Method for controlling a lithography system

Abstract

To provide a method for controlling a lithographic system.SOLUTION: A lithographic system comprises a radiation source and a lithographic apparatus. The radiation source provides radiation to the lithographic apparatus. The lithographic apparatus uses the radiation for imaging a pattern on multiple target areas on a photoresist layer on a semiconductor substrate. The imaging requires a predetermined dose of radiation. The system is controlled to set a level of the power of the radiation in accordance with the magnitude of the predetermined dose.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS)

[0001] This application claims priority from EP Application No. 19164206.5, filed March 21, 2019, which is incorporated herein by reference in its entirety.

[0002]

[0002] The present invention relates to a method for controlling a lithography system, and also to a lithography system and control software configured for use with the lithography system. [Background technology]

[0003] A lithographic apparatus is a machine constructed to apply a desired pattern onto a substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus can, for example, project a pattern in a patterning device (e.g. a mask) onto a layer of radiation-sensitive material (resist) provided on the substrate.

[0004]

[0004] To project a pattern onto a substrate, a lithographic apparatus may use electromagnetic radiation. The wavelength of this radiation determines the minimum size of features that can be formed on the substrate. Lithographic apparatus using extreme ultraviolet (EUV) radiation having a wavelength in the range of 4-20 nm, e.g., 6.7 nm or 13.5 nm, can be used to form smaller features on a substrate than lithographic apparatus using radiation having a wavelength of, e.g., 193 nm.

[0005]

[0005] An EUV lithography system includes a radiation source configured to generate EUV radiation and a lithography apparatus configured to receive the EUV radiation from the lithography source and 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 mass-limited fuel targets into plasma one by one. This plasma generates the EUV radiation. The EUV radiation is thus provided in a pulse sequence, e.g., at a rate of 50 kHz or 100 kHz. The lithography apparatus is, for example, a scanner, which can irradiate each target area on the substrate by scanning a pattern imaged by a radiation beam in a given direction while simultaneously scanning the substrate parallel or anti-parallel to this direction. In general, to increase the throughput (i.e., number of substrates per hour) of the lithography apparatus, it is desirable to minimize the time required to image a pattern onto a substrate.

[0006]

[0006] The amount of radiant energy delivered to a unit surface area of ​​the substrate is called a dose. A typical dose size is, for example, 20 mJ / cm 2 ~70mJ / cm 2 It is desirable to precisely control the radiation dose delivered to the substrate. Summary of the Invention

[0007] According to a first aspect of the present invention, there is provided a method of controlling a lithography system comprising a radiation source and a lithography apparatus. The radiation source is configured to provide radiation to the lithography apparatus. The radiation source may, for example, be of the type known as an LPP source. The lithography apparatus is configured to use the radiation to image a pattern onto a plurality of target areas of a photoresist layer on a semiconductor substrate. A predetermined radiation dose is required for the imaging. The method includes setting a level of power of the radiation according to a magnitude of the predetermined dose.

[0008]

[0008] To date, in the operation of lithography systems, a fixed time-averaged energy level is used in the radiation source. This energy level is selected to be appropriate for all possible photoresists. In other words, the average energy level is selected to be appropriate for even the most sensitive photoresists. The inventors have recognized that, in practice, as a result, the selected energy level is lower than necessary 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 to maximize throughput. The method of the present invention is advantageous because, by controlling the operating power of the radiation source according to the required dose, the throughput of the lithography system, i.e., the number of substrates processed per unit time, can be optimized. As will be explained in more detail below, the dose is proportional to the ratio of the (time-averaged) energy per pulse from the radiation source to the scanning speed of the scanner. The scanner throughput (the time it takes the scanner to handle one substrate) increases with increasing scanning speed. To maintain a dose equal to the required magnitude, the energy per pulse must also increase. However, increasing the energy can lead to instabilities in the energy generated by the radiation source, resulting in the radiation source delivering insufficient energy to the scanned area. Such target areas may require re-exposure in a second pass of the scanner through the substrate because the scanner's first pass through the substrate did not deliver the required amount of energy. Such a second pass is also known as a "die repair." Therefore, the greater the source's energy per unit time (i.e., the greater the power), the greater the number of instabilities, which generally leads to the need for a second pass with more die repairs. Therefore, by setting the source power according to the required dose, an optimum can be found between a high scan speed for exposure and the number of die repairs required as a result of the set power level, maximizing the scanner's throughput.

