FIELD OF INVENTION

The present invention generally relates to nanoporous membranes, and more particularly to a method for use in forming nanoporous membranes which using silicon nanowires.

BACKGROUND

A nanoporous membrane is conventionally known as a substantially thin membrane having nanopores that are within 1 to 100 nm in diameter. It has been observed that the rapid growth in using nanoporous membranes in a variety applications such as in highly selective transfer masks; filtering means for biochemical purposes, biomedical and material researches and studies; as part of sensing membrane layer; anti-reflection surface for solar cells; and as photonic crystals gradually necessitates superior developments focusing in its fabrication methods, and in some cases on the ability to control the physical and chemical properties of the pores.

At present a large number of nanoporous membranes are fabricated using lithographic methods which in various occasions would lead to resolution and cost imposed limitations, in addition to using material (s) that is prone to chemical structure alterations. Apart from the above discussed unsettling tribulations, applications using such flimsy materials are limited and in many cases the respective processing methods are not compatible with the flow of semiconductor device fabrication.

Whilst many prior art and technology substitutions may be expedient and considerably enhanced in regards to the fabrication of nanoporous membranes, the current conditions or challenges to to provide a method that is at least independent of chemical structures has yet to be thoroughly resolved.

Proceeding from the above, there is a need to provide a device and method that is able to resolve the abovementioned drawbacks in regards to the fabrication of nanoporous membranes.

The present invention is particularly developed to overcome the aforementioned complications.

It is therefore a primary object of the present invention to provide a method for use in fabricating nanoporous membranes that is independent of chemical structures.

It is further object of the present invention to provide a method thereof for use in fabricating or forming nanoporous membranes using silicone nanowires. It is yet another object of the present invention to provide a method for use in fabricating or forming a nanoporous membrane which is independent of lithographic resolution.

In another object of the present invention there is provided a method for use in fabricating or forming a nanoporous membrane which is compatible for semiconductor device processing.

Further objects and advantages of the present invention may become apparent upon referring to the preferred embodiments of the present invention as shown in the accompanying drawings and as described in the following description.

SUMMARY OF INVENTION

There is disclosed a method for use in forming a nanoporous membrane using silicon nanowires . The primary steps of the present invention includes providing a substrate; forming a catalyst layer on said substrate; growing silicon nanowires on said substrate; depositing membrane layer materials as a base for formation of nanopores; and etching the silicon nanowires selectively . BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

In order to provide a comprehensive understanding of the nature of the invention, reference should be made to the accompanying drawings and the subsequent description. Briefly, the drawings are :

FIG 1 shows the nanoporous membrane formed in accordance with the preferred embodiments of the present invention;

FIG 2 shows a surface and cross sectional view of these nanopores in accordance with a preferred embodiment of the present invention; FIG 3 and FIG 4 provide a flow chart for the steps involved in the fabrication process to form the nanopores, which is extended to another process of transferring the nanoporous pattern into a substrate for formation of flexible polymers films; FIG 5 shows the steps involved for pattern transfer of nanoporous membrane to substrate in accordance with a preferred embodiment of the present invention;

FIG 6 shows the steps involved for formation of flexible nanoporous polymer. DETAILED DESCRIPTION

In addition to the drawings, further understanding of the object, construction, characteristics and functions of the invention, a detailed description with reference to the embodiments is given in the following.

It should be noted that the preferred embodiments which will be described in detail herein are provided to assist in further understanding of the invention. The steps involved in attaining the outcome based on the scope of the appended claims are described in their best mode and sequential order, said sequential order may vary and thus the best mode which will be described herein should not be construed as restricting the scope of the invention.

FIG 1 shows the nanoporous membrane formed in accordance with the preferred embodiments of the present invention. The nanoporous membrane (10) of the present invention may be fabricated onto silicon, glass, metal or polymer type substrate as long as it can withstand the growth temperature of the silicon nanowires, which is typically above 350 °C . FIG 2 shows a surface and cross sectional view of these nanopores (12) in accordance with a preferred embodiment of the present invention. Accordingly, the diameter of the pores is directly dependent on the diameter of the grown silicon nanowires. As for the height of the nanopores, they are dependent on the thickness of the membrane material.

