JP4673278B2 - Wafer inspection method - Google Patents

Description

  The present invention relates to an in-line inspection method for inspecting a deposited film thickness, a pattern dimension, a pattern overlay accuracy, a hole conduction state, etc. of a wafer in the process of manufacturing a semiconductor element, an imaging element, a display element, etc. It relates to the device.

In the manufacture of semiconductor elements, imaging elements, display elements, etc., it is indispensable to increase the density of transistors and the like in order to increase the functionality and performance of the elements. For example, the density of semiconductor devices has been increased at a rate of about 2.5 times / 3 years. Taking the ASIC transistor density listed in the semiconductor technology roadmap as an example, a 20MTr. / Cm ² , in 2002, 54MTr. / Cm ² , 133 MTr. / Cm ² , and in 2011 811MTr. / Cm ² is predicted. In order to realize such high density, it is essential to improve the structure of the MOS transistor together with the miniaturization of the pattern. With regard to the structure of the MOS transistor, it is considered that the current planar transistor will shift to a vertical transistor. As shown in FIG. 17, the vertical transistor has a structure in which a source, a gate, and a drain are arranged in a vertical direction. From the standpoint of in-line inspection, the change to the vertical transistor from the standpoint of in-line inspection is that the measurement of the most important parameter that determines the gate performance, that is, the transistor performance, is changed to the measurement of the film thickness, not the measurement of the pattern dimensions. .

JP-A-10-213422 JP-A-11-265679

  In order to measure the gate length of the vertical transistor, that is, the thickness of the gate electrode in-line, the target is a local region of about several hundreds of nanometers on the premise that sampling inspection can be performed with a reasonable throughput on a wafer in production. Therefore, it is a problem to perform a micro-region / high-precision measurement with a measurement variation of nm or less.

  Currently, in-line film thickness inspection of deposited films, thermal oxide films, and the like, an optical interference type film thickness measuring device and ellipsometer using a light beam are generally used for pilot wafers dedicated to inspection. However, it is a well-known fact that in the very near future, these technologies will not be able to meet the increasingly demanding accuracy requirements. Future candidates for a more accurate film thickness measurement method include (1) an ellipsometer that uses UV light as irradiation light, (2) a method of measuring reflected X-rays by irradiating X-rays at measurement points, and (3) Examples include a method of irradiating a measurement site with laser light to measure elastic waves and the like, and (4) a method of measuring a scattered ion by irradiating a measurement site with a medium-speed ion beam. However, in any method, it is extremely difficult to perform film thickness measurement for a local region of about several hundred nm.

  For example, the gate length measurement accuracy required for a vertical transistor with a gate length of 50 nm (including all measurement variations such as sample-induced variations and instrument differences) is 1 nm or less, and the required film thickness measurement accuracy is as high as possible. The only techniques with spatial resolution that can be achieved are the atomic force microscope (AFM) and the transmission electron microscope (TEM) or scanning transmission electron microscope (STEM) that forms a transmission electron image. Since AFM has extremely low throughput, at present, only TEM or STEM has the possibility. However, even in the case of a TEM or STEM, it is not possible to perform a sampling inspection with a reasonable throughput, which is a premise of in-line inspection, which is a practical problem.

  In view of such circumstances, an object of the present invention is to provide an in-line inspection means using a TEM or STEM for enabling highly accurate film thickness measurement in a local region of about several hundred nm.

  The use of TEM or STEM is the only solution that can realize highly accurate film thickness measurement in a very small region. However, increasing the throughput is the biggest challenge. In order to achieve high throughput, it is essential that (1) the sample can be prepared at high speed and (2) the sample can be observed in a short time. For (1), combining with a focused ion beam apparatus (FIB apparatus) of a method of cutting out a sample using a sputtering action of a focused ion beam is an optimal choice. In this case, the time required for substantial in-line inspection is determined by the sample preparation time of the FIB apparatus. In the FIB apparatus, in order to enable high-speed sample preparation and sample observation in a short time, according to a pre-registered sample preparation recipe, a plurality of designated locations on the wafer are targeted, and sample extraction locations are determined. Positioning is performed automatically, the sample is automatically cut out, the cut sample is automatically mounted on an observation sample holder used in TEM or STEM, and a recipe for observing the sample with TEM or STEM is created. In TEM or STEM, in order to enable sample observation in a short time, according to the observation recipe created by the FIB apparatus and input to TEM or STEM, a plurality of samples mounted on the observation sample holder are targeted. The observation area is automatically aligned and a predetermined sample image is acquired.

  On the other hand, in order to make film thickness measurement with a TEM or STEM more accurate, a stepped cross-section sample capable of confirming and correcting the parallelism between the incident direction of the electron beam and the observation film surface, and a predetermined observation pattern In order to obtain an observation cross section accurately formed at a position, a cross-section observation sample is used which is composed of a plurality of pattern groups in which the observation pattern is gradually shifted in a direction perpendicular to the processing cross section.

  According to the present invention, 'sample observation by TEM / STEM' is combined with 'sample preparation by FIB apparatus', and the FIB apparatus targets a plurality of designated locations on a wafer according to a pre-registered sample preparation recipe. Automatic positioning of the sample extraction location, automatic sample extraction, automatic mounting of the extracted sample on an observation sample holder used in TEM or STEM, and creation of a recipe for observing the sample with TEM or STEM On the other hand, in the TEM or STEM, according to the observation recipe created by the FIB apparatus and input to the TEM or STEM, the observation region is automatically aligned with respect to a plurality of samples mounted on the observation sample holder, By acquiring a predetermined sample image and obtaining observation data, a local region of about several hundred nm is targeted. Te, it becomes possible to perform high-precision in-line thickness measurement.