[0009] In one embodiment of the method of the present invention, the total time length for imaging the plurality of target areas includes a first time length for imaging the plurality of target areas in a first pass of the semiconductor substrate and a second time length for imaging one or more specific target areas of the plurality of target areas in a second pass of the semiconductor substrate. The one or more specific target areas are those that did not receive a predetermined dose in the first pass. The method includes setting a level of power of the radiation to keep the total time length substantially at or near a minimum. During the first pass of the substrate, the actual radiation dose received by one or more target areas of the substrate may be less than the desired dose. This can be compensated for by a subsequent second exposure pass (i.e., a so-called die repair or re-exposure pass). The total throughput of a lithography system depends on the time required for the first exposure plus the time required for the subsequent second exposure (i.e., for die repair). The inventors have recognized that by controlling the operating power of the radiation source according to the required dose, the total time required to fully expose a substrate can be minimized.

[0010]

[0010] In one embodiment, the method further includes, during the first pass, recording information representing each position on the substrate and the difference between the predetermined dose and the actually received dose for each of one or more specific target areas, and, during the second pass, performing imaging at one or more specific target areas of the plurality of target areas under control of the recorded information.

[0011] During imaging, the amount of energy received per target area is recorded by an appropriate sensor, and the identity of one or more specific target areas is also recorded. As is known in the art, the identity of the target areas is derived from a so-called wafer grid. The wafer grid determines the coordinates of the positions of the target areas on the substrate in the exposure plane. The wafer grid is determined by alignment marks embedded in the substrate. Proper alignment of the substrate with respect to the projection optics is performed by an alignment system. For example, a number of alignment marks on the substrate are measured to derive a coordinate system, which is compared to a modeled grid to derive the positions of features on the substrate. However, substrate distortion can occur due to clamping the substrate to the substrate table or wafer distortion caused by non-lithographic process steps. This can be monitored by comparing the measurements to the grid. A model describing the wafer grid can be generated and used when exposing a substrate to compensate for the distortion. See, for example, U.S. Patent No. 9,310,698 issued to Menchtchikov et al. and assigned to ASML, Inc., incorporated herein by reference.

[0012]

[0012] It will be appreciated that when 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 the true minimum (e.g., within 10%, preferably within 2%, and particularly preferably within 1% of it).

[0013]

[0013] If the desired dose is large, the set energy level can be increased substantially, allowing the nominal operating power of the radiation source to be closer to the maximum power than if a smaller dose is desired (which may also have a substantially lower set energy level). As noted above, in an EUV LPP source, the dose can be delivered by a series of pulses. If a larger total dose is desired, more pulses can be delivered to the target area on the substrate than if a smaller dose is desired. The number of pulses delivered to the target area can be used to determine the energy level. For example, a look-up table or another mathematical model can be used to convert the number of pulses to a particular energy level.

[0014] Another embodiment of the method of the present invention includes estimating in advance the number of specific target areas depending on the level of power and the magnitude of the dose required. This can be done by a mathematical model, for example a look-up table or algorithm that predicts or otherwise determines or estimates the number of target areas that will require re-exposure of a second pass for a given dose depending on the set source power. Such a model or look-up table can be prepared in advance by monitoring the instability of the power delivered by the source for various set control energy levels, or can be derived from simulations.

[0015]

[0015] 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, for example of the EUV LPP type. The lithography apparatus is configured to use the radiation to image a pattern onto a plurality of target areas of a photoresist layer on a semiconductor substrate. A predetermined radiation dose is required for the imaging. The system is configured to set a power level of the radiation depending on the magnitude of the predetermined dose.

