JPH04112551A - Removing method for noise of wafer inspecting device - Google Patents

Abstract

PURPOSE:To remove noise due to Rayleigh scattering light to detect ultrafine particles, 0.05mum and below in particle size, and to remove detrimental charging of a wafer by evacuating a housing under pneumatic pressure to 1/100atm or less by evacuating means. CONSTITUTION:In an inspection of a wafer, the wafer 1 to be inspected is mounted on a spindle 2a, a left side plate 9b is closed, a housing is sealed, and the housing is evacuated under pneumatic pressure to 1/100atm or less by an exhaust pump 10. After the pressure reduction is confirmed, when the spindle 2a is rotated and the wafer is radially moved by an R moving mechanism 2b, a spot is spirally scanned on the surface of the wafer to be inspected. Since the pneumatic pressure in the housing is reduced to 1/100atm or less, both noise due to Rayleigh scattering light and noise generated in a processor due to static electricity to be charged at the wafer are removed, and ultrafine particles, 0.05mum and below in particle size, are detected by excellent S/N. Thus, noise of the processor of a surface inspecting device is removed to avoid an error.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a method for eliminating noise in a wafer inspection device, and more specifically, it eliminates both noise caused by Rayleigh scattered light by air molecules and noise caused by electrification of the wafer. It's about how to do it.

[Prior Art] Semiconductor ICs are manufactured using wafers such as silicon. If foreign matter or defects (hereinafter simply referred to as "foreign matter") are present on the wafer, the quality will deteriorate, so the wafer is inspected by a wafer inspection device.

FIG. 2 shows the basic configuration of an optical system of a laser wafer inspection apparatus. A wafer 1 to be inspected is mounted on a spindle 2a and rotated in the direction of an arrow θ. On the other hand, the laser beam from the light source 3 is made parallel by a collimator 4, passes through a mirror 5, and is focused by a focusing lens 6 to form a spot with a minute diameter on the surface of the wafer 1. The rotating wafer is moved in the direction of the radius R by the R moving mechanism 2b, and the spot scans the wafer surface with a spiral cane. Scattered light due to foreign matter existing on the surface of the evaporator is collected by a condensing lens 7 and received by a photoelectric converter 8, and the foreign matter is detected by the output voltage thereof. The above is the basic configuration; in order to detect even smaller foreign objects with high sensitivity, many improvements have been made to the laser light emitting system and scattered light receiving system to improve detection performance. .

[Problems to be Solved] Recently, the degree of integration of IC memories has become more and more advanced, and the trend is for pattern line widths to be miniaturized to 0.5 μm or less. In such fine patterns, the 10th
Extremely minute foreign particles (ultrafine particles) of 0.05μm or smaller degrade the quality of IC memory, so surface inspection equipment is required to have the ability to detect ultrafine particles of 0.05μm or smaller. There is.

The foreign matter detection performance of the surface inspection device is basically directly proportional to the laser irradiation power PON, the integral scattering cross section σS1 of the foreign matter, and the solid angle of light reception ωC.

The integrated scattering cross section σS is determined by the wavelength λ of the laser and the particle size of the foreign material (
(assuming that the foreign object is spherical) Dp1 Refractive index of the foreign object n1 It is a function with the angle θ of the scattered light as a variable.

Figure 3 shows helium-neon (He-Ne) as a light source.
N wavelength λ=E333 nm) and Arbo7 (Ar, λ=4
Particle size Dp is 0.0 for a laser beam (88 nm)
A calculation curve of the integrated dispersion cross section σS (multiplied by ωC for convenience) of fine particles of 4 to 0.1 μm is shown. Here, n=1.6, θ=500, and ωc=0.7πSr. In general, the change in σS is approximately proportional to the square of the volume of the foreign object, and the curve in the figure shows that when Dp decreases to 0.05 μm, which is half of 0.1 μm, σS decreases to about 1/70°. It is shown that.

