PATTERN TRANSFERRING BY DIRECT CURRENT PLASMA BASED ION IMPLANTATION AND DEPOSITION

FIELD OF THE INVENTION

[0001] The present invention relates to plasma immersion ion implantation and in particular to plasma immersion ion implantation of substantially planar surfaces.

[0002] The invention has been developed primarily as a method and apparatus for pattern transferring by direct current plasma based ion implantation and deposition and will be described hereinafter with reference to this application. However, it will be appreciated that the invention is not limited to this particular field of use.

BACKGROUND OF THE INVENTION

[0003] Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of the common general knowledge in the field.

[0004] Beam-line ion implantation is the traditional means to fabricate commercial silicon-on- insulator devices, but there is a need to scan the ion beam makes it less desirable, especially for large wafers. Plasma immersion ion implantation (PIII) provides an alternative technique for treating large and irregularly shaped components as well as planar samples in many microelectronic applications.

[0005] Plasma immersion ion implantation techniques are typically conducted in a pulsed mode with pulse durations ranging from several microseconds to several tens of microseconds. This pulsed-mode PIII has several drawbacks. These drawbacks typically include, stray ions impacting the edge and bottom parts of the target stage not contributing to the useful dose, they can also sputter metallic ions from these surfaces and reduce the efficiency of the power modulator, the duty cycle in pulsed-mode PIII is typically quite low, and the finite rise and fall times of the voltage pulses can introduce low-energy ion implantation. In particular, a broad oxygen distribution can make precise control of the thickness of the silicon layer in the SPIMOX process difficult.

SUMMARY OF THE INVENTION

[0006] It is an object of the invention in its preferred form to provide a method and apparatus for pattern transferring by direct current plasma based ion implantation using deposition masking.

[0007] According a first aspect of the invention there is provided a method for pattern transferring by direct current plasma based ion implantation and deposition, the method comprising the steps of: providing a vacuum chamber divided into a first part and a second part; wherein the first part and a second part are connected by an aperture having grid proximal to the aperture; producing a plasma of charged ions in the first part; biasing the ions toward the target for providing a controlled trajectory therebetween; and providing a pattern mask within the ion trajectory for transferring the pattern to the target.

[0008] The method preferably further comprises the step of adjusting the configuration of the apparatus for controlling the ion trajectory. The adjusting the configuration of the apparatus can include any one or more of: adjusting the radius of the aperture; adjusting the distance between the grid and the target, and adjusting the radius of the target.

[0009] Preferably the method also comprises the step of: rotating the grid.

[0010] The biasing of the ions toward the target is preferably in the form of a high voltage direct current potential. More preferably, the biasing is in the form of a high voltage direct current potential of between 500V and 20OkV. The biasing is preferably pulsed; wherein the pulse has a suitably long duty cycle. The duration of the pulse is preferably a few hundreds for microseconds.

[001 1] According a second aspect of the invention there is provided an apparatus for pattern transferring by direct current plasma based ion implantation and deposition; the apparatus adapted to perform the steps according to any one of the previous methods.

[0012] According a second aspect of the invention there is provided an apparatus for pattern transferring by direct current plasma based ion implantation and deposition; the apparatus comprising: a vacuum chamber divided into a first part and a second part; the first part and a second part have a connecting aperture; means for producing a plasma of charged ions in the first part; a multi-perforated grid proximal to the aperture for limiting expansion of the ion sheath beyond the grid; an ion target; a means for biasing the ions toward the target for providing a controlled trajectory therebetween; and a pattern mask within the ion trajectory for transferring the pattern to the target.

[0013] The mask is preferably mounted on a side of the grid facing the first part. Alternatively the mask is mounted on a side of the grid facing the second part.

[0014] Preferably, any one or more of: the radius of the aperture; the distance between the grid and the target; and the radius of the target; is adjustable for controlling the ion trajectory.

[0015] The grid is preferably made of an electrically conducting material. The grid is preferably rotatable.

[0016] The means for biasing is preferably a high voltage direct current potential.

[0017] Preferably, the means for biasing is a high voltage direct current potential of between 500V and 20OkV. More preferably, means for biasing is pulsed; wherein the pulse has a suitably long duty cycle. The duration of the duty cycle is preferably a few hundreds for microseconds.

[0018] The target is preferably a spin-coated silicon wafer and polycarbonate.

