WO2013184219A1

WO2013184219A1 - Systems and methods for patterning samples

Info

Publication number: WO2013184219A1
Application number: PCT/US2013/031730
Authority: WO
Inventors: Dirk R. ENGLUND
Original assignee: The Trustees Of Columbia University In The City Of New York
Priority date: 2012-03-30
Filing date: 2013-03-14
Publication date: 2013-12-12

Abstract

Systems and methods for patterning samples are disclosed herein. In one aspect of the disclosed subject matter, a method for patterning a target sample is disclosed. An exemplary method can include coating a flat donor substrate with a release layer. A resist layer can be spin coated onto the release layer. A pattern can be formed in the resist layer. The resist layer can be removed. Then the resist layer can be transferred onto a target sample. In another aspect of the disclosed subject matter, another method for patterning a target sample is disclosed. In another aspect of the disclosed subject matter, a target sample having a pattern formed by the above methods is disclosed. In another aspect of the invention, a pattern on a target sample formed by the above methods is disclosed.

Description

SYSTEMS AND METHODS FOR PATTERNING SAMPLES

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

This invention is made with government support under Grant No. FA9550-11-1-0014 awarded by the Air Force Office of Scientific Research. The Government has certain rights in the invention.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority from U.S. Provisional Application No. 61/618,353, filed March 30, 2012, and U.S. Provisional Application No. 61/748,584, filed January 3, 2013, which are incorporated by reference herein.

BACKGROUND

The disclosed subject matter relates to techniques for patterning samples.

Techniques for forming a two-dimensional pattern on a flat surface can include electron beam lithography, optical lithography, and nano-imprint lithography. However, it can be challenging to pattern certain samples, such as those with non-flat surfaces or small dimensions. Additionally, while electron beam lithography can be enhanced by using a conductive sample, it can be challenging to perform electron beam lithography on non-conductive samples or samples that are not suitable for electron beam lithography for other reasons, such as being susceptible to damage or alteration by electron beams or being incompatible with a vacuum environment.

There is a need for techniques that allow for patterning samples with non-flat surfaces or small areal dimensions. There is also a need for a technique that allows for electron beam lithography of non-conductive samples.

SUMMARY

Systems and methods for patterning samples are disclosed herein. In one aspect of the disclosed subject matter, a method for patterning a target sample is disclosed. An exemplary method can include coating a flat donor substrate with a release layer. A resist layer can be spin coated onto the release layer. A pattern can be formed in the resist layer, and the resist layer removed and transferred onto a target sample.

In some embodiments, the donor substrate can be a silicon substrate. In some embodiments, the donor substrate can be coated with a release layer having a thickness of 10-40 nm. In some embodiments, the pattern can be formed in the resist layer using one or more of electron beam lithography, optical lithography, and nano- imprint lithography.

In some embodiments, the release layer can be removed by dissolving the release layer in water, and at least a portion of the release layer can remain intact during the foiming of the pattern. In some embodiments, the release layer can be a layer of polyvinyl alcohol (PVA). In some embodiments, the resist layer can be a polymer layer that will float on water, and removing the resist layer can include allowing the resist layer to float to the surface of the water.

In some embodiments, transferring the resist layer can include submerging the target sample in water below the resist layer and lowering the water until the resist layer rests on the target sample. In other embodiments, transferring the resist layer can include submerging the target sample in water below the resist layer and lifting the target sample until the resist layer rests on the target sample.

In some embodiments, the resist layer can be bonded to the target sample. In some embodiments, the bonding can include heating the resist layer to bind the resist layer to the target sample.

The method can also include forming the pattern in the target sample and removing the resist layer. In some embodiments, the pattern can be formed by etching the pattern into the target sample. In some embodiments, the etching can be one of dry etching or wet etching. In some embodiments, the resist layer can be a layer of opaque material or have an opaque coating, and the pattern can be formed in the target sample by optical lithography. In some embodiments, the pattern can be formed in the target sample by exposing the target sample to a radiation selected from the group consisting of electron radiation and ion radiation. The radiation can have an acceleration energy such that the radiation is blocked by the resist layer.

