Fluorescent mode for workpiece inspection

Abstract

A light beam is directed to a workpiece comprising a low-k dielectric material, which causes fluorescence emission from the low-k dielectric material. The workpiece is imaged during fluorescence emission. The imaging may use an optical filter that selects at least one wavelength from 300 nm to 900 nm in an imaging path of the light beam.

Description

[0001] Cross - Reference to Related Applications

[0002] This application claims priority to the provisional patent application of U.S. Application No. 63 / 453,526, filed on March 21, 2023, and assigned, the content of which is hereby incorporated by reference. Technical Field

[0003] This disclosure relates to the inspection of workpieces, and more particularly, to semiconductor inspection. Background Art

[0004] The evolution of the semiconductor manufacturing industry has placed higher demands on yield management, and particularly on metrology and inspection systems. Critical dimensions are constantly shrinking, but the industry needs to reduce the time to achieve high-yield, high-value production. Minimizing the total time from detecting a yield issue to resolving the issue maximizes the return on investment for semiconductor manufacturers.

[0005] Manufacturing semiconductor devices (such as logic and memory devices) typically involves processing semiconductor wafers using a large number of manufacturing processes to form various features and multiple levels of semiconductor devices. For example, lithography is a semiconductor manufacturing process that involves transferring a pattern from a photomask to a photoresist disposed 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. The arrangement of multiple semiconductor devices fabricated on a single semiconductor wafer can be separated into individual semiconductor devices.

[0006] The inspection process is used at various steps during semiconductor manufacturing to detect defects on the wafer to promote higher yields in the manufacturing process and thus, obtain higher profits. Inspection has always been an important part of manufacturing semiconductor devices (such as integrated circuits (ICs)). However, as the size of semiconductor devices decreases, inspection becomes even more important for the successful manufacture of acceptable semiconductor devices because smaller defects can cause device failure. For example, as the size of semiconductor devices decreases, the detection of smaller-sized defects becomes necessary because even relatively small defects can cause unwanted aberrations in semiconductor devices.

[0007] However, as design rules shrink, semiconductor manufacturing processes can operate closer to the limits of the process's performance capabilities. Additionally, as design rules shrink, smaller defects can impact the electrical parameters of the device, which drives more sensitive inspection. The smaller defect size results in weaker defect signals and more candidates at the noise floor being flagged as defects. Controlling the number of defects on a workpiece can be difficult. Semiconductor manufacturers attempt to determine whether expected defects exist and, thus, whether process parameters are under control. Determining which defects affect the electrical parameters and yield of the device can allow process control techniques to focus on those defects while largely ignoring others. Additionally, at smaller design rules, in some cases, process-induced failures tend to be systematic. That is, process-induced failures tend to fail in a predetermined design pattern that is typically repeated many times within the design. Eliminating spatially systematic, electrically related defects can impact yield.

[0008] Current optical defect inspectors for IC devices rely on light reflection and scattering. As shown in FIG. 1, there is process noise at each manufacturing step. Although shown as rectangles in FIG. 1, IC features can be irregular and rough. For logic devices, low-k dielectric materials are used for the middle-of-line (MEOL) and back-end-of-line (BEOL) processes as the interlayer dielectric (ILD). Because low-k dielectrics are optically transparent, the light used for inspection travels across the layers and interacts with both the expected pattern structure and process noise. As a result, the signal received by the inspector from the wafer includes light returned from the expected pattern, process noise, and defects. As the defect size shrinks, the cumulative light returned from the noise sources in the stack overwhelms the inspection, which limits defect detection sensitivity.

[0009] Technically, attempts have been made to improve the signal-to-noise ratio (SNR) of defects. Wavelength, illumination angle, polarization, and focus offset have been used to minimize the process noise signal contribution and maximize the defect signal intensity. Design information has been used to isolate wafer regions based on noise contribution, which allows for quieter regions with higher sensitivity. Filter optimization and algorithm parameter tuning have been used to maximize defect and wafer noise discrimination. Different optical device modes have been used to distinguish process noise from defects such that the noise can be filtered to obtain higher sensitivity.

