System for continuous wave laser processing and SEM characterization of samples

Abstract

The present invention relates to a system (10) for processing and characterizing a sample (Ech), comprising: a scanning electron microscope (SEM) comprising: a chamber (Ch); a device (COL) configured to generate an electron beam (FE) and to focus the electron beam on the sample; and at least one first detector (Det); a laser source (LAS) configured to generate a continuous wave laser beam (FL); a two-dimensional scanning device (DS) configured to move the laser beam over the sample at a defined speed (v); and a focusing device (DFOC) configured to focus the laser beam on the sample through a window and to modify the value of the focal length in a controlled manner, wherein the laser source and the focusing device are configured such that the focused spot on the sample has a given power (P) and a given diameter (D).

Description

[Technical Field]

[0001] The present invention relates to the field of sample processing and characterization applied to materials research and engineering, and more particularly to the use of continuous wave lasers for processing and scanning electron microscopes for characterization. [Background technology]

[0002] Recent large-scale developments in industrial processes include the development of materials through additive manufacturing using light / matter interactions. These processes result in the formation of microstructures due to the strong temperature gradients these materials are subjected to, also observed in welding. Understanding the consequences of this non-equilibrium metallurgy requires ever more detailed knowledge of what occurs during these processes, both for research purposes and for optimal practical implementation of these processes.

[0003] Currently, this need for knowledge is only partially met due to the complexity of the resulting microstructures and the performance of light interacting with the material. For example, ultra-high precision characterization of microstructures resulting from additive manufacturing requires parts to be pulled from the manufacturing line and inserted into a scanning electron microscope (SEM). The atmosphere in additive machines is not controlled, and samples can oxidize during processing, making characterization by SEM very difficult, if not impossible.

[0004] The publication "A novel combined device for laser modification in SEM" by K. Wetzig et al. (SCANNING Vol. 9, pages 99-107 (1987)) describes the connection of a pulsed laser to an SEM, and the illumination of a sample placed in the chamber of the SEM by an ultra-high energy pulsed laser. The purpose of this research is to -3 or 10 -8The objective of this system is to carry out in situ studies of physical processes carried out on the submicron scale during irradiation of a surface by a pulsed laser (3 J per pulse with a duration of 10 s). SEM images are taken before and after irradiation. The laser beam is focused and the focal spot is fixed with a biconvex lens, which reduces the size of the laser spot by a factor of 10. The intended application is the laser ablation or deposition of materials. The system is limited to the study / characterization of effects induced on metal samples by an ultra-high energy pulsed laser in a point-like treatment zone for destructive purposes.

[0005] The object of the present invention is to remedy the above-mentioned drawbacks by proposing a versatile system that is capable of treating material samples over a millimeter zone, typically with a beam of energetic light, and characterizing a large number of materials with an electron beam, and that is suitable for a variety of treatments, some of which have recently been developed. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] “A novel combined device for laser modification in SEM” by K.Wetzig et al(SCANNING Vol 9,pages 99-107(1987)) Summary of the Invention [Means for solving the problem]

[0007] The present invention provides a system for processing and characterizing a sample, comprising: a scanning electron microscope, a chamber containing a gas or under vacuum in which the sample is placed and one wall of which contains a window; a device configured to generate an electron beam and focus the electron beam onto a specimen; at least one first detector configured to detect electrons emanating from the sample; and a scanning electron microscope including: a laser source configured to generate a continuous wave laser beam; a two-dimensional scanning device configured to move a laser beam over the sample at a defined speed; a focusing device configured to focus the laser beam through the window onto the sample and to modify the value of the focal length in a controlled manner; Including, the laser source and the focusing device are configured such that the focused spot on the sample has a defined power and a defined diameter; Regarding the system.

[0008] According to one embodiment, the focusing device includes an optical system with a fixed focal length and a device configured to modify the focal length and located upstream of the scanning device.

[0009] According to one embodiment, the system according to the invention comprises a beam splitter arranged upstream of the scanning device, and a display camera arranged in the path of the light beam reflected by the sample and reflected by the beam splitter, and configured to display the sample.

