System to inspect, modify or analyze a region of interest of a sample by charged particles, set of systems to inspect, modify or analyze a region of interest of a sample and method to inspect, modify or analyze a region of interest of a sample by charged particles

Abstract

A system inspects, modifies or analyzes a region of interest of a sample via charged particles. A detector device of the system produces a pixel image having horizontal and vertical pixel resolutions. A charged particle deflection device produces a scanning charged particle beam in a scanning region. The deflection device has horizontal and vertical deflection units controlled by a digital to analog converter having a digital resolution larger than the horizontal pixel resolution and/or the vertical pixel resolution. An operator control interface of the system selects an assignment between respective image pixels of a desired pixel image and digital inputs of the DAC to produce horizontal and/or vertical deflection signals to guide the charged particle beam to the location of the respective image pixel. A reliable image of a sample can be obtained even when there is zooming or panning within an accessible region of the sample.

Claims

1. A system configured to inspect, modify or analyze a region of interest of a sample via charged particles, the system comprising: a charged particle column comprising a charged particle generating device and a charged particle deflection device configured to produce a scanning charged particle beam in a scanning region in which the region of interest is disposable; a sample chamber comprising a sample stage; an alignment subsystem configured to prealign the sample on a sample holder to be later mounted on the sample stage in the sample chamber, the alignment subsystem comprising: an external kinematic mount configured to temporally receive the sample holder, the external kinematic mount having a lateral positioning repeatability relative to the sample holder which is better than 200 um, the external kinematic mount being located external to the sample chamber; an external imaging device to acquire a relative lateral position of the sample on the sample holder when mounted to the external kinematic mount; a fine adjustment device to finely adjust the relative lateral position of the sample on the sample holder when mounted to the external kinematic mount; and a locking unit to lock the sample on the sample holder at a chosen relative lateral position after fine adjustment; an internal kinematic mount to receive the sample holder on the sample stage, the internal kinematic mount having a lateral positioning repeatability relative to the sample holder which is at least the positing repeatability of the external kinematic mount, the internal kinematic mount being located within the sample chamber; and a transfer unit to transfer the sample locked to the sample holder from the external kinematic mount to the internal kinematic mount.

2. The system of claim 1, wherein the charged particle column comprises a member selected from the group consisting of a focused ion beam subsystem and a scanning electron microscopy subsystem.

3. The system of claim 1, wherein the external imaging device comprises a member selected from the group consisting of an optical microscope, an infrared microscope, and a fluorescence microscope.

4. The system of claim 1, wherein the sample stage is configured to enable less than 500 micrometers of relative movement between the sample holder and a frame of the system.

5. A set of systems configured to inspect, modify or analyze a region of interest of a sample via different schemes comprising inspection, modification or analysis by charged particles, wherein: one the systems is a system according to claim 1; and each system comprises: a charged particle column to inspect, modify or analyze a sample in a region in which the region of interest is disposable; a sample chamber having a sample stage, wherein the systems of the set share; a common alignment subsystem configured to prealign the sample on a sample holder to be later mounted on the sample stage in the sample chamber, the alignment subsystem comprising: an external kinematic mount configured to temporally receive the sample holder, the external kinematic mount comprising a lateral positioning repeatability relative to the sample holder which is better than 200 um, the external kinematic mount being located external to the sample chamber; and an external imaging device configured to acquire a relative lateral position of the sample on the sample holder when mounted to the external kinematic mount; a fine adjustment device configured to finely adjust the relative lateral position of the sample on the sample holder when mounted to the external kinematic mount; and a locking unit configured to lock the sample on the sample holder at a chosen relative lateral position after fine adjustment; and an internal kinematic mount to receive the sample holder on the sample stage, the internal kinematic mount having a lateral positioning repeatability relative to the sample holder which is at least the positing repeatability of the external kinematic mount, and the internal kinematic mount being located within the sample chamber.

