In-situ etch rate or deposition rate measurement system

Abstract

The present invention relates to a system for in-situ ion beam etching rate or deposition rate measurement, which comprises: a vacuum chamber; an ion beam source, which is configured to direct an ion beam onto a first surface of a sample located in the vacuum chamber, and etch the first surface of the sample at an etching rate; or a material source, which is configured to deposit material onto a first surface of a sample located in the vacuum chamber at a deposition rate; and an interferometric measurement device, which is at least partially located in the vacuum chamber and is configured to direct light onto a second surface of the sample, and in-situ determine the etching rate of the ion beam or the deposition rate of the deposited material based on light reflected from the sample.

Description

Technical Field

[0001] The invention relates to an in-situ etching rate or deposition rate measurement system and method. Background Art

[0002] Ion beam etching is a common tool used to polish and shape samples of various materials, such as optical components or thin films. Specifically, an ion beam is a charged particle beam composed of ions. There are many ion beam sources, the most common of which have singly charged ions.

[0003] The ion beam is directed onto the sample surface, and the impact of the ions erodes the sample surface, grinding away (etching) a certain amount of material. The amount of material etched away by the ion beam depends on, for example, the ion beam parameters, the material composition of the sample, and the exposure time. The etching rate is defined as the amount of material removed from the sample surface over time.

[0004] The ion beam is typically focused onto the sample surface and has a Gaussian profile with a peak (maximum value of the Gaussian ion beam profile) and a full width at half maximum (FWHM). Therefore, the etch profile of the sample surface can also be characterized by the peak etch rate and FWHM.

[0005] In prior art systems, in order to determine the etching rate of the ion beam of a specific sample, an interferometric measurement device based on surface form interferometry is used, for example, a Fizeau-interferometer is used to predefine the characteristics of a sample probe (reference sample). Subsequently, the sample probe is inserted into a vacuum chamber. The sample probe is ideally of the same material as the actual sample that will be exposed to the ion beam later. Using predetermined beam parameters, the sample probe is exposed to the ion beam for a predetermined amount of time, the so-called footprint etching. The sample probe is removed from the vacuum chamber, and the etching profile is then measured ex situ by an interferometric device based on surface interferometry. Thus, the peak etching rate, FWHM and etching volume can be determined. Thereafter, the actual sample is inserted into the vacuum chamber and processed according to the determined etching parameters of the ion beam.

[0006] However, prior art systems require time-consuming methods to determine the etching rate parameters of the ion beam because, in addition to performing the aforementioned interferometric measurements before and after ion beam etching, the sample probe must also be inserted into and removed from the vacuum chamber.

[0007] Additionally, the sample probe has a limited lifespan, since the fringes of the surface form interferometry can only be resolved for a certain depth of the etch profile. That is, after a certain amount of etching on the sample probe, the depth of the etch profile can no longer be resolved by prior art interferometry devices. Such sample probes must be regularly replaced or re-polished, which is costly.

[0008] Furthermore, to determine the full ion beam profile, prior art systems must use a sample probe that is three to four times the size of the ion beam diameter, which necessitates large reference targets for interferometry and limits metrology while being costly.

[0009] Similar problems arise in conventional deposition methods, in which the deposition rate is measured ex situ, ie, before the sample is inserted into a vacuum chamber for material deposition and after the sample is extracted from the vacuum chamber. Summary of the invention

[0010] The object of the present invention is to overcome the above-mentioned drawbacks of the prior art systems. The present invention is defined by the independent claims. The dependent claims are about preferred embodiments of the present invention.

[0011] According to one aspect of the present invention, a system for in-situ ion beam etching rate or deposition rate measurement is provided, the system comprising: a vacuum chamber; an ion beam source, which is configured to direct an ion beam onto a first surface of a sample located in the vacuum chamber, and etch the first surface of the sample at an etching rate; or a material source, which is configured to deposit material onto a first surface of a sample located in the vacuum chamber at a deposition rate; and an interferometric measurement device, which is at least partially located in the vacuum chamber and is configured to direct light onto a second surface of the sample, and in-situ determine the etching rate of the ion beam or the deposition rate of the deposited material based on light reflected from the sample.

