Systems and methods for liquid distribution and coverage control - Patents.com

Abstract

Light can be used to monitor the coating of a liquid onto a substrate. By directing light at a spot on the substrate, as the liquid passes through the spot, some of the light is reflected and some of the light is scattered. Monitoring this behavior can indicate whether the substrate has been successfully coated with the liquid, as well as the identification of defects. Additionally, the coating time can be monitored to make process adjustments.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Patent Application No. 63 / 019,017, filed May 1, 2020, and U.S. Patent Application No. 17 / 196,189, filed March 9, 2021, each of which is incorporated by reference in its entirety herein. [Background technology]

[0002] FIELD OF THE DISCLOSURE This disclosure relates to semiconductor manufacturing, and in particular to the distribution of materials onto a substrate.

[0003] Semiconductor manufacturing includes several processing steps that involve depositing liquids or fluids onto a substrate. These processing steps include, among others, coating the wafer, developing latent patterns, etching materials on the wafer, and cleaning / rinsing the wafer.

[0004] In a typical microfabrication process, a thin layer of a photosensitive material, such as photoresist (i.e., resist), is coated on the working surface (top surface) of a substrate. The photosensitive material is then patterned by photolithography to define a mask pattern, which is then transferred to an underlying layer by etching using the patterned resist as an etch mask. Patterning of the photosensitive material generally involves the steps of coating, exposing, and developing. The working surface of the substrate is coated with a thin film of the photosensitive material. The thin film of the photosensitive material is exposed to a radiation source through a reticle (and associated optics), for example, using a microlithography system. The patterned exposure is followed by a development process during which soluble regions of the photosensitive material are removed using a developing solvent. Depending on the tone of the photoresist and the developing solution used, the soluble regions can be irradiated or non-irradiated regions.

[0005] During the coating process, the substrate is placed on a substrate holder and rotated at high speed while the resist solution is dispensed onto the top surface of the substrate. The high speed rotation speed can be several thousand revolutions per minute (rpm). For example, when the resist solution is dispensed at the center of the substrate, it spreads radially across the substrate due to the centrifugal force exerted by the substrate rotation. Wet etching and cleaning processes are performed similarly. In the developing process, a solvent developer is deposited on the substrate spinning at high speed. The solvent developer dissolves the soluble portion of the photoresist, and then the developer and dissolved photoresist are removed radially across the substrate by centrifugal force. Wet etching, cleaning and rinsing processes are performed in a similar manner, where a liquid is deposited on the rotating wafer and centrifuged. It operates similarly to a development process in that it is removed by a force to remove or clean off certain materials or residues. Summary of the Invention [Means for solving the problem]

[0006] The present disclosure provides a method of dispensing a liquid onto a substrate, the method including: rotating a substrate on a substrate holder about an axis; dispensing a liquid onto a work surface of the substrate while the substrate is rotated on the substrate holder, where the rotation of the substrate causes the work surface of the substrate to be coated with the liquid proceeding from a center of the substrate to an edge of the substrate; directing a laser beam at an edge location on the work surface of the substrate; monitoring light from the edge location of the substrate to identify a monitored light pattern indicative of the liquid reaching the edge location on the substrate; identifying an actual coating time of the liquid from initiating dispensing of the liquid onto the work surface to when the liquid reaches the edge location of the work surface; and comparing the actual coating time of the liquid to an expected coating time of the liquid.

[0007] In one embodiment, monitoring the light from the edge includes monitoring scattered light from a laser beam.

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

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

[0010] In one embodiment, the method further includes adjusting a given dispensing operation based on comparing an actual coating time of the liquid to an expected coating time of the liquid.

[0011] In one embodiment, the method further includes adjusting a given dispensing operation in response to identifying a difference between the actual coating time and the expected coating time that is greater than a predetermined threshold.

[0012] In one embodiment, adjusting a given dispense operation can include dispensing more liquid.

[0013] In one embodiment, adjusting a given dispense operation can include increasing the rotational speed of the substrate.

[0014] In one embodiment, the method further includes indicating an error in response to identifying a difference between the actual coating time and the expected coating time that is greater than a predetermined threshold.

[0015] In one embodiment, the method further includes monitoring a plurality of dispenses of the plurality of spin-on films and comparing the actual coating time to the expected coating time for each of the deposited films.

[0016] In one embodiment, the method further includes monitoring light from an edge location of the substrate to identify a pattern of the monitored light that is indicative of a defect in the film formed from the liquid.

[0017] In one embodiment, monitoring the light from the edge includes monitoring light from a plurality of light sources.

[0018] The present disclosure also provides a system for dispensing liquid onto a substrate, the system comprising: a substrate holder configured to hold and rotate the substrate about an axis; a dispensing unit configured to dispense liquid onto a working surface of the substrate while the substrate is rotated 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 positioned to capture scattered light from the laser beam directed to the edge position of the substrate; and a processor configured to monitor the scattered light from the laser beam directed to the edge position on the substrate to identify a pattern of scattered light indicative of liquid reaching the edge position on the substrate, the processor being further configured to identify an actual coating time of the liquid from the start of a given dispensing of the liquid onto the working surface to the liquid reaching the edge position of the working surface, and to compare the actual coating time of the liquid with an expected coating time of the liquid.

[0019] In one embodiment, the processor is configured to monitor scattered light from a laser beam directed at an edge location on the substrate to identify a pattern of scattered light that is indicative of a film formed from the liquid having coverage defects.

[0020] In one embodiment, the system further comprises a second detector positioned to capture reflected light from the laser beam directed to the edge position of the substrate, and the processor is configured to monitor the reflected light from the laser beam directed to the edge position on the substrate to identify a pattern of reflected light indicative of liquid reaching the edge position on the substrate.

[0021] The present disclosure also provides a system for dispensing liquid onto a substrate, the system comprising: a substrate holder configured to hold a substrate and rotate the substrate about an axis; a dispensing unit configured to dispense liquid onto a working surface of the substrate while the substrate is rotated 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 positioned to capture reflected light from the laser beam directed to the edge position of the substrate; and a processor configured to monitor the reflected light from the laser beam directed to the edge position on the substrate to identify a pattern of reflected light indicative of liquid reaching the edge position on the substrate, the processor being further configured to identify an actual coating time of the liquid from the start of a given dispensing of the liquid onto the working surface to the liquid reaching the edge position of the working surface, and to compare the actual coating time of the liquid with an expected coating time of the liquid.

[0022] In one embodiment, the processor is configured to monitor reflected light from a laser beam directed at an edge location on the substrate to identify a pattern of reflected light that indicates that a film formed from the liquid has coverage defects.

[0023] In one embodiment, the system further comprises a second detector positioned to capture scattered light from the laser beam directed to the edge position of the substrate, and the processor is configured to monitor the scattered light from the laser beam directed to the edge position on the substrate and identify a pattern of scattered light indicative of liquid reaching the edge position on the substrate.

