WO2002037537A2

WO2002037537A2 - Phase transition design to maintain constant line length through focus

Info

Publication number: WO2002037537A2
Application number: PCT/US2001/031442
Authority: WO
Inventors: John L. Nistler
Original assignee: Advanced Micro Devices, Inc.
Priority date: 2000-11-02
Filing date: 2001-10-09
Publication date: 2002-05-10
Also published as: WO2002037537A3; TW519678B; AU2001296722A1

Abstract

Various embodiments of a phase shifting mask and a method of utilizing the same are provided. In one aspect, a mask (86) is provided that includes a substrate (90) and an opaque structure (92) thereon. The opaque structure (92) has an end (128) with a first corner (159c) and a second corner (159d). The first corner (159c) and the second corner (159d) are operable to produce diffraction intensity maximums. A first phase shifting region (115a) is provided that has a first phase. A second phase shifting region (122) is provided that has a second phase that is phase shifted relative to the first phase. The first and second phase shifting regions (155a, 122) are arranged to define a first phase transition (156) between the first corner (159c) and the second corner (159d). The first phase transition (156) is operable to produce a plurality of intensity nodes that are superpositioned with the diffraction intensity maximums.

Description

PHASE TRANSITION DESIGN TO MAINTAIN CONSTANT LINE LENGTH THROUGH FOCUS

BACKGROUND OF THE INVENTION

1. Field of the Invention ■ This invention relates generally to semiconductor processing, and more particularly to a phase shifting mask design and to a method of patterning a photosensitive film.

2. Background Art

Optical photolithography is the most common technique currently used to pattern the minute features in modern semiconductor devices. In general, optical photolithography involves the projection of light through a mask and onto a photosensitive film. The mask includes a pattern of opaque areas and transparent areas. The opaque areas, frequently composed of chrome, block the light and thereby cast shadows and create dark areas, while the transparent areas allow light to pass and thereby create bright areas. The projection of bright and dark images onto the photosensitive film results in the exposure of some, and the shadowing of other portions of the photosensitive film. The exposure changes the chemical properties of the photosensitive film, rendering some portions thereof either soluble or unsoluble in a developing solvent. In some processes, light is passed through a reduction lens prior to striking the photosensitive film. Following exposure, an appropriate developing solvent is applied to the photosensitive film which dissolves selected portions of the photosensitive film.

All optical lithography systems utilizing opaque mask structures direct electromagnetic radiation past various edges and through various slits, and thus involve light diffraction to one degree or another. The edges and slits are natural features of the patterns of polygonal structures on conventional reticles and masks, and may number in the hundreds, thousands, or even millions, depending on the complexity of the mask. The general effect of diffraction is a spreading of the radiation into regions that are not directly exposed to the oncoming waves.

One problem associated with diffraction effects is loss of line length, that is, the creation of a line pattern in a resist film that has a shorter length than the overlying opaque mask structure. The problem is particularly acute at locations on the mask where the end of a chrome line is separated from the orthogonally oriented edge of an adjacent chrome structure. Diffraction effects between the adjacent end of the chrome line and the edge of a neighboring chrome structure produce enough constructive interference to effectively expose portions of the resist film beneath the end of the chrome line. The resulting line patterned in the resist film will have a shorter than desired length. The line shortening may be exacerbated during subsequent etching of films underlying the resist film. This is due to the propensity for resist corners to be etched at a higher rate than other resist surfaces due to the higher concentration and volume of available etchants proximate the resist corners.

Phase shift masking has been in use for a number of years as a means of increasing the effective resolution of optical lithography. Typically, a phase shifting involves passing light through a mask that is fabricated with a plurality of transparent areas, some of which are phase shifted and some of which are non- phase shifted. The phase shifting properties of the phase shifted openings are provided by either altering the thickness of the phase-shifted openings relative to the non-phase shifted openings or by using a material with different refractive index than the non-phase shifted openings. In either case, light passing through the phase shifted openings is phase shifted relative to light passing through the non-phase shifted openings. Diffraction effects may be reduced by combining both phase shifted light and non-phase shifted light so that constructive and destructive interference takes place.

Generally, a summation of constructive and destructive interference of phase-shift masks results in improved resolution and in improved depth of focus of a projected image of an optical system. However, conventional phase-shift masks may not adequately solve the problem of line length loss at mask locations where chrome lines terminate in close proximity to the edges of adjacent chrome structures.

