WO2001071778A2 - Nanometric scale coherently controlled deposition - Google Patents

Abstract

A method for the controlled nanometer-scale deposition of atomic or molecular species on a surface (24), by means of coherently controlled optical focusing. The coherent control is conveniently performed by inducing a linear superposition of excited atomic states or molecular bound states respectively, by means of electromagnetic fields supplied by an applied laser beam (13). The optical focusing is conveniently performed by passing a beam (10) of such suitably prepared species through another electromagnetic field supplied by a standing wave (14, 18) induced by two interacting laser beams (20, 22). Altering the characteristics of the laser beams alters the forces operating on the species, thus directing them to the desired position on the surface (24). Selection of the frequencies, intensities, and relative phases of the electromagnetic fields, as well as the geometry of the interaction between the beam and the electromagnetic fields, enables deposition of aperiodic patterns (26) on the surface with a resolution of 10 to 15 nanometers. Such nanoscale focusing of atoms or molecules by coherent light can be used for executing nanometric lithographic processes.

Description

NANOMETRIC SCALE COEERENTLY CONTROLLED

DEPOSITION

FIELD OF THE INVENTION

The present invention relates to the field of the controlled deposition of molecules and atoms on surfaces on a nanometric scale.

BACKGROUND OF THE INVENTION

The optical manipulation of atoms in their ground state constituting an atomic beam has been widely studied over the past few years. It has been shown, for instance in the article "Calculation of Atomic Positions in Nanometer-scale Direct-write Optical Lithography with an Optical Standing Wave", by K.K. Berggren et al., published in Journal of the Optical Society of America B, Vol.l 1, pp. 1166-1176 (1994), and in the references thereto, that an atomic beam can be focused to sub-micron scale dimensions by using the dipole forces exerted on the atoms by an electromagnetic field, such as that present in a standing light wave. One possible application of this phenomenon is in direct-write atomic nanolithography, which offers the possibility of microfabrication applications in the microelectronic industry, at resolutions well below the wavelength of ultra-violet light, as commonly used.

In U.S. Patent 5,360,764 to R. J. Celotta and J. J. McClelland, hereby incorporated by reference in its entirety, there is described the use of a combination of laser cooling techniques and periodic standing wave electromagnetic fields to enable the focusing of atoms and their subsequent deposition on a substrate, on a nanometric scale. However, the technique described therein has a number of disadvantages; firstly, it is limited to the controlled deposition of atoms, and there are many practical chemical processes, where the presence of molecules rather than atoms is preferable; and secondly, it is limited to the formation of periodic structures on the surface. The technique is thus both limited to atomic species as the type of materials that can be deposited, and also in the range of positions capable of deposition.

A method of depositing molecules is also described in the above mentioned Celotta et al. patent, whereby more than one atomic species are concurrently evaporated onto the desired substrate surface. One of the atomic species is focused into the desired pattern on the substrate by selecting the conditions to ensure that it is in resonance with the applied laser field, and the other, or others, are applied uniformly. At the positions of focus, the two atomic species react chemically to form the desired molecular deposit. Using this scheme, a method for the formation of an array of spots of Cr0₂ is described therein. It is evident that this method for the deposition of molecules is complicated to perform, is limited to only specific molecules, and may prove difficult to achieve good stoichiometry.

Methods of direct manipulation of the molecules of a molecular beam by means of optical focusing, analogous to the methods described above of atomic beam manipulation, have not yet proved particularly successful. The concepts associated with molecular manipulation have indeed been considered for several years, such as is described, for instance, in the article entitled "Deflection of Neutral Molecules Using a Nonresonant Dipole Force" by H. Stapelfeldt et al., published in Physical Review Letters, Vol. 79, pp.2787-2788, 1997, and in the earlier references cited therein. However, in the work of Stapelfeldt et al., high intensity pulsed lasers were used to affect the motion of molecules in a beam, without showing how this could be applied for general deposition work, and certainly not for nanoscale sized structures. Furthermore, both the high fields required and the short laser pulses required are disadvantages of this approach.

There therefore exists an important need for a method for the controlled deposition of molecules on surfaces on a nanometric scale. In addition, the ability to perform controlled deposition of atoms in non-periodic patterns on a nanometric scale is also a needed technique which is hitherto unavailable.

The disclosures of each of the publications mentioned in this section, and of those in the other sections of this specification, are hereby incorporated by reference, each in its entirety.

SUMMARY OF THE INVENTION

The present invention seeks to provide a new method and apparatus for the optical focusing of atomic or molecular beams, such that the atoms or molecules can be deposited in aperiodic structures, with resolutions of down to 10-15 nanometers. The ability to deposit atoms or molecules on surfaces at a nanometric scale has important applications in the semiconductor industry for the purposes of direct deposition etching and for other lithographic processes. The nature of the pattern formed, including the position and width of the component parts of the pattern, are altered by varying a number of parameters associated with the beam preparation and with the electromagnetic fields to which the beam is subjected.

A beam of atoms or molecules, aimed at the surface on which the deposition is required, is preferably sent through a skimmer to minimize velocity components perpendicular to the direction of the beam. The beam is then preferably further collimated by means of laser cooling or by sympathetic cooling or supersonic expansion, in order to reduce the transverse velocity to minimal levels. The better the collimation, the finer the resolution of the focusing effect achieved. The laser cooling can be performed by any of the methods known in the art. One such method is described in the article co-authored by one of the present applicants, entitled "Complete population transfer to and from a continuum and the radiative association of cold Na atoms to produce translationally cold Na₂ molecules in specific vib-rotational states" published in Optics Express, Vol. 4, pp.91-106 (Jan., 1999), hereby incorporated in its entirety by reference. Other methods are also given in the many references cited therein. Alternatively, for an atomic beam, laser cooling may be achieved by passing the atoms through counterpropagating laser fields, though this method is not fully developed at the time of this application for use with molecular beams. It may also be possible to use only mechanical cooling techniques, as described by Drodofsky et al. in an article in Microelectronic Eng. Vol. 30, p. 383ff, (1996), though the beam intensities in this method are very small, and the deposition rates are thus very much slower.

The transverse- velocity cooled atomic or molecular beam is then subjected to an electromagnetic field such as may be provided by one or more laser beams, either pulsed or CW, which prepares a linear superposition of states. For the molecular case, this superposition could preferably be of bound states primarily through a two photon absorption process. For the atomic case, the superposition could preferably be formed of Rydberg states. This operation is another application of the process of coherent control, which has been developed recently to affect atomic and molecular processes by means of quantum interference. Up to now, coherent control has been used to control the outcome of unimolecular processes such as photodissociation, and more recently, collisional and scattering processes. Details of the theory and some applications of the technique of coherent control are contained in the articles "Polarization Control of Branching Ratios in Photodissociation" by C. Asaro, P. Brumer and M. Shapiro, published in Physical Review Letters, Vol. 60, pp. 1634-1637 (1988) and in "Coherent Control of Reactive Scattering" by A. Abrashkevich, M. Shapiro and P. Brumer, published in Physical Review Letters, Vol. 81, pp. 3789-3792 (1998), and in the many references cited therein.

