Method for controlling a lithography system

Abstract

A lithography system includes a radiation source and a lithography apparatus. The radiation source provides radiation to the lithography apparatus. The lithography apparatus uses the radiation to image a pattern onto a plurality of target areas on a photoresist layer on a semiconductor substrate. Imaging requires a predetermined dose of radiation. The system is controlled to set a power level of the radiation according to the magnitude of the predetermined dose.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the priority of European application 19164206.5 filed on March 21, 2019, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present invention relates to a method for controlling a lithography system. The present invention also relates to a lithography system and to control software configured for use in a lithography system. Background Art

[0004] A lithographic apparatus is a machine configured to apply a desired pattern to a substrate. A lithographic apparatus can be used, for example, to manufacture integrated circuits (ICs). A lithographic apparatus can, for example, project a pattern at a patterning device (e.g., a mask) onto a layer of radiation-sensitive material (resist) disposed on a semiconductor substrate.

[0005] To project a pattern onto a substrate, a lithographic apparatus may use electromagnetic radiation. The wavelength of the radiation determines the minimum size of features that can be formed on a substrate. A lithographic apparatus using extreme ultraviolet (EUV) radiation having a wavelength in the range of 4 nm to 20 nm (e.g., 6.7 nm or 13.5 nm) may be used to form smaller features on a substrate, compared to a lithographic apparatus using radiation having a wavelength of, for example, 193 nm.

[0006] The EUV lithography system includes: a radiation source configured to generate EUV radiation; and a lithography apparatus configured to receive EUV radiation from the lithography source and configured to use the EUV radiation to image a pattern onto a substrate (i.e., a semiconductor wafer) provided with a photosensitive resist. The radiation source is typically a laser produced plasma (LPP) source, in which a high power laser converts a mass-limited fuel target into a plasma one at a time. The plasma generates EUV. Therefore, EUV radiation is provided in the form of a pulse sequence at a rate of, for example, 50kHz or 100kHz. The lithography apparatus can be a scanner, for example, in which each target area on the substrate can be irradiated by scanning the pattern to be imaged by a radiation beam in a given direction while synchronously scanning the substrate parallel or antiparallel to the direction. Generally, it is necessary to minimize the time spent imaging the pattern onto the substrate in order to increase the throughput of the lithography apparatus (i.e., the number of substrates per hour).

[0007] The amount of radiation energy delivered to a unit surface area of ​​the substrate is called the dose. Typical values ​​for dose are, for example, 20 mJ / cm 2 Up to 70mJ / cm 2 The dose of radiation delivered to the substrate needs to be accurately controlled. Summary of the invention

[0008] According to a first aspect of the invention, a method for controlling a lithography system comprising a radiation source and a lithography apparatus is provided. The radiation source is configured to provide radiation to the lithography apparatus. The radiation source is of a type, for example, called an LPP source. The lithography apparatus is configured to use radiation to image a pattern onto a plurality of target areas on a photoresist layer on a semiconductor substrate. Imaging requires a predetermined dose of radiation. The method comprises: setting a power level of the radiation according to the magnitude of the predetermined dose.

[0009] So far, a fixed time-averaged energy level of a source has been used to operate a lithography system. This energy level is selected to be suitable for all possible photoresists. In other words, the average energy level is selected to be suitable for even the most sensitive photoresists. The inventors have recognized that, in practice, this results in a selected energy level that is lower than the energy level required for most applications. It has been found that by setting the time-averaged energy level (power level) according to the desired dose, the operating power of the radiation source can be optimized, thereby maximizing the throughput. The method of the present invention is advantageous because the throughput of the lithography system (i.e., the number of substrates processed per unit time) can be optimized by controlling the operating power of the radiation source according to the required dose. As will be further explained in detail below, the dose is proportional to the ratio of the (time-averaged) energy per pulse from the radiation source and the scanning speed of the scanner. The throughput of the scanner (the time spent for the scanner to handle the substrate) increases as the scanning speed increases. In order to keep the dose equal to the required value, the energy per pulse will also increase subsequently. However, increasing the energy may cause the energy generated by the radiation source to be unstable. Sometimes, the radiation source provides insufficient energy to the target area being scanned. This target area will then need to be re-exposed in a second pass of the substrate by the scanner, since the first pass did not deliver the required amount of energy. This second pass is also called a "die repair". Therefore, in the case of higher energy per unit time of the radiation source (i.e., in the case of higher power), the number of instabilities will generally increase, resulting in the need for an increased number of second passes with die repairs. Therefore, setting the power of the radiation source according to the required dose makes it possible to find an optimum between the high scanning speed of the exposure and the number of die repairs required due to the power level setting, thereby maximizing the throughput of the scanner.

