KR20030050320A - Method and apparatus for inspecting semiconductor substrate - Google Patents

Abstract

PURPOSE: A method for inspecting a semiconductor substrate is provided to improve work efficiency and reduce a time interval of an inspection process by including a data conversion unit for converting a pattern image of a semiconductor substrate obtained from a scanning electron microscope(SEM) into digital image data and a data analyzer for analyzing the image data. CONSTITUTION: The semiconductor substrate(900) is settled in an XY stage(302) of the SEM. The image focus of the pattern formed on the semiconductor substrate is aligned. The XY stage for forming an image in a particular part of the semiconductor substrate is transferred. An electron beam(100) is irradiated into the particular part and the secondary electrons(102) emitted from the particular part is detected. The image of the particular part is formed from the detected secondary electrons. A reference image of the particular part is inputted. The data analyzer(312) having an image data analyzing program compares the image of the particular part with the reference image to determine whether the semiconductor substrate is defective.

Description

Method and apparatus for inspecting semiconductor substrate

The present invention relates to a method and apparatus for inspecting a semiconductor substrate using a scanning electron microscope (SEM). More particularly, the present invention relates to a method and an apparatus for inspecting a critical dimension (CD) of a pattern formed on a semiconductor substrate.

In general, a semiconductor device is manufactured by repeatedly performing a unit process such as film formation, etching, diffusion, metal wiring, or the like for forming a pattern having electrical characteristics on a semiconductor substrate. Recently, the semiconductor device has been highly integrated and miniaturized in order to realize high capacity and high speed response speed. Accordingly, the importance of an analytical device or technology required for structural and chemical analysis of finer regions is increasing.

As an apparatus for measuring the critical dimension of the fine pattern, a scanning electron microscope having excellent resolution is mainly used. Scanning electron microscopes are the most widely used analytical instruments for observing microstructures and shapes in the solid state, and those having a resolution of about 50 Hz have been commercialized, and products having a resolution of less than 10 Hz have recently been released.

Briefly describing a method for inspecting a semiconductor substrate using the scanning electron microscope, an electron beam generated from an electron gun is scanned to a specific region on the semiconductor substrate through a focusing lens, a scanning coil, an objective lens, and the like, and is emitted from the specific region. Detect secondary electrons Subsequently, the detected secondary electrons are converted into image data and displayed on a monitor, and the operator directly checks the image on the monitor with the naked eye. As an example of inspecting a semiconductor substrate using the scanning electron microscope, US Patent No. 5,555,319 (issued to Tsubusaki, et al.) Has a method for measuring and measuring a critical dimension having a circuit for filtering image data provided from a scanning electron microscope. Is disclosed.

In the micro-pattern inspection process using the scanning electron microscope as described above, the task of directly checking the critical dimension of the pattern by the naked eye is difficult to perform easily due to the automation of the semiconductor device manufacturing process and the miniaturization of the pattern. In addition, a problem arises in that the reliability of the semiconductor device is lowered due to a worker's judgment error. In addition, direct judgment by the worker has been pointed out as a problem of lowering the productivity of the semiconductor device and the efficiency of the manufacturing process.

The present invention for solving the above problems is to provide a semiconductor substrate inspection method and apparatus in which a comparative analysis using a reference image of a specific portion of the semiconductor substrate is automatically performed.

1 is a schematic diagram illustrating a semiconductor substrate inspection apparatus according to an embodiment of the present invention.

FIG. 2 is a plan view showing the XY stage shown in FIG. 1. FIG.

3 is a cross-sectional view illustrating an alignment position sample shown in FIG. 2.

4 is a flowchart for explaining a semiconductor substrate inspection method using the semiconductor substrate inspection apparatus shown in FIG. 1.

Explanation of symbols on the main parts of the drawings

100: electron beam 102: secondary electron

200: electron beam providing unit 202: column

204: electron gun 206: axis adjustment coil

208: focusing lens 210: scanning coil

212: objective lens 300: sample chamber

302: XY stage 304: door

306: cassette 308: secondary electron detector

310: data converter 312: data analyzer

314: monitor 316: data storage

318: optical microscope 320: XY coordinate controller

322: drive unit 324: fixed pin

326: alignment position sample 900: semiconductor substrate

The present invention for achieving the above object,

Iii) placing a semiconductor substrate on an XY stage of a scanning electron microscope;

Ii) aligning an image focus of a pattern formed on the semiconductor substrate;

Iii) moving the XY stage to form an image of a particular portion of the semiconductor substrate;

Iii) detecting secondary electrons emitted by scanning an electron beam at the specific site;

Iii) forming an image of the specific site from the detected secondary electrons, and

And a step of determining whether the semiconductor substrate is defective by comparing and analyzing the image of the specific region and the reference image with a data analyzer having a reference image of the specific region and an image data analysis program installed therein. Provide a test method.