[0016] In one embodiment of the lithography system, the total length of time for imaging the plurality of target areas includes a first length of time for imaging the plurality of target areas in a first pass of the semiconductor substrate and a second length of time for imaging one or more specific target areas of the plurality of target areas in a second pass of the semiconductor substrate, the one or more specific target areas not receiving a predetermined dose in the first pass. The lithography system is configured to set a level of power of the radiation to keep the total length of time substantially at or near a minimum value.

[0017]

[0017] In another embodiment, the lithography system is configured to record, during a first pass, for each of one or more specific target areas, information representing each position on the semiconductor substrate and the difference between the predetermined dose and the actually received dose, and to control imaging at one or more specific target areas of the plurality of target areas under control of the recorded information during a second pass.

[0018] In another embodiment, the lithography system is configured to estimate in advance the number of specific target areas depending on the power level and the required dose size.

[0019] In another embodiment, the radiation source is operable to provide EUV radiation and is of the laser-produced plasma type.

[0020] The present invention further relates to control software configured for use in a lithography system comprising a radiation source and a lithography apparatus. The control software can be provided on a data carrier or another machine-readable medium. Alternatively, the control software can be provided over a data network, for example for downloading to the lithography system. The radiation source is configured to provide radiation to the lithography apparatus. The lithography apparatus is configured to use the radiation to image a pattern onto a plurality of target areas of a photoresist layer on a semiconductor substrate. The imaging requires a predetermined radiation dose. The control software includes first instructions configured to receive data representing a magnitude of the predetermined dose, and second instructions configured to set a level of power of the radiation in response to the predetermined dose magnitude.

[0021] In one embodiment of the control software, the total length of time for imaging the plurality of target areas includes a first length of time for imaging the plurality of target areas in a first pass of the semiconductor substrate and a second length of time for imaging one or more specific target areas of the plurality of target areas in a second pass of the semiconductor substrate, the one or more specific target areas not receiving a predetermined dose in the first pass. The control software includes third instructions configured to set a level of power of the radiation to keep the total length of time substantially at or near a minimum value.

[0022]

[0022] In one embodiment, the control software includes fourth instructions configured to record, during a first pass, for each of one or more specific target areas, information representing each location on the semiconductor substrate and the difference between the predetermined dose and the actual received dose, and fifth instructions configured to control imaging at one or more specific target areas of the plurality of target areas under control of the recorded information during a second pass.

[0023] Another embodiment includes sixth instructions configured to pre-estimate the number of specific target areas depending on the level of power and the required dose size, and the sixth instructions include seventh instructions for accessing a mathematical model, such as an algorithm or a look-up table, configured to generate this number.

[0024] Typical doses (e.g., 40 mJ / cm 2 ) has the advantage that the EUV radiation source is 20mJ / cm 2 This results in a maximum re-exposure of 0.5%. 2 A dose of about 3.5% increases the substrate throughput per hour. [Brief explanation of the drawings]

[0025]

[0025] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which:

[0026] [Figure 1] 1 depicts a schematic representation of a lithography system comprising a lithographic apparatus and a radiation source; [Figure 2] FIG. 10 shows the total time required to expose a substrate, including die repair, as a function of source power for a given dose. [Figure 3] FIG. 10 shows the estimated number of die repairs per substrate as a function of source power for two dose levels. DETAILED DESCRIPTION OF THE INVENTION

[0027] 1 shows a lithography system comprising a radiation source SO and a lithography apparatus LA. The radiation source SO is configured to generate a beam of EUV radiation B and to provide the beam of EUV radiation B to the lithography apparatus LA. The lithography 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.

[0028]

[0027] 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 facetted field mirror device 10 and a facetted pupil mirror device 11. Together the facetted field mirror device 10 and the facetted pupil mirror device 11 provide the EUV radiation beam B with a desired cross-sectional shape and a desired intensity distribution. The illumination system IL may include other mirrors or devices in addition to or instead of the facetted field mirror device 10 and the facetted pupil mirror device 11.

