Method for improving substrate uniformity during photolithography

Abstract

A method for processing a substrate having a metal oxide resist layer formed thereon is provided, the method comprising the steps of: exposing the substrate to patterned radiation to form a pattern comprising a plurality of features in the metal oxide resist layer; and exposing a portion of the substrate comprising at least one of the features to modulated radiation, thereby causing the metal oxide resist layer to shrink in the portion. Also provided are a computer program for causing a computer apparatus to perform the method, and a computer program product having such a computer program stored thereon, such as an apparatus having a processor adapted to perform the method or run the program, such as a lithographic apparatus. The method and apparatus can result in improved critical dimension uniformity.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority from European application 19207681.8, filed on November 7, 2019, and the entire contents of said European application are incorporated herein by reference. Technical Field

[0003] The present invention relates to a method for improving the uniformity of a substrate during a lithography process. In particular, but not exclusively, the present invention relates to improving the critical dimension (CD) uniformity of features on a substrate and / or increasing the exposure latitude. The present invention can be used in all types of lithography equipment. Background Art

[0004] A lithographic apparatus is a machine configured to apply a desired pattern to a substrate. For example, a lithographic apparatus can be used in the manufacture of integrated circuits (ICs). A lithographic apparatus can, for example, project a pattern (often also referred to as a "design layout" or "design") of a patterning device (e.g., a mask) onto a layer of radiation-sensitive material (resist) disposed on a substrate (e.g., a wafer).

[0005] 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 the substrate. A lithographic apparatus that uses EUV radiation (which is electromagnetic radiation having a wavelength in the range of 4 nm to 20 nm) can be used to form smaller features on a substrate than a lithographic apparatus that uses DUV radiation (e.g., having a wavelength of 193 nm).

[0006] Some lithography tools, particularly those using EUV radiation, use substrates with metal oxide photoresist (MOR) as the light-sensitive layer or photoresist. These substrates are patterned using a single EUV exposure and then post-processed, which may include a post-exposure bake and development, and possibly a hard bake. As a result of this processing, the resulting CD uniformity may be lower than desired. Summary of the Invention

[0007] An object of the present invention is to provide a method of processing a substrate, said method improving the critical dimension uniformity of said substrate.

[0008] In an embodiment of the present invention, a method for processing a substrate is provided, wherein the substrate has a metal oxide resist layer formed thereon, the method comprising the following steps: exposing the substrate to patterned radiation to form a pattern including a plurality of features located in the metal oxide resist layer; exposing a portion of the substrate including at least one of the features to modulated radiation, thereby causing the metal oxide resist layer to shrink in the portion.

[0009] In further embodiments of the present invention, a computer program comprising computer-readable instructions is provided, which, when executed on a suitable computer device, causes the computer device to perform the method of the above-described embodiment, and a computer-readable medium having such a computer program stored thereon is provided.

[0010] In another embodiment of the present invention, a device having a processor is provided. The processor is specifically adapted to execute the steps of the method of the first embodiment and / or run the computer program of the embodiment. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which corresponding reference numerals indicate corresponding parts or components, and in which:

[0012] Figure 1 is a schematic illustration of a lithographic system including a lithographic apparatus and a radiation source; and

[0013] Figure 2 is a graph showing the effect of the method according to an embodiment of the present invention on exposure latitude. DETAILED DESCRIPTION

[0014] Figure 1 is a schematic illustration of a lithography system. The lithography system comprises a radiation source SO and a lithography apparatus LA. The radiation source SO is configured to generate an extreme ultraviolet (EUV) radiation beam B. The lithography 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 on 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 comprise a previously formed pattern. In this case, the lithography apparatus aligns the patterned radiation beam B with the pattern previously formed on the substrate W.

[0015] The radiation source SO, illumination system IL, and projection system PS may all be constructed and arranged so as to be isolated from the external environment. A gas (e.g., hydrogen) at a pressure below atmospheric pressure 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.

[0016] Figure 1The radiation source SO shown in FIG is of a type that may be referred to as a laser produced plasma (LPP) source. A laser 1 (which may comprise a CO2 laser, for example) is arranged to deposit energy via a laser beam 2 into a fuel, such as tin (Sn), provided from a fuel emitter 3. Although tin is mentioned 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 an 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 on the tin at the plasma formation region 4. The laser energy is deposited into the tin, thereby generating a plasma 7 at the plasma formation region 4. During de-excitation and recombination of the ions of the plasma, radiation, including EUV radiation, is emitted from the plasma 7.

