EP1502153A2

EP1502153A2 - Photolithography mask comprising absorber/phase-shifter elements

Info

Publication number: EP1502153A2
Application number: EP03749925A
Authority: EP
Inventors: Philippe Thony; Bernard Aspar; Gilles Fanget
Original assignee: Commissariat a lEnergie Atomique CEA
Current assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 2002-05-07
Filing date: 2003-05-06
Publication date: 2005-02-02
Also published as: US20050158634A1; WO2003096121A2; FR2839560A1; WO2003096121A3; FR2839560B1; JP2005524877A

Abstract

The invention relates to an exposure mask comprising a transparent substrate (100) with at least one absorber/phase-shifter element (112) disposed therein, such as to form a one-piece assembly with said substrate. The invention can be used for photolithography.

Description

MASK FOR PHOTOLITHOGRAPHY WITH ABSORBENT ELEMENTS / DEPHASEURS INCLUDED.

Technical Field The present invention relates to a photolithography mask with absorbing / phase-shifting elements included.

Photolithography masks are widely used for the manufacture of components in the fields of microelectronics, microsystems and integrated optics. They allow in particular to fix the shape and dimensions of components, parts of components, or even intermediate structures used for the production of components.

The invention finds applications in the technical fields indicated above, and in particular for the production of very small patterns, by means of a short wavelength insolation light.

State of the prior art.

Photolithography is one of the fundamental techniques of microelectronics. It uses photosensitive intermediate and sacrificial layers. These layers, for example resin, are deposited on layers of material to be treated. After exposure and development, the resins, formed, can constitute masks for etching or doping the underlying layers to be treated. To give the photosensitive resins a desired pattern, they are themselves insolated through an exposure mask. This corresponds, possibly on a larger scale, to the desired pattern. Insolation light is generally a coherent monochromatic light from a laser. An optical system associated with the mask, and receiving the insolation light, makes it possible to form an image of the pattern of the mask on the layer of photosensitive resin. The exposure masks can advantageously be installed in a photo-repeater for successively exposing different fields of a support, exactly according to the same pattern.

FIG. 1 appended illustrates, in a simplified manner, an exposure mask of known type.

The mask of FIG. 1 comprises a transparent substrate 10 made of silica or quartz. On this substrate are absorbing / phase-shifting elements 12. These correspond to the sunshine pattern or to a complementary pattern, depending on whether the photosensitive resin is of the positive or negative type. The absorber / phase-shifting elements can be opaque or semi-transparent elements.

Opaque absorbers / phase shifters, such as chrome elements, for example, can be used to make a binary insolation mask. Furthermore, absorber / phase-shifting elements made of a semi-transparent material, such as an alloy of silicon and molybdenum, make it possible to produce a phase shift insolation mask. The light that crosses the elements absorbers / phase shifters in fact undergoes a phase shift with respect to the light which passes outside the elements.

Above the absorbing / phase-shifting elements of the mask is a covering film 20. This is, for example, a polymer film. The film 20 is kept away from the absorber / phase-shifter elements 12 by means of a frame 22 bonded to the substrate 10. The role of the film is essentially to prevent dust from settling on the face of the substrate carrying the absorbent elements / phase shifters.

The image of the mask that is formed on a photosensitive layer to be exposed corresponds to the image of the absorber / phase-shifting elements. In other words, the optical system associated with the mask is developed for a focal plane conjugated to the face of the substrate 10 carrying the absorbing / phase-shifting elements. Thus, the spacing between the film 20 and the absorber / phase-shifter elements 12 of the mask makes it possible to move the image of any dust or scratches out of the field of sharpness.

The contrast of the blurred dust image is then sufficiently low so that the resin to be exposed is not sensitive to it.

