Method of forming patterned material layer and apparatus for forming patterned material layer

Abstract

The invention relates to a method and apparatus for forming a patterned layer of material on a substrate. In one arrangement, selected portions of a surface of a substrate are irradiated during a deposition process. The irradiation locally drives the deposition process in the selected portion and thereby forms a patterned layer of material in a pattern defined by the selected portion. A bias voltage having alternating polarity is applied to the substrate during the irradiation to periodically drive secondary electrons generated inside the substrate by the irradiation toward the surface in the selected portion.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to European application 22196803.5 filed on September 21, 2022, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present disclosure relates to methods and apparatus for forming a patterned material layer. The methods and apparatus are particularly suitable for providing patterns of two-dimensional materials, such as for use in fabricating FET devices. Background Art

[0004] As semiconductor manufacturing processes continue to advance, the size of circuit elements has continued to decrease, while the number of functional elements such as transistors per device has steadily increased, following a trend commonly referred to as "Moore's Law." To keep up with Moore's Law, the semiconductor industry is seeking technologies that can produce smaller and smaller features.

[0005] For some types of electronic devices, scaling down device features can cause performance challenges, such as the short channel response that occurs in MOSFETs when the channel length becomes comparable to the width of the depletion layer at the source and drain junctions. These challenges can sometimes be addressed using two-dimensional materials that are atomically thin and can have a relatively low dielectric constant. Two-dimensional materials can also have properties that are desirable for other situations. Where a high dielectric constant is required, two-dimensional materials can be used instead of gate oxides. Where high conductivity is preferred, two-dimensional materials can be used to replace interconnects.

[0006] There are various deposition techniques for making two-dimensional materials. Such deposition techniques include chemical vapor deposition (CVD), mechanical cutting (stripping), molecular beam epitaxy (MBE), atomic layer deposition (ALD), liquid phase spalling and other deposition techniques. A challenge with many of these deposition techniques has been the high temperatures required for the process to work efficiently (at high speed and high quality). High temperatures may degrade or damage previously deposited layers and / or limit the range of previously deposited layers that can be used. Previously deposited layers must be formed so that they can withstand high temperatures to an acceptable degree, for example by having a melting point higher than the temperature reached during the deposition process.

[0007] In the exfoliation-based approach, 2D materials can be grown offline without temperature restrictions, but it is difficult to perform the exfoliation and transfer process with high throughput and low defectivity.

[0008] Patterning two-dimensional materials presents other challenges due to the fragile nature of two-dimensional materials. Two-dimensional materials can be very easily damaged or delaminated. Two-dimensional materials can be damaged, for example, by traditional patterning processes such as coating with resists, photolithography, etching, and resist stripping. Typical photoresists used for DUV and EUV lithography may also be incompatible with two-dimensional materials because they are hydrophilic while two-dimensional materials are hydrophobic. Even with great care during processing, this physical incompatibility can cause resist residues to adhere to the structure unnecessarily and reduce the quality of contact between the structure and other layers.

[0009] Laser etching has been proposed to pattern two-dimensional materials. Laser etching uses a laser to locally heat a surface to gradually melt the material and remove it by evaporation. Laser processing techniques rely on point-by-point scanning, which reduces yield relative to some alternative methods.

[0010] It is possible to use EUV radiation to induce deposition of material in a selected pattern. However, high throughput has proven difficult to achieve due to the need for very high EUV doses. Summary of the invention

[0011] It is an object of the present invention to provide an alternative or improved method and apparatus for forming a patterned layer of material on a substrate.A particular object is to improve throughput and / or quality.

[0012] According to one aspect, an apparatus for forming a patterned material layer on a substrate is provided, comprising: a projection system configured to irradiate a selected portion of a surface of a substrate during a deposition process; an environmental control system configured to contain the substrate in a controlled gaseous environment during the irradiation of the selected portion, the controlled gaseous environment supporting the deposition process; and a bias voltage unit configured to apply a bias voltage with alternating polarity to the substrate during the irradiation to periodically drive secondary electrons generated inside the substrate by the irradiation toward the surface in the selected portion.

[0013] The apparatus may be configured such that the irradiation drives the deposition process locally in the selected portion, and thereby forms a patterned material layer in a pattern defined by the selected portion. The irradiation produces secondary electrons, and the bias voltage increases the proportion of the secondary electrons that may promote or contribute to the drive of the deposition process. The bias voltage is configured to have alternating polarity to avoid accumulation of excess charge on the substrate. The bias voltage improves the deposition rate per unit area, thereby improving throughput. The bias voltage may also improve the spatial confinement of radiation-induced deposition, thereby improving the quality of the pattern formed on the substrate.

[0014] In an embodiment, said irradiating comprises irradiating with electromagnetic radiation having a wavelength of less than 100 nm. This allows efficient generation of secondary electrons and facilitates high spatial resolution.

[0015] In an embodiment, the bias voltage has a non-sinusoidal bias voltage waveform. Providing a non-sinusoidal bias voltage makes it possible to reduce the variation of the electric field in the internal volume of the substrate adjacent to the surface, thereby reducing the energy range of secondary electrons driven to the surface. Reducing the energy range of secondary electrons means that a larger proportion of the secondary electrons can optimally promote or contribute to driving the deposition process, thereby improving production throughput.

[0016] In an embodiment, the bias voltage waveform is periodic and each period includes: a negative bias portion during which secondary electrons in the substrate are driven toward the surface in the selected portion; and a positive bias portion during which secondary electrons in the substrate are driven away from the surface in the selected portion. In such an arrangement, the voltage of the bias voltage waveform may also be arranged 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 irradiating from the plasma onto the substrate during the negative bias portion. Compensating for the charging of the substrate in this manner promotes or helps reduce the energy range of secondary electrons irradiated on the target layer by reducing variations in the electric field in an internal volume of the substrate adjacent to the surface in the selected portion.

[0017] In an embodiment, said variation in voltage of said bias voltage waveform during said negative bias portion is substantially linear during at least a majority of said negative bias portion. It has been found that such an approach provides a good balance between ease of implementation and effective compensation of charging of said substrate and reduction of variations in said electric field in said internal volume of said substrate adjacent to said surface in said selected portion.

[0018] In an embodiment, the variation in voltage of the bias voltage waveform during the negative bias portion maintains a substantially time-invariant electric field in an internal volume of the substrate adjacent to the surface of the substrate in the selected portion during the negative bias portion. Maintaining a substantially time-invariant electric field in the internal volume adjacent to the surface facilitates a high level of control over the energy of secondary electrons reaching the surface, thereby facilitating high throughput.