[0024] It should be noted that this Summary section does not specify all embodiments and / or inherently novel aspects of the invention described in this disclosure or claims. Instead, this Summary provides only a preliminary discussion of different embodiments and corresponding points of novelty over the prior art. For further details and / or possible aspects of the invention and embodiments, the reader is directed to the Detailed Description section and corresponding figures of the present disclosure, which are discussed further below.

[0025] A more detailed understanding of various embodiments of the present invention and many of the attendant advantages thereof will become readily apparent by reference to the following detailed description taken in conjunction with the accompanying drawings, in which: The drawings are not necessarily to scale, emphasis instead being placed upon illustrating features, principles, and concepts. [Brief description of the drawings]

[0026] [Figure 1] 1 is a schematic cross-sectional view of an exemplary distribution system according to embodiments disclosed herein. [Diagram 2] 1A-1D are top views of an exemplary substrate segment illustrating the flow of an exemplary coating process according to embodiments disclosed herein. [Diagram 3] 1A-1D are top views of an exemplary substrate segment illustrating the flow of an exemplary coating process according to embodiments disclosed herein. [Figure 4] 1A-1D are top views of an exemplary substrate segment illustrating the flow of an exemplary coating process according to embodiments disclosed herein. [Diagram 5] 1A-1D are top views of an exemplary substrate segment illustrating the flow of an exemplary coating process according to embodiments disclosed herein. [Figure 6] 1A-1D are top views of an exemplary substrate segment illustrating a flow of an exemplary removal process according to embodiments disclosed herein. [Figure 7] 1A-1D are top views of an exemplary substrate segment illustrating a flow of an exemplary removal process according to embodiments disclosed herein. [Figure 8] 1A-1D are top views of an exemplary substrate segment illustrating a flow of an exemplary removal process according to embodiments disclosed herein. [Figure 9] 1A-1D are top views of an exemplary substrate segment illustrating a flow of an exemplary removal process according to embodiments disclosed herein. [Figure 10]The behavior of reflected and scattered light over time for light directed at the edge of a flat substrate is shown as the liquid is spread across the substrate, particularly 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 well covered the edge of the substrate. [Figure 11] The behavior of reflected and scattered light over time for light directed at the edge of a flat substrate is shown as liquid is spread across the substrate, particularly 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 defects remain. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] The technology herein includes systems and methods for dispensing liquids onto a substrate with real-time coverage and removal control. The technology herein is applicable to various manufacturing operations including coating a substrate (e.g., a semiconductor wafer), developing a film, wet etching a material, and cleaning and rinsing a substrate. Various embodiments use a laser beam light directed at one or more predetermined locations on a substrate to monitor the behavior of scattered and / or reflected light from those one or more predetermined locations. Monitoring this scattered / reflected light behavior can indicate the location of a given liquid on the work surface of the substrate when it interacts with the laser beam, which can then flag the substrate as defective or generate feedback data for modifying the corresponding dispensing operation in real time, such as by increasing / decreasing the dispensed volume of fluid or increasing / decreasing the rotational speed of the substrate. Monitoring can be manual or automatic.

[0028] Although there are a variety of manufacturing operations that involve liquid materials being dispensed onto a rotating substrate, the description of the exemplary embodiments will focus primarily on coating the substrate for convenience in describing the technology herein. Conventional, conventional microfabrication techniques involve photolithography, in which a film (photoresist) is coated onto a substrate, exposed to a pattern of actinic radiation, and then developed to remove the soluble material.

[0029] Conventionally, more photoresist (i.e., resist) is dispensed than is necessary to completely cover the substrate. An excess or overcoat of resist is dispensed to ensure that the entire substrate is evenly coated. The substrate (typically a semiconductor wafer) is spun at a relatively high speed (the spinning speed) while the liquid resist is dispensed onto the wafer's work surface. The spinning wafer then uses centrifugal force to push the resist to the edge of the substrate (typically a circular wafer). A given resist, developer, or other fluid has a line of travel that does not always have a uniform edge. That is, the photoresist does not have an outer edge or outer meniscus that extends uniformly in the radial direction like a uniformly expanding perfect circle. Instead, the outer edge of the photoresist is not uniform, and some areas of the photoresist may reach the edge of the substrate before other areas. The result is visible as a jagged edge of the photoresist at the edge of the substrate. This incomplete coverage is not visible while the substrate is rotating. Instead, due to the blurring of the liquid as it is spun, the spinning substrate appears to be completely coated.

[0030] One approach for coverage control is to visually monitor the progress of the coating liquid across the substrate, for example with a stroboscope or camera. Visual monitoring can be effective for some liquids and film thicknesses, but less effective in others. For example, some photoresists and films have a coverage thickness on the order of tens of nanometers. Films of this thickness are relatively thin, and as a result, the film can be essentially transparent. Correspondingly, it becomes difficult to visually determine when the wafer is completely coated with a given film. Monitoring with scattered / reflected light can solve such problems.

[0031] For many applications, a uniform and complete coating of photoresist on the work surface of the substrate is necessary. To meet this requirement, excess resist is dispensed so that the spinning substrate can be completely coated. The excess resist falls off the edge of the wafer and becomes wasted resist. Traditionally, manufacturers may deposit as much as 400% or more of excess photoresist and other liquid chemicals as a safety factor that accounts for several different variables that may affect complete coverage. One factor is the dispensing capacity of the dispensing system itself. For example, some photoresist compositions can coat a substrate with about 0.2 cc of resist. Due to dispensing variability, it is common to dispense about 0.8 cc of resist.

[0032] There are various factors or variables that contribute to excessive fluid being dispensed. Some factors are related to the capabilities of the dispense system itself. This includes variability in valve response, conduits, measurement means, etc. Another factor is the performance of a given photoresist or liquid chemistry. Even if the chemical formula is the same, slight variations in the photoresist composition can cause a given amount of liquid dispensed to be more or less viscous at any given dispense. Viscosity variations must be addressed, which usually causes an increase in the amount of safety stock by dispensing more chemical. Another factor that affects coverage is the physical characteristics of the substrate surface itself. During the manufacture of semiconductor devices on a wafer, there are different materials used at different stages of manufacture. Moreover, the surface topography can differ depending on the manufacturing stage and the type of device being manufactured (e.g., memory vs. logic). A given material and / or topography can increase the viscosity of the photoresist spreading across this surface. The wetting of the substrate is an important factor, as there can be significant variations in the interaction of the liquid with the substrate. This interaction usually causes bias in the flow of the liquid across the substrate. When these safety factors are mixed, manufacturers may end up using substantially more chemical than is actually needed for complete coverage. Some manufacturers may work with four or more times the extra volume compared to the volume actually needed.