[0012] That is, the system can be used to determine the ion beam etch rate or the deposition rate of a material deposition technique. The deposition technique can be any of the following: chemical vapor deposition (CVD); physical vapor deposition (PVD); low-pressure chemical vapor deposition (LPCVD); plasma-enhanced chemical vapor deposition (PECVD); or plasma-assisted CVD.

[0013] In deposition rate determination, material from a material source is deposited onto a sample surface, and the deposition rate can be determined as a change in thickness (increase) over time. In contrast, in ion etching rate determination, material is removed from a sample surface, and the etching rate can be determined as a change in thickness (decrease) over time.

[0014] As mentioned above, the interferometry device may be located at least partially within the vacuum chamber, for example, the sensors and optical fibers may be located within the vacuum chamber, while other elements, such as a power supply, controller, and other components of the interferometry device may be located outside the vacuum chamber.

[0015] The interferometric measurement device can be configured to determine the etching rate while etching the first surface of the sample, preferably after a predetermined stabilization time, preferably greater than 2 minutes, more preferably greater than 3 minutes, even more preferably greater than 4 minutes, and most preferably 4-5 minutes or longer. That is, the etching rate measurement can be performed while etching is in progress.

[0016] The interferometric measurement device may be configured to determine the deposition rate while the material is being deposited onto the first surface of the sample. That is, the deposition rate measurement may be performed while the deposition is taking place.

[0017] The etch rate may be defined as the amount of material removed from the first surface of the sample over time.

[0018] The deposition rate may be defined as the amount of material deposited onto the first surface of the sample over time.

[0019] The interferometric measurement device may be a high precision optical low-coherence interferometer (HP-OLCI).

[0020] The HP-OLCI as an analysis unit may be a stripe interferometer and may be based on optical coherence tomography (OCT) technology. It may comprise two inner arms and two outer arms. One inner arm may be equipped with a voice coil which provides a working area via its pitch. The second inner arm may be movable to provide a scanning range (preferably 0-135 mm in thickness).

[0021] One outer arm can be formed by the sensor itself in the ion beam figuring (IBF) vacuum chamber. The second arm can be an adjustable reference. This reference can be formed by an air gap. The two outer arms can provide signals; by determining the distance between the two signals the thickness is measured. For example, a 1550 nm DFB laser can serve as a scale.

[0022] The reference arm can be used to set the air gap with the optical thickness of the sample. The air gap can be created by a movable (e.g. 135 mm) glass plate (e.g. fused silica) and a mirror. HP-OLCI can take into account only the interference pulse of the interface and can compare it with the interference pulse of the air gap interface (transition zone of fused silica to air). If the two signals are on top of each other, the thickness difference is zero. If the sample surface is etched away by the ion beam, the interference pulse is away from the reference pulse. The distance between the two is determined with high precision by the maximum of the two pulses and the DFB laser interference signal (scale). The change over time can be output in nm / s and can be measured with an accuracy better than 0.1 nm / s.

[0023] In other words, the HP-OLCI is a highly accurate comparative thickness measurement device. The reference signal is usually generated by a sample of precisely known thickness, and the difference to this reference sample is determined. The absolute thickness is not important for the present invention. Instead, the change over time is determined. Therefore, an air gap can be used, which has the advantage of being variable.

[0024] The second surface of the sample can be opposite to the first surface of the sample. That is, one side of the sample can be etched using an ion beam, and the opposite side can be used to measure the etch rate. Similarly, material can be deposited onto one side of the sample, and the opposite side can be used to measure the deposition rate.

[0025] The interferometry device can be configured to determine the thickness of the sample over time, and determine the etching rate or deposition rate based on the change in thickness of the sample over time.

[0026] The interferometry device may include a sensor configured to direct light onto the second surface of the sample and collect light reflected back from the sample.

[0027] The sensor may include optical components to direct light onto the second surface of the sample and collect light reflected back from the sample.

[0028] The sensor may be located within the vacuum chamber.

[0029] The sensor may contain the sample. That is, according to a preferred embodiment, the sample may be located inside the sensor.

[0030] The sensor may include a housing, and the sample may be located inside the housing, preferably the optical components are also located inside the housing.

