JP2002090979A - Auxiliary features for use in lithographic projection - Google Patents

Abstract

(57) [PROBLEMS] To project a high-density form such as a contact hole of an integrated circuit onto a substrate using a lithographic projection apparatus.
To provide an improved mask capable of accurately forming an image of such an isolated area and projecting it at a predetermined position without deformation. The array of isolated features (110) representing contact holes has a critical dimension of the mask pattern and a resolution limit of a lithographic apparatus in which the mask is to be used,
A plurality of auxiliary features 151, 15 that do not remain on the developed substrate
2 are arranged to increase the symmetry of this array. As a result, the mask is improved by reducing the aberration of the aerial image of the mask pattern, particularly the odd aberration, by the diffraction effect.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithographic projection apparatus, comprising: an illumination system for providing a projection beam of radiation; a first object table having a first object holder for holding a mask; Typically, using a lithographic apparatus that includes a second object table with a second object holder for imaging and a projection system for imaging an illuminated portion of the mask onto a target portion of the substrate.
Providing a mask carrying a pattern on the first object table, providing a substrate having a radiation-sensitive layer on the second object table, and bonding the illuminated portion of the mask on the target portion of the substrate; An assist feature for use in a device manufacturing method including an imaging step.
t features).

[0002] For the sake of simplicity, the projection system may hereinafter be referred to as a "lens", which terms include, for example, refractive optics, reflective optics, catadioptric optics, and charged particle optics. It should be construed broadly to encompass various types of projection systems, including elements. The illumination system may also include elements that operate according to any of these principles to direct, shape, or control the projection beam, and such elements are collectively or individually referred to below as "lenses." I might call. Moreover,
The first and second object tables may be referred to as a "mask table" and a "substrate table", respectively.

[0003] In this document, the terms "radiation" and "beam" are used to refer to ultraviolet radiation (eg, 365 nm, 248
nm, 193 nm, 157 nm or 126 nm) and extreme ultraviolet radiation (EUB), but not limited to them, but in principle these terms are used to X-rays, electrons and ions are also included. The invention will now be described using a reference system in orthogonal X, Y and Z directions, and the rotation about an axis parallel to the I direction is denoted by Ri. Further, unless the context demands otherwise, the term "vertical (Z)" as used herein does not imply any particular orientation of the device, but is perpendicular to the substrate or mask plane, or It is intended to point in a direction parallel to the optical axis of the optical system.

[0004]

2. Description of the Related Art Lithographic projection apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, the mask (reticle) may include a circuit pattern corresponding to an individual layer of the IC, and the pattern may be applied to a target portion of a substrate (silicon wafer) coated with a layer of radiation-sensitive material (resist). Alternatively, it can be imaged on an exposed area (eg, including one or more dies). In general, a single wafer will contain a whole network of adjacent target portions that are successively irradiated via the reticle, one at a time. In one type of lithographic projection apparatus, each target portion is irradiated by exposing the entire mask pattern onto the target portion at once; such an apparatus is commonly referred to as a wafer stepper. In an alternative device C, commonly referred to as a step-and-scan device C, the mask pattern is sequentially scanned under a projection beam in a given reference direction (the "scan" direction), while the projection system is generally Is the magnification M (generally <1), and the speed V of scanning the substrate table is the speed of scanning the mask table multiplied by the magnification M. Therefore, the substrate table is synchronized in parallel or anti-parallel with this direction. Each target portion is irradiated by scanning. Further information on a lithographic apparatus as described herein can be gleaned, for example, from International Patent Application WO 97/33205.

[0005] Generally, a lithographic apparatus includes a single mask table and a single substrate table. But,
Machines with at least two independently movable substrate tables have become available; see, for example, International Patent Application WO 98 /
See multistage apparatus described in 28665 and WO 98/40791. The basic operating principle behind such a multi-stage device is that the second substrate table can be moved to the loading position while the first substrate table is below the projection system to expose the first substrate above it, Ejecting the previously exposed substrate, picking up a new substrate, making some initial measurements on the new substrate, and then as soon as the exposure of the first substrate is completed, place the new substrate in an exposed position below the projection system. Wait to transfer to it; and then repeat this cycle; in this way, the throughput of the machine can be significantly increased, which in turn improves the cost of owning the machine. It should be understood that this same principle can be used with only one substrate table moving between the exposure position and the loading position.

