JP4719554B2 - Focused ion beam device - Google Patents

Description

  The present invention relates to a focused ion beam apparatus using a gas assist process for performing deposition and etching, and a sample processing method using the focused ion beam apparatus.

  A focused ion beam (FIB) apparatus scans an FIB on the surface of the sample, drills the surface of the sample by sputtering, blows a film source gas onto the sample, and scans the FIB for protection. This is an apparatus for depositing a metal film for adhesion or performing etching by blowing an etching gas to make the processed surface uneven by making the processed surface uneven by the difference in etching rate depending on the substrate constituent material. Observation and microfabrication devices such as FIB with scanning electron microscope (SEM) and FIB with scanning transmission electron microscope (STEM) are mainly used only in offline defect analysis departments. In recent years, however, in addition to this, the wafer was taken out in the middle of the process, and after cross-sectioning a certain point, it was observed by SEM on the spot to check for connection voids due to contact voids and residual film. Used for process monitoring to observe process performance, and for in-depth analysis, take out a micro sample containing a defective part out of the device, fill the hole after cross-section processing, and return it to the process line again Is also progressing. It is necessary to feed back the results of defect analysis by these devices to the production process quickly and take measures against defects. The reason is to minimize the loss due to defects and improve the yield. For this reason, improving the throughput of the apparatus and reducing the down time have become particularly important in recent years.

  In a series of cross-sectional observation and microsample taking operations, the gas assist processing operation for performing deposition and etching processing and the probe contact operation for taking out the microsample take a large proportion of time. How this processing time can be shortened is important in improving the throughput. In Japanese Patent Laid-Open No. 2005-108472, the optical system settings (magnification, etc.) and beam residence time are set so that an optimum scanning method can be obtained based on the scan period dependency of the deposition rate and etching rate stored in advance for a desired beam irradiation region. The scanning interval is determined. A method is disclosed in which the deposition rate is set to the optimum beam stay time, the scanning interval is adjusted to the beam diameter, and the scanning cycle is set to the optimum value to obtain the maximum value. Japanese Patent Laid-Open No. 2002-210581 calculates the amount of gas consumed by automatic processing, and if the remaining gas amount is insufficient to complete all registered processes, an alarm is issued and the wafer is not processed. It is described to do so. In Japanese Patent No. 2829232, the pressure in the processing chamber is monitored, the gas control valve is controlled to open and close based on the pressure, the ion beam is irradiated with a high-intensity ion source, and the local reaction is performed by reacting with the gas. Is described.

JP 2005-108472 A JP 2002-210581 A Japanese Patent No. 2829232

As a result of intensive studies on the prior art by the present inventors, the following three problems have been recognized.
(1) Gas assist (deposition, etching process) processing speed is low.
Conventionally, in gas assist processing, since the processing conditions are not optimum, the processing speed is slow and the processing takes time. Therefore, the throughput of the apparatus has been reduced. Further, even if the processing conditions that give the fastest processing speed are obtained on a trial basis, the processing speed is lowered because the processing conditions deviate from the optimal conditions due to the change of the beam over time.

  FIG. 19 shows a scanning method of the focused ion beam 11. FIG. 19A is a perspective view, and FIG. 19B is a top view. The focused ion beam 11 is scanned at a beam scanning interval 82 within the beam scanning region 81 of the sample surface 10. When viewed from above, the beam 11 stays for a certain time (beam staying time), then moves by the beam scanning interval, and scans the entire field of view (scanning region).

  FIG. 20 is a diagram showing the characteristics of the deposition rate, with the beam scanning interval on the horizontal axis and the deposition rate on the vertical axis. As shown in this figure, the deposition rate becomes maximum at the scanning interval≈beam diameter. When the beam diameter becomes larger than the scanning interval, the effect of sputtering becomes remarkable at the overlapping portion, and the deposition rate decreases. Conversely, when the beam diameter becomes smaller than the scanning interval, the average deposition rate also decreases. The beam diameter at the processing point varies depending on the following factors.

(a) Change in beam diameter with time of ion source FIG. 18 shows a structural diagram of an LMIS (liquid metal source). The surface of the emitter 110 of the LMIS is initially covered with the ionized material 111, but the sputtered matter 112 from the extraction electrode 113 and the beam aperture 114 is attached by the irradiation of the focused ion beam 11. When the sputtered material 112 adheres to the beam emission point, the beam divergence angle changes, so that the beam diameter may change at the processing point. In both the beam aperture 114 and the variable aperture 102, the hole diameter is initially increased due to the sputtering phenomenon caused by beam irradiation. As the hole diameter increases, the beam reduction magnification is constant, so the beam size at the processing point changes. In this case, it is possible to recover to a certain level by flashing temporarily until the lifetime of the LMIS, but the deterioration proceeds.

(b) Beam diameter change due to change of optical system with time When sputter processing is performed, the sputtered material is reattached around the processing point. When spatter adheres to parts around the beam trajectory and the material is an insulator, the charged ion beam trajectory changes due to the electric force to charge, increasing off-axis aberrations, reducing resolution, and defocusing. This causes problems such as misalignment. Such an abnormality can be adjusted by the beam adjustment by the operator if the degree is large, but if it occurs between the beam adjustment operations, or if it cannot be recognized by the operator, it is processed in a state where the deposition rate and the etching rate are reduced. Cause a decrease in throughput.

(c) Beam diameter change due to sample height change When the processing position (height) changes due to the sample height change, the beam irradiation optical conditions (beam extraction system, focusing lens system, objective lens conditions, etc.) are the same. However, the beam diameter at the processing point changes. When the optical system is simplified, the light source image is formed at the processing point by the objective lens. The beam size at the processing point is a function of the distance B between the objective lens principal point and the processing point when the focal length f of the objective lens is constant. When B changes, the focus shifts and the beam size at the processing point changes. Depending on the processing conditions, a change in image (beam at the processing point) size due to the difference in B may be a problem.