In U.S. Patent No. 5,256,849, to M. O. Scully, there is described a method of increasing the refractive index of a material by means of the creation of superpositions of states therein, by means of coherent control of the atomic levels of the material. Alteration of the refractive index of a material is operative to affect the motion of light through the material. The use of coherent control in the present invention, unlike any of the methods described in the prior art, is operative to affect the motion of the atoms or molecules themselves, by means of optical focusing.

The prepared atomic or molecular beam then preferably passes through two or more standing electromagnetic fields directed parallel to the surface, which too may be produced by means of interacting laser beams. By varying the characteristics of the laser beams, the atomic or molecular properties, the distance of the stationary fields from the surface, and the properties of the stationary electromagnetic fields, the nature of the pattern deposited on the surface can be controlled, including the position, intensity and resolution of the component parts of the pattern. In general, the pattern displays a large background with several relatively low intense peaks when there is no atomic or molecular coherence, whereas the peaks become intense and the background weak when the atomic or molecular coherence is introduced.

In the case of atomic beam deposition, since the superposition may be formed from Rydberg excited states of the atoms, this affords the possibility of much higher polarizabilities, and hence requires much lower laser powers than for molecular beam deposition.

There is thus provided in accordance with a preferred embodiment of the present invention, a method of depositing atoms or molecules in a predetermined pattern onto a surface by means of coherently controlled optical focusing of a beam of the atoms or molecules.

There is further provided in accordance with yet other preferred embodiments of the present invention, a method as described above and consisting of the steps of providing a collimated beam of atoms or molecules to be deposited, directing the beam through a first electromagnetic field, typically produced by a laser beam, operative to produce a superposition of states of the atoms or molecules, and thereafter directing the beam through a second electromagnetic field, typically produced by two or more standing waves, such that the atoms or molecules are focused onto the surface in the predetermined pattern.

In accordance with still another preferred embodiment of the present invention, there is provided a method as described above and also consisting of the step of cooling the beam before production of the superposition of bound states, the cooling being effected by means of a laser cooling process.

There is further provided in accordance with still another preferred embodiment of the present invention, a method as described above and wherein the superposition of bound states of the molecules is formed by means of a two-photon absorption process.

In accordance with a further preferred embodiment of the present invention, there is also provided a method as described above and wherein the beam is cooled by a mechanical cooling process such as by expansion through a supersonic nozzle, either exclusively, or before it is subjected to the laser cooling process.

There is provided in accordance with yet a further preferred embodiment of the present invention, a method as described above and wherein the first laser is either a CW or a pulsed laser.

There is even further provided in accordance with a preferred embodiment of the present invention, a method as described above and wherein the standing waves are formed by one or more laser beams.

Furthermore, in accordance with yet another preferred embodiment of the present invention, there is provided a method as described above and wherein the predetermined pattern is aperiodic and may be determined at least by the parameters of the first electromagnetic field and by the parameters of the second electromagnetic field.

There is also provided in accordance with a further preferred embodiment of the present invention, a method as described above and also consisting of the step of directing the beam through a third electromagnetic field, arranged approximately orthogonally to the second electromagnetic field, and in effectively the same common plane, such that the atoms or molecules are focused onto the surface in a predetermined array pattern, which could have a resolution of less than 50 nanometers. In accordance with yet another preferred embodiment of the present invention, there is provided a method of depositing atoms or molecules in a predetermined pattern onto a surface as described above, and wherein the atoms or molecules are operative to perform applications such as nanolithography, micro-etching, the writing of information on a storage medium, the formation of photolithographic masks, the production of doped regions within the surface, the production of high profile tip structures on the surface, or the production of optical grating structures on the surface.

There is further provided in accordance with yet another preferred embodiment of the present invention, a system for the deposition of atoms or molecules in a predetermined pattern onto a surface by means of coherently controlled optical focusing of a beam of the atoms or molecules.

In accordance with still another preferred embodiment of the present invention, there is provided a system for the deposition of atoms or molecules as described above, and consisting of a source emitting a beam of the atoms or molecules, a laser cooling stage for minimizing the transverse velocity components of the molecules of the beam, a first electromagnetic field through which the beam is directed, operative to produce a superposition of states of the atoms or molecules, and a second electromagnetic field, through which the beam is thereafter directed, such that the atoms or molecules are focused onto the surface in the predetermined pattern.

There is provided in accordance with yet a further preferred embodiment of the present invention, a system for the deposition of atoms or molecules as described above and wherein the first electromagnetic field is formed by at least one first laser beam.

There is even further provided in accordance with a preferred embodiment of the present invention, a system for the deposition of atoms or molecules as described above and wherein the second electromagnetic field consists of at least two standing waves formed by laser beams. BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood and appreciated more fully from the following detailed description, taken in conjunction with the drawings in which:

Fig.l is a schematic representation of a system for performing coherently controlled atomic or molecular beam optical focusing, such as is suitable for executing nanolithography, according to a preferred embodiment of the present invention;

Figs. 2(a) to 2(d) show how the density distribution of deposition of molecules and the optical potential vary along the z-direction, both in the presence of and in the absence of molecular coherence;

Figs. 3(a) to 3(d) are plotted under the same conditions as Figs. 2(a) to 2(d), but show an enlarged section in the z-direction;

Figs. 4(a) to 4(d) show the separate contributions to the molecular density as a function of z, due to the first and second SW fields, taking into account only the non-interference term of the optical potential;

Figs. 5(a) to 5(f) show the dependence of the deposition density on different superpositions of states, using the superposition ( |000> + |v00>), where v takes the values 1 to 6;

Figs. 6(a) to 6(f) show the dependence of the deposition density on different superpositions of states, using the superposition ( |000> + |v20>), where v takes values of 0 to 5;

Figs. 7(a) to 7(f) show the dependence of the deposition density on |c₂|² for six different values of |c₂|², for the superposition between the |000> and |020> states;

Figs. 8(a) to 8(d), show plots of the optical potential for the superposition between |000> and |020> states, with and without molecular coherence, and for different values

;

Figs. 9(a) to 9(c) displays the density distribution for three different values of phase between the two standing waves, for the superposition |000> + |020>;

Figs. 10(a) to 10(f) illustrate the variation in the form and intensity of the strongest peak shown in Fig. 9(b) at z_s = 0.49, as a function of six different values of the relative phase between the two standing waves;

Figs. 11(a) to 11(f) show the variation in the form and intensity of the strongest peak shown in Fig. 9(b), as a function of the intensity of the two S W fields, for six different values of the field of SW2;

Figs. 12(a) to 12(c) show plots of the density distribution for three different values of the interaction time, T^, for the superposition |000> + |020>;

Figs. 13(a) to 13(d) show the density distribution of deposition as a function of free flight distance, L_ff for four different values of L_f

Figs. 14(a) to 14(d) show the width of a typical deposited peak as a function of the rotational temperature of the molecules, for four different values of T_r ; and

Figs. 15(a) to 15(d) are graphs which show the density distribution for the deposition of atomic rubidium for different interaction times, both in the presence of and in the absence of coherent control.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Reference is now made to Fig. 1, which schematically illustrates a preferred embodiment of an apparatus for the execution of coherently controlled atomic or molecular beam optical focusing, such as is suitable for the performance of nanolithography. The source 2 produces a beam of atoms or molecules, which is preferably cooled by thermal expansion through a supersonic nozzle 3, such as is well known in the art. The beam may then preferably be further collimated mechanically by an exit aperture 8. After this initial cooling, the transverse velocity spread is preferably reduced to minimal levels by means of laser cooling, such as by an optical pumping and trapping process. Alternatively and preferably, not all of these cooling processes may be used in performing the molecular deposition, but the outcome may be poorer spatial resolution, and, if at least the laser cooling process is not used, very much slower deposition rates.

