JP3186171B2 - Foreign object observation device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a foreign matter observation apparatus for easily searching for a minute foreign matter or a defect on a wafer.

[0002]

2. Description of the Related Art Conventionally, evaluation of minute foreign matters locally present on a wafer is performed by an optical type as described in Nikkei Micro Devices Magazine (June 1990, pages 71 to 72). It is difficult with a surface foreign matter inspection device alone, and it is made by providing information such as the coordinates of foreign matter obtained by the optical surface foreign matter inspection device to a scanning electron microscope and performing observation or analysis at high magnification. I was

As a result, it is easy to find foreign matter with a scanning electron microscope or the like, and the foreign matter is quickly identified.

[0004]

The size of the foreign matter is as follows:
If it is as large as 0 μm, if the magnification with a scanning electron microscope is selected to be about 1000 times, it will be observed as several tens of mm on an observation CRT, and it is possible for human eyes to find foreign substances sufficiently. This is because if the size of an observation CRT of a scanning electron microscope is 200 mm × 200 mm, 20
It means that a foreign substance within the range of 0 μm □ can be put in the visual field of the observation CRT. In other words, this means that the foreign matter cannot be put into the field of view of the observation CRT without the accuracy of specifying the coordinates of the foreign matter in the range of 200 μm □, that is, ± 100 μm. Further, when the coordinate identification accuracy provided by the optical surface foreign matter inspection device and the scanning electron microscope is ± 100 μm, the magnification at which the foreign matter can enter the field of view of the observation CRT is 100
0 times means the limit.

Here, the size of foreign matter on the wafer is 1 μm.
m, the observation magnification of 1000 times,
Observation is only 1 mm or less on a CRT, and it is difficult to find foreign matter.

SUMMARY OF THE INVENTION An object of the present invention is to provide a foreign substance observing apparatus which is easy to observe with an electron microscope by compensating for the low accuracy of foreign substance coordinates which can be specified by an optical surface foreign substance inspecting apparatus with an electron microscope.

[0007]

In order to achieve the above object, the level of the size of a foreign substance provided by an optical surface foreign substance inspection apparatus is determined. The area is connected to the optical surface
Divided into N × M with a size larger than the coordinate error with the microscope ,
Each divided area is sequentially searched by an electron microscope.

[0008]

The coordinates of the local foreign matter on the wafer obtained by the optical surface foreign matter inspection apparatus are provided to the electron microscope through a medium such as communication or FD. Therefore, when it is desired to observe a foreign substance at a high magnification with an electron microscope, the size level of the foreign substance is determined, and when the size level is equal to or less than a certain value, the observation region can be divided within the range of the coordinate identification accuracy. With a microscope, foreign substances can be easily found and observed simply by sequentially searching the divided areas.

[0009]

FIG. 1 is a schematic diagram showing the configuration of an apparatus according to the present invention, and FIG. 2 is an explanatory diagram of its operation. First, the wafer 1 to be measured is transferred to the optical surface foreign matter inspection device 2.
In the optical surface foreign matter inspection apparatus, first, in order to specify at which position on the measured wafer the foreign matter exists, the wafer coordinates based on an arbitrary point on the wafer are determined. The method of detecting foreign matter inside the optical surface foreign matter inspection device is to irradiate light on the wafer, capture the scattered light from the foreign matter, and detect the number and size of the foreign matter. By irradiating the entire surface of the wafer, it is possible to easily know at what position on the wafer and what size foreign matter is present. These foreign substance information 3 (location of foreign substance and size information / classified in several levels) is managed by the CPU 4 inside the optical surface foreign substance inspection apparatus. Therefore, it is easy to capture and observe a foreign substance at an arbitrary place with the optical surface foreign substance inspection device. However, the optical surface foreign matter inspection apparatus has a very low magnification (up to 10) due to the limit of the wavelength of light.
Observation magnification can only be increased up to
It is difficult to observe a minute foreign matter of about 1 μm. Therefore,
The wafer 1 to be measured is transported to the scanning electron microscope 5 for observation in order to observe the minute foreign matter in an enlarged manner. However, since it is difficult for the scanning electron microscope to obtain information on the position on the wafer where the foreign matter exists, the foreign matter information 3 is simultaneously provided from the optical surface foreign matter inspection device. By utilizing the foreign substance information, the location of the foreign substance can be known, and the observation of the foreign substance on the scanning electron microscope side becomes easy.