6. A method, comprising: providing the system of claim 1; attaching a sample to the sample holder; mounting the sample holder to the external kinematic mount; acquiring a relative position of the sample on the sample holder using the external imaging device; fine adjusting the relative position of the sample on the sample holder using the fine adjustment device to enable inspection, modification or analysis of the region of interest in a subsequent inspection, modification or analyzing step; locking the sample on the sample holder after fine adjustment; transferring the sample holder with the finely adjusted sample from the external kinematic mount to the internal kinematic mount inside a sample chamber of the system; inspecting modifying or analyzing the region of interest of the sample with the system; unloading the sample on the sample holder from the internal kinematic mount from the system, and allowing a time to pass; and reloading the sample into the same system and finding the region of interest within 500 um of the scanned region.

7. The system of claim 1, wherein: the charged particle column comprises a member selected from the group consisting of a focused ion beam subsystem and a scanning electron microscopy subsystem; and the external imaging device comprises a member selected from the group consisting of an optical microscope, an infrared microscope, and a fluorescence microscope.

8. The system of claim 7, wherein the sample stage is configured to enable less than 500 micrometers of relative movement between the sample holder and a frame of the system.

9. The system of claim 1, wherein: the charged particle column comprises a member selected from the group consisting of a focused ion beam subsystem and a scanning electron microscopy subsystem; and the sample stage is configured to enable less than 500 micrometers of relative movement between the sample holder and a frame of the system.

10. The system of claim 1, wherein: the external imaging device comprises a member selected from the group consisting of an optical microscope, an infrared microscope, and a fluorescence microscope; and the sample stage is configured to enable less than 500 micrometers of relative movement between the sample holder and a frame of the system.

11. The system of claim 1, wherein the sample stage is configured to allow a range of motion of at most one millimeter in a first direction, and the sample stage is configured to allow a range of motion of at most one millimeter in a second direction perpendicular to the first direction.

12. The system of claim 1, wherein the sample stage comprises a piezo mechanical flexure stage.

13. The system of claim 1, wherein the sample stage is rigidly fixed to a frame of the system.

14. The system of claim 13, wherein the sample stage prevents relative movement between the sample holder and the frame of the system.

15. The set of systems of claim 5, further comprising a transfer unit locked to the sample holder from the external kinematic mount to the internal kinematic mount.

16. The set of systems of claim 15, wherein the systems share the transfer unit.

17. The method of claim 6, wherein the period of time is at most 10 minutes.

18. The method of claim 6, wherein the period of time is at least one day.

19. The method of claim 6, wherein the sample is reloaded with a higher precision compared to a precision with which the sample was originally placed during the initial inspection, modification or analyzing.

20. The method of claim 6, wherein the sample is reloaded into the system with a repeatability of positioning that is greater than one millimeter.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Illustrative embodiments of the disclosure herein after are described with respect to the accompanying figures, in which:

(2) FIG. 1 shows in a schematical sectional view an embodiment of an inspection system to inspect a region of interest of a sample by charged particles;

(3) FIG. 2 also in a schematical sectional view components of an alignment subsystem to prealigne a sample on a sample holder including an external kinematic mount to temporally receive the sample holder;

(4) FIGS. 3 and 4 momentary situations of a process to produce a sample holder and an external kinematic mount according to FIG. 2;

(5) FIG. 5 one example of an assignment between (1) a two dimensional bit space spanned up by the digital to analog converters (DACs) of a horizontal deflection voltage generating unit and of a vertical deflection voltage generating unit of a charged particle deflection device of the inspection system and (2) a corresponding pixel image of the sample, wherein each adjacent pixel in the pixel image corresponds to an increment of 1 bit in the DAC code of the bit space, wherein this assignment is an example of certain known technology;

(6) FIG. 6 in a depiction similar to that of FIG. 5 an assignment between the bit space and the pixel image according to the disclosure, wherein the adjacent pixel in the pixel image correspond to an increment of 1024 bits in the DAC code;

(7) FIG. 7 in a depiction similar to that of FIG. 5 an assignment between the bit space and the pixel image according to the disclosure, wherein each adjacent pixel in the pixel image corresponds to an increment of 512 bits in the DAC code;

