JP2002537202A - Method for preparing library using combined molecular beam epitaxy (COMBE) device - Google Patents

Abstract

SUMMARY OF THE INVENTION The present invention relates to apparatus and methods for the synthesis and identification of complex metal oxides formed as a variation of a combination by molecular beam epitaxy on a substrate, and the results of such synthesis (ie, It relates to a combinatorial array (or library) of samples consisting of stable or metastable composite oxides, multilayers, and superlattices. A position-addressable combinatorial library of composite oxides having a thermally labile structure comprises a multi-region substrate and is formed on a region of the substrate, which is of the formula (A ₁ ) _x1 (A ₂ ) _{x2. n)} a thermostable or metastable oxides having _xn O _y, wherein at least one element component a _i is a metal, x _i, y is a natural number or a fraction containing 0, n =. 2 to 20, wherein the stoichiometry or structure of the oxide varies systematically and in a known manner in at least one elemental component, with one pair of opposing side regions and one side region It travels between the other side area. Further disclosed is the use of the library in identifying composite oxides having desired properties (eg, high temperature superconductivity).

Description

DETAILED DESCRIPTION OF THE INVENTION

FIELD OF THE INVENTION The present invention relates to devices and methods for the synthesis and identification of complex metal oxides formed on substrates as combinatorial changes by molecular beam epitaxy, and the results of such synthesis (ie, Arrays of sample combinations include stable or metastable complex oxides, multilayers, and superlattices). Various aspects of the synthesis process may be performed by a program control processor.

(1) Ivan Bozovic et al., Physica C235-240: 1
78-181 (1994) [2] D. Xiang et al., Science 268: 1738-1740 (
1995) [3] Gabriel Briceno et al., Science 270: 273-
275 (1995) [4] Earl Daniels et al., Nature 389: 944-94.
8 (1997) [5] Earl Daniels et al., Science 279: 837-8.
39 (1998) [6] Ivan Bozovic et al. Superconductivit
y7: 187-195 (1994) [7] Ivan Bozovic and J. et al. N. Eckstein, Appl
ied Surface Science 113-114: 189-197 (1
997) [8] A. Kraus and O.M. Auciello, Ed. (John Wi
Lee and Sons, New York, 1999)
CTERIZATION OF THIN FILM GROWTH PROC
Chapter 3 of ESSES VIA IN SITU TECHNIQUES, Iva
n Bozovic et al., "Reflection High-Energy El"
Electron Diffraction as a Tool for Rea
l Time Characterization of Growth of
 Complex Oxides "[9] C.I. J. Kraisinger and D.S. G. FIG. Schlom, J .;
Vacuum Science and Technology (1998) seal
During printing [10] E. FIG. Klausmeier-Brown et al., Applied P
physics Letters 60: 657-659 (1992) [11] Bauer, Report of Progress in P
physics 57: 895-938 (1994) [12] S. Altman et al., Surface Rev. and Let
t. 5: 1129-1141 (1998) [13] A.I. R. Kraus et al., Materials Research Soc.
ieety Bulletin 20 (5): 18-23 (1995) (Background of the Invention) Complex (ternary, quaternary, etc.) oxides are a subject of increasing interest in science and technology.
Was. These composites include a high temperature superconductor (La_2-xSr_xCuO_Four, YBa_TwoCu _Three O_7-x, Or Bi_2-xPb_xSr_TwoCa_n-1Cu_nO_{2n + 4 + y}And others)
Electric body (Pb_1-xyLa_xZr_yTiO_ThreeOr Ba_1-xSr_xTiO_ThreeEtc.), Iwayu
(La) exhibiting a strong magnetoresistance effect_1-xySr_xCa_yMnO_ThreeEtc.)
And various other functionalities (pyroelectric, piezoelectric, photoconductive and luminescent
And other oxides [1].

From the above several composition formulas, the number of possible compositions for ternary oxides is already enormous due to the large number of possible stoichiometric ratios. In fact, the complexity increases exponentially with the number of elements combined. To understand the magnitude of this problem (and why nothing is known about such compounds),
0, that is, a compound containing the given element, that is, the general formula (A ₁ ) _x1 (A ₂ ) _x2 . . . _Let us speculate that it would be desirable to search for compounds having (A ₁₀ ) _x10 O _y . In particular,
Given that the phases are different when the index of at least one element differs, for example by more than 0.01, under these assumptions there will be more than 10 ¹⁶ different compositions to try. .

[0004] The traditional search approach for new inorganic materials is to mix and react predetermined amounts of some starting elements or compositions, and perform some characterization to determine the properties of the sample. It was to determine the structure or some physical properties. With this feedback, the synthesis of other samples, such as different compositions, can proceed. In general, such a sequential search is slow and obviously inadequate when dealing with more complex compositions without a very strong intuition of where to look.

For a faster and more systematic search, one would like to employ some parallel processing. That is, many (100, 1000 or even more) batches of samples are synthesized at one time with a systematic and known stoichiometric variation over a series. Ideally, one would like to test the samples in parallel (ie, all at once). If this sample is coded in some way by a one-dimensional or two-dimensional matrix, it can be known which composition under study provides the optimal value.

[0006] This idea is known as combinatorial search for new materials, and combinatorial chemistry has indeed been widely used with great success in drug research for quite some time. More recently, combinatorial chemistry has also been implemented in inorganic chemistry, particularly in search for new complex oxides, as follows [2,3]. For example, an array of 10.times.10 substrates
It is exposed to several atomic or molecular beams emanating from the sputter source. (
Alternatively, a single large area substrate can be used, which can then be cut. 2.) A mask is used to selectively block one substrate or the other, whereby different amounts of a given composition are deposited on different substrates. When this is complete, the samples are all heated to react the composition. This technique has been successfully used to find new phosphors in a variety of colors and more efficient than those currently used in cathode ray tubes. [4,5] This particular physical property is more acceptable in a parallel test-simply irradiating the sample array with ultraviolet light and observing which particular sample shines the most.

