METHOD FOR FURTHER IMPROVING LASER PULSED DEPOSITION EFFICIENCY

Abstract

A thin film deposition apparatus comprising: a laser pulse generator to generate a laser pulse; optical elements to optionally P-polarize and optionally rotate the laser pulse polarization with a polarization angle φ based on the cavity chamber and deposition material; focusing optics to focus the laser pulse; a source of deposition material having refractive index n.sub.2; said deposition material mounted within an evacuated chamber having a refractive index n.sub.1; a rotation and / or translation device to alter and / or direct said laser pulse onto said source of deposition material at an incidence angle θ to produce a plasma to be deposited on a substrate; wherein the polarization angle φ and incidence angle θ are defined by the area under the graphical representation of the ellipse of equation

[00001]$\frac{{\left(\theta -{\theta }_0\right)}^2}{a^2}+\frac{{\left(\phi -{\phi }_0\right)}^2}{b^2}=1$

where θ.sub.0=0.8× arctan (n.sub.2/n.sub.1), φ.sub.0=0, a=0.4× arctan (n.sub.2/n.sub.1) and b=0.5× arctan (n.sub.2/n.sub.1).

Claims

1-42. (canceled)

43. A thin film deposition apparatus comprising: a laser pulse generator to generate a laser pulse; optical elements to P-polarize and rotate the laser pulse polarization with a polarization angle φ based on the cavity chamber and deposition material; focusing optics to focus the laser pulse; a source of deposition material having refractive index n.sub.2; said deposition material mounted within an evacuated chamber having a refractive index n.sub.1 a rotation and / or translation device to alter and / or direct said laser pulse onto said source of deposition material at an incidence angle θ to produce a plasma to be deposited on a substrate; wherein the polarization angle φ and incidence angle θ are defined by the area under the graphical representation of the ellipse of equation $\begin{array}{l}\frac{{\left(\theta -{\theta }_0\right)}^2}{a^2}+\frac{{\left(\phi -{\phi }_0\right)}^2}{b^2}=1\text{where}{\text{θ}}_0=0.8\times \text{arctan}\left({\text{n}}_2/{\text{n}}_1\right),{\text{φ}}_0=\\ 0,\text{a}=0.4\times \text{arctan}\left({\text{n}}_2/{\text{n}}_1\right)\text{and b}=0.5\times \text{arctan}\left({\text{n}}_2/{\text{n}}_1\right)\end{array}$ .

44. The thin film deposition apparatus according to claim 43 wherein the laser pulse generator comprises an excimer laser pulse generator.

45. The thin film deposition apparatus according to claim 44 wherein the excimer laser pulse generator comprises KrF as gain medium.

46. The thin film deposition apparatus according to claim 43 wherein the laser pulse generator comprises ArF as gain medium.

47. The thin film deposition apparatus according to claim 43 wherein the laser pulse wavelength is less than 1064 nm.

48. The thin film deposition apparatus according to claim 43 wherein the laser pulse wavelength is less than 600 nm.

49. The thin film deposition apparatus according to claim 43 wherein the laser pulse wavelength is about 532 nm.

50. The thin film deposition apparatus according to claim 43 wherein the laser pulse wavelength is in the range 213 to 355 nm.

51. The thin film deposition apparatus according to claim 43 wherein the laser pulse wavelength is in the range 126 to 348 nm.

52. The thin film deposition apparatus according to claim 43 wherein the laser pulse wavelength is 248 nm or about 248 nm.

53. The thin film deposition apparatus according to claim 43 wherein the laser pulse wavelength is 198 nm or about 198 nm.

54. The thin film deposition apparatus according to claim 43 wherein the laser pulse wavelength is 193 nm or about 193 nm.

55. The thin film deposition apparatus according to claim 43 wherein the pulse duration is in the range 1 femtosecond to 50 nanoseconds.

56. The thin film deposition apparatus according to claim 43 wherein the pulse duration is in the range 5-30 nanoseconds.

57. The thin film deposition apparatus according to claim 43 wherein the optical elements to P-polarize and rotate the laser pulse polarization comprises one or more of a film polarizer, a crystal polarizing cube, a wire grid polarizer, a Brewster window, a λ/4 plate, a λ/2 plate, and a faraday rotator.

