Patent Application
20230209661
The invention relates to metrology or testing methods and devices for characterizing a temperature-dependent process performed on a surface or substrate.
Metrology techniques may be used to characterize processes in which the temperature of a substrate affects one or more parameters of a treatment process of the substrate. The examples given in this description relate to semiconductor or metallurgical fabrication processes performed on a substrate such as a silicon wafer. However, other processing techniques in other contexts may likewise require a substrate or surface to be at a particular temperature during processing. Such processing techniques may include coating, deposition, etching, abrasion, washing, annealing, sintering, polishing or other processes which are affected by the substrate temperature. Metrology techniques can be used to obtain characterization information which can be used to calibrate or adjust process parameters to obtain the desired process result on the substrate, in dependence on the substrate temperature. For example, it may be desired to identify an optimum temperature for depositing a particular characteristic (eg thickness or crystallographic structure) of a particular material deposited on a particular substrate, or to determine the characteristic(s) of the deposited material at each of various substrate temperatures.
It is known to characterize a temperature-dependent silicon fabrication process by performing the process on one or more test wafers, with the test wafers at a different temperature for each test. The characterization may be performed with one test wafer, heated to a first temperature, then a second, then a third, etc, and with different regions of the wafer exposed to the fab process for each test. Or different wafers may be used for each test. In order to achieve a useful characterization of the process variation with temperature, many tests are needed, and many wafers, and the testing process takes a great deal of time. A fine-grained characterization would be out of the question.
By way of example, it is known in some thin-film fabrication methods to elevate the substrate (target) temperature in order to obtain a particular desired deposition rate and/or crystallographic structure of the deposited elements. Likewise, the substrate temperature may be varied to obtain a desired etch rate of a particular etching process, for example. In the growth of Neodymium Iron Boron (NeFeB) magnetic films, for example, the material may be deposited using sputtering with the substrate at a temperature (TD) in the range 20° C. to 500° C. (https://doi.org/10.1063/1.2710771). Post deposition annealing up to 750° C. for multiple minutes enables crystallization and promotes grain growth. This annealing step is not only sensitive to the annealing temperature (TA) and annealing time (tA), but also the temperature ramp rate during heating (dT/dtA+) and cooling (dT/dtA-). This simple example includes five temperature-related parameters. If one were to scan the parameter space with just 4 values of each parameter, there would be 45 = 1024 possible combinations. In practice, processes are characterized for a much smaller number of combinations on grounds of time and cost.
The present invention aims to overcome at least some of the disadvantages of the prior art. To this end, a metrology device according to the invention is described in claim 1, a metrology array according to the invention is described in claim 6 and characterization methods according to the invention are described in claims 9 and 10.
The invention will now be described in detail with reference to the attached drawings, in which:
It should be noted that the figures are provided merely as an aid to understanding the principles underlying the invention, and should not be taken as limiting the scope of protection sought. Where the same reference numbers are used in different figures, these are intended to indicate similar or equivalent features. It should not be assumed, however, that the use of different reference numbers is intended to indicate any particular degree of difference between the features to which they refer.
This invention proposes to use arrays of MEMS hot plates as deposition substrates (targets). Such an array may consist of individual elements, arrays of 2×2 elements or 10×10 or more. As each element can be set to a well-defined temperature a total of 100 deposition temperatures could be tested simultaneously. Post deposition etching or thermal treatments could again be performed simultaneously and individualized for each plate. Consequently, finding the optimal thermal conditions for deposition, annealing, end etching could be accomplished 100× faster. The method described is applicable for deposition, annealing, and etching processes which occur at vacuum, at pressures typically, but not limited to, below 2×10-2 mbar. Such deposition methods may include, but are not limited to, Low pressure Cold Wall Chemical Vapor Deposition (CVD), Plasma Enhanced CVD, Sputtering, Reactive Ion Sputtering, Magnetron Sputtering, Atomic Layer Deposition (ALD), and Physical Vapor Deposition (PVD) (including thermal and e-beam evaporation). The etching may take place in a reactive ion etching system, where an RF voltage creates a plasma which results in an an-isotropic etch of the substrate. Annealing may occur in vacuum or rarified gas (low pressure). As often processes are temperature dependent, the MEMS hotplate elements enable the efficient optimization of deposition, etching and annealing parameters.