One drawback of this method is that only thermodynamically stable compositions can be formed in this method, and most samples end up in (generally not useful) multiphase mixtures. And even a single phase is polycrystalline, complicating the determination of its intrinsic material properties.

[0008] ALL-MBE (Atomic Stacked Molecular Beam Epitaxy) is a technology developed in the last decade for the deposition of single crystal thin films of copper salt superconductors and other complex oxides. [
[1,6,7] ALL-MBE systems consist of an ultra-high vacuum chamber with many thermal transition sources (Knudsen cells) with computer-controlled shutters. Atomic flux monitoring was found to be most useful because atomic absorption spectroscopy was accurate enough to detect changes of less than 1 percent and fast enough to allow real-time feedback control. By using a pure ozone beam, sufficient oxidation can be achieved under high vacuum conditions,
Enables in situ monitoring of surface structures by HEED (reflective high energy electron diffraction) and other surface analysis tools. [8] Thin-film growth by ALL-MBE typically shows an atomically flat surface and, in the case of superlattices and multilayers, shows a substantially perfect interface. next,
Surfaces and interfaces can be controlled. For example, it is grown, or the surface layer of the cleaved _{Bi 2 Sr 2 CaCu 2 O 8} + x single crystal and most probably Bi-O
Layer-This is the natural termination plane as well as the easiest cleavage plane. However, the stack growth may terminate at any desired atomic monolayer, such as at the CuO ₂ plane. If one wishes to switch to another compound at that point, the starting plane can again be optionally selected. This provides great flexibility in adjusting the surface and interface, as long as surface reconstruction can be avoided, and opens up new avenues in the fabrication of devices such as, for example, three-layer (ie, sandwich) bonding. Traditionally, a barrier layer is inserted between two natural termination layers of the host material (bottom electrode and top electrode).
Here, it is possible to insert a layer of a heterogeneous compound between two “inner” planes of the host compound that are not the natural termination plane.

[0009] Stack growth, in turn, facilitates depositing a portion of a monolayer of a given atomic species.
To complete a monolayer with other elements. Thus, without bulk diffusion, simply
Optionally, the layers can be chosen to be doped. Dopants have different valences
Can be selected to modify and control the local charge carrier density.
Modulation doping was achieved in this way. [7] Next, some energetically degenerate (degenerate) occurs in the complex compound.
e) Phases or near-degenerate phases are often found. A well-known example is Bi_TwoSr_TwoCa _n-1 Cu_nO_{2n + 4 + x}The phases in the family, 2201, 2212, 2223
, 2234, etc. In general, cooling the melt mixes these phases.
Compounds are obtained for entropic reasons. However, stack growth is like this
Between different phases, i.e., selectively achieve only those desired.
To make it longer. Because phase separation requires extensive bulk diffusion,
Even if the temperature does not rise, the phase spatial barrier prevents the phase from growing. this
In this way, Bi_TwoSr_TwoCa_n-1Cu_nO_{2n + 4 + x}And BiSr_TwoCa_n-1Cu_nO_{Two n + 3 + x} (N is up to 10).
Were the first true "artificial" high-Tc materials. [1,6] (Summary of the Invention) In one aspect, the present invention provides a compound having a thermally stable or metastable structure.
Includes composite oxide location-addressable combinatorial library. This library is
On a substrate having a substrate surface bounded by two or more pairs of opposing side regions
A plurality of surface regions are formed and defined at known locations with respect to the side regions. This
Formed on these regions is the formula (A)₁)_x1(A_Two)_x2... (A_n)_xnO_yWith
Is a thermally stable or metastable oxide, wherein the elemental component A_iSmall of
At least one is metal, x_i, Y include zero i = 1, 2,. . . n (here
Where n = 2-20) is a natural number or a fraction, and the oxide stoichiometry or
The structure changes in a known manner systematically and in at least one elemental composition.
At that time, proceeding between the one side region and the other side region in the pair of the opposite side regions.
I do.

In a preferred embodiment, when at least one of the elemental components A ₁ , A ₂ is a metal, the oxide has an n-value of 2 and the oxide of the elemental components A ₁ , A ₂ and A ₃ If at least two of them are metals, they have an n value of 3 and the elemental components A ₁ , A ₂ , A ₃
And when at least three of A ₄ are metals, they have an n value of 4, and when at least three of the elemental components A _i are metals, they have an n value of 5 or more.

In one general embodiment, x _i , associated with one of the elemental components A _i , varies in a systematic manner, wherein a pair of opposing side regions is connected to one side region. X _j associated with the other side region and associated with the other elemental component A _j changes in a systematic manner, with another pair of opposing side regions and one side region It progresses with the other side area.

In another general embodiment, x _i associated with one of the elemental components A _i varies in a systematic manner, wherein a pair of opposing side regions has one side region and the opposing side region. Between the two sides, and y changes in a systematic manner, with another pair of opposite side areas proceeding between one side area and the opposite side area.

Further, in another general embodiment, the oxide in the library is a multilayer or superlattice, and the structure of the oxide changes in a known manner systematically and with one or more of the following variables: To: (a) the total number of atomic layers forming the structure; (b) the chemical composition of the same (single compound) oxide layer found in the multilayer oxide structure; Thickness of homogeneous (single compound) oxide layers and (d) sequence of homogeneous (single compound) oxide layers found in the multi-layer oxide structure.