[0010] In an embodiment of the method of the present invention, the total length of time for imaging on a plurality of target areas comprises: a first length of time for imaging on the plurality of target areas during a first pass of the semiconductor substrate; and a second length of time for imaging on one or more specific target areas of the plurality of target areas during a second pass of the semiconductor substrate, the one or more specific target areas failing to receive a predetermined dose during the first pass. The method comprises: setting a power level of the radiation so that the total length of time is kept substantially at or near a minimum. During the first pass of the substrate, there is a probability that one or more target areas of the substrate receive an actual dose of radiation that is less than the desired dose. This can be compensated for by a second subsequent exposure pass (i.e., a so-called die repair or re-exposure pass). The total throughput of the lithography system depends on the sum of the time spent for the initial exposure and the time spent for the second subsequent exposure (i.e., for die repair). The inventors have recognized that the total time spent to fully expose the substrate can be minimized by controlling the operating power of the radiation source according to the desired dose.

[0011] In an embodiment, the method further comprises: during a first pass, for each corresponding target area among one or more specific target areas, recording information representing a corresponding location on the substrate and a corresponding difference between a predetermined dose and an actually received dose; during a second pass, under control of the recorded information, imaging onto one or more specific target areas among the multiple target areas.

[0012] During imaging, the amount of energy received per target area is being recorded via a suitable sensor and the identification of one or more specific target areas. As is known in the art, the identification of the target area is derived from the so-called wafer grid. The wafer grid determines the coordinates of the position of the target area of ​​the substrate in the exposure plane. The wafer grid is determined by alignment marks embedded in the substrate. Proper alignment of the substrate relative to the projection optics is performed by an alignment system. For example, several alignment marks on the substrate are measured to derive a coordinate system, which is compared with the modeled grid to derive the position of the features on the substrate. However, the clamping of the substrate on the substrate stage or the wafer distortion occurring in the non-lithographic process step may cause the distortion of the substrate, which can be monitored by comparing the measurement results with the grid. A model describing the wafer grid can be created, which is used when exposing the substrate in order to compensate for the distortion. See, for example, U.S. Pat. No. 9,310,698 to Menchtchikov et al., which is assigned to ASML and incorporated herein by reference.

[0013] It will be appreciated that, as used in this context, minimizing the sum of the first time period and the second time period is intended to mean achieving a sum of the first time period and the second time period that is at or close to a true minimum (e.g., within 10% of that minimum, preferably within 2% of that minimum, and particularly preferably within 1% of that minimum).

[0014] For a larger desired dose, the energy level setting may be substantially higher so that the nominal operating power of the radiation source is closer to the maximum power, compared to a situation where a smaller dose is desired, in which case the energy level setting may be substantially lower. As discussed above, the dose may be delivered via a series of pulses in the EUV LPP source. More pulses may be delivered to a target area on a substrate where a larger total dose is desired than where a smaller dose is desired. The energy level may be determined using the number of pulses to be delivered to the target area. For example, a lookup table or another mathematical model may be used to convert the number of pulses to a specific energy level.