[0019] The ion is preferably Argon. The ion density is preferably between 10 ⁸ and 10 ¹² m ^"3 . The working pressure is preferably between 10 ^"4 and 5x10 ^" * Torr.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

FIG. 1 is an example schematic view of an apparatus for pattern transferring by direct current plasma based ion implantation using deposition masking according to the invention;

FIG. 2 is an example of field lines about a stage of an apparatus of FIG. 1, shown for different configurations of the stage;

Figures 3A through 3E are examples of plasma ion trajectory of an apparatus of FIG. 1, shown for different configurations of the stage;

FIG. 4 is an example of implantation area of an apparatus of FIG. 1, shown for different configurations of the stage;

FIG. 5 is an example of implantation area of an apparatus of FIG. 1, shown for different configurations of the stage; FIG. 6 is an example partial schematic an apparatus of FIG. 1 , shown using a rotatable fine grate;

FIG. 7 is an example partial schematic an apparatus of FIG. 1, shown using a course grate;

FIG. 8 is an example flowchart of a method for pattern transferring by direct current plasma based ion implantation using deposition masking according to the invention;

FIG. 9 is an example result obtained by an apparatus and method according to the invention;

FIG. 10 illustrates schematically an alternative apparatus for pattern transfer; FIG. 1 1 illustrates an example masked used in the apparatus of Fig. 10;

FIG. 12 illustrates a photograph of the experimental results produced; FIG. 13 illustrates an alternative mask used in the apparatus of Fig. 10;

FIG 14 illustrates a photograph of the experimental results produced for the mask of FIG. 13; FIG. 15 and FIG. 16 are SEM photographs of the experimental results of Fig.

14;

FIG. 17 illustrates an alternative mask used for protein cell attachment;

FIG. 18A, FIG. 18B, FIG. 19, FIG. 2OA, FIG. 2OB are photographs of results obtained utilising the mask of FIG. 17; and

FIG. 21 illustrates the results of a simulation of the utilisation of an ion focusing lense.

DESCRIPTION OF THE PREFERRED AND OTHER EMBODIMENTS

[0021] It would be appreciated that pattern transferring to a substrate is used in semiconductor fabrication. A method of transferring a pattern can consist of five steps, including

1) spin coating a thin polymer on a substrate;

2) transfers a shadow of the pattern to the spin coated substrate by Lithography;

3) formation of pattern on the spin coated polymer by selective etching;

4) transferring the real pattern to the substrate by non-selective ion implantation;

5) remove of the remaining spin-coated polymer.

[0022] Because substrates have to be treated in different chambers and transported to different sectors of the laboratory, this complex series of treatments makes a successful pattern transfer difficult. It will be appreciated that yield is an important measure in semi-conductor device fabrication.

[0023] In an embodiment, a selective plasma based ion implantation method has been developed that can restrict the need to conduct the above five step procedure. An Ion beam is generated, focused, and directed in a ion beam column. The ion beam will be deflected and stigmatized by electrostatic or magnetic lens system. A stage system is used to position the fabrication area.

[0024] A steady-state directed-current PIII (DC-PIII) is preferably utilised. This techniques can be controlled to provide a suitable method and apparatus for the processing of planar objects, for example a silicon wafer. This process typically

provides a higher quality, a higher throughput, and a low-instrument footprint, then pulsed mode PIII. Further, only a direct current power supply is required instead of more expensive power modulator typically used in conventional PIII.

[0025] In an embodiment, DC-PIII techniques includes a vacuum chamber which is separated into two parts with a conducting grid made of a compatible material (such as silicon coating) to avoid contamination. An extracting aperture is provided that links the two parts of the vacuum chamber. It would be appreciated that the size of this aperture can be fixed or adjustable. A plasma of a selected gas in the first part of the vacuum chamber. A conducting grid spans the aperture for substantially confining the plasma sheath inside the first part of chamber, to limit the expansion of ion sheath beyond the grid to substantially avoid plasma extinction, and to substantially enhance stability thereby enabling long-pulse and DC operation.

[0026] In an embodiment, DC-PIII techniques includes the target stage, on which a target sample can be placed for supporting it in an appropriate position with a device. This target stage is biased using a negative direct-current (DC) voltage. It would be appreciated that the location of the target stage can be either fixed or adjustable. It would be further appreciated that the radius of the target stage may be fixed or adjustable. By way of example, adjustability of the target stage can be achieved by selectively placing circumferential guard-ring around the stage or by adopting a bevelled edge on the bottom of the target stage.

[0027] The selection of the grid can effect both the amount of the "drifting out" ions and implantation area, alleviate ion loss, and minimize contamination due to sputtering of the side and bottom of the target stage.

[0028] The control of the implantation area is typically provided by selecting any one or more of:

> the radius of the extraction aperture,

> the distance between the conducting grid and the target sample, and

> the radius of the target stage.

[0029] Referring to FIG. 1, by way of example only, an apparatus for steady-state directed-current PIII (DC-PIII) is disclosed. The target stage 1 10, is biased using a

negative DC voltage generated by a high voltage DC power supply 115. The vacuum chamber 120 is separated into a first part 121 and a second part 122 by a conducting grid 125 that spans a connecting aperture. This grid is typically made of a compatible material, for example silicon coating, to avoid contamination. The pressure in the vacuum chamber is maintained by a vacuum pump 123.

[0030] A gas is introduced though a port 130. A plasma of this gas is generated in the first part 120 of the chamber by operation of an RF power supply 135 and matching network 136 coupled to antenna coils 137.