For use in identifying oxides having high temperature superconducting properties, composite metal oxides can be formed as alternating copper oxide and metal or metal oxide monolayers.

For use in identifying an oxide having the desired ferroelectric properties, the oxide may be an alternating titanium oxide, niobium oxide, tantalum oxide, or boron oxide, and a metal or metal oxide monolayer. It is formed.

[0016] For use in identifying oxides having strong magnetoresistance properties, the oxides are formed as alternating manganese oxide and metal or metal oxide monolayers.

In another aspect, the invention includes a method for identifying a composite oxide having desired solid-state properties. The method includes forming a position-addressable, combinatorial library of complex oxides having a thermally stable or metastable structure of the type described above. Individual oxides on the substrate are tested for the desired solid state properties, and the structure of the oxide having the desired properties is determined according to the known synthesis history of the substrate-region location and its array location.

The library is formed by placing a substrate having a substrate surface joined by two or more pairs of opposing side regions in a vacuum chamber containing a plurality of element sources having shutters. The substrate defines a plurality of surface regions at known locations relative to a region on its side. Layer continuous atoms, on the substrate array region, ozone, oxygen plasma, in the presence of gaseous source of NO ₂ or some other suitable active oxygen,
Deposited, while depositing conditions are varied in at least one process variable in a known and systematic way, with a pair of opposing side regions between one side region and the other side region. proceed. The process variables are: (i) the amount of at least one elemental component deposited from one or more elemental sources; (ii) the order of deposition from the elemental sources (ie, source shuttering order); (iii) the temperature of the substrate region;
(Iv) the partial pressure of ozone or atomic oxygen in the substrate region, or (v) the thickness of the barrier layer in a multilayer structure.

Varying the process variable of the amount of material deposited from the elemental source across the substrate array creates a network mask between the source and the target that is effective to produce a desired gradient of atomic flux through the mask. In this case, a mesh mask, which is effective to generate a uniform atomic flux through the mask or to proceed between the one side region and the other side region in the opposite side regions of the pair of substrates, is disposed. Can be achieved.

Varying the process variable of the amount of material deposited from the elemental source additionally or alternatively places a movable shutter between the source and the target at each of the plurality of selected locations. This can be achieved.

Varying the temperature of the substrate region heats the substrate to create a temperature gradient that progresses between one side region and the other side region in opposite side regions of the pair of substrates. This can be achieved by:

Varying the partial pressure of ozone or atomic oxygen in the substrate region can be achieved by directing ozone at an almost grazing angle to the substrate surface from a source located in one side region of the substrate array.

The deposition conditions for one or more process variables can be changed under the control of a program control processor. Accordingly, a program control processor can be used to control the placement of the mesh mask between the source and the target at each of the selected plurality of locations, thereby producing a desired gradient of the atomic flux through the mask, Or it may be used to control the placement of a movable shutter between a source and a target at each of a plurality of selected locations.

A combined library of complex oxides can be generated using a combined molecular beam epitaxy apparatus.

These and other objects and features of the invention will become more fully apparent when the following detailed description of the invention is read in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION FIG. 1 schematically shows a rectangular substrate 11 joined by four side regions and having a surface 12 defining 36 position-addressable surface regions. Formed on the surface region is a library of complex oxides generally identified by the formula A _x B _1-x C _y D _1-y O ₃ , where each A, B, C and D is a metal Where x and y are
It changes from 0 to 1.0 in increments of 0.2 in the direction shown.

A. Key Parameters The key parameters that affect the results of the ALL-MBE growth experiment are: Stoichiometry, or chemical composition. This is determined by the amount of each element provided and deposited on the substrate. 2. Shuttering order. In the case of ALL-MBE, the order in which the elements are supplied affects the film structure, since the film growth is at least partially kinetic controlled.
This is most evident from the fact that other superlattices and multilayers that do not form naturally can be grown.

However, because the surface is at or near thermodynamic equilibrium, a major role is also played by the following thermodynamic parameters: 3. Substrate temperature, Ts. This generally affects the phase diagram and provides several windows in which certain phases can be formed. 4. Oxygen partial pressure. In order to operate at high vacuum conditions, ALL-MBE generally does not use ordinary molecular oxygen (O ₂ ), but rather a more reactive gas such as ozone (O ₃ ) or atomic oxygen such as oxygen plasma. other gases source, NO ₂ gas or other suitable active oxygen sources are used. Ozone has a much higher oxidizing power (10 ⁴ to 10 ⁵ times) than oxygen (O ₂ ), which depends somewhat on the substrate temperature. Therefore, reading the background gas pressure is insufficient and it is necessary to know the ratio of O _{3 to} O ₂ . However, given the much higher reactivity of ozone, we can ignore O ₂ and focus on the ozone partial pressure p for: 5. The layer thickness, parameters (1) to (4) above, are important in determining the result of the synthesis of any oxide film, single phase or multilayer, while in the latter case, determine the device characteristics Another important parameter is the thickness of the barrier. For example, a three-layer or sandwich type SNS (superconductor / normal metal / superconductor) or SI
This is exactly the case when making S (superconductor / insulator / superconductor) junctions. The same is true for many of the physical properties of the various superlattices, depending on the thickness of the alternating layers, and often even in a rather unexpected manner.

In order to maximize the effectiveness of the next generation combination ALL-MBE machine, we have the ability to change all of the above parameters (1)-(5) one at a time or simultaneously in a combination method. Ran.

