Multi-Stage/Multi-Chamber Electron-Beam Inspection System

Abstract

Techniques for yield management in semiconductor inspection systems are described. According to one aspect of the present invention, columns of sensing mechanism are configured with different functions, weights and performances to inspect a sample to significantly reduce the time that would be otherwise needed when all the columns were equally applied.

Claims

1. A semiconductor inspection system comprising: columns of sensing mechanism; a moving mechanism to position a sample under the columns of sensing mechanism; and a controller executing a module configured to configure the columns to carry out a type of inspection according to at least one of functions, weights and performances so that the columns are adaptively used to sense a sample being inspected.

2. The inspection system as recited in claim 1, wherein the controller is caused to access an outline or layout of the sample so that the columns are properly configured to minimize a time that would be otherwise spent by the columns when equally configured to proceed with the type of inspection.

3. The inspection system as recited in claim 2, wherein areas of the sample are simultaneously sensed by the columns configured with different tasks.

4. The inspection system as recited in claim 3, wherein the columns are divided into at least two groups, one for inspection and the other for review, the columns in different groups work in time order.

5. The inspection system as recited in claim 3, wherein the columns are set with different weight values, the columns with higher weight values are primarily used in scanning.

6. The inspection system as recited in claim 3, wherein the columns with different performances are assigned with different scanning jobs or for different areas of the sample.

7. The inspection system as recited in claim 1, wherein the columns are equipped in at least one vacuum chamber at least one stage.

8. The inspection system as recited in claim 1, wherein the columns are equipped in each of some of N vacuum chambers, each of the N chambers including at least one stage, the N vacuum chambers provided to perform different inspections.

9. The inspection system as recited in claim 8, wherein the N vacuum chambers are assigned orderly, wherein the vacuum chambers close to an input port to receive the sample are labeled with lower order while the vacuum chambers close to output ports to exit passed samples have higher order.

10. The inspection system as recited in claim 9, wherein a path of inspecting the sample through some of the N vacuum chambers is determined by the order.

11. The inspection system as recited in claim 10, wherein up to N samples can be inspected simultaneously.

12. The inspection system as recited in claim 11, wherein the semiconductor sample is a wafer or a mask.

13. The inspection system as recited in claim 1, wherein the sensing mechanism is based on an electron beam.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where:

[0013] FIG. 1 shows an exemplary inspection system in which the present invention may be applied to significantly improve the throughput without sacrificing the sensitivity or performance thereof;

[0014] FIG. 2A, it shows a conceptual diagram of a controller programmed or caused to control N stations, where N is at least two (2);

[0015] FIG. 2B illustrates an internal functional block diagram of a computing device that may be used as the controller in FIG. 2A;

[0016] FIG. 3A shows a wafer/mask being inspected or routed from chamber 1 to chamber 3 with increasing inspection precision, where three chambers are arranged in a linear path;

[0017] FIG. 3B shows a chamber with three stages arranged in a linear path;

[0018] FIG. 4A and FIG. 4B show another embodiment in which four chambers/stages are arranged in a system to provide multiple paths to enhance the throughput of the inspection system;

[0019] FIG. 5 shows a flowchart or process of conducting an inspection of a sample along a multi-path;

[0020] FIG. 6A shows a section of exemplary columns, not all columns are used equally, where the columns are assigned with different functions;

[0021] FIG. 6B shows another section of exemplary columns, where columns with higher weights have higher priority in scanning;

[0022] FIG. 6C shows that columns with different performance scan different areas; and

[0023] FIG. 7 shows a flowchart or process of assigning columns with different functions.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] The detailed description of the present invention is presented largely in terms of procedures, steps, logic blocks, processing, or other symbolic representations that directly or indirectly resemble the operations of inspection instruments or devices. These descriptions and representations are typically used by those skilled in the art to most effectively convey the substance of their work to others skilled in the art. Numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will become obvious to those skilled in the art that the present invention may be practiced without these specific details. In other instances, well known methods, procedures, components, and circuitry have not been described in detail to avoid unnecessarily obscuring aspects of the present invention.

[0025] Reference herein to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments.

[0026] Embodiments of the present invention are discussed herein with reference to FIGS. 1-7. However, those skilled in the art will readily appreciate that the detailed description given herein with respect to these figures is for explanatory purposes as the invention extends beyond these limited embodiments.