[0033] Note that because a given photoresist coating a substrate reaches the edge of the substrate at different rates, there is typically a safety stock of the amount needed for complete coverage. This minimum extra photoresist is usually about 2-20% extra. Thus, a given substrate can be fully coated with 102-120% of the resist that would actually need to be deposited for complete coverage, according to calculations. However, due to various performance factors, manufacturers routinely deposit 300%-500% more photoresist (or developer) than is actually needed. The extra is simply a safety stock. It is not the amount needed to coat / rinse the substrate, but is included only to ensure that the substrate is never partially coated.

[0034] The technology herein includes spin-on dispense process sensors and defect monitors for coverage control for depositing spin-on films on substrates such as semiconductor wafers. Each substrate can be characterized by the behavior of scattered and / or reflected light from a laser beam directed at a predetermined location on the substrate as it interacts with the liquid. For example, a laser can be directed to the edge of the substrate to detect when the liquid has completely covered the substrate. Liquid dispensed near the center of the rotating substrate will gradually begin to cover the substrate as it flows outward toward the laser / substrate edge. When the edge of the liquid and the laser beam interact, a momentary change in the behavior of the scattered and reflected light will occur, which can be detected by one or more optical detectors for detecting the scattered and / or reflected light and can indicate the progress of the liquid / substrate coverage. Additional lasers or other types of light sources can be targeted to other areas of the substrate to obtain further progress / coverage information. The system can flag a substrate as defective if it does not have adequate liquid coverage, or the system can use a feedback control loop (e.g., advanced process control (APC)) to ensure that the exact amount of volume is deposited, which greatly reduces the volume of safety stock dispensed. Thus, instead of having a safety stock that is 300%, or 400%, or 500% more than required, the systems and methods herein can over-deposit photoresist, developer, or other liquid by less than 50%, less than 20%, or even less than 2%. This can eliminate waste, reduce the need for chamber cleaning, and reduce tool downtime. Each substrate being processed by deposition of liquid can be monitored in real time with one or more optical detectors to detect reflected and / or scattered light, and points along the edge of the liquid across the substrate can be mapped versus time each time the edge interacts with the laser beam. This edge can be the outer edge of the liquid coating the substrate or the inner edge of the liquid being removed from the substrate.

[0035] Based on an analysis of the progress or behavior of the liquid, some actions or modifications to the dispensing system can be made. For example, in some dispenses, it may be observed that the photoresist progresses relatively quickly and moves past the edge of the substrate resulting in premature coating. By the system tracking the progress of the coating and identifying when the coating is complete (or will be complete by identifying the rate of progress), the system can indicate (provide feedback) when or when complete coating has been or will be achieved and stop dispensing liquid. If the system observes or determines that the edge of the resist is decelerating and moving slowly, action 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.

[0036] Traditionally, analysis of coating performance is performed after the coating process. Essentially, the substrate is stopped from spinning or removed from the process chamber to check the coating coverage. To the naked eye, the coating progress may appear uniform because the high speed of rotation obscures non-uniformities. However, the technology herein looks at data on scattered or reflected light and optionally applies that data as real-time feedback to provide a real-time status of the future coating of the substrate and its coating capabilities, for example by identifying dispense or rotation stop points. A processor can be connected to the scattered or reflected light detector and can analyze the scattered / detected light to check whether a given dispense is acceptable and whether coating is required, collect process statistics (e.g., yield statistics), or adjust the spin speed and dispense rate / amount. Such control can adapt to variable process conditions in real-time. Thus, instead of estimating the substrate wettability and photoresist viscosity to calculate safe dispense amounts and spin times, photoresist can be deposited on a rotating substrate without initially knowing the stop point. As the photoresist spreads across the substrate, a processor receiving scattered and / or reflected light data on this progression can identify the rate of progression as a function of time as if the substrate background were stationary, and can therefore accurately indicate a stopping point. Accordingly, the system can stop a given coating operation when the substrate is completely coated, without needing to know the substrate wetting properties and photoresist viscosity. In other words, instead of estimating stopping times and estimating the volume of liquid dispensed, the exact dispensed volume and stopping time can be calculated in real time based on observation of scattered / reflected light indicative of the progression of the liquid.

[0037] In some embodiments, a first substrate may have fluid dispensed thereon, and then the scattered / reflected light data is used to identify the spin and dispense times required for complete coating. This dispense time and volume data can then be used for subsequent dispenses.

[0038] In some embodiments, statistics of deposition yield as a function of process conditions (including dispense volume, spin speed profile, etc.) can be collected. A dispense process can be defined based on the statistics and the desired process yield. During production, deposition yield statistics can be collected and process drift can be continuously monitored. In production (including high volume manufacturing (HVM)), deposition yield can be continuously monitored and process adjusted to ensure that the coating process is within specifications, thereby continuously correcting process or environmental drift. If a defect is detected in HVM, the substrate can be immediately sent for repair. Process matching through coverage yield allows the system to account for variations and offset the effects of tool variations (process bowl, dispense system, etc.), environmental effects (fab temperature, humidity), chemical variations, drift (bottle-to-bottle effects or interpolated life effects), etc.

[0039] The techniques herein measure scattered and / or reflected light from the substrate to detect the passage of the spreading liquid front. The techniques can also detect radial striation type defects. Thus, the sensor can determine whether a particular deposition was successful or unsuccessful.

[0040] The technology herein will now be described with reference to the accompanying drawings. Referring to FIG. 1, system 100 is a system for dispensing liquid 117 onto substrate 105. Substrate holder 122 is configured to hold and rotate substrate 105 around an axis. Motor 123 can be used to rotate substrate holder 122 at a selectable rotational speed. While substrate 105 is rotated by substrate holder 122, dispensing unit 118 is configured to dispense liquid onto the working surface of substrate 105. Dispensing unit 118 can be located directly above substrate holder or can be located elsewhere. If located away from substrate holder, conduit 112 can be used to deliver fluid to substrate. Fluid can exit through nozzle 111. FIG. 1 shows liquid 117 being dispensed onto the working surface of substrate 105. A collection system 127 can then be used to capture or collect excess liquid 117 that is shaken off substrate 105 during a given dispensing operation.

[0041] The dispense components can include a nozzle arm 113 and a support member 115 that can be used to move the position of the nozzle 111 over the substrate 105 or to a resting position away from the substrate holder 122, such as for resting upon completion of a dispense operation. Alternatively, the dispense unit 118 can be embodied as a nozzle itself. Such a nozzle can have one or more valves in communication with the system controller 160. The dispense unit 118 can have various embodiments configured to control the dispense of selectable volumes of fluid onto a substrate.

