A METHOD FOR CREATING STRUCTURES OR DEVICES USING AN ORGANIC ICE RESIST

Abstract

The invention relates to a method for creating an organic resist on a surface of a cooled substrate, the method comprising the steps of condensing a vapour into a solid film on the surface of the cooled substrate; patterning at least part of the solid film by exposing selected portions of said solid film to at least one electron beam thereby creating the organic resist on 5 the surface of the cooled substrate in accordance with a predetermined pattern; wherein the created organic resist remains essentially intact at ambient conditions; and using the created organic resist as a mask for creating semiconductor structures and/or semiconductor devices.

Claims

1. A method for creating an organic resist on a surface of a cooled substrate, the method comprising the steps of a) condensing a vapour into a solid film on the surface of the cooled substrate; b) patterning at least part of the solid film by exposing selected portions of said solid film to at least one electron beam thereby creating the organic resist on the surface of the cooled substrate in accordance with a predetermined pattern; wherein the created organic resist remains essentially intact at ambient conditions; and c) using the created organic resist as a mask for creating semiconductor structures and/or semiconductor devices.

2. A method according to claim 1, wherein the semiconductor structures and/or the semiconductor devices are created in the underlying substrate.

3. A method according to claim 2, wherein the semiconductor structures and/or the semiconductor devices are created in the underlying substrate using an etching process, such as reactive ion etching.

4. A method according to claim 2, further comprising the step of removing the organic resist.

5. A method according to claim 1, wherein the substrate comprises a semiconductor substrate, such as a silicon substrate.

6. A method according to claim 1, wherein the vapour is created from one or more of the following classes of chemicals: hydrocarbon C6-C16, sulfur containing compounds, halogen containing compounds, oxygen containing compounds, nitrogen containing compounds, monomers, and ALD and CVD precursors for metallic layers.

7. A method according to claim 1, wherein the substrate, during exposure of the solid film, is cooled to temperatures below 200 K, such as below 170 K, such as below 150 K, such as below 130 K, such as below 110 K, such as below 90 K, such as around 70 K.

8. A method according to claim 1, wherein the patterning of the solid film is performed by electron beam lithography.

9. A method according to claim 1, wherein the roughness of the edges of the created semiconductor structures and/or semiconductor devices is less than 10 nm, such as less than 8 nm, such as less than 6 nm, such as less than 4 nm, such as less than 2 nm, such as less than 1 nm.

10. A method according to claim 1, wherein a half pitch of the created semiconductor structures and/or semiconductor devices is less than 50 nm, such as less than 40 nm, such as less than 30 nm, such as less than 20 nm, such as less than 10 nm.

11. A method according to claim 1, wherein the cooled substrate is arranged on a cryosystem being arranged in a high vacuum chamber.

12. A method according, to claim 11, wherein the vapour is introduced into the high vacuum chamber via a gas injection system.

13. A method according to claim 11, wherein the solid film has a vapour pressure being smaller than the pressure in the high vacuum chamber in order to prevent sublimation.

14. A method according to claim 1, wherein the vapour comprises molecules with a molecular mass smaller than 100 Daltons.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0072] The invention will now be described in further details with reference to the accompanying drawings, in which:

[0073] FIG. 1 illustrates a formation of an organic resist on a provided substrate,

[0074] FIG. 2 illustrates a vacuum chamber for a solid film formation and subsequent EBL patterning,

[0075] FIG. 3 illustrates a use of an organic resist as a mask for transferring structures to the underlying substrate,

[0076] FIG. 4 illustrates a 3-step manufacturing process for manufacturing a 3D solid structure,

[0077] FIG. 5 illustrates a 2-step manufacturing process for manufacturing a 3D solid structure, and

[0078] FIG. 6 shows in a) AFM profiles and in b) a SEM picture of silicon nanowires.

[0079] While the invention is susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and will be described in detail herein. It should be understood, however, that the following description relates to examples of embodiments, and the invention is not intended to be limited to the particular forms disclosed. Rather, the invention covers all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. Furthermore, all the drawings are not to scale, and therefore any ratio extracted from the drawings is not relevant.

DETAILED DESCRIPTION OF THE INVENTION

[0080] In its most general aspect, the present invention relates to the formation of a solid structure on a surface of a cooled substrate. The solid structure formed on the surface of the cooled substrate remains essentially intact when the substrate is brought from the cooled state to ambient temperatures. Preferably, the solid structure involves an organic resist that may be used as a mask for creating semiconductor structures and/or semiconductor devices.

[0081] FIG. 1 illustrates a step by step process of the formation of the solid structure. FIG. 1a illustrates a substrate 100 which is provided in a high vacuum chamber and which is cooled down to a temperature of for example 110 K. In the next step a vapour which is introduced into the vacuum chamber is condensed when it gets in contact with the surface of the cooled substrate.

[0082] A potential candidate for the vapour is to be condensable under certain circumstances. Typically, the vapour comprises molecules with a molecular mass smaller than 100 Daltons. The vapour may be created from one of the following condensable chemical compounds: common gasses such as carbon dioxide, ammonia, sulfur dioxide or nitrous oxide; noble gases such as xenon; alkanes such as isobutene, heptane, nonane, decane; alcohols such as ethanol and isopropanol; organic solvents such as acetonitrile, chloroform, ethyl acetate, anisole-jenny, anisole or 1.4 dichlorobenzene; organics such as sulfur trioxide or naphthalene; monomers such as styrene.

[0083] The condensed vapour forms a solid film 101 as illustrated in FIG. 1b. FIG. 1c illustrates exposure of selected portions of the solid film 101 to three electron beams 102 in order to form solid structures in the form of an organic resist on the surface of the cooled substrate in accordance with a predetermined pattern. The exposure to the electron beams is performed in the vacuum chamber at low temperatures. An energetic electron beam locally changes the chemical properties of the solid film 101 whereby the organic resist is formed.

