The disclosure relates to computer-implemented methods for the simulation of an energy-filtered ion implantation (EFII).
In commercially oriented micro technical production processes, masked and/or non-masked doping elements are to be introduced by means of ion implantation into materials, such as semiconductors (silicon, silicon carbide, gallium nitride) or optical materials (glass, LiNbO3, PMMA), with predefined depth profiles in the depth range from a few nanometers up to a plurality of 10 micrometers.
Ion implantation is a method to achieve doping or production of defect profiles in a material, such as semiconductor material or an optical material, with predefined depth profiles in the depth range of a few nanometers to a plurality of tens of micrometers. Examples of such semiconductor materials include, but are not limited to silicon, silicon carbide, and gallium nitride. Examples of such optical materials include, but are not limited to, LiNbO3, glass and PMMA.
There is a need to produce depth profiles by ion implantation which have a wider depth distribution than that of a doping concentration peak or defect concentration peak obtainable by monoenergetic ion irradiation or to produce doping or defect depth profiles which cannot be produced by one or a few simple monoenergetic implantations. The doping concentration peak can often be represented approximately by a Gaussian distribution or more precisely by a Pearson distribution. However, there are also deviations from such distributions, especially when so-called channeling effects are present in the crystalline material. Related art methods produce the depth profile using a structured energy filter in which the energy of a monoenergetic ion beam is modified as the monoenergetic ion beam passes through a micro-structured energy filter component. The resulting energy distribution leads to a creation of the depth profile ions in the target material. This is described, for example, in European Patent no. EP 0 014 516 B1. An energy filter for tailoring depth profiles in a semiconductor doping application is know from CSATO CONSTANTIN ET AL (“Energy filter for tailoring depth profiles in semiconductor doping application”, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH. SECTION B: BEAM INTERACTIONS WITH MATERIALS AND ATOMS, vol. 365, pages 182-186, XP029313812, ISSN: 0168-583X, DOI: 10.1016/J.NIMB.2015.07.102). Ion beam irradiation of nanostructures is disclosed BORSCHEL C ET AL (“Ion beam irradiation of nanostructures A 3D Monte Carlo simulation code”, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH. SECTION B: BEAM INTERACTIONS WITH MATERIALS AND ATOMS, vol. 269, no. 19, pages 2133-2138, XP028266956, ISSN: 0168-583X, DOI: 10.1016/J.NIMB.2011.07.004).
An example of such an ion implantation device 20 is shown in
On the other hand, the lower ion beam 10-2 passes through an area 25max in which the membrane of the energy filter 25 is at its thickest. The energy E2 of the lower ion beam 10-2 on the left-hand side is absorbed substantially by the energy filter 25 and thus the energy of the lower ion beam 10-2 on the right-hand side is reduced and is lower than the energy of the upper ion beam, i.e., E1>E2. The result is that the more energetic upper ion beam 10-1 is able to penetrate to a greater depth in the substrate material 30 than the less energetic lower ion beam 10-2. This results in a differential depth profile in the substrate material 30, which is, for example, part of a semiconductor wafer.
This depth profile is shown on the right-hand side of the
For typical ion species (N, Al, B, P) in the energy range from 1 MeV up to some tens of MeV (e.g., 40 MeV) it can be observed that low energy ions tend to have a large scattering angle and high energy ions tend to have a small scattering angle. The reason for this different scattering behavior is the energy dependence of the underlying stopping mechanisms. Ions with high kinetic energy preferentially lose their energy by so-called electronic stopping, i.e., excitations of the electron system of the substrate. This usually results in only small directional deviation, i.e., small scattering angles. Ions with low kinetic energy preferentially lose their energy by elastic collisions with the atoms of the substrate, so-called nuclear stopping. This results in large angle scattering.
For a static implantation arrangement (i.e., filter and substrate are not moved with respect to each other), which is one aspect for the simulation of doping depth profiles, the distance between filter and substrate plays the decisive role. As can be seen in
In summary for a given ion species, a given initial ion energy, a given filter design and a given substrate material and a given filter-substrate distance a certain energy distribution and angular distribution of the filter transmitted ions will be generated.