  In addition, when TEM or STEM is used, composition analysis, structural analysis, and electronic state analysis of a very small region can be easily performed in conjunction with high-resolution sample image formation. Since this analysis / analysis information can be used in combination, it is difficult to measure the thickness of each layer of in-line laminated film, measure the three-dimensional shape of the pattern, measure the pattern overlay accuracy, and connect the wiring. Thus, it is possible to accurately and accurately measure the conduction state of the film, measure the particle size of the film-forming substance, measure the composition distribution of the trace impurities in the film, and compare the defect with a predetermined reference image.

  Further, by handling these in-line measurement data in an integrated manner, more advanced process management and transistor characteristic analysis are realized. For example, if the gate insulating film thickness and the dopant concentration profile of the source / drain region are measured in-line simultaneously with the gate length, the electrical characteristics of the transistor such as the threshold voltage can be accurately predicted in real time. In other words, data for precisely managing device performance / reliability and yield, which has never been achieved before, can be acquired by in-line inspection.

  In addition, since the inspected sample can be stored, it can be taken out of the storage and reexamined when the yield or reliability problem occurs later. This facilitates failure analysis that is forced to be difficult without the actual product.

  The wafer inspection method, focused ion beam apparatus, and transmission electron beam apparatus according to the present invention are as follows.

(1) In a wafer inspection method in a semiconductor device manufacturing process, a step of loading a wafer to be inspected into a focused ion beam device, and a step of automatically positioning a sample cut-out location on the wafer according to a pre-read sample preparation recipe A step of cutting a predetermined sample from the wafer by a focused ion beam, a step of mounting the cut sample on the observation sample holder, information on the mounting position of the cut sample on the observation sample holder, and the sample A step of creating an observation recipe described in association with information on the inspection conditions, a step of loading the observation sample holder in a transmission electron beam device, a step of reading the observation recipe by the transmission electron beam device, and reading Automatically positioning the sample on the observation sample holder according to the observation recipe, Method of inspecting a wafer, characterized in that the determined sample and a step of acquiring a predetermined observation data according to the observation recipe.

  In the sample preparation process using the focused ion beam apparatus, it is possible to quickly prepare a sample by appropriately using a shaped beam, a variable shaped beam, or a cell projection beam as the focused ion beam. The cell projection can be composed of at least a C-shape and a spot. A TEM or STEM can be used as the transmission electron beam apparatus. It is preferable to transmit the observation recipe between the focused ion beam apparatus that executes the sample preparation process and the transmission electron beam apparatus that executes the sample observation process online via a LAN or the like.

(2) In the wafer inspection method according to (1), the step of creating the observation recipe includes a step of reading a code written on the observation sample holder, and a step of loading the observation sample holder using the code as a key. A method for inspecting a wafer, wherein a recipe for a transmission electron beam apparatus for observing a sample is prepared.

  When the sample is cut out by the FIB apparatus, the transmission electron beam apparatus recipe for observing the sample is automatically or automatically set using the code on the sample, which is a number unique to the sample attached to the sample using the FIB, as a key. You may make it produce semi-automatically.

(3) In the wafer inspection method according to (1) or (2), in the step of obtaining the observation data, at least one data among sample image data, composition analysis data, structure analysis data, and electronic state analysis data is obtained. A method for inspecting a wafer, comprising: obtaining the wafer.

  The obtained observation data includes film thickness measurement, pattern shape measurement, pattern overlay measurement, wiring connection continuity measurement, particle size measurement, dopant concentration profile measurement, and defect measurement compared to a predetermined reference image. Can be used for Measurement data can be used for process management and device characteristic analysis.

(4) A sample stage that is movable while holding a wafer, a stage driving unit that drives the sample stage, a means for forming a focused ion beam, and a wafer that holds the focused ion beam on the sample stage. In the focused ion beam apparatus including a deflector for scanning, a detector for detecting a sample signal generated from the sample by irradiation of the focused ion beam, a sample manipulator for sample handling, and a control unit, the control unit includes: A function for automatically positioning a sample cutting position on a wafer by controlling the stage driving unit and / or the deflector according to a pre-registered sample preparation recipe, and a control for cutting a predetermined sample using the focused ion beam And the sample cut out by controlling the sample manipulator is mounted on the observation sample holder used in the observation device. Function, the sample mounting position on the observation sample holder, the information described in the sample preparation recipe of the sample, and the information stored in advance read from the memory based on the information And a function of creating an observation recipe to be used in the observation apparatus.

  The cut sample may be imprinted with a focused ion beam with a code for identifying the sample. The sample cut out from the wafer is once fixed to the sample manipulator, and then one or both of the sample manipulator and the observation sample holder are moved and mounted at a predetermined address position of the observation sample holder. For fixing the sample to the sample manipulator, an ion beam assisted film deposition method or an electrostatic adsorption action between the manipulator and the sample can be used.

(5) A sample stage that is movable while holding an observation sample holder on which a sample is mounted, a stage driving unit that drives the sample stage, a means for squeezing the electron beam to irradiate the sample, and the electron beam In a transmission electron beam device including a deflector for deflecting, a transmission electron detector for detecting an electron beam transmitted through a sample, and a control unit, the control unit is an observation recipe created by the focused ion beam device. And a function for performing automatic control of positioning an observation region for a sample on an observation sample holder produced by the focused ion beam device, and a function for acquiring predetermined observation data, Transmission electron beam device.

