TWI627512B - Lithographic apparatus and device manufacturing method - Google Patents

Abstract

A level sensor senses a localized height of a portion of a surface of a semiconductor substrate. The level sensor includes an optical system having a projection grating and a detector. In operational use in the presence of the substrate, the optical system images the projection grating onto the detector via reflections away from the surface. The level sensor senses the local height by virtue of the imaging of the projection grating on the detector. The level sensor includes an actuator for adjusting the imaging by the optical system.

Description

Microlithography device and device manufacturing method

The present invention relates to a level sensor and a lithography apparatus including the same.

A lithography apparatus is a machine that applies a desired pattern onto a substrate, typically applied to a target portion of the substrate. The lithography apparatus can be used, for example, in the fabrication of integrated circuits (ICs). In this case, a patterned device (which is alternatively referred to as a reticle or pleated reticle) can be used to create a circuit pattern to be formed on individual layers of the IC. This pattern can be transferred to a target portion (eg, including portions of a die, a die, or a plurality of dies) on a substrate (eg, a germanium wafer). Transfer of the pattern is typically performed via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of sequentially adjacent adjacent target portions. Conventional lithography apparatus includes a so-called stepper in which each target portion is irradiated by exposing the entire pattern to a target portion at a time; and a so-called scanner in which a given direction ("scanning" Each of the target portions is irradiated by scanning the pattern via the radiation beam while scanning the substrate in parallel or anti-parallel in this direction. It is also possible to transfer the pattern from the patterned device to the substrate by imprinting the pattern onto the substrate.

In lithography, the flatness of a substrate (eg, a wafer) can be measured and stored, for example, as a height map. A height map can be used to position the relevant target portion of the substrate at an appropriate height Where so as to specify that when the pattern is projected onto the target portion of the substrate, the target portion is positioned within the focus range (focus depth) of the projection system (eg, the projection lens) of the lithography apparatus. The compiled height map is also referred to as "level sensing." The level sensing can be performed by a level sensor. The level sensor can be integral with the lithography device or can be a separate measurement configuration. The level sensor can use optical metrology by projecting a measuring beam onto a substrate and detecting its reflection. In some detection schemes, a grating can be used in the optical path of the measuring beam, for example, a projection grating upstream of the substrate and a detection grating downstream of the substrate.

Consider a level sensor with a projection grating, a detection grating, and a detector. The projection grating is imaged on the surface of the substrate at an angle relative to the (ideal) surface normal. The image is reflected by the surface of the wafer and re-imaged onto the detection grating. Due to the oblique incidence, the change in the height of the substrate will cause the image of the projection grating to be shifted over a certain distance over the detected grating. The shifted image of the projection grating is partially transmitted by the detection grating. The detector detects the intensity of the transmitted image. The intensity indicates the local height of the substrate. In other words, a change in the height of the surface of the substrate causes a change in the image transmitted by the detection grating, thereby allowing the height information to be derived from the detector signal. In the applicable measurement principle, the optical path of the image of the projection grating should be accurately set to specify that the projection grating is correctly imaged onto the detection grating.

Manual calibration of the position of the projection grating and the detection grating relative to each other can be performed during fabrication and/or calibration of the lithography apparatus or level sensor. During such (re)calibration, a calibration beam can be applied and the relative positions of the projection grating and the detection grating can be manually adjusted to specify that the calibration beam correctly projects the projection grating onto the detection grating.

In addition to the fact that the level sensor calibration at the customer site can increase the downtime of the lithography program, the accuracy of such manual calibration can be limited: on the one hand, it can be used for this reason: for safety reasons Reason, usually used compared to the measurement applied during the level sensing The beam is at different wavelengths of light to perform the calibration. Moreover, when the lithography apparatus system is turned off and sufficiently adjusted, the environmental conditions (e.g., temperature) at which the calibration is performed may be different than the environmental conditions during the level sensing of the operational use. The distance between the projection grating and the detection grating can be relatively large. For example, the temperature difference between calibration and operational use can cause the optical frame (grating mounting to the optical frame) to exhibit a thermal deformation effect. The thermal deformation effect of the optical frame can cause the relative position of the grating to deviate from the position set or adjusted during calibration during operation of the lithographic apparatus.

There is a need to provide an improved level sensor calibration.

One aspect of the present invention is directed to a level sensor configured to sense a localized height of a portion of a surface of an object. The level sensor includes an optical system. The optical system includes a projection grating and a detector. In operational use in the presence of the article, the optical system is operable to image the projection raster onto the detector via reflections away from the surface. The level sensor is configured to sense the local height by relying on the imaging of the projection grating on the detector. The level sensor includes an actuator for adjusting the imaging by the optical system.

In an embodiment, the actuator is configured to adjust at least one of: a position of the projection grating; an additional position of the detector; an orientation of the projection grating; and the detection One of the detectors is otherwise oriented.

In an additional embodiment, the optical system includes a detection grating. In operation in the presence of the object, the optical system is operable to image the projection grating onto the detector via reflection from the surface and transmission through the detection grating. The actuator is configured to adjust at least one of: a position of the detection grating; and an orientation of the detection grating.

