Systems and methods for fluid distribution and coverage control

Abstract

Light can be used to monitor the coating of liquid onto a substrate. By directing light to a point on the substrate, some light is reflected and some is scattered as the liquid passes through that point. Monitoring this behavior can indicate whether the substrate has been successfully coated with the liquid and identify defects. Furthermore, coating time can be monitored for process adjustments.

Description

[0001] Cross-referencing of jointly pending applications

[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 019,017, filed May 1, 2020, and U.S. Non-Provisional Patent Application No. 17 / 196,189, filed March 9, 2021, the entire contents of which are incorporated herein by reference. Background Technology

[0003] This disclosure relates to semiconductor manufacturing, and more specifically to the distribution of materials on a substrate.

[0004] Semiconductor manufacturing involves multiple processing steps involving the deposition of liquids or fluids on a substrate. These processing steps include, in particular, coating the wafer, developing a potential pattern, etching material onto the wafer, and cleaning / rinsing the wafer.

[0005] In conventional microfabrication processes, a thin layer of photosensitive material, such as photoresist, is coated onto the working surface (upper surface) of a substrate. Subsequently, the photosensitive material is patterned using photolithography to define a mask pattern, which is then transferred to the underlying layer by etching using the patterned photoresist as an etching mask. The patterning of the photosensitive material typically involves coating, exposure, and development steps. A thin film of photosensitive material is coated onto the working surface of the substrate. Using, for example, a microlithography system, this thin film is exposed to a radiation source through a photomask (and associated optics). Following the patterned exposure is a development process, during which a developing solvent is used to remove soluble areas of the photosensitive material. Depending on the hue of the photoresist and developer used, the soluble areas can be irradiated or non-irradiated.

[0006] During the coating process, the substrate is positioned on a substrate holder and rotated at high speed while a resist solution is distributed onto the upper surface of the substrate. The high rotation speed can be thousands or tens of thousands of revolutions per minute (rpm). For example, when the resist solution is distributed in the center of the substrate, it diffuses radially across the substrate due to the centrifugal force exerted by the substrate's rotation. Wet etching and cleaning processes can be performed similarly. During development, a solvent developer is deposited on the rapidly rotating substrate. The solvent developer dissolves the soluble portions of the photoresist, and then, due to centrifugal force, the developer and the dissolved photoresist are radially removed from the substrate. The wet etching, cleaning, and rinsing processes are performed similarly to the development process, where liquid is deposited on the rotating wafer and removed by centrifugal force, thereby removing or eliminating specific materials or residues. Summary of the Invention

[0007] This disclosure discloses a method for dispensing liquid onto a substrate. The method includes: rotating the substrate about an axis on a substrate holder; dispensing liquid onto a working surface of the substrate while the substrate is rotating on the substrate holder, the rotation of the substrate causing the liquid to coat the working surface of the substrate, progressing from a central portion of the substrate to an edge of the substrate; directing a laser beam to an edge position on the working surface of the substrate; monitoring light from the edge position of the substrate to identify a pattern of the monitored light indicating that the liquid has reached the edge position on the substrate; identifying an actual coating time of the liquid, the actual coating time from the start of dispensing the liquid onto the working surface until the liquid reaches the edge of the working surface; and comparing the actual coating time of the liquid with an expected coating time of the liquid.

[0008] In one embodiment, monitoring light from the edge portion includes monitoring scattered light from the laser beam.

[0009] In one embodiment, monitoring light from the edge portion includes monitoring reflected light from the laser beam.

[0010] In one embodiment, monitoring light from the edge portion includes monitoring both scattered light from the laser beam and reflected light from the laser beam.

[0011] In one embodiment, the method further includes adjusting a given dispensing operation based on comparing the actual coating time of the liquid with the expected coating time of the liquid.

[0012] In one embodiment, the method further includes adjusting a given assignment operation in response to identifying that the difference between the actual coating time and the expected coating time is greater than a predetermined threshold.

[0013] In one embodiment, adjusting a given dispensing operation may include dispensing more liquid.

[0014] In one embodiment, adjusting a given allocation operation may include increasing the rotational speed of the substrate.

[0015] In one embodiment, the method further includes indicating an error in response to identifying that the difference between the actual coating time and the expected coating time is greater than a predetermined threshold.

[0016] In one embodiment, the method further includes monitoring multiple dispensings of multiple spin-coated films and comparing the actual coating time and expected coating time of each deposited film.

[0017] In one embodiment, the method further includes monitoring light from a substrate edge location to identify a pattern of the monitored light that indicates a defect in the liquid-formed film.

[0018] In one embodiment, monitoring light from the edge portion includes monitoring light from multiple light sources.

[0019] This disclosure also discloses a system for dispensing liquid on a substrate, the system comprising: a substrate holder configured to hold the substrate and rotate it about an axis; a dispensing unit configured to dispense liquid on a working surface of the substrate while the substrate is rotating on the substrate holder; a laser configured to guide a laser beam to an edge position on the working surface of the substrate; a first detector positioned to capture scattered light from the laser beam guided to the edge position on the substrate; a processor configured to monitor the scattered light from the laser beam guided to the edge position on the substrate to identify a pattern of scattered light indicating that the liquid has reached the edge position on the substrate; the processor is further configured to determine the actual coating time of the liquid and compare the actual coating time of the liquid with the expected coating time of the liquid, the actual coating time being from the start of the given dispensing of the liquid onto the working surface until the liquid reaches the edge of the working surface.

[0020] In one embodiment, the processor is configured to monitor scattered light from a laser beam directed to an edge location on the substrate to identify a pattern of scattered light that indicates a covering defect in the film formed from the liquid.

[0021] In one embodiment, the system further includes a second detector positioned to capture reflected light from a laser beam directed to an edge location on the substrate; and the processor is configured to monitor reflected light from a laser beam directed to an edge location on the substrate to identify a pattern of reflected light indicating that the liquid has reached the edge location on the substrate.

[0022] This disclosure also discloses a system for dispensing liquid on a substrate, the system comprising: a substrate holder configured to hold the substrate and rotate it about an axis; a dispensing unit configured to dispense liquid on a working surface of the substrate while the substrate is rotating on the substrate holder; a laser configured to guide a laser beam to an edge position on the working surface of the substrate; a first detector positioned to capture reflected light from the laser beam guided to the edge position on the substrate; a processor configured to monitor the reflected light from the laser beam guided to the edge position on the substrate to identify a pattern of reflected light indicating that the liquid has reached the edge position on the substrate; the processor is further configured to determine the actual coating time of the liquid and compare the actual coating time of the liquid with the expected coating time of the liquid, the actual coating time being from the start of the given dispensing of the liquid onto the working surface until the liquid reaches the edge of the working surface.

[0023] In one embodiment, the processor is configured to monitor reflected light from a laser beam directed to an edge location on the substrate to identify a pattern of reflected light that indicates a covering defect in the film formed by the liquid.