  The observation data can include sample image data, composition analysis data, structure analysis data, electronic state analysis data, and the like. The transmission electron beam apparatus can include a characteristic X-ray analyzer, an Auger electron spectrometer, an energy analyzer of characteristic loss electrons, and the like. The composition analysis data can be acquired by, for example, providing a characteristic X-ray analyzer or an energy spectrometer in the transmission electron beam apparatus, and the structural analysis data can be acquired by providing a two-dimensional array detector of transmission electrons. The electronic state analysis data can be obtained by providing a transmission electron energy spectrometer.

  Based on the obtained observation data, film thickness measurement, pattern shape measurement, pattern overlay measurement, wiring connection continuity measurement, particle size measurement, dopant concentration profile measurement, defect measurement compared to a predetermined reference image And so on. The obtained measurement data can be used for process management and device characteristic analysis. Observation data, measurement data, process management data, etc. can be output as electronic data. The process management data to be output can be, for example, a wafer map indicating whether or not the inspection is successful, or data collected as an inspection failure rate, the number of inspection failures, and a defect classification result. The transmission electron beam apparatus preferably has an observation magnification calibration function based on a crystal lattice image.

(6) A means for loading / unloading the sample holder, a storage means for storing a sample observation recipe, a sample holder identification means for identifying the sample holder, and a control means, the control means comprising: And transmitting the observation recipe corresponding to the sample holder from the storage means based on the identification result by the sample holder identification means, and controlling each part based on the observation recipe to observe the sample. Electron beam device.

  The cross-section observation sample produced by the focused ion beam apparatus can be produced so that the observation pattern is composed of a plurality of pattern groups that are formed by shifting little by little in a direction perpendicular to the processing cross section. In observing the cross-sectional observation sample, an optimum observation pattern is selected by adopting a pattern having the largest dimension as a test pattern.

  When a cross-section observation sample having at least one step in the cross-section for observation is used, the incident angle formed by the cross-section and the observation beam can be obtained from the transmission image. The information on the incident angle of the observation beam can be used to control the tilt angle of the sample or the incident beam with a deflector to control the beam incident angle to a predetermined value. Alternatively, the measurement data can be corrected based on the obtained incident angle.

  According to the present invention, highly accurate in-line film thickness measurement can be performed.

  FIG. 1 shows a schematic configuration of an example of an FIB apparatus according to the present invention. The FIB apparatus is comprehensively controlled by the control unit 31. The ion beam 12 extracted from the ion gun 11 is accelerated to a predetermined energy, and then is focused by the focusing lens 13 and the objective lens 14, and is placed on the surface of the wafer 23 mounted on the XY stage 22 in the sample chamber 21. Irradiated. The XY stage 22 is driven by the stage drive unit 32 under the control of the control unit 31. The ion beam 12 irradiated on the wafer 23 is deflected by the deflector 15 and scanned on the wafer 23. A cell projection diaphragm 16 is disposed below the converging lens 13. On the other hand, secondary electrons 24 are emitted from the wafer portion irradiated by the ion beam 12. The secondary electrons 24 are detected by the secondary electron detector 25, subjected to signal processing such as amplification and A / D conversion by the signal amplification / processing unit 33, and then stored in the memory 34. The image signal stored in the memory 34 is supplied to a display 35 that is scanning in synchronization with ion beam scanning, and a sample image is displayed on the display 35. This sample image is called a SIM image.

  The sample chamber 21 includes a wafer loading / unloading unit 42 for loading or unloading a wafer held on the wafer carrier 41 with respect to the XY stage 22, and a holder for holding a TEM or STEM observation sample cut out by the FIB apparatus. An observation sample holder loading / unloading unit 43 for loading / unloading, a sample manipulator driving unit 44, and a reactive gas introduction unit 45 are provided. An optical microscope 26 is also provided in the sample chamber.

  The control unit 31 sets a sample cutting position for TEM or STEM observation based on the obtained sample image according to the read sample preparation recipe 37, and performs ion beam processing while monitoring the sample image. The processed sample is cut out from the wafer and used for observation by TEM or STEM. The control unit 31 controls each unit to control the cutting of the observation sample and creates an observation recipe 88 described later. The created observation recipe 88 is temporarily stored in the memory 34, and is output to the TEM or STEM for sample observation and the database via the LAN. The observation recipe will be described later.

  FIG. 2 shows a schematic configuration of a TEM or STEM according to the present invention. The apparatus is comprehensively controlled by the control unit 81. The electron beam 62 emitted from the electron gun 61 is accelerated to a predetermined energy, and is then narrowed down by the converging lens 63 and irradiated onto the sample surface on the sample holder 66 mounted on the XY stage 65. The XY stage 65 is driven by the stage drive unit 82 under the control of the control unit 81. The transmitted electrons 71 that have passed through the sample are detected by the transmitted electron detector 73 through the objective lens 72, subjected to signal processing such as amplification / A / D conversion by the signal amplification / processing unit 83, and then stored in the memory 84. The image signal stored in the memory 84 is supplied to a display 85 that is scanned in synchronization with the electron beam scanning, and a sample image is displayed on the display 85. The sample holder 66 holding the sample is loaded on the XY stage 65 or unloaded by the sample holder loading / unloading unit 86 under the control of the control unit 81.