In an additional embodiment, the optical system includes an optical component. The optical component includes at least one of: a lens and a mirror. The actuator is configured to adjust the following At least one of: one of the optical components; and one of the optical components.

In an additional embodiment, the detector is operative to detect a property of the image of the projected raster on the detector. The level sensor has a control device configured to drive the actuator under the control of the attribute.

The invention also relates to a lithography apparatus configured to image a patterned radiation beam onto a substrate under the control of a height map of a substrate. The lithography apparatus includes a level sensor as discussed above. The level sensor is operative to compile the height map by sensing respective local height values of respective portions of the substrate.

△h‧‧‧ height difference

ACT‧‧‧ actuator

AD‧‧‧ adjuster

B‧‧‧radiation beam

BD‧‧•beam delivery system

C‧‧‧Target section

CO‧‧‧ concentrator

CON‧‧‧Control device

CONV‧‧‧ conversion factor

DB‧‧‧measuring beam

DEF‧‧ defocus distance

DET‧‧Detector

DG‧‧‧Detection grating

FDB‧‧‧Light

IF‧‧‧ position sensor

IL‧‧‧Lighting system/illuminator

IN‧‧‧ concentrator

IO‧‧‧Lighting optics/input optics

LG‧‧‧ light source

M1‧‧‧mask alignment mark

M2‧‧‧Photomask alignment mark

MA‧‧‧patterned device/mask

MAX‧‧‧max

MT‧‧‧Photomask support structure/mask table

OE ₁ ‧ lens

OE ₂ ‧ lens

P1‧‧‧ substrate alignment mark

P2‧‧‧ substrate alignment mark

PG‧‧‧projection grating

PG-DG def‧‧‧relative distance/defocus distance/defocus

PM‧‧‧First Positioning Device

POF‧‧‧Focus plane/focus point

PS‧‧‧Projection System

PW‧‧‧Second Positioning Device/Second Positioner

SO‧‧‧radiation source

TW‧‧‧ test wedge

W‧‧‧Substrate

WT‧‧‧ substrate table

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which FIG. a lithography apparatus of one embodiment; - Figure 2 depicts a height diagram of a level sensor in accordance with an embodiment of the present invention; and - Figures 3A, 3B, and 3C depict the setting of the level sensor to A graphic that focuses on the way.

Figure 1 schematically depicts a lithography apparatus in accordance with one embodiment of the present invention. The apparatus includes an illumination system (illuminator) IL configured to condition a radiation beam B (eg, UV radiation or any other suitable radiation); a reticle support structure (eg, a reticle stage) MT constructed to A patterned device (eg, reticle) MA is supported and coupled to a first locating device PM configured to accurately position the patterned device in accordance with certain parameters. The device also includes a substrate table (eg, wafer table) WT or "substrate support" that is configured to hold a substrate (eg, a resist coated wafer) W and is connected to a configuration to be Parameter to accurately position the second positioning device of the substrate PW. The apparatus further includes a projection system (eg, a refractive projection lens system) PS configured to project a pattern imparted by the patterned device MA to the radiation beam B to a target portion C of the substrate W (eg, including one or more crystals) On the grain).

The illumination system can include various types of optical components for guiding, shaping, or controlling radiation, such as refractive, reflective, magnetic, electromagnetic, electrostatic, or other types of optical components, or any combination thereof.

The reticle support structure supports (ie, carries) the patterned device. The reticle support structure holds the patterned device in a manner that depends on the orientation of the patterned device, the design of the lithographic device, and other conditions, such as whether the patterned device is held in a vacuum environment. The reticle support structure can use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterned device. The reticle support structure can be, for example, a frame or table that can be fixed or movable as desired. The reticle support structure ensures that the patterned device is, for example, in a desired position relative to the projection system. Any use of the terms "folder" or "reticle" herein is considered synonymous with the more general term "patterned device."

The term "patterned device" as used herein shall be interpreted broadly to mean any device that can be used to impart a pattern to a radiation beam in a cross section of a radiation beam to create a pattern in a target portion of the substrate. It should be noted that, for example, if the pattern imparted to the radiation beam includes a phase shifting feature or a so-called auxiliary feature, the pattern may not exactly correspond to the desired pattern in the target portion of the substrate. Typically, the pattern imparted to the radiation beam will correspond to a particular functional layer in the device (such as an integrated circuit) produced in the target portion.

The patterned device can be transmissive or reflective. Examples of patterned devices include photomasks, programmable mirror arrays, and programmable LCD panels. Photomasks are well known in lithography and include reticle types such as binary, alternating phase shift and attenuated phase shift, as well as various hybrid reticle types. An example of a programmable mirror array uses a matrix configuration of small mirrors, each of these small mirrors One can be tilted individually to reflect the incident radiation beam in different directions. The tilted mirror imparts a pattern in the radiation beam reflected by the mirror matrix.

The term "projection system" as used herein shall be interpreted broadly to encompass any type of projection system suitable for the exposure radiation used or for other factors such as the use of a immersion liquid or the use of a vacuum, including refraction, Reflective, catadioptric, magnetic, electromagnetic, and electrostatic optical systems, or any combination thereof. Any use of the term "projection lens" herein is considered synonymous with the more general term "projection system."