[0029] After being so conditioned, the EUV radiation beam B interacts with the patterning device MA. This interaction results in a patterned EUV radiation beam B'. The projection system PS is configured to project the patterned EUV radiation beam B' onto the substrate W. To this end, the projection system PS may comprise a plurality of mirrors 13, 14, which are configured to project the patterned radiation beam B' onto the substrate W, which is held by a substrate table WT. The projection system PS may apply a demagnification factor to the patterned radiation beam B' to form images of features that are smaller than corresponding features on the patterning device MA. For example, a demagnification factor of 4 or 8 may be applied. Although in Figure 1 the projection system PS is illustrated as having only two mirrors 13, 14, the projection system PS may include a different number of mirrors, for example 6 or 8 mirrors.

[0030]

[0029] The substrate W may include a previously formed pattern. If this is the case, the lithographic apparatus LA aligns the patterned EUV radiation beam B' with the previously formed pattern on the substrate W.

[0031] A relative vacuum, ie a small amount of gas (eg hydrogen) at a pressure well below atmospheric pressure, may be provided in the source SO, the illumination system IL and / or the projection system PS.

[0032] The radiation source SO shown in FIG. 1 is of a type sometimes referred to as a laser-produced plasma (LPP) source. A laser system 1, which may include, for example, a CO2 laser, is arranged to deposit energy via a laser beam 2 onto a mass-limited target (e.g., droplets) of fuel, such as tin (Sn), provided by a fuel emitter 3. While the following description refers to tin, any suitable fuel may be used. The fuel may be, for example, in liquid form or may be, for example, a metal or alloy. The fuel emitter 3 may include a nozzle configured to direct the tin, for example, in droplet form, along a trajectory towards a plasma formation region 4. The laser beam 2 is incident on the tin in the plasma formation region 4. Deposition of the laser energy onto the tin generates a tin plasma 7 in the plasma formation region 4. Radiation, including EUV radiation, is emitted from the plasma 7 during de-excitation and recombination of electrons with the plasma ions.

[0033]

[0032] The EUV radiation from the plasma is collected and focused by a collector 5. The collector 5 may include, for example, a near-normal incidence radiation collector 5 (sometimes more commonly referred to as a normal incidence radiation collector). The collector 5 may have a multi-layer mirror structure arranged 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 with two foci. A first of the foci may be at the plasma formation region 4 and a second of the foci may be at an intermediate focus 6, as discussed below.

[0034]

[0033] The laser system 1 may be spatially separated from the radiation source SO. If this is the case, the laser beam 2 may be passed from the laser system 1 to the radiation source SO by a beam delivery system (not shown), which may include, for example, appropriate directing mirrors and / or beam expanders and / or other optics. The laser system 1, the radiation source SO and the beam delivery system together may be considered as a radiation system.

[0035]

[0034] 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 the plasma present in the plasma formation region 4. The image of the intermediate focus 6 acts as a virtual radiation source for the illumination system IL. The radiation source SO is arranged such that the intermediate focus 6 is located at or near an opening 8 of a closing structure 9 of the radiation source SO.

[0036]

[0035] Although Figure 1 illustrates the radiation source SO as a laser-produced plasma (LPP) source, any suitable radiation source may be used to generate EUV radiation, such as a discharge-produced plasma (DPP) source or a free electron laser (FEL).

[0037] As mentioned above, the mass-limited fuel targets ("droplets") are converted into plasma one after the other. This process can be carried out at a frequency of, for example, 50 kHz or 100 kHz. The EUV radiation beam B therefore consists of a time-sequence of discrete EUV pulses. Consider now a lithographic apparatus LA used in a so-called scan mode. In scan mode, the mask MA and substrate W are scanned synchronously while a pattern imparted to the radiation beam B is projected onto a target area of ​​the substrate W. The velocity and direction of the substrate W relative to the mask MA can be determined by the (de-)magnification and image reversal characteristics of the projection system PS. The total amount of radiant energy delivered by the lithographic apparatus LA to a unit surface area on the surface of the substrate W is called the "dose". The desired dose is to achieve a modification or hardening 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, a highly sensitive photoresist may require a relatively small dose (e.g. 20 mJ / cm ) to image a pattern onto the substrate W. 2 However, for less sensitive photoresists, a higher dose (e.g., 70 mJ / cm 2 ) may be desirable.

