JPH10197462A - Pattern inspecting instrument - Google Patents

Abstract

PROBLEM TO BE SOLVED: To rapidly improve the life of MCP(microchannel plate) maintaining a fast and highly sensitive defect detecting performance by inspecting a pattern on a sample surface continuously moving an X-Y stage based on an output signal from a position detecting means. SOLUTION: Secondary electrons 110 are generated from a sample 6 by a primary irradiation beam 100 irradiated from a primary column 3 as electron beam irradiation means comprising an electron gun 1 for forming a square electron beam and a tetrapolar lens system 2. The secondary electrons 110 generated from on the surface of the sample 6 are trapped by a projection type secondary electron detection column 4 to be expansively projected onto an MCP assembly detector 5. As directed by a CPU 10, an X-Y stage 7 is driven by a stage drive means and positional information thereof is transmitted to a TDI type CCD camera drive control means 8 from a laser interferometer unit 9 to sequentially supply a sample image to the CPU 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for inspecting a pattern of a wafer, a mask or the like using an electron beam, and more particularly to a detection apparatus for detecting at least one of secondary electrons, reflected electrons and backscattered electrons. It relates to the configuration of the vessel.

[0002]

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.

Conventionally, as a pattern inspection apparatus using an electron beam, there are, for example, JP-A-5-258703 and JP-A-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.

[0005]

However, in the conventional detector as described above, an MCP (micro channel plate) is used, but a secondary electron image signal generated from the sample surface also irradiates the sample surface. Since the aspect ratio becomes long in the X-axis direction, which is the same as the shape of the electron beam, the area of the sample image projected on the MCP becomes very small.

[0006] In general, the relative gain of an MCP is reduced to about 60% when the total output charge per unit area reaches 0.1 C / cm2. The small use area of the MCP causes a problem that the life of the MCP is shortened. An object of the present invention is to provide a pattern inspection apparatus using a detector in which the life of an MCP is dramatically improved while maintaining high-speed and high-sensitivity defect detection performance.

[0007]

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. A pattern inspection apparatus for inspecting a pattern on a sample surface having an electron detection unit for detecting, wherein the electron detection unit doubles at least one of secondary electrons, reflected electrons, and backscattered electrons from the sample. An MCP, a fluorescent unit for optically converting the electron group doubled from the MCP to the MCP image receiving unit, a TDI array CCD irradiated with light excited from the fluorescent unit; Control means for driving and controlling the TDI array CCD in accordance with the position signal of the electron beam irradiation surface, wherein the irradiation beam surface from the electron beam irradiation means is placed on a sample surface mounted on the XY stage. A pattern on a sample surface is inspected while the XY stage is continuously moved based on an output signal from the position detecting means in a state where the XY stage is stopped at a predetermined position above.

According to a second aspect of the present invention, in addition to the first aspect, the shape of the electron beam irradiation surface is rectangular. In claim 3 of the present invention, the shape of the electron beam irradiation surface is an elliptical shape. According to a fourth aspect of the present invention, an electron beam irradiating means for irradiating an electron beam on a sample surface, an XY stage on which the sample is mounted, and a secondary beam from the sample surface irradiated by the electron beam. What is claimed is: 1. A pattern inspection apparatus for inspecting a pattern on a sample surface, comprising: electron detection means for detecting at least one of electrons, reflected electrons, and backscattered electrons, wherein said electron detection means comprises secondary electrons from said sample. An MCP for doubling at least one of reflected electrons and backscattered electrons, a fluorescent section for optically converting an electron group doubled from the MCP, and light excited from the fluorescent section. Control means for driving and controlling the TDI array CCD in accordance with a position signal of the electron beam irradiation surface from the position detecting means. , In a state where the X-Y stage was still in place, it has a configuration provided with a moving mechanism for horizontally moving the electron beam irradiation surface on the inspection target position on the sample.

According to a fifth aspect of the present invention, an irradiating means for irradiating the sample surface with an electron beam, an XY stage for moving the sample to the electron beam irradiation surface, and detecting a position of the XY stage Pattern for inspecting a pattern on a sample surface, comprising: a position detecting means for detecting the position of the electron beam, and electron detecting means for detecting at least one of secondary electrons, reflected electrons and backscattered electrons from the sample surface irradiated by the electron beam. In the inspection apparatus, the electron detecting means may include an MCP that doubles at least one of secondary electrons, reflected electrons, and backscattered electrons from the sample, and an electron that is doubled from the MCP in the MCP image receiving unit. A configuration comprising: a fluorescent portion for converting a group of light; a TDI array CCD for irradiating light excited by the fluorescent portion; and a shielding unit for shielding a light amount applied to the TDI array CCD; It was.

