Patent Description:
In the production or manufacturing of semiconductor devices, such as integrated circuits, optical lithography may be used to fabricate the semiconductor devices. Optical lithography is a printing process in which a lithographic mask or photomask or reticle is used to transfer patterns to a substrate such as a semiconductor or silicon wafer to create the integrated circuit (I. Other substrates could include flat panel displays, holographic masks or even other reticles. While conventional optical lithography uses a light source having a wavelength of <NUM>, extreme ultraviolet (EUV) or X-ray lithography are also considered types of optical lithography in this application. The reticle or multiple reticles may contain a circuit pattern corresponding to an individual layer of the integrated circuit, and this pattern can be imaged onto a certain area on the substrate that has been coated with a layer of radiation-sensitive material known as photoresist or resist. Once the patterned layer is transferred the layer may undergo various other processes such as etching, ion-implantation (doping), metallization, oxidation, and polishing. These processes are employed to finish an individual layer in the substrate. If several layers are required, then the whole process or variations thereof will be repeated for each new layer. Eventually, a combination of multiples of devices or integrated circuits will be present on the substrate. These integrated circuits may then be separated from one another by dicing or sawing and then may be mounted into individual packages. In the more general case, the patterns on the substrate may be used to define artifacts such as display pixels, holograms, directed self-assembly (DSA) guard bands, or magnetic recording heads. Conventional optical lithography writing machines typically reduce the photomask pattern by a factor of four during the optical lithographic process. Therefore, patterns formed on the reticle or mask must be four times larger than the size of the desired pattern on the substrate or wafer.

A method includes inputting an array of pixels, where each pixel in the array of pixels has a pixel dose. The array of pixels represents dosage on a surface to be exposed with a plurality of patterns, each pattern of the plurality of patterns having an edge. A target bias is input. An edge of a pattern in the plurality of patterns is identified. For each pixel which is in a neighborhood of the identified edge, a calculated pixel dose is calculated such that the identified edge is relocated by the target bias. The array of pixels with the calculated pixel doses is output.

A method includes inputting a plurality of patterns to be exposed on a surface, where each pattern has an edge. The method also includes inputting a target bias, and rasterizing the plurality of patterns to create an array of pixels, where each pixel in the array of pixels represents an exposure dosage. Dosages of pixels in the array of pixels are calculated, where the calculated dosages relocate the edge of a pattern in the plurality of patterns. The relocation is based on the target bias. The array of pixels is output, including the calculated pixel dosages.

A system for biasing shapes to be written onto a surface includes a device configured to input an array of pixels. Each pixel comprises a pixel dose, and the array of pixels represents dosage on a surface to be exposed with a plurality of patterns. Each pattern of the plurality of patterns has an edge. The system also includes a device configured to identify an edge of a pattern in the plurality of patterns; a device configured to calculate a calculated pixel dose for pixels which are in a neighborhood of the identified edge, so that the identified edge is relocated by a target bias; and a device configured to output the array of pixels with the calculated pixel doses. The system can also include a device configured to determine the dosages in the pixel array, using a set of geometric shapes. The system can also include a device configured to expose the surface with the outputted array of pixels. The device configured to calculate the pixel doses may operate simultaneously with the device configured to expose the surface, in an inline fashion. The device configured to expose the surface may comprise multiple beams.

A system includes a device configured to expose a pattern onto a resist-coated surface using an electron beam, and a device configured to compute a constant distance bias. The device configured to expose may expose the resist with multiple beams. The device configured to expose and the device configured to compute may operate in an inline fashion. The device configured to compute may comprise a graphics processing unit (GPU).

Methods and systems are presented for biasing the dimensions of patterns to be exposed onto a surface. The methods improve the ability to produce constant distance biasing for edges of a pattern, and improve the efficiency of biasing computations compared to conventional methods. The methods use an array of pixels that represent dosages, to identify the edge of the pattern and relocate the edge to achieve a target bias. In some embodiments, dose margin can also be enhanced as part of the biasing operations. In performing the biasing, dosage calculations can be performed using dosage data only for pixels neighboring the edge. The calculations of the present methods may be performed in an inline fashion with exposing the patterns on a surface.

The present disclosure is related to lithography, and more particularly to the design and manufacture of a surface which may be the surface of a reticle, a wafer, or any other surface, using charged particle beam lithography. Although embodiments shall be described in terms of a semiconductor wafer or a photomask, the methods and systems described herein can also be applied to other components used in the manufacturing of semiconductor devices. The embodiments may also be applied to the manufacturing of various electronic devices such as flat panel displays, micro-electromechanical systems, and other microscopic structures that require precision by electron beam writing. Accordingly, a reference to shots being delivered onto a surface shall apply to, for example, a surface of a semiconductor wafer, or a surface of a reticle or photomask.

