Process control method for semiconductor devices processed by lithography

Abstract

The present disclosure provides a process control method and a corresponding apparatus for a semiconductor device to be processed by lithography. An exposure tool assembly is used to expose a photoresist layer to an exposure beam, wherein the photoresist layer is coated on a semiconductor substrate, and wherein, for each exposure, a current exposure parameter set including at least a defocus value and an exposure dose is used. The exposed photoresist layer is developed, wherein a resist pattern is formed from the photoresist layer. Characteristic properties of the resist pattern and / or characteristic properties of a substrate pattern obtained from the resist pattern are measured. In response to a deviation of the measured characteristic properties from target characteristic properties, the current exposure parameter set is updated. Uncorrected characteristic properties of a hypothetical resist pattern that would be formed without updating the exposure parameter set are estimated. In response to information obtained from the uncorrected characteristic properties, the measurement strategy for the characteristic properties can be changed or the current exposure parameter set can be updated.

Description

Technical Field

[0001] Embodiments relate to the manufacture of semiconductor devices such as volatile and non-volatile memory devices, logic circuits, microprocessors, power semiconductor devices, and flat panel devices, where an exposure process transfers a pattern into a photoresist layer on a semiconductor wafer. The exposure process can use APC (Advanced Process Control) to determine exposure parameters for a current exposure based on metrology results from a previously exposed semiconductor wafer. Embodiments further relate to a wafer manufacturing assembly including an exposure tool assembly. Background Art

[0002] During the manufacturing process of semiconductor devices, various physical components of functional elements such as transistors, diodes, capacitors, resistors, and wiring connections are formed in and on a semiconductor substrate, for example, as doped regions in the semiconductor substrate and doped regions in layers deposited on the processed surface of the semiconductor substrate. These solid components can be formed layer by layer by combining the deposition of one or more layers on the processed surface and using a patterning process to transfer a specific pattern into the layer, where the patterning process (e.g., by etching) locally modifies or removes multiple parts of the relevant layer. Fluctuations in the patterning process result in deviations from the target dimensions and may adversely affect the process yield or may result in a relatively wide distribution of parameters of the final semiconductor device.

[0003] Patterning by photomasking includes depositing a photoresist layer on the processed surface of a semiconductor wafer. The exposure process projects the reticle pattern of a photomask into the photoresist layer, where, in the photoresist layer, the photoactive component is selectively modified in the exposed part relative to the unexposed part, such that after exposure, the photoresist layer contains a latent image of the reticle pattern. The development process selectively removes the modified or unmodified parts. The developed resist layer can be used as an etch mask or an implant mask.

[0004] The physical dimensions of a resist pattern depend particularly on the exposure dose and the defocus value. The exposure dose represents the energy of the exposure radiation used to expose a photoresist layer in a specific pattern. Defocus refers to the distance between the wafer surface and the focal plane of the exposure radiation. The physical dimensions of certain critical patterns in the photoresist layer can be measured and compared with the target dimensions. APC can adjust the exposure dose and / or defocus for the next exposure based on the measurement results for the critical dimensions.

[0005] There is a need to improve the physical dimension uniformity of the resist pattern across the wafer (e.g., in-wafer uniformity) and between wafers (e.g., between-wafer uniformity) with less effort, and / or there is a need to reduce metrology work without adversely affecting the in-wafer uniformity and the between-wafer uniformity. Summary of the Invention

[0006] In one aspect, an embodiment provides an advanced process control method, including: using an exposure tool assembly to expose a photoresist layer coated on a semiconductor substrate to an exposure beam, wherein, for each exposure, using a current exposure parameter set including at least a defocus value and an exposure dose; developing the exposed photoresist layer to form a resist pattern; measuring characteristic features of the resist pattern and / or characteristic features of a substrate pattern obtained from the resist pattern, and updating the current exposure parameter set in response to a deviation between the measured characteristic features and target characteristic features; estimating uncorrected characteristic features of a hypothetical resist pattern formed without updating the exposure parameter set; and at least one of the following operations: (i) changing the measurement strategy for the characteristic features in response to information obtained from the uncorrected characteristic features, and (ii) updating the current exposure parameter set in response to information obtained from the uncorrected characteristic features.

[0007] According to another aspect, an embodiment provides a wafer manufacturing assembly, including: an exposure tool assembly configured to (i) expose a photoresist layer coated on a semiconductor substrate to an exposure beam according to a current exposure parameter set, and (ii) form a resist pattern through the exposed photoresist layer; a metrology unit configured to measure characteristic features of at least one of the resist pattern and a substrate pattern obtained from the resist pattern; an APC unit configured to update the exposure parameter set in response to a deviation between the measured characteristic features and target characteristic features; and a calculation unit configured to estimate uncorrected characteristic features of a hypothetical resist pattern formed without updating the exposure parameter set. Brief Description of the Drawings

[0008] Figure 1 is a schematic block diagram of a part of a semiconductor device manufacturing component including an advanced process control unit for controlling exposure parameters according to a reference example, for illustrating a background useful for understanding embodiments.

[0009] Figure 2 is a schematic block diagram of a part of a semiconductor device manufacturing component according to an embodiment, the semiconductor device manufacturing component including a calculation unit for estimating uncorrected characteristics of a hypothetical structure formed without updating exposure parameters.

[0010] Figure 3 is a schematic flowchart illustrating a method for advanced process control according to an embodiment related to exposure parameter update.

[0011] Figure 4 is a schematic block diagram of a part of a semiconductor device manufacturing component including a calculation unit according to an embodiment related to controlling correction data for an exposure tool component.

[0012] Figure 5 is a block diagram schematically illustrating an advanced process control method according to an embodiment.

[0013] Figure 6 is a schematic diagram illustrating a measured and uncorrected critical dimension, for illustrating Figure 4 the effects of embodiments.

