Methods for designing alignment marks

Abstract

A method for configuring a mark, the mark comprising a groove etched into a substrate, the method comprising: a) obtaining a relationship between a range of height variations throughout a surface of a trial layer deposited on a trial groove having a trial depth and the thickness of the trial layer; b) determining the range of height variations throughout the surface of the layer deposited on the mark, allowing a measurement system to determine the position of the mark; and c) configuring the mark by determining the depth of the groove based on the relationship, the range of height variations, and the thickness of the process layer deposited on the mark.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to European application No. 19198332.9 filed on September 19, 2019 and European application No. 19204856.9 filed on October 23, 2019, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present invention relates to a lithographic apparatus and a method for manufacturing a device. Background Art

[0004] A lithographic apparatus is a machine that applies a desired pattern to a substrate (usually to a target portion of the substrate). A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that case, a pattern forming device (which may alternatively be referred to as a mask or reticle) can be used to produce a circuit pattern to be formed on a single layer of an IC. This pattern can be transferred to a target portion (e.g., a portion including a die, a die, or several dies) on a substrate (e.g., a silicon wafer). The transfer of the pattern is usually performed via imaging onto a layer of radiation-sensitive material (resist) disposed on the substrate. Typically, a single substrate will contain a network of adjacent target portions that are patterned in succession. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing the entire pattern to the target portion at once; and so-called scanners, in which each target portion is irradiated by scanning the substrate synchronously in a given direction (the "scanning" direction) while scanning the pattern through a radiation beam, parallel to or anti-parallel to such a scanning direction. It is also possible to transfer the pattern from the patterning device to a substrate by imprinting the pattern onto the substrate.

[0005] The manufacturing process of semiconductor structures or other structures on a substrate usually involves multiple lithography steps and other processing steps, whereby a pattern is applied on the substrate, followed by steps such as selective etching, layer growth, ion implantation, diffusion, etc. The multiple patterns will be aligned with each other so that alignment marks can be set on the substrate. The alignment marks can be formed by patterns such as grooves and can interact with the alignment beam of the alignment measurement system of the lithographic equipment.

[0006] When manufacturing, for example, high voltage or high power electronic devices, a relatively thick process layer may be applied on the substrate. Ion implantation may be applied in the process layer in order to provide a desired amount of charge carriers in the layer. Such a relatively thick process layer may be grown stepwise, whereby thinner layers are applied and ion implantation is performed, these process steps may be repeated until the desired thickness of the process layer is reached.

[0007] Alignment marks may be required on the process layer. However, due to the thickness of the process layer, alignment marks covered by the process layer may disappear. Therefore, additional process steps may be required between the repeated steps of growing the thinner layer and the ion implantation in order to be able to transfer the original marks to the top of the process layer thus obtained. Summary of the invention

[0008] It would be desirable to be able to reduce the number of process steps required to transfer alignment marks onto the top of a relatively thick layer on a substrate.

[0009] According to one aspect of the present invention, there is provided a method for designing an alignment mark on a substrate, the alignment mark comprising at least one groove etched into the substrate, the method comprising:

[0010] - Get the relationship between:

[0011] - the range of height variations across the surface of the trial layer deposited on the trial mark having the trial mark groove having the trial depth, and

[0012] - the thickness of the trial layer;

[0013] wherein the trial mark represents the alignment mark, and wherein the trial layer represents a process layer deposited on the alignment mark;

[0014] - determining a desired range of height variations across the surface of the trial layer deposited on the trial mark, the height variations within the desired range enabling determination of the position of the trial mark by a calibration system based on the height variations across the surface of the trial layer on the trial mark; and

[0015] - configuring the alignment mark by determining a desired depth of at least one trench of the alignment mark using the relationship, the desired range of height variation, and a predetermined thickness of the process layer deposited over the alignment mark.

[0016] According to another aspect of the present invention, an alignment mark designed according to the method of the present invention is provided.

[0017] According to yet another aspect of the present invention, there is provided a method for aligning a substrate during a photolithography process, the method comprising:

[0018] - providing a substrate comprising an alignment mark according to the invention, and - providing a process layer having a predetermined thickness on said substrate, and - performing an alignment measurement of the height variation of said process layer throughout said alignment mark. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which corresponding reference numerals indicate corresponding parts, and in which:

[0020] - Figure 1 depicts a lithographic apparatus in which embodiments of the present invention may be employed;

[0021] - Figure 2 depicts a flow chart illustrating a method of designing a mark according to an embodiment of the present invention; - Figure 3A and Figure 3B A trial mark, a trial mark with a trial layer are depicted respectively;

[0022] - Figure 4 describing the relationship between the depth of elevation variation across the surface of the trial layer and the thickness of the trial layer;