[0038]

[0037] When a target area of ​​the substrate W receives a dose different from the desired dose, this is called a dose error. Specifically, a dose error is the difference between the actual dose received by the target area and the desired dose. A dose error can be "positive" (i.e., when the target area receives a dose greater than the desired dose) or "negative" (i.e., when the target area receives a dose less than the desired dose). Any dose error will cause some printing error in the photosensitive resist. A negative dose error can be corrected by applying an additional dose to compensate for a previous deficiency. However, a positive dose error may not be correctable because an excessive dose (e.g., causing overexposure) has already been applied and the changes in the photoresist are generally irreversible. This may result in irreversible damage to the substrate W.

[0039] It will be appreciated that, depending on manufacturing tolerances, a certain level of positive dose error can be considered acceptable. For example, depending on the requirements, a positive dose error of up to 1%, in particular up to 0.5%, can be considered acceptable. As referred to in this specification, excessive dose means a dose that is outside the acceptable tolerance level.

[0040] As mentioned above, during scanning of the target area to be exposed, the radiation beam delivers pulses of EUV radiation energy to the target area. That is, the energy or dose received by a unit surface area of ​​the target area is equal to the sum of the energies of each pulse incident on the unit surface area being scanned. The number of pulses delivered to the target area of ​​the substrate W depends, among other things, on the operating power of the radiation source SO and the scan speed. With regard to the role of the scan speed, it is noted that the EUV radiation reaches the substrate W through a slit, beneath which the substrate is moved. The substrate W comprises a number of target areas, each having a length "l" and a width "w". During exposure of a target area (or "die"), the substrate W is moving with a relative velocity "v" in a direction parallel to the length "l" of the target area. The time Tscan required to expose a target area is equal to l / v. If the radiation source SO delivers energy at a rate of N pulses per second, the number of pulses received by the area l·w is equal to N·Tscan=N·(l / v). If each pulse has a constant energy E, then the energy received by an area l·w is N·(l / v)·E. The parameter "dose" is defined as the energy received per unit area, so the delivered dose is N·(l / v)·E / (w·l)=N·E / (v·w). Dose can therefore be adjusted by controlling at least one of the pulse rate, energy per pulse, and scan speed. A given dose level is given by the ratio E / v. To maximize the scan speed, and therefore the throughput of the lithography system for a given dose level, it is necessary to maximize the energy per pulse so that the ratio remains constant.

[0041] In practice, the energy of an EUV pulse may vary from pulse to pulse. This may be due to variations in fuel droplet size or velocity, variations in laser pulse timing, etc. Therefore, the energy of each EUV pulse is tracked. For this purpose, one or more EUV sensors configured to detect the EUV generated per pulse may be housed within the enclosure 9. For further background, see, for example, U.S. Pat. No. 9,360,600 issued to Pate et al., assigned to ASML, and incorporated herein by reference. In the operation of the radiation source SO, a so-called dose margin controllably sets the EUV energy level averaged over a certain length of time (also referred to as controlled energy or power) below the maximum output power of the radiation source (also referred to as open-loop energy). A non-zero dose margin makes it possible to compensate for temporary drops in EUV energy, for example by adjusting one or more pulse lengths or by adjusting the energy of one or more laser pulses that ignite one or more of the following fuel droplets. For further information on dose control, see, e.g., U.S. Pat. No. 9,693,440 issued to Ershov and assigned to ASML, Inc., and U.S. Pat. No. 8,872,122 issued to Schafgans et al. and assigned to ASML, Inc., both of which are incorporated herein by reference. See also U.S. Patent Application Publication No. 20180253014 issued to Everts et al. and assigned to ASML, Inc., which are incorporated herein by reference. See also U.S. Pat. Nos. 8,653,437 and 9,390,827 issued to Partlo et al. and assigned to Cymer, Inc., a subsidiary of ASML, which are incorporated herein by reference.

[0042]

[0041] If an excessive number of consecutive EUV pulses deliver too low an energy to an exposure target area of ​​the substrate, the final dose delivered to the target area may be too small. Such dose reductions and their associated target areas are recorded. This information is then used to expose such areas in a second pass of the substrate to correct the dose in those areas.

