Energy filter components for ion implantation systems used in wafer production

Abstract

The present invention relates to an energy filter element of an ion implantation system for producing wafers, and in particular to an implantation device, an implantation system and a method. The implantation device comprises a filter frame and a filter fixed by the filter frame, wherein the filter is designed to be irradiated by an ion beam.

Description

[0001] This application is a divisional application of Chinese patent application No. 201780029666.1, whose application date is April 4, 2017 and whose invention name is “Energy filter element for ion implantation system for producing chips”. Technical Field

[0002] The present invention relates to an implantation device comprising an energy filter (implantation filter) for ion implantation, use thereof, and an implantation method. Background Art

[0003] By ion implantation, doping or defect distribution can be achieved in any desired material such as semiconductor materials (silicon, silicon carbide, gallium nitride) or optical materials (LiNbO3) for a predetermined depth distribution in the depth range of a few nanometers to hundreds of micrometers. It is particularly desirable to produce a depth distribution characterized by a wider doping concentration peak or defect concentration peak than can be obtained by monoenergetic ion radiation, or to produce a doping or defect depth distribution that cannot be produced by one or more simple monoenergetic implantations. Summary of the invention

[0004] In an embodiment of the present invention, an implantation apparatus for implanting ions in a target substrate includes a filter frame and a filter fixed by the filter frame, the filter being configured to be irradiated by an ion beam passing through the filter. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Figure 1 The basic principle of an energy filter is shown: the energy of a monoenergetic ion beam is modified as a function of the entry point while passing through a microstructured energy filter assembly. The resulting ion energy distribution leads to a change in the depth profile of the implanted species in the substrate matrix.

[0006] Figure 2 On the left is shown the wafer wheel on which the substrate to be implanted is held in place. During processing / implantation, the wheel is tilted by 90° and set in rotation. The ion beam, shown in green, thus "writes" concentric circles on the wheel. In order to irradiate the entire wafer surface, the wheel is moved vertically during processing. On the right, Figure 2 An energy filter installed in the beam opening area is shown.

[0007] Figure 3 Schematic diagram showing various doping profiles (dopant concentration as a function of depth in the substrate) of energy filter microstructures of different configurations (side view and top view shown in each case):

[0008] (a) The triangular prism-shaped structure produces a rectangular doping profile;

[0009] (b) Smaller triangular prism-shaped structures produce doping profiles with shallower depth profiles;

[0010] (c) The trapezoidal prismatic structure produces a rectangular doping profile with a peak at the beginning of the profile;

[0011] (d) The pyramidal structure produces a triangular doping profile that increases in height with increasing depth in the substrate.

[0012] Figure 4 A cross section of the filter frame used to hold the energy filter chip is shown.

[0013] Figure 5 A top view of a filter frame for securing an energy filter element with locking elements and a mounted energy filter is shown.

[0014] Figure 6 Shown is a typical installation for fixing the energy filter element to the framework in the beam path of an ion implanter. In this example, the filter fixture is arranged on a side of chamber wall. In this example, this side is the inner side of chamber wall, i.e., facing the side of wafer (not shown) during implantation. The filter chip has been inserted into the framework therein and pushed into the filter fixture, covering the opening through which ion beam passes in the chamber wall during implantation subsequently.

[0015] Figure 7 A partial frame (left side in the figure) and a complete frame (far right in the figure) are shown, and each frame can be constructed of the same material as the energy filter (eg, monolithic) and / or a different material.

[0016] Figure 8 The use of one or more rods for connecting a filter frame or any other passive scattering element surrounding the filter is shown.

[0017] Fig. 9 The use of single or multiple suspension elements for connecting a filter frame or any other scattering element surrounding the filter is shown.

[0018] Fig.10 The use of a magnetic field for connecting a filter frame or any other scattering element surrounding the filter is shown.

[0019] Fig.11 A simple implementation of a multi-filter is shown. Three filter elements of different shapes are combined in a filter holder frame to form a complete energy filter. The ion beam passes uniformly through all individual filter elements.

[0020] In the embodiment of the invention (left), the dopant depth profile shown on the right is thus produced. This profile contains three depth profiles, numbered 1, 2 and 3. Each of these sub-distributions originates from one of the three sub-filters shown on the left, i.e. from the sub-filter provided with the corresponding number.

[0021] Fig.12 A detailed view of the multi-filter concept is shown. On the left are three filter elements shown by way of example. The four elements are described by number. For a given ion species and primary energy, a dopant depth profile is produced by each filter element. The weighting, i.e. the produced concentration, can be adjusted by varying the size of the individual filter element surfaces. For this example, it is assumed that the filter and the substrate have the same energy-dependent stopping power. However, this is usually not the case.

[0022] Fig.13 Shows when Fig.12 The sum distribution obtained when all filter elements described in are mounted together as a complete filter with appropriate weighting and uniformly exposed to an ion beam with suitable primary energy.

[0023] Fig.14 An exemplary configuration of individual filter elements in a multi-filter is shown. The individual elements F1 , F2 , F3 etc. shown here are cut with a bevel and mounted directly on top of each other.

[0024] Fig.15 The filter arrangement is shown installed in an ion implantation system. A cooling line, which is supplied with coolant by an external cooling device, is integrated in the filter holder that holds the filter frame. The cooling line can also be arranged on the surface of the filter holder (not shown).

[0025] Fig.16 An energy filter with a large surface area is shown, which is only partially irradiated per unit time. Thus, the non-irradiated areas can be cooled by radiation cooling. As mentioned above, this embodiment can also be configured as a multi-filter. That is, it can be configured as a filter comprising several different filter elements. In the example shown, the frame with the filter oscillates in a direction perpendicular to the direction of the ion beam. The area of ​​the filter covered by the ion beam is smaller than the total surface area of ​​the filter, so that per unit time, only part of the filter is exposed to the beam. Due to the oscillating motion, this part changes continuously.

[0026] Fig.17Another arrangement of the configuration of the energy filter is shown, which rotates around a central axis. Again, the illumination per unit time is only partial, and the non-irradiated elements can thereby cool down. This embodiment can also be configured as a multi-filter.

[0027] Fig.18 The "migration of peaks" is schematically shown. By implanting ions into the energy filter with the aid of a trapezoidal prism-shaped structure, a rectangular distribution can be produced in the substrate. The initial peak is implanted into the energy filter. This implantation distribution has the advantageous property of starting directly on the substrate surface, which is very important for the application of energy filters.

[0028] Fig.19 The figure shows how ions are implanted into a PMMA substrate with the aid of an energy filter during static implantation. The ions disrupt the molecular structure of PMMA. The subsequent development process reveals the energy distribution of the ions. Areas of high energy deposition are dissolved away. Areas of low or no energy deposition of the ions are not dissolved by the developer solution.

[0029] Fig. 20 A monitoring system for identifying filters and monitoring compliance with filter specifications (maximum temperature, maximum accumulated ion dose) is shown.

[0030] Fig.21 The collimator structure is shown, attached to the filter holder. The aspect ratio determines the maximum angle α. If the available distance to the injected substrate is not large enough, the collimator can consist of several collimator units with smaller openings arranged side by side. This can be arranged in a honeycomb pattern, for example.

[0031] Fig. 22 The collimator structure built directly onto the filter is shown. The aspect ratio determines the maximum angle α. Here the filter is placed in the ion beam in a back-to-front configuration. If designed properly, the collimator has a beneficial mechanical stabilizing effect on the filter and improves radiative cooling due to the increased surface area of ​​the filter chip.

[0032] Fig.23 The collimator structure built directly onto the filter is shown. The aspect ratio determines the maximum angle α. In this example, the filter is placed in the ion beam in a front-to-back configuration.

[0033] Fig.24 A collimator structure built directly onto the filter is shown. The collimator structure can have a layered, striped, tubular or honeycomb structure, depending on the layout of the filter and the maximum angular distribution required.

[0034] Fig.25A collimator structure built directly on the target substrate is shown. The collimator structure can have a layered, striped, tubular or honeycomb structure, depending on the layout of the substrate structure and the desired maximum angular distribution.

[0035] Fig.26 Doping profiles obtained using the same filter but a different collimator structure are shown.

[0036] Fig. 27 The doping profiles obtained by implantation through multiple filters with and without a collimator structure are shown.

[0037] Fig.28 The "flipping" of the filter is schematically shown. (A) The filter is used in a regular arrangement, which means that the microstructures point away from the beam. (B) The filter can be flipped, which means that the microstructures point towards the beam. This has a favorable effect on the sputtering effect in the filter.

[0038] Fig.29 The "tilting" of the filter is schematically shown. If the energy filter is made of anisotropic material, there may be a channeling effect. This can be prevented by tilting the energy filter.

[0039] Fig.30 Various doping profiles (dopant concentration as a function of depth in the substrate) for energy filter microstructures of various shapes are schematically shown (shown in side and top view in each case). (A) A triangular prism-shaped structure produces a rectangular doping profile. (B) A smaller triangular prism-shaped structure produces a doping profile with a shallower depth profile. (C) A trapezoidal prism-shaped structure produces a rectangular doping profile with a peak at the beginning of the profile. (D) A pyramid-shaped structure produces a triangular doping profile that rises as it extends through the depth of the substrate.

[0040] Fig.31 Various target distribution shapes based on the same primary ions and the same primary energy for different target materials are shown. In each case, the filter material is silicon.

[0041] Fig.32 The variation of stopping power as a function of energy is shown [4] (SRIM simulation).

[0042] Fig.33 The starting materials for a simple multilayer filter are shown. Filter materials with suitable holding power are arranged one on top of another by suitable deposition methods.

[0043] Fig.34It is shown that with a suitable configuration of a stack of materials with different stopping powers, even with simple filter geometries (here: striped triangles) complex dopant depth profiles can be achieved.

[0044] Fig.35 The general principle of constructing an energy filter from materials 1-6 is shown, with each individual filter structure having a different geometry.

[0045] Fig.36 The equilibrium charge state of the ions (black line: Thomas-Fermi estimation; blue line: Monte Carlo simulation; red line: experimental results) is shown as a function of the kinetic energy of the ions as they pass through the membrane. Ions: sulfur; membrane: carbon

[27] .

[0046] Fig.37 Heating of the energy filter by ion bombardment is shown: 6MeV C ions in an energy filter that is opaque under these conditions [2].

[0047] Fig.38 An embodiment of a filter arrangement is shown in which, for the purpose of suppressing secondary electrons, the filter is fixed in a filter frame at a defined (positive) potential relative to the filter holder.

[0048] Fig.39 The work functions of various components are shown.

[25] Materials Science-Poland, Vol.24, No.4, 2006.

[0049] Fig.40 An arrangement is shown for energy filter injection in which complete illumination of a static substrate is achieved by an ion deflection system before the filter and by choosing a suitable distance between the filter and the substrate (typically in the range of a few cm to a few m).

[0050] Fig.41 A configuration is shown in which energy filter injection is achieved for complete illumination of the substrate using a large filter surface that is larger than the substrate surface. The diameter of the illuminated filter area is larger than the diameter of the substrate.