[0042] The dispensing unit 118 can be embodied using a variety of technologies. A variety of valves, flow controllers, filters, nozzles, etc. can be used. The various dispensing technologies selected for use can provide different levels of volume control and delay. The techniques herein can benefit from precise volume control by using a bladder-based dispensing unit such as that described in U.S. Patent Application Publication No. 2018 / 0046082 (U.S. Patent Application No. 15 / 675,376), entitled "High-Purity Dispense Unit." However, such a precise dispensing system is not necessary. Accordingly, the techniques herein can be implemented using conventional dispensing systems.

[0043] The dispensing unit may be configured to dispense a selective amount of photoresist, negative developer, or other liquid onto the substrate based on input from a system controller. The dispensing unit may include a dispensing nozzle positioned above a working surface of the substrate.

[0044] The system 100 includes at least one laser 130 configured to send a laser beam 131 to a predetermined location (i.e., a target) on the substrate 105. The laser 130 can be a laser diode or a light emitting diode with beam forming optics. The predetermined location can be where knowledge of the coverage progression or defect detection of the liquid 117 is desired. Various predetermined locations can be used herein. For example, the laser 130 can be configured to direct the laser beam 131 to the edge of the substrate 105 (or within a few millimeters of the edge) to know if the entire substrate 105 has been covered by the liquid 117. In another embodiment, two or more laser devices 130 can be used. For example, a second laser beam can be directed between the edge and the center of the substrate 105 to monitor the intermediate progression of the liquid 117. In another embodiment, a different light source can be used instead of or in addition to the laser beam 131. Any laser (e.g., green or red) can be used as long as it does not activate the given photoresist being dispensed.

[0045] A reflected light detector 132 is positioned to capture reflected light from the laser beam 131. When the laser beam 131 hits and reflects from a location on the substrate 105, if the location is smooth, a large portion of the laser beam 131 will be reflected toward and detected by the reflected light detector 132 (rather than the scattered light detector 133). A smooth location may indicate that the location is not yet covered by the liquid 117, or that the location is well covered by the liquid 117. It is noted that more than one reflected light detector may be used. For example, if a first laser beam is directed toward the edge of the substrate, a first reflected light detector may be used to detect reflected light from the edge of the substrate. If a second laser beam is directed toward the interior of the substrate, a second reflected light detector may be used to detect reflected light from the interior of the substrate.

[0046] A scattered light detector 133 is positioned to capture scattered light from the laser beam 131. When an edge of the liquid 117 interacts with the laser beam 131, more light will be scattered and less light will be reflected. This edge of the liquid 117 can spread liquid or a sliver (mouse bite) radially onto the substrate 105 that is not yet covered with the liquid 117. Detection of 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. It is noted that more than one scattered light detector can be used. For example, if a first laser beam is directed at the edge of the substrate, a first scattered light detector can be used to detect scattered light from the edge of the substrate. If a second laser beam is directed towards the interior of the substrate, a second scattered light detector can be used to detect scattered light from the interior of the substrate.

[0047] It should be noted 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 can have both scattered light detector 133 and reflected light detector 132, although this is not necessary.

[0048] The reflected light detector 132 and the scattered light detector 133 can use conventional techniques for detecting light. For example, the reflected light detector 132 and the scattered light detector 133 can include photodetectors for detecting light. Additionally, additional components can be disposed in the system 100 to direct the laser beam 131, the scattered light and / or the reflected light to corresponding target locations. Examples of such components can include mirrors, elliptical collectors, quarter wave plates, polarizing beam splitters, focusing lenses, collimator / cylindrical lenses, etc. In one embodiment, a polarizing beam splitter is used to direct the reflected light to the reflected light detector, while a primary mirror directs the scattered light to a secondary mirror, which directs the scattered light to the scattered light detector.

[0049] The detected scattered and / or reflected light information can be sent to or collected by the processor 150. The processor 150 is configured to consider 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 flag the substrate if it has a defect (e.g., a sliver). 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 on the work surface of the substrate 105 until the liquid reaches a predetermined location (e.g., edge, interior) of the work surface. 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 the liquid 117 on the substrate. By analyzing the scattered and / or reflected light, the processor 150 can determine how complete the propagation of the edge of the fluid is or determine the dewetting conditions among others. This edge progress data can then be provided to a system controller 160. The system controller 160 is connected to the substrate holder 122 and to the dispense unit 118. The system controller 160 can be configured to adjust the volume of liquid dispensed onto the working surface of the substrate based on the feedback data while the substrate is rotating with the liquid 117 on the substrate. For example, a dedicated control loop or an APC control loop or a feedback control loop connected to the system controller 160 can be configured to control a corresponding dispense system and / or substrate spin mechanism.

[0050] One or more scattered light detectors and / or reflected light detectors are located relative to the detected scattered and reflected light, respectively. A processor 150 is connected to or accessible by the system 100 and configured to analyze the scattered and / or reflected light received from their corresponding detectors. The processor 150 may be configured to generate feedback data while the substrate 105 is rotating with the liquid 117 thereon. Feedback data may also be generated and provided after the dispensing operation. The processor 150 may also be configured to monitor the progress of the coating of photoresist across the work surface of the substrate 105 based on an inspection of the scattered and / or reflected light, and generate feedback data indicative of when sufficient photoresist has been dispensed for complete coverage of the work surface of the substrate 105. This indication may be predictable based on the rate of progress.

[0051] The processor 150 can be configured to identify patterns of scattered and / or reflected light that indicate that the liquid 117 has reached the target location on the substrate 105 or that a film formed from the liquid 117 has coverage defects. Steady state behavior of the scattered and reflected light may indicate that the liquid 117 has not yet reached the target location (i.e., the location of the laser beam 131) or that the target location is well covered. Spikes / unsteady state behavior of the scattered or reflected light may indicate that the edge of the liquid 117 has just reached the target location or that a coverage defect exists. Examples of such behavior are provided later in this disclosure.

[0052] A system controller 160 is connected to the substrate holder 122 and to the dispensing unit 118. The system controller 160 is configured to adjust the volume of liquid 117 dispensed onto the working surface of the substrate 105 based on the feedback data while the substrate 105 rotates with the liquid 117 thereon. The system controller 160 can be further configured to adjust the rotational speed of the substrate holder 122 based on the feedback data.

[0053] The system controller 160 can be configured to dispense an initial volume of liquid 117 onto the working surface of the substrate 105, and then dispense an additional volume of liquid 117 onto the working surface of the substrate, the additional volume of liquid 117 being sufficient to complete full coverage of the liquid 117 on the working surface of the substrate 105. In other words, if it is determined that more fluid is needed to completely cover the wafer, more fluid can be dispensed.

