JPS63210606A - Method and apparatus for inspecting pattern - Google Patents

Abstract

PURPOSE:To shorten inspection time to a large extent while keeping high accuracy, by a method wherein scanning is performed along the contour line of an object to be inspected using charged particle beam converged into a smaller diameter and the pattern surface of the object to be inspected is scanned using charged particle beam converged into a larger diameter. CONSTITUTION:The position, direction and length of the contour line L1 of a pattern P are preliminarily calculated from the data of the planning note of said pattern P and the pattern P is minutely scanned by the first charged particle beam converged into a smaller diameter so as to cross the contour line L1 at a right angle to detect, for example, a flaw 59. Further, raster scanning is performed with respect to the surface containing the pattern P by the second particle beam converged into a larger diameter as compared with the first particle beam to detect the flaws 60, 61 inside and outside the pattern P. Generally, a fine flaw is concentrated to the contour line L1 and not generated on the plane of the pattern P. By this method, inspection time is shortened to a large while high accuracy is kept.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to defect inspection of patterns formed on masks and reticles used in the manufacture of semiconductor devices, and is particularly suitable for inspection using a charged particle beam. The present invention relates to a pattern defect inspection method and apparatus.

[Conventional technology]

In the production of semiconductor integrated circuits, a mask is made as an original plate,
This is done by transferring the pattern on the mask onto the wafer using light, xi,'', etc. Since transfer is performed from one mask to a large number of wafers, if there is a defect on the mask, there will be a large number of defects. Therefore, pattern inspection on the mask is extremely important.

Conventionally, the ability to detect defects in mask patterns was
As described in No. A35-85767, the mask is scanned with an electron beam at a constant speed, the reflected electrons or secondary electrons are detected, and the detected signal is binarized using an appropriate threshold value, and then a predetermined typing is performed. A method has been proposed in which defects are detected using digital image processing.

In the case of an X-ray mask, there is also a method of detecting a pattern by scanning the mask with an electron beam at a sieve acceleration voltage and detecting the particles passing through the mask.

FIG. 2 shows an example of a normal mask pattern, and FIG. 6 shows an example of a defect occurring on the mask pattern. 51 is a mask pattern base material, 52 is a pattern, 53 is a cow short, 54
is chipped, 55 is short, and 56 is broken.

57 is a pinhole defect, and 58 is an isolated defect. All defects occur along the pattern contours, except for pinholes and isolated defects. The size of the defect to be detected is generally 1/2 to 1/3 of the pattern line width, so for a mask used for xsm light, the size is about 0.1 μm. On the other hand, the thickness of the mask pattern is about 1 μm. Pattern defects that occur along pattern contours occur mainly during pattern drawing and patterning, and micro defects of about 0.1 μm often occur. However, pinholes and isolated defects are caused by foreign matter attached to the pattern surface being transferred to the pattern during pattern film formation or patterning. In some cases, sharp edges are difficult to form. Therefore, minute pinholes and isolated defects of about 0.1 μm are extremely unlikely to occur.

However, in the conventional method, as shown in Fig. 4, the electron edge is scanned over the entire mask surface at a constant beam diameter, at a constant speed, and at a pitch equal to the beam diameter, and the detection signal is transmitted at a constant rate equal to the beam diameter. Sampled at intervals. Therefore, in order to detect micro defects even in areas where micro defects do not occur, except near the pattern outline, inspection must be sampled in detail, which poses the problem of requiring a considerable amount of inspection time. Was.

[Problem that the invention seeks to solve]

The conventional technology described above performs raster scanning under the same beam conditions and performs pattern detection under the same conditions, including areas where micro defects are likely to occur and areas where micro defects are unlikely to occur. It's easy to get stuck 4! This results in an inspection with a higher resolution than that, and there is a problem in that it takes an enormous amount of inspection time to inspect the entire mask surface.

The purpose of the present invention is to
An object of the present invention is to provide a mask pattern inspection method and apparatus that can be inspected at high speed.

[Means for solving problems]

The above purpose is to provide a means for changing the diameter of the electron beam, an electromagnetic deflection means for deflecting the electron beam along the ideal pattern contour, and a deflection of the cryptographic beam by the electromagnetic deflection means at a constant minute deflection width at right angles. By combining the two deflection means, the electron beam is scanned so as to be always perpendicular to the ideal pattern contour, and the position of the actual pattern contour is Micro-defects on the pattern contour are detected by comparing the position of the pattern contour with the ideal pattern contour, and in areas other than the pattern contour, a mask is scanned with a large electron beam diameter and sampling is performed at a coarser sampling interval than before. Therefore, defects are detected by detecting the pattern at high speed and comparing it with an ideal pattern.