[0023] - Figure 5 depicts a graphical representation illustrating the use of the relationship, the desired range of height variation, and a predetermined thickness of a process layer deposited over the alignment mark to determine a desired depth of at least one trench of the alignment mark;

[0024] - 6A to 6F depicts a graph illustrating the measurement results of the alignment beam as a function of the bottom critical dimension of the alignment mark at different alignment beam wavelengths; and - Fig. 7A and Figure 7B An alignment mark and an alignment mark with a process layer are respectively depicted, which are designed according to the described method. DETAILED DESCRIPTION

[0025] Figure 1 A lithographic apparatus according to an embodiment of the invention is schematically depicted. The apparatus comprises an illumination system IL, a support structure MT, a substrate table WT and a projection system PS.

[0026] The illumination system is configured to condition a radiation beam B. The support structure MT (e.g. a mask table) is configured to support a patterning device MA (e.g. a mask) and is connected to a first positioner PM configured to accurately position the patterning device according to certain parameters. The substrate table WT (e.g. a wafer stage) is configured to hold a substrate W (e.g. a resist-coated wafer) and is connected to a second positioner PW configured to accurately position the substrate according to certain parameters. The projection system PS is configured to project a pattern imparted to the radiation beam B via the patterning device MA onto a target portion C (e.g. comprising one or more dies) of the substrate W.

[0027] 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.

[0028] The term "radiation beam" as used herein encompasses all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g., having a wavelength of or about 365 nm, 355 nm, 248 nm, 193 nm, 157 nm, or 126 nm) and extreme ultraviolet (EUV) radiation (e.g., having a wavelength in the range of 5 to 20 nm), as well as particle beams, such as ion beams or electron beams.

[0029] The support structure MT supports the pattern forming device MA, i.e. bears the weight of the pattern forming device MA. The way in which the support structure MT holds the pattern forming device MA depends on the orientation of the pattern forming device MA, the design of the lithographic equipment, and other conditions, such as, for example, whether the pattern forming device MA is held in a vacuum environment. The support structure MT can use mechanical, vacuum, electrostatic or other clamping techniques to hold the pattern forming device MA. The support structure MT can be, for example, a frame or a table that can be fixed or movable as required. The support structure MT can ensure that the pattern forming device MA is in a desired position, for example relative to the projection system PS.

[0030] The term “patterning device” as used herein should be broadly interpreted as referring to any device that can be used to impart a radiation beam B with a pattern in its cross-section, such as to create a pattern in a target portion C of a substrate W. It should be noted that the pattern imparted to the radiation beam B may not exactly correspond to the desired pattern in the target portion C of the substrate W, for example if the pattern includes phase-shifting features or so called assist features. Typically, the pattern imparted to the radiation beam will correspond to a specific functional layer in a device (such as an integrated circuit) created in the target portion C.

[0031] The pattern forming device MA can be transmissive or reflective. Examples of pattern forming devices include masks, programmable mirror arrays, and programmable LCD panels. Masks are well known in lithography and include mask types such as binary masks, alternating phase shift masks, and attenuated phase shift masks, 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 to reflect an incident radiation beam B in different directions. The tilted mirrors impart a pattern in the radiation beam B reflected by the mirror matrix.

[0032] The term "projection system" as used herein should be broadly interpreted to include any type of projection system, including refractive, reflective, refractive-reflective, magnetic, electromagnetic, and electrostatic optical systems, or any combination thereof, as appropriate, appropriate to the exposure radiation being used or other factors (such as the use of immersion liquid or the use of a vacuum).

[0033] As depicted here, the device is transmissive (eg, using a transmissive mask). Alternatively, the device may be reflective (eg, using a programmable mirror array of the type described above, or using a reflective mask).

[0034] The lithographic apparatus may be of a type having two (dual stage) or more substrate tables WT (and / or two or more mask tables). In such a "multi-stage" machine, the extra tables may be used in parallel, or preparatory steps may be performed on one or more tables while one or more other tables are being used for exposure. In addition to one or more substrate tables WT, the lithographic apparatus may have a measurement stage which is arranged to be located at a position below the projection system PS when the substrate table WT is away from the position below the projection system PS. Instead of supporting the substrate W, the measurement stage may be provided with a sensor for measuring properties of the lithographic apparatus. For example, the projection system may project an image onto a sensor on the measurement stage to determine image quality.

[0035] The lithographic apparatus may also be of a type in which at least a portion of the substrate W 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 and the substrate. Immersion liquid may also be applied to other spaces in the lithographic apparatus, for example, between the pattern forming device MA and the projection system PS. It is well known in the art that immersion techniques are used to increase the numerical aperture of the projection system. The term "immersion" as used herein does not mean that structures such as the substrate W must be immersed in the liquid, but only means that the liquid is located between the projection system PS and the substrate W during exposure.