  If a spatial distribution signal of the transmitted electrons 71 is obtained by irradiating the electron beam 62 at one point, a transmitted electron image can be obtained. On the other hand, when the irradiation electron beam is scanned by the deflector 64 and the time change signal of the transmitted electrons 71 is obtained, a scanned transmission electron image can be obtained. As a detector, in addition to the transmission electron detector 73, an X-ray detector 75 for detecting characteristic X-rays 74 generated from the sample by electron beam irradiation, an energy spectrometer 76 for performing energy spectroscopy on the transmission electrons 71, and the like are provided. . The observation of the sample is performed according to the observation recipe 88 created by the FIB apparatus and transmitted via the LAN, for example.

  FIG. 3 is a diagram showing the concept of in-line inspection in the semiconductor device manufacturing process according to the present invention. An in-line inspection process is provided in the middle of the wafer process and the semiconductor process processes 91 and 92 before and after the illustrated process. The in-line inspection process is roughly divided into two processes, a sample preparation process in the FIB apparatus and a sample inspection process in the TEM / STEM.

  In the sample preparation process in the FIB apparatus, in accordance with a pre-registered sample preparation recipe 37, a plurality of designated locations on the wafer are targeted, sample extraction locations are automatically positioned, the sample is automatically extracted, and the sample is extracted. An observation recipe 88 for observing a sample with TEM / STEM is created while being automatically mounted on an observation sample holder used in TEM / STEM.

In the specimen inspection process in TEM / STEM, the observation area is automatically aligned for multiple specimens mounted on the specimen holder for observation according to the observation recipe 88 produced by the FIB apparatus and input to the TEM / STEM. Then, by acquiring a predetermined sample image, an inspection is performed on a local region of about several hundred nm. Each will be described below.
Initially, with reference to FIG.4 and FIG.5, the sample preparation process in a FIB apparatus is demonstrated. In this step, sample cutting, observation sample preparation, and observation recipe 88 creation by TEM / STEM are performed.

  FIG. 4 is a flowchart for explaining processing for preparing an observation sample holder for loading a sample cut out by the FIB apparatus. First, in step 11, a sample holder carrier containing an empty observation sample holder is attached to the observation sample holder loading / unloading unit 43 of the FIB apparatus. Next, in step 12, the observation sample holder is taken out from the sample holder carrier, and is confirmed to be empty by a detector attached to the load / unload unit 43. Then, the process proceeds to step 13 to load / The holder number written on the holder is read by a holder number reader attached to the unloading section. Thereafter, in step 14, the observation sample holder is transported and loaded into a predetermined position in the sample chamber 21 of the FIB apparatus. The holder number of the observation sample holder is a code unique to each observation sample holder, and is used to identify each observation sample holder. In addition, the main body of the observation sample holder itself can be reused repeatedly.

  Note that the process for preparing the observation sample holder shown in FIG. 4 may be completed before step 30 using the free time of the sample preparation and observation recipe creation process shown in FIG.

  FIG. 5 is a flowchart showing the flow of the sample preparation process and the observation recipe creation process. In step 21, the wafer carrier 41 containing the wafer to be inspected is mounted on the wafer load / unload unit 42. In step 22, the wafer to be inspected is taken out from the wafer carrier, and in the next step 23, it is transferred to the pre-alignment unit and pre-aligned. The pre-alignment is an operation for detecting the orientation flat or notch of the wafer and aligning the mounting direction of the wafer with the direction of the XY stage 22 of the FIB apparatus using this as a reference.

  After the wafer is pre-aligned, in step 24, the wafer number formed on the wafer is read by a wafer number reader (not shown) incorporated in the FIB apparatus. The wafer number is a code unique to each wafer, and is used to identify the individual wafer or the product name / in-process name of the wafer. In step 25, using the read wafer number as a key, the sample preparation recipe 37 corresponding to this wafer registered in advance is read. The sample preparation recipe 37 defines a sample cutting procedure, a cutting condition, and a cutting result output condition from a wafer, and is generally set for each type of product / working process name to which the wafer belongs. Subsequent operations are automatically or semi-automatically performed according to the recipe 37.

  After reading the recipe, in step 26, the wafer is transferred and loaded onto the XY stage 22 in the sample chamber 21. In a subsequent step 27, the wafer 23 loaded on the XY stage 22 is aligned using an optical microscope 26 mounted on the upper surface of the sample chamber 21 and an alignment pattern formed on the wafer 23. The alignment is an operation for aligning the coordinate system of the wafer 23 and the coordinate system of the XY stage 22, and the optical microscope image of the alignment pattern is compared with an alignment pattern reference image registered in advance, and the field of view is referred to. The stage position coordinates are corrected so as to overlap the visual field of the image for use. In step 28, the aligned wafer 23 is stage-moved to a predetermined sample cutting position, and the cutting position is positioned using the SIM image.

  After positioning the cut-out location, the process proceeds to step 29 where a focused ion beam shaped so that the beam shape is suitable for high-speed processing is irradiated to cut out a section of a predetermined size (for example, several μm square and several hundred nm thick). The cut sample is fixed to the sample manipulator.

  FIG. 6 is a diagram for explaining a sample cutting process from the wafer 23 by the focused ion beam. When cutting out the sample, for example, a cell projection diaphragm 16 as shown in FIG. 7 is used in order to achieve both high-speed rough machining and finishing with high positioning accuracy. The cell projection diaphragm 16 includes a C-shaped cell unit 101 having a C-shaped beam transmission unit 102 and a spot beam unit 105. The central portion 103 of the C-shaped cell portion 101 is a cut-out sample portion, and a beam-like portion 104 that connects the central portion 103 to the peripheral portion is a sample support portion during processing.