[0024] In one embodiment, the system further includes a second detector positioned to capture scattered light from a laser beam directed to an edge location on the substrate; and the processor is configured to monitor the scattered light from the laser beam directed to an edge location on the substrate to identify a pattern of scattered light indicating that the liquid has reached the edge location on the substrate.

[0025] Please note that the Summary of this Exploration does not specify every embodiment and / or additional novel aspect of this disclosure or the claimed invention. Rather, the Summary provides only a preliminary discussion of different embodiments and corresponding novel points that outperform conventional techniques. For additional details and / or possible perspectives on the invention and embodiments, the reader should refer to the Detailed Description section of this disclosure and the accompanying drawings, as discussed further below. Attached Figure Description

[0026] A more complete understanding of the various embodiments of the invention and its many incidental advantages will become very clear by referring to the following specific embodiments considered in conjunction with the accompanying drawings. The drawings are not necessarily drawn to scale, but rather focus on illustrating features, principles, and concepts.

[0027] Figure 1 This is a schematic cross-sectional view of an example allocation system according to the embodiments disclosed herein.

[0028] Figure 2 This is a top view of an example substrate fragment, illustrating the flow of an example coating process according to embodiments disclosed herein.

[0029] Figure 3 This is a top view of an example substrate fragment, illustrating the flow of an example coating process according to embodiments disclosed herein.

[0030] Figure 4 This is a top view of an example substrate fragment, illustrating the flow of an example coating process according to embodiments disclosed herein.

[0031] Figure 5 This is a top view of an example substrate fragment, illustrating the flow of an example coating process according to embodiments disclosed herein.

[0032] Figure 6 This is a top view of an example substrate fragment, illustrating the flow of an example removal process according to embodiments disclosed herein.

[0033] Figure 7This is a top view of an example substrate fragment, illustrating the flow of an example removal process according to embodiments disclosed herein.

[0034] Figure 8 This is a top view of an example substrate fragment, illustrating the flow of an example removal process according to embodiments disclosed herein.

[0035] Figure 9 This is a top view of an example substrate fragment, illustrating the flow of an example removal process according to embodiments disclosed herein.

[0036] Figure 10 It demonstrates the behavior of reflected and scattered light guided to the edge of the substrate over time when the liquid spreads on a flat substrate, especially when the liquid has not yet reached the edge of the substrate, when the liquid is at the edge of the substrate, and after the liquid has successfully covered the edge of the substrate.

[0037] Figure 11 It demonstrates the behavior of reflected and scattered light guided to the edge of the substrate over time when the liquid spreads on a flat substrate, especially when the liquid has not yet reached the edge of the substrate, when the liquid is at the edge of the substrate, and after the liquid has covered the edge of the substrate but left a defect. Detailed Implementation

[0038] This document describes techniques for dispensing liquids onto a substrate under real-time cover and remove control. These techniques are applicable to a variety of manufacturing operations, including substrate coating (e.g., semiconductor wafers), film development, wet etching of materials, and substrate cleaning and rinsing. Various embodiments use a laser beam directed to one or more predetermined locations on the substrate to monitor the behavior of scattered and / or reflected light from these locations. Monitoring this scattered / reflected light behavior as the liquid interacts with the laser beam can indicate the position of a given liquid on the working surface of the substrate, allowing the substrate to be flagged as defective or generating feedback data for real-time modification of the corresponding dispensing operation, such as by increasing / decreasing the volume of fluid dispensed or increasing / decreasing the substrate rotation speed. Monitoring can be manual or automated.

[0039] Although various manufacturing operations involving liquid materials dispensed onto a rotating substrate exist, for the sake of describing the techniques herein, the description of exemplary embodiments will focus primarily on substrate coating. Conventional microfabrication techniques involve photolithography, in which a film (photoresist) is coated onto a substrate, exposed to a photochemical radiation pattern, and then developed to remove soluble materials.

[0040] Traditionally, more photoresist (i.e., photoresist) is applied than is needed to completely cover the substrate. Applying extra or excessive photoresist is to ensure uniform coating across the entire substrate. The substrate (typically a semiconductor wafer) is rotated at a relatively high speed (rotation speed) while liquid photoresist is applied to the wafer's working surface. The rotating wafer then uses centrifugal force to push the photoresist to the edges of the substrate (typically a circular wafer). The path of advance of a given photoresist, developer, or other fluid does not always have uniform edges. That is, the outer edges or outer menisci of the photoresist do not spread radially uniformly (e.g., expand uniformly in a perfect circle). Instead, the outer edges of the photoresist are uneven, and photoresist in some areas may reach the edge of the substrate before photoresist in other areas. The result may appear as jagged edges of the photoresist at the substrate edges. This incomplete coverage is not visible while the substrate is rotating. Instead, due to the blurring effect of the liquid, the rotating substrate may appear to be completely coated while rotating.

[0041] One method for controlling coating coverage is to visually monitor the progress of the coating liquid on the substrate, for example, using a stroboscope or camera. Visual monitoring may be effective for some liquids and film thicknesses, but is less effective for others. For example, some photoresists and films have coverage thicknesses on the order of tens of nanometers. Films of this thickness are relatively thin and therefore can be essentially transparent. Therefore, it is difficult to visually determine when a wafer is fully coated with a given film. Monitoring with scattered / reflected light can overcome these problems.

[0042] For many applications, it is required to uniformly and completely coat the working surface of the substrate with photoresist. To meet this requirement, additional resist is dispensed so that the rotating substrate can be completely coated. This extra resist falls off the wafer edges and is wasted. Traditionally, as a safety factor to account for several different variables that could affect complete coverage, manufacturers may deposit up to 400% or more of additional photoresist and other liquid chemicals. One factor is the dispensing capability of the dispensing system itself. For example, some photoresist compositions can coat the substrate with approximately 0.2 cc of resist. Due to dispensing variables, it is common to dispense approximately 0.8 cc of resist.

[0043] Various factors or variables can cause excess fluid to be dispensed. Some factors relate to the capabilities of the dispensing system itself. These include variability in valve response, conduit variability, and measurement methods. Another factor is the properties of a given photoresist or liquid chemical. With slight variations in the photoresist composition (even within the same chemical formula), a given amount of dispensing liquid may have more or less viscosity at any given dispensing. These viscosity differences need to be addressed and often necessitate increasing the safety margin by dispensing more chemical. Another factor affecting coverage is the physical properties of the substrate surface itself. Different materials are used at different stages of semiconductor device fabrication on wafers. Furthermore, surface morphology can vary depending on the manufacturing stage and the type of device being manufactured (e.g., memory versus logic). A given material and / or morphology can increase the viscosity of the photoresist spread on the surface. Substrate wettability is an important factor because the interaction between the liquid and the substrate can vary significantly. This interaction often causes deviations in liquid flow on the substrate. When these safety factors are taken into account, manufacturers may then use significantly more chemical than is actually required to achieve complete coverage. Some manufacturers can use four times or more of the extra volume compared to what is actually needed.