The evolution of microelectronics techniques towards the manufacturing of ever faster and more efficient components, leads to the production of ever smaller photolithography patterns. As part of this development, improvements in exposure equipment may relate to optical components. projection of the mask image. This is, for example, an increase in their openness. Another important parameter is the wavelength of the insolation light. One trend is to reduce the wavelength from 193 nm for current photo-repeaters to 157 nm for future production units. Reducing the wavelength allows the projection of finer details.

A difficulty arises, however, with a wavelength as short as 157 nm. It is linked to a limited transmission of light through the mask and through the optical projection means.

The substrate of the mask, as well as the projection lenses, can possibly be made of materials capable of offering a satisfactory light transmission. On the other hand, the covering film 20 absorbs a large amount of insolation light for short wavelengths. The same applies to the air located in the space between the substrate 10 of the mask and the covering film 20. A significant absorption harms the contrast of the projected image and therefore the resolution of lithography.

One solution envisaged consists in replacing the flexible covering film 20, which is made of polymer, by a film of a hard material having better light-transmitting properties. The use of a hard material for the covering film is however liable to disturb more significantly the path of a light beam of sunshine. This can lead to deformations of the image of the mask projected onto a layer of photosensitive material to be exposed. In addition, the installation of a covering film of a hard material increases the complexity and the cost of manufacturing the masks.

Furthermore, to avoid absorption of light by the air contained in the free space between the substrate and the covering film, a system can be provided for purging this space before use. This operation is however delicate and also has a negative influence on the final cost of the mask.

A further illustration of the state of the art can be found in documents (1) and (2), the full references of which are given at the end of the description.

There is another type of mask: alternate type PSM masks called self-aligned. This state of the art is illustrated by document (3), the full reference of which is given at the end of the description. These masks include chrome patterns and quartz engravings for the phase shifters. The phase shifters are first produced on the substrate. Then, a layer of chromium is deposited. Then, the chrome patterns are made in this layer. These masks are called SCAA for "Sidewall Chrome Alterning Aperture".

The production of this type of mask poses a problem because the technological process must comprise two stages, one relating to quartz for producing the phase mask and the other relating to chromium to produce the chromium mask, these two stages being carried out on the same substrate. It is difficult to achieve a flawless chromium deposit on the etched surface of the substrate. It is also difficult to produce the patterns in the chromium layer, again because of the topology of the surface (spreading of resin and exposure by electron beam or by laser).

Statement of the invention.

The object of the present invention is to propose a photolithography mask which does not have the limitations and difficulties mentioned above.

One aim is in particular to propose a mask compatible with short wavelengths of sunshine, and in particular with a wavelength of the order of 157 nm, or even less.

An aim is thus to propose a mask which does not introduce significant deformations of the projected image and which does not significantly absorb the insolation light.

Another object is to propose a mask which does not require a purge and whose manufacturing cost is moderate. To achieve these goals, the invention relates more precisely to a mask for photolithography comprising a transparent substrate, the substrate comprising a first portion of substrate and a second portion of substrate, integral with the first portion of substrate, at least one absorber / phase-shifter element being embedded in the substrate, characterized in that the first part of the substrate is bonded, without adding material, to the second part of the substrate.

Although the mask may have only one absorber / phase-shifter element, possibly of complex shape, it generally includes several.

In the rest of the text, reference is thus made to a plurality of absorbing / phase-shifting elements.

The absorber / phase-shifting elements are considered to be included in the substrate and to form a monolithic assembly with the substrate, when they are embedded therein so that the mask does not have a cavity in contact with the absorbing / phase-shifting elements, or when a possible cavity is small enough not to significantly absorb a light beam capable of passing through the substrate.

