectric material. The processor is configured to generate an image of the workpiece that includes the fluorescence emission.

[0019] The workpiece can be a semiconductor wafer. In one example, the low-k dielectric material is a dielectric oxide.

[0020] The processor may be configured to quantify the k-value of the low-k dielectric material based on the spectral shape and / or intensity level of the fluorescence emission.

[0021] The processor may be configured to determine the uniformity of the k-value of the low-k dielectric material.

[0022] The processor may be configured to inspect the low-k dielectric material for defects.

[0023] The tunable optical filter may be configured to tune the wavelength between a first value from 190 nm to 700 nm and a second value from 300 nm to 900 nm.

[0024] This system may have a polarizer on the path of the optical beam. The polarizer may be configured to tune the polarization of the optical beam.

[0025] This system may have a condenser optical filter on the path of the optical beam between the stage and the detector. The condenser optical filter may be configured to be tunable at wavelengths from 400 nm to 900 nm.

[0026] For an understanding of the nature and objects of the present disclosure, reference should be made to the following detailed description taken in conjunction with the accompanying drawings set forth below.

Brief Description of the Drawings

[0027] [Figure 1] It is a cross-sectional view of a typical BEOL (back end of line) IC stack with various structures represented by metal lines (Mx) and interlayer dielectrics (ILDx), having surface roughness and irregular metal structures. [Figure 2] It is a schematic diagram of an embodiment of an optical system according to the present disclosure. [Figure 3] It is a chart showing an excitation spectrum (dashed line) capable of generating 550 nm fluorescence emission, and a fluorescence emission spectrum (solid line) brought about by 400 nm excitation light in a low-k dielectric material. [Figure 4] It is a chart showing fluorescence emission spectra of two types of low-k dielectric materials with k = 2.55 and k = 3.0, indicating that intensity differences and spectral shifts can be used to discriminate low-k materials having different k-value targets and to monitor the uniformity of the k-values of dielectrics used within an IC device.

Modes for Carrying Out the Invention

[0028] The subject matter recited in the claims is described by specific embodiments, but other embodiments also exist within the technical scope of the present disclosure, including embodiments in which not all of the benefits and features described herein are provided. Various structural, logical, process step, and electronic modifications can be made without departing from the technical scope of the present disclosure. Thus, the technical scope of the present disclosure is defined solely by reference to the appended claims.

[0029] Improved imaging modes can be provided for generating signals that can enhance sensitivity to defects by detecting fluorescence emission from low-k dielectric materials. In the embodiments disclosed herein, fluorescence emission from low-k dielectric materials is captured to enhance the optical inspection sensitivity of layers containing low-k dielectrics. Based on this fluorescence behavior in low-k dielectric materials, a novel signal generation mechanism makes it possible to enhance the optical inspection sensitivity of layers containing low-k dielectrics. Furthermore, the intensity and fluorescence emission spectrum change depending on the low-k dielectric material. This optical property can be used to discriminate between low-k dielectric materials and to achieve quantitative uniformity of the k value. Since the k value of dielectric materials affects the electrical performance of logic devices, the ability to monitor the k value of dielectrics within those devices using fluorescence emission can be used to control the electrical performance of the IC, resulting in improved yield.

[0030] Figure 2 is a schematic diagram of one embodiment of the optical system 100. This system 100 can provide single-mode or multi-mode inspection methods. Fluorescence mode imaging can be incorporated into this optical system 100.

[0031] The system 100 has a light source 101 that generates an optical beam 102. The light source 101 can be, for example, a mercury light source, a laser light source, a lamp, a laser-sustained plasma light source, or other light sources. The wavelength of the optical beam 102 can be 190 nm to 900 nm. For example, the wavelength of the optical beam 102 can be 190 nm to 700 nm. When the optical beam 102 is projected along its own path, the optical beam 102 can pass through the adjustable optical filter 104, the first lens 103, the polarizer 105, and the second lens 106. The adjustable optical filter 104 is shown prior to the first lens 103 with respect to the path of the optical beam 102, but it can also be placed between the first lens 103 and the beam splitter 107.

[0032] The wavelength range of the adjustable optical filter 104 in the path of the light beam 102 should be selected so as to maximize the excitation of the low-k dielectric material and, consequently, pump the fluorescence emission. In that case, the focusing optical filter 111 in the imaging path should be selected so as to collect the maximum fluorescence emission from the low-k dielectric material. Figure 3 shows the excitation and fluorescence emission spectra obtained from an example of a low-k dielectric material. In this example, the strongest excitation wavelength is approximately 310 nm, and the strongest fluorescence emission is approximately 550 nm.