FIG 3 provides a flow chart for the steps involved in the fabrication process to form the nanopores (12) , which is extended to another process of transferring the nanoporous pattern into a substrate for formation of flexible polymers films. As mentioned in the preceding paragraphs, the method of the present invention is substantially independent of lithographic resolution and chemical structure of the respective nanoporous material.

Referring to FIG 3 and FIG 4, the first stage is to form nanoporous membrane silicon oxide or silicon nitride. It should be noted that nanoporous membrane material is not limited to silicon dioxide or silicon nitride, as the preferred materials would be in the category of materials with high resistant to the etching methods so as to enable removal of the silicon nanowires for the purpose of the present invention. For instance, the membrane material can be extended to polymer type material such as polyimide, which is highly resistant to potassium hydroxide (KOH) etching.

For this stage, the first step is depositing a thin layer of metal catalyst (13) for silicon nanowire growth (S200) on a substrate (14), whereby the growth may be performed by plasma enhanced chemical vapour deposition (PCVD) (S300) . The next step is the deposition (S400) of silicon oxide or silicon nitride as membrane layer, in which these layers (16) can be deposited by low pressure chemical vapour deposition (LPCPVD) . Then the silicon nanowires (15) are removed so as to form nanopores in the membrane material by means of highly selective etching devoid of damaging the membrane layer. Preferred etching methods include wet etching by potassium potassium hydroxide (KOH) or tetramethylammonium hydroxide (TMAH) ; or by plasma etching with hydrogen bromide (HBr) or sulphur hexafluoride (SF6) .

FIG 5 shows the steps involved for pattern transfer of nanoporous membrane to substrate in accordance with a preferred embodiment of the present invention. In this stage, upon completion in forming the nanoporous membrane, the nanopores are transferred to the underlying layer or substrate (S500) . Using silicon dioxide or silicon nitride as masking layer, the nanopores is etched (S600) into the underlying silicon substrate by wet chemical etching by potassium hydroxide (KOH) or tetramethylammonium hydroxide (T AH) ; or by plasma etching with hydrogen bromide (HBr) or sulphur hexafluoride. Subject to the desired application, the membrane layer can then be selectively removed . Silicon oxide and silicon nitride membrane can be removed (S700) using hydrofluoric acid (HF) . Silicon nitride can also be removed by phosphoric based acid.

FIG 6 shows the steps involved for formation of flexible nanoporous polymer. In this stage, an example of polymer may include polyimide (50) , whereby the membrane layer can be detached from its underlying substrate thus forming flexible nanoporous polymer film. The first step as seen in FIG 6 is to provide the polymer on the substrate (40) . This process is then followed by etching (T200) the silicon nanowires (60) and then releasing (T300) the polymer from the substrate (40) . As an example, for polyimide (50) the membrane layer can be released in hydrofluoric based acid (HF) .

In an alternative approach, the polymer membrane (50) which is formed (F200) on the substrate (40) can be removed (F300) prior to removing the silicon nanowires (60) . An advantage of this method is the etching time for the silicon nanowires ( 60) in wet chemical solution can be reduced by halve because the etchant may attack the nanowires from both sides of the membrane. It should be noted that the nanopores of the nanoporous membrane formed with the method of the present invention has a diameter which is directly dependant on the diameter of the silicon nanowire, and preferably within the range of lOnm to 200nm. The height of the nanopores of the membrane is directly dependent on the thickness of the deposited membrane material.

Although the present invention has been described in terms of the presently preferred embodiments, it is to be understood that such disclosure is not to be interpreted as limiting. Various alterations and modifications will no doubt become apparent to those skilled in the art after having read the above disclosure. The appended claims should be interpreted as covering all alterations and modifications as fall within the scope of invention .