Patent Application
20080089470
The accompanying drawings illustrate various embodiments of the principles being described in this specification and are a part of the specification. The illustrated embodiments are merely examples and do not limit the scope of the principles described herein.
Throughout the drawings, identical reference numbers designate similar, but not necessarily identical, elements.
The present specification describes exemplary methods and systems that facilitate alignment of a patterning tool and a substrate for contact lithography. To improve the accuracy, precision, and vibration tolerance of the alignment between the patterning tool and substrate, a capacitive alignment system is incorporated into the patterning tool and substrate. This capacitive alignment system uses a signal transmitted through capacitively paired conductors that are disposed respectively on the patterning tool and substrate to determine the proper alignment of the patterning tool with respect to the substrate or vice versa. Because the capacitive alignment system is integrated into the patterning tool and substrate being aligned, the issues associated with having an alignment system experience different vibrations than the members being aligned are ameliorated.
As used herein and in the appended claims, the term “contact lithography” generally refers to any lithographic methodology that employs a direct or physical contact between a patterning tool or means for providing a pattern and a substrate or means for receiving the pattern, including a substrate having a pattern receiving layer thereon. Specifically, “contact lithography” as used herein includes, but is not limited to, any form of imprint lithography or photographic contact lithography.
As mentioned above, and by way of example, in imprint lithography, the patterning tool is a mold that transfers a pattern to the substrate through an imprinting process. In some embodiments, physical contact between the mold and a layer of formable or imprintable material on the substrate transfers the pattern to the substrate. Imprint lithography, as well as a variety of applicable imprinting materials, are described in U.S. Pat. No. 6,294,450 to Chen et al. and U.S. Pat. No. 6,482,742 B1 to Chou, both of which are incorporated herein by reference in their respective entireties.
In photographic contact lithography, a physical contact is established between a patterning tool, in this case called a photomask or, more simply, a mask, and a photosensitive resist layer on the substrate that serves as the pattern receiving layer. During the physical contact, visible light, ultraviolet (UV) light, or another form of radiation passing through selected portions of the photomask exposes the photosensitive resist or photoresist layer on the substrate. The photoresist layer is then developed to remove portions that don't correspond to the pattern. As a result, the pattern of the photomask is transferred to the substrate.
For simplicity in the following discussion, no distinction is generally made between the substrate and any layer or structure on the substrate (e.g., a photoresist layer or imprintable material layer) unless such a distinction is helpful to the explanation. Consequently, reference herein is generally to the “substrate” irrespective of whether a resist layer or an imprintable material layer is or is not employed on the substrate to receive the pattern. One of ordinary skill in the art will appreciate that a resist or imprintable material layer may always be employed on the substrate of any contact lithography methodology according to the principles being described herein.
As shown in
The surface (132) of the substrate that receives the pattern may be a natural surface of the substrate (130) or may be a layer of material specifically deposited on the substrate (130) to receive the pattern of the patterning tool (110). The arrow (105) represents the action of applying pressure between the mold (112) and the substrate (130) to from a desired structure on the substrate (130) corresponding to the main pattern (112) of the patterning tool (110).
On the left side of the patterning tool (110) and substrate (130), as illustrated in the example of
As will be appreciated by those of ordinary skill in the art, each of the conductors in the two arrays (151-154) can be paired with a respective conductor on the other of the patterning tool (110) or substrate (130) to form a capacitor. The spacing between the patterning tool (110) and substrate (130), which is typically filled with air at normal atmospheric pressure, provides the dielectric element between each of the two respective conductors that form a capacitor.
As shown in
Two corresponding arrays (153, 154) are disposed on the patterning tool (110). The configuration of the arrays (153, 154) on the patterning tool (110) will match that of the arrays (151, 152) on the substrate (130). Consequently, when the patterning tool (110) and substrate (130) are brought into close proximity and aligned, the two arrays (153, 154) on the patterning tool (110) will match up spatially with the two arrays (151, 152) on the substrate (130) such that each element of each array (153, 154) on the patterning tool (110) is aligned with a corresponding element of an array (151, 152) on the substrate (130) to form a capacitor.
Turning again to the arrays (151, 152) on the substrate (130), each element of the first array (151) is electrically connected (157) to one of a pair of terminals (131). Each element of the second array (152) is electrically connected (158) to the other of the pair of terminals (131). A corresponding pair of terminals (133) is disposed on the patterning tool (110).
The two pairs of terminals (131, 133) include conductors located on the surfaces of the patterning tool (110) and substrate (130) respectively such that when the patterning tool (110) and substrate (130) are brought into close proximity, the terminals (131, 133) form a pair of capacitors in the same manners as the matched elements of the arrays (151-154) described above.