(B. Embodiment of Combined Molecular Beam Epitaxy (COMBE)) A conventional ALL-MBE system is described in, for example, the document [1]. The following modifications and improvements may cause the combined search capability to be implemented.

1. 1. Mesh Mask Prior to each elemental metal source (Knudsen cell), a transmission ("mesh") mask 22-a simple stainless steel with a number of holes 22a drilled therein (
Or other suitable metal) pieces should be added (FIGS. 2A and 2B).

The mask 22 is preferably mounted on a linear motion feed-through actuator (or rocking stick) 23 with a bellows 23a, and in the extended position shown in FIG. 2A and the retraction in the nipple shown in FIG. 2B. Be able to move between positions. With the gate valve 24 movable in the directions shown between the open and closed positions, the spool including the mask 22 and the linear motion actuator 23 is moved to the main high vacuum chamber (
(See FIG. 9) and can be opened. In this way, the mask 22 can be cleaned or replaced without having to vent the growth chamber (see FIG. 9). Mounted on the source nipple (or mounted on its water-cooled jacket) is a rigid frame 25 (see also FIG. 2C), which receives the mask 22 sliding into the frame 25. Adapted. This ensures that the mask 22 is always locked in the same position when extended.

The gradient of the atomic flux across the substrate (or array of substrates) 11 depends on the distribution of the holes 22a. For example, as shown in FIG. 3, the square mask 22 is divided into 4 × 4 equal fields 22b and 4 × 4 holes in each of these fields in the first left-hand side row, each in the second row. With 3 × 3 holes, 2 × 2 holes in each of the third row, and a single hole in the last row. Clearly, the atomic beam transmitted by such a mask has a varying steepness of flux from the highest on the left hand side to the lowest on the right hand side.

Although this illustration is oversimplified, it is clear that by using such a transfer mask 22, an atomic beam can optionally be formed. All possible variations, from virtually zero gradient, ie uniform deposition rate over the entire substrate area, to very steep gradients, ie 100% on one side to 0% on the other side Is possible.

What is important here is the size and distribution of the holes 22a, which should be selected in such a way as to ensure the desired gradient of the atomic flux across the substrate (or array of substrates). At the same time, it is important to maintain high permeability so that there is no need to raise the source temperature too much (and lose more source material) to maintain a reasonable deposition rate. This mounting allows the composition gradient to be controlled separately for each element.

For better uniformity, pairs of identical sources located opposite one another can be used. That is, the atom beam is bombarded at the same angle to the substrate but from the opposite side. If the sources are arranged on a circumference centered on an axis perpendicular to the substrate, this means that the pairs of complementary sources are arranged at 180 degrees to each other. Using a simple transmission mask 22 placed over one of these two sources, the corresponding flux gradient across the substrate is set to its maximum value (when one source is completely blocked and the other is open). From its minimum value (when both sources have the same intensity)
Until you can control. For example, by adjusting the temperature of each source, another method is provided in which two opposing sources of the same element have different atomic fluxes. Yet another simplest approach is to use different shuttering times for the two sources, i.e., keep one of them open longer than the other, corresponding to the desired slope.

(2. Sample Shadow Mask) Next, as shown in FIG. 4, two shutters 28 and 29 can be inserted in front of the substrate holder 27 on each of the linear motion feed-through actuators 31 and 32, respectively. Shutters 28 and 29 are oriented at 90 degrees to each other (eg, one 29 is vertical, and one 28
Is horizontal). These shutters 28 and 29 can be operated automatically, that is, computer controlled as part of a programmed growth approach.
Each shutter 28 and 29 should allow some distributed number of positions, from a fully open position without shadowing of the substrate to a fully closed position without deposition. In the simplest example shown below, only one intermediate (half-closed) shutter position is assumed, where half of the substrate array is in the shadow and the other half does not interfere with deposition. This arrangement provides digital layer thickness control in a multilayer structure, as required by item (2) in section A above. For example, when investigating the optimal barrier thickness in a three-layer conjugate, one unit cell thickness barrier on the film on the first substrate, two unit cell thickness barriers on the second substrate, and three unit cells on the next substrate Thickness barriers, etc., can be made.

Combination with source shutter already existing in ALL-MBE system
Effectively changes the shuttering order for different samples in the array.
It is also possible to do. This is illustrated by the following simple example. Main source shutter shutter
The chattering sequence is single phase Bi_TwoSr_TwoCa_ThreeCu_FourO_{12 + x}To deposit
Assume that it is rammed. The auxiliary substrate shadowing shutters 28 and 29
May be used to selectively block some of the substrates as part of the
Different phases are then deposited on these substrates as shown in FIG. 5A. The present inventors
, These are Bi, as seen in FIG. 5B._TwoSr_TwoCa_TwoCu_ThreeO_{10 + x}(Nori
Tc = 110K), Bi_TwoSr_TwoCaCu_TwoO_{8 + x}(Tc = 85K), Bi _Two Sr_TwoCuO_{6 + x}(Tc = 10K), and Bi_TwoSr_TwoCa_ThreeCu_FourO_{12 + x}Is
.

As will be described in more detail with reference to FIG. 10, control of the source shutter, mesh mask 22 or sample shadow shutters 28 and 29 is controlled by a program (ie, software) of instructions written according to the present disclosure. It can be executed by a suitable digital computer operating under its own control or controlled using functionally equivalent hardware modules constructed using known discrete components, application specific integrated circuits (ASICs), etc. obtain.