In the context of semiconductor fabrication, the invention may MEMS hot plates as a tool for thin-film deposition, reactive etching, and thermal treatment methods. The MEMS hot plates enable high level of control of the temperature of the deposition substrate, deposition mass and post deposition thermal treatment. Lastly, the MEMS can also enable intrinsic characterization of the deposited thin-film. The ability to create an array of MEMS hotplate elements allows the user scan the thermal landscape with high precision. The ability to test deposition, etching, and post deposition thermal treatment parameters in parallel, along with in-situ feedback, improves the efficiency in optimizing thin-film growth protocols.
The heating elements create an array of deposition targets.
Each target can be held at a unique, well defined temperature during deposition (TD) or etching (TE).
The temperature can be monitored using the resistance of the heating elements
The temperate can be changed (dT/dt+) in millisecond time scales (tramp) (which is interesting for multi-layer depositions were each layer can be deposited at a unique substrate temperature).
By adding an electrode below the heating elements, the elements can be resonated. The change in resonance frequency (f0) is a direct measure of the mass of the deposited material. (The deposition rate may be temperature dependent).
After deposition, the heating elements can be used as annealing elements. In this case the temperature (TA), temperate ramp rates (dT/dtA) and annealing temperature time (tA) can be set individually for each heating element.
The resonance can be used to monitor the annealing effects. For example: if a magnet is being annealed then and external homogeneous field will induce a torque on the magnets. This restoring torque will result in a frequency change of a torsion mode. Therefore, the frequency shift in the torsion mode due to an applied external field can be used as a measure of the magnetization of the deposited film.
The modular system would also allow the chip containing the thermal array to be mounted in a specially developed socked in characterization systems. This includes, but is not limited to, material characterization systems such as optical microscopy (with vacuum chambers), Scanning Electron Microscopes (SEM), Vacuum Atomic Force Microscopes (AFM), Vacuum X-ray diffractometers (XRD), and Raman Spectrometers, etc. The array enables the characterization of materials deposited on the hotplates over a wide thermal parameter space, with respects to surface morphology, crystallography, and chemical bond vibrations which may alter as a function of temperature or during thermal annealing processes.
A small die, such as 2.5×2.5 mm2 may contain, for example, an individual hot plate with a diameter or up to 1×1 mm2, or for example, an array of 2×2 hot palate with a diameter of 0.5 mm each or for example, an array of 3×3 with a diameter of 0.2 mm each, etc. up to an array, for example of 10×10 with a diameter of 0.05 mm each.
To summarize: These arrays can be used to optimize growth, post growth annealing conditions and etching, in particular related to thermal treatment. Implemented as resonators they can be used for real-time feedback of deposition rates, etch rates, and serve to track and quantify changes in material properties due to annealing treatments.
The device described may advantageously be made of a single material. One could also add a stack or a conformal coating to ensure chemical compatibility. For example, it is known that a conformal ALD deposited layer of Al2O3 will chemically separate incompatible materials such as silicon and gold, at elevated temperatures.
The MEMS hotplate device 1 depicted in
The central plate can be heated using the heating elements to 500 deg C or over 1000 deg C or over 2000 deg C up to 4000 deg C if the heating elements and the central plate are made of refractory ceramic materials such as, but not limited to HfC, TaC, or TaHfC. The heating elements suspend the central plate element above the substrate such that it is not touching the substrate. The void between the plate and the substrate is typically 2-20 microns deep, but may be larger. The heating elements are such that they can expand, flex and bend as they are heated. This flexure releases the thermal stresses that occur as the heating elements and the central plate are heated to high temperatures. The structures are made of a single material. The material is curved to the substrate at the anchors. This has two functions; 1 it physically attaches the heaters to the substrate and 2 it creates an overhand so that deposited material does not short out the devices. This is depicted in the inset of
The central plate element is typically 50-100 microns in diameter, but depending on the application smaller diameters, down to 10 microns or smaller can are interesting when larger arrays are desired (described below), or the thermal time constants are needed to be very small, such as well below 1 millisecond. Correspondingly, much larger central plate elements may be of interested, 200 microns, or even 400 microns or even 600 microns in diameter. The MEMS hotplate devices with larger diameter central plates will tend to have larger number of heating elements, they will have a slower thermal response time which defines the time needed to heat or cool the MEMS hotplate devices, and will typically not be able to heat to as high a temperature due to the thermal radiation cooling effects. For these reasons the larger plates will have a maximum temperature in the range of 1000 K or up to 2000 K depending on geometry, material and number of heating elements. To minimize this cooling effect, materials with low emission coefficient are best suited for larger MEMS hotplate device with larger plates.