In the related art there are a number of principles disclosed for the fabrication of the energy filter 25. Typically, the energy filter 25 will be made from bulk material with the surface of the energy filter 25 etched to produce the desired pattern, such as the triangular cross-sectional pattern shown from
A further construction principle is shown in the German Patent application DE 10 2019 120 623.5, in which the energy filter comprises spaced micro-structured layers which are connected together by vertical walls.
The maximum power from the ion beam 10 that can be absorbed through the energy filter 25 depends on three factors: the effective cooling mechanism of the energy filter 25, the thermo-mechanical properties of the membrane from which the energy filter 25 is made, as well as the choice of material from which the energy filter 25 is made. In a typical ion implantation process around 50% of the power is absorbed in the energy filter 25, but this can rise to 80% depending on the process conditions and filter geometry.
An example of the energy filter is shown in
In order to optimize the wafer throughput in the ion implantation process for a given ion current for the ion beam 10 and thus use the ion beam 10 efficiently, it is one aspect to only irradiate the membrane of the energy filter 25 and not the frame 27 in which the membrane is held in place. It is likely that at least part of the frame 27 will also be irradiated by the ion beam 10 and thus heat up. It is indeed possible that the frame 27 is completely irradiated. The membrane forming the energy filter 25 is heated up but has a very low thermal conductivity as the membrane is thin (i.e., between 2 μm and 20 μm, but up to 200 μm). The membranes are between 2×2 cm 2 and 35×35 cm2 in size and correspond to the size of the target wafers. There is little thermal conduction between the membranes and the frame 27. Thus, the monolithic frame 27 does not contribute to the cooling of the membrane and the only cooling mechanism for the membrane, which is relevant, is the thermal radiation from the membrane.
As shown in
The layouts or three-dimensional structures of energy filters 25 shown in
In general, one may simulate energy filtered ion implantation. However, the fundamental problem of simulating energy filtered ion implantation lies in the different geometric dimensions of the implantation structure. The energy filter structural elements are typically triangular structures, e.g., made of silicon with a height difference between minimum and maximum membrane thickness of about 1 μm over about 16 μm up to 100 μm. A plurality of such structural elements, arranged side by side, form an energy filter. The dimensions of an energy filter structural element in a direction perpendicular to the ion beam direction are also in the order of a few micrometers to a few 100 μm. For the energy filters used in practice, macroscopic dimensions of the energy filter membrane are required from 2×2 cm, over 17×17 cm up to 40×40 cm. Substrate sizes are also in this range. The distances between the energy filter and the substrate, on the other hand, are typically in the millimeter or centimeter range.
For a static setup according to
In the following section, this irradiation arrangement of
Initial situation: filter dimensions of the energy filter 25 are y≈1000 μm, z≈1000 μm with a plurality of unit cells (full triangular structure) arranged in a side-by-side manner, with unit cell dimensions of x=16 μm, y≈11 μm, translation symmetry in z. The implanted ion is aluminum (Al), primary energy 12 MeV, filter material is equal to substrate material, is equal to silicon.
In real energy-filtered irradiation, it is one aspect to achieve a laterally homogeneous concentration and energy distribution of the ions analogous to the situation shown in
For the simulation of energy-filtered ion implantation, a static arrangement is assumed. To achieve a desired degree of lateral homogenization and avoid particle loss, the boundary condition is that the resulting energy spectrum of the simulated energy filter must be independent of the spatial coordinates y-z on the wafer. In other words, the full energy-angle spectrum of a unit cell must be found on any y-z position on the wafer.
Ion implantation is a process “composed” of a large number of individual events. One needs a large number of single ions (typically 1E12 cm-2-1E15 cm-2) in order to form typical distributions in the substrate due to statistical scattering processes. The use of Monte Carlo techniques is therefore widespread in the field of ion implantation.
