Height detection system for electron beam measurement tools

Abstract

The light beam is directed towards a workpiece on the stage. The workpiece is positioned at a certain absolute distance from the electron beam tube. The light beam reflected from the workpiece is received by a sensor. The light beam is used to determine the reference distance between the electron beam tube and the workpiece on the stage.

Description

Technical Field

[0001] The present disclosure relates to a measurement system for semiconductor wafers.

Background Art

[0002] With the development of the semiconductor manufacturing industry, the demand for yield management, particularly measurement and inspection systems, has been increasing. The critical dimensions continue to shrink, and the industry still needs to reduce time to achieve even higher yields and high-value production. By minimizing the total time from detecting a yield problem to correcting it, the return on investment of semiconductor manufacturers is maximized.

[0003] Manufacturing semiconductor devices such as logic devices and memory devices typically involves processing semiconductor wafers using a number of manufacturing processes to form semiconductor devices of various shapes and multiple levels. For example, lithography is a semiconductor manufacturing process that includes transferring a pattern from a reticle to a photoresist disposed on a semiconductor wafer. Further examples of semiconductor manufacturing processes include, but are not limited to, chemical mechanical polishing (CMP), etching, deposition, and ion implantation. The arrangement of multiple semiconductor devices manufactured on a single semiconductor wafer may be separated into individual semiconductor devices.

[0004] Measurement processes are used in various stages of semiconductor manufacturing to monitor and control the process. Unlike inspection processes, which detect defects on a wafer, measurement processes are used to measure one or more characteristics of a wafer that cannot be determined using existing inspection tools. One or more characteristics of a wafer can be measured using measurement processes, thereby allowing the efficiency of the process to be determined from one or more characteristics. For example, a measurement process can measure the dimensions of shapes formed on a wafer during the process (e.g., line width, thickness, etc.). In addition, if one or more characteristics of a wafer are unacceptable (e.g., outside a predetermined range), the measured values ​​of one or more characteristics of the wafer can be used to modify one or more parameters of the process so that further wafers manufactured by the process have acceptable characteristics. Many measurement processes are performed using electron beam tools.

[0005] The absolute distance between the electron beam tube in the measuring tool and the workpiece on the measuring tool's stage is used to achieve the desired focus. Traditionally, a metal L-shaped target was machined onto the workpiece to allow mechanical alignment in the X, Y, and Z directions. The L-shaped target forms an intersection. A uniform intersection allows for alignment in the X and Y directions. Alignment in the Z direction, such as absolute distance, may include finding the best focus position. The best focus can be determined by finding where the image of the workpiece has the sharpest edge and / or the highest contrast. Because the L-shaped target is machined, it may have roughness, scratches, unevenness, or deposits. Determining the focus position can be difficult due to these imperfections in the L-shaped target. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] U.S. Patent Application Publication No. 2009 / 0309022 [Overview of the project] [Problems that the invention aims to solve]

[0007] Due to the limitations of the tooling machinery, large shape sizes cannot provide sufficient pattern complexity for complete measurement and / or evaluation of optical performance. Furthermore, machined metal trenches are rough, which can cause scattering that negatively impacts measurements. Additionally, the target may not be at the same height as the workpiece, affecting alignment accuracy. This can impact the performance of the height sensor.

[0008] New systems and technologies are needed. [Means for solving the problem]

[0009] In a first embodiment, a system is provided. The system includes a stage configured to hold a workpiece, an electron beam tube configured to direct an electron beam onto a workpiece on the stage, a light source configured to generate a light beam onto the workpiece on the stage, a sensor configured to receive the light beam reflected from the workpiece, a mirror configured to reflect the light beam received from the workpiece back onto the sensor, and a processor that electronically communicates with the sensor. The processor is configured to use measurements from the sensor to determine the displacement from a reference distance between the electron beam tube and the workpiece on the stage.

[0010] The system may include a second mirror and a third mirror. The second and third mirrors are positioned within the path of the light beam. The second mirror is positioned to direct the light beam from the light source towards the workpiece. The third mirror is positioned to direct the light beam from the workpiece towards the mirror. The second and third mirrors may each be folding mirrors.