Now, when light is irradiated onto air molecules, scattered light called Rayleigh is scattered. The size of each air molecule is at most nm or less, and its integrated scattering cross section σR is extremely small. However, the number L (Loschmidt number) of air molecules within a unit volume is very large, and the total integrated scattering cross section Lσ
R has a value comparable to that of the above foreign matter. However, the number of air molecules that contribute to the scattered light in this case is the number within the volume where the laser spot is irradiated and where the light is received, and is therefore the Roschmidt number multiplied by the light receiving volume. . In FIG. 3, the calculated values of the Rayleigh scattered light LσR at 0° C. and 1 atmosphere are also shown, with a light receiving volume of 10 μm in spot diameter and 1 mm in length. LσR is Dp=0.04μ
It is approximately equal to σS of the foreign matter of m. Therefore, ~0.05 μm
It is said that the following foreign substances are difficult to detect because Rayleigh scattered light forms a wall.

Next, since the surface inspection apparatus shown in FIG. 2 uses a rotational scanning method and the rotational speed is high, for example, 2500/min, the wafer is charged with high-voltage static electricity due to air friction. Such charges sometimes discharge and generate noise in various circuits of the surface inspection apparatus, which has the drawback of causing errors in signal or data processing.

This invention was made in view of the above, and in order to detect ultrafine particles of ~0.05 μm or less in a wafer surface inspection device, it eliminates the noise caused by the Rayleigh scattered light, and also eliminates the harmful charging of the wafer. The purpose is to provide a method to eliminate

[Means for Solving the Problems] The present invention is a noise elimination method in a wafer surface inspection apparatus that scans the surface of a wafer to be inspected with a laser spot, receives the scattered light, and inspects the surface. A casing capable of maintaining airtightness, a means for exhausting air inside the casing, and a light source and projection lens system for the laser beam described above and a light receiver for the scattered light described above are provided outside the casing, respectively, A rotational movement mechanism for rotating/moving the wafer in response to spot scanning is provided inside the housing, and a glass window for transmitting the laser beam and a condensing lens for condensing the scattered light are provided on the lid of the housing. . In inspecting the surface of a wafer, the air inside the housing is reduced to at least 1/100 atmosphere by an exhaust means to eliminate both noise caused by Rayleigh scattered light and noise caused by electrification of the wafer.

[Operation] In the surface inspection device to which the above noise elimination method is applied, a laser beam from a light source outside the housing is focused by a projection lens and introduced into the interior through a glass window provided in the lid of the housing. A spot is formed on the surface of a wafer to be inspected placed on a rotary movable table, and the surface of the wafer being rotated or moved by the rotary movable table is scanned. If a foreign object is present on the wafer, the scattered light is collected by a condensing lens provided on the lid of the casing, and is received by a light receiver provided outside the casing to detect the foreign object. On the other hand, the laser beam also irradiates air molecules within the housing, causing Rayleigh scattered light to be scattered. The Rayleigh scattered light is proportional to the number of irradiated air molecules, and the number is proportional to the air pressure inside the housing, that is, the Rayleigh scattered light is proportional to the air pressure. During wafer surface inspection, the air pressure inside the housing is reduced to 1/100th of an atmosphere or less using the exhaust means, so the noise caused by Rayleigh scattered light is also reduced to 1/100th or less, improving the S/N. Ultrafine particles of 0.05 μm or less can be detected well. Further, by reducing the air pressure, static electricity charged on the wafer is reduced and discharge is suppressed, thereby eliminating noise in the processing circuit of the surface inspection apparatus and avoiding the occurrence of errors.