[0010] According to one embodiment, the system according to the invention includes a thermal sensor configured to measure the temperature of a zone containing the laser focal spot on the sample.

[0011] According to one embodiment, the system according to the invention further comprises a device for injecting a defined gas into the chamber (DIG).

[0012] According to one embodiment, the first detector is a secondary electron detector.

[0013] According to one embodiment, the system according to the present invention further comprises a second removable detector configured to detect electrons backscattered by the sample.

[0014] According to one embodiment, the system according to the invention further comprises a detachable crystallographic camera (CC) configured to detect electrons backscattered by the sample.

[0015] According to one embodiment, the system according to the present invention includes a removable calorimeter for calibrating the laser output power.

[0016] According to one embodiment, the scanning electron microscope is an environmental type scanning electron microscope.

[0017] According to one embodiment, the laser source is coupled to an optical fiber, and further, the laser source, the two-dimensional scanning device, and the focusing device are disposed in a single housing, and the system further includes a coupling configured to interface the housing and the scanning electron microscope.

[0018] According to another aspect, the present invention provides a method for processing and characterizing a sample, comprising placing the sample in a chamber of a scanning electron microscope, the chamber containing a gas or under vacuum, and a wall of the chamber containing a window; - generating a continuous wave laser beam with modifiable power 100; - a processing step 200 comprising focusing a laser beam on a sample by passing the laser beam through a window, the value of the focal length being modifiable in a controlled manner, and scanning the laser beam in two dimensions to move the laser beam over this sample at a defined speed, the focused spot on the sample having a defined power and a defined diameter; a characterization step 300, which consists in generating a first image, called a post-processing image, in a scanning electron microscope by illuminating the sample with a focused electron beam and detecting the electrons leaving the sample; The present invention relates to a method comprising:

[0019] According to one embodiment, the method according to the invention further comprises, before the processing step 200, a step 50 consisting in generating a second image, called a pre-processing image, with a scanning electron microscope.

[0020] The following description presents some exemplary embodiments of the device of the present invention, and these examples do not limit the scope of the invention. These exemplary embodiments include not only features essential to the invention, but also additional features related to the embodiment in question.

[0021] The invention will be better understood and other features, objects and advantages of the invention will become apparent from the following detailed description given by way of non-limiting example and with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0022] [Figure 1] 1 illustrates a system for processing and characterizing a sample according to the present invention. [Figure 2] 1 shows an example of an implementation of a system according to the invention, where the SEM operates in "SE" mode and includes a viewing camera and a thermal camera. [Figure 3] 1 shows an example of an implementation of a system according to the invention, in which the SEM operates in "BSE" mode and includes a device for injecting a defined gas. [Figure 4] 1 shows an example of an implementation of a system according to the invention, in which the SEM is operated in "EBSD" mode and includes a crystallography camera. [Figure 4a] 1 illustrates an example implementation of a system according to the present invention in which a laser source, an output optical fiber, a two-dimensional scanning device, and a focusing device are arranged in a single housing, and the system includes a coupling configured to interface the housing and the SEM. [Figure 5] 1 shows a first example of the use of the system according to the invention with characterization in SEM mode. [Figure 6] FIG. 1 shows a second example of the use of the system according to the invention, with characterization in EBSD mode, where SEM image A was taken before processing and SEM image B was taken after processing. [Figure 7] 10 shows a third example of the use of the system according to the invention with characterization in BSE mode. DETAILED DESCRIPTION OF THE INVENTION

[0023] A system 10 according to the invention for processing and characterizing a sample is illustrated in Fig. 1. The system 10 comprises a scanning electron microscope SEM comprising a chamber Ch under vacuum or partial gas pressure in which the sample to be processed / characterized is placed. One of the walls of the SEM comprises a window H. In a known manner, the SEM comprises a device COL (commonly called a column) configured to generate an electron beam FE and to focus this electron beam on the sample, and at least one detector Det configured to detect electrons emerging from the sample.

[0024] Furthermore, the system 10 according to the invention comprises a laser source LAS configured to generate a continuous wave laser beam FL, a focusing device DFOC configured to focus the laser beam onto the sample through a window H and to modify the value of the focal length in a controlled manner, and a two-dimensional scanning device DS configured to move the laser beam over this sample at a defined speed v.