  As shown in FIG. 6A, the C-shaped cell portion 101 on the left side of the beam stop 16 is irradiated with a focused ion beam to form a C-shaped beam, and after rough cutting, the beam irradiation position on the stop 16 is set. A thin spot beam is formed by switching to the spot beam portion 105 on the right side, and finishing is performed as shown in FIG. In the processing portion of the wafer, an observation sample portion 106 is formed corresponding to the central portion 103 of the C-shaped cell portion 101 of the beam stop 16, and a support portion 107 is formed corresponding to the beam-like portion 104. At the time of cutting, in order to obtain a high processing speed and a smooth processing cross section, a reactive gas for assisting ion etching is introduced from the reactive gas introduction part 45 to make the vicinity of the ion beam irradiation point a reactive gas atmosphere. For example, a fluorine-based gas is introduced into the vicinity of a processing location for processing a silicon oxide film and a chlorine-based gas for processing a metal wiring. A section or a plane is selected as the slice according to the observation purpose.

  As shown in FIG. 6C, after the wafer is tilted and the lower part of the sample section is cut, the sample is fixed to the sample manipulator 108. The sample is fixed to the sample manipulator 108 by, for example, bringing the tip of the manipulator into contact with the upper surface of the sample in an atmosphere of tungsten compound gas and irradiating the contact portion with an ion beam to form the tungsten film 109. The sample is supported on the tungsten film 109 and fixed to the sample manipulator 108 as shown in FIG. After that, as shown in FIG. 6E, the sample 110 is cut out by cutting the support portion 107 with a focused ion beam. The sample is fixed to the manipulator by bringing the tip of the manipulator into contact with the sample surface, controlling the manipulator driving unit 44 to apply a voltage to the manipulator, and generating an attractive force using an electrostatic action between the sample and the sample. The manipulator may be fixed by electrostatic adsorption.

  Returning to FIG. 5, in step 30, the sample 110 fixed to the sample manipulator 108 is moved onto the observation sample holder loaded at a predetermined position in the sample chamber 21 by the movement of the sample manipulator and / or the observation sample holder. Moved to. FIG. 8 is a schematic view showing an example of a sample fixed to the observation sample holder 66. FIG. 8A is a top view of an observation sample holder loaded with a sample, and FIG. 8B is a cross-sectional view taken along line AA ′. The illustrated observation sample holder 66 includes a carbon thin film 123 supported by a metal mesh 122 at one end of a cylindrical main body 121, and an address is assigned to each section defined by the metal mesh 122. The cut samples 131 to 134 are loaded into pre-registered address positions designated by the sample preparation recipe 37 on the observation sample holder or read from the memory based on the sample preparation recipe.

  On the other hand, in step 31, the control unit 31 of the FIB apparatus uses information such as the product name related to the sample, the in-process name, the address number of the die to which the sample belongs, the address position on the observation sample holder, and the inspection contents. Then, an observation recipe 88 using the holder number as a key is created. The observation recipe 88 defines the observation procedure, observation conditions, and observation result output conditions for the sample mounted on the observation sample holder. If the TEM / STEM recipe for the holder number of the observation sample holder carried into the sample chamber 21 of the FIB apparatus already exists in the memory 34 of the FIB apparatus before the observation recipe 88 is created in step 31, Since it is a recipe relating to a sample that has been observed before, the recipe data is deleted and the contents of the observation recipe are initialized.

  In step 32, with respect to the wafer on the XY stage, it is determined whether or not the sample cutting and mounting on the observation sample holder at all the locations specified in the sample preparation recipe 37 have been completed. The processing from step 28 to step 31 is repeated until the cutting is completed.

  In step 33, the observation sample holder that has finished loading the sample and the wafer that has been cut out of the sample are returned to their respective carriers. On the other hand, since the observation recipe 88 created in step 31 is input to the TEM / STEM used for inspection, in step 34, the observation recipe 88 is output via a communication line or using a storage medium. If unprocessed wafers to be inspected remain in the wafer carrier in the determination in the next step 35, the processing from step 21 is repeated for those wafers.

  FIG. 9 shows a description item example of the observation recipe 88. In the illustrated observation recipe 88, information such as a product holder number, information on a wafer from which a sample has been cut out, information such as a product name, a lot name, a wafer number, and a die address are described. Further, as the inspection information, information such as the sample address in the holder, the inspection item, the inspection procedure, the acceleration voltage, the beam current, the detection signal, and the detection result output are described. In the illustrated example, for example, the sample mounted on the sample address A-1 in the holder should be inspected for polysilicon film thickness by an STEM using a type 3 inspection procedure at an acceleration voltage of 100 kV and a beam current of 1 nA. The result is instructed to be output as a type 2 wafer map. In FIG. 9, types such as inspection procedure and inspection output mean that data registered in advance is called and used.

  Among these pieces of information, the sample holder number is acquired in step 14 of FIG. 4, and information such as the product name, lot name, wafer number, die address, and the like regarding the wafer from which the sample is cut out is stored in the sample preparation recipe 37. This is the information that was written. Among the inspection information, information such as the sample address in the holder, the inspection item, the inspection procedure, the acceleration voltage, the beam current, the detection signal, and the detection result output are based on the information described in the sample preparation recipe 37 or based on it. This is pre-registered information read from the memory. In this way, the control unit 31 of the FIB apparatus cuts out the sample from the designated location of the wafer designated according to the sample preparation recipe and loads the sample into the observation sample holder, and specifies the sample on the TEM / STEM side. An observation recipe is created by combining necessary information, that is, information on an observation sample holder loaded with the sample and address information on the holder, and information on the inspection method of the sample inherited from the sample preparation recipe. Via TEM / STEM and database.