[0006] In order to improve the image projected on the resist, and eventually the developed device, it is known to provide the mask with so-called "auxiliary features". Auxiliary forms are not intended to appear on resist developed devices,
In this embodiment, a mask is used to utilize a diffraction effect so that a developed image more closely resembles a desired circuit pattern. Auxiliary forms are generally “sub-resolution”,
It means that they are at least one dimension smaller than the smallest feature of the mask that is actually resolved on the wafer. Auxiliary features are those that define the minimum width of a feature or the minimum spacing between features of a mask, and often a fraction of the "critical dimension", which is the resolution limit of the lithographic projection apparatus in which the mask should be used. May have. However, since the mask pattern is typically projected at a magnification of less than 1, for example, 1/4 or 1/5, the auxiliary features on the mask will have larger physical dimensions than the smallest features on the wafer. Particular mention may be made. Two types of assistance are known. Scatter bars are lines of sub-resolution width placed on one or both sides of an isolated conductor to simulate the proximity effect that occurs in a tightly packed area. Serifs are used to bring the end or corner of a line closer to a right angle or circle, as desired.
Additional areas of various shapes placed at the corners and ends of the conductors, or corners of the rectangular form (note that in this context, the auxiliary form, commonly referred to as the "hammer head", is considered a form of serif) . Further information on the use of scattering bars and serifs can be found, for example, in US 5,242,770 and US 5,707,765, which are incorporated herein by reference.

[0007] Contact holes, or via holes, in integrated circuits present special problems in imaging. Since the contact holes often must be made through multiple or relatively thick process layers previously created on the wafer, they must be patterned into a relatively thick layer of photoresist, which creates an aerial image of this mask pattern. Requires a deep depth of focus.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an improved mask for better imaging of regularly or irregularly spaced, dense features, such as contact holes, and the like. It is an object of the present invention to provide a method of making such a mask and a device manufacturing method using the improved mask.

[0009]

According to the present invention, there is provided a mask for use in a lithographic projection apparatus, the mask comprising a plurality of isolated regions that contrast with the background and represent features to be printed in device fabrication. A mask is provided wherein the isolated regions are generally arranged in an array, wherein the mask is characterized by a plurality of auxiliary features which are smaller than the isolated regions and arranged to make the array more symmetric.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS These assist features tend to reduce aerial image aberrations by reducing the asymmetry of the array, ideally all the asymmetric aberrations caused by odd aberrations such as three wavefronts and coma. Is located to decrease. In an array that already has some degree of symmetry, these assist features may add additional symmetry or may make the unit (simple) cells more symmetric within themselves. In this way, the invention can provide an improvement in imaging symmetry, largely independent of the exposure device and the illumination or projection settings. In many cases, these isolated forms occupy grid points of a regular array (although these isolated forms may be slightly off the ideal grid points), but one or more of this unit or simple cell Can be seen as empty. In this case, these auxiliary features are placed on at least some of the open grid points.

Arrays that are themselves regular, for example in the form of a mask having one or more rotational or reflective symmetry degrees, are necessarily finite and thus lack translational symmetry; unit cells at the edges of the array Is not exactly equivalent to the central one, because they have only a few neighbors. Thus, auxiliary features according to the present invention may be placed around the exterior of the array to create pseudo-neighbors for the outermost features of the array. Of course, a wide variety of auxiliary features in different locations may be used in the array, for example, placing the auxiliary features within the array to make the array more rotational or reflective symmetric, and placing it outside the array to surround the outermost features. You may make it more similar to an internal form.

These assist features may be detectable in an aerial image and may partially expose the photo (energy sensitive) resist, but at least in one dimension so as not to appear in the developed pattern of the resist. Should be small enough. Accordingly, these assist features are generally smaller than the critical dimension of the mask pattern and the resolution limit of the lithographic apparatus in which the mask is to be used.

[0013] These isolated regions may mean, for example, contact holes to be made in a DRAM array. These isolated areas and assist features may be transparent areas on a relatively opaque background or vice versa. In a reflective mask, these isolated areas and assist features will have different reflectivity than the background. In a phase shift mask, these isolated regions and assist features may introduce a different phase shift and / or different attenuation from the background. It is not necessary that these assist features have the same "tone" as the isolated area.

According to another aspect of the invention, a method of making a mask for use in a lithographic projection apparatus forms a plurality of isolated regions that are contrasting with a background and represent features to be printed in device fabrication. And a method comprising the steps wherein the isolated regions are generally arranged in an array,
A method characterized by the further step of forming a plurality of assist features smaller than the isolated area and arranged to make the array more symmetric.