[0054] The system controller 160 can be configured to increase the rotational speed of the substrate holder 122 based on feedback data indicating insufficient coverage of the liquid 117 on the working surface of the substrate 105. Such an increase in the rotational speed can help spread the film across the substrate 105. Alternatively, the system controller 160 can decrease the rotational speed of the substrate holder 122 based on feedback data indicating, for example, a turbulent state of the liquid 117 on the working surface of the substrate 105 or excessive resist splashing off the substrate 105. The system controller 160 can increase the volume of the liquid 117 dispensed on the working surface of the substrate 105 based on feedback data indicating insufficient coverage of the liquid 117 on the working surface of the substrate 105.

[0055] The processor 150 can have many functions. The processor 150 can be configured to generate feedback data while the substrate 105 is rotating with the liquid 117 thereon, and a given dispensing operation can be adjusted while the substrate 105 is rotating with the liquid 117 thereon. Based on an inspection of scattered / reflected light indicative of the position / movement of the liquid 117, the processor 150 can monitor the progress of an outer meniscus of the liquid 117 as it coats the work surface of the substrate 105. The processor 150 can also monitor the progress of an inner meniscus of the liquid 117 as it is shaken off the work surface of the substrate 105. The progress of the coating of the liquid 117 can be monitored to generate feedback data indicating that a greater or lesser volume of the liquid 117 should be dispensed, resulting in a minimum volume being dispensed that results in the work surface of the substrate 105 being completely coated, and / or to identify when the work surface of the substrate 105 is completely covered.

[0056] The system controller 160 may be configured to perform a variety of actions. For example, the system controller 160 may adjust the volume of liquid 117 dispensed onto the working surface of the substrate 105 based on feedback data while the substrate 105 is rotating. The rotational speed of the substrate holder 122 may be adjusted based on feedback data. Based on collected data indicating the movement of the liquid 117, the volume of liquid 117 dispensed may be less than 150% of the coverage volume required to completely cover the working surface of the substrate 105. Based on feedback data indicating a turbulent state of the liquid 117 on the working surface of the substrate 105, the system controller 160 may reduce the rotational speed of the substrate holder 122, thereby preventing damage to the substrate 105. The system controller 160 may also stop dispensing fluid in response to receiving feedback data indicating that the working surface of the substrate 105 is completely covered.

[0057] The progress of coating the initial volume of liquid 117 on the work surface of the substrate 105 is monitored by the processor 150 and feedback data can be generated that indicates insufficient coverage of the work surface of the substrate 105. Based on an inspection of the scattered and / or reflected light that indicates adequate coverage, the processor 150 can calculate the total volume of liquid 117 to be dispensed onto the substrate 105 to cover the substrate 105 with an excess volume below 50%. The processor 150 can also monitor and generate feedback data that indicates a dewetting condition and when sufficient photoresist has been dispensed for complete coverage of the substrate 105. In response to receiving feedback data that indicates when sufficient photoresist has been dispensed for complete coverage of the substrate 105, the system controller 160 can stop the dispense operation. The scattering and / or reflection behavior can also be analyzed to monitor the progress of an outer meniscus of the liquid 117 as it coats the substrate or the progress of an inner meniscus of the liquid 117 as it is shaken off the substrate.

[0058] One embodiment includes a system for dispensing liquid onto a substrate. The system includes a substrate holder configured to hold the substrate and rotate the substrate about an axis. A dispensing unit is configured to dispense liquid onto a working surface of the substrate while the substrate is rotated 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 at an edge of the substrate.

[0059] The edge of the liquid 117 can be tracked with high accuracy. This can be useful for identifying areas of poor coverage (sometimes referred to as "mouse bite" occurrences) or other uneven edge progression to ensure that the substrate 105 is completely covered. For example, with respect to the deposition of photoresist to cover the substrate 105, uncovered formation can occur at the edge of the photoresist progression. This uncovered area and its formation can be tracked as a function of time prior to formation. Such tracking can be useful to ensure complete coating and minimize excess liquid 117 material. This progression can be tracked as a function of time during the spinning of the photoresist by tracking the leading edge of the photoresist propagation as it moves past the edge of the substrate 105. The processor 150 can then calculate the position of that function of time and then determine where the edge of the photoresist is and how close a given edge is to actually having a mouse bite occur. Identifying uncoated portions can then automatically trigger responses such as marking the substrate 105 as defective, incrementally depositing more photoresist, or accelerating the rotation speed to achieve complete coverage. Such 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 has completely covered (or will completely cover) the substrate 105, and this coverage rate can then be used to indicate when to stop dispensing photoresist onto the substrate.

[0060] Due to uneven distribution of liquid chemistry, some excess of liquid 117 is necessary to completely cover a given substrate. 105 However, with precise control, this excess can be as low as 2-50% of the excess material dispensed.

[0061] FIG. 2 shows a top view of a substrate segment showing the working surface of the substrate 105. The substrate 105 is rotating at a relatively high speed, for example, 2-3 thousand revolutions per minute. It is common for semiconductor wafers to have a notch 126 or straight edge at one location on the substrate. This notch 126 may be V-shaped, while it may be a short flat edge of a circular wafer. When the notch 126 interacts with the laser beam 131, it may cause a change in the behavior of the scattered and reflected light. Knowing this, the laser beam 131 may be directed away from the notch 126, or the processor 150 may anticipate and filter out the scattered / reflected light caused by the notch 126.

[0062] In Figure 2, liquid 117 is shown on the working surface of substrate 105. This could be, for example, photoresist deposited at or near the center point of substrate 105. As substrate 105 rotates at high speed, liquid 117 spreads out in a radial direction. Figure 3 shows the continued radial progression of liquid 117. Note that outer meniscus 129 has an uneven edge. In other words, liquid 117 does not spread evenly or perfectly evenly.

[0063] FIG. 4 shows the progression of the liquid 117 after some of the liquid 117 has reached the outer edge of the substrate. Note that there are some areas of slivers (mouse bites) that are still not covered with the liquid 117. If the coating operation were to stop at this point, there would be insufficient coverage (i.e., a defect). Each time the laser beam 131 hits a sliver, the behavior of the scattered and reflected light will be erratic. By monitoring this behavior, it can be shown that the coverage is not complete. This can trigger either to mark the substrate 105 as defective or to continue to rotate the substrate 105 if the liquid 117 is still spreading outward. Other actions can include increasing the rotation speed of the substrate 105 or expelling more liquid 117 on the substrate 105. Based on an evaluation of the scattered or reflected light data, the total surface area of ​​the uncovered areas can be accurately calculated or estimated, and therefore the additional volume to be dispensed can be accurately determined. The system controller 160 can then receive this feedback or instruction from the processor 150 and then control the dispensing unit 118 to dispense incrementally more volume sufficient to complete full coating coverage with the minimum amount of more volume dispensed. The result is shown in Figure 5. Accordingly, a given substrate 105 can be fully coated with the minimum amount of excess liquid 117 dispensed.