The laser cooling may be preferably performed for an atomic beam by passing the beam through two counter-propagating laser beams 5 and 6, produced by reflecting one laser beam back along itself by means of an end mirror 7. The laser is tuned to the appropriate frequency to effect the cooling as is known in the art. If lower transverse velocities are required then additional laser cooling methods known in the art, such as Sisyphus, can be used. Molecules are preferably cooled to a single rotational state. In order to provide good focusing of the beam, necessary to achieve a resolution of approximately lOnm, the beam should preferably be collimated to have a residual transverse velocity of less than 10 nm/t_d, where t_d is the flight time in seconds from the beam source to the surface. The highly collimated beam 10 propagates along the x direction and then passes through a preparatory electromagnetic field 12, which produces a linear superposition of states of the atoms or molecules. The electromagnetic field is preferably produced by means of a laser 13.

The beam then preferably passes through two standing waves (SW) 14, 16 of a radiation field, preferably formed by retro-reflecting off a mirror 18, two near resonant, CW laser beams 20, 22, positioned above the substrate 24 onto which the molecules are to be deposited. While passing through the SW radiation field, the atoms or molecules experience a dipole force, due to the SW-induced optical potential (OP), which acts as an array of lenses, causing those atoms or molecules in the beam with kinetic energy less than the depth of the OP to focus into predefined patterns 26 as they deposit onto the substrate 24. Those atoms or molecules with kinetic energy greater than the depth of the OP skip over the potential well and are lost to the ordered deposition process.

According to a preferred method of embodiment of the present invention, the kinetic energy of the beam in the x-direction v is approximately fixed and is much larger than the magnitude of the OP, such that a majority of the atoms or molecules are indeed focused as desired. In the y-direction, perpendicular to the direction of the two SW's, the focusing region is essentially uniform. The focusing effect is then described by an effective one dimensional OP along the z-direction. The atoms or molecules in the beam execute motion according to the Hamilton's equation: m_N i_i = p_i (1) d_ and P, = - dz ^Vc op tzi.pi (2)

where V_op is the optical potential and the subscript i symbolizes the i-th atom or molecule in the beam, treated as a point-like particle. The result of focusing by means of a one-dimensional OP along the z-direction is a pattern of lines of deposited atoms or molecules, of essentially uniform intensity in the y-direction, the lines being spaced in the z-direction and of width and intensity in accordance with the deposition parameters used.

According to another preferred embodiment of the present invention, it is possible to deposit an array of spots rather than an array of lines, by adding another electromagnetic field, preferably produced by another pair of laser beam standing waves, preferably directed orthogonally to the first pair of SW's and in the same plane thereto. The second electromagnetic wave then produces an additional OP directed along the y-direction, thus focusing the atomic or molecular beam in this direction also. The result of this preferred embodiment is therefore an array of deposited spots, in positions and of intensity according to the parameters chosen.

One preferred application is the direct deposition of hydrogen chloride or chlorine molecules on the surface of a microelectronic substrate for purposes of direct write etching. Another application is in the direct writing of nanometer scale information for high density information storage. Other preferred applications in the semiconductor industry include the production of nanometric scale photolithographic masks for subsequent conventional etching, the production of such masks for plasma etching, the doping of selected areas of a wafer on a nanometric scale for the production of high resolution structures, the deposition of high profile tip structures such as are used in field emission devices, and the generation of high resolution shaped optical grating structures. It should be emphasized that unlike the methods available in the prior art, since the present invention enables the deposition of complete molecules, the stoichiometry of the deposited layers or structures can be more readily maintained.

In order to produce the desired deposition distribution on the substrate, the optical coherence of the ordering and focusing laser beams, the atomic or molecular coherence, and the atomic or molecular beam itself must be arranged such that the optical potential interacts with the beam to direct the atoms or molecules to their correct positions. Methods of calculation are now presented, according to preferred embodiments of the present invention, to illustrate how these necessary parameters are derived to ensure the desired nature and extent of the focusing effect and the deposition pattern. The calculations are now performed for the preferred embodiment of the focusing of a beam of nitrogen molecules, N₂, though it is to be understood that similar methods of calculating the deposition pattern may be derived for other molecular or atomic species.

As a first step, the molecular coherence is calculated. It is assumed that the molecular beam passes through a preparatory laser field to produce a superposition state composed of two Hamiltonian eigenstates. An extension to a superposition state involving more than two eigenstates is also possible. The superposition state is given by:

|ψ(t)> = _Cl|_φι> e-^ffiι^t/h + c₂|φ₂> e^⁷* (3)

where |cpi> represents the Hamiltonian eigenstates of energy Ej. This coherent state is prepared by two-photon absorption using a laser of frequency ω_L and amplitude E _L. Application of perturbation theory methods, such as is known in the art, leads to the evaluation of the population of the upper level as:

where ^ - (E_m-E_n)/h and Δ_2ωL ⁼ Ω₂₁ - 2ω_L≡ (E₂-Ei)/h - 2ω is the detuning of the two-photon absorption from resonance, and γ is the linewidth of the transition between two superposition states where m and n represent the quantum numbers corresponding to the rotational, vibrational and electronic states. Note that within the perturbation regime |c₂|² < 0.2, which restricts the power of the pump laser. Assuming a negligible value of Δ_2ω , a restriction on two parameters results, viz., |c₂|² and γ. Table I shows the value of the pump field E_L required as a function of γ, for |c₂|² = 0.2. The pump laser is set at the frequency CD required for a resonant two-photon absorption process between the levels of the ground electronic state ]φχ> = |v=0,J=0,M=0> and |φ₂> = |v=0,J=2,M=0>.

Table 1 γ (Hz) E_L (V/m)

8.3 xlO⁶ 1.0 xlO⁷

1.0 xlO⁹ 1.1 xlO⁸ In this calculation of the optical potential are included the ground electronic state X∑ and six electronic excited states viz., b ∑* , c ,'ι¹l ∑ v +

e ∑⁺ _u , b¹TT_tl , c^lTT_u and o¹TT_u whose transition dipole matrix elements between the ground and excited states are non-zero. Eigenstates involved in the superposition are taken to be in the X∑⁺ _g state. Defining |v_i5 Jj, Mj > as the i-th

eigenstate, the constraints of the selection rules mandate taking a superposition involving states where J₂=Jι or J₂=Jι+2. Here vj and J,- are the vibrational and rotational quantum numbers respectively and Mj is the component of Ji along the direction of polarization of the external field. A linearly polarized pump laser is used to achieve the allowed coefficient |c₂|² < 0.2.

As an example, Table 2 below lists the values of E_L needed to achieve different values of |c₂|² for superpositions of the ground electronic state between

|v=0, J=0, M=0 > and |v=0, J=2, M=0 >, where a realistic value of γ=1.0xl0⁹ Hz is assumed for N₂ molecules, and negligible detuning is assumed, i.e. Δ_2ωL « γ.

