Pre-aligning a substrate in a lithographic apparatus, device manufacturing method, and device manufactured by the manufacturing method

A method of pre-aligning a substrate in a lithographic apparatus is described. The substrate has at least one alignment mark provided on a side of the substrate. The method includes determining a relationship between a position of the at least one alignment mark, at least part of an edge of the substrate, and a center of the substrate. A substrate support is provided to support a substrate, the substrate support having at least one optical view window at a predetermined location to view a part of the side of the substrate. The substrate is placed on the substrate support on the basis of the relationship to position the at least one alignment mark in the at least one optical view window.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to pre-aligning a substrate in a lithographic apparatus, a lithographic apparatus containing an alignment system containing a pre-alignment device configured to perform a pre-alignment method, a device manufacturing method, and a device manufactured according to the device manufacturing method.

2. Description of the Related Art

In a manufacturing process using a lithographic projection apparatus, a pattern in a patterning device is imaged onto a substrate positioned on a substrate support. The substrate is at least partially covered by a layer of energy-sensitive material (also termed resist). Prior to, and after this imaging step, the substrate may undergo various procedures, such as a post-exposure bake (PEB), development, a hard bake, and measurement and/or inspection of the imaged features. These procedures are used as a basis to pattern an individual layer of a device, e.g., an integrated circuit (IC). Such a patterned layer may then undergo various processes such as etching, ion-implantation (doping), metallization, oxidation, chemo-mechanical polishing, etc., all intended to finish off an individual layer. If several layers are required, then the whole procedure, or a variant thereof, will have to be repeated for each new layer. Eventually, an array of devices will be present on the substrate. These devices are then separated from each other by a technique such as dicing or sawing, after which the individual devices can be mounted on a carrier, connected to pins, etc.

Alignment is the process of positioning the image of a specific point on the patterning device to a specific point on the substrate that is to be exposed. Typically, one or more alignment marks, such as a small pattern, are provided on each of the substrate and the patterning device. As indicated above, a device such as an IC may consist of many layers that are built up by successive exposures with intermediate processing steps. Before each exposure, alignment is performed to minimize any positional error between the new exposure and the previous ones, such error being also termed overlay error. A substrate generally may be provided with alignment marks at both sides of the substrate.

An alignment process involves a pre-alignment procedure in which the edge and the center of a (generally circular) substrate are determined, and an alignment procedure in which the substrate is accurately aligned using the one or more alignment marks provided on the substrate. After a substrate has been pre-aligned in a pre-alignment device, the substrate is transferred to a substrate support by a substrate handler, which usually is a robot having an arm for transferring the substrate from the pre-alignment device to the substrate support.

In a pre-alignment procedure, different devices may be used. In a known substrate pre-alignment procedure, a pre-alignment device is used having a pre-alignment support provided with mechanical pins abutting predetermined edge portions of the substrate. Use of such a pre-alignment device presupposes a known diameter of the substrate. If the diameter of the substrate may vary, an offset in the determination of the orientation of the center of the substrate may be introduced, both in terms of an offset in an X direction, an offset in a Y direction, and an offset in a φ (angular) direction (where the substrate essentially extends in an X-Y plane, and φ denotes an angle of rotation of the center of the substrate). In fact, the offset defines a difference between the substrate's geometrical coordinate system and a coordinate system based on the alignment marks provided on the substrate. The offset may be determined when the diameter of the substrate is known. Alternatively, a pre-alignment device may be used having a substrate edge detector relative to which the substrate is rotated on a pre-alignment support of the pre-alignment device. By rotating the substrate and simultaneously measuring the location of the edge, a center X, Y and φ offset may be determined. As a further alternative, a pre-alignment device may be used having a number of spaced substrate edge detectors located along an expected edge portion of a substrate. No rotation of the substrate is necessary to determine a center of substrate, although, if the diameter of the substrate may vary, an X, Y, and φ offset in the determination of the orientation of the center of the substrate may be introduced. These offsets may be determined when the diameter of the substrate is known.

Once the offset referred to above has been determined, an orientation of the particular substrate can be chosen such that the substrate may be placed correctly on a substrate support to perform an alignment procedure.

Following a pre-alignment procedure, in an alignment procedure of a substrate on a substrate support, the image of an alignment mark on the patterning device is positioned accurately to an image of an alignment mark on the substrate.

It is observed that in some technologies, such as micro system technology (MST) and micro electromechanical systems (MEMS), devices are fabricated from both sides of a substrate. Exposures performed on one side of the substrate must be accurately aligned with features previously exposed on the other side of the substrate.

