ION IMPLANTATION DEVICE COMPRISING ENERGY FILTER AND ADDITIONAL HEATING ELEMENT

Abstract

An ion implantation device (20) is provided comprising an energy filter (25) with a structured membrane, wherein the energy filter (25) is heated by absorbed energy from the ion beam, and at least one additional heating element (50a-d, 55a-d, 60, 70) for heating the energy filter (25).

Claims

1. An ion implantation device (20) comprising: an energy filter (25) with a structured membrane, wherein the energy filter (25) is heated by absorbed energy from the ion beam; and at least one additional heating element (50a-d, 55a-d, 60, 70) for heating the energy filter (25).

2. The ion implantation device (20) of claim 1 wherein the additional heating element is a resistive element connected by electrical contacts (50a-d) to an electrical conductor (55a-d).

3. The ion implantation device (20) of claim 2, wherein the resistive element is at least one of an energy-filter membrane, bulk material (23) or a layer (21)), in particular the resistive element is made of silicon, silicon carbide, carbon, a composite or of a multilayer material.

4. The ion implantation device (20) of claim 1, wherein the at least one additional heating element energy filter (25) is an external heating element (60, 70).

5. The ion implantation device (20) of claim 4, wherein the external heating element is a heatable chuck (60) or an external light source (70) mounted in a housing (410; 510).

6. A method of implanting ions in a substrate material (30) with an ion depth profile comprising: pre-heating (500) an energy filter (25) to at least a predetermined temperature, wherein the energy filter (25) comprises a structured membrane; directing (510) an ion beam (10) through the energy filter (25) to the substrate material (30) for a pre-determined length of time; and cooling (520) the energy filter (25).

7. The method of claim 6, wherein the cooling (520) of the energy filter (25) is carried in a pre-set manner.

8. The method of claim 6, wherein the cooling (520) of the energy filter (25) is carried out by thermal radiation.

9. The method of claim 6, wherein the pre-heating (500) of the energy filter (25) comprises pre-heating separately of at least part of a membrane in the energy filter (25) or part of a frame of the energy filter (25).

10. The method of claim 6, wherein the pre-heating (500) of the energy filter (25) is carried out using an additional heating element (50a-d, 55a-d, 60, 70).

11. The method of claim 6, wherein the pre-heating (500) of the energy filter (25) is carried out using a temperature profile.

12. The method of claim 10, wherein the additional heating element (50a-d, 55a-d) is one of a resistive element (50a-d, 55a-d) an external lamp (70), or a heatable chuck (60) on which the substrate material (30) is mounted.

13. The method of claim 6, further comprising a post-implantation heating step (530).

14. The method of claim 13, wherein the post-implantation heating step (530) is performed in a separate location.

15. The method of claim 6, wherein different parts of the energy filter (35) are heated differently.

16. The method of claim 6, wherein at least parts of the energy filter (35) are heated during the directing of the ion beam (10) on the energy filter (25).

17. The method of claim 8, wherein the pre-heating (500) of the energy filter (25) comprises pre-heating separately of at least part of a membrane in the energy filter (25) or part of a frame of the energy filter (25).

Description

DESCRIPTION OF THE FIGURES

[0022] FIG. 1 shows the principle of the ion implantation device with an energy filter as known in the prior art.

[0023] FIG. 2 a structure of the ion implantation device with the energy filter.

[0024] FIG. 3A shows the temperature dependence of the filter with increasing ion current density.

[0025] FIG. 3B shows the difference in temperature rise between the membrane and the filter as a function of time.

[0026] FIGS. 4A-4E show five embodiments of the energy filter with a heating element.

[0027] FIG. 5 shows the method of ion implantation.

DETAILED DESCRIPTION OF THE INVENTION

[0028] The invention will now be described on the basis of the drawings. It will be understood that the embodiments and aspects of the invention described herein are only examples and do not limit the protective scope of the claims in any way. The invention is defined by the claims and their equivalents. It will be understood that features of one aspect or embodiment of the invention can be combined with a feature of a different aspect or aspects and/or embodiments of the invention.

[0029] FIGS. 4A-D show three examples of an energy filter 25 in a housing with heating elements. The energy filters 25 illustrated use the same reference numerals to show the same elements as in FIG. 1. The heating elements are used to heat up the energy filter 25 before, during and after the use of the energy filter 25 for ion implantation. It can be seen from considering FIG. 3A that the additional energy dissipated in the energy filter 25 due to the ion implantation beam 10 is much smaller at higher temperatures (e.g. above around 200 to 400° C.). This means that the temperature difference between the irradiated parts of the energy filter 25 and the unirradiated parts of the energy filter 25 will be generally less than 50-200° C. which results in much lower thermal stress in the energy filter 25.

[0030] FIG. 4A illustrates one example of the heating element. In this example, the heating element is due to the resistive heating of the frame 27 in which the energy filter 25 is mounted as well as the membrane. In this example, contacts 50a and 50c are mounted connected to the bulk silicon layer 23 and a current flows from electrical conductor 55a to electrical conductor 55c (or vice versa) through the frame 27 and the frame 27 warms up due to the electrical resistance of the material in the frame 27, i.e. the bulk silicon 23, contacts 50b and 50d are connected to corresponding electrical conductors 55b and 55d as seen in this figure. A current flows from the electrical contact 50b to the electrical contact 50d (or vice versa) through the membrane formed from the silicon layer 21 and the membrane warms up due to the electrical resistance of the material in the silicon layer 21.