Optical proximity correction schemes have been employed in the past as a means of reducing the deleterious effects of edge diffraction induced line length loss. Common examples of these include both rules based and model based. However, such techniques have limited success in situations where resist exposure occurs away from optimum focus.

The present invention is directed to overcoming or reducing the effects of one or more of the foregoing disadvantages.

DISCLOSURE OF INVENTION In accordance with one aspect of the present invention, a mask is provided that includes a substrate and an opaque structure thereon. The opaque structure has an end with a first corner and a second corner. The first corner and the second corner are operable to produce diffraction intensity maximums. A first phase shifting region is provided that has a first phase. A second phase shifting region is provided that has a second phase that is phase shifted relative to the first phase. The first and second phase shifting regions are arranged to define a first phase transition between the first corner and the second corner. The first phase transition is operable to produce a plurality of intensity nodes that are superpositioned with the diffraction intensity maximums. In accordance with another aspect of the present invention, a mask is provided that includes a substrate, a first opaque structure and a second opaque structure. The first opaque structure has a first end separated from the second opaque structure to define a gap capable of transmitting radiation. The first end has a first corner and a second corner. The first corner and the second corner are operable to produce diffraction intensity maximums. A first phase shifting region is provided that has a first phase. A second phase shifting region is provided that has a second phase that is phase shifted relative to the first phase. The first and second phase shifting regions are arranged to define a first phase transition between the first corner and the second corner. The first phase transition is operable to produce a plurality of intensity nodes that are superpositioned with the diffraction intensity maximums.

In accordance with another aspect of the present invention, a mask is provided that includes a substrate, a first phase shifting region that has a first phase, and a second phase shifting region that has a second phase that is phase shifted about 180° relative to the first phase. A first opaque structure is positioned on the substrate between the first and second phase shifting regions and has a first end with a first corner and a second corner. The first corner and the second corner are operable to produce diffraction intensity maximums. A second opaque structure is positioned on the substrate in spaced-apart relation to the first opaque structure to define a gap capable of transmitting radiation. A third phase shifting region is provided that has a third phase that is phase shifted about 60° relative to the first phase. A fourth phase shifting region is provided that has a fourth phase that is phase shifted about 60° relative to the third phase and about 120° relative to the second phase. The third and fourth phase shifting regions are arranged to define a first phase transition in the gap. The first phase transition is operable to produce a first plurality of intensity nodes that are superpositioned with the diffraction intensity maximums. In accordance with another aspect of the present invention, a mask is provided that includes substrate capable of transmitting radiation, a first phase region and a second phase region adjacent to the first phase region and defining a first phase transition therebetween. The first and second phase regions are out of phase whereby transmitted radiation destructively interferes and results in an intensity drop off at the first phase transition. A third phase region is provided along with a fourth phase region adjacent to the third phase region and defining a second phase transition therebetween that is substantially aligned with the first phase transition.

The third and the fourth phase regions are out of phase whereby transmitted radiation destructively interferes and produces an intensity drop off at the second phase transition that is less than the intensity drop off at the first phase transition.

In accordance with another aspect of the present invention, a method of patterning a photosensitive film is provided that includes providing the photosensitive film on a substrate and exposing the photosensitive film with radiation. During the exposure, selected portions of the photosensitive film are masked with a mask that has a first opaque structure, a second opaque structure, a first phase shifting region and a second phase shifting region. The first opaque structure has a first end with a first corner and a second corner that are operable to produce diffraction intensity maximums. The first phase shifting region has a first phase, and the second phase shifting region has a second phase that is phase shifted relative to the first phase. The first and second phase shifting regions are arranged to define a first phase transition between the first corner and the second corner that is operable to produce a plurality of intensity nodes that are superpositioned with the diffraction intensity maximums. The exposed photosensitive film is then developed.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and other advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings in which:

FIG. 1 is a plan view of an exemplary embodiment of an integrated circuit in accordance with the present invention;

FIG. 2 is a plan view of a conventional mask for patterning a photoresist layer which may be used to pattern the integrated circuit of FIG. 1;

FIG. 3 is a plan view of a selected portion of the mask shown in FIG. 2;

FIG. 4 is a plan view of a small portion of a resist film patterned by the portion of the mask shown in FIG. 3;

FIG. 5 is a plan view of a portion of a conventional phase shifting mask; FIG. 6 is a plan view of an exemplary embodiment of a phase shifting mask that may be used to pattern the structures of the integrated circuit depicted in FIG. 1 in accordance with the present invention;

