NL2024448A - Methods for Improving Uniformity in Substrates in a Lithographic Process - Google Patents

Abstract

A method of processing a substrate having a metal oxide resist layer formed thereon is provided, the method including the steps of: exposing the substrate to patterning radiation to form a pattern including a plurality of features in the metal oxide resist layer; exposing a portion of the substrate including at least one of said features to conditioning radiation thereby causing shrinkage of the metal oxide resist layer in said portion. Computer programs which cause a computer apparatus to perform the above method and computer program products having such computer programs stored thereon are also provided, as are apparatuses, such as lithographic apparatuses, having a processor adapted to carry out the above method or run the above program. The methods and apparatuses can lead to an improvement in critical dimension uniformity.

Description

Background [0002] A lithographic apparatus is a machine constructed to apply a desired pattern onto a substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus may, for example, project a pattern (also often referred to as '‘design layout” or “design”) of a patterning device (e.g., a mask) onto a layer of radiation-sensitive material (resist) provided on a substrate (e.g., a wafer).

[0003] The wavelength of radiation used by a lithographic apparatus to project a pattern onto a substrate determines the minimum size of features that can be formed on that substrate. A lithographic apparatus that uses EUV radiation, that is electromagnetic radiation having a wavelength within the range 4-20 nm, may be used to form smaller features on a substrate than a lithographic apparatus using DUV radiation (for example with a wavelength of 193 nm).

[0004] Some lithographic apparatuses, in particular those using EUV radiation, use substrates with a metal oxide photoresist (MOR) as the light-sensitive layer. These substrates are patterned by single exposure EUV followed by post-processing, which may include post-exposure bake and development and possibly a hard bake. As a result of this processing, the resulting CD uniformity can be less than is desirable.

SUMMARY [0005] An object of the present invention is to provide methods of processing a substrate which improve the critical dimension uniformity of the substrate.

[0006] In an embodiment of the present invention there is provided a method of processing a substrate having a metal oxide resist layer formed thereon, the method including the steps of: exposing the substrate to patterning radiation to form a pattern including a plurality of features in the metal oxide resist layer; exposing a portion of the substrate including at least one of said features to conditioning radiation thereby causing shrinkage of the metal oxide resist layer in said portion.

[0007] In further embodiments of the present invention there is provided a computer program comprising computer readable instructions which, when run on suitable computer apparatus, cause the computer apparatus to perform the method of the above embodiment, and a computer readable medium having stored thereon such a computer program.

[0008] In a further embodiment of the present invention there is a provided an apparatus having a processor specifically adapted to carry out the steps of the method of the first embodiment above and/or to run the computer program of the embodiment above.

Brief Description of the Drawings [0009] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:

[0010] Figure 1 is a schematic illustration of a lithographic system comprising a lithographic apparatus and a radiation source; and [0011] Figure 2 is a plot showing the effect on exposure latitude of a method according to an embodiment of the present invention.

Detailed Description [0012] Figure lisa schematic illustration of a lithographic system. The lithographic system comprises a radiation source SO and a lithographic apparatus LA. The radiation source SO is configured to generate an extreme ultraviolet (EUV) radiation beam B. The lithographic apparatus LA comprises an illumination system IL, a support structure MT configured to support a patterning device MA, a projection system PS and a substrate table WT configured to support a substrate W. The illumination system IL is configured to condition the radiation beam B before it is incident upon the patterning device MA. The projection system is configured to project the radiation beam B (now patterned by the patterning device MA) onto the substrate W. The substrate W may include previously formed patterns. Where this is the case, the lithographic apparatus aligns the patterned radiation beam B with a pattern previously formed on the substrate W.

[0013] The radiation source SO, illumination system IL, and projection system PS may all be constructed and arranged such that they can be isolated from the external environment. A gas at a pressure below atmospheric pressure (e.g. hydrogen) may be provided in the radiation source SO. A vacuum may be provided in the illumination system IL and/or the projection system PS. A small amount of gas (e.g. hydrogen) at a pressure well below atmospheric pressure may be provided in the illumination system IL and/or the projection system PS.

[0014] The radiation source SO shown in Figure 1 is of a type that may be referred to as a laser produced plasma (LPP) source. A laser 1, which may for example be a C02 laser, is arranged to deposit energy via a laser beam 2 into a fuel, such as tin (Sn) that is provided from a fuel emitter 3.

Although tin is referred to in the following description, any suitable fuel may be used. The fuel may for example be in liquid form, and may for example be a metal or alloy. The fuel emitter 3 may comprise a nozzle configured to direct tin, for example, in the form of droplets, along a trajectory towards a plasma formation region 4. The laser beam 2 is incident upon the tin at the plasma formation region 4. The deposition of laser energy into the tin creates a plasma 7 at the plasma formation region 4. Radiation, including EUV radiation, is emitted from the plasma 7 during deexcitation find recombination of ions of the plasma.