As depicted herein, the device is of the transmissive type (eg, using a transmissive reticle). Alternatively, the device may be of a reflective type (eg, using a programmable mirror array of the type mentioned above, or using a reflective mask).

The lithography apparatus may have two (dual stage) or more than two substrate stages or "substrate supports" (and/or two or more than two mask stages or "mask holders") Types of. In such "multi-stage" machines, additional stages or supports may be used in parallel, or one or more stages or supports may be subjected to preliminary steps while one or more other stages or supports are used exposure.

The lithography apparatus can also be of the type wherein at least a portion of the substrate can be covered by a liquid (eg, water) having a relatively high refractive index to fill the space between the projection system and the substrate. The immersion liquid can also be applied to other spaces in the lithography apparatus, such as the space between the reticle and the projection system. Wetting techniques can be used to increase the numerical aperture of the projection system. The term "wetting" as used herein does not mean that a structure such as a substrate must be immersed in a liquid, but rather only means that the liquid is located between the projection system and the substrate during exposure.

Referring to Figure 1, illuminator IL receives a radiation beam from radiation source SO. For example, when the source is a pseudo-molecular laser, the source and lithography devices can be separate entities. Under such conditions, the source is not considered to form part of the lithographic apparatus, and the radiation beam is comprised by, for example, a suitable guiding mirror and/or beam. The beam delivery system BD of the expander is passed from the source SO to the illuminator IL. In other cases, for example, when the source is a mercury lamp, the source can be an integral part of the lithography apparatus. The source SO and illuminator IL along with the beam delivery system BD (when needed) may be referred to as a radiation system.

The illuminator IL can include an adjuster AD configured to adjust the angular intensity distribution of the radiation beam. In general, 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 the pupil plane of the illuminator can be adjusted. In addition, the illuminator IL may include various other components such as a concentrator IN and a concentrator CO. The illuminator can be used to adjust the radiation beam to have a desired uniformity and intensity distribution in its cross section.

The radiation beam B is incident on a patterned device (e.g., reticle MA) that is held on a reticle support structure (e.g., reticle stage MT) and is patterned by the patterned device. In the case where the reticle MA has been traversed, the radiation beam B is transmitted through the projection system PS, and the projection system PS focuses the beam onto the target portion C of the substrate W. With the second positioning device PW and the position sensor IF (for example, an interference measuring device, a linear encoder or a capacitive sensor), the substrate table WT can be accurately moved, for example, to position different target portions C on the radiation beam. In the path of B. Similarly, the first positioning device PM and another position sensor (which is not explicitly depicted in Figure 1) can be used, for example, with respect to the radiation beam after mechanical extraction from the reticle library or during scanning. The path of B is to accurately position the mask MA. In general, the movement of the reticle stage MT can be achieved by means of a long stroke module (rough positioning) and a short stroke module (fine positioning) forming part of the first positioning device PM. Similarly, the movement of the substrate table WT or the "substrate support" can be achieved using a long stroke module and a short stroke module that form part of the second positioner PW. In the case of a stepper (relative to the scanner), the reticle stage MT can be connected only to the short-stroke actuator or can be fixed. The mask MA and the substrate W can be aligned using the mask alignment marks M1, M2 and the substrate alignment marks P1, P2. Although the substrate alignment marks occupy a dedicated target portion as illustrated, the marks may be located between the target portions In space (these marks are called scribe line alignment marks). Similarly, in the case where more than one die is provided on the reticle MA, a reticle alignment mark may be located between the dies.

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

1. In the step mode, when the entire pattern to be applied to the radiation beam is projected onto the target portion C at a time, the mask table MT or "mask support" and the substrate table WT or "substrate support" are caused. It remains substantially stationary (ie, a single static exposure). Next, the substrate stage WT or the "substrate support" is displaced in the X and/or Y direction so that the different target portions C can be exposed. In step mode, the maximum size of the exposure field limits the size of the target portion C imaged in a single static exposure.

2. In the scan mode, when the pattern to be applied to the radiation beam is projected onto the target portion C, the mask table MT or "mask support" and the substrate table WT or "substrate support" are synchronously scanned (also That is, a single dynamic exposure). The speed and direction of the substrate stage WT or "substrate support" relative to the mask stage MT or the "mask support" can be determined by the magnification (reduction ratio) and image reversal characteristics of the projection system PS. In the scan mode, the maximum size of the exposure field limits the width of the target portion in a single dynamic exposure (in the non-scanning direction), and the length of the scanning motion determines the height of the target portion (in the scanning direction).

3. In another mode, when the pattern to be applied to the radiation beam is projected onto the target portion C, the reticle stage MT or "mask support" is held substantially stationary, thereby holding the programmable patterning device And move or scan the substrate table WT or "substrate support". In this mode, a pulsed radiation source is typically used and the programmable patterning device is updated as needed between each movement of the substrate table WT or "substrate support" or between successive pulses of radiation during a scan. This mode of operation can be readily applied to matte lithography utilizing a programmable patterning device, such as a programmable mirror array of the type mentioned above.