[0044] Note that because a given photoresist reaches the substrate edges at varying rates, a certain amount of safety margin is typically required to complete coverage. This minimum amount of extra photoresist is usually around 2% to 20%. Therefore, by calculation, a given substrate can be coated with 102% to 120% of the resist actually needed to achieve complete coverage. However, due to various performance factors, manufacturers often deposit 300% to 500% more photoresist (or developer) than actually needed. This extra amount is simply a safety margin. It is not the amount absolutely necessary for coating / rinsing the substrate, but merely to ensure that the substrate is never partially coated.

[0045] The techniques described herein include spin-coating process sensors and defect monitors for coverage control during spin-coating film deposition on substrates such as semiconductor wafers. Each substrate can be characterized by the behavior of scattered and / or reflected light from a laser beam as it interacts with a liquid at a predetermined location on the substrate. For example, to detect that the liquid has completely covered the substrate, the laser can be directed to the edge of the substrate. Liquid already dispensed near the center of the rotating substrate will gradually begin to cover the substrate as it flows outward toward the laser / substrate edge. The behavior of scattered and reflected light changes instantaneously as the liquid edge interacts with the laser beam, which can be detected by one or more optical detectors for detecting scattered and / or reflected light and indicating the progress of the liquid / coverage of the substrate. Additional lasers or other types of light sources can be targeted to other areas of the substrate to obtain further progress / coverage information. If the substrate does not achieve proper liquid coverage, the system can mark the substrate as defective, or the system can use a feedback control loop (e.g., advanced process control (APC)) to ensure accurate volumetric deposition, thereby significantly reducing the safety margin for dispensing. Therefore, instead of having a safety margin of 300%, 400%, or 500% more than required, the systems and methods of this paper can deposit photoresist, developer, or other liquids in excess of less than 50%, 20%, or even 2%. This eliminates waste, reduces the need for chamber cleaning, and minimizes tool downtime. Each substrate being processed by liquid phase deposition can be monitored in real time using one or more optical detectors for detecting reflected and / or scattered light, and time points can be plotted along the liquid edge moving on the substrate each time the substrate interacts with the laser beam. This edge can be the outer liquid edge coating the substrate or the inner liquid edge cleaning the substrate.

[0046] Based on the analysis of the liquid's progress or behavior, measures or modifications can be taken to the dispensing system. For example, in some dispensing processes, it may be observed that the photoresist progresses relatively quickly and moves to the edge of the substrate, achieving early coating. If the system tracks the coating progress and identifies when coating is completed (or identifies when coating will be completed by identifying the progress rate), the system can instruct (provide feedback) when or at what point complete coating is achieved or will be achieved, in order to stop dispensing the liquid. If the system observes or determines that the edge of the resist is slowing down and moving slowly, actions can be taken to accelerate the rotation of the substrate holder and / or dispense additional resist onto the substrate to achieve complete coating or wetting.

[0047] Traditionally, coating performance analysis is performed after the coating process. Essentially, the substrate is stopped rotating or removed from the processing chamber to examine the coating coverage. To the naked eye, coating progress may appear uniform because high-speed rotation blurs inhomogeneities. However, the technique presented here provides a real-time view of the future of substrate coating and the capability of that coating by examining data on scattered or reflected light and applying that data as real-time feedback, for example, to identify stopping points for dispensing and / or rotation. A processor can be connected to a scattered or reflected light detector and can analyze the scattered / detected light to determine whether a given dispensing is acceptable, whether coating is necessary, collect process statistics (e.g., yield statistics), or adjust rotation speed and dispensing rate / amount. Such control can be adjusted in real time to adapt to variable process conditions. Thus, instead of estimating the substrate wettability and photoresist viscosity to calculate safe dispensing amounts and rotation times, photoresist can be deposited on a rotating substrate without initially knowing the stopping point. As the photoresist spreads across the substrate, the processor, receiving data on this progress of scattered and / or reflected light, can identify the rate of progress changing over time and can then accurately indicate the stopping point. Accordingly, it is not necessary to know the substrate wettability and photoresist viscosity, because the system can stop a given coating operation when the substrate is fully coated. In other words, the precise dispensing volume and stopping time can be calculated in real time based on observations of scattered / reflected light indicating liquid progress, rather than estimating the stopping time and the volume of liquid to be dispensed.

[0048] In some embodiments, fluid may be dispensed onto the initial substrate, and then scattered / reflected light data is used to identify the rotation time and dispensing time required for complete coating. This dispensing time and volume data can then be used for subsequent dispensing.

[0049] In some embodiments, deposition yield statistics that vary with process conditions, including dispensing volume, rotational speed profiles, etc., can be collected. The dispensing process can be defined based on the statistics and the desired process yield. During production, deposition yield statistics can continue to be collected and process deviations monitored. In production (including high-volume manufacturing (HVM)), deposition yield can continue to be monitored and the process adjusted to ensure the coating process conforms to specifications, thereby continuously correcting process or environmental deviations. When defects are detected in HVM, the substrate can be immediately sent for rework. Process matching by coverage yield allows the system to account for and offset the effects of tooling variability (e.g., process bowls, dispensing systems, etc.), environmental influences (plant temperature, humidity), chemical variability, deviations (bottle-to-bottle, or shelf-time effects), etc.

[0050] The technique described in this paper measures scattered and / or reflected light from the substrate and detects the passage of the dispersed liquid front. It can also detect radial stripe-type defects. Therefore, the sensor can determine whether a particular deposition was successful.

[0051] The techniques described herein will now be explained with reference to the accompanying drawings. (References) Figure 1 System 100 is a system for dispensing liquid 117 onto substrate 105. A substrate holder 122 is configured to hold substrate 105 and rotate substrate 105 about an axis. A motor 123 can be used to rotate substrate holder 122 at a selectable rotational speed. A dispensing unit 118 is configured to dispense liquid onto the working surface of substrate 105 as substrate 105 is rotated by substrate holder 122. Dispensing unit 118 can be positioned directly above substrate holder, or it can be positioned at another location. If positioned away from substrate holder, fluid can be delivered to substrate using conduit 112. Fluid can be discharged through nozzle 111. Figure 1 The dispensing of liquid 117 onto the working surface of substrate 105 is demonstrated. Excess liquid 117 ejected from substrate 105 during a given dispensing operation can then be captured or collected using collection system 127.

[0052] The dispensing component may include a nozzle arm 113 and a support member 115, which can be used to move the nozzle 111 in position above the substrate 105, or to be removed from the substrate holder 122 to a resting position, such as for resting when the dispensing operation is complete. Alternatively, the dispensing unit 118 may be implemented as the nozzle itself. Such a nozzle may have one or more valves communicating with the system controller 160. The dispensing unit 118 may have various embodiments configured to control the dispensing of optional volumes of fluid onto the substrate.

