ION IMPLANTER HAVING ENERGY FILTER WITH ADDITIONAL THERMAL ENERGY DISSIPATION SURFACE AREA - Patent application

Abstract

An ion implanter (20) including an energy filter (25), the energy filter (25) having a thermal energy dissipation surface area, the energy filter (25) including a membrane having a first surface and a second surface disposed opposite the first surface, the first surface being a structured surface.

Description

[Technical field]

[0001] Interrelationship with other applications This application claims priority to and the benefit of Luxembourg Patent Application Publication No. 101807, filed May 15, 2020, the contents of which are incorporated herein by reference in their entirety.

[0002] The present invention relates to an apparatus for an ion implanter including an energy filter (implant filter) for ion implantation, and the use thereof and an implantation method. [Background technology]

[0003] Ion implantation is a method for achieving doping or creation of defect profiles in materials, such as semiconductor materials or optical materials, with predefined depth profiles ranging from a few nanometers to tens of micrometers in depth. 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.

[0004] There is a need to generate ion implantation depth profiles with a broader depth distribution than that of doping or defect concentration peaks obtainable by monoenergetic ion bombardment, or to generate doping or defect depth profiles that cannot be generated by one or more simple monoenergetic implants. Prior art methods of generating depth profiles are known, using structured energy filters, where the energy of a monoenergetic ion beam is modified as it 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 EP 0014516 B1 (Bartko) or US 2019 / 122850 A1.

[0005] FIG. 1 shows an example of such an ion implanter 20, in which the ion beam 10 impinges on a structured energy filter 25. 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 0.5-3.0 MeV / nucleon or preferably 1.0-2.0 MeV / nucleon. In a particular embodiment, the ion beam source produces an ion beam 10 having an energy of 1.3-1.7 MeV / nucleon. The total energy of the ion beam 10 is 1-50 MeV, in a preferred embodiment 4-40 MeV, in a preferred embodiment 8-30 MeV. The frequency of the ion beam 10 can be 1 Hz-2 kHz, for example 3 Hz-500 Hz, in one embodiment 7 Hz-200 Hz. The ion beam 10 can also be a continuous ion beam 10. Examples of ions in the ion beam 10 include, but are not limited to, aluminum, nitrogen, hydrogen, helium, boron, phosphorus, carbon, arsenic, and vanadium.

[0006] 1, it can be seen that the energy filter 25 is made from a membrane having a triangular cross-sectional shape on the right side, however, this type of shape does not limit the invention and other cross-sectional shapes can be used. The upper ion beam 10-1 passes through the energy filter 25 with little reduction in energy because the area 25 where the upper ion beam 10-1 passes through the energy filter 25 is min has a minimum thickness of the membrane in 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 membrane resulting in absorption of at least a portion of the energy of the ion beam 10 in the membrane).

[0007] On the other hand, the lower ion beam 10-2 is focused on the area 25 max, where the membrane of the energy filter 25 has its maximum thickness. The energy E2 of the left bottom ion beam 10-2 is substantially absorbed by the energy filter 25, and therefore the energy of the right bottom ion beam 10-2 is reduced and is less than the energy of the top ion beam, i.e. E1>E2. As a result, the more energetic top ion beam 10-1 can penetrate to a greater depth in the substrate material 30 than the less energetic bottom ion beam 10-2. This results in a differential depth profile in the substrate material 30 that is part of the wafer.

[0008] This depth profile is shown on the right side of Figure 1. The chopped triangular area shows that ions penetrate the substrate material at a depth of d1 to d2. The Gaussian curve shows the depth profile without the energy filter 25, with a maximum depth of d3. It should be understood that the depth d3 is greater than the depth d2 because some of the energy of the ion beam 10-1 is absorbed in the energy filter 25.

[0009] In the prior art there are several known principles for manufacturing the energy filter 25. Typically the energy filter 25 is manufactured from a bulk material with the surface of the energy filter 25 etched to generate a desired pattern, such as the triangular cross-sectional pattern shown in Figure 1. In DE 102016106119 B4 (Csato / Krippendorf) energy filters are described that are manufactured from layers of materials with different ion beam energy reduction properties. The resulting depth profile of the energy filter described in this Csato / Krippendorf patent application depends on the structure of the layers of material and the structure of the surface.

[0010] In the applicant's co-pending patent application DE 102019120623.5 A1, the details of which are incorporated herein by reference, a further construction principle is presented, in which an energy filter comprises spaced apart microstructured layers connected together by vertical walls.

