JP4394707B2 - Sample surface defect inspection system - Google Patents

Description

  The present invention relates to a defect inspection apparatus for inspecting minute foreign matters / defects existing on the surface of a semiconductor substrate or the like with high sensitivity and high speed.

  In a production line for semiconductor substrates, thin film substrates, and the like, in order to maintain and improve product yield, defects and foreign substances existing on the surface of semiconductor substrates, thin film substrates, etc. are inspected. For example, in a sample such as a semiconductor substrate before forming a circuit pattern, it is necessary to detect minute defects or foreign matters having a surface area of 0.05 μm or less. In order to improve the manufacturing yield, it is important to periodically inspect whether or not such minute defects or foreign matters are generated in the manufacturing equipment in each process.

  In the conventional inspection apparatus, in order to detect such minute defects and foreign matters, a laser beam focused on a sample surface of several tens of μm is used as in, for example, “Patent Document 1” or “Patent Document 2”. Irradiated to collect and detect scattered light from defects and foreign objects. Further, as a technique for discriminating the type of defect, as in "Patent Document 3" or "Patent Document 4," scattered light from the defect is detected in multiple directions to determine the directionality of the scattered light. There is something.

JP-A-9-304289 US Pat. No. 5,903,342 JP 2001-255278 A US Pat. No. 6,894,302

  The distribution of scattered light generated by a defect having a size about 1/10 of the illumination wavelength is isotropic. For this reason, by adding signals detected in multiple directions, the SN ratio is improved and minute defects can be detected. On the other hand, in a defect in which the scattered light distribution is anisotropic, the SN ratio is lowered by adding signals detected in multiple directions, and the detection sensitivity is lowered. In defect inspection of semiconductor substrates, high-sensitivity inspection is required regardless of the type of defect.

  By adding the detection signals of scattered light detected in multiple directions to detect minute defects and processing each detection signal individually, it is possible to avoid overlooking anisotropic defects. The main specific means are as follows.

  The configuration of the first means irradiates a focused laser beam on the surface of the sample to be inspected, condenses the scattered light generated on the surface of the sample to be inspected in multiple directions, and photoelectrically converts the collected scattered light. In the apparatus for inspecting the defects existing on the surface of the specimen to be inspected, the detection signals detected in multiple directions are added to detect minute defects, and the detection signals detected in multiple directions are individually processed to perform anisotropy. A defect inspection apparatus characterized by detecting a defect.

  The configuration of the second means irradiates a focused laser beam on the surface of the sample to be inspected, condenses the scattered light generated on the surface of the sample to be inspected in multiple directions, and photoelectrically converts the scattered light thus collected. In this case, the inspection apparatus has a first plurality of photoelectric conversion elements that are detected in multiple directions and a second plurality of photoelectric conversion elements that are detected in multiple directions. The first plurality of photoelectric conversion elements are arranged with a first elevation angle with respect to the surface of the sample to be inspected, and the second plurality of photoelectric conversion elements have a second elevation angle larger than the first elevation angle. A defect inspection apparatus characterized by being arranged.

  The configuration of the third means irradiates a focused laser beam on the surface of the specimen to be inspected, condenses the scattered light generated on the surface of the specimen to be inspected in multiple directions, and photoelectrically converts the collected scattered light. In this case, the inspection apparatus has a first plurality of photoelectric conversion elements that are detected in multiple directions and a second plurality of photoelectric conversion elements that are detected in multiple directions. The first plurality of photoelectric conversion elements are arranged with a first elevation angle with respect to the surface of the sample to be inspected, and the second plurality of photoelectric conversion elements have a second elevation angle larger than the first elevation angle. The defect inspection apparatus is characterized in that the first and second plurality of photoelectric conversion elements can be individually adjusted in sensitivity.