[0031] The housing may include an opening, and the sample may be located at the opening such that the ion beam or the material to be deposited may reach the first surface of the sample via the opening. In other words, the first surface of the sample may be located at the opening of the housing.

[0032] The housing may comprise a graphite outer surface. Thus, only the sample exposed is left to the ion beam or material to be deposited.

[0033] The interferometry device may include a cooling device, such as a copper cooling device, in contact with the sample and may be configured to cool the sample.

[0034] The interferometric measurement device may include a positioning device configured to position the light at at least one predetermined position on the second surface of the sample. The positioning device may be an x, y, z stage on which the optical component may be mounted so that the optical component can be moved in three dimensions. In some embodiments, a two-dimensional x, y stage may also be sufficient to move the optical component in two dimensions, preferably parallel to the second surface of the sample.

[0035] The controller may be configured to control the positioning device to position the light at a position on the second surface of the sample corresponding to the center of the ion beam to determine a peak etching rate of the ion beam.

[0036] The peak etch rate may be defined as the etch rate at the maximum intensity of the ion beam, where the ion beam has a substantially Gaussian form.

[0037] The controller may be further configured to control the positioning device to position the light at a plurality of positions on the second surface of the sample corresponding to positions within the ion beam profile to determine an etching rate of the ion beam profile.

[0038] For example, by obtaining several measurements at different locations corresponding to locations within the ion beam profile, a Gaussian fit can be used to determine the volume etch rate of the ion beam profile.

[0039] The controller may be further configured to control the positioning device to position the light at a plurality of locations on the second surface of the sample to determine the deposition rates at the plurality of locations.

[0040] The system may further include an alignment device configured to align the ion beam relative to the first surface of the sample.

[0041] The alignment device may include a Faraday cup and a position camera or feature definition device configured to define features of the ion beam by spot scanning and calculate the offset to an initial starting point.

[0042] According to another aspect of the present invention, a method for in-situ ion beam etching rate or deposition rate measurement is provided. The method comprises: directing an ion beam onto a first surface of a sample located in a vacuum chamber, etching the first surface of the sample at an etching rate; or depositing material onto a first surface of the sample located in the vacuum chamber at a deposition rate; directing light from an interferometric measurement device at least partially located in the vacuum chamber onto a second surface of the sample; and determining the etching rate or the deposition rate of the ion beam in-situ based on light reflected from the sample.

[0043] Typically, a sample as described herein (also referred to as a sample probe) may be related to an actual sample on which ion beam processing or deposition will ultimately be performed, or to a test sample used to determine an ion beam etch rate or deposition rate. Such a test sample should ideally be of the same material as the actual sample on which ion beam processing or deposition will ultimately be performed.

[0044] In particular, if the sample is thin enough, the present invention can be used to measure the sample while it is being etched or while material is being deposited onto the sample, without the need for a test sample. For example, this "real-time" measurement of an actual sample while etching or depositing can be used to determine the etching rate or deposition rate by determining the center thickness of an optical lens. If the expected temperature is high, a thin sample (e.g., an optical thickness of up to 135 mm) can be advantageous because heat dissipation is easier in a thin sample than in a thick sample. In other words, since optical materials can tend to be poor thermal conductors, it may be more efficient to remove heat from a thin sample.

[0045] However, in the case where the interior of the sample is constant temperature, there is no restriction on the sample thickness. In any case, it is preferred that the interior of the sample has a constant temperature.

[0046] As is apparent from the above description of the invention, the present invention provides a system and method that reduces processing time because interferometric measurement of a sample can be performed in situ. Thus, time-consuming insertion and extraction of the sample into and from a vacuum chamber can be avoided. In addition, it is not necessary to measure the sample before and after ion beam etching or material deposition, which saves additional time.

[0047] Additionally, with the present invention, since thickness-based interferometry is used, samples can be used more often (re-used) without having to replace or re-polish the samples, and thus costs can be saved.

[0048] Furthermore, because thickness-based interferometry is used, the present invention does not require a sample size of three to four times the ion beam diameter in order to determine the etch profile of the ion beam, which again saves costs.

