Patent Application
20210223696
This application claims priority of EP application 16190865.2 which was filed on Sep. 27, 2017 and which is incorporated herein in its entirety by reference.
The present invention relates to a substrate, a substrate holder, a substrate coating apparatus, a method for coating the substrate and a method for removing the coating.
A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. comprising part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
It is desirable that when a substrate is first loaded onto a substrate holder in preparation for exposure it is held freely so that any stresses can be released. During the loading process, the substrate is supported by so-called e-pins which hold it at three positions. Therefore, the weight of the substrate causes it to distort and it is desirable that this distortion be released before exposures. On the other hand, it is desirable that the substrate be held very firmly during exposure. There are two reasons for this. Firstly, the substrate is subjected to very large accelerations during an exposure sequence in order to achieve a high throughput and must not move on the substrate holder. Secondly, the substrate absorbs energy from the projection beam during exposure and therefore heats up locally. Such local heating can cause thermal expansion causing slip between substrate and burls leading to overlay errors. By holding the substrate firmly to the substrate holder such distortion can be resisted.
A substrate holder conventionally has a plurality of burls to support the substrate. The total area of the burls that contacts the substrate is small compared to the total area of a substrate.
The substrate is conventionally clamped to the substrate holder during exposures. Two clamping techniques are commonly used. In vacuum-clamping a pressure differential across the substrate is established, e.g., by connecting the space between the substrate holder and the substrate to an under-pressure that is lower than a higher pressure above the substrate. The pressure difference gives rise to a force holding the substrate to the substrate holder. In electrostatic clamping, electrostatic forces are used to exert a force between the substrate and the substrate holder. Several different arrangements are known to achieve this. In one arrangement a first electrode is provided on the lower surface of the substrate and a second electrode on the upper surface (also referred to as the clamp surface) of the substrate holder. A potential difference is established between the first and second electrodes. In another arrangement two semi-circular electrodes are provided on the substrate holder and a conductive layer is provided on the substrate. A potential difference is applied between the two semi-circular electrodes so that the two semi-circular electrodes and the conductive layer on the substrate act like two capacitors in series.
It is commonly observed that clamping of a flat or non-flat (curved) substrate results in substrate deformation. This is caused by friction forces, occurring between the substrate and the substrate holder, preventing a stress-free flattening of the substrate when it is placed on the clamp surface of the substrate holder. These forces are directed within the plane of the substrate and result in significant compressive and/or tensile stress components. By elastic deformation these stress components cause translation of product features or markers on the substrate which result in significantly worse alignment and/or overlay performance of the lithographic apparatus. The friction forces need however to be sufficiently large to keep the substrate firmly attached to the substrate holder during the lithographic process. This dual character of the friction forces poses a problem when aiming for lithographic processing of substrates that need to remain free of stress components and positioned stably with respect to the substrate holder.
The problem can be solved by controlling the friction forces between the substrate and the substrate holder; a low friction force must be present during loading of the substrate to the substrate holder and a higher friction force must be present when the substrate is clamped to the substrate holder while being subject to a lithographic process.
According to an embodiment, there is provided a substrate for a lithographic process, the substrate comprising a backside configured to be clamped to a substrate holder of an apparatus, the backside is at least partially provided with a monomolecular layer configured to reduce a friction coefficient of the backside.
According to another embodiment, there is provided a substrate holder for a lithographic apparatus, the substrate holder comprising a clamp surface configured to clamp a substrate, the clamp surface is at least partially provided with a monomolecular layer configured to reduce a friction coefficient of the clamp surface.
According to another embodiment, there is provided a substrate coating apparatus, the substrate coating apparatus comprising a vapor supply system providing a vapor adjacent to the backside of the substrate, the vapor creating a monomolecular layer on at least a part of the backside of the substrate.
According to another embodiment, there is provided a method for creating a monomolecular layer on a substrate, the method comprising bringing a vapor adjacent to the substrate.
An effect of applying the monomolecular layer to the backside of the substrate is that the friction forces between the substrate backside and the substrate holder become small when the substrate is loaded on the substrate holder; i.e., when the substrate does not experience full clamping force. This allows a stress-free relaxation of the substrate. After loading the substrate on the substrate holder full clamping force is exerted in order to fix the substrate with respect to the substrate holder.