[0011] The system may further include a plano-convex lens positioned in the path of the light beam between the second mirror and the workpiece.

[0012] The system may include a beam splitter positioned in the path of the light beam between the workpiece and the light source. The beam splitter directs at least a portion of the light beam towards the sensor.

[0013] The light source may be a light-emitting diode.

[0014] The system may include a convex lens in the path of the light beam between the light source and the workpiece.

[0015] The system may include a slit in the path of the light beam between the light source and the workpiece.

[0016] The mirror may be a spherical mirror.

[0017] The workpiece may be a semiconductor wafer.

[0018] In a second embodiment, a method is provided. This method includes directing a light beam from a light source to a workpiece on a stage. The workpiece is positioned at a certain absolute distance from the electron beam tube. The light beam is reflected by the workpiece. The light beam reflected from the workpiece is received by a sensor. A processor is used to determine the displacement from a reference distance between the electron beam tube and the workpiece on the stage.

[0019] The workpiece may be a semiconductor wafer.

[0020] This method may include using a mirror to reflect the light beam reflected from the workpiece. By reflecting the light beam from the workpiece, the light beam is directed towards the mirror.

[0021] The directing may include reflecting the light beam from a second mirror disposed in the path of the light beam between the light source and the workpiece.

[0022] Reflecting the light beam from the workpiece may include reflecting the light beam from a third mirror disposed in the path of the light beam between the workpiece and the mirror.

[0023] The method may include splitting the light beam reflected from the workpiece using a beam splitter. A portion of the light beam is directed by the beam splitter to a sensor.

[0024] The directing may include focusing the light beam.

[0025] The method may include redirecting the light beam reflected from the workpiece back to the same point on the workpiece before the light beam is received by the sensor.

[0026] The method may include adjusting the height of the stage based on the displacement from a reference distance.

[0027] To more fully understand the nature and objects of the present disclosure, reference should be made to the following detailed description taken in conjunction with the accompanying drawings.

Brief Description of the Drawings

[0028] [Figure 1] It is a block diagram of an embodiment of a system according to the present disclosure. [Figure 2] It is a block diagram of an optical system used in the system of FIG. 1. [Figure 3] It shows exemplary test results using the system of FIG. 1. [Figure 4] It shows a double pass using an embodiment of the system of FIG. 1 compared to a single pass. [Figure 5] It shows a calibration method of the system of FIG. 1. [Modes for carrying out the invention]

[0029] While the claimed subject matter is described in relation to specific embodiments, other embodiments, including those that do not provide all of the advantages and features described herein, are also within the scope of this disclosure. Various structural, logical, processing, and electronic modifications can be made without departing from the scope of this disclosure. Accordingly, the scope of this disclosure is defined solely by reference to the appended claims.

[0030] A height detection system can measure the displacement from a reference distance between the electron beam tube and the workpiece on the stage of the measuring tool. For example, the absolute distance may be between the top surface of the workpiece on the stage and the bottom surface of the objective lens in the electron beam tube. The use of a particular measurement may require a reference distance (which can be an absolute distance, a point along the absolute distance, or a range within the absolute distance) between the electron beam tube and the workpiece on the stage of the measuring tool to achieve the desired electron beam focus. The height detection system can be used during workpiece scanning to verify that the electron beam tube is positioned at this reference height relative to the workpiece. This may be done during measurement preparation or at other times during the operation of the measuring tool.

[0031] The absolute distance can be affected by the structure on the workpiece, the shape of the workpiece (e.g., curvature, thickness variations, etc.), changes in the stage height, and / or inaccurate movement of the stage (e.g., too much or too little movement). These differences can also affect the placement of the reference distance.

[0032] Figure 1 is a block diagram of system 100. System 100 may be part of a measurement tool. System 100 includes a stage 102 configured to hold a workpiece 101. The workpiece 101 may be a semiconductor wafer, a Calchip, or another type of substrate. The stage 102 is movable in the X, Y, and Z directions using actuators. System 100 also includes an electron beam tube 103 configured to direct an electron beam onto the workpiece 101 on the stage 102. The distance between the end of the electron beam tube 103 and the top surface of the workpiece 101 is the absolute distance in Figure 1 (shown by the dotted line 115).

