Edge placement by spatial light modulator writing

Abstract

A method of preparing pixel data for imaging with an SLM includes the step S10 of obtaining data representing a pattern. At S20 the data is rasterized into a grid of pixels. The rasterization includes the step S22 of assigning edge adjustment values ​​to pixels that cover an edge of the pattern. At S30 the rasterized pattern is divided into a number of rasterized pattern planes associated with respective radiation exposures. At S32 the sum of the radiation exposures of the fully covered pixels exceeds a threshold for activating a radiation sensitive layer on a substrate on which the pattern is to be printed. At S34 the sum of the radiation exposures for the pattern edge pixels corresponds to an amount sufficient to shift the location where the sum of the radiation exposures reaches the activation threshold by a distance corresponding to the edge adjustment value. At S40 the data representing the rasterized pattern planes is output.

Description

[Technical field]

[0001] The present technology relates generally to imaging, such as mask writing or direct writing, and in particular to methods and arrangements for spatial light modulators. [Background technology]

[0002] To obtain high quality pattern printing, spatial light modulators (SLMs), such as digital micromirror devices (DMDs), liquid crystal displays (LCDs), grating light valves (GLVs), planar light valves (PLVs), microshutter arrays (MSAs), analog spatial light modulators (ASLMs) and / or liquid crystal on silicon (LCSs), are often used. The SLM has an array of individually controllable elements arranged to generate a grid of pixels in a stamp area on a target surface. The SLM translates the pattern of the controllable elements in the SLM into an exposure of a portion of a substrate having a radiation sensitive coating. The SLM moves continuously relative to the substrate during one operation, allowing successive short pulses of radiation to illuminate the array of controllable elements in the SLM. This results in an instantaneous pattern of controllable elements that reflect or transmit light being "stamped" into some area of ​​the substrate. The pattern of the controllable elements that control the light may then be altered before introducing the next pulse of radiation, and the substrate surface is gradually covered with a patterned exposure. This exposure is of a binary nature. That is, the exposure is either sufficient to change the properties of the radiation sensitive coating or it is not. In other words, if the radiation exceeds a threshold level, the radiation sensitive coating will react. Each controllable element corresponds to a particular area of ​​the substrate called a machine pixel.

[0003] A printed structure can be mapped onto a machine grid of machine pixels. Machine pixels that fall entirely within the printed structure are assigned a full exposure, ensuring that the radiation level of every part of the machine pixel is above a threshold level. Machine pixels that are entirely outside the printed structure are assigned no exposure, ensuring that the radiation level of every part of the machine pixel is below the threshold level.

[0004] For machine pixels covering the edge of a printed structure, the situation is a little more complicated. Some radiation will also enter the edge-related machine pixel from adjacent machine pixels covered by the printed structure. However, this radiation level will be below the threshold and will fall towards any "unexposed" adjacent machine pixels. However, by adding radiation from a lower radiation exposure to the edge-related machine pixels, the total dose closest to the machine pixel covered by the structure may exceed the threshold. This will move the edge of the region of the substrate that exceeds the threshold towards the adjacent unexposed machine pixels. In this way, by accommodating the additional radiation exposure, an edge placement accuracy significantly better than the size of the machine pixel may be achieved.

[0005] A problem arises when using the on / off radiation principle in SLM writing: additional exposures can be provided by multiple exposures, which changes the total radiation dose. However, if the required edge placements can vary significantly, a large number of additional exposures may be required to provide different additional radiation exposures tailored to the individual edge-related machine pixels. Each additional exposure reduces the overall production speed.

[0006] Therefore, there is a need for improved methods and arrangements for accurate edge placement of SLMs. Summary of the Invention

[0007] A general objective of the present technique is to improve edge placement of spatial light modulators.

[0008] The above objects are achieved by a method and an apparatus as claimed in the independent claims. Preferred embodiments are defined in the dependent claims.

[0009] Generally speaking, in a first aspect, a method of preparing pixel data for rendering with a spatial light modulator includes obtaining data representing a pattern to be printed by an input interface of a rasterization module. The pattern to be printed is rasterized in a processing unit of the rasterization module into a grid of pixels. The rasterization step includes assigning an edge adjustment value to pixels covering an edge of the pattern to be printed. The edge adjustment value is a fraction of the pixel width where the edge is located relative to adjacent pixels covered by the pattern to be printed. The rasterized pattern is divided in the processing unit into n rasterized pattern planes. Each of the rasterized pattern planes is associated with a respective radiation exposure. The sum of the radiation exposures of the rasterized pattern planes of pixels completely covered by the pattern to be printed exceeds a threshold for activating a radiation sensitive layer on a substrate on which the pattern is printed. The sum of the radiation exposures of the rasterized pattern planes of pixels associated with the edge of the pattern to be printed corresponds to an amount sufficient to shift the position where the sum of the radiation exposures reaches the threshold for activating the radiation sensitive layer by a distance corresponding to the edge adjustment value. Data representing the n rasterized pattern planes is output by an output interface of the rasterization unit, at least two of the respective radiation exposures being different.

[0010] In a second aspect, a method for imaging with a spatial light modulator includes step a) of acquiring data representative of n rasterized pattern planes associated with a pattern to be printed. The rasterized pattern planes are acquired by the method according to the first aspect. In step b) the spatial light modulator is positioned according to a stamp area of ​​the first rasterized pattern plane. In step c) a substrate having a radiation sensitive layer is exposed with a radiation dose corresponding to the radiation exposure associated with the first rasterized pattern plane. In step e) steps b) and c) are repeated for the n rasterized pattern planes by exposing with the respective associated radiation exposure. In step f) steps b), c) and e) are repeated for additional stamp areas according to a scanning scheme.