The clamping force causes local removal of the monomolecular layer, resulting in a direct contact between the substrate backside and the clamp surface of the substrate holder. This direct contact results in a strong increase of the friction force between the substrate and the substrate holder. The increased friction force is beneficial for positional stability of the substrate with respect to the substrate holder during lithographic processing.
According to another embodiment, there is provided a method for removing a monomolecular layer from a substrate, the method comprising a step of exposing the substrate to a light source.
According to another embodiment, there is provided a lithographic apparatus comprising a substrate, the substrate comprising a backside configured to be clamped to a substrate holder of the lithographic apparatus, the backside is at least partially provided with a monomolecular layer configured to reduce a friction coefficient of the backside.
According to another embodiment, there is provided a metrology apparatus comprising a substrate, the substrate comprising a backside configured to be clamped to a substrate holder of the metrology apparatus, the backside is at least partially provided with a monomolecular layer configured to reduce a friction coefficient of the backside.
According to another embodiment, there is provided a lithographic apparatus comprising a substrate holder, the substrate holder comprising a clamp surface configured to clamp a substrate, the clamp surface is at least partially provided with a monomolecular layer configured to reduce a friction coefficient of the clamp surface.
According to another embodiment, there is provided a metrology apparatus comprising a substrate holder, the substrate holder comprising a clamp surface configured to clamp a substrate, the clamp surface is at least partially provided with a monomolecular layer configured to reduce a friction coefficient of the clamp surface.
According to another embodiment, there is provided a lithographic apparatus comprising a substrate coating apparatus, the substrate coating apparatus comprising a vapor supply system providing a vapor adjacent to the backside of the substrate, the vapor creating a monomolecular layer on at least a part of the backside of the substrate.
According to another embodiment, there is provided a metrology apparatus comprising a substrate coating apparatus, the substrate coating apparatus comprising a vapor supply system providing a vapor adjacent the backside of the substrate, the vapor creating a monomolecular layer on at least a part of the backside of the substrate.
According to another embodiment, there is provided a spin coating apparatus comprising a substrate coating apparatus, the substrate coating apparatus comprising a vapor supply system providing a vapor adjacent to the backside of the substrate, the vapor creating a monomolecular layer on at least a part of the backside of the substrate.
Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:
an illumination system (illuminator) IL configured to condition a radiation beam B (e.g. UV radiation or DUV radiation);
a support structure (e.g. a mask table) MT constructed 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 in accordance with certain parameters;
a support table, e.g. a sensor table to support one or more sensors or a substrate support apparatus 60 constructed to hold a substrate (e.g. a resist-coated production substrate) W, connected to a second positioner PW configured to accurately position the surface of the table, for example of a substrate W, in accordance with 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 patterning device MA onto a target portion C (e.g. comprising part of, one, or more dies) of the substrate W.
The illumination system IL may include various types of optical components, such as refractive, reflective, magnetic, electromagnetic, electrostatic or other types of optical components, or any combination thereof, for directing, shaping, or controlling radiation.
The support structure MT holds the patterning device MA. It holds the patterning device MA in a manner that depends on the orientation of the patterning device MA, the design of the lithographic apparatus, and other conditions, such as for example whether or not the patterning device MA is held in a vacuum environment. The support structure MT can use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device MA. The support structure MT may be a frame or a table, for example, which may be fixed or movable as required. The support structure MT may ensure that the patterning device MA is at a desired position, for example with respect to the projection system PS. Any use of the terms “reticle” or “mask” herein may be considered synonymous with the more general term “patterning device.”
The term “patterning device” used herein should be broadly interpreted as referring to any device that can be used to impart a radiation beam with a pattern in its cross-section such as to create a pattern in a target portion of the substrate. It should be noted that the pattern imparted to the radiation beam may not exactly correspond to the desired pattern in the target portion of the substrate, for example if the pattern includes phase-shifting features or so called assist features. Generally, the pattern imparted to the radiation beam will correspond to a particular functional layer in a device being created in the target portion, such as an integrated circuit.
The patterning device MA may be transmissive or reflective. Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography, and include mask types such as binary, alternating phase-shift, and attenuated phase-shift, as well as various hybrid mask types. An example of a programmable mirror array employs a matrix arrangement of small mirrors, each of which can be individually tilted so as to reflect an incoming radiation beam in different directions. The tilted mirrors impart a pattern in a radiation beam which is reflected by the mirror matrix.