Therefore, simulation methods can support or shorten development processes or facilitate the accurate design and dimensioning of processes and products. In order to be able to carry out a reasonable simulation in terms of time and cost with sufficient statistics, a method must therefore be used which takes into account the different size ratios and in this way drastically reduces the complexity and the computational effort for the simulation without loss of accuracy.
The typical dimensions of interesting simulation areas for ion implantation process simulation in semiconductor technology are perpendicular to the ion beam in the size range of a plurality of micrometers up to a plurality of millimeters or even centimeters and parallel to the ion beam (depth profile) in the range of a plurality of micrometers up to 100 micrometers. The typical resolution requirement in all directions is at least 5 or 10 nanometers. To achieve the required spatial resolution, these areas must be subdivided into a fine grid in the nanometer range and simulated with a correspondingly high number of events to resolve relevant characteristics with high event density.
It is an object of the present disclosure to provide a method, which allows the simulation of doping depth profiles of energy filtered ion beams by means of a so-called “Monte Carlo” algorithm. In particular to provide a method for complex ion implantation processes, such as the EFII process, to be efficiently simulated using the Monte Carlo method in order to be able to reproduce the real physical process and its effects in the substrate as accurately as possible and without artifacts.
By implementing the ion implantation arrangement in a Monte Carlo simulation environment, the complex structure of such an array implies a high workload for the implementation of the involved structures. In general, the widely varying dimensions of the microscopic filter structure compared to the filter-substrate spacing results in a poor ratio of total simulation volume SV, e.g., shown in
It is an object of the present disclosure to provide a method for embedding the simulation of energy-filtered ion implantation into the tool landscape for technology simulation of semiconductor electronic devices (TCAD).
It is an object of the present disclosure to provide a computer-implemented method to significantly improve the efficiency of the Monte Carlo simulation of an energy-filtered implantation process, i.e., to reduce the effort for the implementation of the model, to reduce the complexity of the computer simulation and ultimately to reduce the computing time or to reduce the requirements on the performance of the computer hardware. With respect to the geometric simulation model, the present disclosure improves the ratio of the total simulation volume SV to the simulation area g. The present disclosure enables the reduction of the number of simulation events while maintaining a high event density in the simulation area g. As a result, simulation time can be saved.
Therefore, there is a need to improve a method for simulating energy filtered ion implantation.
According to a first aspect the disclosure a computer-implemented method for the simulation of an energy-filtered ion implantation (EFII), comprising the steps of: determining at least one part of an energy filter; determining at least one part of an ion beam source; determining a simulation area in a substrate; Implementing the determined at least one part of the energy filter, the determined at least one part of the ion beam source, the determined simulation area in the substrate; determining a minimum distance between the implemented at least one part of the energy filter and the implemented substrate for enabling a desired degree of a lateral homogenization of the energy distribution in a doping depth profile of the implemented substrate; determining a maximum expected scattering angle of the energy filter by simulating an energy-angle spectrum for the energy filter; and defining a total simulation volume. Thereby, it is possible to provide a simulation volume Sv as small as possible and to provide a simulation volume Sv in a simplified manner. A static filter-substrate arrangement can be further provided independent of a static or dynamic real implantation setup. Therefore, the method enables the simplification of the geometry to be implemented by considering the energy-angle distribution and the associated geometric constraints.
In one aspect of the method, the minimum distance between the energy filter and the substrate is between 100 μm and 1000 μm for the simulation of the EFII process of Al-ions with a kinetic primary energy of 12 MeV.
In another aspect of the method, the energy filter by the determined maximum expected scattering angle defines the number of filter unit cells arranged next to each other.
In another aspect of the method, the simulation area to be analyzed in the substrate is between 1 μm to 500 μm in either direction.
