NL1036635A1 - Method of providing alignment marks, device manufacturing method and lithographic apparatus. - Google Patents

Description

METHOD OR PROVIDING ALIGNMENT MARKS, DEVICE MANUFACTURING METHOD AND LITHOGRAPHIC EQUIPMENT

Field [0001] The present invention relates to a method of providing a set of alignment marks on a substrate, a device manufacturing method and a lithographic apparatus. The invention also relates to a method of determining the relative displacement or at least two layers provided with the alignment marks.

Background [0002] 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., including 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.

In general, the wafer is covered with a plurality of layers, placed on top of each other. In the layers patterns are exposed, in the pattern of a layer has to fit exactly on the previous one. In practice, there will always be an offset between consecutive layers. The offset or displacement of the layers relative to one is referred to as the overlay error or overlay. The overlay is determined by one or more alignment sensors arranged to measure the positions of substrate alignment marks arranged for that purpose on the layers.

Several methods exist to determine the overlay capability of a lithographic apparatus. First of all, use can be made or one or more of the alignment sensors typically present in the lithographic apparatus. The alignment sensor measures the relative position of an alignment mark in a first layer with respect to the position of the same or similar alignment mark in a second layer, placed on top of the first layer. However, the overlay measurements rely on alignment marks or similar overlay targets with dimensions that are much larger than the typical product features to be provided on the substrate. Furthermore, the alignment sensors are designed for an accuracy that is much larger than the typical product features as well. 0005] Alternative use may be made or separate metrology tool. For instance, the location of the outer box / frame in the first layer with respect to the location of the inner box in the second layer may be determined with the metrology tool. This method is relatively slow and involves removing the substrate from the lithographic apparatus after having provided the first layer on the substrate. Finally, the measurement of the overlay may be SEM tool based. The location of a set of lines in a first layer may be measured at resolution (ie, with an accuracy having the same order of magnitude of the typical product features in the layer) with respect to the location of a second set of lines at resolution in a second layer. However, this SEM tool-based method is comparatively time consuming and complex (or equally impossible) to accomplish when the first layer target is located in a product layer.

SUMMARY

It is desirable to provide a method and apparatus for providing accurate and high-quality alignment marks on a substrate.

[0007] It is further desirable to provide a method and apparatus for providing alignments marks in the overlay error may be determined fast and with a high accuracy.

[0008] It is also desirable to provide a method and apparatus for providing alignments marks in the overlay error may be determined at resolution.

[0009] According to an aspect of the invention a method of providing a set of alignment marks on a substrate is provided, the method including: - exposing a first pattern on at least one exposure area or a layer of a substrate, the first pattern including a repetitive set of elements having a first element size; - exposing a second pattern on the least one exposure area on top of the first pattern, the second pattern including a repetitive set of elements or a second element size, the second element size being larger or narrower than the first element size; in the elements of the first and second patterns partly overlap and combined form a set of repetitive large-sized alignment marks, such that the edges of the alignment marks in the direction of repetition are formed by small-sized elements.

[0010] According to another aspect of a method of calibration of a projection system or of a lithographic apparatus is provided, the method including: a) when the projection system is in an initial condition, exposing a first pattern on at least one exposure area of a layer of a substrate, the first pattern including a repetitive set of small-sized elements and exposing a second pattern including a set of large-sized elements on the least one exposure area on top of the first pattern, containing the elements of the first and second patterns partly overlap and combined form a set of repetitive large-sized alignment marks, such that the edges of the alignment marks in the direction of repetition are formed by small-sized elements; b) when the projection system is in heated condition, repeating the exposure process a); c) determining information about the distortion of the alignment marks as a function of the temperature or at least a portion of the projection system.

[0011] According to another aspect of the invention or determining the relative displacement or at least two layers provided with respective sets of alignment marks, is provided, including the method: - producing a first set of combined alignment marks on a first layer and a complimentary, second set of combined alignment marks on a second layer, provided on top of the first layer, - irradiating the two sets of combined alignment marks; - detecting the relative displacement between the first and second sets of alignment marks.

According to another aspect a device manufacturing method is provided, the method including transferring at least one pattern from a patterning device onto a substrate of the device, transferring a pattern comprising: - transferring a first pattern at least one exposure area or a layer or a substrate, the first pattern including a repetitive set of elements having a first element size; - transfer ring a second pattern on the least one exposure area on top of the first pattern, the second pattern including a repetitive set of elements or a second element size, the second element size being larger or narrower than the first element size; in the elements of the first and second patterns partly overlap and combined form a set of repetitive large-sized alignment marks, such that the edges of the alignment marks in the direction of repetition are formed by small-sized elements.

[0013] According to another aspect of a lithographic apparatus arranged to provide a pattern of alignment marks from a patterning device onto a substrate, is provided, the apparatus is arranged and constructed so as to: - expose a first pattern on at least one exposure area of a layer of the substrate, the first pattern including a repetitive set of elements having a first element size; - expose a second pattern on the least one exposure area on top of the first pattern, the second pattern including a repetitive set of elements or a second element size, the second element size being larger or narrower than the first element size; in the elements of the first and second patterns partly overlap and combined form a set of repetitive large-sized alignment marks, such that the edges of the alignment marks in the direction of repetition are formed by small-sized elements.

Further details, features and advantages of the present invention will be elucidated in the following description.