(8) FIG. 8 in a depiction similar to that of FIG. 5 an assignment between the bit space and the pixel image according to the disclosure, wherein the adjacent pixel in the pixel image corresponds to an increment of 100 bits in the DAC code;

(9) FIG. 9 in a depiction similar to that of FIG. 5 an assignment between the bit space and the pixel image according to the disclosure, wherein the adjacent pixel in the pixel image corresponds to an increment of 100 bits in the DAC code, wherein further the pixel image is shifted as compared to FIG. 8.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

(10) An inspection system 1 serves to inspect a region of interest (ROI) 2 of a sample 3 by charged particles 4, e.g. ions and/or electrons. The system includes a charged particle device 5, e.g. a scanning electron microscope (SEM) or a focused ion beam (FIB) device. The charged particle device 5 is designed as a column and is mounted on a frame 6 of a sample processing chamber 7. The charged particle device 5 has a charged particle generating unit 8 followed by a charged particle deflection device 9 to produce a scanning beam of the charged particles 4 in a scanning region in which the ROI 2 can be placed.

(11) To facilitate the description of orientations and dimensions, in the following a Cartesian xyz coordinate system is used. In FIG. 1 the x axis is directed to the right. The y axis is directed perpendicular to the drawing plane away from the view and the z axis is directed upwards.

(12) The deflection device 9 is connected to a horizontal deflection voltage generating unit 10 and a vertical deflection voltage generating unit 11. The horizontal deflection voltage generating unit 10 produces a horizontal deflection voltage for horizontal scanning movement, i.e. movement in +/?x-direction of the charged particle beam. The vertical deflection voltage generating unit 11 produces a vertical deflection voltage for vertical scanning movement, i.e. movement in the +/?y-direction of the charged particle beam.

(13) The deflection voltage generating units 10, 11 are part of a control electronics 11a which is in signal connection with further components of the system 1 as described below. Such signal connection is visualized in FIG. 1 with double arrows.

(14) The horizontal deflection voltage generating unit 10 includes a digital to analog converter (DAC) 12. The vertical deflection voltage generating unit 11 includes a digital to analog converter (DAC) 13. The DACs 12, 13 are contained within the adjacent control electronics 11a and are part of the deflection voltage generating units 10 and 11. The horizontal deflection is provided by the horizontal deflection voltage generating unit 10 within the control electronics 11a including the DAC 12. The vertical deflection is provided by the vertical deflection voltage generating unit 11 within the control electronics 11a including the DAC 13.

(15) Further, the inspection system 1 has an imaging detector 14 to produce a pixel image of the ROI 2 having a horizontal pixel resolution and vertical pixel resolution. Such imaging detector 14 herein after also is referred to as a detector device or as an image control device. The image detector 14 is in signal connection with the control electronics 11a.

(16) On the right hand side of FIG. 6 an example of such pixel image 15 is shown with an exemplified sample structure image 16 having the shape of the letter F. The pixel image 15 has a total of 1024?1024 image pixels. The pixel image 15 has a horizontal pixel resolution and a vertical pixel resolution of 1024?1024. Such pixel image resolution thus is 10 bit.

(17) In a further embodiment, the horizontal pixel resolution of the pixel image 15 may be different to its vertical pixel resolution.

(18) The DACs 12, 13 of the deflection voltage generating units 10, 11 have a digital resolution which is larger than the corresponding horizontal and vertical pixel resolution.

(19) The digital resolutions of the DACs 12, 13 may be 20 bit as is exemplified in a bit space 17 also shown in FIG. 6. Such bit space includes in both directions x, y 2.sup.20=1048575 bits.

(20) The digital resolution of the DACs 12, 13 may be at least two times larger than the pixel resolution.

(21) The pixel resolution of the pixel image 15 and/or the digital resolution of the DACs 12, 13 may be described by a power of 2. Some SEM or FIB instruments might achieve a beam deflection with currents in coils rather than with voltage on electrodes. In such case, the signals from the DACs 12, 13 are simply converted to currents.

