JP2762313B2 - Inspection method for foreign substances on lattice face plate - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for inspecting a foreign substance on a lattice face plate, and more particularly, to separating a silicon wafer into individual IC chips.
This is a foreign matter inspection method for a lattice face plate which is formed by etching a lattice groove by a process called photo, and separated by the boundary.

[Prior art] A semiconductor IC chip is made of a silicon wafer, and a silicon oxide film (or a silicon nitride film) is deposited on a surface of the silicon IC chip, a photoresist is applied, a photomask is projected and transferred,
And multi-step processes such as development processing are repeated
Chips are manufactured.

To improve the productivity of IC chips, multiple IC chips are formed on a silicon wafer and each IC is diced.
A method of dividing into chips has been performed. FIG. 2 (a),
In (b), a lattice groove 1b is formed in the silicon wafer 1 by etching by a process called L photo, and the silicon wafer 1 is separated into a plurality of lattice plane plates 1a with the boundary as a boundary. After the wiring pattern is formed on each lattice face plate as described above, the wafer is divided into individual IC chips along the lattice grooves.

When foreign matter adheres to the surface of the silicon wafer, the quality of the IC deteriorates, and depending on the degree, the IC becomes defective. Therefore, the foreign matter on the wafer is inspected by a foreign matter inspection device, and when a wiring pattern is formed, an electric current is applied. The test is performed.

FIG. 3 shows the basic calibration of the optical system of the foreign matter inspection apparatus. For the wafer 1 to be inspected, a material having a smooth surface is used, and the wafer 1 is mounted on the moving table 2. On the other hand, the laser beam from the light source 3 is converted into parallel light by the collimator 4a of the light projecting optical system 4, and is focused on the spot by the focusing lens 4c via the mirror 4b and irradiated. When the spot scans the surface of the wafer by moving or rotating the movable table 2, the spot scatters the scattered light due to foreign substances present on the surface. This scattered light is collected by the condenser lens 5,
Light is received by the photoelectric converter 6 and foreign matter is detected.

The above optical system has a basic configuration, and various improvements have been made to the light projecting optical system and the light receiving optical system in order to improve the detection performance for foreign substances or to shorten the inspection time. With respect to the formed wafer, a method has been developed in which the influence of the pattern is removed by a comparison method of the same pattern to detect foreign matter.

[Problem to be Solved] In response to the recent increase in the degree of integration of ICs, the tendency of foreign substances to adhere to wafers has been increasingly severely restricted. For this reason, it is necessary to inspect foreign substances adhering to each lattice face plate at the stage when the lattice grooves are formed by the above-mentioned L photo process. When this inspection is performed by the optical system shown in FIG. 3, scattered light from the grating grooves is detected at the same time, and foreign matter adhering to the grating face plate is not discriminated. On the other hand, it is possible to apply a foreign substance inspection method to the above-mentioned comparison method, but it is not efficient because the processing is complicated and the processing time is long, and a method capable of performing inspection in a short time by a simple and clear principle is desirable. .

The present invention has been made in view of the above, and an individual IC
For silicon wafers with lattice grooves for etching separated into chips, a method is provided for detecting foreign matter adhering to each lattice face plate separated by the lattice grooves by eliminating the influence of scattered light from the lattice grooves. It is intended to do so.

[Means for Solving the Problems] The present invention is a foreign matter detection method for a lattice face plate separated by a lattice groove formed in a silicon wafer as a boundary. Scanning is performed by irradiating a laser spot with a foreign matter inspection device. The inspection device has a dark field light receiving system that detects scattered light,
A bright-field light receiving system for detecting a change in the direction of regular reflection light caused by unevenness or inclination of the reflection surface; Foreign matter adhering to the edges of the grating grooves and the grating face plate is respectively detected by the dark field light receiving system and stored in the first area of the memory. At the same time, the edge of the grating groove is detected by the bright-field light receiving system and stored in the second area of the memory. The data stored in the second area is subtracted from the data stored in the first area to obtain detection data for foreign matter attached to the lattice face plate.

[Operation] In the method for detecting foreign matter on a lattice face plate according to the present invention,
A silicon spot to be inspected is irradiated with a laser spot and scanned by a foreign substance inspection device. The inspection apparatus is provided with a dark-field type and a bright-field type light receiving system. Since the dark-field method has good detection performance for scattered light, it detects not only the foreign matter adhering to the lattice face plate but also the scattered light due to the edge of the lattice groove, and these detection data are stored in the first area of the memory. It is memorized. On the other hand, the bright-field method has almost no power of detecting foreign matter scattered light, but instead, the reflection direction of the incident laser,
That is, the detection ability in the direction of the regular reflection light is excellent, whereby the change in the direction of the regular reflection light of the laser due to the convex surface of the edge of the grating groove is detected, and this detection data is stored in the second area of the memory. . By subtracting the data of the second area from the data stored in the first area, the detection data for the edge of the lattice groove is deleted,
Data on the detection of foreign matter adhering to the lattice face plate is obtained.

