Ion implantation apparatus including an energy filter and an additional heating element

Abstract

An ion implantation apparatus (20) is provided that includes an energy filter (25) having a structured film, the energy filter (25) being heated by absorbed energy from an ion beam, and at least one additional heating element (50a-d, 55a-d, 60, 70) for heating the energy filter (25).

Description

Technical Field

[0001] Interrelation with Other Applications This application claims the priority and benefit of Luxembourg Patent Application Publication No. 101808, filed on May 15, 2020. The content of Luxembourg Patent Application Publication No. 101808 is hereby incorporated by reference in its entirety into this specification.

[0002] The present invention relates to equipment for an ion implantation apparatus including an energy filter (implantation filter) for ion implantation, its use, and an implantation method.

Background Art

[0003] Ion implantation is a method for achieving doping or generation of a defect profile within a material, such as a semiconductor material or an optical material, with a predefined depth profile in a depth range from several nanometers to several tens of micrometers. Examples of such semiconductor materials include, but are not limited to, silicon, silicon carbide, gallium nitride, gallium arsenide, cadmium telluride, and zinc selenide. Examples of such optical materials include, but are not limited to, LiNbO3, fused silica, or polymers such as potassium titanyl phosphate and PMMA.

[0004] There is a need to generate an ion implantation depth profile having a wider depth distribution than that of a doping concentration peak or a defect concentration peak obtainable by single-energy ion irradiation, or to generate a doping or defect depth profile that cannot be generated by one or more simple single-energy implantations. Conventional techniques for generating depth profiles using structured energy filters are known, in which case the energy of a single-energy ion beam is changed as the single-energy ion beam passes through a microstructured energy filter component. The resulting energy distribution results in the generation of depth-profile ions, materials. This is described, for example, in European Patent No. 0014516B1 (Bartko).

[0005] FIG. 1 shows an example of such an ion implantation apparatus 20, in which case the ion beam 10 hits a structured energy filter 25 within a vacuum housing. The ion beam source 5 can be, for example, a radio frequency linear accelerator that generates ions having an energy of 0.3 to 3.0 MeV / ion, but this does not limit the present invention. The ion beam source 5 can also be a cyclotron, a tandem accelerator or a single-ended electrostatic accelerator. In other embodiments, the energy of the ion beam source 5 is 0.5 to 3.0 MeV / nucleon or preferably 1.0 to 2.0 MeV / nucleon. In a specific embodiment, the ion beam source generates an ion beam 10 having an energy of 1.3 to 1.7 MeV / nucleon. The total energy of the ion beam 10 is 1 to 50 MeV, in a preferred embodiment 4 to 40 MeV, and in a preferred embodiment 8 to 30 MeV. The frequency of the ion beam 10 can be 1 Hz to 2 kHz, for example 3 Hz to 500 Hz, and in one embodiment 7 Hz to 200 Hz. The ion beam 10 can also be a continuous ion beam 10. Examples of ions within the ion beam 10 include, but are not limited to, aluminum, nitrogen, hydrogen, helium, boron, phosphorus, carbon, arsenic and vanadium.

[0006] In FIG. 1, it can be seen that the energy filter 25 is manufactured from a film having a triangular cross-sectional shape on the right side, but this type of shape does not limit the present invention and other cross-sectional shapes can be used. The upper ion beam 10-1 passes through the energy filter 25 with little energy reduction because the area 25 through which the upper ion beam 10-1 passes through the energy filter 25 min has the minimum thickness of the film within the energy filter 25. In other words, if the energy of the upper ion beam 10-1 on the left side is E1, the energy of the upper ion beam 10-1 will have substantially the same value E1 on the right side (with only a small energy loss due to the stopping power of the film that causes at least partial absorption of the energy of the ion beam 10 within the film).