58. The thin film deposition apparatus according to claim 43 wherein the deposition material comprises one or more of: a carbon source, a graphite, highly oriented pyrolytic graphite, a complex metal oxide, Lithium Niobate (LiNbO.sub.3), a high temperature superconductor, LiTi.sub.2O.sub.4, Li.sub.4Ti.sub.5O.sub.12, YBa.sub.2Cu.sub.3O.sub.7, a ferroelectric material, Ba.sub.xSr.sub.1-xTiO.sub.3, a piezoelectric, Ta.sub.2O.sub.5, a fast ion conductor, Y.sub.2(Sn.sub.yTi.sub.1-y).sub.2O.sub.7, a liquid petroleum gas sensor, and Pd-doped SnO.sub.2.

59. The thin film deposition apparatus according to claim 43 wherein the pressure within the evacuated chamber is in the range 10.sup.-4 to 10.sup.-8 Torr.

60. The thin film deposition apparatus according to claim 43 wherein the pressure within the evacuated chamber is in the range 10.sup.-6 to 10.sup.-8 Torr.

61. The thin film deposition apparatus according to claim 43 wherein the polarization angle φ and incidence angle θ are defined by the area under the graphical representation of the ellipse of equation $\frac{{\left(\theta -{\theta }_0\right)}^2}{a^2}+\frac{{\left(\phi -{\phi }_0\right)}^2}{b^2}=1$ where θ.sub.0=arctan (n.sub.2/n.sub.1), φ.sub.0=0, a=1 and b=1.

62. A thin film deposition apparatus comprising: an excimer laser pulse generator with KrF as gain medium to generate a laser pulse with wavelength of 248 nm and pulse duration of 5 to 30 nanoseconds; a set of optical elements, comprising a sequence of λ/4 plate, then λ/2 plate then λ/4 plate to linearly P-polarize the laser pulse and rotate the laser pulse polarization with a polarization angle φ based on the cavity chamber and deposition material; focusing optics to focus the laser pulse; a source of deposition material comprising highly oriented pyrolytic graphite and having refractive index n.sub.2; said deposition material mounted on a rotation and / or translation device within an evacuated chamber having a refractive index n.sub.1 and pressure within the evacuated chamber in the range 10-.sup.6 to 10.sup.-8 Torr; a rotation and / or translation device comprising a dielectric mirror, for readily altering and directing said laser pulse onto said source of deposition material at an incidence angle θ to produce a plasma; a substrate; means for positioning said substrate to be in the path of said plasma so that said plasma is directed towards said substrate; wherein the polarization angle φ and incidence angle θ are defined by the area under the graphical representation of the ellipse of equation $\begin{array}{l}\frac{{\left(\theta -{\theta }_0\right)}^2}{a^2}+\frac{{\left(\phi -{\phi }_0\right)}^2}{b^2}=1\text{where}{\text{θ}}_0=\text{arctan}\left({\text{n}}_2/{\text{n}}_1\right),{\text{φ}}_0=\\ 0,\text{a}=1\text{and b}=1.\end{array}$ .

Description

DESCRIPTION OF THE DRAWINGS

[0047] FIG. 1 shows an example Pulsed Laser Deposition system of this invention with a linearly polarized laser beam focussed onto a target material with an incidence angle θ.sub.B corresponding to the Brewster angle.

[0048] FIG. 2 shows an electromagnetic wave propagating along the Z axis, with the electric field component (plain line) oscillating along the Y axis and the magnetic field component (dashed line) oscillating along the X axis.

[0049] FIG. 3 illustrates the definition of S and P polarizations for linearly polarized pulse laser beam

[0050] FIG. 4 shows the definition of the polarization angle φ between the electric field component of the pulsed laser beam and the plane of incidence, thereby defining S (φ=π/2), P (φ=0) and arbitrary linear polarizations (0<φ<π/2).

[0051] FIG. 5 shows the calculated reflectance of a graphite target as function of the laser beam incidence angle with respect to the normal of the target for (A) 266 nm, (B) 355 nm and (C) 532 nm incident wavelengths.

[0052] FIG. 6 shows the calculated surface temperature on a graphite deposition source as function of the fluence of a 532 nm pulsed laser.

[0053] FIG. 7 shows the calculated kinetic energy of different carbon species vaporized from a graphite deposition source by a 532 nm pulsed laser at 15 J/cm.sup.2 for two incidence angles, 45 deg and Brewster angle.