[0033] Turning to Figure 2, the adjustable optical filter 104 allows the wavelength or wavelength group to be tuned between a first value of 190 nm to 700 nm and a second value of 300 nm to 900 nm. For example, the adjustable optical filter 104 may include several optical filters. A specific optical filter can be selected from the adjustable optical filter 104 for a particular application or workpiece.

[0034] The polarization of the light beam 102 can be tuned using the polarizer 105. To reduce leading layer noise, the polarizer 105 can control light penetration within the workpiece 109. By limiting the optical interaction with the surface of the workpiece 109 using the polarizer 105, noise in the fluorescence mode can be further reduced. Limiting the optical interaction may be useful if the workpiece 109 has a wafer stack.

[0035] The light beam 102 is directed towards the beam splitter 107. After passing through the beam splitter 107 and the third lens 108, the light beam 102 is directed towards the workpiece 109. The workpiece 109 is placed on a stage 110 configured to hold the workpiece 109 along the path of the light beam 102.

[0036] The workpiece 109 may be a semiconductor wafer, but it may be any other workpiece. In one example, the workpiece 109 is a wafer stack. The workpiece 109 contains a low-k dielectric material, such as a dielectric oxide. The light beam 102 induces fluorescence emission from the low-k dielectric material within the workpiece 109. For example, the low-k dielectric material to be fluorescent may have a k value of less than 3, but other low-k materials with different k values ​​that produce the same effect can also be used.

[0037] The detector 112, for example, a camera, receives the light beam 102 (shown by the dashed line) reflected from the workpiece 109. The light beam 102 may be passed through a focusing optical filter 111 along the path between the workpiece 109 and the detector 112. The focusing optical filter 111 can be configured to be tunable to wavelengths or wavelength groups from 400 nm to 900 nm. The focusing optical filter 111 may include several optical filters. A specific optical filter can be selected from the focusing optical filter 111 for a particular application or workpiece.

[0038] The processor 113 communicates electronically with the detector 112. The processor 113 may be programmed in software and / or firmware to perform the functions described herein and may have appropriate digital and / or analog interfaces for connection with other elements of the system 100. Alternatively, the processor 113 may have hardwired and / or programmable hardware logic circuits that perform at least some of the functions of the processor 113. For simplicity, the processor 113 is shown in Figure 2 as a single planar block, but in practice, the processor 113 may comprise a plurality of interconnected control units and may have appropriate interfaces for receiving and outputting signals depicted in the figure and described in the text. Program code or instructions for causing the processor 113 to perform the various methods and functions disclosed herein may be stored in a readable storage medium, such as memory.

[0039] The processor 113 is configured to generate an image of the workpiece 109, including fluorescence emission, using information from the detector 112. The processor 113 may have additional functions. For example, the processor 113 may be configured to quantify the k-value of the low-k dielectric material of the workpiece 109 based on the spectral shape and / or intensity level of fluorescence. In another example, the processor 113 may be configured to determine the uniformity of the k-value in the low-k dielectric material of the workpiece 109 by, for example, monitoring whether the fluorescence intensity at a particular wavelength is below a threshold. In yet another example, the processor 113 may be configured to inspect the low-k dielectric material within the workpiece 109 for defects.

[0040] During operation, the workpiece 109 is placed on the stage 110 within the system 100. The workpiece 109 is illuminated with a light beam 102, for example, having a wavelength of 300 nm to 900 nm. Illuminating the workpiece 109 with the light beam 102 can induce fluorescence emission from the low-k dielectric material within the workpiece 109. The workpiece 109 is then imaged during this fluorescence emission.

[0041] The workpiece 109 can be inspected in fluorescence mode using fluorescence emission from low-k dielectrics. Unwanted noise is not generated from materials on the workpiece 109 that do not fluoresce. For example, MEOL and BEOL materials in advanced logic devices contain dielectrics and metals. In fluorescence mode, only dielectric materials fluoresce, so noise sources from metal lines are automatically suppressed, leading to noise reduction. In addition, since the only signal emitting from the wafer stack is from the low-k dielectric material, amplified signal generation in fluorescence mode can occur at oxide etching defects. This can result in increased defect signals and enhanced defect detection.