[0049] Furthermore, the present invention allows etch rate measurements to be made at non-orthogonal impact angles. This is particularly advantageous for highly curved samples, where the respective positioning system may not allow for a perfectly orthogonal impact angle throughout the entire extension of the sample.

[0050] More specifically, the etch rate is highly affected by the impact angle and varies between different materials. The possibility to determine the etch rate for such non-orthogonal impact angles is one of the advantages of the present invention.

[0051] These and other features, advantages and aspects of the present invention will become apparent from the following description of the figures summarizing exemplary embodiments of the present invention. The following description of exemplary embodiments of the present invention should not be construed as limiting the scope of the present invention. On the contrary, the exemplary embodiments are intended to provide some non-exhaustive examples of how to implement the present invention. It will be apparent to those with ordinary knowledge in the art that the present invention is not limited by the combination of features of the following exemplary embodiments. On the contrary, if not explicitly stated otherwise, the features of different exemplary embodiments may be combined with the features of other exemplary embodiments. That is, the scope of the present invention is defined only by the features of the independent claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Some preferred embodiments are now described with reference to the accompanying drawings, in which:

[0053] Figure 1 A preferred embodiment of the system of the present invention is shown.

[0054] Figure 2 Another embodiment of the system of the present invention is shown.

[0055] Figure 3 A flow chart showing a preferred embodiment of the method of the present invention is shown,

[0056] Figure 4 shows a sample probe having footprints etched in different ways using different ion beam parameters,

[0057] Figure 5 shows the in-situ raw etch rate measurements of samples using different ion beam parameters,

[0058] Figure 6 shows the in-situ raw etch rate measurement performed on the sample,

[0059] Figures 7a to 7e 48 hours of measurement results showing source stability for each hour of measurement;

[0060] Figure 8 A diagram showing the sample thickness during geometry determination;

[0061] Fig. 9 shows the sample thickness during geometry determination, and

[0062] Fig.10 Another preferred embodiment of the system of the present invention is shown. DETAILED DESCRIPTION

[0063] refer to Figure 1 , describing a preferred embodiment of the system of the present invention. Figure 1A system 100 for in-situ ion beam etch rate measurement is shown. The system includes a vacuum chamber 110, an ion beam source 111, and an interferometric measurement device 114.

[0064] The ion beam source 111 is configured to direct an ion beam 112 onto a first surface 113 a of a sample 113 located in the vacuum chamber 110 , and to etch the first surface 113 a of the sample 113 at a certain etching rate.

[0065] The interferometry device 114 is at least partially located within the vacuum chamber 110 and is configured to direct light 115 onto the second surface 113 b of the sample 113 and determine in situ an etch rate of the ion beam 112 based on light reflected from the sample 113 .

[0066] The interferometric device 114 may be a low-coherence interferometer, constructed, for example, from two entangled Michelson interferometers, with an adjustment arm having a scanning range of approximately 400 microns, a measuring range arm (adjustable between 0-135 mm thickness), an actual measuring arm adjusted on a reference sample, and an adjustable reference arm providing a reference signal for thickness measurement. The light source may be a combination of superluminescent diodes with central wavelengths of 1280 nm and 1310 nm. As a measure, a distributed feedback, DFB laser with a coupling wavelength of 1550 nm is used for interferometric measurement of the path. This is only one example of an interferometric device that can be used with the present invention. However, the present invention is not limited thereto. Any interferometric device 114 capable of determining the thickness of the sample 113 may be used with the present invention. However, in terms of accuracy, the aforementioned arrangement of the interferometric device 114 may be superior to other such interferometric devices.

[0067] Figure 2 Another embodiment of the system 100 of the present invention is shown. Specifically, Figure 2 Show referenced Figure 1 Features described and additional optional features of system 100.

[0068] Specifically, Figure 2 The vacuum chamber 110, ion beam 112, sample 113, light 115, optical components 116, sensor 117, optical fiber 118, high precision optical low coherence interferometer (HP-OLCI) frame 119, display and input device 120, ion beam shaping IBF control computer 121, network device 122 and adjustable thickness reference module 123 are shown.

[0069] Ion beam 112, sample 113, light 115, optical components 116, sensor 117, and a portion of optical fiber 118 are located within vacuum chamber 110. Sample 113 and optical components 116 are located within sensor 117.

