Method for forming a patterned material layer, and apparatus for forming a patterned material layer - Patents.com

Abstract

The present disclosure relates to a method and apparatus for forming a patterned layer of material on a substrate. In one configuration, selected portions of a surface of a substrate are irradiated during a deposition process. The irradiation locally enhances the deposition process at the selected portions, thereby forming a patterned layer of material in a pattern defined by the selected portions. During the irradiation, a bias voltage having alternating polarity is applied to the substrate so as to periodically drive secondary electrons generated within the substrate by the irradiation toward the surface of the selected portions.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to European Application No. 22196803.5, filed September 21, 2022, which is incorporated herein by reference in its entirety.

[0002] This disclosure relates to methods and apparatus for forming patterned layers of material, which are particularly applicable in providing two-dimensional patterns of material, such as for the fabrication of FET devices. [Background technology]

[0003]

[0003] As semiconductor manufacturing processes continue to improve, the dimensions of circuit elements have continued to shrink, while the amount of functional elements, such as transistors, per device has steadily increased for decades, following a trend commonly referred to as "Moore's Law." To keep up with Moore's Law, the semiconductor industry pursues technologies that enable the creation of smaller and smaller features.

[0004]

[0004] For some types of electronic devices, shrinking device features can create performance challenges, such as the short channel effect in MOSFETs, which occurs when the channel length becomes comparable to the width of the depletion layer at the source and drain junctions. These challenges can sometimes be resolved by using two-dimensional materials that are atomically thin and can have relatively low dielectric constants. Two-dimensional materials may also have desirable properties when used in other contexts: they can be used in place of gate oxides, which require a high dielectric constant; and they can be used as a replacement for interconnects, where high electrical conductivity is preferred.

[0005]

[0005] Various deposition techniques exist for producing two-dimensional materials. These deposition techniques include chemical vapor deposition (CVD), mechanical cleavage (exfoliation), molecular beam epitaxy (MBE), atomic layer deposition (ALD), and liquid phase exfoliation. A challenge with many of these deposition techniques is the high temperatures required for the process to operate efficiently (at high speed and high quality). High temperatures can degrade or damage previously deposited layers and / or limit the usable extent of the previously deposited layers. The previously deposited layers must be formulated to withstand high temperatures to an acceptable degree, such as by having a melting point higher than the temperatures reached during the deposition process.

[0006]

[0006] Although exfoliation-based approaches allow offline growth of two-dimensional materials without temperature limitations, the exfoliation and transfer process is difficult to achieve with high throughput and low defect rates.

[0007]

[0007] Patterning two-dimensional materials presents additional challenges due to their fragile nature. Two-dimensional materials can be highly susceptible to damage or tearing. Two-dimensional materials can be damaged by conventional patterning processes, such as resist coating, lithography, etching, and resist stripping. Typical photoresists for DUV and EUV lithography may also be incompatible with two-dimensional materials; for example, two-dimensional materials are hydrophobic, while photoresists are hydrophilic. Even with careful attention during processing, this physical incompatibility can result in unwanted adhesion of resist residue to the structure and poor contact quality between the structure and other layers.

[0008]

[0008] Laser etching has been proposed for patterning two-dimensional materials. Laser etching uses a laser to locally heat a surface, gradually melting and vaporizing the material to remove it. Laser processing techniques rely on point-to-point scanning, resulting in lower yields compared to some alternative approaches.

[0009]

[0009] EUV radiation can be used to cause the deposition of materials in selected patterns, however, achieving high throughput has proven difficult due to the very high EUV doses required. Summary of the Invention

[0010] The present invention aims to provide an alternative or improved method and apparatus for forming a patterned layer of material on a substrate, in particular with improved throughput and / or quality.

[0011] According to one aspect, there is provided an apparatus for forming a patterned layer of material on a substrate, the apparatus including: a projection system configured to irradiate selected portions of a surface of the substrate during a deposition process; an environmental control system configured to contain the substrate within a controlled gaseous environment during irradiation of the selected portions, the controlled gaseous environment being an environment that supports the deposition process; and a bias voltage unit configured to apply a bias voltage having alternating polarity to the substrate during irradiation to periodically drive secondary electrons generated within the substrate by the irradiation toward the surface of the selected portions.

[0012]

[0012] The apparatus can be configured such that the irradiation locally enhances the deposition process in selected portions, thereby forming a patterned layer of material in a pattern defined by the selected portions. The irradiation generates secondary electrons, and the bias voltage increases the proportion of secondary electrons that can contribute to enhancing the deposition process. Configuring the bias voltage to have alternating polarity prevents excessive charge buildup on the substrate. The bias voltage improves the deposition rate per unit area, thereby increasing throughput. The bias voltage can also improve the spatial definition of the radiation-induced deposition, thereby improving the quality of the pattern formed on the substrate.

[0013] In one embodiment, the irradiation comprises irradiation with electromagnetic radiation having a wavelength of less than 100 nm, which allows for efficient generation of secondary electrons and facilitates high spatial resolution.

[0014]

[0014] In one embodiment, the bias voltage has a non-sinusoidal bias voltage waveform. Providing a non-sinusoidal bias voltage can reduce the change in the electric field within the interior volume of the substrate adjacent to the surface, thereby reducing the range of energy of secondary electrons driven to the surface. A smaller range of energy of secondary electrons means that a greater proportion of secondary electrons can contribute to facilitating the deposition process in an optimal manner, thereby improving throughput.

[0015] In one embodiment, the bias voltage waveform is periodic, with each period including a negative bias portion during which secondary electrons in the substrate are driven toward the surface of the selected portion and a positive bias portion during which secondary electrons in the substrate are driven away from the surface of the selected portion. In such a configuration, the voltage of the bias voltage waveform may be further configured to vary during at least a majority of the negative bias portion in a manner that at least partially compensates for charging of the substrate caused by ions impinging on the substrate from the plasma during the negative bias portion. Compensating for substrate charging in this manner reduces changes in the electric field within the interior volume of the substrate adjacent the surface of the selected portion, thereby contributing to a smaller range of energies of secondary electrons impinging on the target layer.

[0016] In one embodiment, the voltage change of the bias voltage waveform during the negative bias portion is substantially linear during at least a majority of the negative bias portion. This approach has been found to balance ease of implementation with efficiently compensating for substrate charging to reduce changes in the electric field within the interior volume of the substrate adjacent the surface of the selected portion.

[0017] In one embodiment, the voltage of the bias voltage waveform during the negative bias portion is varied to maintain a substantially time-invariant electric field within an interior volume of the substrate adjacent a selected portion of the substrate surface during the negative bias portion. Maintaining a substantially time-invariant electric field within the interior volume adjacent the surface facilitates high control over the energy of secondary electrons reaching the surface, thereby facilitating high throughput.