Table 2

|c₂|² E_L (V/m) I_L (W/cm²)

0.20 1.1 xlO⁸ 6.42 xlO⁹

0.10 9.3 xlO⁷ 4.59 xlO⁹

0.01 6.3 xlO⁷ 2.11 xlO⁹

0.001 2.9 xlO⁷ 1.54 xlO⁹

As a further example, Table 3, shows the value of the pump field E_L and the intensity I_L and ω_L required for different supeφositions of the ground electronic state between |v_ls J=0, M=0 > and |v₂, J=2, M=0 >, where as before, γ = 1.0 x 10 Hz, and |c₂| = 0.2, and negligible detuning are assumed. Table 3 i v₂ E_L (V/m) I_L (W/cm²) ω_L (Hz)

0 1 4.6 xlO⁸ 9.18 xlO¹⁰ 2.1988 x 10¹⁴

0 2 4.72 xlO⁸ 1.18 xlO^π 4.3673 x 10¹⁴

0 3 4.74 xlO⁸ 1.19 xlO¹¹ 6.5077 x 10¹⁴

0 4 7.5 xlO⁸ 2.98 xlO¹¹ 8.6241 x 10¹⁴

In the next step the beam downstream of the cooler is assumed to have a

Gaussian transverse speed distribution, f(v_λ) , where n is the

number of particles used for simulation. The center of the distribution v_x is zero or very close to zero, and the spread of the distribution is σ_vl . Calculations show that the deposition associated with a particular width σ_v may be approximately calculated by computing the deposition using a zero transverse velocity width and then broadening the computed peaks by 2 t_d σ_vι , where t_d is the time it takes for an atom or molecule to get from the collimated source to the deposition surface. The value for the longitudinal speed υn of the beam is taken to be 600 m/s. This value can be obtained from the expression:

where K is the Boltzmann constant, M_buff is the mass of the buffer gas atom used, γ is the specific heat ratio of the buffer gas and T₀ is the initial temperature. This expression is derived in the book "Atomic and Molecular Beam Methods" edited by G. Scoles, published by Oxford University Press, (1988). The effect of as described above aberrations due to the longitudinal speed distribution has been omitted here. The effect of the optical coherence of the standing waves, and the resulting optical potential, are now considered. The prepared N₂ beam is subjected to two standing CW fields, whose intensity is uniform over a distance of Lint, the length of interaction along x , but is zero elsewhere. A free flight distance L j can also be introduced between the field and the surface to observe its effect on the deposition.

The wave vectors of the two standing waves (SW) are \k \z — ψ-z and \k₂\z = ψ-z, where λi and λ₂ are the optical wave length of the two standing waves and z is the unit vector along the propagation direction. The combined SW field is of the form

E(z, t) = [2E{⁰⁾ cos(k_lZ)e^iωit + c.c] + [2E₂ ^] cos(k₂z + θ_F)e^iω2t + c.c]

≡ [E(ω₁) + c.c.] + [E(ω₂) + c.c] (5)

where c.c. denotes the complex conjugate of the terms preceeding it, θp is the relative phase of the two SW, E1⁰⁾ and E₂ ^{0) are given by E[⁰⁾ = (2 ώa)^{i 2} _and _E ⁽°⁾ ₌ (²l α)ⁱ/² _reSp_ectively with c, μ₀ and I being the speed of the light, permeability of the vacuum and the intensity of the i-th SW field. The phase Θ_F changes the position of the nodes and antinodes of E(z, t) along z and affects the position of the minima in the SW-induced OP. Choosing ω₂ — ω_x = Ω₂ι = &jJL_{} s0} that excitation of > by )ι and of

> by ω₂ lead to the same energy E = Eι + ωι = E₂ + hω₂. The interaction between the molecule and incident field is given by (—μ • E), where, within first order perturbation theory and neglecting state line widths, the dipole moment can be obtained as:

μ = μ(ω_x) + μ(-ω_x) + μ(ω₂) -f μ(-ω₂) + μ(ω₂₁ + ω_x) + μ(-ω_2ϊ - ω_x) +μ(ω_2x - ω₂) + μ(-ω_2i + ω₂)

= χⁱⁿ(ω_l)E(ω_l) + χⁿⁱ(ω_l)E(ω_l) + χⁱⁿ(ω₂)E(ω₂) + χⁿⁱ(ω₂)E(ω₂) +Xⁱⁿ(ω₂ι + ω )E'(ω_2l + ω_x) + χⁱⁿ(ω_2l - ω₂)E'(ω_2l - ω₂) + c.c. (6) O 01/71778

17

where E(ωi) are defined above, E'(ω_2l + ω_x) = E[⁰⁾ cos(kχz) exp[(ω₂ι + ωχ)t], and E'(ω₂ι - ω₂) = E^ cos(k₂z + Θ_F) exp[(ω₂₁ - ω₂)t], and μ(-ω) = μ(ω)*. The susceptibilities x above are given by

(^ω2^j - r ft 2^cι

1 1 1

ft ω i -f- U> ϋJji — Lϋ₂

ft ^■*— ' ω₅-ι -I- α>ι u)_j2 — ω_x

where ω_mn

>, n being the unit vector along the direction of polarization of the external field. Since both the SW are linearly polarized along the z axis (Eq.(6)) only the zz component of the polarizability, denoted χ_zz, need be considered. Here the superscripts "in" and "ni" refer to the interference and non-interference terras respectively of χ, where the interference terms are the direct consequence of the coherent superposition of the \φχ > and | ₂ > state. Control over χ(ω{) is obtained by changing various parameters, e.g., I -f_oil) l^cι|ι i^c2|) θjyi and θ , where ΘM is the relative phase of ci and c . The nonlinear dipole optical potential experienced by molecules in the N₂ molecular beam motion is

V_op = -μ.E = - ∑ V_ijlm (7) i=l,2 j=l,2;l=+,—,m=+,- where V{_ji_m ~ μ(lωϊ)E(mω_j). Here the components of dipole moment(Eq.(6)) other than those at frequencies ω_x and ω₂ are ignored. Note that there are three types of terms in Eq.(7) : (1) i=j ,1 ≠ m where Eq.(7) has only time independent parts, (2) l=m where Eq.(7) has terms which oscillate faster than ω_x or ω₂ and (3) i -ψ j, l φ m where Eq.(7) has terms which oscillate slower than either ω or ω₂. Adopting the rotating wave approximation(RWA) results in the exclusion of terms corresponding to case (2). The final expression for the optical potential is then

V_op = -2[R Vχχ₊-) + (V₂₂₊-) + M Vχ₂₊_) + &(V₂χ₊-)] = V£ + V£ (8)

where 5 denotes the real part and

-V₀

+ 4E₂<⁰⁾² cos²(k₂z + θp)χ™(ω₂) +4Eχ^{{ )}E₂ ^{{ )} cos(kχz) cos(k₂z + θ_F)χⁿⁱ(ω_x) 003( _! - ω₂)t +4Eχ^{{ )}E₂ ^{{ )} cos(kχz) cos(k₂z + θ_F)χⁿⁱ(ω₂) cos(ω₂ - ω_x)t] (9)