[0054] FIG. 8 shows the calculated kinetic energy of neutral carbon atom ablated from a graphite deposition source as function of the incidence angle for 3 different polarization states of a 248 nm pulsed laser with a fluence of 60 J/cm.sup.2.

[0055] FIG. 9 shows the calculated kinetic energy increase for carbon species between a P-polarized pulsed laser beam at Brewster angle incidence against a circularly polarized pulsed laser beam at 45 deg incidence for different wavelengths.

[0056] FIG. 10 shows the contour plot of the percentage increase of kinetic energy of ejected carbon atoms from a graphite source of deposition material as function of both the polarization angle φ of the pulsed laser beam and the incidence angle θ for a 60 J/cm.sup.2 pulsed laser fluence at 248 nm.

[0057] FIG. 11 shows the isolines for fixed percentage increase of the kinetic energy of neutral atoms (0%, 5%, 10%, 15%, 20%, 25%, 30%, 35% and 40%), ablated from a graphite source of material deposition with a 248 nm pulsed laser at a 60 J/cm.sup.2 fluence. The fitted ellipses for each fixed percentage increase of the kinetic energy are shown as dashed lines and the ideal fitted ellipse centred at θ.sub.0=0.8×θ.sub.B and φ.sub.0=0, with a long and short axis equal to 0.5×θ.sub.B and 0.4×θ.sub.B respectively, is shown as a plain line.

[0058] FIG. 12 shows an apparatus for steering the incident pulsed laser beam onto the target at different incidence angles.

[0059] FIG. 13 shows the Brewster angle in degrees as function of the target refractive index assuming a refractive index in the vacuum chamber n.sub.1=1. Several materials with different refractive indices at 248 nm wavelength are shown as examples.

[0060] FIGS. 14A-14D shows the isolines for fixed percentage increase of the kinetic energy of neutral atoms (from 0% to the maximum percentage increase with a 5% increment), ablated from a (A) a Silver, (B) gold, (C) TiO.sub.2 and (D) Ta.sub.2O.sub.5 source of material deposition with a 248 nm pulsed laser at a 60 J/cm.sup.2 fluence. The ideal fitted ellipse centred at θ.sub.0=0.8×θ.sub.B and φ.sub.0=0, with a long and short axis equal to 0.5×θ.sub.B and 0.4×θ.sub.B respectively, is shown as a plain line for each of the figures.

DETAILED DESCRIPTION OF THE INVENTION

[0061] Referencing FIG. 1, a basic embodiment of the present invention is illustrated. Generally, the PLD system includes a pulsed laser source 1, polarization optics 2 and focussing optics 3, to produce a linearly P-polarized laser beam focussed into the target material 4 at an incidence angle θ.sub.B, corresponding to the Brewster angle and defined as the arctan of the ratio of the refractive indices of the target and its surrounding environment. The polarization rotation optics 2, which can be a λ/2 plate, a Faraday rotator or any other polarization rotation device known to someone skilled in the art, is meant for a linearly polarized laser source. If the laser source is linearly polarized, then a λ/2 plate will allow to rotate the polarization axis along the preferred axis (p-polarized). If the laser source is circularly polarized, then a λ/4 plate will transform the circular polarization into a linear one and the addition λ/2 plate will allow to rotate the polarization axis along the preferred axis (p-polarized). If the laser source is randomly polarized (elliptical polarization for example for an excimer/gas plasma lasers), then a λ/4 plate + λ/2 plate + λ/4 plate will transform any polarization state into an arbitrary polarization output, preferentially a P-polarized beam. A polarizer (film, crystal, wire grid) behaves like a filter and only allows a specific polarization to go through. The selection of the polarization is performed by rotating the polarized and matching its fast axis with the desired polarization output. The main disadvantage with a polarizer is that all the light that is not transmitted through the polarizer is lost thereby negating the advantage provided by the invention. A Brewster window is similar to a polarizer although only P-polarized light can go through (i.e. no selection possible). A faraday rotator is very similar to a λ/2 plate, but can be remotely driven by a magnetic field to rotate the polarization. In particularly preferred embodiments comprising an excimer laser, a combination of λ/4 plate + λ/2 plate + λ/4 plate is preferred.