[0018]

[0018] According to one aspect, there is provided a method for forming a patterned material layer on a substrate, the method comprising irradiating selected portions of a surface of the substrate during a deposition process, the irradiation being such that the deposition process is locally enhanced in the selected portions to form a patterned material layer in a pattern defined by the selected portions, and applying a bias voltage having alternating polarity to the substrate during the irradiation, thereby periodically driving secondary electrons generated within the substrate by the irradiation toward the surface of the selected portions. [Brief explanation of the drawings]

[0019]

[0019] Some embodiments of the present invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which: [Figure 1] 1 depicts a first example lithography system including a lithographic apparatus and a radiation source; [Figure 2] 2 depicts a second example lithography system comprising a lithographic apparatus and a radiation source; [Figure 3] 1 shows schematically how selected portions of a substrate are irradiated to locally enhance the deposition process. [Figure 4] 10A and 10B show schematic diagrams of the formation of a patterned layer of material defined by selected portions. [Figure 5] 1 shows an apparatus for forming a patterned layer of material. [Figure 6] 10 shows a schematic representation of the average trajectory of secondary electrons from the focal region towards the surface of the substrate with no bias voltage applied to the substrate. [Figure 7] In the configuration of FIG. 6, the average trajectory of secondary electrons is shown schematically when a bias voltage is applied to the substrate. [Figure 8] 1 shows a schematic representation of how the substrate voltage varies with time during the transient phase immediately after the bias voltage is first turned on. [Figure 9] 1 shows a schematic representation of how the substrate voltage varies over time in steady state. [Figure 10] 1 is a graph showing the energy distribution of secondary electrons, plotted as the number of electrons having energy E, N(E), versus energy E, for two different bias voltage waveforms. [Figure 11] 1 is a graph showing the energy distribution of secondary electrons when no bias voltage is applied, with overlaid rectangles showing the approximate range of energies that favor three different types of bond dissociation. [Figure 12] 1 shows an example of a non-sinusoidal bias voltage waveform. [Figure 13] 1 is a graph illustrating three exemplary non-sinusoidal bias voltage waveforms having different amplitudes. [Figure 14] 14 is a graph showing the energy distribution of secondary electrons for the three bias voltage waveforms shown in FIG. 13. DETAILED DESCRIPTION OF THE INVENTION

[0020] A lithographic apparatus is a machine constructed to apply a desired pattern onto a substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus can, for example, project a pattern in a patterning device (such as a mask) onto a layer of radiation-sensitive material (resist) provided on the substrate.

[0021] To project a pattern onto a substrate, a lithographic apparatus may use electromagnetic radiation. The wavelength of this radiation determines the minimum size of features that can be patterned on the substrate. Typical wavelengths currently in use are 365 nm (i-line), 248 nm, 193 nm, and 13.5 nm. Lithographic apparatus using extreme ultraviolet (EUV) radiation having a wavelength of less than 100 nm, optionally a wavelength in the range of 5 to 100 nm, optionally a wavelength in the range of 4 nm to 20 nm, for example 6.7 nm or 13.5 nm, can be used to form smaller features on a substrate than lithographic apparatus using radiation with a wavelength of, for example, 193 nm.

[0022]

[0022] In this document, the terms "radiation" and "beam" are used to encompass all types of electromagnetic radiation, including ultraviolet radiation (e.g., having a wavelength of 365 nm, 248 nm, 193 nm, 157 nm, or 126 nm), EUV (extreme ultraviolet radiation, e.g., having a wavelength in the range of about 5 to 100 nm), as well as electron beam radiation, unless otherwise specified.

[0023] 1 schematically depicts a lithographic apparatus LA comprising: an illumination system IL (also referred to as an illuminator) configured to condition a radiation beam B (e.g. UV radiation, DUV radiation or EUV radiation), a mask support (e.g. a mask table) MT constructed to support a patterning device (e.g. a mask) MA and coupled to a first positioner PM configured to accurately position the patterning device MA according to certain parameters, a substrate support (e.g. a wafer table) WT constructed to hold a substrate (e.g. a resist-coated wafer) W and coupled to a second positioner PW configured to accurately position the substrate support according to certain parameters, and a projection system (e.g. a refractive projection lens system) PS configured to project a pattern imparted to the radiation beam B by the patterning device MA onto a target portion C (e.g. comprising one or more dies) of the substrate W.

[0024]

[0024] In operation, the illumination system IL receives a radiation beam from the radiation source SO, for example via the beam delivery system BD. The illumination system IL may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic and / or other types of optical components, or any combination thereof, for directing, shaping and / or controlling the radiation. The illuminator IL is used to condition the radiation beam B so that it has a desired spatial and angular intensity distribution in its cross-section in the plane of the patterning device MA.

[0025]

[0025] The term "projection system" PS as used herein should be interpreted broadly to encompass various types of projection systems, including refractive, reflective, catadioptric, anamorphic, magnetic, electromagnetic and / or electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation being used and / or other factors such as the use of an immersion liquid or a vacuum. Any use of the term "projection lens" herein should be considered as synonymous with the more general term "projection system" PS.

[0026]

[0026] The lithographic apparatus LA may be of a type in which at least a portion of the substrate is covered by a liquid having a relatively high refractive index (e.g. water) so as to fill a space between the projection system PS and the substrate W, which is also known as immersion lithography. Further information about immersion techniques can be found in US Patent No. 6,952,253, which is incorporated herein by reference.

[0027] The lithographic apparatus LA may be of a type that includes two or more substrate supports WT (also known as "dual stage"). In such a "multi-stage" machine, the substrate supports WT can be used in parallel and / or a substrate W placed on one substrate support WT can be prepared for a next exposure of that substrate W while another substrate W on another substrate support WT is used to expose a pattern onto that other substrate W.

[0028] In addition to the substrate support WT, the lithographic apparatus LA may comprise a measurement stage. The measurement stage is arranged to hold a sensor and / or a cleaning device. The sensor may be arranged to measure a property of the projection system PS or a property of the radiation beam B. The measurement stage may hold multiple sensors. The cleaning device may be arranged to clean part of the lithographic apparatus, for example part of the projection system PS or part of the system for supplying immersion liquid. The measurement stage may be moved below the projection system PS when the substrate support WT is spaced apart from the projection system PS.

[0029]

[0029] In operation, a radiation beam B is incident on a patterning device (e.g. mask) MA, which is held on a mask support MT, and is patterned according to a pattern (design layout) present on the patterning device MA. Having passed through the mask MA, the radiation beam B passes through a projection system PS, which focuses the beam onto a target portion C of a substrate W. The substrate support WT can be accurately moved using the second positioner PW and the position measurement system IF to position different target portions C, for example, at aligned and focused positions in the path of the radiation beam B. Similarly, the patterning device MA can be accurately positioned relative to the path of the radiation beam B using the first positioner PM and possibly further position sensors (not explicitly shown in Figure 1). The patterning device MA and substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks P1, P2 as illustrated occupy dedicated target portions, they may be located in spaces between the target portions. When the substrate alignment marks P1, P2 are located between target portions C, they are known as scribe-lane alignment marks.