(3. Multiple Filament Heater) It is possible to insert a heater system 61 similar to that currently used, but this heater system 61 has several heater filaments, and each heater filament Has its own current control. (Instead of a bare filament, a commercial UHV compatible heater lamp can also be used, while the principle remains the same). For example, considering the base holder 62, the base holder 62 is 4 × 4
It has a hole 62a for a 1 cm ² substrate, the back side of the substrate being metal (eg Ti-P
(t-Au multilayer) and exposed to irradiation from an array of heater filaments 63 in a 4 × 4 individually controlled bare or quartz lamp 64 (FIG. 6). The temperature of each substrate in the matrix can be read using an optical pyrometer.

In this way, a uniform temperature over the substrate matrix can be easily achieved,
Or, if desired, Ts may have a large temperature gradient from one side to the other, for example, a 100 ° C difference.

Instead of this matrix of small substrates, the same heater system 61 can easily accommodate one annular 3 inch (or larger) wafer.

4. Multi-Nozzle Ozone Delivery System The last remaining factor needed to complete control over the desired variable set of parameters for the combinatorial search is the oxidizing power. Control of this gradient can also be performed by using a multiple nozzle system 70 for supplying ozone to the substrate 11. For example, there may be four nozzles 71, 72, 73 and 74, arranged at a steep angle to the substrate holder 62 and the substrate 11, every 90 ° around the substrate, and each having a needle valve and a flow meter. Is provided (FIG. 7). In this way, the four nozzles 71, 72, 7
A choice can be made between the most uniform configuration, emanating from all three and 74, and the most asymmetric configuration, with only one nozzle operating. Assuming that the surface 12 of the substrate 11 to which the ozone beam is directed is rather hot, typically about 700 ° C., the amount of differential pumping, the pumping speed of the MBE system in question, and the size and position of the nozzle, will result in significant ozone Decomposition and recombination to (less reactive) molecular oxygen is expected. Thus, it is possible to achieve significant gradients in the partial pressure of ozone across the substrate matrix, for example a factor of 5 to 10 differences between sites experiencing the highest and lowest values of p.

In summary, the four devices described above (mesh or transmission mask 22, shadow masks or shutters 28 and 29, multiple filament heaters 61, and multiple nozzle ozone delivery system 70) use a powerful parallel combinatorial search technique. Thus, for a given target single-phase film or hetero-structure, the film composition, shuttering order, layer thickness, substrate temperature Ts and ozone partial pressure p can be optimized. These four devices are shown in FIG.

C. Mathematical Aspects of Implementing Combinatorial MBE While the concepts detailed above are practically qualitatively valid for practical implementation, the mesh mask 22 It is necessary to optimize the shape of the orifice (ie, hole 22a) at and the shape of the ozone delivery system 70. This requires a numerical simulation of the atomic beam flux gradient. In a molecular flow regime, if the orifice can be considered a point source, the gas flow can be described using the following Knudsen equation:

I = (I ₀ / r ² ) cosΘcos (Θ + φ) (1) where I is the atomic collision velocity (the deposition rate is proportional if Ts is constant over the substrate region), and φ is perpendicular to the substrate. Angle between and perpendicular to the surface containing the pinhole,
角度 is the angle between the direction in which the deposition rate is calculated and perpendicular to the surface containing the pinhole,
And r is the distance from the pinhole to the point on the substrate surface where the deposition rate is calculated [9]. This near value is valid when the mean free path λ of the atom or molecule is large compared to the orifice diameter d, and in the distal field where the distance R from the pinhole to the center of the substrate is also large compared to d. Note that there is.

The mathematical task is as follows. Given the configuration and operating pressure of the MBE system, this defines the range of values of R, φ and r and Θ of interest, as well as the mean free path λ of the molecule. Put the mask under consideration on the mask (x ₁ , y ₁ ), (x ₂ , y ₂ )
,. . , (X _N , y _N ), diameters d ₁ ,. . . , _DN . For any given mask, calculating the distribution of deposition rates across the substrate array area is straightforward. However, we are actually interested in the opposite optimization problem. For a given deposition rate gradient distribution, an optimal mask design that most closely approximates this distribution must be found and transmission through the mask must be maximized. Iterative numerical simulation can accomplish this. As noted above, for better uniformity, pairs of identical sources located opposite one another may be used, i.e., the atomic beam is at the same angle to the substrate but impinges from the opposite side. obtain. By using a simple transmission mask placed at one of these two sources, we can go from a maximum (if one source is completely blocked and the other is open) to a minimum. (If both sources have the same intensity), the gradient of the corresponding atomic flux over the substrate can be controlled. Whenever analytically reversal results are possible, they can be used to accelerate these numerical simulations. Optimization of the number, shape and positioning of the ozone nozzles can be similar. In particular, this should take into account the collimation of the source and the finite thickness of the mesh mask. Further processing goes beyond the simple Knudsen equation (1) and includes higher order corrections and deviations from the ideal gas flow regime.

D. Oxel Combined Molecular Beam Epitaxy (COMBE) Apparatus In one preferred embodiment of the apparatus of the present invention, Bremen's Oxel
Combined molecular beam epitaxy (COMB) at the GmbH Laboratory
E) The system was implemented, which is described in this section and shown in FIG.

A multi-chamber ultra-high vacuum (UHV) with a base pressure in the 10 ⁻¹¹ Torr range
2.) The system is located in two adjacent laboratory facilities and connected at its transport chamber through its walls, which transport chamber also acts as a wafer storage chamber.
One of these experimental facilities is the clean room area, where substrate-filled (unfilled) chambers and major microfabrication steps (metallization, insulation, surface cleaning and oxidation, and ion-milling) are performed without breaking vacuum. The resulting processing chamber is housed. The second experimental facility houses a main growth chamber, an annealing chamber, and a second wafer introduction chamber.