  10 and 11 are diagrams for explaining an example of how to cut out a sample in the FIB apparatus. The sample cut out from the wafer needs to have a cross section at the center of the pattern in order to measure the hole pattern or the like with high accuracy. Even if the accuracy of the irradiation position of the focused ion beam is slightly worse, in order to produce a cross section near the center of any pattern, the observation pattern is gradually changed in a direction perpendicular to the processing cross section as shown in FIG. It is preferable to use a sample for cross-sectional observation composed of a plurality of pattern groups arranged in a shifted manner. 10A is a top view of the wafer including the sample cutout portion 140, and FIG. 10B is a cross-sectional view. In this sample, the inspection pattern 142 having the maximum lateral length appearing in the cross section is determined to be the optimum inspection pattern in which the cross section is formed at the substantially central portion.

  Further, in order to make the film thickness measurement with TEM / STEM more accurate, it is necessary to make the incident direction of the electron beam parallel to the observation film surface. In order to be able to confirm or correct the parallelism between the incident direction of the electron beam and the observation film surface, a step 152 may be formed on the observation cross section 151 of the sample 150 as shown in FIG.

When the sample 150 shown in FIG. 11 is observed with a TEM / STEM, the incident direction of the electron beam of the TEM / STEM is not parallel to the observation film surface of the film 153 for measuring the thickness, as shown in FIG. Thus, a transmission image in which the film is discontinuous between the stepped portion 152 and the non-stepped portion is obtained. In this case, the film thickness T2 measured on the sample image includes an error. On the other hand, when the incident direction of the electron beam of TEM / STEM is parallel to the observation film surface, the film 15 3 of the upper surface 154 and lower surface 155 are each stepped portion 152 as shown in FIG. 12 (a) and the non-stepped portion A continuous transmission image can be obtained. The measured value T1 in this case accurately represents the film thickness of the film 153. Accordingly, by tilting the XY stage of the TEM / STEM or adjusting the incident direction of the electron beam 62, the film thickness is measured so as to form a TEM image or STEM image as shown in FIG. Since it is ensured that the incident direction of the electron beam is parallel to the observation film surface, an accurate film thickness measurement value can be obtained.

  Next, an inspection method using TEM or STEM and an output method of inspection results will be described. FIG. 13 is a flowchart showing the flow of processing in the TEM or STEM.

  In step 41, the sample holder carrier on which the observation sample holder to be inspected is placed is automatically transported or carried by the operator from the FIB apparatus to the TEM / STEM and mounted on the load / unload unit 86 of the sample holder carrier. In step 42, the holder number written on the observation sample holder is read by the holder number reader attached to the load / unload unit 86. In step 43, using the read holder number as a key, an observation recipe 88 corresponding to the observation sample holder that has been created in advance by the FIB apparatus and transferred and overwritten in the TEM / STEM is read out. Subsequent operations are automatically or semi-automatically performed according to the observation recipe 88.

  In step 44, the observation sample holder to be measured is taken out from the holder carrier and then loaded in a predetermined direction on a XY stage 65 in the sample chamber held in a vacuum. In the following step 45, the observation sample holder 66 loaded on the XY stage 65 is moved to the address where the first sample specified by the observation recipe 88 is located, and the observation point is positioned.

  When positioning the observation location, if the observation pattern is composed of a plurality of pattern groups as shown in FIG. 10, for example, by selecting the cross section of the inspection pattern that maximizes the horizontal line length, An inspection pattern with a cross section near the center is selected as the observation location. In addition, when a step as shown in FIG. 11 is formed in the processed cross section of the sample, the incident direction of the electron beam 62 or the inclination of the XY stage 65 is adjusted, and a non-step portion as shown in FIG. By observing the lines of the film upper surface and the film lower surface formed by the step portion as a straight line, the electron beam and the observation film surface can be made parallel. Instead of adjusting the incident direction of the electron beam 62 or the inclination of the XY stage 65, the angle formed by the electron beam 62 and the observation film surface is obtained, and the obtained film thickness is used to correct the film thickness measurement data. May be.

  Next, the process proceeds to step 46, and the sample is irradiated with the electron beam 62 in accordance with the instruction of the observation recipe 88, elemental analysis using transmission electron image formation or characteristic X-ray analysis, and transmission electrons using the electron energy spectrometer 76. Energy analysis. The transmission electron image may be a projection image obtained by a normal transmission electron microscope or a scanning image obtained by a scanning transmission electron microscope. The scanned image is easier to interpret and easier to handle than the projected image because there is no change in diffraction contrast due to a slight difference in focal position.

  Then, the obtained transmission electron image and / or elemental analysis information are analyzed, and the film thickness of the predetermined portion of the thin film, the shape dimension of the pattern as shown in the cross-sectional example of the hole pattern in FIG. (Diameter d1, bottom diameter d2, height h, inclination angle θ), overlay d3 of pattern 161 and pattern 162 as shown in the cross-sectional example of FIG. 14B, and cross-sectional example of FIG. 14C. Conduction and non-conduction of the hole 163, the crystal grain size of the deposited film as shown in the cross-sectional example of FIG. 14D (164 is the crystal grain, 165 is the grain boundary), and shown in the cross-sectional example of FIG. Detection of defects 168 in comparison with a pre-stored reference image as shown in the dopant concentration profile 167 in the dopant layer 166, and a deposited film cross-sectional example in FIG. 14 (f) (compare the sample image with the reference image). To detect the difference and missing the difference. Output as 168) such as to obtain predetermined inspection data. The analysis of the observation data may be performed in real time, or the transmission image or data for each sample may be acquired and stored, and the analysis may be performed offline.