[0062] A circularly polarized or elliptically polarized pulsed laser source would require more complex polarization optics with a polarizer such as a film polarizer, crystal polarizing cube, wire grid polarizer, Brewster window or any other light polarizing device known to someone skilled in the art, to linearly polarize the pulsed laser beam, in addition to the aforementioned polarization rotation apparatus.

[0063] The ablation of the source of deposition material occurs in a high vacuum chamber 5, under a pressure ranging from 10.sup.-4 to 10.sup.-12 Torr or in some preferred embodiments, 10.sup.-4 to 10.sup.-8 Torr or 10.sup.-6 to 10.sup.-8 Torr, allowing the creation of a plasma plume of ejected atom and ionized species 6 from the source of deposition material, each time a single pulse from the P-polarized pulsed laser source hits the source of deposition material. The plasma plume 6, propagating inside the vacuum chamber 5, reaches the substrate 7, where it condenses to form a thin film 8.

[0064] The source of deposition material can be mounted on a rotation/translation device 9, allowing for the incoming laser beam to hit a different spot on the source of deposition material surface and to maintain the source of deposition material surface at the focal point of the focussing optics 2.

[0065] For clarity, we define the pulsed laser beam as an electromagnetic wave as shown in FIG. 2, propagating along the Z axis, with an oscillating electric field perpendicular to the propagation axis and an oscillating magnetic field perpendicular to both the propagation axis and the oscillating electric field. Someone skilled in the art will appreciate that while the electric field is represented in FIG. 2 as oscillating along the Y axis, it can be oscillating along the X axis or anywhere in the XY pane as long as it remains perpendicular to the propagation axis Z. The same applies for the magnetic field which has been represented in FIG. 2 as oscillating along the X axis. If the electric field does not rotate around the propagation axis as the electromagnetic wave propagates, the electromagnetic wave is defined as being linearly polarized. If the electric field rotates around the propagation axis as the electromagnetic wave propagates, the electromagnetic wave is defined as being unpolarized. The nature of the polarization can be further defined by the angle between the plane of incidence onto the source of deposition material and the electric field of a linearly polarized beam. As shown in FIG. 3, the electromagnetic wave is described as P-polarized when the electric field is parallel to the incidence plane onto the source of deposition material and S-polarized when the electric field is perpendicular to the incidence plane onto the source of deposition material. Therefore, one can define an angle φ, as shown in FIG. 4 between the electrical field component of the propagating pulsed laser beam and the plane of incidence of the pulsed laser beam onto the source of material deposition which characterized more accurately the state of polarization such as a P-polarized pulsed laser beam having an angle φ=0, while S-polarization having an angle φ=π/2. Circular polarization is a unique case wherein two orthogonal electrical fields with the same amplitude and phase difference of π/2 propagates along the same axis. This is equivalent to having an angle φ= π/4 or the average between S and P polarizations.

[0066] To demonstrate the advantages related to the present invention we have investigated the deposition of a diamond like carbon film with graphite as the source of deposition material.

[0067] The reflectance of a graphite source of deposition material was calculated at 3 different wavelengths for S-polarized (φ= π/2), P-polarized (φ= 0) and circularly polarized (φ= π/4) laser beams as previously defined. The results of these calculations are shown in FIG. 5. The reflectance of a P-polarization beam can be reduced to zero, regardless of the wavelength, at the Brewster angle. The reader will note that the Brewster angle slightly changes as a function of the considered pulsed laser wavelength in this specific example as the refractive index of the source of material deposition is a function of the wavelength among other variables. The reader will also understand from the teachings of this disclosure that any move away from the widely reported 45 deg incidence angle towards the Brewster angle, with a P-polarized laser pulse, for the particular deposition material will reduce the surface of deposition material reflectance, thereby improving the ablation efficiency, with increasing effect the closer the incidence angle is to the Brewster angle.

[0068] The temperature at the surface of the graphite source of deposition material was also calculated, following the formalism of equation (1), and the results shown in FIG. 6 for a 532 nm excitation, as function of the laser fluence for the 3 polarization states aforementioned and two distinct incidence angles: 45 degrees and the Brewster angle (θ.sub.B=67.59 degrees with respect to the normal on the graphite source of deposition material).