[0019] According to one aspect, a method for forming a patterned material layer on a substrate is provided, comprising: irradiating a selected portion of the surface of the substrate during a deposition process, the irradiation locally driving the deposition process in the selected portion and thereby forming a patterned material layer having a pattern defined by the selected portion; and applying a bias voltage having alternating polarity to the substrate during the irradiation to periodically drive secondary electrons generated inside the substrate by the irradiation toward the surface in the selected portion. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which:

[0021] Figure 1 Depicting a first example of a lithographic system including a lithographic apparatus and a radiation source;

[0022] Figure 2 depicts a second example of a lithographic system including a lithographic apparatus and a radiation source;

[0023] Figure 3 schematically depicting irradiating selected portions of a substrate to locally drive a deposition process;

[0024] Figure 4 schematically depicting the formation of a patterned material layer defined by selected portions;

[0025] Figure 5 Describing an apparatus for forming a patterned layer of material;

[0026] Figure 6 schematically depicts the average trajectory of secondary electrons from the focusing region towards the surface of the substrate in the absence of a bias voltage applied to the substrate;

[0027] Figure 7 Schematically depicting the case where a bias voltage is applied to the substrate Figure 6 The average trajectory of the secondary electrons in the arrangement of ;

[0028] Figure 8 schematically depicting the variation of substrate voltage with respect to time during a transient period shortly after initial switch-on of a bias voltage;

[0029] Fig. 9 schematically depicting the variation of substrate voltage with respect to time in steady state;

[0030] Fig.10 is a graph showing energy distribution of secondary electrons for two different bias voltage waveforms, the graph being plotted as the relationship between the number of electrons N(E) at energy E and the energy E;

[0031] Fig.11 is a graph showing energy distribution of secondary electrons without applied bias voltage, wherein superimposed rectangles show approximate energy ranges that are favorable for three different types of bond dissociation;

[0032] Fig.12 depicting an example non-sinusoidal bias voltage waveform;

[0033] Fig.13 is a graph showing three example non-sinusoidal bias voltage waveforms having different amplitudes;

[0034] Fig.14 It is shown that for Fig.13 Graphs of the energy distribution of secondary electrons for three bias voltage waveforms are shown. DETAILED DESCRIPTION

[0035] A lithographic apparatus is a machine configured to apply a desired pattern onto a substrate. A lithographic apparatus may be used, for example, in the manufacture of integrated circuits (ICs). For example, a lithographic apparatus may project a pattern at a patterning device (e.g., a mask) onto a layer of radiation-sensitive material (resist) disposed on a substrate.

[0036] To project a pattern onto a substrate, a lithographic apparatus may use electromagnetic radiation. The wavelength of this radiation determines the minimum size of the features patterned onto the substrate. Typical wavelengths currently in use are 365 nm (i-line), 248 nm, 193 nm, and 13.5 nm. Compared to a lithographic apparatus using radiation having a wavelength of, for example, 193 nm, a lithographic apparatus using extreme ultraviolet (EUV) radiation having a wavelength of less than 100 nm, optionally in the range of 5 nm to 100 nm, optionally in the range of 4 nm to 20 nm (e.g., 6.7 nm or 13.5 nm) may be used to form smaller features on a substrate.

[0037] Herein, unless otherwise stated, 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) and EUV (extreme ultraviolet radiation, e.g., having a wavelength in the range of about 5 nm to 100 nm), as well as electron beam radiation.

[0038] Figure 1A lithographic apparatus LA is schematically depicted. The lithographic apparatus LA comprises an illumination system (also referred to as an illuminator) IL configured to condition a radiation beam B (e.g., UV radiation, DUV radiation, or EUV radiation), a mask support (e.g., a mask stage) MT configured to support a patterning device (e.g., a mask) MA and connected to a first positioner PM configured to accurately position the patterning device MA according to certain parameters, a substrate support (e.g., a wafer stage) WT configured to hold a substrate (e.g., a resist-coated wafer) W and connected 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.

[0039] In operation, the illumination system IL receives a radiation beam from a radiation source SO, for example via a beam delivery system BD. The illumination system IL may include various types of optical components for directing, shaping and / or controlling the radiation, such as refractive, reflective, magnetic, electromagnetic, electrostatic and / or other types of optical components, or any combination thereof. The illuminator IL may be used to condition the radiation beam B so that it has a desired spatial and angular intensity distribution in its cross-section at the plane of the patterning device MA.

[0040] The term "projection system" PS as used herein should be broadly interpreted as covering various types of projection systems suitable for the exposure radiation used and / or for other factors such as the use of immersion liquid or the use of a vacuum, including refractive, reflective, catadioptric, anamorphic, magnetic, electromagnetic and / or electrostatic optical systems or any combination thereof. Any use of the term "projection lens" herein may be considered synonymous with the more general term "projection system" PS.

[0041] The lithographic apparatus LA may be of a type in which at least a portion of the substrate may be covered by a liquid having a relatively high refractive index, such as water, so as to fill the space between the projection system PS and the substrate W, which is also referred to as immersion lithography. More information on immersion techniques is given in US6952253, which is incorporated herein by reference.

[0042] The lithographic apparatus LA may also be of a type having two or more substrate supports WT (also referred to as a "dual stage"). In such a "multi-stage" machine, the substrate supports WT may be used in parallel, and / or a step of preparing a substrate W for subsequent exposure may be performed on a substrate W located on one of the substrate supports WT while another substrate W on another substrate support WT is being used to expose a pattern on another substrate W.

[0043] In addition to the substrate support WT, the lithographic apparatus LA may also comprise a metrology platform. The metrology platform is arranged to hold sensors and / or cleaning means. The sensors may be arranged to measure properties of the projection system PS or properties of the radiation beam B. The metrology platform may hold a plurality of sensors. The cleaning means may be arranged to clean parts of the lithographic apparatus, for example a part of the projection system PS or a part of the system for providing immersion liquid. The metrology platform may be moved under the projection system PS when the substrate support WT is away from the projection system PS.

[0044] In operation, a radiation beam B is incident on a patterning device MA (e.g. a mask) held on a mask support MT and is patterned by a pattern (design layout) present on the patterning device MA. Having traversed the mask MA, the radiation beam B passes through a projection system PS which focuses the beam onto a target portion C of the substrate W. With the aid of a second positioner PW and a position measurement system IF, the substrate support WT can be accurately moved, for example in order to position different target portions C in the path of the radiation beam B at focus and alignment positions. Similarly, a first positioner PM and possibly a further position sensor (which may be located in the substrate support WT) may be used to position the radiation beam B. Figure 1 The patterning device MA may be accurately positioned relative to the path of the radiation beam B using the mask alignment marks M1, M2 and the substrate alignment marks P1, P2. Although the substrate alignment marks P1, P2 as shown occupy dedicated target portions, the marks may be located in spaces between target portions. When the substrate alignment marks P1, P2 are located between target portions C, they are referred to as scribe line alignment marks.