LETTER DESCRIPTION OF THE DRAWINGS

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: [0016] - Figure 1 depicts a lithographic apparatus according to an embodiment of the invention; - Figure 2 depicts a schematic diagram or a laser step alignment apparatus; - Figure 3A depicts a schematic representation of an embodiment or a first alignment pattern; Figure 3B depicts a schematic representation of an embodiment or second alignment pattern, combined with the alignment pattern of Figure 3A, to form an alignment mark; - Figure 4A depicts an alignment mark resulting from a known exposure method; Figure 4B depicts an embodiment of an alignment mark resulting from an exposure method according to an embodiment of the present invention; - Figures 5A-5F depict various alignment patterns according to an embodiment of the present invention for determining overlay; - Figure 6A depicts a top view of a wafer containing a distorted features; Figure 6B depicts a top view in more detail of the die of Figure 6A; - Figure 6C depicts a top view of an example or a sample mark to be applied to the die of Figure 6B; Figure 6D depicts a top view of the die of Figure 6B, provided with a variety of sample marks for measuring the product distortion; - Figures 7A-7C depict respective schematic views in a cross-section or further in a DPT application; - Figures 8A-8D depict schematic views in cross-section or further expanded showing contrast versus pattern density requirements; Figure 8E depicts a top view of the embodiment shown in Figure 8D; - Figures 9A-9C depict schematic views in cross-section or further further in spacer technology application; - Figures 10A-10D depict schematic views in a cross-section or further in a deep trench application; - Figures 11 A-1 IB depict schematic views in cross-section or further, in another deep-trench application; and - Figures 12A-12C depict schematic views in cross-section or further, in a via layer application.

DETAILED DESCRIPTION

Figure 1 schematically depicts a lithographic apparatus according to one embodiment of the invention. The apparatus comprises: an illumination system (illuminator) IL configured to condition a radiation beam B (e.g., UV 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 in accordance with certain parameters; a substrate table (e.g., a wafer table) WT constructed to hold a substrate (e.g., a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate 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., including one or more dies) of the substrate W.

The illumination system 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 supports, i.e., bears the weight of, the patterning device. It holds the patterning device in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions, such as for example whether or not the patterning device is a hero in a vacuum environment. The support structure can use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. The support structure may be a frame or a table, for example, which may be fixed or movable as required. The support structure may ensure that the patterning device is at a desired position, for example with respect to the projection system. Any use of the terms "reticle" or "mask" may be considered synonymous with the more general term "patterning device." The term "patterning device" used 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 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 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 radiation exposure 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" may also be considered as synonymous with the more general term "projection system".

As shown here, the apparatus is of a reflective type (e.g., employing a reflective mask). Alternatively, the apparatus may be of a transmissive type (e.g., employing a transmissive mask).

The lithographic apparatus may be of a type having two (dual stage) or more substrate tables (and / or two or more mask tables). In such "multiple stage" machines the additional 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 also be a type of at least a portion of the substrate may be covered by a liquid having a relatively high refractive index, eg, water, so as to fill a space between the projection system and the substrate . Liquid immersion may also be applied to other spaces in the lithographic apparatus, for example, between the mask and the projection system. Immersion techniques are well known in the art for increasing the numerical aperture of projection systems. The term "immersion" as used does not mean that a structure, such as a substrate, must be submerged in liquid, but rather only means that liquid is located between the projection system and the substrate during exposure.

Referring to Figure 1, the illuminator IL receives a radiation beam from a radiation source SO. The source and the lithographic apparatus may be separate entities, for example when the source is an excimer laser. In such cases, the source is not considered to be part of the lithographic apparatus and the radiation beam is passed from the source SO to the illuminator IL with the aid of a beam delivery system BD including, for example, suitable directing mirrors and / or a beam expander. In other cases the source may be an integral part of the lithographic apparatus, for example when the source is a mercury lamp. The source SO and the illuminator IL, together with the beam delivery system BD if required, may be referred to as a radiation system.

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

The radiation beam B is incident on the patterning device (e.g., mask MA), which is a hero on the support structure (e.g., mask table MT), and is patterned by the patterning device. Having traversed the mask MA, the radiation beam B passes through the projection system PS, which is the beam onto a target portion C or the substrate W. With the aid of the second positioner PW and position sensor IF2 (eg, an interferometric device, linear encoder or capacitive sensor), the substrate table WT can be moved accurately, eg, 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 IF1 can be used to accurately position the mask MA with respect to the path of the radiation beam B, eg, after mechanical retrieval from a mask library, or during a scan. In general, movement of the mask table MT may be realized with the aid of a long-stroke module (coarse positioning) and a short-stroke module (fine positioning), which form part of the first positioner PM. Similarly, movement of the substrate table WT may be realized using a long-stroke module and a short-stroke module, which form part of the second positioner PW. In the case of a stepper (as opposed to a scanner) the mask table MT may be connected to a short-stroke actuator only, or may be fixed. Mask MA and substrate May be aligned using mask alignment marks M1, M2 and substrate alignment marks P1, P2. Although the substrate alignment marks as illustrated occupy dedicated target portions, they may be located in spaces between target portions (these are known as scribe-lane alignment marks). Similarly, in situations in which more than one that is provided on the mask MA, the mask alignment marks 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 mask table MT and the substrate table WT are kept essentially stationary, while an entire pattern imparted to the radiation beam is projected onto a target portion C at one time (ie, a single static exposure). The substrate table WT is then shifted in the X and / or Y direction so that a different target portion 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 mask table MT and the substrate table WT are scanned synchronously while a pattern beamed to the radiation beam is projected onto a target portion C (i.e., a single dynamic exposure). The velocity and direction of the substrate table WT relative to the mask table 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) or the target portion in a single dynamic exposure, whereas the length of the scanning motion has the height (in the scanning direction) of the target portion.

3. In another mode, the mask table MT is kept essentially stationary holding a programmable patterning device, and the substrate table WT is moved or scanned while a pattern is imparted to the radiation beam 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 table WT or in between successive radiation pulses during a scan. This mode of operation can be readily applied to maskless lithography that utilizes programmable patterning device, such as a programmable mirror array or a type as referred to above. Combinations and / or variations on the modes described above or use or entirely different modes or use may also be employed.

