Apparatus for analyzing surfaces using fast atom diffraction in a high pressure environment

Abstract

The present invention relates to an apparatus (1) for characterizing the surface (SE) of a sample (E), comprising: - a chamber (C) including a medium (PE) for the sample, the chamber being connected to a pump, referred to as a main pump (PP), which is adapted to maintain a temperature below 10°C within the chamber. ‑2 A pressure of mbar; a source (SN) for generating an incident beam (NB) of neutral atoms or molecules with energies of 50 eV and 5 keV and a divergence of less than or equal to 0.05°, said source being arranged to direct the incident beam (NB) through an inlet (EF) into the chamber at an incident angle (θ) of less than or equal to 10° relative to the plane of said surface. in The incident beam (NB) is directed toward the surface (SE) to be characterized, and the neutral atoms or molecules of the incident beam (NB) are scattered forward by the surface (SE) to form a diffracted beam (DB); - a detection housing (ZDU) connected to the chamber and to a pump, referred to as the UHVP pump, which includes: - a concentric tube assembly (Ens), each tube (T1, T2) having one end, referred to as the inlet end, having an opening (O1, O2), the assembly including tubes having a minimum radius (T1) and a length L; - a position-sensitive detector (Det) adapted to detect the diffraction pattern (FD) of the neutral atoms or molecules of the diffracted beam; the length L and the openings (O1, O2) are adapted to deliver the diffracted beam to the detector without losing spatial information about the surface (SE), and the openings and the UHVP pump are adapted to maintain a depth below 10°C within the detection housing. ‑5 mbar pressure.

Description

Technical Field

[0001] This invention relates to an apparatus for characterizing surfaces. More specifically, the apparatus of this invention enables the determination of the crystal structure of a surface and the monitoring of the growth of thin layers. Background Technology

[0002] RHEED (Reflection High Energy Electron Diffraction) is the most widely used tool for characterizing in-situ crystalline layers. Its advantage lies in its compatibility with molecular beam epitaxy (MBE), one of the most widely used crystal layer growth methods. RHEED can fully characterize the crystal structure of a surface. It also allows for real-time monitoring of the layer-by-layer crystal growth through MBE.

[0003] According to document FR2903494, it is known to characterize crystal surfaces using grazing incidence diffraction equipment that utilizes neutral molecules or atoms. This technique is called GIFAD (grazing incidence fast atom diffraction) and shares many similarities with the RHEED tool. In addition to providing the same information about crystal layer structure as the RHEED method, the GIFAD method has several advantages related to the use of neutral particles:

[0004] -Because its penetration depth for neutral molecules or atoms is significantly reduced compared to electrons, it exhibits unique sensitivity to the last layer of the surface.

[0005] Measurements are based on electron density distribution rather than atomic nucleus positions.

[0006] - Insensitive to electromagnetic fields, and

[0007] - It can be operated without damaging fragile materials.

[0008] Figure 1 The apparatus described in document FR2903494 is schematically illustrated. This apparatus is a molecular epitaxy machine 1000 equipped with GIFAD surface characterization equipment. Machine 1000 consists of a housing 1100 connected to a pumping system 5 that generates an ultra-high vacuum within the housing. Effusion units 1200 for generating molecular beams extend into the housing 1100. Supports 1300 for a substrate 3', on which the surface 3 will be epitaxially deposited, are positioned in front of these units. The apparatus 1 for generating high-energy atomic or molecular beams is adapted to emit them into the housing 1100 via an inlet 1400. A position-sensitive detection device 4, consisting of, for example, a microchannel wafer coupled to a fluorescent screen observed by a camera, is arranged within the wall of the housing 1100.

[0009] Beam 2 has a possible variable incident angle θ of no more than about 10° (grazing incidence). incThe target surface 3 is guided towards the surface to be characterized. Here and below, the plane measurement angle is relative to the target surface 3. As in the RHEED technique, the space directly above surface 3 is left empty, allowing molecular beam epitaxy growth and measurement to occur simultaneously.