[0045] Figure 2 A lithographic system is shown comprising a radiation source SO and a lithographic apparatus LA. The radiation source SO is configured to generate an EUV radiation beam B and to supply the EUV radiation beam B to the lithographic apparatus LA. The lithographic 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.

[0046] The illumination system IL is configured to condition the EUV radiation beam B before it is incident on the patterning device MA. In addition, 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 a desired cross-sectional shape and a desired intensity distribution for the EUV radiation beam B. The illumination system IL may also include other mirrors or arrangements in addition to or instead of the faceted field mirror arrangement 10 and the faceted pupil mirror arrangement 11.

[0047] After being so conditioned, the EUV radiation beam B interacts with the pattern forming device MA. As a result of this interaction, a patterned EUV radiation beam B' is generated. The projection system PS is configured to project the patterned EUV radiation beam B' onto the substrate W. For the stated purpose, the projection system PS may include a plurality of mirrors 13, 14 configured to project the patterned EUV radiation beam B' onto the substrate W held by the substrate table WT. The projection system PS may apply a reduction factor to the patterned EUV radiation beam B', thereby forming an image having features that are smaller than corresponding features on the pattern forming device MA. For example, a reduction factor of 4 or 8 may be applied. Although the projection system PS is Figure 2 Although illustrated in FIG. 1 as having only two mirrors 13 , 14 , the projection system PS may comprise a different number of mirrors (eg six or eight mirrors).

[0048] The substrate W may include a previously formed pattern. In this case, the lithographic apparatus LA aligns an image formed by the patterned EUV radiation beam B′ with a pattern previously formed on the substrate W.

[0049] A relative vacuum, ie a small amount of gas (eg hydrogen) at a pressure well below atmospheric pressure, may be provided in the radiation source SO, in the illumination system IL and / or in the projection system PS.

[0050] The radiation source SO may be a laser produced plasma (LPP) source, a discharge produced plasma (DPP) source, a free electron laser (FEL) or any other radiation source capable of generating EUV radiation.

[0051] As mentioned in the introduction of the specification, although there is interest in using two-dimensional materials in semiconductor manufacturing processes, there are challenges in achieving sufficiently high crystalline quality and / or production volume and / or low defectivity. Deposition processes such as CVD and ALD require high temperatures, which may damage the underlying layer. For example, a typical CVD process for producing a high-quality monolayer of two-dimensional crystals may require temperatures above 800°C, while temperatures above 500°C are generally incompatible with back-end process CMOS technology. For example, the thermal budget for Si FinFet (fin field effect transistor) is less than 1050°C for the front-end process (FEOL) and less than 400°C for the back-end process (BEOL). For 2D-FET (field effect transistor based on two-dimensional materials), this budget is much lower (typically 450°C to 500°C for both FEOL and BEOL). The process based on peeling avoids these thermal constraints because the deposition of two-dimensional materials can be performed at the separation site, but the transfer process is complex and it is difficult to avoid high defectivity. Traditional patterning processes such as coating resists, photolithography, etching, and resist stripping are also problematic because they may damage the two-dimensional material. Additionally, conventional photolithography techniques present challenges for patterning 2D material layers. Due to the nature of these materials, the resulting structures are contaminated and / or damaged by rough edges after the (dry, wet) etching steps following photolithography (DUV, EUV, EBL). The contact with other layers (e.g., source and drain electrodes) is not optimal, resulting in a Schottky barrier that is approximately 3.5 times larger than if a clean and sharp interface were provided.

[0052] Alternative methods using EUV-induced deposition can directly form patterns of two-dimensional materials without any resist processing. Examples of such deposition are described in WO2019166318, WO2020207759 and EP3875633A1, all of which are incorporated by reference. However, in the case of EUV-induced deposition, it may be difficult to achieve sufficiently high growth rates for two-dimensional materials. In practice, the EUV dose (the amount of energy deposited per unit area by EUV radiation) is constrained by production throughput requirements. Typically, increasing the dose reduces production throughput. For example, a typical EUV dose limit can be 100 mJ / cm 2 .

[0053] Embodiments of the present disclosure provide methods and apparatus for forming a patterned layer 23 of material on a substrate W that addresses the above challenges. The formation of the patterned layer 23 involves irradiation of the substrate W. The above reference can be used to see Figure 1 and Figure 2Thus, an apparatus for performing the method may include a projection system PS, such as that described above with reference to Figure 1 and Figure 2 A projection system PS is described which is configured to irradiate a substrate W by projecting a patterned radiation beam onto the substrate W.

[0054] In some embodiments, Figure 3 to Figure 4 As illustrated in , during the deposition process, the substrate W is irradiated to form a patterned layer 23. The method includes irradiating 20 a selected portion 22 of the surface of the substrate W during the deposition process. The irradiation can thereby apply a dose in the selected portion 22 and not in any other portion on the surface during at least one step of the deposition process. In an embodiment, the patterned layer 23 includes a two-dimensional material, is substantially composed of a two-dimensional material, or is composed of a two-dimensional material. A two-dimensional material is a material that exhibits significant anisotropic properties in the lateral direction within the plane of the material compared to the direction perpendicular to the plane of the material. A class of two-dimensional materials is sometimes referred to as a single layer material or a single layer, and may include a crystalline material composed of a single layer of atoms or a small number of single layers of atoms stacked on top of each other. In some embodiments, the two-dimensional material includes one or more of the following, is substantially composed of one or more of the following, or is composed of one or more of the following: one or more 2D allotropes, such as graphene and antimonene; or one or more inorganic compounds, such as MXene, hexagonal boron nitride (hBN) and transition metal dichalcogenides (TMD) (MXene 2 A type of semiconductor that can be atomically thin, where the letter M refers to a transition metal atom (e.g., Mo or W) and the letter X refers to a chalcogen atom (e.g., S, Se, or Te)), such as WS 2 , MoS 2 ,WSe 2 , MoSe 2Etc. The two-dimensional material may include a layer of M atoms sandwiched between two layers of X atoms. The two-dimensional material may include any semiconductor two-dimensional material suitable for use as a transistor channel. As mentioned above, the two-dimensional material may include a 2D allotrope, such as graphene or antimonene, or an inorganic compound. The two-dimensional material may include a monolayer (or multiple monolayers if the deposition process is repeated). In the embodiment shown, the deposition process is an atomic layer deposition process. In other embodiments, different deposition processes or combinations of deposition processes are used, including, for example, using one or more of the following independently or in combination: atomic layer deposition; chemical vapor deposition; plasma enhanced chemical vapor deposition; epitaxy; sputtering; and electron beam induced deposition. The formation of the patterned layer 23 may constitute a step in a method of forming at least one layer of a device to be manufactured (such as a semiconductor device). For example, the two-dimensional material may form a channel or a metal cap or an interconnect or a diffusion barrier in an interconnect of a FET.