[0027] Referring now to the drawings, in which like numerals refer to like parts throughout the several views, FIG. 1 shows an exemplary inspection system 100 in which the present invention may be applied to significantly improve the throughput without sacrificing the sensitivity or performance thereof. The exemplary system 100 is shown to include a chamber 102 and a chamber 104, each of the chambers 102 and 104 is shown to have N stages, where N is an integer and at least one. Traditionally, items to be inspected or samples 106 (e.g., wafers or masks) are routed into the chamber 102, each of the samples 106 go through each of the stages therein for predefined inspections. Those samples that have passed the chamber 102 are now to go through the chamber 104, where additional inspections are to be conducted thereon. It can be observed that the throughput of the system 100 is essentially controlled by the number of the stages in a chamber together with the test procedures at each of the stages. Given the linear arrangement of the stages or chambers, the more chambers/stages there are in an inspection system, the lower the throughput for the system.

[0028] In reality, not all samples have to go through each of the stages in a chamber or all the chambers, if there are any. Further it is much more efficient to carry out a serial of inspections over several stages rather than completing a comprehensive inspection at one stage. One of the benefits, advantages and objectives in one embodiment of the present invention is to enhance the throughput by dynamically routing a sample (e.g., wafer/mask) from one station to another. Unless explicitly stated, as used herein, a station means a stage or a chamber. As the name suggests, a stage is a set of test procedures to be performed on a sample for a designated inspection in an entire inspection process while a chamber is a relatively standalone process in which there are a set of particular inspections to be performed collectively on a sample to detect if there are one or more particular defects on the sample. In other words, a chamber may include several stages while an inspection instrument includes at least one chamber.

[0029] According to one embodiment, a stage is a platform that holds a sample and has a mechanism to move in a direction so that the sample may be inspected (e.g., by an electron beam microscope). A stage must be situated inside a chamber. A chamber is a vacuum chamber that holds one or more stages.

[0030] Referring now to FIG. 2A, it shows a conceptual diagram of a controller 200 programmed or caused to control N stations, where N is at least two (2). Depending on implementation, the controller 200 may be part of an inspection instrument or a computing device provided to control the operation of these stations. According to one embodiment, test items or samples are not sequentially set to go through each of these stations. Instead, depending on the test result from a station, the controller is designed to route a sample to a next station deemed most appropriate without delay to carry out a next inspection task on the sample. According to another embodiment, some of the stations are duplicated to improve the throughput, which means each of the duplicated stations performs an identical task. For example, a certain task at a station takes a longer time to finish than tasks at other stations. Instead of waiting for a station to complete a designated task, the duplicated stations thereof can be used to start the task on other test samples, hence minimizing a time gap between two adjacent stations.

[0031] Referring now to FIG. 2B, it illustrates an internal functional block diagram 220 of a computing device that may be used as the controller in FIG. 2A. The computing device includes a microprocessor or microcontroller 222, a memory space 224 (e.g., RAM or flash memory) in which there is a control module 226, an input interface 228, a screen driver 230 to drive a display screen 232 and a station interface 234. According to one embodiment, the control module 226 is implemented to realize one embodiment of the present invention. Depending on implementation, the control module 226 may be loaded into the memory space 224 via an interface (e.g., a storage medium or a data network). When the control module 226 is executed by the microcontroller 222, a plurality of (test) stations can be effectively controlled and test samples can be seamlessly routed among the stations to carry out necessary inspection tasks so as to enhance the throughput without scarifying the performance of the inspection system.

[0032] The input interface 228 includes one or more input mechanisms. A user may use an input mechanism to interact with the device 220 by entering a command. In the context of the present invention, the input interface 228 receives test signals (e.g., scanning signals at preset resolutions), the microcontroller 222 is caused to perform processing and analysis of the test signals. Based on the results from the test signals, the microcontroller 222 executing the control module 226 controls which station is called upon to carry out a next inspection task.

[0033] The driver 230, coupled to the microcontroller 222, is provided to take instructions therefrom to drive the display screen 232. In one embodiment, the driver 230 is caused to drive the display screen 232 to display a test result of a sample, for example, an indication of pass or fail of the sample. In one embodiment, the display screen 232 is caused to display which station is the next for a sample being inspected with a set of parameters to show the pass or fail of the sample from a previous station. The display screen 232 allows an operator (e.g., a fab manager) to assess the current status of the manufacturing process. The network interface 234 is provided to allow the device 220 to communicate with or control all the stations via a designated medium (e.g., a data bus or network).