Referring now to the drawings, wherein like numbers refer to like items, <FIG> illustrates an embodiment of a lithography system, such as a charged particle beam writer system, in this case an electron beam writer system <NUM>, that employs a variable shaped beam (VSB) to manufacture a surface <NUM>. The electron beam writer system <NUM> has an electron beam source <NUM> that projects an electron beam <NUM> toward an aperture plate <NUM>. The plate <NUM> has an aperture <NUM> formed therein which allows the electron beam <NUM> to pass. Once the electron beam <NUM> passes through the aperture <NUM> it is directed or deflected by a system of lenses (not shown) as electron beam <NUM> toward another rectangular aperture plate or stencil mask <NUM>. The stencil <NUM> has formed therein a number of openings or apertures <NUM> that define various simple shapes such as rectangles and triangles. Each aperture <NUM> formed in the stencil <NUM> may be used to form a pattern in the surface <NUM> of a substrate <NUM>, such as a silicon wafer, a reticle or other substrate. An electron beam <NUM> emerges from one of the apertures <NUM> and passes through an electromagnetic or electrostatic reduction lens <NUM>, which reduces the size of the pattern emerging from the aperture <NUM>. In commonly available charged particle beam writer systems, the reduction factor is between <NUM> and <NUM>. The reduced electron beam <NUM> emerges from the reduction lens <NUM> and is directed by a series of deflectors <NUM> onto the surface <NUM> as a pattern <NUM>. The surface <NUM> is coated with resist (not shown) which reacts with the electron beam <NUM>. The electron beam <NUM> may be directed to overlap a variable portion of an aperture <NUM>, affecting the size and shape of the pattern <NUM>. Blanking plates (not shown) are used to deflect the beam <NUM> or the shaped beam <NUM> so to prevent the electron beam from reaching the surface <NUM> during a period after each shot when the lenses directing the beam <NUM> and the deflectors <NUM> are being re-adjusted for the succeeding shot. Typically the blanking plates are positioned so as to deflect the electron beam <NUM> to prevent it from illuminating aperture <NUM>. Conventionally, the blanking period may be a fixed length of time, or it may vary depending, for example, on how much the deflector <NUM> must be re-adjusted for the position of the succeeding shot.

In electron beam writer system <NUM>, the substrate <NUM> is mounted on a movable platform or stage <NUM>. The stage <NUM> allows substrate <NUM> to be repositioned so that patterns which are larger than the maximum deflection capability or field size of the charged particle beam <NUM> may be written to surface <NUM> in a series of subfields, where each subfield is within the capability of deflector <NUM> to deflect the beam <NUM>. In one embodiment the substrate <NUM> may be a reticle. In this embodiment, the reticle, after being exposed with the pattern, undergoes various manufacturing steps through which it becomes a lithographic mask or photomask. The mask may then be used in an optical lithography machine to project an image of the reticle pattern <NUM>, generally reduced in size, onto a silicon wafer to produce an integrated circuit. More generally, the mask is used in another device or machine to transfer the pattern <NUM> on to a substrate (not illustrated).

The minimum size pattern that can be projected with reasonable accuracy onto the surface <NUM> is limited by a variety of short-range physical effects associated with the electron beam writer system <NUM> and with the surface <NUM>, which normally comprises a resist coating on the substrate <NUM>. These effects include forward scattering, Coulomb effect, and resist diffusion. Beam blur, also called βf, is a term used to include all of these short-range effects. The most modern electron beam writer systems can achieve an effective beam blur radius or βf in the range of <NUM> to <NUM>. Forward scattering may constitute one quarter to one half of the total beam blur. Modern electron beam writer systems contain numerous mechanisms to reduce each of the constituent pieces of beam blur to a minimum. Since some components of beam blur are a function of the calibration level of a particle beam writer, the βf of two particle beam writers of the same design may differ. The diffusion characteristics of resists may also vary. Variation of βf based on shot size or shot dose can be simulated and systemically accounted for. But there are other effects that cannot or are not accounted for, and they appear as random variation.

The shot dosage of a charged particle beam writer such as an electron beam writer system is a function of the intensity of the beam source <NUM> and the exposure time for each shot. Typically the beam intensity remains nominally fixed, and the exposure time is varied to obtain variable shot dosages. The exposure time may be varied to compensate for various long-range effects such as backscatter, fogging and loading effects in a process called proximity effect correction (PEC). Electron beam writer systems usually allow setting an overall dosage, called a base dosage, which affects all shots in an exposure pass. Some electron beam writer systems perform dosage compensation calculations within the electron beam writer system itself, and do not allow the dosage of each shot to be assigned individually as part of the input shot list, the input shots therefore having unassigned shot dosages. In such electron beam writer systems, all shots implicitly have the base dosage, before PEC. Other electron beam writer systems do allow explicit dosage assignment on a shot-by-shot basis. In electron beam writer systems that allow shot-by-shot dosage assignment, the number of available dosage levels may be <NUM> to <NUM> or more, or there may be a relatively few available dosage levels, such as <NUM> to <NUM> levels. For scanned multi-beam systems, dosage adjustment may be done by scanning the surface multiple times.