The term “projection system” used herein should be broadly interpreted as encompassing any type of projection system, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof, as appropriate for the exposure radiation being used, or for other factors such as the use of an immersion liquid or the use of a vacuum. Any use of the term “projection lens” herein may be considered as synonymous with the more general term “projection system”.
As here depicted, the lithographic apparatus is of a transmissive type (e.g. employing a transmissive mask). Alternatively, the lithographic apparatus may be of a reflective type (e.g. employing a programmable mirror array of a type as referred to above, or employing a reflective mask).
The lithographic apparatus may be of a type having two or more tables (or stage(s) or support(s)), e.g., two or more substrate tables or a combination of one or more substrate tables and one or more sensor or measurement tables. In such “multiple stage” machines the multiple tables may be used in parallel, or preparatory steps may be carried out on one or more tables while one or more other tables are being used for exposure. The lithographic apparatus may have two or more patterning device tables (or stage(s) or support(s)) which may be used in parallel in a similar manner to substrate, sensor and measurement tables. The lithographic apparatus may be of a type that has a measurement station, at which there are various sensors for characterizing a production substrate prior to exposure and an exposure station, at which the exposures are commanded out.
The lithographic apparatus is of a type wherein at least a portion of the substrate W may be covered by a immersion liquid 10 having a relatively high refractive index, e.g. water such as ultra pure water (UPW), so as to fill an immersion space 11 between the projection system PS and the substrate W. An immersion liquid 10 may also be applied to other spaces in the lithography apparatus, for example, between the patterning device MA and the projection system PS Immersion techniques can be used to increase the numerical aperture of projection systems. The term “immersion” as used herein does not mean that a structure, such as a substrate W, must be submerged in immersion liquid 10; rather “immersion” only means that an immersion liquid 10 is located between the projection system PS and the substrate W during exposure. The path of the patterned radiation beam B from the projection system PS to the substrate W is entirely through immersion liquid 10.
Referring to
The illuminator IL may comprise an adjuster AD for adjusting the angular intensity distribution of the radiation beam B. Generally, at least the outer and/or inner radial extent (commonly referred to as σ-outer and σ-inner, respectively) of the intensity distribution in a pupil plane of the illuminator IL can be adjusted. In addition, the illuminator IL may comprise various other components, such as an integrator IN and a condenser CO. The illuminator IL may be used to condition the radiation beam B to have a desired uniformity and intensity distribution in its cross-section. Similar to the source SO, the illuminator IL may or may not be considered to form part of the lithographic apparatus. For example, the illuminator IL may be an integral part of the lithographic apparatus or may be a separate entity from the lithographic apparatus. In the latter case, the lithographic apparatus may be configured to allow the illuminator IL to be mounted thereon. Optionally, the illuminator IL is detachable and may be separately provided (for example, by the lithographic apparatus manufacturer or another supplier).
The radiation beam B is incident on the patterning device (e.g., mask) MA, which is held on the support structure (e.g., mask table) MT, and is patterned by the patterning device MA. Having traversed the patterning device MA, the radiation beam B passes through the projection system PS, which focuses the beam onto a target portion C of the substrate W. With the aid of the second positioner PW and position sensor IF (e.g. an interferometric device, linear encoder or capacitive sensor), the substrate support apparatus 60 can be moved accurately, e.g. so as to position different target portions C in the path of the radiation beam B.
Similarly, the first positioner PM and another position sensor (which is not explicitly depicted in
In the case of a stepper (as opposed to a scanner) the support structure MT may be connected to a short-stroke actuator only, or may be fixed. Patterning device MA and substrate W may be aligned using patterning device 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 target portions C (these are known as scribe-lane alignment marks). Similarly, in situations in which more than one die is provided on the patterning device MA, the patterning device alignment marks M1, M2 may be located between the dies.
The depicted apparatus could be used in at least one of the following modes:
1. In step mode, the support structure MT and the substrate support apparatus 60 are kept essentially stationary, while an entire pattern imparted to the radiation beam B is projected onto a target portion C at one time (i.e. a single static exposure). The substrate support apparatus 60 is then shifted in the X and/or Y direction so that a different target portion C can be exposed. In step mode, the maximum size of the exposure field limits the size of the target portion C imaged in a single static exposure.