[0033] The light source 104 is configured to generate a light beam 111 onto the workpiece 101 on the stage 102. The light source can be a light-emitting diode (LED) or a laser. The light beam 111 can be visible light. For example, the light beam 111 can mainly use red wavelength light. The spot on the workpiece 101 formed by the light beam 111 can vary. For example, the spot on the workpiece 101 may be a 2 mm diameter or a 2 mm x 2 mm square.

[0034] The light beam 111 may have an oblique angle of incidence to the workpiece 101. This allows for avoidance of many mechanical components within the system 100 and can result in high reflectivity. For example, the light beam 111 may have an incidence angle of 3.5 ± 0.5 degrees with respect to the plane of the workpiece 101.

[0035] Sensor 112 is configured to receive a light beam 111 reflected from the workpiece 101. Sensor 112 can be a bicell photodiode connected to or part of a printed circuit board (PCB). The bicell photodiode can be read when the image signal is in the upper or lower half of the bicell photodiode. The height adjustment of the stage 102 can be based on the position of the image signal on sensor 112.

[0036] The mirror 110 can be configured to reflect the light beam received from the workpiece 101 toward the sensor 112. The mirror 110 may be a spherical mirror, but other types of mirrors may perform this function. For example, the light reflected from the workpiece 101 can be reflected back to the workpiece 101 using the mirror 110. This reflected light can then be directed toward the sensor 112 after being reflected by the workpiece 101.

[0037] The processor 113 communicates electronically with the sensor 112. The processor 113 can also communicate electronically with the actuator of the stage 102 or other components in the system 100. Using the measurements from the sensor 112, the processor 113 can determine the relative displacement from a reference distance. The reference distance can be determined relative to the best focus of the electron beam on the workpiece 101. The processor 113 can also determine the adjustment of the stage 102 in the Z direction to allow the workpiece 101 to be in a desired focus position and / or position within the reference distance.

[0038] The processor 113 typically comprises a programmable processor programmed with software and / or firmware to perform the functions described herein, along with appropriate digital and / or analog interfaces for connection to other elements of the system 100. Alternatively or additionally, the processor 113 comprises hardwired and / or programmable hardware logic circuits that perform at least some of the functions of the processor 113. For simplicity, the processor 113 is shown in Figure 1 as a single monolithic functional block, but in practice, the processor 113 may comprise a plurality of interconnected control units having appropriate interfaces for receiving and outputting signals shown in the figure and described herein. Program code or instructions for the processor 113 to perform the various methods and functions disclosed herein may be stored in memory within the processor 113 or in other readable storage media such as memory.

[0039] The focal length of the electron beam tube 103 can be fixed. Instead of changing the focus of each optical component within the electron beam tube 103, actuators associated with the stage 102 can be used to move the workpiece 101 closer to or further away from the fixed focal plane (i.e., move it in the Z direction). A Z height sensor for the stage 102 can monitor the height of the stage 102, but with only a Z height sensor, it may be difficult to know when the stage 102 has moved to the best focus position in the Z direction. Various workpieces 101 can have various heights, and a single workpiece 101 can have height differences across the workpiece 101.

[0040] System 100 may include a second mirror 107 and a third mirror 109. The second mirror 107 and the third mirror 109 may be folding mirrors, but other mirrors or optical components that perform this function may be used. For example, the second mirror 107 and / or the third mirror 109 may be pentaprisms. The second mirror 107 and the third mirror 109 may be positioned in the path of the light beam 111 such that the second mirror 107 directs the light beam 111 from the light source 104 to the workpiece 101, and the third mirror 109 directs the light beam 111 from the workpiece 101 to the mirror 110. The second mirror 107 and the third mirror 109 can also receive reflected light in the opposite direction of the path of the light beam 111.

[0041] The system may include a composite lens 108 positioned in the path of the light beam 111 between the second mirror 107 and the workpiece 101. Although two lenses are shown as part of the composite lens 108, more or fewer lenses may be used. The composite lens 108 focuses the light beam 111 onto the workpiece 101. In one example, the composite lens 108 is a plano-convex lens. An additional set of composite lenses may be positioned between the second mirror 107 and the beam splitter 106.