[0055] In an embodiment, the irradiation is performed with radiation capable of locally driving a deposition process. In an embodiment, the radiation comprises, consists essentially of, or consists of any type of EUV radiation (having a wavelength less than 100 nm) capable of locally driving a deposition process. The use of EUV radiation provides high spatial resolution. In some other embodiments, the irradiation is performed with radiation comprising, consisting essentially of, or consisting of higher wavelength radiation, optionally in combination with an immersion liquid, as described below. The higher wavelength radiation may be in the range of 100 nm to 400 nm (including DUV radiation).

[0056] The irradiation locally drives the deposition process in the selected portions 22 to cause the formation of a patterned layer 23, such as Figure 4 As schematically depicted in . The pattern of the patterned layer 23 is defined by the selected portion 22. The pattern is therefore formed without the need for any resist. Therefore, no process for removing the resist is required, which reduces the risk of damaging the patterned material layer 30 or damaging any fragile underlying material. This method is particularly desirable in cases where resist residues may significantly affect the properties of the fragile underlying material and / or where the stripping of the resist may significantly damage the fragile underlying material. Examples of fragile underlying materials include very thin film coatings, 2D materials such as graphene or transition metal dichalcogenides (TMDs), and free-standing diaphragms or films. Compared to conventional lithography-based semiconductor manufacturing processes, radiation is being used to drive one or more chemical reactions involved in the deposition process, rather than being used to destroy or cross-link molecules in the resist.

[0057] Atomic layer deposition is a known thin film deposition technique in which each of at least two chemical species (which may be referred to as precursor materials) is reacted with the surface of the material in a sequential, self-limiting manner. In contrast to chemical vapor deposition, the two precursor materials are typically not present simultaneously above the substrate W.

[0058] In at least some embodiments using atomic layer deposition, the atomic layer deposition includes at least a first step and a second step. In the first step (an example of which is Figure 3 In a second step (illustrated in FIG. 1 ), a first precursor material 24 is reacted with the surface of a substrate W. In a second step (illustrated in FIG. Figure 4 In the embodiment of the present invention (depicted in FIG. 1 ), the second precursor material 26 is caused to react with the substrate W in the region (in this example, the selected portion 22 ) where the first precursor 24 reacted with the substrate W in the first step.

[0059] Figure 5 An apparatus 30 for performing the method is schematically depicted. Thus, the apparatus 30 forms a patterned layer 23 of material on a substrate W. The apparatus 30 comprises a projection system PS. The projection system PS may form part of a lithographic apparatus LA. The projection system PS irradiates selected portions 22 by projecting a patterned radiation beam from a patterning device MA onto the substrate W. The projection system PS may be as described above with reference to Figure 1 as described above (e.g., when the irradiation comprises DUV radiation and / or immersion lithography is required) or as described above with reference to Figure 2 The lithographic apparatus LA is configured in the manner described (eg when the radiation comprises EUV radiation).

[0060] In an embodiment, the lithographic apparatus LA is configured to perform immersion lithography. In such an embodiment, the atomic layer deposition process may include a step of irradiating the selected portion 22 while the selected portion 22 is in contact with the immersion liquid. Thus, for example, the atomic layer deposition process may include: a first step comprising adsorbing a precursor from a gaseous precursor material to the substrate W; and a second step in which the adsorbed precursor in the selected portion 22 is modified by irradiation via the immersion liquid (e.g., to remove byproducts of the adsorption process). Any byproducts produced by the irradiation via the immersion liquid may be conveniently carried away by the flow of immersion liquid. In an embodiment, the irradiated substrate W is then dried and any other desired treatment is performed on the dried substrate W.

[0061] In an embodiment, an environmental control system 32 is provided. The environmental control system 32 allows the composition of the environment 34 above the substrate W to be controlled in a manner that allows the deposition process to proceed. In an 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 by the patterned beam. The chamber 35 can provide a sealed environment 34 that contains a selected portion 22 of the surface of the substrate W. The chamber 35 can include a pellicle 37 (e.g., a thin film) that is substantially transparent to the patterned beam 20 while still being used to limit or prevent particles from moving through the pellicle 37. The pellicle 37 can, for example, seal the chamber 35 and be substantially transparent to EUV radiation. The patterned radiation beam passes through the pellicle 37 to the target layer 22 during irradiation. The chamber 35 should generally be able to maintain the controlled gaseous environment at a pressure substantially below atmospheric pressure. The chamber 35 can be configured to provide conditions similar to those provided in, for example, an EUV scanner vacuum environment.

[0062] In some embodiments, the entirety of the substrate W will be located within the chamber 35 during the deposition process (e.g., an atomic deposition process). In an embodiment, a material exchange system 36 (e.g., a port into the chamber 35 and associated valves and / or conduits) is provided, which allows materials to be added to and removed from the sealed environment 34 to allow different composition environments to be established within the sealed environment 34. Materials can be provided to and from the material exchange system 36 by a flow manager 38. The flow manager 38 can include any suitable combination of reservoirs, pipes, valves, tanks, pumps, control systems, and / or other components necessary to provide the required material flow into and out of the chamber. The different composition environments achieved in this manner can correspond to different corresponding stages of the deposition process. In some embodiments, the materials added to and removed from the chamber are gaseous, thereby providing composition environments composed of different combinations of gases. In embodiments where one or more steps of a deposition process are performed by irradiating the substrate W through an immersion liquid, the environmental control system 36 may be configured to allow switching between maintaining a controlled liquid environment above the substrate W (e.g., during exposure in an immersion lithography mode) and maintaining a controlled gaseous environment above the substrate W (e.g., during adsorption of precursors from a gaseous precursor material).

[0063] In some embodiments, driving the deposition process in the selected portion 22 includes driving a chemical reaction involving a precursor material. The precursor material will be provided as part of the composition environment established above the substrate W during irradiation. Driving the chemical reaction can cause the chemical reaction to continue at a faster rate than in the absence of irradiation. Alternatively, the chemical reaction can be a chemical reaction that does not occur at all in the absence of irradiation. In an embodiment, the chemical reaction is endothermic and the irradiation provides the energy necessary to allow the chemical reaction to continue. In some embodiments, the chemical reaction is at least partially driven by heat generated in the substrate W by irradiation. Therefore, the chemical reaction driven by irradiation can include a chemical reaction that requires an elevated temperature to continue or continues more rapidly at an elevated temperature. In some embodiments, the chemical reaction includes a photochemical reaction driven by irradiation. Therefore, at least one substance involved in the chemical reaction directly absorbs photons from the irradiation, and the absorption of photons allows the chemical reaction to continue. In some embodiments, the photochemical reaction includes a multiphoton photochemical reaction, which involves the absorption of two or more photons by each substance in at least one substance involved in the photochemical reaction. Compared to what would exist for a single-photon photochemical reaction, the requirement to absorb two or more photons makes the chemical reaction much more sensitive to changes in the intensity of the irradiation (i.e., the rate of the chemical reaction varies more strongly with changes in intensity). The increased sensitivity to intensity provides improved lateral contrast. In an embodiment, a combination of photochemical reaction and radiation-induced heating is used to provide a well-defined process window in which the chemical reaction is locally driven to produce a pattern. In an embodiment, the chemical reaction is driven by a plasma generated by the interaction between the radiation and the substrate W, a layer formed on the substrate W, and / or a gas present above the substrate. In an embodiment, the plasma generated is generated in a localized region defined by the irradiation. In an embodiment, the chemical reaction is driven by electrons provided by the irradiation. The electrons may include photoelectrons or secondary electrons (electrons generated by inelastic scattering events of photoelectrons or electrons from an electron beam). In an embodiment, the photons absorbed by the substrate W may provide high-energy electrons (e.g., secondary electrons, as described below) that participate in the deposition process near the surface of the substrate W. In an embodiment using a combination of electromagnetic radiation and an electron beam, a portion of the deposition process may be driven by electrons from an electron beam.