[0051] Fig.42 An only partially active filter is shown where mechanical scanning is performed in one direction.

[0052] Fig.43 The modification of the doping profile in the substrate by means of a sacrificial layer in the case of masked energy-filtered implantation is shown. In the embodiment shown here, the start of the implantation profile is migrated into the sacrificial layer. This principle can be used similarly for unmasked energy-filtered ion implantation.

[0053] Fig.44The lateral modification of the doping profile in the substrate by means of a sacrificial layer in the case of unmasked energy-filtered ion implantation is shown. The lateral depth modification is produced by lateral differences in the thickness of the sacrificial layer. This principle can be used analogously for masked energy-filtered implantation.

[0054] Fig.45 The coupling of the vertical movement of the filter and the substrate in the y direction is shown. By rotating the wafer wheel, the wafer is guided behind the substrate in the x direction. For example, the ion beam (not shown) expands in the x direction and, due to the vertical oscillation of the implantation chamber, it scans the entire surface of the multi-filter. The surface consists of an effective filter area and an ineffective fixture area. The configuration shown in (A) is an unfavorable configuration. When considering the irradiated filter surfaces at y1 and y2, three filters are irradiated at y1, while no filter is irradiated at y2. Therefore, a laterally non-uniform stripe pattern is obtained on the wafer. The configuration shown in (B) is a possible embodiment of a better configuration. Two filters are irradiated at y1 and y2. This is true for all y. Therefore, a laterally uniform doping over the entire surface of the wafer is achieved.

[0055] Fig.46 A wafer wheel is shown with an arrangement of wafers to be irradiated and monitoring structures located between the wafers.

[0056] Fig.47 A monitoring mask is shown for one example of a configuration employing various mask structures Ma1-Ma10 that are transparent or partially transparent to the ion beam.

[0057] Fig.48 A cross section of a monitoring mask and monitoring material is shown.

[0058] Fig.49 An example of a concentration depth profile produced by an energy filter is shown.

[0059] Fig.50 An example of a mask structure for monitoring depth-dependent dose distribution is shown.

[0060] Fig.51 The monitoring of the injection process by means of a monitoring structure is shown.

[0061] Fig.52 The monitoring of the injection process by means of a monitoring structure is shown.

[0062] Fig.53 Monitoring of the maximum projection range is shown.

[0063] Fig.54 The mask structure is shown.

[0064] Fig.55Another example of a mask structure is shown.

[0065] Fig.56 Another example of a mask structure is shown.

[0066] Fig.57 A mask structure for monitoring an asymmetric angular distribution is shown.

[0067] Fig.58 Various configurations of mask structures for detecting ion angular distributions in various directions are shown.

[0068] Fig.59 A clever adaptation of the transition between the two injection profiles A and B is shown so that the resulting total concentration profile will result in a desired profile, for example a uniform profile. This can (but does not necessarily) be advantageous in particular in cases where the layer system consists of two layers, as shown in the figures here.

[0069] The following sequence of processes is recommended:

[0070] (1) doping the lower layer (implant B),

[0071] (2) Growth upper layer, and

[0072] (3) Doping the upper layer.

[0073] There are still only limited possibilities for the construction of the high-energy tail of implant A. However, the low-energy tail of implant B can be influenced specifically by the introduction of a sacrificial layer, as described in “15: Modification of the doping profile in the substrate by sacrificial layers”.

[0074] The following sequence of processes is recommended:

[0075] (1) Growth of sacrificial layer;

[0076] (2) doping the lower layer (implant B);

[0077] (3) removing the sacrificial layer;

[0078] (4) Growth upper layer;

[0079] (5) Doping the upper layer. DETAILED DESCRIPTION

[0080] Figure 1A method for producing a depth profile known from [7] is shown. In this case, for the purpose of wafer processing, an ion beam is implanted into a substrate with the aid of a structured energy filter in a system for ion implantation. The implantation method and the dopant distribution or defect distribution in the wafer after processing are shown. Specifically shown is how the energy of the monoenergetic ion beam is modified when it passes through a microstructured energy filter assembly, depending on its entry point. The energy distribution of the ions produced leads to a change in the depth distribution of the implanted substance in the substrate matrix. Figure 1 This depth profile is also shown in , which is rectangular in the example shown here.

[0081] Figure 2 A system for ion implantation is shown. The system comprises an implantation chamber in which several wafers can be arranged on a wafer wheel. The wafer wheel rotates during implantation so that the individual wafers repeatedly pass through a beam opening in which an energy filter is arranged and through which the ion beam passes to the implantation chamber and thereby strikes the wafers. Figure 2 The wafer wheel with the substrate to be implanted can be seen on the left. During processing / implantation, the wheel is tilted 90° and set to rotate. The ions of the ion beam, shown in green, "write" concentric circles on the wheel. In order to irradiate the entire wafer surface, the wheel is moved vertically during processing. The energy filter installed in the ion beam opening can be Figure 2 See on the right side.

[0082] Figure 3 Several arrangements or three-dimensional structures of filters are shown by way of example to illustrate the principle of how a wide variety of dopant depth profiles can be produced by appropriate filter selection. Figure 3 The individual filter profiles shown in can be combined with one another to obtain additional filter profiles and thus additional dopant depth profiles. In each case a cross section of an energy filter is shown (far left in the figure) as well as a top view of the energy filter and a curve showing the variation of the obtained dopant concentration with respect to the depth in the wafer (as a function of depth). The "depth" of the wafer is the direction perpendicular to the wafer surface where the ions are implanted. As Figure 3 As shown, (a) a triangular prism-shaped structure produces a rectangular doping distribution; (b) a smaller triangular prism-shaped structure produces a rectangular dopant distribution that extends to a depth less than that in (a) (thus, the depth of the distribution can be adjusted by selecting the size of the structure); (c) a trapezoidal prism-shaped structure produces a rectangular doping distribution with a peak at the beginning of the distribution; and (d) a pyramid-shaped structure produces a triangular doping distribution that increases in height with increasing depth in the substrate.

[0083] For a number of reasons, the energy filters (injection filters) or energy filter elements known in the past are not suitable for achieving high throughputs, i.e. many wafers per hour. It is particularly desirable to have a high wafer throughput per hour, to be easy to handle, to be easy to produce and to achieve any desired distribution shape. Static or removably mounted filters are known from the literature [2], [3], [4], [5], [6], [7], [8], [9],

[10] , which are produced monolithically, i.e. made from a solid block of material and are individually mounted in the ion beam. In contrast to silicon, the shape of the doped regions in SiC wafers is generally not changed by the outward diffusion of the dopant distribution [2], [4], [5], [6]. The reason for this is that the diffusion constants of common dopants such as Al, B, N and P are very small even at high temperatures. These diffusion constants are many orders of magnitude below the comparative values ​​for silicon. For this reason, it has not been possible to economically realize doped regions, in particular those with a high aspect ratio, i.e. a small ratio of substrate area to depth, until now.

[0084] The dopant depth profile in the semiconductor wafer can be produced by in-situ doping during epitaxial deposition or by (masked) monoenergetic ion implantation. In the case of in-situ doping, a high level of imprecision may occur. Even in the case of uniform dopant distribution, the nature of the method means that significant deviations from the ideal doping will be expected on the wafer, i.e. from the middle to the edge. For gradient depth profiles, this imprecision also extends to the vertical direction of the doped region, because now the local dopant concentration depends on a large number of process parameters, such as, for example, temperature, local doping gas concentration, topology, the thickness of the Prandtl boundary layer, growth rate, etc. The use of a monoenergetic ion beam means that many separate implants must be performed to obtain a dopant distribution with an acceptable vertical waviness. This method can only be scaled up to a certain extent, and it soon becomes economically unfeasible.

[0085] Various embodiments of the present invention relate to the structure of an energy filter element for an ion implantation system, which makes it possible to meet the requirements for using the energy filter element in the industrial production of semiconductor components, in particular components based on SiC semiconductor materials. With regard to the use of the energy filter element, the production conditions are defined by, for example:

[0086] 1. Technical convenience of filter replacement

[0087] In a production environment, ie in a factory, production is even performed on ion implanters by industrial workers ("operators"), who in most cases are not trained engineers.

[0088] The energy filter is an extremely fragile microstructured membrane that is difficult to handle without destroying it. Therefore, in order for this filter technology to be economically usable, it should be ensured that after a short period of instruction even non-specialists (i.e. non-engineers) can replace the filter as if it were a tool that was becoming worn or exchange it for another one in the injection system.

[0089] 2. Any desired vertical distribution shape

[0090] Novel semiconductor components such as superjunction components or optimized diode structures require inhomogeneous doping profiles. However, the simple energy filters described in [1-6] only produce a constant distribution. Complex filter structures such as those described in Rüb [8] are technically very delicate and difficult to realize based on the state of the art production methods. The goal is to achieve complex vertical distribution shapes by using uncomplicated, i.e. easy to produce, filter structures.

[0091] 3. High output - cooling system combined with filter movement

[0092] Production conditions refer, for example, to an ion implanter (typical terminal voltage on a tandem accelerator > 1 MV to 6 MV) with a flow rate of about 2x10 per wafer. 13 cm -2 The implantation rate should usually produce more than 20-30 wafers with a diameter of 6" per hour. Therefore, in order to produce the desired number of wafers in this case, an ion current of more than 1 pμA to several tens of pμA must be used; or a power of more than several watts must be used, for example, on a filter (typical surface area 1-2cm 2 )Deposition 6W / cm 2 This causes the filter to heat up. The problem is to cool the filter by appropriate measures.

[0093] 4. Simple, low-cost production of filter structures for obtaining uniform, uniform depth distribution

[0094] The filter structure can be produced by anisotropic wet chemical etching. In the simplest form, the filter structure consists of long triangular flakes of appropriate size (e.g., 6 μm high, 8.4 μm apart, and a few millimeters in length), which are periodically arranged on the thinnest possible membrane. The production of triangular flakes with sharp corners is cost-intensive because wet chemical anisotropic etching must be precisely adjusted. Sharp corners, i.e. non-trapezoidal flakes, are expensive because the etching rate and etching time must be precisely coordinated with each other to obtain sharp flakes. In practice, this will lead to a lot of process control work during etching; and, due to the uneven treatment expected on a chip with hundreds of flakes during etching (the etching rate of a wet chemical process can never be perfectly reproduced and will never be uniform over a large area), this will lead to yield losses, i.e. imperfectly structured filter elements. The goal will be to achieve a simple and low-cost method for the production of energy filters.

[0095] 5. High lateral uniformity of the generated dopant or defect regions

[0096] The energy filters for ion implantation described in the previously cited documents [2], [3], [4], [5], [6], [7], [8], [9],

[10] have an internal three-dimensional structure which causes the ions to travel different distances as they pass through the filter. These differences in travel distance (depending on the stopping power of the filter material) produce a change in the kinetic energy of the transmitted ions. Thus, a monoenergetic ion beam is converted into a beam consisting of ions with different kinetic energies. The energy distribution is determined by the geometry and material of the filter; that is, the filter structure is transferred into the substrate by ion lithography.