The position, shape and size of these assist features are calculated by calculating the aberrations at the wavefront that the pattern would create without them, and then predicting the aberrations, especially the three and one wavefront (coma) aberrations. May be determined by determining a location or the like for these assist features.

According to a further aspect of the invention, a lithographic projection apparatus is provided, comprising: an illumination system for providing a projection beam of radiation; a first object table with a first object holder for holding a mask; and a substrate. Manufacturing a device using a lithographic apparatus that includes a second object table with a second object holder for holding, and a projection system for imaging an illuminated portion of the mask onto a target portion of the substrate. Providing a mask carrying a pattern on the first object table, wherein the mask includes a plurality of isolated areas that are in contrast to the background and represent features to be printed in the manufacture of the device. A step in which the isolated regions are generally arranged in an array;
Providing a substrate having a radiation-sensitive layer on an object table, and imaging the illuminated portion of the mask onto the target portion of the substrate, wherein the mask is positioned above the isolated region. A method is provided, comprising a plurality of auxiliary features that are small and arranged to make the array more symmetric.

In a manufacturing process using a lithographic projection apparatus according to the invention, a pattern in a mask is imaged onto a substrate that is at least partially covered by a layer of radiation-sensitive material (resist). Prior to the imaging step, the substrate may undergo various processes, such as, for example, priming, resist coating, and soft baking. After exposure,
The substrate may undergo other processing, such as, for example, post-exposure bake (PEB), development, hard bake, and image morphology measurement / inspection. This series of processes is used as a basis for patterning individual layers of a device, eg, an IC. The layers so patterned are then subjected to various processes, all intended to finish the individual layers, such as etching, ion implantation (doping), metallization, oxidation, chemical and mechanical polishing, etc. May receive. If several layers are required, the whole process or its modification would have to be repeated for each new layer. Eventually, an array of devices (dies) will be present on the substrate (wafer). These devices can then be separated from each other by techniques such as dicing or sawing, from which the individual devices can be attached to a carrier, connected to pins, etc.
Further information on such processes can be found, for example, in Peter Van Zandt's "Manufacturing Microchips: A Practical Guide to Semiconductor Processing," 3rd Edition.
Edition, McGraw-Hill Publishing Company, 1997, ISBN 0-07-067250-4
Can be obtained from this book.

Although this text may refer specifically to the use of the device according to the invention in the manufacture of ICs, it is expressly understood that such a device has many other possible uses. Should. For example, it may be used in the manufacture of integrated optical systems, magnetic domain memory inductive detection patterns, liquid crystal display panels, thin film magnetic heads, and the like. One of ordinary skill in the art will appreciate that in the context of such alternative applications, any of the terms "reticle", "wafer" or "die" as used herein will be replaced by the more general terms "mask", "substrate" and ""Targetarea" or "Exposure area"
You will find that you should think that it can be replaced by.

While this specification focuses on a lithographic apparatus and method for patterning a radiation beam entering a projection system using a mask, the invention presented herein provides a general method for patterning the radiation beam. It should be noted that it should be seen in the broad context of a lithographic apparatus and method that employs an appropriate "patterning means". As used herein, the term "patterning means" refers to a means that can be used to provide an incident radiation beam with a patterned cross section corresponding to a pattern to be created on a target portion of the substrate; The term is also used in this context. Generally, the pattern will correspond to a particular functional layer in a device being created in this target portion, such as an integrated circuit or other device. In addition to the mask on the mask table, examples of such patterning means include: a programmable mirror array. An example of such a device is a matrix-addressable surface having a viscoelastic control layer and a reflective surface. The basic principle behind such a device is that (for example) the addressed area of this reflective surface reflects the incident light as diffracted light, while the unaddressed area reflects the incident light as undiffracted light. It is. Using an appropriate filter, the undiffracted light can be filtered out of the reflected beam, leaving only the diffracted light behind; thus, this beam is patterned according to the addressing pattern of the matrix-addressable surface. Will be done. The necessary addressing can be performed using suitable electronic means. Further information on such mirror arrays can be found, for example, in US Pat.
91 and US 5,523,193, which are incorporated herein by reference. A programmable LCD array. An example of such a configuration is given in US Pat. No. 5,229,872, which is incorporated herein by reference. This specification and claims should be construed to include such general patterning means as an alternative to a mask.