[0064] It should be noted that some coating processes do not coat on perfectly flat substrates, but on substrates with structures (trenches, holes, mesas, etc.). These patterned structures can modify the light reflection and scattering. Even if the substrate is properly coated, the scattered / reflected light can behave erratically. Thus, the structures can be accounted for by comparing the scattered / reflected light signal to a signal from a reference / target substrate that is considered defect-free. The behavior of the scattered and / or reflected light can be compared to the results from this reference substrate to determine when the substrate is acceptably coated with the film and whether any defects are present. Essentially, any deviation in the behavior of the scattered / reflected light from the target substrate can indicate the presence of a liquid edge. Alternatively or in addition, the detected light from an uncoated substrate can be used as a reference for the same substrate after it is coated with the liquid. If the substrate has a similar pattern of reflected and scattered light before and after it is coated with the liquid, it may indicate that the substrate is acceptably coated. In another embodiment, the patterned structures can be taken into account by the processor or software and filtered out.

[0065] As can be understood, the embodiments herein are not limited to coating photoresist on a wafer, but can be applied to many additional microfabrication techniques that use liquids deposited on a rotating substrate. For example, the scattered / reflected light analysis herein can benefit the distribution of developer liquid. After a layer of photoresist is exposed to patterned actinic radiation, the soluble parts need to be developed. In film development, the objective is not simply to coat the substrate, but to dissolve and completely remove the soluble material. In development, typically a larger volume of fluid is dispensed compared to photoresist. The substrate can be monitored by analyzing the scattered / reflected light. Irregular changes in the behavior of the detected light can indicate the completion of dissolution of the soluble material, flow dynamics, etc.

[0066] The techniques herein may benefit from development with a variety of developers, including negative tone developers. In practice, it is common that about 6-8 ccs of negative tone developer may be dispensed while about 30-50 ccs of other developers may be dispensed. Regardless of the developer used, dewetting may be an issue during development, especially at the edge of the wafer. Development is slower than photoresist deposition. During development, solutes may be picked up, resulting in a weakened photoresist solution. The solution may move faster along the scribe lanes than it moves in other areas. If the solution becomes saturated, photoresist may deposit on the substrate, again causing defects. Also, if the developer dries in one area before the dissolved photoresist is removed from the substrate, that photoresist may be redeposited on the substrate. Thus, the techniques herein may monitor the removal of developer from the substrate. Both the leading edge and the follow etch may be monitored. If gas is also used to clean the wafer, the air jet interaction (nitrogen puff) at the trailing edge may be monitored in real time.

[0067] These techniques and monitoring are equally applicable to wet etching. Scattered / reflected light monitoring of the substrate fluid can be used to ensure that the developer dispensing and contents have not changed due to changes in surfactant conditions. Pattern recognition of the detected scattered / reflected light can identify the etch rate and developer consumption. By using such light detection techniques to identify specific conditions (completion, turbulence), the dispensing system can take corresponding action such as stopping developer / etchant dispensing or slowing the rotation speed in response to the turbulent condition. Minimizing the amount of developer or etchant used can reduce overall waste, benefiting green processing initiatives. Certain developers can be expensive, and minimizing the volume dispensed can also provide economic benefits.

[0068] The embodiments herein apply equally to cleaning and rinsing. Various rinsing or cleaning operations can use piranha, SC1, SC2, deionized water, etc. Knowing the progress of the rinse or clean can provide benefits including yield and throughput. Some rinse fluids, such as deionized water, are relatively economical compared to resist and developer fluids, and therefore using substantially more than required may not incur significant environmental or material costs. However, yield and throughput can benefit from real-time feedback. Knowing the exact completion point allows the rinse and etch to be stopped sooner compared to conventional techniques, where safety stocks or spin times must be considered to ensure a given substrate is completely cleaned or etched. With respect to defect reduction, some structures being microfabricated may be relatively sensitive at certain stages. If the rinse fluid goes from laminar to turbulent, this turbulence can damage or destroy the structures being built. Thus, monitoring the turbulent flow state can improve yield. Knowing exactly when the rinse or clean is complete can increase throughput. If a given rinse or cleaning process were completed and then immediately stopped based on analysis of the scattered and / or reflected light feedback, the number of wafers processed per hour could be increased. In some rinse operations, the system could be embodied with an array of nozzles, for example, to spray liquid onto the substrate.

[0069] 6-9 illustrate exemplary developing, etching or rinsing operations. In FIG. 6, dispensing of liquid 117 has been stopped. As a rinse or developer, this fluid continues to move radially to the edge of the substrate 105. This may cause the inner meniscus 121 to move outward (FIG. 7). This inner meniscus 121 may be monitored, such as to look for undesirable flow conditions that may damage devices thereon. If such conditions are identified, the controller may reduce the rotation speed. In FIG. 8, it may be identified that nearly all of the liquid 117 has been shaken off. The processor may calculate or identify when the liquid 117 has in fact been all but removed from the substrate (FIG. 9) and responsively stop the corresponding dispensing operation. Other operations may be performed. For example, if the scattered / reflected light detection analysis indicates redeposition of material, more liquid may be dispensed to dissolve / remove such material.

[0070] Accordingly, real-time control can be provided for precise coating, developing, etching, rinsing and cleaning.

[0071] Examples of results will not be discussed. It should be noted that with respect to liquid coverage, the liquid front, which is the moving edge of the liquid, may cause a temporary change in the reflected / scattered light when interacting with the laser beam. FIG. 10 shows an example of a pattern showing successful liquid coating, where the laser beam 131 is directed at the edge of the substrate 105. The reflected light 1001 and scattered light 1002 are detected by their corresponding detectors and plotted against time. Initially, as shown during time 10a, the reflected light 1001 and scattered light 1002 show a clear steady state behavior, which may indicate that the moving edge of the liquid 117 has not yet reached / interacted with the laser beam 131. Then, as shown during time 10b, the reflected light 1001 and scattered light 1002 deviate from their previous behavior and instead show an irregular, unsteady behavior, which may indicate that the moving edge of the liquid 117 has reached and interacted with the laser beam 131. The amount of reflected light 1001 has temporarily decreased while the amount of scattered light 1002 has temporarily increased compared to their corresponding magnitudes during time 10a. Finally, when the liquid 117 properly covers the edge of the substrate 105, the behavior of the scattered light 1002 and reflected light 1001 will stabilize again, as shown at time 10c. The times at time 10a and time 10b are summed by the processor 150 to obtain the actual coating time, which can be compared to the predicted coating time. If the predicted and actual coating times have a difference greater than a predetermined threshold, an error can be indicated or system operation can be adjusted.