(2) The processing speed until a microsample including a defective part is cut out and taken out is slow.
In a series of processes in which the microsample is cut out from the wafer and taken out of the apparatus, the probe is brought into contact with the cut out microsample, and a tungsten deposit is adhered in the vicinity of the contact point to be removed from the wafer. Next, in order to take this sample out of the apparatus, there is a step of adhering to the cartridge and cutting off the probe. Conventionally, in order to shorten the processing time, the distance to the wafer is measured by the Z sensor, and the probe is moved at a high speed to a position near the microsample from the measurement result, and then contacted to protect the probe. Until then, the movement speed was reduced.

  FIG. 21 shows the reflected light when a single wavelength 115 such as a laser beam is incident on the patterned wafer. In the drawing, for the sake of simplicity, the path change due to refraction at the time of entering and exiting the resist 119 is ignored. In addition, the pattern is a single layer, but in reality, it is almost a multilayer. In the case of a wafer with a pattern, as shown in the drawing, the Z sensor has a reflected light 116A on the surface of the resist or the like and a reflected light 116B on the internal silicon wafer when the silicon wafer 10 has a resist, oxide film 119 or the like. Since the light is incident on the light receiver 117, the center of gravity of the light 120 incident on the sensor that is the light receiver 117 is shifted, and a measurement error is generated. Further, the same measurement error as described above occurs even when patterns having different reflectivities are dense. In order to prevent this, there is a method of reducing this error by using a multi-wavelength light source. However, in order to obtain a constant amount of reflected light, it is necessary to increase the incident angle of the Z sensor and take up installation space. In some cases, the installation may be impossible.

  As described above, since the measurement accuracy is low, in order to prevent the probe from being damaged, the probe is moved over the sample with considerable likelihood. As a result, the distance until the probe is brought into contact with the probe is increased, and it takes time to move the probe, which is an obstacle to high-speed sampling processing.

(3) Due to a decrease in measurement accuracy due to changes in the contact condition of the temperature sensor immediately after maintenance, the gas passage temperature falls below the gas sublimation temperature, the gas re-solidifies, reattaches inside the nozzle, and the gas nozzle is clogged. There are things to do. In addition, with the use of the gas source, the gas may decrease and the gas supply amount to the processing point may decrease. In either case, the supply amount of gas source molecules decreases, and the processing speed decreases. When the degree of vacuum in the sample chamber is not monitored, for example, when depositing is performed, the sputtering effect has an advantage over the depositing due to the lack of the gas source, the defective part is scraped, and the cause of the defect cannot be specified. The problem of becoming may occur. In addition, when etching is performed, there is a problem in that a sufficient etching rate cannot be obtained or a difference in etching rate due to constituent materials cannot be obtained, so that a sufficient contrast cannot be obtained.

  When the pressure value in the sample chamber is constantly monitored, in the conventional method, if the pressure value falls below a certain threshold value, an alarm is issued and the wafer is discharged, the gas source is replenished, and then the wafer is transferred again. → Move to the location → Continue to continue processing, increase processing time, and in the worst case, the interrupted processing surface is contaminated and cannot be processed continuously, and the wafer must be discarded As a result, problems such as a decrease in the throughput of the apparatus and an increase in the down time of the apparatus occurred.

  An object of the present invention is to improve the throughput of a focused ion beam apparatus and a sample processing method.

For example, the following problems are solved by the following means.
(1) It has a stage that can adjust the height of the wafer so as to measure the beam diameter at a processing point in a certain cycle, and the measured value of the beam diameter and the scanning interval are substantially the same based on the measurement result. The beam irradiation conditions such as the optimum processing magnification, interlace, and beam stay time are determined. When the beam diameter measurement result becomes an abnormal value compared with the threshold value, an alarm is displayed on the screen. Further, when the beam diameter is in a normal range but deviates from a predetermined value, a means for adjusting the beam diameter is provided.

(2) In order to measure the hole diameter of the variable aperture, the current value of the focusing lens is changed, the beam is focused on the variable aperture surface, and this beam is scanned with a deflector arranged upstream of the variable aperture. The hole diameter of the variable aperture is measured by a detection system that detects secondary electrons and reflected electrons emitted from the beam irradiation point. In addition, the amount of charge irradiated to the variable aperture is obtained, and this value is compared with a threshold value. When the value is exceeded, an alarm is issued and maintenance of the variable aperture is performed.

(3) In order to improve measurement accuracy by the Z sensor, several points near the machining point are measured, an average value of the measured values is obtained, and a deviation from the average value is obtained. When this deviation exceeds a certain threshold value, this is regarded as an abnormal value and excluded from the data group. An approximate expression was created again from the excluded data by the least square method or the like, and the height at the machining point was obtained. In addition, the height is obtained in a region free of obstacles such as a pattern, for example, around the alignment mark, the inclined plane equation is obtained, and the height at the processing point is obtained.

(4) While the gas assist process is being performed, the degree of vacuum in the sample chamber is monitored. If the degree of vacuum in the normal process is shifted to the high vacuum side by a certain threshold, this is recognized as an abnormal state. The main cause is insufficient gas source or clogged gas nozzle. By increasing the gas source and gas nozzle temperature from normal times, the clogging of the gas nozzle is eliminated, and by increasing the pressure of the gas source, the gas supply amount that is insufficient at the processing point is increased and the processing is continued. did. Also, if the pressure does not reach the desired value even when the temperature is raised, an alarm is issued and maintenance is performed.

  According to the present invention, it is possible to prevent a reduction in processing speed due to changes in the ion source and optical system over time and changes in the processing point height, so that the gas assist processing speed such as deposition and etching can be increased, and the processing of the apparatus Helps improve throughput.

  Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing a configuration example of a focused ion beam apparatus according to the present invention. The sample chamber 1 is evacuated by an exhaust system 2 composed of a dry pump and a turbo molecular pump, and is maintained at a high vacuum of about 10 ⁻⁴ to 10 ⁻⁵ Pa. In the sample chamber 1, a FIB column 3, a projector, a laser-reflective Z-sensor 4 separated from the light receiver, a gas gun 5 having a gas nozzle 36 for performing deposition and etching, and a microsample from the sample 10 are extracted. There are a micro sampling unit 6 having a probe 12, a Pirani or Penning vacuum gauge 7 for measuring the degree of vacuum in a sample chamber, and a 5-axis stage 8. Each unit has a central control unit 20 that is connected to the controllers 13 to 18 and controls them in an integrated manner. A console 19 and an image treatment device 21 are connected to the central control unit 20. The console 19 includes a GUI (Graphic User Interface) operation screen, a screen for displaying SIM and SEM images, an input unit such as a keyboard and a mouse, and the like.

  FIG. 17 shows the optical system of the FIB column 3. An LMIS (liquid metal source) 100 includes an emitter 110 to which a liquid metal shown in FIG. 18 is attached, an ionizing material 111 around the emitter 110, and an extraction electrode 113 to which a negative voltage of several kV is applied to the emitter 110. The beam aperture 114 is used to extract only the center of the beam. After the ion beam 11 extracted from the LMIS 100 passes through the acceleration and focusing lens 101, only the center of the beam is extracted by the variable aperture 102, the beam is scanned by the deflector 106A, condensed by the objective lens 107, and the sample 10 Irradiate. Beam alignment and astigmatism correction are performed by an aligner and stagma 103. The blanker 104 scans the Faraday cup 105 with a beam and measures the beam current. Secondary electrons and reflected electrons 109 emitted from the sample 10 are incident on the beam detector 108A by a drawing electric field.

  The above is the description of the liquid metal ion source FIB, but there is no problem with the gas gas FIB. As the gas source, argon, oxygen, nitrogen, neon gas, or the like is used. When these gas gas sources are used, the minimum focusing diameter of the beam is generally larger than that of the liquid metal source, so the resolution is reduced, but the sample can be cut out without contamination by metal such as gallium. Since it can, the wafer can be processed cleanly, and it has a great feature in that it can be applied in-line without worrying about contamination.

  The microsampling unit 6 has a structure that can move in three axial directions of the X, Y, and Z axes. In order to extract the defective part from the sample 10 and mount it on the mesh, the driving movement distance of each axis needs to be about several millimeters. A linear actuator, a piezo element, or the like is used for driving, and the probe can be moved with submicrometer positional accuracy. A vacuum bellows is used as a partition between the vacuum and the atmosphere, but it is necessary to select a drive system having a thrust that can sufficiently overcome the force pushed by the atmosphere of the bellows. The probe 12 is made of tungsten and has a sharp shape with a tip having a curvature of about 1 micrometer or less. When the gas gas FIB is used as the ion source, silicon is used as a probe in order to prevent metal contamination of tungsten. In some cases, a certain amount of metal is doped in order to provide conductivity.

  The stage 8 is movable in the X, Y (horizontal direction), Z (vertical direction), R (rotation), and T (tilt) axes. The T-axis is used for cross-sectional observation after sputter processing by FIB, when microsampling is extracted from a sample, and the like. The tilt angle is a maximum of 60 °. Axial misalignment due to tilt is corrected to prevent visual field misalignment. Since the wafer 10 uses a diameter of 300 mm, the movement distance in the X and Y axis directions is 320 mm and moves in several seconds. A laser is used for wafer positioning, and the accuracy is about submicrometer. For driving in the Z-axis direction, a ball screw and nut, a DC motor, and an encoder are used as in the X and Y axes. The movement in the Z-axis direction employs a wedge structure, and has a positioning accuracy of about submicron. In FIG. 1, the column includes only the FIB for simplification of the drawing. However, the FIB with SEM or the FIB with STEM may be used. By using the SEM in combination, operations such as searching for a defect site can be performed without using gallium ions, so that contamination of the wafer can be minimized. In addition, since SEM is added, two-dimensional to three-dimensional observation is possible. Therefore, when the probe 12 is brought into contact with the microsample, the operation can be easily performed at a high speed. When STEM is used, the sample internal structure can be observed with sub-nanometer resolution. For this reason, a more detailed analysis and analysis of a defective part is attained.

  In addition, as an SEM, an automatic review function ADR (Auto Defect Review) that automatically collects high-definition images of fine defects detected by an inspection apparatus, and automatically collected defects are classified and the occurrence status of each defect type is related. A review SEM having an automatic defect classification (ADC) function that collects information may be used. By combining the review SEM and FIB, it is possible to select and classify the defective portion classified by class. By taking this out of the apparatus and analyzing and analyzing it with a higher-resolution STEM or TEM apparatus, it becomes possible to know the cause of the defect at a higher speed and with higher accuracy, and to take countermeasures quickly.

As the deposition gas, tungsten carbonyl W (CO) ₆ is used for forming a protective film in a defective portion, bonding the probe and the microsample, and bonding the microsample and the mesh. Tungsten carbonyl W (CO) ₆ is heated to a temperature at which it is gasified from a solid (sublimation temperature) or higher, and this gas is irradiated to a processing point to form a tungsten film by decomposition by FIB. In addition, after micro-sampling, the processing hole is filled in order to prevent foreign matter from entering the processing hole and becoming a source of contamination, or to cause defects such as cracks in post-processing such as CMP (Chemical Mechanical Polishing). However, for this, orthokeisan tetraethyl (TEOS) or the like is used. TEOS forms a silicon oxide film by decomposition with FIB. The thickness of the protective film is determined so that the defective portion is not sputtered by the bottom beam when the sample is cut out. The adhesion film thickness is determined mainly from the adhesive strength and the like. For filling a hole, it is necessary to fill a hole about the hole filling volume. In any case, these film formations take several minutes to several tens of minutes, and occupy a large proportion of the time required to extract a series of samples.

