JPH10197463A - Pattern inspection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive pattern inspection device which can improve the service life of an MCP(micro channel plate) while maintaining a highly sensitive defect detecting ability and can perform high-speed processing. SOLUTION: A pattern inspection device which inspects the pattern of a sample is provided with a lighting means 3 which projects an electron beam upon the surface of a sample, an X-Y stage 7 which moves the sample for exposing the surface of the sample to the electron beam, a position detecting means 9 which detects the position of the stage 7, an electron detector 5 which detects at least one of secondary electrons, reflected electrons, and back scattered electrons from the surface of the sample irradiated with the electron beam as the image beam of the sample, and a projection type electrooptic system 4 which forms the image of the image beam of the sample on the electron detector 5 as the image of the sample. The inspection device continuously inspects the pattern on the surface of the sample by inverting the image of the sample formed on the detector 5 by controlling the electrooptic system 4 in accordance with the variation of the moving direction of the stage 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

2. Description of the Related Art With the recent high integration of LSIs, the sensitivity of detecting defects on a sample surface such as a wafer and a mask has been increasing. For example, a detection sensitivity of 0.1 μm is required for the size of a defect to be detected on a pattern size of a 0.25 μm wafer pattern of a 256 MDRAM. In addition, there has been an increasing demand for an inspection apparatus that satisfies both high detection sensitivity and high inspection speed. In order to meet these requirements, a surface inspection device using an electron beam has been developed.

2. Description of the Related Art Conventionally, as a pattern inspection apparatus using an electron beam, there are, for example, Japanese Patent Application Laid-Open Nos. 5-258703 and 7-249393. As a typical example of the prior art, JP-A-7-249393 will be briefly described. FIG. 10 is an overall configuration diagram of a conventional pattern inspection apparatus. It comprises a primary column 81 composed of an electron gun for generating a rectangular electron beam and a quadrupole lens system, and a projection type secondary electron detection column 84 for detecting secondary electrons or reflected electrons from a sample. By using an electron optical system consisting of a rectangular cathode and a quadrupole lens system,
The beam shape to be irradiated on the sample surface 82 can be easily formed arbitrarily. This apparatus is characterized in that the inspection time for scanning the entire surface of the sample can be greatly reduced with high detection sensitivity by a rectangular beam having an appropriate aspect ratio.

Next, various detection systems have been proposed as secondary electron detection systems for detecting secondary electrons from a sample. As an example, a secondary electron detector using an MCP / phosphor screen / linear image sensor will be described. FIG. 11 is a sectional view of a conventional secondary electron detector. Secondary electrons emitted from the sample pass through the secondary electron detection column,
An image is formed on the detection surface. A fiber plate 73 coated with a fluorescent screen 72 is arranged at the subsequent stage, and the signal of the doubled electron group is converted into an optical signal, and is converted again into an electric signal by a MOS type linear image sensor 74.

[0004]

However, in the above prior art, considering the processing speed for continuously inspecting the wafer, the TDI array CCD has a bidirectional imaging function in order to minimize the turnaround time of the stage. It is necessary to adopt a camera with a certain point. However, two-way TD
In the I camera, the number of integrated lines of TDI cannot be set variably, and the number of integrated lines must be fixed. In this case, the TDI camera must be selected with the highest priority given to the conditions under which the device can operate stably. Good or bad environment
(The magnitude of the floor vibration, the magnitude of the fluctuating magnetic field, etc.), there is a problem in that the degree of freedom in setting the conditions for optimization or the like is lost.

[0005] To develop a TDI camera capable of bidirectional imaging and capable of changing the number of integrated lines requires enormous development costs, complicates the internal structure of the CCD, and increases the aperture ratio of the CCD. And the effect of line integration is reduced. SUMMARY OF THE INVENTION An object of the present invention is to provide a pattern inspection apparatus capable of improving the life of an MCP and maintaining high-speed processing at low cost while maintaining high-sensitivity defect detection performance.