[0025] The laser source LAS and the focusing device DFOC are configured so that the focused spot on the sample has a defined power P and a defined diameter D. To vary P, the power of the adjustable laser is changed, and to vary D, the value of the focal length is changed. The beam FL enters the chamber Ch through an interface window H, which is preferably laser-quality treated (specific surface treatment). The window is transparent to the wavelength of the laser and also ensures the sealing of the chamber. The window seals the chamber and allows the laser beam FL to enter the chamber Ch and access the sample.

[0026] Typically, SEM images of the sample are taken after laser treatment and, optionally, before treatment for comparison.

[0027] Thus, the present invention allows processing and characterizing material samples in the same instrument using a continuous wave laser beam whose parameters (P, D, v) can be modified.

[0028] With continuous wave lasers, the energy input is constant over time and follows a well-controlled temperature gradient, allowing the study and implementation of physical and chemical processes such as: - Material modification, e.g., change of state or phase, change of microstructure or surface condition, evolution of roughness, assembly, etc. -Restoration or repair (solidification or resolidification)

[0029] With the system according to the invention, the spot parameters P (power) and D (size) can be adjusted to adapt the surface energy density incident on the sample and the temperature gradient experienced (which can reach 1 million degrees / cm). Typically, the beam diameter varies depending on the application over a range within the interval [45-500 μm].

[0030] Additionally, the sample is processed in the controlled atmosphere of the SEM chamber Ch (vacuum, humidity, neutral or reducing gas, etc.), for example, laser processing under vacuum protects the sample from moisture and oxidation damage.

[0031] Tuning the scanning speed v of the device DS typically provides multi-scale characteristics, with accessible scanning amplitudes ranging from microns to millimeters, and further allows for complex scanning geometries (scanning strategies).

[0032] Thus, time, temperature and atmospheric factors are controlled.

[0033] The system according to the present invention, which integrates the control of the above-mentioned parameters, allows for the improvement of the surface quality and the mechanical properties of the material of the sample. Furthermore, new properties of the laser-treated material can be obtained by changing the local microstructure of the material, and the changes produced by the laser treatment can be characterized.

[0034] Systems according to the present invention can be implemented in a variety of materials (eg, ceramic, mineral, metallic, polymeric, etc.).

[0035] Scientific studies of the results obtained with the system according to the invention will expand the field of experimental and numerical knowledge.

[0036] The system according to the invention can be used to replicate heat treatments similar to those performed in various industrial processes (additive manufacturing, heat treatment, annealing, tempering, welding, etc.), understand the nature of the interaction between industrial lasers and materials during these processes, and suggest optimized heat treatments during and / or after these processes.

[0037] Furthermore, the system according to the invention can be located, for example, in industrial centers of additive manufacturing or surface structuring, and can control the in situ evolution of materials treated by a laser, integrating the system according to the invention upstream or downstream of a process to verify the result or results of modifying manufacturing parameters on the evolution of the material's microstructure.

[0038] Thus, the system for processing and characterizing samples according to the present invention is extremely versatile and, as discussed above, fills a heretofore unmet instrument need.

[0039] The system according to the present invention has various embodiments that can be combined with each other.

[0040] According to the embodiment illustrated in Fig. 2, the focusing device comprises an optical system L with a fixed focal length and a device 20 configured to modify the focal length and arranged upstream of the scanning device, device 20 itself being arranged upstream of optical system L. Device 20 is for example a varioScan® which comprises a diverging lens that makes the beam diverge at the laser output and thus makes it possible to modify the size of the laser spot impinging on the sample.

[0041] The scanning device is, for example, a goniometric mirror.

[0042] The accessories also illustrated in Figure 2 allow visualization of the zone of influence of the beam on the sample.

[0043] According to one embodiment, the system further comprises a beam splitter BS arranged upstream of the scanning device and a viewing camera CV arranged in the path of the light beam FLR reflected by the sample and then by the beam splitter BS. The viewing camera thus reproduces the light reflected by the sample and makes it possible to visualize the surface of the sample, the future path of the laser and also the position through which the laser spot is passing.