  The configuration of the fourth means irradiates a focused laser beam on the surface of the sample to be inspected, condenses the scattered light generated on the surface of the sample to be inspected in multiple directions, and photoelectrically converts the collected scattered light. In this case, the inspection apparatus has a first plurality of photoelectric conversion elements that are detected in multiple directions and a second plurality of photoelectric conversion elements that are detected in multiple directions. The first plurality of photoelectric conversion elements are arranged with a first elevation angle with respect to the surface of the sample to be inspected, and the second plurality of photoelectric conversion elements have a second elevation angle larger than the first elevation angle. The first and second plurality of photoelectric conversion elements can set a threshold value for distinguishing whether a detection signal is a noise or a defect signal according to a level of shot noise generated by the photoelectric conversion element. With a defect inspection device characterized by is there.

  By adding the detection signals of scattered light detected in multiple directions to detect minute defects and processing each detection signal individually, it is possible to avoid overlooking anisotropic defects.

  Further, by automatically analyzing the obtained defect data, it is possible to determine whether the defect is caused by a problem of the apparatus or originally exists on the substrate.

  One embodiment of the present invention will be described below.

  1, 2 and 3 show an example of an apparatus for detecting defects / foreign particles on a semiconductor wafer before forming a circuit pattern. 1 is a side view, FIG. 2 is a plan view of a low angle detection system, and FIG. 3 is a plan view of a high angle detection system. 1 schematically includes an illumination optical system 101, a detection optical system 102, and a wafer stage 103. The illumination optical system 101 includes a laser light source 2, an attenuator 3, a beam expander 4, wave plates 5 and 6, and a condenser lens 8.

  The laser beam emitted from the laser light source 2 is adjusted to the required light quantity by the attenuator 3, the beam diameter is enlarged by the beam expander 4, the polarization direction of the illumination is set by the wave plates 5 and 6, and the condenser lens 8 is used. The detection area on the wafer 1 is condensed and illuminated. 7a and 7b are mirrors for changing the illumination light path, and are used as necessary. Wave plates 5 and 6 set the polarization of illumination to S-polarized light, P-polarized light, and circularly polarized light. The illumination elevation angle θi is preferably 5 to 25 degrees.

  The attenuator 3 is composed of a half-wave plate and a polarizing beam splitter. The light beam passing through the PBS (Polarized Beam Splitter) is changed by tilting the polarization angle of the emitted beam (linearly polarized light) of the laser light source with a half-wave plate. By rotating the half-wave plate, the polarization axis changes, and the amount of light can be adjusted.

  The detection optical system 102 includes a low-angle detection system and a high-angle detection system, and includes scattered light detection lenses 9 and 12, analyzers 10 and 13, and photoelectric conversion elements 11 and 14, and foreign matter existing in the detection area. The scattered light from the defect is almost condensed on the light receiving surfaces of the photoelectric conversion elements 11 and 14 by the scattered light detection lenses 9 and 12. The photoelectric conversion elements 11 and 14 generate electric signals having a magnitude proportional to the amount of light received and scattered, detect the foreign matter / defects by performing signal processing with a signal processing circuit (not displayed), and detect the size and location .

The photoelectric conversion elements 11 and 14 are used to receive and photoelectrically convert the scattered light collected by the detection optical system 102, such as a TV camera, a CCD linear sensor, a TDI sensor, or a photomultiplier tube. . The analyzers 10 and 13 are used for detecting only components in a specific direction included in the scattered light. The detection elevation angle (center angle) θ ₁ of the low angle detection system is preferably 15 ° to 35 °, and the detection elevation angle (center angle) θ ₂ of the high angle detection system is preferably 45 ° to 70 °.

  The wafer stage 103 includes a chuck 15 for holding the wafer 1, a rotation mechanism 17 for rotating the wafer 1, and a linear feed mechanism 16 for linearly feeding the wafer 1 in the radial direction. By rotating and scanning the wafer 1 in the horizontal direction on the wafer stage 103 and moving it straight, it becomes possible to detect foreign matter / defects and classify the defects in the entire area of the wafer 1.

FIG. 2 is a plan view of the low-angle detection system, and multi-directional detection is possible. In this embodiment, six-direction detection is shown. The output of each photoelectric conversion element 11 is subjected to addition, subtraction, division, etc. depending on the application. The detection azimuth angle (center angle) is 20 to 50 ° (φ ₁ ), -20 to -50 ° (φ ₂ ), 70 to 110 ° (φ ₃ ), -70 to -110 ° ( _{φ 4), 130~160 ° (φ} 5), - 130~160 ° (φ 6) it is preferable.