[Embodiments] FIGS. 1A, 1B and 1C are a block diagram of an optical system, a block diagram of a data processing circuit, and a grid in an embodiment of a method for detecting foreign matter on a grid plate according to the present invention. FIG. 4 is an explanatory diagram of a principle of detecting foreign matter attached to a face plate. In FIG. 5A, a laser beam from a laser light source 3 is collimated by a collimator 4a and passes through a center hole of a first hole mirror 7a, and a mirror 7b to an incident point deviated from a center point O of a focusing lens 7c. The incident light is focused and a spot is formed on the wafer 1. The dark-field light receiving system includes a condenser lens 5 and a photoelectric converter 6-1 provided diagonally to the scanning point of the spot. The bright-field light receiving system is a focusing lens 7c,
Mirror 7b, first and second hole mirrors 7a, 7d, and
It is constituted by the second and third photoelectric converters 6-2 and 6-3. When there is no foreign matter on the surface of the wafer, no irregularity or inclination, the photoelectric converter 6-1 has no light-receiving current, but its specular reflection light passes through the above-mentioned point of symmetry of the incident point of the focusing lens 7c, receiving power I ₂ is output is received by the photoelectric converter 6-2 bright field light receiving system. Now, when the laser spot illuminates the grating grooves, the laser spot is scattered by its edge, the scattered light is received is condensed by the condenser lens 5 to the photoelectric converter 6-1, the light-receiving current I ₁ output Is done. At the same time, the direction of the specularly reflected light changes due to the convex surface of the edge of the lattice groove, and is received by the photoelectric converter 6-3 along the path between the one-dot chain line and the two-dot chain line in the drawing.
I ₃ is output. Correspondingly, receiving current I ₂ by the direction of the change in specular reflected light is reduced. Next, when the laser spot is applied to the foreign matter by adhering to the lattice face plate,
Light scattered by the foreign matter is received by the photoelectric converter 6-1 dark-field light-receiving system, receiving current I ₁ is output. However, since the direction change of the specular reflection light by the foreign matter it is very weak, not received in the bright-field light receiving system, the photoelectric converter 6-2 is output constant photocurrent I _2.

It should be noted that the light receiving systems for the dark field and the bright field are not limited to those described above, and may be constituted by other methods.

In block diagram of Fig. 1 (b), the light-receiving current I ₁ of the photoelectric converter 6-1 is adjusted to a suitable level by the amplifier 8, the digital current [I _1] by A / D converter 10-1 becomes The data is stored in a first area of a memory (MEM) 13 under the control of a microprocessor (MPU) 12 via an interface (I / F) 11. The address of the first area is an address number corresponding to the coordinate position of the wafer to be inspected. Next, the light-receiving current I _2, I ₃ of the photoelectric converter 6-2 and 6-3, the difference current is input to the subtractor 9 (I ₃ -I ₂₎ is created. By thus taking the difference between the two currents, the detection sensitivity to the change in the direction of the specularly reflected light is doubled. The difference current (I ₃ −I ₂ ) is A / D
The current is converted into a digital current [I ₃ −I ₂ ] by the converter 10-2, and is stored at the address of the second area of the MEM 13 by the MPU 12 via the I / F 11. This address number is the first
It is set corresponding to the address number of the area.

FIG. 1 (c) shows the difference current [I ₃ −I ₂ ] of the bright field light receiving system.
And the edge db of the grating groove stored in the second area of the MEM 13 and the edge db of the grating groove detected by the light receiving current [I ₁ ] of the dark field receiving optical system and stored in the first area. And foreign matter da adhering to the lattice face plate
Is shown. By subtracting the data in the second area from the data in the first area, the data at the edge db is erased,
Only the detection data da for the foreign matter attached to the lattice face plate is detected.

[Effects of the Invention] As is apparent from the above description, in the method for detecting foreign matter on the lattice face plate according to the present invention, the silicon wafer is scanned by the laser spot of the inspection apparatus, and the foreign matter adhering to the lattice face plate by the dark field light receiving system. And the edge of the grating groove are both detected and stored in the memory, and the edge of the grating groove is detected and stored in the memory by the bright-field light receiving system, and by subtracting the data of these memories, the edge of the grating groove is detected. The detection data is erased, and only the detection data of the foreign substance attached to the lattice face plate is obtained. The detection principle is simple and clear, the time required for inspection is short, and the foreign substance inspection is performed on the lattice face plate formed by the L photo process. There is a great effect that can be performed efficiently.

[Brief description of the drawings]

FIGS. 1 (a), 1 (b) and 1 (c) show a configuration of an optical system, a block diagram of a data processing circuit, and a configuration of a lattice face plate in an embodiment of a method for inspecting foreign matter on a lattice face plate according to the present invention. 2 (a) and 2 (b) are explanatory views of a lattice groove and a lattice face plate formed by an L-photo process, and FIG. 3 is an optical diagram of a foreign substance inspection apparatus for a material wafer. It is a basic block diagram of a system. DESCRIPTION OF SYMBOLS 1 ... Silicon wafer, 1a ... Lattice surface plate, 1b ... Lattice groove, 2 ... Moving table, 3 ... Laser light source, 4 ... Projection optical system, 4a ... Collimator, 4b ... Mirror, 4c ... … Focusing lens, 5… condensing lens, 6… photoelectric converter, 6-1 …… dark field light receiving system photoelectric converter, 6-2, 6-3… bright field light receiving system photoelectric converter, 7a, 7d: Hole mirror, 7b: Mirror, 7c: Focusing lens, 7e: Condensing lens, 8: Amplifier, 9: Subtractor, 10: A / D converter, 11: Interface (I / F), 12: Microprocessor (MPU), 13: Memory (MEM).

Claims (1)

(57) [Claims] An object inspection apparatus irradiates a laser spot on a lattice surface plate separated by a lattice groove formed in a silicon wafer as a boundary, and scans the lattice plane. A field-of-view light-receiving system, and a bright-field light-receiving system that detects a change in the direction of specularly reflected light caused by the unevenness or inclination of the reflection surface are provided. Each is detected and stored in a first area of a memory, the edge of the grating groove is detected by the bright-field light receiving system and stored in a second area of the memory, and the data stored in the first area is A foreign matter inspection method for a lattice face plate, wherein data detected in a foreign substance adhering to the lattice face plate is obtained by subtracting data stored in the second area.