[0007] On the one hand, the lower ion beam 10-2 passes through the area 25 max In this case, the film of the energy filter 25 has its maximum thickness. The energy E2 of the lower ion beam 10-2 on the left side is substantially absorbed by the energy filter 25. Therefore, the energy of the lower ion beam 10-2 on the right side is reduced and is less than the energy of the upper ion beam, that is, E1>E2. As a result, the upper ion beam 10-1 with higher energy can penetrate to a greater depth within the substrate material 30 than the lower ion beam 10-2 with lower energy. This results in a differential depth profile within the substrate material 30 which is part of the wafer.

[0008] On the right side of FIG. 1, this depth profile is shown. The indented triangular area indicates that the ions penetrate the substrate material at a depth of d1 to d2. The Gaussian curve shows the depth profile with a maximum value at a depth of d3 without the energy filter 25. It should be understood that the depth d3 is greater than the depth d2 because part of the energy of the ion beam 10-1 is absorbed within the energy filter 25.

[0009] In the prior art, there are several known principles for manufacturing the energy filter 25. Usually, the energy filter 25 is manufactured from a bulk material having a surface of the energy filter 25 etched to produce a desired pattern such as the triangular cross-sectional pattern shown in FIG. 1. German Patent Application Publication No. 102016106119 B4 (Csato / Krippendorf) describes an energy filter manufactured from layers of materials having different ion beam energy reduction characteristics. The depth profile resulting from the energy filter described in this Csato / Krippendorf patent application depends on the structure of the layers of materials and the structure of the surface.

[0010] In the specification of the applicant's concurrently filed German Patent Application Publication No. 102019120623.5, the details of which are incorporated herein by reference, further structural principles are shown, where the energy filter includes spaced-apart microstructured layers connected together by vertical walls.

[0011] The maximum output from the ion beam 10 that can be absorbed within 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 manufactured, and the choice of material from which the energy filter 25 is manufactured. In a normal process, about 50% of the output is absorbed within the energy filter 25, which can increase up to 80% depending on the process state.

[0012] An example of an energy filter is shown in FIG. 2, where in this case the energy filter 25 is manufactured from a triangular structured membrane mounted within a frame 27. In a non-limiting example, the energy filter 25 can be manufactured from a single piece of material such as silicon-on-insulator, which includes a silicon dioxide layer 22 having a thickness of 0.2 - 1 μm, for example an insulating layer, sandwiched between a silicon layer 21 (which is typically 2 - 20 μm thick but can be up to 200 μm thick) and bulk silicon 23 (which is about 400 μm thick). The structured membrane can be manufactured from, for example, silicon, but can also be manufactured from silicon carbide or another carbon-based material or ceramic.

[0013] To optimize the wafer throughput in an ion implantation process for a given ion current of the ion beam 10 and thus use the ion beam 10 efficiently, it is preferred to irradiate only the membrane of the energy filter 25 and not the frame 27 in which the membrane is held in place. In practice, at least a part of the frame 27 will also be irradiated by the ion beam 10 and thus heated. In fact, the entire frame 27 may be irradiated. The membrane forming the energy filter 25 is heated, but the membrane has a very low thermal conductivity because it is thin (i.e., 2 - 20 μm thick but can be up to 200 μm thick). The membrane has a size of 2 × 2 cm2 ~35×35 cm 2 and corresponds to the size of the wafer. There is almost no heat conduction between the membrane and the frame 27. Therefore, the monolithic frame 27 does not contribute to the cooling of the membrane, and the only cooling mechanism for the associated membrane is thermal radiation from the membrane.

[0014] Heating of the membrane within the energy filter 25 increases the thermal stress between the heated portions of the membrane and the frame 27 that form the energy filter 25. This is shown in FIG. 3B, which shows that due to the different heat capacities of the membrane and the frame 27, the smaller membrane heats up much faster than the bulkier frame. This difference results in thermal stress between the membrane and the filter, which can lead to mechanical deformation.