[0015] Another embodiment of the method of the present invention includes estimating in advance the number of specific target areas according to the power level and according to the magnitude of the required dose. This can be implemented via a mathematical model (e.g., implemented in a lookup table or algorithm) that predicts or otherwise determines or estimates the number of target areas that will need to be re-exposed during the second pass according to the source power setting and for a given dose. The model or lookup table can be prepared in advance by monitoring instabilities in the power delivered by the radiation source for various controlled energy levels as set, or can be derived from simulations.

[0016] The invention also relates to a lithography system comprising a radiation source and a lithography apparatus. The radiation source is configured to provide radiation to the lithography apparatus and is, for example, of EUV LPP type. The lithography apparatus is configured to use the radiation to image a pattern onto a plurality of target areas on a photoresist layer on a semiconductor substrate. Imaging requires a predetermined dose of radiation. The system is configured to set a power level of the radiation according to the magnitude of the predetermined dose.

[0017] In an embodiment of the lithography system, the total length of time for imaging on the plurality of target areas comprises: a first length of time for imaging on the plurality of target areas during a first pass of the semiconductor substrate; and a second length of time for imaging on one or more specific target areas of the plurality of target areas during a second pass of the semiconductor substrate, the one or more specific target areas failing to receive a predetermined dose during the first pass. The lithography system is configured to set a power level of the radiation to keep the total length of time substantially at or near a minimum value.

[0018] In another embodiment, the lithography system is configured to: during a first pass process, for each corresponding target area among one or more specific target areas, record information representing a corresponding location at the semiconductor substrate and a corresponding difference between a predetermined dose and an actually received dose; and during a second pass process, control imaging on one or more specific target areas among the multiple target areas under the control of the recorded information.

[0019] In another embodiment, the lithography system is configured to estimate in advance the number of specific target areas according to the power level and according to the magnitude of the required dose.

[0020] In another embodiment, the radiation source is operable to supply EUV radiation and the radiation source is of the laser produced plasma type.

[0021] The invention further relates to a control software configured to be used in a lithography system comprising a radiation source and a lithography apparatus. The control software may be provided on a data carrier or on another machine-readable medium. Alternatively, the control software may be provided via a data network, for example, for downloading on the lithography system. The radiation source is configured to provide radiation to the lithography apparatus. The lithography apparatus is configured to use radiation to image a pattern onto a plurality of target areas on a photoresist layer on a semiconductor substrate. Imaging requires a predetermined dose of radiation. The control software comprises: a first instruction configured to receive data representing a magnitude of a predetermined dose; and a second instruction configured to set a power level of the radiation according to the magnitude of the predetermined dose.

[0022] In an embodiment of the control software, the total length of time for imaging on the plurality of target areas comprises: a first length of time for imaging on the plurality of target areas during a first pass of the semiconductor substrate; and a second length of time for imaging on one or more specific target areas of the plurality of target areas during a second pass of the semiconductor substrate, the one or more specific target areas failing to receive a predetermined dose during the first pass. The control software comprises a third instruction configured to set a power level of the radiation to keep the total length of time substantially at or near a minimum value.

[0023] In an embodiment, the control software includes: a fourth instruction configured to: during a first pass process, for each corresponding target area in one or more specific target areas, record information representing a corresponding location at the semiconductor substrate and a corresponding difference between a predetermined dose and an actually received dose; and a fifth instruction configured to control imaging on one or more specific target areas among the multiple target areas under the control of the recorded information during a second pass process.

[0024] Another embodiment includes sixth instructions configured to estimate in advance the number of specific target areas according to the power level and according to the magnitude of the required dose. The sixth instructions include seventh instructions for accessing a mathematical model (e.g., an algorithm or a lookup table) configured to generate the number.

