JP3367204B2 - Semiconductor inspection equipment - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor inspection apparatus suitable for measuring minute dimensions such as the width of a pattern of a semiconductor integrated circuit. 2. Description of the Related Art A confocal scanning laser microscope has been conventionally used mainly for measuring dimensions such as the width of a pattern formed on a wafer or a mask when manufacturing a semiconductor integrated circuit. FIGS. 4A and 4B show the principle of a confocal scanning laser microscope. 4A, a laser beam 2a emitted from a laser oscillator 1 is reflected by a turning mirror 3, collected by a lens 4, and passed through a pinhole 5. FIG. The laser beam 2 a passing through the pinhole 5 is transmitted through the beam splitter 6, is converged by the objective lens 7, and is irradiated on the sample (wafer, mask, or reticle) 8. The reflected light 2b reflected by the surface of the sample 8 is reflected by the beam splitter 6, passes through the pinhole 9, is photoelectrically converted by the photomultiplier tube 10, and is detected as an electric signal. When measuring the dimensions with such a laser microscope, the position of the focal point F of the laser beam 2a is fixed to the position below (or above) the pattern 11 as shown in FIG. I do. The sample 8 is slowly moved in the Y-axis direction on an XY stage (not shown) while the sample 8 is scanned in the X-axis direction at a high frequency by the scan controller 12. At this time, when the beam spot passes under the pattern 11 as shown in FIG.
All pass through the pinhole 9, the photomultiplier tube 1
The output of 0 is the highest. On the other hand, when the beam spot passes over the pattern 11 as shown in FIG. 4B, the reflected light 2 b is not focused at the position of the pinhole 9 and most of the reflected light 2 b Since the light is blocked, the output of the photomultiplier tube 10 becomes the lowest. Therefore,
The brightness according to the output of the photomultiplier tube 10 is adjusted in synchronism with the scan by the scan controller 12.
By drawing sequentially on the top, the enlarged image 1 of the pattern
4 is displayed on the television monitor 13 and the enlarged image 14
, It is possible to automatically measure the line width of the pattern 11 with high accuracy. A specific example of a confocal scanning laser microscope based on the above principle will be described with reference to FIG. FIG. 5 is an apparatus configuration diagram of a confocal scanning laser microscope (trade name: Siscan-IIA), which is a product of Siscan-Systems, USA. This confocal scanning laser microscope includes an optical module 16 and a workstation 17 interconnected by a signal cable 15. In the optical module 16, an XY stage 20 is mounted on a base 19 supported by an air suspension 18, and a scanner 21 is further mounted on the XY stage 20. The sample is chucked and held on the scanner 21 by vacuum suction. A focusing device 22 is disposed above the scanner 21, and converges a laser beam emitted from the laser head 23 by the objective lens 7 and irradiates the sample on the scanner 21. And
In the laser head 23, as shown in FIG.