[0015] Furthermore, local heating of the membrane due to absorption of energy from the ion beam in only a portion of the membrane also results in thermal stress within the membrane, which can lead to mechanical deformation or damage to the membrane within the energy filter 25. Heating of the membrane occurs within a very short time period, i.e., less than 1 second, often at the millisecond level. The cooling effect on the non-irradiated portion of the energy filter results in a temperature gradient within the energy filter 25. This cooling effect is particularly pronounced in the case of the pulsed ion beam 10 and the scanned ion beam 10. These temperature gradients can result in defects and the formation of distinct phases within the material in which the membrane of the energy filter 25 is fabricated, and possibly unexpected material changes (due to the implanted species).

[0016] The energy filter 25 has also been found to heat up much more rapidly due to the ion beam 10 when the temperature of the energy filter is below 200°C to less than 400°C, and this is shown in FIG. 3A. FIG. 3A shows an example of the dependence of the temperature in °C on the particle flux density during continuous irradiation for the absorption of ions having different energies. The solid line shows the simulation of ions with an energy of 2 MeV, and the upper line is for ions with an energy of 8 MeV. The middle line is for ions of 4 MeV and 6 MeV as shown in FIG. 3A. The example shown in FIG. 3A is for illustrative purposes only and depends on the filter design and process conditions.

SUMMARY OF THE INVENTION

MEANS FOR SOLVING THE PROBLEM

[0017] This specification teaches an ion implantation apparatus including an energy filter, and the energy filter is for adding an additional heating element to the energy filter. The addition of the additional heating element is for preheating the energy filter in order to reduce the temperature gradient resulting from the ion beam passing through the energy filter.

[0018] In one aspect, the additional heating element can be a resistive element connected to a conductor by an electrical contact. The current flows through the bulk silicon forming the frame of the energy filter and / or the film of the energy filter and heats the material.

[0019] In another aspect, the additional heating element is is, but is not limited to, an external heating element such as a heatable chuck or an external light source mounted within a housing.

[0020] This specification also describes a method of implanting ions into a substrate material with an ion depth profile. The method outlined in this specification includes preheating an energy filter to at least a predetermined temperature, directing an ion beam through the energy filter onto the substrate material for a predetermined length of time, and then cooling the energy filter.

[0021] Preheating the energy filter may include separately preheating at least a portion of a film within the energy filter or a portion of the frame of the energy filter, and is carried out by using additional heating elements such as resistive elements, external lamps, or a heatable chuck to which the substrate material is attached.

Brief Description of the Drawings

[0022]

Figure 1

Figure 2

Figure 3A

Figure 3B

Figures 4A-4E

Figure 5

Modes for Carrying Out the Invention

[0023] Here, the present invention will be described based on the drawings. It should be understood that the embodiments and aspects of the present invention described in this specification are merely examples and in no way limit the scope of protection of the claims. The present invention is defined by the claims and their equivalents. It should be understood that the features of one aspect or embodiment of the present invention may be combined with the features of one or more different aspects and / or embodiments of the present invention.

[0024] Figures 4A to 4D show three examples of the energy filter 25 within the housing having the heating element. The energy filter 25 shown uses the same reference numerals as that in FIG. 1 to denote the same elements. The heating element is used to heat the energy filter 25 before, during, and after the use of the energy filter 25 for ion implantation. From the consideration of FIG. 3A, it can be seen that the additional energy dissipated within the energy filter 25 due to the ion implantation beam 10 is much smaller at higher temperatures (e.g., above about 200 to 400 °C). This means that the temperature difference between the irradiated portion and the non-irradiated portion of the energy filter 25 generally results in a much smaller thermal stress within the energy filter 25, which is less than 50 to 200 °C.

[0025] FIG. 4A shows an example of the heating element. In this example, the heating element is by resistive heating of the energy filter 25 and the frame 27 to which the film is attached. In this example, as observed in this figure, the contacts 50a and 50c are attached in a state connected to the bulk silicon layer 23, and the current flows from the conductor 55a to the conductor 55c (or vice versa) through the frame 27. The frame 27 is heated due to the electrical resistance value of the material within the frame 27, i.e., the bulk silicon 23, and the contacts 50b and 50d are connected to the corresponding conductors 55b and 55d. The current flows from the electrical contact 50b to the electrical contact 50d (or vice versa) through the film formed from the silicon layer 21, and the film is heated due to the electrical resistance value of the material within the silicon layer 21.