[0064] In some embodiments, the flow dynamics of gaseous / liquid co-reactants and / or catalysts and / or precursors are controlled during the deposition process. Control of the flow dynamics can improve the quality of the deposited material. Control of the flow dynamics can include controlling the direction of the flow (or the vector flow field of the flow). Alternatively or additionally, control of the flow dynamics can include controlling the rate of the flow, including, for example, providing a pulsed flow. In an embodiment, control of the flow dynamics is performed so as to locally generate high density related particles near the deposition site in space and / or time and generate low density particles near other surfaces (e.g., optical devices).

[0065] In some embodiments, the composition environment is controlled to provide different gas mixtures at different times. Different gas mixtures can be provided to deposit different materials or switch between a mode of depositing a material and a mode of etching away a material. Different gas mixtures can also be used to controllably vary the deposition rate over time, which can be used, for example, to produce features with well-defined edges and / or shapes.

[0066] In some embodiments, a bias voltage is applied to the substrate W during irradiation. Figure 5 As schematically depicted in , a bias voltage can be applied using a bias voltage unit 40. The bias voltage unit 40 may include a voltage source that can be configured to provide a desired bias voltage waveform. In the arrangement shown, the substrate W is attached to the substrate table WT via an electrostatic chuck 42. The bias voltage unit 40 can apply a bias voltage indirectly by applying a voltage to the substrate table WT and / or the electrostatic chuck 42, or can apply the bias voltage directly to the substrate W (for example, applying a bias voltage from the side of the substrate W opposite to the selected portion 22 of the surface of the irradiated substrate W). The bias voltage can be applied by a matching box or a blocking capacitor network 41. As explained below, the bias voltage can increase the degree of contribution of the secondary electrons generated by the irradiation to driving the deposition process in the selected portion 22, thereby increasing the rate of the deposition process and improving the yield. The bias voltage can achieve this situation by increasing the proportion of secondary electrons reaching the surface of the substrate W with suitable energy and / or trajectory.

[0067] Figure 6 and Figure 7 The average trajectory of secondary electrons from the focusing region 48 towards the surface of the substrate W is schematically depicted (dashed arrows). Figure 6 Indicates the case where no bias voltage is applied. Figure 7Represents the case where a bias voltage is applied. In each case, secondary electrons can be generated by irradiated photons that interact with the substrate material to produce primary electrons with relatively high energy. The primary electrons then further interact with the substrate material to produce secondary electrons with lower energy. A portion of the secondary electrons generated in the substrate W will arrive at the surface with an energy and trajectory suitable for escaping from the surface and promoting or facilitating the driving of the deposition process at the surface of the substrate W. The secondary electrons can drive the deposition, for example, by causing the dissociation of precursor molecules at the surface. The dissociation of the precursor molecules can drive a chemical reaction that causes the desired material to be deposited on the surface.

[0068] exist Figure 6 In the case represented in , without an applied bias voltage, a portion of the irradiated secondary electrons originating from the focal region 48 reach the surface of the substrate W, but the secondary electrons are relatively spread out. A relatively large proportion of the secondary electrons also reach the surface with relatively shallow trajectories (e.g., trajectories that are closer to being parallel to the surface of the substrate than being perpendicular to the surface of the substrate). Secondary electrons that reach the surface with energies below the work function will be reflected and will not contribute to the deposition of initiating material on the surface. Secondary electrons that reach the surface with energies above the work function but with shallow trajectories will also be reflected if the energy associated with the propagation component perpendicular to the surface is less than the work function.

[0069] exist Figure 7 In the case represented in FIG. 1 , with the bias voltage applied, the bias voltage causes an electric field to be established between the focusing region 48 and the surface. The maximum magnitude of the electric field will depend on the amplitude of the bias voltage waveform. Electric fields in the range of several GV / m can be achieved in the substrate W and will be sufficient to modify the trajectory of the secondary electrons sufficiently strongly to have a useful effect. For example, it has been found that SiO deposited by ALD techniques 2 A thin substrate can withstand an electric field of several GV / m without breakdown. The electric field changes the trajectory of the secondary electrons so that the secondary electrons are irradiated onto the surface at a steeper angle and in a more restricted area. This results in a larger proportion of secondary electrons being able to overcome the work function and promote the deposition of the induced material on the surface. In addition, the electric field focuses the secondary electrons into a more spatially restricted area on the surface, thereby increasing the intensity of the secondary electrons reaching the surface. The rate of radiation-induced deposition per unit area is thereby increased by the applied bias voltage. In addition, the bias voltage promotes improved spatial confinement of radiation-induced deposition, thereby improving the quality of the pattern formed on the substrate W by radiation-induced deposition.

[0070] In an embodiment, the bias voltage has an alternating polarity. The bias voltage thus repeatedly changes sign. The bias voltage can be defined by a periodic (regularly repeated) bias voltage waveform. The bias voltage drives the secondary electrons generated inside the substrate by irradiation periodically toward the surface in the selected portion 22. The use of a bias voltage with alternating polarity limits the charging of the substrate W during irradiation. Excessive charge accumulation on the substrate W is undesirable because it may cause deposition to be induced on an area wider than the desired area, for example, regardless of the pattern defined by the irradiation (for example, outside the selected portion 22).

[0071] In some embodiments, the bias voltage waveform is sinusoidal. Figure 8 and Fig. 9 An example curve 46 is schematically depicted showing the variation in voltage at the surface of a substrate W with respect to time during application of a sinusoidal bias voltage waveform. Figure 8 Depicted is the transient period immediately after the bias voltage waveform is first applied. Fig. 9 Describes the steady-state operating condition that is reached after a short time. Figure 8 As shown, the voltage at the surface may drift during the transient phase because the surface becomes negatively charged due to the greater mobility of relatively light negatively charged electrons in the plasma generated by irradiation out of the substrate compared to the heavier positively charged ions in the plasma. In the presence of a well-tuned matching box or blocking capacitor network 41, the voltage drifts until the waveform is such that no net charging of the surface occurs when considered over the entire cycle (period) of the applied bias voltage waveform. The DC shift observed in steady state can be referred to as the DC bias voltage.