[0042] The beam splitter 106 may be positioned within the path of the light beam 111 between the workpiece 101 and the light source 104. The beam splitter 106 may direct at least a portion of the light beam 111 towards the sensor 112. For example, the beam splitter 106 may be located within the path of the light beam 111 between the light source 104 and the second mirror 107.

[0043] The system may include a convex lens 105 in the path of the light beam 111 between the light source 104 and the workpiece 101. For example, the convex lens 105 may be in the path of the light beam 111 between the light source 104 and the beam splitter 106. The convex lens 105 can collimate the light beam 111. Although one convex lens 105 is shown, a set of lenses may also be used. The convex lens 105 may be part of a Köhler illumination system.

[0044] The slit 114 may be positioned within the path of the light beam 111 between the light source 104 and the workpiece 101. For example, the slit 114 may be located within the path of the light beam 111 between the light source 104 and the beam splitter 106, such as downstream of the convex lens 105. In one example, the slit 114 has dimensions of 2 * 0.12 mm. The slit 114 may be fixed or adjustable.

[0045] The pattern effect can be controlled within system 100 by adjusting the illumination uniformity of light source 104, the slit focus of slit 114, the spherical mirror focus of mirror 110, or the mesiality of the primary and secondary beams. This can be seen in the diagram shown in Figure 5. Figure 5 shows an L-shaped target on the workpiece. The beam profiler in Figure 5 can collect alignment images as shown in Figures 3 and 5.

[0046] Figure 2 is a block diagram of the optical system used in system 100 of Figure 1. The stage control unit can move the stage in the Z direction. The stage control unit may include actuators that can move the stage at least in the Z direction. The stage control unit can electronically communicate with a processor ("stage PC") which may be the same as or different from the processor 113 in Figure 1. In one example, the stage control unit is part of the processor 113. In another example, the stage control unit is an additional processor that electronically communicates with the processor 113.

[0047] During operation of the embodiment shown in Figure 2, a beam of light from the light source (i.e., an optical beam) is directed towards a workpiece on the stage. As shown in Figure 1, the workpiece is positioned at a certain absolute distance from the electron beam tube. Returning to Figure 2, the optical beam is reflected by the workpiece and received by the sensor. If the workpiece position is not referenced, the bicell photodiode generates a voltage difference for feedback control of the stage 102.

[0048] A processor can be used to determine the relative displacement from a reference distance. The reference distance can be determined relative to the best focus of the electron beam on the workpiece. The system can then be aligned to this specific height.

[0049] The absolute distance between the electron beam tube and the workpiece on the stage can also be determined. A signal difference may indicate that the absolute distance is outside the specifications.

[0050] For example, as shown in Figure 2, light from a light beam imaging the top or bottom of a bicell photodiode within a PCB means that the absolute distance or displacement from the reference distance is outside the specifications. The stage height can be adjusted in the Z direction to bring the absolute distance or displacement within the specifications. The stage height can be adjusted to accommodate different workpiece heights, different wafer curvatures, or different chuck designs.

[0051] The light beam reflected from the workpiece may be further reflected using a mirror. By reflecting the light beam from the workpiece, the light beam can be directed towards the mirror.

[0052] The light beam may be reflected by a second mirror positioned in the path of the light beam between the light source and the workpiece. The light beam reflected from the workpiece may be reflected by a third mirror in the path of the light beam between the workpiece and the mirror.

[0053] The light beam reflected from the workpiece may be split using a beam splitter. At least a portion of the light beam is directed towards the sensor by the beam splitter.

[0054] A light beam can be focused as it is transmitted along its path.

[0055] Alignment and focusing can be performed by collecting images of the pattern on the wafer using a height sensor tool camera. For example, alignment can be performed in the X and Y directions using the street between dies on the workpiece. Focus or field tilt can be adjusted using a geometric pattern.

[0056] Figure 3 shows exemplary test results using System 100. Figure 3 is used to determine the height sensor conjugate reference during the alignment process. The change in slit height is shown for tool #4, which can include an embodiment of System 100. This is compared with a bench tool and two other tools (tool #1 and tool #2) having one embodiment of System 100. The image on the left is the L target. The image on the right is the corresponding wafer image at different conjugate positions for the various tools.