[0053] Various techniques can be used to implement the dispensing unit 118. Various valves, flow controllers, filters, nozzles, etc., can be used. The various dispensing techniques chosen can provide various levels of volume control and delay. The techniques herein can benefit from precise volume control achieved by using a capsule-based dispensing unit as described in U.S. Patent Application Publication No. 2018 / 0046082 (U.S. Serial No. 15 / 675,376), entitled "High-Purity Dispense Unit." However, such a precise dispensing system is not required. Accordingly, conventional dispensing systems can be used to practice the techniques herein.

[0054] The dispensing unit can be configured to dispense a selected amount of photoresist, negative tint developer, or other liquid onto a substrate based on input from a system controller. The dispensing unit may include a dispensing nozzle positioned above the working surface of the substrate.

[0055] System 100 includes at least one laser 130 configured to direct a laser beam 131 to a predetermined location (i.e., a target) on substrate 105. Laser 130 may be a laser diode or a light-emitting diode with beam-forming optics. The predetermined location may be a place where it is desired to observe the progress of liquid 117 coverage or to perform defect detection. Different predetermined locations may be used herein. For example, to determine whether the entire substrate 105 has been covered by liquid 117, laser 130 may be configured to direct the laser beam 131 to the edge of substrate 105 (or within a few millimeters of the edge). In another embodiment, more than one laser 130 may be used. For example, a second laser beam may be directed between the edge and the center portion of substrate 105 to monitor intermediate progress of liquid 117. In another embodiment, a different light source may be used in place of or to supplement laser beam 131. Any laser (e.g., green or red) may be used, as long as it does not activate the given photoresist being applied.

[0056] A reflected light detector 132 is positioned to capture reflected light from the laser beam 131. When the laser beam 131 strikes a predetermined location on the substrate 105 and is reflected away, if the predetermined location is smooth, most of the laser beam 131 will be reflected to the reflected light detector 132 (instead of the scattered light detector 133) and detected by it. A smooth predetermined location indicates that the location is not yet covered by the liquid 117, or that the location has been successfully covered by the liquid 117. Note that more than one reflected light detector can be used. For example, if the first laser beam is directed to the edge of the substrate, a first reflected light detector can be used to detect reflected light from the substrate edge. If the second laser beam is directed to the interior portion of the substrate, a second reflected light detector can be used to detect reflected light from the interior portion of the substrate.

[0057] A scattered light detector 133 is positioned to capture scattered light from the laser beam 131. When the edge of the liquid 117 interacts with the laser beam 131, more light is scattered and less light is reflected. This edge of the liquid 117 can be radially dispersed liquid or a fragment (mouse bite) on the substrate 105 not yet covered by the liquid 117. Detecting an increase in scattered light (or a decrease in reflected light) can indicate that the liquid 117 has reached a predetermined location on the substrate 105, or that the substrate 105 has a defect. Note that more than one scattered light detector can be used. For example, if the first laser beam is directed to the edge of the substrate, a first scattered light detector can be used to detect scattered light from the edge of the substrate. If the second laser beam is directed to the interior portion of the substrate, a second scattered light detector can be used to detect scattered light from the interior portion of the substrate.

[0058] Note that in one embodiment, system 100 has at least one detector for capturing reflected light. In another embodiment, system 100 has at least one detector for capturing scattered light. System 100 may have both a scattered light detector 133 and a reflected light detector 132, but this is not always necessary.

[0059] The reflected light detector 132 and the scattered light detector 133 can use conventional techniques to detect light. For example, the reflected light detector 132 and the scattered light detector 133 can have photodetectors for detecting light. Furthermore, additional components can be placed in the system 100 to guide the laser beam 131, the scattered light, and / or the reflected light to their respective target locations. Examples of such components may include mirrors, elliptical collectors, quarter-wave plates, polarizing beam splitters, focusing lenses, collimators / cylindrical lenses, etc. In one embodiment, a polarizing beam splitter is used to guide the reflected light to the reflected light photodetector, while the primary mirror guides the scattered light to the secondary mirror, and the secondary mirror guides the scattered light to the scattered light photodetector.

[0060] The detected scattered and / or reflected light information can be transmitted to or collected by the processor 150. The processor 150 is configured to examine the scattered and / or reflected light information received from the scattered light detector 133 and / or the reflected light detector 132. The processor 150 can mark whether the substrate has defects (e.g., cracks). The processor 150 can also monitor the coating time. The processor 150 can identify the actual coating time of the liquid 117, from the start of dispensing the liquid 117 onto the working surface of the substrate 105 until the liquid reaches a predetermined location on the working surface (e.g., edge, inner portion). Furthermore, the processor 150 can compare the actual coating time of the liquid 117 with the expected coating time. The processor 150 can also be configured to generate feedback data while the substrate 105 is rotating with liquid 117 on it. By analyzing the scattered and / or reflected light, the processor 150 can, in particular, determine the degree of completion of fluid edge propagation or the dehumidification status, etc. This edge progress data can then be fed to the system controller 160. System controller 160 is connected to substrate holder 122 and to dispensing unit 118. System controller 160 is configured to adjust the volume of liquid dispensed onto the working surface of the substrate based on feedback data while the substrate is rotating with liquid 117 on it. For example, a specially constructed control loop, APC control loop, or feedback control loop connected to system controller 160 is arranged to control the corresponding dispensing system and / or substrate rotation mechanism.

[0061] One or more scattered light detectors and / or reflected light detectors are positioned to detect scattered light and reflected light, respectively. Processor 150 is connected to or accessible by system 100 and is configured to analyze the scattered light and / or reflected light received from the respective detectors. Processor 150 can be configured to generate feedback data while substrate 105 is rotating with liquid 117 on it. Feedback data can also be generated and provided after a dispensing operation. Processor 150 can also be configured to monitor the coating progress of photoresist on the working surface of substrate 105 based on the examination of scattered and / or reflected light and generate feedback data indicating when sufficient photoresist has been dispensed to completely cover the working surface of substrate 105. This indication can be anticipated based on the progress rate.

[0062] Processor 150 can be configured to recognize patterns of scattered and / or reflected light that indicate whether liquid 117 has reached a target location on substrate 105 or whether the film formed by liquid 117 has coverage defects. Steady-state behavior of scattered and reflected light can indicate that liquid 117 has not yet reached the target location (i.e., the location of laser beam 131) or that the target location has been successfully covered. Spike / non-steady-state behavior of scattered or reflected light can indicate that the edge of liquid 117 has just reached the target location or that coverage defects exist. Examples of such behavior will be given later in this disclosure.

[0063] System controller 160 is connected to substrate holder 122 and to dispensing unit 118. System controller 160 is configured to adjust the volume of liquid 117 dispensed onto the working surface of substrate 105 based on feedback data while substrate 105 is rotating with liquid 117 on it. System controller 160 may be further configured to adjust the rotational speed of substrate holder 122 based on feedback data.