[0097] 6. Monitoring the "end of life" of energy filters

[0098] Due to the interaction of the ion beam with the core of the filter material and due to the thermal load, in particular for each ion implantation process with an energy filter, a typical service life of the filter occurs. For a silicon energy filter with a support layer thickness of about 2 μm, a conventional prong structure of about 8 μm and an implantation method with a current of about 0.1 pμA at 12 MeV nitrogen, the maximum production is about 100 wafers (6″).

[0099] For the risk of the machine operator and the safety of the filter manufacturer, the total number of wafers processed using a specific filter should be monitored.

[0100] 7. Limitations of the angular distribution of transmitted ions

[0101] In order to produce masked dopant regions, ie regions with limited lateral dimensions, especially in the case of high aspect ratios, the angular spectrum of the transmitted ions must be limited to avoid implanting ions under the mask layer.

[0102] 8. Minimize filter wear through the sputtering effect

[0103] 9. Avoid channeling (lattice guiding effect) by arranging the filter relative to the ion beam

[0104] 10. Complex dopant depth profiles achieved with simple filter geometry

[0105] 11. Electronic suppression during filter use

[0106] It is known that during the transport of ions through a solid, the charge of the ions assumes a state of equilibrium. Electrons of the primary beam can be released to the solid or accepted by it. That is, depending on the properties of the filter material and the primary energy, the transported ions have on average a higher or lower charge state after passing through the filter

[26] . This can result in positive or negative charging of the filter.

[0107] At the same time, high kinetic energy secondary electrons can be generated by ion bombardment of the front or back side of the filter.

[0108] At high current densities such as those expected in industrial production, the energy filter heats up. Hot electrons are generated as a function of the temperature and the work of the filter material due to thermionic emission (Richardson-Dushman law).

[0109] The distance of the ion accelerator between the filter and the substrate (in a high vacuum) is typically only a few centimeters or less. That is, the diffusion of hot electrons (from thermionic emission) and the behavior of fast electrons (from ion bombardment) distort the measurement of the ion current on the substrate by, for example, a Faraday cup mounted there.

[0110] 12. Alternative production methods by injection molding, casting or sintering

[0111] In publications [2]-

[15] , microtechnological methods are proposed for producing energy filters. Specifically, for producing the filters, photolithographic methods are used in combination with wet-chemical or dry-chemical etching. For filter production, anisotropic wet-chemical etching methods in silicon by alkaline etchants (e.g., KOH or TMAH) are preferred.

[0112] In the case of filters produced by the above-mentioned method, the functional filter layer is made of single-crystalline silicon. It must therefore always be assumed that channeling effects will in principle influence the effective energy losses in the filter layer in an uncontrollable manner when it is bombarded with high-energy ions.

[0113] 13. Configuration for irradiating static substrates

[0114] An irradiation configuration is used which allows irradiation of static materials with high lateral uniformity over the entire surface of the substrate under energy filtering. Reason: The end station of the irradiation system usually does not have full mechanical capability to scan the entire wafer (wafer wheel) with a point-shaped or nearly point-shaped beam spot. Instead, many systems have an electrostatically expanded beam (= strip in the x-direction), which, for example, electrostatically scans the wafer (y-direction). In some cases, a partial mechanical scanner is used. That is, the beam expands in the x-direction, while the wafer is (slowly) moved mechanically in the y-direction.

[0115] 14. Configurations that take advantage of large filter surfaces

[0116] An irradiation configuration must be used which makes it possible to irradiate static or movable substrates with high lateral uniformity over the entire surface of the substrate and over large filter surfaces under energy filtering. This makes it possible to reduce thermal and degradation effects in the filter.

[0117] 15. Changing the doping profile in the substrate through a sacrificial layer

[0118] Energy filters are tools for manipulating doping profiles in substrates. For certain requirements, it is desirable to manipulate the doping profile that can be produced in the substrate after the energy filter, i.e., at a position downstream of the energy filter. Specifically, it is desirable to "push" the near-surface start of the doping profile away from the substrate. This can be particularly advantageous when the start of the doping profile in the substrate cannot be properly adjusted by the filter due to various reasons (particularly by scattering loss of ions). This doping profile manipulation after the energy filter can be achieved by implanting into a sacrificial layer on the substrate.

[0119] 16. Lateral modification of the doping profile in the substrate by means of a sacrificial layer

[0120] For certain applications, it is desirable that the doping profile in the substrate exhibits lateral variations. In particular, variations in the implantation depth of a uniform doping profile can be advantageously used for edge termination in semiconductor components. Such lateral adjustment of the doping profile can be achieved by providing a sacrificial layer with lateral thickness variations on the substrate.

[0121] 17. Adjustment of distribution transition between several injection distributions

[0122] For some applications, it is desirable to connect two or more profiles to each other along a "seam" at a certain depth, because otherwise there would be insulation between the layers. This problem occurs in layer systems, in particular when the lower end of an upper doping profile or the upper end of a lower doping profile below it comprises a "tail" of slowly decreasing concentration.

[0123] 18. Specific configuration of the multi-filter concept for coupled oscillatory motions

[0124] If the multi-filter is connected to a part of a movable substrate chamber that can be moved linearly back and forth in front of the beam (for example, in the case of a rotating wafer wheel with a vertical scanning direction), the multi-filter can be easily moved relative to the beam simply by moving the substrate chamber. By means of a magnetic or electrostatic scanning device that scans in one direction in front of the filter, a very large multi-filter surface can be used, which is equal to, for example, the product of the vertical oscillation distance multiplied by the horizontal scanning distance. The movement of wafer and filter is coupled in this configuration, which can lead to problems with the lateral uniformity of doping. By the rotation of the wafer wheel, the ion beam "writes" lines on the wafer. Due to the above-mentioned configuration, the position of the horizontal irradiation line on the wafer can, for example, be coupled to a certain vertical position on the multi-filter. For example, the gaps between the individual filter elements lead to unevenly doped lines on the wafer. Therefore, the arrangement of the filter components in the multi-filter must be chosen so that lateral uniformity is ensured despite the coupling of the linear movement of the filter and substrate.

[0125] Examples of energy filters, injection devices or partial injection devices which meet the aforementioned production conditions are explained below. It should be mentioned that the measures and concepts explained below can be combined with one another in any desired manner, but each of them can also be applied individually in itself.

[0126] Point 1: Technical convenience of filter replacement

[0127] It is envisaged that a frame which allows easy handling of the injection filter is mounted on the filter in question, which is hereinafter referred to as a "filter chip". Figure 4-6 As shown, this frame can be configured in such a way that it can be used on an ion implantation system in a previously installed frame fixture of appropriate size. The frame protects the energy filter, makes it easy to handle, and is responsible for electrical and thermal dissipation and / or electrical insulation (see Fig.36 ). The frame can be provided with the filter chips by the manufacturer of the filter element in a dust-free environment and delivered to the ion implantation system in a dust-free package.

[0128] Figure 4 and 5 Examples of geometric and mechanical structures of filter frames are shown. The filter held thereby may have any desired surface structure, selected according to the desired doping profile to be obtained therewith. The filter holder and / or the filter frame may be provided with a coating which prevents abrasion of material from the filter frame and the filter holder.

[0129] The filter frame and the filter holder can be made of metal, preferably of high-grade steel or the like. During the implantation process, sputtering effects in the local environment of the energy filter caused by scattered ions must be expected. That is, it must be expected that material at and near the frame and filter surfaces will be carried away. Metal contamination on the substrate wafer may be an undesirable result. The coating prevents such contamination, wherein the coating is composed of a non-contaminating material. What material is non-contaminating depends on the properties of the target substrate used. Examples of suitable materials include silicon and silicon carbide.

[0130] Figure 4 Shown is a cross section of the filter frame used to hold the energy filter chip. Also shown in Figure 4 The energy filter chip can be attached to the frame in various ways, such as by using an adhesive or by mechanical springs. Figure 5 The device for fixing the energy filter element (which is also shown in Figure 5 The filter frame comprises a locking element by which the frame can be opened and closed to allow the filter to be replaced. Figure 6 An example of mounting a frame for securing an energy filter element in the beam path of an ion implanter is shown. Figure 6 The upper part of the figure shows a cross section of the chamber wall and a filter holder arranged therein. In an embodiment, the filter holder is arranged on the inner side surface of the chamber wall, i.e., the side facing the wafer (not shown) during the implantation process. During the implantation process, the ion beam passing through the opening in the chamber wall and through the filter arranged in front of the opening is also Figure 6 The frame with the filter chip inserted into the filter holder covers the opening in the chamber wall through which the ion beam passes during the implantation process. This is shown in Figure 6 , which shows a front view of the chamber wall with the filter holder attached to the chamber wall.

[0131] The frame can be made of the same material as the filter. In this case, the frame can be produced integrally with the filter and can therefore be called a "monolithic frame". As explained above, the frame can also be made of a different material than the filter, such as metal. In this case, the filter can be inserted into the frame. According to another example, the frame comprises a monolithic frame and at least one other frame of a different material than the filter, which is attached to the monolithic frame. The other frame is, for example, a metal frame.

[0132] As explained and shown above, and as Figure 7As shown on the right, the frame may completely surround the filter. According to other examples, the frame does not constitute a border on all (four) sides (edges) of the filter, but only on three, two (opposite) or only one edge of the filter. Therefore, the term "frame" should be understood in conjunction with this description as a solid frame, which completely surrounds the filter on all sides (edges), and as a partial frame, which only extends around some sides of the filter. Examples of such partial frames are also shown in FIG. Figure 7 Therefore, Figure 7 Various partial frames (on the left side of the figure) and complete frames (on the far right of the figure) are shown. Each of these frames can be constructed of the same material as the energy filter (eg, a monolithic piece) or a different material.

[0133] The energy filter or any other scattering element can be mounted in the beam path of the implanter by its frame in various ways, which can be realized according to one of the above examples. The frame inserted into the filter holder explained above is only one of several possibilities. Other possibilities are explained below.

[0134] according to Figure 8 An example shown in, the framework can be installed on the chamber wall by at least one rod. In this case, at least one rod is used as the filter fixing member. Figure 8 Shown in the figure are examples of installation by only one rod, by two rods and by three rods. It is obvious that more than three rods can also be provided.

[0135] According to another example, Fig. 9 As shown, the frame can also be attached to the chamber wall by a hanger or a suspension element. These suspension elements are, for example, flexible and can be installed between the frame and the chamber wall in a way that the frame is firmly fixed in place. The suspension element is used as a filter fixture in this example. Fig. 9 The examples of accessories with only one suspension element, with two suspension elements and with three suspension elements are shown. Of course, more than three suspension elements can also be provided.

[0136] According to another example, Fig.10 As shown, the frame with the filter is fixed by a magnet by a suspension (contactless) mode. For this purpose, the magnet is attached to the front and rear sides of the frame and the chamber wall, In this way, in each case, the magnet on the chamber wall or the fixture attached to the chamber wall is opposite to the magnet on the frame, wherein the relative magnetic poles of the opposite magnets have opposite polarities. Due to magnetic force, the frame floats between the magnet attached to the chamber wall and the magnet attached to the fixture. The magnet on the frame of the filter can, for example, be realized by thermal vapor deposition or any other layer formation method.