[0036] Reference Figure 1 , the illumination system IL receives a radiation beam B from a radiation source SO. The radiation source SO and the lithographic apparatus may be separate entities, for example when the radiation source is an excimer laser. In this case, the source is not regarded as forming part of the lithographic apparatus, and the radiation beam B is transferred from the radiation source SO to the illumination system IL by means of a beam delivery system BD comprising, for example, suitable directional mirrors and / or a beam expander. In other cases, the radiation source SO may be an integral part of the lithographic apparatus, for example when the radiation source is a mercury lamp. The radiation source SO and the illuminator IL, together with the beam delivery system BD (where necessary), may be referred to as a radiation system.

[0037] The illumination system IL may comprise an adjuster AD for adjusting the angular intensity distribution of the radiation beam B. Typically, at least the outer radial extent and / or the inner radial extent (commonly referred to as σ-outer and σ-inner, respectively) of the intensity distribution in a pupil plane of the illumination system may be adjusted. Furthermore, the illumination system IL may comprise various other components, such as an integrator In and a condenser CO. The illumination system IL may be used to condition the radiation beam B to have a desired uniformity and intensity distribution in its cross-section.

[0038] The radiation beam B is incident on the patterning device MT held on the support structure MT and is patterned by the patterning device MA. After having passed through the patterning device MA, the radiation beam B passes through the projection system PS which focuses the beam B onto a target portion C of the substrate W. With the aid of a second positioner PW and a position sensor IF (e.g. an interferometric device, a linear encoder, or a capacitive sensor), the substrate table WT can be accurately moved, for example, in order to position a different target portion C in the path of the radiation beam B. Similarly, the first positioner PM and the further position sensor (not shown) are arranged in a manner similar to those of the first positioner PM and the further position sensor (not shown). Figure 1 The support structure MT may be used to accurately position the pattern forming device MA relative to the path of the radiation beam B, for example after mechanical retrieval from a mask library or during scanning. In general, the movement of the support structure MT may be achieved with the aid of a long-stroke module and a short-stroke module forming part of the first positioner PM. The long-stroke module may provide coarse positioning of the short-stroke module over a large range of movement. The short-stroke module may provide fine positioning of the support structure MT relative to the long-stroke module over a small range of movement. Similarly, the movement of the substrate table WT may be achieved using a long-stroke module and a short-stroke module forming part of the second positioner PW. The long-stroke module may provide coarse positioning of the short-stroke module over a large range of movement. The short-stroke module may provide fine positioning of the substrate table WT relative to the long-stroke module over a small range of movement. In the case of a stepper (as opposed to a scanner), the support structure MT may be connected only to the short-stroke actuator, or may be fixed. The pattern forming device MA and the substrate W may be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks P1, P2 are shown occupying dedicated target portions, they may be located in spaces between target portions C (these are referred to as scribe lane alignment marks). Similarly, where more than one die is provided on the patterning device MA, the mask alignment marks M1, M2 may be located between dies.

[0039] The depicted device can be used in at least one of the following modes:

[0040] In a first mode (described as step mode), the supported structure MT and the substrate table WT are held substantially stationary while an entire pattern imparted to the radiation beam B is projected at once onto a target portion C (i.e. a single static exposure). The substrate table WT 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 that is imaged in a single static exposure.

[0041] In a second mode, the so-called scan mode, the support structure MT and substrate table WT 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 speed and direction of the substrate table WT relative to the support structure MT may be determined by the (or less) magnification and image reversal characteristics of the projection system PS. In scan mode, the maximum size of the exposure field limits the width of the target portion C in a single dynamic exposure (in the non-scanning direction), while the length of the scanning movement determines the height of the target portion (in the scanning direction).

[0042] In a third mode, the support structure MT is held substantially stationary, a programmable patterning device is held, and the substrate table WT is moved or scanned while a pattern imparted to the radiation beam B is projected onto a target portion C. In this mode, a pulsed radiation source is typically used and the programmable patterning device is updated as required after each movement of the substrate table WT or between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography utilising a programmable patterning device, such as a programmable mirror array of the type described above.

[0043] Combinations and / or variations on the above-described modes of use or entirely different modes of use may also be employed.

[0044] Figure 2 A flow chart illustrating a method of designing an alignment mark on a substrate is described. The alignment mark comprises at least one trench etched into the substrate.

[0045] In step 201, the relationship between the following items is obtained:

[0046] - the range of height variations across the surface of a probationary layer deposited on a probationary mark having a probationary mark groove having a probationary depth, and

[0047] - The thickness of the trial layer.