[0030] 2 shows a lithography system including a radiation source SO and a lithography apparatus LA. The radiation source SO is configured to generate a beam of EUV radiation B and to provide this beam of EUV radiation B to the lithography apparatus LA. The lithography apparatus LA comprises an illumination system IL, a support structure MT configured to support a patterning device MA (e.g. a mask), a projection system PS, and a substrate table WT configured to support a substrate W.

[0031]

[0031] The illumination system IL is configured to condition the EUV radiation beam B before it is incident on the patterning device MA. Furthermore, the illumination system IL may include a facetted field mirror device 10 and a facetted pupil mirror device 11. Together the facetted field mirror device 10 and the facetted pupil mirror device 11 provide the EUV radiation beam B with a desired cross-sectional shape and a desired intensity distribution. The illumination system IL may include other mirrors or devices in addition to or as an alternative to the facetted field mirror device 10 and the facetted pupil mirror device 11.

[0032] After being conditioned as described above, the EUV radiation beam B interacts with the patterning device MA. This interaction results in a patterned EUV radiation beam B'. The projection system PS is configured to project the patterned EUV radiation beam B' onto a substrate W. To that end, the projection system PS may include a number of mirrors 13, 14 configured to project the patterned EUV radiation beam B' onto a substrate W held on a substrate table WT. The projection system PS may apply a demagnification factor to the patterned EUV radiation beam B', thereby forming an image having smaller features than corresponding features on the patterning device MA. For example, a demagnification factor of 4 or 8 may be applied. Although in Figure 2 the projection system PS is depicted as having only two mirrors 13, 14, the projection system PS may include a different number of mirrors (e.g. 6 or 8 mirrors).

[0033] The substrate W may include a previously formed pattern, in which case the lithographic apparatus LA aligns the image formed by the patterned EUV radiation beam B′ with the previously formed pattern on the substrate W.

[0034] A relative vacuum, ie a small amount of gas (eg hydrogen) at a pressure significantly below atmospheric pressure, may be provided within the source SO, illumination system IL and / or projection system PS.

[0035]

[0035] The source SO may be a laser-produced plasma (LPP) source, a discharge-produced plasma (DPP) source, a free-electron laser (FEL) or any other source capable of producing EUV radiation.

[0036] As mentioned in the introduction, while there is interest in using two-dimensional materials in semiconductor manufacturing processes, achieving sufficiently high crystal quality and / or throughput and / or low defectivity presents challenges. Deposition processes such as CVD and ALD require high temperatures, which can damage underlying layers. For example, a typical CVD process for producing a single layer of high-quality two-dimensional crystals can require temperatures exceeding 800°C, while temperatures exceeding 500°C are typically incompatible with downstream CMOS technologies. For example, the thermal budget for silicon FinFETs (fin field-effect transistors) is less than 1050°C for front-end (FEOL) and less than 400°C for back-end (BEOL). For 2D-FETs (two-dimensional material-based field-effect transistors), this budget is even smaller (typically 450–500°C for both FEOL and BEOL). Delamination-based processes circumvent these thermal constraints by allowing the deposition of two-dimensional materials off-site, but they also introduce complex transfer processes and make it difficult to avoid high defectivity. Conventional patterning processes, such as resist coating, lithography, etching, and resist stripping, are also problematic because they can damage two-dimensional materials. Furthermore, conventional lithography techniques present challenges in patterning 2D material layers. Due to the nature of these materials, the resulting structures are susceptible to contamination and / or damage due to rough edges after lithography (DUV, EUV, EBL) and subsequent (dry and wet) etching steps. This can result in suboptimal contacts with other layers, such as source and drain electrodes, resulting in Schottky barriers up to 3.5 times larger than would be possible with clean, sharp interfaces.

[0037]

[0037] An alternative approach using EUV-induced deposition allows for direct patterning of two-dimensional materials without resist processing. Examples of such deposition are described in WO2019166318, WO2020207759 and EP3875633A1, all of which are incorporated herein by reference in their entirety. However, achieving a sufficiently high growth rate of two-dimensional materials can be difficult with EUV-induced deposition. The EUV dose (the amount of energy per unit area deposited by EUV radiation) is practically limited by throughput requirements. Increasing the dose typically reduces throughput. Typical EUV dose limits are, for example, 100 mJ / cm 2 It could be.

[0038]

[0038] Embodiments of the present disclosure provide a method and apparatus for forming a patterned layer of material 23 on a substrate W that overcomes the above-mentioned problems. Forming the patterned layer 23 comprises irradiating the substrate W. This irradiation may be performed using any of the arrangements described above with reference to Figures 1 and 2. Accordingly, an apparatus for carrying out the above method comprises a projection system PS as described above with reference to Figures 1 and 2, which is configured to irradiate the substrate W by projecting a patterned beam of radiation onto the substrate W.

[0039] In some embodiments, as illustrated in FIGS. 3 and 4, the substrate W is irradiated during a deposition process to form a patterned layer 23. The method includes irradiating (20) a selected portion (selected portion) 22 of the surface of the substrate W during the deposition process. Thus, the irradiation may impart a dose to the selected portion 22 and not to any other portion of the surface during at least one step of the deposition process. In one embodiment, the patterned layer 23 comprises, consists essentially of, or consists of a two-dimensional material. A two-dimensional material is a material that exhibits a significant anisotropy in properties lateral to the plane of the material compared to a direction perpendicular to the plane of the material. A class of two-dimensional materials, sometimes referred to as monolayer materials or monolayers, may consist of crystalline materials consisting of a single atomic layer or a few single atomic layers stacked on top of each other. In some embodiments, the two-dimensional material comprises, consists essentially of, or consists of one or more 2D allotropes such as graphene and antimonene, MXenes, hexagonal boron nitride (hBN), and one or more inorganic compounds such as transition metal dichalcogenides (TMDs) (e.g., MX type semiconductors such as WS2, MoS2, WSe2, and MoSe2, which may be atomically thin, where the letter M represents a transition metal atom (e.g., Mo or W) and the letter X represents a chalcogen atom (e.g., S, Se, or Te)). The two-dimensional material may include one layer of M atoms sandwiched between two layers of X atoms. The two-dimensional material may include any semiconducting two-dimensional material suitable for use as a transistor channel. As mentioned above, the two-dimensional material may include 2D allotropes such as graphene and antimonene, or inorganic compounds. The two-dimensional material may be composed of a monolayer (or multiple monolayers if the deposition process is repeated). In the illustrated embodiment, the deposition process is an atomic layer deposition process. In other embodiments, a different deposition process or combination of deposition processes is used, including, for example, one or more of atomic layer deposition, chemical vapor deposition, plasma-enhanced chemical vapor deposition, epitaxy, sputtering, and electron beam induced deposition, either alone or in combination.Formation of patterned layer 23 may constitute a step in a method of forming at least one layer of a device to be fabricated, such as a semiconductor device. The two-dimensional material may form, for example, a channel of a FET, a metal cap, an interconnect, or a diffusion barrier within an interconnect.