-V™ = 2[4Ef^? cos(kχz) cos(k₂z + 6_F)χ (ωχ) + 4E₂ ^{0? cos(kχz) cos(k₂z + θ_F)χlⁿ(ω₂) +4Ef⁾E ⁾ cos²(k₂z + θ_F)[χiⁿ(ωχ) 003(0 _! - ω₂)t - χf(ω_x) sm(ω_x - ω₂)t] +4E[⁰⁾Ei⁰⁾ cos²(k_xz){χ™(ω₂) cos(α;₂ - ω_x)t - χf(ω₂) sin(ω₂ - ω_x)t]} (10)

Here χ_r denotes the real part, and χι denotes the imaginary part of the susceptibility. Numerical experiments show that the time-dependent parts in Eqs.(9) and (10) can be neglected; they are found not to cause any significant change in the trajectory. Therefore,

y™ = -{SE?² cos²(kχz)χⁿⁱ(ω_x) + 8^⁰⁾² cos²(k₂z + θ_F)χⁿⁱ(ω₂)} (11) V% = -[8Si⁰⁾² cos(k z) cos(k₂z + θp)χ₇ ⁿ(ω_x) + 8E? cos(kχz) cos(k₂z + θ_F)χ^ⁱ (ω₂)]

(12)

Thus, the optical potential in the absence of molecular coherence consists of two terms each representing the dipole interaction of the field and the induced molecular dipole of the same frequency.

Thus, the molecules experience the above optical potential, which is an oscillating function along the z direction and which acts as an array of lenses. Each minimum of the potential behaves as a focusing center and each maximum behaves as a defocusing center. The results is an inhomogeneous aperiodic distribution of potential minima whose depths vary, depending on z, Ex , E₂ , |cχ|, |c₂|, ΘM and Θ_F. Reference is now made to Figs. 2 and 3 (to be discussed in detail hereinbelow), which show typical results of the molecular density distribution obtained along the ^-direction, together with the corresponding optical potential. It is seen that V™ represents a periodic array of lenses, whereas V_op = V™ + V^ does not. Thus, unlike traditional atomic lithography where the optical potential is purely periodic, different optical potentials can be obtained by altering terms in the potential which enter via quantum interference. This feature of the present invention enables pattern formation not realized in prior art conventional atomic lithographic techniques.

The classical density distribution of molecules on the substrate is now calculated. For an initial uniform spatial distribution of molecules in the beam after the cooling process, p(z, 0) = constant, the classical trajectories can be calculated for every molecule interacting with the optical potential given by Eq.(8) to obtain the spatial distribution of molecule p(z, T) at time T — T_int + ^^1L, where T_int is the actual interaction interaction time between the molecules and the optical potential, and is equal to

The numerical steps in the computation for this molecular density distribution after interacting with the SW-induced OP are as follows : Step 1: At t=0, consider a fixed number of molecules (n=20,000 in the example shown) uniformly distributed over a small portion of the profile of the cooled molecular source —αλ₂ < z^ < α\₂, where α = 2 in the example shown

Step 2: Divide this range of

where i=l, 2, , Nχ S0 that every ΔzW = J^ length of the profile of the cooled molecular source contains n_x = n/N_x number of molecules.

Step 3: Fit these n_x molecules into a transverse speed distribution function given by f(v±). This leads to say, m* molecules having transverse speed υ±. such that j rrij = J f(v±)dυ± = n_x. Every N discrete length of size z^ has the same distribution.

Step 4: Calculate the force at every point

and solve the set of equations given by Eqs. (1) and (2) where Pi is given by m_N2υ±.. For any i, the same equation with the same v_x_. will be solved m-i times.

Step 5: The final distribution p(z_s, T) of the molecule along z_s onto a substrate(s) is obtained by counting the number of particles hitting a particular region along z_s upon their deposition onto a substrate. The length of z_s has been fixed at 4λ₂ for the computational example shown.

This method was used to compute results for various transverse velocity distributions. Below we report results for the case where σ_υχ = 0. This can be corrected for nonzero σ_V by the method described above. The deposition density distribution patterns obtained are functions of the parameters used in performing the coherently controlled optical focusing of the molecular beam. Ideally, every minimum of the Optical Potential OP acts as a focusing center, giving rise after a sufficient time of interaction, to a delta function molecular density distribution, and producing a corresponding pattern on the substrate. The deposition pattern formed, p (z_s, T) can be approximated by the expression:

p (z_s, T) = ∑ |a(z_s,T)| ² f(z,T) δ(z_s-z_m) (13) m where |a(z_s,T)| ² is the intensity of focusing at a given point z_s onto the substrate at time T, and f(z,T) may be chosen as a Lorentzian function. The point Z_m is the position of a minimum in the optical potential. The width of f(z,T) together with |a(z_s,T)| measures the quality of focusing of the molecules, in terms of the intensity and width of the focused beam particle deposits. The focusing quality of the deposition is dependent on a number of parameters, namely, cχ₅ c₂, Θ_F, σ_vj_, IΦ₂ ^>, L_ff, Ti_nt, Eι⁽⁰⁾ and E₂ ⁽⁰⁾ . As illustrative of the method of the present invention, the effect of these parameters on the nature of the resulting molecular deposit is now described.

(a) The Effect of Molecular Coherence:

The parameters C], c₂, Θ_M, |φι> and |φ₂> introduced into the OP are the direct consequence of molecular coherence. As can be seen from the expressions for V_op (equations 11 and 12), these parameters do not affect the location of the OP minima. Hence they have no direct effect on changing the position of the deposition onto a substrate. However, they do have a direct effect on the intensity of the deposition resulting from the change in the magnitude of the OP. If there were no molecular coherence, deposition would be due only to V_op , i.e., the usual dipolar interaction between the molecule and the coherent electric field.

The effect of molecular coherence on the deposition distribution is shown in Figs. 2(a) to 2(d), which show how the density distribution of deposition p(z_s,Ti_n) and the optical potential vary along the z_s direction, both in the presence of and in the absence of molecular coherence. The scale for the optical potential is graduated in meV, while the distance along the z_s direction is measured in μm. The results shown in Figs. 2(a) to 2(d) are calculated using 20,000 molecular trajectories, and under the conditions: σ_v± = 0 m/s, E₂ ⁽⁰⁾ = 1.0 x 10⁶V/cm,

= 1.0 x 10⁴ , Θ_F - -2.65 rad,

T_M ⁼ 0.625μsec, λi = 0.628 μm, λ₂ = 0.736 μm and L_ff = 0. The superposition is created between the |000> and |020> states.

In Fig. 2, and in all of the succeeding figures, the computations were done assuming a transverse velocity of zero. However, the results in the figures may be readily corrected to include a non-zero transverse velocity distribution by assuming that the transverse velocity distribution is Gaussian with a width σ_v±. The result of such a transverse velocity distribution is to broaden the features in the figures by approximately V2t_da_Vi_, where t is the distance from the cooled, collimated source to the deposition surface.

Figs. 2(a) and 2(b) show the effects of the absence of molecular coherence. Fig 2(a) shows the molecular density distribution and Fig. 2(b) shows the corresponding optical potential. The dipole force due to the non-interference term is exerted primarily along the gradient of the light intensity of the field with frequency ω₂ since E₂ » Ei. This results in a force acting on the molecules in the direction of the minima of the intensity of the light field with frequency ω₂, i.e., toward the nodes of the standing wave. This is the standard result realized in the atomic beam manipulation techniques known in the prior art, where deposition forms at the nodes of the SW.