The method may further include displaying an image of the specific site and the determination result, wherein the magnification of the image is set to 8000 to 100,000 times so that the operator can visually observe the naked eye.

The semiconductor substrate inspection apparatus according to the present invention for achieving the above object,

An XY stage on which a semiconductor substrate is placed and driven according to a set XY coordinate;

Electron beam providing means for scanning an electron beam to a specific portion of the semiconductor substrate placed on the XY stage;

A secondary electron detector for detecting secondary electrons emitted from the specific site;

An image data converter converting the detected secondary electrons into image data for generating an image of the specific region; And

And a data analyzer for comparing and analyzing the image data and the reference image data, and determining whether the semiconductor substrate is defective according to the result.

The semiconductor inspection apparatus of claim 5, wherein the XY coordinates are set to overlap an optical microscope for acquiring an image of an alignment pattern formed on the semiconductor substrate, and an image of the obtained alignment pattern and a preset alignment image. And a driving means connected to an XY coordinate controller and the XY coordinate controller to drive the XY stage. The display apparatus may further include a display unit which shows the image of the specific part and the determination result, and a data storage unit which stores the determination result.

Therefore, the pattern formed on the semiconductor substrate is automatically performed by the semiconductor substrate inspection apparatus without depending on the visual inspection of the operator, whereby the reliability and productivity of the semiconductor device can be improved.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a schematic diagram illustrating a semiconductor substrate inspection apparatus according to an embodiment of the present invention.

Referring to FIG. 1, a device for inspecting a fine pattern formed on a semiconductor substrate 900 uses a scanning electron microscope method using an electron beam 100. The inspection apparatus includes an electron beam providing unit 200 providing an electron beam 100 scanned on the semiconductor substrate 900 and a sample chamber 300 provided under the electron beam providing unit 200. The semiconductor substrate 900 is placed on the XY stage 302 provided in the sample chamber 300. One side of the sample chamber 300 is provided with a door 304 on which the semiconductor substrate 900 is loaded, and a cassette 306 in which a plurality of semiconductor substrates are accommodated outside the sample chamber 300 and on one side of the door 304. ) Is loaded.

The electron beam providing unit 200 is provided with an electron gun 204 inside the cylindrical column 202. The role of the electron gun 204 serves to create and accelerate electrons used as a light source. The electron gun 204 supplies a stable electron source used in the form of the electron beam 100, which follows Richardson's law. There are two ways to produce electrons in the electron gun 204. One is to heat the filament to a high temperature so that free electrons are released into the vacuum from the surface of the filament. To emit electrons. The former is called a hot electron and the latter is called a field emission electron.

In the case of the hot electrons, when a metal such as tungsten is heated to a high temperature, electrons confined to the surface atoms are released from the bondage of the atomic nucleus and released into the vacuum. The anode is mainly tungsten, a line filament with a diameter of about 100 micrometers, and bent into a V-shaped hairpin. This filament is heated directly from the current and maintains a high voltage (1-50 kV) during operation. In the case of tungsten, the typical operating temperature is 2700K, allowing 40 to 80 hours of use at a vacuum of 10 to 5 torr. Increasing the temperature increases the electron emission density but decreases the service life. In order to increase the density of generated electrons, B compound having a structure of LaB ₆ is used as a filament, and this material has an advantage of generating a larger amount of electrons at a much lower temperature (1400 to 2000K) than tungsten. Electrons deviating from the metal surface are accelerated to the positive electrode plate having a potential difference of 25 to 30 kV relative to the filament, and proceed to the optical axis through a hole located in the center of the positive electrode.