[0040] In one embodiment, irradiation is carried out with radiation that can locally enhance the deposition process. In one embodiment, the radiation comprises, consists essentially of, or consists of any type of EUV radiation (having a wavelength less than 100 nm) that can locally enhance the deposition process. The use of EUV radiation provides high spatial resolution. In other embodiments, irradiation is carried out with radiation that comprises, consists essentially of, or consists of higher wavelength radiation, optionally in combination with an immersion liquid, as described below. This higher wavelength radiation may be in the range of 100 nm to 400 nm (including DUV radiation).

[0041] The irradiation locally enhances the deposition process at the selected portions 22, thereby forming a patterned layer 23, as shown schematically in FIG. 4 . The pattern of the patterned layer 23 is defined by the selected portions 22. Therefore, the pattern is formed without the need for resist. Therefore, a resist removal process is not necessary, reducing the risk of damage to the layer of patterned material 30 or to fragile underlying materials. This approach is particularly desirable when resist residues can significantly affect the properties of fragile underlying materials and / or when resist stripping can cause significant damage to the fragile underlying materials. Examples of fragile underlying materials include ultrathin film coatings, 2D materials such as graphene and transition metal dichalcogenides (TMDs), and freestanding membranes and thin films. In contrast to conventional lithography-based semiconductor manufacturing processes, radiation is not used to break or crosslink molecules within the resist, but rather to enhance one or more chemical reactions involved in the deposition process.

[0042] Atomic layer deposition is a known thin film deposition technique in which at least two chemicals (sometimes called precursor materials) are reacted sequentially with the surface of a material in a self-limiting manner. In contrast to chemical vapor deposition, the two precursor materials are typically not present on the substrate W at the same time.

[0043] In at least some embodiments using atomic layer deposition, the atomic layer deposition process includes at least a first and a second step. In the first step, an example of which is shown in Figure 3, a first precursor material 24 is reacted with a surface of the substrate W. In the second step, an example of which is shown in Figure 4, a second precursor material 26 is reacted with the substrate W in the area where the first precursor 24 reacted with the substrate W in the first step (selected portion 22 in this example).

[0044]

[0044] Figure 5 shows schematically an apparatus 30 for carrying out this method. The apparatus 30 therefore forms a patterned layer of material 23 on a substrate W. The apparatus 30 includes a projection system PS, which may form part of a lithographic apparatus LA. The projection system PS projects a patterned beam from a patterning device MA onto the substrate W, thereby irradiating the selected portion 22. The lithographic apparatus LA may be configured as described above with reference to Figure 1 (e.g. if the irradiation comprises DUV radiation and / or if immersion lithography is required) or as described above with reference to Figure 2 (e.g. if the irradiation comprises EUV radiation).

[0045] In one embodiment, the lithographic apparatus LA is configured to perform immersion lithography. In such an embodiment, the atomic layer deposition process may include irradiating the selected portion 22 while the selected portion 22 is in contact with an immersion liquid. The atomic layer deposition process may therefore include a first step involving adsorption of precursors from, for example, a gaseous precursor material onto the substrate W, and a second step in which the adsorbed precursors are modified in the selected portion 22 by irradiation through the immersion liquid (e.g., to remove by-products of the adsorption process). Any by-products generated by irradiation through the immersion liquid can be carried away by the flow of the immersion liquid. In one embodiment, the irradiated substrate W is then dried, and the dried substrate W is then subjected to any further required processing.

[0046] In one embodiment, an environmental control system 32 is provided. The environmental control system 32 allows the composition of an environment 34 above the substrate W to be controlled in a manner that allows the deposition process to proceed. In one embodiment, the environmental control system 32 includes a chamber 35. The chamber 35 is configured to contain the substrate W in a controlled gaseous environment during irradiation of the substrate W with the patterned beam. The chamber 35 may provide a sealed environment 34 that includes the selected portion 22 of the surface of the substrate W. The chamber 35 may include a pellicle 37 (e.g., a thin membrane) that is substantially transparent to the patterned beam 20 while also functioning to limit or prevent particle movement through the pellicle 37. The pellicle 37 may, for example, seal the chamber 35 and be substantially transparent to EUV radiation. The patterned radiation beam passes through the pellicle 37 to reach the target layer 22 during irradiation. The chamber 35 should typically be capable of maintaining a controlled gaseous environment at a pressure significantly below atmospheric pressure. The chamber 35 may be configured to provide conditions similar to those provided in the vacuum environment of, for example, an EUV scanner.

[0047] In some embodiments, all of the substrate W resides within the chamber 35 during the deposition process (e.g., an atomic deposition process). In one embodiment, a material exchange system 36 (e.g., ports to the chamber 35 and associated valves and / or conduits) is provided to allow materials to be added to and removed from the enclosed environment 34 so that different compositional environments can be established within the enclosed environment 34. Material exchange with the material exchange system 36 may be performed by a flow manager 38. The flow manager 38 may include any suitable combination of reservoirs, piping, valves, sinks, pumps, control systems, and / or other components necessary to provide the required flow of materials into and out of the chamber. The different compositional environments achieved in this manner may correspond to different stages of the deposition process. In some embodiments, the materials added to and removed from the chamber are gaseous, thereby providing compositional environments comprised of different gas combinations. In embodiments in which one or more steps of the deposition process are performed by irradiating the substrate W through an immersion liquid, the environmental control system 36 may be configured to enable switching between a state in which a controlled liquid environment is maintained above the substrate W (e.g., during exposure in immersion lithography mode) and a state in which a controlled gaseous environment is maintained above the substrate W (e.g., during precursor adsorption from a gaseous precursor material).