[0044] According to another embodiment, the system 10 according to the invention comprises a thermal sensor CT for measuring the temperature of the zone containing the laser focus spot on the sample. Preferably, a two-dimensional thermal camera is used, which makes it possible to perform infrared thermography, for example to visualize the distribution of the temperature field induced by the laser treatment.

[0045] The electron detector shown in Figure 2 is a secondary electron detector commonly referred to as a DES, which is conventionally used in scanning electron microscopy, operating in secondary electron mode. This mode is typically installed as a default setting on commercial SEMs, and allows for the acquisition of topographical contrast images of the observation surface.

[0046] Additionally, FIG. 2 shows a removable protective shield BP that protects the SEM column during laser firing.

[0047] 3 illustrates an embodiment of a system according to the present invention in which the SEM operates in backscattered electron (BSE) mode. This mode produces atomic number contrast images that can provide information about the chemical properties of the observed elements. In this mode, the system includes a second electron detector, a backscattered electron detector (DER). Preferably, this detector is removable and is positioned only when the SEM is required to operate in this mode.

[0048] According to an embodiment also illustrated in FIG. 3, the system 10 includes a device DIG for injecting a defined gas into the chamber Ch, allowing for environmental control during the laser treatment.

[0049] 4 illustrates an embodiment of a system according to the present invention in which the SEM is operated in electron backscatter diffraction (EBSD) mode. In this mode, the system includes a detachable crystallography camera CC configured to detect electrons backscattered / diffracted by the sample. This mode allows viewing the results of laser processing in order to characterize the microstructure from a crystallographic perspective (specific imaging).

[0050] According to one embodiment, the scanning microscope is an environmental type scanning microscope or ESEM, which is able to monitor the gas environment of the part to be treated. Furthermore, by using an ESEM in the system according to the invention, all relevant physical and chemical techniques using particle physics (X-ray spectroscopy, electron diffraction, infrared thermography) can be carried out.

[0051] According to one embodiment, the system includes a removable calorimeter that calibrates the laser output power.

[0052] By way of non-limiting example, the laser LAS is a class 4 fiber laser emitting at a wavelength of 1070±2 nm with adjustable fiber output power (collimated beam) from 20 to 200 W.

[0053] According to one embodiment, the laser is coupled to an output optical fiber. The laser source, the output optical fiber, the two-dimensional scanning device, and the focusing device are arranged in a single housing BT. According to one embodiment, the system further comprises a coupling PA configured to interface the housing and the SEM, as illustrated in Figure 4a. This coupling can confine the focusing lens of the housing.

[0054] Figure 5 shows a first example of the use of the system according to the invention. This secondary electron image (SEM) makes it possible to identify the position and evaluate the width of the zone affected by the laser passage. In this experiment, five laser spots were created with a power of 24 W and a spot size of 60 μm. Tracks 1 to 5 correspond to laser travel speeds of 50, 100, 250, 500, and 1000 mm / s, respectively.

[0055] 6 shows a second example of the use of the system according to the invention, where image A is the image before laser treatment and image B is the image after laser treatment. An electron backscatter diffraction type analysis obtained with an EBSD camera shows the crystallographic characteristics of the material's microstructure and the modification of the material by the laser. A comparison of image A (before laser treatment) and image B (after laser treatment) shows that the grains that make up the microstructure and surface features are modified by the passage of the laser (zone 60).

[0056] Figure 7 shows a third example of the use of the system according to the invention. Backscattered electron imaging (BSE mode) obtained with an electron microscope shows the contrast of the chemical composition that makes up the microstructure of the observed material, as well as the modification of the material by the laser. The lower part (untreated zone) shows a network (brighter image due to chromium and molybdenum enrichment) and cells (interconnected honeycomb network, darker image). The treated upper part shows that the network has been modified, with a significantly reduced network topography and smaller cells. This structural change causes a modification of the material's mechanical properties.