Embodiment FIGS. 1(a) and 1(b) show a side view and a plan view of an embodiment of the noise elimination method for a wafer inspection apparatus according to the present invention. In both figures, reference numeral 9 indicates a housing that can maintain airtightness, and a spindle 2a that places the wafer 1 and rotates on the base 9a of the housing 9, and an R that moves the wafer in the radial direction.
The rotational movement mechanism 2 consisting of the movement mechanism 2b is fixed. The left side plate 9b of the housing can be opened and closed by a hinge, and the wafer 1 is taken in and taken out from here. In addition, an exhaust port 9c is provided on the right side plate, from which the exhaust pump IO is connected to the piping 10a.
Connect. A glass window 11 is provided on the lid 9d of the housing, and the laser beam from the light source 3 is made parallel by a collimator 4, passes through a mirror 5, is focused by a focusing lens 6, and is transmitted through the glass window 11, forming a spot on the surface of the wafer. irradiated.

Further, the condenser lens 7 and the photoelectric converter 8 are connected to a suitable pipe 7a.
Scattered light from the wafer is collected by a condensing lens 7 and received by a photoelectric converter 8.

In wafer inspection, the wafer 1 to be inspected is mounted on the spindle 2a, the left side plate 9b is closed to make the housing airtight, and the air pressure inside the housing is reduced to 1/100th of an atmosphere or less using the exhaust pump 10. After confirming that the pressure has been reduced, the spindle 2a is rotated and the wafer is moved in the radial direction by the R moving mechanism 2b, so that the spot scans the surface of the wafer in a spiral manner and the inspection is performed. The air pressure inside the housing is 100
Since the pressure is reduced to less than 1/2 atm F, noise caused by Rayleigh scattered light and noise generated in the processing circuit due to static electricity charged on the wafer are both eliminated to ~0.05 μm.
Ultrafine particles of m or less can be detected with good S/N.

[Effects of the Invention] As is clear from the above explanation, in the noise elimination method for a wafer inspection apparatus according to the present invention, the air pressure inside the housing is reduced to 1/100th of an atmosphere or less by the exhaust means, so that the noise reduction method due to Rayleigh scattered light is Noise is also reduced to 1/100 or less, S/N is improved, and ultrafine particles of ~0.05 μm or less can be detected satisfactorily. In addition, by reducing the air pressure, the static electricity charged on the wafer is reduced and discharge is suppressed, which eliminates noise in the processing circuit of the surface inspection equipment and avoids errors. The contributing effects are significant.

[Brief explanation of the drawing]

1(a) and (b) are a side view and a plan view showing the structure of an inspection device in an embodiment of the noise elimination method for a wafer inspection device according to the present invention, and FIG. 2 is a diagram of the optical system of the wafer inspection device. The basic configuration diagram, FIG. 3, is a curve diagram of calculated values of the integral scattering cross section of fine particles and Rayleigh scattered light. DESCRIPTION OF SYMBOLS 1... Wafer, 2... Rotation movement mechanism, 2
a...Spindle, 2b...R movement mechanism, 3.
...Light source, 4-...Collimator, 5...
-Mirror 7...Condenser lens, 8...Photoelectric converter, 9a...Base, 9c...Exhaust port, 10...Exhaust pump, 11...Glass window. 6... Focusing lens, 7a... Pipe, 8... Housing, 9b... Left side plate, 9d... Lid, 10a... Piping,

Claims (1)

[Claims] (1) In a wafer surface inspection device that scans a laser spot on the surface of a wafer to be inspected and receives scattered light from the spot to inspect the surface, there is provided a housing that can maintain airtightness, and an interior of the housing. a light source and a projection lens system for the laser beam, and a light receiver for the scattered light are respectively provided on the outside of the housing, and a light source for scanning the spot is provided inside the housing. A rotation movement mechanism for rotating/moving the wafer, a glass window for transmitting the laser beam, and a condensing lens for condensing the scattered light are provided on the lid of the casing, and in the surface inspection of the wafer. The wafer inspection is characterized in that the air inside the housing is depressurized to at least 1/100 atmosphere by the exhaust means to eliminate both noise caused by Rayleigh scattered light and noise caused by the charging of the wafer. How to eliminate noise from equipment.