[0048] In some embodiments, enhancing the deposition process in the selected portion 22 includes enhancing a chemical reaction involving a precursor material. The precursor material is provided as part of the compositional environment established above the substrate W during irradiation. Enhancement of the chemical reaction allows the chemical reaction to proceed at a faster rate than would occur in the absence of irradiation. Alternatively, the chemical reaction may not occur at all without irradiation. In one embodiment, the chemical reaction is endothermic, and the irradiation provides the energy necessary to enable the chemical reaction to proceed. In some embodiments, the chemical reaction is enhanced, at least in part, by heat generated within the substrate W by the irradiation. Thus, a chemical reaction enhanced by irradiation may include a chemical reaction that requires an elevated temperature to proceed or that proceeds more rapidly at elevated temperatures. In some embodiments, the chemical reaction includes a photochemical reaction enhanced by the irradiation. Thus, at least one species involved in the chemical reaction directly absorbs a photon from the irradiation, and this absorption of the photon enables the chemical reaction to proceed. In some embodiments, the photochemical reaction includes a multiphoton photochemical reaction, which involves absorption of two or more photons by each of at least one species involved in the photochemical reaction. Because two or more photons must be absorbed, the chemical reaction is more sensitive to changes in irradiation intensity than single-photon photochemical reactions (i.e., the rate of the chemical reaction varies more significantly as a function of intensity). This increased sensitivity to intensity results in improved lateral contrast. In one embodiment, a combination of photochemical reactions and radiation-induced heating is used to provide a well-defined process window in which the chemical reaction is locally driven to generate the pattern. In one embodiment, the chemical reaction is driven by a plasma generated by interaction between the radiation and the substrate W, a layer formed on the substrate W, and / or gases present on the substrate. In one embodiment, the generated plasma is generated within a localized region defined by the irradiation. In one embodiment, the chemical reaction is driven by electrons provided by the irradiation. Such electrons may include photoelectrons or secondary electrons (electrons generated by inelastic scattering events of photoelectrons or electrons from the electron beam).In one embodiment, photons absorbed by the substrate W may bring energetic electrons (e.g., secondary electrons, as described below) near the surface of the substrate W that participate in the deposition process. In embodiments where a combination of electromagnetic radiation and an electron beam is used, the deposition process may also be facilitated in part by electrons from the electron beam.

[0049] In some embodiments, the flow dynamics of gas / liquid co-reactants and / or catalysts and / or precursors are controlled during the deposition process. Controlling the flow dynamics can improve the quality of the deposited material. Controlling the flow dynamics can include controlling the flow direction (or vector flow field of the flow). Alternatively or additionally, controlling the flow dynamics can include controlling the flow velocity, including, for example, providing a pulsed flow. In one embodiment, the flow dynamics are controlled spatially and / or temporally to produce a high density of relevant particles near the deposition location and a lower density of particles near other surfaces (e.g., optics).

[0050] In some embodiments, the compositional environment is controlled to provide different gas mixtures at different times. The different gas mixtures may be provided to deposit different materials or to switch between a mode of depositing material and a mode of etching and removing material. The different gas mixtures may be used to controllably vary the deposition rate as a function of time, which may be useful, for example, in creating features with well-defined edges and / or shapes.

[0051] In some embodiments, a bias voltage is applied to the substrate W during irradiation. As shown schematically in FIG. 5 , the bias voltage may be applied using a bias voltage unit 40. The bias voltage unit 40 may include a voltage source configurable to provide a desired bias voltage waveform. In the illustrated arrangement, the substrate W is attached to a substrate table WT via an electrostatic chuck 42. The bias voltage unit 40 may apply the bias voltage indirectly by applying a voltage to the substrate table WT and / or the electrostatic chuck 42, or may apply the bias voltage directly to the substrate W (e.g., from the side of the substrate W opposite the surface of the substrate W from the selected portion 22 being irradiated). The bias voltage may be applied via a match box or blocking capacitor network 41. As explained below, the bias voltage may increase the extent to which secondary electrons generated by the irradiation contribute to facilitating the deposition process in the selected portion 22, thereby increasing the rate of the deposition process and improving yield. The bias voltage may achieve this by increasing the proportion of secondary electrons that reach the surface of the substrate W with suitable energy and / or trajectory.

[0052] 6 and 7 schematically illustrate the average trajectories (dashed arrows) of secondary electrons from the focal region 48 toward the surface of the substrate W. FIG. 6 illustrates the case where no bias voltage is applied, and FIG. 7 illustrates the case where a bias voltage is applied. In both cases, secondary electrons can be generated when photons of the illumination interact with the substrate material to generate relatively high-energy primary electrons. The primary electrons then further interact with the substrate material to generate lower-energy secondary electrons. Some of the secondary electrons generated within the substrate W will arrive at the surface with the appropriate energy and trajectory to escape from the surface and contribute to facilitating the deposition process at the surface of the substrate W. The secondary electrons may facilitate deposition, for example, by causing dissociation of precursor molecules at the surface. Dissociation of precursor molecules can facilitate chemical reactions that result in the deposition of a desired material on the surface.

[0053] 6 , in the absence of a bias voltage, some secondary electrons generated from the illumination of the focal region 48 reach the surface of the substrate W, but these secondary electrons are relatively spread out. Furthermore, a relatively large proportion of the secondary electrons reach the surface on relatively shallow trajectories (e.g., trajectories closer to a direction parallel to the surface of the substrate than to a direction perpendicular to the surface of the substrate). Secondary electrons that reach the surface with energies lower than the work function will be reflected and will not be able to contribute to inducing material deposition at the surface. Secondary electrons that reach the surface on shallow trajectories, even if they have energies higher than the work function, may also be reflected if the energy associated with the component of propagation perpendicular to the surface is smaller than the work function.

[0054]

[0054] In the applied bias voltage situation depicted in FIG. 7, the bias voltage establishes an electric field between the focal region 48 and the surface. The maximum magnitude of the electric field will depend on the amplitude of the bias voltage waveform. An electric field in the range of several GV / m can be realized within the substrate W, which is strong enough to alter the trajectories of secondary electrons to have a useful effect. For example, thin SiO2 substrates deposited by ALD techniques have been found to withstand electric fields of several GV / m without being destroyed. The electric field alters the trajectories of secondary electrons so that they impinge at a steeper angle and on a more limited area on the surface. As a result, a larger proportion of secondary electrons can overcome the work function and contribute to inducing material deposition at the surface. Furthermore, the electric field concentrates the secondary electrons in a more spatially limited area on the surface, resulting in a higher intensity of secondary electrons reaching the surface. Therefore, the rate of radiation-induced deposition per unit area increases with the applied bias voltage. Additionally, the bias voltage facilitates improving the spatial definition of the radiation-induced deposition, thereby improving the quality of the patterns formed on the substrate W by the radiation-induced deposition.

[0055] In one embodiment, the bias voltage alternates in polarity. Thus, the bias voltage repeatedly changes sign. The bias voltage may be defined by a periodic (regularly repeating) bias voltage waveform. The bias voltage periodically drives secondary electrons generated inside the substrate by the irradiation toward the surface of the selected portion 22. Using a bias voltage with alternating polarity limits charging of the substrate W during irradiation. Excessive charge accumulation on the substrate W is undesirable because it may induce deposition over a larger than desired area, for example, independent of the pattern defined by the irradiation (e.g., outside the selected portion 22).