[0064] The system controller 160 can be configured to dispense an initial volume of liquid 117 onto the working surface of the substrate, and then dispense an additional volume of liquid 117 onto the working surface of the substrate 105, such additional volume of liquid 117 being sufficient to completely cover the working surface of the substrate 105. In other words, more fluid can be dispensed when it is determined that more fluid is needed to completely cover the wafer.

[0065] System controller 160 can be configured to increase the rotational speed of substrate holder 122 based on feedback data indicating insufficient coverage of liquid 117 on the working surface of substrate 105. This increase in rotational speed can help distribute the film on substrate 105. Alternatively, system controller 160 can decrease the rotational speed of substrate holder 122 based on feedback data indicating, for example, turbulence of liquid 117 on the working surface of substrate 105 or excessive resist being ejected from substrate 105. System controller 160 can also increase the volume of liquid 117 distributed on the working surface of substrate 105 based on feedback data indicating insufficient coverage of liquid 117 on the working surface of substrate 105.

[0066] Processor 150 may have a number of functions. Processor 150 may be configured to generate feedback data while substrate 105 is rotating with liquid 117 on it, and may adjust a given dispensing operation while substrate 105 is rotating with liquid 117 on it. Based on the examination of scattered or reflected light indicating the position / movement of liquid 117, processor 150 may monitor the progress of the outer meniscus of liquid 117 as liquid 117 coats the working surface of substrate 105. Processor 150 may also monitor the progress of the inner meniscus of liquid 117 as liquid 117 is splashed off the working surface of substrate 105. The coating progress of liquid 117 may be monitored to generate feedback data indicating whether more or less volume of liquid 117 should be dispensed to obtain the minimum dispensing volume required to completely coat the working surface of substrate 105, and / or to identify when the working surface of substrate 105 is completely covered.

[0067] System controller 160 can be configured to take various actions. For example, system controller 160 can adjust the volume of liquid 117 dispensed onto the working surface of substrate 105 based on feedback data while substrate 105 is rotating. The rotational speed of substrate holder 122 can be adjusted based on feedback data. Based on collected data indicating the movement of liquid 117, the volume of dispensed liquid 117 can be less than 150% of the coverage volume required to completely cover the working surface of substrate 105. System controller 160 can reduce the rotational speed of substrate holder 122 based on feedback data indicating the turbulence of liquid 117 on the working surface of substrate 105, which can prevent damage to substrate 105. System controller 160 can also stop dispensing fluid in response to receiving feedback data indicating that the working surface of substrate 105 is completely covered.

[0068] The processor 150 can monitor the coating progress of the initial volume of liquid 117 on the working surface of the substrate 105 and generate feedback data indicating insufficient coverage of the working surface of the substrate 105. Based on the inspection of scattered and / or reflected light indicating proper coverage, the processor 150 can calculate the total volume of liquid 117 dispensed on the substrate 105 to cover the substrate 105 with an excess volume of less than 50%. The processor 150 can also monitor and generate feedback data indicating dehumidification status and when sufficient photoresist has been dispensed to completely cover the substrate 105. In response to receiving feedback data indicating when sufficient photoresist has been dispensed to completely cover the substrate 105, the system controller 160 can stop the dispensing operation. Scattering and / or reflection behavior can be analyzed to monitor the progress of the outer meniscus of the liquid 117 when it is coated on the substrate, or the progress of the inner meniscus of the liquid 117 when it is ejected from the substrate.

[0069] One embodiment includes a system for dispensing liquid onto a substrate. The system includes a substrate holder configured to hold the substrate and rotate it about an axis. A dispensing unit is configured to dispense liquid onto a working surface of the substrate as it rotates on the substrate holder. At least one of a scattered light detector and a reflected light detector is positioned to detect scattered or reflected light from a laser beam directed to the edge of the substrate.

[0070] The edges of liquid 117 can be tracked with high accuracy. This helps identify areas that are not adequately covered (sometimes referred to as "mouse bite") or other areas with uneven edge progression, ensuring that substrate 105 is fully covered. For example, regarding photoresist deposition used to cover substrate 105, uncovered areas may form at the edges of photoresist progression. This uncovered area and its formation can then be tracked as a function of time before formation. Such tracking helps ensure that coating is completed and that excess liquid 117 material is minimized. This progress can be tracked as a function of time during photoresist rotation by tracking the leading edge of photoresist propagation as the photoresist moves across the edge 105 of the substrate. Processor 150 can then calculate the location as a function of time and determine where the photoresist edge is and how close a given edge is to the location where a mouse bite actually occurred. Identifying uncoated portions can then automatically trigger responses, such as marking substrate 105 as defective, incrementally depositing more photoresist, or increasing the rotation speed to achieve complete coverage. This edge tracking can also be used to calculate the progress rate in real time. The progress rate can be used to identify or calculate when the photoresist fully covers (or will fully cover) the substrate 105, and therefore the coverage rate can be used to indicate when to stop distributing photoresist on the substrate.

[0071] Due to the non-uniform propagation of liquid chemicals, a certain amount of liquid 117 excess is required to completely cover a given substrate. 105 However, under precise control, this excess can be as low as an additional 2% to 50% of the distributed material.

[0072] Figure 2 A top view of a substrate segment is shown, illustrating the working surface of substrate 105. Substrate 105 rotates at a relatively high speed, such as 2-3 thousand revolutions per minute. Commonly seen in semiconductor wafers, a notch 126 or straight edge is present at a location on the substrate. This notch 126 is V-shaped in some cases, and in others, a short, flat edge of another circular wafer. If the notch 126 interacts with the laser beam 131, it causes a change in the behavior of scattered and reflected light. Knowing this, the laser beam 131 can be guided away from the notch 126, or the processor 150 can predict and filter out the scattered / reflected light caused by the notch 126.

[0073] exist Figure 2 In the diagram, liquid 117 is shown on the working surface of substrate 105. This liquid may be, for example, photoresist deposited at or near the center point of substrate 105. When substrate 105 is rotated at high speed, liquid 117 spreads radially. Figure 3 This illustrates the continued radial progression of liquid 117. Note that the outer meniscus 129 has uneven edges. In other words, liquid 117 does not spread uniformly or completely uniformly.