[0070] The ion beam 112 is directed, for example, through an opening (not shown) in the sensor housing onto a first surface 113a of the sample. Light 115, such as infrared light, is directed (focused) onto an opposite surface (second surface 113b) of the sample 113 by an optical component 116, wherein the light is provided to the optical component 116 via an optical fiber 118.

[0071] The sample 113 is located on the inner surface of the sensor 117 , ie, the sensor housing. An opening (not shown) in the sensor housing is provided so that a first surface 113 a of the sample is partially exposed to the ion beam 112 .

[0072] The optical component 116 is configured to focus the light 115 onto the second surface 113b of the sample and collect the light reflected from the surfaces 113a, 113b of the sample. The light reflected back from the sample surfaces 113a, 113b produces a unique interference pattern. By comparing this interference pattern with the interference pattern of the comparison sample from the adjustable thickness reference module 123, the thickness of the sample 113 can be determined.

[0073] For example, the interference pattern may include interference pulses, wherein the envelope of the interference pulses may be used to determine the thickness of the sample 113. To increase the accuracy of the thickness determination, the distance between the interference pulses may be used to determine the thickness of the sample 113.

[0074] Even better is to evaluate the entire pulse itself to further improve accuracy.

[0075] The HP-OLCI stand 119 is connected to the optical assembly 116 via an optical fiber 118 and to the adjustable thickness reference module 123 via another optical fiber. The HP-OLCI stand 119 includes a power supply, a light source(s) and respective control means for the HP-OLCI. The control means may be used to control the functions of the interferometric device 114 and may include a processing device, such as a processor, which may be configured to determine the thickness of the sample 113 based on the interferometric measurement and subsequently determine the etching rate, i.e. the thickness change over time.

[0076] The system 100 may also provide a display and input device 120 for displaying the results of the etch rate determination and receiving user input to control different functions of the interferometric measurement device, such as the magnification and intensity of the light 115 reaching the second surface 113b of the sample and / or adjusting the adjustable thickness reference module 123.

[0077] Controlling the magnification and intensity of the light 115 is advantageous because the light is reflected from the sample surface and therefore the intensity depends on the material of the sample. In addition, the intensity may decrease as the sample ages. Therefore, in order to provide sufficient reflected light intensity, the magnification and intensity of the light 115 directed to the second surface 133b of the sample may be adjusted.

[0078] The ion beam 112, namely the parameters of the ion beam 112 and the position of the ion beam 112 relative to the sample, is controlled using an IBF control computer 121. Figure 2 Not shown in detail, the IBF machine provides an ion beam 112 and includes a vacuum chamber 110.

[0079] The IBF control computer 121 and the HP-OLCI rack 119 are connected to a network 122 to provide centralized control of the ion beam 112 and the interferometry device 114 .

[0080] Figure 3 A flow chart showing a preferred embodiment of the method of the present invention is shown. Specifically, Figure 3 The first step S10 of directing the ion beam 112 onto the first surface 113 a of the sample 113 in the vacuum chamber 110 to etch the first surface 113 a of the sample 113 at an etching rate is shown.

[0081] In a second step S20 , light 115 of an interferometric measurement device 114 at least partially located within the vacuum chamber 110 is directed onto the second surface 113 b of the sample 113 .

[0082] In step S30 , the etching rate of the ion beam 112 is determined in situ based on the light reflected from the sample 113 .

[0083] Figure 4 A sample probe is shown with a footprint etched in different ways using different ion beam parameters. Specifically, the sample probe surface is characterized, i.e., an interferometric surface measurement is performed on the sample probe, before the sample is inserted into the vacuum chamber. Subsequently, the footprint is etched into the sample probe surface using an ion beam. The ion beam parameters are varied as follows: a) 1000V and 50W ( Figure 4 Upper left center coverage area), b) 1000V and 70W ( Figure 4 Upper right center coverage area), c) 1000V and 100W ( Figure 4 Lower left center coverage area), and d) 800V and 50W ( Figure 4 In a further step, the sample probe is taken out of the vacuum chamber and interferometric surface measurements are again performed to determine the etching rates for the different footprints. This corresponds to the prior art procedure.