[0137] Point 2. Any desired vertical distribution shape

[0138] In principle, the geometrical construction of energy filters for ion implantation systems can make it possible to realize any desired doping profile in the semiconductor material. For complex profiles, this means that geometrically very demanding three-dimensional etched structures of different sizes and possibly different heights, such as pyramids, pits with defined wall slopes, inverse pyramids, etc., must be produced on the same filter chip.

[0139] It is envisaged that any desired distribution can be approximated using rectangular distribution shapes such as those that can be generated by simple triangular structures (multiple filters). Under certain conditions, it is also possible to use non-triangular structures (eg, pyramids) as the basis for the approximation.

[0140] That is, imagine breaking down the desired doping profile into, for example, box profiles, and creating a triangular filter structure for each box profile. The individual filter chips are then mounted in a frame in such a way that the area weighting corresponds to the dopant concentration appropriate for the box profile element in question.

[0141] The decomposition of the dopant depth profile is not limited to the triangular structures shown in this article. Instead, it can include other structures, which in the most general case contain inclined surfaces or even convex or concave rising sides. The sides do not necessarily have to rise as a whole, but they can also contain valleys and depressions. Binary structures with side angles of 90° can also be envisioned.

[0142] In one example, the filter elements are bevel cut and arranged directly adjacent to each other. Bevel cutting has the advantage that no adhesive bonding between the filters is required to block ions at the filter edges. In addition, the irradiation surface can be optimally utilized in this way. For the same overall filter size and a given ion current, this has the effect of increasing wafer yield.

[0143] Fig.11 An example of a simple realization of a multi-filter is shown. In this example, three differently shaped filter elements are combined in the frame of the filter holder to form a complete energy filter. Fig.11 The upper left of FIG. 11 is a cross section of a filter holder with three filter elements, and the lower left of FIG. 12 is a top view of a filter holder with three filter elements. Fig.11 The right side of the figure is a filter profile that can be obtained with the combined filter. When this filter is used as an implantation filter, the ion beam passes uniformly through all the individual filter elements, resulting in Fig.11Dopant depth profile shown on the right. This profile contains three depth profiles, numbered 1, 2, and 3. Each of these depth profiles comes from one of the three sub-filters shown on the left, i.e. from the sub-filters identified by the same number.

[0144] Fig.12 The manner in which three different filter elements which can be combined to form a multi-filter function is shown by way of example. The figure shows the cross-section of each individual filter element, examples of the dimensions of these filter elements, and doping profiles such as those which can be obtained with the individual filter elements. Fig.12 In the example, only the dimensions of the fourth filter element (not shown) are given as an example. The weighting, i.e. the concentration or doping distribution obtained, can be adjusted by varying the dimensions of the surface area of ​​the individual filter elements. For this example, it is assumed that the filter and the substrate have the same energy-dependent stopping power, but this does not necessarily have to be the case. Fig.13 Shows that based on Fig.12 An example of a doping profile that can be obtained when the four filter elements explained are combined into a multifilter and used for implantation. This summed profile results from the addition of the filter elements weighted over the surface in question. For this figure, it is assumed that the Fig.12 The filter elements described are assembled with appropriate weighting to form a complete filter and uniformly exposed to an ion beam of appropriate primary energy so that the indicated sum distribution is obtained.

[0145] Based on Fig.11 In the example explained, the individual filter elements of the multi-filter are separated from each other by a mesh of the frame. According to another example, Fig.14 As shown, individual filter elements can also be directly adjacent to one another. Fig.14 A cross section of a multi-filter comprising several adjacent filter elements F1, F2, F3 is shown. The multi-filter is inserted into a filter frame. In this example, the individual filter elements F1, F2, F3 are cut with a bevel gauge and arranged directly adjacent to each other.

[0146] Point 3. High throughput - cooling system combined with filter movement

[0147] High wafer throughput for a given target doping can only be achieved with high ion currents. Because about 20% to about 99% of the primary energy of the ion beam is deposited in the filter membrane, i.e., the portion of the beam that passes through the injection filter, the use of cooling methods has been proposed as a way to prevent excessive increases in filter temperature even at high ion currents.

[0148] This type of cooling can be accomplished, for example, by one or more of the following measures a to c as explained below.

[0149] a. Coolant flow in filter holder

[0150] In this way, the heated filter chip is cooled by dissipating heat. Fig.15 An example of a filter holder for cooling of this type is shown. Specifically shown is a cross section of a filter holder, which is attached to a chamber wall of an injector. In this example, coolant lines are integrated in the filter holder, which receives the filter frame. Liquid coolant is supplied to these coolant lines by an external cooling device (not shown). Alternatively or in addition, the coolant lines may also be arranged on the surface of the filter holder (not shown).

[0151] b. Movement of filter or ion beam

[0152] It is envisaged that when using a rotating wafer wheel carrying, for example, 10-15 wafers, the filter or filter holder is configured in such a way that it rotates or oscillates in a linear motion. Alternatively, the ion beam may be electrostatically moved over the filter while the filter remains stationary.

[0153] In these variants, the filter is only partially irradiated by the ion beam per unit time. Therefore, the part of the filter that is not irradiated at a specific moment can be cooled by radiation cooling. As a result, a higher average current density for a given filter can be achieved under continuous use conditions. An example of how this can be achieved is Fig.16 and 17 shown.

[0154] Fig.16 An energy filter with a relatively large surface area is shown, which is only partially irradiated per unit time. Therefore, the non-irradiated areas can be cooled by radiation cooling. This embodiment can also be configured as a multi-filter as described above, i.e. as a filter comprising several different filter elements. In the example shown, the frame with the filter oscillates in a direction perpendicular to the schematically shown ion beam direction. The area of ​​the filter covered by the ion beam is smaller than the total area of ​​the filter, so that only part of the filter is irradiated per unit time. This part changes continuously due to the oscillating motion.

[0155] Fig.17 An example of a filter arrangement with multiple filter elements is shown, which are carried by a rotating filter fixture. Each individual filter element can be structured in the same way, but they can also have different structures to obtain a multi-filter. Fig.17 As shown, as the fixture rotates, a single filter element traverses a circular path around the fixture's axis of rotation (central axis). Also in this example, only partial illumination occurs per unit time; i.e., not all filter elements are illuminated simultaneously, allowing non-illuminated filter elements to cool.

[0156] Point 4. Simplified filter design

[0157] The production of filter elements having a tip structure with precise height and perfect angles is demanding in terms of production technology and correspondingly expensive.

[0158] For simple doping profiles (eg uniform doping), which start from the surface of the substrate and require only a simple tip structure, a simplified design and an associated simplified production method will be proposed herein.

[0159] It is envisioned that the microstructured membrane of the filter (e.g., a pointed structure) has terraces on the tips rather than sharp corners, and the thickness of the supporting layer of the membrane is sized so that the forming low-energy dopant peaks are pushed into the supporting layer of the filter and thereby not injected into the substrate. Fig.18 An example of this type of filter is shown in . A cross section (left side in the figure), a top view (middle) and an example of a doping profile that can be obtained by using the filter shown are shown. As shown in the figure, by using a trapezoidal prismatic structure, a rectangular distribution can be produced in the substrate by implanting ions into the energy filter. The peak at the beginning is implanted into the energy filter; that is, there is no peak of the dopant distribution within the substrate. This implantation profile has the advantageous property of starting directly at the substrate surface, which can be crucial for energy filter applications.

[0160] from Fig.18 From the cross-section of the filter in FIG. 1 , it can be seen that the filter structure comprises terraces instead of sharp corners. Therefore, the cross-section of the individual structural elements is trapezoidal. This greatly simplifies the technology for realizing the desired filtering. It is known that triangular structures can be produced in silicon by, for example, wet chemical etching with KOH or TMAH. For this purpose, the tips of the triangles must be masked in lithography. If perfect tips are produced, this leads to the problem that the etching may penetrate under the primer or hard mask structure. Without the envisioned herein, this problem can only be solved by perfect (and therefore complex and cost-intensive) processing. The ideas proposed in this article therefore greatly simplify the production of filter structures. This is similarly true for modern plasma-supported etching methods such as RIBE (reactive ion beam etching) or CAIBE (chemically assisted ion beam etching).

[0161] Point 5. High lateral uniformity of the generated doped or defective areas

[0162] In the case of static implants, the lateral uniformity aspect can be significant.When a rotating wafer platter (wafer wheel) is used with, for example, 11 wafers and a fixed ion beam, the uniformity is determined by the rotational and translational motion of the wafer platter relative to the ion beam.

[0163] Filter-substrate distance: The angular distribution of the transmitted ions is energy-dependent. If the energy of the filter and the ions is coordinated with each other in such a way that especially very low energy ions (nuclear stopping range) leave the filter, there is a broad angular distribution because large angle scattering events occur. If the energy of the filter and the ions is coordinated with each other in such a way that only high energy ions (only in the electron range, dE / dx 电子 >dE / dx 核 ) is coordinated away from the filter, the angular distribution is very narrow.

[0164] The minimum distance is characterized by the fact that the structure of the filter does not pass onto the substrate, i.e., for a given distribution of scattering angles of the transmitted ions, the lateral distance traversed by these ions is at least comparable to the period of the lattice constant of the ion filter.

[0165] The maximum distance is determined by the loss of scattered ions which, for a given distribution of scattering angles, in particular at the edge of the semiconductor wafer, can still be tolerated by the application.

[0166] Fig.19 The experimental results of ion implantation through an energy filter during static implantation of a PMMA (polymethyl acrylate) substrate are shown. The ions destroy the molecular structure of PMMA so that the subsequent development process shows the energy distribution of the ions by dissolving the high energy deposited areas. Areas with low energy deposits or no energy deposits by the ions are not dissolved by the developer solution.

[0167] The idea proposed in this paper is to produce high lateral doping uniformity by choosing the right filter-substrate distance for both dynamic and static implantation setups.

[0168] Point 6. Monitoring the "end of life" of energy filters

[0169] Energy filters degrade as a function of the cumulative implanted ion dose due to nuclear interactions and significant temperature changes (heating of the filter typically reaches several hundred degrees Celsius).

[0170] Once the critical ion dose is reached, the filter chemistry, density and geometry are changed in such a way that the effect on the target distribution to be achieved is no longer negligible. The critical ion dose depends on the filter material used, the implanted ion species, energy, geometry and the permissible variation range (= specification) of the target distribution.

[0171] For each filter implantation process with a given energy, ion species, distribution, etc., specifications including the maximum temperature during implantation and the maximum allowed cumulative ion dose can therefore be defined. According to an example, the use of an energy filter is provided so that the filter cannot be used outside the specified tolerance even if it is not monitored by an engineer. For this purpose, it is envisioned that once the filter is inserted into the filter fixture on the implanter, each filter is detected based on an electronically readable signature, and this signature is read by, for example, a control computer. For this purpose, the signature is stored in an electronically readable memory arranged on the filter. For example, a database stores the signatures and properties of the filters that can be used on a certain implanter, such as the processes (ion species, energy) to which the filter is applicable, and the degree to which the cumulative dose and the maximum temperature are allowed to reach. By reading out the signature and comparing it with the information in the database, the control computer can thus determine whether the filter is suitable for the planned implantation process.