A charged particle beam system may expose a surface with a plurality of individually-controllable beams or beamlets. <FIG> illustrates an electro-optical schematic diagram in which there are three charged particle beamlets <NUM>. Associated with each beamlet <NUM> is a beam controller <NUM>. Beam controller <NUM> can, for example, allow its associated beamlet <NUM> to strike surface <NUM>, and can also prevent beamlet <NUM> from striking the surface <NUM>. In some embodiments, beam controller <NUM> may also control beam blur, magnification, size and/or shape of beamlet <NUM>. In this disclosure, a charged particle beam system which has a plurality of individually-controllable beamlets is called a multi-beam system. In some embodiments, charged particles from a single source may be sub-divided to form a plurality of beamlets <NUM>. In other embodiments, a plurality of sources may be used to create the plurality of beamlets <NUM>. In some embodiments, beamlets <NUM> may be shaped by one or more apertures, whereas in other embodiments there may be no apertures to shape the beamlets. Each beam controller <NUM> may allow the period of exposure of its associated beamlet to be controlled individually. Generally the beamlets will be reduced in size by one or more lenses (not shown) before striking the surface <NUM>. In some embodiments, each beamlet may have a separate electro-optical lens, while in other embodiments a plurality of beamlets, including possibly all beamlets, will share an electro-optical lens.

For purposes of this disclosure, a shot is the exposure of some surface area over a period of time. The area may be comprised of multiple discontinuous smaller areas. A shot may be comprised of a plurality of other shots which may or may not overlap, and which may or may not be exposed simultaneously. A shot may comprise a specified dose, or the dose may be unspecified. Shots may use a shaped beam, an unshaped beam, or a combination of shaped and unshaped beams. <FIG> illustrate some various types of shots. <FIG> illustrates an example of a rectangular shot <NUM>. A VSB charged particle beam system can, for example, form rectangular shots in a variety of x and y dimensions. <FIG> illustrates an example of a character projection (CP) shot <NUM>, which is circular in this example. <FIG> illustrates an example of a trapezoidal shot <NUM>. In one embodiment, shot <NUM> may be a created using a raster-scanned charged particle beam, where the beam is scanned, for example, in the x-direction as illustrated with scan lines <NUM>. <FIG> illustrates an example of a dragged shot <NUM>, disclosed in <CIT>. Shot <NUM> is formed by exposing the surface with a curvilinear shaped beam <NUM> at an initial reference position <NUM>, and then moving the shaped beam across the surface from position <NUM> to position <NUM>. A dragged shot path may be, for example, linear, piecewise linear, or curvilinear.

<FIG> illustrates an example of a shot <NUM> that is an array of circular patterns <NUM>. Shot <NUM> may be formed in a variety of ways, including multiple shots of a single circular CP character, one or more shots of a CP character which is an array of circular apertures, and one or more multi-beam shots using circular apertures. <FIG> illustrates an example of a shot <NUM> that is a sparse array of rectangular patterns <NUM> and <NUM>. Shot <NUM> may be formed in a variety of ways, including a plurality of VSB shots, a CP shot, and one or more multi-beam shots using rectangular apertures. In some embodiments of multi-beam, shot <NUM> may comprise a plurality of interleaved groups of other multi-beam shots. For example, patterns <NUM> may be shot simultaneously, then patterns <NUM> may be shot simultaneously at a time different from patterns <NUM>.

<FIG> illustrates an embodiment of a charged particle beam exposure system <NUM>. Charged particle beam system <NUM> is a multi-beam system, in which a plurality of individually-controllable shaped beams can simultaneously expose a surface. Multi-beam system <NUM> has an electron beam source <NUM> that creates an electron beam <NUM>. The electron beam <NUM> is directed toward aperture plate <NUM> by condenser <NUM>, which may include electrostatic and/or magnetic elements. Aperture plate <NUM> has a plurality of apertures <NUM> which are illuminated by electron beam <NUM>, and through which electron beam <NUM> passes to form a plurality of shaped beamlets <NUM>. In some embodiments, aperture plate <NUM> may have hundreds or thousands of apertures <NUM>. Although <FIG> illustrates an embodiment with a single electron beam source <NUM>, in other embodiments apertures <NUM> may be illuminated by electrons from a plurality of electron beam sources. Apertures <NUM> may be rectangular, or may be of a different shape, for example circular. The set of beamlets <NUM> then illuminates a blanking controller plate <NUM>. The blanking controller plate <NUM> has a plurality of blanking controllers <NUM>, each of which is aligned with a beamlet <NUM>. Each blanking controller <NUM> can individually control its associated beamlet <NUM>, so as to either allow the beamlet <NUM> to strike surface <NUM>, or to prevent the beamlet <NUM> from striking the surface <NUM>. The amount of time for which the beam strikes the surface controls the total energy or "dose" applied by that beamlet. Therefore, the dose of each beamlet may be independently controlled.