[0056] In some embodiments, the bias voltage waveform is sinusoidal. FIGS. 8 and 9 schematically show exemplary curves 46 illustrating how the voltage at the surface of the substrate W changes over time when a sinusoidal bias voltage waveform is applied. FIG. 8 shows the transient phase immediately after the bias voltage waveform is first applied. FIG. 9 shows the steady-state region reached after a short time. As shown in FIG. 8, the voltage at the surface may drift during the transient phase as the surface becomes negatively charged due to the greater mobility of the relatively light, negatively charged electrons in the plasma generated outside the substrate by irradiation compared to the heavier, positively charged ions in the plasma. With a well-tuned matching box or blocking capacitor network 41, the voltage drifts until the waveform is such that no net charging occurs at the surface when considered over the entire cycle of the applied bias voltage waveform. The DC shift observed in the steady state may be referred to as the DC bias voltage.

[0057] The energy of ions impinging on the substrate W from the plasma above it will depend on how the electric field varies in the sheath volume adjacent to the substrate W while the bias voltage is applied. This electric field depends on the voltage difference between the bulk of the plasma and the voltage at the surface of the substrate W. The voltage in the bulk of the plasma varies relatively little as a function of time compared to the voltage in the sheath volume closer to the substrate W. Curve 47 in Figure 9 shows schematically how the voltage in the bulk of the plasma is expected to vary as a function of time. The voltage in the bulk of the plasma varies with a much smaller amplitude than the voltage at the substrate W.

[0058] A bias voltage applied to the substrate W generates an electric field both within the substrate W and within the sheath volume adjacent to the substrate W. The electric field will have the same polarity in both regions and will therefore drive electron movement in the same way in both regions. Thus, when electrons in the plasma are driven toward the substrate W, secondary electrons within the substrate W will be driven in a direction away from the surface of the substrate in the selected portion (i.e., downward in the orientation of FIG. 5). When positive ions in the plasma are driven toward the substrate W, secondary electrons within the substrate W will be driven toward the surface of the substrate W in the selected portion 22. Thus, the shape of the energy distribution of secondary electrons driven toward the surface of the selected portion 22 by the applied bias voltage will be similar to the shape of the energy distribution of ions driven toward the surface by the applied bias voltage.

[0059] When a sinusoidal bias voltage is applied, the electric field varies as a function of time in a manner that results in a relatively wide, bimodal spread in the energy distribution of secondary electrons arriving at the surface. This is shown schematically in curve 41 of FIG. 10, which shows the energy distribution N(E) as a function of secondary electron energy (E) when a sinusoidal bias voltage is applied. Curve 41 is relatively wide (spread over a relatively large energy range) and bimodal (has two clear local minima). The secondary electron energy distribution can be shifted along the energy axis by varying the amplitude of the bias voltage waveform.

[0060] In some embodiments, a non-sinusoidal bias voltage waveform is applied. Applying a non-sinusoidal bias voltage provides flexibility to achieve a more favorable secondary electron energy distribution for inducing desired deposition at selected portions 22 on the surface of the substrate W. For example, the bias voltage waveform can be adjusted so that a majority of the secondary electrons reaching the surface of the substrate W at selected portions 22 have energies within a range that promotes one or more favorable interaction mechanisms with the precursor material. This can be facilitated by selecting a bias voltage waveform such that the energy distribution of the secondary electrons reaching the surface has a single maximum (rather than multiple maxima). Such an energy distribution is sometimes referred to as a unimodal distribution.

[0061] A preferred interaction mechanism may include a preferred type of bond dissociation. FIG. 11 is a graph showing a typical distribution of secondary electron energies at a surface when no bias voltage is applied. The energy range is relatively broad, with a peak in the 3-5 eV range. Dashed rectangles 51-53 superimposed on the graph indicate the approximate energy ranges favorable for three different types of bond dissociation. Rectangle 51 represents the energy range favorable for dissociative electron detachment (DEA). Rectangle 52 represents the energy range favorable for neutral dissociation (ND). Rectangle 53 represents the energy range favorable for dissociative ionization (DI). Applying a sinusoidal bias voltage waveform can provide secondary electrons in a higher energy range than when no bias voltage is applied. For example, applying a bias voltage may enable most of the secondary electrons reaching the surface to arrive at the surface at energies greater than 10 eV, optionally greater than 20 eV, optionally greater than 30 eV, optionally greater than 40 eV, and optionally in the range of 10 eV to 52 eV (the ND and DI regions), instead of arriving at the surface mostly at energies less than 10 eV (the DEA region). This may result in an improvement over the no-bias case by favoring the ND and DI mechanisms over the DEA mechanism, which may be desirable for a range of deposition processes. However, as discussed above with reference to FIG. 10 , the energy distribution achieved by a sinusoidal bias may still be relatively broad, resulting in a significant proportion of secondary electrons arriving at the surface at energies that are too low to favor the desired bond dissociation mechanisms (e.g., ND and DI). Adjusting the non-sinusoidal bias voltage waveform to narrower the spread of the secondary electron energy distribution may allow a larger portion of the secondary electrons to most effectively contribute to driving the deposition process, and therefore, using a non-sinusoidal bias voltage waveform may improve throughput.

[0062] In one embodiment, the non-sinusoidal bias voltage waveform is periodic. An example of such a bias voltage waveform is shown in FIG. 12. The curve in FIG. 12 represents the variation of the applied voltage in the steady state described above with reference to FIG. 9. In the steady state, no significant net charging of the substrate W occurs over a period 65 of the applied voltage waveform. Each period 65 of the bias voltage waveform includes a positive bias portion 66 and a negative bias portion 67. The duration of the positive bias portion 66 plus the duration of the negative bias portion 67 may be equal to the period 65 of the bias voltage waveform.

[0063] The voltage applied during the negative bias portion 67 is such that during the negative bias portion, secondary electrons in the substrate W are driven toward the surface of the substrate W in the selected portion 22 (i.e., the upper side of the substrate W in the orientation of FIG. 5). Thus, during the negative bias portion, the potential at the surface of the substrate W is higher than the potential in the bulk of the substrate W. At the same time, positive ions of the plasma outside the substrate W may be attracted toward the substrate 22.

[0064] The voltage applied during the positive bias portion 66 is such that secondary electrons within the substrate W are driven away from the surface of the substrate W in the selection portion 22 during the positive bias portion 66. Thus, during the positive bias portion, the potential at the surface of the substrate W is lower than the potential in the bulk of the substrate W. At the same time, electrons of the plasma outside the substrate W may be attracted towards the target layer 22.