  The beam detector 22 includes a scintillator that converts electrons incident at 10 kV into light, a light guide that transmits light generated by the scintillator to a photomultiplier tube, and a photomultiplier tube that converts incident light into electrons and doubles it. Yes. A SIM image is displayed on the screen in synchronization with the beam scanning and the signal intensity of the detector.

  FIG. 2 shows the wafer holder 9. The wafer 10 is mounted on a resin wafer mounting table 24 having a diameter of about 5 mm on the wafer holder 9 and is fixed by three nonmagnetic fixing pins 23. One of the three fixed pins has a movable structure, and the movable pin is connected to a bellows filled with a gas at a certain pressure. It is structured to hold and hold the wafer. On the wafer holder 9, there are a copper mesh 90 having a thickness of several tens of micrometers for mounting a microsample 89 that has been microsampled and extracted, a cartridge 25A for fixing the mesh 90 with screws, and the cartridge holder 25B.

  The cartridge 25A has a structure that can be attached to and detached from the cartridge holder 25B. The cartridge holder 25B can be rotated around the axis as shown in the figure, and the inclined surface of the micro sample 89 can be observed freely. The wafer holder 9 is provided with a focus, stigma adjusting jig 26 and a beam diameter measuring jig 27. A sample with a pattern that can adjust the focus and astigmatism is fixed to the jig. Since these patterns are damaged during beam adjustment and deteriorate with time, the jig is fixed with screws so that it can be periodically replaced.

  In the case where the sample 10 is a wafer that has been subjected to various processes such as a patterned wafer, the sample 10 receives a thermal history and thus warps. Even if the height of the bare wafer surface and the surface height of the beam measurement jig are matched using a bare wafer with a small warp as a reference, as described above, if there is a pattern, the warp on the surface of the beam diameter measurement jig A difference of about several hundred μm at maximum occurs between the height and the processing point height on the wafer surface. In order to accurately measure the beam diameter at the machining point height, it is necessary to move the 5-axis stage 9 in the Z direction so that the height of the beam measurement jig matches the height at the machining point.

  Depending on the processing optical conditions, even if the processing point height deviates by several hundred μm, the change in beam diameter at the processing point may be negligible. In this case, the height measurement at the processing point is not performed and the beam is not measured. It is also possible to adopt a measurement value with a diameter measuring jig.

  FIG. 3 shows a beam diameter measuring method. The wiring pattern 28 on the beam diameter measuring jig 27 is made of the same material having a convex portion. An irradiation beam 29 having a chevron beam energy distribution is scanned in this pattern from left to right in the drawing. When the base of the beam reaches the edge of the pattern, secondary electrons begin to be emitted at the edge. When the center part of the beam having a high energy density is applied to the edge part and then comes to the center of the convex part of the pattern, the amount of secondary electron emission becomes maximum. Further, when scanning to the right side, it begins to decrease, and the distribution 30 of the emission amount of secondary electrons and the like due to beam scanning changes as shown in the figure. The beam diameter can be represented by approximately d1-d0 (width of the convex portion of the pattern).

  If the irradiation energy density to the pattern is increased, the pattern may be scraped by sputtering, and the measurement accuracy may be reduced, or the life of the sample may be shortened. Therefore, it is desirable that the pattern material has a low contamination level to the wafer and a low sputtering rate.

  The beam diameter measurement operation can be automatically measured by selecting a command on the GUI screen. A desired command is selected from the GUI operation menu display section on the GUI screen. As described above, the beam diameter measuring jig 27 automatically moves to the processing point, and scans the focused ion beam 11 under a predetermined condition. The secondary electrons that have come out are detected by the beam detector 22, the secondary electron distribution 30 is obtained, and the beam diameter can be obtained by image processing. Image processing for obtaining the beam diameter is performed by the image processing device 21.

  When the measured beam diameter deviates from the set value within a certain threshold, the beam diameter is adjusted to the set value. As one method, the energization value of the objective lens 107 shown in FIG. Precisely, since the lens positions of the LMIS 100, the sample 10, and the processing optical system are determined and cannot be moved, changing the focal length f changes the beam diameter at the processing point, but the beam distribution shape Will also change. For this reason, a sharp beam shape cannot be obtained, but the adjustment can be performed within a range where there is no practical problem.

  FIG. 4 shows an example of the GUI screen 60 displayed on the console 19 when the above operation is performed. The GUI screen 60 includes an alarm display unit 61, a beam parameter display unit 62 displaying information such as an irradiation beam type, an irradiation beam current value, and a processing magnification, and a GUI operation menu display unit 63 such as a job, system, recipe, and dialog. It consists of SEM, SIM screen display unit 64 and the like. When measuring the beam diameter, the alarm display unit 61 displays “currently under beam adjustment”, and the beam parameter display unit 62 displays the beam diameter before and after the adjustment.

  FIG. 5 shows a case where the measured beam diameter is displayed on the alarm display unit 61 when the measured beam diameter deviates by a certain threshold or more. Possible causes are abnormalities in the ion source, processing optical system, etc., and the inner diameter of the variable aperture 102 becoming larger than the threshold value. In the latter case, it can be avoided before it becomes abnormal by the following method. is there.