[0072] FIG. 11 shows an example of a monitored pattern where the substrate 105 is improperly coated leaving striations. Photodetectors are positioned to capture reflected light 1101 and scattered light 1102 from a laser beam 131 directed at the edge of the substrate 105. Initially, as shown during time 11a, the reflected light 1101 and scattered light 1102 exhibit steady state behavior, which may indicate that the moving edge of the liquid 117 has not yet reached / interacted with the laser beam 131. Then, as shown during time 11b, the reflected light 1101 and scattered light 1102 exhibit erratic, unsteady behavior, which may indicate that the moving edge of the liquid 117 has reached / interacted with the laser beam 131. Finally, if the liquid 117 has properly coated the edge of the substrate 105, the scattered light 1102 and reflected light 1101 behavior will stabilize at time 11c (as shown at time 10c in FIG. 10). Instead, during each rotation of the substrate 105, the striations interact with the laser beam 131, causing a downward spike in the reflected light 1101 and an upward spike in the scattered light 1102, indicating a failure in the coating of the substrate 105. This can be recognized by the processor 150 and trigger subsequent actions, such as marking the substrate 105 as defective or adjusting system operation.

[0073] Another embodiment herein is a method of dispensing a liquid onto a substrate. The substrate is rotated about an axis on a substrate holder. A liquid is dispensed onto a work surface of the substrate while the substrate is rotated on the substrate holder. The rotation of the substrate can cause the work surface of the substrate to be coated with the liquid proceeding from a center of the substrate to an edge of the substrate. A laser beam is directed at an edge location on the work surface of the substrate. Light from the edge location of the substrate is monitored to identify a monitored light pattern indicative of the liquid reaching the edge location on the substrate. An actual coating time of the liquid from beginning to dispense the liquid onto the work surface until the liquid reaches the edge of the work surface is identified. The actual coating time of the liquid is compared to an expected coating time. In response to identifying a difference between the actual coating time and the expected coating time that is greater than a predetermined threshold, the dispensing operation can be adjusted or an error can be indicated. Multiple dispensings of multiple spin-on films can be monitored and the actual coating time of each deposited film can be compared to the expected coating time.

[0074] Dispensing the liquid onto the working surface of the substrate can include dispensing the liquid into the center of the substrate and rotating the substrate causes the liquid to spread outward. The outward spreading can be the liquid coating the substrate or the liquid spreading and splashing off the substrate. In another embodiment, the liquid can be dispensed onto the working surface of the substrate before the substrate is spun on the substrate holder.

[0075] Directing the laser beam to an edge location on the work surface of the substrate can include directing the laser beam directly at or near the edge of the substrate, for example within a few millimeters of the edge. Because the substrate is rotating, the entire peripheral edge of the substrate is taken into account during the monitoring of the scattered / reflected light. In other embodiments, additional or alternative light sources can be used. Any laser (e.g., green or red) can be used as long as it does not activate the given photoresist being dispensed.

[0076] The location at which the laser beam is directed is a radius where coverage progress will be monitored and defects will be detected. Additional laser beams can be directed accordingly onto the work surface of the substrate. They can be directed into the interior of the substrate. Light from this interior location can be monitored to indicate when liquid has reached that interior location or that a defect is present at that interior location. The actual coating time can be identified and compared to the expected coating time for that interior location. This actual coating time can be used to predict when all of the substrate will be coated. This prediction can be made based on many different factors such as how much of the substrate has already been coated, how much of the substrate still needs to be coated, the speed at which the substrate is rotating, the properties of the liquid (e.g., viscosity), etc. Furthermore, if this prediction suggests that the substrate will not be adequately coated, system operation can be adjusted. For example, if the interior was expected to be coated in 1-2 seconds but instead is coated in 3 seconds, this may suggest that coverage is lagging behind with the current operating settings. Thus, the operating settings can be adjusted, such as dispensing additional liquid onto the substrate or increasing the rotation speed of the substrate.

[0077] Monitoring the light can include monitoring scattered light from the laser beam at the edge location. If the amount of scattered light increases for a short period of time, this can indicate that liquid has reached the edge location on the substrate. If the amount of scattered light periodically spikes upward, this can indicate defects, such as striations, at the edge location on the substrate.

[0078] Monitoring the light can include monitoring reflected light from the laser beam at the edge location. If the amount of reflected light decreases for a short period of time, this can indicate that liquid has reached the edge location on the substrate. If the amount of scattered light periodically spikes downward, this can indicate defects, such as striations, at the edge location on the substrate.

[0079] Monitoring the light can include monitoring both reflected and scattered light from the laser beam at the edge location. Although the behavior of the scattered or reflected light may be sufficient to indicate coverage and / or errors, both can be monitored and the behavior of the scattered and reflected light can help verify each other's observations.

[0080] Monitoring the light can include monitoring reflected light, scattered light, or both from any additional laser beams that are targeted inside the substrate.

[0081] Identifying a pattern of the monitored light that is indicative of the liquid reaching the edge location on the substrate can include identifying when the monitored light changes behavior from a generally steady state to an unsteady state. Generally, as the light interacts with the edge of the liquid, the amount of reflected light will decrease and the amount of scattered light will decrease. Furthermore, identifying a pattern of the monitored light that is indicative of the liquid having adequately covered the edge location on the substrate (i.e., no defects remain) can include identifying when the monitored light returns to a steady state. Additionally, identifying a pattern of the monitored light that is indicative of a defect (e.g., striations) can include identifying when the monitored light periodically spikes. Generally, striations will cause the scattered light to spike upwards and the reflected light to spike downwards. Assuming the substrate is rotating at a constant speed, the spikes will be periodic.

[0082] Identifying the actual coating time may include measuring the time between the start of dispensing the liquid onto the work surface of the substrate and when the liquid reaches a target location on the work surface, which may be an edge or an interior, and is set by directing a laser beam at the target location. If multiple target locations are used, multiple coating times may be measured.

[0083] Comparing the actual coating time to the expected coating time can include adjusting a given dispensing operation and / or indicating an error in response to identifying a difference between the actual coating time and the expected coating time that is greater than a predetermined threshold. The expected coating time and the predetermined threshold can be based on previous successful coating times under similar operating conditions or any other prior art known in the art. The desired process yield can be a factor when determining the predetermined threshold.

[0084] Adjusting the dispensing operation can include selectively varying a volume of liquid dispensed onto the work surface of the substrate. Adjusting the dispensing operation can include selectively varying a rotational speed of the substrate holder. Adjusting the dispensing operation of the liquid on the work surface of the substrate can include dispensing a minimized additional volume to an amount sufficient to complete full coating coverage of the work surface of the substrate.

[0085] Indicating the error can include tagging the substrate. The substrate can be marked for rework. Operating conditions, such as substrate rotation speed, actual coating time, amount of liquid dispensed, etc., can be recorded for future analysis and troubleshooting.

[0086] Monitoring the multiple dispensing of the multiple spin-on films can further include comparing actual coating times to expected coating times for each of the deposited films. This information can be stored for analysis, e.g., to make more accurate predictions of future expected coating times, to find more optimal predetermined thresholds, more optimal operating conditions, etc.