[0048] A trial mark etched in a tentative or preliminary or trial substrate is used as a starting point. A trial layer is deposited on the trial mark. The trial substrate, trial layer and trial mark may be physical or may be simulated in a process simulation. The trial mark represents an alignment mark and the trial layer represents a process layer deposited on the alignment mark. This relationship may be determined experimentally or based on simulations, as described below with reference to Figure 3A , Figure 3B and Figure 4 as described.

[0049] In step 202, an expected range of height variation throughout the surface of the trial layer deposited on the trial mark is determined. The height variation under the expected range enables the position of the trial mark to be determined by the calibration system based on the height variation of the surface of the trial layer over the trial mark. The height variation in the expected range can be understood as the range of height variation as required by the alignment system so that the position of the basic alignment mark can be detected based on the height variation in the trial layer (i.e., based on the bumps or undulations). Therefore, the expected range of height variation can be understood as a characteristic of the alignment system. The expected range of height variation can be determined by a trial alignment system, such as a physical alignment system that interacts with a physical trial layer on a physical trial mark, or a simulated alignment system that interacts with a simulated trial layer on a simulated trial mark. The trial calibration system can represent a calibration system as applied to determine the position of the alignment mark based on the height variation of the process layer over the entire alignment mark.

[0050] In step 203, the alignment mark is configured (ie, designed) by determining a desired depth of at least one trench of the alignment mark using:

[0051] -relation,

[0052] - highly variable expected range, and

[0053] - a predetermined thickness of a process layer deposited on said alignment mark.

[0054] The alignment mark can be understood as a structure in or on the surface of a substrate, which can be detected by an alignment measurement system. The alignment mark may include one or more grooves, for example, elongated grooves formed in the top surface of the substrate. The alignment mark may, for example, be composed of a main mark. A process layer may be understood as a layer disposed on the substrate (for example, disposed on the top surface of the substrate), such as a semiconductor material layer. The process layer may, for example, be an epitaxial layer, a laminated layer or a plurality of (thinner) layers (such as an epitaxial layer), or any other suitable layer, such as a layer of crystalline impurity atoms (such as silicon, germanium), and may contain compounds such as gallium nitride (GaN), gallium arsenide (GaAs). The layer may be formed of a crystalline material, such as an epitaxial layer of different materials. In another embodiment, the layer may be formed of a dielectric material, such as an oxide, a nitride, or other materials deposited by using chemical vapor deposition or by other means. The height variation may be understood as a bump or undulation located on the top surface of the trial layer and the process layer, respectively.

[0055] The trial mark may be a trial, experimental or pioneer version of a mark. The trial mark may have a similar dimensional design as the alignment mark, or the dimensional design may be different, such as having a smaller groove depth. The trial mark may be a physical mark, or may be a simulated mark in a simulated design environment.

[0056] Similarly, the trial layer may be a trial version, an experimental version, or a pioneer version of the process layer. The trial layer may have a similar dimensional design to the trial layer, or the dimensional design may be different, such as having a smaller thickness. The trial layer may be a physical layer, or may be a simulated layer in a simulated design environment.

[0057] The height variation can be understood as the spatial variation of the height of the surface of the trial layer and the process layer, respectively. The height variation can be understood as concavity or convexity. Therefore, the range of the height variation can be understood as the height difference of concavity or convexity.

[0058] Figure 3A A trial mark outline (eg, a cross-sectional view) of a trial mark MK provided on a trial substrate W is depicted. The trial mark is formed by a trench TR etched into the top surface of the trial substrate W. The depth of the trench is indicated by DPT. Figure 3BA trial layer LAY is depicted which is arranged on the trial substrate W and in particular is arranged throughout the trial mark MK. When the layer is arranged on the trial mark, a height difference HD (i.e., a range of height variation HV) results in a top surface of the trial layer, the height variation being caused by the trench TR in the top surface. In order to obtain a relationship between the thickness of the trial layer on the trial mark and the range of height variation throughout the surface of the trial layer, a height difference in the top surface of the trial layer can be determined in response to at least two different trial layer thicknesses on the trial substrate. The relationship can be determined based on a change in the height variation of the top surface of the trial layer as a function of a change in the thickness of the trial layer. For example, a (trial) first epitaxial layer is arranged on the trial substrate, and a height variation on the surface of the first epitaxial layer covering the trial mark is determined. Then, a (trial) second epitaxial layer is arranged on the (trial) first epitaxial layer, and a height variation on the surface of the (trial) second epitaxial layer covering the trial mark and the (trial) first epitaxial layer is determined. The height variation as a function of the thickness of the trial layer can be determined based on experiments and / or simulations (e.g., using a process model).