[0011] In a third aspect, a rasterization module for preparing pixel data for rendering with a spatial light modulator comprises a processing unit, a memory, an input interface and an output interface. The input interface is configured to receive data representing a pattern to be printed. The processing unit is configured to rasterize the pattern to be printed into a grid of pixels. The rasterizing step includes assigning an edge adjustment value to pixels covering an edge of the pattern to be printed. The edge adjustment value is a fraction of the pixel width where the edge is located relative to adjacent pixels covered by the pattern to be printed. The processing unit is further configured to divide the rasterized pattern into n rasterized pattern planes. Each of the rasterized pattern planes is associated with a respective radiation exposure. The sum of the radiation exposures of the rasterized pattern planes of pixels completely covered by the pattern to be printed exceeds a threshold for activating a radiation sensitive layer on a substrate on which the pattern to be printed is printed. The sum of the radiation exposures of the rasterized pattern planes of pixels associated with an edge of the pattern to be printed corresponds to an amount sufficient to move a position where the sum of the radiation exposures reaches a threshold for activating the radiation sensitive layer by a distance corresponding to the edge adjustment value. The output interface is configured to output data representative of the n rasterized pattern planes. The processing unit is further configured to select the radiation exposures such that at least two of the respective radiation exposures are different.

[0012] In a fourth aspect, a pattern generator includes a control module and an imaging module. The imaging module is arranged to image a pattern in the stamp area by a spatial light modulator. The spatial light modulator has an array of individually controllable elements arranged to generate a grid of pixels in the stamp area on the target surface. Illumination of individual pixels is controlled by each element. The control module is configured to obtain data representing n rasterized pattern planes associated with the pattern to be printed from the rasterization module according to the third aspect. The imaging module is configured to position the spatial light modulator in alignment with the stamp area of ​​a first rasterized pattern plane. The imaging module is configured to expose a substrate having a radiation sensitive layer with a radiation dose corresponding to the radiation exposure associated with the first rasterized pattern plane. The imaging device is configured to repeat the positioning of the spatial light modulator and the exposure of the n rasterized pattern planes by exposing with the respective associated radiation doses. The imaging device is further configured to repeat the positioning of the spatial light modulator, the exposure, and the repeating for additional stamp areas according to a scanning scheme.

[0013] One advantage of the proposed technique is that more accurate edge placement can be achieved, other advantages will become apparent from reading the detailed description. [Brief description of the drawings]

[0014] The invention, together with further objects and advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawings, in which: [Figure 1] FIG. 1 shows a schematic representation of an SLM-based pattern generator. [Diagram 2] FIG. 2 shows a schematic representation of a portion of a target surface. [Diagram 3] FIG. 3 shows a schematic representation of a portion of a target surface with a displaced stamp area. [Figure 4] FIG. 4 is a diagram showing the radiation dose at the target surface. [Diagram 5] FIG. 5 shows a schematic representation of a portion of a target surface where the pattern does not coincide with pixel boundaries. [Figure 6] FIG. 6 is a diagram showing radiation dose with partial radiation dose at the target surface. [Figure 7] FIG. 7 is a diagram showing the relationship between the radiation dose and edge movement. [Figure 8] FIG. 8 shows a schematic of illumination by a series of rastered pattern planes. [Figure 9] FIG. 9 shows diagrammatically the end result of the illumination of FIG. [Figure 10] FIG. 10 is a flow diagram of the steps of an embodiment of a method for preparing pixel data for imaging by an SLM. [Figure 11] FIG. 11 is a flow diagram of the steps of an embodiment of a method for writing with an SLM. [Figure 12] FIG. 12 illustrates an embodiment of a series of radiation exposures to multiple rasterized pattern planes. [Figure 13] FIG. 13 illustrates an embodiment of a series of radiation exposures to multiple rasterized pattern planes. [Figure 14] FIG. 14 illustrates an embodiment of a series of radiation exposures to multiple rasterized pattern planes. [Figure 15] FIG. 15 illustrates an embodiment of a series of radiation exposures to multiple rasterized pattern planes. [Figure 16] FIG. 16 illustrates a schematic of one embodiment of the rasterization module. [Figure 17] FIG. 17 illustrates a schematic of one embodiment of a pattern generation system. [Figure 18] FIG. 18 illustrates a schematic of one embodiment of a pattern generator. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Throughout the drawings, the same reference numbers are used for similar or corresponding elements.

[0016] To better understand the proposed technology, it may be useful to start with a brief overview of some principles of spatial light modulators (SLMs).

[0017] Figure 1 shows diagrammatically a pattern generator 1 based on an SLM 2. The SLM 2 is shown here as an array 3 of individually controllable elements 4, in this embodiment radiation reflecting elements. Light 5 incident on the array 3 is reflected into a series of exposure beams 6 towards a target surface 10, which is typically supported by a target support 12. The individual elements 4 of the SLM 2 are controllable to either allow reflection or suppress reflection. Elements 4 of the SLM 2 may alternatively be set to disabled, thereby reducing the active portion of the array 3.

[0018] Light emerging from the active part of the SLM 2 is directed towards a target surface 10, on which it forms a grid 20 of pixels 22. The pixels 22, i.e. the imaging elements, together form the stamp area 14. The illumination of each of the individual pixels 22 is thereby controlled by a respective element 4 of the SLM 2. Typically there is a nominal optical scaling of the stamp area 14 with respect to the SLM grid 20. This nominal scaling is a uniform scaling determined by different design parameters such as different distances and conventional optics. Arrangements for achieving such a nominal scaling are well known to those skilled in the art and will not be discussed further.