The optical system shown in FIG. Further, a television camera 24 with a zoom lens for photographing an image near the laser irradiation position of the sample is disposed downwardly adjacent to the laser head 23. Further, below the base 19, an electric circuit chassis 25, various indicators 26 such as vacuum equipment for chucking a sample, a laser power supply 2
And a robot controller for handling the sample, setting it on the scanner 21, and removing it from the scanner 21. On the other hand, an operation panel (keyboard) 28, a television monitor 13, a printer 2
9. A control device 30 including a CPU is provided so that the optical module 16 can be operated from the workstation 17 and the television monitor 13 has
An observation image by the laser beam, an image photographed by the television camera 24, a menu necessary for operation, and the like are displayed. Next, FIG. 6 shows a system configuration of the confocal scanning laser microscope shown in FIG. The sample 8 is transferred onto the scanner 21 by the wafer handling robot 31 and chucked. The laser beam 2a from the laser oscillator 1 is emitted from the objective lens 7 via the optical module 16 and irradiates the sample 8. Then, the reflected light 2b is received and detected by the photomultiplier tube 10. The computer of the workstation 17
The system 30 controls each unit via a bus 32. That is, the wafer handler control unit 33 drives the wafer handling robot 31 to carry out and carry in the sample 8. The XY stage motor control unit 34
The XY stage 20 is driven to position a desired portion to be inspected on the sample 8 as a scan range of the laser beam 2a. Further, the Z-axis focus control unit 35
Is moved up and down to focus below or above the pattern on the sample 8. Then, when there is a focus, the height of the objective lens 7 is fixed there. [0010] The scan control and synchronization circuit 36 performs reading of a scan waveform and synchronization control as scan control. Line scan waveform memory 37
Stores a scan waveform such as a sine wave, and reads out the stored scan waveform at a high speed (for example, 2 kHz) in response to a command from the scan control and synchronization circuit 36. The read scan waveform is converted into an analog waveform by the D / A converter 38, and the actuator (voice coil motor, piezoelectric element, etc.) of the scanner 21 is driven in the X-axis direction via the amplifier 39a, and the laser light 2a
Scan the irradiation position. The scanning speed is maintained at a specified speed by speed feedback. The output of the photomultiplier tube 10 is converted into a digital signal by an A / D converter 40 via a preamplifier 39b. Pixel timing and synchronization circuit 4
Numeral 1 designates a correspondence relationship between the detection information of the photomultiplier tube 10 continuously obtained in each scan and the position on the X-axis. An address on one scan line is given and taken into the line scan pixel memory 42. The line scan distortion memory 43 corrects a deviation between the scan waveform and the actual movement of the scanner 21 and the like, so that an accurate pattern is taken into the line scan pixel memory 42. The scanning of the sample 8 is performed on the XY stage 2
It is performed while slowly moving the Y axis of 0 at a constant speed,
At this time, the contents of the line scan pixel memory 42 are stored in the video display memory 4 for each scan.
4, the pattern images in a desired range on the XY plane are displayed in the display area of the image monitor 45 on the television monitor 13. In the display area of the graphic monitor 46 on the television monitor 13, a detected waveform of the photomultiplier tube 10 in the X-axis direction at the Y-axis position indicated by the cursor on the image monitor 45 is displayed. In the measurement of the pattern width, the image monitor 45
For the area indicated by the cursor above,
The number of pixels of the pattern stored in the display memory 44 is counted, the average value of the count value at each position in the Y-axis direction in the cursor is automatically calculated, and the result is displayed on the television monitor 13 as a numerical value. . In the above-described semiconductor inspection apparatus, the intensity of the laser beam output from the laser oscillator fluctuates due to output fluctuation or noise of the laser oscillator serving as a light source. For this reason, when an attempt is made to measure the dimensions of a film formed on a wafer or a mask with a precision of several nanometers, a signal indicating the dimensional information of the film detected by a photomultiplier tube indicates that the laser light There is a problem that the intensity fluctuation becomes a noise component and the reproducibility of the measurement decreases. SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and the reproducibility of measurement can be improved even when the laser beam output from the laser light source, which is a light source, includes an intensity fluctuation. It is an object of the present invention to provide a semiconductor inspection apparatus in which the semiconductor device does not decrease. [0015] In order to solve the above-mentioned problems, a semiconductor inspection apparatus according to the present invention comprises: a laser oscillating means for irradiating a laser beam to an object; A first detecting means for detecting the intensity, a second detecting means for detecting the intensity of the laser light, and a dividing means for generating information obtained by dividing the intensity of the reflected light by the intensity of the laser light. And forming information representing a surface shape of the object based on the information. According to the semiconductor inspection apparatus of the present invention, the signal indicating the intensity of the reflected light of the device under test, which is the output of the first detecting means, is the output of the second detecting means by the dividing means. It is divided by a signal indicating the intensity of the laser light. Thus, the noise component included in the information representing the surface shape of the object obtained as the output signal of the first detection means is removed. An embodiment of the present invention will be described below with reference to FIGS. The semiconductor inspection apparatus of the present embodiment is based on the confocal scanning laser microscope described above, and is configured by adding the following devices to remove noise components included in the output signal of the photomultiplier tube. It has become. In the semiconductor inspection apparatus according to the present invention, FIG.