If, however, the full optical potential V_op is applied, as given by the sum V_op ^(m) + V_op ⁽ the distribution of the focusing centers changes significantly. Figs. 2(c) and 2(d) show the density distribution and optical potential for the same conditions as in Figs. 2(a) and 2(b), but including the effects of molecular coherence. A rather irregular deposition is obtained, with peaks of different intensities, some significantly stronger than others. For the value

= 0.625 μsec used in the example shown in plotting Figs. 2(a) to (d), the weaker spots appear at intervals of approximately 0.5λ₂ , with the brighter spots appearing at larger intervals. By contrast, without molecular coherence, as is seen from Fig. 2(a), there is a uniform array of deposition peaks of lower intensity than the maximum peaks obtained with molecular coherence, appearing at a regular interval of 0.5λ₂.

Figs. 3(a) to 3(d) are plotted under the same conditions as Figs. 2(a) to 2(d), but show an enlarged section in the z_s direction, to better illustrate the differences between the bright and weak deposition spots.

Reference is now made to Figs. 4(a) to 4(d) which show the separate contributions to the molecular density as a function of z_s, due to the first and second SW fields, Eχ⁽⁰⁾ and E₂ ⁽⁰⁾, taking into account only the non-interference term V_op ^(m) of the optical potential. The parameters used for this example are identical to those used for calculating the distributions shown in the various plots of Figs. 2 and 3. Fig. 4(a) shows a plot of p for the first field, Fig. 4(b) shows the values of V_op ^(m) for the first field, Fig. 4(c) shows a plot of p for the second field, and Fig. 4(d) shows the values of V_op ^(m) for the second field. It is observed that since E » Eι_; the contribution of the SW field of frequency ω_x is small compared with that of ω₂ . It should also be noted that Fig. 4(c) and Fig. 3(a) are essentially equivalent.

Figs. 5(a) to 5(f) and Figs. 6(a) to 6(f) show the dependence of p(z_s,Ti_nt) on different superpositions of states. Figs. 5(a) to 5(f) show the results using the superposition ( |000> + |v00>), where v takes the values 1 to 6 for Figs. 5(a) to 5(f) respectively, while Figs. 6(a) to 6(f) show the results using the superposition ( |000> + |v20>), where v takes values of 0 to 5 for Figs. 6(a) to 6(f) respectively. In the calculations used for plotting all parts of Figs. 5 and 6, the values γ = lxlO⁹ Hz and |c₂|² = 0.2 are assumed, and the other parameters used are identical to those used in Figs. 2 to 4, except that in fig. 5, Θ_F = 2.65 rad.

Figs. 7(a) to 7(f) show the dependence of p(z_s,Ti_nt) on |c₂|² for six different values of |c₂|² . For Fig. 7(a), |c₂|² = 0.01, for (b) 0.1, for (c) 0.15, for (d) 0.2, for (e) 0.4 and for (f) 0.5. The superposition used is between the |000> and |020> states, and all of the parameters used, with the exception of the variable |c₂|², are those used in Figs. 6. Clearly, the structure of the deposition distribution changes with changing |c₂| .

Reference is now made to Figs. 8(a) to 8(d), which show calculated plots of the optical potential corresponding to the parameters E₂ ⁽⁰⁾ = l.OxlO⁶ V/cm, Θ_F = -2.65 rad, λi = 0.628μm, λ₂ = 0.736μm, γ = lxlO⁹ Hz and |c₂|² = 0.2, and for the superposition between |000> and |020> states. The different plots show the results corresponding to four different cases, namely: (a) without molecular coherence and with E₂ ⁽⁰VEi⁽⁰⁾ = 1.0 x 10⁴ , (b) with molecular coherence and E₂ ⁽⁰⁾/Eι⁽⁰⁾ = 1.0 x 10⁴, (c) with molecular coherence and E₂ ⁽⁰⁾/Eι⁽⁰⁾ = 10, and (d) with molecular coherence and E₂ ⁽⁰VE_I ⁽⁰⁾ = 1.0 . Plots corresponding to cases (b), (c) and (d) show V_op for 50 different values of Θ_M. It is observed that change in the phase difference between C_! and c₂, i.e. change in the parameter Θ_M, does not significantly alter the shape of the optical potential, except for minor changes in the depth of the well. As such, the deposition pattern on the surface cannot be altered significantly by means of changing Θ_M.

(b) The Effect of Optical Coherence.

Figs. 9(a) to 9(c) displays the density distribution p(z_s,Ti_nt) obtained for three different values of Θ_F , for the supeφosition |000> + |020>. In Fig. 9(a), Θ_F = -2.65 rad, in Fig 9(b), Θ_F = -2.0 rad., and in Fig. 9(c), Θ_F = -1.0. The other parameters are those as used in the calculations for the previous relevant figures, such as Figs. 6(a), 7(a), 8(b), etc. The parameter Θ_F is seen to directly alter the position of the peaks, as well as their width and intensity.

Figs. 10(a) to 10(f) illustrate the variation in the form and intensity of the strongest peak shown in Fig. 9(a), at z_s = -0.49, as a function of the relative phase of the two standing waves. In Figs. 10(a) to 10(f), the absolute value of Θ_F is set at -2.65, -2.55, -2.45, -2.35, -2.25 and -2.15 radians respectively. It is seen that the shaφest peak in the deposition density is obtained for Θ_F = -2.65 rad., and that the peaks become weaker and broader as Θ_F changes from -2.65 to -2.15 radian. In other words, there is an optimum value for Θ_F that results in the most intense and highest resolution peak.

Figs. 11(a) to 11(f), using similar calculations, show the variation in the form and intensity of the strongest peak shown in Fig. 9(a), as a function of the intensity of the two SW fields. In Figs. 11, the value of E₂ ⁽⁰VEI⁽⁰⁾ is set at l.OxlO⁴ and E₂ ⁽⁰⁾ = (a) l.OxlO⁶, (b) 0.97xl0⁶, (c) 0.94xl0⁶, (d) 0.91xl0⁶, (e) 0.88xl0⁶, and (f) 0.85xl0⁶ V/cm. Approximately optimum values of E₂ ⁽⁰⁾ = 1.0xl0⁶V/cm and E₂ ⁽⁰VEι⁽⁰⁾ = l.OxlO⁴ result in a deposition density distribution peak with maximum intensity and minimum width. As is seen from Figs. 11(b) to 11(f), deviation from these values results in the peak becoming fainter and broader.

(c) Effect of Beam Parameters

The beam parameters, T^_t , L_ff and σ_v also have an effect on the deposition density distribution. This effect is illustrated in the density plots shown in Figs. 12(a) to 12(c) and Figs. 13(a) to 13(d). Since the SW-induced optical potential is comprised of a series of harmonic-type potential wells of varying depth, the time of interaction Ti_nt plays a crucial role in determining the nature of the deposition. In general, if T_int is longer than the quarter period of oscillation of the molecule in any of the potential wells, shaφ peaks will not be formed in the molecular density distribution. Instead the distribution will have large number of smaller peaks. Expressed mathematically, a single shaφ peak in the region of the potential minima will be formed only when T_m- _t ~ (2n+l)T/4, where T is the period of harmonic oscillation for a particular potential well. When Tj_nt ≠ (2n+l)T/4, every peak formed at every potential minima after a time T/4, or (2n+l) multiples of T/4, splits into many weaker peaks.