[0025] Typical doses (e.g., 40 mJ / cm 2 ) is that compared to 20 mJ / cm 2 The EUV radiation source can be operated at a power level of about 5% higher - with a re-exposure of at most 0.5%. This results in a power level of 40 mJ / cm 2 The substrate throughput per hour increased by about 3.5% under the dose. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:

[0027] - Figure 1 schematically depicts a lithography system including a lithography apparatus and a radiation source;

[0028] - Figure 2 is a diagram illustrating the total time required to expose a substrate including die repair as a function of source power at a given dose; and

[0029] - Figure 3 is a graph illustrating the estimated number of die repairs per substrate as a function of source power for two dose levels. DETAILED DESCRIPTION

[0030] Figure 1 A lithographic system is shown comprising a radiation source SO and a lithographic apparatus LA. The radiation source SO is configured to generate an EUV radiation beam B and to supply the EUV radiation beam B to the lithographic apparatus LA. The lithographic apparatus LA comprises an illumination system IL, a support structure MT configured to support a patterning device MA (e.g. a mask), a projection system PS, and a substrate table WT configured to support a substrate W.

[0031] The illumination system IL is configured to condition the EUV radiation beam B before it is incident on the patterning device MA. In addition, the illumination system IL may include a faceted field mirror arrangement 10 and a faceted pupil mirror arrangement 11. The faceted field mirror arrangement 10 and the faceted pupil mirror arrangement 11 together provide a desired cross-sectional shape and a desired intensity distribution for the EUV radiation beam B. In addition to or instead of the faceted field mirror arrangement 10 and the faceted pupil mirror arrangement 11, the illumination system IL may also include other mirrors or arrangements.

[0032] After being so conditioned, the EUV radiation beam B interacts with the patterning device MA. As a result of this interaction, a patterned EUV radiation beam B' is generated. The projection system PS is configured to project the patterned EUV radiation beam B' onto a substrate W. For this purpose, the projection system PS may include a plurality of mirrors 13, 14 configured to project the patterned EUV radiation beam B' onto a substrate W held by a substrate table WT. The projection system PS may apply a reduction factor to the patterned EUV radiation beam B', thereby forming an image having features that are smaller than corresponding features on the patterning device MA. For example, a reduction factor of 4 or 8 may be applied. Although the projection system PS is Figure 1 1. Although illustrated in FIG. 1 as having only two mirrors 13, 14, the projection system PS may comprise a different number of mirrors (eg six or eight mirrors).

[0033] The substrate W may include a previously formed pattern. In this case, the lithographic apparatus LA aligns an image formed by the patterned EUV radiation beam B′ with a pattern previously formed on the substrate W.

[0034] A relative vacuum, ie a small amount of gas (eg hydrogen) at a pressure well below atmospheric pressure, may be provided in the radiation source SO, in the illumination system IL and / or in the projection system PS.

[0035] Figure 1 The radiation source SO shown in FIG. 1 is of a type that may be referred to as a laser produced plasma (LPP) source, for example. A laser system 1 (the laser system 1 may, for example, include a CO2 laser) is configured to deposit energy via a laser beam 2 into a mass-limited target (e.g., droplets) of a fuel such as tin (Sn), which is provided from, for example, a fuel emitter 3. Although tin is mentioned in the following description, any suitable fuel may be used. The fuel may, for example, be in liquid form and may be, for example, a metal or an alloy. The fuel emitter 3 may include a nozzle configured to direct tin, for example, in the form of droplets, along a trajectory toward a plasma formation region 4. The laser beam 2 is incident on the tin at the plasma formation region 4. The deposition of laser energy into the tin generates a tin plasma 7 at the plasma formation region 4. During de-excitation and recombination of electrons with ions of the plasma, radiation including EUV radiation is emitted from the plasma 7.

[0036] EUV radiation from the plasma is collected and focused by a collector 5. The collector 5 includes, for example, a near normal incidence radiation collector 5 (sometimes more generally referred to as a normal incidence radiation collector). The collector 5 may have a multilayer mirror structure configured to reflect EUV radiation (e.g., EUV radiation having a desired wavelength such as 13.5 nm). The collector 5 may have an elliptical configuration having two focal points. A first of the focal points may be at the plasma formation region 4, and a second of the focal points may be at the intermediate focus 6, as discussed below.

