JPH0746079B2 - Foreign object detection method and apparatus - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a foreign matter inspection on a mask used for exposure of a semiconductor or the like, and particularly to a foreign matter suitable for detecting extremely small foreign matter on an X-ray exposure mask. The present invention relates to a detection method and device.

[Conventional technology]

As a first conventional technique, there is known a device for inspecting a minute foreign substance by using an integrating sphere. In this method, a laser having a wavelength of 488 nm or 780 nm is used to scan a spot on a wafer, and scattered light generated from a foreign substance is detected by an integrating sphere.

Further, Japanese Patent Application Laid-Open No. 59-186324 is known as a second conventional technique.

In this conventional technique, a method of obliquely irradiating a laser is used in order to inspect only foreign matters without being affected by the circuit pattern on the mask.

[Problems to be Solved by the Invention]

In the first prior art described above, the wavelength of the illumination light is shortened and the spot diameter for scanning on the wafer is reduced to 0.1.
It is possible to detect minute foreign matters of up to 0.2 μm, but this is not a target when there are uneven circuit patterns on the wafer surface.

Even if the second conventional technique is used, the minimum foreign matter that can be detected is 2 μm, and foreign matter below this size cannot be detected. Furthermore, no consideration is given to surface irregularities.

In order to solve the above problems, an object of the present invention is to provide a foreign matter detection method and apparatus capable of detecting extremely small foreign matter even if irregularities occur on the foreign matter adhesion prevention film on the surface or the protective film of the circuit pattern. .

Another object of the present invention is to provide a foreign matter detection method and apparatus for an X-ray mask, which can detect foreign matter present on the surface of a protective film having a concavo-convex pattern formed by forming a protective film on a circuit pattern like an X-ray mask. To provide.

[Means for Solving the Problems]

In order to achieve the above object, in the present invention, a sample having a protective film on a circuit pattern is irradiated with light such that the protective film absorbs the light, and the irradiated light protects from scattered light generated on the surface of the protective film. The method was to detect foreign substances existing on the film. Further, as a means for realizing this method, a foreign matter detection device is provided with a holding means for holding a sample having a protective film on a circuit pattern and a light which is absorbed by the protective film on the sample held by the holding means. Irradiating means for irradiating, condensing means for condensing scattered light generated on the surface of the protective film by the light irradiated by the irradiating means, and foreign matter existing on the protective film by photoelectrically converting the condensed scattered light. And a detection means for detecting.

[Action]

The irradiated light having a wavelength in a specific region is absorbed or reflected by the organic protective film and does not reach the circuit pattern. Therefore, scattered light due to the circuit pattern is not detected.

On the other hand, if there is a foreign substance on the organic protective film, the irradiation light is strongly scattered by the foreign substance. Therefore, if the scattered light from the surface of the protective film is constantly detected, the foreign substance can be detected.

Here, when the surface of the organic protective film has irregularities, the specularly reflected light and the diffracted light at the irregularities are detected together with the foreign substance scattered light. For this reason, it is impossible to discriminate between the foreign matter and the unevenness, which causes erroneous detection.
Therefore, if the light is detected within the Brewster angle, or if it is detected by an integrating sphere that inserts a light shielding plate that shields the specularly reflected light and the low-order diffracted light from irregularities that cause erroneous detection, only the foreign substance scattered light can be detected. It will be possible.

〔Example〕

Examples of the present invention will be described below. FIG. 1 shows the configuration of an X-ray mask 1 coated with an organic protective film, illumination, and an integrating sphere detection system. As shown in FIG. 1, the X-ray mask 1 includes a supporting material 101 and a boron nitride (B
N), a base material 102 made of silicon nitride (Si ₃ N ₄ ) or the like, an Au circuit pattern 103, and an organic protective film (for example, a polyimide film: polyimide / iso / indolokiinazolindone).
Polyimide iso-indroquinazolinedione)) 104.

Here, since the base material 102 is sufficiently thick on the support material 101 side, there is no surface irregularity of the base material. Therefore, on the substrate side, the light 5a scattered from the foreign matter is collected by the detection system 2 including only the integrating sphere 301a and received by the photoelectric conversion element 302a, and the detection signal 303a is output to detect the foreign matter.

That is, 104 is an organic film coated on the circuit pattern 103, 12 is a stage provided with a holder portion 11 for holding the mask 1, and 203a and 203b are for inspecting foreign matter 5a from a laser oscillator 14 having a wavelength of 380 nm or less. Inspection light, 15a and 15b are beam expanders, 16a and 16b are condenser lenses, 17a and 17b are carb mirrors oscillated by motors 20a and 20b, 2 and 3 are scattered light detection systems, and 2
Reference numeral 0 represents a condensing point, 13 represents a moving direction of the stage 12, 21 represents a light scanning direction, and 205a and 205b represent scattered light from the foreign matter 5. 1
Reference numeral 9 is a half mirror that splits a laser beam 18 of 380 nm or shorter.