[00015]$T_s=\frac{F\left(1-R\right)\alpha }{\rho C_F}$

F is the laser fluence (J/cm.sup.2), R, α (5.68×10.sup.4 cm.sup.-1), ρ (1.4 g/cm.sup.3) and C.sub.F (710 J kg.sup.-1 K.sup.-1) are the target reflectance, absorption coefficient, density and heat capacitance respectively.

[0069] It can be clearly seen, in FIG. 6, that the surface temperature varies linearly with the pulse laser fluence and that the maximum surface temperatures are obtained for a P-polarized beam incidence at the Brewster angle. Selecting a P-polarized beam over a S-polarized beam allows for a 28% increase of the surface temperature at the same fluence and 12% increase for a circularly polarized beam regardless of the incidence angle. A further 9% increase of the surface temperature is achieved by changing the incidence angle of a P-polarized beam from 45 degree to the Brewster angle.

[0070] Similarly, the kinetic energy of the ejected carbon atom can be calculated from their velocity (E=0.5mv.sup.2) where the total velocity (v) is the sum of three different contributions, the thermal velocity v.sub.T, the plasma expansion velocity v.sub.k and the Coulomb acceleration v.sub.c for the charge species.

[00016]$v_T=\sqrt{\frac{8k{T}_s}{\pi \text{}m}}$

[0071] Where T.sub.s is the surface temperature, m the mass of the considered species, and k the Boltzmann constant (1.38×10.sup.-23 m.sup.2 kg s.sup.-2 K.sup.-1).

[00017]$v_K=\sqrt{\frac{\gamma kT}{m}}$

[0072] Where y is the adiabatic coefficient (y=1.67 for monoatomic species).

[00018]$v_C=\sqrt{\frac{2ez{V}_0}{m}}$

[0073] Where e is the electron charge (1.602×10.sup.-19 C), z the charge state (i.e. 1+, 2+, 3+ or 4+) and V.sub.0 the equivalent plasma acceleration voltage (~70 V measured experimentally from the electron velocity).

[0074] It can be seen in FIG. 7 that the kinetic energy of the ablated material from the source of deposition material is always higher when using a P-polarized beam compared to both the S-polarized and circularly polarized pulsed laser source, regardless of the incidence angle. Increasing the incidence angle from 45 degrees to the Brewster incidence angle further increases the kinetic energy of the ablated carbon atoms and ion species. The same trend is further demonstrated in FIG. 8, which shows the kinetic energy of neutral carbon atoms ablated from a graphite source of deposition material as a function of the incidence angle. It can be clearly seen in FIG. 8 that using a P-polarized pulsed laser offers significant benefits compared with the other polarization states (i.e. S-polarized and circular polarization) regardless of the incidence angle. However, the kinetic energy reaches a maximum when the P-polarized pulsed laser is impinging the source of deposition material at the Brewster angle. A person skilled in the art would also appreciate that any deviation from the absolute value of the Brewster angle and polarization angle φ=0 defining the P-polarisation state will still provide some improvement on the kinetic energy of the ablated atoms and ion species as shown in FIG. 8.

[0075] The increase of the kinetic energy is not the same for all generated species. The kinetic energy of highly charged ions is dominated by the Coulomb acceleration which is independent of the plasma temperature in the formalism used here. The increase of kinetic energy for neutral species, which are not influenced by the Coulomb acceleration follows the increase of the plasma temperature as a function of the incidence angle and polarization.

[0076] The benefit of this approach is even greater at shorter wavelengths, as it can be seen in FIG. 9 which shows the calculated kinetic energy increase for carbon species between a P-polarized pulsed laser beam at Brewster angle incidence against a circularly polarized pulsed laser beam at 45 deg incidence for different wavelengths.

[0077] In relation to optimal wavelengths to be used, preferably they are in the UV region of the optical spectrum, ranging from 126 to 355 nm and typically 193 or about 193 nm, or 198 or about 198 nm or 248 nm or about 248 nm.

[0078] In some embodiments, shorter wavelengths are used, for example with an excimer laser, for example Ar.sub.2 at 126 nm, Kr.sub.2 at 146 nm, F.sub.2 at 157 nm, Xe.sub.2 at 172 nm. Such shorter wavelengths are generally less efficient and more difficult to handle.