[0172] Fig. 20 A monitoring system for identifying filters and monitoring compliance with filter specifications (maximum temperature, maximum accumulated ion dose) is shown. Once the filter has been identified by means of built-in sensors (charge integrator and temperature sensor), the accumulated dose and the temperature of the filter are continuously measured. The injection process is terminated when one of the specified parameters is reached or exceeded, i.e. when the filter, for example, becomes overheated or the maximum permissible dose has been injected through the filter. That is, when a certain value no longer complies with the specifications, a signal is sent to the control computer, which terminates the injection process.

[0173] Point 7: Limitations in the angular distribution of transmitted ions

[0174] For applications requiring blank areas on the target substrate, a masking material may be applied to the target substrate.

[0175] In order to avoid lateral "blurring" of the structure by an overly broad ion distribution caused by the filter, it is envisaged to collimate the ion beam transmitted through the filter. The collimation can be done by strip, tube, grid or hexagonal structures with a high aspect ratio, which are arranged in the transmitted beam after the energy filter. The aspect ratio of these structures defines the maximum angle allowed.

[0176] Examples include Figure 21-25 as shown in . Fig.21A cross section of the implanter chamber wall in the region of the beam opening, a filter fixture fixed to the chamber wall with an inserted filter and a collimator attached to the side of the filter fixture facing away from the chamber wall in this example is shown. The aspect ratio of the collimator is determined by the length and width of the collimator, determining the maximum angle α relative to the length direction of the collimator at which the ion beam can be introduced into the collimator and still pass through the collimator. Segments of the ion beam that are beamed at relatively large angles hit the wall of the collimator and therefore do not pass through it. If the available distance between the filter and the substrate to be implanted with ions is insufficient for the desired aspect ratio, the collimator can also consist of several collimator units with smaller openings arranged adjacent to each other. They can be arranged in a honeycomb pattern, for example.

[0177] Alternatively, the collimator structure can also be arranged directly on the filter element. This type of element can be produced as a whole or by micro-bonding methods. Two examples of collimator structures arranged directly on the filter are Fig. 22 As shown in . This type of collimator structure arranged directly on the filter can mechanically stabilize the filter and have a cooling effect, because the collimator structure can be used as a cooling body with a surface area larger than the surface area of ​​the filter. Here, the maximum angle α is also defined by the aspect ratio of the individual collimator structures (each including a length and a width) arranged on the filter. The collimator structure can be attached to the filter by using an adhesive, for example, by bonding or by some similar method.

[0178] exist Fig. 22 In the example shown, the collimator structures are arranged on a structured side of the filter, ie the filter has elevations and depressions. In this example, the structures are trapezoidal. Fig.23 Shows Fig. 22 In this example, the collimator surface is arranged on the unstructured side of the filter. In both cases, the collimator structure is arranged relative to the direction of the ion beam (in Fig.21 and 22 The collimator structure (indicated by arrows in FIG. 1 ) is arranged downstream of the filter and in such a way that the ion beam passes through the collimator structure only after passing the filter.

[0179] Fig.24 A top view of a collimator structure according to various examples is shown. In the example shown, the collimator structure is arranged on a filter which, when viewed from above, has a layered structure. The cross-section of a single "filter lamina" can be, for example, triangular or trapezoidal, as already explained above. However, the layered structure of the filter is only an example. Any other type of filter structure as explained above can also be used. On the left and in the middle, Fig.24An example is shown in which the collimator structure is arranged in a strip-like manner; i.e. it comprises several parallel strips, each strip extending over the entire width of the filter. Each pair of adjacent strips forms a collimator, wherein the width of such a collimator is determined by the distance between adjacent strips. The length of the collimator is determined by the height of the individual strips. The "height" of a strip is its dimension in a direction perpendicular to the plane of the drawing. The strips of the collimator structure may be perpendicular to the thin layers of the filter, e.g. Fig.24 , or they can be parallel to the lamellae, as shown in the center of the figure. Fig.24 On the right side of is an example in which the collimator structure appears as a lattice in top view, thereby forming a plurality of collimators, whose geometry is determined by the geometry of the lattice. In the example shown, the individual collimators are rectangular, in particular square, in top view, so that the collimators are in the form of rectangular tubes. However, this is only an example; the lattice can also be implemented in such a way that the individual collimators are circular, elliptical or hexagonal (honeycomb) in top view or have any other desired polygonal geometry.

[0180] Alignment through a hard mask on the target substrate

[0181] For masked implantation, as an alternative or in addition to the collimator on the filter, a mask can be applied to the target wafer and used as a collimator structure. A condition for such masking may be that the stopping power of the mask must correspond at least to the average range of the transmitted ion beam in the target substrate material. Thus the desired limitation of the angular distribution can also be achieved by the mask, so that the aspect ratio of the mask can be adjusted accordingly. Figure 25 shows an example of a collimator structure of this type, which is arranged directly on the target substrate. Such a collimator structure can have any of the aforementioned geometries; thus it can be, for example, layered, strip-shaped, tubular or honeycomb-shaped, depending on the layout of the substrate structure and the desired maximum angular distribution. The aspect ratio of such a collimator structure is the ratio of the height (h in Figure 25) to the width (h) of the blank areas of the mask on the substrate forming the collimator structure. Fig.25 The ratio of b) in .

[0182] It is found that the collimator structure not only affects the scattering in the lateral direction, but also affects the depth distribution. Fig.26 , which shows the doping profiles for three different implantation methods, each of which is performed with the same filter but with a different collimator structure. In this example, each filter has a layered structure with a trapezoidal cross section. However, this is only an example. On the left side in this figure, an implantation method is shown, in which the implantation is performed without a collimator structure. The implantation profiles thus obtained start at the surface of the substrate.

[0183] exist Fig.26In the middle and right side of the figure, an implantation method is shown, wherein a collimator structure is used for implantation, wherein the aspect ratio of the collimator structure in the case of the example on the right is higher than that of the example in the middle. As can be seen, the doping distribution obtained by these implantation methods does not start from the substrate surface, but is a certain distance from it, wherein the higher the aspect ratio, the further away the doping distribution is from the surface, and the flatter its rise is. The explanation for this is that the dopant distribution in the near-surface region of the substrate is caused by ions with lower energy that are more strongly blocked in the filter. This ion with low energy is more strongly scattered by the filter than the ion with higher energy, so these ions with lower energy have a wider angular distribution than the ions with higher energy. Therefore, the number of low-energy ions that can pass through the collimator structure will be less than the number of ions with higher energy, wherein the larger the aspect ratio of the collimator structure, the more significant the effect, i.e., the smaller the maximum value of the angle that allows ions to still pass through the collimator structure.

[0184] Thus, despite the presence of the collimator structure, a nearly uniform doping profile can be produced starting from the surface, and the filter can be designed so that low energy ions are "preferred." That is, more low energy ions pass through the filter than high energy ions. Fig. 27 An example of a filter of this type is shown in . In this example, the filter has different filter areas, each with a maximum and minimum thickness. The maximum thickness is the same in all three areas, but the minimum thickness is different. This is achieved in this example because the filter has a trapezoidal structure arranged on a substrate in each individual area, wherein the substrate has different heights or thicknesses and the trapezoidal structure therefore has different heights. In the first part, the base is the thinnest and the trapezoidal structure is the highest, so the distance CD1 between adjacent structures is the largest in this part. In the third part, the base has the largest thickness and the trapezoidal structure is the lowest, so the distance CD3 between adjacent structures is the smallest in this part. In the second part, the thickness of the substrate is between the thickness of the first part and the thickness of the third part. Correspondingly, the height of the trapezoidal structure in this part is between the height of the first part and the height of the third part, and in this part, the distance CD2 between adjacent structures is between the distance CD1 in the first part and the distance CD3 in the third part. The individual parts can be identical in terms of surface area, but they can also be of different sizes. It is also obvious that more than three parts with different minimum filter thicknesses can be provided.

[0185] Fig. 27On the left is shown the implantation profile obtained by implantation with the filter described previously when the implantation is carried out without a collimator structure. This implantation profile starts at the surface, but the doping concentration decreases gradually with increasing depth. In the figure, CD1 represents the area of ​​the doping profile that can be attributed to the first part of the filter; CD2 represents the area of ​​the doping profile that can be attributed to the second part of the filter; and CD3 represents the area of ​​the doping profile that can be attributed to the third part of the filter. On the basis of the doping profile, it can be seen that the greater the minimum thickness of the substrate of the relevant part, the shallower the ions that penetrate the filter area in question penetrate into the substrate, i.e. the lower their energy. The doping profile also shows that more low-energy ions pass through the filter than high-energy ions. Since, as explained above, low-energy ions are scattered more strongly than high-energy ions and therefore fewer low-energy ions pass through the collimator structure than high-energy ions, an almost uniform doping profile starting from the surface can be obtained by using such a filter in combination with a collimator structure. This Fig. 27 , which shows an implantation method using the illustrated filter and collimator structure. The collimator structure in this example is located on the substrate, but it can also be arranged on the filter.

[0186] Point 8. Less filter wear caused by sputtering effect

[0187] Implantation configuration of the filter relative to the substrate: in one case the tip faces the substrate, in the other case the tip faces away from the substrate (→ sputtering, scattering on impact). During the implantation methods explained previously and those to be explained below, the filter can in each case be used in such a way that the microstructure of the filter faces the substrate, i.e. away from the ion beam, e.g. Fig.28 Alternatively, the filter can also be rotated so that the microstructure of the filter faces away from the substrate, i.e., faces the ion beam, as shown in FIG. Fig.28 (b) The latter can have a favorable influence on the sputtering effect.

[0188] Point 9: Avoid channeling by arranging the filter relative to the ion beam

[0189] Tilt of filter and / or substrate

[0190] Whenever the filter and / or substrate are made of crystalline materials, undesirable channeling may occur. That is, the ions can reach an increased range along certain crystal directions. The magnitude of the effect and the acceptance angle are functions of temperature and energy. The implantation angle and the crystal surface orientation of the starting materials for the filter and substrate play a crucial role. In general, the channeling effect cannot be reliably reproduced on a wafer, because the above parameters can vary from wafer to wafer and from one implantation system to another.

[0191] Channeling should therefore be avoided. Tilting the filter and substrate can prevent channeling. Channeling in the filter or in the substrate, especially when the filter and substrate consist of different materials, can have a completely different effect on the depth profile of the implanted dopant.

[0192] Fig.29 Schematically shown is a filter which is tilted relative to the substrate during the implantation process in such a way that the base surface of the filter forms an angle greater than zero with the surface of the substrate. For example, the angle is greater than 3°, greater than 5°, or greater than 10° and less than 30°. In particular when the energy filter is made of anisotropic material, channeling can be prevented or reduced in this way.