FIG. 7 is a plan view of a selected portion of the mask shown in FIG. 6 in accordance with the present invention; FIG. 8 is a cross-sectional view of FIG. 7 taken at section 8-8 in accordance with the present invention; FIG. 9 is a plan view of a portion of a photosensitive film patterned with the mask shown in FIG. 7 in accordance with the present invention;

FIG. 10 is a Boissung plot taken at section 10-10 of FIG. 9 in accordance with the present invention; FIG. 11 is a cross-sectional view of FIG. 9 taken at section 10-10 in accordance with the present invention;

FIGS. 12-15 are three-dimensional representations of small portions of a photosensitive film patterned using the mask of FIG. 7 with various values of defocus in accordance with the present invention; and

FIG. 16 is a plan view of an alternate exemplary embodiment of a phase shifting mask in accordance with the present invention.

MODES FOR CARRYING OUT THE INVENTION In the drawings described below, reference numerals are generally repeated where identical elements appear in more than one figure. Turning now to the drawings, and in particular to FIG. 1, therein is shown a plan view of an exemplary embodiment of an integrated circuit 10 implemented on a semiconductor substrate 12. Two of the plurality of circuit devices are designated 14 and 16 respectively. The circuit devices may be laid out in any of a myriad of different arrangements to implement a desired circuit function. For the purposes of illustration, the devices of the integrated circuit are laid out in pairs forming a plurality of memory cells, one of which consists of the circuit devices 14 and 16. As is common in modern integrated circuits, the integrated circuit 10 includes one or more conductor lines 18 and 20 that are routed past the transistor devices 14 and 16. A conventional mask 22 for patterning a photoresist layer which may be used to pattern the integrated circuit 10 is illustrated in FIG. 2. The mask 22 includes a glass substrate 24 upon which a pattern of opaque structures 25, 26, 27, 28 and 29 are formed. The opaque structures 25, 26 and 27 correspond to the desired layout for the transistor devices 14, 16 and 17 while the opaque structure 28 corresponds to the desired layout of conductor line 20. The opaque structures 29 correspond to other features in FIG. 1. The opaque structures 25, 26, 27, 28 and 29 are typically composed of an opaque and highly reflected material such as chrome or the like.

The details of the mask structures 25, 26, 27, 28 and 29 may be understood by referring now also to FIG. 3, which is magnified plan view of the portion of FIG. 2 circumscribed by the dashed box 30. The mask features 25 and 26 are typically fabricated with a pitch Xj which corresponds to the minimum critical dimension ("CD") for the prevailing process technology and with a length Yj which is preselected to provide the resulting circuit devices 14 and 16 shown in FIG. 1 with a length that produces a desired electrical function. The gaps 33 between the ends 32 of the mask features 25 and 26 and the adjacent edge 34 of the mask feature 28 have a dimension Y₂ that is also typically quite small and may correspond to the minimum critical dimension of the prevailing process technology. The same is true for the gaps 35 between the structures 25, 26 and 27 and the structures 29. The patterning of a resist film using the mask 22 depicted in FIG. 2 may be understood by referring to

FIG. 3 and also to FIG. 4, which is a plan view of a small portion of a resist film 36 patterned by the portion of the mask 22 shown in FIG. 3. As is well-known in the art, the mask 22 is placed over the resist film 36 and illuminated with an ultraviolet or other type of electromagnetic radiation source to expose portions of the resist film 36 that are not covered by the mask structures 25, 26, 27, 28 and 29. Following exposure, the resist film 36 is developed in the usual way to leave a pattern of resist structures 38, 40, 42 and 44. The length Y₃ of the mask structures 38, 40 and 44 is considerably shorter than the length Y_t of the mask structures 25, 26 and 27. The dashed images 46 represent the lengths of the mask structures 25, 26 and 27 and thus the desired lengths for the resist structures 38, 40 and 44. This loss of line length, that is, the difference between Y_x and Y₃, is the result of diffraction effects occurring in the gaps 33 and 35 shown in FIG. 3. The length Y₃ of the resist structures 38, 40 and 44 may be further reduced during subsequent etching of films underlying the resist film 36. As noted above, this is due to the propensity for resist corners to be etched at a higher rate then other resist surfaces due to the higher concentration and volume of available etchants proximate the resist corners. The diffraction effects between the adjacent edges of the mask structures 25, 26 and 27 and the mask structure 28 and the mask structures 29 produces enough constructive interference to effectively expose portions of the resist film 36 beneath the ends of the mask structures 25, 26 and 27. This undercutting exposure results in the eventual production of the shortened resist structures 38, 40 and 44 as shown in FIG. 4.