[0019] The light 5 incident on the array 3 is uniform in the sense that every individually controllable element 4 receives essentially the same initial dose. Thus, while control of the elements 4 will provide on / off operation for each individual pixel 22, the dosimetry of any light that reaches the target surface 10 is determined by the dose of the incident light 5. By controlling this dose of incident light 5 during different exposures of different areas of the target surface 10, different radiation doses can be achieved at different locations. However, every location where an element 4 is "on" will be delivered the same dose for each exposure.

[0020] After exposing the stamp area 14 according to the individual settings of elements 4 of the SLM 2, the stamp area 14 can be moved. This may typically be done by mechanically moving the SLM 2 relative to the target support 12, by moving the target support 12, the SLM 2 or both. The movement of the stamp area 14 may also be performed at least partly by optical means.

[0021] The relative movement may be performed in such a way that one stamp area 14 of one exposure is placed end-to-end with another previous stamp area 14. However, the relative movement may also result in an overlap between the stamp areas 14 of the various exposures. Such an overlap may concern only the edge areas of the stamp areas 14, for example to reduce edge effects. However, in other applications a larger overlap may be used, resulting in a multiple exposure strategy, which is used in the present technique and will be discussed in more detail below.

[0022] As explained in the Background, the SLM 2 can be constructed in a variety of ways. The details of the operation of the SLM 2 are not critical to the concepts of the present invention, so long as individual control of the elements 4 is provided and the SLM 2 generates a grid 20 of pixels 22 within the stamp area 14 on the target surface 10.

[0023] FIG. 2 shows a schematic representation of a portion of the target surface 10. The stamp area 14 in the current position of the SLM is shown as a grid 20 of pixels 22. The pixels 22 are arranged with a first pitch D1 in a first direction 101 and with a second pitch D2 in a second direction 102. In this figure, the number of pixels is reduced for illustrative purposes. In the current situation, some of the elements of the SLM allow radiation to be directed towards the stamp area 14 and are marked as black. The selection of the elements in the SLM is performed according to print data representing the pattern 30 to be printed. The target pattern 30 is shown in dotted lines only for reference and is not physically present in the stamp area 14. However, it is easy to see that the pixels 22 corresponding to the items in the pattern 30 are illuminated, whereas the pixels 22 corresponding to the areas between the items in the pattern 30 are not illuminated. The areas of the target pattern 30 outside the current stamp area 14 are marked with diagonal lines and will be processed by the previous or next printing step.

[0024] It will be appreciated that in certain applications the illumination may be a negative counterpart to the pattern 30, i.e. only pixels 22 outside the intended pattern are illuminated. However, this would resemble a "negative" pattern 30.

[0025] With reference to FIG. 3, if a stamp area 14 is illuminated, a movement of the stamp area 14 may be performed before the next exposure is performed. In FIG. 3, an example of the next position is shown at 14 ″. Part of the pattern 30 is still covered by the next stamp area 14 ″ and may receive an additional exposure dose if the SLM allows it. Other parts of the pattern that were previously illuminated will be outside the new stamp area 14 ″. Similarly, parts of the pattern 30 that were previously outside the exposure area will now be inside the new stamp area 14 ″. In this way, the entire surface of the target surface 10 can be covered and each pixel 22 will achieve an exposure dose that is the sum of the doses when the pixel 22 is covered by a stamp area.

[0026] In other words, each point on the target surface 10 may be exposed multiple times with multiple exposures where the stamp area 14 moves only a portion of the width of the stamp area 14. Alternatively, multiple exposures of the same stamp area 14 can be performed, i.e., without any movement between exposures.

[0027] The pattern to be printed is typically rasterized into a grid 20 of pixels 22. Each pixel is intended to be exposed to radiation from one or more exposures. For a pixel completely covered by the pattern to be printed, the sum of the doses from such exposures is configured to exceed the threshold for activating the radiation-sensitive layer on the substrate on which said pattern is printed over the entire pixel surface. In this way, the pixel becomes "exposed".

[0028] This is shown diagrammatically in FIG. 4. A one-dimensional radiation dose 102 for a number of pixels is shown. The total dose is achieved by covering a first group of pixels 22A entirely with the pattern to be printed and turning the corresponding element of the SLM "on". The second group of pixels 22B is positioned outside the pattern to be printed and the corresponding element of the SLM is in the "off" position. The radiation envelope is not perfectly sharp, so some radiation dose will appear in the areas of the pixels 22B that are not intended to be exposed to radiation. However, the magnitude of the radiation dose 102 is lower than the activation level 101 of the radiation-sensitive layer on the substrate, so that no "print" will appear in the pixels 22B that are not intended to be exposed to radiation. It should be noted that the shape of the radiation dose is drawn diagrammatically for illustrative purposes and does not correspond to an actual measured example.

[0029] This works well as long as the edges of the printed pattern coincide with the pixel grid. However, in the general case, it is not known whether the printed pattern can be positioned to the pixel grid. Figure 5 shows an example where the edge 31 of the printed pattern 30 is located in the middle of a pixel of the grid 20 of the rasterized pattern 15. There is a fully covered pixel 22A, a fully empty pixel 22B and a partially covered pixel 22C. The fully covered pixel 22A and the fully empty pixel 22B are easily provided. For the partially covered pixel 22C, additional measures need to be taken. Here, the stamp area 14 is a sub-area of ​​the rasterized pattern 15, and to print the complete pattern 30, several stamp areas 14 need to be printed.