[0193] Key Point 10: Complex doping depth profiles using simple filter geometries

[0194] As explained above, more complex dopant depth profiles can be achieved by adjusting the geometrical design of the filter element.For simplicity, in the following explanation, all types of scattering effects are neglected.

[0195] For the case where the stopping power (dE / dx) of ions is the same in the filter and substrate materials, the following may occur: Fig.30 The situation shown as an example in . Fig.30 Schematic diagrams showing various doping profiles (dopant concentration as a function of depth in the substrate) for energy filters of different designs, each energy filter being shown in side and top views. As shown, (a) a triangular prism-shaped structure produces a rectangular doping profile; (b) a smaller triangular prism-shaped structure produces a doping profile with a shallower depth profile than the larger triangular prism-shaped structure shown in (a); (c) a trapezoidal structure produces a rectangular doping profile with a peak at the beginning of the profile; (d) a pyramid-shaped structure produces a triangular doping profile that increases in height as the depth of the substrate increases.

[0196] For example, when, for example, silicon is used as the substrate material to be doped with boron, and when the energy filter is made of a different material, a variation of the dopant depth profile in the substrate is obtained depending on the density of the filter and the variation of dE / dx as a function of the actual kinetic ion energy. Only when the same material is used for the filter and the substrate can a completely uniform, i.e. a constant variation of the doping in the depth direction be achieved. This is like Fig.31 , which shows doping profiles in various substrate materials (target materials) obtained by the same implantation method, i.e. an implantation method with the same primary ions and the same primary energy. In each case, the filter material is silicon. Due to the different substrate materials, the doping profiles are different.

[0197] Fig.32 Shown for Fig.31The graphs in Figure 4 are based on the variation of the stopping power as a function of energy for various substrate materials [4] (SRIM simulation).

[0198] It is now envisaged that for a given surface geometry, the energy-dependent variation of the stopping power is adjusted by designing the filter, for example, as a multilayer system.

[0199] The variation of stopping power as a function of ion energy (i.e., as a function of vertical position in the filter tip for a given ion species and primary energy) is envisioned to be modeled in such a way that overall (i.e., from the ion entering the filter until the final position in the irradiated substrate), the total loss of kinetic energy is modeled as a function of the entry position on the filter (more precisely, the actual path of the ion through the filter and substrate). Thus, the energy losses in the filter are no longer determined solely by the irradiation length of the filter material, but by the position-dependent variation of the stopping power.

[0200] Thus, for example, with appropriate modeling and fixed geometry, it is possible to produce a doping profile that rises or falls in the depth direction. Thus, the stopping power becomes a function of the lateral position. Examples of such filters are Figure 33-35 The lateral position in each of these figures is denoted by "y".

[0201] Fig.33 A multilayer starting material for a multilayer filter is shown. In this example, the starting material comprises four different layers, labeled 1-4. However, the use of four layers is only an example. Less than four layers or more than four layers can be used. The individual layers differ not only in the material used, but also in their thickness. Two layers can also contain the same material and be separated by two or more layers of different materials. The individual layers can be deposited or produced one on top of the other by a suitable deposition method.

[0202] With a suitable structure of stacked materials with different stopping powers, complex dopant depth profiles can be achieved even with simple filter geometries. Fig.34 Shows the Fig.33 The cross section of the filter realized from the starting material produced in and comprising in the example shown a substrate and triangular structures arranged on the substrate. These triangular structures can be in the form of strips, i.e., they can extend in a direction perpendicular to the plane of the drawing, or they can be part of a pyramidal structure.

[0203] like Fig.35As shown, the filter can also be realized in such a way that a plurality of structures are arranged adjacent to each other in the transverse direction (y direction), these structures comprising different geometries and / or different stacks, i.e. stacks with different configurations with respect to the sequence of the individual layers and / or the materials of the individual layers. For example, six different materials are used in the filter shown, these layers being indicated by 1-6.

[0204] For example, silicon, silicon compounds or metals are suitable as materials for the individual layers, although the choice is not limited to these materials. Silicon compounds include, for example, silicon carbide (SiC), silicon dioxide (SiO2) and silicon nitride (SiN). Suitable metals include, for example, copper, gold, platinum, nickel and aluminum. According to one example, at least one layer of silicon compound is grown on the silicon layer, and the metal layer is vapor deposited on the at least one layer of silicon compound. The metal layer can also be vapor deposited directly on the silicon layer. There is also the possibility of producing different metal layers on top of each other by vapor deposition so that filters with different layers are obtained.

[0205] Point 11. Electronic suppression

[0206] It is known that during the transmission of ions through a solid, electrons of the primary beam remain in the solid or are absorbed by the ions. That is, depending on the characteristics of the filter material and the primary energy, the transmitted ions have on average a higher or lower charge state after passing through the filter

[26] . Electrons are either rejected by the filter or accepted.

[0207] Fig.36 The equilibrium charge state of the ions is shown as a function of the kinetic energy of the ions upon irradiation of the film (black line: Thomas-Fermi estimation, blue line: Monte Carlo simulation; red line: experimental results). Ions: sulfur. Film: carbon

[27] .

[0208] Due to the ion bombardment, secondary electrons with high kinetic energy can be generated both on the front and rear sides of the filter. At high current densities, such as those expected in industrial production, the energy filter will heat up. Due to thermionic electron emission (Richardson-Dushman law), hot electrons are generated as a function of the temperature and work function of the filter material. This is Fig.37 , which shows the heating of an energy filter by ion bombardment. The curve shown is based on an experiment in which the filter was irradiated with carbon (C) ions having a high energy of 6 MeV. The filter in this case is a non-transparent energy filter [2].

[0209] The distance of the ion accelerator between the filter and the substrate (in a high vacuum) is typically only a few centimeters or less. Therefore, ion current measurements at the substrate by means of, for example, a Faraday cup attached thereto are disturbed by the diffusion of hot electrons (from thermionic emission) and by the behavior of fast electrons (from ion bombardment).

[0210] As mentioned above, from the filter's perspective, there are both processes that generate electrons (stripping of primary ions) and processes that emit electrons. Therefore, the potential of an electrically insulating filter installed is not well defined. Instead, it varies during the injection process as a function of ion current, vacuum conditions, temperature, etc. A net negative charge will promote electron emission, while a net positive charge has a tendency to suppress electron emission. Various ways in which this charging effect can be prevented will be explained below.

[0211] (a) Energy filter element at a defined (positive) potential

[0212] It is envisaged that the energy filter is designed and mounted in such a way that the filter is always at a defined potential during ion bombardment. Fig.38 A cross section of a filter arrangement that ensures this is shown. With this filter arrangement, the filter in the filter frame is fixed at a defined (positive) potential relative to the filter holder to suppress secondary electrons. The filter frame is connected to a voltage source and is electrically insulated from the filter holder and the chamber wall of the implanter.

[0213] The potential of the filter holder can be adjusted. This can be implemented, for example, in such a way that, independent of the charge balance resulting from the implantation process, a constant potential relative to the potential of the substrate to be implanted or relative to ground potential is maintained during the implantation. For this purpose, a controlled feed of positive or negative charge by means of a current source can be provided.

[0214] The potential to be maintained can be selected in particular in such a way that, for example, electron emission from the filter is completely suppressed and thus only the (positive) charge of the transported ion current is measured in a Faraday cup adjacent to or above the substrate. Typical values ​​of such a (positive) potential are in the range between tens of volts and several kilovolts.

[0215] In the case of energy filters which are very highly resistive due to their material composition, it is envisaged that the filter is provided on one or both sides with a thin, highly conductive layer with a thickness ranging from a few nanometers to tens of nanometers. When designing the filter, the stopping power of this layer must be introduced into the overall balance of the stopping power. Care must be taken to ensure that the applied layer (even when applied to the side facing away from the substrate) in principle cannot lead to any destructive contamination of the substrate material to be injected. For the processing of SiC substrates, this layer can consist of carbon, for example.

[0216] (b) Energy filter coated with a material with a high work function

[0217] In order to reduce strong thermal electron emission, it is envisaged that the energy filter is coated on one or both sides with a material having a high electron work function, thereby causing only the minimum possible thermal electron emission at a given temperature. The work function of some elements is as Fig.39 As shown in

[25] , Materials Science Poland, Vol. 24, No. 4, 2006. In particular, materials having a work function greater than 3.5 eV, greater than 4 eV or greater than 4.5 eV are suitable.

[0218] The stopping power of this layer should be included in the overall balance of stopping power calculated when designing the filter. Care must be taken to ensure that the applied layer (also when applied on the side facing away from the substrate) does not in principle lead to any harmful contamination introduced into the substrate material.

[0219] Point 12. Alternative production methods using injection molding, casting or sintering

[0220] Implantation filters can be produced by microtechnological methods such as photolithography in combination with wet-chemical or dry-chemical etching. In particular, anisotropic wet-chemical etching by alkaline etchants (e.g., KOH or TMAH) is used to produce filters from silicon. In this type of filter, the functional filter layer is made of single-crystal silicon. During bombardment with high-energy ions, the channeling effect can therefore influence the effective energy losses in the filter layer in a difficult to control manner. An example of how to avoid this effect will be explained below.

[0221] (a) In one example, for production by typical microtechnological methods, wet chemical anisotropic etching, which requires single-crystalline materials, is replaced by dry chemical etching, which means that polycrystalline or amorphous starting materials are used for the filter membrane. Due to its material structure, the obtained filter shows improved performance with respect to the channeling effect.

[0222] (b) In another example, a filter is provided which is not produced by the typical sequence of microtechnological methods, but by embossing, injection molding, casting or sintering. The core idea is to implement the above process in such a way that the mold or mold insert determines the final shape of the energy filter membrane. Now for the method in question, the selected filter material is processed in a familiar manner. That is, the desired geometry is given in a soft state (for embossing), liquid state (for injection molding and casting) or granular state (sintering) by means of predetermined casting molds, mold inserts, molds, etc.

[0223] One advantage of using the above method is that single-crystal filter membranes are generally not obtained, and channeling is therefore suppressed. Another advantage is that the range of available filter membrane materials is very large. For example, the use of sintered SiC filter membranes for producing a uniform doping profile in a SiC substrate is particularly advantageous.

[0224] Another advantage is that by using the above-described molding method, the costs of mass-producing filter elements can be significantly reduced compared to production costs by microtechnology.

[0225] Point 13. Irradiation of static substrates

[0226] A uniform energy-filtered radiation of a static substrate can be achieved by "wobbling" (= controlled deflection) of the ion beam before the filter, arranging the filter between the wobbling unit (= ion beam deflection system) and the static substrate; and choosing the right deflection angle and the distance d between the filter and the substrate (usually a few centimeters to a few meters), e.g. Fig.40 As shown in the example. Fig.40 A configuration for implanting a substrate through an energy filter is shown. This configuration comprises an ion beam deflection device arranged before the filter. For implantation purposes, the ion beam deflection that can be achieved by this deflection device is coordinated with the distance between the filter and the substrate (usually in the range of a few centimeters to a few meters) in such a way that the substrate can be fully irradiated, i.e. its entire surface can be irradiated.