The present invention will be described below with reference to examples and the accompanying schematic drawings. In these drawings, similar reference symbols indicate similar parts.

Lithographic Projection Apparatus FIG. 1 schematically depicts a lithographic projection apparatus that can be used with the present invention. This device comprises: a radiation system Ex, IL for supplying a projection beam PB of radiation (eg UV rays). In this special case, the radiation system also includes a radiation source LA; comprising a mask holder for holding a mask MA (eg a reticle), with a first positioning means for accurately positioning the mask with respect to the member PL. A combined first object table (mask table) MT; comprising a substrate holder for holding a substrate W (e.g. a resist-coated silicon wafer), for positioning the substrate accurately with respect to the member PL; Second object table (substrate table) coupled to two positioning means
WT;-the target portion C of the substrate W
Including a projection system ("lens") PL (e.g., a refractive, catadioptric, or reflective system) for imaging on (e.g., including one or more dies). As depicted herein, the apparatus is transmissive (ie, has a transmissive mask). However, in general, it may be of a reflective type, for example (with a reflective mask). Instead,
The apparatus may use other types of patterning means, such as a programmable mirror array of the type mentioned above.

This radiation source LA (eg a lamp, laser or discharge plasma chamber) produces a beam of radiation. This beam is directly or, for example, a beam expander Ex
, And then into the lighting system (illuminator) IL. The illuminator IL may include adjusting means AM for setting the outer and / or inner radial extent (commonly referred to as σ-outer and / or σ-inner, respectively) of the intensity distribution of the beam. Moreover, it generally includes various other components, such as an integrator IN and a capacitor CO. In this way,
The beam PB incident on the mask MA has a desired uniformity and intensity distribution in its cross section.

Referring to FIG. 1, the radiation source LA may be within the housing of the lithographic projection apparatus (as is often the case when the radiation source LA is, for example, a mercury lamp), but from the lithographic projection apparatus. It should be noted that it is possible to be far away and direct the produced radiation beam to this device (for example, using a suitable directing mirror); this latter scenario is the case where the source LA is an excimer laser. This is often the case. The current invention and claims encompass both of these scenarios.

The beam PB is then transmitted to the mask table MT
Crosses the mask MA held above. After traversing the mask MA, the beam PB passes through a lens PL, which focuses this beam on a target portion C of the substrate W. With the help of the second positioning means (and the interferometer measuring means IF), the substrate table WT can be moved precisely, for example, to place different target portions C in the path of the beam PB. Similarly, for example, after mechanically retrieving a mask MA from a mask library or during a scan, the first
The mask MA can be precisely positioned with respect to the path of the beam PB by using the positioning means. In general, movement of the object tables MT, WT is realized with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), not explicitly shown in FIG. However, in the case of a wafer stepper (as opposed to a step-and-scan apparatus) the mask table MT may only be connected to a short-stroke actuator, or may be fixed.

The apparatus shown can be used in two different modes: In the step mode, the mask table MT is kept essentially fixed and the entire mask image is placed on the target portion C at one time (ie, (With a single "flash"). The substrate table WT is then moved in the x and / or y direction so that different target portions C can be illuminated with the beam PB; in scan mode, a given target portion C is not exposed in a single "flash" Except for that, essentially the same scenario applies. Instead, the direction in which the mask table MT is given (the so-called “scanning direction”, eg, y
Direction) at a velocity v so that the projection beam PB is caused to scan over the mask image; at the same time, the substrate table WT
Is moved therewith in the same or opposite direction at a speed V = Mv, where M is the magnification of the lens PL (typically M = 1
/ 4 or 1/5). In this way, a relatively large target portion C can be exposed without having to compromise on resolution.

[0026]

EXAMPLE 1 FIG. 2 shows a portion of a conventional 6% attenuated phase shift mask pattern that can be used in a lithographic projection apparatus as described above to make contact holes (vias) in a DRAM device. The mask pattern has an array of transparent regions 110 in a substantially opaque field that exposes radiation to expose the resist in the regions where contact holes are to be made. These transparent areas are 111, 112, 11
You will see that the three groups, labeled 3, are arranged in a regularly repeating manner. These contact holes
0.2 μm square with 0.2 μm spacing between contacts. Also shown is a reference area 120 of 0.4 × 1.6 μm ² .