[0059] Figure 4 A graphical view is depicted of the variation of the trial mark depth as a function of the layer thickness, in this example expressed as the number of (e.g. epitaxial) layers on the trial substrate. In this example, the depth of the trial mark groove is 1 micron. After applying the (trial) first epitaxial layer, the resulting height difference of the height variation on the surface of the (trial) first epitaxial layer is entered in the graph, and the same operation is repeated after applying the (trial) second epitaxial layer on the (trial) first epitaxial layer. Thus, a plurality of data points can be obtained, and from this a relationship between the resulting height variation and the thickness of the trial layer can be derived. For example, the relationship can be obtained by curve fitting the obtained data points, for example, fitting a linear approximation to the obtained data points, such as Figure 4 As another example, a polynomial curve may be applied. Since the relationship may be different at different parts of the surface of the substrate, the depth and the relationship obtained may be determined at different parts of the surface of the substrate. Correspondingly, a second curve is determined from the second set of data points, as indicated by REL2. For example, the second curve may be related to a (trial) mark at a lower groove depth.

[0060] In this example, the relationship is determined as a straight line, i.e., a linear relationship, which can provide a low overall error to match the data points. For example, a linear approximation can provide a certain degree of averaging, thereby tolerating, i.e., tolerating, data points that deviate, such as irregular data points, to a certain extent, thereby providing a relatively robust, i.e., robust relationship. Alternatively, a curve (such as a polynomial curve) can be applied, for example, using a curve fitting algorithm, to fit the curve to the data points using a fitting criterion (such as minimization of an error function). For example, a second-order or third-order curve can be fitted to the data points. Thus, a more accurate or more precise relationship can be defined.

[0061] The relationship may be derived from the increments, for example, based on the change in height variation of the trial layer due to a change in thickness of the trial layer. Figure 4 In the example schematically depicted in , the relationship may represent a reduction in the variation in height of the trial layer due to an increase in the thickness of the trial layer.

[0062] In order to enable an alignment system (i.e., an alignment measurement system) to determine the position of the mark based on the height variation of the layer throughout the mark, an expected range of height variation across the surface of the trial layer deposited on the trial mark is determined. The expected range of height variation enables the alignment system to determine the position of the mark with a desired accuracy. The expected range of height variation can be determined by experimentation and / or simulation. For example, in the case of an alignment measurement beam in the visible or near infrared wavelength range, the expected range of height variation may be between 300 nanometers and 500 nanometers.

[0063] Figure 5 A graphical view is depicted of the variation of the depth of a trial mark with the layer thickness, in this example, expressed as the number of (e.g. epitaxial) layers on the trial substrate. Figure 4 As depicted, the determined curves REL1 and REL2 are also as Figure 5 As described in Figure 5 As explained, the alignment mark is designed by determining a desired depth of at least one trench of the alignment mark using:

[0064] -relation,

[0065] - highly variable expected range, and

[0066] - a predetermined thickness of the process layer deposited on the alignment mark.

[0067] For this purpose, the desired depth is depicted in the curve, (i.e. in the present example) between 300 nm and 500 nm. Starting from a predetermined (e.g. desired) thickness DT of the process layer, e.g. 42 microns in the present embodiment, i.e. 6 epitaxial layers of 7 nanometers each. Starting from the predetermined thickness of the process layer and using the relationship between the resulting height variation and the thickness of the trial layer, the desired depth of the alignment mark can be determined using the relationship (e.g. as in the present example by extrapolation using the determined (linear) relationship). Figure 5 As depicted in , the steepest of the relationships, relationship REL2, is applied to account for the "worst case" degradation of the alignment mark when the layer is applied to the substrate. Thus, based on a desired depth of 300 nanometers to 500 nanometers, the slope of REL2, and a desired thickness of the 6 times 7 micron epitaxial layer, a mark trench depth of approximately 2.2 micrometers to 2.4 micrometers, i.e., a desired depth DD, would be desired.

[0068] When using the determined relationship for extrapolation, the trial mark and the trial layer may use different layer thicknesses, such as more common, more readily available or known layer thicknesses, thereby simplifying the process of deriving the relationship based on the trial mark and the trial layer.

[0069] The determined mark groove depth may be used to design the alignment mark.

[0070] The bottom critical dimension of the mark can be further determined, as shown in reference 6A to 6F as described. FIG. 6A to FIG. 6C Plotted are simulations of the alignment sensor signal strength WQ as a function of the bottom critical dimension CD at corresponding resulting mark depths, ie, for the resulting unevenness in the process layer of 300, 400 and 500 nanometers, respectively. FIG. 6D to FIG. 6F Depicted for bottom critical dimensions between 0 and 1 micron, FIG. 6A to FIG. 6C In this example, the simulations were performed for different wavelengths, such as 532 nm (A), 635 nm (B), 780 nm (C), and 850 nm (D).