[0010] Neutral molecules or atoms in beam 2 are reflected by surface 3 at a reflection angle θ. ref ≈θ inc It undergoes diffraction in the azimuth direction, that is, it is parallel to surface 3 due to the structure of surface 3. Figure 2 In the diagram, the incident atomic or molecular beam is represented by reference numeral 2-i, the specular reflection beam by 2-0 (because this is "zero-order" diffraction), and the first non-spectral reflection beam by 2-1 (first-order diffraction). As in RHEED, the angle φ formed by the projections of the beam diffracted in the first-order 2-1 order and the beam diffracted in the zero-order 2-0 order onto a plane parallel to the plane of surface 3, relative to the motion of the incident atoms or molecules, is indirectly related in the transverse direction to the lattice parameter a of the crystal surface 3 through the following relationship: d.tanφ=nλ, where n is an integer and d is the period of the beam, which is related to a by a simple proportional relationship that depends on the crystal structure and the viewing direction. Therefore, for the first-order diffraction, the angle is derived... Where λ is the de Broglie wavelength of the incident particle. The diffraction pattern FD is then detected by detection device 4.

[0011] The GIFAD method proposed in document FR2903494 has proven its effectiveness in studying surface structure and monitoring thin film growth, especially in methods operating in extremely low-pressure chambers such as MBE. The existing GIFAD method in housing 1100... -10 mbar to 10 -5 The operation is within a pressure range of mbar, which is limited by two reasons:

[0012] - The type of detector used (a microchannel chip connected to a fluorescent screen) when the pressure exceeds 10... -5 At mbar, its useful signal becomes difficult to manipulate, and

[0013] - When the atomic beam passes through the shell, the coherence of the atomic beam needs to be maintained by limiting the probability of collision with the residual gas; otherwise, the contrast of the fringes in the diffraction pattern will be reduced, and the pattern may become unusable.

[0014] However, some thin film growth methods (e.g., magnetron plasma deposition, chemical vapor deposition, or pulsed laser ablation), surface modification (plasma treatment or chemical modification), or catalysis under high pressure environments (up to 10) -2 It operates in mbar or above and is therefore incompatible with existing technology devices.

[0015] This invention aims to overcome some limitations of the prior art. Therefore, one object of this invention is a device for characterizing sample surfaces using GIFAD, wherein differential pumping of a detection housing is implemented, and a diffraction pattern is detected within the detection housing. Thus, a detection housing with a resolution of less than 10 is obtained, compatible with microchannel detection. -5 The pressure is mbar, and the chamber containing the sample can have up to 10 mbar pressure, which is compatible with thin film growth or surface modification methods operating under high pressure. -2 mbar pressure. Summary of the Invention

[0016] Therefore, one object of the present invention is an apparatus for characterizing the surface of a sample, comprising:

[0017] - A chamber, including a support for the sample, the chamber being connected to a so-called main pump adapted to maintain a pressure of less than 10 ppm within the chamber. -2 mbar pressure;

[0018] A source for generating an incident beam of neutral molecules or atoms with an energy of 50 eV to 5 keV and a divergence of less than or equal to 0.05°, the source being arranged via an inlet in the chamber to guide the incident beam toward the surface to be characterized at an incident angle of less than or equal to 10° relative to the plane of the surface, the neutral molecules or atoms of the incident beam being scattered forward by the surface to form a diffracted beam; and

[0019] - The detection housing, connected to the chamber and to the so-called UHVP pump, includes:

[0020] - A concentric tube assembly, each tube having a so-called inlet end with an opening, the assembly comprising tubes of a smaller radius having a length L;

[0021] - A position-sensitive detector suitable for detecting the diffraction pattern of neutral molecules or atoms in the diffraction beam;

[0022] - The length L and the opening are adapted to transmit the diffraction beam to the detector without losing information about the surface; the opening and the UHVP pump are adapted to maintain a pressure of less than 10 within the detection housing. -5 mbar pressure.

[0023] Advantageously, the opening of each tube has a diameter that differs from the other tubes and decreases according to the radius of the tube.

[0024] Advantageously, the smaller diameter opening has a diameter of less than or equal to 5 mm.

[0025] Advantageously, the so-called high-pressure distance between the inlet and the inlet end of the tube is less than the decoherence length of the incident beam and the diffracted beam.

[0026] Advantageously, each tube has a so-called outlet end with a collar extending in a direction substantially perpendicular to the tube to guide airflow in that direction at the outlet of each tube, and the coupling port of the UHVP pump is disposed in the detection housing, facing the space formed by the collar.

[0027] Advantageously, the detector includes a microchannel wafer coupled to a fluorescent screen observed by a camera.

[0028] Advantageously, the source is adapted to allow the incident angle to be varied, and the device further includes a translation and / or rotation stage for the tube assembly to adjust the position of the opening according to the incident angle.

[0029] Another object of the present invention is a magnetron plasma deposition system comprising an apparatus according to the invention, the apparatus being arranged to characterize the surface of a sample during deposition. Attached Figure Description

[0030] Other features, details, and advantages of the invention will become apparent from the description taken with reference to the accompanying drawings, which are given by way of example and illustrate, respectively:

[0031] Figure 1 This is a schematic diagram of an apparatus for characterizing sample surfaces using GIFAD technology, based on existing techniques.