[0084] The organic resist is created through a chemical reaction between the solid film 101 and the electron beam 102. Namely, an energetic electron beam 102 locally changes the chemical properties and structure of the solid film 101 thereby changing the chemical composition of the exposed regions of the solid film 101 forming the organic resist.

[0085] Once the exposure of the solid film 101 is completed, the substrate, and thereby also the organic resist, is exposed to ambient conditions. The solid film 101 acts as a negative resist, i.e. parts of the solid film which were not exposed to the electron beams will sublimate, i.e. will be removed, while the exposed parts 103 will remain essentially intact thanks to tight chemical bonds formed between the atoms comprised in the solid film, thereby forming the organic resist 103 as illustrated in FIG. 1d. The organic resist 103 may then be used as a mask for creating semiconductor structures and/or semiconductor devices in the substrate 100.

[0086] FIG. 2 illustrates a vacuum chamber 200 together with a majority of additional features required for the creation of the solid structure. A vapour 201 to be condensed is stored in a vapour chamber 202 and may be introduced into the vacuum chamber 200 through a nozzle 203 mounted above a cryostage 204 and deposited ballistically onto a cold sample 205. The sample is placed onto a sample holder 206 which is connected to a sample transfer arm 207. The sample 205 can be moved inside the vacuum chamber via the sample transfer arm 207. Using the same arm, the sample 205 can be withdrawn from the vacuum chamber, as the arm can be moved back and forth, as indicated by the arrow 208. After the vapour is condensed onto the sample, the solid film created is exposed to at least one electron beam 209 and the solid film is patterned in accordance with a predetermined pattern. The vacuum chamber and the cryostage are cooled by a liquid-nitrogen dewars 210, 211.

[0087] FIG. 3 illustrates a use of the organic resist as a mask for transferring structures to the underlying substrate. In a first step, shown in FIG. 3a, which is performed in a vacuum chamber 300, a vapour 301 is condensed onto a cooled substrate. In this case, the substrate is nonplanar, consisting of a base 302, what may be silicon-on-insulator, a metal layer 303, and a carbon nanotube 304. The next step is exposing the solid film to an electron beam 305, as shown in FIG. 3b, where an organic resist 306 is formed in accordance with a predetermined pattern 307. This step is also performed in the vacuum chamber 300. When the entire structure is taken out from the vacuum chamber to ambient conditions, unexposed parts of the solid film will sublimate, as shown in FIG. 3c. Now, the organic resist 306 may serve as a mask for transferring structures to the underlying metal layer 303 using for example an etching process, such as reactive ion etching 308, as illustrated in FIG. 3d. A small portion of the organic resist 306 is etched away as well during the removal of the underlying metal layer 303. The final step involves the removal of the remaining part of the organic resist 306 The result is a final structure 307, shown in FIG. 3e, which may be a final functional semiconductor device.

[0088] FIG. 4 illustrates how printing of 3D nano-patterns may be performed. Firstly, a solid film 404 is created in a vacuum chamber by condensing a vapour (not shown) onto a substrate 400 and exposing the solid film 404 to electron beams 401 as shown in FIG. 4a. In accordance with a first pattern 402, a first solid structure 403 is formed. Unexposed parts of the solid film 404 will evaporate when exposed to ambient conditions, while the first solid structure 403 will remain intact, as it is shown in FIG. 4b. The next step in the 3D nano-printing process, cf. FIG. 4c, is performed in the vacuum chamber where the vapour 405 is condensed onto the first solid structure 403 and the substrate 400, forming a second solid film 406. FIG. 4d illustrates exposure of the second solid film 406 to the electron beams 407 in accordance with a second pattern 408 whereby a second solid structure 409 is formed. When the structure shown in FIG. 4d is brought to room temperature, the unexposed regions of the solid film 406 sublimate, cf. FIG. 4e. By repeating steps shown in FIGS. 4c-4e additional structures may be provided, cf. FIGS. 4f-4h, whereby advanced 3D structures 410, cf. FIG. 4i, may be formed.

[0089] FIG. 5 illustrates another way of 3D nano-patterns printing. Firstly, a solid film 504 is created in a vacuum chamber by condensing a vapour (not shown) onto a substrate 500 and exposing the solid film 504 to electron beams 501 as shown in FIG. 5a. In accordance with a first pattern 502, a first solid structure 503 is formed. The next step in the 3D nano-printing process, cf. FIG. 4b, is also performed in the vacuum chamber where the vapour is condensed onto the first solid structure 503 and the solid film 504, forming a second solid film 506. FIG. 5b also illustrates exposure of the second solid film 506 to the electron beams 507 in accordance with a second pattern 508 whereby a second solid structure 509 is formed. By repeating steps shown in FIG. 5b additional structures may be provided, cf. FIG. 5c. When the structure shown in FIG. 5c is brought to room temperature, the unexposed regions of the solid film 510 sublimate cf. FIG. 5d. After this sublimation, advanced 3D structures 511, cf. FIG. 5e, may be formed.

[0090] FIG. 6a shows fabrication of silicon nanowires by plasma etching in that FIG. 6a shows AFM profiles evolution of organic ice resist lines on a silicon substrate at three different steps during the etch process: as deposited (upper profile), after silicon etch (middle profile), and after removal (lower profile) of the residual organic ice resist. The etch selectivity between patterned organic ice resist and silicon is 1:6. FIG. 6b shows a SEM view of 400-nm-tall silicon fins made with organic ice resist and plasma etching.