[0043]

[0042] For a given operating power, a more sensitive photoresist may receive fewer pulses to achieve the desired dose to image the pattern onto the substrate W than a less sensitive photoresist. In practice, the output of the pulsed radiation source SO varies over time. If the energy of individual pulses is higher or lower than the nominal or desired output energy of each pulse, this will contribute to a dose error. The fewer pulses a target area receives, the greater the effect such individual pulse energy error has on the total dose.

[0044]

[0043] When the dose margin is reduced and therefore the radiation source SO is operating closer to maximum power, increasing the scan speed can reduce the time to expose a single substrate. However, operating the radiation source SO closer to maximum power also increases the likelihood that a particular target area of ​​the substrate W will have to be re-exposed in a second pass. This is because if the EUV energy delivered to the target area by a previous EUV pulse is reduced, there may not always be enough energy available in the limited number of EUV pulses that subsequently impinge on that target area to compensate for the EUV energy reduction. Therefore, the total time Ttotal required to successfully complete exposure of a substrate W is the exposure time Texpose required to expose the substrate W in the first pass plus the re-exposure time Tre-expose required to perform a re-exposure in the second pass of the substrate W to deliver one or more missing doses.

[0045] For a given required dose, both parameters T expose and T re-expose depend on the scan speed v and the dose margin (in other words, on the level of control energy that is set). It has been found that the parameter T expose is a monotonically decreasing function of the control energy, while the parameter T re-expose is a non-linear monotonically increasing function of the control energy. Thus, there exists a minimum magnitude of the total time T total as a function of the control energy, i.e., for a level of control energy at which the sum of the derivatives [δ T expose / δ control energy] and [δ T re-expose / δ control energy] equals zero. For a given required dose N·E / (v·w), setting the control energy at or near that level generally minimizes the throughput time per substrate W. For this reason, it is necessary to have information on how the number of re-exposures per wafer varies with the control energy. This can be determined and modeled, for example, by monitoring the output of the radiation source SO for different levels of control energy, so as to obtain a profile of the radiation source's behavior. The above is illustrated in the diagrams of FIGS.

[0046] The diagram in Figure 2 shows the curve Texpose, which indicates the time required to expose a substrate W for a given dose in the absence of instabilities, as a function of radiation power. As the instability of the radiation source power increases with increasing power, the number of die repairs also increases. The curve Tre-expose shows the time required to re-expose a substrate W as a function of radiation source power. The curve Ttotal shows the sum of the time required for exposure and the time required for re-exposure as a function of radiation source power.

[0047] The diagram in FIG. 3 shows two different dose levels, namely 20 mJ / cm 2 and 70 mJ / cm 2 1 shows the estimated number of die repairs required per substrate (wafer) as a function of source power for .

[0048] In summary, increasing the scan speed v can increase throughput. However, for a given dose, i.e., a given ratio of E / v, the average energy E must also be increased to keep this ratio constant. Increasing the average energy E, i.e., reducing the dose margin, causes increased instability, which increases the required die repair, i.e., the required second pass of the substrate for re-exposure becomes longer. The inventors propose setting the energy level E within a range where the total time Ttotal is short. This energy E determines the scan speed v for a given magnitude of the required dose E / v. In the second pass, the missing dose is delivered to target areas that received an incomplete dose in the first pass. The missing dose can be controlled by changing E, changing v, or both. See, for example, the above-mentioned U.S. Patent No. 8,653,437 and U.S. Patent No. 9,390,827.

[0049]

[0048] Although specific reference may be made in this text to the use of lithographic apparatus in the manufacture of ICs, it will be appreciated that the lithographic apparatus described herein have other applications, such as in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, etc.