An axis adjustment coil 206, a focusing lens 208, a scanning coil 210, and an objective lens 212 are provided below the electron gun 204. If the central axis of the electron gun 204 and the central axis of the focusing lens 208 are mechanically scattered, the electron beam radiated from the electron gun 204 to enter the focusing lens 208 may be displaced. This causes lens aberration and degrades resolution. At this time, the axis adjustment coil 206 under the electron gun 204 deflects the direction of the electron beam by an appropriate amount in the X-Y axis direction to match the axis of the focusing lens 208. The focusing lens 208 collects the electron beams exiting the electron gun 204 and becomes a secondary factor that determines the intensity of the electron beams. The objective lens 212, which determines the size of the electron beam 100 irradiated onto the semiconductor substrate 900, is also called an electron beam forming lens. In order to make the small electron beam 100, the focal length is short and the surface of the semiconductor substrate 900 is short. Keep it close. The scan coil 210 is positioned between the focusing lens 208 and the objective lens 212 and serves to deflect the electron beam 100 to a point at the center of the objective lens 212. At this point, it is magnified again by the objective lens 212 and serves to cause the electron beam 100 to reciprocate with time. In general, the size of the electron beam 100 from the electron gun 204 is about 10 to 50 micrometers, and the sequential adjustment coil 206, the focusing lens 208, the scanning coil 210 and the objective lens 212 are sequentially The size of the semiconductor wafer 900 which is finally passed through and is finally scanned is about 5 nm to about 200 nm, which is about 1/10000 of the size of the initial electron beam 100.

The upper one side of the sample chamber 300 is provided with a secondary electron detector 308 for detecting secondary electrons 102 emitted by the reaction of the semiconductor substrate 900 and the electron beam 100. The electron beam 100 incident on the semiconductor substrate 900 with an energy of 20 to 30 keV collides with the atoms of the semiconductor substrate 900 in an elastic and inelastic manner, and the secondary electrons 102, backscattered electrons, X-rays and visible light Produces the same signal. A bias voltage of about 125 to 250V is applied to the secondary electron detector 308, and among the signals, the secondary electron 102 having a relatively low energy is detected. The secondary electrons 102 detected by the secondary electron detector 308 are converted into image data through the image data converter 310. The image data converter 310 includes a photomultiplayer tube (PMT, not shown) and an A / D converter (not shown), and the secondary electrons amplified through the optical amplifier are 102 are converted into electrical signals. The electrical signal is again converted into image data having a digital signal form through an A / D converter.

The image data is sent to the data analyzer 312. In the data analyzer 312, reference image data of a specific portion of the semiconductor substrate 900 to be inspected is pre-input, and an image data analysis program is installed. The data analyzer 312 compares and analyzes the input reference image data and the image data, and determines whether the semiconductor substrate 900 is defective according to the result. That is, when the critical dimension of the pattern is larger than the error range compared with the input image data, the defect is determined, and even when contaminants such as particles are found on the semiconductor substrate 900, the defect is determined.

The data analyzer 312 is connected to the monitor 314, and the operator can check the determination result on the monitor 314. In addition, the operator is configured to be able to check the reference image and the measured image simultaneously or selectively on the monitor 314. The operator can visually check the images and can visually check the critical dimension of the pattern.

In addition, the data storage unit 316 connected to the data analyzer 312 stores the result of the determination so that it can be used later to improve the process.

On the other hand, the inspection of the plurality of semiconductor substrates accommodated in the cassette 306 can selectively perform a full inspection or a sampling inspection depending on the situation. When the semiconductor substrate accommodated in the cassette 306 is transferred into the sample chamber 300 by a transfer robot (not shown) and seated on the XY stage 302, an accurate image of the pattern shape formed on the semiconductor substrate 900 is provided. The focus is to be obtained to obtain the. At this time, the magnification of the image can be visually confirmed by the operator and should be set to be suitable for analyzing the image data. For the same reason as above, the magnification is set to about 8000 to 100,000 times. If the magnification of the image is too small, the shape of the pattern may not be known exactly. On the contrary, if the magnification of the image is too large, the inspection area may be too narrow.

The semiconductor substrate 900 placed on the XY stage 302 is aligned using the optical microscope 318 provided on the upper part of the sample chamber 300. Alignment is an operation of correcting the coordinate system of the pattern formed on the semiconductor substrate 900 and the coordinate system of the XY stage 302. Specifically, the stage position coordinates are corrected so as to exactly overlap the reference image by comparing the optical microscope image enlarged by several hundred times the alignment pattern formed on the semiconductor substrate 900 with the reference image of the previously registered alignment pattern. . The image obtained from the optical microscope is transmitted to the XY coordinate controller 320, the XY coordinate controller 320 compares the reference image and the optical microscope image, and thus the drive unit connected to the XY coordinates corrected according to the XY stage 302 To 322. The driving unit 322 moves the XY stage 302 according to the corrected XY coordinates. Next, the XY stage 302 is moved to a specific position registered in the XY coordinate controller 320.