Throughout this specification, reference to an alignment mark being on a particular side of the substrate of course includes the alignment mark being etched into that side of the substrate, and includes the alignment mark having subsequent material deposited on top of it such that it is embedded and is no longer necessarily exposed at the surface.

U.S. Patent Application Publication No. 2002/0109825 A1, which hereby is incorporated by reference in its entirety, discloses a lithographic apparatus which is provided with an optical system, such as a system employing one or more laser beams, built into a substrate table for producing an image of an alignment mark that is provided on the backside of the substrate, i.e., the side of the substrate which is facing the substrate table. The image is located at the plane of the front side of the substrate, and can be viewed by an alignment system from the front side of the substrate. Simultaneous alignment between marks on the back and front of the substrate and a patterning device can be performed using a pre-existing alignment system.

In a production facility where substrates are processed to yield devices, lithographic equipment of different suppliers may be used. The different suppliers generally employ different pre-alignment procedures to determine the edge and the center of the substrate prior to an alignment procedure based on the recognition of one or more alignment marks on the substrate. Therefore, unexpected or at least basically unknown position deviations of the alignment marks may be encountered when processing substrates on different equipment. Moreover, when using one or more alignment marks (sometimes also referred to as alignment targets) on the backside of a substrate, there is a restriction in the positioning of such alignment marks. This restriction stems from the limited physical size of a view window of the optical system used for determining the position of the alignment marks. A pre-alignment method therefore should be designed to place a substrate on a substrate support such that the alignment marks on the backside of a substrate may be viewed in the view window of the optical system, despite the use of lithographic equipment from different suppliers used to produce specific devices.

SUMMARY OF THE INVENTION

It is desirable to provide a pre-alignment method and apparatus allowing the use of equipment from different suppliers while avoiding elaborate pre-alignment processes.

In an aspect of the invention, a method of pre-aligning a substrate in a lithographic apparatus is provided, the substrate having at least one alignment mark provided on a side of the substrate, the method comprising: determining a relationship between a position of the at least one alignment mark, at least part of an edge of the substrate, and a center of the substrate; providing a substrate support to support a substrate, the substrate support having at least one optical view window at a predetermined location to view a part of the side of the substrate; and placing the substrate on the substrate support on the basis of the relationship to position the at least one alignment mark in the at least one optical view window.

According to embodiment of the invention, one or more alignment marks are provided on a side of the substrate in a marking apparatus, such as a lithographic apparatus or other suitable apparatus. By determining the relationship between a position of the at least one alignment mark, the edge and the center of the substrate, and using this relationship when placing, e.g., by a controllable handling apparatus, the substrate on a substrate support of a lithographic apparatus with known characteristics, which may be different from those of the marking apparatus, a substrate may be correctly pre-aligned on the substrate support, with the one or more alignment marks located in a view window of an alignment system of the lithographic apparatus. The relationship may include data indicating a translation and a rotation of a substrate around its center. The data may be stored in, or input to, a control system of the lithographic apparatus.

In another aspect of the invention, a method of pre-aligning a substrate is provided, the method comprising: determining a position of at least part of an edge of the substrate, and a center of the substrate; predetermining a relationship between a position of at least one alignment mark, the at least part of the edge of the substrate, and the center of the substrate; providing the at least one alignment mark on a side of the substrate on the basis of the relationship; providing, in a lithographic apparatus, a substrate support to support a substrate, the substrate support having at least one optical view window at a predetermined location to view a part of the side of the substrate; and placing the substrate on the substrate support to position the at least one alignment mark in the at least one optical view window of the substrate support.

Here, a particular location of the one or more alignment marks may be chosen on the basis of a desired relationship such as to conform to the requirements of a lithographic apparatus in which the substrate is to be processed such as to correctly pre-align the substrate on the substrate support, with the one or more alignment marks located in a view window of an alignment system of the lithographic apparatus. Again, the relationship may include data indicating a translation and a rotation of a wafer around its center, now prior to applying the one or more alignment marks.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The lithographic apparatus may be of a type having two (dual stage) or more substrate tables or “substrate supports” (and/or two or more mask tables or “mask supports”). In such “multiple stage” machines the additional tables or supports may be used in parallel, or preparatory steps may be carried out on one or more tables or supports while one or more other tables or supports are being used for exposure.