[0014] Figure 7 is a block diagram schematically illustrating a method of using information obtained by an advanced process control method according to a further embodiment.

[0015] Figure 8 is a schematic block diagram of a part of a semiconductor device manufacturing component including a calculation unit according to an embodiment related to modifying a sampling plan.

[0016] Figure 9 is a schematic block diagram of a part of a semiconductor device manufacturing component including a calculation unit according to an embodiment related to controlling an etching process.

[0017] Figure 10 is a schematic block diagram of a part of a semiconductor device manufacturing component according to a further embodiment. DETAILED DESCRIPTION

[0018] Figure 1Shows a part of a conventional semiconductor device manufacturing assembly 390 having an exposure tool assembly 320, the exposure tool assembly including a coater unit 322, an exposure unit 324, and a developer unit 326. A plurality of input wafer lots 410 of a pre-processed semiconductor substrate are sequentially provided to the semiconductor device manufacturing assembly 390. For example, the semiconductor substrate can be a semiconductor wafer, a glass substrate on which a semiconductor structure is formed, or an SOI (semiconductor-on-insulator) wafer. Regardless of the type of the semiconductor substrate, the semiconductor substrate is hereinafter referred to as wafer 401.

[0019] The number of wafers 401 in each wafer lot 410 is typically up to 25. The wafers 401 in the same wafer lot 410 can undergo the same process to form the same electronic circuit. For example, the wafers 401 in each wafer lot 410 can be sequentially provided to different processing units of the same type, where the processing units of the same type apply the same process. Alternatively, the wafers 401 can be sequentially provided to the same processing unit, where each processing unit can include one or more sub-units, at which some of the wafers 401 in each wafer lot 410 can be processed in parallel.

[0020] In Figure 1 the example of, the wafers 401 in the wafer lot 410 are provided to the coater unit 322 of the exposure tool assembly 320. The coater unit 322 coats the wafers 401 with a photoresist layer or a photoresist layer system with or without an anti-reflection coating. The coater unit 322 can include a spinner unit that dispenses the resist material on the wafer surface and evenly distributes the resist material by rotating the wafers 401. The coater unit 322 can include heating facilities for evaporating a part of the solvent in the photoresist. The wafers 401 coated at least with the photoresist layer are transferred to the exposure unit 324.

[0021] The exposure unit 324 generates an exposure beam for transferring a target pattern into the photoresist layer, where the exposure beam can selectively activate the photoactive component of the photoresist layer in the exposure portion. The exposure beam can be an electromagnetic radiation beam or a particle beam. For example, the exposure beam is an electron beam that can scan the photoresist layer, where the intensity modulation or blanking of the beam can generate the target pattern. According to another embodiment, the exposure beam includes light or electromagnetic radiation with a wavelength shorter than 365 nm (e.g., 193 nm or less), where the electromagnetic radiation passes through or reflects at a mask and images the mask pattern into the photoresist layer.

[0022] In the portion of the photoresist layer exposed by the exposure beam, the photoactive component affects the polymerization of a previously unpolymerized compound or the depolymerization of a previously polymerized compound.

[0023] Exposure of a wafer 401 can include a single exposure of the entire processed surface or can include multiple exposures in adjacent exposure fields on the processed surface, where the same pattern is imaged into each exposure field. Each exposure is defined by an exposure dose of exposure radiation and a defocus value that indicates the distance between the processed surface and the focal plane of the exposure radiation. The defocus and / or exposure dose can be different for different exposure fields on the same wafer 401, different between different wafers in a wafer lot 410, and / or different between different wafer lots 410. The wafer 401 having the exposed photoresist layer is transferred to a developer unit 326.

[0024] The developer unit 326 removes the exposed portion of the photoresist layer relative to the unexposed portion or removes the unexposed portion relative to the exposed portion. The developer unit 326 can include a heating chamber for post-exposure baking and uses different dissolution rates for the exposed and unexposed portions of the photoresist layer to selectively dissolve the exposed portion relative to the unexposed portion or vice versa. The developer unit 326 can include a heating chamber for evaporating the remaining solvent and for chemically modifying the developed resist layer, e.g., to harden the developed resist layer or to improve the adhesion of the developed resist layer to the wafer surface. The developed resist layer forms a resist pattern including a plurality of resist features.

[0025] A metrology unit 330 can measure the feature characteristics of critical resist features of the resist pattern at sampling points. The metrology unit 330 can be part of the exposure tool assembly 320 or the wafer 401 can be transferred to a remote metrology unit 330. The feature characteristics include the physical dimensions of the critical resist features. The sampling points are positions on the wafer defined in a sampling plan. By way of example, the metrology unit 330 can obtain information about the feature characteristics by OCD (Optical Critical Dimension) scatterometry, inspecting images obtained by SEM (Scanning Electron Microscopy), and inspecting images obtained by optical microscopy.

[0026] By way of example, the feature characteristics of critical resist features can include physical dimensions such as the diameter of a circular resist feature, the lengths of the short and long axes of a non-circular resist feature, the line width of a bar-shaped resist feature, the spacing width between resist features, the sidewall angle of a resist feature, the area of a resist feature, and other properties such as the line edge roughness of a resist feature. Hereinafter, the abbreviation "CD" includes all kinds of feature characteristics and is not limited to the line width and spacing width of critical resist features and the area of critical resist features.

[0027] The post-exposure process can use the resist pattern as, for example, an etch mask for forming grooves and trenches in a semiconductor substrate, as an implantation mask, or as a mask for other modification processes.

[0028] The APC unit 290 receives the measured CD of the measured wafer at selected positions defined in the sampling plan. Based on the CD measured on one or more previous wafers processed at the same exposure tool assembly 320 or at other exposure tool assemblies, the APC unit 290 individually adjusts the exposure dose and / or defocus in the exposure unit 324 for each exposure field, each wafer, and / or each wafer lot.