[0011] 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 film from which the energy filter 25 is fabricated, and the choice of material from which the energy filter 25 is fabricated. In a typical process, approximately 50% of the power is absorbed within the energy filter 25, and this can go up to 80% depending on process conditions.

[0012] An example of an energy filter is shown in Figure 2, where the energy filter 25 is made from a triangular structured membrane mounted in a frame 27. In one non-limiting example, the energy filter 25 can be made from a single piece of material, such as silicon on insulator, including, for example, an insulating layer, silicon dioxide layer 22, having a thickness of 0.2-1 μm, sandwiched between a silicon layer 21 (typical thickness of 2-20 μm, but up to 200 μm) and bulk silicon 23 (about 400 μm thick). The structured membrane is made, for example, from silicon, but can also be made 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 to use the ion beam 10 efficiently, it is preferable to irradiate only the membrane of the energy filter 25 and not the frame 27 on which the membrane is held in place. In practice, it is likely that at least a part of the frame 27 will also be irradiated by the ion beam 10 and thus heated. In practice, it is possible that the whole of the frame 27 will be irradiated. The membrane forming the energy filter 25 is heated, but since the membrane is thin (i.e. between 2 μm and 20 μm, but up to 200 μm) it has a very small thermal conductivity. The membrane is 2×2 cm in size. 2 ~35×35cm 2 and corresponds to the size of the wafer. There is almost no thermal conduction between the membrane and the frame 27. The monolithic frame 27 therefore does not contribute to the cooling of the membrane, and the only cooling mechanism for the associated membrane is thermal radiation from the membrane. Localized heating of the membrane within the energy filter 25 increases thermal stresses between the heated parts of the membrane and the frame that form the energy filter 25.

[0014] Furthermore, localized heating of the membrane due to absorption of energy from the ion beam 10 in only a portion of the membrane also leads to thermal stresses in the membrane, which may result in mechanical deformation or damage to the membrane 25. Heating of the membrane occurs within a very short period of time, i.e., less than a second, often even at the level of milliseconds. The cooling effect of the non-irradiated parts of the membrane leads to temperature gradients in the energy filter 25. This cooling effect is particularly pronounced in the case of pulsed and scanned ion beams 10. These temperature gradients may lead to the formation of defects and distinct phases in the material from which the membrane of the energy filter 25 is made, and possibly unexpected material changes (due to the implanted species).

[0015] In the past, the problem of defects or material modifications has been overcome by defining safe operating conditions for use with a defined maximum ion dose where this problem does not occur. However, the long-term effects of mechanical deformation and damage to the membrane are not addressed. If the long-term effects are ignored, this will result in changes in the profile in the wafer material and therefore in wafers that must be rejected. Summary of the Invention [Problem to be solved by the invention]

[0016] Therefore, there is a need for improved cooling mechanisms for energy filters and temperature uniformity across the filter and frame. [Means for solving the problem]

[0017] The present specification teaches an ion implanter that includes an energy filter having additional thermal energy dissipation surface area to allow for more efficient cooling of the energy filter.

[0018] In one aspect of the ion implantation apparatus, the energy filter includes a membrane having a first surface and a second surface disposed opposite the first surface. At least one of the first structured surface or the second surface has microstructures disposed thereon and forms an additional thermal energy dissipation surface area. The spatial dimensions of the microstructures are 3-5% of the spatial dimensions of the structures on the first structured surface. However, these dimensions are not intended to be limiting of the invention. The microstructures include one of a randomly configured structure or a structure having a triangular cross section.

[0019] In another aspect of the ion implanter, the energy filter includes a plurality of membranes, for example with an additional membrane disposed a distance from a first membrane disposed between the ion beam source and the substrate material. The ion implanter may further include a positioning element for moving a spacing between membranes of the plurality of membranes in either a lateral or horizontal direction to enable different depth profiles to be generated within the substrate.

[0020] In a further aspect, the ion implanter may further include a collimator disposed between one of the first membrane or the further membrane and the substrate material, the collimator absorbing ions in the ion beam that are scattered at a predetermined angle such that the ions reach a location on the substrate and have substantially the same amount of energy and therefore penetration depth.

[0021] In a further aspect of the ion implanter, the housing of the ion implanter further includes a plurality of channels for transporting a cooling fluid to reduce heating and cool the housing and thus the frame and membrane of the ion implanter.