[0079] However, any wavelength may work under the right conditions, provided that the pulse energy is sufficient. The longer the wavelength the higher the energy requirement. In some embodiments, greater wavelengths such as within the visible or Near Infra-Red parts of the spectrum may be used. For example, the wavelengths may be 532 nm (visible), 1064 nm (NIR) or 10.6 .Math.m (IR). However, these are generally not as suitable as they result in higher surface roughness in the deposited thin films which may be detrimental for the envisioned application of the deposited thin film such as for example anti-reflection coatings.

[0080] For diamond like coatings, it is widely believed that C.sup.+ are responsible for generating the Sp3 hybridization which gives these films their unique physical properties. It is also believed that the highest Sp3 fraction is achieved when C.sup.+ kinetic energy reaches 60 eV. Using a frequency double YAG laser (λ=532 nm), circularly polarized at 45 deg incidence angle and following the same formalism for the calculation of the kinetic energy described above, a fluence of ~85 J/cm.sup.2 is required. This fluence requirement falls to ~77 J/cm.sup.2 for a P-polarized beam at the Brewster incidence angle. This value can be further reduced by using shorter wavelengths such as 248 nm produced by an Excimer laser with Krypton Fluoride (KrF) as the gain medium. In this case, only a pulsed laser fluence of 60 J/cm.sup.2 is required to achieve the required C.sup.+ kinetic energy of 60 eV, provided that the pulsed laser beam is P-polarized and the incidence angle on the source of deposition equal the Brewster angle (i.e. θ.sub.B = 69 deg).

[0081] FIG. 10 depicts an even more detailed picture of the enhancement of the kinetic energy of the carbon neutral atoms ejected from the graphite source of deposition material upon its interaction with the pulsed laser beam produced by an excimer laser emitting at 248 nm with a 60 J/cm.sup.2 fluence. The contour plot shown in FIG. 10 shows the percentage increase of kinetic energy as a function of both the incidence angle θ and the polarization angle φ previously defined. The percentage increase has been calculated by normalizing the kinetic energy of every data point by the kinetic energy achieved at normal incidence angle (θ=0), which is the same for all polarization states. Therefore, the normalized values, shown as a percentage increase of the kinetic energy, are independent from the laser fluence for that particular wavelength. As previously demonstrated the maximum enhancement is achieved for a P-polarized pulsed laser beam (φ=0) with an incident angle θ equal to the Brewster angle, thereby yielding a 40% increase of the kinetic energy. However, someone skilled in the art will appreciate that other combination of incidence angle and polarization angle will yield an increase of the kinetic energy of the ablated carbon atoms, albeit lower than the optimal configuration with θ=θ.sub.B and φ=0.

[0082] The isolines of the contour plot, which are delimitating the percentage increase of the kinetic energy of the ablated atom from 0% to the maximum increase (i.e. 40%) with a 5% increment are shown in FIG. 11. Although the isolines have complex non-symmetrical shapes, one can roughly approximate their shapes with ellipses, shown as dashed lines in FIG. 11 for each isoline. The equation (5) describes the ellipse where θ is the angle of incidence, φ the polarization angle, θ.sub.0 and φ.sub.0 the coordinate for the centre of the ellipse, a and b the length of the short and long axis respectively.

[00019]$\frac{{\left(\theta -{\theta }_0\right)}^2}{a^2}+\frac{{\left(\phi -{\phi }_0\right)}^2}{b^2}=1$

[0083] The table 1 shows the parameters used for defining the different ellipses fitting the isolines as function of θ.sub.B. Examining the table 1, someone skilled in the art will appreciate that the higher the isoline threshold, the closer the fitting parameter to the ideal values of θ.sub.0=θ.sub.B and φ.sub.0=0 describing the ideal condition of a P-polarized pulsed laser with an incidence angle equal to the Brewster angle. However, some improvement can be seen even when deviating from the ideal conditions. For example, a linearly polarized pulsed laser beam with a polarization angle φ=20 deg and an incidence angle θ=52 deg will still produce a 15% increase of the ablated atoms kinetic energy. Generally, any combination of incidence and polarization angles, θ and φ defined by the area under the graphical representation of the ellipse of equation (5) with θ.sub.0=0.8 × θ.sub.B, φ.sub.0=0, a=0.4 × θ.sub.B and b=0.5 × θ.sub.B will result in an increase of the kinetic energy as shown in FIG. 11.