Combinations and/or variations or completely different modes of use of the modes of use described above may also be used.

Figure 2 depicts a height diagram of a level sensor as applicable to lithography. The level sensor includes a light source LG that produces a measuring beam. Illumination optics 10 comprise, for example, a lens or lens system that projects a metrology beam onto a projection grating PG. The projection grating PG patterns the incident measuring beam. The thus-measured measurement beam DB projection - for example, using a suitable projection lens - to the height map will be measured on the substrate W. The reflection of the patterned measurement beam DB away from the upper surface of the substrate is projected - for example, using a suitable additional projection lens - onto the detection grating DG. Light from the reflected patterned beam of light transmitted by the detection grating (which is indicated by the EDB in the diagram of Figure 2) is projected onto the detector DET. An example of the implementation of this detector DET is described in U.S. Patent No. 8,351,024, the disclosure of which is incorporated herein by reference.

The projection grating and the detection grating can be formed from any suitable patterned element that is transmissive (as illustrated) or reflective (in another embodiment, not illustrated). The level sensor thus images the projected raster onto the detector via reflections from the upper surface of the substrate (here via the detection grating). The height variation of the surface of the substrate translates into the displacement of the image of the projection grating on the detection grating. This displacement affects the light that is ultimately incident on the detector DET. The detector DET generates a detector output signal indicative of the received light. A detector DET (such as a photodetector) can be configured to generate an output signal indicative of the intensity of the received light. Alternatively, a detector (such as a camera) can be configured to generate an output signal representative of the spatial distribution of the received intensity.

In other embodiments, the detector grating can be omitted and the detector DET can be placed at the location where the detector grating DG is placed in FIG. This configuration provides a more direct detection of the image of the projected raster.

Returning to the embodiment as depicted in Figure 2: Figure 2 depicts two locations of the detection grating DG: The position of the line, wherein the detection grating is in the focus plane POF of the image of the projection grating; and the non-dotted line position, wherein the detection grating is out of focus by the DEF distance.

According to one aspect of the invention, the level sensor further includes an actuator ACT configured to position the projected grating relative to the detection grating or vice versa. Alternatively, the actuator ACT is configured to position the detector DET relative to at least one of the projection raster and the detection raster or vice versa. As is well known, actuators are of the type of motor responsible for moving or controlling a mechanism or system. Figure 2 depicts an example of an actuator positioning detection grating. Alternatively, an actuator (not shown) for positioning the projection grating is provided. As another example, a first actuator that positions a projection grating and provides a second actuator that positions the detection grating is provided. In general, in the embodiment depicted in Figure 2, the actuator sets the relative positions of the projection grating and the detection grating, i.e., the relative positions of the gratings relative to each other. Alternatively, the actuator can (re)locate or redirect the optical elements present in the projection optics of the level sensor. This provision adapts the focal plane of the projection of the projection grating to the detection grating by means of a moving optical element (for example a lens element or mirror). In FIG. 2, an example of such an optical element is indicated as a lens OE1 between the projection grating PG and the substrate W, and another example of this optical element is indicated as projection optics between the substrate W and the detection grating DG. Another lens OE2 in the piece.

In the example where the detection grating is omitted (as described above), the actuator can act on the position of the projection grating, the position of the detector, or the position of the optical element in the projection optics of the level sensor, thus adjusting the projection The position of the focal plane of the projection of the grating and the position of the detector relative to each other. Thus, in general, the actuator is configured to adjust the relative position of the detector and the focal plane of the image of the projected raster (Fig. 2: POF). The actuator can provide any displacement of the focus plane of the image of the projection grating relative to the detector: displacement in the direction parallel to the propagation of the anti-parallel beam, tilt of the focus plane, and/or field of the focus plane The change in curvature. In the latter case, actuated The optical element of, for example, lens OE1 or another lens OE2 in the projection optics can be controllably deformed. The actuator may thus comprise individual actuator elements. The actuator can, for example, comprise a piezoelectric actuator or a Lorentz actuator.

The control device CON drives the actuator to cause the actuator to adjust the relative position of the projection grating and the detection grating. The above relates to (re)adjusting the position of the projection grating, the position of the detection grating, the position of the optical element or the position of the detector by means of an actuator. Similarly, the actuator can be used to (re)adjust the orientation of the projection grating at the far end, detect the orientation of the grating, the orientation of the optical element OE, or the orientation of the detector.

The positioning of the projection grating and the detection grating relative to each other and/or the positioning of the optical elements in the projection optics of the level sensor enable a focused projection onto the detection grating. Thus, accurate level sensing can be performed because the adverse effects associated with defocusing (eg, due to the deviation of the relative positions of the projected grating and the detected grating) can be avoided. Similarly, in the event that the detection grating (as described above) is omitted, the actuator can provide for providing a focus plane of the image of the projection grating at the detection surface of the detector for focus detection. Therefore, accurate level sensing can be performed because the adverse effects associated with defocus can be avoided. Some of these adverse effects are described below.