[0017] EUV radiation is collected and focused by a near normal incidence radiation collector 5 (sometimes more generally referred to as a normal incidence radiation collector). Collector 5 can have a multi-layer structure arranged to reflect EUV radiation (e.g., EUV radiation having a desired wavelength, such as 13.5 nm). Collector 5 can have an elliptical configuration with two elliptical foci. As discussed below, the first focal point can be located at plasma formation region 4, and the second focal point can be located at intermediate focus 6.

[0018] In other embodiments of the laser produced plasma (LPP) source, the collector 5 may be a so-called grazing incidence collector, which is configured to receive EUV radiation at a grazing incidence angle and focus the EUV radiation at an intermediate focus. For example, the grazing incidence collector may be a nested collector comprising a plurality of grazing incidence reflectors. The grazing incidence reflectors may be arranged axially symmetrically around the optical axis O.

[0019] The radiation source SO may include one or more contamination traps (not shown). For example, the contamination trap may be located between the plasma formation region 4 and the radiation collector 5. The contamination trap may be, for example, a rotating vane trap, or may be any other suitable form of contamination trap.

[0020] The laser 1 may be separate from the radiation source SO. In this case, the laser beam 2 may be transferred from the laser 1 to the radiation source SO by means of a beam delivery system (not shown) comprising, for example, suitable directional mirrors and / or beam expanders, and / or other optical devices. The laser 1 and the radiation system SO may be considered together as a radiation system.

[0021] The radiation reflected by the collector 5 forms a radiation beam B. The radiation beam B is focused at a point 6 to form an image of the plasma formation region 4, which serves as a virtual radiation source for the illumination system IL. The point 6 at which the radiation beam B is focused can be referred to as the intermediate focus. The radiation source SO is arranged so that the intermediate focus 6 is located at or near an opening 8 in an enclosure 9 of the radiation source.

[0022] A radiation beam B is passed from a radiation source SO into an illumination system IL which is configured to condition the radiation beam. The illumination system IL may include a faceted field mirror arrangement 10 and a faceted pupil mirror arrangement 11. The faceted field mirror arrangement 10 and the faceted pupil mirror arrangement 11 together provide the radiation beam B with a desired cross-sectional shape and a desired angular distribution. The radiation beam B is passed from the illumination system IL and is incident on a patterning device MA held by a support structure MT. The patterning device MA (which may be, for example, a mask) reflects the radiation beam B and patterns the radiation beam B. The illumination system IL may include other mirrors or devices in addition to or instead of the faceted field mirror arrangement 10 and the faceted pupil mirror arrangement 11.

[0023] After reflection from the patterning device MA, the patterned radiation beam B enters the projection system PS. The projection system comprises a plurality of mirrors 13, 14 configured to project the radiation beam B onto a substrate W held by a substrate table WT. The mirrors 13, 14 forming the projection system may be configured as reflective lens elements. The projection system PS may apply a demagnification factor to the radiation beam so that the image formed has features that are smaller than corresponding features on the patterning device MA. For example, a demagnification factor of 4 may be applied. Although the projection system PS is Figure 1 There are two mirrors 13, 14, but the projection system may comprise any number of mirrors (eg six mirrors).

[0024] The lithographic apparatus can, for example, be used in a scanning mode in which the support structure (e.g., mask table) MT and substrate table WT are scanned synchronously while a pattern imparted to the radiation beam is projected onto the substrate W (i.e., dynamic exposure). The speed and direction of the substrate table WT relative to the support structure (e.g., mask table) MT may be determined by the reduction ratio and image reversal characteristics of the projection system PS. The patterned radiation beam incident on the substrate W may include a stripe of radiation. The stripe of radiation may be referred to as an exposure slit. During a scanning exposure, movement of the substrate table WT and support structure MT may cause the exposure slit to travel across an exposure field of the substrate W.

[0025] Figure 1The radiation source SO and / or the lithographic apparatus shown in FIG. 3 may include components not shown. 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 block other radiation wavelengths (such as infrared radiation).

[0026] In use, the masking system or mask system is arranged so 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 device provides control over the distribution of radiation in a field plane downstream of the lithographic apparatus. Such a field plane includes the plane of the support structure MT (i.e. the plane of the patterning device MA) and the plane of the substrate table WT (i.e. the plane of the substrate W).

[0027] Embodiments of the present invention use a substrate W having a metal oxide photoresist or photoresist layer formed thereon. Metal oxide resists (MORs) are commonly used in EUV lithography and have advantages over conventional chemically amplified resists (CARs). A pattern from a projection system PS is projected onto the photoresist layer in a single exposure to form features in the metal oxide resist layer that are subsequently developed by post-processing operations that may include baking and / or development.