In general, a wafer or substrate is covered with a large number of layers. Each layer starts with the exposure or pattern on the substrate. The pattern has to fit exactly on the previous one. In practice, there will always be an offset between consecutive layers. This offset may for instance be caused by a slight misalignment of the substrate in case the substrate is repositioned, after it has been out for chemical processing, inside the exposure unit so that all patterns of the individual layers fit accurately on top of each other. The offset or displacement of the layers relative to one is referred to as the overlay error or overlay.

The overlay is determined by one or more alignment sensors arranged to measure the positions of substrate alignment marks. Figure 2 shows an example of a laser step alignment arrangement. The arrangement shown in figure 2 comprises a laser source 2, a mirror 10, a semi-transparent mirror 12, a mirror 14, a detector 4, and a processor 6. Also shown in figure 2 are the projection system PS, the substrate W and the substrate table WT, as well as an actuator 8.

In use, the laser source 2 generates a laser beam 16 that is directed to the mirror 10. The mirror 10 reflects the laser beam 16 to the semi-transparent mirror 12. The laser beam 16 axis reflected by the semi-transparent mirror 12 is directed to the mirror 14. The laser beam 16 is reflected by the mirror 14 is directed as an alignment beam 18 to a substrate alignment mark PI on substrate W. The alignment beam 18, as received by the mark P1, is diffracted by the mark P1 as diffracted radiation 16 'back to the mirror 14. The mirror 14 reflects the diffracted radiation 16' to semi-transparent mirror 12. The mirror 12 is semi-transparent and passes a portion of the diffracted radiation 16 'to the detector 4 The detector 4 receives the portion of the diffracted radiation 16 'and generates an output signal for processor 6.

The actuator 8 shown in figure 2 is intended to illustrate that the substrate table WT may be moved to such a position that the mark PI can be aligned with the alignment beam 18. Moreover, the actuator 8 is arranged to move the substrate table WT to allow exposing of the substrate W by exposure light through the projection system PS, as is known to persons skilled in the art. The actuator 8 is controlled by processor 6. Of course, in practice, there may be more than one actuator to allow movement of the WT substrate table in a variety of directions. It is noted that the processor 6 is shown as one single processor unit connected to both the detector 4 and the actuator 8. However, if desired, multiple, different functions or the processor 6 may be implemented in different processors. These processors need not necessarily be within the lithographic apparatus but may be located outside the lithographic apparatus.

The signal received by the processor 6 may be used by the processor 6 to align the layer on which the mark PI is located. To that end various algorithms can be used as is known to persons skilled in the art.

The invention is also applicable with other types of alignment setups, e.g., in a setup with a so-called "Athena" sensor. This alignment sensor measures a position or an alignment mark. During alignment, the alignment mark is illuminated with an alignment beam of radiation. The alignment beam of radiation is diffracted by the alignment mark into several diffraction orders such as +1, -1, +2 and -2. Using optical elements, each set of corresponding diffraction orders (say +1 and -1) may be used to form an image of the alignment mark on a reference plate. The reference plate may contain reference gratings for each set of corresponding diffraction orders to be measured. Behind each reference grating a separate detector may be arranged to measure the intensity of the radiation in the image passing through the reference gratings. By moving the alignment mark relative to the reference plate, the position with the highest intensity for one or more images may be found, which gives the aligned position. 10057] To enhance performance, the intensity of several images may be measured and the alignment beam of radiation may consist of multiple colors. Use of still other types of sensors is not excluded, including sensors based on capacitive or acoustic measurement principles.

Figures 3A and 3B show an example of sets of alignment patterns forming alignment marks in accordance with an embodiment of the present method. The method comprises exposing at an exposure area or a first layer 20 a first dense pattern 21 or repetitively arranged pattern elements. In the embodiment shown the pattern 21 is composed of an array or essentially parallel elements 22 (hereafter referred to as "trenches" although it is understood to be similar to other elements or lines may be applied as well). The trenches are spaced apart with a constant pitch 27 and each trench 22 has a first width (Fi). The first width may be the order of magnitude or typical product features. The dimensions to be achieved nowadays in lithography are in the range of 45 nm or less and may in the future even reach narrower values, such as 32 nm or less. However, in other alternative the first width may also be much larger than the pitch at resolution. For instance, by enlarging the pitch starting from the pitch at resolution, the print error as function or the pitch may be determined, as will be discussed hereafter.

After having exposed the first pattern 21, i.e., the trenches 22 at resolution, the photo resist layer 20 has been developed. During exposure the first layer pattern 21 may have been shifted, for instance due to a lens distortion, a reticle writing error, or any other tool induced offset (e.g., an immersion related shift or lens heating). After exposing layer 20 a second alignment pattern 23 is exposed on the exposure area on top of the first pattern 21. As shown in figure 3B, also the second pattern 23 comprises a set of repetitive elements composed of an array or essentially parallel second trenches 24 , the second trenches 24 having a width (F2) larger than the width (Fi) of the first elements 22. The trenches 24 of the second alignment pattern 23 partly overlap the trenches 22 of the first alignment pattern 21 so as to form a multiple or combined alignment marks 25, as shown in figure 3B. The second trenches are sized and arranged so as to overlap the first trenches in such a way, that the edges of the combined alignment marks 25 are formed by the edges 26 (in the direction of repetition Pr, cf. figure 3 A) of the first elements 22. In this way large-sized alignment marks 25 may be produced, that as a result of their size can be detected by a standard alignment sensor, whereas the accuracy of the alignment marks 25, and also the aligned position, is determined by the small-sized elements 22 of the first pattern 21. Or, in other words, by the double exposure of patterns (images) on the exposure area, one or more double exposure alignment marks 25 may be created, the accuracy of the alignment marks may be improved considerably and the position of an alignment mark can be determined at a much higher resolution than the low resolution of the standard alignment marks would permit.