Thanks to the monolithic nature of the mask, it does not contain, if not very little air or gas absorbing the light of insolation. Furthermore, as the absorber / phase-shifting elements are included, their main faces capable of being exposed to light are covered by the substrate. They are thus protected from dust and possible scratches. More specifically, dust and possible scratches may appear on an external face of the substrate, that is to say outside of a plane or of a region comprising the absorber / phase-shifting elements. The spacing between the absorber / phase shifting elements and a surface likely to be polluted corresponds to the thickness of the substrate or of a part of the substrate that covers the elements, not a cavity. Furthermore, such elements are easily cleaned with standard methods such as chemical baths. At least one absorber / phase-shifter element can be embedded in one of said substrate parts, by being flush with one contact face of the other of said substrate parts. In this embodiment, the second part of the substrate constitutes a cover which exactly covers the face of the first part of the substrate on which the absorber / phase-shifting elements are flush. The first and second parts can be interchangeable. In other words, each of the two parts can both have recessed absorbers / phase shifters and serve as a cover for the other part. Thus, the problems associated with the production of alternate PSM type masks are avoided. Each function (phase mask and chrome mask) is carried out on its own substrate before assembly. There is no interference from the two substrates.

The absorber / phase-shifting elements can be chosen from opaque elements, transparent or semi-transparent elements having a refractive index different from that of the substrate, or a combination of such elements.

Advantageously, the first and second parts of substrate, in direct contact with each other, can be made of identical materials. This makes it possible to avoid any discontinuity in the propagation of light through the mask. The materials can also be chosen different to voluntarily introduce phase shifts of the light. The assembly of the first and second substrate parts is carried out for example by bonding and advantageously the bonding is of the molecular adhesion type.

According to a variant, the absorbing / phase-shifting elements can also be in contact via a filling material placed between the first and second parts of the substrate. The absorber / phase-shifting elements can be embedded in the first and second parts of the substrate. The absorbers / phase shifters can also be embedded in the filling infill layer and sandwiched between the first and second parts ^" of substrate. -

One of the first and second parts of the substrate, or optionally the two parts, can be etched before they are assembled so that at least one first part of the substrate has a face with depressions facing a second part of the substrate. The depressions can be filled with a filling material. It is, for example, the intermediate material between the substrate parts. The cavities, filled with the filling material, can constitute light-shifting elements when the filling material has an optical index different from that of the first and / or second substrate parts. Other characteristics and advantages of the invention will emerge from the description which follows follow, with reference to the figures in the accompanying drawings. This description is given purely by way of non-limiting illustration.

Brief description of the figures.

- Figure 1, already described, is a simplified schematic section of a photolithography mask of known type.

- Figure 2 is a schematic section of a photolithography mask according to the invention, with a substrate in two parts.

- Figure 3 is a schematic section of a photolithography mask according to the invention, with an intermediate filling material. FIGS. 4 and 5 are schematic sections of photolithography masks in accordance with the invention, and constituting variants of the masks of FIGS. 2 and 3.

- Figures 6 and 7 are schematic sections of photolithography masks according to the invention with phase shifting elements.

FIGS. 8 and 9 are schematic sections of photolithography masks according to the invention, and constituting variants of the mask of FIG. 7.

Detailed description of methods of implementing the invention

In the following description, identical, similar or equivalent parts of the different figures are identified by the same reference signs to facilitate the transfer between the figures. Furthermore, and for the sake of clarity of the figures, all the elements are not represented according to a uniform scale. Figure 2 shows a mask according to the invention. It comprises a transparent substrate 100 and, included in this substrate, light absorbing / phase shifting elements 112. The substrate is made of a hard material. It is, for example, made of silica or quartz or any other transparent material for a wavelength of the insolation light.

The light absorbing / phase shifting elements may be made of an opaque material such as a metal. For example, a layer of chrome. They can also be made of a semi-transparent material, such as oSi. When a material is semi-transparent, it makes it possible to introduce a phase shift in the insolation lumen. The transmission coefficient of transparent materials is, for example, of the order of 6 to 12%. The value of the phase shift which exists between the beams which pass through the absorber / phase-shifter elements and those which do not pass through them, can be adjusted by acting on the composition and / or on the thickness of these elements. The composition and the thickness are, for example, adjusted to introduce phase opposition into the beams.