By the above means, the above-mentioned pattern inspection time can be shortened.

[Effect]

FIG. 5 shows an example of the configuration of an electron optical system according to the present invention. In the figure, 57 is an electron gun, 58 is a condenser lens, 59 is a micro deflector using electrostatic deflection, 60 is an electromagnetic main deflector, and 61
62 is an objective lens, 62 is an X-ray mask, 63 is a detection field stop, 64 is a scintillator, 65 is a light guide, and 67 is a photomultiplier tube.

The electrons emitted from the electron a57 pass through the condenser lens 58
The light is focused onto the sample 62 by the objective lens 61 as a minute spot. The main deflector 60 deflects the electron beam along the ideal pattern contour @1, and the micro deflector 3 always deflects the electron beam with a constant scanning width in a direction perpendicular to the main deflector. As a result, the electron beam is deflected as shown in FIG. Since the main deflector needs to scan a scanning width of several hundred micrometers to several millimeters, it must be an electromagnetic deflector that can have a large scanning width. However, electromagnetic deflectors with a large scanning width have a slow step response speed.
Scanning speed unevenness occurs near the scanning start point and scanning end point, and the detected pattern is distorted.As a result, pattern detection distortion is erroneously determined to be a defect. To avoid this, it is necessary to provide a run-up section and perform pattern detection after the scanning speed becomes constant. Compared to the case of raster scanning, in the scanning method shown in FIG. 6, the number of pattern scans is greatly increased, so the number of run-up scans is increased, resulting in a large amount of wasted time that does not contribute to pattern inspection. The present invention divides the scanning shown in FIG. 6 into a component along the ideal pattern outline and a component perpendicular to the pattern, and the main deflector takes charge of the component along the pattern outline, and the component perpendicular to the pattern. An electrostatic deflector is in charge of this. Although electrostatic type deflectors cannot obtain a large scanning width, their fast step response speed eliminates the need for the run-up section required for electromagnetic type deflectors, reducing wasted time that does not contribute to pattern inspection.

For scanning along the pattern outline, an electromagnetic deflector with a slow response speed is sufficient because the beam position only needs to be advanced by one step each time the micro deflector scans once.

The electrons transmitted through the X-ray mask 62 enter the scintillator 64 and generate photons. The photons pass through the light guide 65 and are detected by a photomultiplier tube to obtain a pattern detection signal. When minute scanning is performed from a position at a certain distance toward the inside of the ideal pattern outline, the electron beam is blocked by the pattern portion, so that a detection signal shown by a solid line in FIG. 1 is obtained.

In the figure, the vertical axis is the signal level, and the horizontal axis is time. Furthermore, when this is binarized using a constant threshold value THo, a signal shown in FIG. 8 is obtained. When the beam crosses the pattern contour, the binary signal changes from 1 to 0. If the beam scanning speed is constant, the signal level should always change after a certain time d from the start of scanning. If there is a defect 59 in the pattern, the position of the pattern outline deviates from the position of the ideal pattern outline, and if a! If there is a defect as indicated by 59 in FIG. 6, the time at which the signal level changes will shift as shown by the broken line in FIG. Therefore, a defect can be detected by detecting a case where the time difference at which the signal level changes from 1 to 0 is greater than or equal to a certain tolerance value.

Since there are almost no micro-defects in areas other than the pattern outline, the beam diameter is widened and the pattern is detected by 2-star scanning using only the main deflector.The scanning pitch and sampling interval are also adjusted to the beam diameter. and enlarge it.Figure 91
Here is an example of this. When the beam diameter is increased, the resolution decreases, but since there are almost no micro defects, the defect detection performance does not decrease. An area corresponding to (beam diameter) x (scanning@) can be inspected by - times of scanning, so by increasing the beam diameter, the same area can be inspected with fewer times of scanning.

The beam diameter can be easily increased by lowering the excitation current of the condenser lens. Furthermore, when the reading point beam diameter is increased, the sample irradiation current increases, so an image with a good S/N ratio can be obtained.

Therefore, even if the beam is scanned at a higher speed, a good S/N ratio can be obtained. From the above, by increasing the beam diameter, high-speed scanning is possible, and inspection can be performed with a small number of scans, resulting in a significant reduction in inspection time.