[0010] Current SNR enhancement and noise suppression techniques tend to work when defects have characteristics distinguishable from wafer noise, whether through optical mode selection, design region identification, or image morphology. However, it is challenging to use these noise suppression techniques when the defect size decreases. When the defect intensity approaches or falls below the wafer noise level, it is not feasible to use optical mode optimization to distinguish defects from wafer noise. As the defect size decreases, the signals generated from process noise in all regions become equal to or sometimes even stronger than the signals from the defects. Using design guard bands and focusing defect detection on the quietest regions also becomes ineffective. Algorithm tuning also becomes unmanageable when the signals from noise sources overwhelm the defect signals because defect information is lost in images overwhelmed by wafer noise. When the defect signal is equal to or weaker than the wafer noise, the inspection of combining multiple optical device mode data also faces challenges due to insufficient optical information attributed to the selection of optical modes to distinguish defects from wafer noise.

[0011] Therefore, current techniques may be insufficient when the defect signal is equal to or lower than the process noise. New optical methods are needed to generate additional signals to enhance the defect signal. Summary of the Invention

[0012] In a first embodiment, a method is provided. The method includes placing a workpiece on a stage in an optical inspection system. The workpiece includes a low-k dielectric material. A light beam having a wavelength ranging from 190 nm to 900 nm is generated. The light beam is directed onto the workpiece, thereby causing fluorescence emission from the low-k dielectric material. The workpiece is imaged during the fluorescence emission. The imaging uses an optical filter in the imaging path of the light beam. The optical filter selects at least one wavelength ranging from 300 nm to 900 nm.

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

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

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

[0016] The method may include using a processor to inspect for defects in the low-k dielectric material. In an example, the workpiece further includes metal and all signals used for the inspection are from the low-k dielectric material. The metal may not have fluorescence emission during the directing.

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

[0018] In a second embodiment, a system is provided. The system includes: a light source configured to generate a beam of wavelengths from 190 nm to 900 nm; a stage configured to hold a workpiece in the path of the beam; a tunable optical filter located in the path of the beam; a detector that receives the beam reflected from the workpiece; and a processor in electronic communication with the detector. The workpiece includes a low-k dielectric material. The beam causes fluorescence emission from the low-k dielectric material. The processor is configured to generate an image of the workpiece including the fluorescence emission.

[0019] The workpiece may be a semiconductor wafer. In an 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 for defects in the low-k dielectric material.

[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] The system may include a polarizer in the path of the beam. The polarizer may be configured to tune the polarization of the beam.

[0025] The system may include a collection optical filter in the path of the beam between the stage and the detector. The collection optical filter may be configured to be tunable between 400 nm and 900 nm. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] To more fully understand the nature and objects of the present disclosure, reference should be made to the following detailed description taken in conjunction with the accompanying drawings, in which:

[0027] FIG. 1 is a cross-sectional view of a typical backend-of-line (BEOL) IC stack having a structure representing metal lines (M x ) and interlayer dielectrics (ILD x ) and surface roughness and irregular metal structures;

[0028] Figure 2is a schematic diagram of an embodiment of an optical system according to the present disclosure;

[0029] Figure 3 is a graph showing the excitation spectrum (dashed line) capable of generating a 550 nm fluorescence emission and the fluorescence emission spectrum (solid line) generated by 400 nm excitation light of a low-k dielectric material; and

[0030] Figure 4 is a graph showing the fluorescence emission spectra of two low-k dielectric materials (k = 2.55 and k = 3.0), which shows that the intensity difference and spectral shift can be used to distinguish low-k materials with different k-value targets and to monitor the uniformity of the k-value of the dielectric used in IC devices. Detailed Description

[0031] Although the claimed subject matter will be described in terms of certain embodiments, other embodiments (including embodiments that do not provide all of the advantages and features set forth herein) are also within the scope of the present disclosure. Various structural, logical, process step, and electronic changes can be made without departing from the scope of the present disclosure. Accordingly, the scope of the present disclosure is defined only by reference to the appended claims.

[0032] The fluorescence emission from the low-k dielectric material can provide an improved imaging mode for signal generation, which can enhance the sensitivity to defects. The embodiments disclosed herein capture the fluorescence emission of the low-k dielectric material to enhance the optical inspection sensitivity of the layer containing the low-k dielectric. This fluorescence behavior in the low-k dielectric material enables a new signal generation mechanism to enhance the defect detection of the layer containing the low-k dielectric material. In addition, the intensity and fluorescence emission spectrum change with different low-k dielectric materials. This optical property can be used to distinguish low-k dielectric materials and to provide acceptable uniformity of the k-value. The k-value of the dielectric material affects the electrical performance of the logic device, so the ability to use fluorescence emission to monitor the k-value of the dielectric in the device can be used to control the electrical performance of the IC and can lead to a higher yield.