The inventor has discovered that these contact holes do not image accurately, deform and displace from their nominal position. According to the present invention, auxiliary features are added to this mask pattern to make these arrays more symmetrical. The appropriate position and dimensions of the assist features are determined experimentally by considering the Zernike coefficients representing the wavefront aberrations of the image that would result from this pattern and the assumed assist features.

Wavefront aberrations can be written as a series according to their angular form:

[0029]

(Equation 1)

Here, r and θ are the radial and angular coordinates (r is normalized), and m is an index indicating the contribution of the m-th order aberration. R and R 'are functions of r.

This aberration can also be expressed by a Zernike expansion equation. W = Zif _i (r, θ) + Zjf _j (r, θ) + Zkf _k (r, θ) +... Here, each Z is a Zernike coefficient, and each f is a corresponding Zernike polynomial. These functions f take the form of the product of the polynomial of r and the sin or cos of mθ. For example, coma (m = 1) is expressed as Z7, Z8, Z14, Z15, Z2.
3, Z24, Z34, Z35, etc., and can be represented by a Zernike series, and, for example, the function associated with the Z7 coefficient [f ₇ (r, θ) in the notation above) is: (3r ³ -2r) cos (θ)

Table 1 summarizes the Zernike expansions for low order aberrations. In particular, the inventor has found that odd aberrations (m number is an odd number),
In particular, it has been determined that substantial improvement can be achieved by arranging the assist features to manipulate the Z10 (three wavefront) coefficients. Improvements can also be obtained by arranging the assist features to reduce the aerial image coma (one wavefront). The position, shape and size of the assist features are known as "Solid C", a commercially available software package supplied by Sigma C GmbH, Germany (GmbH) for simulating and modeling optical lithography. However, it can be determined using a known calculation method. “Prolis”
Other suitable software packages, such as those known as, may be used instead.

[0033]

[Table 1]

In the example of a DRAM, six repeating transparent areas (see FIG. 3) are combined into two pairs of triads A, B, C and D,
Considered E and F, the improvement is achieved by each element of the triple occupying one of the four corners of the square (in this example) unit cell. According to the present invention, the auxiliary modes 151 and 152 are provided.
Are located in the fourth corner and include clear squares that are too small to be printed on the developed pattern. These squares may be, for example, 0.12 μm on each side.
It should be noted that these assist features are visible in the aerial image and may partially expose the resist, but are washed away by development of the resist.

The effect of the present invention can be seen in FIG. 4 which is a graph of the intensity corresponding to the aerial image line 130 produced by the mask patterns of FIGS. 4, the solid line represents the intensity of the aerial image created by the mask pattern (FIG. 3) according to the present invention, and the dashed line represents the intensity of the aerial image created by the conventional mask pattern (FIG. 2). The asymmetry of the print can be represented by the distances L and R shown in FIG. 4; these are those that make contact holes, measured at resist threshold, selected at 0.25 in arbitrary units of the graph of FIG. Represents the distance between the wax peaks.
It can be seen that the distance L is reduced in the present invention, so that the asymmetry represented by the difference LR is also reduced.

[0036]

Second Embodiment FIG. 5 shows an alternative arrangement of the contact holes 110.
In this arrangement, pairs of contact holes 211, 212 repeat to form a honeycomb structure. These contact holes may be 0.2 μm square and the spacing between adjacent contacts may be 0.2 μm.
Also shown is a reference area 220 of 0.4 × 0.9 μm ² . According to the invention, an additional auxiliary feature 25 is provided at the center of each honeycomb cell.
By adding 1, the symmetry of the mask pattern is improved as shown in FIG. These auxiliary forms 2
51 may be, for example, a square having sides of 0.12 μm.

The improvement brought about by the present invention in this embodiment 2 is as follows.
Lines 23 of the aerial image created by the mask patterns of FIGS.
This can be seen in FIG. 7, which is a graph of intensity along zero. 4, the solid line represents the intensity of the aerial image created by the mask pattern (FIG. 6) according to the present invention, and the dashed line represents the intensity of the aerial image created by the conventional mask pattern (FIG. 5). It will be clearly seen that the aerial image produced by the mask pattern according to the invention is not very asymmetric.