Defect detection during raster scanning is performed as follows.

Similar to the conventional mask inspection apparatus, an ideal pattern detection signal is generated based on mask pattern design data in synchronization with beam scanning. When the beam is scanning inside the pattern, the beam does not pass through the mask, so an inherently low level detection signal should be obtained. When the pinhole defect 6o is scanned, the beam passes through the defective portion, so a high level signal is detected at the defective portion, as shown in FIG. 10. Therefore, a defect is detected by detecting a signal at a level higher than a threshold value TT (1). is a defect 61, so if a defect exists while scanning the outside of the pattern, a low level signal will be obtained at the defective part as shown in FIG. Defects can be detected by detection.

〔Example〕

Hereinafter, one embodiment of the present invention will be described with reference to FIG. Condenser lens 2° X-direction microelectrostatic deflector 5. Y direction micro electrostatic deflector 4, X direction main electromagnetic deflector 5. Y-direction main electromagnetic deflector 6, objective lens 7,
Line mask 8. Sample stand9. XY stage 10. Scintillator 11. Light guide 12° photomultiplier tube (hereinafter abbreviated as photomultiplier) 16. Photomal amplifier 14. Deflection amplifier 15
, 16.17.18. Deflection method switch 19. Multiplexer 201 Contour sparse vicinity scanning signal generator 22. Micro-scanning clock oscillator 23. X-direction raster scanning signal generator 24.
Y-direction raster scanning signal generator 25. Binarization circuit 26.2
7.28, contour line position determination circuit 29. Multiplexer 3o, inverter 31. Beam diameter changing circuit 52. Design data 34. It consists of a control circuit 35.

In this embodiment, a mask used for xm exposure is inspected. X
The i-mask has a pattern made of a material with a high atomic number and high density, about 1 μm thick, on a base material made of a low atomic number, low density material with a thickness of several μm that transmits X-rays. Therefore, if an electron beam with a sufficiently high acceleration voltage is applied to the mask, the electrons will pass through the mask base portion with almost no scattering, and the electrons will not pass through the patterned portion or will be heavily scattered. Therefore, if mask transmitted electrons within a certain scattering angle are detected, a transmitted electron image is obtained in which the base material part is bright and the pattern part is dark.

The electron beam generated from the electron gun 1 passes through a condenser lens 2,
The light is focused onto the X-ray mask 8 in the form of a spot by the objective lens 7 . It is assumed that the accelerating voltage of the electrons is high enough to pass through the base material portion of the mask 8, and the spot size is as small as the size of the defect to be detected. The electron beam is transmitted through microelectrostatic deflectors 3 and 4 and generated magnetic deflectors 5 and 6.
The mask is scanned two-dimensionally. The electrons that have passed through the mask are converted into photons by a scintillator 11 for detecting transmitted electrons installed below the mask, and then led to a photomultiplier 13 through a light guide 12, where the photons are converted into electrical signals. , obtain a pattern detection signal of the X-ray mask.

The sample stage 9 is fixed on an XY table 10, and a space is secured between the mask 8 and the XY table 10 in which a scintillator 11 for detecting transmitted electrons and a light guide 12 are arranged. Further, a hole is made in the upper surface of the sample stage 9 so that the electron beam can pass therethrough. The path of the electron beam is kept in a vacuum so that the passage of the electrons is not obstructed.

The control circuit 55 is composed of a microcomputer, reads the design data 548 of the object to be inspected, and controls the electromagnetic deflector 5.
6, calculate the direction θ of the pattern contour line and the length l1 of the contour line in the scannable range and the contour origin (Xo, Yo), and send θl1IXo e Yo' to the contour line scanning signal generator 22.
E: Give. Figure 15 shows θ+ l* XO* Yg (
/J shows the definition. Further, the deflection method switch 19 is switched to the contour line scanning signal generator 22 side.

As shown in FIG. 14, the contour line vicinity scanning signal generator 22
is a cosine transformer 36. Sine converter 67, counter 3
8.45. D/A converters 59, 46. Multipliers 41-4
3° adders 71, 72. It consists of an inverter 73.