FIG. 3 is a plan view of the high angle detection system as in FIG. 2, and multi-directional detection is possible. In this embodiment, four-direction detection is shown. The output of each photoelectric conversion element 14 is subjected to addition, subtraction, division, etc. depending on the application. Detection azimuth angle (center angle) is ± 10 degrees (φ ₇ ), 80 to 110 ° (φ ₈ ), -80 to -110 ° (φ ₉ ), 180 ± 10 ° (φ ₁₀ ) Is desirable.

  FIG. 4 shows an example of a signal processing method of the low angle detection system. In this example, a photomultiplier tube is used as the photoelectric conversion element 11. The photomultiplier tube 11 requires a high applied voltage and is supplied from a high voltage DC power source 19. The output of the photomultiplier tube 11 is subjected to current-voltage conversion and necessary voltage amplification by the amplifier circuit 18 and added by the adder circuit 20. At this time, in order to correct the sensitivity difference of the photomultiplier tube 11, the amplification circuit 18 adjusts the amplification factor.

  The output of the adder circuit 20 is removed from the DC component and unnecessary noise component by the band-pass filter 21 and converted to digital by the AD converter circuit 22. The output of the AD conversion circuit 22 is compared with the threshold value by the comparison circuit 23. If the threshold value is exceeded, the AD conversion value and the R · θ coordinate are taken into the defect memory 26. The threshold value is set in the latch 24 from the CPU (not shown) via the interface 25. The contents of the defect memory 26 are read from a CPU (not shown) and used for defect map display, defect classification, and the like. FIG. 5 shows an example of the signal processing method of the high angle detection system, and the content is the same as FIG.

  FIG. 6 shows an example of the scattered light intensity distribution 35 generated by a minute defect when illuminated with P-polarized light. When the size of the defect is about 1/5 or less of the illumination wavelength, the scattered light intensity distribution generated as shown in FIG. 6 is isotropic. In this case, each detection signal has almost the same value (S). Shot noise (N) is generated when photoelectric conversion is performed in the photomultiplier tube 11.

  The short noise (N) output from each photomultiplier tube 11 is random, and the SN ratio of the output signal of each photomultiplier tube 11 is S / N. When all detection signals are added and averaged as shown in FIGS. 4 and 5, the shot noise is averaged to 1 / √6, the SN ratio of the detection signal is improved by √6 times, and each photomultiplier tube 11 is processed individually. More minute defects can be detected. When the scattered light intensity distribution is biased and detected only with one photomultiplier tube 11 as in the case of scratch, the average of the detection is 1/6 and the shot noise is 1 / √6. The S / N ratio is reduced to 1 / √6 compared to the case of processing the photomultiplier tube 11 individually.

  One embodiment for avoiding this is shown in FIG. The same circuit as the processing circuit shown in FIG. 4 is also added to each photomultiplier tube 11. The output of the comparison circuit 23 is logically summed, and when any one of the outputs exceeds the threshold value, the output of all the AD conversion circuits 22 and the R · θ coordinates are taken into the defect memory 26. As a result, it is possible to avoid overlooking an anisotropic defect having directionality in the scattered light intensity distribution.

  FIG. 8 shows an embodiment for correcting the sensitivity difference of the photomultiplier tube 11. Reference numeral 39 denotes a power supply unit capable of adjusting a high voltage applied voltage by an input voltage. As an example of this power supply unit, C4900 manufactured by Hamamatsu Photonics Co., Ltd. can be used. A voltage value is written into the latch 37 via the interface 40, and the voltage value is converted into a voltage value by the DA conversion circuit 38 and given to the power supply unit 39, whereby a high voltage applied voltage can be supplied to the photomultiplier tube 11. By changing the voltage value written into the latch 37, the sensitivity of the photomultiplier tube 11 can be adjusted from the CPU. The sensitivity difference can be easily corrected by the combined use with the amplification factor adjustment by the amplifier circuit 18.