According to a seventh aspect of the present invention, in a pattern inspection method for inspecting a pattern of a sample using an electron beam, a step of moving a position to be inspected on the sample to an electron beam irradiation surface is provided. Continuously moving the inspection target position on the sample to the electron beam irradiation surface in a state where the sample is stopped at a predetermined position; and any one of secondary electrons, reflected electrons, and backscattered electrons from the sample. Detecting by the TDI array CCD.

[0011]

FIG. 1 is an overall configuration diagram of a first embodiment of the present invention. An electron gun 1 for forming a rectangular electron beam
Primary irradiation beam 100 radiated from primary column 3 as an electron beam irradiating means composed of an electron beam and quadrupole lens system 2
As a result, secondary electrons 110 are generated from the sample 6. Sample 6
The secondary electrons 110 generated from the surface of the device are captured by the projection type secondary electron detection column 4 and are enlarged and projected on the MCP assembly detector 5 as electron detection means.

The MCP assembly detector 5 is a TDI system C
The sample image signal is taken out under the control of the CD camera drive control means 8. The sample 6 is placed on the stage 7,
The stage can be moved in the X and Y directions by driving means, and its position can be read by a laser interferometer unit 9 as position detecting means.

The XY stage 7 is driven by the stage driving means in accordance with an instruction from the CPU 10, and its positional information is transmitted from the laser interferometer unit 9 to the TDI CCD camera driving control means 8, and the sample images are sequentially converted. CP
It is supplied to U10. The operation of the pattern inspection apparatus using the electron beam configured as described above will be described below in order.

First, a TDI array CCD will be briefly described. FIG. 2 shows TDI (Time-Delay-Int
2 is a block diagram of an array CCD. The TDI array CCD has C1 to C1 in the horizontal direction.
There are 256 024 line-shaped CCD pixel rows in which 1024 024 lines are arranged in the vertical direction. The accumulated charges on each CCD pixel column are transferred at a time in the vertical direction by one CCD pixel in response to one externally supplied vertical clock signal.

At a certain point in time, 1024
When the image of the pixel moves by one pixel column in the vertical direction and a vertical clock signal is applied in synchronization therewith, Row1
Is transferred to Row2. 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 pixel in the vertical direction and a synchronous clock signal is applied, the stored image is transferred to Row 3 where the image charge is tripled. Thereafter, when the transfer of the charge and the imaging are repeated up to the Row 256 following the movement of the image sequentially, the result of accumulating 256 times the image charge is serially taken out as image data from the horizontal output register.

The operation described above is performed for each pixel row Row1.
Row 256 is performed simultaneously, and a two-dimensional image (1024
It is possible to synchronously extract an image in which image charges of 256 times are accumulated while sending (pixels × 256 pixels) in the vertical direction. Next, the configuration of the MCP assembly detector 5 as the electronic detection means will be described with reference to FIG.
This will be described in detail with reference to FIG.

The sample image beam 36 projected from the projection type secondary electron column enters the first MCP 31.
The sample image beam 36 incident on the first MCP 31 collides with the fluorescent screen 33 via the second MCP 32 while amplifying the amount of current in the MCP. At that time, the first MCP
The potential at the entrance of 31 is set in order to adjust the accelerating voltage of the sample image beam 36 projected from the projection type secondary electron column to the best value of the MCP detection efficiency. For example, when the acceleration voltage of the projection sample image beam 36 is +5 kV, the potential at the entrance of the first MCP 31 is set to -4.5 kV to decelerate the electron energy 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. Also, in order to minimize the spread of the image beam output from the second MCP 32, the second MCP
A voltage of about 4 kV is applied between 32 and the fluorescent screen 33.

At the phosphor screen 33, electrons are converted into photons, and the output image is FOP (fiber optic plate).
34, and the TDI array CCD
The light is applied to the DI 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 about 3: 1.

The operation of the MCP assembly detector on how a sample image is actually taken into the CPU using the components having the above functions will be described. FIG. 4 is an explanatory diagram of the operation of the TDI array CCD at the time of pattern inspection. In FIG. 4, it is assumed that an inspection target area 41 indicated by hatching in a sample (wafer) 6 is inspected. At this time, the irradiation beam area 40 irradiated from the electron beam irradiation means 3 to a predetermined position on the sample is in a fixed state, and the sample 6 placed on the stage is vertically moved at a constant speed by an instruction from the CPU 10. Moving continuously in the direction. The image of the irradiation area 40 on the sample irradiated by the primary irradiation beam 100 is the MCP
Properly magnified and projected onto the assembly detector.