The making of a. mask according to FIG. 2 comprises, for example, the etching of cavities in a first part 110 of the substrate, the deposition of a layer of material suitable for the manufacture of the absorber / phase-shifting elements, then the leveling of this layer with stop on the first part of the substrate. At the end of this operation, absorber / phase-shifting elements 112 are obtained which are flush with one face of the first part of substrate 110. The shape of the elements corresponds to that of the cavities previously etched. The mask is completed by bonding a second part of substrate 120 to the face on which the absorber / phase-shifting elements are flush.

The bonding can be a direct molecular bonding, that is to say without the addition of material. It then results from an appropriate preparation for polishing and cleaning the faces of the first and second parts of the substrate brought into contact. For example, a bonding of hydrophilic type can be carried out. For this, before contacting, the two parts of the substrate are cleaned in order to obtain good hydrophilicity (for example with chemical cleaning of the SCI type). Mechanical-chemical polishing can be carried out in order to attenuate or even eliminate the surface roughness. After assembly, a heat treatment can be carried out to increase the bonding forces and ensure good stability over time (for example this treatment can be carried out at 300 K for 2 hours).

The first and second substrate parts may be made of different materials or, preferably, of the same material. The fact of using the same material makes it possible not to affect the path of a light beam passing from the first part of substrate to the second part of substrate. FIG. 3 shows another possibility of making the photolithography mask. In this example, a layer of opaque or semi-transparent material is deposited on one face of a first portion of substrate 110. This layer is then etched to give it a desired pattern and thus form one or more absorbing / phase-shifting elements 112. The interstices between the absorber / phase shifter elements are then filled with a transparent or semi-transparent filling material 114 such as fused silica or fused silica modified by the addition of chlorinated or fluorinated compounds. This filling material can also be an organo-mineral glass deposited in solution in a solvent, by centrifugation and annealing (sol-gel process). The choice of this material is not particularly critical. The thickness of the absorber / phase-shifter elements 112, and therefore that of the filling material, is generally small. Thus, the filling material does not absorb a large amount of insolation light. You can also choose a quasi-transparent or transparent filling material. After a leveling of the filling material, produced for example by a chemical mechanical polishing process, the first part of substrate 110 is assembled with the second part of substrate 120, also called superstrate, so as to cover the absorbing / phase-shifting elements 112 .

FIG. 4 shows a variant of the photolithography mask of FIG. 3. According to this variant, the filling material covers the absorber / phase-shifting elements 112. During the manufacture of the mask, the leveling of this material does not take place with stop on the absorber / phase-shifting elements, but before reaching these elements. During the assembly of the first and second parts of substrate 110, 120, the filling material can optionally be used for bonding by promoting the adhesion of the first and second parts.

FIG. 5 shows a variant of the photolithography mask of FIG. 2. Before assembling the first and second parts of substrate 110, 120, a layer of transparent material 114, comparable to the filling material, is deposited on the face of the first part substrate 110, to which the absorbing / phase-shifting elements 112. The layer of transparent material 114 is, for example, an adhesive.

FIG. 6 shows a particular embodiment of a photolithography mask according to the invention in which the absorber / phase-shifting elements 112 are associated with phase-shifting elements 118 formed directly in one of the parts 110 of the substrate. It is observed that the first part of substrate 110 has depressions 116 etched from the face carrying the absorber / phase-shifting elements. The depressions can be etched before or after the formation of the absorber / phase shifter elements 112 and are located in particular between the locations provided for these elements. The phase shifting elements 118 are constituted by the combination of the depressions 116 and of a filling material which fills these depressions. In the example illustrated, the depressions are filled with the transparent material of filling 114 already mentioned with reference to the preceding figures. The depressions 116 cause a beam to pass through varying thicknesses of substrate and filling material. Variable phase shifts can thus be introduced into the beams as a function of the depth of the depressions 116.