[0042] Figure 4 shows the emission spectra of low-k dielectric materials with k=2.55 and k=3.0. By using the difference in spectral response, the k value of the low-k dielectric material can be quantified and its uniformity can be checked. Embodiments of the system disclosed herein can be used to determine whether the low-k dielectric material satisfies the k value specification and to quantify the uniformity of the k value over the entire surface or a portion of the surface of the workpiece 109.

[0043] In one embodiment, in fluorescence mode, using a light source 101, excitation light can be supplied to the workpiece 109 by a tunable optical filter 104 located on the illumination path and covering 190-700 nm, and fluorescence emission from the dielectric material can be focused by a focusing optical filter 111 located on the imaging path and covering 400-900 nm. A polarizer 105 can be used to further control light transmission within the workpiece 109 (e.g., within a wafer stack) and control noise. In the fluorescence mode system 100, signals that can provide higher defect sensitivity can be captured in low-k dielectric material quantitative applications. For example, during defect inspection, the fluorescence mode system 100 provides additional signals regarding defects on layers using low-k dielectric material. In another example, the system 100 can quantify the k value of the low-k dielectric within the workpiece 109 and monitor its uniformity. In a further example, intensity and fluorescence emission spectra can be used to (1) distinguish low-k dielectric materials having different target k values, and (2) monitor the k value uniformity of the low-k dielectric material within the workpiece 109.

[0044] Although this disclosure has been described in relation to one or more specific embodiments, other embodiments of this disclosure can be constructed without deviating from the technical scope of this disclosure. That is, this disclosure is considered to be limited only by the attached claims and their reasonable interpretation.

Claims

1. It is a method, A workpiece is placed on a stage within an optical inspection system, provided that the workpiece contains a low-k dielectric material. A light beam is generated with wavelengths ranging from 190 nm to 900 nm. By directing the aforementioned light beam onto the workpiece, fluorescence emission is induced from the low-k dielectric material. The workpiece is imaged during fluorescence emission, and in the imaging, an optical filter is used on the imaging path of the light beam, and at least one wavelength is selected from 300 nm to 900 nm using the optical filter. method.

2. A method according to claim 1, wherein the workpiece is a semiconductor wafer.

3. A method according to claim 1, wherein the low-k dielectric material is a dielectric oxide.

4. A method according to claim 1, further comprising a method for quantifying the k value of the low-k dielectric material based on the spectral shape and / or intensity level of the fluorescence emission using a processor.

5. A method according to claim 1, further comprising a method for determining the uniformity of the k value of the low-k dielectric material using a processor.

6. A method according to claim 1, further comprising a method for inspecting the low-k dielectric material for defects using a processor.

7. A method according to claim 6, wherein the workpiece further contains a metal, and all signals used in the inspection are from the low-k dielectric material.

8. A method according to claim 7, wherein the metal does not emit fluorescence during the orientation.

9. The method according to claim 1, further comprising tuning the wavelength between a first value of 190 nm to 700 nm and a second value of 300 nm to 900 nm using the optical filter.

10. It is a system, A light source configured to generate a light beam with wavelengths from 190 nm to 900 nm, A stage configured to hold a workpiece along the path of the aforementioned light beam, wherein the workpiece contains a low-k dielectric material and the light beam causes fluorescence emission from the low-k dielectric material, A tunable optical filter located on the path of the aforementioned light beam, A detector that receives the light beam reflected from the workpiece, A processor that communicates electronically with the detector and is configured to generate an image of the workpiece which includes the fluorescence emission, A system equipped with these features.

11. The system according to claim 10, wherein the workpiece is a semiconductor wafer.

12. The system according to claim 10, wherein the low-k dielectric material is a dielectric oxide.

13. A system according to claim 10, wherein the processor is configured to quantify the k value of the low-k dielectric material based on the spectral shape and / or intensity level of the fluorescence emission.

14. A system according to claim 10, wherein the processor is configured to determine the uniformity of the k value of the low-k dielectric material.

15. A system according to claim 10, wherein the processor is configured to inspect the low-k dielectric material for defects.

16. A system according to claim 10, wherein the adjustable optical filter is configured to tune the wavelength between a first value of 190 nm to 700 nm and a second value of 300 nm to 900 nm.

17. A system according to claim 10, further comprising a polarizer located on the path of the light beam, wherein the polarizer is configured to tune the polarization of the light beam.

18. A system according to claim 10, further comprising a focusing optical filter in the path of the light beam between the stage and the detector, wherein the focusing optical filter is configured to be tunable in the range of 400 nm to 900 nm.

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