[0074] Figure 4 The progress of liquid 117 is shown after it has partially reached the outer edge of the substrate. Note that there are several areas with nicks (rat bites) that are not yet covered by liquid 117. If the coating operation is stopped at this point, adequate coverage will not be achieved (i.e., there will be defects). The behavior of scattered and reflected light will be unstable each time the laser beam 131 strikes the nicks. By monitoring this behavior, incomplete coverage can be indicated. This can trigger marking the substrate 105 as defective, or continuing to rotate the substrate 105 if the liquid 117 is still spreading outwards. Other measures may include increasing the rotation speed of the substrate 105 or depositing more liquid 117 on the substrate 105. Because the total surface area of ​​the uncovered areas can be accurately calculated or estimated based on the evaluation of the scattered or reflected light data, the additional volume to be allocated can be accurately determined. The system controller 160 can then receive this feedback or instruction from the processor 150 and then control the allocation unit 118 to allocate an additional incremental volume sufficient to complete the full coating coverage with a minimum amount of additional allocation volume. The results are shown in Figure 5 Accordingly, the given substrate 105 can be completely coated with a minimal amount of additional dispensing liquid 117.

[0075] Please note that some coating processes are not performed on a perfectly flat substrate, but rather on a substrate with structures (grooves, holes, mesas, etc.). These patterned structures can alter the reflection and scattering of light. Even if the substrate is properly covered, the scattered / reflected light may exhibit unstable behavior. Therefore, these structures can be considered by comparing their scattered / reflected light signals with signals from a reference / target substrate considered defect-free. The behavior of the scattered and / or reflected light can be compared with the results from that reference substrate to determine when the substrate has been acceptablely covered by the film and whether any defects are present. Essentially, any deviation in the behavior of the scattered / reflected light relative to the target substrate can indicate the presence of a liquid edge. Alternatively or additionally, the light detected from an uncovered substrate can be used as a reference for the same substrate after it has been covered by the liquid. If the substrate has similar reflected and scattered light patterns before and after being covered by the liquid, it can indicate that the substrate has been acceptablely covered. In another embodiment, the patterned structures can be considered and filtered out by a processor or software.

[0076] It is understood that the embodiments described herein are not limited to coating photoresist on a wafer, but can be applied to many other microfabrication techniques using liquids deposited on a rotating substrate. For example, the scattered / reflected light analysis described herein can be beneficial for developer dispensing. After the photoresist layer has been exposed to patterned photochemical radiation, the soluble portions need to be developed. For film development, the purpose is not only to coat the substrate but also to dissolve and completely remove the soluble material. In the case of development, the volume of fluid dispensed is typically larger than that of the photoresist. The substrate can be monitored by analyzing the scattered / reflected light. Detected instability changes in light behavior can indicate the complete dissolution of the soluble material, flow dynamics, etc.

[0077] The technique described herein can be beneficial for development with various developers, including negative-tone developers. In practice, it is common to dispense approximately 6-8 cc of negative-tone developer while simultaneously dispensing approximately 30-50 cc of other developers. Regardless of the developer used, dewetting can be a problem during development, especially at the wafer edges. Development is slower than photoresist deposition. During development, solutes may be absorbed, resulting in a thinner photoresist solution. This solution may move faster along the runner than in other areas. If the solution becomes saturated, the photoresist may redeposit on the substrate, leading to defects. Additionally, if the developer solution dries in an area before the dissolved photoresist is carried away from the substrate, that photoresist may be redeposited on the substrate. Therefore, the technique described herein can monitor the removal of developer from the substrate. Both leading-edge and trailing-edge etching can be monitored. If gases are also used during wafer cleaning, the air jet interaction (nitrogen ejection) at the trailing edge can be monitored in real time.

[0078] These techniques and monitoring methods can be similarly applied to wet etching. Monitoring the scattered / reflected light of the fluid on the substrate can ensure proper dispensing and that the developer content remains consistent regardless of surfactant conditions. Etching rates and developer consumption can be identified by pattern recognition of the detected scattered / reflected light. By using such photodetection techniques to identify specific conditions (complete, turbulent), the dispensing system can take appropriate actions, such as stopping developer / etcher dispensing or slowing rotation in response to turbulent conditions. Minimizing the amount of developer or etchant used reduces overall waste, thus benefiting green processing initiatives. Some developers can be expensive, so minimizing the volume dispensed is also economically advantageous.

[0079] The embodiments described herein are similarly applied to cleaning and rinsing. Various rinsing or cleaning operations can use piranha solutions, SC1, SC2, deionized water, etc. It is known that rinsing or cleaning progress can have benefits including yield and output. Some rinsing liquids (such as deionized water) are relatively economical compared to resists and developers, and therefore using significantly more than required may not incur significant environmental or material costs. However, yield and output can benefit from real-time feedback. By knowing the precise completion point, rinsing and etching can be stopped earlier than conventional techniques that require running a safety reserve or spin time to ensure a given substrate is completely cleaned or etched. Regarding defect reduction, some structures that are microfabricated may be relatively fragile at certain stages. If the rinsing liquid changes from laminar to turbulent, this turbulence can damage or destroy the structure being created. Therefore, monitoring turbulence conditions can improve yield. Output can be increased by knowing precisely when rinsing or cleaning is complete. If a given rinsing or cleaning process is completed and then immediately stopped based on analysis of the scattered and / or reflected light feedback, the number of wafers processed per hour can be increased. For certain rinsing operations, the system can be implemented with an array of nozzles, for example, to spray liquid onto a substrate.

[0080] Figures 6 to 9 Exemplary developing, etching, or rinsing operations are demonstrated. Figure 6 In this process, the dispensing of liquid 117 has ceased. As a rinsing agent or developer, this fluid continues to move radially towards the edge of substrate 105. This may cause the inner meniscus 121 to move outward. Figure 7 This inner curved meniscus 121 can be monitored, for example, to detect unwanted flow conditions that might damage components on it. If such a condition is identified, the controller can reduce the rotational speed. Figure 8 In the process, it can be identified that almost all of liquid 117 has been ejected. The processor can calculate or identify when liquid 117 has indeed completely detached from the substrate. Figure 9This process stops the corresponding dispensing operation in response. Other operations can also be performed. For example, if scattered / reflected light detection analysis indicates that the material has been redeposited, more liquid can be dispensed to dissolve / remove this material.

[0081] Accordingly, real-time control can be provided to achieve accurate coating, development, etching, rinsing and cleaning.

[0082] Examples of the results will not be discussed. Recall that, for liquid coverage, the liquid front (the moving edge of the liquid) causes a temporary change in the reflected / scattered light when it interacts with the laser beam. Figure 10 An example of a pattern indicating successful liquid coating is shown, in which a laser beam 131 is guided to the edge of a substrate 105. Reflected light 1001 and scattered light 1002 are detected by their respective detectors and plotted over time. Initially, as shown during time 10a, reflected light 1001 and scattered light 1002 exhibit fairly steady-state behavior, indicating that the moving edge of liquid 117 has not yet reached / interacted with the laser beam 131. Then, as shown during time 10b, reflected light 1001 and scattered light 1002 deviate from their previous behavior and exhibit unstable, non-steady-state behavior, indicating that the moving edge of liquid 117 has reached and interacted with the laser beam 131. Compared to their corresponding amounts during time 10a, the amount of reflected light 1001 temporarily decreases, while the amount of scattered light 1002 temporarily increases. Finally, if liquid 117 has properly covered the edge of substrate 105, the behavior of scattered light 1002 and reflected light 1001 will stabilize again, as shown during time 10c. Processor 150 can add the times during time 10a and time 10b to obtain the actual coating time and compare it with the expected coating time. If the difference between the expected coating time and the actual coating time is greater than a predetermined threshold, an error can be indicated, or system operation can be adjusted.