In another aspect of the disclosed subject matter, a method for patterning a target sample is disclosed. An exemplary method can include spin coating a resist layer onto a mask layer disposed on a donor layer. A pattern can be formed in the resist layer. The pattern can then be etched into the mask layer. The resist layer and the donor layer can be removed. Then the mask layer can be transferred onto the target sample.

In some embodiments, the pattern can be formed in the resist layer using one or more of electron beam lithography, optical lithography, and nano-imprint lithography. In some embodiments, the pattern can be etched in the mask layer by reactive ion etching.

In another aspect of the invention, a pattern on a target sample formed by one or more of the above methods can be provided.

The accompanying drawings, which are incorporated and constitute part of this disclosure, illustrate embodiments of the invention and serve to explain the principles of the disclosed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and IB show side and top views, respectively, of an example release layer disposed on a donor substrate in accordance with some embodiments of the disclosed subject matter.

FIGS. 2A and 2B show side and top views, respectively, of an example patterned resist layer and a release layer disposed on a donor substrate in accordance with some embodiments of the disclosed subject matter.

FIGS. 3A and 3B show side and top views, respectively, of an example process for removing a patterned resist layer from a donor substrate in accordance with some embodiments of the disclosed subject matter.

FIGS. 4A and 4B show side and top views, respectively, of an example process for transferring a patterned resist layer onto a target sample in accordance with some embodiments of the disclosed subject matter.

FIG! 5A shows an example patterned resist layer disposed on a target sample in accordance with some embodiments of the disclosed subject matter.

FIG. 5B shows an example patterned resist layer disposed on a patterned target sample in accordance with some embodiments of the disclosed subject matter.

FIGS. 5C, 5D, 5E, and 5F collectively show a process of forming a pattern in a target sample in accordance with some embodiments of the disclosed subject matter. FIGS. 6A and 6B show side and top views, respectively, of an example patterned resist layer and a mask layer disposed on a donor layer in accordance with some embodiments of the disclosed subject matter.

FIGS. 7A and 7B show side and top views, respectively, of an example patterned resist layer and a patterned mask layer disposed on a partially patterned donor layer in accordance with some embodiments of the disclosed subject matter.

FIGS. 8A and 8B show side and top views, respectively, of an example patterned mask layer disposed on a selectively etched donor layer in accordance with some embodiments of the disclosed subject matter.

FIGS. 9A and 9B show side and top views, respectively, of an example patterned mask layer disposed on a selectively etched donor layer in accordance with some embodiments of the disclosed subject matter.

FIGS. 10A and 10B show side and top views, respectively, of an example process for transferring a patterned mask layer from a donor layer to a target sample in accordance with some embodiments of the disclosed subject matter.

FIGS. 11 A and 1 IB show side and top views, respectively, of an example patterned mask layer disposed on a target sample in accordance with some embodiments of the disclosed subject matter.

FIGS. 12A and 12B show side and top views, respectively, of an example patterned target sample in accordance with some embodiments of the disclosed subject matter.

FIG. 13 shows an exemplary method for patterning a target sample in accordance with some embodiments of the disclosed subject matter.

FIG. 14 shows an exemplary method for patterning a target sample in accordance with some embodiments of the disclosed subject matter.

Throughout the drawings, similar reference numerals and characters, unless otherwise stated, are used to denote like features, elements, components or portions of the illustrated embodiments. Moreover, while the disclosed subject matter will now be described in detail with reference to the FIGS., it is done so in connection with the illustrative embodiments.

DETAILED DESCRIPTION

The disclosed subject matter presents systems and methods for patterning samples. In certain exemplary embodiments of the disclosed subject matter, a resist layer can be patterned on a flat donor substrate. The resist layer can be removed from the donor substrate and transferred onto the target sample, which can be non-flat, irregularly shaped, and or small. Then the resist layer can be used as a mask for etching, optical lithography, or electron or ion radiation to thus form the pattern on the target sample.