2. In scan mode, the support structure MT and the substrate support apparatus 60 are scanned synchronously while a pattern imparted to the radiation beam B is projected onto a target portion C (i.e. a single dynamic exposure). The velocity and direction of the substrate support apparatus 60 relative to the support structure MT may be determined by the (de-)magnification and image reversal characteristics of the projection system PS. In scan mode, the maximum size of the exposure field limits the width (in the non-scanning direction) of the target portion C in a single dynamic exposure, whereas the length of the scanning motion (and size of the exposure field) determines the height (in the scanning direction) of the target portion C.
3. In another mode, the support structure MT is kept essentially stationary holding a programmable patterning device, and the substrate support apparatus 60 is moved or scanned while a pattern imparted to the radiation beam B is projected onto a target portion C. In this mode, generally a pulsed radiation source is employed and the programmable patterning device is updated as required after each movement of the substrate support apparatus 60 or in between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography that utilizes a programmable patterning device, such as a programmable mirror array of a type as referred to above.
Combinations and/or variations on the above described modes of use or entirely different modes of use may also be employed.
A controller 50 controls the overall operations of the lithographic apparatus and in particular performs an operation process described further below. Controller 50 can be embodied as a suitably-programmed general purpose computer comprising a central processing unit, volatile and non-volatile storage means, one or more input and output devices such as a keyboard and screen, one or more network connections and one or more interfaces to the various parts of the lithographic apparatus. It will be appreciated that a one-to-one relationship between controlling computer and lithographic apparatus is not necessary. One computer can control multiple lithographic apparatuses. Multiple networked computers can be used to control one lithographic apparatus. The controller 50 may also be configured to control one or more associated process devices and substrate handling devices in a lithocell or cluster of which the lithographic apparatus forms a part. The controller 50 can also be configured to be subordinate to a supervisory control system of a lithocell or cluster and/or an overall control system of a fab.
Arrangements for providing immersion liquid between a final optical element of the projection system PS and the substrate W can be classed into three general categories. These are the bath type arrangement, the so-called localized immersion systems and the all-wet immersion systems. An embodiment of the present invention relates particularly to the localized immersion systems.
In an arrangement which has been proposed for a localized immersion system a liquid confinement structure 12 extends along at least a part of a boundary of an immersion space 11 between the final optical element 90 of the projection system PS and the facing surface of the stage or table facing the projection system PS. The facing surface of the table is referred to as such because the table is moved during use and is rarely stationary. Generally, the facing surface of the table is a surface of a substrate W, substrate table WT which surrounds the substrate W or both.
The liquid confinement structure 12 at least partly contains immersion liquid 10 in the immersion space 11 between the final optical element of the projection system PS and the substrate W and/or substrate support apparatus 60. The immersion space 11 is at least partly formed by the liquid confinement structure 12 positioned below and surrounding the final optical element of the projection system PS.
To load a substrate onto the substrate support apparatus 60 for exposures, it is picked up by a substrate handler robot and lowered onto a set of e-pins which project through the substrate holder. The substrate holder is a part of the substrate support apparatus configured to fix the substrate during lithographic processing. The e-pins are actuated so that they can be extended and retracted and may be provided with suction openings at their tips to grip the substrate. They may be three e-pins spaced around the center of the substrate holder. Once the substrate has settled on the e-pins, the e-pins are retracted so that the substrate is supported by the substrate holder. While the substrate is being held by the e-pins, its own weight will cause it to distort, e.g. becoming convex when viewed from above. As the substrate is lowered onto the substrate holder it will contact in some places, e.g. near the edge, before other places, e.g. near the center, and friction between the substrate holder and the lower surface of the substrate may prevent the substrate fully relaxing into a flat unstressed state. Although the curvature of the substrate when supported on the e-pins is small—due to the rigidity of the substrate—and some relaxation does occur when the substrate is on the substrate holder, a residual curvature can nonetheless be sufficient to cause undesirable overlay errors. In addition to the residual curvature of the substrate caused by being held by the e-pins, the substrate may be curved due to processing. For example during manufacturing of 3D NAND structures the substrate will be subject to deposition of various layers. Those layers may be applied at high temperatures, implying that stress components will build up during a cooling down phase of the substrate (in general the substrate and the deposited layers will not have identical thermal expansion coefficients). These stress components may lead to a substantial curvature or deformation of the substrate. Well known deformation geometries resemble a bowl or an umbrella shape of the substrate. Also more complex deformation shapes may occur; for example a saddle shape.