[0031] In the example shown in FIG. 4B, resistive heating is also used to warm up the frame 27. In this case, there are no electrical contacts 50b or 50d applied to the silicon layer 21. The resistive heating of the bulk silicon 23 is identical to the example of FIG. 4A. In this example, no current passes through the membrane FIG. 3B shows that the frame 27 heats up more slowly than the membrane and thus there may be no need to separately heat the membrane.

[0032] The example shown in FIG. 4C does not use resistive heating of the energy filter 25 or the frame 27 but uses the principle of thermal radiation from a heatable chuck 60 on which the substrate material 30 has been placed. The thermal radiation from the heatable chuck 60 was radiated toward the membrane of the energy filter 25 as indicated by the arrow 65. In this example, either the energy filter 25 alone could be heated up or the combination of the energy filter 25 and the frame 27 could be heated.

[0033] A similar principle is employed in the example shown in FIG. 4D. In this case, a light source 70, such as a thermal lamp or a laser, is placed proximate to the energy filter 25 which radiates thermal radiation towards the energy filter 25 to heat up the energy filter 25. The light source 70 could also be located outside of the housing and radiate through a window in the housing. It will be appreciated that FIG. 4D only shows a single one of the light sources 70, but there could be multiple light sources 70 to enable uniform heating of the energy filter 25. There could also be different ones of the light sources 70 on different sides of the energy filter 25.

[0034] In a further example, shown in FIG. 4E, separate heating elements 80 are placed about the frame 27 to heat the frame 27 separately.

[0035] The additional heating elements and their geometry shown in FIGS. 4A-4E are not limiting of the invention and other heating elements and geometries could be employed to heat up the energy filter 25 in order to reduce the localized temperature differences in the membrane of the energy filter 25. This reduces the thermal stress in the energy filter 25 and thus increases the lifetime of the energy filter 25. It will be appreciated that it would be possible to combine two or more of the different heating elements.

[0036] It will be appreciated that heating the energy filter 25 could lead to changes in the properties of the energy filter 25 due to annealing of defects or the diffusion out of gas particles which were trapped in the membrane material of the energy filter 25. Annealing can be beneficial in that defects are healed. It would be possible to change the properties can be minimized by heating the energy filter 25 very quickly (around several milliseconds) and then cooling the energy filter 25 after the ion beam 10 is switched off. In this case, any defects induced in the material of the membrane of the energy filter 25 would not have time to move to energy-favorable positions within the membrane material and will be effectively “frozen” within the membrane material of the energy filter 25. On the other hand, if defects are to be cured then it may be necessary to heat the energy filter 27 more slowly or keep the energy filter 27 at an elevated temperature for a longer time. The additional heating elements shown in FIGS. 4A-4E enable the differential temperature profiles for heating up the energy filter 27 to be created.

[0037] The energy filter 25 is created from a bulk material or by depositing material on a substrate. There are a number of methods known in the art. For example, a mask can be created on the substrate using patterning techniques such as photolithography, e-beam lithography, or laser-beam lithography. The mask is made of 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.

[0038] A method for implantation of ions from the ion beam source 5 into the substrate material 30 to provide a deposition profile, similar to that illustrated with respect to FIG. 1. will now be described with reference to FIG. 5. In a first step 500, the energy filter 25 was pre-heated to at least a predetermined temperature. The pre-determined temperature was preferably chosen such that the rise in temperature of the energy filter 25 due to the passage of the ion beam 10 (see FIG. 3) is reduced. The predetermined temperature could be in the range of 200° C. to 500° C. (or 400° C. in other aspects), for example, but this is not limiting of the invention. It would also be possible to heat different parts of the energy filter 25 differentially.

[0039] The ion beam 10 is directed in step 510 through the energy filter 25 to the substrate material 30 for a pre-determined length of time to implant ions into the substrate material 30, as shown in FIG. 1. The energy filter 25 can also be heated during this stage to reduce temperature gradients within the energy filter 25 (including the membrane and the frame 27 or between the membrane and the frame). Finally, the energy filter 25 is cooled in step 520. The pre-heating step 500 and the cooling step 520 do not have to be carried out uniformly. As noted above, it is possible to design different temperature profiles if required.

[0040] In one aspect, the cooling of the energy filter 25 is carried out by thermal radiation. It would also be possible to use a cooling fluid in the energy filter 25 or the housing of the ion implantation device to cool the energy filter 25 more rapidly. The cooling of the energy filter 25 is taught, for example, in the Applicant's own patent application Ser. No. ______ filed concurrently.

[0041] In a further aspect, the energy filter 25 can be heated in step 530 subsequently after the implantation process is completed, i.e. after the ion beam 10 is removed, to a temperature between, for example, 500° C. to 1100° C. for annealing a silicon membrane to remove defects in the energy filter 25 caused by the ion beam 10. This post-implantation heating step 530 can be carried out in the ion implantation device or the energy filter 25 can be removed from the ion implantation device. This post implantation heating step 530 can be carried out either after every implantation run, after a certain dosage value per unit area has been reached, or at regular time intervals. The post-implantation heating step 530 is, in one aspect, a rapid thermal processing step in order to minimize plastic deformation of the membrane.

REFERENCE NUMERALS

[0042] 5 Ion beam source [0043] 10 Ion Beam [0044] 20 Ion implantation device [0045] 21 Silicon layer [0046] 22 Silicon dioxide layer [0047] 23 Bulk silicon [0048] 25 Energy filter [0049] 27 Filter Frame [0050] 30 Substrate material [0051] 50 Electrical contacts [0052] 55 Electrical conductor [0053] 60 Chuck [0054] 65 Thermal radiation [0055] 70 Light source [0056] 80 Heating elements