[0022] The ion implanter may be provided with a number of absorber elements in thermal contact with the housing to facilitate absorption of thermal radiation, the absorber elements blocking visible and infrared light. [Brief description of the drawings]

[0023] [Figure 1] 1 illustrates the principle of an ion implanter having an energy filter as known in the prior art; [Diagram 2] 1 shows the structure of an ion implanter having an energy filter. [Diagram 3] 1 shows an energy filter having a microstructure. [Figure 4] 1 shows multiple membranes in an energy filter and an open / closed collimation device. [Diagram 5] 1 shows a cooling system for an energy filter. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] The present invention will now be described based on the drawings. It should be understood that the embodiments of the present invention described herein are merely examples and do not in any 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 embodiment of the present invention can be combined with the features of one or more different embodiments of the present invention.

[0025] FIG. 3 illustrates a structure for a membrane of an energy filter 25 according to one embodiment of the present disclosure. FIG. 3A illustrates a structured membrane for an energy filter 25 having a triangular cross-section, as known in the art. FIG. 3B illustrates a microstructure on one surface of the membrane 25 in the energy filter 25, and FIG. 3C illustrates a microstructure on both surfaces of the energy filter 25. In other words, the energy filter 25 has a membrane with additional microstructures on one or more surfaces in addition to its regular triangular cross-sectional morphology.

[0026] 3, the height h of the triangular features is 16 μm and the spacing s is 20 μm. Energy filters 25 can be manufactured to have different dimensions, for example, the height can be from 1 μm to 200 μm and the spacing can be from 1 μm to 400 μm.

[0027] The microstructure will affect the energy profile of the ion beam 10 passing through the energy filter 25. However, by assuming that the energy profile has a tolerance of 3-5%, the microstructure may have a height (labeled in the figure as mh, but not to scale) that is 3-5% of the value of the height h, and a spacing (labeled in the figure as ms, but not to scale) that is 3-5% of the distance of the spacing s. Of course, it should be understood that the change in the energy profile is affected by the microstructure on both sides of the energy filter 20.

[0028] The microstructure is created by etching the energy filter 20 from a bulk material or by depositing a material on a substrate. There are several methods known in the art. For example, a mask can be created on the substrate by using patterning techniques such as photolithography, e-beam lithography or laser beam lithography. The mask is made of 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.

[0029] Self-masked etching techniques may also be used, such as reactive ion etching or the use of potassium hydroxide solutions with additives such as isopropanol in the strong polymerization process area.

[0030] Self-masking deposition techniques such as chemical vapor deposition in selective deposition mode or atomic layer deposition mode can also be used.

[0031] Successive deposition or etching of layers without masking is also known, using femtolaser ablation or focused ion beam deposition or removal of material.

[0032] It should be understood that the creation of the microstructure can be achieved by mechanically roughening the surface of the surface film 25, by adding an additional thin layer of material such as silicon or carbon, or by using other techniques such as laser ablation.

[0033] It is possible that the membrane structure of the energy filter 25 has a different structure and is not in the form of a triangular cross section. For example, the energy filter 25 may be constructed from a series of pyramids, as is known in the art. The microstructures would then be disposed on the surfaces of the pyramids.

[0034] The effect of the microstructure is to provide the membrane of energy filter 25 with a larger surface area that allows for a greater degree of thermal cooling of energy filter 25 due to the larger surface area.

[0035] Further aspects of the invention are shown in Figures 4A and 4B, where energy filter 25 includes multiple membranes 400a-c mounted within multiple frames 27 within housing 410. Housing 410 can be made of steel with an inner coating of silicon carbide or another carbon material. The inner coating is used to reduce or eliminate contamination of the semiconductor substrate. Figure 4A shows multiple multi-layers of energy filter 25, and Figure 4B shows energy filter 25 with triangular cross-section thin film. The membrane of energy filter 25 can also include the microstructure shown in Figure 3.

[0036] A plurality of membranes 400a-c forming the energy filter 25 are disposed within a housing 410. The plurality of membranes 400a-c can be moved within the housing 410 in a direction along the direction of the ion beam 10 to vary the spacing between the individual membranes 400a-c and between the membranes 400a-c and the substrate material 30. The spacing can be varied in both vertical and horizontal directions using positioning elements 430, such as, for example, piezoelectric elements or micromotors.

