JPH0458622B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a fine foreign matter inspection device, and particularly to an LSI inspection device.
This invention relates to an automatic inspection device for fine foreign matter adhering to the surface of photomasks, reticle, clothing, etc.

[Background of the invention]

Generally, LSIs, magnetic bubble memories, etc. are made up of micrometer-sized circuit patterns, but in the process of manufacturing masks and wafers, minute foreign matter may adhere to them, and these foreign matter may This can cause defects in masks, wafer circuit patterns, etc. Since adhesion of foreign matter occurs in many steps of the semiconductor manufacturing process, it is important to detect not only the quantity of foreign matter but also the size and identification of the substance.

Visual inspection was initially performed using a microscope with a magnification of several hundred times to inspect foreign particles on LSI wafers, but this not only caused work fatigue and reduced inspection efficiency, but also caused circuit patterns to become more difficult to inspect. With the miniaturization, it has become extremely difficult to inspect foreign substances in micron units.

Therefore, for example, in the case of an object to be inspected that has a circuit pattern, it has been proposed to irradiate the object with laser light from relatively above and collect the diffusely reflected light from various directions to perform foreign object inspection (for example, , Japanese Patent Publication No. 54-128682, Hitachi Review Vol. 62. No. 11, pp. 15 et seq.).

However, although these foreign object inspection methods can detect the location of the foreign object, they cannot analyze the foreign object, detect the size of the foreign object that is equal to or smaller than the wavelength of light, or analyze the composition of the foreign object. For this reason, recently, a foreign matter inspection device using a scanning electron microscope (hereinafter abbreviated as "SEM") has been used.

Conventionally, as a foreign matter inspection apparatus using such an SEM, one having a configuration as shown in FIG. 1 is known.

Here, 31 is a cathode and 32 is an anode. 3
Although 3 and 34 are both electronic lenses, 33 functions as a condenser lens, and 34 functions as an objective lens. 1 is an LSI wafer, and 35 is a deflection coil for scanning the surface of the LSI wafer 1 with an electron beam. When the LSI wafer 1 is irradiated with an electron beam, secondary electrons, reflected electrons, X-rays, etc. are generated from the surface of the LSI wafer 1 depending on its shape, composition, etc., but these are detected by the detector 36. . Next, 37 is the detector 3
This is an amplifier for amplifying the output from CRT 6, and the amplified output is supplied to the brightness modulation electrode of CRT 38. 40 is a deflection coil of the CRT38.
The output of the scan control circuit 39 is supplied to the electron beam deflection coil 35 and the CRT deflection coil 40. The scanning of the electron beam of the SEM and the scanning of the CRT 38 are synchronized, and the detection signal obtained by the detector 36 is
Displayed on CRT38.

Using such a foreign matter inspection device allows relatively free analysis of foreign matter; however,
For example, when inspecting a mirrored wafer with no circuit patterns for foreign matter, the SEM signal contains a large number of noise components, so the filtering process takes time, and automatic inspection of the entire surface takes a long time. This will require the following. In addition, since semiconductor devices are formed on insulators such as Si and SiO ₂ , if an electron beam is irradiated onto an LSI wafer for a long period of time, a so-called charge-up phenomenon occurs in which electrons become charged on the surface of the LSI wafer. Image quality deteriorates and S/N becomes insufficient. The charge-up phenomenon can be prevented by depositing an Al thin film on the surface of an LSI wafer, but this cannot be applied to LSI wafers that are still in the process. Furthermore, electron beams can cause damage such as contamination (carbon adhesion to the sample surface).
There is a risk of damaging the LSI wafer.

Therefore, using a low-acceleration SEM can prevent these charge-up phenomena and contamination, but it also increases the number of noise components.
Fully automatic inspection requires even more time. moreover,
Wafers on which circuit patterns are formed have the drawback that automatic classification of patterns and foreign objects cannot be performed, and automatic inspection cannot be performed.

[Purpose of the invention]

An object of the present invention is to solve the above-mentioned problems of the prior art by using a scanning electron microscope to detect any position on the object to be inspected, whether it is a mirror wafer or an LSI wafer, without causing damage. It is an object of the present invention to provide a foreign matter inspection device capable of highly sensitive and high speed analysis of minute foreign matter present in the human body.