[0026] In the example shown in FIG. 4B, resistive heating is also used to heat the frame 27. In this case, there is no electrical contact 50b or 50d applied to the silicon layer 21. The resistive heating of the bulk silicon 23 is the same as that in the example of FIG. 4A. In this example, the current does not flow through the film. FIG. 3B shows that there may be a case where the frame 27 heats up slower than the film, and thus it may not be necessary to heat the film separately.

[0027] The example shown in FIG. 4C uses the principle of thermal radiation from a heatable chuck 60 on which the substrate material 30 is disposed, without using resistive heating of the energy filter 25 or the frame 27. The thermal radiation from the heatable chuck 60 is radiated towards the film of the energy filter 25, as indicated by arrow 65. In this example, the energy filter 25 can be heated alone, or a combination of the energy filter 25 and the frame 27 can be heated.

[0028] In the example shown in FIG. 4D, a similar principle is utilized. In this case, a light source 70, such as a heat lamp or a laser, is disposed in the vicinity of the energy filter 25, which radiates thermal radiation towards the energy filter 25 to heat it. The light source 70 can be disposed outside the housing and also radiate through a window in the housing. FIG. 4D shows only a single light source 70, but it should be understood that multiple light sources 70 may be present to enable uniform heating of the energy filter 25. Also, different light sources 70 may be present on different sides of the energy filter 25.

[0029] In a further example shown in FIG. 4E, a separate heating element 80 is disposed around the frame 27 to heat the frame 27 separately.

[0030] The additional heating elements and their shapes shown in FIGS. 4A - 4E do not limit the present invention, and other heating elements and shapes can be utilized to heat the energy filter 25 so as to reduce the local temperature difference within the film of the energy filter 25. This reduces the thermal stress within the energy filter 25 and thus increases the lifespan of the energy filter 25. It should be understood that it would be possible to combine two or more different heating elements.

[0031] It should be understood that heating the energy filter 25 can result in a change in the characteristics of the energy filter 25 due to annealing of defects or diffusion of gas particles trapped within the film material of the energy filter 25. Annealing can be beneficial in that defects are repaired. It is possible to change the characteristics and minimize them by heating the energy filter 25 very rapidly (in about a few milliseconds) and then cooling the energy filter 25 after the ion beam 10 is turned off. In this case, any defects induced within the film material of the energy filter 25 will not have time to move to a position that is energetically favorable within the film material and will be effectively "frozen" within the film material of the energy filter 25. On the other hand, if defect repair is required, it may be necessary to heat the energy filter 27 more slowly or maintain the energy filter 27 at an elevated temperature for a longer period of time. The additional heating elements shown in FIGS. 4A - 4E enable the generation of a differential temperature profile for heating the energy filter 27.

[0032] The energy filter 25 is produced by depositing a material from a bulk material or onto a substrate. There are several known methods in the art. For example, a mask can be produced on a substrate by using patterning techniques such as photolithography, e-beam lithography, or laser beam lithography. The mask is manufactured from a photoresist, silicon dioxide, silicon carbide, chromium, or other materials. Wet chemical etching techniques use, for example, potassium hydroxide, TMAH (tetramethylammonium hydroxide), and other anisotropic etching solutions, plasma etching techniques, and ion beam etching.

[0033] Here, a method for the implantation of ions from an ion beam source 5 into a substrate material 30 to provide a deposition profile similar to that shown with reference to FIG. 1 will be described with reference to FIG. 5. In a first step 500, the energy filter 25 is preheated to at least a predetermined temperature. The predetermined temperature is preferably selected such that the increase in the temperature of the energy filter 25 due to the passage of the ion beam 10 (see FIG. 3) is reduced. The predetermined temperature can be, for example, in the range of 200° C. to 500° C. (or 400° C. in other embodiments), but this is not limiting of the present invention. It would also be possible to differentially heat different parts of the energy filter 25.