  The variable aperture 102 has a gradually increasing inner diameter due to a sputtering phenomenon caused by irradiation of a focused ion beam. Since the reduction ratio of the processing optical system is constant, the beam diameter at the processing point increases. There is a limit to adjusting the beam diameter by changing the energization value of the objective lens. When the variable aperture inner diameter is measured and exceeds a certain threshold, it becomes necessary to replace it. An alarm such as “Please replace the variable aperture” is displayed on the alarm display unit 61 in FIG. 4 to notify the user of the replacement request.

  FIG. 6 shows an optical system in which a portion for measuring the hole diameter of the variable aperture 102 is added to the processing optical system shown in FIG. The main additional parts are a condenser lens 101B, a deflector 106B, and a beam detector 108B. The beam is scanned three-dimensionally on the surface of the variable aperture 102 such that the current value of the condensing lens 101 is changed and condensed by the beam deflector 106B. Secondary electrons and reflected electrons 109 generated at the irradiation point are detected by the beam detector 108B in synchronization with the beam scanning, and the hole diameter of the variable aperture 102 can be measured from the shape of the detected amount. At the end of the hole of the variable aperture 102, it is possible to obtain the hole diameter from the shape dependency of the amount of secondary electron emission, in which the amount of secondary electrons emitted increases due to the edge effect and significantly decreases at the hole. The above measurement is performed at a certain period, and the replacement time of the variable aperture 102 can be accurately known by comparison with a predetermined threshold value. In the case of normal beam processing, the current value of the condenser lens 101A is returned to the original value, and the current values of the deflector 106B and the condenser lens 101B are returned to zero.

  FIG. 7 shows an optical system that measures the current value I flowing through the beam aperture 102 with an ammeter 130. The beam irradiation time t and the current value I are constantly measured, and the charge irradiated to the beam aperture 102 is obtained from the integrated value.

  FIG. 8 is a diagram showing the relationship between the amount of charge applied to the variable aperture 102 and the inner diameter of the variable aperture 102. This relational expression is obtained in advance by a test. When a threshold value is set and exceeded, an alarm such as “Replace aperture” is displayed on the alarm display 61 in FIG.

  One of the factors that cause abnormal beam diameter measurement results is an increase in the inner diameter of the variable aperture. By having a means that can measure the inner diameter of the variable aperture and predict changes in the inner diameter, the beam diameter caused by the aperture The cause of the abnormality can be pursued and countermeasures can be quickly taken.

  When the height of the patterned wafer is measured by a Z sensor using a laser, the measurement error may increase as described above.

  FIG. 9 shows height measurement points on the wafer surface. The X coordinate of the processing point 32 on the wafer 10 surface is assumed to be X1. The measurement points are X1-N × ΔX, X1- (N-1) × ΔX, ..., X1, ..., X1 + (N-1) × ΔX, X1 + N × ΔX, including machining points. . FIG. 9 shows a case where measurement is performed for a total of nine points including processing points. In the figure, the arrangement of measurement points is the X direction, but it may be the Y direction or the XY direction.

  FIG. 10 shows an example of the measurement result at the measurement point in FIG. These data may include an abnormal value 33. The procedure for increasing the measurement accuracy from these measurement results will be described below. First, in a state where the abnormal value 33 is included, a first-order approximation expression 34 is obtained by the least square method. Next, a difference value between the value obtained by the primary approximation formula 34 and the original data is obtained. If there is data whose difference value exceeds a certain threshold, the data is deleted. The first approximation 35 is obtained again by the least square method with the data after the deletion, and the wafer height at the processing point X1 is obtained. By performing this operation, the measurement error can be reduced to about 1 μm even in the patterned wafer. In the case of using a standard wafer with a pattern, the measurement accuracy was improved to about 1 μm in a case where the number of measurement points was 15 and a difference value of 10 μm or more was excluded as an abnormal value. When the measurement accuracy may be lowered, the number of measurement points can be reduced and processing can be performed at high speed.

  FIG. 11 shows another method for measuring the wafer height. In a place where a multilayer film having a complicated pattern is not provided, the light receiver 117 does not cause a displacement of the center of gravity due to reflected light on the upper and lower surfaces of the pattern, and the measurement error is sufficiently small. The position of the complicated pattern without the multilayer film can be known by matching the CAD navigation data storing the wiring pattern data and the actual observation image. For example, the wafer height is measured for each one point 39 in the vicinity of the alignment mark 38 around the chip (die) 37 including the defect portion 84, and the inclined plane 40: Ax + By + Cz + D (A , B, C, D: coefficients), and the height at the processing point 84 in the chip (die) where the pattern exists was obtained from this plane.

  FIG. 12 shows an example in which the height is obtained for the four points 41 around the alignment mark 38 in order to further improve the measurement accuracy, the inclined plane is similarly obtained from this average value, and the height at the machining point is obtained. Show. By obtaining the average value from these four points, the measurement error can be further reduced, and as a result, the measurement accuracy at the machining point 42 can be improved.

  By improving the measurement accuracy of the Z sensor, the probe can be moved safely and reliably to the vicinity of the machining point, so it is possible to shorten the movement time to the machining point when extracting microsampling, and the equipment is improved by improving the processing speed. Throughput can be improved. Further, the probe can be prevented from being damaged, and the downtime of the apparatus accompanying maintenance can be reduced.

FIG. 13A shows an overview of the gas gun 5. The gas source 57 is stored in the gas tank 45. The gas tank 45 is feedback-controlled by a heater, a temperature sensor 46 and a heater controller 47, and is controlled to a predetermined temperature. The heater current is introduced from the atmosphere into the vacuum by the current introduction terminal 48. For example, when W (CO) ₆ is used as the deposition gas source, it is usually controlled at about 60 ° C., which is higher than the sublimation temperature. The shaft 49 of the gas tank is connected to the air cinder 51 via a joint 50 and can be moved in the left-right direction by a bellows 52 and a bearing 53. At the time of the gas assist process, the gas nozzle 36 is moved close to a height of several hundred μm from the processing point of the sample by the air cinder 51 within a few seconds from the retracted position. The sealing plug 55 in the gas tank 45 is opened so as to release gas by compressed air (not shown) when processing.