[0038]

Third Embodiment FIG. 8 shows a rectangular "brick wall" pattern in a conventional staggered array. These rectangles are 0.2x
0.5 μm ² with 0.2 μm spacing between adjacent contacts
It is. The reference area 320 is 0.6 × 0.6 μm ² . According to the present invention, as shown in FIG.
51 is placed between rectangles 310. In these assisting forms, for example, each side may be 0.12 μm.

FIG. 10 is a contour plot of the aerial image created by the unit cell 320 at a 0.25 (arbitrary unit) intensity threshold. The fine dashed line represents the image produced by the present invention (FIG. 9), while the dashed line represents that produced by the conventional mask pattern (FIG. 8). The two-dot chain line represents an ideal aerial image of the mask pattern without three wavefront aberrations. It will be clearly seen that the image provided by the present invention is close to ideal.

[0040]

Fourth Embodiment FIG. 11 shows a mask pattern according to a fourth embodiment of the present invention. The array includes a form, for example, a regular rectangular array of contact holes 410. This array is very regular in nature and has a high degree of internal symmetry. However, by comparing the features in cell 420 to those in cell 421, differences will be seen. Cell 4
Features 410 in 20 have neighbors on all sides, while features 410 in cell 421 have no neighbors outside of them. Thus, according to the present invention, auxiliary features 450 are provided outside the array of features 410 to provide pseudo-adjacents for these features at the edges of the regular array. Thus, cell 421 is more similar to cell 420. Accordingly, these auxiliary features improve the translational symmetry of the array, as it makes the view from the print feature 410 at the edge of the array more similar to the view from the print feature 410 at the center of the array.

Print form 410 and auxiliary form 450
May be similar to those of Examples 1 to 3 and may be modified as desired for a particular application of the invention. If the array created by these print features is not square, these assist features may also be non-square, but must also be small enough to prevent printing. Auxiliary features around the outside of the array may, of course, be used in connection with the auxiliary features within the array itself. Further, if the image of a given auxiliary feature is affected by features that are farther away than its nearest neighbor, additional auxiliary feature columns may be provided as needed. In general, it may be preferable to provide auxiliary features around all sides of the array in printed form, but other features present near the array do not require the provision of auxiliary features all around the array. And / or may be impractical. FIG. 11 shows the assist features spaced from the array by a distance equal to the pitch of the array, but this distance may of course be varied to change the effect of the assist features as desired.

Although a particular embodiment of the invention has been described above, it will be appreciated that the invention may be practiced otherwise than as described. This description is not intended to limit the invention. It should be clearly noted that the present invention is applicable to any mask pattern having a (asymmetric) array or group of features. The present invention relates to a system-on-a-chip, including, for example, a memory and logic or processor on a single device, when the array contains only a portion of the mask pattern.
It should also be clearly noted that it is applicable to device manufacturing.

[Brief description of the drawings]

FIG. 1 shows a lithographic projection apparatus in which an embodiment of the invention can be used.

FIG. 2 shows part of a mask pattern for printing contact holes in the manufacture of a DRAM.

FIG. 3 shows a part of a mask pattern according to the first embodiment of the present invention for printing contact holes in a DRAM.

FIG. 4 is a graph of the intensity of a part of an aerial image created by the mask patterns of FIGS. 2 and 3;

FIG. 5 illustrates a portion of an alternative mask pattern for printing contact holes.

FIG. 6 shows a part of a mask pattern according to a second embodiment of the present invention.

FIG. 7 is a graph of the intensity of a part of the aerial image created by the mask patterns of FIGS. 5 and 6;

FIG. 8 shows a part of a mask pattern for printing a rectangular form.

FIG. 9 shows a part of a mask pattern according to a third embodiment of the present invention for printing a rectangular form.

FIG. 10 is a contour plot of the intensity of a part of the aerial image created by the mask patterns of FIGS. 8 and 9;

FIG. 11 shows a part of a mask pattern according to a fourth embodiment of the present invention.