Referring to FIGS. 1A and 1B, side and top views, respectively, of a release layer 102 disposed on a flat donor substrate 101 are shown. Referring also to FIG. 13, by way of example and not limitation, the flat donor substrate 101 can be coated with a release layer 102 (1301).

Referring to FIGS. 2A and 2B, side and top views, respectively, of a resist layer 103 with a pattern 104 and a release layer 102 disposed on a donor substrate 101 are shown. By way of example and not limitation, the resist layer 103 can be spin coated onto the release layer 102 (1302). A pattern 104 can be formed in the resist layer 103 using any suitable technique (1303). As used herein, "pattern" can refer to any pattern, such as a geometric pattern, a fractal pattern, a linear pattern, or an arbitrary pattern. The flat donor substrate 101 can be any suitable material. For example, if the technique for forming a pattern 104 in the resist layer 103 (1303) is optical or nano-imprint lithography, any flat material can be used for the donor substrate 101. If the technique for forming a pattern 104 in the resist layer 103 ( 1303) is electron beam lithography, the flat donor substrate 101 can be a conductive material. For example, the flat donor substrate 101 can be a doped silicon (Si) substrate or a metallic substrate.

After forming a pattern 104 in the resist layer 103 (1303), the resist layer 103 can be removed (1304). Referring to FIGS. 3 A and 3B, side and top views, respectively, of removing a resist layer 103 with a pattern 104 from a donor substrate

101 are shown (1304). For example, the resist layer 103 can be removed by dissolving the release layer 102 (1304). By way of example and not limitation, the release layer 102 can be of any suitable material and any suitable thickness such that at least a portion of the release layer 102 remains intact during the forming of the pattern 104 (1303) and the release layer 102 dissolves when exposed to a solvent, thereby releasing the resist layer 103 (1304). The release layer 102 can be a polymer material that is water soluble. By way of example and not limitation, the release layer

102 can have a thickness of 5-40 nm, e.g., 10-40 nm. By way of example and not limitation, the release layer 102 can be a layer of polyvinyl alcohol (PVA) having a thickness of 10-40 nm. By way of example and not limitation, the release layer 102 could be any other material, whether water soluble or not, that can be selectively removed by suitable techniques while leaving the patterned resist layer 103 intact. For example, the release layer 102 can be an inorganic material, such as a thin layer of silicon dioxide (SiO₂). which can be removed by hydrofluoric acid.

By way of example and not limitation, the resist layer 103 can be any polymer mat will float on water 111. For example, the resist layer 103 can be poly(methyl methacrylate) (PMMA) or any other positive-tone electron beam lithography material, such as ZEP520, a proprietary resist, or any other electron beam lithography resist (positive tone or negative tone). The resist layer 103 can be removed (1304), e.g., by allowing the resist layer 103 to float to the surface of the water 111 in tank 110.

Referring to FIGS. 4A and 4B, side and top views, respectively, of transferring a resist layer 103 with a pattern 104 onto a target sample 105 are shown (1305). The resist layer 103 can be transferred onto the target sample 105 ( 1305). By way of example and not limitation, the resist layer 103 can be transferred onto the target sample 105 by submerging the target sample 105 in water 111 below the resist layer 103 and lowering the water 111 until the resist layer 103 rests on the target sample 105 (1305). By way of example and not limitation, the resist layer 103 can be transferred onto the target sample 105 by submerging the target sample 105 in water 111 below the resist layer 103 and lifting the target sample 105 until the resist layer 103 rests on the target sample 105 (1305). By way of example and not limitation, the resist layer 103 can be transferred mechanically onto the target sample 105 (1305), such as by elastomer stamping (discussed below). The target sample 105 can be any material, can have any shape including arbitrary shapes, and can have any dimensions including small dimensions, e.g., down to a micron or smaller. By way of example and not limitation, if the resist layer 103 is a polymer resist, the resist layer 103 can deform to cover the surface of a non-flat target sample 105. As used herein, "water suspension" refers to the techniques of transferring a layer, such as the resist layer 103, onto a target, such as the target sample 105, described in the foregoing paragraph.