[0065] The small mass of electrons in the plasma means that they respond very quickly to changes in the electric field direction and flow onto the substrate W essentially only during the positive bias portion 66. In contrast, inertial effects of the much heavier ions will cause them to flow onto the substrate W not only during the negative bias portion 67 but also during at least part of the positive bias portion 66. In some embodiments, the duration of the positive bias portion is selected (e.g., is short enough) so that inertial effects keep ions flowing towards the target layer for the entire duration of the positive bias portion.

[0066] 12, the duration of the positive bias portion 66 is shorter than the duration of the negative bias portion 67. The positive bias portion 66 may be, for example, less than one-quarter of a period 65 of the bias voltage waveform, preferably less than one-fifth of a period 65, preferably less than one-sixth of a period 65, preferably less than one-eighth of a period 65, or preferably less than one-tenth of a period.

[0067] In some embodiments, the voltage of the bias voltage waveform is substantially constant during at least the majority of the positive bias portion 66.

[0068] In some embodiments, the voltage of the bias voltage waveform is varied, at least during a majority of the negative bias portion 67, in a manner that at least partially compensates for charging of the target layer 22 and / or substrate 24 caused by ion bombardment during the negative bias portion. Charging can occur, for example, when the surface and / or subsurface layers are dielectric. Arranging the bias voltage to compensate for charging reduces variations in the electric field in the interior volume of the substrate W adjacent the surface of the selected portion 22, thereby contributing to a reduced energy spread in the energy distribution of secondary electrons reaching the surface.

[0069] 12, the change in voltage of the bias voltage waveform during the negative bias portion 67 is substantially linear (as shown in FIG. 12) at least during a majority of the negative bias portion 67. In some embodiments, the change in voltage of the bias voltage waveform during the negative bias portion 67 is such as to maintain a substantially time-invariant electric field within the interior volume of the substrate W adjacent the surface of the selected portion 22 during the negative bias portion 67.

[0070]

[0070] Using a non-sinusoidal bias voltage waveform facilitates providing a secondary electron energy distribution having a single maximum (unimodal), as illustrated by curve 42 in Figure 10, or a secondary electron energy distribution having multiple maxima that are close together in energy. Thus, a non-sinusoidal bias voltage waveform facilitates providing a secondary electron energy distribution having a high proportion in a range that is favorable for optimal dissociation mechanisms (e.g., the ND and DI mechanisms described above). For example, the bias voltage waveform can be selected to provide a single maximum greater than 10 eV, optionally greater than 20 eV, optionally greater than 30 eV, optionally greater than 40 eV, or optionally in the range of 10 eV to 52 eV.

[0071] As discussed above in connection with the sinusoidal bias voltage waveform, varying the amplitude of the bias voltage waveform can shift the ion energy distribution along the energy axis. This is illustrated in FIG. 13, which shows three different bias voltage waveforms with the same frequency and three different amplitudes. The corresponding distribution of secondary electron energies is shown in FIG. 14. Curve 81 (dashed line) shows the energy distribution resulting from applying the minimum amplitude bias voltage waveform of FIG. 13. Curve 82 (solid line) shows the energy distribution resulting from applying the medium amplitude bias voltage waveform of FIG. 13. Curve 83 (dashed line) shows the energy distribution resulting from applying the maximum amplitude bias voltage waveform of FIG. 13. Curves 81-83 are examples of unimodal curves of the same type as curve 42 shown in FIG. 10. The unimodal morphology is achieved by using each of the non-sinusoidal waveforms shown in FIG. 13. It can be seen that, in contrast to the sinusoidal case discussed above with reference to FIGS. 8-10, the energy spread does not significantly widen or become bimodal with increasing amplitude. Thus, a non-sinusoidal bias voltage waveform allows for flexible control of the secondary electron energy distribution without broadening or bimodality, allowing the secondary electron energy to be flexibly adjusted within a narrow range of optimal energies for inducing the particular deposition process being used.

[0072] In some embodiments, the bias voltage applied by the bias voltage unit 40 comprises a radio frequency waveform. In some embodiments, the frequency of the bias voltage waveform is less than 1 MHz.

[0073] The inventors performed simulations to calculate the magnitude of throughput improvement possible by applying a bias voltage. The maximum theoretically possible improvement varies depending on the material being deposited and the substrate composition, but improvements are generally in the range of 50 to 300. For example, when depositing W on a SiO2 substrate using a tuned square-wave bias voltage and irradiation with EUV radiation, a throughput improvement of over 200 is expected to be achievable. When depositing W on a Sn substrate using the same parameters, a throughput improvement of over approximately 100 is expected. In both cases, applying a bias voltage can achieve a sufficiently high throughput to make this approach practical using currently available EUV lithography tools and currently achievable EUV doses.

[0074]