  The pressure value in the sample chamber is monitored by the vacuum gauge 7 at least during gas assist processing. If the degree of vacuum changes from a certain threshold value to the high vacuum side during processing, there may be a cause such as the gas nozzle clogging 56 due to some cause or the lack of a gas source causing the supply of a sufficient amount of gas to the processing point. It is done.

  FIG. 13B is a detailed view of the gas nozzle tip, and shows a state where the gas source is solidified again at the gas nozzle 36 tip and clogging occurs. In such a case, the gas tank control temperature is raised within an allowable upper limit determined by the gas unit constituent member, and the vacuum degree of the sample chamber is controlled to be a predetermined vacuum degree. For example, when a Viton O-ring is used for a gas seal, the upper limit temperature is about one hundred and several tens of degrees Celsius.

For example, it is 5 × 10 ⁻⁵ (Pa) when no gas is introduced, but 2 × 10 ⁻³ (Pa) when the gas is introduced. The sample chamber pressure value at the time of gas introduction is proportional to the gas flow rate in the general case where the outgas amount and leak amount in the sample chamber are sufficiently smaller than the gas flow rate. When the amount of gas introduced is halved, the pressure value is approximately 1 × 10 ⁻³ (Pa). When a threshold value of the sample chamber pressure value is determined based on an allowable decrease in throughput or the like, and the pressure value in the sample chamber is on the high vacuum side, an alarm display unit 61 in FIG. Is displayed, but processing is continued ", and the wafer is processed to the end. If the specified vacuum level is not reached even when the temperature is increased to the allowable upper limit value, an alarm such as “Processing will be stopped because the gas source is insufficient” is displayed on the alarm display unit 61 as described above. Then, the processing wafer is collected. By the above-described relief treatment, most of the wafer can normally finish the gas assist processing such as deposition and etching.

  According to the present embodiment, it is possible to prevent a decrease in processing performance due to a shortage of gas sources. In addition, it is possible to prevent disposal of the processing wafer due to out of gas, thereby improving cost performance.

  FIG. 14 (1) to FIG. 14 (4) show an example of the entire operation flow including the above-described contents. The general operation procedure is shown below.

(1) Processing for carrying in an inspection wafer and searching for a defective portion.
The focus / stagma adjustment jig 26 is moved to the processing point 32 (S11), and beam adjustment is performed (S12). Using an optical or SEM visual inspection device, etc., detect the position of detected foreign matter, shape defects, VC (voltage contrast) defects, etc. on the detected wafer to coordinate values of the focused ion beam device using coordinate linkage. (S13). Thereafter, the wafer to be observed and processed is carried in (S14). The wafer is moved by the coordinate linkage (S15). The coordinate linkage in step 15 has a positioning accuracy of only a few micrometers, and is positioned visually based on the device pattern information in order to improve the accuracy (S16).

(2) A process of measuring the beam diameter at the position (height) of the defective portion to be processed using a jig.
The height H of the processing point 32 is measured by the Z sensor 4 by the method described in FIGS. 9 to 12 (S21). Next, the beam diameter measuring jig 27 is moved to the processing point 32 (S22). The wafer holder 9 including the beam diameter measuring jig 27 is moved and adjusted in the vertical direction so that the value of H measured in step 22 is obtained (S23). Under the beam irradiation conditions of the processing conditions, the beam diameter at the processing point is measured by the method shown in FIG. 3 (S24). In step 25, it is determined whether or not the measured value is an abnormal value. If the measured value is an abnormal value, an alarm is displayed on the GUI screen 60 on the console 19 as shown in FIG. (S26) The operator who sees it contacts the service person (S27).

  If it is not an abnormal value in the determination in step 25, the process proceeds to step 28 to determine whether the measured value is a predetermined value. If it is determined in step 28 that the value is a predetermined value, the defective portion 84 is moved to the processing point 32, and the wafer holder 9 is moved and adjusted in the vertical direction so as to have the height H (S30). If it is determined in step 28 that the current value deviates from the predetermined value, the energization current value of the objective lens 107 and the like is adjusted so as to become the predetermined value, and the adjustment result is displayed as shown in FIG. 4 (S29). ). Thereafter, the process proceeds to Step 30.

(3) A process of determining beam irradiation conditions and performing a defect positioning mark and protective deposit processing.
The processing magnification M and the interval I (interlace) of the beam scanning dots 80 are determined so that the beam scanning interval 82 becomes substantially the same value as the measured diameter D of the beam 11 (S31). The beam scanning interval 82 is expressed by the following equation. Referring to FIG. 22, GUI screen size = A × B. The beam scanning period is expressed by the following formula.

Beam scanning interval = GUI screen size / magnification / number of dots per side length x interlace
Beam scanning cycle = scanning area / {(beam scanning interval) ² ) x beam residence time

  As an example, A = B = 150 mm on the GUI screen, magnification at processing = 3000, formed by 4096 dots per side of A and B (divided by 4096), and an interlace of 8 (dots) Assuming that the beam stays every 8 pieces and the beam is scanned at the next 8 dots apart after a certain time), the beam scanning interval is 150 (A = B) / 3000 times (processing magnification) / 4096 (dots) Number) × 8 (scanning interval) = 100 nm. Since the beam diameter at the processing point is known in advance by measuring, the interlace is determined so that the beam diameter is equal to the beam scanning interval. For example, when the beam diameter is 100 nm, if interlace = 8, the beam diameter = scanning interval. When the beam diameter = 200 nm, the interlace = 16 and the beam diameter = scanning interval.