This result can be demonstrated by reference to Figs. 12(a) to 12(c), which show plots of the spatial values of p(z_s,Tj_nt) obtained for three different values of T_kt, for the supeφosition |000> + |020>, where γ = lxlO⁹ Hz and |c₂|² = 0.2. The values of T^_t are (a) 0.5μsec (b) 0.625μsec, and (c) 0.8μsec. The other parameters used in calculating the data are: σ_vl = 0 m/sec, E₂ ⁽⁰⁾ = 1.0 10⁶V/cm, E₂ ⁽⁰⁾/Eι⁽⁰⁾ = l.OxlO⁴, Θ_F = -2.65 rad, λi = 0.628μm, λ₂ = 0.736μm and L_ff = 0.

In accordance with the explanation given above, it is seen that the shaφ peak formed for T_int = 0.625μsec in Fig. 12(b) at z_s ~ -0.5μm, splits into two relatively weak peaks at T_int = O.δμsec, as seen in Fig. 12(c). Similarly, for Ti_nt = 0.5μsec (Fig. 12a), an intense single peak is obtained at z_s ~ -1.2μm, because the time period T, corresponding to the potential in the region z_s ~ -1.2μm is such that T/4 ≡ 0.5μsec. Similarly, the most intense peak formed at T^_t = 0.625μsec (Fig. 12b) appears much less intense for Tj_nt = 0.5μsec (Fig. 12a) because Ti_nt <T/4. The shaφ single peak formed for Tj_nt = 0.5μsec at z_s ~ -1.2μm implies that the optical potential well at z_s ~ -1.2μm corresponds to the period of oscillation ~ (0.5 / 4) μsec for N₂.

It is thus observed that the molecular density distribution for different interaction times is a function of the optical potential, and conversely, knowledge of the spatial structure of the deposition density enables information to be obtained about the optical potential.

All of the above results of the application of the present invention are obtained with zero free flight distance, L_f = 0, between the applied field and the surface onto which the molecules are deposited. The addition of any finite free flight distance leads, for the parameters studied, to a deterioration of the quality of the deposition in terms of its intensity and line width. The density distribution of deposition as a function of free flight distance is shown in Figs. 13(a) to 13(d). The other deposition parameters for Figs. 13(a) to 13(d) are the same as those used for the previous examples, such as shown in Fig. 12(b). The values of L_ff used in these figures are: Fig. 13(a), L_ff = 0.0; 13(b), L_ff =25μm; 13(c), L_ff=50μm; and 13(d), L_ff =75 μm. It is observed that the intensity of the deposition peak decreases rapidly with increase of L_ff , and the peak itself broadens and splits into lower peaks.

The effect of the rotational cooling on the quality of the deposition is illustrated in Figs. 14(a) to 14(d), which show the width of a typical deposited peak as a function of the rotational temperature of the molecules. Fig. 14(a) is shown at a temperature T_r of 298°K, 14(b) at 150°K, 14(c) at 50°K, and 14(d) at 10°K. The graphs show that the deposited peaks becomes wider and more erratic with decrease in the rotational temperature. The effect of rotational cooling is thus opposite to that of the translational cooling.

Finally, Figs. 15(a) to 15(d) are graphs of density distributions obtained, for the deposition of atomic rubidium for different interaction times, both in the presence of and in the absence of coherent control, according to another preferred embodiment of the present invention. The coherent control is achieved using a supersposition of Rydberg states of the atoms, in this case the 8s and 8d states. This preparation can be performed by laser exciting the species from the ground atomic state, preferably where the atoms already have, as a result of preliminary laser cooling, a small transverse velocity distribution. The atoms are passed through two laser fields with wavelengths of 3430.8 nm and 13291.9 nm, respectively, and with intensities of only 1.91 x 10^"3 Watt per square cm, and 0.19 Watt per square cm., respectively. Such weak fields are effective because of the high polarizability obtained from Rydberg excited atoms. The results shown in Figs. 15(a) to 15(d) are obtained with the values Θ_M = 1.5 rad and Θ_F = 1.26 rad, where Θ_M and θ_Fare defined above and with lc^² =0.8 and |c₂|² = 0.2.

In Figs. 15(a) and 15(b) the deposition results atoms pass through the field for 0.26 μsec. In the absence of any interference terms, i.e. where the atoms are only subject to V then the resultant deposition is shown in Fig. 15(b). By contrast, when both V^m and V , are present i.e. where the interference term is included, then the deposition is much improved, as observed in Fig. 15(a). Similar results are shown in Figs. 15(c) and 15(d) for interaction times of 0.36 μsec. It is apparent from the examples shown, that, as in the molecular deposition case, for a specified interaction times, the application of coherent control gives much improved, i.e. narrower, peaks. Furthermore, the peaks may have aperiodic symmetry, unlike the previously mentioned prior art methods of atomic beam deposition.

This invention has been described heretowith in terms of the deposition of the atoms or molecules as a layer on the surface of a substrate to produce a predetermined pattern of material. According to further preferred embodiments of the present invention, the deposited atoms or molecules can be implanted into the surface of a semiconductor substrate, in order to produce selectively doped regions of nanometric resolution according to the predetermined pattern desired. This feature is useful in the production of high resolution semiconductor devices. The atoms or molecules used are chosen according to the semiconductor material to be doped, and the type of doping required.

The embodiments enumerated above have been described in terms of coherence arising out of two supeφosition states, and of focusing arising from the passage of the beam through two standing wave fields. According to further preferred embodiments of the present invention, use can be made of supeφosition of more than two states, and alternatively or additionally, of focusing by means of more than two standing wave fields. Use of these preferred embodiments provides more degrees of freedom in the choice of the parameters used to control the focusing of the atomic or molecular beam, thus allowing more flexibility in the achievement of the specific deposition pattern desired.

It will be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described hereinabove. Rather the scope of the present invention includes both combinations and subcombinations of various features described hereinabove as well as variations and modifications thereto which would occur to a person of skill in the art upon reading the above description and which are not in the prior art.

Claims

CLAIMSWe claim:

1. A method of depositing molecules in a predetermined pattern onto a surface by means of coherently controlled optical focusing of a beam of said molecules.

2. The method according to claim 1 and comprising the steps of: providing a collimated beam of molecules; directing said beam through a first electromagnetic field operative to produce a supeφosition of bound states of said molecules; and thereafter directing said beam through a second electromagnetic field, such that said molecules are focused onto said surface in said predetermined pattern.

3. The method according to claim 2 and wherein said second electromagnetic field comprises at least two standing waves.

4. The method according to claim 2 and wherein said supeφosition of bound states of said molecules is formed by means of a two-photon absoφtion process.

5. The method according to claim 2 and also comprising the step of cooling said beam of molecules before production of said supeφosition of bound states.

6. The method according to claim 5 and wherein said step of cooling said beam is effected by means of a mechanical cooling process.

7. The method according to claim 6 and wherein said mechanical cooling process is effected by expansion of said beam through a supersonic nozzle.

8. The method according to claim 5 and wherein said step of cooling said beam is effected by means of a laser cooling process.