It is well known that during the lithography process, a layer, such as a resist layer (also referred to as a "photosensitive layer"), may be provided on the substrate that covers other layers that are etched or otherwise processed. In the case of forming an ideal reflective resist layer on the surface of the substrate, the reflected beam propagates to the detector at a uniform angular intensity distribution (i.e., seen in a direction perpendicular to the direction of propagation) and is projected onto the detector. Due to the optical properties of the resist layer and the other layer below, unevenness in angular intensity distribution can result. Because the level sensor provides the focused imaging of the projection grating to the detection grating or on the detector, the uneven angular intensity is obtained when the uneven reflected beam is imaged as a focus. The degree distribution will not affect or only slightly affect the intensity distribution of light as received at the detector DET. However, in the case where the distance between the projection grating and the detection grating deviates from the ideal distance, the imaging on the projection grating to the detection grating may become out of focus. Similarly, if the detection grating is omitted, the image projected onto the detector can become out of focus. If the image is out of focus, the uneven angular intensity distribution due to, for example, the refractive properties of the resist layer and the underlying layer causes an uneven projection onto the detector DET. The level sensor interprets the displacement of the beam onto the detector (which causes the amount of light received at the detector to change) to be interpreted as a change in height of the substrate. The uneven angular intensity distribution of the measuring beam that has interacted with the substrate (in the case of a resist or the like) can thus be interpreted by the detector as the displacement of the beam at the height of the detector (in-height displacement) Therefore, the measurement error is caused in the case where the projection grating and the detection grating are out of focus.

Therefore, these defocus errors can contribute to the total error budget of the lithography projection program.

By providing an actuator that adjusts the relative position of the focal plane of the image of the projected grating relative to the detector and a control device that controls the position of the actuator, the height variation of the beam on the detector can be reduced - due to (eg The optical properties of the layer on the substrate. Therefore, the level sensing accuracy can be increased.

Thus, instead of turning on the lithography device for manually adjusting the relative position or orientation of the relevant components of the level sensor, the actuator is now in an environmental condition similar to the environmental conditions present in the operational use (eg, temperature, use) Controlled remote adjustment is achieved under light from source LG. This contributes to achieving higher accuracy in producing the height maps mentioned above.

In addition, if the effect of a particular resist layer on the intensity distribution of the measured beam received at the detector is known, the processing of the detector signal can be modified for compiling the height map and/or the actuator to control the focal plane. The positioning is to at least partially compensate for the effect of the resist layer. The control device CON itself can thus be subject to specific information control indicating the optical properties of the layer stack on the substrate W.

In an embodiment, via a suitable transcoder, transponder or another signal conversion device, as needed The output signal of the detector DET (ie, the measurement signal) is supplied to the sensing input of the control device CON. The control device can be configured to drive the actuator, for example, in the calibration mode to set the relative position of the image plane of the projection grating in the focus direction depending on the output signal of the detector. The control device CON can thus be configured to operate in at least two different modes (different operating states): a measurement mode in which the control device can maintain the set position; and a calibration mode in which the control device can set the image plane of the projection grating A new relative position in the focus direction relative to the detector (ie, adjusting the relative position). In the calibration mode, the detector output signal can be applied to control the drive actuator to set the relative position of the image plane of the projection grating relative to the detector in the focus direction. Therefore, the detector output signal can be applied in the calibration mode to set the relative position of the image plane of the projection grating relative to the detector in the focus direction. By using the detector output signal during calibration, very few additional devices will be required and accurate calibration can be performed when the detector output signal itself involves calibration. A number of calibration strategies are envisioned, some examples of which are described below.

The calibration strategy can include the control device being configured to operate in a calibration mode as follows.

The control device drives the actuator to sequentially present a plurality of relative positions of the focal plane of the image of the projected grating relative to the detector, such as shifting the detection grating DG over a range of positions, as depicted in FIG. Detect the position of the grating DG. Thereby, a plurality of different relative positions are sequentially set, for example, stepwise using incremental step sizes of relative positions. For each relative position, the detector output signal is received by the control device. In the case of optimization criteria, the control device derives the best detector output signal from the actual detector output signal. Various examples of such optimization criteria can be suggested by those skilled in the art, some of which will be described below. The control device drives the actuator to set the relative position of the focal plane of the image of the projection raster relative to the detector based on the relative position at which the optimal detector output signal is detected. Therefore, set a plurality of relative Position, and the detector output signal is detected at each relative position.