[Summary of the invention]

In order to achieve the above object, the present invention provides a sample stage on which an object to be inspected such as a mirror wafer or an LSI wafer is placed, a moving means for moving the sample stage at least two-dimensionally, and a moving means for moving the moving means. coordinate detection means for detecting coordinate information of an object to be inspected, such as a mirror wafer or an LSI wafer; a foreign object detecting means for detecting scattered light from the foreign object detecting means; and a recording means for recording at least coordinate information detected by the coordinate detecting means when the presence of the foreign object from the foreign object detecting means is detected;
The position coordinates of the foreign object recorded in the recording means are read out, and the moving means is operated based on the read position coordinates of the foreign object to move the sample stage to remove the foreign object on the object to be inspected using an electron beam. A control means that is positioned within a field of view that can be analyzed, and a charged particle detector that scans and irradiates an electron beam onto a foreign object on an object to be inspected that is positioned within the field of view by the control means, and detects charged particles generated from the foreign object with a charged particle detector. and a scanning electron microscope that analyzes the foreign matter based on the charged particle signal detected by the charged particle detector. Further, in the foreign object inspection apparatus of the present invention, the storage means includes a foreign object map creation means for creating a foreign object map indicating the presence of a plurality of foreign objects on the object to be inspected based on the recorded coordinate information. It is characterized by Further, in the foreign object inspection apparatus of the present invention, the foreign object detection means and the scanning electron microscope are arranged side by side with a desired interval in the horizontal direction, and the moving means moves the sample stage from the field of view of the foreign object detection means. It is characterized by being configured so that it can be moved into the field of view of a scanning electron microscope.
Moreover, the present invention is characterized in that the sample stage is installed in a vacuum sample chamber in the foreign substance inspection apparatus.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings.

Note that the same parts in the drawings are given the same reference numerals. FIG. 2 is a configuration diagram showing an example of a foreign matter inspection device according to the present invention. 10 is a vacuum sample chamber, 11 is a
This is a sample stage on which objects to be inspected such as LSI wafers are placed. 14 is a motor for rotating the sample stage 11, and 15 is an encoder.
Reference numeral 16 denotes a moving stage, which moves between and within the field of view of the foreign object detection unit 12 and the SEM 13 using optical means such as a laser. Reference numeral 19 denotes a motor for moving the moving stage 16, and is connected to the moving stage via a screw 17 and a coupling ring 18. 20 is an encoder. Reference numeral 21 denotes a sample scanning section, which includes motors 14 and 1.
9 to control their drive. 22 is LSI
This is a coordinate storage unit that stores the adhesion position of foreign matter adhering to the sample to be inspected on the wafer 1. The coordinate storage section 22 is configured to receive the foreign object detection signal 23 detected by the foreign object detection section 12 and the outputs from the encoders 15 and 20. When the foreign object detection section 12 detects a foreign object on the LSI wafer 1, the foreign object detection signal 23 becomes, for example, a "High" level. 24 is a control section that controls the entire foreign matter inspection apparatus. Also,
25 is a window for sample exchange, and 26 is a vacuum pump.