  The intensity and distribution of scattered light generated on the wafer surface vary depending on the spatial frequency and roughness of the roughness present on the wafer surface. When the scattered light intensity detected on the wafer surface detected by the photomultiplier tube 11 is Su, the shot noise generated in the photomultiplier tube 11 is √Su. When the scattered light intensity on the wafer surface detected by the photomultiplier tube 11 is different for each photomultiplier tube 11, the generated shot noise is also different, and it is necessary to change the threshold for defect detection. FIG. 9 shows an embodiment for dealing with this, and FIG. 10 shows the processing contents.

The output signal 45 of the amplifier circuit 18 is separated into a wafer signal 46 and a defect signal 47 including shot noise by the band pass filter 21 and the low pass filter 41. A threshold value is created from the wafer signal 46 that has passed through the low-pass filter 41. The signal from the wafer signal 46 is converted to digital by the AD conversion circuit 42, and the threshold value Vth is created by the arithmetic circuit 43 and set in the latch 44. Since the shot noise is proportional to the square root of the wafer signal Su, the threshold value Vth is calculated by equation (1).
Vth = k · √ (Su · Δf) (1)
Here, k is a constant, and Δf is a frequency band of the circuit.

  FIG. 11 shows an example of an inspection flow. Import the inspection recipe and set the necessary parameters in the device. The wafer is loaded and inspected, and defect data is input from the defect memory. When inspection is completed, wafer scanning (rotation and single-axis feed) is stopped and the wafer is unloaded. After that, the defect map is displayed on the GUI screen as necessary.

  FIG. 12 is an example of a GUI. The GUI screen 48 includes at least a defect map 49 and a defect map display sensor selection screen 50 that are displayed after the inspection is completed.

FIG. 13 shows an example of defect discrimination. The ratio of the detection signal V _L of the low angle detection system and the high angle detection system V _H is calculated by the processing circuit 51, and the result is written in the defect memory. The processing contents will be described with reference to FIG. When V _L is plotted on the horizontal axis and V _H is plotted on the vertical axis, the calculation results are plotted. Concave defects (COP, scratch, etc.) are plotted in the area 53 above the threshold curve 52, and convex defects are plotted in the area 54 below. Therefore, appropriate irregularities (defect types) can be discriminated by setting the threshold curve 52.

  In FIG. 14, convex defects are below the dotted line 52, and concave defects are above the dotted line 52. The concave defect is often a defect that originally existed in a Si wafer or the like. The convex defect is often a defect generated in the apparatus. Therefore, it can be said that there are many problems in the manufacturing apparatus if there are more convex defects than concave defects even at the same defect density.

  The above description has been made assuming that the photomultiplier tube 11 is used as the photoelectric conversion element. However, the relationship between the shot noise and the defect detection signal is the same when a CCD or the like is used as the photoelectric conversion element. Therefore, the above description can be applied to the case where an element other than the photomultiplier tube 11 is used as the photoelectric conversion element.

The figure which shows one Example (side view) of this invention The figure which shows one Example (plan view) of this invention The figure which shows one Example (plan view) of this invention The figure explaining a signal processing circuit The figure explaining a signal processing circuit Diagram explaining the intensity distribution of scattered light from minute defects The figure explaining a signal processing circuit The figure explaining the photomultiplier tube sensitivity adjustment method Diagram explaining the threshold setting method The figure explaining the processing content of FIG. Diagram explaining inspection flow Diagram explaining an example of GUI The figure explaining a defect classification processing circuit Diagram explaining the contents of defect classification

Explanation of symbols

1: wafer, 101: illumination optical system, 102: detection optical system, 103: wafer stage,
2: Laser light source, 3: Attenuator, 4: Beam expander,
5, 6: Wave plate, 7: Mirror, 8: Condensing lens, 9, 12: Scattered light detection lens, 10, 13: Analyzer,
11, 14: Photoelectric conversion elements.