FIGS. 3 and 4 are conceptual diagrams showing an embodiment of the present invention. Consider a case where the foreign substance P7 on the wafer to be measured is observed with an optical surface foreign substance inspection device and a scanning electron microscope. For example, if a wafer coordinate system common to both apparatuses is defined and the foreign matter P is defined at the position P (x, y), the same foreign matter P is P1 at the wafer coordinate 8 of the optical surface foreign matter inspection device. (x1, y1), at the wafer coordinate 9 of the scanning electron microscope, it will be observed at a different position of P2 (x2, y2). x1 ≠ x2, y1 ≠ y
The reason for 2 is that the surface foreign matter inspection apparatus and the scanning electron microscope have errors due to the stage accuracy, alignment (setting of wafer coordinates) accuracy, foreign object detection accuracy, etc. I can't do that.

However, in consideration of the coordinate specifying accuracy of each device, a range 10 (hereinafter referred to as a search area) in which the foreign matter P always exists can be specified within a certain range on the wafer. .

Therefore, when observing a foreign substance with a scanning electron microscope, it is possible to find the foreign substance most efficiently by selecting the highest magnification (hereinafter, referred to as a reference magnification) that allows the search area to be within the field of view at one time. However, when the size of the foreign matter is small, the presence of the foreign matter may not be noticed at a low magnification such as the reference magnification. Therefore, the search area is divided into multiple
If each of the divided areas is sequentially enlarged and observed, even a minute foreign substance can be largely observed, which facilitates discovery.

For example, as shown in FIG. 5, a screen 11 of the scanning electron microscope (here, the entire search area is considered to be visible on the screen) is divided into 25 (5 × 5), and each screen is divided into By observing, the observable magnification can be increased to 5 times the reference magnification, and the 1 mm square foreign matter 12 on the observation CRT can be observed as a 5 mm square foreign matter, making it very easy to find the foreign matter. Becomes

The search movement of the divided area can be performed at high speed and with high accuracy by using an electron beam.

Here, in order to observe a foreign substance at a size N times the original reference magnification, it is necessary to divide the screen into N × N. Now, consider a case where an L × L area is scanned with an electron beam as shown in FIG. 6, and this area is divided into N × N, and (R, C) = (1, 1), (1, 2) ,…, (N, m),… (N, N)
(n, m is 1, 2,..., N). If the scanning width of the electron beam is 1 / N, the portion centered on the deflection center O (0,0) 15 can be enlarged by N times.

However, the above search can be performed by shifting the deflection center in order according to the search area and setting the scanning width of the electron beam to 1 / N.

Here, the deflection center 16 in an arbitrary divided area (n, m) is expressed as follows: 0 (x, y) = (-L (N-1) / 2N + Ln / N, L (N-
1) / 2N−Lm / N) (where N> 1), so that the values of n and m are changed from 1 to N
The above search can be performed by changing the order up to. Note that this equation holds even if N is an odd number or an even number. Means for shifting the deflection center is obtained by superimposing a DC component on the voltage center of the deflection waveform that is the source of electron beam scanning. Alternatively, it can be obtained by moving the optical axis of the electron beam using a dedicated electromagnetic coil or an electrostatic plate.

Further, instead of shifting the electron beam, the search position may be moved by moving the stage.
A combination of an electron beam and a stage is also possible.

Since the foreign substance information obtained from the optical foreign substance inspection apparatus includes information on the size of each foreign substance, the division number N is automatically determined based on the foreign substance size information. By doing so, it is possible to efficiently search for foreign substances.

Now, in the foreign matter information from the optical surface foreign matter inspection device, it is assumed that the size is classified into three levels of S, M, L, and each level is a level S... Foreign matter Level M: Foreign matter of 1 μm □ to 10 μm □ Level L: Foreign matter of 10 μm □ or more shall be defined. Assume classifiable. Also, the search area for identifying the presence of a foreign substance is 200 μm
□ and the size of the CRT observed by the scanning electron microscope was 20
If it is 0 μm □, the reference magnification at which foreign matter can be put into the field of view at a time is 1000 times. By the way, the foreign matter of level L can be observed at a reference magnification of 10 μm square or more, and the foreign matter can be easily found without dividing and observing the search area. Conversely, a foreign substance of level S can be observed only at 1 μm or less, and it is difficult to find the foreign substance unless the search area is divided and enlarged and observed. Level M includes a foreign substance having a size that can be sufficiently detected at the reference magnification and a foreign substance that is difficult to detect.