Line length loss can result in a variety of device performance problems. Shorter than anticipated line lengths can produce unanticipated resistivity values for transistor device structures. If line length loss is significant enough, the circuit devices may not perform at all, such as, for example, where a transistor gate no longer is positioned over an active area.

Phase shift masking has been in use for several years as a technique for producing thin device features. FIG. 5 is a plan view of a conventional phase shifting mask 48 that may be used to pattern the resist structures 38, 40, 42 and 44 shown in FIG. 4. The mask 48 includes a light transmitting plate 50 that has a phase of 0°.

Opaque mask structures 52, 54 and 55 are patterned on the plate 50 in the usual way. A phase shifter 56 with a phase of 180° is formed between the mask structures 52 and 54. The interaction of incident radiation passing through the 0° and 180° portions results in a destructive interference effect which produces very thin device features on an underlying resist film (not shown). To ensure that the 0° to 180° phase transition does not produce an underexposure between the corners 58 and 60 of the mask structures 52 and 54 and thus a potential bridging in an underlying resist film, a 120° phase shifter 62 is formed in the plate 50. The 120° to 180° phase transition 64 ensures that the intensity of light passing the corners 58 and 60 is high enough so that the portions of an underlying resist film positioned thereunder will be sufficiently exposed. Corresponding 120° phase shifters 66 and 68 are provided at the lower ends of the mask structures 52 and 54. Sixty degree phase shifters 70, 72, 74 and 76 are provided to lessen the phase shift gradient between the 120° phase shifters 62, 66 and 68 and the surrounding 0° region. Without the phase shifters, the edges of a 120° phase shifter, such as the phase shifter 62, would abut the 0° phase region and potentially produce a pronounced intensity dip and resulting underexposure in the vicinity of the upper and lower corners of the mask structures 52 and 54. Such an underexposure in those regions could produce irregular bulges in the resist film pattern with the mask 48. Note that the 60-to-120° phase transitions 78 and 80 are positioned outside of the gaps 82 and 84 between the mask structures 52 and 54 and the mask structure 55. Indeed, the conventional practice has been to position the phase transitions 78 and 80 substantially outside of the gaps 82 and 84 so that an intensity dip proximate the ends of the structures 52 and 54 is avoided. An exemplary embodiment of a mask 86 in accordance with the present invention that may be used to pattern the structures of the integrated circuit 10 depicted in FIG. 1 may be understood by referring now to FIGS. 6, 7 and 8. FIG. 6 is a plan view of the mask 86, FIG. 7 is a plan view of the portion of FIG. 6 circumscribed by the dashed box 88 in FIG. 6, and FIG. 8 is a cross-sectional view of FIG. 7 taken at section 8- 8. The mask 86 consists of a light transmitting substrate or plate 90 upon which a plurality of opaque mask structures are fabricated, three of which are designated 92, 94, 96, 98, 100, 102 and 104. The plate 90 is composed of a material capable of transmitting electromagnetic radiation, such as, for example, soda-lime glass, borosilicate glass, quartz or the like. The patterned structures 92, 94, 96, 98, 100, 102 and 104 are generally polygonal in shape and may be composed of emulsion, chrome, iron oxide or the like. In the illustrated embodiment, the polygon structures 92, 94, 96, 98, 100, 102 and 104 are composed of chrome. The mask 86 may be dark-field or clear-field as desired. In the illustrated embodiment, the mask 86 is of clear-field polarity. As the skilled artisan will appreciate, commercially available resists are manufactured with sensitivity to a variety of wavelengths. Accordingly, the term "opaque" as used herein and in the claims below, is intended to mean incapable of transmitting electromagnetic radiation with a wavelength(es) to which a given resist is sensitive.