Referring to FIG. 5 A, a resist layer 103 having a pattern 104 disposed on a target sample 105 is shown. The resist layer 103 can be bonded to the target sample 105 (1306a). By way of example and not limitation, the resist layer 103 and/or the target sample 105 can be heated to bind the resist layer 103 to the target sample 105 (1306a). By way of example and not limitation, other bonding techniques can be used, for example chemical binding, such as adhesives.

Referring to FIG. SB, a resist layer 103 having a pattern 104 disposed on a target sample 105 having the pattern 104 is shown. The pattern 104 can be formed in the target sample 104 using the resist layer 103 as a mask (1306b). By way of example and not limitation, the pattern 104 can be etched into the target sample 104 using the resist layer 103 as a mask (1306b). As used herein, "etched" or "etching" refers to either wet or dry etching, unless a specific type of etching is stated. Generally, dry etching can be used, but wet etching can also be suitable unless otherwise stated. By way of example and not limitation, the resist layer 103 can be an opaque material or can have an opaque coating, and the pattern 104 can be formed in the target sample 104 by optical lithography using the resist layer 103 as a mask (1306b).

Referring to FIGS. SC, SD, 5E, and SF, a process of forming a pattern

104 in a target sample 105 using a resist layer 103 as a mask is shown (1306b).

Referring to FIG. 5C, by way of example and not limitation, the target sample 105 can include a sample resist layer 105b and a sample substrate 105a. Referring to FIG. 5D, the target sample 105 can be exposed to radiation 120 using the resist layer 103 as a mask. By way of example and not limitation, me radiation 120 can be electron radiation or ion radiation. By way of example and not limitation, the radiation 120 can be short-wavelength (e.g. 10 nm and below) electromagnetic radiation, such as extreme ultraviolet radiation and X-ray radiation. Such short wavelengths can be ineffective in typical contact mask lithography, which employs an opaque mask on a transparent wafer, such as a chromium (Cr) pattern on a quartz wafer. Quartz can become opaque at such short wavelengths. The radiation 120 can have an

acceleration energy such that the radiation 120 is blocked by the resist layer 103. Referring to FIG. 5E, the resist layer 103 can be removed (1307). By way of example and not limitation, the resist layer 103 can be removed by raising the level of water 111 so that the resist layer 103 floats to the surface of the water 111. By way of example and not limitation, the resist layer 103 can be removed mechanically (1307), such as by elastomer stamping (discussed below). Referring to FIG. SF, the sample resist layer 105b can be developed using known techniques relating to soft mask lithography to form the pattern 104 therein (1306b). In the case of electron radiation, the sample substrate 105a can be a conductive material, and the pattern 104 can be a pattern of holes in the sample resist layer 105b. In the case of ion radiation, the pattern 104 can be a pattern of areas implanted with ions (not pictured) in the sample resist layer 105b.

Referring to FIGS. 6A and 6B, side and top views, respectively, of a resist layer 603 with a pattern 604 and a mask layer 602 disposed on a donor layer

601 are shown. Referring also to FIG. 14, the resist 603 layer can be spin coated onto the mask layer 602, which is disposed on the donor layer 601 (1401). The resist layer 603 can be any suitable material, including any suitable material discussed above with respect to resist layer 103. The donor layer 601 can be any suitable material including any material discussed above with respect to flat donor substrate 101. The mask layer

602 can be any suitable material, including a semiconductor material. By way of example and not limitation, the mask layer 602 can be silicon and the donor layer 603 can be an insulator, such as glass or silicon dioxide. Thus the mask layer 602 and the donor layer 603 collectively can be a silicon-on-insulator (SOI) substrate. By way of example and not limitation, the resist layer 603 can be a polymer resist. A pattern 604 can be formed in the resist layer 603 by any of the techniques discussed above with respect to resist layer 103 and pattern 104 (1402).