In <FIG> beamlets that are allowed to strike surface <NUM> are illustrated as beamlets <NUM>. In one embodiment, the blanking controller <NUM> prevents its beamlet <NUM> from striking the surface <NUM> by deflecting beamlet <NUM> so that it is stopped by an aperture plate <NUM> which contains an aperture <NUM>. In some embodiments, blanking plate <NUM> may be directly adjacent to aperture plate <NUM>. In other embodiments, the relative locations of aperture plate <NUM> and blanking controller <NUM> may be reversed from the position illustrated in <FIG>, so that beam <NUM> strikes the plurality of blanking controllers <NUM>. A system of lenses comprising elements <NUM>, <NUM>, and <NUM> allows projection of the plurality of beamlets <NUM> onto surface <NUM> of substrate <NUM>, typically at a reduced size compared to the plurality of apertures <NUM>. The reduced-size beamlets form a beamlet group <NUM> which strikes the surface <NUM> to form a pattern that corresponds to the pattern of the apertures <NUM>, which are allowed to strike surface <NUM> by blanking controllers <NUM>. In <FIG>, beamlet group <NUM> has four beamlets illustrated for forming a pattern on surface <NUM>.

Substrate <NUM> is positioned on movable platform or stage <NUM>, which can be repositioned using actuators <NUM>. By moving stage <NUM>, beam <NUM> can expose an area larger than the dimensions of the maximum size pattern formed by beamlet group <NUM>, using a plurality of exposures or shots. In some embodiments, the stage <NUM> remains stationary during an exposure, and is then repositioned for a subsequent exposure. In other embodiments, stage <NUM> moves continuously and at a variable velocity. In yet other embodiments, stage <NUM> moves continuously but at a constant velocity, which can increase the accuracy of the stage positioning. For those embodiments in which stage <NUM> moves continuously, a set of deflectors (not shown) may be used to move the beam to match the direction and velocity of stage <NUM>, allowing the beamlet group <NUM> to remain stationary with respect to surface <NUM> during an exposure. In still other embodiments of multi-beam systems, individual beamlets in a beamlet group may be deflected across surface <NUM> independently from other beamlets in the beamlet group.

Other types of multi-beam systems may create a plurality of unshaped beamlets <NUM>, such as by using a plurality of charged particle beam sources to create an array of Gaussian beamlets.

In the process of manufacturing a pattern on a surface, it is desirable to control the widths of shapes projected onto the surface by being able to provide a given constant bias. For example, often, one "mask" is made, then it might be determined that for whatever reason the pattern features on it are slightly too thick or too thin, say by <NUM>. The fabricator would then desire to bias all the edges in the pattern by <NUM> / <NUM> = <NUM> in another iteration to create the next better version. Constant bias is illustrated in <FIG> shows an example pattern <NUM> comprising the text "Hello World". Pattern <NUM> is similar to the original pattern <NUM>, but where the edges which have been positively biased in pattern <NUM> - i.e. the edges have been moved outward - so that the letters are thicker. In biasing, the edges of each figure in a pattern are biased "inwards" or "outwards," to make the width of each pattern narrower or fatter. The scale of the pattern does not change. Biasing may be performed, for example, to account for changes in etching characteristics (over-etching or under-etching).

<FIG> illustrates a conventional method of producing bias, by biasing the input CAD (computer-aided design) shapes geometrically. Element <NUM> is an original pattern, in the shape of an "H". Vectors <NUM> illustrate the direction in which each edge portion of pattern <NUM> is to move during positive biasing. Element <NUM> illustrates the revised pattern after a positive bias. Performing the biasing on shapes is a complex operation:.

This geometric method is not popular, because of the substantial computational effort required to bias the CAD shapes, and the consequent effect on mask turnaround time.

In a variant of the above method, the CAD shapes may be biased as they are read into a mask exposure system. Doing this saves disk input/output (I/O) volume, reducing or eliminating the turnaround time issue. However, this method still has the problem that a geometric constant bias is often not the only correction that is desired.