[0074] Embodiments of the present disclosure are set forth in the following numbered clauses: 1. An apparatus for forming a patterned layer of material on a substrate, comprising: a projection system configured to illuminate selected portions of a surface of the substrate during a deposition process; an environmental control system configured to contain the substrate within a controlled gaseous environment during irradiation of the selected portion, the controlled gaseous environment being one that supports the deposition process; and a bias voltage unit configured to apply a bias voltage having alternating polarity to the substrate during irradiation, thereby periodically driving secondary electrons generated within the substrate by the irradiation toward the surface of the selected portion; An apparatus comprising: 2. The apparatus of clause 1, wherein the bias voltage has a non-sinusoidal bias voltage waveform. 3. The apparatus of clause 2, wherein the bias voltage waveform is periodic. 4. Each cycle is a negatively biased portion where secondary electrons in the substrate are driven toward the surface of the selected portion; and a positive bias portion that drives secondary electrons in the substrate away from the surface of the selected portion. 5. The apparatus described in clause 4, wherein the bias voltage unit is configured to vary the voltage of the bias voltage waveform during at least a majority of the negative bias portion in a manner that at least partially compensates for charging of the substrate caused by ions impinging on the substrate from the plasma during the negative bias portion. 6. The apparatus of clause 5, wherein the bias voltage unit is configured such that the change in voltage of the bias voltage waveform during the negative bias portion is substantially linear, at least during a majority of the negative bias portion. 7. The apparatus of clause 5 or 6, wherein the bias voltage unit is configured such that the change in voltage of the bias voltage waveform during the negative bias portion is such that the change maintains a substantially time-invariant electric field within the interior volume of the substrate adjacent the surface of the selected portion during the negative bias portion. 8. The device of any of clauses 4-7, wherein the duration of the positive bias portion is less than 1 / 4 of the period of the bias voltage waveform. 9. An apparatus as described in any of clauses 4 to 8, wherein the voltage of the bias voltage waveform is substantially constant during at least a majority of the positive bias portion. 10. An apparatus according to any preceding clause, wherein the bias voltage unit is configured to have a bias voltage waveform selected such that the energy distribution of secondary electrons reaching the surface of the selected portion has a single maximum value. 11. The apparatus of any preceding clause, wherein the bias voltage unit is configured to have a bias voltage waveform selected such that the energy distribution of secondary electrons reaching the surface of the selected portion has most secondary electrons with energies greater than 10 eV and / or energies at which neutral dissociation and / or dissociative ionization of the precursor material is more favorable than dissociative electron detachment. 12. An apparatus according to any preceding clause, wherein the projection system is configured to illuminate the selected portion with electromagnetic radiation having a wavelength of less than 100 nm. 13. An apparatus according to any preceding clause, wherein the projection system and environmental control system are configured such that irradiation generates a plasma outside the substrate. 14. Apparatus according to any preceding clause, wherein the projection system and environmental control system are configured to locally enhance the deposition process in the selected portions by irradiating, thereby forming a patterned layer of material in a pattern defined by the selected portions, and optionally the patterned layer comprises a two-dimensional material. 15. A method of forming a patterned layer of material on a substrate, comprising: irradiating selected portions of a surface of the substrate during a deposition process, the irradiation being such that the deposition process is locally enhanced in the selected portions to form a patterned layer of material in a pattern defined by the selected portions; applying a bias voltage having alternating polarity to the substrate during irradiation to periodically drive secondary electrons generated within the substrate by the irradiation toward the surface of the selected portion; A method comprising: 16. The method of clause 15, wherein the bias voltage has a non-sinusoidal bias voltage waveform. 17. The method of clause 16, wherein the bias voltage waveform is periodic. 18. Each period is a negatively biased portion where secondary electrons in the substrate are driven toward the surface of the selected portion; a positive bias portion whereby secondary electrons in the substrate are driven away from the surface of the selected portion. 19. The method of clause 18, wherein during at least a majority of the negative bias portion, the voltage of the bias voltage waveform is varied in a manner to at least partially compensate for charging of the substrate caused by ion impingement on the substrate from the plasma during the negative bias portion. 20. The method of clause 19, wherein the change in voltage of the bias voltage waveform during the negative bias portion is substantially linear, at least during a majority of the negative bias portion. 21. The method of clause 19 or 20, wherein the change in voltage of the bias voltage waveform during the negative bias portion is such as to maintain a substantially time-invariant electric field within the interior volume of the substrate adjacent the surface of the selected portion during the negative bias portion. 22. The method of any of clauses 18-21, wherein the duration of the positive bias portion is less than 1 / 4 of the period of the bias voltage waveform. 23. The method of any of clauses 18-22, wherein the voltage of the bias voltage waveform is substantially constant during at least a majority of the positive bias portion. 24. A method according to any one of clauses 15 to 23, wherein the bias voltage has a bias voltage waveform selected so that the energy distribution of secondary electrons arriving at the surface of the selected portion has a single maximum value. 25. A method according to any one of clauses 15 to 24, wherein the bias voltage has a bias voltage waveform selected such that in the energy distribution of secondary electrons reaching the surface of the selected portion, most secondary electrons have energies greater than 10 eV and / or energies at which neutral dissociation and / or dissociative ionization of the precursor material is more favorable than dissociative electron detachment. 26. The method of any of clauses 15 to 25, wherein the irradiation comprises irradiation with electromagnetic radiation having a wavelength of less than 100 nm. 27. The method of any one of clauses 15 to 26, wherein the irradiation generates a plasma outside the substrate. 28. The method of any one of clauses 15 to 27, wherein the patterned layer comprises a two-dimensional material.

Claims

1. 1. An apparatus for forming a patterned layer of material on a substrate, comprising: a projection system configured to illuminate selected portions of a surface of the substrate during a deposition process; an environmental control system configured to contain the substrate within a controlled gaseous environment during the irradiation of the selected portion, the controlled gaseous environment being one that supports the deposition process; and a bias voltage unit configured to apply a bias voltage having alternating polarity to the substrate during the irradiation, thereby periodically driving secondary electrons generated within the substrate by the irradiation toward the surface of the selected portion; An apparatus comprising:

2. The apparatus of claim 1 , wherein the bias voltage has a non-sinusoidal bias voltage waveform.

3. The apparatus of claim 2 , wherein the bias voltage waveform is periodic.

4. Each period is a negative bias portion where secondary electrons in the substrate are driven toward the surface of the selected portion; a positive bias portion that drives secondary electrons in the substrate away from the surface of the selected portion.

5. 5. The apparatus of claim 4, wherein the bias voltage unit is configured such that, during at least a majority of the negative bias portion, a voltage of the bias voltage waveform varies to at least partially compensate for charging of the substrate caused by ion impingement on the substrate from a plasma during the negative bias portion.

6. 6. The apparatus of claim 5, wherein the bias voltage unit is configured such that the change in voltage of the bias voltage waveform during the negative bias portion is substantially linear, at least during a majority of the negative bias portion.

7. 7. The apparatus of claim 5 or 6, wherein the bias voltage unit is configured such that the change in voltage of the bias voltage waveform during the negative bias portion is such that the change maintains a substantially time-invariant electric field within an interior volume of the substrate adjacent the surface of the selected portion during the negative bias portion.

8. 8. The apparatus of claim 4, wherein the duration of the positive bias portion is less than 1 / 4 of the period of the bias voltage waveform.

9. An apparatus according to any one of claims 4 to 8, wherein the voltage of the bias voltage waveform is substantially constant during at least the majority of the positive bias portion.

10. 10. The apparatus of claim 1, wherein the bias voltage unit is configured to have a bias voltage waveform selected such that the energy distribution of secondary electrons reaching the surface of the selected portion has a single maximum value.

11. 11. The apparatus of claim 1, wherein the bias voltage unit is configured to have a bias voltage waveform selected such that in the energy distribution of secondary electrons reaching the surface of the selected portion, most of the secondary electrons have energies above 10 eV and / or energies at which neutral dissociation and / or dissociative ionization of precursor material are more favorable than dissociative electron detachment.

12. Apparatus according to any preceding claim, wherein the projection system is configured to illuminate the selected portion with electromagnetic radiation having a wavelength of less than 100 nm.

13. Apparatus according to any preceding claim, wherein the projection system and the environmental control system are configured such that the irradiation generates a plasma outside the substrate.

14. 14. The apparatus of any preceding claim, wherein the projection system and the environmental control system are configured such that the deposition process in the selected portions is locally enhanced by the irradiation, thereby forming a patterned layer of material in a pattern defined by the selected portions, optionally the patterned layer comprising a two-dimensional material.

15. 1. A method of forming a patterned layer of material on a substrate, comprising: irradiating selected portions of a surface of the substrate during a deposition process, the irradiation being such that the deposition process is locally enhanced in the selected portions to form a patterned layer of material in a pattern defined by the selected portions; applying a bias voltage having alternating polarity to the substrate during the irradiation to periodically drive secondary electrons generated within the substrate by the irradiation toward the surface of the selected portion; A method comprising:

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