  If the beam scanning period is not set to be longer than the gas adsorption time, the gas assist processing speed is lowered. Therefore, taking the above into consideration, the magnification and interlace are determined. The process for determining these is performed by the central control unit 20.

  As shown in FIG. 15A, marks 69 are formed on both ends of the defect by sputtering so that the position of the defect portion 84 can be seen (S32). Next, the gas nozzle 36 is brought close to the processing point 42 (S33), the gas sealing plug 55 is opened and gas is irradiated (S34), and the focused ion beam 11 is irradiated according to a recipe inputted in advance, and FIG. ) As shown in FIG. At this time, since the pressure value in the sample chamber becomes unstable immediately after the introduction of the deposition gas, it is monitored after a certain time after the introduction (S35).

  When the pressure in the sample chamber exceeds the threshold value and becomes a high vacuum, the gas source is deficient and the gas nozzle is clogged. Therefore, the temperature of the gas source and gas nozzle is raised (S36), and the degree of vacuum in the sample chamber is monitored. (S38). The alarm display unit 61 of FIG. 4 displays “The gas source is insufficient, but processing is continuing”. Even if the temperature is raised to the allowable temperature, if the vacuum does not reach the predetermined value, the process is interrupted and a message to that effect is displayed on the alarm display unit 61 in FIG. If the pressure in the sample chamber rises to a predetermined value, the temperature of the gas source and gas nozzle is maintained to continue the processing, and the deposition process is terminated (S39).

(4) Processing for extracting a microsample.
As shown in FIG. 15A, hole processing 85 on both ends of the mark 69 is performed by the FIB 11 (S41). Next, as shown in FIGS. 15B and 15C, a part of the uncut portion 87 is left and the microsample is cut out (S42). Next, as shown in FIG. 15D, the probe 12 is brought into contact with the microsample 89 (S43). As shown in FIG. 15 (e), the probe 12 and the micro sample 89 are bonded with the deposition film 91 (S44). Next, as shown in FIG. 15F, part of the uncut portion 87 is removed by sputtering, and the microsample 89 is separated from the sample (S45).
(5) A process of mounting the micro sample on the cartridge mesh and taking it out.

  As shown in FIG. 15G, the extracted microsample 89 is adhered to the mesh 90 on the cartridge 25A by the deposition film 92 (S51). As shown in FIG. 15H, the separation process is performed by the sputtering of the probe 12 (S52). Next, the wafer 10 and the cartridge 25A are carried out. Thereafter, the microsample 89 mounted on the mesh 90 of the cartridge 25A is thinned to about several tens of nanometers by an FIB apparatus outside the apparatus. After that, a highly accurate analysis with a resolution of sub-nanometer is performed by STEM or TEM.

Although the above method measures the beam diameter every time a defective part is processed, it takes time and labor, so it is not very practical when used in a mass production line. In order to shorten the time, in order to correct the wafer height by warping the wafer in advance, the height is measured at several points including the outer periphery and the center of the wafer surface, and the wafer surface is, for example,
Z = aX ² + bY ² + cXY + dX + eY + f (a, b, c, d, e, f: coefficients)
It is approximated by a paraboloid represented by In order to improve the approximation accuracy, it may be expressed by a higher order function. If one point on the wafer surface is measured, the wafer height can be calculated from the above paraboloid by calculation over the entire surface of the wafer surface. By correcting the wafer warp and adjusting the height of the wafer holder 9, the beam diameter at the processing point can be kept constant under the same processing conditions, and the processing speed can be kept high. become.

  FIG. 16 is a diagram illustrating the above. Let H be the distance between the FIB column 3 and point A when processing point A on the wafer surface. When machining the point B at the wafer end, if the height of the wafer holder 9 is corrected by the 5-axis stage 8 by ΔH corresponding to the amount of warpage of the wafer, the distance from the FIB column to the point B will be the same at the point B as well. H, and the beam diameter at the processing point can be kept constant.