6 are assigned the same reference numerals as in the conventional semiconductor inspection apparatus shown in FIG. FIG. 1 is a diagram showing an optical system in a semiconductor inspection apparatus according to the present embodiment. In the figure, reference numerals 47, 4
8, 49, 58 and 59 are turning mirrors, 51 is a beam expander, 52 is a collimator lens, and 80 is a second photomultiplier tube (second detecting means). Laser light 2 emitted from laser oscillator 1
a is reflected by the turning mirrors 47 and 48 and enters the beam splitter 6. The laser beam 2a incident on the beam splitter 6 is
Is transmitted to the beam expander 51, is condensed here, passes through the pinhole, and then is incident on the collimator lens 52. The laser light 2 a is collimated by the collimator lens 52 and then reflected by the turning mirror 49 to be incident on the objective lens 7.
The objective lens 7 converges the incident laser beam 2a with high precision and irradiates the sample 8 with the laser beam 2a. The laser beam 2a applied to the sample 8 is modulated and reflected according to the reflectance of a film formed on the surface of the sample 8. Reflected light 2b reflected by this sample 8
Is reflected again by the turning mirror 49, condensed by the collimator lens 52, passes through a pinhole provided in the beam expander 51, is adjusted into parallel rays, and is incident on the beam splitter 6. Then, the reflected light 2b is totally reflected by the beam splitter 6, is changed its traveling direction by a turning mirror 58, and is incident on the photomultiplier tube 10 (first detecting means). The reflected light 2b incident on the photomultiplier tube 10 is photoelectrically converted here, and an intensity change generated according to the reflectance of the film formed on the surface of the sample 8 is detected. As described above, the intensity of the laser beam 2a applied to the sample 8 fluctuates due to fluctuations in the output of the laser oscillator 1 and noise. Therefore, the photomultiplier tube 10 detects, as a noise component, an intensity variation caused by the output variation of the laser oscillator 1 or noise or the like at the same time as the intensity variation caused according to the dimension of the film of the sample 8 to be measured. I do. On the other hand, a part of the laser light 2a, which is the direct light of the laser oscillator, incident on the beam splitter 6, is reflected, the traveling direction is changed by the turning mirror 59, and the laser light 2a is transmitted to the second photomultiplier tube 80. The noise component of the laser beam 2a which is incident and is caused by the output fluctuation of the laser oscillator 1, the noise or the like is detected. Next, FIG. 2 is a system configuration diagram showing an example of a semiconductor inspection apparatus according to the present invention. This semiconductor inspection apparatus is different from the conventional semiconductor inspection apparatus shown in FIG. 6 in that an amplifier 81 for amplifying the output of the photomultiplier tube 80 and an output signal of the photomultiplier tube 10 are output from the photomultiplier tube 80. The configuration is such that a divider 82 for dividing by a signal is added. The intensity change of the laser beam 2b generated according to the width of the film formed on the surface of the sample 8 is converted into an electric signal by the photomultiplier tube 10 and amplified by the preamplifier 39b with high S / N. Thereafter, it is input to the divider 82. Further, a change in the intensity of the laser light 2 a caused by an output fluctuation or noise of the laser oscillator 1 is converted into an electric signal by the photomultiplier tube 80, and the high-
After being amplified by / N, it is input to the divider 82. In the divider 82, the output signal of the photomultiplier tube 10 is divided by the output signal of the photomultiplier tube 80, and is input to the next-stage A / D converter. Here, referring to FIG. 3, the photomultiplier tube 1
The principle of dividing the output signal of 0 by the output signal of the photomultiplier tube 80 to remove noise components caused by output fluctuation of the laser oscillator 1 and noise included in the output signal of the photomultiplier tube 10 will be described in detail. explain. Now, let A be the signal output by the photomultiplier tube 80, B be the signal output by the photomultiplier tube 10, and C be the signal output by the divider 82. The output signal B is a signal obtained by directly photoelectrically converting the laser light 2 a output from the laser oscillator 1 as a light source by the photomultiplier 80, and includes an intensity fluctuation component by the laser oscillator 1.