[0037] The laser system 1 may be spatially separated from the radiation source SO. In this case, the laser beam 2 may be delivered from the laser system 1 to the radiation source SO by means of a beam delivery system (not shown) comprising, for example, suitable guide mirrors and / or beam expanders and / or other optical devices. The laser system 1, the radiation source SO and the beam delivery system may be considered together as a radiation system.

[0038] The radiation reflected by the collector 5 forms an EUV radiation beam B. The EUV radiation beam B is focused at an intermediate focus 6 to form an image at the intermediate focus 6 of a plasma present at the plasma formation region 4. The image at the intermediate focus 6 serves as a virtual radiation source for the illumination system IL. The radiation source SO is configured such that the intermediate focus 6 is located at or near an opening 8 in an enclosure 9 of the radiation source SO.

[0039] although Figure 1 The radiation source SO is depicted as a laser produced plasma (LPP) source, but any suitable source such as a discharge produced plasma (DPP) source or a free electron laser (FEL) may be used to produce EUV radiation.

[0040] As mentioned above, mass-limited fuel targets ("droplets") are converted into plasma one by one. This process can be carried out at a frequency of, for example, 50kHz or 100kHz. Therefore, the EUV radiation beam B consists of a time sequence of discrete EUV pulses. Now consider the lithography apparatus LA being used in the so-called scanning mode. In the scanning mode, the mask MA and the substrate W are scanned synchronously, and the pattern imparted to the radiation beam B is projected onto the target area of ​​the substrate W. The speed and direction of the substrate W relative to the mask MA can be determined by the (reduction rate) magnification and image reversal characteristics of the projection system PS. The total amount of radiation energy per unit surface area delivered by the lithography apparatus LA to the surface of the substrate W is called the "dose". The desired dose will achieve a change or curing of the photoresist layer on the surface of the substrate W. The desired dose may vary depending on the sensitivity of the photoresist. For example, in the case of a highly sensitive photoresist, a relatively small dose (e.g., 20mJ / cm 2) in order to image the pattern onto the substrate W. However, in the case of less sensitive photoresists, a larger dose (e.g., 70 mJ / cm 2 ).

[0041] If the target area on the substrate W receives a dose different from the expected dose, this is called a dose error. Specifically, the dose error is the difference between the actual dose received by the target area and the expected dose. The dose error can be "positive" (i.e., when the target area receives a dose greater than the expected dose) or "negative" (i.e., when the target area receives a dose smaller than the expected dose). Any dose error will result in some printing errors in the photoresist. Negative dose errors can be corrected by providing additional doses to compensate for the aforementioned difference. However, it may be impossible to correct positive dose errors caused by having given too much dose (e.g., causing overexposure), and therefore, changes in the photoresist are generally irreversible. This may result in irreparable damage to the substrate W.

[0042] It will be appreciated that, depending on manufacturing tolerances, a certain level of positive dose error may be considered acceptable. For example, based on requirements, a positive dose error of at most 1% (specifically at most 0.5%) may be considered acceptable. "Excess dose" as referred to herein means a dose that falls outside an acceptable tolerance level.

[0043] As previously mentioned, the radiation beam transfers the energy of the EUV radiation in the pulses to the target area being exposed while the target area is being scanned. That is, the energy received per unit surface area of ​​the target area (i.e., the dose) is equal to the sum of the energies of the individual pulses incident on the unit surface area being scanned. The number of pulses delivered to the target area on the substrate W will depend, among other things, on the operating power of the radiation source SO and the scanning speed. With regard to the role of the scanning speed, it should be noted here that the EUV radiation reaches the substrate W via a slit under which the substrate is traveling. The substrate W accommodates a plurality of target areas, each having a length "1" and a width "w". During exposure of a target area (or: a "die"), the substrate W is traveling at a relative speed "v" in a direction parallel to the length "l" of the target area. The time T taken to expose the target area scan If the radiation source SO delivers energy at a rate of N pulses / second, then the area l·w receives energy equal to N·T scan=N·(1 / v) multiple pulses. If each pulse has a constant energy E, the energy received by the area l·w will be N·(l / v)·E. Since the parameter "dose" is defined as the energy received per unit area, the delivered dose will be N·(l / v)·E / (w·1)=N·E / (v·w). Therefore, the dose can be adjusted by controlling at least one of the pulse rate, the energy per pulse and the scanning speed. A given dose level is determined by the ratio E / v. In order to maximize the scanning speed, and therefore maximize the throughput of the lithographic equipment for a given dose level, one needs to maximize the energy per pulse to keep the ratio constant.