Another known correction method is to bias the dose of the source. If all shapes have a similar dose margin (i.e., edge slope), a desired constant distance bias can be obtained by changing the dose delivered to the surface. This has been the predominant method of biasing. The current method works well when dose margin is a good proxy for all sources of manufacturing variation. There are situations where constant bias in width is desirable. The current method does not work to create bias that is uniform in bias width, except when the following conditions are satisfied:.

Short-range effects cause some non-uniformity in biasing, but with fairly large shots this has been acceptable.

In the most advanced masks, however, some or all of these conditions may be violated:.

In this environment, a dosage change does not produce constant distance biasing.

<FIG>, <FIG>, <FIG> and <FIG> show the results of simulating a <NUM>% dosage bias according to conventional methods, with shapes of differing sizes, and starting with different exposure dosages, with electron beam exposure. <FIG> presents the conditions of the simulation, which was done using two long shots: one shot with a width of <NUM> and one shot with a width of <NUM>. The following simulation conditions were used:.

There are therefore four simulations: two shape widths at each of two dosages. <FIG> presents the results of the simulation.

As can be seen from <FIG>, the change in dimension (Delta CD) from the <NUM>% dose biasing varies between the <NUM> and <NUM> wide shapes, and also between the <NUM> and <NUM> dosages. This illustrates that dose biasing does not provide a constant distance dimensional change across the conditions of the simulation.

<FIG> illustrates dosage profiles for the <NUM> shape, for <NUM> dose, <NUM> dose, <NUM> dose, and <NUM> dose (<NUM> * <NUM>%). Curve <NUM> is the dosage profile for <NUM> dose; curve <NUM> is the dosage profile for <NUM> dose (<NUM> *<NUM>%); curve <NUM> is the dosage profile for <NUM> dose; and curve <NUM> is the dosage profile for <NUM> dose (<NUM>* <NUM>%). <FIG> illustrates the same dosage profiles as <FIG>, but zoomed in near the <NUM> / <NUM> (threshold) dosage point. Point <NUM> indicates that the <NUM> and <NUM> doses (curves <NUM> and <NUM>, respectively) cross the <NUM> threshold value at an x-coordinate of <NUM>. Point <NUM> indicates that both the 1X and 2X doses with <NUM>% bias (curves <NUM> and <NUM>, respectively) have doses of <NUM>*<NUM> = <NUM> at the pre-bias contour (x=<NUM>). Thus, for both the <NUM> dosage curve <NUM> and for the <NUM> dosage curve <NUM>, the dose at an x-coordinate of <NUM> is <NUM>% above the <NUM> threshold value at an x-coordinate of <NUM>. The <NUM>% dose increase at an x-coordinate of <NUM> has therefore been achieved. The amount the edge will move with a <NUM>% dose is determined by where the curve crosses the threshold value of <NUM>. Curve <NUM> intersects dose=<NUM> at x-coordinate <NUM>. Curve <NUM>, which has a higher slope than curve <NUM>, intersects dose=<NUM> at x-coordinate <NUM>, which is closer to x-coordinate <NUM> than is x-coordinate <NUM>. Constant biasing is therefore not achieved.

Thus, improved methods of bias correction are needed.

The present disclosure shall apply to manufacturing patterns using a multi-beam energy source, on any surface such as a mask, wafer, flat panel display (FPD), or FPD mask. The types of energy sources include electron beam (eBeam), proton beam, argon fluoride (ArF) optical laser, multi-frequency lasers (as FPD writers use), and EUV. In multi-beam, a single chamber (often called the column) houses an apparatus that shoots multiple shapes simultaneously either through a single source (e.g., electron gun or light source) or through multiple sources. Multiple shapes may be an array of, for example, <NUM> x <NUM>, but can be any number such as ranging from a total of approximately <NUM> or less, to much more than <NUM> x <NUM>. These shapes, which may be squares, are referred to as pixels in this disclosure.

Embodiments utilize a multi-beam machine to modify the dose of individual pixels to bring about a constant distance bias for every edge of every shape for the whole mask. This can be done inline within the machine, for example by using graphics processing unit (GPU) acceleration for the computing. By computing the simulated effect of a dose change of the pixels, every edge can be biased by approximately plus or minus a portion of the pixel size, while also manipulating the dose profile to enhance dose margin in various ways. The implementation may involve, for example, less than a pixel of bias, such as half a pixel. Larger biases with more complex analyses are also possible. "Enhancing" or improving dose margin is thought of as increasing dose slope (making it steeper) so that it is less susceptible to manufacturing variation. Since calculations for many pixels can be done in parallel, special purpose hardware devices may be used to improve performance over general purpose CPUs. In some embodiments, the special purpose hardware device may be a graphical processing unit (GPU).