FIG. 2shows a wafer W on a wafer table WT, also termed hereinafter: substrate support. Wafer marks WM1and WM2are provided on a side (“back side”) of the wafer W. An optical system is built into the wafer table WT for providing optical access to the wafer marks WM1, WM2on the back side of the wafer W. The optical system comprises a plurality of arms10A,10B. Each arm consists or two mirrors12,14and two lenses16,18. The mirrors12,14in each arm are inclined such that the sum of the angles that they make with the horizontal is 90°. In this way, a beam of light impinging vertically on one of the mirrors will remain vertical when reflected off the other mirror.

In use, light is directed from above the wafer table WT onto mirror12, through lenses16and18, onto mirror14and then onto the respective wafer mark WM1, WM2. Light is reflected off portions of the wafer mark and returns along the arm op the optical system via mirror14, lenses18and16, and mirror12. The mirrors12,14and lenses16,18are arranged such that an image20A,20B of the wafer mark WM1, WM2is formed at the plane of the front (top) surface of the wafer W, corresponding to the front side of the wafer W. The order of the lenses16,18and the mirrors12,14may be different, as appropriate to the optical system. For example, lens18, could be between the mirror14and the wafer W.

It is observed that the arms of the optical system may have different orientations as seen in a plane parallel to the back side of the wafer W, while one end of an arm is situated such that it is below the wafer W, and the opposite end of the arm is situated in the area of the wafer table WT not (fully) covered by the wafer W. It is further noted that the mirrors12,14of an arm of the optical system need not be provided as discrete components, but may be integral with the wafer table WT. For this purpose, appropriate faces may be machined into the wafer table WT, which then may be provided with a coating to improve reflectivity, thus forming the mirrors12,14. As a further alternative, the arms of the optical system may be embodied using optical fibers or coherent optical fiber bundles, and lenses to couple radiation into and out of the fibers.

An alignment system for performing an accurate alignment (following a pre-alignment) may be a through-the-lens (TTL) arrangement, such that the lens system PL between the mask MA and the wafer W is actually the projection lens used for the exposure radiation. However, the alignment system can also be off-axis (OA).

In the method according to an embodiment of the invention, a relationship between the position of at least one alignment mark on a substrate, at least part of an edge of the substrate, and a center of the substrate is to be determined. Such a relationship may be expressed in data which describe an offset between a geometrical coordinate system and an alignment coordinate system coupled to the at least one alignment mark. The offset may be expressed in terms of a translation and a rotation value. The translation value may be a distance between a center of the geometrical coordinate system and a center of the alignment coordinate system, expressed in an X coordinate and a Y coordinate, where the translation is in a X-Y plane. The rotation value may be an angle of rotation around one of the centers, expressed in an angle of rotation φ, where at least part of the edge of the substrate (such as a notch or a flat edge part) may determine a reference angle. This relationship may be established in various ways.

One way of determining a relationship between the position of at least one alignment mark on a substrate, at least part of an edge of the substrate, and a center of the substrate may be seen in performing off-line measurements of the positions on a plurality of substrates, determining an average value of offsets of an X position, a Y position and an angle of rotation of a center of the substrates, and storing the average offset values for the plurality of substrates. Each substrate will have the same (average) relationship assigned to it.

Instead of determining average values for a plurality of substrates, a specific set of values X, Y and φ may be determined for each substrate in an off-line measurement, coupling each set of values to the corresponding substrate, which may be identified by a suitable identifier assigned to it.

An alternative way of determining a relationship between the position of at least one alignment mark on a substrate, at least part of an edge of the substrate, and a center of the substrate may be seen in predetermining this relationship in terms of a selected set of values X, Y and φ previous to providing an alignment mark on the substrate, and only then providing the at least one alignment mark on the substrate in correspondence with the predetermined set of values. This may also be regarded as an off-line procedure.

A further way of determining a relationship between the position of at least one alignment mark on the substrate, at least part of an edge of the substrate, and a center of the substrate may be seen in determining a specific set of values X, Y and φ in an in-line measurement in a pre-alignment device of a lithographic apparatus, before an exposure of the substrate takes place. When the alignment mark is provided at a side (also called: backside) of the substrate opposite to the exposed side of the substrate, the pre-alignment device requires a mark sensor configured to capture an image of the alignment mark while alignment mark is facing a pre-alignment support. Further details of a pre-alignment device are disclosed below.