[0006]

Means for Solving the Problems In order to solve the above problems, according to the present invention, first, in claim 1, an irradiation means for irradiating an electron beam on a sample surface, and applying the sample to the electron beam irradiation surface. A moving XY stage, position detection means for detecting the position of the XY stage, and at least one of secondary electrons, reflected electrons and backscattered electrons from the sample surface irradiated by the electron beam. An electron detector for detecting a sample image beam, and a pattern inspection apparatus for inspecting a pattern of a sample having a projection electron optical system that forms the sample image beam as a sample image on the electron detector, Inverting the sample image formed on the electron detector by controlling the projection electron optical system according to a change in the moving direction of the stage, and continuously inspecting the pattern on the sample surface. did.

According to a second aspect of the present invention, in addition to the first aspect, the electronic detector is a TDI array CCD. In claim 3 of the present invention, in addition to claim 2, the TDI
The array CCD is of a variable integration line type, and the number of the integration lines is variable depending on the state of the sample to be inspected.

According to a fourth aspect of the present invention, in addition to the first aspect, the irradiating means makes the current amount of the primary electron beam variable according to the state of the sample to be inspected.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an overall configuration diagram of an embodiment of the present invention. In the figure, the X axis is used as coordinates indicating the direction of displacement of the stage 6, the Y axis is perpendicular to the paper surface, and θ is the angle around the Z axis. A secondary electron 110 is generated from the sample 6 by a primary irradiation beam 100 irradiated from a primary column 3 as an electron beam irradiation means including an electron gun 1 for forming a rectangular electron beam and a quadrupole lens system 2. Secondary electrons 110 generated from the surface of the sample 6 are captured by the projection type secondary electron detection column 4, and are used as electron detection means.
The image is enlarged and projected on the CP assembly detector 5.

The MCP assembly detector 5 is controlled by a drive control means 8 of a variable integration line type 96-stage TDI CCD camera to extract a sample image signal. The sample 6 is placed on a stage 7, and the stage can be moved in X and Y directions by driving means.
Y and the angle θ can be read by a laser interferometer unit 9 as a position detecting means.

In response to an instruction from the CPU 10, the stage driving means drives the XY stage 7. The position information of the stage is transmitted from the laser interferometer unit 9 to the TDI system C.
The sample images are transmitted to the CD camera drive control means 8, sequentially supplied to the CPU 10, and displayed on the display 12. The operation of the defect inspection apparatus using the electron beam configured as described above will be described in order below.

First, the integration line variable type TDI array CCD will be briefly described. FIG. 2 is a block diagram of a variable integration line 96-stage TDI (Time-Delay-Integration) array CCD. A linear CCD in which 2048 CCD pixels C1 to C2048 are arranged in a horizontal direction.
96 stages of Row1 to Row96 are arranged in the vertical direction. The accumulated charge on each CCD stage is transferred by one stage in the vertical direction at a time by one vertical clock signal supplied from the outside.

When the total number of lines is set to a maximum of 96 lines by an external signal, for example, at a certain point in time,
When the image of 2048 pixels captured in Row 96 moves by one stage in the vertical direction and a vertical clock signal is given in synchronization with the movement, the line image captured in Row 96 becomes R
Transferred to ow95. Then, since the same image is continuously taken, the charge of the stored image is doubled. Subsequently, when the image is further moved by one stage in the vertical direction and a synchronous clock signal is applied, the stored image is transferred to Row 94, where triple image charges are stored.

Thereafter, when the transfer of charges and the imaging are repeated up to Row 1 following the movement of the image, the result of accumulating 96 times the image charges is serially taken out as image data from the horizontal output register. The above operation is
Performed simultaneously in each stage Row1 to Row96, and a two-dimensional image (2
While transmitting (048 pixels × 96 pixels) in the vertical direction, it is possible to synchronously extract an image in which 96 times the image charge is accumulated line by line.

The case where the number of integrated lines is made variable by external control is as follows. In the case of this camera, five types of integration lines, 96, 48, 24, 12, and 6 stages, can be selected. For example, if it is set to 48 levels, CSS4
The transfer charge is cut at the line-shaped portions shown in FIG. That is, in the case of 48-stage setting,
What actually contributes to imaging is limited to Row1 to Row48. If another number of stages is set, CSS2
4, the transfer charge is cut off at CSS12 and CSS6.