The plate 90 includes a 0° phase region and a phase shifting region 106 positioned between the facing edges 108 and 110 of the mask structures 92 and 94. The interaction of incident radiation passing through the 180° phase shifting region 106 and the 0° region provides for the establishment of very thin lines corresponding to the shapes of the mask structures 92 and 94 in a photoresist film (not shown) patterned with the mask 86. The assignment of 0° and 180° to the respective portions of the plate 90 is somewhat arbitrary. The phase of the phase shifter 106 is selected to be approximately 180° out of phase with the non-phase shifted portion of the plate 90 so that sufficient destructive interference leads to the patterning of thin lines in a photosensitive film. A 120° phase shifter 112 is formed between the ends 114 and 116 of the mask structures 92 and 94 and the edge 118 of the mask structure 98. The 120° phase shifter 112 is provided to establish a low angle phase transition with the 180° phase shifter 106 so that the area between the edges 108 and 110 at the 180°-to-120° phase transition 120 is not under exposed and produces a line in an underlying resist pattern. The 120° phase shifters 122 and 124 are similarly provided between the ends 126 and 128 of the mask structures 92 and 94 and the ends 130 and 132 of the mask structures 100 and 102. As with the 120° phase shifter 112, the 120° phase shifters 122 and 124 are provided to establish low angle phase transitions 136 and 138 with the 180° phase shifter 106. The 60° phase shifters 140 and 142 are provided on either side of the phase shifter 112 to provide low angle phase transitions 144 and 146. Again, the assignment of 60° and 120° phase angles is somewhat arbitrary.

As the skilled artisan will appreciate, in the absence of the phase shifters 140 and 142, there would exist a 120° to 0° phase transition at the left and right edges of the phase shiffer 112, which could produce a large enough drop off in intensity at those phase transitions that would produce an underexposure of an underlying resist film and the complete bridging between the patterned resist structures corresponding to the mask structures 92, 94 and 98. However, unlike the conventional phase shifting mask 48 depicted in FIG. 5, the mask 86 in accordance with the present invention is fabricated so that the phase transitions 144 and 146 are positioned between the inner edges 108 and 110 and the outer edges 148 and 150 of the mask structures 92 and 94. The phase transitions 144 and 146 are positioned between the respective edges 108 and 148 and 110 and 150 and in the gaps 152 and 154 between the edge 118 of the structure 98 and the edges 114 and 116 of the mask structures 92 and 94 so that an intensity effect is produced which effectively eliminates the loss of line length depicted in FIG. 4.

Two 60° phase shifters 155a and 155b are positioned adjacent to the 120° phase shifters 122 and 124 and define 60°-to-120° phase transitions 156 and 157 that are positioned in gaps 158a and 158b between the structures between the edges 148 and 108 of the mask structure 92 and the edges 110 and 150 of the mask structure 94. The deliberate positioning of the phase transitions 156 and 157 as depicted in FIG. 7 is intended to provide the same intensity effect proximate the gaps 158a and 158b as the phase transitions 144 and 146 and thus prevent the unwanted diffraction induced exposure of an underlying film positioned directly below ends 128 and 130 of the mask structures 92 and 94 and the corresponding ends of the mask structures 102.

The aforementioned intensity effect is the result of the interactions of: (1) the intensity maximums of the diffraction patterns produced at the respective corners 159a, 159b, 159c, 159d, 159e, 159f, 159g, 159h, 159i, 159j, 159k andl591 of the mask structures 92, 94, 100 and 102; and (2) the intensity nodes of the phase transitions 136, 138, 140, 142, 144, 146, 156, and 157. The phase transitions 144, 146, 156 and 157 are deliberately positioned between the edges 108 and 148 and 110 and 150 of the opaque structures 92 and 94 to produce a superpositioning of the above-referenced corner diffraction intensity maximums and the phase transition intensity nodes. This strategic superpositioning may achieve an overall average intensity maximum that is above the resist exposure threshold of an underlying resist film (not shown).

It is anticipated that the optimum effect will be achieved in circumstances where the phase transitions 144, 146, 156 and 158 are positioned substantially at a mid-point between the edges of the respective mask structure, e.g., 148 and 108 for the mask structure 92 and 110 and 150 for the mask structure 94. However, the beneficial effects of the deliberate positioning of the phase transitions 144, 146, 156 and 158 may be realized so long as the phase transitions 144, 146, 156 and 158 are positioned somewhere between the particular edges of the pertinent mask structure, e.g., 92 or 94.