[0029] Figure 2 Illustrated is a wafer manufacturing assembly 300 that includes means for determining exposure parameters, metrology settings, and advanced process control settings for semiconductor devices to be lithographically processed. The wafer manufacturing assembly 300 can include an exposure tool assembly 320 and a metrology unit 330 having the functions described with reference to Figure 1 as described.

[0030] The APC unit 290 can determine a set of exposure parameters for the current exposure based on the measured CD received from the metrology unit 330. The set of exposure parameters can include dose / focus correction data, e.g., a correction value for focus, a correction value for exposure dose, or correction values for both focus and exposure dose. The APC unit 290 can further consider the previous correction data for a predetermined number of previous exposures multiplied by specific weight factors respectively. In the absence of other information received from the outside, the APC unit 290 outputs the new dose / focus correction data to the exposure tool assembly 320.

[0031] The wafer manufacturing assembly 300 further includes a calculation unit 200 that receives information about specific characteristic properties of the measured wafer. For example, the metrology unit 330 or a MES (Manufacturing Execution System) that receives and manages measurement data obtained by multiple metrology units can transfer the CD defined as above to the calculation unit 200. Additionally, the calculation unit 200 can receive wafer context information WCI that identifies the wafer 401 from which the CD is obtained. By way of example, the wafer context information WCI can include: parameters that identify the source, type, and parameters of the wafer 401, the processing tools and processing units on which the wafer 401 is processed (e.g., the reticle used in the exposure tool assembly 320), the process conditions to which the relevant wafer has been subjected, identifiers of the process gases and process fluids to which the relevant wafer has been exposed, and chronical information including the date and time of the previous process.

[0032] The computing unit 200 also receives and / or holds exposure information that can be used for process correction in the exposure tool assembly 320, e.g., previously applied exposure dose, focus, previous dose / focus correction data, and / or the temperature profile of post-exposure bake. The exposure information available for process correction can be included in the wafer context information WCI or can be directly transmitted from the exposure tool assembly 320 to the computing unit 200.

[0033] The primary stage of the computing unit 200 can determine the dose error and focus error for the current exposure based on the measured CD received from the metrology unit 330 and the exposure information. The exposure information can include the exposure parameters of one or more previous exposures, the dose error and focus error of one or more previous exposures, and / or the focus data obtained by on-product focus measurement, wherein the focus error can be zero in the case where the computing unit 200 receives the data obtained by on-product focus measurement.

[0034] To determine the dose error and focus error, the primary of the computing unit 200 can use a physical model that describes the relationship between CD, exposure dose, and focus. Based on the measured CD, the exposure dose and / or defocus value valid for the sampling point from which the measured CD has been obtained can be obtained by a physical model (i.e., polynomial model) defined by basis functions and coefficients.

[0035] The secondary stage of the computing unit 200 can calculate the alternative uncorrected feature characteristics of the imaginary resist pattern that would be formed without making any updates to the set of exposure parameters. In other words, the computing unit 200 calculates the CD for the case where any advanced process control is omitted. According to an embodiment, the secondary can retrospectively calculate the optimal dose value and the optimal focus value of the previously processed wafers.

[0036] By estimating the imaginary uncorrected feature characteristics that would be caused by the exposure without applying an update process to defocus and / or exposure dose, the computing unit 200 can contribute to calculating and analyzing the parameters of all processes from exposure until at least the first post-exposure processing unit 340, while the basic advanced process control of the exposure remains valid and the processed wafer 401 can meet the normal degree of process tolerance. The computing unit 200 can allow the use of adjustments in different wafer models, wafer context information, APC settings, and / or sampling plans to determine the process correction values and CD uniformity without temporarily bypassing the advanced process control, such that the wafer yield remains unaffected and no wafers are lost due to the absence of advanced process control.

[0037] For this purpose, the result RS obtained from the secondary of the computing unit 200 can be transmitted to the expert system 206, to the user interface 205 that visualizes the result for a human operator (user), to the post-exposure processing unit 340, or to the APC unit 290. The result of the secondary of the computing unit 200 can be used to influence wafer processing, for example, by modifying the settings of advanced process control or by redefining the wafer model, by controlling the post-exposure processing unit 340 in a manner that compensates for parameter drift, or by changing the measurement strategy (e.g., by modifying the sampling plan used by the metrology unit 330).

[0038] For example, based on the information obtained from the computing unit 200, the sampling plan used by the metrology unit 330 can be modified by skipping the sampling points that have the least impact on the determination of the model coefficients of a model that describes the CD distribution across the entire wafer surface according to one or more polynomials.

[0039] Alternatively or additionally, alternative defocus / dose correction parameters can be obtained in a manner that smoothes or minimizes the deviation of the characteristic properties from the target values. For this purpose, the uncorrected CDs can be searched to obtain trends specific to certain parameters of the wafer context information. The alternative dose / focus correction data can be transmitted to the APC unit 290, where the corrected defocus / dose correction parameters can overwrite the conventionally obtained dose / focus correction values for the next exposure.

[0040] The simulation of the behavior of the wafer manufacturing assembly 300 in combination with the simulation of the results of other parameter settings at the user interface 205 allows for the differentiation between different sources or scenarios of CD deviation. The tendency and trend of parameter fluctuations can be evaluated more precisely and without disturbing other effects. Additionally, the impact of different parameter settings on specific characteristic properties can be evaluated to determine which characteristic properties at the original sampling points are the most critical.

[0041] Figure 3 Illustrated are the details of the simulation performed during the process of a method for modifying the exposure dose for a current exposure based on the estimated CD predicted for the current exposure based on the uncorrected CDs of previous exposures. The simulation can be performed by the Figure 2 computing unit 200. For simplicity, the simulation refers to an embodiment that only considers the exposure dose. The simulation can be applied to defocus, to a combination of defocus and exposure dose, and also to further parameters and parameter combinations.