[0044] In practice, the energy of the EUV pulses may vary from pulse to pulse. This may be due to changes in the size or velocity of the fuel droplets, changes in the timing of the laser pulses, and the like. Therefore, the energy of each EUV pulse is tracked. To this end, one or more EUV sensors may be housed in the enclosure structure 9, and one or more EUV sensors are configured to sense the EUV generated by each pulse. For more background information, see, for example, U.S. Patent No. 9,360,600 to Pate et al., which is assigned to ASML and incorporated herein by reference. The radiation source SO operates with a so-called dose tolerance that controllably sets the energy level of the EUV generated averaged over a specific length of time (also referred to as: controlled energy or power) below the maximum output power of the source (also referred to as: open-loop energy). The non-zero dose tolerance can compensate for a brief drop in EUV energy, for example, by adjusting the duration of one or more pulses or by adjusting the energy of one or more laser pulses acting on one or more fuel droplets in subsequent fuel droplets. For more information on dose control, see, for example, U.S. Patent 9,693,440, issued to Ershov and assigned to ASML, and U.S. Patent 8,872,122, issued to Schafgans et al. and assigned to ASML, both of which are incorporated herein by reference. See also U.S. Patent Application Publication 20180253014, filed by Everts et al., which is assigned to ASML and incorporated herein by reference. See further, for example, U.S. Patent 8,653,437 and U.S. Patent 9,390,827, both of which are issued to Partlo et al., assigned to ASML subsidiary Cymer and incorporated herein by reference.

[0045] In the event that too many consecutive EUV pulses deliver too low energy to the target area of ​​the substrate being exposed, the final dose delivered to the target area may be too low. This dose drop is recorded along with the associated target area. This information is then used to expose such areas during a second pass of the substrate in order to correct the dose in those areas.

[0046] For a given operating power, a more sensitive photoresist may receive fewer pulses than a less sensitive photoresist in order to obtain the desired dose to image the pattern onto the substrate W. In practice, the output of the pulsed radiation source SO will vary over time. This will contribute to dose errors if the energy of individual pulses is higher or lower than the nominal or expected output energy of each pulse. The fewer pulses received by the target area, the greater the impact of such errors in individual pulse energy on the total dose.

[0047] If the dose tolerance is made smaller, and therefore if the radiation source SO is being operated at closer to maximum power, the time taken to expose a single substrate can be reduced if the scanning speed is increased. However, operating the source SO at closer to maximum power also increases the probability that certain target areas of the substrate W must be re-exposed during a second pass. The reason for this is that there may not always be enough energy available in the limited number of subsequent EUV pulses incident on a target area in order to compensate for the drop in EUV energy delivered to that target area by the preceding EUV pulse. Therefore, the total time T taken to successfully complete the exposure of the substrate W is total is the exposure time T required to expose the substrate W during the first pass expose Plus the re-exposure time T required to re-exposure during the second pass of the substrate W to deliver the missing dose re-expose .