TABLE-US-00001 Fitting Parameters for the Ellipses Describing the Isolines Isoline threshold - % increase in kinetic energy Fitting parameters 5% 10% 15% 20% 25% 30% 35% 40% θ.sub.0 (deg) 0.83 × θ.sub.B 0.88 × θ.sub.B 0.91 × θ.sub.B 0.93 × θ.sub.B 0.95 × θ.sub.B 0.96 × θ.sub.B 0.98 × θ.sub.B 0.99 × θ.sub.B φ.sub.0 (deg) 0 0 0 0 0 0 0 0 a (deg) 0.36 × θ.sub.B 0.29 × θ.sub.B 0.25 × θ.sub.B 0.21 × θ.sub.B 0.17 × θ.sub.B 0.14 × θ.sub.B 0.10 × θ.sub.B 0.03 × θ.sub.B b (deg) 0.52 × θ.sub.B 0.44 × θ.sub.B 0.36 × θ.sub.B 0.29 × θ.sub.B 0.22 × θ.sub.B 0.14 × θ.sub.B 0.07 × θ.sub.B 0.01 × θ.sub.B

[0084] This reduction of the required fluence obtained with this invention allows for increased deposition speed. For example, with the same laser power output, a larger spot size on the target can be used with a P-polarized beam at the Brewster angle, yielding the same fluence, enabling larger quantities of material being removed from the target, thereby increasing the deposition speed.

[0085] Another benefit of a large incidence angle relates to surface contamination on the optics, especially the window 10 in FIG. 1 which allows for the incoming pulsed laser beam to penetrate the vacuum chamber. Over time the optics, especially when the incidence angle is at or about 45 deg, are subjected to the deposition of the material ablated from the source of deposition material albeit at a much lower rate than the substrate meant to be coated. Increasing the incidence angle towards the Brewster angle reduces the coating rate of the optics, reducing the need for replacing them every so often.

[0086] Furthermore, the larger than standard incidence angle allows for reducing the distance between the source of deposition material and the substrate due to the lower encumbrance. This smaller gap also enables larger deposition rates as it has been shown that the deposition rate is inversely proportional to the distance between the target and the substrate. This is due to the increase of hemispherical expansion of the pulsed laser induced plasma plume with the increase of the source of deposition material to substrate distance. In other words, while positioning the substrate closer to the source of deposition material allows only a smaller surface to be coated, the conservation of the ion flux implies that a thicker coating can be achieved for a given deposition time. This is particularly relevant for the coating of substrates with a small surface area, such as lenses for example.

[0087] When applying PLD to the deposition of complex metal oxides, changing the distance between the target and the substrate can influence the stoichiometry for the deposited material. Using the apparatus and method described allows for an alternative way to achieve better control.

[0088] While for most applications a vacuum chamber will be ideally dedicated to the deposition of a single material to avoid cross contamination and therefore costly down time in an industrial setting, it is easy to envision a simple mechanical device for readily adjusting the incidence angle. Such adjustment may preferably occur within the vacuum chamber to access a wider range of incidence angle as steering the pulsed laser beam outside the chamber would only allow for few degrees variation of the incidence angle. An example of such device is depicted in FIG. 12 where a P-polarized pulsed laser beam 11 is directed onto a mirror 12. The mirror 12 reflects the P-polarized pulsed laser beam 11 onto the target 4 at a predefined incidence angle corresponding to the Brewster angle for the given target 4, to produce a plasma plume 6 of ionized species which will condense on the substrate 7 to form the thin film 8. The position of the mirror 12 can be modified manually through both translation and rotation mechanical devices to adjust the pulsed laser beam incidence angle depending on the nature of the source of deposition material, ensuring that the pulsed laser beam incidence angle moves toward or preferably matches the Brewster angle. Alternatively, these translation and rotation adjustments can be performed through computer controlled motorised translation and rotation mechanical devices.

[0089] The mirror can be provided in any suitable shape or form. Typically, they are either circular or square. Preferably, when used with an excimer laser, the mirror is a dielectric mirror, which reflects only the desired wavelength or wavelength range they are designed to reflect and are otherwise transparent (or semitransparent). Metallic mirrors, such as Aluminium can also be used for UV applications (down to 250 nm) but are not as resilient as dielectric ones as they can not sustain high energy density. In practice, mirrors can be glued on a plate, or mounted on a ring, or clamp.