A first signal generator (140) is connected to one of the terminals (133) on the patterning tool (110). This signal generator (140) produces a periodic electrical signal. This periodic signal may-be, for example, a sine wave or other periodic waveform.
When the patterning tool (110) is in close proximity with the substrate (130), such that the terminals (131, 133) form a pair of capacitors, the periodic signal from the first signal generator (140) will be transmitted through the capacitor formed by a corresponding pair of the terminals (131, 133) and thence to the corresponding array (151) on the substrate (130).
As described above, that corresponding array (151) will also be in a capacitive relationship with an array (154) on the patterning tool (110). Thus, the periodic signal from the signal generator (140) will be transmitted through the capacitors formed by the arrays (151, 154) back to the patterning tool (110). The signal is then input through a connection (155) from that array (154) on the patterning tool (110) to an alignment detection circuit (142) that will be described in more detail below with respect to
A second signal generator (141) is connected to the other of the two terminals (133) on the patterning tool (110). This signal generator (141) produces a periodic electrical signal that is identical to that produced by the first signal generator (140) with the exception that the signal produced by the second signal generator (141) is 180° out of phase with the signal produced by the first signal generator (140).
As described above, when the patterning tool (110) is in close proximity with the substrate (130) such that the terminals (131, 133) form a pair of capacitors, the periodic signal from the second signal generator (141) will be transmitted through the other capacitor formed by a pair of the terminals (131, 133) and to the corresponding array (152) on the substrate (130).
That corresponding array (152) will also be in a capacitive relationship with a corresponding array (153) on the patterning tool (110). Thus, the periodic signal from the second signal generator (141) will be transmitted through the capacitors of the arrays (152, 153) back to the patterning tool (110). The signal is then input through a connection (156) from that array (153) on the patterning tool (110) to the alignment detection circuit (142).
As will be appreciated by those skilled in the art, the configuration described herein is only one example of the principles being disclosed. For instance, the signal generators (140, 141) may, alternatively, be connected to the terminals (131) on the substrate (130) and the alignment detection circuit (142) may, alternatively, be connected to the two arrays (151, 152) on the substrate (130) rather than the arrays (153, 154) on the patterning tool (110). In such an embodiment, the terminals (133) and the arrays (153, 154) on the patterning tool (110) would be interconnected using connections similar to those (157,158) presently shown in connection with the substrate (130).
Within the alignment detection circuit (142), the signal (155, 156) from each array is input respectively, in parallel, to an amplifier (161, 162) and a capacitor (163, 164). Then, each signal (155, 156), after being transmitted in parallel through a respective amplifier/capacitor circuit, is input to a summing amplifier (165).
Because the signals from the two signal generators (140, 141) are 180° out of phase, if all the elements of the arrays (151-154) are properly aligned to form the desired capacitors described above, each of the signals (155, 156) will be equal in amplitude and 180° out of phase. Consequently, the summing amp (165) will add the two signals (155, 156) and produce a null output. If the arrays (151-154) are not properly aligned, some of the capacitive pairs will produce a stronger or weaker relative signal depending on the degree to which each such pair is or is not aligned, and the summing amp (165) will consequently output a non-null signal.
Therefore, when the summing amp (165) outputs a null signal, that indicates that the patterning tool (110) and the substrate (130) are aligned with respect, at least, to the line or axis along with the arrays (151-154,
The alignment processor (170) is also connected to an alignment servo system (171). The alignment servo system (171) is configured to manipulate and adjust the relative alignment of the patterning tool (110) and the substrate (130). In this regard, the alignment servo system (171) may be configured to move the pattering tool (110) relative to the substrate (130), move the substrate (130) relative to the patterning tool (110) or move both the substrate (130) and the patterning tool (110) to adjust their relative positioning and alignment.
If the alignment processor (170) receives a non-null signal from the alignment detection circuit (142), the alignment processor (170) is programmed to drive the alignment servo system (171) to change the relative positioning and alignment of the patterning tool (110) and the substrate (130). As will be described in more detail below, the alignment processor (170) may continued to drive the alignment servo system (171) and reposition the patterning tool (110) and/or the substrate (130) until a null signal is received from the alignment detection circuit (142), indicating a desired alignment between the patterning tool (110) and substrate (130). The alignment processor (170) may also be programmed to determine, based on a change in the signal from the alignment detection circuit (142), in which direction or directions the alignment servo system (171) must move the patterning tool (110) or substrate (130) to produce the desired alignment.