For example, at each relative position of the focal plane of the image of the projected grating relative to the detector, we measure the sensitivity of the detector output signal to the stimulus. The stimuli may be formed, for example, by a movement of the substrate W in a vertical direction (via moving the substrate table WT in a vertical direction, the vertical direction being substantially perpendicular to a top surface of the substrate); or a wedge TW (hereinafter in more detail) Discussed) or movement of another optical component in the optical path of the measuring beam of the level sensor. In the case where the measuring beam of the level sensor is reflected from the substrate table WT itself, the stimulation can be formed by the movement of the substrate table WT in the vertical direction. Due to this stimulus, the detector output signal can be measured for sensitivity to the stimulus, and the detector output signal can be selected to respond optimally to the stimulus. The detector output signal provides the most suitable response to the relative position of the focal plane of the projected raster image relative to the detector to provide the most appropriate relative position of the image plane of the projected raster relative to the detector in the focus direction. The most suitable relative position will then be used during the level sensing in operation. Thus, the control device drives the actuator to set the relative position accordingly. In the case where the stimulus is formed by interference, the optimization criterion may be a minimum value, that is, the relative position of the image plane of the projection grating in which the minimum effect of establishing the interference is located in the focus direction may be provided. The relative position of the best focus. In the case where the stimulation system is formed by the change of the height of the substrate, the optimization criterion may be a maximum value, that is, the relative position at which the maximum sensitivity to the height change is established may be the highest providing the projection grating on the detection grating. The relative position of the good focus.

As described above, the lithography apparatus includes a substrate table WT configured to hold a substrate on which the height map is to be determined, and the lithography apparatus also includes a projection system configured to position the holding substrate relative to the projection system PS of the lithography apparatus. The positioner PW of the substrate stage. In order to perform a sensitive metrology and set the relative position of the focal plane of the image of the projected raster relative to the detector, the control device can be further configured to operate in the calibration mode as follows: the control device communicates with the positioner PW for projection Grating The relative position of the image plane relative to the detector in the focus direction causes the positioner PW to move the position of the substrate stage to a plurality of sequential vertical positions. For example, the positioner PW sequentially moves the substrate table to two, three or more than three vertical positions. A detector output signal of the detector is detected at each of the vertical positions of the substrate stage. Then, for each relative position of the focal plane of the image of the projection grating relative to the detector, the value of the conversion factor CONV is derived from the detector output signal according to the vertical position of the substrate stage. For example, the conversion factor can be a gain factor that changes the amount of change in the output signal indicative of the detector for a unit in the vertical position. The gain value is in fact a measure for contrast. For the sake of clarity: in an imaging system, the image of an object and an object is said to be "best focus" in the case where the contrast of the image is optimal (i.e., the image is as sharp as possible). The contrast becomes poor when moving away from the best focus. For example, when moving the substrate stage in the vertical direction, other possibilities for the conversion factor may include the maximum range of the detector output signal. The optimal relative position of the image plane of the projection grating relative to the detector in the focus direction is established by the maximum value of the self-conversion factor of the control device, that is, the relative position at which the maximum sensitivity is established is regarded as the projection grating focus. The ground is closest to the focus projection onto the detection grating/correspondingly projected to the relative position of the detector.

An example of this conversion factor CONV is depicted in Figure 3A, which represents a curve that is fitted to a (limited number) of values as measured by the conversion factor. The diagram of Figure 3A gives the value of the conversion factor CONV as a function of the relative distance (indicated as "PG-DG def") along the path of the measurement beam between the projection grating and the detection grating as measured. The change in the conversion factor close to the relative position corresponding to the best focus can be low, which is reflected in the relatively flattening of the transition curve near the top. Noise or other interference can affect the process of finding the maximum value MAX in the set of measured conversion factors. Thus, in one embodiment, a second order polynomial is fitted to the value of the conversion factor and the top of the resulting curve is calculated and considered to be the maximum value MAX of the conversion factor CONV. Therefore, noise or other interference can minimally affect the determination of the maximum value of the conversion factor.

In the case where the conversion factor is implemented as the maximum range of the detector output signal, for example, when the substrate stage is moved in the vertical direction, the second-order polynomial can be similarly fitted to the measurement and can be similarly obtained as shown in the figure. The curve of the curve shown in 3A, by which the top of the curve indicates the maximum value of the conversion factor.

Preferably, the set accuracy of the actuator ACT operating on the projection grating or on the detection grating or on the detector is determined. It should be noted that the actuator ACT can be implemented by a piezoelectric actuator. It is well known that piezoelectric actuators can achieve positional adjustment in small increments and exhibit high stiffness, thus providing a stable positioning relative to mechanical vibrations and the like. Alternatively, the actuator may comprise a voice coil actuator also referred to as a "Laurentz actuator."

In piezoelectric actuators, hysteresis can occur, introducing inaccuracies between the actuation voltage and the position. The effect of hysteresis can be avoided by implementing a position feedback control loop. However, for cost reasons and for available capacity, it is preferred to operate the actuator ACT in an open loop mode (i.e., without an internal position feedback control loop). Therefore, a method different from the above method for measuring the most advantageous position (focus position) of an object (projection grating, detection grating or detector) positioned by the actuator is proposed. The proposed method is as follows.