As shown in FIG. 9, the main growth chamber 90 contains a metal source 81.
6 arms 91 to 106 are provided. This source 81 is easily replaceable,
The system is modular. Each arm 91-106 has a gate valve 24 and a dedicated small (701 / s) turbo-molecular pump and autonomous pumping with a roughing line. Thus, it is possible to valve off, refill, repair, replace, or outgas each source without having to break the vacuum and interrupt the functioning of the main chamber 90. The metal source 81 (see FIG. 8) can be a thermal transition cell (low temperature, high temperature, or dual filament cell) or a rod-fed (
rod-fed), which is accessible to most elemental metals in the periodic system.

The source 81 is aimed at the substrate 11 (see FIG. 1) at about 20 °, which allows a large composition diffusion (gradient) over the substrate array area. Each source 8
1 comprises a linear motion feedthrough actuator 23 and a mounted mesh mask 22 and further comprises computer controlled pneumatic linear motion feedthrough actuators 31 and 32, each of which is as described in Section B above. It may have shadow masks 28 and 29, respectively. Next, each arm 91-106 includes four optical ports (two next to the source and two behind the shutter) and, by atomic absorption spectroscopy [10], on either side of the shutter. Enables accurate online (real-time) monitoring of atomic flux.

The main chamber 90 itself has two large (1,000 1 / s) turbo-molecular pumps (with magnetic bearings and mounted on special spools for vibration isolation).
(Not shown in FIG. 9). To further minimize sample vibration relative to the electron microscope (see below), the entire chamber 90 is placed on a passive (with air damper) vibration isolation frame. A sample vibration damper is also provided.

The chamber 90 further includes a sample manipulator to allow sufficient sample rotation and translation. The manipulator has a water-cooled sample heater system 61, which includes four UHV-compatible quartz mercury lamp heaters, arranged in a linear array (see FIG. 6B). Each lamp 64 is separately controlled, allowing a temperature gradient to be maintained along one direction across the substrate array, or to achieve uniform heating of the entire array. The same sample manipulator also has a set of four water-cooled nozzles 70 for the delivery of an ozone or other active oxygen gas source (see FIG. 7). The nozzles 71-74 move with the substrate holder 27 (see FIG. 4) in such a way as to maintain a fixed position with respect to the sample array, while the latter rotates or translates. The chamber 90 then comprises a set of state-of-the-art analytical tools. These include a Quartz Crystal Speed Monitor (QCM) on a separate motor manipulator that allows for full and computer controlled x, y, z movement, so that the deposition rate is determined at each location in the substrate array at each source. Can be mapped correctly. Reflected high energy electron (RHEED) systems also have the ability to quickly switch from one substrate to another substrate location in a 16-sample array (ie, the ability to scan), and use multiple screens to simultaneously scan 16 films each. Has the ability to display RHEED patterns from Both innovations have been specifically implemented to enhance the capacity of this device for combinatorial synthesis and searching.

The chamber 90 is further equipped with a low energy electron microscope (LEEM) to enable real-time (video speed) images of the growth film surface at nanometer scale resolution [11]. This makes it possible to observe, study,
And quantification, island nucleation (island nucleation)
ion) or growth mechanisms such as step flow growth [12]. The same device is also used as a low energy electron diffraction (LEED) system,
Alternatively, it can function as a light-excited electron microscope (PEEM), with the latter also providing a UV source. Finally, time-of-flight ion scattering and recoil spectroscopy (TOF-I
A SARS) system is provided, comprising a plurality of detectors and analyzers at several angles, including a recoil ion mass spectroscopy (MSRI) analyzer [13]. Since this is a very accurate surface analysis tool, it provides quantitative information on the chemical composition of the surface monolayer in real time even during film growth.

Overall, the Oxxel COMBE system uses LEEM and TOF-IS
Optimized for high-throughput combinatorial search through massive phase space, further assisted by advanced analysis tools such as ARS and multiple read RHEED and scan QCM systems, both of which are compatible with oxide MBE systems It was not previously integrated.

As described above and as will be appreciated by those skilled in the art, various aspects of the present invention (
That is, the source shutter, mesh mask 22, shadow mask shutters 28 and 29, or mapping source deposition rate control) can be performed using a processor-controlled device such as a digital computer. FIG. 10 is a functional block diagram of a typical computer system 200 that can be used to implement one or more of these aspects of the invention. As shown, the computer system 200 includes a bus 201 interconnecting a central processing unit (CPU) 202, which includes a processing circuit such as a microprocessor, a random access memory (RAM) 203 and a read only memory. (ROM) 2
4 represents a system memory with various memory elements such as 04, as well as multiple device interfaces (ie, controllers). The input controller 205 comprises one or more input devices 2 such as a keyboard, mouse, trackball, etc.
06 represents an interface circuit connected to the device. Display controller 207
Represents an interface circuit that connects to one or more display devices 208, such as a computer monitor. I / O controller 209 represents an interface circuit that connects to one or more I / O devices 211, such as a modem or a network connection. The storage controller 212 includes one or more storage devices 2 such as a magnetic disk or tape drive, an optical disk drive, and a semiconductor storage device.
13 represents an interface circuit connected to the device. The printer controller 214
Represents an interface circuit that connects to one or more printer devices 215, such as a laser, inkjet printer or plotter. No particular type of computer system is important to perform the computer-controllable aspects of the present invention. Any suitable computer system or processor control device may be used.