The skilled artisan will appreciate that the benefits of the present invention may be applied to mask designs that involve opaque structures that do not terminate proximate other opaque structures and thus do not present a gap per se like the gaps 152, 154, 158a and 158b. For example, the same type of strategic positioning of the phase transition 156 may be utilized in circumstances where the adjacent mask structure 100 is not present. In this circumstance, the intensity maximums of the diffraction patterns produced at the corners 159c and 159d may be deliberately superpositioned with the intensity nodes of the phase transitions 136, 140 and 156.

Various well-known techniques may be used to fabricate the various phase shifting regions. For example, various portions of the plate 90 may be sequentially etched to selected depths.

FIG. 9 depicts a plan view of a portion of a photosensitive or resist film 160 that has been patterned, that is, exposed and developed using the mask image depicted in FIG. 7. Experiment has shown that the resist structures 162, 163 and 164 corresponding to the mask structures 92, 94 and 96 in FIG. 7 are patterned with a length Y₃', which is substantially the same as the length Y of the mask structures 92, 94 and 96 as shown in FIG. 7. Thus, the resist structures 162, 163 and 164 may be patterned without substantial line length loss. Small hillocks 165 may be patterned in the resist structure 166 as a result of the positioning of the phase transitions of the mask 86 shown in FIG. 7. The skilled artisan will appreciate that the preservation of line length at the expense of line width or

CD will not necessarily result in an improved process. However, the mask design in accordance with the present invention provides for diminished line length loss without substantial sacrifice of line width or CD critical dimension. This is illustrated in FIGS. 10 and 11, which are, respectively, a Boissung plot taken at section 10-10 of FIG. 9 and a cross-sectional view of FIG. 9 taken at section 10-10. The Boissung plot of FIG. 10 illustrates three curves 167, 168 and 170 at three different exposure energy levels. Exposure is performed with light at a wavelength of 248 nm and a partial coherence of 0.60, and through a 0.54 numerical aperture lens. The first curve 167 represents an exposure dosage of 20 mJ/cm². The second curve 168 represents an exposure dosage of 15mJ/cm² and the third plot 170 represents an exposure dosage of 10 mJ/cm². The dashed lines 172 represent a target critical dimension range plus or minus 10 % above and below a design CD of 0.2 μm. Note that the plot 168 corresponding to 15 mJ/cm² illustrates that the mask design of the present invention provides an isofocal CD that falls within the design CD of 0.2 μm plus or minus 10 % over a defocus interval of about -0.45 μm to about -0.18 μm. This data suggests that line width may be maintained over a substantial interval of defocus.

The two-dimensional profile of the resist structures 162, 164 and 165 are illustrated in FIG. 11. In one exemplary embodiment, the critical dimension for the top is 0.29 μm, the critical dimension at the bottom is

0.345 μm the average sidewall angle is about 85° and the thickness loss is about 0.4 %.

Three-dimensional representations of the mask 160 for various values of defocus, a single exposure dosage of 15 mJ/cm², and a design CD of 0.2 μm are illustrated in FIGS. 12, 13, 14 and 15. Exposure is performed with light at a wavelength of 248 nm and a partial coherence of 0.60 and a 0.54 numerical aperture lens. FIG. 12 depicts the mask 160 at -0.45 μm defocus, FIG. 13 depicts the mask 160 at -0.15 μm defocus,

FIG. 14 depicts the mask 160 at 0.15 μm defocus and FIG. 15 depicts the mask 160 at -0.65 μm defocus. Note that, while there is a fair degree of image degradation at -0.65 μm defocus as shown in FIG. 15, there is, nevertheless, very little loss of line length throughout the entire range of defocus from 0.15 to -0.65 μm. Furthermore, line width is relatively constant, through the interval 0.15 to -0.45 μm of defocus. An alternate exemplary embodiment of the multiphase mask, now designated 86', may be understood by referring now to FIG. 16. In the exemplary embodiment depicted in FIGS. 6, 7 and 8, a single phase transition, such as the phase transition 144, is positioned between opposing edges 148 and 108 of a mask structure 92 to achieve a desired phase transition diffraction effect between the upper end 114 of the mask structure 92 and the edge 118 of the mask structure 98. In this illustrative embodiment shown in FIG. 16, multiple phase shifting regions are positioned adjacent to the 120° phase shifting region 112 and between the opposing edges 148 and 108 and 110 and 150 of the mask structures 92. More specifically, 60° phase shifting regions 174 and 176 may be positioned adjacent to the phase shifting region 112, and 30° phase shifting regions 178 and 180 may be positioned adjacent to the 60° phase shifting regions 174 and 176. In this way, the 60° phase shifting regions 174 and 176 may modulate the 120° phase shifting region 112 at the phase transitions 182 and 184 as described above and the 30° phase shifting regions 178 and 180 may establish very low angle phase transitions 186 and 188 with the 0° phase portions of the mask 86'. The exact number and phase angles for the plurality of phase shifting regions employed between the opposing edges 148 and 108 and 110 and 150 may be subject to great variety.