[0033] Figure 2 is a schematic diagram of an embodiment of an optical system 100. The system 100 can provide a single-mode or multi-mode inspection scheme. The optical system 100 can include fluorescence mode imaging.

[0034] System 100 includes a light source 101 that generates a light beam 102. The light source 101 can be, for example, a mercury source, a laser source, a lamp, a laser sustained plasma source, or other light sources. The light beam 102 can have a wavelength ranging from 190 nm to 900 nm. For example, the light beam 102 can have a wavelength ranging from 190 nm to 700 nm. As the light beam 102 is projected along its path, the light beam 102 can pass through a tunable optical filter 104, a first lens 103, a polarizer 105, and a second lens 106. Although shown in front of the first lens 103 with respect to the path of the light beam 102, the tunable optical filter 104 can also be positioned between the first lens 103 and a beam splitter 107.

[0035] The wavelength range of the tunable optical filter 104 in the path of the light beam 102 can be selected such that the low-k dielectric material can be maximally excited to pump fluorescence emission. Then, the collection optical filter 111 in the imaging path can be selected to collect the maximum fluorescence emission from the low-k dielectric material. Figure 3 The excitation and fluorescence emission spectra obtained from an exemplary low-k dielectric material are shown. In this example, the strongest excitation wavelength is about 310 nm, and the strongest fluorescence emission is about 550 nm.

[0036] Return Figure 2 , the tunable optical filter 104 can tune the wavelength between a first value ranging from 190 nm to 700 nm and a second value ranging from 300 nm to 900 nm. For example, the tunable optical filter 104 can include a number of optical filters. A specific optical filter for a specific application or workpiece can be selected from the tunable optical filter 104.

[0037] The polarizer 105 can tune the polarization of the light beam 102. To reduce previous layer noise, the polarizer 105 can control the light penetration inside the workpiece 109. The polarizer 105 can limit the interaction of light with the surface of the workpiece 109 to further reduce the noise in the fluorescence mode. If the workpiece 109 includes a wafer stack, limiting the light interaction can be helpful.

[0038] The light beam 102 is directed to the beam splitter 107. After passing through the beam splitter 107 and a third lens 108, the light beam 102 is directed to the workpiece 109. The workpiece 109 is placed on a stage 110 configured to hold the workpiece 109 in the path of the light beam 102.

[0039] The workpiece 109 can be a semiconductor wafer, but other workpieces are also possible. In an example, the workpiece 109 is a wafer stack. The workpiece 109 includes a low-k dielectric material, such as a dielectric oxide. The light beam 102 induces fluorescence emission from the low-k dielectric material in the workpiece 109. For example, the fluorescent low-k dielectric material can have a k value lower than 3, but other low-k materials with different k values that provide the same effect are also possible.

[0040] Detector 112 (e.g., a camera) receives a light beam 102 (shown in dashed lines) reflected from workpiece 109. The light beam 102 can pass through a collection optical filter 111 along the path between the workpiece 109 and the detector 112. The collection optical filter 111 can be configured to be tunable to one or more wavelengths between 400 nm and 900 nm. The collection optical filter 111 can include a number of optical filters. A specific optical filter can be selected from the collection optical filter 111 for a particular application or workpiece.

[0041] Processor 113 is in electronic communication with detector 112. Processor 113 can be programmed in software and / or firmware to perform the functions described herein, along with suitable digital and / or analog interfaces for connecting to other components of system 100. Alternatively or additionally, processor 113 can include hardwired and / or programmable hardware logic circuitry that performs at least some of the functions of processor 113. Although Figure 2 processor 113 is shown as a single monolithic functional block for simplicity, in practice, processor 113 can include multiple interconnected control units, and suitable interfaces for receiving and outputting signals, which are illustrated in the figures and described in the text. Program code or instructions for processor 113 to implement the various methods and functions disclosed herein can be stored in a readable storage medium (e.g., a memory).

[0042] Processor 113 is configured to use the information from detector 112 to generate an image of workpiece 109 that includes fluorescence emission. Processor 113 can also include additional functionality. For example, processor 113 can be configured to quantify the k-value of the low-k dielectric material of workpiece 109 based on the spectral shape and / or intensity level of the fluorescence. In another example, processor 113 can be configured to determine the uniformity of the k-value in the low-k dielectric material of workpiece 109 (e.g., by monitoring whether the fluorescence intensity at a specific wavelength is below a threshold). In yet another example, processor 113 can be configured to inspect for defects in the low-k dielectric material of workpiece 109.