[0071] The wavelength of the alignment beam may be selected based on the height variation and subsequently the CD may be selected to optimize the alignment sensor signal strength (WQ). The wavelength of the alignment beam may be selected for the bottom CD variation of 0 to 1 um. The optimization criterion is to use the alignment signal strength, for example 1%.

[0072] Fig. 7AAn illustrative cross-sectional view of an alignment mark MK in a substrate W designed by the disclosed method is depicted. The alignment mark MK may be embodied as a physical alignment mark or as a design, for example, a data file comprising design parameters capable of reproducing the alignment mark designed by the described method. The alignment mark comprises a trench TR having a desired depth DD as determined by the method.

[0073] Therefore, if Figure 7B As depicted in , when a process layer LAY having a predetermined thickness DT is applied throughout the mark MK in the substrate W, a height variation HV having a height difference HD is provided in the top surface of the process layer, the height variation enabling the position of the mark MK to be determined by an alignment measurement system (particularly in a horizontal plane substantially perpendicular to the surface of the substrate). Thus, the alignment measurement system, instead of interacting with the trench TR of the mark MK, can thereby interact with the height variation resulting from the top surface of the layer as a result of the base alignment mark designed according to the presently disclosed method.

[0074] In addition to using the methods to design / configure alignment marks, any other marks including at least trenches etched into a substrate may also be configured according to the methods as disclosed in this document. For example, a bottom grating (mark) included in an overlay mark (e.g., a mark extending across two layers deposited on the substrate) may be configured according to any of the methods as described in this document. A metrology system (e.g., a scatterometer) may then be used instead of the alignment system to determine the position of the bottom grating (relative to the top grating (mark) included in the overlay mark).

[0075] In an embodiment, a method for configuring a mark is provided, the mark comprising a groove etched into a substrate, the method comprising: a) obtaining a relationship between a range of height variations throughout a surface of a trial layer deposited on a trial groove having a trial depth and a thickness of the trial layer; b) determining a range of height variations throughout the surface of a layer deposited on the mark, allowing a measurement system to determine a position of the mark; and c) configuring the mark by determining a depth of the groove based on the relationship, the range of height variations, and the thickness of the layer.

[0076] In an embodiment, the mark is (part of) an alignment mark or an overlay mark.

[0077] Other embodiments of the invention are disclosed in the following list of numbered aspects:

[0078] 1. A method for designing an alignment mark on a substrate, the alignment mark comprising at least one trench etched into the substrate, the method comprising:

[0079] a) obtaining a relationship between a range of height variation across a surface of a trial layer deposited on a trial mark having a trial mark groove having a trial depth and a thickness of the trial layer, wherein the trial mark represents the alignment mark, and wherein the trial layer represents a process layer deposited on the alignment mark;

[0080] b) determining an expected range of height variations across the entire surface of the trial layer deposited on the trial mark, the height variations within the expected range enabling a calibration system to determine the position of the trial mark based on the height variations across the surface of the trial layer on the trial mark; and

[0081] c) configuring the alignment mark by determining a desired depth of at least one trench of the alignment mark using the relationship, the desired range of height variation, and a predetermined thickness of the process layer deposited over the alignment mark.

[0082] 2. A method according to aspect 1, wherein the relationship is determined based on at least two different thicknesses of the trial layer and at least two corresponding ranges of height variation across the surface of the trial layer deposited on the trial mark in response to the at least two different thicknesses of the trial layer.

[0083] 3. The method of aspect 2, wherein determining the relationship comprises fitting a curve using at least two different height changes determined in response to the at least two different thicknesses of the trial layer.

[0084] 4. The method according to aspect 3, wherein the curve is a linear curve.

[0085] 5. A method according to aspect 3 or 4, wherein the predetermined thickness of the process layer exceeds the at least two thicknesses of the trial layer, and the desired depth is determined using extrapolation of the curve.

[0086] 6. A method according to any one of aspects 2 to 7, wherein the at least two corresponding ranges of height variation across the surface of the trial layer deposited on the trial marking are determined using a process model.

[0087] 7. A method according to any of the preceding aspects, wherein the expected range of height variations across the surface of the trial layer deposited on the trial mark is determined using a simulation of the interaction of the alignment system with height variations across the surface of the trial layer.

[0088] 8. The method of clause 7, wherein simulations are performed for a plurality of bottom critical dimensions of the trial mark trenches, the method further comprising using results of the simulations to select the bottom critical dimension of the trial mark.