Referring to FIGS. 7A and 7B, side and top views, respectively, of a resist layer 603 with a pattern 604 and a mask layer 603 with a pattern 604 disposed on a donor layer 601 that is partially patterned 604 are shown. The pattern 604 can be formed in the mask layer 602 by any of the techniques discussed above with respect to forming a pattern in the target substrate 105 or sample resist layer 105b. By way of example and not limitation, the pattern 604 can be etched into the mask layer 602 using the resist layer 603 as a mask (1403). By way of example and not limitation, the pattern 604 can be reactive ion etched into the mask layer 602 using the resist layer 603 as a mask (1403). The resist layer 603 can be removed by any suitable method, such as dissolving the resist layer in a solvent or mechanically removing the resist layer (1404). By way of example and not limitation, if the resist layer 603 is a polymer photoresist, it can be dissolved by a solvent such as acetone (1 04). By way of example and not limitation, oxygen plasma etching can also be used to remove the resist layer 603. For example, oxygen plasma etching can be used in order to keep the sample dry. Referring to FIGS. 8 A and 8B, side and top views, respectively, of a mask layer 602 with a pattern 604 disposed on a donor layer 601 that is selectively etched are shown. The donor layer 601 can be removed by any suitable method (1405). By way of example and not limitation, the donor layer 601 can be selectively etched (1405). By way of example and not limitation, the donor layer 601 can be selectively etching by buffered-oxide etching (1405). By way of example and not limitation, if the donor layer 601 is silicon dioxide and the mask layer 602 is silicon, the donor layer 601 can be selectively etched by a solvent 611 such as hydrofluoric acid or a solution of hydrofluoric acid and water. By way of example and not limitation, the donor layer 601 and the mask layer 602 can be submerged in the solvent 611, which is contained in tank 610. Referring to FIGS. 9A and 9B, side and top views, respectively, of a mask layer 602 with a pattern 604 disposed on a donor layer 601 that is selectively etched are shown.

Referring to FIGS. 10A and 10B, side and top views, respectively, of transferring a mask layer 602 with a pattern 604 from a donor layer 601 to a target sample 605 (1406) are shown. The mask layer 602 can be transferred onto the target sample 605 by any suitable method, including any of the methods discussed above for transferring resist layer 103 (1406). By way of example and not limitation, the mask layer 602 can be transferred by water suspension, as described above.

By way of example and not limitation, the mask layer 602 can be transferred to the target sample 605 (1406) by any of the techniques disclosed in commonly assigned U.S. Provisional Application No. 61/705,896, which is hereby incorporated by reference in its entirety. As used herein, "elastomer stamping" refers to any of the techniques for micro- and/or nano-device transfer disclosed in commonly assigned U.S. Provisional Application No. 61/705,896. For purpose of illustration and not limitation, such techniques can include using a metal tip covered with an elastomer to transfer the mask layer 602 to the target sample 605. The metal tip can be formed from, for example, tungsten. The elastomer can include, for example, polydimethylsiloxanepolydime (PDMS). The elastomer-coated tip can be contacted with the mask layer 602 such that the elastomer deforms and thereby creates a contact surface, thus attaching the mask layer 602 to the tip via the adhesive force between the elastomer and the mask layer 602. The tip can then be positioned over a predetermined location of the target sample 605. The elastomer can relax to its original shape, thus decreasing the contact surface area, and releasing the mask layer 602 onto the target sample 60S (1406).

The target sample 60S can be any material, can have any shape including arbitrary shapes, and can have any dimensions including small dimensions. By way of example and not limitation, if the mask layer 602 is rigid, such as a silicon mask layer 602, the mask layer 602 can remain flat and not deform over small feature sizes (on the scale of microns) on the surface of the target sample 60S when transferred thereto, while the mask can deform to cover the surface for larger scale features (on the scale of tens of microns or more). Conformity to the surface of the target sample 60S can depend on the flexibility of the mask layer 602 that is used, which can depend on the material's Young's modulus and its thickness.