[0031 ] The grid substantially confines the plasma inside the first chamber 121, and substantially limits the expansion of ion sheath beyond the grid. It would be appreciated that the grid further enhances stability, thereby enabling suitable long-pulse and DC operation. It would also be appreciated that, as the plasma is substantially confined above the grid, the loss of ions and electrons in the plasma is subsequently small which can improve the efficiency of the plasma source.

[0032] A variable extracting connecting aperture can efficiently control both the amount of the "drifting out" ions and implantation area, alleviate ion loss, and minimize contamination due to sputtering of the side and bottom of the exposed target stage. It would be appreciated that as there is no voltage rise or fall time in DC-PIII, and therefore the low-energy ion component can be dramatically reduced. It would be further appreciated that normal angle implantation across substantially the entire wafer can be achieved because, in steady-state DC-PIII, the ion sheath has already propagated to the grid and ions only track the electric field between the grid and the top surface of the target sample.

[0033] The implanted area can be varied by appropriately adjusting any one or more of: the radius of the extraction aperture 140 (G ₁ . ), the distance between the conducting grid 125 and the target stage H O (H ), and the radius of the target stage 1 10 ( r ).

[0034] By way of example only, the lower part of the chamber desirably has a cylindrical symmetry. In this embodiment, it would be appreciated that a planar simulation, taken along a line adjacent the axis of symmetry can be used to model the

chamber. The extension of the potential beneath the grid can be solved by Laplace's equation in two-dimensional (2-D) cylindrical coordinates as:

dr ² r dr dz ²

[0035] The centered difference approach is used to approximate the potential, whereby:

dr ² ~ (dr) ²

[0036] Therefore, the Laplace's equation can be expressed in a 2-D coordinate system as:

[0037] The trajectories and motions of ions are governed by Newton's equation of motion in cylindrical coordinates.

[0038] By way of example only, the interior dimensions of the apparatus are such that the:

> vacuum chamber 120 radius is 38cm;

> vacuum chamber 120 height is 100 cm; > silicon wafer target stage 110 is 5.6 cm thick; and

> support rod 1 12 radius is 0.65 cm and has a variable length.

[0039] The radius of the extraction aperture 140 ( G ₁ . ), the distance between the conducting grid 125 and the target stage 110 (H), and the radius of the target stage 110 ( r ). can be varied.

[0040] Hydrogen ions are selected for the simulation and experiments since a high hydrogen implant dose creates blistering on the silicon surface which enables easy determination of the implantation area. It would be appreciate that this apparatus and method is not limited to Hydrogen ion implantation. In this embodiment, Hydrogen implantation is carried out using 2OkV target stage bias at a working pressure at 3.5 10 ^"3 torr for 3 minutes. The implantation dose based on previous secondary ion mass spectrometry (SIMS) analysis is in the range of 1 to 2 10 ¹⁷ cm ² and to create surface blistering, the silicon wafer target sample is annealed in air at 55O ⁰ C for 1 hour.

[0041] It would be appreciated that the incident angle of the ions does not depend on the charge state and mass of the ions, but is inherently determined by the local electric field in the second part 122 of the vacuum chamber 120. Different placements and geometry of the target stage 110 can affect the local electric field and the ion trajectories. In this example, it is the tangential angle of the change of the axial potential, and the change of the radial potential:

[0042] Referring to FIG.2, the potential contour plot for a target stage at 2OkV applied voltage for varying heights and diameter is shown. These example figures shows the potential contour plot for a target stage diameter of 100mm and a height of 20cm 210, a target stage diameter of 150mm and a height of 20cm 211, a target stage diameter of 100mm and a height of 70cm 212, and a target stage diameter of 150mm and a height of 70cm 213.

[0043] It would be appreciated that flatter contours are observed when the target stage 220 is closer to the grid 212 and 213. It would be further appreciated that the potential contours change when using different target stage geometry, for example, by

increasing the dimension of the target stage by using a guard-ring or by adopting a bevelled edge on the bottom of the target stage.

[0044] Since in steady-state DC-PIII the ion sheath has already reached the grid, ions from the first part of the vacuum chamber are pulled immediately through the grid by the electric field exerted by the sample target stage. It will be appreciated that flat field contours reduce non-normal angle incidence while not distorting and broadening the depth profile. This is preferable for ion-cut/layer transfer and SPIMOX for substantial control of the thickness of silicon on insulator (SOI) as well as reduction of a damaged zone.

[0045] Referring to FIG 3A through FIG. 3E, five example ion trajectories indicative of the influence of the implantation area using different instrumental configurations are shown.

[0046] FIG. 3A and 3B, show example ion trajectories exhibited for a target stage diameter of 150mm and a grid radius of 30cm. It will be appreciated that, the incident ions substantially impact the midplane of the target stage, with some ion trajectories overlapping across each other. In this example, moving the target stage closer to the grid did not overcome overlapping of the impinging ions trajectories, as shown in FIG. 3B.