[0057] The system according to the invention therefore allows for in-situ comparison before / after treatment without having to move the sample between laser treatment and characterization. This comparison of images taken in-situ represents a significant time saving and the use of the system according to the invention results in more reliable measurements as the measurements are performed under a controlled atmosphere. According to another aspect, the present invention relates to a method for processing and characterizing a sample. The sample is placed in a chamber Ch of an SEM, which may contain a gas or be under vacuum. The chamber wall includes a window H. The method includes a step 100 of generating a continuous-wave laser beam FL having a modifiable power P. Next, in a processing step 200, the laser beam is focused on the sample by passing it through the window and scanned in two dimensions so as to move the laser beam over the sample at a defined speed v. The value of the focal length can be modified in a controlled manner, and the focused spot on the sample has a defined power P and a defined diameter D. Finally, in a characterization step 300, a first image, called a post-processing image, is generated in the SEM by illuminating the sample with a focused electron beam FE and detecting electrons emerging from the sample.

[0058] According to one embodiment, the method according to the invention further comprises, before the processing step 200, a step 50 consisting in generating a second image in the SEM, called a pre-processing image.

Claims

1. A system (10) for processing and characterizing a sample, comprising: a scanning electron microscope (SEM), a chamber (Ch) containing a gas or under vacuum, in which the sample is placed and one wall of which contains a window (H); a device (COL) configured to generate an electron beam (FE) and to focus said electron beam on said sample; at least one first detector (Det) configured to detect electrons leaving the sample; a scanning electron microscope (SEM) comprising: a laser source (LAS) configured to generate a continuous wave laser beam (FL); a two-dimensional scanning device (DS) configured to move said laser beam over said sample at a defined speed (v); a focusing device (DFOC) configured to focus the laser beam through the window onto the sample and to modify the value of the focal length in a controlled manner; Including, the laser source and the focusing device are configured so that the focused spot on the sample has a defined power (P) and a defined diameter (D); System (10).

2. 2. The system of claim 1, wherein the focusing device comprises an optical system (L) with a fixed focal length and a device (20) configured to modify the focal length and located upstream of the scanning device.

3. 3. The system of claim 1 or 2, comprising a beam splitter (BS) arranged upstream of the scanning device, and a display camera (CV) arranged in a path of a light beam (FLR) reflected by the sample and by the beam splitter, and configured to display the sample.

4. The system according to any one of claims 1 to 3, comprising a thermal sensor (CT) configured to measure the temperature of a zone containing a laser focal spot on the sample.

5. The system according to any one of claims 1 to 4, further comprising a device (DIG) for injecting a defined gas into the chamber.

6. The system of any one of claims 1 to 5, wherein the first detector is a secondary electron detector (DES).

7. The system of any one of claims 1 to 6, further comprising a second removable detector (DER) configured to detect electrons backscattered by the sample.

8. The system of any one of claims 1 to 7, further comprising a detachable crystallographic camera (CC) configured to detect electrons backscattered by the sample.

9. A system according to any preceding claim, including a removable calorimeter for calibrating the laser output power.

10. The system according to any one of claims 1 to 9, wherein the scanning electron microscope is an environmental scanning electron microscope (ESEM).

11. 11. The system of claim 1, wherein the laser source is coupled to an optical fiber, and the laser source, the two-dimensional scanning device, and the focusing device are disposed in a single housing, and the system further comprises a coupling configured to interface the housing and the scanning electron microscope.

12. 1. A method for processing and characterizing a sample, comprising placing the sample in a chamber (Ch) of a scanning electron microscope (SEM), the chamber containing a gas or under vacuum, and a wall of the chamber containing a window (H); - generating 100 a continuous wave laser beam (FL) with modifiable power (P); - a processing step 200 comprising focusing the laser beam on the sample by passing it through the window, the value of the focal length being modifiable in a controllable manner, and scanning the laser beam in two dimensions to move the laser beam over the sample at a defined speed (v), the focused spot on the sample having a defined power (P) and a defined diameter (D); a characterization step 300 consisting in generating a first image, called a post-processing image, in the scanning electron microscope by illuminating the sample with a focused electron beam (FE) and detecting the electrons leaving the sample; A method comprising:

13. 13. The method of claim 12, further comprising, prior to said processing step 200, a step 50 of generating a second image with said scanning electron microscope, called a pre-processing image.

Images