A chromeless embodiment of the multiphase mask, now designated 86", may be understood by referring now to FIG. 17. A central 180° phase shifting region 190 is bordered laterally by a 0° phase portion of the mask 86". The phase of the phase shifter 190 is selected to be approximately 180° out of phase with the non-phase shifted or 0° phase portion of the mask 86" so that sufficient destructive interference leads to the patterning of thin lines in a photosensitive film. The phase transitions 192 and 194 between the phase shifting region 190 and the 0° region thus supplant the opaque mask structures described above. Two 120° phase shifters 196 and 198 are formed at the upper and lower borders of the 180° phase shifter 190. The 120° phase shifters 196 and 198 are bracketed respectively by 60° phase shifters 200 and 202. The 120° phase shifters 196 and 198 are provided to establish low angle phase transitions 204 and 206 with the 180° phase shifter 190 so that the areas between the phase transitions 192 and 194 at the 180°-to-120° phase transitions 204 and 206 are not under exposed and produce a line in an underlying resist pattern. The 60° phase shifters 200 and 202 are provided to establish low angle phase transitions 208 and 210 with the 120° phase shifters 200 and 202. Again, the assignment of °0, 60°, 120° and 180° phase angles is somewhat arbitrary.

The mask 86" in accordance with the present invention is fabricated so that the portions 212 and 214 of the phase transitions 208 and 210 are in substantial alignment with the 180°-to-0° phase transition 192 and the portions 216 and 218 of the phase transitions 208 and 210 are similarly in substantial alignment with the 180°-to-0° phase transition 194. This configuration produces the same type of intensity effect as the strategically positioned phase transitions 144 and 146 depicted in FIG. 7 above, and thus effectively eliminates the loss of line length depicted in FIG. 4 in circumstances involving chromeless masks. While the invention may be susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and have been described in detail herein. However, it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the invention as defined by the following appended claims.

Claims

CLAIMSWhat is claimed is:

1. A mask (86), comprising:

A substrate (90) capable of transmitting radiation; an opaque structure (92) on the substrate (90) and having an end (128) with a first corner (159c) and a second corner (159d), the first corner (159c) and the second corner (159d) being operable to produce diffraction intensity maximums; a first phase shifting region (122) having a first phase; a second phase shifting region (155a) having a second phase that is phase shifted relative to the first phase; and whereby the first and second phase shifting regions (122, 155a) are arranged to define a first phase transition (156) between the first corner (159c) and the second corner (159d), the first phase transition (156) being operable to produce a plurality of intensity nodes, the plurality of intensity nodes being superpositioned with the diffraction intensity maximums.

2. A mask (86), comprising: a substrate (90) having a first opaque structure (92) and a second opaque structure (100), the first opaque structure (92) having a first end (128) separated from the second opaque structure (100) to define a gap (158a) capable of transmitting radiation, the first end (128) having a first corner (159c) and a second corner (159d), the first corner (159c) and the second corner (159d) being operable to produce diffraction intensity maximums; a first phase shifting region (155a) having a first phase; a second phase shifting region (112) having a second phase that is phase shifted relative to the first phase; and whereby the first and second phase shifting regions (155a, 112) are arranged to define a first phase transition (156) between the first corner (159c) and the second corner (155d), the first phase transition (156) being operable to produce a plurality of intensity nodes, the plurality of intensity nodes being superpositioned with the diffraction intensity maximums.

3. The mask of claims 1 or 2, wherein the first end of the first opaque structure has a midpoint, the first phase transition being positioned substantially at the midpoint.

4. The mask of claims 1 or 2, wherein the second phase is shifted relative to the first phase by about 60°.

5. The mask of claim 4, wherein the first phase is 60° and the second phase is 120°.

6. The mask of claims 1 or 2, comprising a third phase shifting region adjacent to the first phase shifting region.

7. The mask of claim 6, wherein the third phase shifting region has a third phase that is phase shifted relative to the first phase shifting region.