(22) The deflection voltage output of the DACs 12, 13 may be in a range between ?10 V and +10 V.

(23) A setting time of a setting of a chosen voltage output value of the DACs 12, 13 may be 1 ?s at most.

(24) The control electronics 11a includes an image zoom capability 18 and an image shifting capability 19 which are exemplified as respective units 18, 19. The image zoom capability 18 serves to alter an image magnification of the ROI 2. The image shifting capability 19 serves to alter an image position within the ROI 2.

(25) The inspection system 1 further includes an operator control interface 20 being in signal connection with the control electronics 11a which is further connected to the image detector device 14. The operator control interface 20 herein after also is referred to as an image selecting device. The capabilities or units 18, 19 may be part of the image selecting device 20 or (as shown) of the control electronics 11a.

(26) The image selecting device 20 allows the operator or automated software algorithms to select an assignment between respective image pixels of the chosen pixel image 15 and digital inputs of the DACs 12, 13 to produce horizontal and vertical deflection voltage output values used to guide the charged particle beam to the location of the respective image pixel. In particular, the imaging selecting device 20 or operator control interface allows the operator to select an assignment between individual x and y pixels of the desired image 15 and the horizontal and vertical DAC output values within the bit space 17. Such assignment is simplified through a graphical user interface that allows the user to specify intuitive variables like image resolution, image field of view (FOV), and x and/or y image shift, and possibly rotations or distortions of the image. Once such assignment is established, the image acquisition proceeds with the DACs 12, 13 generating the output values to guide the charged particle beam to the location of the respective image pixel.

(27) To produce the voltage outputs via the DACs, no amplifier interchange is necessary within the whole bit space 17 provided by the DACs 12, 13.

(28) The respectively selected assignment via the operator control interface may include an approximation step to choose between different possible digital inputs which are close to the desired deflection voltage output value. For example, such approximation step helps to decide whether a bit x.sub.i, x.sub.i+1 and/or y.sub.i, y.sub.i+1 of the bit space 17 is the appropriate one to approximate the desire x/y voltage output value.

(29) Such approximation provided by the operator control interface may include a randomization process. Further, such assignment may include a provision of image correction demands.

(30) The working principle of the image selecting device 20 further is described by reference to FIGS. 5 to 9.

(31) FIG. 5 shows a certain known assignment between a bit space 21 of DACs and a pixel image 22 in a system of the certain known technology. Here, each adjacent pixel in the pixel image 22 corresponds to an increment of 1 bit in a code of the respective DAC. Both the bit space 21 and the pixel image 22 have a 1024?1024 resolution.

(32) FIG. 6 to 9 show different pixel image selection results provided by the operator control interface 20 of the inspection system 1 according to the disclosure.

(33) In FIG. 6 each adjacent pixel in the image 15 (image pixel increment=1) corresponds to an increment of 1024 bit in the DAC code of the bit space 17.

(34) An integral and differential linearity of the DACs 12, 13 may be better than 1 least significant bit (LSB). In the FIG. 6 embodiment the full bit space 17 is programmed via the operator control interface 20 to produce output voltages with DAC code increments of 1024 bits. The 1024 resulting bit use of e.g. the horizontal DAC 12 would be 0, 1023, 2047, . . . 1048575. By an alternative assignment, also a pixel image with a pixel resolution more than 1024?1024 is possible, i.e. 2048?2048, 4096?4096, . . . until even 1048576?1048576.

(35) FIG. 7 shows the situation where a central ? area 23 of the available bit space 17 is used to generate output voltages assigned to respective pixels of a magnified pixel image 24. An increment of each DAC value of the bit space 17 within such central area 23 would then be 512. Accordingly, the resulting pixel image 24 has a magnification of 2? as compared to the pixel image 15 of FIG. 6. No change of an amplifier is necessary to achieve this magnification change.