[0047] FIG. 3C and 3D, show example ion trajectories exhibited for a target stage diameter of 100mm and a grid radius of 20cm. It would be appreciated that, although overlapping is reduced, some of the ions are still implanted into the edge of the target stage or supporting rod.

[0048] FIG. 3E show example ion trajectories exhibited for a target stage diameter of 150mm and a grid radius of 15 cm. It would be appreciated that, this provides substantially a 100% top surface implantation and controls the implantation area.

[0049] A preferred relationship of the radius of the target stage, radius of the grid, and distance between the grid to the top of the target stage ( r : R; H; D ) for DC-PIII can be 1:4:2.5:2. It would be appreciated that this ratio can also be applied to long pulse PIII. It would be further appreciated that a disk-like chamber, unlike cylindrical chambers typically used in pulsed mode PIII, is preferable for DC-PIII (or for long pulse PIII).

[0050] By way of example only, two series of experiments were carried out to further investigate the relationship between G ₁ . (the radius of the extraction aperture) and H (the distance between the conducting grid and the target stage). In this example a silicon wafer target stage of 150-mm diameter were implanted using hydrogen DC-PIII at a hydrogen pressure of 0.35mtorr for 3 minutes. The target stages were subsequently annealed in air at 550°C for 1 hour to achieve surface blistering and reveal the implanted area. During annealing, the implanted hydrogen atoms coalesce along the implant- projected range where there is a high density of defects after implantation to form buried micro-cavities. Upon annealing, the internal pressure causes local surface exfoliation manifesting in surface blistering. Surface blistering only takes place at the hydrogen implanted region and there are only very minor effects of implantation area caused by lateral hydrogen diffusion. The surface bubbles about lμm in diameter were visible under the naked eyes and easily observed using scanning electron microscopy (SEM).

[0051] Referring to FIG. 4, by way of example, a first set of samples are implanted using a constant H , the implanted area increases with a larger aperture radius G ₁ .. The figure shows simulation results as a solid line. The experimental implantation area is shown with error bars indicative of the unclear blistering boundaries.

[0052] Referring to FIG. 5, by way of example, a first set of samples are implanted using a constant aperture radius G ₁ .. This figure show shows simulation results as a solid line. The experimental implantation area is shown with error bars indicative of the unclear blistering boundaries.

[0053] It would be appreciated that quantitative agreement with the theoretical data is shown in FIG.4 and FIG. 5.

[0054] In an embodiment, varying H is shown to change the potential contours in the lower chamber while changing G ₁ . is shown to affect the numbers of hydrogen ions diffusing from the top chamber. Preferably, G ₁ . should be below 25cm with respect to the placement of the target sample to the conducting.

[0055] It would be appreciated that, a guard-ring-type extension can be added to the sample chuck to flatten the electric field in the vicinity of the target sample to achieve

primarily normal incidence. It would be farther appreciated that, the extraction aperture radius G _r has a substantial effect on the control of the implanted area, while the placement of the sample to the conducting grid H has a relatively lesser effect.

[0056] Referring to FIG. 1, a mask 150 is placed in the ion trajectory for transferring a pattern to the target sample. It would be appreciated that this masking can be used to deposit ion in a target sample for the creation of semiconductor devices, including metal oxide semiconductors (MOS). In an embodiment the four main steps are:

(a) initial oxidisation on n-type silicon;

(b) ion implantation of boron to for a p-type region; (c) grow a thin film of oxide to form a contact; and

(d) deposit aluminium; wherein steps b) though d) require a pattern transfer to the substrate.

[0057] It would be appreciated that pattern transferring is an important mechanism in device fabrication of semiconductor industry.

[0058] Direct current (DC) plasma based ion implantation and deposition (PBIID), by way of example, comprises:

(a) a vacuum chamber separated into two parts by a conducting grid, for example a fine mesh;

(b) the conducting grid is adapted to stop the ion sheath extending from a first part to a second part of the chamber;

(c) plasma based ion implantation for voltage pulse between 5OkV and 10OkV with duration of a few hundreds for microseconds; and

(d) adjusting the implantation area to a focused small area by adjusting the geometry of the second part of the chamber.

[0059] The voltage pulse can be between 500V and 2OkV. The duration is preferably provided at 2kHz but it would be appreciated that other frequencies are suitable. The conducting grid in the form of a fine mesh is typically made from stainless steel.

[0060] By way of example only, direct current plasma based ion implantation and deposition (DC-PBIID), facilitates a pattern transfer by:

(a) overlapping the conducting grid with mask; wherein the mask can have a dedicated pattern;

(b) controlling the geometry of the second part of the chamber for adjusting the size of the transferred pattern; and (c) performing plasma based ion implantation and deposition for transferring the pattern to the target sample.