[0084] For comparison, a sample of the same material (in this case fused silica) was measured using the present invention (i.e. in situ), while using the same beam parameters. The original raw values ​​obtained by the in situ measurement, i.e. the thickness over time, are shown in FIG5 (together with the rolling average). Each measurement was performed for 20 minutes, and a new measurement was started 5 minutes after the previous measurement.

[0085] As Figure 5 It can be seen that initially, i.e. within the first 4-5 minutes, the thickness increases, which is due to thermal expansion effects and changes in the optical index with increasing temperature. By using active cooling of the sample, it is possible to reach stable conditions after 4-5 minutes, depending on the neutralizer and beam power.

[0086] The beam geometry can be obtained by running a point scan, i.e. measuring at different locations on the surface. The first measurement point requires an initial heating time (4-5 minutes), all other points only require a 1-2 minute heating time to stabilize the measurement. The measurement points are preferably scanned in a spiral fashion, starting in the center and moving more outwards. Thus, the energy input can be kept almost constant and the time required for each measurement point can be reduced.

[0087]

[0088] Table 1

[0089] Table 1 shows nine comparative measurements between conventional interferometry on 3-inch probe fused silica and a 1-inch 1 mm sample of the measuring device according to the invention (in-situ etch rate measurement - ISERM). Depending on the manufacturing process of the material, the etch rate can vary significantly. Therefore, the reference sample of the measuring device should be made of the same material as the sample to be processed. Otherwise, correction factors can be determined in advance to take into account the individual variations.

[0090] Figure 6 A beam scan showing the signal and average of the etch rate over time using the present invention. After the initial heating of the sample, the etch rate continues to decrease.

[0091] Figures 7a to 7e The 48-hour measurement results of the source stability are plotted. Specifically, measurements are taken every hour to obtain the peak etch rate over time (see Figure 7d )、Full Width at Half Maximum (FWHM) ( Figure 7b ) stable values ​​and their respective deviations ( Figure 7c and Figure 7e ). Figure 7a One example measurement is shown for a 48 hour measurement. As can be seen from the figure, stable peak etch rate and FWHM are achieved during the long term measurements using the present invention.

[0092] Figure 8 is a graph showing sample thickness during geometry determination. Likewise, after initial heating of the sample (wherein the sample thickness increases), the relative sample thickness decreases over time.

[0093] Fig. 9 The etch rate measurements at different locations on the sample surface are shown, along with the respective Gaussian fits used to obtain the etch rate of the ion beam profile, i.e., the volume etch rate. Fig. 9 In FIG. 5 , the y-axis shows the normalized etch rate value and the x-axis shows the displacement of the respective scan from the center.

[0094] A Gaussian fit is used to obtain the volume etch rate, which corresponds to the Gaussian profile of the ion beam. As can be seen, the present invention can be used to determine the volume etch rate in situ.

[0095] The spot scan functionality of the present invention allows the light directed to the sample surface to be centered relative to the ion beam by calculating the offset from the configured position. In addition, the ion beam etch rate geometry can be visualized, similar to the electrical geometry visualization using Faraday scanning. By using a 3D Gaussian fit, the volume etch rate can be calculated. Spot scanning is subject to the same limitations as epak etch rate measurements, and therefore the exposure time for each point must be selected to match the process requirements of the deviation level.

[0096] As is apparent from the above description, in-situ measurements can be used to determine etch rates in-situ in a short time with process matching accuracy. No costly reference probes are required and lockout procedures are eliminated. Samples can be reused many times before having to be replaced, and sample materials can be easily replaced.

[0097] refer to Fig.10 , describing another preferred embodiment of the system of the present invention. Fig.10 A system 100 for in-situ deposition rate measurement is shown. The system includes a vacuum chamber 110, a material source 111a, and an interferometric measurement device 114.

[0098] The material source 111 a is configured to direct the material 112 a onto the first surface 113 a of the sample 113 located in the vacuum chamber 110 , and deposit the material 112 a onto the first surface 113 a of the sample 113 at a certain deposition rate.

[0099] The interferometry device 114 is at least partially located within the vacuum chamber 110 and is configured to direct light 115 onto the second surface 113 b of the sample 113 and determine in situ a deposition rate of the deposited material 112 a based on light reflected from the sample 113 .