[0042] Initialization step 510 initializes the value of counter n (the counter can count individual wafers or wafer lots), the correction value CorrVal(1) for the first wafer or wafer lot, and the exposure dose ExpDos(1) for the first exposure, where the first exposure dose can be obtained only from the target CD and device parameters. Counter step 520 can increment counter n by one. In exposure step 530, the exposure tool exposes one or more wafers assigned to counter value n with the initial exposure dose. At least one critical dimension on an individual wafer or multiple wafers (e.g., all wafers assigned to the same lot) is obtained by measurement step 540. Based on the measured CD, estimation step 550 estimates the uncorrected critical dimension CD(n) by adding or subtracting the portion caused by the correction dose to the measured CD, where for n = 1, the estimated CD(1) is equal to the measured CD.

[0043] Up to a predefined number n0 of wafers or wafer lots, a loose APC setting can calculate the exposure dose for the next individual wafer or wafer lot in APC step 570 based on one or more previously measured critical dimensions CD(n), CD(n - 1).

[0044] In the case where the number of measurements exceeds the predefined number n0 and there is sufficient information in the estimated uncorrected critical dimensions CD(1)…CD(n), predictor step 582 can calculate the hypothetical critical dimension PCD(n + 1) for the next individual wafer or wafer lot based on the previously estimated uncorrected CD and alternative dose corrections. For this purpose, predictor step 582 can interpret the wafer context information regarding the current wafer and previous wafers to obtain the context. Correction step 584 can determine the alternative dose correction for the next exposure based on the previously estimated CD.

[0045] The following table illustrates by way of example Figure 3 of the embodiments. Exposure with an exposure dose of 25 mJ / cm 2 to a given reticle results in a target CD of 30 nm. Close to an exposure dose of 25 mJ / cm 2 an exposure dose fluctuation of +1 mJ / cm 2 results in a 1 nm reduction in CD.

[0046] In the example of Table 1, exposure of the first wafer lot with an exposure dose of 25 mJ / cm 2 results in a measured CD of 32 nm, which deviates from the target CD by +2 nm. Considering the model that describes the relationship between dose and CD, an additional 1 mJ / cm 2 results in a 1 nm reduction in the line, so APC increases the exposure dose by +2 mJ / cm 2A correction dose to reduce the CD by 2 nm to meet the target CD. However, due to process variations as discussed above, the average measured CD of the second wafer lot may deviate from the expected 30 nm again and may be, for example, 30.5 nm. For the exposure of the next wafer lot, the APC can further increase the correction dose by 0.5 mJ / cm 2 , to offset the remaining CD deviation of +0.5 nm. Similarly, further process fluctuations affected the average measured CD of the third wafer lot to be 29.7 nm, such that for the fourth wafer lot, the correction dose was reduced by 0.3 mJ / cm 2 .

[0047]

[0048] Table 1

[0049] Table 2 relates to an example of how an uncorrected CD value can be estimated based on the measured CD and the corrected CD due to the correction dose. For the first lot, since no correction dose was used to generate the corrected CD, the uncorrected CD is equal to the measured CD. For the second lot, a correction dose of 2 mJ / cm 2 was used, resulting in a 2 nm linewidth reduction. Thus, without the correction dose, the actual linewidth would be 32.5 nm instead of 30.0 nm. For the third lot, the measured CD is 29.7 nm, but the correction dose (a total of 2.5 mJ / cm 2 ) reduces the linewidth by 2.5 nm, such that the uncorrected CD is 32.2 nm.

[0050]

[0051] Table 2

[0052] The uncorrected CD can be searched for trends, periodicity, or context-dependency, or the absence of trends and periodicity or context-dependency.

[0053] Figure 4 Relates to a wafer manufacturing assembly 300 having a computing unit 200 for improving the correction values of the exposure dose and / or defocus in an exposure tool assembly 320. A metrology unit 330 can obtain the CD from a wafer 401 and transmit the CD to an APC unit 290 and the computing unit 200.

[0054] The metrology unit 330 transmits the measured CD to the calculation unit 200. The calculation unit 200 can directly use the measured CD to first obtain a model that describes the CD distribution across the entire wafer surface according to one or more polynomials and to calculate the uncorrected feature characteristics of the imaginary resist pattern. According to another embodiment, the calculation unit 200 uses the relationship between the CD and the exposure dose and defocus to obtain the dose error and the focus error, and then uses the dose error and the focus error, or the dose setting and the focus setting - for example, to determine the model coefficients of the model that describes the focus error and the dose error or the optimal dose and / or the optimal focus for each point of the model, such that the model coefficients do not depend on the type of CD.

[0055] The APC unit 290 and the calculation unit 200 can be assigned to different hardware components, for example, a controller, a server, a computer connected through a data transfer interface, and / or assigned to different software modules that exchange data through a data interface. The APC unit 290 can be connected to the calculation unit 200 through a data interface. The APC unit can be configured to update the exposure parameter set in response to the information received from the calculation unit 200.

[0056] For example, the APC unit 290 can include a controller unit that runs a program for conventional focus / dose control and includes an interface for receiving at least one of the following: i) alternative parameter settings for determining improved focus / dose control parameters, and ii) improved focus / dose control parameters for overriding the conventionally obtained parameters before passing the focus / dose control parameters to the exposure tool assembly 320.

[0057] The calculation unit 200 can be an additional device, for example, an additional controller or an additional software module for a computer to run programs other than the advanced process control in the APC unit 290, where the results obtained by the calculation unit 200 can affect the change of the parameter settings of the APC unit 290, the replacement of the focus / dose correction values in the APC unit 290, or can be directly transmitted to the exposure tool assembly 320. According to another embodiment, the APC unit 290 is one of several modules or stages integrated in the calculation unit 200, where the calculation unit 200 can completely replace the conventional APC unit 290.

