An automated calibration method for a film thickness gauge

Abstract

The application belongs to the technical field of semiconductor, and particularly relates to an automatic calibration method of a film thickness instrument, which comprises the following steps: first, moving a moving platform to chain a mirror into a light path, using the mirror to chain a position into the light path, the surface of the position is blackened, has optical properties of surface roughness, no light passes through the area to return to the light path, a spectrometer in the light path obtains pure dark noise data DN, and dark noise calibration is completed; second, moving the moving platform to chain a reference sheet into the light path, and at this time, reference sheet reflected light intensity is obtained on the spectrometer, and reference sheet calibration is completed; the problems that a traditional calibration mode is slow, a process is complicated, wafer pollution is easily caused, and automatic completion is impossible are solved.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor measurement technology, specifically an automated calibration method for a film thickness gauge. Background Technology

[0002] When measuring the thickness of a thin film on a wafer surface using a reflective film thickness gauge, necessary calibrations must be performed first, including dark noise calibration and reference film reflectivity calibration.

[0003] Currently, these two calibration methods are mainly manual. The manual method involves: 1. The operator places the light-absorbing material on the measuring stage, and the computer collects data using a spectrometer to obtain the dark noise; 2. The operator places a reference wafer with a known film structure on the measuring stage, and the computer similarly collects data using a spectrometer to obtain the reflected light intensity of the reference wafer. It is evident that this calibration method is slow, cumbersome, prone to wafer contamination, and cannot be automated. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by employing a combined optimization of dark noise and reference film calibration. An automated calibration method for film thickness gauges is designed, which enables intelligent control to complete dark noise and reference film calibration without the need for frequent manual placement of light-absorbing materials and reference films on the measuring stage. This solves the problems of slow speed, cumbersome process, easy wafer contamination, and inability to automate the traditional calibration method.

[0005] To achieve the above objectives, the following technical solution is adopted: An automated calibration method for a film thickness gauge includes the following steps: Step 1: Move the motion platform so that the reflector links into the optical path. Use the reflector to link position 7 into the optical path as well. The surface of the position is blackened and roughened so that no light returns to the optical path through this area. The spectrometer in the optical path obtains pure dark noise data DN, thus completing the dark noise calibration. The second step involves moving the motion platform to link the reference film into the optical path. At this point, the spectrometer displays the intensity of the light reflected from the reference film. Complete the calibration of the reference film; Preferably, the tray used to hold the wafer has two small holes cut out in its central part: one for placing a shaped reference wafer and the other for placing a mirror. The coordinates of the center of these two small holes are known by design.

[0006] The second preferred embodiment is a wafer-carrying tray with two platforms at its edge: one for placing a shaped reference wafer and the other for placing a mirror. The coordinates of these two platforms are known through design.

[0007] Compared with the prior art, the beneficial effects of the technical solution of the present invention are: This invention employs a method to eliminate reflected light for calibration, and designs an automated calibration method for film thickness gauges. This allows for the elimination of reflected light through intelligent control, eliminating the need for frequent manual placement of light-absorbing materials on the measuring stage. This solves the problems of traditional calibration methods being slow, cumbersome, prone to wafer contamination, and unable to be automated.

[0008] The second preferred pallet solution involves stopping the measurement process when a wafer is being measured, as calibration is required. Since the positions of the reflector and reference wafer do not overlap with the measured wafer, the measurement is stopped via built-in software logic, and resumed only after calibration. This solution ensures real-time calibration and more reliable measurement results. Attached Figure Description

[0009] Figure 1 This is a schematic diagram of the first preferred scheme for calibrating dark noise DN using the method (mirror) for eliminating reflected light in this invention; Figure 2 for Figure 1 Enlarged view of point A in the middle Figure 3 This is a schematic diagram of the second preferred embodiment of the present invention.

[0010] The components include: 1. Reference film; 2. Measurement optical path; 3. Working surface; 4. Support; 5. Spectrometer; 6. Tray; 7. Position; 8. Reflector. Detailed Implementation

[0011] like Figure 1 and Figure 2 As shown, an automated calibration method for a film thickness gauge includes the following steps: The first step is to use mirror 8 to reflect the light path 2 to position 7. Since the surface of position 7 is black (blackened) and rough, no light can return to the light path. The spectrometer measures the dark noise DN. The second step involves moving the motion platform to link reference piece 1 into the optical path. At this point, the intensity of the light reflected from the reference piece is obtained on the spectrometer 5. Complete the calibration of reference piece 1; The purpose of this invention is to calibrate the dark noise DN and the reflected light intensity of the reference film. Through formula The reflectivity of the wafer under test can then be calculated. .

[0012] Specific thin films are grown on the surface of a wafer. The thickness (t) and refractive index (n, k) of these films must meet design requirements; otherwise, specific electrical performance requirements cannot be met. A reflective film thickness gauge measures the intensity of reflected light from the wafer surface. This intensity is compared with the intensity of reflected light from a wafer surface with a known film structure (therefore, the reflectivity can be theoretically calculated) to obtain the reflectivity of the wafer surface under test. Furthermore, based on the initial value of tnk of the wafer surface under test, a nonlinear optimization algorithm is used to give the accurate value of tnk.