[0061] The mask is typically placed proximal to the grid but can be above or below the grid. In a preferred embodiment the mask makes a tight contact with the grid. In other embodiments the mask can be spaced apart from the grid.

[0062] In this example, Argon ions are selected for the experiments since a high Argon implant dose creates cross-linking on the polycarbonate surface which enables easy determination of the patterns being transferred. It would be appreciate that this apparatus and method is not limited to Argon ion implantation. In this embodiment, Argon implantation is carried out using 15kV target stage bias at a working pressure at 4.0 1 O^ torr for one and a half hour at a frequency of 50Hz and a pulse duration of 100 microseconds.

[0063] In this embodiment, the ion density is preferably at values between 10 ⁸ and 10 ¹² m ^"3 to avoid ion repletion for a sharp and clear pattern transferred.

[0064] In this embodiment, the working pressure is preferably at values between 1 O^ and 5XlO ^"4 Torr to avoid ion scattering from the background gas molecules for a sharp and clear pattern transferred.

[0065] Referring to FIG. 6, the grid 610 is preferably a fine mesh. It would be appreciated that a more course mesh 710 can be used, as shown in FIG. 7, but is less effective in containing the plasma sheath. The grid can be rotated to substantially reduce any shallow effect.

[0066] Referring to FIG. 6, the ratio of the mask pattern 620 and the transferred pattern 630 can be adjusted, and includes 1 :1, 1 : 100 and 1 : 1000. It would be appreciated that micro-meter and nano-meter sized transferred patterns are achievable using disclosed techniques. In other embodiments the mask pattern can be enlarged when transferred to the target sample.

[0067] Referring again to FIG. 1, an apparatus for pattern transferring by direct current plasma based ion implantation and deposition is disclosed, wherein the apparatus comprises:

(a) a vacuum chamber 120 divided into a first part 121 and a second part 122; the first part and a second part have a connecting aperture 140;

(b) means for producing a plasma of charged ions (135, 136 and 137) in the first part;

(c) a multi-perforated grid 140 proximal to the aperture for limiting expansion of the ion sheath beyond the grid; (d) an ion target 110;

(e) a means for biasing the ions 115 toward the target for providing a controlled trajectory therebetween; and

(f) a pattern mask 150 within the ion trajectory for transferring the pattern to the target.

[0068] The grid may be rotated to substantially reduce the shallow effect.

[0069] Referring to FIG. 8, there is shown a method for pattern transferring by direct current plasma based ion implantation and deposition is disclosed, wherein method comprises the steps of:

(a) providing a vacuum chamber divided into a first part and a second part; wherein the first part and a second part are connected by an aperture having grid proximal to the aperture; 810;

(b) producing a plasma of charged ions in the first part 820;

(c) biasing the ions toward the target for providing a controlled trajectory therebetween 830; and

(d) providing a pattern mask within the ion trajectory for transferring the pattern to the target 850.

[0070] In this embodiment the grid may be rotated to substantially reduce the shallow effect.

[0071] It would be appreciated that this technique is applicable to many industries including semiconductor fabrication and medical device fabrication. It would be further appreciated that the target sample can be any suitable material, including spin-coated silicon and 1 mm thick polycarbonate.

[0072] It would be appreciated that the implantation area can be controlled by: adjusting the radius of the extraction aperture, the distance between the conducting grid and the sample, and the radius of the target stage. It would be further appreciated that an embodiment can perform a pattern transfer to any suitable substrate by selective direct current (DC) plasma based ion implantation and deposition (PBIID).

[0073] Referring to FIG. 9, there is shown an example result, showing a pattern transferred to the target. In an embodiment the target is a spin-coated silicon wafer and polycarbonate. In other embodiments the target can be of other suitable material.

[0074] A further embodiments based on this design are provided below, by way of example only.

[0075] As shown in Fig. 10, when a patterned metal mask 150 is overlapped with the metal grid/mesh 125, the shadow of the pattern will be projected to the sample substrate by the implanted ions. The mask is typically placed proximal to the grid, and can be above or below the grid. In a preferred embodiment the mask makes a tight contact with the grid. Unlike the projection of a light beam, ions can be scattered by background gas. Therefore, it is preferred that the working pressure is low such that the ion mean free path is bigger than the gap between the metal mask and the sample stage. By way of example, by selecting an Ar ion kinetic energy of 7OeV, a mean free path of 10cm requires a working pressure of O.όmTorr.

[0076] A low ion density is also preferred for transfer well-defined images because when two ions are close to each other, an electric force proportional to l/r ² will repel the ions - where r is the distance between the ions. It will be appreciated that, a plasma density of 10 ⁹ cm ^"3 has an average ion distance of 1 x 10 ^"5 meters. The electric force between ions will be in the order of 2.31 x 10 ¹⁸ N. An electric field strength greater than 14.42 Vm ^"1 can be used to manipulate this plasma.