[0058] As long as the APC unit 290 does not receive other information, for example, from the calculation unit 200 or from the user interface 205, the APC unit 290 can perform conventional ("loose") control of the exposure dose and / or focus. In the case where the APC unit 290 receives enhanced correction data for the exposure dose and defocus, the APC unit 290 forwards the enhanced correction data instead of forwarding the loose correction data. According to another embodiment, the APC unit 290 can receive alternative parameter settings (e.g., weight settings of previous CDs or previous correction values), and overwrite the previous parameter settings with the received alternative parameter settings.

[0059] The calculation unit 200 calculates the uncorrected CD of an imaginary structure in the resist pattern (which would be formed in the resist pattern without any update to the exposure parameter set), and can transmit the uncorrected CD to the user interface 205 and / or the external expert system 206. Alternatively or additionally, the calculation unit 200 can internally perform an expert-level evaluation of the uncorrected CD.

[0060] The user, the expert system 206, or the expert level of the calculation unit 200 can associate the uncorrected CD with the context information of the wafer and / or wafer lot, and can search for parameters in the wafer context information to obtain the correlation between the corresponding parameters and the uncorrected CD value. If a correlation between the parameters in the wafer context information and the uncorrected CD value is found, the user, the expert system 206, or the expert level alerts the calculation unit 200 to estimate the enhanced correction value based only on such previous exposures involving the same parameter in the wafer context information.

[0061] For example, if the user, the expert system 206, or the expert level identifies that a certain CD trend of the parameters identifying a specific coater unit is significantly different from the CD trends of other coater units, the user, the expert system 206, or the expert level can alert the calculation unit 200 to use different parameter settings (using only the exposure history of wafers processed at the same coater unit) to determine the enhanced CD correction value.

[0062] Before actually using different parameter settings to determine the focus / dose correction value, the simulation level of the calculation unit 200 can simulate the impact of different parameter settings on the CD. The results of the simulation can be transmitted to the user interface 205, where the user can approve the different parameter settings.

[0063] After approving the different parameter settings, the calculation unit 200 or the user can update the parameter settings in the APC unit 290. According to another embodiment, the calculation unit 200 can directly transmit the focus / dose correction value obtained with the new parameter settings to the exposure tool assembly 320, such that the APC unit 290 is bypassed.

[0064] Based on the measured CD and the calculated exposure dose and / or defocus at the sampling points on the wafer 401, the secondary stage of the calculation unit 200 can determine the coefficients of the model for estimating the dose / focus in regions on the wafer 401 not directly covered by the sampling points, and / or for separating possible systematic parts from random parts. The model can be or can include a wafer-level model, which describes the dose / focus distribution across the entire wafer surface according to one or more polynomials (e.g., odd and even Zernike polynomials, Legendre polynomials, and / or radial basis functions determined using TPS (thin plate spline) technology).

[0065] The measured CD conveys values only at the sampling points. The modeling algorithm calculates the model coefficients, for example, for a Zernike polynomial or a Legendre polynomial that best matches the base values (i.e., the measured CD at the sampling points). By identifying all the model coefficients of the polynomial, the polynomial can be evaluated to estimate the dose / focus correction data for each point on the wafer surface.

[0066] The model can also include one or more models for a single exposure field (field-fine model) or a field model that generalizes multiple exposure fields of the wafer 401 (e.g., all exposure fields of the wafer 401).

[0067] The model provides dose / defocus for a dense grid of points across the entire wafer surface. The order of the secondary and primary stages can be changed, and the two stages can operate in parallel or one after the other.

[0068] A new setting can involve new model coefficients for estimating relevant CD information of the exposure field. For example, the new setting can change the order of at least one of the model polynomials, e.g., from an nth-order Zernike polynomial to an (n - m)th or (n + m)th-order Zernike polynomial. The new setting can also change the model type, e.g., from a model described by Zernike polynomials to a Legendre model. The effect of the new model can be simulated by the simulation stage of the calculation unit 200 and visualized on the user interface 205.

[0069] By calculating the uncorrected CD of a hypothetical structure that would be formed on the same wafer without APC, better CD correction values can be searched for, while the basic advanced process control of the exposure remains valid and the processed wafer 401 meets the normal degree of process tolerances. On the other hand, knowledge of the uncorrected CD allows, for example, differentiation between different tools or chambers in which the wafer 401 is processed in parallel.

[0070] Exploratory data analysis (EDA) can be used to analyze uncorrected CDs to visually summarize their main characteristics, for example, where EDA can use statistical models.

[0071] Another metrology unit 350 can measure the dimensions of critical substrate features (substrate CDs). The calculation unit 200 can use at least one of the substrate CD and the resist CD as the measured CD.

[0072] According to an embodiment, Figure 4 the calculation unit 200 and the APC unit 290 can cooperate to perform Figure 5 the advanced process control method illustrated in Figure 5 where each functional block in Figure 4 corresponds to a method step executed in one of the units depicted in

[0073] The functional blocks in the right column relate to the wafer being inspected at a certain point in time (the current wafer) and the current wafer data obtained from and assigned to the current wafer. The current wafer data can include current CD measurements at predefined measurement sites and data obtained from the current CD measurements, for example, current defocus data and error data. The current wafer data can include wafer context information related to the current wafer, information about the applied defocus correction and error correction, etc. The measurement sites can be defined in a sampling plan.

[0074] The functional blocks in the left column relate to the previously processed and inspected wafers (historical wafers) inspected before the current wafer and the historical wafer data obtained from and assigned to the historical wafers. The historical wafer data can include historical CD measurements at predefined measurement sites and historical defocus data and dose data. The historical wafer data can further include wafer context information, for example, information identifying the processing unit in which the wafer has been processed and the processing conditions the wafer has undergone.