According to a second aspect of the disclosure a computer-implemented method for the simulation of an energy-filtered ion implantation (EFII), comprising the steps of: approximating an energy filter in at least one base element; selecting at least one of the at least one base element such that the desired geometry and material composition of the energy filter to be simulated can be assembled from the selected base elements. Determining the energy-angle spectrum for the selected at least one base element; determining a virtual ion beam source based on the determined energy-angle spectrum of the selected at least one base element; and simulating the implantation effects in a simulation area in a substrate. Thereby, the more complex simulation task can be separated into the definition of a virtual ion beam source (i.e., EFIIS-source), and the subsequent simulation of ion implantation effects for arbitrary substrates. The method enables the simulation task in a sequence of process steps in conjunction with simulations that make it possible to reduce the overall simulation volume and thus increase efficiency of carrying out the simulation. Therefore, the method enables even the simulation of more complex energy filters. This results from the improved ratio of total simulation volume Sv to simulation area g, where here the simulation volumes are independent of each other in the steps of the determination of the virtual ion beam characteristic, and the simulation of simulation area g by means of the previously defined virtual ion beam. This also allows a better simulation efficiency, in which the dimensions of the energy filter and the simulation area are very different. Furthermore, the event densities and grid densities of the two process steps of the method can be defined independently of each other, which allows the simulation to be optimized according to the requirements.
In one aspect of the method, the at least one base element is one of at least one part of at least one energy filter element, a filter unit cell of the energy filter, or a set of discrete energy filters.
In one aspect of the method, the energy filter is triangular-shaped, pyramid-shaped, inverted pyramid-shaped, or free-form shaped.
In another aspect of the method, the filter unit cell of the energy filter is composed of a plurality of base elements of different geometry, different material compositions of different layer structures.
In one aspect of the method, the implantation effects are one of defect generation, doping profile, masking effects.
In another aspect of the method, new filter geometry, new filter material selection, new layer composition of the energy filter, new primary ion, new primary ion energy, new primary ion implantation angle and a new virtual ion beam source are determined.
In one aspect of the method, the method comprises the step of storing the least one base element in a data base.
In one aspect of the method, the method comprises the step of storing the virtual ion beam source in a data base.
In another aspect of the method, the method comprises the step of parametric analyzing a masking structure on the substrate for optimization of the masking thickness, material composition, and masking layout and for optimizing the 3D-doping profile in the substrate, which is influenced by the masking structure. The mask structure can significantly influence the 3D-doping profile through its composition, thickness (partial transparency) and the angle of its “slopes” (partial implantation at a flat angle). These influences can be analyzed very well with the method according to the present disclosure or the doping profiles and the masks can be optimized.
In one aspect of the method, the optimization of the masking structure and/or 3D-doping profile on the substrate is carried out using a Monte Carlo simulation. The mask structure can significantly influence the 3D-doping profile through its composition, thickness (partial transparency) and the angle of its “slopes” (partial implantation at a flat angle). These influences can be analyzed very well with the method according to the present disclosure or the doping profiles and the masks can be optimized.
The disclosure will now be described on the basis of figures. It will be understood that the aspects of the disclosure described in the figures are only examples and do not limit the protective scope of the claims in any way. The disclosure is defined by the claims and their equivalents. It will be understood that features of one aspect of the disclosure can be combined with a feature of a different aspect of the disclosure. This disclosure becomes more obvious when reading the following detailed descriptions of some examples as part of the disclosure under consideration of the enclosed drawings, in which:
The maximum expected scattering angle α of a filter unit cell 30 is to be determined. For this purpose, the energy-angle spectrum for a given filter unit cell 30 is simulated and the maximum scattering angle α (which is still experienced by a relevant number of ions) is determined. In particular, with a high number of simulated ions, there will always be a few ions that have scattering angles close to 90°. Therefore, the angle α could be defined in a way that the angle α includes the relevant part of the scattered ions, i.e., not considering the scattered ions with a scattering angle larger than the angle α, which in total make up less than 1% or 2% of the total number of ions. This lowers the accuracy but simplifies the simulation. As shown in
The total dimension of the simulation is calculated with the formula L=l+g, wherein the width l of the ion beam source 5 and the energy filter 25 is calculated with, the following formula:
½=fs tan(α)
wherein α=the maximum scattering angle, and fs=distance 50 between the energy filter 25 and the substrate 26.