Next, the MCP assembly detector will be described. FIG. 3 is an explanatory diagram of the configuration of the MCP assembly detector. The sample image beam 36 projected from the projection type secondary electron column enters the first MCP 31. First M
The sample image beam 36 incident on the CP 31 collides with the fluorescent screen 33 via the second MCP 32 while amplifying the current amount in the MCP.

At this time, the potential at the entrance of the first MCP 31 is set in order to adjust the acceleration voltage of the sample image beam 36 projected from the projection type secondary electron column to a value with the best MCP detection efficiency. You. For example, when the acceleration voltage of the projection sample image beam 36 is +5 kV, the first MCP
The potential at the inlet of 31 is set to -4.5 kV and decelerated,
The electron energy is set to about 0.5 keV.

The amplification rate of the sample image beam current is defined by the voltage applied between the first MCP 31 and the second MCP 32. For example, an amplification factor of 1 × 10 ⁴ is obtained when 1 kV is applied. Further, in order to minimize the spread of the image beam output from the second MCP 32, the second MCP 3
A voltage of about 4 kV is applied between 2 and the fluorescent screen 33.

On the phosphor screen 33, the electrons are converted into photons, and the output image is converted to a FOP (fiber optic plate) 3.
4 and a TD equipped with the TDI array CCD.
The light is emitted to the I-type CCD camera 35. In order to match the image size on the phosphor screen 33 with the imaging size of the TDI array CCD, the FOP 34 is designed so that the image is reduced and projected approximately 3: 1.

The following describes how the sample image is actually taken into the CPU by using the components having the above functions. In FIG. 4, it is assumed that the inspection target area 43 indicated by oblique lines in the sample (wafer) 44 is inspected. It is assumed that the sample 44 continuously moves in the vertical direction at a constant speed according to the instruction from the CPU. Further, the linear image beam 40 from the sample area irradiated by the primary irradiation beam 100
Assume that the image is properly enlarged and projected on the P assembly detector.

Now, when the inspection is started from the position shown in FIG. 4, the coordinates (X1, Y1) of the inspection target area 43 are changed to (X20
The sample image up to 48, Y1) is the RDI of the TDI array CCD.
Imaged and stored in ow96. Due to the vertical movement of the sample 44,
When the primary beam irradiation position moves by one pixel in the moving direction 42, the laser interferometer unit 8 sends one vertical clock signal to the TDI camera control unit 9.

Then, Row 96 of the TDI array CCD is used.
Is transferred to Row95, and the sample images from (X1, Y1) to (X2048, Y1) are transferred to Row95 of the TDI array CCD and from (X1, Y2) until the next clock comes.
The sample image up to (X2048, Y2) is captured in Row 96. Similarly, Row96 of the primary irradiation beam 41 is
When the camera reaches the sample coordinate position from (X1, Y96) to (X2048, Y96) and finishes imaging, (X1, Y1) returns to (X2048, Y96).
The sample images up to Y1) are first output to the CPU 10 via the TDI camera control unit 9. From the next vertical clock signal, (X1, Y2) to (X20
The sample images up to 48, Y2) are output to the CPU 10, and the images are sequentially acquired by the CPU, and the inspection is performed.

FIG. 5 shows a flow of the inspection as viewed from the whole wafer to be inspected. In the drawing, the locus 50 of the irradiation beam position due to the movement of the XY stage is shown. As shown in this figure, after the inspection by continuous movement of the stage in one direction,
In the next inspection, the processing speed is fastest if the moving direction of the stage is opposite. Therefore, in this embodiment, since the integration direction of the TDI array CCD cannot be changed, a means for inverting the mapping is used inside the projection type secondary electron detection column 2.

FIG. 6 is a diagram for switching between erect and inverted mapping.
It is a light beam schematic diagram of an imaging mode. In order to invert the image, the number of times of image formation by the electrostatic lens should be increased or decreased by one. The lens configuration is designed in advance so that the magnification difference generated at that time can be sufficiently absorbed. FIG. 6A conceptually illustrates a mode in which the sample image on the sample surface is erectly formed on the MCP detector surface. Cathode lens 6
By means of 1 and the transfer lens 62, the sample image is formed on the field aperture 65 at a certain magnification. Furthermore, the first projection lens 63 and the second projection lens 6 in the subsequent stage
By 4, the sample image is formed on the MCP surface.