[0075] The first step 710 stores the results of the historical CD measurements at the measurement sites and the historical exposure data of multiple historical wafers and makes these results and data available. The second step 720 converts the historical CD measurements into exposure errors that describe the deviation of the CD measurements from the target CD in terms of defocus and dose errors. The second step 720 can use a polynomial model that relates the CD deviation from the target value to the defocus and dose errors that cause the CD deviation. The defocus and dose errors can be only defocus, only dose error, or can include both defocus and dose errors. The defocus and dose errors describe the residual defocus and dose errors of the historical wafers.

[0076] The third step 730 calculates the effect of historical process corrections at the measurement site. The historical process corrections correspond to the focus corrections and dose corrections actually applied to each historical wafer, and can form another example of the uncorrected characteristics as discussed above.

[0077] For each CD measurement site on the historical wafer, the fourth step 740 adds the residual defocus and dose errors determined in the second step 720 to the defocus and dose actually applied to the same historical wafer to obtain the optimal focus and / or the optimal dose. The optimal focus and the optimal dose are retrospectively obtained values: if the exposure had used these values in the past, the exposure would have resulted in the minimum CD deviation.

[0078] The fifth step 750 can determine the coefficients of a model that provides the optimal focus or the optimal dose for a dense grid of points across the entire historical wafer. According to an embodiment, the fifth step 750 can provide the coefficients of a first model and the coefficients of a second model, the first model providing the optimal focus for a dense grid of points across the entire historical wafer, and the second model providing the optimal dose for a dense grid of points across the entire historical wafer. Steps 710 to 750 can be repeated for multiple historical wafers.

[0079] Based on the historical optimal focus values and optimal dose values, the sixth step 760 calculates alternative dose corrections and error corrections obtained only from historical data. The sixth step 760 can use the EWMA (exponentially weighted moving average) method to obtain the historical optimal focus values and optimal dose values. The EWMA method can track the exponentially weighted moving average of the historical optimal focus and / or optimal dose in a timely manner, where the method weights the historical optimal focus values and optimal dose values in a geometrically decreasing order such that the most recent optimal focus values and optimal dose values are weighted the highest, while the oldest samples contribute only little.

[0080] For example, the sixth step 760 can predict the optimal dose z of the next wafer (which can be the current wafer) by adding the weighted prediction error of the previous historical wafer n to the optimal dose z of the previous historical wafer n n where the prediction error is the difference between the applied dose x n+1 and the optimal dose z n as given in equation (1): n

[0081] (1) z n+1 = z n + λ(x n - z n )

[0082] Equation (2) is based on the dose values x1…x applied historicallyn Describes the optimal dose z for the next wafer n+1 :

[0083] (2) z n+1 = λx n +(1 - λ)λx n-1 +...+(1 - λ) n-1 λx1+(1 - λ) n x0

[0084] In Equation (1), the weight parameter λ satisfies the condition 0 ≤ λ ≤ 1, where, for λ = 0, the EWMA method takes the average value x0 of the historical optimal dose values. λ can take any value within the range between the lower limit and the upper limit, where, for example, the lower limit can be 0.05 or 0.1, and the upper limit can be 0.2 or 0.3. λ may be close to the lower limit when the sample values are noisy, and λ may be close to the upper limit when the sample values (at least for multiple subsequent samples) approximate a definable function.

[0085] Alternatively or additionally, the sixth step 760 may predict the optimal focus value for the next wafer, or predict both the optimal dose value and the optimal focus for the next wafer.

[0086] The sixth step 760 may also use the historical wafer context information and the wafer context information of the current wafer to select only a subset of the historical wafers to determine alternative dose correction values and error correction values. For example, the sixth step 760 may only consider such historical wafers that are processed at the same level of the same exposure tool as the current wafer. Based on the predicted optimal focus and optimal dose, the sixth step predicts the alternative defocus correction and dose error correction for the next wafer.

[0087] The seventh step 810 makes the results of the CD measurement at the measurement site of the current wafer n + 1 available. The eighth step 820 converts the current CD measurement into an exposure error, which describes the deviation of the CD measurement from the target CD in terms of defocus and dose errors. To obtain the defocus and dose errors based on the deviation of the CD measurement from the target CD, the eighth step 820 may use the same polynomial model as the second step 720. The defocus and dose errors describe the residual defocus and dose errors of the current wafer.

[0088] The ninth step 830 calculates the effect of the previous process correction at the measurement site. The previous process correction corresponds to the focus correction and dose correction actually applied to the current wafer.

[0089] For each measurement site on the current wafer, the tenth step 840 adds the residual defocus and dose error obtained in the eighth step 820 to the actual defocus and dose error of the current wafer obtained in the ninth step 830 to obtain an optimal focus correction and dose correction for the current wafer, where the optimal focus correction and dose correction are exposure parameters obtained retrospectively: if the optimal exposure parameters had been used in the past for the exposure, the exposure would have resulted in a minimum CD deviation.

[0090] The eleventh step 870 calculates the effect of the alternative focus correction and dose correction obtained at the measurement site of the current wafer in the sixth step 760.

[0091] The twelfth step 880 obtains an alternative focus error and dose error by calculating the difference between the effect of the alternative focus correction and dose correction obtained from the historical wafers in the eleventh step 870 and the best dose and best focus obtained for the current wafer in the tenth step 840. The thirteenth step 890 may convert the alternative focus error and dose error into an alternative CD value.

[0092] Figure 6 Illustrated by way of an example involving process deviations caused by the coater unit Figure 4 is an embodiment. Line 601 connects the measured CD deviations ΔCD of n wafers, and line 602 connects the uncorrected CD deviations ΔcCD of these same wafers. The uncorrected CD deviations can be assigned to three different context groups 611, 612, 613, where each context group includes a plurality of wafers. The uncorrected CD deviations of the wafers assigned to the first context group 611 exhibit a different correlation from the correlations between the uncorrected CD deviations of the other wafers.