[0030] One way to achieve edge placement with precision greater than the pixel size is to irradiate the pixel with a partial radiation dose that is lower than the radiation dose of a fully covered pixel. As shown diagrammatically in FIG. 6, a small radiation dose 105 at the partially covered pixel 22C will be added to the radiation dose 102 provided by the adjacent fully covered pixel 22A. The sum of such doses is shown by graph 103 and will reach an activation level 101 of the radiation sensitive layer on the substrate at point 106. Thus, the portion of pixel 22C to the right of this point 106 will be "exposed", whereas the portion of pixel 22C to the left of this point 106 will be "unexposed". In other words, the edge of the printed pattern has shifted by a distance Δ.

[0031] The distance Δ preferably corresponds to the position of a pattern edge. With respect to the adjacent pixel 22A covered by the printed pattern, an edge adjustment value 107 can be defined as a fraction of the pixel width 108 over which the edge is located.

[0032] Thus, as shown in the diagram of Figure 7, there is a relationship 104 between the additional radiation dose allowed in a pixel and the edge adjustment into that pixel. This relationship 104 depends on the actual radiation dose distribution of the SML, but may be easily calibrated for each installation or type of installation. Note that the curve in Figure 7 is for illustrative purposes only and does not correspond to an actual measured relationship. This means that by changing the radiation dose of a pixel, it is possible to move the edge towards an adjacent pixel.

[0033] As mentioned above, all pixels in the grid are provided with essentially the same radiation dose. However, by utilizing multiple exposures, differences in radiation doses may occur at different pixels. In a very basic sense, the same stamp area can be exposed multiple times, but with different pixel selections. For example, if five exposures of the same imaged area are performed with the same impinging radiation exposure, different pixels can be provided with 0%, 20%, 40%, 60%, 80% or 100% of the maximum available dose, and the edge positions can be shifted accordingly.

[0034] This principle of multiple exposure also works well in combination with the partially overlapping exposures mentioned above. In FIG. 8, the pattern 30 to be printed is exposed in successive stamp areas 14 which move relative to the substrate during each exposure. The filled squares indicate pixels which are controlled to allow exposure at different times. In this example, each location of the pattern 30 is exposed by up to six exposures. The stamp areas 14 are thus selected areas of the rasterized pattern plane 16, which together form the rasterized pattern. The six exposures are thus controlled by the respective rasterized pattern plane 16. This means that the stamp areas 14 of each sixth exposure are selected from the same rasterized pattern plane 16. If an edge shift is performed for a pixel, i.e. only a part of the pattern covers the corresponding pixel, then the pixel is exposed in one exposure but not in the other exposures. The final result is shown diagrammatically in FIG. 9, where pixels corresponding to the central part of the pattern 30, i.e. where the pixel is completely covered by the pattern 30, are shown as black areas. Some pixels at the edge of the pattern 30 receive a lower dose of radiation, as indicated by hatching, and the dose of radiation at these edge pixels is adapted to cause edge movements that are consistent with the original pattern 30. Small edge movements are caused by small amounts of additional radiation dose, and larger edge movements are caused by larger amounts of additional radiation dose.

[0035] FIG. 10 shows a flow diagram of steps of one embodiment of a method for preparing pixel data for rendering by a spatial light modulator, e.g., mask rendering or direct rendering. In step S10, data representing a pattern to be printed is obtained. In step S20, the pattern to be printed is rasterized into a grid of pixels. In this process, as shown in step S22, rasterization includes assigning edge adjustment values ​​to pixels that cover an edge of the pattern to be printed. The edge adjustment value is a fraction of the pixel width at which the edge is located, relative to the adjacent pixels covered by the pattern to be printed. In other words, the edge adjustment value indicates how far the nearest pattern edge of a fully covered pixel needs to move across the area of ​​partially covered pixels.

[0036] In step S30, the rasterized pattern is divided into n rasterized pattern planes, whereby each rasterized pattern plane is associated with one exposure of the multiple exposure process during the next pattern writing. Such multiple exposure process may be performed by totally overlapping exposures or partially overlapping exposures. Each of the rasterized pattern planes is associated with a respective radiation exposure. Various alternatives to this will be considered in more detail below. The division into rasterized pattern planes is performed such that the sum of the radiation exposures of the rasterized pattern planes for pixels completely covered by the printed pattern exceeds a threshold for activating a radiation-sensitive layer on the substrate on which the pattern is printed, as shown in step S32. In the same manner, the division into rasterized pattern planes corresponds to an amount sufficient to shift the position at which the sum of the radiation exposures of the rasterized pattern planes for pixels associated with an edge of the printed pattern reaches a threshold for activating the radiation-sensitive layer by a distance corresponding to an edge adjustment value, as shown in step S34. In step S40, data representative of the n rasterized pattern planes is output. This data can then be utilized in imaging methods using spatial light modulators.

[0037] FIG. 11 shows a flow diagram of steps of an embodiment of a method for imaging with a spatial light modulator, such as mask imaging or direct imaging. In step S50, data representing n rasterized pattern planes associated with a pattern to be printed is obtained. The rasterized pattern planes are obtained, for example, by a method according to the techniques presented above. In step S55, the spatial light modulator is aligned with the stamp area of ​​the first (first or initial) rasterized pattern plane. In step S60, a substrate having a radiation-sensitive layer is exposed with a radiation dose corresponding to the radiation exposure associated with the first (first or initial) rasterized pattern plane.

[0038] In one embodiment, the coincident exposures of the rasterized pattern planes are performed in the same area on the substrate. In such an embodiment, in step S70, iterations of steps S55 and S60 are performed for n rasterized pattern planes. The iterations for the n rasterized pattern planes are performed by exposing each with an associated radiation dose.