Now, when the inspection is started from the position shown in the figure, the coordinates (X1, Y1) of the inspection target area 41 are changed to (X
Sample images up to 1024, Y1) are stored in the TDI array CC.
The image is captured and stored in Row 1 of D. When the primary beam irradiation position moves by one pixel of the CCD in the movement direction 42 due to the vertical movement of the sample 6, the laser interferometer unit 9
One vertical clock signal is sent to the DI CCD camera drive control means 8. Then, the image picked up in Row1 of the TDI array CCD is transferred to Row2 and (X1, Y1) to (X102) until the next clock signal comes.
The sample image up to 4, Y1) is the RDI of the TDI array CCD.
At ow2, the sample images from (X1, Y2) to (X1024, Y2) are captured at Row1.

Similarly, Row1 of the irradiation area 40 by the primary irradiation beam is changed from (X1, Y256) to (X102).
When the imaging reaches the sample coordinate position up to (4, Y256) and the imaging is completed, the sample image from (X1, Y1) to (X1024, Y1) is output to the CPU 10 for the first time via the camera drive control means 8. Begin to be. From the next vertical clock signal, sample images from (X1, Y2) to (X1024, Y2) are output to the CPU 10, and the images are sequentially acquired by the CPU to perform inspection.

As described above, according to the present invention, the MCP
The shape of the electron beam illuminated is rectangular, with a large area
(Corresponding to 1024 horizontal pixels and 256 vertical pixels), so that the life of the MCP can be dramatically increased.
Table 1 shows an example in which the performance of one embodiment of the present invention is compared with that of a conventional example.

[0024]

[Table 1]

As described above, the present invention makes it possible to increase the life of the MCP by about 256 times in principle. However, since the aperture ratio of the TDI CCD to the incident light of the CCD is lower than that of a normal line CCD, it is necessary to slightly increase the total output current of the MCP. Taking this into account, it is possible to expect a life improvement of about 200 times.

Next, a second embodiment will be described. In addition, if the TDI array CCD employed in the present invention is used in a frame mode, it is possible to observe a sample image without moving the sample. This is called frame mode observation. Here, the frame mode means that after an image is captured on the TDI array CCD for a certain period of time, the image irradiation on the TDI array CCD is temporarily shielded by a shielding means 13 such as a mechanical shutter or an electron beam blanker and stored in the TDI array CCD. This is a mode in which all the obtained two-dimensional images are sequentially taken into the CPU from Row 256. Then, the TDI array CCD is replaced with a normal two-dimensional C
It can be used as an image sensor similar to a CD. As described above, storing the image information in the memory 11 of the CPU and displaying the image information on the display screen 12 automatically and continuously stops the sample inspection during the sample inspection, and temporarily stops the sample inspection. This is a very effective means when the operator wants to visually observe the sample image.

According to the present invention, the current density of the electron beam irradiating the sample can be reduced to about 2 without deteriorating the inspection speed.
Since it can be reduced to 1/56, the effect of significantly reducing damage such as charge-up and contamination of the sample due to electron beam irradiation can also be expected. Further, in the first embodiment of the present invention, the shape of the electron beam irradiating the sample surface is a rectangular shape having a large area (corresponding to 1024 horizontal pixels and 256 vertical pixels). It goes without saying that any shape, such as an elliptical shape, may be used as long as it includes the shape.
Therefore, it is not necessary to make the tip of the electron gun tip extremely high in aspect, and the electron beam shape required to irradiate the sample surface can be easily obtained as compared with the conventional technique. Improved stability and lower cost can be expected.

In addition to the example in which the sample stage is moved as shown in the first embodiment, the X on which the sample is placed is set.
The present invention is also applied to a system in which the -Y stage 7 is fixed and the moving mechanism 14 is provided so as to mechanically horizontally move the electron beam irradiation means 3 on the primary column side with respect to the inspection surface. No problem. At this time, the irradiation beam may be controlled by primary column deflection control.

In this embodiment, the detected electrons are secondary electrons, but may be reflected electrons or backscattered electrons. Since the electron beam column used in the application as described in the present invention can be constituted by an electrostatic deflector or an electrostatic lens, it is possible to make the electron beam column body very small. In recent years, as wafers have become increasingly large,
Although the size of the inspection device has been inevitably increased, a system for moving the small electron beam column side by providing a moving mechanism capable of mechanically moving the electron beam irradiation means instead of moving the wafer is provided. Then, it is possible to reduce the external dimensions of the pattern inspection apparatus using an electron beam.