The LSI wafer 1, which is the object to be inspected, is placed in the sample exchange window 2.
5 and placed on the sample stage 11 in the vacuum sample chamber 10. A foreign object detection unit 12 using optical means such as a laser detects foreign objects on the LSI wafer 1 which is moved in a spiral by motors 14 and 19, as shown in FIG. 3a, for example. When a foreign object is detected,
Foreign object detection signal 23 changes from “Low” level to “High”
rise to the level. At the rising edge, encoder 1
The outputs of 5 and 20 are latched in the coordinate storage section 22,
The position of the foreign object on the LSI wafer 1 is stored. Therefore, the position of the foreign object can be obtained in polar coordinates. When the entire surface of the LSI wafer 1 or several chips have been inspected, the moving stage 16 is moved by the motor 19 to the SEM
Move within the field of view of 13. The position coordinates of the detected foreign object are stored in the coordinate storage section 22, so the sample scanning section 21 controls the motors 14 and 1 based on the data.
9 is minutely driven to position the sample stage 11 and the movement stage 16. This makes it possible to obtain an SEM signal of the foreign object at the position desired to be observed.
In the case of a mirror-finished LSI wafer having no circuit pattern on it, the foreign object detection section 12 has the configuration shown in FIG. 4, for example. Laser 5 is applied to LSI wafer 1 placed on sample stage 11 that can rotate or translate.
A laser beam is irradiated from almost directly above. Scattered light from foreign matter 3 attached to the surface of LSI wafer 1 is detected by detector 6, and the detected value is amplified by amplifier 7 and based on position coordinate data detected by encoder 15 shown in FIG. Then, the position and size of the foreign object 3 are stored in the memory 8 (coordinate storage section). By repeating this process, the memory 8 (coordinate storage unit 2
2) The position and size of the foreign matter present on the LSI wafer 1 are stored, and a foreign matter map on the LSI wafer 1 is created by the foreign matter map creator 9. In this way, the size of the foreign object is also stored in the memory 8 (coordinate storage unit 2).
2), information on the size of the foreign object can also be used in the analysis of the foreign object in the SEM 13. Since the sample stage 11 can rotate or translate, the LSI wafer can be moved so that the laser beam scans the LSI wafer 1 in a spiral shape as shown in FIG. 3a.
It is also possible to scan as shown in FIG. 3b. Further, in the case of an LSI wafer with a circuit pattern, the foreign matter inspection section 12 has the configuration shown in FIG. 5, for example. In FIG. 5, an S-polarized laser 27 irradiates the LSI wafer 1 with S-polarized laser light at an angle. is approximately 1 degree. Here, polarized light that vibrates perpendicularly to the plane formed by the irradiated laser beam and the wafer normal (Z-axis) is called S-polarized light, and polarized light that vibrates parallel to it is called P-polarized light. At this time, the polarization direction of the scattered light from the pattern portion on the LSI wafer 1 does not change, and it continues toward the objective lens 28 as S-polarized light shown by the solid line, but the polarization direction of the laser light that hits the foreign object changes. Therefore, it contains a large amount of P-polarized light component shown by the dotted line. Therefore,
A polarizing plate 29 that blocks S-polarized light is provided behind the objective lens 28, and by detecting the light that has passed through the polarizing plate 29 with a photoelectric element 30, only the scattered light (P-polarized light component) from the foreign object is detected. This makes it possible to detect the location of a foreign object on an LSI wafer with a circuit pattern. As a result, the coordinate storage unit 22 stores the position coordinates of all foreign particles attached to arbitrary positions on the LSI wafer. Next, the control unit 24 reads out the position coordinates of each foreign object stored in the coordinate storage unit 22 and drives and controls the motor 19 via the sample scanning unit 21 to move the moving stage 16 below the lens barrel of the SEM 13. Then, the motor 19 and the motor 14 are driven and controlled to finely move the moving stage 16 and the sample stage 11 so that each foreign object exists within the field of view of the SEM 13. Note that the SEM 13 can have the configuration shown in FIG. 1, for example, and the details thereof are omitted since they have been described above. As described above, the control unit 24 controls all the foreign objects on the LSI wafer 1 detected by the foreign object detection unit 12 based on the position coordinates of each foreign object stored in the coordinate storage unit 22.
Position it within the field of view of SEM13. As a result,
SEM13 analyzes each foreign substance by analyzing the SEM signal (X-ray image, AE image, elemental analysis, etc. as shown in Figure 1 using an electron beam) detected from each foreign substance. be able to. Note that when the foreign object detection signal 23 becomes "Low" level when a foreign object is detected on the LSI wafer 1, the outputs of the encoders 15 and 20 are latched in the coordinate storage section 22 at the fall of the foreign object detection signal 23. , the position of the foreign object on the LSI wafer is memorized.

Next, another embodiment of the present invention will be described based on FIG. This embodiment is provided with a mechanism that allows the foreign object detection section 12 and the SEM 13 to work more effectively on the sample at the same position. That is, the laser beam irradiated from the laser 42 is focused on the LSI wafer 1 via the beam expander 43 and the optical lens holder 44. Detector 45 detects light scattered by foreign objects
The foreign object detection section 12 detects the foreign object by the motor 46.
It can be taken in and out of the sample stage 11. FIG. 6 shows the foreign object detection unit 1 based on the mode command from the control unit 24 that controls the entire system.
2 shows the mode at the time of foreign object detection. This is done based on the mode command from the control unit 24.
In the foreign matter analysis mode using the SEM 13, the optical lens holder 44 moves to the right in the figure. In the above foreign object detection mode, the foreign object detection signal sequentially output from the amplifier 7 and the encoder 1 are
Based on the coordinate signals output from 5 and 20,
The coordinate storage unit 22 stores the position and size of the foreign object on the LSI wafer 1. In the foreign substance analysis mode, the control unit 24 first reads out the position coordinates of each foreign substance stored in the coordinate storage unit 22, controls the motor 19 and the motor 14 via the sample scanning unit 21, and controls the SEM 13. The movement stage 16 and the sample stage 11 are controlled to move finely so that each foreign object is present within the field of view. This result SEM1
Images of all foreign objects placed on the LSI wafer 1 within the field of view 3 can be observed.
When the LSI wafer 1 detects a foreign object, the motors 14 and 1
9 continuously moves in a spiral shape, and during observation and analysis by SEM, the coordinate storage unit 22 and sample scanning unit 21 move the required amount. If the SEM 13 does not have a long focus (long working distance), the Z-axis mechanism 47 is used as necessary. The Z-axis mechanism 47 can move the LSI wafer 1 to the focal position of the SEM 13, for example, position 49, by means of a motor 48, so that a clear SEM image can be obtained.