For example, the method 200 further requires that the minimum distance 50 (fs) between the energy filter 25 and the substrate 26 is between 100 μm and 1000 μm for the simulation of the EFII process of Al-ions with a kinetic primary energy of 12 MeV. The method 200 further comprises that the maximum expected scattering angle α of the filter unit cell 30 is 70° for the simulation of the EFII process of Al-ions with a kinetic primary energy of 12 MeV and the minimum distance 50 of 500 μm. The method 200 further comprises that the simulation area g in the substrate 26 is in one-dimension 2 μm. The method 200 further comprises that the total width l of the energy filter 25 by the determined maximum expected scattering angle α is the number of filter unit cells arranged next to each other. For example, the minimum distance 50 (fs) between the energy filter 25 and the substrate 26 can also be 0 μm (no homogenization) over 100 μm up to 1000 μm or up to some millimeters (full homogenization). For light ions (hydrogen) and very high energies and large filter structures (e.g., 100 μm thickness) larger distances 50 than 1000 μm will be necessary.
As shown in
After the first process step, in the next step, the relevant properties of the ion beam characteristics (energy and angle, y-z coordinates dependency of energy and angle of the ions), which act on the simulation area g due to the filter properties and the properties of the primary ions, are calculated for all of the selected basic elements 25a-1, 25a-2, . . . , 25a-n. The method 300 according to the present disclosure is not limited to triangular-shaped ones of the energy filters 25. Rather, pyramidal, inverted pyramidal, or more generally free-form structures for the energy filters 25 can also be simulated using the method 300. For example, the energy filter 25 or filter unit cell 30 can be composed of a plurality of base elements 25a-1, 25a-2, . . . , 25a-n of different geometry, different material composition or different layer structure. Tilting of the energy filter 25 or mirroring about an axis perpendicular to the ion beam 10 is also possible.
As shown in
The method 300 for the simulation of the energy-filtered ion implantation (EFII), comprising as the second process step also the step of simulating 305 the implantation effects in the simulation area g in the substrate 26. In the next step, a virtual ion beam source 5 with an energy-angle characteristic is defined, which is composed of the ion beam characteristics of the base elements 25a-1, 25a-2, 25a-3, . . . , 25a-n selected in the first process step of method 300. Thus, this composite virtual ion beam source 5 corresponds exactly (or approximates) the ion beam characteristics (energy and angle distribution) of the overall energy filter 25 to be simulated. As shown in
Therefore, for each new filter geometry, new filter material selection, new layer composition of the energy filter 25, new primary ion, new primary ion energy, new primary ion implantation angle (i.e., distribution) a new virtual ion beam source 5, i.e., EFIIS source 5, is defined. The ion beam source 5, i.e., EFIIS source 5, can be used to simulate and analyze the effects of ion implantation on any substrate 26. The ion beam source 5, i.e., EFIIS source 5, and also the underlying base elements 25a-1, 25a-2, 25a-3, . . . , 25a-n of the energy filters 25 can be stored in databases (not shown) in the first process step of the method 300. Furthermore, it is possible to successively improve the virtual ion beam source 5, i.e., EFIIS source 5, by matching simulation results with experimental results.
As shown in
Further significant advantages result from a systematic investigation of a simulation area g, with variation of a geometry parameter in the simulation area. This is shown, for example, in
As shown in
As shown in
Number | Date | Country | Kind |
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LU 102558 | Aug 2021 | LU | national |
This application is a U.S. National Stage Application of, and claims the benefit of, International PCT Application Number PCT/EP2022/054400, filed on 10 Feb. 22, 2022, which claims the benefit of and priority to Luxembourg Patent Application LU 102558, filed on 24 Feb. 2021. The entire disclosure of Luxembourg Patent Application LU 102558 is hereby incorporated by reference.
Filing Document | Filing Date | Country | Kind |
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PCT/EP2022/054573 | 2/23/2022 | WO |