[0034] According to one implementation, the control module 226 is loaded in the memory 224 and executed by the controller 222 to reconfigure the columns in a multicolumn electron-beam inspection tool used in at least one of the stations. Instead of uniformly using all the columns, the columns of a system are allocated by the control module 226 by their functions, weights, and/or performances. More importantly, based on test results from a previous station, the columns are allocated effectively for a particular sample or a particular area thereof to reduce the time or/and inspection effort or details spent by the columns on the sample or the area thereof. As a result, the overall throughput for the station is considerably enhanced to make it possible for use in-line in a semiconductor fabrication facility.

[0035] FIG. 3A shows an exemplary flow 300 of three chambers being organized to form one or more paths for wafer/mask inspection. The inspection procedure in each chamber is determined by its order in the path and the relative columns used. The assignment of the functions of the chambers follows a methodology to maximize the total throughput. The wafer/mask is then inspected or reviewed in different chambers for the features of certain types and care areas, and transferred according to the order of the pipeline. For a system with N chambers, a maximum number of N wafers can be processed simultaneously.

[0036] Various modes of inspection, which are mainly categorized into linear-path or multi-path by the pipeline, can be arranged flexibly. For the linear-path inspection, such as in the three-chamber system, the wafer/mask is inspected in the chambers in a serial order. The first chamber is used to perform a coarse inspection (e.g., pixel size around 20 nm). The second chamber is used to perform a fine inspection (e.g., pixel size around 5 nm), and the third chamber is used to perform defects review (e.g., pixel size less than 2 nm). The wafer/mask is then inspected or routed from chamber 1 to chamber 3 with increasing inspection precision as shown in FIG. 3A. Those skilled in the art can appreciate that the linear-path inspection as shown in FIG. 3A is designed to increase the throughput. For example, if a sample is inspected with a system including one chamber and one stage, the total inspection time is assumed T. For a system with one chamber including three parallel stages, the average time at each stage is roughly assumed T/3. But the total inspection would be larger than T when the transfer time is taken into account, e.g., 1.2T. However, when the sample is moved to one of three stages, one of the remaining two staged can inspect a next sample, and a third sample can be followed on the remaining stage, making the inspection procedures of the three samples almost in parallel. Thus a sample can be finished with this system about every 0.4T. For a whole period of 60T, a one-stage-one-chamber system would finish 60 samples while a one-chamber-three-stage system according to FIG. 3A could finish more than 150 samples (less than 180 samples since the first/last sample does not have sample before/after it). As a result, the throughput is greatly increased.

[0037] FIG. 3B shows a chamber with three stages arranged in a linear path. Similar to FIG. 3A, each of the three stages is set for inspecting a series of samples for defects within a limit. The sample is first inspected with a normal inspection sensitivity (a larger pixel size), and a wider area. If no defect is found, the sample is unloaded for quick throughput. If, however, defects or possible defects are found, the sample is loaded to the next stage and inspected with a higher sensitivity (a smaller pixel size) so that the defects are studied to figure out the issues with the manufacturing process. The inspection with the higher sensitivity is conducted in a much smaller, targeted area so that the throughput is not negatively affected. As a result, the overall throughput of the three stages can be enhanced.

[0038] With more chambers/stages, the transfer connections can be set up and arranged more flexibly, giving more flexibility to the inspection arrangement and scheduling. For example, FIG. 4A and FIG. 4B show the schematics of another embodiment of this invention, where four chambers/stages are configured in a system. The first chamber/stage (for coarse inspection) is connected to two chambers/stages (namely Chamber/Stage 2 and 2a, for inspection with pixel size around 5 nm). When the coarse inspection in chamber1/stage1 is done, the control (i.e., the control module 226) is configured to decide in which chamber/stage the next fine inspection should take place. If one of chamber/stage 2 or 2a is busy, then the sample should logically be sent to the other, therefore greatly reducing the chance of “traffic jam” of the inspection work flow. The wafer/mask can be inspected in Chamber/Stage 2 or 2a after Chamber/Stage 1 inspection, and later be transferred to Chamber/Stage 3 for review. Chamber 2 and Chamber 3 each is connected to an output port, where Chamber 2 exits those samples that have no need for review in Chamber/Stage 3. Thus, the multiple paths include: 1.fwdarw.2.fwdarw.3, 1.fwdarw.2a.fwdarw.3, and 1.fwdarw.2.

[0039] Given the description above, those skilled in the art can easily understand how more chambers/stages in an inspection system can be configured to route a sample without causing a traffic jam. It can also be understood that the multi-path configuration increases the flexibility in scheduling the inspection tasks and increases the efficiency of the entire inspection process. The configuration ensures that a potential blockade at some spots along the inspection line would not block the whole processing.