[0039] In another embodiment, an additional step S65 is introduced, in which the spatial light modulator is scanned relative to the substrate by a distance in the scan direction equal to the width of the stamp area in the scan direction divided by n, so that in this embodiment step S70 is performed with the respective stamp area moved according to the scan distance, thereby overlapping the previous exposure.

[0040] In step S75, steps S55, S60 and S70, and, if applicable, step S65, are repeated for additional stamp areas according to the scanning scheme.

[0041] If the radiation exposure of each of the rasterized pattern planes is equal, the number n of rasterized pattern planes makes it possible to achieve n different equidistant levels of total radiation dose for each pixel. This means that the pattern edge can be moved to n different positions within the width of a single pixel. However, increasing the number of rasterized pattern planes will also slow down the printing speed. If the number of rasterized pattern planes is doubled, i.e. the edge position accuracy is doubled, the printing speed will also be reduced by a factor of two.

[0042] However, by allowing the radiation exposure of the rasterized pattern planes to differ, an increase in the number of achievable edge location moves can be achieved. FIG. 12 illustrates various radiation exposures 110 of a series of rasterized pattern planes. Rasterized pattern planes 1-3 are associated with maximum radiation exposure, and rasterized pattern planes 4-7 are associated with reduced radiation exposure. In order to illuminate all pixels by every rasterized pattern plane, the rasterized pattern plane in which each pixel is "on" may be selected depending on which edge move is required. In the radiation exposure of the series of rasterized pattern planes presented in FIG. 12, a total of 62 different edge moves may be selected.

[0043] The radiation exposure associated with the various rasterized pattern planes can be varied by various methods, each of which is known to those skilled in the art. One option is to use light intensity filters. Alternatively, acousto-optical or electro-optical modulators can be used. Some lasers also allow direct modulation of the laser output. Other types of methods of influencing intensity can also be used. These methods are known per se to those skilled in the art and will not be described in more detail.

[0044] However, the adaptation to achieve more accurate edge movement comes at some cost. The maximum radiation exposure available at some rasterized pattern planes is less than achievable, so the total available dose across all rasterized pattern planes is reduced. To compensate for this total dose loss, it is necessary to increase the maximum available radiation exposure or extend the exposure time. Increasing the maximum radiation exposure typically comes at a higher cost. Increasing the exposure time is also undesirable as it reduces the overall throughput. Thus, the choice of radiation exposure scheme must be tailored to the application and is typically a compromise between edge movement accuracy and radiation equipment utilization.

[0045] In one embodiment, at least two of the respective radiation exposures are different. Each different radiation exposure increases the number of selectable edge movements, up to a factor of two in the most efficient setup.

[0046] In applications that require very high precision in edge movements, but are not sensitive to radiation power availability, it is preferable to increase the number of different radiation exposures. Figure 13 shows various radiation exposures of a series of rasterized pattern planes that maximize the number of selectable edge movements for a given number of rasterized pattern planes. In this embodiment, each radiation exposure is different.

[0047] In this embodiment, every radiation exposure has twice the dose of the other one, except for the weakest one. This embodiment provides 62 different intermediate edge movements between no edge movements and the "maximum movement", i.e., maximum illuminated pixels. However, at the same time, the printing speed is reduced by a factor of six and the radiation efficiency is reduced to 33%. This approach has been shown to provide excellent edge positioning accuracy in test runs. In comparison, six pattern planes rasterized with the same radiation exposure would have only five different intermediate edge movements, and the printing speed would be reduced by a factor of six, but would utilize 100% of the available radiation power.

[0048] Even in embodiments where none of the radiation exposures except one has twice the radiation dose of the other of the respective radiation exposures, the concept of the dose relationship between the different radiation exposures being equal to two is often advantageous. Thus, in one embodiment, at least a majority of the respective radiation exposures have twice the radiation dose of the other of the respective radiation exposures. An example of such an embodiment is the set shown in Figure 12. This embodiment provides 62 possible intermediate edge movements and utilizes 56% of the available radiation power, at the expense of a seven-fold reduction in printing speed.

[0049] Another drawback of the embodiment of FIG. 13 is that one or a few rasterized pattern planes are very dominant in terms of exposure. If the pulse energy fluctuates for such a high-power exposure or if the actual placement of the dose is slightly off, the final result will be greatly affected. In other words, the sensitivity to operational disturbances may be high. By having several pulses of approximately the same magnitude together to produce the main radiation portion, the sensitivity to single unpredictable disturbances is reduced. For such reasons, an embodiment such as that of FIG. 12 may be preferred. However, the selection of the radiation exposure distribution is preferably performed taking into account the requirements of the application to which it is applied.

[0050] Yet another approach uses a constant difference between the different radiation exposures. In other words, in one embodiment, at least a majority of the respective radiation exposures differ in radiation dose from another one of the respective radiation exposures by a constant difference. The advantage of such a constant difference is that each available edge movement can be achieved by several different combinations of exposures. This can be beneficial in some applications where the selection of radiation exposure or rasterized pattern plane may also be determined by other requirements. Figure 14 shows such an embodiment, where all radiation exposures are related to each other by a constant difference. This embodiment provides 54 possible intermediate edge movements, utilizing 55% of the available radiation power, at a tenfold reduction in printing speed.

[0051] Another aspect of the selection of dose levels includes the sequence of radiation exposure: if there are small variations in radiation power, it may be wise to separate the rasterized pattern planes with high doses in time, so that a temporary deviation in radiation power only affects one or at least a small portion of the high dose rasterized pattern planes.