In one embodiment, execute a program of instructions residing in RAM, which may be taken from ROM 204, storage device 213, or obtained from a network server or other source through I / O device 211. As a result, C
The PU 202 controls the operation of the shutters 28 and 29. More broadly, the program of instructions (ie, software) may be carried by any medium readable by CPU 202 or other suitable program control processor. Such media include various magnetic media such as discs or tapes, various optical media such as compact discs, and electromagnetic spectrum, including carrier waves coded to convey baseband or broadband signals and instructions programs. And various communication paths.

Alternatively, control of shutters 28 and 29 may be performed by functionally equivalent hardware using discrete components, application specific integrated circuits (ASICs), and the like. Such hardware may be physically integral with CPU 202, or may be a separate element. If the hardware is a separate element, the computer 202
It can be embodied within itself or on a computer card that can be inserted into a valid card slot of computer 200.

Accordingly, the term “program control processor” as used herein covers both a processor operating under the control of appropriate software and a device having appropriate programming incorporated therein. It is intended.

In addition to shutters 28 and 29, various other aspects of the library synthesis method can also be computer controlled to control the source shutter, mesh mask 22, or source deposition rate according to the teachings herein. Including. With these teachings, those skilled in the art will be able to write (or write) specific code, or design functionally equivalent hardware to implement control of these features (or Designed).

It will be apparent to those skilled in the art that many obvious changes and modifications can be made to such a system, such as changing the number of sources or heater filaments, or the number and shape of ozone nozzles, and the like. Clearly, however, this does not represent a substantial modification or improvement to the invention.

[Brief description of the drawings]

FIG. 1 shows A _x B _1-x C _y made on a substrate at x, y = 0, 0.2, 0.4, 0.6, 0.8 and 1.0. 2 shows a two-dimensional library of D _1-y O ₃ samples.

2A and 2B illustrate a transmission mesh mask useful for practicing the method of the present invention, showing the movement of the mask between an operating position (FIG. 2A) and a retracted position (FIG. 2B). .
FIG. 2C shows a side view of the frame adapted to receive the transmission mask when in the operating position.

FIG. 3 shows details of a source mask or mesh designed to produce a right-to-left gradient atomic flux, with the deposit on the left side of the sample array being much higher than on the right side.

FIG. 4 shows the moved position of both the lateral and vertical shadow masks located between the transition source and the substrate array.

FIG. 5A provides a shadow mask shuttering sequence for the combined growth of four separate BiSrCaCuO oxides, and FIG. 5B shows a corresponding map of the phases formed.

FIGS. 6A and 6B show a front view and a side view, respectively, of a sample holder configured to generate differential heating of an array region in a sample.

FIGS. 7A and 7B show a front view and a side view, respectively, of a sample holder configured to generate a partial pressure difference in ozone across an array region in a sample.

FIG. 8 shows a system for use in generating a combined library of complex oxides by molecular beam epitaxy according to the present invention.

FIG. 9 shows a schematic of the main growth chamber of the Oxxel COMBE system, showing 16 water-cooled arms containing elemental metal sources with gate valves. RHEE
D, TOF-ISARS, and LEEM are also shown. There are supporting vibration-insulating frames, turbo molecular pumps (16 small ones on the arm and two
Two large objects), sample and QCM manipulator, electrical, water and gas connections are not shown.

FIG. 10 is a functional block diagram of a typical computer that can be used to control various aspects of the present invention.

──────────────────────────────────────────────────続 き Continuation of front page (81) Designated country EP (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, IT, LU, MC, NL, PT, SE ), JP, KR, US

Claims (23)