The focus alignment operation as described above may be performed by an alignment position sample. 2 and 3, the pin 324 is provided on the XY stage 302 so that the semiconductor substrate 900 is placed at a designated position. That is, a plurality of fixing pins 324 are provided at predetermined positions so that alignment may be performed based on a flat zone of the semiconductor substrate 900. An alignment position sample 326 is formed on one side of the portion where the semiconductor substrate 900 is placed. The alignment position sample 326 has a structure in which the metal film holder 328 and the metal film sample 330 are bonded to each other with the insulating adhesive 332 interposed therebetween, as shown in the cross-sectional view of FIG. 3. In this case, the metal film holder 328 is made of a metal material, for example, aluminum (Al), and the metal film sample 330 is made of copper (Cu). The electron beam provided from the electron gun 204 is irradiated to the alignment position sample 326, thereby detecting the secondary electrons emitted, and the XY stage 302 can be aligned through the alignment position image generated by the secondary electrons. Can be. In this case, the XY coordinate controller 320 is connected to the data analyzer 312 and corrects the XY coordinates according to a result of comparing the alignment position image data provided from the data converter 310 with the reference alignment position image data registered in advance. do.

Next, a method of inspecting a pattern formed on a semiconductor substrate will be described with reference to the flowchart of the semiconductor substrate inspection method illustrated in FIG. 4.

First, a cassette containing a plurality of semiconductor substrates is mounted on a stage provided outside the sample chamber. Then, the semiconductor substrate selected from the cassette is mounted on the XY stage provided in the sample chamber by using the transfer robot (S100).

Subsequently, the focus is aligned by comparing the image of the alignment pattern obtained from the optical microscope with the image of the previously registered alignment pattern.

Subsequently, the XY stage is moved to reach the specific beam to be inspected (S300).

Then, the electron beam provided from the electron gun is scanned on the specific site, and the secondary electrons emitted from the specific site are detected by the electron beam (S400).

The detected secondary electrons are transmitted to the image data conversion unit, and the image data conversion unit forms image data of the specific region from the detected secondary electrons (S500).

The image data then forms an image on the monitor and is also sent to the image analyzer. The image analyzer compares and analyzes the input reference image data with the image data. That is, by comparing the digitized image data, it is determined whether the pattern formed on the semiconductor substrate is defective. And, the result of the determination is shown so that the work can be confirmed on the monitor (S600).

The operator can optionally visually check the inspection image and the reference image on the monitor, and the defect determination result is stored as data in the data storage.

According to the present invention as described above, by providing a data converter for converting the pattern image of the semiconductor substrate obtained from the scanning electron microscope into digital image data and a data analyzer for analyzing the image data, to improve the work efficiency of the operator, The time for the inspection process can be shortened.

In addition, a decrease in reliability of the semiconductor device due to an operator's judgment error is prevented, and the productivity of the semiconductor device as a whole is improved.

Although described above with reference to a preferred embodiment of the present invention, those skilled in the art will be variously modified and changed within the scope of the invention without departing from the spirit and scope of the invention described in the claims below I can understand that you can.

Claims (6)

Iii) mounting the semiconductor substrate on the XY stage of the scanning electron microscope; Ii) aligning an image focus of a pattern formed on the semiconductor substrate; Iii) moving the XY stage to form an image of a particular portion of the semiconductor substrate; Iii) detecting secondary electrons emitted by scanning an electron beam at the specific site; Iii) forming an image of the specific site from the detected secondary electrons; And And a step of determining whether the semiconductor substrate is defective by comparing and analyzing the image of the specific region and the reference image with a data analyzer having a reference image of the specific region and an image data analysis program installed therein. method of inspection. The semiconductor substrate inspection method of claim 1, further comprising displaying an image of the specific portion and the determination result. The semiconductor substrate inspection apparatus according to claim 1, wherein the magnification of the image is 8000 to 100,000 times so that the critical dimension of the pattern can be visually observed. An XY stage on which the semiconductor substrate is placed and driven according to the set XY coordinates; Electron beam providing means for scanning an electron beam onto a specific portion of the semiconductor substrate placed on the XY stage; A secondary electron detector for detecting secondary electrons emitted from the specific site; An image data converter converting the detected secondary electrons into image data for generating an image of the specific region; And And a data analyzer which compares and analyzes the image data and the input reference image data, and determines whether the semiconductor substrate is defective according to the result. The optical microscope of claim 4, further comprising: an optical microscope for acquiring an image of an alignment pattern formed on the semiconductor substrate; An XY coordinate controller configured to set the XY coordinates such that the image of the obtained alignment pattern and a preset alignment image overlap each other; And And a driving means connected to the XY coordinate controller and driving the XY stage. The display apparatus of claim 4, further comprising: a display unit configured to display an image of the specific portion, the reference image, and the determination result; And And a data storage unit connected to the data analyzer and storing the determination result.