[0013] in, It refers to light intensity, superscript. Indicates arrival at the spectrometer. Referring to the reference film, It is the wafer to be tested. It is dark noise in the optical path system. It's reflectivity. The film structure and material parameters of the reference film are known, therefore... It can be obtained through theoretical calculations. To obtain... Pre-calibration is required. and Then measure .in, The reflectance can be directly obtained from the spectrometer 5 and then calculated. The reason for determining dark noise by eliminating reflected light instead of turning off the light source is that after calibrating dark noise by turning off the light source and then turning it back on, the light emitted by the light source needs a longer time to stabilize to a measurable level. This method of eliminating reflected light automates the process, eliminating the need for operators to frequently remove and place the light-absorbing material on the measurement stage. Through this second preferred solution, calibration can be performed at any time during wafer measurement.

[0014] As a preferred approach, in the first step, a light path 2 is used directly above the reference wafer 1, perpendicular to the measurement surface of the reference wafer 1 or the wafer under test. A light source and a spectrometer are located at the other end of the light path to emit light to the reference wafer 1 and collect the light reflected back from the reference wafer 1.

[0015] As an optional approach, the second step also includes setting a bracket 4 on a working surface, placing the optical path 2 on the bracket 4 so that the optical path 2 is perpendicular to the working surface, then fixing the tray 6 on the working surface, while making the reference sheet 1 parallel to the working surface, and connecting the end of the optical path 2 away from the working surface to the input end of the spectrometer 5 through an optical fiber.

[0016] During calibration, the dark noise can be measured by automatically moving the reflector 8 directly below the optical path 2.

[0017] Because reflective film thickness gauges are highly sensitive to changes in light intensity and require frequent calibration, it is crucial that reference plate 1 is placed directly at a predetermined position on tray 6 (chuck) to facilitate automatic computer calibration. The reflector 8 reflects the light in the optical path to a roughened, blackened area far from the working surface 3, effectively blocking the light path. Therefore, when the light path is aligned with reflector 8, only dark noise data is obtained on the spectrometer, without reflected light. This allows for on-the-fly calibration of dark noise by rotating tray 6. After calibration, tray 6 can be removed via the motion platform to begin calibration, which is very convenient and quick. This design is also the foundation for intelligent calibration. Furthermore, position 7 on the support 4 is recessed to further lock in the light, preventing reflection and further improving the accuracy of dark noise calibration.

[0018] The second preferred option is a wafer tray 6 with two platforms at its edges: one for placing the trimmed reference wafer 1 and the other for placing the reflector 8. The coordinates of these two platforms are known through design. During measurement downtime or when real-time calibration is required during measurement, the chuck is moved rapidly by a computer program to collect dark noise and reference reflected light intensity on the reflector and reference wafer. Calibration is performed during measurement intervals, thus improving the wafer per hour (WPH).

Claims

1. An automated calibration method for a film thickness gauge, characterized in that, Includes the following steps: Step 1: Move the motion platform and link the reflector (8) into the optical path. Use the reflector (8) to link the position (7) into the optical path as well. The surface of the position (7) is blackened and has the optical property of rough surface. No light returns to the optical path through this area. The spectrometer (5) in the optical path obtains pure dark noise data DN and completes the dark noise calibration. The second step involves moving the motion platform to link the reference film into the optical path. At this point, the spectrometer displays the intensity of the light reflected from the reference film. Complete the calibration of reference piece (1).

2. The automated calibration method for a film thickness gauge according to claim 1, characterized in that, In the second step, an optical path (2) is set directly above the reference plate (1), making the optical path (2) perpendicular to the measurement surface of the reference plate (1). This is used to receive the perpendicular light reflected from the reference plate (1) and to perpendicularly illuminate the reference plate (1) with the light emitted from the optical path (2), thereby measuring the light intensity of the reference plate (1). .

3. The automated calibration method for a film thickness gauge according to claim 2, characterized in that, In the second step, the perpendicular light reflected from the reference plate (1) is transmitted to the spectrometer (5) through the optical path (2), thereby measuring the light intensity through the spectrometer (5). .

4. The automated calibration method for a film thickness gauge according to claim 2, characterized in that, In the first step, a reflector (8) is used so that the reflector (8) reflects the light output from the light path (2) to outside the light path (2), and then the light reflected on the reflector (8) is eliminated outside the light path (2).

5. The automated calibration method for a film thickness gauge according to claim 1, characterized in that, The second step also includes setting a bracket (4) on a working surface, setting the optical path (2) on the bracket (4) so ​​that the optical path (2) is perpendicular to the working surface, and then fixing the reference piece (2) on the working surface, while making the reference piece (2) parallel to the working surface. The end of the optical path (2) away from the working surface is connected to the input end of the spectrometer (5) through an optical fiber.

6. The automated calibration method for a film thickness gauge according to claim 5, characterized in that, Place a tray (6) on the work surface, and cut out two small holes in the center. One hole is used to place the cut reference piece (1), and the other hole is used to place a reflector (8).

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