[0037] The configuration of Figures 4A and 4B also includes an (optional) collimator 420 for collimating the ion beam 10 after it passes through the plurality of membranes 400a-c. The collimator 420 can be open or closed at the ends. It should be understood that each membrane of the plurality of membranes 400a-c absorbs a portion of the energy of the ion beam 10 passing therethrough, and thus the membrane 400a-c from which the energy filter 25 is fabricated absorbs less energy than a single one of the membranes 400a, 400b or 400c. The plurality of membranes 400a-c are cooled through thermal emission.

[0038] The configuration of energy filter 25 shown in Figures 4A and 4B also allows different depth profiles to be generated for ions penetrating through substrate material 30. Although the multiple membranes 400a-c are shown as similar in Figures 4A and 4B, each of the multiple membranes 400a-c can have a different profile, if desired.

[0039] 4, three membranes 400a-c are shown, it should be understood that the number of membranes 400a-c can be much greater. Increasing the number of membranes 400a-c allows more energy to be dissipated. The maximum amount of energy that can be dissipated in a single one of the membranes 400a-c is 1.6 W / cm to avoid damage. 2 If it is assumed that the ion beam 10 has an energy of 10 MeV and 50% of the energy is required to create a deposition pattern in the substrate material 30, then the ion current in the ion beam 10 is 0.23 μA / cm 2 In the case of five membranes 400a-c, it is assumed that each membrane 400a-c can absorb the same amount of energy, and the maximum ionic current is 1.6 μA / cm 2 It becomes.

[0040] A further embodiment of the invention is shown in Figure 5, where the energy filter 25 is mounted in a cooling housing 500. The cooling housing 500 has one or more flow passages 510 in a wall 520 of the cooling housing 500 through which a cooling fluid 530 passes. The cooling fluid 530 is, for example, water. Thermal radiation emitted from the energy filter 25 is absorbed by the wall 520 and the heat is then dissipated through the cooling fluid 520.

[0041] In a further embodiment, the inside of the wall 520 comprises an absorber element 540, for example of a silicon or carbon based material, and may have a thickness in the range of micrometers to millimeters. The absorber element 540 absorbs the radiant heat energy from the energy filter 25. [Explanation of symbols]

[0042] 5. Ion beam source 10 Ion Beam 20 Ion mounting device 21 Silicon layer 22 Silicon dioxide equipment 23 Bulk Silicon 25 Energy Filter 27 Filter Frame 30 Base material 400a~c membrane 410 Housing 420 Collimator 430 Positioning elements 500 Cooling Housing 510 Flow Path 520 Wall 530 Cooling fluid 540 Absorber element

Claims

1. 1. An ion implanter comprising an energy filter and a housing, the energy filter has a thermal energy dissipative surface area, the energy filter including a membrane having a first surface and a second surface disposed opposite the first surface, the first surface being a structured surface; the energy filter is mounted within the housing; The ion implanter, wherein the housing further includes a plurality of absorber elements in thermal contact with the housing that block visible and infrared light.

2. 2. The ion implanter of claim 1, wherein the first structured surface or the second surface has microstructures disposed thereon to form additional thermal energy dissipation surface areas, the spatial dimensions of the microstructures being 3-5% of the spatial dimensions of the structures on the first structured surface.

3. The ion implanter of claim 2 , wherein the microstructures comprise one of a randomly arranged structure or a structure having a triangular cross section.

4. 10. The ion implanter of claim 1, wherein the energy filter comprises a plurality of membranes having an additional membrane disposed a distance from a first membrane.

5. 5. The ion implanter of claim 4, further comprising an ion beam source, a substrate material, and a plurality of membranes disposed between said ion beam source and said substrate material.

6. An ion implantation apparatus as described in claim 5, further comprising a collimator disposed between one of the first film or further films and the substrate material.

7. 7. The ion implanter of claim 4, further comprising a positioning element for varying the spacing between any of said plurality of membranes.

8. 3. The ion implanter of claim 2, wherein the structures on the first surface are of triangular cross-section or are pyramidal in shape.

9. The ion implanter of claim 1 , wherein the energy filter is fabricated from a silicon membrane.

10. The ion implanter of claim 1 , wherein the housing further comprises a plurality of channels for transporting a cooling fluid.

11. The ion implanter of any preceding claim, further comprising a filter frame, the energy filter being carried by the filter frame.

12. A housing for an energy filter of an ion implantation apparatus as described in any one of claims 1 to 11, the housing including a plurality of flow paths for transporting a cooling fluid.

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