On the other hand, the signal B is the laser light 2 output from the laser oscillator 1.
The sample 8 is irradiated with the laser beam 2a, and the laser beam 2a undergoes an intensity change due to the difference in the reflectance of the film formed on the surface of the sample 8, and the reflected light 2b reflected by the photomultiplier 10 is photoelectrically converted by the photomultiplier tube 10. This is the obtained signal. Therefore, signal B is
On the intensity change component due to the film formed on the surface of the sample 8, the intensity change caused by the output fluctuation of the laser oscillator 1 as a light source or noise is superimposed as a noise component. From the above, assuming that the intensity change component due to the film formed on the surface of the sample 8 is D, the signal B becomes (A
× D). Therefore, the photomultiplier tube 10
The signal B output by the photomultiplier tube 80 is the signal A output by the photomultiplier tube 80.
The signal C output from the divider 82 is expressed as C = (A × D) / A = D, and the noise component due to the output fluctuation of the laser oscillator 1 which is the light source and the intensity fluctuation caused by the noise is expressed as follows. Only the intensity change component D due to the film formed on the surface of the sample 8 after being removed is output. As described above, according to the semiconductor inspection apparatus of this embodiment, the noise component due to the output fluctuation of the laser oscillator 1 and the intensity fluctuation caused by the noise included in the output signal of the photomultiplier tube 10 is the laser light. It is removed by dividing by the output signal of the third photomultiplier tube 80 for detecting the intensity fluctuation of 2a. As a result, as the output signal of the divider 82, only a signal related to the dimension of the film formed on the surface of the sample 8 is output, and the reproducibility of the dimension measurement is improved. Although one embodiment of the semiconductor inspection apparatus according to the present invention has been described above, the present invention is not limited to the above-described embodiment, and various design changes can be made in the specific configuration of each part. Of course. As described above in detail, according to the semiconductor inspection apparatus of the present invention, the noise component included in the information representing the surface shape of the object obtained as the output signal of the second detection means Is removed, and the reproducibility of measurement of minute dimensions is improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing an example of an optical system of a semiconductor inspection device according to the present invention. FIG. 2 is a system configuration diagram showing an example of a semiconductor inspection device according to the present invention. FIG. 3 is a diagram illustrating the principle of noise cancellation of the semiconductor inspection device according to the present invention. FIG. 4 is a diagram illustrating a measurement principle of a conventional confocal scanning laser microscope. FIG. 5 is a front view showing an example of a conventional semiconductor inspection device. FIG. 6 is a system configuration diagram showing an example of a conventional semiconductor inspection device. [Description of Signs] 1 Laser oscillator 6 Beam splitter 7 Objective lens 8 Sample 10 Photomultiplier tube (first detection means) 51 Beam expander 52 Collimator lens 80 Second photomultiplier tube (second detection means) 81 Preamplifier 82 Divider

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01B 11/24 G02B 27/00 H01L 21/66

Claims (1)

(57) [Claims] [Claim 1] Laser light emitted from laser oscillation means
Is irradiated on the sample, and the intensity of the reflected light obtained from the sample is detected.
Semiconductor inspection that measures the minute dimensions of the sample
Inspection device, which reflects a part of the laser light emitted from the laser oscillation means.
While transmitting the remaining laser light, and
A beam splitter that totally reflects the reflected light
Rain was condensed with data, the laser beam transmitted through the beam splitter
Beam expander that passes through the hole and the laser light emitted from the beam expander with high accuracy
An objective lens for converging and irradiating the sample, and an objective lens and a beam expander for reflecting the light from the sample
Of the reflected light that has passed through and totally reflected by the beam splitter
Detecting means for detecting the intensity of the laser light partially reflected by the beam splitter.
Detecting the intensity of the reflected light obtained from the second detecting means and the first detecting means;
Divide by the intensity of the reflected light obtained from the detecting means 2
The intensity of the laser light included in the intensity of the reflected light
A semiconductor inspection apparatus , comprising: division means for removing fluctuation .