[0093] A user, an expert system, or an expert level of the computing unit 200 can search the wafer context information of the relevant wafers to identify the common context of the wafers in the first context group 611, the common context of the wafers in the second context group 612, and the common context of the wafers in the third context group 613. If the common context of the wafers in the first context group 611 can be identified, the computing unit can be prompted to determine the correction value of the next wafer including the same parameters in the wafer context information only based on the previous correction values of the wafers involving the first context group 611.

[0094] In Figure 7In [the context], the computing unit 200 is data-connected to the main unit 910 of an EDA (electronic design automation) system. The main unit 910 can be a computer running on a computer system or a server. The computing unit 200 transmits information about the exposure performed by the exposure tool component to the main unit 910. The main unit 910 further receives layout information that specifies the pattern to be imaged onto the photoresist layer. Through the convolution of the layout data with the model of the exposure beam, the main unit 910 obtains information about the energy distribution in the exposed photoresist layer, enabling the main unit 910 to simulate the effects of certain exposure parameters, defocus, and dose deviations on the dimensions of selected layout features.

[0095] Typically, the main unit 910 uses the maximum values of defocus and dose errors to identify critical layout features. By using the actual defocus and dose errors obtainable through the computing unit 200, the test for criticality becomes more precise, and the EDA can let go of layout features that would otherwise be marked as critical.

[0096] Figure 8 Embodiments relate to using the results of calculations performed by the computing unit 200 to enhance the accuracy and / or efficiency of the metrology unit 330.

[0097] The wafer manufacturing component 300 includes at least the exposure tool component 320, the APC unit 290, the metrology unit 330, and the post-exposure processing unit 340 as described above.

[0098] A sampling plan 333 is transmitted to the metrology unit 330. The sampling plan 333 can include wafer identification information for identifying a specific wafer 401 in the wafer lot 410, and further includes position information identifying the metrology sites selected for inspection on the wafer 401. The metrology sites can have a circular, elliptical, or rectangular shape. The size of the metrology sites depends on the measurement method. The diameter or edge length of the metrology sites can be about 100 μm for scattering measurement methods and can be about 1 μm, or less than 1 μm, for measurements using electron microscopy.

[0099] The metrology unit 330 inspects the wafer 401 and obtains characteristic features of the relevant wafer 401 at the metrology sites identified in the sampling plan 333. The characteristic features may include geometric dimensions, such as the height, width, and / or length of structures on the surface of the wafer 401 within the measurement area, e.g., the width of a line or the vertical extension of a step or trench, the sidewall angle of a protrusion extending from the surface of the wafer 401, or the sidewall angle of a trench extending into the surface of the wafer 401. Alternatively or additionally, the characteristic features may include information about the thickness and / or composition of the topmost layer covering the wafer 401, or information about other physical properties or characteristics, such as line edge roughness, line width roughness, overlay data, wafer shape, wafer deformation, defect density, and information about the results of defect and electrical measurements.

[0100] At a first level, the metrology unit 330 inspects the wafer 401 according to an original sampling plan using a first number of sampling points and transmits the inspection results to the APC unit 290. The APC unit 290 receives the inspection results, calculates corrected exposure parameters, and transmits the corrected exposure parameters to the exposure tool assembly 320.

[0101] The computing unit 200 may receive the inspection results and the corrected exposure parameters and simulate the CDs of characteristic features of multiple subsets of the sampling points. Further examples may compare the actual deviations with the measured CD values and may modify the sampling plan according to an optimal strategy.

[0102] For example, the computing unit 200 may pass information describing the uncorrected values to the user interface 205, and the user modifies the sampling plan in response to the information presented to him at the user interface 205, where the modification is intended to omit sampling points that do not improve system performance.

[0103] According to other embodiments, the computing unit 200 may pass information describing the uncorrected values to an expert system, or the computing unit 200 may include an expert level that modifies the sampling plan according to an optimal strategy without further user interaction.

[0104] For example, the computing unit 200, the expert system, or the user may compare the actual deviation of the critical dimension with the deviation in the case where one or more sampling points in the original sampling plan are omitted. In the case where the hypothetical deviation is equal to, less than, or only slightly worse than the actual deviation, the computing unit 200, the expert system, or the user removes the (multiple) sampling points in question from the sampling plan such that at least the metrology unit 330 uses only the updated sampling plan 334.

[0105] According to an embodiment, the computing unit 200 determines a first model coefficient of the wafer model based on an original sampling plan and determines a second model coefficient of the wafer model based on a proper subset of the sampling points of the original sampling plan. If the deviation between the first model coefficient and the second model coefficient is lower than a predefined threshold, the computing unit 200 may be controlled to replace the original sampling plan with a new sampling plan including the proper subset of the sampling points. According to an embodiment, the computing unit 200 may output information describing the first model coefficient and the second model coefficient.

[0106] For the next wafer 401, the metrology unit 330 uses fewer sampling points without sacrificing the quality of APC. Another metrology unit 350 may use the updated sampling plan 334.

[0107] Figure 9 Embodiments relate to advanced process control for a patterning process (e.g., an etching process) as described above.

[0108] The wafer 401 coated with the patterned and developed photoresist layer is transferred to the post-exposure processing unit 340. The processing unit 340 may include an etching tool that images the resist pattern into the wafer, e.g., into the substrate and / or into a layer or layer stack deposited on the substrate, wherein a substrate pattern is formed in the wafer 401.

[0109] In the substrate pattern, CDs such as pattern depth, line width, tilt angle, line roughness, etc. depend on parameters of the etching process, such as etchant concentration, etching temperature, etching time, plasma voltage, and plasma frequency. Another metrology unit 350 obtains the CDs of the substrate pattern at predefined measurement sites, which may be defined in the sampling plan.