[0048] Given the desired dose, parameter T expose and T re-expose Both depend on the scanning speed v and the dose tolerance (or in other words: on the level of controlled energy as set). Parameter T expose It is proved to be a monotonically decreasing function of the controlled energy, and the parameter T re-expose It is proved to be a nonlinear monotonically increasing function of the controlled energy. Therefore, there is a total time T that varies with the controlled energy total , i.e., for the level of controlled energy for which the derivative [εT expose / εcontrolled engery] and [δT re-expose / δcontrolled engery] is equal to zero. Given a desired dose N·E / (v·w), setting the controlled energy at or near that level will generally minimize the throughput time per substrate W. To do this, one needs to have information about how the number of re-exposures per wafer changes with changes in the controlled energy. This has been determined, for example, by monitoring the output of the radiation source SO for different levels of controlled energy and modeling in order to be able to outline the behavior of the radiation source. Figure 2 and Figure 3 is described in the schematic diagram.

[0049] Figure 2 The schematic diagram shows the curve T expose , curve T expose The time required to expose a substrate W with a given dose is shown as a function of source power in the absence of instabilities. Since the instability of the source power increases with increasing power, the number of die repairs also increases. Curve T re-expose The time required to re-expose the substrate W is shown as a function of the source power. Then, the curve T total It is the sum of the time required for exposure and the time required for re-exposure, which varies with the source power.

[0050] Figure 3 Schematic diagram of the two different dose levels (20 mJ / cm 2 and 70mJ / cm 2 ) illustrates the estimated number of die repairs required per substrate (wafer) as a function of source power.

[0051] Summary: If the scanning speed v is increased, the throughput can be increased. However, for a given dose (i.e. for a given ratio E / v), the average energy E will then also be increased to keep the ratio constant. Increasing the average energy E (i.e. reducing the dose tolerance) leads to more instabilities requiring more die repairs (i.e. requiring a longer second pass of the substrate for re-exposure). The inventors propose to set the energy level E at a reduced total time T total The energy E then determines the scanning speed v by a given magnitude of the desired dose E / v in the range of . During the second pass, the missing dose is supplied to the target area that received an incomplete dose during the first pass. The missing dose can be controlled by changing E, changing v, or changing both. See, for example, U.S. Pat. No. 8,653,437 and U.S. Pat. No. 9,390,827 mentioned above.

[0052] Although the present invention may specifically refer to the use of lithographic equipment in IC manufacturing, it should be understood that the lithographic equipment described herein may have other applications. Possible other applications include manufacturing integrated optical systems, guidance and detection patterns for magnetic domain memory, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, etc.

[0053] Where context permits, embodiments of the present invention may be implemented in hardware, architecture, software, or any combination thereof. Embodiments of the present invention may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by one or more processors. A machine-readable medium may include any mechanism for storing or transmitting information in a form that can be read by a machine (e.g., a computer device). For example, a machine-readable medium may include a read-only memory (ROM); a random access memory (RAM); a magnetic storage medium; an optical storage medium; a flash memory device; an electrical, optical, acoustic, or other form of propagation signal (e.g., a carrier wave, an infrared signal, a digital signal, etc.); and other media. In addition, architectures, software, processes, instructions may be described in the present invention as performing certain actions. However, it will be understood that such descriptions are merely for convenience, and such actions are in fact caused by a computer device, processor, controller, or other device that executes the architecture, software, process, instructions, etc., and in doing so may cause an actuator or other device to interact with the physical world.

[0054] Although specific embodiments of the present invention have been described above, it will be appreciated that the present invention may be practiced in other ways than those described. The above description is intended to be illustrative, not restrictive. Therefore, it will be apparent to those skilled in the art that the present invention as described may be modified without departing from the scope of the claims set forth below.

Claims

1. A method of controlling a lithography system comprising a radiation source and a lithography apparatus, wherein: The radiation source is configured to provide radiation to the lithographic apparatus; The lithographic apparatus is configured to image a pattern onto a plurality of target areas on a photoresist layer on a semiconductor substrate using the radiation; The imaging requires a predetermined dose of radiation; The method comprises: setting a power level of the radiation according to a magnitude of the predetermined dose; and Wherein, the total time length for performing the imaging on the plurality of target areas includes: a first length of time for performing said imaging on said plurality of target areas during a first pass of said semiconductor substrate; and a second length of time for performing said imaging on one or more specific target areas of said plurality of target areas during a second pass of said semiconductor substrate, said one or more specific target areas failing to receive said predetermined dose during said first pass; and The method comprises setting the power level of the radiation so that the total time length is kept substantially at or close to a minimum value.