The data on the contour direction θ output from the control circuit 35 is sent to a cosine converter 36. By the sine converter 37,
The values of θ and ainθ are determined. When the scan start pulse Cs is output, the counter 68 is cleared to 0, and the counter 45 is set to -d (minus d). The counter 45 counts the output pulses of the clock oscillator 23 2d times. The count value is converted into an analog value by the D/A converter 46. When the count value reaches d, -d is set again and counting is repeated. As a result, the output of the D/A converter 46 becomes a sawtooth wave having an amplitude of d around 0 as shown in FIG. The output of the D/A converter 46 and the output of the sine converter 37 are multiplied by the multiplier 41 and applied to the X-direction microelectrostatic deflector 3 via the deflection amplifier 15, and the output of the cosine converter 36 is multiplied by the inverter 73. After the sign is inverted, the output of the D/A converter 46 and the output of the inverter 37 are multiplied by the multiplier 42, and then applied to the Y-direction microelectrostatic deflector 4 via the deflection amplifier 16. It is scanned repeatedly with a width of 2d perpendicular to the contour line. Further, the pulse interval of the clock oscillator 23 is set to be the time required for the electron beam to move by the beam diameter. Furthermore, the beam diameter at this time is narrowed down to be smaller than the minimum detectable defect size.

Every time the counter 45 counts up to d, the counter 38
The value of is incremented by 1, and when the counter 38 counts up to l, the output of the OD/A converter 39, which returns the pulse Ce to the control circuit, becomes a stair-step waveform of l steps. D/
The output of the A converter 59 and the cosine converter 36. Multiply the output of the sine converter 37 by 1!1. 43 and 44, and add the output l of the multiplier 43 to the X origin data Xo in an adder 71. Yo to adder 7
When the result added in step 2 is applied to the Y-direction electromagnetic deflector 6 via the deflection amplifier 18, it moves in the θ direction shown in FIG. 15! the beam is deflected by When the deflections caused by the noise deflector 344 are combined, the scanning shown in FIG. 6 is performed. When the control circuit 65 receives the count end pulse Ce from the counter 38, the control circuit 65 calculates θ, l, Xo,
Find Yo and perform scanning in the same way. While scanning along the contour line, the multiplexer 20 supplies the output of the photomultiplier 14 to the 21 conversion circuit 26. 2
The digitizing circuit 26 binarizes the input signal using a threshold value THO. The contour line position determination circuit 29 includes a latch circuit 47. Differential circuit 48. Absolute value circuit 49. It consists of a comparison circuit 50. Contour running! The value of the counter 45 in the signal generation circuit 22 is latched and held when the output of the binarization circuit 26 changes from 1 to 0. The difference circuit 48 calculates the difference from the output ad of the latch 47. Further, an absolute value circuit 49 obtains its absolute value. Here, at is the number of pulses of the oscillator 25 output while scanning the length of the minimum detectable defect size.

The comparison circuit 50 further compares the output of the absolute value circuit 49 with dt, and determines that there is a defect when the value of the absolute value circuit output is larger.

When the electromagnetic deflectors 5 and 6 have finished scanning all T contour lines within the scannable range, the scanning method switch 19 is moved to the raster scanning signal generator 24, 25 side, and the multiplexer 20 is moved to the raster scanning signal generator 24, 25 side.
It is cut out on the multiplexer 50 side. Further, the beam diameter changing circuit 62 weakens the excitation current of the condenser lens 2 to increase the beam diameter to about the size of a vine defect occurring in a region other than the vicinity of the contour line.

The control circuit 65 uses the raster scanning signal generator 24.25 to determine the range that can be scanned by the main electromagnetic deflection a5.6.
Raster scan as shown in the figure. During raster scanning, the electrostatic deflectors 3 and 4 do not scan. In synchronization with raster scanning, the control circuit 35 outputs the output of the multiplexer 30 to the binarization circuit 27 when the electron beam is inside the ideal pattern based on the data of the design data 34, and outputs the output of the multiplexer 30 to the binarization circuit 27, If it is outside (on the board), it is output to the binarization circuit 28, and if it is on the outline of the ideal pattern, it is not output anywhere.

The binarization circuit 27 binarizes the input signal with a threshold value TH1 to detect pinholes in the pattern.

Further, the binarization circuit 28 binarizes the input signal using a threshold value TH2, and further inverts the logic using an inverter 31 to detect isolated defects.

When scanning the contour, the control circuit 55 outputs the output of the contour position determination circuit 29 to the inside of the contour (on the pattern).
When raster scanning is performed, the output of the binarization circuit 27 is
When scanning outside the contour line, the output of the inverter 31 is used as a defect detection signal, thereby correctly determining defects.