FIG. 6B shows that the number of times of image formation is reduced by one by changing the applied voltage of the first projection lens 63 and the second projection lens 64. Thus, the image of FIG. 6B is the inverted image of FIG. 6A. The magnification adjustment is performed by adjusting the applied voltage of each lens. According to the above-described method, it is possible to inspect the flow as shown in FIG. 5 without using a TDI camera capable of bidirectional image integration.

[0026]

According to the present invention, the number of integrated lines in the TDI camera can be selected, so that the primary beam current can be optimized to some extent in accordance with the surface condition and surface material of the sample. Become. Therefore, damage such as charge-up and contamination due to primary beam irradiation of the sample can be minimized.

Further, even if the TDI array CCD and the camera control unit are specially developed so that the configuration of the pixel and the configuration of the number of integrated lines optimal for the apparatus can be selected,
Since the unidirectional TDI method is sufficient, the development cost can be greatly reduced. For example, the maximum possible value of the number of TDI integrated lines is designed to be 512 lines, and the selection can be made 512, 256, 128, 64, 32, 16, or 8, which is easy and stable. In addition, it is possible to inexpensively develop a device that enables high-speed inspection.

In the present invention, the image inversion by means of the applied voltage of the electrostatic lens is used as the image inversion means, but other rotation means such as image rotation by a deflector or image rotation by an electromagnetic lens may be used. Needless to say. In the present invention, since the image can be rotated by 180 degrees when the sample stage is turned back, even if a unidirectional TDI camera is used, the same processing speed as when a bidirectional TDI camera is employed can be obtained. In addition, since a TDI camera capable of variably setting the number of integrated lines can be employed, the number of integrated lines and the amount of primary electron beams in the TDI camera can be optimized according to the case.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of the overall configuration of the present invention.

FIG. 2 is a block diagram of a TDI type array CCD.

FIG. 3 is a configuration diagram of an electronic detection unit (MCP assembly detector).

FIG. 4 shows a TDI array CC during pattern inspection.
Operation | movement explanatory drawing of D.

FIG. 5 is an explanatory diagram of a sample stage operation during pattern inspection.

FIG. 6 is a conceptual explanatory diagram of a mapping imaging mode.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 electron gun 2 quadrupole lens system 3 electron beam irradiation means (primary electron column composed of electron gun and quadrupole lens system) 4 secondary electron detection column 5 electron detection means (MCP assembly detector) 6 sample 7 X- Y stage 8 TDI array CCD camera drive control unit 9 Interferometer unit (XY stage position detection unit) 10 CPU 11 Memory 12 Display 13 Shielding unit 14 Electron beam irradiation unit moving mechanism 31, 32 MCP image receiving unit 33 Fluorescent unit 34 Fiber Opt plate (FOP) 35 Camera with TDI array CCD 100 Primary irradiation beam 110 Electron beam emitted from sample

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI H01L 21/66 G01R 31/28 L

Claims (4)

[Claims] 1. An irradiation means for irradiating an electron beam onto a sample surface, and an X-ray moving means for moving the sample to the electron beam irradiation surface.
Y stage, position detecting means for detecting the position of the XY stage, and at least one of secondary electrons, reflected electrons, and backscattered electrons from the sample surface irradiated by the electron beam as a sample image beam. A pattern inspection apparatus for inspecting a pattern of a sample, comprising: an electron detector to be detected; and a projection electron optical system that forms the sample image beam as a sample image on the electron detector. A pattern inspection apparatus characterized in that a pattern on a sample surface is continuously inspected by inverting a sample image formed on the electron detector by controlling the projection electron optical system according to a change. 2. The electronic detector according to claim 1, wherein the electronic detector is a TDI array CCD.
The pattern inspection apparatus according to claim 1, wherein 3. The pattern inspection apparatus according to claim 2, wherein the TDI array CCD is of a variable integration line type, and the number of the integration lines is variable according to the state of a sample to be inspected. 4. The pattern inspection apparatus according to claim 1, wherein said irradiating means changes the setting of the current amount of the primary electron beam according to the state of the sample to be inspected.