[0083] Figure 11 An example of a detected pattern is shown where substrate 105 has been improperly coated, leaving stripes. A photodetector is set up to capture reflected light 1101 and scattered light 1102 from a laser beam 131 directed to the edge of substrate 105. Initially, as shown during time 11a, reflected light 1101 and scattered light 1102 exhibit steady-state behavior, indicating that the moving edge of liquid 117 has not yet reached / interacted with the laser beam 131. Then, as shown during time 11b, reflected light 1101 and scattered light 1102 exhibit unstable, non-steady-state behavior, indicating that the moving edge of liquid 117 has reached / interacted with the laser beam 131. Finally, if liquid 117 has properly covered the edge of substrate 105, the behavior of scattered light 1102 and reflected light 1101 will stabilize during time 11c (as shown). Figure 10(As shown in time 10c). Conversely, during each rotation of the substrate 105, the stripes and the laser beam 131 interact, resulting in a downward spike in the reflected light 1101 and an upward spike in the scattered light 1102, indicating that the substrate 105 has not been successfully coated. This can be identified by the processor 150 and trigger subsequent actions, such as marking the substrate 105 as defective or adjusting system operation.

[0084] Another embodiment of this document is a method for dispensing liquid onto a substrate. The substrate is rotated about an axis on a substrate holder. While the substrate is rotating on the substrate holder, liquid is dispensed onto a working surface of the substrate. The rotation of the substrate allows the liquid to coat the working surface of the substrate, progressing from the center of the substrate to the edge. A laser beam is directed to an edge position on the working surface of the substrate. Light from the substrate edge position is monitored to identify a pattern of the monitored light indicating that the liquid has reached the edge position on the substrate. The actual coating time of the liquid is confirmed from the start of dispensing the liquid onto the working surface until the liquid reaches the edge of the working surface. The actual coating time of the liquid is compared with an expected coating time. In response to confirming that the difference between the actual coating time and the expected coating time is greater than a predetermined threshold, the dispensing operation can be adjusted, or an error can be indicated. Multiple dispensings of multiple spin-coated films can be monitored, and the actual coating time of each deposited film can be compared with the expected coating time.

[0085] Distributing liquid on the working surface of a substrate may include distributing liquid at the center of the substrate, with rotation of the substrate causing the liquid to spread outwards. This outward spreading may be the liquid coating the substrate or the liquid being flung off the substrate. In another embodiment, the liquid may be distributed on the working surface of the substrate before the substrate is rotated on a substrate holder.

[0086] Directing the laser beam to an edge location on the substrate working surface can include directing the laser beam directly to the substrate edge, or approximately close to the edge, such as within a few millimeters of the edge. Since the substrate is rotating, the entire edge around the substrate will be considered during scattered / reflected light monitoring. In other embodiments, additional or alternative light sources may be used. Any laser (e.g., green or red) can be used, as long as it does not activate the given photoresist being dispensed.

[0087] The laser beam is directed to a radius around which the coating progress is monitored and defects are detected. Accordingly, additional laser beams can be directed onto the working surface of the substrate. These can be directed into the interior portions of the substrate. Light from these interior locations can be monitored to indicate when the liquid has reached that location or if a defect exists there. The actual coating time for these interior locations can be confirmed and compared to the expected coating time. This actual coating time can be used to predict when to coat the entire substrate. Predictions can be made based on many different factors, such as how much of the substrate has already been coated, how much more needs to be coated, the substrate's rotation speed, and the properties of the liquid (e.g., viscosity). Furthermore, if the prediction indicates that the substrate will not be properly coated, the prediction can be used to adjust system operation. For example, if an interior portion should have been coated in 1-2 seconds but was actually coated in 3 seconds, this could indicate that the coating is lagging behind the current operating settings. Therefore, operating settings can be adjusted, such as dispensing additional liquid onto the substrate or increasing the substrate's rotation speed.

[0088] The monitoring light can include the scattered light from a laser beam originating from an edge location. A brief increase in the amount of scattered light may indicate that liquid has reached the edge location on the substrate. Periodic upward spikes in the amount of scattered light may indicate the presence of defects, such as streaks, at the substrate edge location.

[0089] The monitoring light can include the reflected light from a laser beam originating from an edge location. A brief decrease in the amount of reflected light may indicate that liquid has reached the edge location on the substrate. Periodic downward spikes in the amount of scattered light may indicate a defect, such as streaks, at the substrate edge location.

[0090] Monitoring light can include both reflected and scattered light from a laser beam originating from an edge location. While the behavior of either the scattered or reflected light is sufficient to indicate coverage and / or error, both can be monitored, where the behavior of the scattered and reflected light can help verify the observations of the other.

[0091] The monitoring light may include reflected light, scattered light, or both, from any additional laser beam directed to the interior of the substrate.

[0092] Identifying the pattern of monitored light indicating that the liquid has reached the substrate edge can include identifying when the monitored light will change behavior, from a generally steady state to a non-steady state. Generally, when light interacts with the liquid edge, the amount of reflected light decreases, while the amount of scattered light decreases. Furthermore, identifying the pattern of monitored light indicating that the liquid has properly covered the substrate edge (i.e., without leaving any defects) can include identifying when the monitored light returns to a steady state. Additionally, identifying the pattern of monitored light indicating defects (e.g., streaks) can include identifying when the monitored light periodically spikes. Generally, streaks cause upward spikes in scattered light and downward spikes in reflected light. Assuming the substrate rotates at a constant speed, the spikes will be periodic.

[0093] Determining the actual coating time can include measuring the time between the start of liquid dispensing on the substrate's working surface and the time between the liquid reaching a target location on the working surface. This target location can be an edge or an inner portion and is defined by guiding a laser beam to that location. If multiple target locations are used, multiple coating times can be measured.

[0094] Comparing the actual coating time with the expected coating time may include adjusting a given assignment operation and / or indicating an error in response to identifying that the difference between the actual and expected coating times is greater than a predetermined threshold. The expected coating time and the predetermined threshold may be based on previous successful coating times under similar operating conditions, or any other conventional technique known in the art. The desired process yield may be a factor in determining the predetermined threshold.

[0095] Adjusting the dispensing operation may include selectively modifying the volume of liquid dispensed on the working surface of the substrate. Adjusting the dispensing operation may include selectively modifying the rotational speed of the substrate holder. Adjusting the liquid dispensing operation on the working surface of the substrate may include dispensing an additional volume that is minimized to a sufficient amount to achieve complete coating coverage of the working surface of the substrate.