[0227] Point 14. Configurations that utilize large filter surface areas

[0228] (a) Configuration where the entire filter surface is effective

[0229] Fig.41 A configuration for energy filter implantation (i.e. implantation through an energy filter) is shown, in which the ion beam is amplified by suitable measures and the irradiated filter surface area is larger than the substrate surface area, so that the substrate can be completely irradiated and a large filter surface can be utilized. The diameter of the irradiated filter area is larger than the diameter of the substrate. The substrate can be stationary or movable. Due to this configuration, large filter surfaces can be used (=reduced degradation effects and thermal effects in the filter) and it is ensured that the entire surface of the substrate can be irradiated. The use of this type of configuration is particularly advantageous in cases where the required filter structures are "large". For the doping of high-barrier Si-IGBTs or Si power diodes with protons, penetration depths of >100 μm are required. Therefore, for such applications, filter structures with a "tip height" of >100 μm must be provided. Even for large substrates (e.g. 6" or 8"), such filter structures can be produced very easily with sufficient mechanical stability.

[0230] In the configuration described herein, a certain minimum distance should be maintained between substrate and filter, which ensures that there is sufficient lateral homogenization of the implanted ions due to scattering effects.

[0231] (b) Configurations where the filter surface is partially inactive

[0232] First, the same configuration as described in section 14(a) is used: a configuration for energy filter implantation, in which the ion beam area is enlarged by suitable measures and the irradiated filter surface is larger than the substrate surface. However, the entire filter surface is not active here. Instead, only a certain part of the filter surface is active. This means that the filter consists of a configuration of multiple filter elements, for example in the form of strips. These filter elements can be made from the substrate in an integral form, for example, by suitable production methods. The other (inactive) part of the filter surface serves to stabilize the filter membrane. This part causes the ion beam to cast a shadow. In this configuration, the substrate or the filter must therefore be moved in order to compensate for the shadow effect. Due to this configuration, a large filter surface can be utilized (= degradation effects and thermal effects in the filter are reduced) and it is ensured that the entire surface of the substrate can be irradiated. Fig.42 A filter with inactive components and with mechanical scanning in one direction is shown.

[0233] Point 15. Modifying the doping profile in the substrate with the help of a sacrificial layer

[0234] In addition, a sacrificial layer of appropriately chosen thickness and barrier capacity can be applied to the substrate so that the implant profile migrates in the desired manner along the depth direction in the substrate. This type of sacrificial layer can be used for masked ion implantation (compare Fig.43 ), and can also be used for unmasked ion implantation. In particular, this method makes it possible to "push" the undesired beginning of the doping profile away from the substrate and into the sacrificial layer, ie to implant the beginning of the profile into the sacrificial layer.

[0235] Fig.43 The modification of the doping profile in the substrate obtained by means of a sacrificial layer in the case of masked energy-filtered implantation is shown. In the example shown here, the beginning of the implantation profile is pushed into the sacrificial layer. Fig.43 Conversely, this principle can be used analogously for unmasked energy-filtered ion implantation, ie for implantation in which no masking layer is present.

[0236] Point 16. Lateral modification of the doping profile in the substrate by means of a sacrificial layer

[0237] By applying to the substrate a suitably selected sacrificial layer of varying stopping power and thickness over the wafer surface, the implant profile can be shifted as desired in depth into the substrate as a function of lateral position on the wafer. This type of sacrificial layer can be used for both masked and unmasked ion implantation (compare Fig.44 ). In particular, a variation of the implantation depth of a uniform doping profile can be advantageously used for edge termination in semiconductor components.

[0238] Fig.44 The lateral modification of the doping profile in the substrate by a sacrificial layer in the case of unmasked energy-filtered ion implantation is shown. Here, the lateral modification of the implantation depth is achieved by varying the thickness of the sacrificial layer in the lateral direction. The principle can be used analogously for masked energy-filtered implantation.

[0239] Point 17. Applicability of distribution transitions between several injection distributions

[0240] Two or more doping profiles can be cleverly overlapped so that the desired overall doping profile is obtained, especially in the overlapping area. This technique is particularly advantageous for the growth and doping of multiple layers. A representative example consists of the growth of several SiC-epi layers and their energy-filtering doping. Good contact between the layers must be ensured.

[0241] Point 18. Special configuration of the multi-filter concept with coupled oscillating motion

[0242] Clever arrangements can be used so that despite coupled oscillatory motion of the filter and substrate, ie, no relative vertical movement between the filter and substrate, lateral uniformity of the ion distribution can still be achieved. Fig.45 A configuration of this type is shown in . The wafer is guided by rotation of the wafer wheel behind the substrate in the x-direction. The ion beam (not shown) expands, for example, in the x-direction and scans the entire multi-filter surface by a vertical oscillating movement of the implantation chamber. The filter surface consists of an effective filter area and an ineffective fixture area. Configuration (A) is an unfavorable configuration. When considering the irradiated filter surfaces for y1 and y2, three filters are irradiated at y1, while no filter is irradiated at all at y2. As a result, a laterally non-uniform stripe pattern is obtained on the wafer. Configuration (B) shows a possible example of a better configuration. Two filters are irradiated for both y1 and y2. This is true for all y. As a result, a laterally uniform doping on the wafer surface is achieved.

[0243] like Fig.45As shown, the vertical movement of the filter and the substrate in the y direction are coupled. By rotating the wafer wheel, the wafer is guided in the x direction along the back of the filter. The ion beam (not shown) is extended, for example, in the x direction and scans the entire multi-filter surface by the vertical oscillating movement of the implantation chamber. The filter surface consists of an effective filter area and an ineffective fixture area. Configuration (A) is a rather unfavorable configuration. When considering the irradiated filter surface for y1 and y2, three filters are irradiated at y1, while no filter is irradiated at all at y2. Therefore, a laterally non-uniform stripe pattern is obtained on the wafer. Configuration (B) shows a possible example of a better configuration. Two filters are irradiated for both y1 and y2. This is true for all y. Therefore, laterally uniform doping on the wafer surface is achieved.

[0244] Point 19. Monitoring

[0245] Another aspect aims to solve the problem of monitoring important parameters of the ion implantation modified by the energy filter. These parameters are, for example, the minimum or maximum "projected range", the depth concentration distribution determined by the filter geometry, and the (energy-dependent) angular distribution. The monitoring of other parameters such as the implanted ion species etc. may also be useful. In particular, monitoring should be possible on the wafer in which the ions are implanted or (simultaneously) on (several) structures near the wafer. According to one aspect, the monitoring should be carried out without the need for any further processing of the monitored structures or the wafer.

[0246] Monitoring can be performed by measuring optical parameters such as spectral absorption, spectral emission, spectral reflectance, refractive index change, global absorption (wavelength range depends on the measurement device) and global emission and reflectance (wavelength range depends on the measurement device).

[0247] According to one aspect, for monitoring the above-mentioned implantation parameters, a configuration of mask and substrate materials is provided, which (1) are arranged at suitable locations on the surface to be implanted, for example on a wafer wheel, and (2) due to ion implantation, for example in an "as-implanted" manner, i.e. without further post-treatment, change their optical properties in such a way that the change is proportional to the implanted ion dose of a given ion species. Such materials cited in (2) are, for example, PMMA (Plexiglas), PMMA, SiC, LiNbO3, KTiOPO4, etc.

[0248] In case the material optically sensitive to the ionizing radiation is at the same time the material of the target substrate, the target substrate (eg a SiC wafer) can be used directly for optical monitoring.

[0249] In addition to changes in optical properties, it is known that materials such as PMMA change their solubility in certain acids and solvents after ion irradiation. Therefore, the depth of the structure (or etch rate or etch geometry obtained, etc.) changed after ion irradiation can be used as a measure of the implanted ion dose.

[0250] Monitoring other changes in physical parameters by ion irradiation is conceivable. Such changes may include, for example, monitoring mechanical properties of the material, monitoring electrical properties of the material, or even monitoring nuclear physical activation of the material by high energy ion irradiation.

[0251] According to one aspect, the detection should be based on changes in optical properties. An embodiment of this type is described below. For the often occurring situation where no monitoring is performed on the target substrate to be implanted, an embodiment of a separate monitoring structure is envisaged. The monitoring structure consists of a configuration of a suitable substrate material with one or more mask structures. For example Fig.47 and 48 as shown in .

[0252] like Fig.46 As shown, one or more monitoring structures (monitoring chips) are arranged at a suitable location, such as on a wafer wheel. For example, the readout of the monitoring chip is completed after implantation without further post-processing. In some cases, the mask must be removed from the monitoring substrate to read the measurement value. According to one aspect, the mask is reusable.

[0253] The mask material and the substrate material of the monitoring chip can also be made of different materials. The criteria for selecting the mask material are, for example, its compatibility with the material of the target substrate (to exclude contamination caused by sputtering effects). Another criterion is the stopping power of high-energy ions, which allows the production of mask structures with high aspect ratios.

[0254] The mask material and the substrate material of the monitoring chip can also be made of the same material. The mask and the substrate can also be produced as a whole. In this case, it is usually not possible to reuse the mask or the substrate.

[0255] Performance and evaluation of masking structures after ion implantation:

[0256] 1. The performance of ion implantation modified by energy filters;

[0257] 2. Mask removal - possible but not absolutely necessary, since the readout measurement can also be performed by reflection from the rear surface of the substrate;

[0258] 3. Optical measurement:

[0259] a. Absorption spectrum, wavelength resolution

[0260] b. Transmission spectrum, wavelength resolution

[0261] c. Reflectivity, wavelength resolution

[0262] d. Simple global absorption, i.e. non-wavelength-resolved

[0263] e. Simple global emission, i.e. non-wavelength-resolved

[0264] f. Measurement of refractive index changes

[0265] g. Changes in polarization

[0266] 4. Compare with the calibration curve or reference standard to determine if the injection process was performed as expected.

[0267] By using the explained monitoring structure, the following injection parameters can be tested:

[0268] A. Depth-dependent dose

[0269] This is therefore a test for degradation of the filter and a test to determine if the injectant dosage is set correctly on the machine side.

[0270] B. Maximum / minimum projection range

[0271] It is therefore a test for the correct injection of energy, for filter degradation and for the correctness of the resulting filter structure.

[0272] C. Angular distribution of implanted ions

[0273] This is therefore a test for degradation of the filter, a test for correct formation of the filter, and a test for correct geometrical configuration in the injection chamber.

[0274] A. Monitoring the depth distribution of implanted ions

[0275] Point A. Depth-dependent dose

[0276] Figure 49-52 The monitoring of the depth distribution of the implanted ion dose set by the energy filter is shown as an example. In this example, the following simplifying assumptions apply:

[0277] -The change in optical properties is caused only by the local implanted ion dose and the inherent defects caused by it.

[0278] - ions, for example, only pass through the depth region III with ion concentration C1 ( Fig.51 ) (so that they reach concentration region C2) without causing further changes in the optical properties.

[0279] - It is conceivable that this change in optical properties might be observed precisely in PMMA, for example, due to electron blocking effects.