[0015] The EUV radiation is collected and focused by a near normal incidence radiation collector 5 (sometimes referred to more generally as a normal incidence radiation collector). The collector 5 may have a multilayer structure that is arranged to reflect EUV radiation (e.g. EUV radiation having a desired wavelength such as 13.5 nm). The collector 5 may have an elliptical configuration, having two ellipse focal points. A first focal point may be at the plasma formation region 4, and a second focal point may be at an intermediate focus 6, as discussed below.

[0016] In other embodiments of a laser produced plasma (LPP) source the collector 5 may be a socalled grazing incidence collector that is configured to receive EUV radiation at grazing incidence angles and focus the EUV radiation at an intermediate focus. A grazing incidence collector may, for example, be a nested collector, comprising a plurality of grazing incidence reflectors. The grazing incidence reflectors may be disposed axially symmetrically around an optical axis O.

[0017] The radiation source SO may include one or more contamination traps (not shown). For example, a contamination trap may be located between the plasma formation region 4 and the radiation collector 5. The contamination trap may for example be a rotating foil trap, or may be any other suitable form of contamination trap.

[0018] The laser 1 may be separated from the radiation source SO. Where this is the case, the laser beam 2 may be passed from the laser 1 to the radiation source SO with the aid of a beam delivery system (not shown) comprising, for example, suitable directing mirrors and/or a beam expander, and/or other optics. The laser 1 and the radiation source SO may together be considered to be a radiation system.

[0019] Radiation that is reflected by the collector 5 forms a radiation beam B. The radiation beam B is focused at point 6 to form an image of the plasma formation region 4, which acts as a virtual radiation source for the illumination system IL. The point 6 at which the radiation beam B is focused may be referred to as the intermediate focus. The radiation source SO is arranged such that the intermediate focus 6 is located at or near to an opening 8 in tin enclosing structure 9 of the radiation source.

[0020] The radiation beam B passes from the radiation source SO into the illumination system IL, which is configured to condition the radiation beam. The illumination system IL may include a facetted field mirror device 10 and a facetted pupil mirror device 11. The faceted field mirror device and faceted pupil mirror device 11 together provide the radiation beam B with a desired crosssectional shape and a desired angular distribution. The radiation beam B passes from the illumination system IL and is incident upon the patterning device MA held by the support structure MT. The patterning device MA (which may for example be a mask) reflects and patterns the radiation beam B. The illumination system IL may include other minors or devices in addition to or instead of the faceted field mirror device 10 and faceted pupil minor device 11.

[0021] Following reflection from the patterning device MA the patterned radiation beam B enters the projection system PS. The projection system comprises a plurality of minors 13, 14 that are configured to project the radiation beam B onto a substrate W held by the substrate table WT. The mirrors 13,14 which form the projection system may be configured as reflective lens elements. The projection system PS may apply a reduction factor to the radiation beam, forming an image with features that are smaller than conesponding features on the patterning device MA. A reduction factor of 4 may for example be applied. Although the projection system PS has two minors 13, 14 in Figure 1, the projection system may include any number of mirrors (e.g. six mirrors).

[0022] The lithographic apparatus may, for example, be used in a scan mode, wherein the support structure (e.g. mask table) MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam is projected onto a substrate W (i.e. a dynamic exposure). The velocity and direction of the substrate table WT relative to the support structure (e.g. mask table) MT may be determined by the demagnification and image reversal characteristics of the projection system PS. The patterned radiation beam that is incident upon the substrate W may comprise a band of radiation. The band of radiation may be referred to as an exposure slit. During a scanning exposure, the movement of the substrate table WT and the support structure MT may be such that the exposure slit travels over an exposure field of the substrate W.

[0023] The radiation source SO and/or the lithographic apparatus that is shown in Figure 1 may include components that are not illustrated. For example, a spectral filter may be provided in the radiation source SO. The spectral filter may be substantially transmissive for EUV radiation but substantially blocking for other wavelengths of radiation such as infrared radiation.

[0024] In use, the masking system is disposed such that it can be moved into and out of the optical path of radiation between the illumination system IL and the projection system PS. Such a masking apparatus provides control over the distribution of radiation in field planes of the lithographic apparatus that are downstream of the apparatus. Such field planes include the plane of the support structure MT (i.e. the plane of a patterning device MA) and the plane of the substrate table WT (i.e. the plane of a substrate W).

[0025] Embodiments of the present invention use a substrate W on which a metal oxide photoresist layer is formed. Metal oxide resists (MORs) are often used in EUV lithography and they have advantages over the traditional chemically amplified resists (CARs). The pattern from the projection system PS is projected onto the photoresist layer in a single exposure to form features in the metal oxide resist layer which are subsequently developed by post-processing operations which may include baking and/or development.