8. The mask of claim 7, wherein the third phase is shifted relative to the second phase by about 60°.

9. A mask (86), comprising: a substrate (90); a first phase shifting region (106) having a first phase; a second phase shifting region (0°) having a second phase that is phase shifted about 180° relative to the first phase; and a first opaque structure (92) positioned on the substrate (90) between the first and second phase shifting regions (106), (0°) and having a first end (114), the first end (114) having a first corner (159a) and a second corner (159b), the first corner (159a) and the second corner (159b) being operable to produce diffraction intensity maximums; a second opaque structure (98) positioned on the substrate in spaced-apart relation to the first opaque structure (92) to define a gap (152) capable of transmitting radiation; a third phase shifting region (112) having a third phase that is phase shifted about 60° relative to the first phase; a fourth phase shifting region (140) having a fourth phase that is phase shifted about 60° relative to the third phase and about 120° relative to the second phase; and whereby the third and fourth phase shifting regions (112, 140) are arranged to define a first phase transition (144) in the gap (152), the first phase transition (144) being operable to produce a first plurality of intensity nodes, the first plurality of intensity nodes being superpositioned with the diffraction intensity maximums.

10. The mask of claim 9, wherein the first end of the first opaque structure has a midpoint, the first phase transition being positioned substantially at the midpoint.

11. The mask of claim 9, comprising a fifth phase shifting region positioned between the first phase shifting region and the fourth phase shifting region and having a fifth phase that is phase shifted about

30° relative to the first and fourth phase shifting regions, the fourth and fifth phase shifting regions being arranged to define a second phase transition in the gap that is operable to produce a second plurality of intensity nodes, the second plurality of intensity nodes being superpositioned with the diffraction intensity maximums.

12. The mask of claim 9, comprising a third opaque structure adjacent to a second end of the first opaque structure and defining a gap therebetween, and a phase shifting region adjacent to the second phase shifting region and defining a phase transition region in the gap between third opaque structure and the second end of the first opaque structure.

13. The mask of claim 12, wherein the second end of the first opaque structure has a midpoint, the first phase transition being positioned substantially at the midpoint of the second end.

14. A mask (86"), comprising: a first phase region (0°); a second phase region (190) adjacent to the first phase region (0°) and defining a first phase transition (192) therebetween, the first and second phase regions (0°, 190) being out of phase whereby transmitted radiation destructively interferes and results in an intensity drop off at the first phase transition (192); a third phase region (196); and a fourth phase region (200) adjacent to the third phase region (196) and defining a second phase transition (212) therebetween that is substantially aligned with the first phase transition, the third and the fourth phase regions (196, 200) being out of phase whereby transmitted radiation destructively interferes and produces an intensity drop off at the second phase transition (212) that is less than the intensity drop off at the first phase transition (192).

15. The mask of claim 14, wherein the first phase region and the second phase region are out of phase by about 180°.

16. The mask of claim 14, wherein the third phase region and the fourth phase region are out of phase by about 60°.

17. The mask of claim 14, wherein the first phase region and the second phase region are out of phase by about 180° and the third phase region and the fourth phase region are out of phase by about 60°.

18. A method of patterning a photosensitive film (160), comprising: providing the photosensitive film (160) on a substrate; exposing the photosensitive film (160) with radiation while masking selected portions thereof with a mask (90) having a first opaque structure (92) and a second opaque structure (98), the first opaque structure (92) having a first end (114) separated from the second opaque (98) structure to define a gap (152) capable of transmitting radiation, the first end (114) having a first corner (159a) and a second corner (159b), the first corner (159a) and the second corner (159b) being operable to produce diffraction intensity maximums, a first phase shifting region (140) having a first phase,, and a second phase shifting region (112) having a second phase that is phase shifted relative to the first phase whereby the first and second phase shifting regions (140, 112) are arranged to define a first phase transition (144) between the first corner (159a) and the second corner (159b), the first phase transition (144) being operable to produce a plurality of intensity nodes, the plurality of intensity nodes being superpositioned with the diffraction intensity maximums; and developing the exposed photosensitive film (160).

19. The method of claim 18, wherein the photosensitive film comprises a positive photosensitive material such that members are patterned into the photosensitive film having shapes corresponding to the shapes of the first and second opaque structures.

20. The method of claim 18, wherein the photosensitive film comprises a negative photosensitive material such that trenches are patterned into the photosensitive film having shapes corresponding to the shapes of the first and second opaque structures.