Next, the search / observation operation of this embodiment will be described with reference to FIG.
This will be specifically described based on the flowchart of FIG.

<Step 100> First, foreign matter information such as a coordinate value and a size level of the foreign matter obtained by the optical surface foreign matter inspection apparatus is read and stored by the scanning electron microscope.

<Step 101> Next, the stage is moved according to the coordinate values of the foreign substance to be observed.

<Step 102> Here, the size level of the foreign matter is determined, and a primary determination is made as to whether or not the foreign matter can be found at the reference magnification.

<Steps 103 and 104> Since the foreign matter passing through this step is relatively large, the foreign matter is searched at the reference magnification without dividing the search area. After the discovery, the foreign substance is moved to the center of the visual field, and the observation is performed with the magnification increased.

<Steps 105, 106, 107 and 10>
8> Since foreign matter passing through this step includes both those that can be found at the reference magnification and those that are difficult, the observation is first made at the reference magnification, and if the foreign matter cannot be found, the search area is divided and observed. I do. Since the minimum foreign matter size is 1 μm square, the division number N of about 5 is sufficient.

<Step 109> Since the maximum size of a foreign substance passing through this step is 1 μm square, it is impossible to find the foreign substance at the reference magnification, and the search area is divided and observed from the beginning.
Although the number of divisions N differs depending on the size of the target foreign substance, a value larger than that in step 108 is required.

With the above-described series of operations, it is possible to efficiently and easily search and observe even a minute foreign matter on a wafer.

In the above description, the case where the size level of the foreign matter is classified into three levels has been described. However, if the number of classifications is large, the number of divisions of the search area can be determined more efficiently. In the above-described embodiment, the search area is equally divided and searched in order. However, if the search area is partially overlapped and an image is captured, the search for a minute foreign matter near the search boundary can be prevented. There is.

[0030]

According to the present invention, even a very small foreign substance detected by an optical surface foreign substance observation apparatus having a very low foreign substance detection position accuracy can be easily and quickly searched on the scanning electron microscope side. There is an effect that can be done.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a device configuration of the present invention.

FIG. 2 is a conceptual diagram for explaining the operation of the device of the present invention.

FIG. 3 is a coordinate diagram for explaining the concept of the present invention.

FIG. 4 is a coordinate diagram for explaining the concept of the present invention.

FIG. 5 is a schematic view showing one embodiment of the present invention.

FIG. 6 is a schematic view showing another embodiment of the present invention.

FIG. 7 is a flowchart illustrating the operation of the present invention.

[Explanation of symbols]

Reference numeral 1: wafer to be measured, 2: optical surface foreign matter inspection device, 3
... foreign matter information, 4 ... CPU, 5 ... scanning electron microscope, 6 ... C
PU, 7: Foreign matter P, 8: Wafer coordinate of optical surface foreign matter inspection device, 9: Wafer coordinate of scanning electron microscope, 10
... range in which the presence of foreign matter can be specified, 11 ... CRT screen, 1
2: foreign matter, 13: scanning area, 14: division number, 15: deflection center O (0, 0), 16: deflection center O (x, y).

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01N 21/84-21/958 G01B 11/00-11/30 H01L 21/66

Claims (2)

(57) [Claims] 1. An optical surface foreign matter inspection device for wafers and similar devices, and an electron microscope for observing or analyzing the shape of foreign matter or defects using wafer coordinates and foreign matter information provided by the device. Means for determining the level of the size of foreign matter provided by the optical surface foreign matter inspection device and similar devices, when the foreign matter level is less than a certain value, the observation area of the wafer The optical surface foreign matter inspection device and the
A foreign matter observing apparatus characterized in that the electron microscope is divided into N × M divided areas with a size larger than a coordinate error with respect to an electron microscope, and the electron microscope has means for performing divided observation for each divided area. 2. The number N of divisions of the divided area is equal to the size of the foreign matter.
The electron microscope is automatically determined on the basis of the information, and the electron microscope searches the N × M divided areas at a high magnification while moving an electron beam or a stage for each divided area. 2. The foreign matter observation device according to 1.