In further detail the small-sized elements may be sized at resolution, i.e., at the smallest level of detail that can be seen or imaged by the lithographic tool, nowadays typically about 45 nm, as mentioned earlier. Examples of how the small-sized pattern elements are sized at resolution are given hereafter.

In the embodiment described above, both the first pattern and the second pattern are exposed in the same layer. Instead of this double exposure in the same layer (i.e., a double patterning (DPT) application), the first pattern may be exposed in a first layer and the second pattern may be exposed in a second layer, overlaying the first layer. In this way the contrast or an alignment mark may be enhanced. By combining the second pattern in the second layer with the first pattern in the first layer, the resulting mark may have a higher contrast than a standard mark defined in the first layer. Due to design requirements, it may just not be possible to define a mark in a first layer with enough contrast. Especially when a Hard Mask is used for a third layer exposure and alignment to the first layer is needed, the alignment mark according to the present invention may be applied, as will be discussed hereafter.

One may even determine the position of a previous layer without actually having an alignment pattern in that layer, for instance in the DPT process.

Furthermore, in cases of exposing the first and second patterns in different layers, the resulting alignment marks can be aligned using the alignment system already present in the lithographic apparatus. The contrast is made by the second layer exposure and the aligned position is determined by the first layer exposure. It is understood that a second layer of overlay error has no effect on the aligned position provided that the error remains narrower than ± F / 2, where F is the smallest pattern element size printed in the first layer.

As will be discussed hereafter, the whole sequence of applying first and second patterns on one or more layers can be reversed, ie, the large-sized pattern element is exposed in the first layer and the dense pattern of small-sized elements ( for instance trenches) is exposed in the second layer, placed on top of the first layer. In that case the aligned position is determined by the second layer pattern.

In alignment of the invention the alignment mark is composed of a single large-sized pattern element partly overlapping at least two small-sized pattern elements. More specifically, the large-sized element has a width that is larger than the mutual distance between consecutive small-size elements so that the large-sized element will overlap at least to some extent at least two of the small-sized elements. In other variants, however, more than one large-sized pattern element and a large number or small-sized pattern elements is employed. In order to ensure that in the latter times the first and second patterns are matched to one another, the width (W, cf. figure 3B) or the space between consecutive large-sized pattern elements is chosen to be an integer number times the pitch 27 of the small-sized pattern elements 22.

Figures 4A and 4B are further examples of alignment marks. Figure 4A shows three sets 30 of alignment marks 25 that are the result of a single exposure. Due to last trench (line) imaging effects the quality of the outer two trenches (or lines) 25'may be poor. The quality of trenches 25 'is crucial for determining the aligned position and therefore for ensuring a high alignment accuracy. Since these two trenches are semi-dense, this is not an easy task to perform. Figure 4B shows three sets 30 of alignment marks 25 that are the result of a double exposure in accordance with an embodiment of the present invention. The outer trenches (or lines) 25 'now result from a dense pattern 21 and the edges of the patterns formed by the last trenches 25'are well-defined so that high-quality alignments marks are formed on the substrate.

In the described described in connection with figures 3 A and 3B, the first exposure creates a first pattern of relatively small-sized pattern elements 22, while the second exposure creates a second pattern of relatively large-sized pattern elements 23. In other otherwise, however, the situation is reverse. In a first exposure a first pattern of relatively large-sized pattern elements 23 has been created, while the second exposure creates a second pattern of relatively small-sized pattern elements 22.

In further embodiments of the present invention a method is provided for determining the relative displacement or at least two layers provided with respective sets of alignment marks. The method comprises producing a first set of combined alignment marks on a first layer and a complimentary, second set of combined alignment marks on a second layer, provided on top of the first layer. Thereafter the two sets of combined alignment marks are irradiated and the relative displacement between the first and second sets of alignment marks is determined with high accuracy. An example of such an embodiment is shown in figures 5A-5F. Figure 5 A shows a first pattern 21 created at a first exposure area in a first layer 20 or a substrate. The first pattern is of the type including a variety or consecutive small-sized elements 22, which may be the form of a dense pattern at resolution. At another exposure area of the same first layer 20 a second pattern of the type including a multiple or consecutive large-sized elements 24 is exposed, as shown in figure 5D. Next a second layer 29 is placed on top of the first layer 20. At the same exposure area of figure 5 A a third pattern is exposed on the second layer 29, the third pattern is of the type having a multiple or large-sized elements 24 partly overlapping the first pattern (cf. figure 5B). Similarly, on top of the large-sized elements 24 is exposed at the same exposure area or figure 5D a variety or small-sized elements is 22, as shown in figure 5E. Figures 5C and 5F now show the resulting alignment marks 30.31 at both exposure areas. The alignment mark 30 is representative of the X, Y position (at resolution) or the first layer 20, while alignment mark 31 is representative of the X, Y position (at resolution) or the second layer 29. The difference between both positions renders the overlay offset or overlay at resolution. Overly, for determining the overlay at resolution use may be made of overlay sensors present in the lithographic apparatus, for instance alignment sensors of the SMASH type (cf. EP 1 372 040 A2) or Athena type (cf. EP 0 906 590 A1) or any other diffraction / phase grating type or detection system. Moreover, camera or image based systems may be used as well to detect the position of the structures at resolution. In this way it is possible to measure overlay at resolution (or the features of the substrate) by way of an alignment sensor capable of measurement at a lower resolution.