Improving the uniformity of dose margins across the mask is an important agenda for mask shops. This has been because mask shops in some situations want to modify dose to achieve a relatively constant edge bias for all shapes in the mask. The present methods offer a superior alternative to that methodology in providing a way to achieve edge bias correction without any turnaround time penalty of another iteration of CAD.

In <FIG>, shaded quarter circle <NUM> represents a section of a pattern to be written onto a surface. Each pattern has at least one edge, such that a plurality of patterns for a surface has a plurality of edges. The quarter circle <NUM> portion of the pattern comprises edge <NUM>. As can be seen in the example of <FIG>, a pattern may cover fractional portions of pixels <NUM> in the array of pixels. Each pixel <NUM> has a corresponding dose. In this example, the dose for pixels fully covered by the pattern is <NUM>; doses for pixels at or near an edge of the pattern have a non-zero fractional amount (e.g., <NUM> to <NUM>); and pixels that are outside of the pattern or pattern edge have a dose of zero. The pixel coverage can be used to generate the location of the desired edge within each pixel, as well as the local dose slope gradient.

<FIG> illustrates rasterization of a portion of a surface into a grid, or array, of pixels. Pixels are typically <NUM>, although they may be <NUM>, <NUM>, or any other size. The values illustrated in each pixel of the <FIG> grid represent dosage values to be exposed onto the surface from <FIG> pattern <NUM>. In this example, the dose threshold is <NUM>.

Using the pixel array of <FIG>, a shape edge can be calculated. In some embodiments, interpolation can be used to determine the x and y coordinates where dosage crosses the dose threshold. For each specified pixel in which an edge of a pattern has been identified, a location and an orientation of the identified edge is determined. <FIG> illustrates the pixel array of <FIG>, with identified edge <NUM> also illustrated. Desirably, calculation of identified edge <NUM> can be done using dosages only from pixels in the neighborhood of the edge, which facilitates parallel processing in doing the calculations. The neighborhood of the edge may be, for example, within <NUM>-<NUM> pixels away from the edge.

Knowing the shape edge <NUM>, the mathematical gradient of this edge may be calculated at any point on the edge. <FIG> graphically illustrates the gradient vectors <NUM> extending from edge <NUM>, in the direction of a positive bias. For negative bias, each gradient vector would point in an opposite direction.

<FIG> illustrates the pixel array, where pixel dosages have been calculated to relocate edge <NUM> by the target bias amount, to position <NUM>.

The calculations described above are repeated for each pixel near any of the plurality of edges in the plurality of patterns. As indicated in the above example, calculations required for edge biasing using pixel dosage arrays can be done for each pixel using dosage information for only nearby pixels. This allows parallel processing of calculations. In some embodiments, the parallel processing may comprise use of graphical processing units (GPUs) or other specialized hardware.

Dose margin enhancement can also be accomplished with pixel dosage array shape data. As is known to those skilled in the art, in a leading edge mask process in semiconductor device manufacturing, for example, when shapes smaller than approximately <NUM> in mask dimensions are exposed with a normal <NUM> dose shot, the edge will have a lower dose margin than for larger shots. <FIG> illustrate how biasing can be combined with dose margin enhancement. <FIG> illustrates an example pixel dose array <NUM> to be exposed using an electron beam exposure system. In this example, the pixel size is <NUM> in both X and Y directions. A calculated edge <NUM> is determined from this data, representing a line end pattern. As shown in <FIG>, the width of the line end pattern in this example is <NUM>.

<FIG> a pixel array in which pixel dosages have been calculated to negatively bias edge <NUM>, relocating it to position <NUM>. The biased pattern with edge position <NUM> has a width of <NUM>, using a target bias of <NUM> from the original <NUM> width. The maximum pixel dosage is <NUM>. Pixel <NUM>, for example, through which the target edge traverses, has a dosage of <NUM>. As is known to those skilled in the art, a <NUM> wide line end pattern exposed with a normal <NUM> dose will have an undesirably low dose margin because of the characteristics of electron beam exposure systems when exposing patterns which are this small.

Dose margin can be improved by increasing the dose of pixels near edge <NUM>, as illustrated in <FIG>. In pixel array <NUM> of <FIG>, the maximum pixel dosage is set to <NUM>, meaning <NUM> time a normal dose. Pixel array <NUM> has a higher dose margin for the biased edge <NUM> than does pixel array <NUM>. In pixel array <NUM>, pixels in the center of the line end pattern remain at <NUM> dose, since increasing the dose of these pixels is less effective at improving dose margin than providing increased dosage closer to the edge <NUM>. Pixel <NUM>, which corresponds to <FIG> pixel <NUM>, has a dose of <NUM> - less than pixel <NUM>, which is necessary to maintain the target edge with the adjacent interior pixel having a dose of <NUM>.