[0040] For systems with N chambers/stages, a preferred setting is to assign the chambers/stages with different inspection steps orderly when N is small (e.g., 2-3). The chambers/stages close to the input ports are labeled with lower order while those close to the output ports have higher order. Chambers/stages with higher order are usually assigned with finer inspection task. The path of wafer/mask transfer is then determined by the order. When the inspection for one wafer/mask in the i.sup.th chamber (or at the i.sup.th stage) is finished, the wafer/mask is moved to the next (i+1.sup.th) chamber/stage for next-step inspection (usually with finer resolution) if the inspection of the wafer/mask in the next (i+1.sup.th) chamber/stage has also been completed. If the next (i+1.sup.th) chamber/stage is still occupied, then the current wafer/mask will stand by until the next chamber/stage is ready. Up to N wafers/masks can be inspected simultaneously.

[0041] If N is larger (≧4), multiple paths is created and the order of the chambers/stages is configured flexibly. A chamber/stage (order i.sup.th) can be connected to two or more chambers/stages (with same order or different order), thus wafers/masks can be set to follow different paths for different types of inspection. The setting can be modified if needed. It is possible to change the order of the chambers/stages or switch between different paths (e.g., from linear path to multi-path or reversed). By combining with various multi-columns, more specific inspection needs can be satisfied.

[0042] Referring now to FIG. 5, it shows a flowchart or process 500 of conducting an inspection of a sample along a multi-path. The process 500 may be implemented in software as a module or in combination with software and hardware. To facilitate the description of the process 500, the previous drawings shall be referred to.

[0043] According to one embodiment, a plurality of samples are moved along a moving mechanism (e.g., a convey belt or a mechanical arm) through a set of stations. The process 500 starts when one of the samples is moved into a station that is set to conduct one type of inspection. At 502, the station, also referred to as first station, is caused to examine if the sample is in place. For example, a wafer is moved onto a platform in the station, a camera is used to check if the sample is in place for inspection. In operation, an image from the camera is sent back to a module (e.g., the control module 226 of FIG. 2B). After the image is processed, a decision can be inferred whether the sample is in place or not. If not, the sample can be repositioned. Once it is determined that the sample is in place, the process 500 moves to 504 to conduct the type of inspection specifically at the station. According to one embodiment, the first station is designed to conduct an inspection with larger pixel size (e.g., 20 nm) and to inspect a wider area. When the first inspection is finished, the process 500 moves to 506 to determine if further inspection is needed. If there would be no need to conduct further inspection, the sample will be unloaded from the system. If it is determined further inspection is warranted, the process 500 goes to 508 to determine which one of the next (second) stations available to conduct another type of inspection on the sample. According to one embodiment, the second station is designed to conduct an inspection with smaller pixel size (e.g., 5 nm).

[0044] As described above, there are more than one second stations. The control module 226 of FIG. 2B is configured to minimize any time duration between two stations by determining an immediately available second station to take in the sample. In operation, the sample existing from the first station and automatically routed to the chosen second station is conducted the second type of inspection. The process 500 comes to 510 to determine whether the sample needs to be reviewed, based on the results of the inspection result. If it is determined the sample needs to be reviewed, it will be again routed to a next (third) station to have a review inspection thereon, otherwise, the sample will be unloaded from the system.

[0045] The process 500 is described above with respect to two levels of test stations (e.g., stages or chambers). It can be appreciated by those skilled in the art that the process 500 is applicable to several levels of stations, and for a system with N stations, a maximum number of N samples can be processed simultaneously.

[0046] A station (i.e., stage or chamber) may employ various technologies to detect possible defects on a sample. According to one embodiment of the present invention, at least one station employs a multicolumn electron beam or e-beam tool for the detection of electrical defects that may be present in the sample. Within an electron column, the electron beam is generated under vacuum, focused to a small diameter, and scanned across the surface of a specimen by electromagnetic deflection coils. By using multiple columns, a sample can be simultaneously imaged (e.g., by electron detectors or other imagers) by more than one column usually (maybe all of the columns in the best case), significantly increasing the throughput of the inspection.

[0047] In one embodiment of the present invention, there are roughly 200 columns distributed over a 300 mm diameter wafer. Each column covers a footprint of 20×20 mm in size over the wafer. In another embodiment of the present invention, this column footprint can be 40×40 mm, corresponding to approximately 56 columns over a 300 mm diameter wafer.