[0077] In an embodiment, high density plasma of 1 x 10 ¹² cm ^"3 , the ion angle and energy distributions are showed not to be disturbed when subtracted through a hole of size much smaller than the ion sheath generated from the bulk plasma. In principle, the metal mesh 125 can be removed providing the line width of the patterns less than the ion sheath.

[0078] It will be appreciated that, this embodiment is capable of transferring a pattern to a substrate by ion implantation using the concept of combining a metal mask and a fine mesh. This embodiment operates under predefined processing conditions, such as low working pressure and low plasma density.

[0079] In a further embodiment, whereby a high negative voltage bias of -15kV is used, the ion sheath generated by the huge negative voltage can overwhelm the ion sheath from the bulk plasma. A non-uniform electric field can be created at the pattern exits, diversifying the ion trajectories. Diversification of the subtracting ions can be avoided by providing an electric field that is smoothed out by the fine mesh overlapped on top of the metal mask.

[0080] The system of FIG. 10 includes a small cylindrical vacuum chamber of about 40cm in height and 40cm in diameter, a radio frequency (RF) helicon plasma source, and a RUP 6-25 solid-state pulsed power supply (GBS Elektronik, GmbH). The chamber is evacuated to less than 1x10 ⁵ Torr by a combination of turbo and mechanical pumps. Argon gas is supplied to the chamber at a flow rate of 0.5 seem. The working pressure is 3x10^ Torr. Argon plasma is generated by the helicon plasma source working in inductive couple mode by turning off the magnetic field. Two reasons for turning off the magnetic field include, maintaining lower plasma density and avoiding twisting of the subtracting ions by ExB field. 50W of power is input to the helicon antenna through a matching box and the reflected power is 25W. The plasma density in this embodiment is estimated to be 10 ⁶ cm ^"3 .

[0081] By way of example only, four (4) letters "USYD" were mechanically cut into a mask made of stainless steel. Referring to FIG. 1 1, the selected mask thickness is lmm and the selected line width of the letters is 6mm. The letter "U" 1 110 is opened in space allowing ions to be subtracted from the plasma generating chamber towards the processing chamber. The letters "Y" 1 130 and "D" 1 140 were covered by a fine mesh

made of stainless steel, 120 mesh per inch and 0.0026 inch wire diameter. The letter "S" 1 120 is covered by a very fine mesh made of Ni, 2000 mesh per inch and 5 μm wire diameter.

[0082] Referring to FIG. 12, this overlapping of a fine mesh with the mask is shown to transfer a clear pattern. Ar+ ions were implanted to a lmm thick polycarbonate sample. - 15kV voltage pulses were applied to the sample stage at a frequency of 2 kHz for a total time of 30mins. The pulse duration is 100 msec. The sample is 6 cm from the metal mask. The letters "Y" 1230 and "D" 1240 were implanted into the lmm thick polycarbonate sample, and are relatively clear. The dark image is caused by carbonization of the polymer when high energy Ar ions implanted to the surface of the polycarbonate substrate. The image of the letter "U" 1210 is burry and more difficult to identify. When observing the results, it will be appreciated that mesh covering the bottom of the letter "S" 1220 was folded - as indicated by 1225. As the mask letter "S" 1125 is covered by a very fine mesh made of Ni, 2000 mesh per inch and 5 μm wire diameter, the thinness and softness of the mesh made it difficult to smoothly stack to the mask. By overlapping a smooth mesh on top of the mask, the electric field strength at the mask can be smoothed out, and a relatively clear image transferred. In this example, the line width of the letters "Y" and "D" is reduced from 6mm measured at the mask to 2mm measured at the substrate. The 1 mm thick mask plate can deform the electric field strength when a -15kV negative voltage is applied to the sample stage.

[0083] According to another example, the system of FIG. 10, includes a metal mask with fine details. As shown in FIG. 13 the mask includes:

> four (4) letters "USYD" 1310 with line width 1 mm in the top left hand corner;

> an Australian Flag 1320 with line width of 1 mm in the bottom left hand corner;

> an image of Darth Vader 1330 made up by 0.2mm (200 microns) holes in the top right hand corner; and

> an electronic circuit 1340, with line width 0.14mm (140 microns) in the bottom right hand corner was.

[0084] These four patterns were cut into 0.1 , 0.2, and 0.3 mm thick metal plates by laser within an area of 2.5x2.5 cm2. The area is covered by a fine mesh made of Ni, 2000 mesh per inch and 5 μm wire diameter. To provide a smooth contact between the mask and the mesh, the Ni 2000 mesh is sandwiched by the 0.2 and 0.3 metal plates.

[0085] A substrate is a two (2) inch silicon wafer that is carbon coated (40nm).