In the embodiment shown in figures 6A-6D the small-sized elements of a pattern are formed by product features at an overlay target area. Figure 6A shows a wafer 40 having a large numbers or dies to be exposed. Figure 6B shows a blown up detail of one of the dies 4 of the wafer 40. It shows the product features 44 of a die 41 ', for instance a large number or parallel word lines in a DRAM memory, trenches, bit lines or control gates. Distortions of the parallel elements, for instance due to lens and reticle distortions, errors which are immersion related, errors in the mask, substrate table or errors caused by lens heating, are present. On top of the photo resist features of figure 6B a second layer is exposed by a number of alignment patterns 42 is provided, each having a set of repetitive alignment pattern elements 43. The resulting product is shown in figure 6D. Each alignment pattern 42 forms together with the existing product features 44, an alignment mark that can be used to determine to local distortion of the die. In fact the distortion may be determined as a function of the location on the die. While in figure 6D three alignment marks 42 are depicted, the number of alignment marks may vary, depending on the product characteristics.

The method may also be used to calibrate for lens heating effects. During exposure or subsequent fields on the substrate the lens or lenses or the projection system is heated up. The heating process influences the characteristics of the lens, i.e., when the lens is heated in the exposure process, the lens distortion has changed. Therefore the lens distortion when the first field is exposed generally differs from the lens distortion when a further field is exposed. Exposed, the pattern exposed on the substrate may be used to determine information about the effects of heating on the lens distortion. Based on this information a calibration of the projection system can be performed, for instance by manipulating the projection system to account for the expected changes in lens distortion during exposure of a substrate. 10071] Although in the above range a constant pitch is used, in other vary a varying pitch or the small-sized elements may be employed as well, for instance varying from almost isolated (ISO) lines, ie, lines having a relatively large pitch , but narrower than the pitch of the large sized elements (alignment mark), to the dense lines shown in figure 6. These small-sized elements are exposed by the exposure light, the exposure light typically having a relatively short wavelength, eg, " blue "light with a wavelength (λ) or about 193 nm. The structures for forming the small-sized elements on the substrate are present on the mask (or reticle) and diffraction of the "blue" light occurs. The diffracted light then passes the exposure lens. Light diffracted from an ISO structure and light from a dense structure pass the lens in different ways. ], 0072] Therefore, patterns with different pitches (ie, small-sized pitches in comparison with the larger pitch or alignment forming the large-sized elements forming the alignment mark) are diffracted differently by the exposure light and experience a different lens distortion ( optical path is different though the exposure lens). The different lens distortion causes a different displacement (offset) or the features on the substrate. By exposing a second pattern with a large-sized pitch on the first pattern (having small-sized elements), the displacement (offset) may be determined. 10073] Alignment is generally performed by one or more alignment sensors, whether an alignment sensor has a light source generating light with a relatively large wavelength, e.g., red light with a wavelength or 633 nm. This light causes diffraction of the elements with a large-sized pitch, i.e., the pitch of the large-sized elements. The alignment sensors are configured to detect the light diffracted from these large-sized elements with a large-sized pitch and therefore are able to perform an alignment process. However, in accordance with an embodiment, the position of the alignment marks is determined by the pattern of small-sized elements and therefore by the different small-sized elements. Since each individual small-sized pitch ends up differently at the substrate (aberration induced displacement), a set of patterns having different pitches may be used to determine information about the effects of the pitches of the features (eg, isolated (ISO) lines and dense lines) on the alignment signal sensed by the alignment sensors. Based on this information an ISO-dense calibration may be performed.

Figures 7A-7B relate to a further embodiment of the invention. In this embodiment alignment marks are defined in a double patterning (DPT) application. The figures show a substrate 45 on top on which a hard mask 46 has been applied. In a fist patterning step a first pattern with relatively small-sized pattern elements or trenches 48 is patterned in the layer 46. The result after the first patterning process is depicted in Figure 7A. Then a second patterning step is performed and a second pattern with relatively large-sized elements 49 is patterned in layer 46. Referring to figure 7B, the combination of the small-sized elements 48 and the large-sized elements 49 renders with an alignment mark. More specifically, the alignment mark itself is defined in the second patterning process, while the aligned position is defined in the first patterning process.

Figure 7C shows an alternative embodiment after the second patterning process some protrusions (lines) 47 remain present in the area occupied by the large-sized pattern elements 49 or Figure 7B. Or, in other words, during patterning of the large-sized elements a subset of the small-sized elements at the areas of the large-sized elements is kept substantially intact. The number of protrusions should be kept small enough to create sufficient contrast for the combined alignment mark to be created, while at the same time the number should be large enough to meet with the pattern density requirements, for instance demanded by the chips manufacturer.

Figures 8A-8E relate to a further embodiment of the present invention, corresponding, similar to the described in connection with figures 7A-7C, an alignment pattern is created in a hard mask layer in a double patterning (DPT) application , more specifically a double exposure application. The object of the present embodiment is to define in a first exposure a pattern (mark) having a good contrast and to add a follow, in a second exposure, the respective process segmentation in order to fulfill a pattern density requirements. The figures show a substrate 45 on top on which a hard mask 46 has been applied. In a fist patterning step a first pattern with relatively large-sized pattern elements or trenches 50 is patterned in the layer 46. The result after the first patterning process is depicted in figures 8A and 8B. In figure 8A a number of large-sized pattern elements 50 is provided, while in figure 8B a similar pattern with large-sized pattern elements 51 is provided with a number of small-sized elements, for instance lines 52, is kept intact. However, the areas 53 in between the small-sized elements 52 are large enough to keep a pattern with essentially large-size pattern elements 51.