[0072] The energy of ions impinging on the substrate W from the plasma above the substrate W will depend on how the electric field varies in the sheath space adjacent to the substrate W during the applied bias voltage. This electric field depends on the voltage difference between the bulk of the plasma and the voltage at the surface of the substrate W. Compared to the voltage in the sheath space closer to the substrate W, the voltage in the bulk of the plasma varies relatively very little over time. Fig. 9 The curve 47 in Schematically depicts how the voltage in the bulk of the plasma is expected to vary with time. Compared to the voltage in the substrate W, the voltage in the bulk of the plasma varies with a much smaller amplitude.

[0073] The bias voltage applied to the substrate W generates an electric field both within the substrate W and in the sheath space adjacent to the substrate W. The electric field will have the same polarity in both regions and will thus drive the electrons in both regions to move in the same sense. Thus, when the electrons in the plasma are driven toward the substrate W, the secondary electrons inside the substrate W will be driven away from the surface of the substrate in the selected portion (i.e., in the Figure 5 When the positive ions in the plasma are driven toward the substrate W, the secondary electrons in the substrate W will be driven toward the surface of the substrate W in the selected portion 22. Therefore, the energy distribution of the secondary electrons driven to the surface in the selected portion 22 by the applied bias voltage is similar in form to the energy distribution of the ions driven toward the surface by the applied bias voltage.

[0074] When a sinusoidal bias voltage is applied, the electric field varies with time in a manner that results in a relatively broad and bimodal spread of the energy distribution of the secondary electrons reaching the surface. This situation is schematically depicted in Fig.10 , which shows the energy distribution N(E) as a function of the secondary electron energy (E) with an applied sinusoidal bias voltage. Curve 41 is relatively broad (spread over a relatively large energy range) and bimodal (having two distinct local minima). The energy distribution of the secondary electrons can be shifted along the energy axis by varying the amplitude of the bias voltage waveform.

[0075] In some embodiments, a non-sinusoidal bias voltage waveform is applied. Applying a non-sinusoidal bias voltage provides flexibility to achieve an energy distribution of secondary electrons that is more conducive to inducing desired deposition in a selected portion 22 on the surface of the substrate W. For example, the bias voltage waveform can be adapted so that a larger proportion of secondary electrons reaching the surface of the substrate W in the selected portion 22 have energies within a range that promotes one or more favorable mechanisms of interaction with the precursor material. This can be facilitated by selecting a bias voltage waveform to provide an energy distribution having a single maximum value (rather than multiple local maxima) for the secondary electrons reaching the surface. This energy distribution can be referred to as a unimodal distribution.

[0076] Favorable interaction mechanisms may include favorable types of bond dissociation. Fig.11is a graph showing a typical secondary electron energy distribution at the surface without applying a bias voltage. The range of energies is relatively wide, with peaks in the range of 3 eV to 5 eV. Dashed rectangles 51 to 53 are superimposed on the graph, which show the approximate energy ranges that are favorable for three different types of bond dissociation. Rectangle 51 depicts an energy range that is favorable for dissociative electron stripping (DEA). Rectangle 52 depicts an energy range that is favorable for neutral dissociation (ND). Rectangle 53 depicts an energy range that is favorable for dissociative ionization (DI). Applying a sinusoidal bias voltage waveform can provide a range of secondary electrons at higher energies than when no bias voltage is applied. For example, instead of a majority of secondary electrons arriving at the surface at energies less than 10 eV (in the DEA operating state), applying a bias voltage can allow a majority of secondary electrons arriving at the surface to arrive at the surface at energies above 10 eV, optionally above 20 eV, optionally above 30 eV, optionally above 40 eV, optionally in the range of 10 eV to 52 eV (in the ND and DI operating states) and / or at energies that are more favorable to neutral dissociation (ND) and / or dissociative ionization (DI) of the precursor material than to dissociative electron stripping (DEA). This can provide an improvement over the unbiased case by promoting the ND and DI mechanisms relative to the DEA mechanism, which can be advantageous for a range of different deposition processes. However, as described above with reference to Fig.10 As discussed, the energy distribution achieved by a sinusoidal bias voltage may still be relatively spread out, such that a significant proportion of secondary electrons may arrive at the surface with energies that are too low to be conducive to the desired bond dissociation mechanisms (e.g., ND and DI). Adapting a non-sinusoidal bias voltage waveform to provide a narrower spread in the energy distribution of the secondary electrons can allow a larger proportion of the secondary electrons to contribute to the deposition process in the most efficient manner. Therefore, using a non-sinusoidal bias voltage waveform can improve production throughput.

[0077] In an embodiment, the non-sinusoidal bias voltage waveform is periodic. Fig.12 An example of such a bias voltage waveform is shown in . Fig.12 The curve in the figure represents the Fig. 9 The variation of the applied voltage in the steady state is described. In the steady state, no significant net charging of the substrate W occurs within the 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 sum of the durations of the positive bias portion 66 and the negative bias portion 67 may be equal to the period 65 of the bias voltage waveform.

[0078] The voltage applied during the negative bias portion 67 causes the secondary electrons in the substrate W to be directed toward the surface of the substrate W in the selected portion 22 (i.e., during the negative bias portion). Figure 5Therefore, during the negative bias portion, the potential at the surface of the substrate W is higher than the potential within the volume of the substrate W. At the same time, positive ions of the plasma outside the substrate W can be attracted toward the substrate 22.

[0079] The voltage applied during the forward bias portion 66 causes secondary electrons in the substrate W to be driven away from the surface of the substrate W in the selected portion 22 during the forward bias portion 66. Therefore, during the forward bias portion, the potential at the surface of the substrate W is lower than the potential within the volume of the substrate W. At the same time, electrons of the plasma outside the substrate W may be attracted toward the target layer 22.

[0080] The low mass of the electrons in the plasma means that the electrons will respond very quickly to changes in the direction of the electric field, and will essentially flow onto the substrate W only during the positive bias portion 66. In contrast, heavier ions will flow onto the substrate W due to inertial effects not only during the negative bias portion 67, but also during at least a portion of the positive bias portion 66. In some embodiments, the duration of the positive bias portion is selected (e.g., short enough) so that the ions continue to flow to the target layer due to inertial effects during the entire positive bias portion.

[0081] In some embodiments, Fig.12 As illustrated in FIG, 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 a quarter of the period 65 of the bias voltage waveform, preferably less than 1 / 5 of the period 65, preferably less than 1 / 6 of the period 65, preferably less than 1 / 8 of the period 65, preferably less than 1 / 10 of the period.