9. The method according to claim 8 and wherein said step of cooling said beam also comprises a mechanical cooling step.

10. The method according to claim 9 and wherein said mechanical cooling process is effected by expansion of said beam through a supersonic nozzle.

11. The method according to claim 2 and wherein said first electromagnetic field is formed by at least one first laser beam.

12. The method according to claim 11 and wherein said first laser is a CW laser.

13. The method according to claim 11 and wherein said first laser is a pulsed laser.

14. The method according to claim 3 and wherein said standing waves are formed by beams from at least one second laser.

15. The method according to claim 1 and wherein said predetermined pattern is aperiodic.

16. The method according to claim 2 and wherein said predetermined pattern is determined at least by the parameters of said first electromagnetic field and by the parameters of said second electromagnetic field.

17. The method according to claim 2 and also comprising the step of directing said beam through a third electromagnetic field, arranged approximately orthogonally to said second electromagnetic field, and in effectively the same common plane, such that said molecules are focused onto said surface in a predetermined array pattern.

18. The method according to claim 1 and wherein said predetermined pattern has a resolution of less than 50 nanometers.

19. The method according to claim 1 and wherein said predetermined pattern has a resolution of less than 20 nanometers.

20. A method of depositing molecules in a predetermined pattern onto a surface by means of coherently controlled optical focusing of a beam of said molecules, wherein said molecules are operative to perform nanolithography.

21. A method of depositing molecules in a predetermined pattern onto a surface according to claim 1, wherein said surface is a storage medium, and said molecules are operative to write information on said storage medium.

22. A method of depositing molecules in a predetermined pattern onto a surface according to claim 1, wherein said molecules in said predetermined pattern constitute a photolithographic mask.

23. A method of depositing molecules in a predetermined pattern onto a surface according to claim 1, wherein said molecules produce doped regions within said surface.

24. A method of depositing molecules in a predetermined pattern onto a surface according to claim 1, wherein said molecules produce a high profile tip structure on said surface.

25. A method of depositing molecules in a predetermined pattern onto a surface according to claim 1, wherein said molecules produce an optical grating structure on said surface.

26. A method of depositing molecules in a predetermined pattern onto a surface according to claim 1, wherein said molecules are operative to perform micro-etching.

27. A system for the deposition of molecules in a predetermined pattern onto a surface by means of coherently controlled optical focusing of a beam of said molecules.

28. A system for the deposition of molecules according to claim 27, and comprising: a source emitting a beam of said molecules; a cooler for minimizing the transverse velocity components of said molecules of said beam; a first electromagnetic field through which said beam is directed, operative to produce a supeφosition of bound states of said molecules; and a second electromagnetic field, through which said beam is thereafter directed, such that said molecules are focused onto said surface in said predetermined pattern.

29. A system for the deposition of molecules according to claim 28, and wherein said cooler is a laser cooler.

30. A system for the deposition of molecules according to claim 29, and also comprising a mechanical cooler.

31. A system for the deposition of molecules according to claim 30, and wherein said mechanical cooler comprises a device for the expansion of said beam through a supersonic nozzle.

32. A system for the deposition of molecules according to claim 28 and wherein said first electromagnetic field is formed by at least one first laser beam.

33. A system for the deposition of molecules according to claim 28 and wherein said second electromagnetic field comprises at least two standing waves formed by laser beams.

34. A method of depositing atoms in a predetermined pattern onto a surface by means of coherently controlled optical focusing of a beam of said atoms.

35. The method according to claim 34 and comprising the steps of: providing a collimated beam of atoms; directing said beam through a first electromagnetic field operative to produce a supeφosition of excited states of said atoms; and thereafter directing said beam through a second electromagnetic field, such that said atoms are focused onto said surface in said predetermined pattern.

36. The method according to claim 35 and wherein said excited states are Rydberg states.

37. The method according to claim 35 and wherein said second electromagnetic field comprises at least two standing waves.

38. The method according to claim 35 and also comprising the step of cooling said beam of molecules before production of said supeφosition of excited states.

39. The method according to claim 38 and wherein said step of cooling said beam is effected by means of a laser cooling process.

40. The method according to claim 39 and wherein said step of cooling said beam also includes a mechanical cooling step.

41. The method according to claim 40 and wherein said mechanical cooling process is effected by expansion of said beam through a supersonic nozzle.

42. The method according to claim 35 and wherein said first electromagnetic field is formed by at least one first laser beam.

43. The method according to claim 42 and wherein said first laser is a CW laser.

44. The method according to claim 42 and wherein said first laser is a pulsed laser.

45. The method according to claim 37 and wherein said standing waves are formed by beams from at least one second laser.

46. The method according to claim 34 and wherein said predetermined pattern is aperiodic.

47. The method according to claim 35 and wherein said predetermined pattern is determined at least by the parameters of said first electromagnetic field and by the parameters of said second electromagnetic field.

48. The method according to claim 35 and also comprising the step of directing said beam through a third electromagnetic field, arranged approximately orthogonally to said second electromagnetic field, and in effectively the same common plane, such that said atoms are focused onto said surface in a predetermined array pattern.

49. The method according to claim 34 and wherein said predetermined pattern has a resolution of less than 50 nanometers.

50. The method according to claim 34 and wherein said predetermined pattern has a resolution of less than 20 nanometers.

51. A method of depositing atoms in a predetermined pattern onto a surface by means of coherently controlled optical focusing of a beam of said atoms, wherein said atoms are operative to perform nanolithography.

52. A method of depositing atoms in a predetermined pattern onto a surface according to claim 34, wherein said surface is a storage medium, and said atoms are operative to write information on said storage medium.

53. A method of depositing atoms in a predetermined pattern onto a surface according to claim 34, wherein said atoms in said predetermined pattern constitute a photolithographic mask.

54. A method of depositing atoms in a predetermined pattern onto a surface according to claim 34, wherein said atoms produce doped regions within said surface.

55. A method of depositing atoms in a predetermined pattern onto a surface according to claim 34, wherein said atoms produce a high profile tip structure on said surface.

56. A method of depositing atoms in a predetermined pattern onto a surface according to claim 34, wherein said atoms produce an optical grating structure on said surface.

57. A system for the deposition of atoms in a predetermined pattern onto a surface by means of coherently controlled optical focusing of a beam of said atoms.

58. A system for the deposition of atoms according to claim 57, and comprising: a source emitting a beam of said atoms; a cooler for minimizing the transverse velocity components of said atoms of said beam; a first electromagnetic field through which said beam is directed, operative to produce a supeφosition of excited states of said atoms; and a second electromagnetic field, through which said beam is thereafter directed, such that said atoms are focused onto said surface in said predetermined pattern.

59. The method according to claim 58 and wherein said excited states are Rydberg states.

60. A system for the deposition of atoms according to claim 58, and wherein said cooler comprises a laser cooler.

61. A system for the deposition of atoms according to claim 60, and also comprising a mechanical cooler.

62. A system for the deposition of atoms according to claim 61, and wherein said mechanical cooler comprises a device for the expansion of said beam through a supersonic nozzle.

63. A system for the deposition of atoms according to claim 58 and wherein said first electromagnetic field is formed by at least one first laser beam.

64. A system for the deposition of atoms according to claim 58 and wherein said second electromagnetic field comprises at least two standing waves formed by laser beams.