In both situations a pattern having a relatively high contrast is achieved. Then the second patterning step is performed and a second pattern with relatively small-sized elements or trenches 54 is patterned in layer 46. Starting from the situation of figure 8A, trenches 54 are patterned in a direction parallel to the grating period, resulting in the layout shown in figure 8C. The combination of the small-sized elements 54 and the large-sized elements 50 renders an alignment mark. The alignment mark shown in figure 8 A has a high contrast that might be required in order to be able to perform the second exposure. However, the mark 8A might violate the customer design rules. This may be or particular use in DPT applications or when a mask is followed by a so-called trim mask.

Starting from the situation of Figure 8B, some parts of the original lines or small-sized elements 52 have been kept intact, the trenches cannot be patterned in the direction parallel to the grating period. Instead of the trenches 55 are patterned in a direction perpendicular to the grating period (cf. the gray areas), resulting in the alignment marks as shown in the cross-section of figure 8D and the top view of figure 8E. At this point, the alignment mark is in compliance with the design rules and the underlying substrate can be etched.

Figures 9A-9C illustrate a further embodiment of the present invention. Figure 9A shows a substrate 45 on top of which a hard mask 60 has been applied. In a manner known as such in the art, the hard mask 60 has been provided with a variety of spacers 62. In other words, on the hard mask 60 features are patterned, a film is formed on the hard mask and its features, the film is partly etched away so that the horizontal surfaces of the features are exposed, leaving only the film material on the sidewalks and the original patterned features are removed. The result is that only the film material is left, the film material forming the spacers 62, as shown in Figure 9A. The spacers consist of a first pattern or small-sized pattern elements.

In a further step and trim mask, applied, removing, a part of the spacers, and resulting in the pattern shown in Figure 9B. The trim mask partly removes the spacers 62 and thus produces a repetitive set of relatively large-sized pattern elements 63. The combination of the small-sized pattern elements (spacers 62) and the large-seized pattern elements 63 forms an alignment mark. Again, the alignment mark is defined in the trim mask while the aligned position is defined by the layer of spacers.

Figure 9C illustrates another embodiment with an alternative layout. The trim mask removes a number of spacers 62, but keeps several spacers 64 in the area occupied by the large-sized element 63 in figure 9B intact in order to be able to comply with certain pattern density requirements.

Figures 10A and 10B illustrate a further embodiment of the present invention. The figures show a substrate, typically a part of a memory chip having a large number of capacitors, in which substrate a deep trench layer 65 is present. Deep trench layer 65 contains a number of deep trenches 67 (depth typically 8 pm or more), typically arranged to form a repetitive set or relatively small-sized pattern elements. Furthermore, the deep trenches 67 (i.e., the small sized pattern elements) are arranged into groups or deep trenches 67 to form a set or repetitive large-sized pattern elements. The groups of deep trenches 67 together form an alignment mark. In figure 10A the alignment mark is comprised of three groups of deep trenches 67. This number may vary and in most applications will be larger than three. Now in order to enhance the contrast of the alignment mark, a part of the upper portion of the deep trench layer 65, at the location of the deep trenches, may be removed, for an instance by an Active Area exposure process. The resulting pattern is illustrated in figure 10B. The removal is performed in such a way that a number of large-sized pattern elements 69 has been created in such a way that the large-sized pattern elements 69 partly overlap a large or small-sized pattern elements 67, while the edges of the large -sized elements 69 are formed by original deep trenches 67. The presence of the large-sized pattern elements improves the contrast of the alignment mark, but the positioning of the alignment mark is still determined by the deep trenches 67.

Contrast enhancement may be especially beneficial in situations where an alignment mark is defined in a deep trench layer underneath a hard mask in one of the subsequent layers. This situation is shown schematically in figure 10C. Figures 10C illustrates the layout of figure 10A, on top of the deep trench layer 65 a further layer 76 and a hard mask 70 have been applied. Due to the presence of the further layer 76 and especially the hard mask 70 the contrast or the alignment mark (cf. figure 10C) might be too low. When the contrast enhancing process or removing a part of the upper portion of the deep trench layer 65, more specifically the Active Area exposure process (or any other processing step that can be used to enhance the contrast), is applied (cf. figure 1 OB) and the subsequent layer 76 and hard mask 70 are provided on top of the processed deep trench layer 65, this results in an alignment mark with a better contrast (cf. figure 10D). The contrast may be enhanced to such extent, the aligned position can be determined by the deep trenches or the first layer (i.e., the deep trench layer 65) even though a hard mask (forming a third layer) is present.

Figures 11A and 11B illustrate a further embodiment of the present invention, in a configuration similar to the configuration described in connection with figures 10A-10D. In the present edition a substrate comprises a deep trench layer 71 in which a variety of deep trenches 72 has been provided. The deep trenches 72 are not grouped, but are more or less equally distributed along the deep trench layer 71. On top of the deep trench layer 71 a further layer 74 and a hard mask 75 has been applied. This configuration, with no alignment mark is defined, is shown in figure 11 A. In order to provide the substrate with an alignment mark, at several locations the upper portion of the deep trenches 72 has been removed so that a number of large-sized elements or recesses 77 are present in the upper portion of the deep trench layer 71. The recesses can be made by any process, for instance by Active Area exposure process. When the recesses have been made, the further layer 74 and further the hard mask 75 is applied on top of the deep trench layer 71. The recesses 77 together with the deep trenches 72 form an alignment mark. The contrast of this alignment mark is determined by the recesses 77, while the aligned position is determined by the trenches 72 in the deep trench layer 71.