Apart from low friction characteristics the monomolecular layer 102 may also (i) provide hydrophobic properties to the substrate backside known to be beneficial for water management. This is caused by the water repelling properties of the non-polar tails 302 of the molecules 300. In addition a conductive group 303 may be added to the molecules 300 to provide (ii) anti-static properties to the substrate 100. The presence of the monomolecular layer may further (iii) prevent adhesion of particles to the substrate backside. These three additional properties all reduce the likelihood of particles between the substrate backside 101 and the substrate holder surface 201, limiting issues due to contamination of the substrate holder. The hydrophobic property of the monomolecular layer is particularly useful when the substrate is processed in an immersion lithography tool. The water repellent substrate backside prevents the immersion liquid (water) to accumulate on the substrate holder surface.
Resuming it can be concluded that the monomolecular layer 102 on the substrate backside 101 both achieves having a low friction between the substrate and clamp surface during substrate relaxation while the presence of a clamping force during substrate processing causes displacement of the monomolecular layer resulting in a sufficiently large friction force between the substrate and the clamp surface to ensure positional stability of the substrate.
The disclosed implementations for a substrate 100 and a substrate holder 200 are especially relevant for lithographic apparatus where the allowable pattern position shifts during substrate loading are very small and where substrates are subject to high acceleration forces during process steps (exposure). However the inventions as disclosed herein are not limited to use within such apparatus, but also applicable to substrate holders within eg metrology apparatus (measuring characteristics of features on substrates), coating apparatus (spin coating of wafers) and other substrate processing apparatus (chemical mechanical polishing, etching, ion implant and the like).
Substrate Coating Apparatus
The apparatus 800 or 801 may be implemented as a separate tool, integrated within a semiconductor apparatus (lithographic apparatus, metrology apparatus) or integrated within a (spin) coating apparatus for semiconductor substrates (eg track). An advantage of integrating the tool 800/801 within another apparatus is that the process of providing the monomolecular layer may be executed in parallel with another process. An example is given in
In some cases removal of the monomolecular layer may be necessary. This may be the case when the substrate has to undergo a processing step which is affected by the presence of molecules of the monomolecular layer. Various methods of removing the monomolecular layer are proposed in this document.
Although specific reference may be made in this text to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, liquid-crystal displays (LCDs), thin film magnetic heads, etc. The skilled artisan will appreciate that, in the context of such alternative applications, any use of the terms “wafer” or “die” herein may be considered as synonymous with the more general terms “substrate” or “target portion”, respectively. The substrate referred to herein may be processed, before or after exposure, in for example a track (a tool that typically applies a layer of resist to a substrate and develops the exposed resist), a metrology tool and/or an inspection tool. Where applicable, the disclosure herein may be applied to such and other substrate processing tools. Further, the substrate may be processed more than once, for example in order to create a multi-layer IC, so that the term substrate used herein may also refer to a substrate that already contains one or multiple processed layers.
Further embodiments are disclosed in the list of numbered clauses below:
The terms “radiation” and “beam” used herein encompass all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g. having a wavelength of or about 436, 405, 365, 248, 193, 157 or 126 nm). The term “lens”, where the context allows, may refer to any one or combination of various types of optical components, including refractive and reflective optical components.
While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described.
Any controllers described herein may each or in combination be operable when the one or more computer programs are read by one or more computer processors located within at least one component of the lithographic apparatus. The controllers may each or in combination have any suitable configuration for receiving, processing, and sending signals. One or more processors are configured to communicate with the at least one of the controllers. For example, each controller may include one or more processors for executing the computer programs that include machine-readable instructions for the methods described above. The controllers may include data storage media for storing such computer programs, and/or hardware to receive such media. So the controller(s) may operate according the machine readable instructions of one or more computer programs.
The descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims set out below.
| Number | Date | Country | Kind |
|---|---|---|---|
| 16190865.2 | Sep 2016 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2017/071179 | 8/23/2017 | WO | 00 |