[0043] During operation, workpiece 109 is positioned on stage 110 in system 100. Workpiece 109 is illuminated with a light beam 102 that can have a wavelength from 300 nm to 900 nm. Illuminating workpiece 109 with the light beam 102 can cause fluorescence emission from the low-k dielectric material in workpiece 109. Then, the workpiece 109 is imaged during this fluorescence emission.

[0044] Low-k dielectric fluorescence emission can be used to inspect workpiece 109 in a fluorescence mode. Materials on the workpiece 109 that do not fluoresce will not generate unwanted noise. For example, the MEOL and BEOL materials of advanced logic devices include dielectrics and metals. In the fluorescence mode, since only the dielectric material fluoresces, noise sources generated from metal lines are automatically suppressed, resulting in reduced noise. Additionally, because the only signal from the wafer stack of the emission signal is the low-k dielectric material, oxide etch defects can have amplified signal generation in the fluorescence mode. This can result in higher defect signals and enhanced defect detection.

[0045] Figure 4 Emission spectra of low-k dielectric materials with k = 2.55 and k = 3.0 are shown. The difference in spectral response can be used to quantify the k value and inspect the uniformity of the low-k dielectric. Embodiments of the systems disclosed herein can be used to determine whether the low-k dielectric material meets the k-value specification and can quantify the uniformity of the k value over the entire surface or a portion of the surface of the workpiece 109.

[0046] In an embodiment, the fluorescence mode can use a light source 101 and a tunable optical filter 104 covering 190 nm to 700 nm in the illumination path to deliver the excitation light to the workpiece 109, and a collection optical filter 111 covering 400 nm to 900 nm in the imaging path to collect the fluorescence emission from the dielectric material. To further control the light transmission in the workpiece 109 (e.g., in the wafer stack) for noise control, a polarizer 105 can be used. The fluorescence mode capture of the system 100 can provide signals with higher defect sensitivity in low-k dielectric qualification applications. For example, for defect inspection, the fluorescence mode of the system 100 will provide additional signals for defects on the layer using the low-k dielectric material. In another example, the system 100 can quantify and monitor the uniformity of the k value of the low-k dielectric in the workpiece 109. In yet another example, the intensity and fluorescence emission spectrum can be used to (1) distinguish low-k dielectric materials with different target k values and (2) monitor the k-value uniformity of the low-k dielectric material in the workpiece 109.

[0047] Although the present disclosure has been described with respect to one or more particular embodiments, it should be understood that other embodiments of the present disclosure can be made without departing from the scope of the present disclosure. Accordingly, the present disclosure is considered to be limited only by the appended claims and their reasonable interpretations.

Claims

1. A method, comprising: Placing a workpiece on a stage in an optical inspection system, wherein the workpiece comprises a low-k dielectric material; Generating a light beam having a wavelength ranging from 190 nm to 900 nm; Directing the light beam onto the workpiece, thereby causing fluorescence emission from the low-k dielectric material; Imaging the workpiece during the fluorescence emission, wherein the imaging uses an optical filter in the imaging path of the light beam, and wherein the optical filter selects at least one wavelength ranging from 300 nm to 900 nm.

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

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

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

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

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

7. The method according to claim 6, wherein the workpiece further comprises metal, and wherein all signals for the inspection are from the low-k dielectric material.

8. The method according to claim 7, wherein the metal does not have fluorescence emission during the directing.

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

10. A system, comprising: A light source configured to generate a light beam having a wavelength ranging from 190 nm to 900 nm; A stage configured to hold a workpiece in the path of the light beam, wherein the workpiece comprises a low-k dielectric material, and wherein the light beam causes fluorescence emission from the low-k dielectric material; An adjustable optical filter located in the path of the light beam; A detector that receives the light beam reflected from the workpiece; And A processor in electronic communication with the detector, wherein the processor is configured to generate an image of the workpiece including the fluorescence emission.

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

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

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

16. The system according to claim 10, wherein the tunable optical filter is 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.

17. The system according to claim 10, further comprising a polarizer in the path of the beam, wherein the polarizer is configured to tune the polarization of the beam.

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

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