[0052] Similarly, as discussed further below, when performing corrections based on measured exposures, it is advisable to plan for the different magnitudes of radiation exposure available throughout the sequence.

[0053] 15 shows an embodiment in which the rasterized pattern planes with the highest dose are spread throughout the sequence. Thus, this approach presents a solution where the radiation exposure varies non-monotonically for each sequence of n rasterized pattern planes. Within one and the same sequence, there are both increases and decreases in dose between successive rasterized pattern planes.

[0054] Another principle used to distribute the radiation exposures is to create multiple instances of one high dose surrounded by two lower doses, and preferably one low dose surrounded by two higher doses, In other words, in one embodiment, for the majority of each radiation exposure, the doses of the nearest previous radiation exposure and the nearest subsequent radiation exposure will either both be high or both be low.

[0055] When performing actual writing, this results in the radiation exposure frequently varying between high and low doses. In other words, in one embodiment of the writing method, the rasterized pattern planes are selected in time such that at least two rasterized pattern planes are surrounded in time by rasterized pattern planes associated with lower radiation exposures, resulting in a non-monotonic time variation of the radiation exposure for all pixels.

[0056] Many current pattern generators using SLMs offer the possibility to actually measure the exposure level of a pixel. This is known per se in the prior art and depends on the actual configuration of the pattern generator. For this reason, the details of such measurements will not be considered further. Indeed, it is assumed that a person skilled in the art has the knowledge and skills to be able to carry out such measurements.

[0057] In such cases, the technique may be further exploited. The exposure level of a pixel is measured after a step of exposing the substrate by one of the rasterized pattern planes. If a deviation from the expected exposure is detected, the planning of any remaining rasterized pattern planes may be modified. In other words, if the measurement and evaluation are fast enough and there are remaining rasterized pattern planes to be used to irradiate the measured pixel, a compensatory measure may be implemented. The remaining rasterized pattern planes and their respective radiation exposures may then be recombined to come as close as possible to the remaining required exposure of the pixel in question. In other words, the not yet used parts of the rasterized pattern planes are adjusted to compensate for any deviation from the expected exposure level. The mixture of high-dose and low-dose rasterized pattern planes discussed above is beneficial in such cases, since it is possible to find the appropriate adjustment relocation of the rasterized pattern planes that are either "on" or "off" for the pixel in question.

[0058] Alternatively, an adjustment of the exposure may be performed, for example, during one return pass, if the measured exposure is lower than the expected exposure, but such an adjustment is not possible if the detected exposure is too high.

[0059] Although the inventive concept is applicable to any kind of writing method, the initial target technical field was its application to lithography or photomask lithography systems. For this reason, in a preferred embodiment, the pattern generator is a lithography or photomask lithography system. In mask writing systems, the requirements on the edge position are typically very high, whereas the actual printing speed is less important. This means that the inventive concept is particularly advantageously applied to mask writing systems. However, it should be noted that the same principles are also useful for example for different types of direct printing.

[0060] In Fig. 16 an embodiment of a rasterization module 60 for preparing pixel data for imaging with an SLM is shown. As explained above, the SLM has an array of individually controllable elements arranged to generate a grid of pixels in a stamp area on a target surface, with the illumination of individual imaging elements being controlled by each element. The rasterization module comprises a processing unit 62, a memory 64, an input interface 66 and an output interface 68. The input interface 66 is configured to obtain data representative of the pattern to be printed. The data representative of the pattern to be printed is preferably stored in the memory 64. The processing unit 62 is configured to rasterize the pattern to be printed into a grid of pixels. The rasterization comprises the assignment of an edge adjustment value to pixels covering an edge of the pattern to be printed. The edge adjustment value is a fraction of the pixel width where the edge is located relative to the adjacent pixels covered by the pattern to be printed. Instructions for the processing unit to perform the rasterization are preferably stored in a retrievable manner in the memory 64. The processing unit 62 is further configured to divide the rasterized pattern into n rasterized pattern planes. Each of the rasterized pattern planes is associated with a respective radiation exposure. The sum of the radiation doses of the rasterized pattern planes for pixels that are completely covered by the printed pattern exceeds a threshold for activating a radiation sensitive layer on the substrate on which the pattern is printed. Furthermore, the sum of the radiation exposures of the rasterized pattern planes for pixels associated with an edge of the printed pattern corresponds to an amount sufficient to shift the location at which the sum of the radiation exposures reaches the threshold for activating the radiation sensitive layer by a distance corresponding to the edge adjustment value. The output interface 68 is configured to output data representative of the n rasterized pattern planes.

[0061] In one embodiment, processing unit 62 is further configured to select the radiation exposures such that at least two of the respective radiation exposures are different.

[0062] In an additional embodiment, processing unit 62 is further configured to select the radiation exposures such that all of the respective radiation exposures are different.

[0063] In one embodiment, processing unit 62 is further configured to select the radiation exposures such that at least a majority of the respective radiation exposures have twice the radiation dose as another one of the respective radiation exposures.

[0064] In one embodiment, processing unit 62 is further configured to select the radiation exposures such that at least a majority of the respective radiation exposures have a radiation dose that differs by a constant difference relative to another one of the respective radiation exposures.

[0065] In one embodiment, processing unit 62 is further configured to select the radiation exposure to vary non-monotonically for each sequence of n rasterized pattern planes.

[0066] In an additional embodiment, for a majority of each radiation exposure, the doses of the nearest previous radiation exposure and the nearest subsequent radiation exposure are either both high or both low.