In the example of <FIG>, the maximum pixel dosage is <NUM>. Use of even higher pixel dosages can further improve dose margin. However, in some multi-beam exposure systems, the exposure time for the surface is determined by the maximum dosage pixel(s) in the pattern. Higher maximum pixel dosages lengthen the overall exposure time, increasing turnaround time and cost.

<FIG> illustrates an example flowchart for performing bias corrections, in accordance with some embodiments. The input is a set of shapes <NUM>, such as from a computer-aided design (CAD) system. The set of shapes <NUM> may be a plurality of patterns, for example, a set of geometric shapes. Each pattern in the plurality of patterns has an edge. In step <NUM>, the input shapes are rasterized by determining the pixel doses in a <NUM>-dimensional array of pixels, using the plurality of patterns, to create a <NUM>-dimensional array of dosages <NUM> which represent dosages for a pixelized representation of a surface to be exposed. Each pixel in the array of pixels represents an exposure dosage. The pattern data of the plurality of patterns - e.g., the geometric shape data of the patterns - is rasterized to create the array of pixels. Using the array <NUM>, in step <NUM> the edges of the patterns are identified, and the gradient vectors along each of the edges are calculated. Identification of the edges in step <NUM> may include calculating a location of the edge using pixel dosages of the array of pixels. Step <NUM> also uses as input the target bias <NUM>. The direction of the gradient vectors is determined by whether the desired bias is positive (outward) or negative (inward).

In step <NUM> pixel dosages are calculated which will cause edges to be relocated by the target bias <NUM>. Step <NUM> uses as input the array <NUM> and the target bias <NUM>. Additionally, step <NUM> may input a predetermined maximum pixel dose <NUM>. In some embodiments, step <NUM> includes calculating the dose margin of each relocated edge, and adjusting pixel dosages to increase the dose margin in locations where the dose margin is less than a pre-determined minimum acceptable value. For example, the dose margin may be improved by increasing the pixel dose of a pixel near the relocated edge. The dose margin may be maximized, within a constraint of a predetermined maximum pixel dose, or it may be improved to at least a predetermined minimum dose margin. In other embodiments, step <NUM> includes maximizing the dose margin of each edge, subject to the maximum pixel dose. In some embodiments, step <NUM> may also include correction for non-linearities in the exposure system hardware. Step <NUM> outputs dosage array <NUM>, which is the array of pixels with the calculated pixel dosages. In step <NUM>, a surface is exposed in a multi-beam exposure system using the dosage array <NUM>.

In some embodiments, calculating the calculated pixel dose in step <NUM> can include compensating for a mid-range scattering. In one embodiment, mid-range exposure effects are calculated in step <NUM> from dosage array <NUM>. Step <NUM> outputs a mid-range dosage array <NUM>. The mid-range dosage array <NUM> may be coarser than array <NUM> - i.e. each pixel in array <NUM> represents a larger area than in dosage array <NUM>. In step <NUM>, dosage from a pixel in mid-range dose array <NUM> is subtracted from each calculated pixel dosage before outputting the dosage to array <NUM>.

Other quantities at the edges of the patterns can be adjusted using the same pixel methodology, such as compensating for eBeam non-linearity.

As described above, in the present methods all the calculations for the bias are local. Ordinarily, to do this sort of biasing geometrically, one would first need to analyze and combine the various geometric primitives together, which is an expensive operation. In contrast, by performing the biasing after the geometric data has been rasterized into pixels as in the present methods, it is possible to perform the biasing as a set of small local calculations, modifying each pixel based on nothing more than its immediate neighbors. Such local calculations enable the processing to be parallelized. In some embodiments, calculations may be performed in real time as an inline process, during the exposure of the surface by a multi-beam exposure system. In other embodiments, calculations may be performed during the exposure of another surface, in a pipelined fashion. In a pipelined system, the next surface to be written on the machine is calculated while the previous surface is being written on the machine. A pipelined system is effective for improving the throughput of many surfaces, if the surfaces have similar write times and compute times. An inline (real time) system is effective for improving the throughput as well as the turnaround times of each surface.

The present methods can be used offline, pipelined, or inline. Being fast enough to be able to process inline is most desirable. Inline processing is most desirable particularly when the number of total pixels that needs to be written is very large. For example, for semiconductor device manufacturing for multi-beam eBeam writing of masks, over <NUM> T-Bytes of data are required to store all the pixel data. Since multi-beam eBeam machines need to write the pixels extremely quickly, storing such data on hard disk or even solid state disk may not be practical in cost. In inline processing, unlike in offline or pipelined processing, there is no need to store the data because the machine consumes the data to write the pixels soon after the data is computed. This is another reason why inline processing that the present methods enable is valuable. As mentioned above, the same methodology can be used for adjusting pixel doses to improve dose margin (i.e., edge slope).