[0057] As shown in Figure 3, tool #1 has a sharper outer edge compared to a standard wafer result with good pattern effect (PE). There is a difference in image quality between the L target and the wafer.

[0058] Changing the slit height with tool #4 sharpens the DataRay image. Finally, the RS pattern can be seen. When the slit height changed from 0.4mm to -1.2mm, the pattern effect decreased by approximately 450nm. This change resulted in a 240nm pattern effect.

[0059] Figure 4 shows a double pass using one embodiment of the system in Figure 1, compared to a single pass. A single pass may be insufficient when the workpiece is a high-contrast wafer. The system may read this as a height difference, which is incorrect because the wafer is planar. High-contrast wafers include a brighter side on the right, representing a higher height. This problem can be avoided by using a double pass, as performed in the embodiment of Figure 1. Using a spherical mirror and passing the light beam twice means that the images cancel each other out, as shown in the example in the lower right.

[0060] While this disclosure has been described in relation to one or more specific embodiments, it will be understood that other embodiments of this disclosure can be made without departing from the scope of this disclosure. Therefore, this disclosure is deemed to be limited only by the appended claims and their reasonable interpretation.

Claims

1. It is a system, A stage configured to hold a workpiece, An electron beam tube configured to direct the electron beam towards the workpiece on the stage, A light source configured to generate a light beam onto the workpiece on the stage, A sensor configured to receive the light beam reflected from the workpiece, A mirror configured to reflect the light beam received from the workpiece toward the sensor, and A system comprising a processor that electronically communicates with the sensor, wherein the processor is configured to determine the displacement from a reference distance between the electron beam tube and the workpiece on the stage using measurements from the sensor.

2. The system according to claim 1, further comprising a second mirror and a third mirror, wherein the second mirror and the third mirror are positioned in the path of the light beam, the second mirror is positioned to direct the light beam from the light source to the workpiece, and the third mirror is positioned to direct the light beam from the workpiece to the mirror.

3. The system according to claim 2, further comprising a plano-convex lens disposed in the path of the light beam between the second mirror and the workpiece.

4. The system according to claim 2, wherein the second mirror and the third mirror are each folding mirrors.

5. The system according to claim 1, further comprising a beam splitter positioned in the path of the light beam between the workpiece and the light source, wherein the beam splitter directs at least a portion of the light beam toward the sensor.

6. The system according to claim 1, wherein the light source is a light-emitting diode.

7. The system according to claim 1, further comprising a convex lens in the path of the light beam between the light source and the workpiece.

8. The system according to claim 1, further comprising a slit in the path of the light beam between the light source and the workpiece.

9. The system according to claim 1, wherein the mirror is a spherical mirror.

10. The system according to claim 1, wherein the workpiece is a semiconductor wafer.

11. It is a method, The light beam from the light source is directed towards a workpiece on the stage, at which time the workpiece is positioned at a certain absolute distance from the electron beam tube. The light beam is reflected from the workpiece. The light beam reflected from the workpiece is received by a sensor, and A method comprising using a processor to determine the displacement from a reference distance between the electron beam tube and the workpiece on the stage.

12. The method according to claim 11, wherein the workpiece is a semiconductor wafer.

13. The method according to claim 11, further comprising using a mirror to reflect the light beam reflected from the workpiece, wherein the reflection of the light beam from the workpiece directs the light beam toward the mirror.

14. The method according to claim 13, wherein the directing includes reflecting the light beam from a second mirror positioned in the path of the light beam between the light source and the workpiece.

15. The method according to claim 14, wherein the reflection of the light beam from the workpiece includes reflecting the light beam from a third mirror positioned in the path of the light beam between the workpiece and the mirror.

16. The method according to claim 11, further comprising using a beam splitter to split the light beam reflected from the workpiece, wherein a portion of the light beam is directed to the sensor by the beam splitter.

17. The method according to claim 11, further comprising directing the light beam to focus it.

18. The method according to claim 11, further comprising redirecting the light beam reflected from the workpiece to the same point on the workpiece before the light beam is received by the sensor.

19. The method according to claim 11, further comprising adjusting the height of the stage based on the displacement from the reference distance.

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