[0067] 17 shows an embodiment of a pattern generation system 70 comprising a rasterization module 60 and a pattern generator 80. In this embodiment, the rasterization module 60 provides data representing n rasterized pattern planes associated with the pattern to be printed. In this embodiment, the rasterization module 60 is shown as a separate unit. The rasterized pattern can then be transferred to the pattern generator 80 by a communication connection 61 or wireless alternative. Alternatively, the data representing the rasterized pattern can be provided by the rasterization module 60 in a data storage unit that is physically provided to the pattern generator 80 for access.

[0068] However, in other embodiments, as indicated by the dotted lines, the rasterization module 60 may be provided as part of the pattern generator 80, with processing power preferably being shared by the pattern generator 80 and the rasterization module 60. The transfer of the rasterized pattern from the rasterization module 60 to the pattern generator 80 is then performed by internal means.

[0069] 18 illustrates generally one embodiment of a pattern generator 80. The pattern generator 80 comprises a control module 82 and an imaging module 84. The imaging module 84 is arranged to image a pattern into the stamp area. The imaging module comprises an SLM 2 having an array 3 of individually controllable elements 4 arranged to generate a grid of pixels in the stamp area on the target surface 10. Illumination of the individual imaging elements is controlled by the respective elements 4 based on instructions from the control module 82.

[0070] The control module 82 is configured to obtain data from the rasterization module representing the n rasterized pattern planes associated with the pattern to be printed. As explained above, this rasterized pattern can be provided in a variety of ways from an internal source or an external source, according to the principles further explained above.

[0071] The imaging module 84 is configured to position the SLM in line with a stamp area of ​​a first rasterized pattern plane. The imaging module 84 is configured to expose a substrate having a radiation sensitive layer with a radiation dose corresponding to a radiation exposure associated with the first rasterized pattern plane. The imaging module 84 is configured to repeat the positioning of the SLM and exposing the n rasterized pattern planes by exposing them with their associated radiation doses. The imaging module 84 is further configured to repeat the positioning, exposing and repeating of the SLM for additional stamp areas according to a scanning scheme.

[0072] In one embodiment, the imaging device is further configured to scan the spatial light modulator relative to the substrate by a distance in the scan direction equal to the width of the stamp area in the scan direction divided by n. The repetitions of positioning and exposing the SLM are performed with each stamp area offset according to the scan distance, thereby partially overlapping with previous exposures. The positioning, exposing and repetitions of the SLM further include repetitions of scanning the spatial light modulator for each rasterized pattern plane.

[0073] In one embodiment, the control module 82 is further configured to select the rasterized pattern plane to be used by the imaging module 84 in a timely manner such that at least two rasterized pattern planes are surrounded in time by the rasterized pattern plane associated with a lower radiation exposure, resulting in a non-monotonic time variation of the radiation exposure of all pixels.

[0074] In one embodiment, the pattern generator further comprises an exposure level measurement unit configured to measure the exposure level of the pixels after exposing the substrate. The control module 82 is further configured to adjust unused portions of the rasterized pattern plane to compensate for any deviations from the expected exposure level.

[0075] The above-described embodiments should be understood as some examples of the present invention. It will be understood by those skilled in the art that various modifications, combinations and changes can be made to the embodiments without departing from the scope of the present invention. In particular, different part solutions in different embodiments can be combined in other configurations, where technically possible. However, the scope of the present invention is defined by the appended claims.

Claims

1. A method for generating pixel data for rendering using a spatial light modulator (2), comprising the steps of: - obtaining (S10) data representative of the pattern (30) to be printed by an input interface (66) of a rasterization module (60); a step (S20) of rasterizing, in a processing unit (62) of said rasterization module (62), said pattern (30) to be printed on a grid (20) of pixels (22), The rasterizing step (S20) includes a step (S22) of assigning an edge adjustment value (107) to pixels (22C) covering an edge (31) of the pattern (30) to be printed; the edge adjustment value (107) is a fraction of the pixel width (108) within which the edge (31) is located, relative to the adjacent pixels (22A) covered by the printed pattern (30); - a step (S30) of dividing the rasterized pattern (15) into n rasterized pattern planes (16) in the processing unit (62), Each of said rasterized pattern planes (16) is associated with a respective radiation exposure (102, 105, 110); the sum of the radiation exposures (102, 105, 110) of the rasterized pattern plane (16) for pixels (22A) that are completely covered by the pattern (30) to be printed exceeds a threshold (101) for activating a radiation-sensitive layer on a substrate (10) onto which the pattern (30) is printed; a sum of radiation exposures (102, 105, 110) of the rasterized pattern plane (16) for pixels (22C) associated with an edge (31) of the pattern (30) to be printed corresponds to an amount sufficient to shift the location at which the sum of radiation exposures reaches the threshold (101) for activating the radiation-sensitive layer by a distance (Δ) corresponding to the edge adjustment value (107); - outputting (S40) data representative of said n rasterized pattern planes (16) by an output interface (68) of said rasterization unit (60), at least two of said respective radiation exposures (102, 105, 110) are different.

2. 2. The method of claim 1, wherein all of said respective radiation exposures (102, 105, 110) are different.

3. 3. The method of claim 1 or 2, characterized in that at least a majority of said respective radiation exposures (102, 105, 110) have a radiation dose that is twice as high as another one of said respective radiation exposures (102, 105, 110).

4. 3. The method of claim 1, wherein at least a majority of said respective radiation exposures (102, 105, 110) differ in radiation dose from another one of said respective radiation exposures (102, 105, 110) by a constant difference.

5. 3. A method according to claim 1 or 2, characterized in that the radiation exposure (102, 105, 110) varies non-monotonically across each sequence of n rasterized pattern planes (16).