[0030]

According to the present invention, the following effects can be expected. In the present invention, it is possible to increase the use area of the MCP by 256 times as compared with the prior art, so that the life of the MCP can be extended by 256 times under the same condition of the MCP output current. Becomes

The MCP output current is the same and the used area is 256
If it is doubled, the current density becomes 1/256, but TDI
Since the CCD of the system is used, the same image can be captured 256 times. Therefore, the S / N ratio of the sample image obtained as a result can be made equal to that of the conventional technique, and high sensitivity detection performance can be maintained. Furthermore, since a TDI array CCD capable of a data rate comparable to that of the linear image sensor (line CCD) described in the above-mentioned prior art can be employed, the characteristics can be inherited even in high-speed processing performance.

[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 a conceptual configuration diagram of a conventional defect inspection apparatus using an electron beam method.

FIG. 6 is a configuration diagram of a conventional MCP.

[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

Claims (6)

[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 electron detection for detecting at least one of secondary electrons, reflected electrons and backscattered electrons from the sample surface irradiated by the electron beam A pattern inspection apparatus for inspecting a pattern on a sample surface, comprising: an MC for doubling at least one of secondary electrons, reflected electrons, and backscattered electrons from the sample.
P, the MCP image receiving unit includes a fluorescent unit for optically converting the group of electrons doubled from the MCP, a TDI array CCD irradiated with light excited from the fluorescent unit, and the electron from the position detecting unit. TD according to the position signal of the beam irradiation surface
Control means for driving and controlling the I-array CCD, and controlling the irradiation beam surface from the electron beam irradiation means to the X-
While the XY stage is continuously moved on the basis of an output signal from the position detecting means in a state where the XY stage is stationary at a predetermined position on the sample surface mounted on the Y stage, the pattern on the sample surface is A pattern inspection apparatus for inspecting a pattern. 2. The pattern inspection apparatus according to claim 1, wherein said electron beam irradiation surface has a rectangular shape. 3. The pattern inspection apparatus according to claim 1, wherein said electron beam irradiation surface has an elliptical shape. 4. An electron beam irradiation means for irradiating an electron beam onto a sample surface, an XY stage on which the sample is mounted, and secondary electrons and reflection from the sample surface irradiated by the electron beam. What is claimed is: 1. A pattern inspection apparatus for inspecting a pattern on a sample surface, comprising: electron detection means for detecting at least one of electrons and backscattered electrons, wherein the electron detection means comprises secondary electrons and reflected electrons from the sample. And MC for doubling at least one of backscattered electrons
P, the MCP image receiving section includes a fluorescent section for converting the number of electrons doubled from the MCP into a light, a TDI array CCD irradiated with light excited from the fluorescent section, and the electron beam from the position detecting means. The TDI according to the position signal of the irradiation surface
Control means for driving and controlling an array CCD, wherein the electron beam irradiation means horizontally moves an electron beam irradiation surface at a position to be inspected on the sample while the XY stage is stationary at a predetermined position. A pattern inspection apparatus comprising a moving mechanism for moving. 5. An irradiation means for irradiating a sample surface with an electron beam, and an X-ray beam moving said sample to said electron beam irradiation surface.
Y stage, position detecting means for detecting the position of the XY stage, and electron detection for detecting at least one of secondary electrons, reflected electrons and backscattered electrons from the sample surface irradiated by the electron beam A pattern inspection apparatus for inspecting a pattern on a sample surface, comprising: an MC for doubling at least one of secondary electrons, reflected electrons, and backscattered electrons from the sample.
P, the MCP image receiving section includes a fluorescent section for converting the number of electrons doubled from the MCP into light, a TDI array CCD to which light excited from the fluorescent section is irradiated, and the TDI array C
A pattern inspection apparatus comprising: a shielding unit that shields a light amount applied to a CD. 6. A pattern inspection method for inspecting a pattern of a sample using an electron beam, comprising: moving an inspection target position on the sample to an electron beam irradiation surface; and stopping the electron beam irradiation surface at a predetermined position. Continuously moving the inspection target position on the sample to the electron beam irradiation surface in a state where the electron beam is irradiated. One of secondary electrons, reflected electrons, and backscattered electrons from the sample is transferred by the TDI array CCD. Detecting the pattern.