The calculations described or referred to in this disclosure may be accomplished in various ways. Due to the large amount of calculations required, multiple computers or processor cores of a CPU may also be used in parallel. In one embodiment, the computations may be subdivided into a plurality of <NUM>-dimensional geometric regions for one or more computation-intensive steps in the flow, to support parallel processing. In another embodiment, a special-purpose hardware device, either used singly or in multiples, may be used to perform the computations of one or more steps with greater speed than using general-purpose computers or processor cores. Specialty computing hardware devices or processors may include, for example, field-programmable gate arrays (FPGA), application-specific integrated circuits (ASIC), or digital signal processor (DSP) chips. In one embodiment, the special-purpose hardware device may be a graphics processing unit (GPU). In another embodiment, the optimization and simulation processes described in this disclosure may include iterative processes of revising and recalculating possible solutions. In yet another embodiment, calculations may be performed in a correct-by-construction method, so that no iterations are required.

<FIG> illustrates an example of a computing hardware device <NUM> that may be used to perform the calculations described in this disclosure. Computing hardware device <NUM> comprises a central processing unit (CPU) <NUM>, with attached main memory <NUM>. The CPU may comprise, for example, eight processing cores, thereby enhancing performance of any parts of the computer software that are multi-threaded. The size of main memory <NUM> may be, for example, <NUM>-bytes. The CPU <NUM> is connected to a Peripheral Component Interconnect Express (PCIe) bus <NUM>. A graphics processing unit (GPU) <NUM> is also connected to the PCIe bus. In computing hardware device <NUM>, the GPU <NUM> may or may not be connected to a graphics output device such as a video monitor. If not connected to a graphics output device, GPU <NUM> may be used purely as a high-speed parallel computation engine. The computing software may obtain significantly-higher performance by using the GPU for a portion of the calculations, compared to using CPU <NUM> for all the calculations. The CPU <NUM> communicates with the GPU <NUM> via PCIe bus <NUM>. In other embodiments (not illustrated) GPU <NUM> may be integrated with CPU <NUM>, rather than being connected to PCIe bus <NUM>. Disk controller <NUM> may also be attached to the PCIe bus, with, for example, two disks <NUM> connected to disk controller <NUM>. Finally, a local area network (LAN) controller <NUM> may also be attached to the PCIe bus, and provides Gigabit Ethernet (GbE) connectivity to other computers. In some embodiments, the computer software and/or the design data are stored on disks <NUM>. In other embodiments, either the computer programs or the design data or both the computer programs and the design data may be accessed from other computers or file serving hardware via the GbE Ethernet.

In some embodiments, a system for biasing shapes to be written onto a surface includes a device configured to input an array of pixels. Each pixel comprises a pixel dose, and the array of pixels represents dosage on a surface to be exposed with a plurality of patterns. Each pattern of the plurality of patterns has an edge. The system also includes a device configured to identify an edge of a pattern in the plurality of patterns; a device configured to calculate a calculated pixel dose for pixels which are in a neighborhood of the identified edge, so that the identified edge is relocated by a target bias; and a device configured to output the array of pixels with the calculated pixel doses. In some embodiments, the system includes a device configured to determine the dosages in the pixel array, using a set of geometric shapes. In some embodiments, the system can also include a device configured to expose the surface with the outputted array of pixels. The device configured to calculate the pixel doses may operate simultaneously with the device configured to expose the surface, in an inline fashion. The device configured to expose the surface may comprise multiple beams.

In some embodiments, a system includes a device configured to expose a pattern onto a resist-coated surface using an electron beam, and a device configured to compute a constant distance bias. The device configured to expose may expose the resist of the resist-coated surface with multiple beams. The device configured to expose and the device configured to compute may operate in an inline fashion. The device configured to compute may comprise a graphics processing unit (GPU).

Claim 1:
A method comprising:
inputting a pattern to be exposed on a surface, wherein the pattern comprises an edge;
inputting a target bias;
rasterizing the pattern to create an array of pixels, wherein each pixel in the array of pixels represents an exposure dosage;
identifying the edge of the pattern using the array of pixels;
calculating calculated pixel dosages in the array of pixels, for each pixel that is in a neighborhood of the edge, wherein the calculated pixel dosages relocate the edge of the pattern, wherein the edge may be relocated by a portion of each pixel, wherein the relocation is the target bias, and wherein calculating the calculated pixel dosages comprises a simulated effect of a dose change; and
outputting the array of pixels, including the calculated pixel dosages.