Patent Application
20080090160
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 pattern of magnetic material is formed on the substrate while a magnetic sensor capable of detecting the pattern of magnetic material is integrated with the patterning tool, e.g., a mold or mask.
Additionally, in some examples, multiple layers of structure are created on top of each other using contact lithography with alignment of a patterning tool and the substrate being performed for each such layer using the pattern of magnetic material and the magnetic sensor. It will be readily appreciated that the alignment of the patterning tool for each such layer with the substrate and any preceding layers is very important to the ultimate quality and reliability of the device being fabricated.
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.
Further, as used herein and in the appended claims, the term “deformation” refers to both a plastic deformation and an elastic deformation. As used herein, “plastic deformation” means an essentially non-reversible, non-recoverable, permanent change in shape in response to an applied force. For example, a “plastic deformation” includes a deformation resulting from a brittle fracture of a material under normal stress (e.g., a cracking or shattering of glass) as well as plastic deformations that occur during shear stress (e.g., bending of steel or molding of clay). Also, as used herein, “elastic deformation” means a change in shape in response to an applied force where the change in shape is essentially temporary and/or generally reversible upon removal of the force.
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 deposited on the substrate (130) specifically to receive the pattern of the mold (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 mold (110).
On the left side of the mold (110), as illustrated in
In the example of
As this occurs, the magnetic material (121) loaded onto the additional imprint feature (120) is embedded in the corresponding pattern formed on the substrate (130). In this way, a pattern of magnetic material is formed on the substrate (130) which will be used to align subsequent molds with the substrate (130) as will be described in more detail below.
In this example, the pattern of magnetic material is formed on the substrate (130) at the same time that the mold (110) imprints the main pattern (112) into the substrate (130). Consequently, the pattern of magnetic material is then particularly useful, as will be described below, for aligning subsequent molds that form subsequent layers of structure with the substrate (130) and the structure previously formed on the substrate (130) by the first mold (110) or succeeding molds. As will be appreciated by those skilled in the art, relatively alignment between a first and subsequent patterns transferred or imprinted to the substrate (130) is very important, perhaps more important than the initial alignment of the substrate (130) with a first mold (110) forming a first layer of structure.
As shown in
As in the example of
As will be appreciated by those skilled in the art, the two preceding examples pertain to forming a pattern of magnetic material on a substrate in the context of imprint lithography.
The technique of using a pattern of magnetic material to align a patterning tool and substrate will be described in detail below. It will be clear to those skilled in the art, however, that this technique can be applied with equal utility to both imprint and photographic lithography.
As illustrated in
Due to the relief of this pattern (200) of magnetic material, different magnetic field strengths will occur a set distance above the substrate (130) in the area of the pattern (200). This varying magnetic field will correspond to the high and low points of the pattern (200) or, in other words, the varying distance from that set distance above the substrate to a point on the pattern (200) of magnetic material directly below.
The magnetic field will be relatively strong at points directly above the peaks of the pattern (200) and will decrease in strength to a minimum at points directly above the troughs or valleys of the pattern (200). It is this variation in magnetic field strength that allows the pattern (200) to be used for precise alignment of a mold or other patterning tool with the substrate (130), as will be described in more detail below.
In the example of
During alignment, the distance between a mold and substrate being aligned is generally on the order of tens of nanometers. Consequently, the magnetic field created by the patterned magnetic material (200) can be adequately detected even if the pattern (200) is covered under one or more layers of deposited patterning material.
In some examples, the substrate (130) may have an initial patterned layer (133) already formed thereon. In such cases, another layer of patterning material (211) is provided over the initial patterned layer (133) so that a next patterned layer can be formed therein.
A magnetic sensor head (321) is also incorporated with the patterning tool (310). This magnetic sensor head (321) may include a number of magnetic sensors (320) that are sensitive to the local strength of a magnetic field. These sensors (320) may be disposed on the sensor head (321) in a pattern or with a spacing that corresponds to the spacing of relief features in the pattern (200) of magnetic material on the substrate (130). The sensors (320) may be, for example, Giant Magneto Resistance (GMR) sensors.
When the patterning tool (310) is brought into close proximity with the substrate (130), the sensors (320) of the sensor head (321) on the patterning tool (310) will register the varying magnetic field produced by the pattern (200) of magnetic material on the substrate. As described above, features with a relatively high relief, e.g., peaks, in the pattern (200) will produce a stronger magnetic field at the level of the sensor head (321) than do features with a relative low relief, e.g., troughs or valleys.
Consequently, the sensor head (321) will output a maximized signal when, for example, each of the sensors (320) is precisely aligned with a corresponding peak in the pattern (200) of magnetic material. Alternatively, the sensor head (321) will output a minimized signal when the sensors (320) are precisely aligned over the low points of the pattern (200). In this way, precise alignment between the patterning tool (310) and the substrate (130) can be verified.