[Explanation of symbols]

 C target part IL illumination system MA mask MT first object table PB projection beam PL projection system W substrate WT second object table 110 isolated area 151 auxiliary mode 152 auxiliary mode 251 auxiliary mode 310 isolated area 350 auxiliary mode 410 isolated area 450 auxiliary mode

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Johannes Jacobs Mateus Baselmans Netherlands Oil Shot, De Cruik 1 (72) Inventor Marx Schulter Eindhoven, Netherlands Evarihof 187 (72) Inventor Donis George Flagello USA Arizona, Scottsdale, E, Juan Tabo Road 8118 (72) Inventor Robert John Soca USA California, Campbell, Monte Villa Court 137 F-term (reference) 2H095 BA02 BB02 BB03 BB07 BB36 BC09 5F046 AA25 BA03 BA08 CB17

Claims (20)

[Claims] A mask for use in a lithographic projection apparatus, comprising a plurality of isolated areas (11) that contrast with the background and represent features to be printed in the manufacture of the device.
0,310,410), wherein the isolated areas are entirely arranged in an array, the plurality of auxiliary features positioned to be smaller than the isolated areas and to make the array more symmetric. The mask is characterized by. 2. The mask according to claim 1, wherein
A mask wherein the isolated areas are arranged in groups forming unit cells and the auxiliary features are positioned to make the unit cells more symmetric. 3. The mask according to claim 2, wherein
A mask wherein the isolated region is positioned at or near some point of one or more regular unit cells, and wherein the assist feature is positioned at a point not occupied by the isolated region of the regular unit cell . 4. The mask according to claim 3, wherein
A mask wherein the isolated area is positioned at three corners of a rectangular unit cell and the assist feature is positioned at a fourth corner. 5. The method according to claim 1, wherein:
The mask of claim 1, wherein the assist feature is positioned to reduce the effects of at least one odd aberration of a wavefront created by the mask pattern when illuminated by exposure light at the lithographic projection apparatus. . 6. The mask according to claim 1, wherein the auxiliary features are formed around a feature at or near an edge of the array and inside the array. A mask positioned along at least a portion of an edge of the array to more closely resemble the perimeter of the array. 7. The mask according to claim 1, wherein the auxiliary feature comprises a wavefront created by the mask pattern when illuminated by exposure radiation with the lithographic projection apparatus. 3 wavefronts and / or
Alternatively, a mask positioned so as to reduce the influence of coma (one wavefront) aberration. 8. The mask according to claim 1, wherein the auxiliary feature has the same contrast as a background of the mask as compared with the isolated region. 9. The mask according to claim 1, wherein the isolated area is more transparent to the exposure radiation of the lithographic projection apparatus than the background. 10. The mask according to claim 1, wherein the isolated area is more reflective than the background to exposure radiation of the lithographic projection apparatus. 11. The mask according to claim 1, wherein the isolated region has a phase shift different from that of the background. 12. The mask according to claim 1, wherein the auxiliary feature is smaller than a critical dimension of the mask. 13. The mask according to claim 12, wherein the auxiliary feature is smaller than a resolution limit of the lithographic projection apparatus. 14. A method of making a mask for use in a lithographic projection apparatus, the method comprising forming a plurality of isolated regions that are contrasting with a background and represent features to be printed in device fabrication, wherein the isolated regions are generally A method comprising the steps of being arranged in an array, the method characterized by the additional step of forming a plurality of auxiliary features that are smaller than the isolated regions and arranged to make the array more symmetric. 15. The method of claim 14, further comprising: determining a wavefront aberration of an aerial image that the pattern of the isolated regions will produce in the lithographic apparatus; and for the plurality of assist features. Determining the position, shape and size of the aerial image so as to reduce aberrations of the aerial image. 16. The method of claim 15, wherein the positions for the plurality of assist features are determined to reduce three and / or one wavefront (coma) aberrations. 17. A lithographic projection apparatus, comprising: an illumination system for providing a projection beam of radiation; a first object table having a first object holder for holding a mask; a second object for holding a substrate. A method of manufacturing a device using a lithographic apparatus comprising: a second object table having a holder; and a projection system for imaging an illuminated portion of the mask onto a target portion of the substrate, the method comprising: Providing a mask carrying a pattern on an object table, wherein the mask includes a plurality of isolated areas that are contrasted with a background and represent features to be printed in device fabrication, wherein the isolated areas are generally Arranging a substrate having a radiation-sensitive layer on the second object table; and arranging the irradiated portion of the mask on the second object table. Imaging on the target portion of the substrate, wherein the mask comprises a plurality of assist features positioned to be smaller than the isolated area and to make the array more symmetric. And how. 18. The method according to claim 16, wherein said device comprises a memory array, in particular a DRAM. 19. A device manufactured according to the method of claim 17. 20. A method according to any one of claims 17 to 19, wherein a maximum dimension of the auxiliary feature is less than 50% of a wavelength of the projection beam, preferably of a wavelength of the projection beam. A method that is in the range of 30-40%.