[0100] The interferometric measurement device 114 may be the same device as described with reference to the etch rate determination. Therefore, further description is omitted at this time to avoid unnecessary repetition.

[0101] As the invention can be embodied in several forms without departing from the scope or essential characteristics thereof, it should be understood that the above-described embodiments are not to be limited to any details of the foregoing description unless otherwise indicated, but are to be interpreted broadly within the scope as defined in the appended claims, and all changes and modifications that fall within the invention are therefore intended to be covered by the appended claims.

[0102] Furthermore, in the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single unit may fulfill the functions of several features recited in the claims. The terms "substantially", "about", "approximately" and the like in conjunction with an attribute or value also specifically and precisely define the attribute or precisely define the value. Any element signs in the claims should not be construed as limiting the scope.

Claims

1. A system (100) for in-situ ion beam volume etching rate measurement, comprising: a vacuum chamber (110); an ion beam source (111) configured to direct an ion beam (112) onto a first surface (113a) of a sample (113) located in the vacuum chamber (110) and etch the first surface (113a) of the sample (113) at a volume etching rate; and an interferometric measurement device (114) at least partially located within the vacuum chamber (110) and configured to direct light (115) onto a second surface (113b) of the sample (113) and to determine in situ the volume etch rate of the ion beam (112) based on light reflected from the sample (113), The second surface (113b) of the sample (113) is opposite to the first surface (113a) of the sample (113), and the volume etching rate is related to the etching rate of the ion beam profile.

2. The system (100) of claim 1, wherein the interferometry device (114) is configured to determine the volume etch rate while etching the first surface (113a) of the sample (113).

3. The system (100) of claim 1 or 2, wherein the volume etch rate is the amount of material removed from the first surface (113a) of the sample over time.

4. The system (100) of claim 1 or 2, wherein the interferometric measurement device (114) is a high precision optical low coherence interferometer (HP-OLCI).

5. The system (100) of claim 1 or 2, wherein the interferometry device (114) is configured to determine the thickness of the sample (113) over time, and to determine the volume etch rate based on the change in thickness of the sample (113) over time.

6. The system (100) of claim 1 or 2, wherein the interferometric measurement device (114) comprises a sensor (117) configured to direct light (115) onto the second surface (113b) of the sample (113) and to collect light reflected back from the sample (113).

7. The system (100) of claim 6, wherein the sensor (117) comprises an optical component (116) to direct light (115) onto the second surface (113b) of the sample (113) and to collect light reflected back from the sample (113).

8. The system (100) of claim 7, wherein the sensor (117) comprises a housing and wherein the sample (113) is located inside the housing.

9. The system (100) of claim 8, wherein the housing comprises a graphite outer surface.

10. The system (100) of claim 1 or 2, wherein the interferometric measurement device (114) comprises a cooling device, the cooling device being in contact with the sample (113) and being configured to cool the sample (113).

11. The system (100) of claim 1 or 2, wherein the interferometric measurement device (114) comprises a positioning device configured to position the light (115) at at least one predetermined position on the second surface (113b) of the sample (113).

12. The system (100) of claim 11, further comprising a controller configured to control the positioning device to position the light (115) at multiple positions of the second surface (113b) of the sample (113) corresponding to positions within the ion beam profile to determine the etching rate of the ion beam profile.

13. The system (100) of claim 1 or 2, further comprising an alignment device configured to align the ion beam (112) relative to the first surface (113a) of the sample (113).

14. A method for in-situ ion beam volume etch rate measurement, wherein the method comprises: directing an ion beam (112) onto a first surface (113a) of a sample (113) located in a vacuum chamber (110) to etch the first surface (113a) of the sample (113) at a volume etching rate; or directing light (115) from an interferometric measurement device (114) at least partially located in the vacuum chamber (110) onto a second surface (113b) of the sample (113), wherein the second surface (113b) of the sample (113) is opposite to the first surface (113a) of the sample (113); and The volume etch rate of the ion beam (112) is determined in situ based on light reflected from the sample (113), wherein the volume etch rate is related to an etch rate of an ion beam profile.

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