As indicated above, when the alignment detection circuit (142) outputs a null signal, the substrate (130) and patterning tool (110) are aligned with respect to an axis along which the arrays (151-154,
A second alignment detection circuit (143) is also provided to receive the outputs of this second capacitive alignment system. The alignment processor (170) is accordingly programmed to fully align the patterning tool (110) and substrate (130) using the output of both the first alignment detection circuit (142) and the second alignment detection circuit (143). The alignment processor (170) drives the alignment servo system (171) until both the first and second alignment detection circuits (142, 143) both produce a null signal.
When a null signal is received from both the first and second alignment detection circuits (142, 143), this indicates to the alignment processor (170) that the patterning tool (110) and the substrate (130) are fully aligned with respect to two mutually orthogonal axes and are, therefore, aligned such that the contact lithography process can commence to transfer the pattern (112,
In the example of
This pair of arrays (180) is also electrically connected to a pair of terminals (131) in the manner illustrated in
Additionally, a second pair of arrays (181) is arranged as a single linear array that is aligned with a second or X axis of the substrate (130). As indicated above, this pair of arrays may be arranged as alternating elements within the linear pair of arrays (181).
This pair of arrays (180) is also electrically connected to a separate pair of terminals (130-1), again, in the manner illustrated in
Consequently, the terminals (131) and the pair of arrays (180) correspond to the terminals (131) and pair of arrays (151, 152) shown on the substrate (130) illustrated in
Additionally, the terminals (131-1) and the pair of arrays (181) shown in
Consequently, by aligning the first pair of arrays (180) with corresponding arrays on a patterning tool and aligning the second pair of arrays (181) with other corresponding arrays on a patterning tool, the substrate (130) is fully aligned with the patterning tool with respect to both the mutually-orthogonal X and Y axes. However, further rotational alignment may be needed.
It may be noted that the capacitive alignment system will also detect any rotation of either the substrate (130) or a corresponding patterning tool about either of the X or Y axes. If the system that physically moves the patterning tool and substrate allows for such relative rotation about either of the axes in the XY plane, that relative rotation will cause the distance between the conductive arrays on the patterning tool and substrate to vary along the length of at least one of the arrays. Consequently, the null signal being sought by the alignment processor (170,
The capacitance arrays (180) and (181) provide for one point of alignment between the substrate and patterning tool in the XY plane. However, either or both of the substrate and patterning tool may be rotated within in the XY plane. Consequently, a second point of alignment can be used to ensure that the substrate and patterning tool are fully aligned, both as to the plane and rotation within the plane. Consequently, a second set of arrays (190, 191), identical to arrays (180, 181), can also be provided to determine a second point of alignment which accounts for rotational alignment within the XY plane. These arrays (190, 191) are operated, respectively, through terminals (131-2, 131-2) in the same manner described above with respect to the arrays (180, 181). The second set of arrays (190, 191) is located some distance from the first set of arrays (180, 181) as shown in
As will be appreciated by those skilled in the art, the patterning tool and substrate are initially brought into proximity such that the arrays of conductive elements on the patterning tool and substrate can begin to function as capacitors, even if not precisely aligned. Additionally, the initial optical alignment brings the patterning tool and substrate into sufficient alignment such that the system operates within a single desired phase of the signals output by the signal generators (140, 141).
As will be appreciated by those of ordinary skill in the art, the systems being described herein can be implemented with an opaque patterning tool and substrate. However, an optically transparent patterning tool or substrate can also be used. Having an optically transparent patterning tool or substrate may facilitate the rough optical alignment being performed (step 190) in the method of
Next, fine alignment adjustments can be made (step 191) using the capacitive alignment systems described above. For example, as described above with respect to
The alignment-servo system effects adjustment to the relative positions and orientation of the patterning tool and the substrate until the conductive arrays aligned along the X axis are producing a null signal (determination 192). Similarly, the alignment servo system effects adjustment to the relative positions and orientation of the patterning tool and the substrate until the conductive arrays aligned along the Y axis are also producing a null signal (determination 193).
As will be appreciated by those skilled in the art, the step of making fine adjustments (step 191) to the relative positions and orientation of the patterning tool and substrate can be performed with respect to the axes in any order. For example, the alignment may be performed first with respect to either the X or Y axis or may be performed with respect to both axes simultaneously.
When a null signal is achieved from both the X-axis arrays (determination 192) and the Y-axis arrays (determination 193), the patterning tool and substrate are satisfactorily aligned (step 194). The method of
The preceding description has been presented only to illustrate and describe examples of the principles discovered by the applicants. This description is not intended to be exhaustive or to limit these principles to any precise form or example disclosed. Many modifications and variations are possible in light of the above teaching.