The hotplate device includes electrical leads, 10 one of which may be ground 12. To improve the efficiency these leads can be metallized 14, which reduced the electrical resistance in the leads. Typical resistance of each heating element is 1000 Ohms, but can be lower or higher. Typical resistance of the metallized leads is below 1 Ohm. Beneath the central plate 4 and the heating elements 6 there is a void. Beneath the void there is an electrode 16, which may be segmented. This electrode make is possible to mechanically actuate and/or sense the corresponding displacement of the central plate 4. Such sensing can be capacitive sensing, or optical sensing or piezoresistive sensing. The actuation can be thermal, capacitive (electrostatic) or piezo-electric using a shaker platform. Such actuation is typically alternating, resulting a vibrational motion of the pate. Ideally this is on resonance or close to resonance. For the devices presented the resonant frequency is typically between 10 kHz and 1 MHz. For larger plates this can be as low as 100 Hz, or for smaller plates this can be as high as 10 MHz or even 100 MHz. Depending on the actuation method the resonant mode can be out of plane, in plane or a torsional mode.
The MEMS hotplate device 1 can be placed in an array as illustrated in
The MEMS hotplate devices 1 are used to heat the central plate 4. The heat is applied by passing a current though the heater devices 6. The current is driven by applying a voltage bias, typically between 0-5 volts between the leads 10 and 12. These leads are metallized 14 to reduce electrical losses between the power source and the heating elements. The voltage bias drives a current thought the device, proportional to the device resistance. The resistance is typically a function of temperature and may be linear or not. The hotplates are calibrated and a look-up table can be used to determine their temperature by comparing the hot pate element electrical resistance change with respect to a reference temperature. For materials such as metal, or highly doped semiconductors, as is the case with highly doped silicon with phosphor, the resistance increases with temperature. This temperature dependence means that monitoring the resistance, for example by measuring the current resulting from the applied voltage bias, can be used to determine the temperature of the hotplate of a calibrated device. The increasing resistance with rising temperature also helps stabilize the MEMS hotplate device as the heating becomes self-limiting. (If the heating elements are made of a material with a decreasing resistance with increasing temperature then it is preferred to apply a current bias instead of a voltage bias.) The voltage bias can be constant, ramped or modulated. A square wave, or individual square pulse can be applied. By monitoring the resulting current one can calculate the thermal time constant tT. For known material properties and MEMS hotplate device geometries one can use this to calculate the thermal load. If the thermal properties are known and the thermal load is measured then this information can be used to determine the mass of the material deposited or etched from the central hotplate. Hence, the thermal control and feedback module can used to 1) set a target temperature, b) set a thermal annealing profile and c) used to measure thermal time constants from which material properties and/or deposition and etch rates can be deduced. As outlined in the next paragraph the thermal control and feedback module can also d) measure piezoresistive changes of the resistance of the heating elements and e) thermo-mechanically actuate the device.
The MEMS hotplate devices include an electrode 16 placed below the central plate. This electrode can be used to capacitively sense the distance between the central plate and the electrode. Applying a voltage to electrode 16 will result in the electrostatic attraction of the plate. Resonant or pulsed signals can be used to actuate mechanical modes in the MEMS hotplate device. These modes can be sensed using the same capacitive electrode, optically, by reflecting a laser off the surface of the central hotplate, and/or piezoresistivity, by measuring changes in the resistance of the heating arms, which are also the flexural elements of said resonator. Changes in the resonance frequency, f, of the modes (at a fixed temperature) can be used to measure changes in mass, m:
The changes in mass, measured though changes in the thermal response time or preferably by changes in resonance frequency (equivalent to the mechanical response time) can be used to determine deposition or etch rates, an important feedback feature enabled by the MEMS hotplate devices. Of both mechanical and thermal timescales are precisely measured, then this information can be used to calculate both the mass (mechanical mass) and the thermal load (thermal mass) of the deposited material. Like this it is possible to determine a deposition rate or etch rate for each element of the MEMS hotplate device array independently and in-situ of the thin film deposition or etching system.