[0082] In some embodiments, the voltage of the bias voltage waveform is substantially constant during at least a majority of the forward bias portion 66 .

[0083] In some embodiments, the voltage of the bias voltage waveform varies during at least a majority of the negative bias portion 67 so as to at least partially compensate for charging of the target layer 22 and / or substrate 24 caused by irradiation of ions during the negative bias portion. Charging may occur, for example, where the surface and / or layers below the surface are dielectrics. Arranging the bias voltage to compensate for charging reduces changes in the electric field in the interior volume of the substrate W adjacent to the surface in the selected portion 22, thereby promoting a reduction in the energy spread of the energy distribution of secondary electrons reaching the surface.

[0084] In some embodiments, Fig.12 As illustrated in FIG. 1 , the variation in voltage of the bias voltage waveform during the negative bias portion 67 is substantially linear during at least a majority of the negative bias portion 67 (e.g., Fig.12In some embodiments, the variation in voltage of the bias voltage waveform during the negative bias portion 67 maintains a substantially time-invariant electric field in the interior volume of the substrate W adjacent to the surface in the selected portion 22 during the negative bias portion 67.

[0085] The use of a non-sinusoidal bias voltage waveform facilitates providing an energy distribution of secondary electrons having a single maximum (single peak), as indicated by Fig.10 , or provide an energy distribution of secondary electrons with multiple local maxima that are close together in energy. The non-sinusoidal bias voltage waveform thereby facilitates providing an energy distribution of secondary electrons that has a high proportion in a range that is conducive to optimal dissociation mechanisms (e.g., the ND and DI mechanisms discussed above). For example, the bias voltage waveform can be selected so as to provide a single maximum value above 10 eV, optionally above 20 eV, optionally above 30 eV, optionally above 40 eV, optionally in the range of 10 eV to 52 eV.

[0086] As explained above in the context of a sinusoidal bias voltage waveform, the energy distribution of the ions can be shifted along the energy axis by varying the amplitude of the bias voltage waveform. This is illustrated in Fig.13 In. Fig.13 , three different bias voltage waveforms with three different amplitudes and the same frequency are shown. Fig.14 The corresponding distribution of secondary electron energy is shown. Curve 81 (dashed line) shows the Fig.13 Curve 82 (solid line) shows the energy distribution caused by applying the bias voltage waveform with the lowest amplitude. Fig.13 Curve 83 (dashed line) shows the energy distribution caused by applying a bias voltage waveform with an intermediate amplitude. Fig.13 The energy distribution caused by the bias voltage waveform with the highest amplitude in the curves 81 to 83 is Fig.10 An exemplary single peak curve of the same type as curve 42 shown in FIG. Fig.13 The corresponding non-sinusoidal waveform shown in FIG. 1 realizes a single peak form. Compared with the above reference Figure 8 and Fig.10 For the discussed sinusoidal case, the spread of visible energy neither increases significantly in width nor becomes double-peaked as the amplitude increases. Thus, the non-sinusoidal bias voltage waveform allows for flexible control of the energy distribution of the secondary electrons without the distribution becoming spread out or double-peaked. Thus, the energy of the secondary electrons can be flexibly tuned to be within a small range of optimal energies for initiating the particular deposition process being used.

[0087] In some embodiments, the bias voltage applied by the bias voltage unit 40 includes a radio frequency waveform. In some embodiments, the frequency of the bias voltage waveform is less than 1 MHz.

[0088] The inventors have performed simulations to calculate the magnitude of throughput improvement that may be achieved by applying a bias voltage. The maximum improvement may vary in theory depending on the material deposited and the composition of the substrate. However, improvements in the range of 50 to 300 have been found to be typical. For example, for a SiO2 substrate deposited using an adapted square wave bias voltage, the maximum improvement may vary depending on the material deposited and the composition of the substrate. 2 For deposition of W on Sn substrates and irradiation with EUV radiation, a throughput improvement of greater than 200 is expected. For deposition of W on Sn substrates using the same parameters, a throughput improvement of greater than about 100 is expected. In both cases, application of the bias voltage allows sufficiently high throughput to be achieved using currently available EUV lithography equipment and currently achievable EUV doses to make the method practical.

[0089] Embodiments of the present disclosure are explained in the following numbered aspects.

[0090] 1. An apparatus for forming a patterned material layer on a substrate, comprising:

[0091] a projection system configured to irradiate selected portions of a surface of a substrate during a deposition process;

[0092] an environmental control system configured to contain the substrate in a controlled gaseous environment during irradiation of the selected portions, the controlled gaseous environment supporting the deposition process; and

[0093] A bias voltage unit is configured to apply a bias voltage having an alternating polarity to the substrate during irradiation to periodically drive secondary electrons generated inside the substrate by the irradiation toward the surface in the selected portion.

[0094] 2. The apparatus of clause 1, wherein the bias voltage has a non-sinusoidal bias voltage waveform.

[0095] 3. The apparatus of clause 2, wherein the bias voltage waveform is periodic.

[0096] 4. The apparatus of clause 3, wherein each cycle comprises:

[0097] a negative bias portion during which secondary electrons in the substrate are driven toward the surface in the selected portion; and

[0098] A forward bias portion during which secondary electrons in the substrate are driven away from the surface in the selected portion.

[0099] 5. An apparatus according to aspect 4, wherein the bias voltage unit is configured so that the voltage of the bias voltage waveform varies during at least most of the negative bias portion in a manner that at least partially compensates for charging of the substrate caused by ions irradiating from the plasma onto the substrate during the negative bias portion.

[0100] 6. The apparatus of clause 5, wherein the bias voltage unit is configured such that a variation in voltage of the bias voltage waveform during the negative bias portion is substantially linear during at least a majority of the negative bias portion.

[0101] 7. An apparatus according to aspect 5 or 6, wherein the bias voltage unit is configured so that a change in the voltage of the bias voltage waveform during the negative bias portion maintains a substantially time-invariant electric field in an internal volume of the substrate adjacent to the surface in the selected portion during the negative bias portion.

[0102] 8. A device according to any one of clauses 4 to 7, wherein the duration of the positive bias portion is less than 1 / 4 of the period of the bias voltage waveform.

[0103] 9. An apparatus according to any one of clauses 4 to 8, wherein the voltage of the bias voltage waveform is substantially constant during at least most of the forward bias portion.

[0104] 10. An apparatus according to any preceding numbered aspect, wherein the bias voltage unit is configured such that the bias voltage has a bias voltage waveform selected to provide an energy distribution having a single maximum value for secondary electrons arriving at the surface in the selected portion.