[0087] 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 dispensed. Accordingly, monitoring the light from the edge can include monitoring light from multiple light sources.

[0088] In the above description, specific details have been described, such as the particular shape of the processing system and a description of various components and processes used therein. However, it should be understood that the technology herein may be practiced in other embodiments that deviate from these specific details, and such details are for the purposes of explanation and not for the purposes of limitation. The embodiments disclosed herein have been described with reference to the accompanying drawings. Similarly, for the purpose of explanation, specific numbers, materials, and configurations have been set forth to provide a thorough understanding. Nevertheless, the embodiments may be practiced without such specific details. Components having substantially the same functional configurations are indicated by similar reference symbols, and therefore any redundant description may be omitted.

[0089] To facilitate understanding of various embodiments, various techniques have been described as multiple discrete operations. The order of description should not be construed as to imply that these operations are necessarily order dependent. In fact, these operations need not be performed in the order presented. The described operations may be performed in a different order than in the described embodiments. Various additional operations may be performed and / or described operations may be omitted in additional embodiments.

[0090] As used herein, "substrate" or "target substrate" refers generally to an object to be processed according to the present invention. The substrate may include any material portion or structure of a device, particularly a semiconductor or other electronic device, and may be a base substrate structure, such as a semiconductor wafer, a reticle, or a layer on or overlying a base substrate structure, such as a thin film. Thus, the substrate is not limited to any particular base structure, underlying layer, or overlying layer, whether patterned or not, but rather is contemplated to include any such layer or base structure, and any combination of layers and / or base structures. Although the description may refer to a particular type of substrate, this is for illustrative purposes only.

[0091] Those skilled in the art will also understand that there may be many variations that can be made to the operation of the techniques described above while still achieving the same objectives of the present invention. Such variations are intended to be included within the scope of the present disclosure. Thus, the above description of the embodiments of the present invention is not intended to be limiting. Rather, any limitations to the embodiments of the present invention are presented in the following claims.

Claims

1. 1. A system for dispensing a liquid onto a substrate, comprising: a substrate holder configured to hold a substrate and rotate the substrate about an axis; a dispensing unit configured to dispense a liquid onto a working surface of the substrate while the substrate is rotated on the substrate holder; a first laser configured to direct a first laser beam at an edge of the work surface of the substrate; a first detector positioned to capture scattered light from the first laser beam directed at the edge of the work surface of the substrate; a second laser configured to direct a second laser beam into the work surface of the substrate; a second detector positioned to capture scattered or reflected light from the second laser beam directed toward the interior of the work surface of the substrate; and monitoring scattered or reflected light from the second laser beam directed toward the interior of the work surface of the substrate to monitor intermediate progress of the liquid; and a processor configured to monitor scattered light from the second laser beam at the work surface of the substrate and identify a pattern of scattered light indicative of the liquid reaching the edge of the substrate; the processor is further configured to identify an actual coating time of the liquid from the start of a given dispense of the liquid on the work surface until the liquid reaches the edge of the work surface, and compare the actual coating time of the liquid to an expected coating time of the liquid; The system, wherein the processor is further configured to indicate an error or adjust system operation if the predicted coating time and the actual coating time have a difference greater than a predetermined threshold.

2. 2. The system of claim 1, wherein the processor is configured to monitor scattered light from the first laser beam directed at an edge of the work surface of the substrate to identify a pattern of scattered light that indicates a film formed from the liquid has coverage defects.

3. a third detector positioned to capture reflected light from the first laser beam directed at the edge of the work surface of the substrate; 10. The system of claim 1, wherein the processor is configured to monitor reflected light from the first laser beam directed at the edge of the work surface of the substrate to identify a pattern of reflected light that indicates that liquid has reached the edge of the substrate.

4. 1. A system for dispensing a liquid onto a substrate, comprising: a substrate holder configured to hold a substrate and rotate the substrate about an axis; a dispensing unit configured to dispense a liquid onto a working surface of the substrate while the substrate is rotated on the substrate holder; a first laser configured to direct a first laser beam at an edge of the work surface of the substrate; a first detector positioned to capture reflected light from the first laser beam directed at the edge of the work surface of the substrate; a second laser configured to direct a second laser beam into the work surface of the substrate; a second detector positioned to capture scattered or reflected light from the second laser beam directed toward the interior of the work surface of the substrate; and a processor configured to monitor scattered or reflected light from the second laser beam directed toward the interior of the work surface of the substrate to monitor intermediate progress of the liquid, monitor reflected light from the first laser beam directed to the edge of the work surface of the substrate, and identify a pattern of reflected light indicative of the liquid reaching the edge of the substrate; the processor is further configured to identify an actual coating time of the liquid from the start of a given dispense of the liquid on the work surface until the liquid reaches the edge of the work surface, and compare the actual coating time of the liquid to an expected coating time of the liquid; The system, wherein the processor is further configured to indicate an error or adjust system operation if the predicted coating time and the actual coating time have a difference greater than a predetermined threshold.

5. 5. The system of claim 4, wherein the processor is configured to monitor reflected light from the first laser beam directed at an edge of the work surface of the substrate to identify a pattern of reflected light that indicates that a film formed from the liquid has coverage defects.

6. a third detector positioned to capture scattered light from the first laser beam directed at the edge of the work surface of the substrate; 5. The system of claim 4, wherein the processor is configured to monitor scattered light from the first laser beam directed at the edge of the work surface of the substrate to identify a pattern of scattered light that is indicative of liquid reaching the edge of the substrate.

7. The system of claim 1 , wherein the first laser is aimed directly at an edge of the work surface of the substrate.

8. The system of claim 4 , wherein the first laser is aimed directly at an edge of the work surface of the substrate.

9. 1. A system for dispensing a liquid onto a substrate, comprising: a substrate holder configured to hold a substrate and rotate the substrate about an axis; a dispensing unit configured to dispense a liquid onto a working surface of the substrate while the substrate is rotated on the substrate holder; a laser configured to direct a laser beam to an edge location on the work surface of the substrate; a first detector positioned to capture scattered light from the laser beam directed at the edge location of the substrate; a second detector positioned to capture reflected light from the laser beam directed at the edge location of the substrate; a processor configured to monitor scattered and reflected light from the laser beam directed at the edge location on the substrate to identify a pattern of scattered light and a pattern of reflected light, respectively, indicative of the liquid reaching the edge location on the substrate; The processor is further configured to identify an actual coating time of the liquid from a start of a given dispense of the liquid on the work surface until the liquid reaches the edge location of the work surface, and compare the actual coating time of the liquid to an expected coating time of the liquid; The system, wherein the processor is further configured to indicate an error or adjust system operation if the predicted coating time and the actual coating time have a difference greater than a predetermined threshold.

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