2. The method of claim 1, comprising: During the first pass, recording, for each respective one of the one or more specific target areas, information representing a respective location at the semiconductor substrate and a respective difference between the predetermined dose and an actually received dose; During the second pass, imaging is performed on the one or more specific target areas of the plurality of target areas under control of the recorded information.

3. The method according to claim 1 or 2, comprising: Depending on the power level and depending on the magnitude of the required dose, the number of specific target areas is estimated in advance.

4. The method according to claim 1 or 2, wherein: The radiation source is operable to supply EUV radiation and is of the laser produced plasma type.

5. A lithography system comprising a radiation source and a lithography apparatus, wherein: The radiation source is configured to provide radiation to the lithographic apparatus; The lithographic apparatus is configured to image a pattern onto a plurality of target areas on a photoresist layer on a semiconductor substrate using the radiation; The imaging requires a predetermined dose of radiation; The lithography system is configured to set a power level of the radiation according to a magnitude of the predetermined dose; and Wherein, the total time length for performing the imaging on the plurality of target areas includes: a first length of time for performing said imaging on said plurality of target areas during a first pass of said semiconductor substrate; and a second length of time for performing said imaging on one or more specific target areas of said plurality of target areas during a second pass of said semiconductor substrate, said one or more specific target areas failing to receive said predetermined dose during said first pass; and The lithography system is configured to set a power level of the radiation so that the total time length is kept substantially at or close to a minimum value.

6. The lithography system of claim 5, wherein the lithography system is configured to: During the first pass, recording, for each respective one of the one or more specific target areas, information representing a respective location at the semiconductor substrate and a respective difference between the predetermined dose and an actually received dose; and During the second pass, imaging is performed on the one or more specific target areas of the plurality of target areas under control of the recorded information.

7. The lithography system of claim 5 or 6, wherein the lithography system is configured to estimate in advance the number of the specific target areas according to the power level and according to the magnitude of the required dose.

8. The lithography system according to claim 5 or 6, wherein: The radiation source is operable to supply EUV radiation and is of the laser produced plasma type.

9. A computer program product configured for use in a lithography system comprising a radiation source and a lithography apparatus, wherein: The radiation source is configured to provide radiation to the lithographic apparatus; The lithographic apparatus is configured to image a pattern onto a plurality of target areas on a photoresist layer on a semiconductor substrate using the radiation; The imaging requires a predetermined dose of radiation; as well as The computer program product comprises: first instructions configured to receive data representing a magnitude of the predetermined dose; and second instructions configured to set a power level of the radiation according to a magnitude of the predetermined dose; and Wherein, the total time length for performing the imaging on the plurality of target areas includes: a first length of time for performing said imaging on said plurality of target areas during a first pass of said semiconductor substrate; and a second length of time for performing said imaging on one or more specific target areas of said plurality of target areas during a second pass of said semiconductor substrate, said one or more specific target areas failing to receive said predetermined dose during said first pass; and Wherein, the computer program product comprises: The third instructions are configured to set a power level of the radiation so that the total time length is maintained substantially at or close to a minimum value.

10. The computer program product of claim 9, comprising: fourth instructions configured to: record, for each respective one of the one or more specific target areas, information representing a respective location at the semiconductor substrate and a respective difference between the predetermined dose and an actually received dose during the first pass; as well as Fifth instructions are configured to control the imaging performed on one or more specific target areas of the plurality of target areas under control of the recorded information during the second pass.

11. The computer program product of claim 9 or 10, comprising sixth instructions configured to estimate in advance the number of the specific target areas according to the power level and according to the magnitude of the required dose.

12. The computer program product of claim 11, wherein: The sixth instructions include a seventh instruction for accessing a mathematical model configured to generate the number.

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