6. 6. The method of claim 5, wherein for a majority of the respective radiation exposures (102, 105, 110), the doses of the nearest previous radiation exposure (102, 105, 110) and the nearest subsequent radiation exposure (102, 105, 110) are either both high or both low.

7. A method for imaging on a spatial light modulator (2), comprising: a) obtaining (S50) data representative of n rasterized pattern planes (16) associated with a pattern to be printed, said rasterized pattern planes (16) being obtained by a method according to claim 1 or 2; -b) positioning (S55) a spatial light modulator (2) in line with the stamp areas (14, 14'') of said first rasterized pattern plane (16); -c) exposing (S60) a substrate with said radiation-sensitive layer with a radiation dose corresponding to said radiation exposure (102, 105, 110) associated with said first rasterized pattern plane (16); - e) repeating steps b) and c) for the n rasterized pattern planes (16) by exposing them with their associated radiation doses (S70); - f) repeating (S75) steps b), c) and e) for additional stamp areas (16) according to a scanning scheme.

8. 8. The method according to claim 7, further comprising a step (S65) of: - d) scanning the spatial light modulator (2) relative to the substrate by a distance in the scanning direction equal to the width of the stamp area (14, 14") in the scanning direction divided by n, said step e) being carried out with each of said stamp areas (16) moved according to said scanning distance, thereby overlapping with a previous exposure; The method, wherein the repeating of step f) further comprises step d).

9. 8. The method of claim 7, wherein the rasterized pattern planes (16) are selected in time such that at least two rasterized pattern planes (16) are surrounded in time by rasterized pattern planes (16) associated with lower radiation exposures (102, 105, 110), resulting in a non-monotonic time variation of the radiation exposure of all pixels (22).

10. - after said step c) of exposing the substrate, measuring the exposure level of the pixels (22); 8. The method of claim 7, further comprising the step of adjusting unused portions of the rasterized pattern plane (16) to compensate for any deviations from the expected exposure level.

11. A rasterization module (60) for preparing pixel data for rendering using a spatial light modulator (2), comprising a processing unit (62), a memory (64), an input interface (66) and an output interface (68), said input interface (66) being configured to obtain data representative of a pattern (30) to be printed; the processing unit (62) is configured to rasterize the pattern (30) to be printed into a grid (20) of pixels (22); said rasterization comprising the assignment of edge adjustment values ​​(107) to pixels (22C) covering the edges (31) of said pattern (30) to be printed; the edge adjustment value (107) is a fraction of the pixel width (108) within which the edge (31) is located, relative to the adjacent pixels (22A) covered by the printed pattern (30); The processing unit (62) is further configured to divide the rasterized pattern (15) into n rasterized pattern planes (16); Each rasterized pattern plane (16) is associated with a respective radiation exposure (102, 105, 110); the sum of the radiation exposures (102, 105, 110) of the rasterized pattern plane (16) for pixels (22A) that are completely covered by the pattern (30) to be printed exceeds a threshold (101) for activating a radiation-sensitive layer on a substrate on which the pattern (30) is printed; the sum of the radiation exposures (102, 105, 110) of the rasterized pattern plane (16) for pixels (22C) associated with an edge (31) of the pattern (30) to be printed corresponds to an amount sufficient to shift the location at which the sum of the radiation exposures reaches the threshold (101) for activating the radiation-sensitive layer by a distance (Δ) corresponding to the edge adjustment value (107); the output interface (68) is configured to output data representing the n rasterized pattern planes (16); A rasterization module, wherein the processing unit (62) is further configured to select the radiation exposures (102, 105, 110) such that at least two of the respective radiation exposures (102, 105, 110) are different.

12. 12. The rasterization module of claim 11, wherein the processing unit (62) is further configured to select the radiation exposures (102, 105, 110) such that all of the respective radiation exposures (102, 105, 110) are different.

13. a control module (82); and an imaging module (84) arranged to image a pattern on a stamp area (14) by a spatial light modulator (2), the spatial light modulator (2) having an array (3) of individually controllable elements (4) arranged to generate a grid (20) of pixels (22) within the stamp area (14, 14") on the target surface (10), the illumination of each pixel (22) being controlled by each of the elements (4); the control module (82) is configured to obtain data representing n rasterized pattern planes (16) associated with a pattern (30) to be printed from a rasterization module (60) according to claim 11 or 12, the imaging module (84) is configured to position the spatial light modulator (2) in alignment with a stamp area (14, 14") of the first rasterized pattern plane (16); the imaging module (84) is configured to expose a substrate having the radiation-sensitive layer with a radiation dose corresponding to the radiation exposure (102, 105, 110) associated with the first rasterized pattern plane (16); the imaging module (84) is configured to repeat the steps of positioning the spatial light modulator (2) and exposing the n rasterized pattern planes (16) by exposing them with their associated radiation doses; The imaging module (84) is further configured to repeat the steps of positioning the spatial light modulator (2), exposing, and repeating such steps for additional stamp areas (14, 14") according to a scanning scheme.

14. 14. The pattern generator of claim 13, wherein the control module (82) is further configured to select in time the rasterized pattern planes (16) used by the imaging module (84) such that at least two rasterized pattern planes (16) are surrounded in time by the rasterized pattern planes (16) associated with lower radiation exposures (102, 105, 110), resulting in a non-monotonic time variation of the radiation dose of all pixels (22).

15. 14. The pattern generator of claim 13, further comprising an exposure level measurement unit configured to measure the exposure level of the pixels after exposing the substrate, whereby the control module is further configured to adjust unused portions of the rasterized pattern surface (16) to compensate for any deviation from expected exposure levels.

Images