FIGS. 3 and 4illustrate a pre-alignment device30for performing a pre-alignment procedure to be elucidated below. The pre-alignment device30includes a pre-alignment support32for supporting a substrate33(inFIG. 4the substrate is indicated with broken lines), the pre-alignment support32being rotatable around an axis34such that an angle of rotation of the pre-alignment support32may be measured and controlled in a manner known per se, and not shown or explained in more detail. The pre-alignment support32includes vacuum chambers36which are open at the side facing the substrate33. By lowering a gas pressure in the vacuum chambers36relative to the ambient gas pressure, the substrate33may be engaged fixedly on the pre-alignment support32. The pre-alignment device30further includes an arm-shaped translation actuator38having a vacuum chamber40which is open at a side facing the substrate33. The translation actuator38is movable in the directions of double arrow42by drive devices known per se, and not shown or explained in more detail. The movement of the translation actuator38may be measured and controlled in a manner known per se, and not shown or explained in more detail. By lowering a gas pressure in the vacuum chamber40relative to the ambient gas pressure, the substrate33may be engaged fixedly on the translation actuator38(while at the same time disengaging the substrate33from the pre-alignment support32) and translated as required. On the other hand, the substrate33will be disengaged from the translation actuator while being engaged on the pre-alignment support. The pre-alignment device30further includes an edge sensor44, e.g., embodied as a linear CCD (Charge Coupled Device) sensor, mounted on a structure not shown on which also the pre-alignment support32is mounted. The edge sensor44may optically measure part of the edge of the substrate33located in a recess of the edge sensor44. By rotating the substrate33fixedly engaged on the pre-alignment support32, a predetermined part of the edge of the substrate33may be measured, and from the data produced by the edge sensor, a geometrical center of the substrate33may be determined, as well as the location of specific edge parts such as notches or flat edge parts. The pre-alignment device30further includes an optical mark sensor46interacting with an optical device48. The optical device48basically corresponds to an optical arm10A,10B shown inFIG. 2, and has an alignment mark end50and a mark sensor end52. The alignment mark end50is configured for taking an image of the side of the substrate facing the pre-alignment support32. The mark sensor end52is configured to provide the image to the mark sensor46. In an embodiment, the alignment mark end of the optical device48may be moved relative to the pre-alignment support32in the directions of double arrow42to scan a ring-shaped or ring-section shaped area of the backside of the substrate33(when rotating the substrate33) in order to locate an alignment mark provided on the backside of the substrate33. In a further embodiment, the optical device48may be moved as a whole relative to the pre-alignment support32in the directions of double arrow42to scan a ring-shaped or ring-section shaped area of the backside of the substrate33(when rotating the substrate33) in order to locate an alignment mark provided on the backside of the substrate33. In a further embodiment, the mark sensor46may be moved relative to the optical device48in the directions of double arrow42to scan a ring-shaped or ring-section shaped area of the backside of the substrate33(when rotating the substrate33) in order to locate an alignment mark provided on the backside of the substrate33. In a further embodiment, a combination of two or three of these movements may be established. In any of these movements, the position of the moving object is measured and controlled.

With the measurements made by the edge sensor44, and the combination of the mark sensor46and the optical device48, a relationship between the position of at least one alignment mark on (the backside of) the substrate33, at least part of an edge of the substrate33, and a center of the substrate33may be determined, and may be expressed in a set of offset values X, Y, and φ for the particular substrate33, where the substrate extends in an X-Y plane, and axis34is an axis of rotation.

Subsequently, a desired orientation of the substrate33may be established by the pre-alignment device30while the substrate still is supported in the pre-alignment device30, before a transfer of the substrate from the pre-alignment support32to the substrate support WT takes place, such that the at least one alignment mark will be positioned in the at least one optical view window of the substrate support. In this process, a control device is used to control an angle of rotation of the pre-alignment support32, and a translation of the translation device38on the basis of measurements from the edge sensor44and the mark sensor46. To reach a desired orientation in the pre-alignment device30, the translation actuator38may be used to provide a required translation, and the pre-alignment support32may be used to provide a required rotation. This procedure allows for a transfer using a simple transfer structure, such as a pick and place robot (not shown in detail).

Further, the substrate33may be transferred by the transfer structure from the pre-alignment device30to the substrate support WT without first establishing a desired orientation of the substrate33. In this situation, the desired orientation is established by the transfer structure after taking the substrate33from the pre-alignment device30, and before bringing the substrate33into contact with the substrate support WT such that the at least one alignment mark is positioned in the at least one optical view window of the substrate support. This procedure requires a transfer structure configured to set a desired orientation during the transfer of the substrate33from the pre-alignment device30to the substrate support WT.

Substrates produced on an apparatus of one supplier may be processed on an apparatus of a different supplier using the pre-alignment method and device according to embodiments of the present invention.