Oxygen ions, mainly O ₂ ⁺ , were implanted onto the surface through the mask by applying a 5kV negative voltage pulse of 100Hz for 30mins. The pulse duration is 9.5ms. The metal mask is 2mm away from the substrate. As best shown in FIG. 14, the carbon layer is modified by the implanted oxygen ions and the patterns 1310, 1320, 1330 and 1340 is transferred (having relatively well defined boundaries) to the substrate as 1410, 1420, 1430 and 1440 respectively. FIG. 15 shows a section of the transferred pattern, as viewed through a Scanning Electron Microscope (SEM). FIG. 16 shows 20 micron wide lines - for example 1610 and 1620 - having relatively well defined boundaries within the transferred 0.14mm lines. It will be appreciated that patterns with feature size - or line widths - in the order of microns can be implanted into a substrate.

[0086] According to another examples, the system of FIG. 10 is adapted to patterns transfer techniques on bio -applications, and in particular polymers' surface functionality modification.

[0087] It will be appreciated that a surface that can promote protein activities and/or strongly attach - or bind - protein is applicable to bio-applications. These bio- applications include the fabrication of Cell-on-Chips devices and bio-sensors. Polymers are typically used for biomedical application because they are relatively light-weight, easily formed, low cost and corrosion resistance. Their surfaces are relatively highly inert hydrophobic, and treatments for improving their biocompatibility are sought.

[0088] By way of example only, a system of FIG. 10 is adapted to transfer a pattern with good contrast in protein/cell attachment. As shown in FIG. 17, a cross like shape 1710, having dimensions of 3cm x 3cm, is cut into a lmm thick Aluminum metal mask. The central cross is covered by a fine stainless steel, 120 mesh per inch with 0.0026 inch wire diameter. The other cross like shapes - for example 1720 - were covered by tape. A plurality of polymers were placed on the substrate stage. Ar plasma is generated at working pressure of 0.15 mTorr. A -5kV voltage pulse is applied to the

stage and Ar ions were implanted to the polymers. The sample stage is positioned 5cm from the metal mask.

[0089] A contrast between the treated (inside the cross) and untreated (outside the cross) areas is achieved, using predetermined plasma immersion ion implantation (PIII) parameters. In PIII, the sample is immersed in a plasma. Negative high voltage pulses are applied to the sample stage. When the sample is negatively biased, an ion sheath is established and ions are implanted to the sample surface. If the sample is immune to plasma, the surface is modified by ion implantation. However, if a polymer is not immune to plasma, the mixture of plasma and ion implantation effects can be observed after PIII treatment. By way of example only, using a pulsing frequency of 50Hz provides a duty cycle of 0.02 sec, and therefore a pulse duration of 20 microseconds takes only 0.1% of the cycle. In this scenario, after a total treatment time of 800 seconds the polymers will expose to a plasma for 799.2 seconds. It will be appreciated that the polymers' surface treatment will be substantially dependant on effect caused by the plasma. It will be also be appreciated that the plasma effect will be dependant on the system configuration.

[0090] The surface energy can be measured by contact angle of small water droplets. The biocompatibility can be measured by the protein attachment and functional assay of Horesradish Peroxidase (HRP) enzyme.

[0091] For a system according to FIG. 11 and using predetermined PIII parameters, a lmm polycarbonate sample were implanted at IkHz, 600 microseconds (60% of the cycle), a voltage of -5kV, and total time of 4mins. It will be appreciate that this provides 2.4mins of ion implantation and l.όmins of plasma exposure. Similarly a 0.5mm Teflon sample is implanted at IkHz, 800 microseconds (80% of the cycle), a voltage of -5kV, and total time of 20mins. It will be further appreciate that this provides 16mins ion implantation and 4mins plasma exposure.

[0092] Referring to FIG. 18, and using these predetermined PIII parameters, a suitable contrast in water contact angle of the polycarbonate sample is achieved.

[0093] Referring to FIG. 18A and FIG. 18B respectively show water contact angle measurement of a PIII treated polycarbonate sample and Teflon sample. In each, water

contact angle measurement show a cross transferred to the surfaces, for example though differences in the angle between drops labelled 1810 and 1820 and between 1815 and 1825. This shows that the endurance of polycarbonate to the plasma effect is 2mins in this system configuration. It is also found that the endurance for 0.5mm thick Teflon is 5mins for this system configuration. As depicted in FIG 18 A, the surface energy of the treated polycarbonate inside the cross is increased, while the surface energy of the untreated (unpolluted) area outside the cross did not change. As depicted in FIG 18B, and due to different textural structure of the Teflon, the surface energy of the treated Teflon decreased.

[0094] In an embodiment, by way of example only, the treated polymer samples were further placed in a Phosphate Buffered Saline (PBS) buffer containing 0.05mg/ml HRP enzyme for 24 hours. This is typically facilitated in a peri dishes placed on a rocking platform. The surface of the polymers will be substantially saturated with HRP. After one day, the samples were rinsed five times in PBS for 20mins each, whereby the weakly bound HRP can be rinsed away. 150 μL 3,3 ',5,5' TetraMethylBenzidine (TMB) liquid substrate system for membranes, is then added to the surfaces. Upon incubation, a dark blue reaction product developed on membrane (surface) sites where peroxidase (HRP) is present. After the TMB testing, the same samples were rinsed in pH 7.4 PBS with ultra sound to remove the TMB and reaction product from the surfaces. These samples were stored in PBS for several days. TMB testing is repeated after several days of storage.