FIG. 7 shows another possible embodiment of a photolithography mask comprising two types of absorber / phase-shifting elements 112a, 112d. Two layers of materials are successively deposited on a portion of substrate 110 and shaped by etching according to desired patterns. It is, in order, a layer of transparent or semi-transparent material having an optical index different from that of the first portion of substrate 110, then a layer of opaque material. The etching of these layers makes it possible to form phase-shifting elements 112d and absorbing elements 112a corresponding respectively to the transparent / semi-transparent layer and to the opaque layer.

It can be observed that absorbing elements 112a can partially cover and obscure phase-shifting elements 112d. The space between the absorber elements and phase shifters is filled with filling material 114 in the manner already described. If necessary, the filling material can also constitute phase-shifting elements.

Figures 8 and 9 simply illustrate alternative embodiments of the photolithography mask of Figure 7, also with absorbing elements 112a and phase-shifting elements 112d. In the case of FIG. 8, the absorbing elements 112a are formed on an assembly face of the first part 110 of the substrate while the phase-shifting elements 112d are embedded in the second part 120 of the substrate. A transparent material 114 coats the absorbing elements 112a. It can be observed that the absorbent elements of the second part of substrate 120 coincide with certain gaps left between absorbent elements of the first part of substrate. It should be noted that in an embodiment of the mask according to FIG. 8, the phase-shifting elements 112d can be solid or gaseous.

In the last example, given in FIG. 9, phase-shifting elements 112d are defined on the second part 120 of the substrate, for example by etching a layer, and absorbing elements, 112a are defined on the first part of substrate 110.

The first and second parts are then assembled by comparing the absorber / phase-shifting elements and connecting them by means of a layer 114 of transparent filling material. This layer coats the elements.

In a particular embodiment, after the first and second parts of the substrate have been bonded, at least one of the parts is thinned in order to obtain a thickness of substrate less than the sum of the thicknesses of the two parts. The installation of the mask in the equipment is thus facilitated. CITED DOCUMENTS (D

"Mechanical analysis of hard pellicles form 157 nm lithography" by Philip L. Reu et al., Optical

Microlithography XIV, Proceedings of SPIE, vol.

4346 (2001), pages 1166-1174, (2)

"157-nm Photomask Handling and Infrastructure: Requirements and Feasibility", by Jerry Cullings,

Ed Muzio, Optical Microlithography XIV, Proceedings of SPIE, vol. 4346 (2001) pages 52-60. (3)

"Phase Phirst! An improved strong-PSM paradigm" by Marc D. Levenson et al., Proc. of SPIE 4186, 20 ^th

Annual BACUS Symposium on Photomask Technology and

Management, ed. Brian J. Grenon, Giang T. Dao

(January 2001).

Claims

1. Mask for photolithography comprising a transparent substrate (100), the substrate comprising a first portion of substrate (110) and a second portion of substrate (120), integral with the first portion of substrate, at least one absorber / phase-shifter element ( 112) being embedded in the substrate, characterized in that the first part of the substrate is bonded, without adding material, to the second part of the substrate.

2. Mask according to claim 1, characterized in that it comprises a first part of substrate bonded by molecular adhesion to a second part of substrate.

3. Mask according to claim 1, wherein at least one absorber / phase shifter element is embedded in each of the first and second substrate portions.

4. Mask according to claim 1, in which at least one absorber / phase-shifter element (112) is embedded in one of said substrate parts, by being flush with one contact face of the other of said substrate parts.

5. Mask according to claim 1, wherein the absorber / phase shifter element is in contact with a filler material (114) between the first and second substrate portions (110, 120).

6. Mask according to claim 5, wherein at least one mask element is sandwiched between a first and a second part of the substrate.

7. Mask according to claim 1, in which at least one absorber / phase-shifter element is chosen from opaque elements, semi-transparent elements having a refractive index different from the substrate, and a combination of such elements.

8. Mask according to claim 1, in which at least a first part of the substrate (110) has a face with depressions (116) facing a second part of the substrate (120), the depressions being filled with a filling material. (114).