Elemental information obtained from elemental analysis and transmission electron energy analysis not only determines the composition state, but also determines the film thickness, pattern geometry, hole conduction / non-conduction, crystal grain size, dopant concentration profile, etc. Indispensable for. For example, when measuring the film thickness of a SiO ₂ / Si ₃ N ₄ laminated film, the contrast difference between the two appearing in the transmission electron image is small. It is difficult to determine accurately. However, by detecting and comparing characteristic X-rays, Auger electrons, characteristic energy loss electrons, etc., it becomes possible to determine the boundary between them more precisely.

  The transmission electron image and element concentration profile are compared with the pre-stored reference image of the inspection location, and the defects detected as the difference between them are not only in the film thickness, shape and dimension, but also in the hole filling portion and plug. Pinholes, poor coverage of deposited films, crystal defects such as stacking faults, and the like. The detected defects are classified according to a predetermined automatic defect classification algorithm.

  Returning to FIG. 13, the inspection of all the samples on the observation sample holder is performed by repeating the processing from step 45 to step 46. If it is determined in step 47 that the inspection of all the samples on the sample holder has been completed, the process proceeds to step 48 where the observation sample holder is unloaded onto the sample holder carrier. Subsequently, the process proceeds to step 49, where an inspection result is created and output based on the measurement data obtained in step 46. If it is determined in step 50 that there is an uninspected observation sample holder in the sample holder carrier, the processing from step 42 to step 49 is repeated.

  The form of the inspection result output in step 49 may be the sample image or the observation data as it is. However, in general, as shown in FIG. Or it outputs in the form of defect classification results. If the inspection die is clicked on the wafer map, the sample image corresponding to the die and the raw data of observation can be displayed together. Note that not only charts such as wafer maps and charts but also a predetermined report format can be processed and output. In general, the data is output to a higher-level inspection data management system via a communication line or a storage medium, but can also be output as a printed matter.

  Further, by handling these in-line measurement data in an integrated manner, data for more advanced process management and transistor characteristic analysis can be obtained. For example, by performing in-line measurement of the gate insulating film thickness and the dopant concentration profile of the source / drain region simultaneously with the gate length, data for accurately predicting the electrical characteristics of the transistor such as a threshold voltage in real time can be provided. These data are output to a higher-level production management system and used to precisely manage device performance / reliability and yield.

  The sample holder carrier that has been inspected is sent to a sample storage unit connected to the TEM or STEM by a transporter, and the inspected sample is stored in the sample storage unit while being placed on the observation sample holder. These samples are stock-managed using the wafer number, product name / work-in-process name, holder number, etc. as keys, and are taken out and re-investigated if yield or reliability issues occur later. The Note that the sample storage can be arranged between the FIB apparatus and the TEM / STEM as a buffer as shown in FIG. 16 in consideration of the consistency of processing time between the FIB apparatus and the TEM / STEM. Good.

  Note that TEM or STEM magnification calibration is performed by observing a crystal lattice image. As a result, measurement data with very accurate dimensions and shapes can be obtained. Both the wafer carrier and the sample holder carrier are kept in a clean atmosphere. In particular, when the composition of a sample is analyzed, the sample holder carrier used is considered so that the sample is not contaminated with molecules.

  In this embodiment, the SIM image is used to position the cut-out position. However, a high-resolution optical microscope or scanning electron microscope (SEM) is built in the focused ion beam device, and the optical microscope image or SEM image is used. It is also possible to position. By positioning using an optical microscope image or SEM image instead of the SIM image, damage to the wafer due to positioning can be further reduced.

  In this embodiment, the observation sample holder is numbered, and the TEM / STEM inspection is controlled using the holder number. However, instead of using the holder number, focusing is performed along with sample preparation. The sample number may be imprinted on each sample with an ion beam, and the observation recipe 88 may be created using the sample number to control the inspection work.

  In the present embodiment, a case where a plurality of samples cut out from one wafer is placed on one observation sample holder is shown, but a plurality of samples cut out from one wafer are a plurality of observation samples. Samples cut from a plurality of wafers may be collectively placed on one observation sample holder. As for the inspection contents, it is possible to perform a plurality of types of inspections on one sample, or to change the inspection contents individually for the samples in the observation sample holder.

  In the present embodiment, the case in which the designation of the sample extraction location in the FIB apparatus is determined in advance for each product name and in-process step name, but the specification of the sample extraction location in the recipe is performed using the defect position coordinate data of the defect inspection apparatus, It can be overwritten differently for each wafer, as in the case of position coordinate designation on the wafer map of the operator. In addition to determining the cutting location for each product name and work-in-process name, if it is possible to overwrite the defect position coordinate data for each wafer, it can be used for review inspection after defect inspection, etc. .

In this embodiment, the tungsten support film is used for fixing the sample to the sample manipulator, but the fixing deposition film is not limited to this.
In the present embodiment, the case where both the FIB apparatus and the TEM / STEM are configured as a stand-alone is shown, but it is also possible to configure as a single apparatus including the FIB apparatus and the TEM / STEM. It is also possible to connect a plurality of TEM / STEMs to one FIB apparatus.