In FIGS. 2 and 6, if electrons are used as the excitation source and primary electrons reflected from the LSI wafer 1 are detected by the detector 36, slow electron energy loss spectrum analysis can be performed, and surface analysis is possible. Even the vibrational state of molecules can be investigated. Similarly,
If the Auger electrons from the LSI wafer 1 are detected by the detector 36, elemental analysis becomes possible. Furthermore, if a detector 36 for detecting X-rays is provided, elemental analysis of minute parts is also possible. In this way, detailed observation and analysis including the composition of minute foreign matter can be performed.

〔Effect of the invention〕

According to the present invention, it is possible to analyze a large number of foreign substances attached to an object to be inspected such as an LSI wafer using a high-resolution scanning electron microscope, without missing anything, and in a short time, that is, at high speed. The test can be carried out without damaging the inspection object due to charge-up, etc., and as a result, it is possible to investigate the cause of foreign matter in the manufacturing process of semiconductors, etc., and the effect is that it can significantly improve the yield of semiconductors and other products. play.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram showing the configuration of a scanning electron microscope.
Fig. 2 is a block diagram showing the configuration of a foreign matter inspection device according to an embodiment of the present invention, Fig. 3 is a schematic diagram showing the scanning direction on an LSI wafer, and Fig. 4 shows an object to be inspected with a circuit pattern attached. FIG. 5 is a block diagram showing the structure of the foreign object detecting section in the foreign object inspection apparatus according to the present invention when there is no circuit pattern; FIG. The figure is a configuration diagram showing the configuration of a foreign matter inspection device according to another embodiment of the present invention. 1...LSI wafer, 3...Foreign object, 11...Sample stage, 12...Foreign object detection unit, 13...Scanning electron microscope, 14, 19, 46, 48...Motor,
15, 20...Encoder, 16...Movement stage, 21...Sample scanning unit, 22...Coordinate storage unit,
23... Foreign object detection signal, 24... Control unit, 27...
...S-polarized laser, 28...Objective lens, 29...
Polarizing plate, 30... Photoelectric element, 31... Cathode, 32
... Anode, 33, 34 ... Electron lens, 35, 4
0... Deflection coil, 36, 45... Detector, 38
... CRT, 39 ... Scanning control circuit, 42 ... Laser, 43 ... Beam expander, 44 ... Optical lens holder, 47 ... Z-axis mechanism.

Claims (1)

[Claims] 1. A sample stage on which an object to be inspected is placed, a moving means for moving the sample stage in at least two dimensions, and coordinates for moving the moving means to detect coordinate information of the object to be inspected. a detection means; a foreign matter detection means for irradiating a light beam onto the surface of the object to be inspected placed on a sample stage and detecting scattered light from foreign matter present on the surface; recording means for recording at least coordinate information detected by the coordinate detection means when presence is detected;
The position coordinates of the foreign object recorded in the recording means are read, and the moving means is operated based on the read position coordinates of the foreign object to move the sample stage within the sample chamber to remove the foreign object on the object to be inspected. A control means positioned within a field of view that can be analyzed and analyzed by an electron beam, and a charged particle detected by irradiating and scanning a foreign object on an object to be inspected positioned within the field of view with an electron beam to detect charged particles generated from the foreign object. What is claimed is: 1. A foreign matter inspection device comprising: a scanning electron microscope that analyzes the foreign matter based on a charged particle signal detected by the charged particle detector. 2. The storage means includes a foreign matter map creation means for creating a foreign matter map indicating the presence of a plurality of foreign matter on the object to be inspected based on the recorded coordinate information. Foreign matter inspection device described. 3. The foreign object detection means and the scanning electron microscope are arranged side by side with a desired spacing in the horizontal direction, and the moving means is configured to be able to move the sample stage from the field of view of the foreign object detection means to the field of view of the scanning electron microscope. A foreign matter inspection device according to claim 1, characterized in that: 4. The foreign matter inspection apparatus according to claim 1, wherein the sample stage is installed in a vacuum sample chamber.