[0050] Where the context permits, embodiments of the present invention may be implemented in hardware, firmware, 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 readable by a machine (e.g., a computing device). For example, machine-readable media may include read-only memory (ROM), random-access memory (RAM), magnetic storage media, optical storage media, flash memory devices, electrical, optical, acoustic, or other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.), and others. Furthermore, firmware, software, routines, and instructions may be described herein as performing certain actions. However, it should be understood that such description is merely for convenience and that such actions actually result from computing devices, processors, controllers, or other devices executing the firmware, software, routines, instructions, etc., and that, in performing these actions, actuators or other devices may interact with the physical world.

[0051]

[0050] While specific embodiments of the present invention have been described above, it will be understood that the invention may be practiced otherwise than as described. The foregoing description is illustrative and not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set forth below.

Claims

1. 1. A method of controlling a lithography system comprising a radiation source and a lithographic apparatus, the method comprising: the radiation source is configured to provide radiation to the lithographic apparatus; the lithographic apparatus is configured to use the radiation to image a pattern onto a plurality of target areas in a photoresist layer on a semiconductor substrate; said imaging requires a predetermined radiation dose; the method includes setting a power level of the radiation in response to the predetermined dose size; The total length of time for the imaging at the plurality of target areas is: a first length of time for the imaging at the plurality of target areas in a first pass of the semiconductor substrate; a second length of time for the imaging of one or more specific target areas of the plurality of target areas in a second pass of the semiconductor substrate, the one or more specific target areas not receiving the predetermined dose in the first pass; setting the level of the power of the radiation of the radiation source in the first pass and the second pass to keep the total time length substantially at or near a minimum value.

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

3. 3. The method of claim 1, wherein the radiation source is operable to provide EUV radiation and is of the laser-produced plasma type.

4. 1. A lithography system comprising a radiation source and a lithographic apparatus, the radiation source is configured to provide radiation to the lithographic apparatus; the lithographic apparatus is configured to use the radiation to image a pattern onto a plurality of target areas in a photoresist layer on a semiconductor substrate; said imaging requires a predetermined radiation dose; the system is configured to set a power level of the radiation in response to the predetermined dose; The total length of time for the imaging at the plurality of target areas is: a first length of time for the imaging at the plurality of target areas in a first pass of the semiconductor substrate; a second length of time for the imaging of one or more specific target areas of the plurality of target areas in a second pass of the semiconductor substrate, the one or more specific target areas not receiving the predetermined dose in the first pass; a lithography system configured to set the level of the power of the radiation of the radiation source in the first pass and the second pass so as to keep the total time length substantially at or near a minimum value.

5. During the first pass, for each of the one or more specific target areas, recording information representative of each location on the semiconductor substrate and the difference between the predetermined dose and the actual dose received; during the second pass, imaging at the one or more specific target areas of the plurality of target areas under control of the recorded information; The lithography system of claim 4 , configured as follows:

6. 6. A lithography system according to claim 4 or 5, wherein the radiation source is operable to provide EUV radiation and is of the laser-produced plasma type.

7. 1. Control software configured for use in a lithography system comprising a radiation source and a lithographic apparatus, the control software comprising: the radiation source is configured to provide radiation to the lithographic apparatus; the lithographic apparatus is configured to use the radiation to image a pattern onto a plurality of target areas in a photoresist layer on a semiconductor substrate; said imaging requires a predetermined radiation dose; The control software first instructions configured to receive data representing a magnitude of the predetermined dose; and second instructions configured to set a level of power of the radiation in response to the magnitude of the predetermined dose; The total length of time for the imaging at the plurality of target areas is: a first length of time for the imaging at the plurality of target areas in a first pass of the semiconductor substrate; a second length of time for the imaging of one or more specific target areas of the plurality of target areas in a second pass of the semiconductor substrate, the one or more specific target areas not receiving the predetermined dose in the first pass; The control software and third instructions configured to set the level of the power of the radiation of the radiation source in the first pass and the second pass to keep the total time length substantially at or near a minimum value.

8. fourth instructions configured to record, for each of the one or more specific target areas during the first pass, information representative of each location on the semiconductor substrate and a difference between the predetermined dose and an actually received dose; fifth instructions configured to control imaging of the one or more specific target areas of the plurality of target areas under control of the recorded information during the second pass; 8. The control software of claim 7, comprising:

Images