[0034] In step 510, the ion beam 10 is directed through the energy filter 25 to the substrate material 30 for a predetermined length of time to implant ions into the substrate material 30, as shown in FIG. 1. At this stage, the energy filter 25 can also be heated to reduce the temperature gradient within the energy filter 25 (including the membrane and frame 27 or between the membrane and the frame). Finally, in step 520, the energy filter 25 is cooled. The preheating step 500 and the cooling step 520 do not need to be performed uniformly. As described above, different temperature profiles can be designed as required.

[0035] In one embodiment, the cooling of the energy filter 25 is performed by thermal radiation. It would also be possible to use a cooling fluid within the energy filter 25 or the housing of the ion implantation device to cool the energy filter 25 more rapidly. Regarding the cooling of the energy filter 25, for example, it is taught in the patent application of the present applicant filed simultaneously, application number 2022-569462 of the specification.

[0036] In a further aspect, in step 530, after the injection process is completed, i.e., after the ion beam 10 is removed, the energy filter 25 can be heated to a temperature, for example, between 500 °C and 1100 °C, to anneal the silicon film in order to remove the defects in the energy filter 25 caused by the ion beam 10. This post-injection heating step 530 can be performed within the ion implantation apparatus or the energy filter 25 can be removed from the ion implantation apparatus. This post-injection heating step 530 can be performed after all injection runs, after reaching a specific dose / unit area, or at regular time intervals. In one aspect, the post-injection heating step 530 is a rapid thermal processing step to minimize plastic deformation of the film.

Explanation of Signs

[0037] 5 Ion beam source 10 Ion beam 20 Ion implantation apparatus 21 Silicon layer 22 Silicon dioxide layer 23 Bulk silicon 25 Energy filter 27 Filter frame 30 Substrate material 50 Electrical contact 55 Conductor 60 Chuck 65 Thermal radiation 70 Light source 80 Heating element

Claims

1. An ion implantation apparatus, comprising: An energy filter having a structured film, the energy filter being heated by the absorption energy from the ions of the ion beam induced to pass through the structured film; and At least one additional heating element for heating the energy filter.

2. The ion implantation apparatus according to claim 1, wherein the additional heating element is a resistive element connected to a conductor by an electrical contact.

3. The resistive element is at least one of an energy filter film, a bulk material or a layer. In particular, the resistive element is made of silicon, silicon carbide, carbon, a composite material or a multilayer material. The ion implantation apparatus according to claim 2.

4. The ion implantation apparatus according to any one of claims 1 to 3, wherein at least one additional heating element for heating the energy filter is an external heating element.

5. The ion implantation apparatus according to claim 4, wherein the external heating element is an external light source mounted in a heatable chuck or housing.

6. A method of implanting ions into a substrate material with an ion depth profile, comprising: - Preheating an energy filter to at least a predetermined temperature, the energy filter including a structured film; - Inducing an ion beam through the structured film of the energy filter into the substrate material for a predetermined length of time; and - Cooling the energy filter.

7. The method according to claim 6, wherein the cooling of the energy filter is performed in a preset manner.

8. The method according to claim 6 or 7, wherein the cooling of the energy filter is performed by thermal radiation.

9. The preheating of the energy filter includes preheating at least a part of the film in the energy filter or a part of the frame of the energy filter. The method according to any one of claims 6 to 8.

10. The preheating of the energy filter is performed using an additional heating element. The method according to any one of claims 6 to 9.

11. The preheating of the energy filter is performed using a temperature profile. The method according to any one of claims 6 to 10.

12. ​ The method according to claim 10, wherein the additional heating element is one of a resistive element, an external lamp, or a heatable chuck to which the base material is attached.

13. The method according to any one of claims 6 to 12, further comprising a heating step after implantation.

14. The method according to claim 13, wherein the heating step after implantation is performed at a separate location.

15. The method according to any one of claims 6 to 14, wherein different portions of the energy filter are heated separately.

16. The method according to any one of claims 6 to 15, wherein at least a part of the energy filter is heated while guiding the ion beam to the energy filter.

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