[0032] Figure 2 This is a diagram illustrating the diffraction of incident atomic or molecular beams through a sample surface using GIFAD technology, based on existing techniques.

[0033] Figure 3 This is a schematic diagram of an apparatus according to the present invention for characterizing the surface of a sample using GIFAD technology.

[0034] Figure 4 This is an enlarged schematic diagram of the casing ZDU of the device of the present invention.

[0035] Figure 5 This is a schematic diagram of a magnetron plasma deposition system including the apparatus according to the invention, used to characterize the surface of a sample by GIFAD technology during deposition.

[0036] Unless otherwise stated, the elements in the accompanying drawings are not drawn to scale. Detailed Implementation

[0037] Figure 3 An apparatus 1 according to the invention is shown, which is used to characterize the surface SE of a sample E using the GIFAD technique. The apparatus includes a chamber C, which includes a support PE for the sample E.

[0038] Device 1 includes a source SN for generating an incident beam NB of neutral molecules or atoms with energies from 50 eV to 5 keV and a divergence less than or equal to 0.05°. This source is known from the prior art and is described in more detail in document FR2903494. Therefore, for the sake of brevity, its description will not be repeated here. Simply put, it typically comprises three stages: a generator of the atomic or molecular ion beam, a neutralizer, and a collimator. The ion source includes a set of electrodes and electrostatic focusing optics, which enable the ions to be accelerated to the desired energy by applying an electrostatic field. The charge of the ions makes them easier to accelerate, select, and generate as a pulsed beam when needed, compared to neutral particles. The ion beam is then neutralized by charge exchange in a gas-filled cell. The atomic or molecular beam leaving the neutralizer typically has too high a divergence to be observed at the target surface SE, therefore collimation is performed using a collimator, typically consisting of a pair of apertures.

[0039] In the device of the present invention, the source SN is arranged to guide the incident beam NB into the chamber C via the input EF. The beam NB is subjected to grazing incidence conditions (i.e., an incident angle θ relative to the surface plane). in The incident beam is guided towards the surface SE (at an angle less than or equal to 10°) to be characterized. This grazing incidence condition ensures minimal penetration of neutral molecules or atoms within the sample, thus ensuring sensitivity to the last layer of the sample. On the other hand, excessively high incident angles significantly reduce the diffraction signal. As mentioned above, neutral molecules or atoms in the incident beam NB are scattered forward by the surface SE, and due to the crystal structure of the surface, the reflection angle θ... ref ≈θ inc The incident beam undergoes diffraction in the azimuth direction. Neutral molecules or atoms in the incident beam NB are scattered forward, forming a diffracted beam DB, which transmits the characteristic spatial information of the surface SE as a far-field diffraction pattern FD. Figure 3 Illustration including a perspective view of the detector Det and the diffraction pattern FD.

[0040] Unlike the characterization devices of the existing GIFAD technology, the detection in the existing technology is performed at a frequency of less than 10. -5 The device 1 of the present invention performs differential pumping of a detection housing ZDU, within which diffraction pattern detection is performed separately from the chamber C. As a reminder, differential pumping is a technique consisting of several different volumes juxtaposed therebetween, maintaining a high pressure differential, each volume separated by a small-sized opening and pumped by a corresponding pump. Specifically, in the present invention, the chamber C and the housing ZDU are connected by several separate volumes, which are pumped by a so-called UHVP (see below). Thus, a pressure of less than 10 mbar, compatible with microchannel wafer detection, is obtained within the detection housing ZDU. -5 The pressure is mbar, while the pressure in chamber C containing sample E can be as high as 10 mbar. -2mbar (hereinafter referred to as "high pressure") is compatible with thin film growth or surface modification methods operated under high pressure.

[0041] For this purpose, chamber C is connected to a so-called main pump PP via a coupling port (not shown), which is adapted to maintain a pressure of less than 10 ppm within chamber C. -2 The pressure is mbar. Preferably, chamber C is pumped by a main pump PP and an additional turbomolecular pump. This configuration is rationalized because it requires maintaining an ultra-high vacuum (pressure below 10 mbar) (excluding gas injection). -9 (mbar) to maintain sample quality, as GIFAD technology is extremely sensitive to surface contamination.