[0096] Indicating errors may include marking the substrate. The substrate may be marked as requiring rework. Operating conditions, such as substrate rotation speed, actual coating time, and dispensed liquid volume, may be recorded for future analysis and troubleshooting.

[0097] Monitoring multiple spin-coated films over multiple assignments can include comparing the actual coating time and the expected coating time for each deposited film. This information can be stored for analysis, such as making more accurate predictions about future expected coating times, better predetermined thresholds, and better operating conditions.

[0098] Multiple light sources can be monitored. For example, any laser (e.g., green or red) can be used, as long as it does not activate the given photoresist being applied. Accordingly, monitoring light from edge portions can include monitoring light from multiple light sources.

[0099] In the foregoing description, specific details, such as the particular geometry of the processing system and the description of the various components and processes used therein, have been set forth. However, it should be understood that the techniques described herein may be practiced in other embodiments departing from these specific details, and such details are for illustrative purposes and not for limitation. Embodiments disclosed herein have been described with reference to the accompanying drawings. Similarly, specific figures, materials, and configurations have been set forth for illustrative purposes to provide a thorough understanding. However, embodiments may be practiced without such specific details. Components having substantially the same functional construction are indicated by similar reference numerals, and therefore any redundant description may be omitted.

[0100] Various techniques have been described as multiple discrete operations to aid in understanding the various embodiments. The order of description should not be construed as implying that these operations are necessarily order-dependent. In fact, these operations do not need to be performed in the order presented. The described operations may be performed in a different order than in the described embodiments. In additional embodiments, various additional operations may be performed and / or the described operations may be omitted.

[0101] As used herein, "substrate" or "target substrate" generally refers to the object being processed according to the present invention. A substrate may include any material portion or structure of a device (especially a semiconductor or other electronic device) and may be, for example, a base substrate structure (such as a semiconductor wafer, photomask), or a layer on or overlying a base substrate structure (such as a thin film). Therefore, a substrate is not limited to any particular base structure, lower layer, or upper layer, whether patterned or unpatterned, but is contemplated to include any such layer or base structure, and any combination of layers and / or base structures. This description may refer to specific types of substrates, but this is for illustrative purposes only.

[0102] Those skilled in the art will also understand that many changes can be made to the technical operations described above, while still achieving the same objectives of the invention. The scope of this disclosure is intended to cover these changes. Therefore, the foregoing description of embodiments of the invention is not intended to be limiting. Rather, any limitations on embodiments of the invention are set forth in the appended claims.

Claims

1. A system for dispensing a liquid on a substrate, the system comprising: A substrate holder configured to hold a substrate and allow the substrate to rotate about an axis; A dispensing unit configured to dispense liquid onto the working surface of the substrate while the substrate is rotating on the substrate holder; A laser that is fixed relative to the substrate holder and configured to constantly guide a laser beam to a position corresponding to the edge of the working surface of the substrate when held by the substrate holder. A first detector is positioned to capture scattered light from a laser beam directed to the edge of the working surface of the substrate; A processor configured to monitor scattered light from a laser beam directed to the edge of a working surface of the substrate, in order to identify a pattern of scattered light indicating that the liquid has reached the edge of the substrate. The processor is further configured to: identify the actual coating time of the liquid, the actual coating time being from the start of the liquid being applied to the working surface until the liquid reaches the edge of the working surface; compare the actual coating time of the liquid with the expected coating time of the liquid; and indicate an error or adjust system operation in response to the difference between the expected coating time and the actual coating time being greater than a predetermined threshold.

2. The system as claimed in claim 1, wherein, The processor is configured to monitor the scattered light from a laser beam directed to the edge of the working surface of the substrate in order to identify a pattern of scattered light that indicates a covering defect in the film formed by the liquid.

3. The system of claim 1, further comprising: A second detector is positioned to capture reflected light from a laser beam directed to the edge of the working surface of the substrate; and The processor is configured to monitor reflected light from a laser beam directed to the edge of the working surface of the substrate in order to identify a pattern of reflected light that indicates that the liquid has reached the edge of the substrate.

4. The system according to claim 1, wherein, The laser is configured to direct the laser beam directly to the edge of the working surface of the substrate.

5. A system for dispensing a liquid on a substrate, the system comprising: A substrate holder configured to hold a substrate and allow the substrate to rotate about an axis; A dispensing unit configured to dispense liquid onto the working surface of the substrate while the substrate is rotating on the substrate holder; A laser that is fixed relative to the substrate holder and configured to constantly guide a laser beam to a position corresponding to the edge of the working surface of the substrate when held by the substrate holder. A first detector is positioned to capture reflected light from a laser beam directed to the edge of the working surface of the substrate; A processor configured to monitor reflected light from a laser beam directed to the edge of a working surface of the substrate, in order to identify a pattern of reflected light indicating that the liquid has reached the edge of the substrate. The processor is further configured to: identify the actual coating time of the liquid, the actual coating time being from the start of the liquid being applied to the working surface until the liquid reaches the edge of the working surface; compare the actual coating time of the liquid with the expected coating time of the liquid; and indicate an error or adjust system operation in response to the difference between the expected coating time and the actual coating time being greater than a predetermined threshold.

6. The system of claim 5, wherein, The processor is configured to monitor reflected light from a laser beam directed to the edge of the working surface of the substrate to identify patterns in the reflected light that indicate coverage defects in the film formed by the liquid.

7. The system of claim 5, further comprising: A second detector is positioned to capture scattered light from a laser beam guided to the edge of the working surface of the substrate; and The processor is configured to monitor the scattered light from a laser beam directed to the edge of the working surface of the substrate in order to identify a pattern of scattered light that indicates that the liquid has reached the edge of the substrate.

8. The system according to claim 5, wherein, The laser is configured to direct the laser beam directly to the edge of the working surface of the substrate.

9. A system for dispensing a liquid on a substrate, the system comprising: A substrate holder configured to hold a substrate and allow the substrate to rotate about an axis; A dispensing unit configured to dispense liquid onto the working surface of the substrate while the substrate is rotating on the substrate holder; A laser configured to direct a laser beam to an edge position on the working surface of the substrate; A first detector is positioned to capture scattered light from a laser beam directed to an edge location of the substrate; A second detector is positioned to capture reflected light from a laser beam directed to an edge location on the substrate; A processor configured to monitor scattered and reflected light from a laser beam directed to an edge location on the substrate, to identify patterns in the scattered and reflected light, respectively, that indicate the liquid has reached the edge location on the substrate. The processor is further configured to: identify the actual coating time of the liquid, the actual coating time being from the start of the liquid being applied to the working surface until the liquid reaches the edge of the working surface; compare the actual coating time of the liquid with the expected coating time of the liquid; and indicate an error or adjust system operation in response to the difference between the expected coating time and the actual coating time being greater than a predetermined threshold.

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