As discussed above, the level sensor images the projected grating onto the substrate to produce an array of illuminated discrete spots on the substrate. Consider a dedicated test substrate or dedicated structure on the substrate table itself (also referred to as a "fiducial"). A dedicated test substrate or dedicated structure on the substrate stage has two adjacent regions that are optically different. The two regions can have different layer stacks. Different stacks are selected such that the reflected beam that exits the different stacks exhibits the greatest possible difference in angular dependence of reflectivity (also known as "apodization"). Each of the plurality of spots in the array now sequentially illuminates the different regions. That is, an area is picked up at the beginning All spots are received and the other area does not receive any spots, and gradually, the number of spots in the first mentioned area decreases and the number of spots in the last mentioned area increases. Therefore, the detector output signal in this sequence indicates a gradual transition from one region to the adjacent region. The output signal can be interpreted as a "height value". The difference between the interpreted height values as measured by the level sensor depends linearly on the defocus distance "PG-DG def" between the projected grating and the detected grating. When the associated object (projection grating or detection grating or detector) is moved through the best focus position, the height difference is measured along with the contrast (eg, via a gain as mentioned earlier). The maximum of the second order polynomial discussed above can then be determined based on the measured height difference.

Figure 3B shows the height difference thus interpreted as a function of the relative distance between the projected grating and the detecting grating along the path of the measuring beam (indicated as "PG-DG def") as measured. Illustration of Δh. The range of relative distances at which the measurements are taken includes the distance associated with the best focus. The linear curve is fitted via the measurement points.

Subsequently, the actuator ACT is repeatedly set by setting and re-measuring the value of the height difference Δh until a specific value corresponding to the height difference of the optimum focus is achieved. It should be noted that the absolute value of the height or the (eg, thermal) drift of the level sensor will not affect the particular value of the height difference corresponding to the best focus. This is illustrated in the diagram of Figure 3C, which gives a conversion factor CONV that varies according to the height difference Δh.

Examples of stimuli provided by operating the test wedge TW are provided below. The test wedge TW is located, for example, between the input optics 10 and the projection grating PG. The test wedge TW, as schematically illustrated in Fig. 2, can be moved under the control of the control device CON, for example, by means of a suitable test wedge actuator (not shown). The control device can be configured to perform the following operations in the calibration phase: placing the test wedge in the optical path between the input optic and the projection grating at each relative position of the focal plane of the image of the projection grating relative to the detector Move between the two positions. In an embodiment, the wedge It is configured to be immediately adjacent to the projection grating at the side of the projection grating facing the input optic 10 such that light is incident on the projection grating at a non-zero average angle. This provides a non-telecentric imaging system. Therefore, we obtain the output signal of the detector (that is, the measured height of the substrate) to the optical path length between the projection grating and the detection grating (that is, the amount of defocus PG-DG def) Sensitivity. This relationship between the measured height and the amount of defocus is thus a linear relationship. In the case where the insertion/removal of the test wedge does not cause a change in the output signal of the detector, the level sensor is focused: the projection grating is respectively focused on the detection grating or projected on the detector. In other words, the control device receives, from the detector, a signal indicative of the displacement of the beam incident on the detector at each relative position of the focal plane of the image of the projection grating relative to the detector, the displacement being due to the test wedge being optical The movement in the path. The test wedge provides asymmetry in the measurement beam as projected onto the detector (as seen perpendicular to the direction of propagation of the measurement beam). As explained above, the greater the effect of this asymmetry in the beam profile, the more the projection raster is imaged onto the detector grating or the more defocused on the detector. Therefore, the more defocusing of the level sensor, the greater the interference of the test wedge. Thus, the optimal relative position of the focal plane of the image of the projected grating relative to the detector can thus be established by the minimum or zero value of the displacement of the control device from the beam due to the movement of the test wedge into the optical path . For example, this interference factor causes a linear change with respect to the defocus "PG-DG def". The minimum interference caused by the test wedge will then indicate the relative position of the projection grating and the detection grating, wherein the projection grating and the detection grating are properly positioned, i.e., positioned to focus.

In the above examples, the test substrate or reference on the substrate stage was used with different optical properties as discussed above to control the set accuracy of the actuator. Another approach involves tilting the substrate table. In this approach, we look at the so-called "Tilt-Independent-Point" (or: TIP) shift induced by PG-DG defocus.

TIP is defined as the (X position or) Y position that is sensed by the level sensor without changing in the case where the substrate table will pivot about an axis passing through the position ((Ry or) Rx inclination). Only the TIP in the Y position is considered for the purposes of the present invention. As is well known, the Y direction is the scanning direction of the lithography apparatus.

The control device drives the positioner to tilt the substrate table into two different positions that are inclined relative to each other. Thus, the measuring beam interacts with at least two locations of the substrate or reference member (i.e., at least two locations on the substrate). Detects the detector output signal at two locations. The height difference is derived from the detector output signals at two locations that are tilted relative to one another. Similar to the above, the derived height difference is associated with the respective relative positions of the focal planes of the image of the projected grating relative to the optical detector. In this alternative, instead of applying two regions having different optical properties, the substrate or reference member is tilted about the Rx axis to provide a predetermined measurement beam that is reflected at a different portion of the measurement beam near the focus of the measurement beam. For example, if the measuring beam is incident on the surface of the substrate (or reference member) more or less close to the focus point POF of the diffracted measuring beam, the tilt may cause a change in the detector output signal. Therefore, the detector output signal is measured at at least two locations that differ from each other in the Rx tilt angle. Again, a curve of the response of the detector output signal to the Rx tilt angle relative to the actuator position can be obtained. This curve can be linear. Due to, for example, the refractive properties of the resist as explained above, reflections outside the focus point will affect the height measurement. Thus, in this embodiment, at least two different tilting locations of the substrate can be used in place of the two different regions on the test substrate. Thus, instead of using a particular test substrate or a particular reference on a substrate stage, a normal substrate (such as an unprocessed substrate) or a flat surface of the substrate table can be used for such measurements.