[0048] The configurations of columns in a prior art multicolumn electron-beam inspection systems set each column with same function and equal priority. The care areas or areas of interest on wafers, however, may not be located in a way that guarantees all of the care areas are covered or that the columns are used most effectively, thus resulting in low efficiency in scanning. According to one embodiment, the columns of a system are allocated by their functions, weights, and performances. The columns of certain function (e.g. inspection, review) are used for certain type of scanning, and the columns with different performances (e.g., spot size) are assigned for different jobs or care areas accordingly.

[0049] According to one embodiment, there are three basic modes of allocation and control of the columns:

1. By function: Columns are divided into groups with different functions, for example, inspection and review. The columns with different functions work in time order as controlled;
2. By weight: Columns are set with different weight values, the columns with higher weight are primarily used in scanning; and
3. By performance: Columns with different performance are assigned with different scanning jobs or for different care areas.
For various patterns or care areas, combination of these modes can be applied flexibly by following certain rules and algorithms.

[0050] Referring now to FIG. 6A, it shows that a section of exemplary columns, not all columns are used equally. As shown in FIG. 6A, one group of columns are chosen to carry out a certain inspection, e.g., coarse inspection, while another group of columns are used for subsequent inspection, e.g., fine inspection. In one embodiment, after a wafer is inspected, a review process is applied to the wafer in order to further analyze and classify defects. Sometimes, only certain critical areas of the sample need to be inspected. In this case, the critical areas can be collectively inspected by using a customized, or calculated inspection path so that all of the critical regions will be covered by either of the chosen columns in an optimal way, such as with the shortest travel distance, or fastest inspection speed.

[0051] FIG. 6B shows that another section of exemplary columns, where columns with higher weights have higher priority in scanning. FIG. 6C shows that columns with different performance scan different areas. For various patterns or care areas, combination of these modes can be applied flexibly by following certain rules and algorithms. For example, an optimization problem can be formed, given the care area locations and tasks on a sample, the configurations of the columns (the function, the weight, and the performance) and the cost factors of various actions of the e-beam tool, to minimize the distance a stage must travel to cover all the care areas, or set the functions in a specific order. In one embodiment, the inspections can be carried out in increasing precisions. The purpose is to minimize the time that would have to spend on inspecting the sample.

[0052] The weight value of a column can be determined by their location, performance or other factors, and the columns with higher weights share higher priority in scanning. Scanning jobs can then be assigned by the function, weight, and performance of the columns, or by some certain combination of these factors (following certain algorithm).

[0053] Referring now to FIG. 7, it shows a flowchart or process 700 of configuring columns based on three factors: function, weight, and performance. The process 700 may be implemented in software as a module or in combination with software and hardware. To facilitate the description of the process 700, the previous drawings shall be referred to.

[0054] According to one embodiment, a plurality of samples are moved along a moving mechanism (e.g., a convey belt or a mechanical arm) through a set of stations. To effectively use the columns of inspection tools or sensors (e.g., e-beams) at a station, at 702, the layout of the samples are accessed. In operation, the layout of the samples is analyzed to determine which area of a sample needs what sensors to sense or review, and often at what resolutions. The purpose is to minimize the time needed for various inspections of the sample.

[0055] The process 700 moves to 704 to configure the columns per the layout obtained the 702. FIG. 6A, FIG. 6B and FIG. 6C are some examples that the columns may be configured therefor. At 706, when one of the samples is moved into a station that is set for inspection by the columns. One of the columns or other sensors are provided to ensure that the sample is positioned correctly for the inspection. Once the sample is ensured that it is right in the position, the inspection proceeds as specified at 708.

[0056] As described above, the columns configured in accordance with 704 are placed to perform their respective tasks. Depending on the configuration, some do scanning, some do reviewing and analysis while others may look at different areas of the sample at same or different resolutions. Optionally, the process 700 move to 710, where the columns at the same station may be configured in time to change with different functions, weights or performance for a different type of inspection.

[0057] Those skilled in the art that the present invention leads to higher average usage rate, shorter scanning time, thus higher efficiency, which translates to higher throughput, for any multicolumn electron-beam inspection system.

[0058] The present invention has been described in sufficient details with a certain degree of particularity. It is understood to those skilled in the art that the present disclosure of embodiments has been made by way of examples only and that numerous changes in the arrangement and combination of parts may be resorted without departing from the spirit and scope of the invention as claimed. Accordingly, the scope of the present invention is defined by the appended claims rather than the foregoing description of embodiments.