The sensor head (321) will output a signal to a processor or controller (325). The processor (325) is programmed to interpret the signal from the sensor head (321) as an indication of whether the sensor head (321) is precisely aligned over the pattern of magnetic material (200).
As will be appreciated by those skilled in the art, a number of different methods could be used to verify, using the magnetic field of the pattern (200), that the sensor head (321) and the patterned magnetic material (200) are precisely aligned, for example, when the output of the sensor head (321) is maximized by aligning individual sensors (320) with high points of the pattern (200) of magnetic material.
The processor (325) will accordingly drive an alignment servo system (330). The alignment servo system (330) may be or comprise any system or device able to adjust the relative positions and orientation of the patterning tool (310) and the substrate (130) on a micro or nano-scale.
The alignment servo system (330) may move both the patterning tool (310) and the substrate (130), just the patterning tool (310) or just the substrate (130). In any of these cases, the alignment servo system (330) is able to change and adjust the relative positions and orientation of the patterning tool (310) and the substrate (130). As indicated, the alignment servo system is capable of making very fine adjustments, on the order of nanometers, to the relative positions and orientation of the patterning tool (310) and the substrate (130).
If the output of the sensor head (321) indicates to the processor (325) that the patterning tool (310) and substrate (130) are not properly or completely aligned, the processor (325) will control the alignment servo system (330) to accordingly adjust the relative positions and orientation of the patterning tool (310) and the substrate (130). This process continues until the signal from the sensor head (321) indicates to the processor (325) that the sensor head (321) and the patterned magnetic material (200) are precisely aligned. This is taken to mean that the patterning tool (310), on which the sensor head (321) is disposed, and the substrate (130), on which the magnetic pattern (200) is disposed, are correspondingly precisely aligned.
When this occurs, the processor (325) stops driving the alignment servo system (330). The patterning tool (310) and substrate (130) are then aligned and prepared for a lithographic transfer of the pattern (312) of the patterning tool (310) to the substrate (130), e.g., into patterning material layer (211). As noted, either imprint or photographic lithography may be used to pattern the material layer (211).
After the pattern (312) has been used to form a desired corresponding structure in the patterning material layer (211), the process may be repeated to form as many additional layers of patterning as are desired. Specifically, another layer of patterning material is deposited over the previous layer, e.g., layer (211). The sensor head (321) is then used to again detect the patterned magnetic material (200) and align a patterning tool with the substrate. The pattern of the patterning tool is then lithographically used to form a desired structure on the uppermost layer of material on the substrate (130). As indicated, this process may be repeated to form as many additional layers of patterning as are desired.
Additionally, a layer of patterning material (step 401) is prepared to lithographically receive a pattern in the form of a desired structure. As indicated above, this layer may be an original, natural surface of the substrate, may be a layer of patterning material deposited on the surface of the substrate or may be a layer of patterning material deposited over a preceding layer of patterning material.
Next, the patterning tool that will form the desired the structure in the layer of material is registered over the substrate. As indicated above, the patterning tool and substrate must be precisely aligned to optimize the production and utility of the device being fabricated.
As described above, a pattern of magnetic material on the substrate produces a spatially varying magnetic field that can be detected by a corresponding sensor head to determine the alignment between the patterning tool and the substrate (step 402). The alignment between the patterning tool and the substrate, as indicated by detection of the magnetic field of the patterned magnetic field, is compared to some standard that indicates that the patterning tool and substrate are properly aligned. This standard may be, for example, a particular signal strength, such as a maximized signal strength, produced by the magnetic sensor head when the sensor head is precisely aligned with the pattern in the magnetic material.
If the magnetic pattern and sensor head are properly aligned (determination 403), the corresponding patterning tool and substrate are considered to be properly and precisely aligned. The pattern on the patterning tool is then lithographically transferred to the pattern-receiving layer or surface of the substrate to form a desired structure therein (step 405).
If, however, the magnetic pattern and sensor head are not properly aligned (determination 403), an alignment system, such as the servo system described above, will be used to adjust the relative positions and orientation of the patterning tool and substrate (step 404). The alignment of the magnetic pattern with the sensor head is then again determined (determination 403).
This loop of the method shown in
After a layer has been lithographically patterned (step 405), the determination is made whether all the desired layers have been completed (determination 406). As indicated herein, a number of patterned layers may be stacked to produce a desired device.
If all the desired layers have been completed (determination 406), the method ends. If, however, additional layers are desired, another layer of patterning material is prepared or deposited on the substrate (step 401). The following steps of the method are then repeated. Specifically, the patterning tool and substrate are aligned (step 402), the alignment is verified (determination 403), the current layer is lithographically patterned (step 405) until all desired layers are completed (determination 406).
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.