[0089] 9. An alignment mark, wherein the alignment mark is designed according to the method of any one of the preceding aspects.

[0090] 10. A method for aligning a substrate during a photolithography process, the method comprising:

[0091] - providing a substrate comprising an alignment mark according to aspect 10, and

[0092] - providing a process layer having a predetermined thickness on said substrate, and

[0093] - performing an alignment measurement of the height variation of the process layer across the alignment mark.

[0094] 11. A computer program comprising a sequence of one or more machine readable instructions describing a method according to any one of the preceding aspects.

[0095] 12. A data storage medium, wherein the computer program according to aspect 11 is stored in the data storage medium.

[0096] 13. A computer system configured to execute the computer program according to aspect 11.

[0097] 14. A method of configuring a mark, the mark comprising a trench etched into a substrate, the method comprising:

[0098] a) obtaining a relationship between the range of height variation across the surface of a trial layer deposited on a trial groove having a trial depth and the thickness of the trial layer;

[0099] b) determining the extent of height variations across the surface of a layer deposited on said mark, allowing a metrology system to determine the position of said mark; and

[0100] c) configuring the mark by determining a depth of the groove based on the relationship, the range of height variation, and the thickness of the layer.

[0101] 15. The method of clause 14, wherein the mark is a portion of an overlay mark or an alignment mark.

[0102] 16. A method according to aspect 14 or 15, wherein the relationship is determined based on at least two different thicknesses of the trial layer and at least two corresponding ranges of height variation across the surface of the trial layer deposited on the trial mark in response to the at least two different thicknesses of the trial layer.

[0103] 17. The method of aspect 16, wherein determining the relationship comprises fitting a curve using at least two different height changes determined in response to the at least two different thicknesses of the trial layer.

[0104] 18. The method of clause 17, wherein the curve is a linear curve.

[0105] 19. A method according to aspects 17 or 18, wherein the predetermined thickness of the process layer exceeds the at least two thicknesses of the trial layer, and the desired depth is determined using extrapolation of the curve.

[0106] 20. The method of any one of aspects 17 to 19, wherein a process model is used to determine the at least two corresponding ranges of height variation across the surface of the trial layer deposited on the trial marking.

[0107] 21. A method according to any one of aspects 15 to 20, wherein the expected range of height variations across the surface of the trial layer deposited on the trial mark is determined using a simulation of the interaction of the alignment system with height variations across the surface of the trial layer.

[0108] 22. The method of clause 21, wherein simulations are performed for a plurality of bottom critical dimensions of the trial mark trenches, the method further comprising using results of the simulations to select the bottom critical dimension of the trial trenches.

[0109] 23. An alignment mark designed according to the method of any one of aspects 14 to 22.

[0110] 24. A method for aligning a substrate during a photolithography process, the method comprising:

[0111] - providing a substrate comprising an alignment mark according to clause 24, and

[0112] - providing a layer on said substrate, and

[0113] - performing alignment measurements of the height variations of the layer across said alignment marks.

[0114] 25. A computer program comprising a sequence of one or more machine readable instructions describing a method according to any one of clauses 14 to 24.

[0115] 26. A data storage medium having the computer program according to aspect 25 stored therein.

[0116] 27. A computer system configured to execute the computer program according to aspect 25.

[0117] Although the use of lithographic equipment in IC manufacturing may be specifically mentioned herein, it should be understood that the lithographic equipment described herein may have other applications, such as manufacturing integrated optical systems, guidance and detection patterns for magnetic domain memory, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, etc. It should be understood by those skilled in the art that in the context of these alternative applications, any use of the term "wafer" or "die" in the present disclosure may be considered synonymous with the more general term "substrate" or "target portion", respectively. The substrates mentioned herein may be processed in, for example, a coating and developing system or track (a tool that typically applies a resist layer to a substrate and develops the exposed resist), a measurement tool, and / or an inspection tool before or after exposure. Where applicable, the disclosure herein may be applied to such substrate processing tools and other substrate processing tools. In addition, the substrate may be processed more than once, for example, to produce a multi-layer IC, so that the term substrate used herein may also refer to a substrate that already contains multiple processed layers.

[0118] Although specific reference has been made above to embodiments of the invention being used in the context of optical lithography, it should be understood that the invention may be used in other applications, such as imprint lithography, and is not limited to optical lithography where the context permits. In imprint lithography, the topography in the patterning device defines the pattern produced on the substrate. The topography of the patterning device may be imprinted into a layer of resist provided to the substrate, the resist being cured by applying electromagnetic radiation, heat, pressure, or a combination thereof. The patterning device is removed from the resist, leaving the pattern behind after the resist has cured.