Once the derived height difference has been correlated with the respective relative positions of the focal plane of the image of the projected raster relative to the detector, the associated height difference can be applied to provide a relative focal plane relative to the detector with respect to the image of the projected raster Feedback from the location. The control device has driven the actuator to project the projection The control device can verify the relative position of the focal plane of the image of the projected grating relative to the detector as follows: the position of the focal plane of the image of the grating relative to the relative position of the detector is set to the optimal position as follows: The determination of the height difference is performed, and the height difference between the determined height difference and the relative position is compared. In the event that the measured height difference does deviate from the height difference associated with the expected relative position, the control device can drive the actuator to correct the relative position and repeat the position verification and actuator drive as needed, thereby repeating The ground reaches the expected location.

A level sensor as described in this document can be included in a lithography apparatus such as a lithography apparatus that uses a transmissive or reflective projection lens.

The control device may be formed from a separate control system including, for example, a data processing system having suitable program instructions, or may be implemented as a task or program on an existing data processing system of a level sensor or lithography device. Although reference may be made herein specifically to the use of lithographic devices in IC fabrication, it should be understood that the lithographic devices described herein may have other applications, such as fabricating integrated optical systems, for magnetic domain memory. Lead to detection patterns, flat panel displays, liquid crystal displays (LCDs), thin film heads, and more. Those skilled in the art will appreciate that in the context of the content of such alternative applications, any use of the terms "wafer" or "die" herein may be considered as the more general term "substrate" or "target portion", respectively. Synonymous. The methods mentioned herein may be treated before or after exposure, for example, in a coating development system (a tool that typically applies a layer of resist to the substrate and develops the exposed resist), a metrology tool, and/or a testing tool. Substrate. Where applicable, the disclosure herein may be applied to such and other substrate processing tools. In addition, the substrate can be processed more than once, for example, to create a multilayer IC, such that the term "substrate" as used herein may also refer to a substrate that already contains multiple processed layers.

Although the use of embodiments of the present invention in the context of the content of optical lithography can be specifically referenced above, it should be appreciated that the present invention can be used in other applications (eg, imprint lithography), and in content The background is not limited to optical lithography. In imprint lithography, the topography in the patterned device defines the pattern produced on the substrate. The patterning device can be configured to be pressed into a resist layer that is supplied to the substrate where the resist is cured by application of electromagnetic radiation, heat, pressure, or a combination thereof. After the resist is cured, the patterned device is removed from the resist to leave a pattern therein.

The terms "radiation" and "beam" as used herein encompass all types of electromagnetic radiation, including ultraviolet (UV) radiation (eg, having a 2020 nm, 248 nm, 193 nm, 157 nm or 126 nm wavelength) and extreme ultraviolet (EUV) radiation (for example, having a wavelength in the range of 5 nm to 20 nm), and a particle beam such as an ion beam or an electron beam.

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

Although the specific embodiments of the invention have been described above, it is understood that the invention may be practiced otherwise than as described. For example, the present invention can 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, a semiconductor memory, disk or optical disk) ), which has this computer program stored in it.

The above description is intended to be illustrative, and not restrictive. Therefore, it will be apparent to those skilled in the art that the invention as described herein may be modified without departing from the scope of the appended claims.

Claims (4)

A level sensor configured to sense a localized height of a portion of a surface of an object, wherein: the level sensor includes an optical system; the optical system includes a projection grating and a detector In operation in the presence of the object, the optical system is operable to image the projection grating onto the detector via reflections away from the surface; the level sensor is configured to be from the projection grating The imaging on the detector senses the local height; the level sensor includes an actuator for adjusting the imaging by the optical system, wherein the actuator is configured to adjust At least one of: a position of the projection grating; an additional position of the detector; and an additional orientation of the detector, wherein the detector is operable to detect the projection grating One of the properties of the imaging on the detector; and the level sensor has a control device configured to drive the actuator under the control of the attribute. A level sensor according to claim 1, wherein: the optical system comprises a detection grating; wherein the optical system is operable to leave the table in operation in the presence of the object Reflecting the surface and imaging the projection grating onto the detector via transmission of the detection grating; and the actuator is configured to adjust at least one of: one location of the detection grating And one of the detection gratings is oriented. A level sensor according to claim 1, wherein: the optical system comprises an optical component; the optical component comprising at least one of: a lens and a mirror; the actuator configured to adjust the following At least one of: one of the optical components; and one of the optical components. A lithography apparatus configured to image a patterned radiation beam onto a substrate under control of a height map of a substrate, wherein the lithography apparatus comprises a request item 1, 2 or 3 A level sensor; the level sensor is operative to compile the height map by sensing respective local height values of respective portions of the substrate.