  Confirmation and correction of cross-section observation sample consisting of multiple pattern groups in which the observation pattern is slightly shifted in the direction perpendicular to the processed cross-section, and the parallelism between the observation beam incidence direction and the observation film surface As can be done, the cross-sectional sample with the step processed is not limited to TEM / STEM, and can be used for various observation devices such as SEM and optical microscope.

  In this embodiment, the manufacture of semiconductor elements is taken as an example, but the present invention can also be applied to the manufacture of similar elements such as image pickup elements and display elements.

  Combining 'sample observation by TEM or STEM' with 'sample preparation by FIB apparatus', (1) In the FIB apparatus, sample extraction is performed for a plurality of designated locations on the wafer according to a pre-registered sample preparation recipe Positioning automatically, cutting out the sample automatically, mounting the cut sample on the sample holder for observation used in TEM / STEM, and creating a recipe for observing the sample with TEM / STEM, (2) In the TEM / STEM, according to the observation recipe created by the FIB apparatus and input to the TEM / STEM, a plurality of samples mounted on the observation sample holder are targeted, and the observation region is automatically aligned. Performing in-line film thickness measurement with high accuracy for a local region of about several hundred nanometers by acquiring a predetermined sample image It can become.

  In addition, when TEM / STEM is used, it is possible to perform composition analysis, structural analysis, and electronic state analysis of a very small region in combination with high-resolution sample image formation. Since this analysis / analysis information can be used in combination, it is difficult to measure the thickness of each layer of in-line laminated film, measure the three-dimensional shape of the pattern, measure the pattern overlay accuracy, and connect the wiring. Thus, it is possible to accurately and accurately measure the conduction state of the film, measure the particle size of the film-forming substance, measure the composition distribution of the trace impurities in the film, and compare the defects with a predetermined reference image. Further, by handling these in-line measurement data in an integrated manner, more advanced process management and transistor characteristic analysis are realized. For example, if the gate insulating film thickness and the dopant concentration profile of the source / drain region are measured in-line at the same time as the gate length, the transistor electrical characteristics such as threshold voltage can be accurately predicted in real time. That is, data that can accurately manage the performance / reliability and yield of the device, which has never been obtained before, can be acquired by in-line inspection.

  In addition, since the inspected sample can be stored, it can be taken out of the storage and reexamined when the yield or reliability problem occurs later. This facilitates failure analysis that is forced to be difficult without the actual product.

  Furthermore, since the crystal lattice image can be observed, the magnification calibration of the apparatus can be performed very accurately, and measurement data with very accurate dimensions and shapes can be obtained.

It is a figure which shows schematic structure of an example of the FIB apparatus by this invention. It is a figure which shows schematic structure of TEM or STEM by this invention. It is a conceptual diagram of the in-line test | inspection in the semiconductor device manufacturing process by this invention. It is a flowchart explaining the process for preparing the sample holder for observation. It is a flowchart explaining a sample preparation process and an observation recipe preparation process. It is explanatory drawing of the process of cutting out the sample from a wafer using a focused ion beam. It is a figure which shows the example of the aperture_diaphragm | restriction for cell projection for obtaining the shaped ion beam. It is the schematic which shows the example of the sample fixed to the sample holder for observation. It is a figure which shows the example of a description item of the recipe for observation. It is a figure explaining the example of how to cut out the sample by a FIB apparatus. It is a figure which shows the example of a cross-sectional sample with a level | step difference. It is a figure which shows the example of the transmitted image of the cross-sectional sample with a level | step difference. It is a flowchart which shows the flow of a process in TEM or STEM by this invention. It is a figure for demonstrating the application example of the test | inspection in this invention. It is a figure which shows the example of an output of a test result. It is a figure which shows the example of arrangement | positioning of a sample storage. It is a figure which shows the schematic diagram of the structure of a vertical MOS transistor.

Explanation of symbols

  11: ion gun, 12: ion beam, 23: wafer, 61: electron gun, 62: electron beam, 65: XY stage, 66: sample holder, 71: transmission electron, 73: transmission electron detector, 88: for observation Recipe, 150: Sample, 151: Observation cross section, 152: Step, 153: Film

Claims (2)

Loading a semiconductor wafer to be inspected into one apparatus composed of a focused ion beam apparatus and a scanning transmission electron microscope;
Cutting a sample from a semiconductor wafer by a focused ion beam;
Mounting the cut-out sample on an observation holder;
Measuring a scanning transmission image from a direction in which an observation film surface appearing in a section of the cut-out sample and a sample incident direction of an electron beam are parallel to each other by the scanning transmission electron microscope,
The step of measuring with a scanning transmission electron microscope a scanning transmission image from a direction in which the observation film surface appearing in the cut section of the sample is parallel to the sample incident direction of the electron beam is an observation film appearing in the cross section of the sample A step of measuring the film thickness of the observation film surface from a direction in which the surface and the specimen incidence direction of the electron beam are parallel and a direction perpendicular to the observation cross section to be measured; and a scanning electron microscope A method for inspecting a semiconductor wafer, comprising: making a sample incident direction of the electron beam parallel to an observation film surface of the sample. The inspection method according to claim 1,
A step of forming a step in the observation cross section for measuring the film thickness of the sample cut out by the focused ion beam,
In the step of making the specimen incident direction of the electron beam parallel to the observation film surface, a scanning transmission image is obtained in which the upper surface and the lower surface of the film whose thickness is to be measured are continuous at the step portion and the non-step portion, respectively. A method for inspecting a semiconductor wafer, characterized by adjusting.

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