Claims (14)

A focused laser beam is irradiated on the surface of the sample to be inspected, and scattered light generated on the surface of the sample to be inspected is collected in multiple directions, and the collected scattered light is photoelectrically converted to exist on the surface of the sample to be inspected. In a device for inspecting a defect to be detected, a detection signal detected in multiple directions is added and compared with a first threshold value, and whether or not the added detection signal is larger than the first threshold value And detecting whether or not there is a micro defect , comparing each of the detection signals detected in multiple directions with a second threshold value, and at least one of the detection signals is the second detection signal A defect inspection apparatus for detecting whether or not an anisotropic defect is present depending on whether or not it is larger than a threshold value . Of the detected signal based on the scattered light generated by the specimen surface, according to claim 1, characterized in that to create a defect detection threshold using a signal from the inspection surface of the sample has passed through the low-pass filter Defect inspection equipment. 2. The method according to claim 1, wherein if any one of the plurality of detection signals detected in multiple directions exceeds the preset second threshold value, it is determined that the defect is an anisotropic defect. Defect inspection apparatus as described.   The defect inspection apparatus according to claim 1, wherein the photoelectric conversion is performed by a photomultiplier tube.   The defect inspection apparatus according to claim 4, wherein the photomultiplier tube is capable of setting sensitivity individually. A focused laser beam is irradiated on the surface of the sample to be inspected, and scattered light generated on the surface of the sample to be inspected is collected in multiple directions, and the collected scattered light is photoelectrically converted to exist on the surface of the sample to be inspected. In a defect inspection apparatus for inspecting defects
The defect inspection apparatus has a first plurality of photoelectric conversion elements that are detected in multiple directions and a second plurality of photoelectric conversion elements that are detected in multiple directions, and the first plurality of photoelectric conversion elements are samples to be inspected. Arranged with a first elevation angle with respect to the surface, and the second plurality of photoelectric conversion elements are arranged with a second elevation angle greater than the first elevation angle,
The detection signals detected in multiple directions are added by the first plurality of photoelectric conversion elements and compared with a first threshold value. The added detection signal is larger than the first threshold value. And detecting whether or not there is a micro defect, and comparing each of the detection signals detected in multiple directions with a second threshold value, and at least one of the detection signals is the detection signal Whether it has an anisotropic defect depending on whether it is greater than the second threshold,
The detection signals detected in multiple directions are added by the second plurality of photoelectric conversion elements and compared with a first threshold value, and the added detection signal is larger than the first threshold value. And detecting whether or not there is a micro defect, and comparing each of the detection signals detected in multiple directions with a second threshold value, and at least one of the detection signals is the detection signal A defect inspection apparatus for detecting whether or not an anisotropic defect is present depending on whether or not it is larger than a second threshold value .   The defect inspection apparatus according to claim 6, wherein the laser beam is incident on the surface of the sample to be inspected at a third elevation angle, and the third elevation angle is smaller than the first elevation angle.   The defect inspection apparatus according to claim 6, wherein the first elevation angle is 15 degrees to 35 degrees, and the second elevation angle is 45 degrees to 70 degrees.   The defect inspection apparatus compares the detection data from the first plurality of photoelectric change elements and the detection data from the second photoelectric conversion element to determine the type of defect. Defect inspection apparatus as described.   For a plurality of defects, a plot is output in which the output from the first plurality of photoelectric conversion elements is on the vertical axis and the output from the second plurality of photoelectric conversion elements is on the horizontal axis. The defect inspection apparatus according to claim 6.   The defect inspection apparatus according to claim 6, wherein sensitivities of the first and second plurality of photoelectric conversion elements can be individually adjusted.   The defect inspection apparatus according to claim 11, wherein the photoelectric conversion element is a photomultiplier tube.   The first and second plurality of photoelectric conversion elements can set a threshold value for distinguishing whether a detection signal is a noise or a defect signal according to a level of shot noise generated by the photoelectric conversion element. The defect inspection apparatus according to claim 6.   The defect inspection apparatus according to claim 13, wherein the photoelectric conversion element is a photomultiplier tube.

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