Figures 12A-12C illustrate a further embodiment of the invention, the concept of combining different alignment patterns to form an alignment mark is applied to via layers. Figure 12A shows a substrate 89 composed of a variety of layers 78-84 placed on top of each other. Layers 81 and 82 port provided with groups 85 of metal contacts or vias 86 for interconnecting metal layers 80 and 82. The vias 86 form a repetitive set of small-sized pattern elements in the sense of the present invention. The vias are also arranged in groups 85, each group forming an element or a set of relatively large-sized elements. In situation these small-sized pattern elements are not further processed, they may be considered to form an alignment mark. In figure 12A three groups of vias 86 are depicted, although in practice the number of groups forming together an alignment mark may be different. However, the contrast of this type of alignment may prove to be insufficient. In order to improve the contrast of the alignment mark (while keeping the accuracy of the original alignment mark defined by the vias 86), the upper portion of the vias may undergo a metal exposure process to render the configuration shown in figure 12B.

The metal exposure process causes the upper portion of the vias to define a repetitive set of large-sized elements 87, each element 87 being sized and arranged to partly overlap the group 85 or vias 86. The combination of the small sized pattern elements (ie, the vias 86) and the large size elements (ie, the metal exposed portions) form an alignment mark. The contrast of this alignment mark is improved since it is determined by the large-sized metal exposed portions 87, while the accuracy (aligned position) is determined by the small-sized vias 86 (since the edges of the alignment mark are formed by vias 86, as can be seen in Figure 12B).

In Figure 12C, another embodiment of the present invention is illustrated. In this embodiment the vias 86 are sized and arranged for a set of repetitive small-sized pattern elements, similar to the illustrated discussed in connection with figure 12 A, but the small-sized pattern elements are not grouped into a set forming relatively large -sized elements 85. The present version of the alignment mark is only formed after a metal exposure process to provide the configuration as shown in figure 12C. The metal exposed portions 88 define a set of large-sized elements, that, in combination with the small-sized elements formed by the vias 86, form an alignment mark. The metal exposed portions 88 are sized and arranged so that the edges of the alignment are formed by vias 86 and not by the metal exposed portions, as shown in figure 12C. Due, the alignment mark provides a good contrast since it is determined by the large-sized metal exposed portions 88, while the accuracy (aligned position) is high since this is determined by the small-sized vias 86. In this edition the vias are exposed as trenches, while in other occasions the vias are exposed as contact holes.

The method comprises providing the first and second patterns in one or more scribe lanes between exposure fields of the substrate. For instance, by providing the first pattern of relatively small sized pattern elements in the left one of the scribe lanes or a first field of a substrate, providing the second pattern of relatively large sized pattern elements in the right scribe lane of the first field and repeating the steps of providing the first and second patterns in the scribe lanes of a second field of the substrate, the second field abutting the first field so that the pattern provided in one of the scribe lanes of the first field overlaps the pattern provided in one or the scribe lanes of the second field, for instance by overlappingly exhibiting the first and second field (stitching), an alignment mark in the scribe line may be achieved. A similar process in possible in case of an alignment mark provided in the upper and lower scribe lane of the field.

As will be appreciated, in several of the illustrated in the Figures, the marks are substantially rectangular. As will be further appreciated, the marks need not be perfectly rectangular, but may include minor irregularities in shape including, for example, comers that are not perfectly square, and sides that are not perfectly straight and even. Instead, they are just ought to be sufficiently rectangular to act as gratings for alignment purposes.

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 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 "Read may be considered as synonymous with the more general terms" substrate "or" target portion ", respectively. The substrate referred to may be processed, before or after exposure, in for example a track (a tool that typically applies to a layer of resist to a substrate and develops the exposed resist), a metrology tool and / or an inspection tool. Where applicable, the disclosure 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 the term substrate used may also refer to a substrate that already contains multiple processed layers.

Although specific reference may have been made above to the use of the invention in the context of optical lithography, it will be appreciated that the invention may be used in other applications, for example imprint lithography, and where the context allows , is not limited to optical lithography. In imprint lithography a topography in a patterning device the pattern created on a substrate. The topography of the patterning device may be pressed into a layer or resist supplied to the substrate whereupon the resist is cured by applying electromagnetic radiation, heat, pressure or a combination thereof. The patterning device is moved out of the resist leaving a pattern in it after the resist is cured.

The terms "radiation" and "beam" used include compass and all types of electromagnetic radiation, including ultraviolet (UV) radiation (eg, having a wavelength of or about 365.355.248.193, 157 or 126 nm) and extreme ultra-violet (EUV radiation (eg, having a wavelength in the range of 5-20 nm), as well as particle beams, such as ion beams or electron beams.

The term "lens", where the context allows, may refer to any one or combination of various types of optical components, including refractive, reflective, magnetic, electromagnetic and electrostatic optical components.

While specific expired of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described. For example, the invention may take the form of a computer program containing one or more sequences of machine-readable instructions describing a method as disclosed above, or a data storage medium (eg, semiconductor memory, magnetic or optical disk) having such a computer program stored therein.