[0119] Although specific embodiments of the present invention have been described above, it should be understood that the present invention may be practiced in ways other than those described. For example, the present invention may be in the form of a computer program comprising one or more machine-readable instruction sequences describing the methods disclosed above, or a data storage medium (e.g., a semiconductor memory, a magnetic disk, or an optical disk) having a computer program stored therein.

[0120] The above description is intended to be illustrative rather than limiting. Accordingly, those skilled in the art will appreciate that modifications may be made to the described invention without departing from the scope of the claims set forth below.

Claims

1. A method for designing an alignment mark on a substrate, the alignment mark comprising at least one trench etched into the substrate, the method comprising: a) obtaining a relationship between a range of height variation across a surface of a trial layer deposited on a trial mark having a trial mark groove having a trial depth and a thickness of the trial layer, wherein the trial mark represents the alignment mark, and wherein the trial layer represents a process layer deposited on the alignment mark; b) determining a desired range of height variations across the surface of the trial layer deposited on the trial mark, the height variations within the desired range enabling determination of the position of the trial mark by an alignment system based on the height variations across the surface of the trial layer on the trial mark; and c) configuring the alignment mark by determining a desired depth of the at least one trench of the alignment mark using the relationship, the desired range of height variation, and a predetermined thickness of the process layer deposited over the alignment mark.

2. The method according to claim 1, wherein: The relationship is determined based on at least two different thicknesses of the trial layer and at least two corresponding ranges of height variation across the surface of the trial layer deposited on the trial indicia in response to the at least two different thicknesses of the trial layer.

3. The method of claim 2, wherein determining the relationship comprises fitting a curve using at least two different height changes determined in response to the at least two different thicknesses of the trial layer. The method according to claim 3 , wherein the curve is a linear curve.

5. A method according to claim 3 or 4, wherein the predetermined thickness of the process layer exceeds at least two thicknesses of the trial layer, the desired depth being determined using extrapolation of the curve.

6. The method according to claim 2, wherein: The at least two corresponding ranges of height variation across the surface of the trial layer deposited on the trial indicia are determined using a process model.

7. The method according to claim 1, wherein: The expected range of height variations across the surface of the trial layer deposited on the trial mark is determined using simulations of the interaction of the alignment system with height variations across the surface of the trial layer.

8. The method of claim 7, wherein the simulation is performed for a plurality of bottom critical dimensions of the trial mark trench, the method further comprising using a result of the simulation to select the bottom critical dimension of the trial mark.

9. A computer program product for designing an alignment mark on a substrate, the alignment mark comprising at least one trench etched into the substrate, the computer program product comprising machine readable instructions configured to: a) obtaining a relationship between a range of height variation across a surface of a trial layer deposited on a trial mark having a trial mark groove having a trial depth and a thickness of the trial layer, wherein the trial mark represents the alignment mark, and wherein the trial layer represents a process layer deposited on the alignment mark; b) determining an expected range of height variation across the surface of the trial layer deposited on the trial mark, the height variation within the expected range enabling the alignment system to determine the position of the trial mark based on the height variation across the surface of the trial layer on the trial mark; and c) configuring the alignment mark by determining a desired depth of the at least one trench of the alignment mark using the relationship, the desired range of height variation, and a predetermined thickness of the process layer deposited over the alignment mark.

10. The computer program product according to claim 9, wherein: The relationship is determined based on at least two different thicknesses of the trial layer and at least two corresponding ranges of height variation across the surface of the trial layer deposited on the trial indicia in response to the at least two different thicknesses of the trial layer.

11. The computer program product of claim 10, wherein determining the relationship comprises fitting a curve using at least two different height changes determined in response to the at least two different thicknesses of the trial layer.

12. The computer program product of claim 11, wherein the curve is a linear curve.

13. The computer program product of claim 11 or 12, wherein the predetermined thickness of the process layer exceeds the at least two thicknesses of the trial layer, the desired depth being determined using extrapolation of the curve.

14. The computer program product of claim 10, wherein: The at least two corresponding ranges of height variation across the surface of the trial layer deposited on the trial indicia are determined using a process model.

15. The computer program product of claim 9, wherein: The expected range of height variation across the surface of the trial layer deposited on the trial mark is determined using simulations of the alignment system and height variation across the entire surface of the trial layer.

16. The computer program product of claim 15, wherein the simulation is performed for a plurality of bottom critical dimensions of the trial mark trench, The results of the simulation are used to select the bottom critical dimension of the trial mark. 17 . A data storage medium, wherein the computer program product according to claim 9 is stored.

18. A computer system configured to execute the computer program product according to claim 9.

Images