(36) FIG. 8 shows a further magnification example, where a further limited central area 25 of the bit space 17 corresponding to a DAC bit increment of 100 to produce a pixel image 25a again with pixel resolution of 1024?1024. Such DAC bit increment of 100 corresponds to a magnification of approximately 10?. Accordingly, a small section of the overall structure 16 is now shown in the pixel image 25a.

(37) Of course, via different selections of the DAC bit increment via the operator control interface 20 also other magnifications up to a magnification value of 1000? is possible.

(38) The selection of the magnification is achieved using the image zoom unit 18 of the operator control interface.

(39) With respect to FIG. 9 the operation of the operator control interface 20 together with the image shifting unit 19 is exemplified. Here, a respective assignment between the respective image pixels of the image 26 and the digital inputs according to the DAC bit values in the bit space 17 is set via the image shifting unit. In the FIG. 9 embodiment, this is done by shifting the area 25 of FIG. 8 to a new shifted position resulting in a shifted bit area 27 within the bit space 17. Within such shifted bit area 27, the DAC bit increment also is 100 as in the FIG. 8 embodiment. So while the magnification of the image 25a is unchanged relative to 26, a different region of the sample has been imaged. Such image shift also does not require an interchange between different voltage amplifiers.

(40) Further, the inspection system 1 includes an alignment subsystem 31 whose main components are shown in FIG. 2. Such alignment subsystem 31 serves to prealign the sample 3 on a sample holder 32 externally, whereas such sample holder 32 later is mounted on an internal kinematic mount 33 of a sample stage 34 of the inspection system 1.

(41) The alignment subsystem 31 includes an external kinematic mount 35 to temporally receive the sample holder during the alignment of the sample 3 relative to the sampler holder 32. The external kinematic mount 35 is located external to the sample chamber 7. The external kinematic mount has recesses 36 in which hardened balls 37 are pressed during manufacturing of the external kinematic mount 35. In FIG. 2, two of such recess/ball pairs 36, 37 are shown. Also another number of such pairs, in particular three recess/ball pairs 36, 37, is possible. This serves as an example of a kinematic mounting system where the sample holder can be positioned repeatedly. Other designs might include cylinders, cones, or even magnets to assure repeatable positioning.

(42) FIGS. 3 and 4 show momentary situations during the manufacturing of the external kinematic mount 35. The internal kinematic mount 33 may be manufactured in the same way.

(43) FIG. 3 shows the external kinematic mount 35, the balls 37 and the sample holder 32 as raw prefabricated parts.

(44) After positioning of the balls 37 in the raw recesses 36 of the external kinematic mount 35, counter recesses 38 which are provided in the sample holder 32 are aligned to the prepositioned balls 37. To each recess 36 of the external kinematic mount 35 a dedicated counter recess 38 of the sample holder 32 is aligned. After such alignment, the external kinematic mount 35 and the sample holder 32 are pressed together with an impressing force F.sub.i (FIG. 4). During such impressing step, the balls 37 are pressed into the respective recesses 36 in the external kinematic mount. Such impressing relative position of the ball 37 to the recesses 36 is such that the respective balls 37 perfectly fit to their respective counter recesses 38. After the impressing step of FIG. 4 the fabrication of the kinematic positionally assigned components of the sample holder 32 and the external kinematic mount 35 is completed. Such external kinematic mount provides a repeatable dismounting and remounting of the sample holder with position repeatability of the sample holder 32 with respect to the external kinematic mount 35 or the internal kinematic mount 33 which is better than 500 um, such position repeatability may be better than 100 um, may be better than 20 um and also might be better than 2 um and in particular might be better than 1 um.

(45) In particular, the lateral positioning repeatability in the x and/or in the y direction is better than the ?m values given above.

(46) Further, the alignment subsystem 31 has an external imaging device 39 to acquire a relative position, in particular a relative lateral position, of the sample 3 on the sample holder 32 when mounted to the external kinematic mount 35. The external imaging device 39 may be an optical microscope, an infrared (IR) microscope or a fluorescence microscope.