[0042] To perform differential pumping, the detection housing ZDU is connected to chamber C and via a coupling port PC to the UHVP pump. Both the PC and UHVP pumps are typically turbomolecular pumps. The housing ZDU includes concentric tube assemblies Ens, each tube T1, T2 having a so-called inlet end with corresponding openings O1, O2 positioned near the sample E. This tube assembly allows for defining a juxtaposition volume that separates the chamber from the environment surrounding the detector Det through small-diameter openings to perform differential pumping. The diameters of openings O1, O2 and the pump UHVP are suitably maintained within the detection housing ZDU at less than 10 mm. -5 mbar pressure.

[0043] Figure 4 It shows relative to Figure 3 A magnified schematic diagram of the ZDU outer casing.

[0044] To perform detection, the housing ZDU includes a position-sensitive detector Det, which is adapted to detect the diffraction pattern FD of neutral molecules or atoms in the diffraction beam FD. For example, the detector consists of a microchannel wafer coupled to a fluorescent screen observed by a camera.

[0045] Therefore, differential pumping can ensure that the ZDU housing temperature is below 10. -5 A vacuum of mbar ensures that the signal-to-noise ratio of the diffraction pattern on the detector is sufficient to determine the surface structure, while the chamber C has a high pressure (up to 10 mbar). -2 Therefore, the present invention provides a feasible solution to the lack of tools capable of monitoring growth in a magnetron plasma deposition framework, and provides a technique that operates under high pressure and is widely used in research and industry, where RHEED is unavailable due to the electromagnetic field strength present in the chamber during deposition.

[0046] Importantly, there is no information loss in the diffraction beam path between the sample and the detector Det, meaning that a portion of the diffraction pattern FD associated with the characterizing surface SE is not interrupted by the path in the tube assembly Ens. In the device of the present invention, the diffraction beam is transmitted in a smaller radius tube T1 with a length L. Furthermore, the aforementioned condition implies that the length L and the openings O1, O2 are suitable for transmitting the diffraction beam to the detector Det without information loss. For this purpose, the openings at the tube ends have gradually increasing diameters along the path of the diffraction beam DB, decreasing according to the radius of the tube. That is, the larger radius tube T2 has a smaller diameter opening O2 and is placed closer to the sample compared to the opening O1 of the smaller radius tube T1. In fact, the diffraction beam DB diverges from the sample, and the openings should accommodate this divergence. As a non-limiting example, in order not to truncate the relevant diffraction signal while allowing differential pumping to the detection housing to less than 10 -5 With a pressure of mbar, when the distance between the sample and the opening is typically 5cm, the smaller diameter opening O2 usually has a diameter of less than or equal to 5mm.

[0047] Preferably, the diameters of openings O1 and O2 are large enough that the detected diffraction pattern includes all intensities scattered by the surface as well as the portion of the direct beam (not diffracted by the surface). The portion of the direct beam (not diffracted by the surface) serves as an angular reference and facilitates the correct interpretation of the diffraction pattern.

[0048] In the device of this invention, assuming a higher pressure in chamber C, the probability of atoms or molecules in the beams DB and NB colliding with the residual gas in chamber C is higher than in prior art GIFAD devices. These collisions result in an exchange of angular momentum and / or energy, which can disrupt the coherence of the atomic or molecular beam, thereby reducing the contrast of the diffraction pattern fringes. To obtain an operable diffraction pattern FD on detector Det, in this invention, the so-called high-pressure distance LHP between the inlet EF and the opening O2 is less than the decoherence length of the incident beam. It should be understood that this decoherence length depends on the energy of the atoms or molecules in the beams DB and NB and the pressure in chamber C. For example, through simulation, the inventors have calculated that approximately 10 -2 At a pressure of mbar and an energy of approximately 1 keV, a high-pressure distance of less than 10 cm (LHP) allows for partial conservation of the quantum properties of the atomic or molecular beam and yields operable diffraction patterns. Notably, this distance is sufficient to allow for the integration of surface treatment systems (deposition or etching) within chamber C.

[0049] exist Figure 3 and Figure 4In the device shown, only two tubes are illustrated as a non-limiting example; however, it should be understood that the invention can be implemented using more than two tubes. The use of more than two tubes makes it easier to maintain a larger pressure differential between the chamber C and the outer casing ZDU, while transmitting the beam DB without losing the information about the surface SE carried by the diffraction pattern FD.

[0050] exist Figure 4 In one embodiment of the device, each tube has a so-called "outlet" end with a collar Col extending in a direction substantially perpendicular to the tube to guide the airflow pumped by the UHVP pump in that direction at the outlet of each tube. Furthermore, the coupling port PC of the UHVP pump is disposed within the detection housing, facing the space SP formed by the collar. These optional features ensure that the amount of residual gas present in the housing ZDU in the environment surrounding the detector is minimized.