[0105] 11. An apparatus according to any of the aforementioned numbered aspects, wherein the bias voltage unit is configured so that the bias voltage has a bias voltage waveform selected to provide an energy distribution of secondary electrons reaching the surface in the selected portion, in which energy distribution, a majority of the secondary electrons have an energy higher than 10 eV and / or have an energy that is more conducive to neutral dissociation and / or dissociative ionization of the precursor material than dissociative electron stripping.

[0106] 12. Apparatus according to any preceding numbered aspect, wherein the projection system is configured to irradiate the selected portion with electromagnetic radiation having a wavelength of less than 100 nm.

[0107] 13. The apparatus of any preceding numbered aspect, wherein the projection system and environmental control system are configured such that the irradiating generates a plasma external to the substrate.

[0108] 14. An apparatus according to any of the preceding numbered aspects, wherein the projection system and the environmental control system are configured so that the irradiation drives the deposition process locally in the selected portion and thereby forms a patterned material layer in a pattern defined by the selected portion, the patterned layer optionally comprising a two-dimensional material.

[0109] 15. A method for forming a patterned material layer on a substrate, comprising:

[0110] irradiating selected portions of the surface of the substrate during a deposition process, said irradiation driving the deposition process locally in said selected portions and thereby forming a patterned layer of material in a pattern defined by said selected portions; and

[0111] A bias voltage having an alternating polarity is applied to the substrate during the irradiation to periodically drive secondary electrons generated inside the substrate by the irradiation toward the surface in the selected portion.

[0112] 16. The method of clause 15, wherein the bias voltage has a non-sinusoidal bias voltage waveform.

[0113] 17. The method of clause 16, wherein the bias voltage waveform is periodic.

[0114] 18. The method of clause 17, wherein each cycle comprises:

[0115] a negative bias portion during which secondary electrons in the substrate are driven toward the surface in the selected portion; and

[0116] A forward bias portion during which secondary electrons in the substrate are driven away from the surface in the selected portion.

[0117] 19. The method of clause 18, wherein the voltage of the bias voltage waveform varies during at least a majority of the negative bias portion in a manner to at least partially compensate for charging of the substrate caused by ions impinging from the plasma onto the substrate during the negative bias portion.

[0118] 20. The method of clause 19, wherein a variation in voltage of the bias voltage waveform during the negative bias portion is substantially linear during at least a majority of the negative bias portion.

[0119] 21. A method according to aspects 19 or 20, wherein the variation in the voltage of the bias voltage waveform during the negative bias portion maintains a substantially time-invariant electric field in an internal volume of the substrate adjacent to the surface in the selected portion during the negative bias portion.

[0120] 22. A method according to any one of aspects 18 to 21, wherein the duration of the positive bias portion is less than 1 / 4 of the period of the bias voltage waveform.

[0121] 23. A method according to any one of aspects 18 to 22, wherein the voltage of the bias voltage waveform is substantially constant during at least most of the forward bias portion.

[0122] 24. A method according to any one of aspects 15 to 23, wherein the bias voltage has a bias voltage waveform selected to provide an energy distribution having a single maximum for secondary electrons reaching the surface in the selected portion.

[0123] 25. A method according to any one of aspects 15 to 24, wherein the bias voltage has a bias voltage waveform selected to provide an energy distribution of secondary electrons reaching the surface in the selected portion, in which energy distribution, a majority of the secondary electrons have energies higher than 10 eV and / or have energies that are more conducive to neutral dissociation and / or dissociative ionization of the precursor material than dissociative electron stripping.

[0124] 26. The method of any one of aspects 15 to 25, wherein the irradiating comprises irradiating with electromagnetic radiation having a wavelength less than 100 nm.

[0125] 27. The method of any one of aspects 15 to 26, wherein the irradiating generates a plasma external to the substrate.

[0126] 28. The method of any one of aspects 15 to 27, wherein the patterned layer comprises a two-dimensional material.

Claims

1. An apparatus for forming a patterned material layer on a substrate, comprising: a projection system configured to irradiate selected portions of a surface of a substrate during a deposition process; an environmental control system configured to contain said substrate in a controlled gaseous environment during said irradiating of selected portions, said controlled gaseous environment supporting said deposition process; as well as A bias voltage unit is configured to apply a bias voltage having an alternating polarity to the substrate during the irradiation to periodically drive secondary electrons generated inside the substrate by the irradiation toward the surface in the selected portion.

2. The device according to claim 1, wherein The bias voltage has a non-sinusoidal bias voltage waveform.

3. The device according to claim 2, wherein: The bias voltage waveform is periodic.

4. The device according to claim 3, wherein: Each cycle includes: a negative bias portion during which secondary electrons in the substrate are driven toward the surface in the selected portion; and A forward bias portion during which secondary electrons in the substrate are driven away from the surface in the selected portion.

5. The device according to claim 4, wherein: The bias voltage unit is configured such that a voltage of the bias voltage waveform varies during at least most of the negative bias portion in a manner to at least partially compensate for charging of the substrate caused by ions irradiated from a plasma onto the substrate during the negative bias portion.

6. The device according to claim 5, wherein: The bias voltage unit is configured such that a variation in the voltage of the bias voltage waveform during the negative bias portion is substantially linear during at least a majority of the negative bias portion.

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

8. The device according to any one of claims 4 to 7, wherein: The duration of the positive bias portion is less than 1 / 4 of the period of the bias voltage waveform.

9. The device according to any one of claims 4 to 8, wherein: The voltage of the bias voltage waveform is substantially constant during at least a majority of the forward bias portion.

10. Apparatus according to any preceding claim, wherein: The bias voltage unit is configured so that the bias voltage has a bias voltage waveform selected to provide an energy distribution having a single maximum value of secondary electrons reaching the surface in the selected portion.

11. Apparatus according to any preceding claim, wherein: The bias voltage unit is configured so that the bias voltage has a bias voltage waveform selected to provide an energy distribution of secondary electrons reaching the surface in the selected portion, in which energy distribution a majority of the secondary electrons have energies higher than 10 eV and / or have energies that are more conducive to neutral dissociation and / or dissociative ionization of the precursor material than dissociative electron stripping.

12. Apparatus according to any preceding claim, wherein: The projection system is configured to irradiate the selected portion with electromagnetic radiation having a wavelength 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 irradiating generates a plasma external to the substrate.

14. Apparatus according to any preceding claim, wherein: The projection system and the environmental control system are configured such that the irradiation drives the deposition process locally in the selected portion and thereby forms a patterned layer of material in a pattern defined by the selected portion, the patterned layer optionally comprising a two-dimensional material.

15. A method for forming a patterned material layer on a substrate, comprising: irradiating selected portions of the surface of the substrate during a deposition process, said irradiation driving said deposition process locally in said selected portions and thereby forming a patterned layer of material in a pattern defined by said selected portions; and A bias voltage having an alternating polarity is applied to the substrate during the irradiation to periodically drive secondary electrons generated inside the substrate by the irradiation toward the surface in the selected portion.

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