[0110] The APC unit 290 may control one or more of the parameters of the etching process in the manner described above for the focus and exposure dose of the exposure tool.

[0111] Figure 10 Embodiments relate to advanced process control effective for a combination of an exposure process and a post-exposure process (e.g., an etching process).

[0112] The defocus and exposure dose used in the exposure tool assembly 320 may be controlled in the manner described with reference to Figures 2 to 5 provided that the computing unit 200 uses the CDs of the substrate pattern obtained at another metrology unit 350 that inspects the wafer 401 after the post-exposure process. The CD drift caused by fluctuations in the etching parameters may be compensated by appropriate settings in the exposure tool assembly 320.

Claims

1. An advanced process control method, comprising: Exposing a photoresist layer coated on a semiconductor substrate to an exposure beam using an exposure tool assembly, wherein, for each exposure, a current exposure parameter set including at least a defocus value and an exposure dose is used; Developing the exposed photoresist layer to form a resist pattern; Measuring characteristic properties of the resist pattern and / or characteristic properties of a substrate pattern obtained from the resist pattern, and updating the current exposure parameter set in response to a deviation between the measured characteristic properties and target characteristic properties; Estimating uncorrected characteristic properties of a hypothetical resist pattern formed without updating the exposure parameter set; and Changing the measurement strategy of the characteristic properties by modifying a sampling plan in response to information obtained from the uncorrected characteristic properties, the sampling plan including position information about sampling points on the surface of the semiconductor substrate, wherein the characteristic properties are measured at the sampling points, and wherein modifying the sampling plan includes omitting sampling points that will not improve system performance.

2. The method according to claim 1, further comprising: Exposing a photoresist layer coated on a semiconductor substrate to an exposure beam using the exposure tool assembly, wherein an updated exposure parameter set is used.

3. The method according to claim 1, comprising: Updating the current exposure parameter set in response to information obtained from the uncorrected characteristic properties and from wafer context information, wherein the wafer context information contains information about the process history of the semiconductor substrate.

4. The method according to claim 3, wherein Updating the current exposure parameter set only considers semiconductor substrates assigned to a substrate group, wherein the semiconductor substrates assigned to the substrate group share at least one common parameter in the wafer context information, and wherein the substrate group includes a proper subset of the semiconductor substrates.

5. The method according to claim 4, wherein The uncorrected characteristic properties of the semiconductor substrates assigned to the substrate group exhibit a different correlation from the correlation between the uncorrected characteristic properties of all other semiconductor substrates.

6. The method according to claim 1, comprising: Determining a first model coefficient of a wafer model based on an original sampling plan including a first number of sampling points; Determining a second model coefficient of the wafer model based on a proper subset of the sampling points; And If the deviation between the first model coefficient and the second model coefficient is below a predefined threshold, replacing the original sampling plan with a new sampling plan including the proper subset of the sampling points.

7. The method according to claim 1, wherein The resist pattern and / or the substrate pattern includes a plurality of resist features, and the characteristic properties include at least one of the following: the diameter of a circular resist feature, the sidewall angle of a resist feature, the height dimension of a resist feature, the minor axis length of a non-circular resist feature, the major axis length of a non-circular resist feature, the line width of a strip resist feature, the spacing width between resist features, the area of a resist feature, and the line edge roughness of a resist feature.

8. A wafer manufacturing component, comprising: an exposure tool component configured to i) expose a photoresist layer coating a semiconductor substrate to an exposure beam according to a current set of exposure parameters, and ii) form a resist pattern through the exposed photoresist layer; a metrology unit configured to measure a characteristic property of at least one of the resist pattern and a substrate pattern obtained from the resist pattern; an APC unit configured to update the set of exposure parameters in response to a deviation between the measured characteristic property and a target characteristic property; and a calculation unit configured to estimate uncorrected characteristic properties of a hypothetical resist pattern formed without updating the set of exposure parameters, wherein the calculation unit is further configured to change a measurement strategy of the characteristic properties of the metrology unit by modifying a sampling plan, the sampling plan including position information about sampling points on a surface of the semiconductor substrate, wherein the characteristic properties are measured at the sampling points, and wherein modifying the sampling plan includes omitting sampling points that do not improve system performance.

9. The wafer manufacturing component according to claim 8, wherein the calculation unit is configured to update the current set of exposure parameters in response to information obtained from the uncorrected characteristic properties.

10. The wafer manufacturing component according to claim 9, wherein the calculation unit is configured to: update the current set of exposure parameters in response to information obtained from the uncorrected characteristic properties and information obtained from wafer context information, wherein the wafer context information includes information about a process history of the semiconductor substrate.

11. The wafer manufacturing component according to claim 10, wherein the calculation unit is configured to: update the current set of exposure parameters only based on semiconductor substrates assigned to a substrate group, wherein the semiconductor substrates assigned to the substrate group share at least one common parameter in the wafer context information, and wherein the substrate group includes a proper subset of the semiconductor substrates.

12. The wafer manufacturing component according to claim 11, wherein the uncorrected characteristic properties of the semiconductor substrates assigned to the substrate group exhibit a correlation different from the correlation between the uncorrected characteristic properties of all semiconductor substrates.

13. The wafer manufacturing component according to claim 8, further comprising: a data interface connecting the calculation unit and the APC unit, wherein the APC unit is configured to update the set of exposure parameters in response to information received from the calculation unit.

14. The wafer manufacturing component according to claim 8, wherein the calculation unit is configured to: determine first model coefficients of a wafer model based on an original sampling plan including a first number of sampling points, determine second model coefficients of the wafer model based on a proper subset of the sampling points of the original sampling plan, and output information describing the first model coefficients and the second model coefficients.

15. The wafer manufacturing component according to claim 8, wherein The computing unit is configured to simulate uncorrected feature characteristics of a hypothetical resist pattern for alternative settings of at least one of a sampling plan, an automated process control, and a wafer model.

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