(47) Further, the alignment subsystem 31 has a x and y fine adjustment device 40 to adjust the relative lateral position of the sample 3 on the sample holder 32 when mounted to the external kinematic mount 35.

(48) Further, the alignment subsystem 31 includes a locking unit 41 to lock the sample 3 on the sample holder 32 at a chosen relative lateral position after fine adjustment via the fine adjustment device 40.

(49) In one embodiment, the x and y positioning device 40 is realized as x and y precision micrometers which cause the sample 3 to slide across the sample holder 32. In another embodiment, the positioning device 40 is realized as a motorized lead screw or a piezomechanical positioning system. Generally, the operator would cause the sample to be adjusted while absorbing its position with the viewing microscope, i.e. the external imaging device 39, until a recognizable feature of interest or fiducial is observed. The sample 3 is then locked or mechanically attached to the sample holder 32. This attachment can be achieved with a temporary adhesive as is customarily used in microscopy to affix samples to holders. Examples include silver paint, carbon paint, epoxy, glue, mechanical clamping mechanisms or magnetic clamping mechanisms.

(50) The external imaging device 39 may be aligned relative to the external mount 35 in the same way that the charged particle beam 4 is positioned relative to the internal mount 33.

(51) With the same process steps as described above with respect to FIGS. 3 and 4, the internal kinematic mount 33 of the sample stage 34 is produced. During such production, the same sample holder 32 may be used which also was used during production of the external kinematic mount 35. The internal kinematic mount 33 also has recesses 36 and balls 37. The internal kinematic mount 33 serves to receive the sample holder 32 on the sample stage 34. The internal kinematic mount 33 has a lateral positioning repeatability regarding the lateral x/y positioning of the internal kinematic mount 33 relative to the sample holder 32 which is comparable to the positioning repeatability of the external kinematic mount 35. The internal kinematic mount 33 is located within the sample chamber 7.

(52) Further, the inspection system 1 includes a transfer unit 42 schematically shown in FIG. 2 which serves to transfer the sample 3 locked to the sample holder 32 from the external kinematic mount 35 to the internal kinematic mount 33 via a respective air lock (not shown) of the sample chamber 7.

(53) Depending on the specific embodiment, the sample stage 34 may be mounted to a moving stage 43 permitting a very limited relative movement between the sample holder 32 and the frame 6 of the inspection system 1.

(54) The alignment subsystem 31 may be shared by several systems for which the system 1 is an example. The systems sharing the alignment subsystem 31 may constitute a set of systems to inspect, modify or analyze the ROI 2 of the sample 3 by different schemes through the use of charged particles. Further, all of the individual systems include an internal kinematic mount similar to the internal kinematic mount 33. All of these individual systems of the set share the alignment subsystem 31.

(55) In a method to inspect the region of interest 2 of the sample 3 using the inspection system 1, the sample 3 rests on top of the sample holder 32. Then, the sample holder 32 is mounted to the external kinematic mount 35. After that, the relative position of the sample 3 on the sample holder 32 is acquired using the external imaging device 39. Then a fine adjusting of the relative position of the sample 3 on the sample holder 32 takes place using the fine adjustment device 40. Such adjustment is such that a given relative position results which enables an inspection of the ROI 2 in a subsequent inspection step. After such adjustment, the sample 3 on the sample holder 32 is locked using the locking unit 41 to fix the relative position of the sample 3 on the sample holder 32. Then the sample holder 32 with the finely adjusted and locked sample 3 is transferred from the external kinematic mount 35 to the internal kinematic mount 33 using the transfer unit 42. After that, the region of interest 2 of the sample 3 is inspected with the respective system.

(56) The inspection system 1 further has a gas injection subsystem 45 including a gas duct 46 for delivery of a process gas to the ROI 2, a shut off valve 47 within such gas duct. The process gas is delivered via a heated crucible 48 which is in gaseous connection with the gas duct 46.

(57) Further, the sample chamber 7 is in fluid connection to a vacuum pump 50 via a pump channel 49 being connected to the sample chamber 7.