[0090] Another option is to change the position of the target, through similar rotation and translation mechanical devices, to modify the incidence angle without having to adjust the pulsed laser optical pathway. However, this option would only work for flat targets and not cylindrical ones. Furthermore, tilting the source of deposition material will also tilt the generated plasma plume created upon impact of the pulsed laser beam onto the target, as it is always perpendicular to the target surface, therefore requiring the substrate to be repositioned with respect to the target accordingly. Consequently, while technically feasible, this approach is more complex than steering the pulsed laser beam. Any variation of the aforementioned pulsed laser beam steering architecture or any other means of steering the incident laser beam onto the target material 4 would be adequate for matching the incidence angle with the Brewster angle, or moving towards the Brewster angle from the standard 45 deg.

[0091] The reader will appreciate that this is only one of many potential applications for this invention which relates to the optimum polarization and incidence angle for pulsed laser beams in PLD. Changing from one source of deposition material to another will require adjustment of the pulsed laser beam incidence angle to the Brewster angle according to the refractive index of the source of deposition material as shown in FIG. 13. While PLD, and therefore this invention, can be used for the deposition of virtually any materials, including metals, semiconductors and organic materials such as polymers, this deposition method and the present invention are particularly suited for the deposition of complex metal oxides such Lithium Niobate (LiNbO.sub.3), high temperature superconductors such as LiTi.sub.2O.sub.4, Li.sub.4Ti.sub.5O.sub.12 and YBa.sub.2Cu.sub.3O.sub.7, ferroelectric materials such as Ba.sub.xSr.sub.1-xTiO.sub.3, piezoelectric such as Ta.sub.2O.sub.5, fast ion conductors Y.sub.2(Sn.sub.yTi.sub.1-y).sub.2O.sub.7 and liquid petroleum gas sensors such as Pd-doped SnO.sub.2 to name a few, which are known to be difficult to achieve with any other physical or chemical deposition methods due to their complex stochiometric composition. The aforementioned advantages (i.e. lower energy requirement, higher ablation efficiency, higher deposition speed and so on), demonstrated with Diamond Like Carbon deposition from a graphite source of deposition, can be replicated with any material.

[0092] The same calculations, as previously shown for graphite ablation and the resulting carbon atom increase of kinetic energy, have been reproduced with other materials commonly used in physical deposition methods such as silver, gold, titanium dioxide (TiO.sub.2) and tantalum pentoxide (Ta.sub.2O.sub.5). These materials have been selected to demonstrate the viability of this invention over a wide range of refractive index n.sub.2 from 1.3 to 2.6 at 248 nm for the source of deposition material. FIGS. 14A-14D shows, similarly to FIG. 11, the isolines describing the percentage increase of the ablated atoms from each of these materials ((A): silver, (B):gold, (C): TiO.sub.2 and (D): Ta.sub.2O.sub.5) upon interaction with the pulsed laser beam as a function of the polarization angle and incidence angle. Someone skilled in the art will appreciate that the magnitude of enhancement (i.e. percentage increase of the resulting kinetic energy of the ablated specie) is highly dependent on the nature of the material and more specifically on its heat capacitance and absorbance at the considered wavelength. Nevertheless, a significant increase of the kinetic energy can be observed for all the materials studied, ranging from over 15% for gold to over 30% for TiO.sub.2. It will be also noted that the best fitting ellipse, shown on each plot of FIG. 13 is a plain line, described by the equation 5, with θ.sub.0=0.8 × θ.sub.B, φ.sub.0 = 0, a = 0.4 × θ.sub.B and b=0.5 × θ.sub.B is consistently overlapping the area of the different plots of FIG. 14 where there is a significant enhancement of the kinetic energy compared to the standard ablation conditions with a 45 deg incidence angle and unpolarized pulsed laser.

[0093] It is convenient to describe the invention herein in relation to particularly preferred embodiments. However, the invention is applicable to a wide range of embodiments and it is to be appreciated that other constructions and arrangements are also considered as falling within the scope of the invention. Various modifications, alterations, variations and or additions to the construction and arrangements described herein are also considered as falling within the ambit and scope of the present invention.