To protect the electrical leads from the deposition material, or the reactive ion etching, they may be covered. Such masking is illustrated in
Depending on the deposition and etch processes performed, it may also be possible to only mask the heater elements 6, as is illustrated in
The MEMS hotplate device array is built on a chip, typically 1×1-10×10 mm2. This chip 104 is mounded in a chip holder, typically a ceramic chip holder 102 as illustrated in
In the CWLPCVD realization the fabrication and analysis platform includes a thermometer 118 for temperature monitoring and calibration but no multiplexing element. In this case each element is addressed directly using the commination electrodes 122b which are fed out of the vacuum chamber through electrical vacuum feedthrough port 148 to a control and communication module 200. This module may be stand alone or interface with a computer, tablet or smart phone, for example using a USB connection or wireless communication protocols.
The second example, illustrated in
In this example of the implementation the on the fabrication and analysis platform includes a multiplexing element 120 which can address a large array and transfer signals between the fabrication and analysis platform (such as temperature information) and the MEMS heating devices (such as the set voltage and measured device resistance) and the control and communication modules 200a and 200b. In this example the wire bundle 122 and feedthrough 148 may contain fewer cables as the information is digital, compared to the direct electrical access to the devices described previously. There are two independent control and communication modules. Control and communication module 200a is used to set and monitor the temperature profile of the MEMS hotplate device array, were the control and communication module 200b is used for monitoring the resonance frequency, of the mechanical displacement of the MEMS hotplate device array. As discussed above, this information can be used to determine deposition rates and additional material properties. In either case the modules can be stand alone or interface with a computer 202, tablet or cell phone using USB or Bluetooth communication.
The provided thin-film deposition examples are illustrative and not limiting. Using the same methodology, the system described can also be included in other, standardized thin-film deposition systems, such as, but not limited to, Physical Vapor Deposition System (in which case the fabrication and analysis platform 100 is inverted, facing down, as the material flux would typically come from below), Atomic Layer Deposition, Sputtering, and Reactive Ion Sputtering.
Thin-film etching can be performed by reactive ion etching (RIE). Such a setup is illustrated in
In the Homogeneous Field Setup depicted in
Inhomogeneous Field Setup depicted in
The examples illustrated the annealing of a magnetic thin-film in the presence of a magnetic field. The same setup can be used in other material characterizations systems, with the requirement that the MEMS hotplate device array is in vacuum. Examples include, but are not limited to SEMs, vacuum AFMs, vacuum XRD, and vacuum Raman Spectrometers, along with optical microscopes interfacing with a vacuum chamber though an optical window. In particular the SEM is a simple interface as the SEM chambers tend to be large and are held under high vacuum. The fabrication and analysis platform 100 can be mounted on the SEM stage. Most SEM chambers also have electrical feedthrough options, so interfacing with a thermal control and feedback module is possible. This makes it possible to observe changes in surface morphology with regards to the annealing protocol chosen. AFM systems mounted in vacuum chambers can perform surface topology analysis to much higher degree of precision. One advantage of the MEMS hotplate devices is the high rate at which they heat or cool. Hence, one can heat, hold, cool and image at relatively high rates (thermal cycling timescales can be as low as 1-10 ms) to observe changes over time and thermal profiles, while all measurements are performed at ambient temperatures. This is particularly important for AFM measurements which include direct contact between the AFM tip and the sample, requiring that there not be a larger thermal gradient which can prohibit useful measurements. The high temperatures which can be applied by the MEMS hotplate devices may not only anneal the deposited structures, such as changing the crystal structure or domains, but can also induce phase changes (melting or evaporating) and chemical reactions in multi-material depositions. Hence, the platform can be used to measure thermal and chemical properties of the deposited materials.
| Number | Date | Country | Kind |
|---|---|---|---|
| 3067973 | Jan 2020 | CA | national |
| 3079443 | Apr 2020 | CA | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/050879 | 1/15/2021 | WO |