After inspecting all the ranges that can be scanned by the main electric deflectors 5 and 6, the control circuit 55 drives the XY stage 10,
0 or more operations for inspecting uninspected areas on the X-ray mask 8 are repeated to inspect the entire inspection range on the X-ray mask 8.

In this example, the target is an X-ray mask, and the pattern is detected by detecting transmitted electrons. However, when inspecting an object such as a glass mask through which electrons do not pass, it is possible to use reflected electrons or , it is sufficient to detect secondary electrons. In that case, since the shading of the pattern is reversed, the same defect determination can be performed after inverting the output of the photomal amplifier using an inverter.

〔Effect of the invention〕

According to the present invention, the inspected portion can be inspected by transmitting or reflecting a charged particle beam, which has the effect of significantly shortening inspection time while maintaining high accuracy in defect detection performance.

[Brief explanation of the drawing]

Figure Wc1 is a block diagram of an embodiment of the present invention, Figure 2 is a diagram showing an example of a normal mask pattern, Figure 5 is a diagram showing an example of a defect occurring on the mask pattern, and Figure 4 is a diagram showing a beam according to the prior art. Figure 5 is a diagram showing an example of a beam scan according to the present invention. Figure 5 is a diagram showing an example of a beam scan according to the present invention. Figure 1 is a diagram showing an example of beam scanning according to the present invention. Figure 8 is a graph representing the electron beam intensity as a function of time corresponding to the scanning distance. Figure 8 is a binarized graph of Figure 1. Figure 9 is the scanning by the main deflector when the beam diameter is increased. 10 is a diagram showing the intensity signal of the transmitted electron beam when scanning a pinhole defect, W, 11 is a diagram showing the intensity signal of the transmitted electron beam when scanning a pinhole defect.
Figure 12 is a diagram showing the intensity signal of the transmitted electron beam when scanning a residual defect. Figure 13 is a diagram showing the binary signal of the signal in Figure 12. FIG. 14 is a diagram for explaining the details of the near-contour scanning signal generator 22 in FIG. 1, FIG. 15 is a diagram showing parameters related to scanning, and FIG. FIG. 17, which is a diagram showing an example of a sawtooth wave that provides scanning, is a diagram for explaining details of the contour line position determination circuit 29 in FIG. 1. 1...Electron gun, 2...Palon beam. 3... Condenser lens. 4... Deflection coil, 5... Objective lens. 7... Mask, 9... Transmission electron detector 1
DESCRIPTION OF SYMBOLS 1... CAD data database 12... CAD data reader 15... Format converter 14... Outline vicinity signal generator 1 15... Beam diameter modulator, 16... Beam deflector. 18...Multiplexer, 19... Edge detection circuit. 22... contour line vicinity scanning signal generator. 29...Contour line position determination circuit

Claims (1)

[Claims] 1. Scanning along the pattern outline on the object to be inspected using a charged particle beam focused to a first spot diameter;
A pattern inspection method comprising scanning the pattern of the object to be inspected using a charged particle beam focused to a spot diameter of . 2. In the pattern inspection method according to claim 1, the charged particle beam having the first spot diameter is finely scanned so as to intersect the pattern outline, and the second spot diameter is finely scanning the charged particle beam having the first spot diameter. A pattern inspection method in which the pattern of the object to be inspected is raster-scanned by a charged particle beam having a spot diameter larger than the spot diameter of the object. 3. In the pattern inspection method according to claim 1, the scanning includes a process of knowing the outline position of the pattern from the design data of the pattern provided on the object to be inspected, and a process of determining the outline position of the pattern provided on the object to be inspected. A pattern inspection method that includes a process of determining the actual position of a contour line from the rising or falling portion of a detection signal. 4. A charged particle source that generates charged particles, a means for focusing the charged particles from the charged particle source onto the object to be inspected with at least two different spot diameters, and an electrostatic type capable of two-dimensionally scanning the spot. a deflection means, an electromagnetic deflection means capable of two-dimensionally scanning the same spot, detecting charged particles transmitted or reflected from the object to be inspected or secondary charged particles generated from the object to be inspected, and detecting the pattern; A pattern inspection device comprising: a means for detecting a defect; a means for reading design data of the object to be inspected to calculate a pattern outline position, direction, and length; and a means for detecting a defect from the design data and a detection signal of the pattern. .