[0280] - This is not a problem in principle for the possibility of evaluation, but Fig.51 and 52 In the example, it is excluded for simplicity.

[0281] Fig.50 The mask structures shown or described in are staggered with respect to thickness and number, depending on the desired depth resolution, i.e. configured as "inclined planes" or as continuous slopes. Thus, for maximum thickness, for example, the following condition applies: "Thickness of the mask" > R p，max .

[0282] Depending on the requirements of the readout device, the lateral dimensions of the individual structures may be in the range of square micrometers to square millimeters to square centimeters.

[0283] Point B. Monitoring the maximum projection range

[0284] Fig.53 A structure suitable for monitoring the maximum projection range is shown.

[0285] A similar structure using the evaluation steps as described in A can also be used to measure or monitor the minimum projection range.

[0286] Point C. Monitoring the angular distribution of implanted ions

[0287] It is well known that energy filters used for ion implantation produce energy-dependent angular spectra of ions after they pass through the filter.

[0288] In principle, for monoenergetic ions arriving perpendicular to the filter surface, the resulting low-energy ions after the filter are indeed scattered more strongly than the high-energy ions.

[0289] The resulting angular distribution is therefore a function of the filter geometry, geometry changes during the filter's useful life, the incidence of channeling, the ion species used, the primary energy, the resulting maximum and minimum energies of the transmitted ions, and the geometric configuration in the implantation chamber. All of these parameters can be kept track of by monitoring the angular distribution.

[0290] In order to monitor a single parameter, different masking structures that can be arranged in the monitoring chip are proposed, such as Figure 55-58 As shown and described in .

[0291] It must be remembered that for the evaluation of the angular distribution, usually only the aspect ratio of the mask structure is important.

[0292] The dimensions of the openings in the mask structure of a thin mask which is only slightly thicker than the maximum projected area in the mask material can therefore lie in the micrometer or submicrometer range.

[0293] Such monitoring structures are preferably configured as an array consisting of many individual structures, so that an overall optical evaluation (i.e., within a few mm) can be performed. 2 or cm 2 on the surface of the ).

[0294] In contrast, for the same aspect ratio and mask thickness in the millimeter range, for example, the opening size can be in the millimeter or centimeter range. In these cases, individual structures that are not arranged in an array can also be evaluated without special technical effort.

[0295] Proposed mask structure:

[0296] 1. Fixed mask thickness, various geometric mask openings → aspect ratio changes;

[0297] 2. Variable mask thickness, fixed geometry of mask opening → change in aspect ratio;

[0298] 3. Combination of 1 and 2;

[0299] 4. By configuring several arrays (or single structures), each consisting of 1, 2 or 3 angles different from each other, the directional dependence of the angular distribution can be monitored.

[0300] A circular configuration is also conceivable.

[0301] like Fig.58 As shown, in addition to concentric circular rings, single circles and rings of various sizes are also particularly advantageous for monitoring the angular distribution of ions transmitted by the energy filter.

[0302] The core of the above-mentioned aspects is that the (substantially) dose-dependent modification of the (preferably) optical parameters of the material is to be used for the "as-implanted" monitoring of the energy filter implantation process. Thus, by optical measurements (for example), the implantation obtained can be monitored as completely as possible with respect to its most important parameters, without the need for any complex post-processing (e.g. annealing and application of metal contacts).

[0303] Defective implants can thus be detected cheaply and quickly, and the affected wafers can be identified.

[0304] Fig.59A clever adjustment of the distribution transition between the two injection distributions A and B is shown, so that the overall concentration distribution obtained can, for example, produce the desired uniform distribution. This can (but does not necessarily have to) be particularly advantageous for the layer system of two layers shown in the figure. It is envisaged to be achieved by the following process sequence:

[0305] (1) Doping the lower layer (implant B);

[0306] (2) Growth upper layer;

[0307] (3) Doping the upper layer. There are only limited possibilities for configuring the high-energy tail of implant A, but the low-energy tail of implant B can be influenced in particular by introducing a sacrificial layer as described in “Point 15. Modification of the doping profile in the substrate by means of a sacrificial layer”.

[0308] The idea is to implement this in the following order:

[0309] (1) Growth of sacrificial layer;

[0310] (2) doping the lower layer (implant B);

[0311] (3) removing the sacrificial layer;

[0312] (4) Growth upper layer;

[0313] (5) Doping the upper layer.

[0314] The concepts explained above make it possible to develop production-worthy implantation methods for the semiconductor industry, i.e., economical applications of implantation methods in industrial production processes. In addition to the uniform doping to be achieved by a simple triangular filter structure, the concepts explained in this article make it particularly possible to achieve complex vertical doping concentration profiles in a highly flexible manner (multi-filter concept) using low angular distributions of implanted ions. Specifically, all types of doping concentration profiles can be approximated by using a triangular filter structure in combination with a collimator structure. Another important aspect relates to the suppression of artifacts that interfere with the measurement of ion currents on the substrate.

[0315] In summary, it should be pointed out again that the measures described under points 1-19 above can be applied alone or in any desired combination with each other. For example, the explained "end of life" detection can be applied to filters installed in a frame, but it can also be applied to filters installed in some other way.

[0316] Furthermore, the wafer may be a semiconductor wafer, but it may also be composed of some other material to be implanted, such as PMMA.

[0317] References

[0318] [0]Energy filter for ion implantation systems.M.Rüb,Research Reportof the University of Applied Sciences(Ernst-Abbe-Hochschule)Jena, 2013 / 2014.

[0319] [2]Constantin Csato,Florian Krippendorf,Shavkat Akhmadaliev,Johannesvon Borany,Weiqi Han,Thomas Siefke,Andre Zowalla,Michael Rüb: Energy filterfor tailoring depth profiles in semiconductor dopingapplications.Nucl.Instr.Meth.,B,2015,

[0320] http: / / dx.doi / org / 10.1016 / j.nimb.2015.07.102.

[0321] [4]Investigation of dopant profiles,losses and heating using anenergy filter for ion implantation.Krippendorf,Csato,Rüb,DPG SpringConference, Dresden,March 2014.

[0322] [5]Energy filter for ion implantation.F.Krippendorf,C.Csato,T.Bischof,S.Bupta,W.Han,M.Nobst,University of Applied Sciences Jena;C.Ronning, Friedrich Schiller University Jena;R.Rupp,Infineon TechnologiesAG, Neubiberg;A.Schewior,University of Applied Sciences Jena;W.Wesch,Friedrich Schiller University Jena;W.Morgenroth,Institute for PhotonicTechnologies e.V.,Jena;M.Rüb,University of Applied Sciences Jena.MicrosystemTechnology Congress,Aachen,October 2014,“Energy filter for ion implantationsystems.Idea–preliminary experiments–Application,C.

[0323] [6]C.Csato,T.,Bischof,S.,Gupta,W.Han,F.Krippendorf,W.Morgenroth,M.Nobst,C.Ronning,R.Rupp,A.Schewior,W.Wesch,M.Rüb,June 12, 2013,Workshop“IonBeams–Research and Application”,2013,Leibnitz Institute for SurfaceModification,Leipzig;M.Rüb,B.Sc.,T.Bischof,M.Sc., C.Csato,B.Sc.,S.Gupta,B.Sc.,W.Han,M.Sc.,F.Krippendorf,B.Sc.,A.Schewior,B.Sc.,C. Energy filterfor ion implantation systems,research report of University of AppliedSciences Jena,2011 / 2012.

[0324] [7]EP 8 030 037A1.

[0325] [8]Rüb:Energy filter for high-energy ion implantation,IP.comDisclosure No.:IPCOM000018006D,original publication date:December 1,2001.Included in the prior art database:July 23,2003and Siemens AG,2001,SiemensTechnical Report,December 2001,9pages.

[0326] [9]DE 10 2011 075 350 A1.

[0327]

[10] J.Meijer,B.Burchard,High-energy ion projection for deep ionimplantation as a low-cost,high-throughput alternative for subsequent epitaxyprocesses.J.Vac.Sci.Technol.,B22(1).

[0328]

[11] U.Weber,G.Kraft:Design and construction of a ripple filter forsmoothed depth dose distribution in conformal particle therapy.Phys.Med.Biol.,44(1999),2765-2775.

[0329]

[12] Y.Takada et al.:A miniature ripple filter for filtering a ripplefound in distal part of a proton SOBP,Nuclear Instruments and Methods inPhysics Research A 524(2004)366-373.

[0330]

[16] DE 19 652 463 C2.

[0331]

[18] US 7,385,209 B2.

[0332]

[19] US 2002-0050573 A1.

[0333] [19-1]Energy filter for ion implantation systems.M.Rüb,researchreport of the University of Applied Sciences Jena,2013 / 2014.

[0334] [19-2]DE 102 39 312 B4

[0335]

[25] Materials Science-Poland,Vol.24,No.4,2006.

[0336]

[26] M.Nastasi et al.:Ion-Solid Interactions.Fundamentals andApplications.Cambridge University Press,1996.

[0337]

[27] O.Osman:Irradiation effects of swift heavy ions inmatter.Dissertation,Essen,2011。

Claims

1. An implantation device for implanting ions into a target substrate, the device comprising: filter framework, a filter held by the filter frame, the filter configured to be irradiated by an ion beam passing through the filter, and A collimator structure is arranged on the filter, or arranged in the transmitted beam after the filter, or arranged on the target substrate.

2. The injection device according to claim 1, wherein The collimator structure is arranged on the filter, and wherein the collimator structure is attached to the filter by using an adhesive or by bonding, or wherein the collimator structure is formed integrally with the filter.

3. The injection device according to claim 2, wherein: The collimator structure is arranged downstream of the filter with respect to the direction of the ion beam.

4. The injection device according to claim 3, wherein: The collimator structure is arranged on the structured side of the filter.

5. The injection device according to claim 1, wherein The filter frame is fixed in the filter holder.

6. The injection device according to claim 5, wherein: The collimator structure is arranged on the filter holder in the transmitted beam after the filter.

7. The injection device according to claim 1, wherein: The collimator structure includes a plurality of collimator units arranged in a predetermined pattern.

8. The injection device according to claim 7, wherein: The collimator units form a layered structure or a grid in a top view.

9. The injection device according to claim 7, wherein: The collimator unit is rectangular, circular, elliptical, hexagonal, or has other polygonal geometric shapes in a top view.

10. The injection device according to claim 7, wherein: At least one of the collimator units comprises a tube having a length and a width, wherein a ratio of the width to the length is less than 1, less than 2, less than 5 or less than 10.

11. The injection device according to claim 1, wherein: The collimator structure is disposed on the target substrate, wherein the collimator structure is formed as a hard mask on the target substrate.

12. A method for doping a target substrate, comprising: Ions are implanted into the target substrate by irradiating the target substrate with an ion beam using an implantation apparatus, the implantation apparatus comprising: filter framework, a filter held by the filter frame, the filter configured to be irradiated by an ion beam passing through the filter, A collimator structure is arranged on the filter, or arranged in the transmitted beam after the filter, or arranged on the target substrate.

Images