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. Other aspects of the invention are set out as in the following numbered clauses: 1. A method of providing a set of alignment marks on a substrate, the method including: exposing a first pattern on at least one exposure area or a layer of a substrate , the first pattern including a set of repetitive elements having a first element size; exposing a second pattern about the first pattern, the second pattern including a set of repetitive elements or a second element size, the second element size being different from the first element size, being the elements of the first and second patterns at least partly overlap and combine to form a set of repetitive large-sized alignment marks, such that edges of the alignment marks in the direction or repetition are formed by small-sized elements. 2. A method as claimed in claim 1, whether a width (W) or a space between consecutive large-sized pattern elements is an integer number of times a pitch or the small-sized pattern elements. 3. A method as claimed in claim 1 or 2, the first pattern comprising small-sized elements and the second pattern comprising large-sized elements. 4. A method as claimed in claim 1 or 2, the first pattern comprising large-sized elements and the second pattern comprising small-sized elements. 5. A method as claimed in any of the preceding claims, the first pattern is exposed in a first layer and the second pattern is exposed in a second layer, at least partially overlaying the first layer. 6. A method as claimed in any of the claims 1-4, both the first pattern and the second pattern are exposed in the same layer. 7. A method as claimed in any of the preceding claims, the alignment marks are for use in imaging a pattern and the small-sized elements are sized at resolution. 8. A method as claimed in claim 7, including aligning the combined alignment marks at a resolution of the small-sized elements. 9. A method as claimed in any of the preceding claims, including determining a position or a combined alignment mark at a resolution of the small-sized elements. 10. A method as claimed in any of the preceding claims, including determining a contrast between a combined alignment mark and its surroundings at a resolution of the large-sized elements. 11. A method as claimed in any of the preceding claims, including: providing a first set of alignment marks according to the first pattern in a first layer comprising small-sized elements and the second pattern in a second layer comprising large-sized elements; providing a second set of alignment marks according to the first pattern in a first layer comprising large-sized elements and the second pattern in the second layer comprising small-sized elements; determining a position of the first layer from the first set of alignment marks; determining a position of the second layer from the second set of alignment marks; and determining an overlay offset from the determined position of the first layer and the determined position of the second layer. 12. A method as claimed in any of the preceding claims, in which the small-sized elements form a dense pattern formed by lines or trenches. 13. A method as claimed in any of the preceding claims, each element is substantially rectangular, and the large-sized elements have a width that is larger than a mutual distance between consecutive small-size elements. 14. A method as claimed in any of the preceding claims, the small-sized elements or a pattern formed by product features at an overlay target area. 15. A method as claimed in any of the preceding claims, whether during patterning of the large-sized elements a subset of the small-sized elements at the areas of the large-sized elements are kept substantially intact. 16. A method as claimed in any of the preceding claims, including providing a variety of alignment marks having varying pitch between the small-sized pattern elements. 17. A method of calibrating a projection system or a lithographic apparatus, including the method: a) when the projection system is in an initial condition, exposing a first pattern on at least one exposure area or a layer of a substrate, the first pattern including a repetitive set of small-sized elements and exposing a second pattern including a set of large-sized elements on the least one exposure area on top of the first pattern, including the elements of the first and second patterns partly overlap and combined form a set of repetitive large-sized alignment marks, such that the edges of the alignment marks in the direction of repetition are formed by small-sized elements; b) when the projection system is in heated condition, repeating the exposure process a); c) determining information about the distortion of the alignment marks as a function of the temperature or at least a portion of the projection system. 18. A method as claimed in claim 17, including adapting the characteristics of the projection system as a function of the temperature based on the predetermined information about said distortion. 19. A method as claimed in any of the preceding claims, the first and second patterns are provided in one or more scribe lanes between exposure fields of the substrate. 20. A method as claimed in any of the preceding claims, including: providing the first pattern of relatively small sized pattern elements in one of the scribe lanes or a first field of a substrate; providing the second pattern of relatively large sized pattern elements in an opposite scribe lane or the first field; and repeating the steps of providing the first and second patterns in the scribe lanes of a second field of the substrate, the second field abutting the first field so that the pattern provided in one of the scribe lanes of the first field overlaps the pattern provided in one of the scribe lanes of the second field. 21. A method as claimed in claim 20, the alignment mark is provided according to a method as claimed in any of claims 1-19. 22. A method of determining a relative displacement or at least two layers provided with respective sets of alignment marks, including: producing a first set of combined alignment marks on a first layer and a complimentary, second set of combined alignment marks on a second layer , provided on top of the first layer, in accordance with any of claims 1-19; irradiating the two sets of combined alignment marks; and detecting the relative displacement between the first and second sets of alignment marks. 23. A device manufacturing method including transferring at least one pattern from a patterning device on a substrate of the device, transferring a pattern comprising: transferring a first pattern on at least one exposure area or a layer of a substrate, the first pattern including a repetitive set of elements having a first element size; transfer ring a second pattern on the least one exposure area on top of the first pattern, the second pattern including a repetitive set of elements or a second element size, the second element size being larger or narrower than the first element size, being the elements of the first and second patterns partly overlap and combine to form a set of repetitive large-sized alignment marks, such that the edges of the alignment marks in the direction of repetition are formed by small-sized elements. 24. A device manufacturing method according to claim 23, the alignment marks are provided by a method as claimed in any of claims 1 -22. 25. A lithographic apparatus arranged to provide a pattern of alignment marks from a patterning device on a substrate, in which the apparatus is arranged and constructed so as to: - expose a first pattern on at least one exposure area or a layer of the substrate, the first pattern including a repetitive set of elements having a first element size; - expose a second pattern on the least one exposure area on top of the first pattern, the second pattern including a repetitive set of elements or a second element size, the second element size being larger or narrower than the first element size, being the elements or the first and second patterns partly overlap and combine to form a set of repetitive large-sized alignment marks, such that the edges of the alignment marks in the direction of repetition are formed by small-sized elements. 26. An apparatus as claimed in claim 25, where the apparatus is arranged to provide a set of alignment marks in accordance with any of claims 1-22.

Claims (1)

A lithography device comprising: an illumination device adapted to provide a radiation beam; a carrier constructed to support a patterning device, the patterning device being capable of applying a pattern in a section of the radiation beam to form a patterned radiation beam; a substrate table constructed to support a substrate; and a projection device adapted to project the patterned radiation beam onto a target area of the substrate, characterized in that the substrate table is adapted to position the target area of the substrate in a focal plane of the projection device.