[0051] Preferably, according to an embodiment of the present invention, the generating source SN is adapted such that the incident angle θ inc It can change. The angle of incidence θ inc The change in the reflection angle θ ref The same changes. To transmit the diffraction beam without losing spatial information, the device also includes a translation and / or rotation stage for the tube assembly. Figure 4 (not shown in the image) so that the position of the opening can be adjusted according to the angle of incidence.

[0052] Figure 5 A system 2 for magnetron plasma deposition is shown, comprising apparatus according to the invention for characterizing the surface SE of sample E during deposition of sample E using the GIFAD technique. Figure 3 Compared to the apparatus of the present invention shown, system 2 further includes a channel CA for supplying gas G from which plasma P, such as argon, is generated. The system also includes two electrodes between which a voltage generator GT applies a voltage: a magnetron cathode EC and an anode EA (shown here connected to ground). The voltage between the anode EA and the cathode EC achieves ionization cascade through gas impingement and plasma P generation. Due to the electromagnetic field strength present in the chamber during deposition, RHEED cannot be used for in-situ monitoring of this technique. For example, using a magnetron-type magnetic trap coupled to the cathode EC allows electrons in plasma P to be confined near the surface of the target Ci to increase plasma density, and also allows it to operate at less than 10... -2 Operating at mbar, this is fully compatible with the device described in this invention. Then, ions of gas G are accelerated toward the cathode and then strike the surface of the target Ci, ejecting atoms At from the target. These atoms have sufficient kinetic energy to reach the surface of the sample, thereby forming a layer SE.

[0053] Due to the presence of gas G and plasma, the pressure in chamber C is typically 10 during magnetron plasma deposition. -3 mbar to 10 -2 mbar. With the differential pumping of the device of the present invention, GIFAD technology can be implemented during magnetron plasma deposition.

Claims

1. An apparatus for characterizing the surface of a sample, comprising: - A chamber, including a support for the sample, the chamber being connected to a main pump, the main pump being adapted to maintain a pressure of less than 10 ppm within the chamber. -2 mbar pressure; - A source for generating an incident beam of neutral molecules or atoms with an energy of 50 eV to 5 keV and a divergence of less than or equal to 0.05°, the source being arranged to guide the incident beam toward the surface to be characterized at an incident angle of less than or equal to 10° relative to the plane of the surface via an inlet in the chamber, the neutral molecules or atoms of the incident beam being scattered forward by the surface to form a diffracted beam; and - A detection housing, connected to the chamber and connected to the UHVP pump, comprising: - A concentric tube assembly, each tube having an inlet end with an opening, the assembly including a smaller radius tube T1 having a length L, the radius of tube T1 being smaller than the radius of tube T2; - A position-sensitive detector suitable for detecting the diffraction pattern of neutral molecules or atoms in the diffraction beam; The length L and the opening are adapted to transmit the diffraction beam to the position-sensitive detector without losing information about the surface, and the opening and the UHVP pump are adapted to maintain a depth of less than 10 within the detection housing. -5 mbar pressure.

2. The device according to claim 1, wherein, The opening of each tube has a diameter that differs from the other tubes and decreases as the radius of the tube increases.

3. The device according to any one of claims 1 to 2, wherein, Smaller diameter openings have a diameter of 5 mm or less.

4. The device according to any one of claims 1 to 2, wherein, The high-pressure distance between the inlet and the inlet end of the tube is less than the decoherence length of the incident beam and the diffracted beam.

5. The device according to claim 4, wherein, The high-voltage distance is less than 10 cm.

6. The device according to any one of claims 1 to 2, wherein, Each tube has an outlet end with a collar extending in a direction substantially perpendicular to the tube to guide airflow in that direction at the outlet of each tube. The coupling port of the UHVP pump is located in the detection housing, facing the space formed by the collar.

7. The device according to any one of claims 1 to 2, wherein, The position-sensitive detector includes a microchannel chip coupled to a fluorescent screen observed by a camera.

8. The device according to any one of claims 1 to 2, wherein, The source is adapted to allow the incident angle to be varied, and the device further includes a translation and / or rotation stage for the concentric tube assembly to adjust the position of the opening according to the incident angle.

9. A magnetron plasma deposition system comprising the apparatus according to any one of claims 1 to 8, the apparatus being arranged to characterize the surface of the sample during deposition.

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