Referring to FIGS. 11 A and 1 IB, side and top views, respectively, of a mask layer 602 having a pattern 604 disposed on a target sample 60S having the pattern 604 are shown. The pattern 604 can be formed in the target sample 60S using the mask layer 602 as a mask by any suitable technique (1407) including any of the techniques discussed above with respect to target sample 10S. By way of example and not limitation, the pattern 604 can be etched into the target sample 60S using the mask layer 602 as a mask (1407).

Referring to FIGS. 12A and 12B, side and top views, respectively, of a target sample 60S having a pattern 604 are shown. The mask layer 602 can be removed by any suitable technique (1408). By way of example and not limitation, the mask layer 602 can be removed from the target sample 60S by any of the techniques discussed above for transferring the mask layer 602 (1408). By way of example and not limitation, the mask layer 602 can be removed by selective etching (1408).

The foregoing merely illustrates the principles of the disclosed subject matter. Various modifications and alterations to the described embodiments will be apparent to those skilled in the art in view of the teachings herein. For example, suitable materials different than those discussed above can be used for the various substrates, layers, and target samples. For example, different patterns can be implemented. For example, different techniques can be used for forming the various layers, forming the patterns, transferring the various layers, and removing various layers. It will thus be appreciated that those skilled in the art will be able to devise numerous techniques which, although not explicitly described herein, embody the principles of the disclosed subject matter and are thus within its spirit and scope.

Claims

1. A method for patterning a target sample, comprising:

coating a flat donor substrate with a release layer,

spin coating a resist layer onto the release layer;

forming a pattern in the resist layer;

removing the resist layer; and

transferring the resist layer onto the target sample.

2. The method of claim 1 , wherein the removing comprises dissolving the release layer in water.

3. The method of claim 2, wherein at least a portion of the release layer remains intact during the forming.

4. The method of claim 3, wherein the coating comprises depositing a layer of polyvinyl alcohol (PVA).

5. The method of claim 3, wherein the spin coating comprises depositing a polymer layer that will float on water, and wherein the removing further comprises allowing the resist layer to float to the surface of the water.

6. The method of claim 5, wherein the transferring comprises:

submerging the target sample in water below the resist layer; and lowering the water until the resist layer rests on the target sample.

7. The method of claim 5, wherein the transferring comprises:

submerging the target sample in water below the resist layer; and lifting the target sample until the resist layer rests on the target sample.

8. The method of claim 1, further comprising bonding the resist layer to the target sample.

9. The method of claim S, wherein the bonding comprises heating the resist layer to bind the resist layer to the target sample.

10. The method of claim 1 , the method further comprising:

forming the pattern in the target sample; and

removing the resist layer.

11. The method of claim 10, wherein the forming the pattern in the target sample comprises etching the pattern into the target sample.

12. The method of claim 10, wherein the resist layer comprises a layer of opaque material, and wherein the forming the pattern in the target sample comprises forming the pattern in the target sample by optical lithography.

13. The method of claim 10, wherein the forming the pattern in the target sample comprises forming the pattern by exposing the target sample to a radiation selected from the group consisting of electron radiation and ion radiation, the radiation having an acceleration energy such that the radiation is blocked by the resist layer.

14. A method for patterning a target sample, comprising:

spin coating a resist layer onto a mask layer disposed on a donor layer; forming a pattern in the resist layer;

etching the pattern into the mask layer;

removing the resist layer;

removing the donor layer; and

transferring the mask layer onto the target sample.

15. The method of claim 14, wherein the etching comprises reactive ion etching.

16. The method of claim 14, wherein the removing the resist layer comprises dissolving the resist layer.

17. The method of claim 14, wherein the removing the donor layer comprises selectively etching the donor layer.

18. The method of claim 14, wherein the transferring comprises transferring the mask layer by a technique selected from the group consisting of water suspension and elastomer stamping.

19. A target sample having a pattern formed by the method of claim 10.

20. A pattern on a target sample, formed by the method of claim 10.