[Claims] 1. A combination library of position-addressable composite oxides having a thermally stable or metastable structure, said library comprising a substrate surface bounded by two or more pairs of opposing side regions. A substrate having
A thermal substrate having a substrate defining a plurality of surface regions at known locations relative to the side regions, and having a formula (A ₁ ) _x1 (A ₂ ) _x2 ... (A _n ) _xn O _y A stable or metastable oxide is formed on the region, wherein at least one elemental component A _i is a metal, x _i , y are natural numbers or fractions including 0, and n = 2-20 The stoichiometry or structure of the oxide varies systematically and in a known manner for at least one elemental component, with one side region and the other in a pair of opposing side regions. A library that progresses to and from the side area. 2. The library according to claim 1, wherein the oxide is: (i) n = 2 and at least one of the elemental components A ₁ and A ₂ is a metal (Ii) an oxide wherein n = ₃ and at least two of the elemental components A ₁ , A ₂ and A ₃ are metals; (iii) n = 4 and the elemental components A ₁ , A ₂ , A ₃ and An oxide wherein at least three of A ₄ are metals; (iv) an oxide wherein n is 5 or more and at least three of the elemental components A _i are metals. 3. The library of claim 2, wherein x _i associated with one of the elemental components A _i is one side region and the other side in a pair of opposing side regions. X _j associated with another elemental component A _j , which changes in a systematic manner as it travels between the two side areas, one side area and the other side area in another pair of opposing side areas. A library that changes in a systematic way as it progresses to and from regions. 4. The library of claim 2, wherein x _i associated with one of said elemental components A _i is one side region and the other side in a pair of opposing side regions. Changes in a systematic manner as it travels between the side regions, and y changes in the system when traveling between one side region and the other side region in another pair of opposing side regions. A library that changes in a typical way. 5. The library of claim 2, wherein the composite metal oxide is formed as an alternating layer of copper oxide and a single metal or metal oxide layer, and wherein A library, at least some of which are high-temperature superconductors. 6. The library of claim 2, wherein the composite metal oxide is an oxide and a metal or metal selected from the group consisting of titanium oxide, niobium oxide, tantalum oxide, and boron oxide. Formed as alternating layers of oxide monolayers,
The library, wherein at least some of the oxides in the library have ferroelectric properties. 7. The library of claim 2, wherein the composite metal oxide is formed as an alternating layer of manganese oxide and a metal or metal oxide monolayer;
A library, wherein at least some of the oxides have ferromagnetic resistance properties. 8. The library of claim 1, wherein the library comprises at least 100 different oxides. 9. The library of claim 1, wherein the oxide is a multilayer or superlattice, and the structure of the oxide is one or more of the following variables: The total number of atomic layers forming the structure; (b) the number of layers in the uniform multilayer, in an oxidized structure comprising a uniform multilayer alternating with layers of different compositions; (c) the layers of different compositions of the multilayer. A library, which systematically and in a known manner, varies in the composition of one or more of the multilayer components in an oxidized structure comprising a uniform multilayer alternating with: 10. A method for identifying a composite oxide having desired solid state properties, said method comprising: forming on a substrate having a substrate surface bounded by two or more pairs of opposing side regions. And defining a plurality of surface regions at known locations relative to the side regions, wherein a library of thermally stable or metastable oxides has the formula (A ₁ ) _x1 (A ₂ ) _x2.
• (A _n ) _xn O _y , wherein at least one elemental component A _i is a metal;
x _i , y are natural numbers or fractions including 0, n = 2 to 20, and the stoichiometry or structure of the oxide varies in at least one elemental component in a systematic and known manner. Then proceeding between one side region and the other side region in a pair of opposing side regions, testing each oxide on the substrate for the desired solid state properties Identifying the structure of the oxide having the desired property according to the array location and a known synthesis history of the array location. 11. The method of claim 10, wherein the method is used in selecting a composite oxide having high-temperature superconducting properties, wherein the composite metal oxide on the substrate is used. The method wherein the article is formed as an alternating layer of copper oxide and a metal oxide monolayer. 12. The method of claim 11, wherein the selecting step tests the oxide at each of the substrate regions at each of a series of temperatures and exceeds the maximum temperature. Identifying an oxide that exhibits conductivity.
Method. 13. The method of claim 10, wherein the method is used in selecting a composite oxide having desired ferroelectric properties, wherein the oxide comprises (i) A) an oxide selected from the group consisting of titanium oxide, tantalum oxide, niobium oxide, and boron oxide; and (ii) formed as an alternating layer of another metal or metal oxide layer, and the oxide in the library. At least some of the methods have ferroelectric properties. 14. The method according to claim 10, wherein the method is used in selecting a composite oxide having desired ferromagnetic resistance properties, wherein the composite metal oxide is selected from the group consisting of: A method formed as alternating layers of manganese oxide and a metal or metal oxide monolayer. 15. A method for producing a combinatorial library of complex oxides, comprising: combining a shutter, two or more pairs of opposite side regions in a vacuum chamber containing a plurality of elemental sources. Arranging a substrate having a substrate surface, and defining a plurality of surface regions at known locations relative to the side regions, continuing over the substrate array region in the presence of a gaseous source of oxygen atoms. Depositing an atomic layer, during said depositing step, being known about at least one process variable in proceeding between one side region and the other side region in a pair of opposing side regions; Changing deposition conditions in a systematic manner, wherein the process variables include: (i) the amount of at least one elemental component deposited from one or more elemental sources; (ii) the element (Iii) the temperature of the substrate region, (iv) the partial pressure of oxygen atoms in the substrate region, and (v) the thickness of the barrier layer in the multilayer structure. _Forming a thermally stable or metastable oxide having the formula (A ₁ ) _x1 (A ₂ ) _x2 ... (A _n ) _xn O _y by the deposition step. , Where at least one
The two element components A _i are metals, x _i and y are natural numbers or fractions including 0, and n
= 2 to 20 and the stoichiometry or structure of the oxide varies systematically and in a known manner in at least one elemental component, with one side in a pair of opposing side regions Proceeding between the side region and the other side region. 16. The method of claim 15, wherein changing the process variable of an amount of material deposited from an elemental source comprises a mesh mask between the source and the target. Wherein the mask is effective to generate a desired gradient of the atomic flux, wherein one side region and the other side of the pair of opposing side regions of the substrate are included. A method that proceeds between and to a side area. 17. The method of claim 15, wherein the step of altering the process variable of an amount of material deposited from an elemental source comprises a mesh mask between the source and the target. And wherein said mask is effective to produce a uniform atomic flux therewith. 18. The method of claim 15, wherein altering the process variable of an amount of material deposited from an elemental source comprises a step between each of the source and the target. A method comprising positioning a movable shutter at a plurality of selected locations. 19. The method according to claim 15, wherein the step of changing the temperature of the substrate region comprises the steps of: forming one side region and the other of a pair of opposed side regions of the substrate. Heating the substrate so as to create a temperature gradient as it travels between the side regions. 20. The method according to claim 15, wherein the step of changing the partial pressure of the oxygen atoms in the substrate region comprises changing a partial pressure of the oxygen atoms from a source located in one side region of the gradient. Directing ozone at an almost grazing angle to the substrate surface. 21. The method of claim 15, wherein at least one
The method wherein the deposition conditions for one process variable are changed under the control of a programmed processor. 22. The method of claim 18, wherein the step of disposing the movable shutter between the source and the target at each of the plurality of selected locations comprises program controlling. A method controlled by a configured processor. 23. The method of claim 15, wherein the combined library of composite oxides is manufactured on a combined molecular beam epitaxy apparatus.