The figure which shows the structure of the whole apparatus. The figure which shows a wafer holder. The figure which shows the measuring method of a beam diameter. The figure which shows a GUI screen. The figure which shows a GUI screen. The figure which shows FIB optical system. The figure which shows FIB optical system. The figure which shows the relationship between a variable aperture internal diameter and the amount of irradiation charges. The figure which shows a sample height measurement point. The figure which shows the measurement result of sample height. The figure which shows another measuring method of sample height. The figure which shows another measuring point of sample height. The figure which shows the structure of a gas gun. The figure which shows the whole processing flow. The figure which shows the whole processing flow. The figure which shows the whole processing flow. The figure which shows the whole processing flow. The figure which shows the microsampling method. The figure which shows the method of keeping the height of a process point constant. The figure which shows FIB optical system. The figure which shows the structural drawing of LMIS (liquid metal ion source). The figure which shows the beam scanning method. The figure which shows a beam scanning space | interval, a deposit, and an etching rate. The figure which shows the measurement error which generate | occur | produces in the conventional sample height measurement. The figure which shows beam scanning conditions.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Sample chamber, 2 ... Exhaust system, 3 ... FIB column, 4 ... Laser reflection type Z sensor, 5 ... Gas gun, 6 ... Micro sampling unit, 7 ... Vacuum gauge, 8 ... 5-axis stage, 9 ... Wafer holder DESCRIPTION OF SYMBOLS 10 ... Sample (wafer), 11 ... Focused ion beam, 12 ... Probe, 13 ... Micro sampling unit, 14 ... FIB controller, 15 ... Z sensor controller, 16 ... Gas gun controller, 17 ... Vacuum gauge controller, 18 ... Stage Controller 19, console 20, central controller 21 image processor 22 beam detector 23 wafer fixing pin 24 wafer mount 25 A cartridge 25 B cartridge holder 26 focus Stagma adjustment jig, 27 ... Beam diameter measurement jig, 28 ... Wiring pattern, 29 Irradiation beam, 30 ... secondary electron quantity distribution, 31 ... height measurement point, 32 ... machining point, 33 ... abnormal value, 34 ... primary approximation, 35 ... primary approximation, 36 ... gas nozzle, 37 ... tip ( 38 ... alignment mark, 39 ... height measurement point, 40 ... approximate plane, 41 ... height measurement point, 42 ... processing point, 45 ... gas tank, 46 ... heater and temperature sensor, 47 ... heater controller, 48 ... Current introduction terminal, 49 ... Shaft, 50 ... Joint, 51 ... Air cylinder, 52 ... Bellows, 53 ... Bearing, 55 ... Sealing plug, 56 ... Clogging, 57 ... Gas source, 60 ... GUI screen, 61 ... Alarm Display unit, 62 ... Beam parameter display unit, 63 ... GUI operation menu display unit, 64 ... SIM, SEM screen display unit, 80 ... Dot, 81 ... Beam scanning area, 82 ... Between beam scanning , 84 ... Defect part, 85 ... Processing hole, 86 ... Deposition film, 87 ... Uncut part, 89 ... Microsample, 90 ... Cartridge mesh, 100 ... LMIS (liquid metal source), 101 ... Acceleration, focusing lens, 102 ... variable aperture, 103 ... aligner, stagma, 104 ... blanker, 105 ... Faraday cup, 106A, 106B ... deflector, 107 ... objective lens, 108A, 108B ... beam detector, 109 ... secondary and reflected electrons, 110 ... Emitter, 111 ... Ionized material, 112 ... Sputtered material, 113 ... Extraction electrode, 114 ... Beam aperture, 116A, 116B ... Reflected light, 117 ... Light receiver, 119 ... Resist, oxide film, 122 ... Actual processing region, 130 ... Ammeter

Claims (7)

A sample holder placed in the sample chamber and carrying the sample;
A vacuum gauge for measuring the degree of vacuum of the sample chamber;
A focused ion beam optical system for irradiating a sample mounted on the sample holder with a focused ion beam;
A detector for detecting secondary particles generated from the sample by irradiation of the focused ion beam;
An image processing unit for processing a scanned image of the sample obtained from the detection signal of the detector;
A display unit for displaying a sample image and apparatus conditions;
A control unit for controlling each unit,
It has means for measuring the hole diameter of a variable aperture installed in the focused ion beam optical system, and the control unit determines the life of the aperture based on the measured hole diameter. Focused ion beam device. A sample holder placed in the sample chamber and carrying the sample;
A vacuum gauge for measuring the degree of vacuum of the sample chamber;
A focused ion beam optical system for irradiating a sample mounted on the sample holder with a focused ion beam;
A detector for detecting secondary particles generated from the sample by irradiation of the focused ion beam;
An image processing unit for processing a scanned image of the sample obtained from the detection signal of the detector;
A display unit for displaying a sample image and apparatus conditions;
A control unit for controlling each unit,
Means for integrating the irradiation beam current value to the variable aperture installed in the focused ion beam optical system, and the control unit determines the lifetime of the aperture based on the integrated current value Focused ion beam device characterized by. A sample holder placed in the sample chamber and carrying the sample;
A vacuum gauge for measuring the degree of vacuum of the sample chamber;
A focused ion beam optical system for irradiating a sample mounted on the sample holder with a focused ion beam;
A detector for detecting secondary particles generated from the sample by irradiation of the focused ion beam;
An image processing unit for processing a scanned image of the sample obtained from the detection signal of the detector;
A display unit for displaying a sample image and apparatus conditions;
A gas gun that blows process gas on the sample;
A control unit for controlling each unit,
The control unit monitors the degree of vacuum in the sample chamber based on the output of the vacuum gauge, and when the degree of vacuum becomes higher than a predetermined threshold during processing using the gas gun, the gas A focused ion beam apparatus characterized in that the temperature of the gun is raised so that the degree of vacuum in the sample chamber becomes a predetermined degree of vacuum. 4. The focused ion beam apparatus according to claim 3, wherein the control unit displays a control result of the degree of vacuum of the sample chamber on the display unit. A sample holder placed in the sample chamber and carrying the sample;
A vacuum gauge for measuring the degree of vacuum of the sample chamber;
A focused ion beam optical system for irradiating a sample mounted on the sample holder with a focused ion beam;
A detector for detecting secondary particles generated from the sample by irradiation of the focused ion beam;
A first image processing unit for processing a scanned image of the sample obtained from the detection signal of the detector;
A display unit for displaying a sample image and apparatus conditions;
In order to measure the beam diameter of the focused ion beam, a beam diameter measuring member installed on the sample holder;
A second image processing unit for measuring the beam diameter of the focused ion beam from the scanned image of the beam diameter measuring member;
A controller that determines the irradiation conditions of the focused ion beam based on the measured beam diameter,
The control unit obtains the height of a processing point by the focused ion beam from a measured value in a region having no pattern that causes a measurement error in the beam diameter measuring member. .   6. The focused ion beam apparatus according to claim 5, wherein gas assist treatment is performed by blowing gas from a gas gun to the sample, the degree of vacuum in the sample chamber in which the sample is placed is monitored, and the degree of vacuum is higher than a predetermined threshold value. A focused ion beam apparatus, wherein when the vacuum is reached, the temperature of the gas gun is raised to control the degree of vacuum of the sample chamber to a predetermined degree of vacuum.   7. The focused ion beam apparatus according to claim 6, wherein a result of controlling the degree of vacuum of the sample chamber is displayed.

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