[0026] One embodiment of the present invention uses post-patterning exposure (prior to postprocessing of the substrate) by means of light (e.g. at 248nm, 193nm or 13.5nm) or electrons (e-beam) to increase the exposure latitude (EL) of the metal oxide resist. This further exposure may be a flood exposure which illuminates an area of the substrate (or indeed all of the substrate), or may be localized and/or patterned.

[0027] Further exposure of the metal oxide resist layer to light or electrons results in shrinkage of the resist remaining after patterning. This is a result of the metal oxide resist chemistry and means that use of a metal oxide resist can give a higher exposure latitude (or reduced critical dimension). By shrinking locally it is possible to improve dose sensitivity and thus achieve better uniformity in critical areas.

[0028] Additionally, it is possible to adj List or control the degree of shrinkage by changing the dose of the post-patterning exposure.

[0029] Figure 2 shows a plot of the exposure latitude (y axis) achieved against the pitch. The theoretical 10 NILS limit is shown for comparison against post-patterning exposure to an e-beam and shows that an improvement of -25% in the EL can be achieved which correspondingly would result in a decrease in the dose-driven contribution to critical dimension uniformity by a similar amount. [0030] Figure 2 also shows that the impact of the post-patterning exposure varies according to pitch. This dependency can be used to tailor the gain in exposure latitude and give better control of the critical dimension.

[0031] A single example of exposure to a higher post-processing dose is also shown (8 frame exposure) which illustrates how different degrees of shrinkage and EL and dose sensitivity can be obtained.

[0032] Whilst Figure 2 shows the impact of post-patterning exposure to e-beam radiation on exposure latitude, similar effects will arise from post-patterning exposure to other forms of radiation, including DUV and EUV.

[0033] The embodiments of the invention may also allow optical proximity correction cooptimization and a way to control shrinkage in certain areas of a substrate.

[0034] Although the above embodiments have been described with reference to EUV lithography, the principles are applicable to any lithographic process in which a metal oxide resist layer is used on the substrate. The present invention is therefore not limited to EUV lithography.

[0035] Although specific reference may be made in this text to embodiments of the invention in the context of a lithographic apparatus, embodiments of the invention may be used in other apparatus.

Embodiments of the invention may form part of a mask inspection apparatus, a metrology apparatus, or any apparatus that measures or processes an object such as a wafer (or other substrate) or mask (or other patterning device). These apparatus may be generally referred to as lithographic tools. Such a lithographic tool may use vacuum conditions or ambient (non-vacuum) conditions.

[0036] The term EUV radiation may be considered to encompass electromagnetic radiation having a wavelength within the range of 4-20 nm, for example within the range of 13-14 nm. EUV radiation may have a wavelength of less than 10 nm, for example within the range of 4-10 nm such as 6.7 nm or 6.8 nm.

[0037] Although specific reference may be made in this text to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications. Possible other applications include the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, liquidcrystal displays (LCDs), thin film magnetic heads, etc.

[0038] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described.

[0039] The descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the clauses set out below. Other aspects of the invention are set out as in the following numbered clauses:

1. A method of processing a substrate having a metal oxide resist layer formed thereon, the method including the steps of:

exposing the substrate to patterning radiation to form a pattern including a plurality of features in the metal oxide resist layer;

exposing a portion of the substrate including at least one of said features to conditioning radiation thereby causing shrinkage of the metal oxide resist layer in said portion.

2. The method according to clause 1 wherein the conditioning radiation is electromagnetic radiation.

3. The method according to clause 1 wherein the conditioning radiation is electron beam radiation.

4. The method according to any one of the preceding clauses wherein the step of exposing a portion of the substrate to conditioning radiation includes exposing a plurality of portions of the substrate to conditioning radiation.

5. The method according to clause 4 wherein at least two of said plurality of portions are exposed to different doses of conditioning radiation.

6. The method according to any one of the preceding clauses wherein the conditioning radiation is uniform across the exposed portion.

7. The method according to any one of clauses 1 to 5 wherein the conditioning radiation varies in intensity across the exposed portion so as to form a pattern on the exposed portion.

8. A method of forming a pattern on a substrate by photolithography, the method including the method of processing a substrate according to any one of the preceding clauses.

9. The method of clause 8 further including the step of, after said step of exposing a portion of the substrate to conditioning radiation, developing the pattern formed by the patterning radiation.

10. A computer program comprising computer readable instructions which, when run on suitable computer apparatus, cause the computer apparatus to perform the method of any one of the preceding clauses.

11. A computer readable medium having stored thereon the computer program of clause 10.

12. An apparatus having a processor specifically adapted to carry out the steps of the method as clauseed in any one of clauses 1 to 9 and/or to run the computer program of clause 10.

13. An apparatus according to clause 12 which is specifically configured as a lithographic apparatus operable to perform a lithographic process on substrates.

Claims (1)

1. Claim:

   1. Een inrichting ingericht voor het belichten van een substraat.

   1/2

   

   WT

   Inpria EL through pitch

   

   Pitch inpria line (nm)