[0028] One embodiment of the present invention uses patterned post-exposure (before post-processing of the substrate) to increase the exposure latitude (EL) of the metal oxide resist by light (e.g., 248 nm, 193 nm, or 13.5 nm) or electrons (e-beam). This further exposure can be a flood exposure, irradiating a region of the substrate (or indeed the entire substrate), or can be localized and / or patterned.

[0029] Further exposure of the metal oxide resist layer to light or electrons causes the remaining resist after patterning to shrink. This is a result of the metal oxide resist chemistry and means that using metal oxide resists can give higher exposure latitude (or reduced critical dimensions). By shrinking locally, it is possible to improve dose sensitivity and thus achieve better uniformity in critical areas.

[0030] Furthermore, it is possible to adjust or control the degree of shrinkage by varying the dose of the post-patterning exposure.

[0031] Figure 2 A graph of the exposure latitude achieved versus pitch (y-axis) is shown. The theoretical 10 NILS limit is shown for comparison with post-patterning exposure for an electron beam, and shows that an improvement of approximately 25% in EL can be achieved, which in turn will result in a similar amount of reduction in the dose drive contribution to critical dimension uniformity.

[0032] Figure 2 It is also shown that the effect of post-patterning exposure varies depending on the pitch. This dependence can be used to adjust the gain in exposure latitude and better control the critical dimension.

[0033] Also shown is a single example (8 frame exposure) for exposure to a higher post-treatment dose, illustrating how different degrees of shrinkage, and EL, and dose sensitivity can be obtained.

[0034] Although Figure 2 The effect of post-patterning exposure to e-beam radiation on exposure latitude is shown, but post-patterning exposure to other forms of radiation, including DUV and EUV, will also have similar effects.

[0035] Embodiments of the present invention may also allow for co-optimization of optical proximity effect correction and a manner to control shrinkage of certain regions of the substrate.

[0036] Although the above embodiments have been described with reference to EUV lithography, these principles are applicable to any lithographic process using a metal oxide resist layer on the substrate.Therefore, the present invention is not limited to EUV lithography.

[0037] Although embodiments of the present invention may be specifically mentioned herein in the context of lithographic equipment, embodiments of the present invention may be used in other equipment. Embodiments of the present invention may form part or component of mask inspection equipment, metrology equipment, or any equipment that measures or processes targets such as wafers (or other substrates) or masks (or other patterning devices). These equipment may generally be referred to as lithographic tools. Such lithographic tools may use vacuum conditions or ambient (non-vacuum) conditions.

[0038] The term "EUV radiation" may be taken to encompass electromagnetic radiation having a wavelength in the range of 4 nm to 20 nm, for example in the range of 13 nm to 14 nm. EUV radiation may have a wavelength less than 10 nm, for example in the range of 4 nm to 10 nm, such as 6.7 nm or 6.8 nm.

[0039] Although specific reference may be made herein to the use of lithographic apparatus in IC fabrication, it will be appreciated 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, liquid crystal displays (LCDs), thin film magnetic heads, and the like.

[0040] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described.

[0041] The above description is intended to be illustrative rather than restrictive.Thus, it will be apparent to those skilled in the art that modifications may be made to the invention as described without departing from the scope of the aspects set forth hereinafter.

Claims

1. A method for processing a substrate having a metal oxide resist layer formed thereon, the method comprising the steps of: exposing the substrate to patterned radiation to form a pattern comprising a plurality of features in the metal oxide resist layer; A portion of the substrate including at least one of the features is exposed to conditioning radiation, thereby causing the metal oxide resist layer to shrink in the portion.

2. The method of claim 1, wherein the conditioning radiation is electromagnetic radiation. The method of claim 1 , wherein the conditioning radiation is electron beam radiation.

4. A method according to any one of the preceding claims, wherein the step of exposing a portion of the substrate to conditioning radiation comprises exposing a plurality of portions of the substrate to conditioning radiation. The method of claim 4 , wherein at least two of the plurality of portions are exposed to different doses of conditioning radiation.

6. A method according to any preceding claim, wherein the conditioning radiation is uniform across the exposed portion.

7. A method according to any one of claims 1 to 5, wherein the intensity of the conditioning radiation varies 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 comprising the method of processing a substrate according to any one of the preceding claims.

9. The method of claim 8, further comprising the step of developing the pattern formed by the patterned radiation after the step of exposing a portion of the substrate to conditioning radiation.

10. A computer program comprising computer readable instructions which, when executed on suitable computer equipment, cause the computer equipment to carry out the method of any preceding claim.

11. A computer-readable medium having stored thereon the computer program according to claim 10.

12. A device having a processor specially adapted to perform the steps of the method according to any one of claims 1 to 9 and / or to run the computer program according to claim 10.

13. The apparatus of claim 12, being specifically configured as a lithographic apparatus operable to perform a lithographic process on a substrate.

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