[0095] Referring to FIG. 19, after day 4 a cross-like shape 1910 is observed for the PIII treated polycarbonate sample, indicating that HRP activities or attachment is not maintained by the PIII treatment. These results were reproduced in all 4 PIII treated polycarbonate samples.

[0096] Referring to FIG, 2OA and FIG. 2OB. As shown in FIG, 2OA, a positive cross 2010 is observed for the Teflon sample, implying that HRP activities or attachment is maintained by the PIII treatment. As shown in FIG. 20B, three of the PIII treated Teflon samples showed a sharp boundary cross 2015, believed to be a result of the ions flux being different when treating the Teflon samples. This method and system can transfer a pattern with suitable contrast in protein/cell attachment. A negative cross like

shape is observed for the polycarbonate sample and positive cross like shape is observed for the Teflon samples.

[0097] This method and system can also be applied to one-step large area selective nano-pattern transferring methods. The method can enable:

a) a non-contact and one-step process, which is applicable to nano-electronic devices since nano-structures are typically easily destroyed by wet etching;

b) a mask being made of stainless steel, where duration is not a problem;

c) transferred patterns to be reproducible; and

d) large area in cm ² of complex patterns to be transferred in a relatively short period oftime.

[0098] It will be appreciated that this method can be applied to overcome problems associated with many techniques. By way of example only some problems include:

^ diblock copolymer self-assembly can produce 20 nm holes or lines, but lacks control of pattern registration over large;

> dip pen lithography can write complicated patterns with 15 nm line width

(atomic microscopy tip), but patterning speed and reproducibility is typically are not practical;

^ focused ion or electron beam (FIB/E) proximity or projection lithography can define features finer than 20 nm, but require fragile stencil masks with equally fine features;

> imprint lithography is a low-cost, high throughput fabrication process but typically has a resolution in the sub-10-nm regime;

> imprint lithography is a contact process, whereby defects can be introduced during the stamping process and also undergoes ageing of the imprint mask; and

> nanopantography is reported as a method for massively parallel patterning of nano-sized features, but an ion focusing lens must be transferred to the substrate and this technique is typically only efficient when identical nano-patterns are transferred to each 50 microns lens.

[0099] A cell on chip device is a micro-fabricated system that can present cells with multiple environmental impacts. The cells vary in time and space in a controllable and reproducible fashion, which typically cannot easily be achieved by a standard tissue culture. It will be appreciated that these impacts can include gradients of cytokines and secreted proteins from neighbouring cells, biochemical and mechanical interactions with the extracellular matrix (ECM), and direct cell-cell contacts. This enables them to be used to link cell culture with integrated analytical devices that can probe the biochemical processes that govern cell behaviour.

[00100] Different polymers' surface functionality has been modified such that a pattern with relatively suitable contrast in protein/cell attachment is achieved. It would be appreciated that this method has suitability to fabrication of micro-cells-on-chips. The PIII parameters can be optimised to obtain polymer substrate of suitable contrast in:

a) attaching and promoting protein or cells; and/or

b) depressing any attachment of protein, cells, or bacteria; and/or

c) selectively attaching a particular protein or cell.

[00101] Referring to FIG. 21, in relation to particle-in-cell simulation, the ions beam after passing the metal mask can be precisely control by a simple ion focusing lens. It will be appreciated that a combination of ion focusing and ion defocusing lens may be used to transfer a clear nano-pattern with well-defined boundaries to any substrate.

[00102] Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise", "comprising", and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to".

[00103] As used herein, unless otherwise specified the use of the ordinal adjectives "first", "second", "third", etc., to describe a common object, merely indicate that different instances of like objects are being referred to, and are not intended to imply that the objects so described must be in a given sequence, either temporally, spatially, in ranking, or in any other manner.

[00104] Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment, but may refer to the same embodiment. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments.

[00105] Similarly it should be appreciated that in the above description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the Detailed Description are hereby expressly incorporated into this Detailed Description, with each claim standing on its own as a separate embodiment of this invention.

[00106] Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination.

[00107] Furthermore, some of the embodiments are described herein as a method or combination of elements of a method that can be implemented by a processor of a computer system or by other means of carrying out the function. Thus, a processor with the necessary instructions for carrying out such a method or element of a method forms a means for carrying out the method or element of a method. Furthermore, an element described herein of an apparatus embodiment is an example of a means for carrying out the function performed by the element for the purpose of carrying out the invention.

[00108] In the description provided herein, numerous specific details are set forth.

However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.

[00109] Although the invention has been described with reference to a specific example, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.