A polyimide film was used for the organic protective film 104. The spectral transmittance of the polyimide film is shown by the wavelength (n
m) and transmittance as shown in FIG.
The following light has a property that the transmittance is extremely small. On the other hand, for shorter wavelengths (1 to 20 nm) such as X-rays, the transmittance of the polyimide film has a value close to 100%.

Therefore, as shown in FIG. 2, the organic film 10 is formed on the X-ray mask.
If a polyimide film is applied as 4, foreign matter in the air 5
Adheres onto this polyimide film. In the foreign matter inspection, when light 203b having a wavelength of 380 nm or less is irradiated from above, the light hitting the polyimide film is absorbed by the polyimide film and does not generate scattered light, but hits the foreign material 5 on the polyimide film. Since the light generates scattered light 205b, it is possible to detect a foreign substance only by detecting the scattered light 205b by the scattered light detection system 3.

As shown in FIG. 4, the mask 1 coated with such an organic film 104 is set on a stage 12 that moves in a uniaxial direction, and moved in the direction of the arrow 13 of the moving direction. On the other hand, the laser expander 1 outputs laser light 18 from the laser oscillator 14 with a wavelength of 380 nm or less.
The beam diameter is expanded by 5a and 15b, and further, it is condensed as a laser spot by the condenser lenses 16a and 16b. Then, the laser spot is swung in the scanning direction 21 by the carbano mirrors 17a and 17b. As a result, the laser spot scans the entire surface of the circuit pattern area on the substrate side and the organic protective film side of the mask 1, so the scattered light 205a, 205b is condensed by the scattered light detection systems 2, 3 and the photoelectric conversion elements 302a, 302b are collected. The minute foreign matter 5 can be detected by detecting with.

Next, the film thickness of the organic protective film 104 of the X-ray exposure mask will be described. That is, assuming that the light reflected and scattered from the circuit pattern 103 of the mask with and without the organic protective film is I ₁ and I ₂ , respectively, and the incident light is I ₀ , in the present invention, the film thickness of the organic protective film is The pattern scattered light ratio I ₁ / I ₀ when there is no organic protective film needs to be 0.1%.

On the other hand, since there is a relationship of T = 10 ^{−3.0 l} between the transmittance T of the organic protective film at the used wavelength of 325 nm and the thickness 1 μm of the organic protective film, the scattered light ratio I ₁ / I ₀ of the circuit pattern 103 is In order to achieve 0.1%, an organic protective film with a thickness of 1 μm is required. Since incident light travels back and forth through the organic protective film, the required thickness of the organic protective film is 0.5 μm. become. Therefore, in order to reduce the scattered light to 10 ⁻³ or less, the minimum thickness of the organic protective film needs to be 0.5 μm or more. However, this film thickness is necessary to protect the circuit pattern 103.

FIG. 5 is an explanatory view of an X-ray exposure mask. In this X-ray exposure mask, the mask 1 is, for example, boron nitride (BN),
A substrate 102 made of silicon nitride (Si ₃ N ₄ ) or the like,
This substrate 10 is made up of a frame portion 101b made of silicon (Si).
Gold (Au) having a thickness of, for example, about 1 μm is formed on the organic protective film 104a which transmits X-rays having a thickness of about 3 μm deposited on the organic protective film 104a.
An organic protective film 104b for passing X-rays is further formed on the circuit pattern 103 by about 5 μm.
It is attached about m.

The X-ray exposure mask having the above structure is used for the substrate 10
Inspection light 203a, 203 of 380nm or less from both the 2nd side and the opposite side
Irradiation with b, and foreign matter 5 on the mask 1 as in the above-described embodiment.
Is inspected.

In the above embodiments, an example using an X-ray exposure mask coated with an organic protective film that absorbs light has been described, but it is not limited to the X-ray exposure mask as long as it has the same function. Absent. It is obvious that the same effect can be obtained in a semiconductor device having a circuit pattern and an organic protective film formed on the circuit pattern.

As described above, it is possible to detect minute foreign particles of 0.15 μm or less, which was impossible until now, without being affected by the circuit pattern.
For example, in the case of an X-ray exposure mask, if a foreign substance is detected, it becomes possible to remove the foreign substance by washing or the like.
As a result, the exposure can be performed in a state where no foreign matter is attached, which can greatly contribute to the yield of LSI.

By the way, since the organic protective film 104 is thin on the side of the circuit pattern, unevenness occurs on the surface of the organic protective film due to the step of the circuit pattern 103. Foreign matter scattered light from the foreign matter 5b as shown in FIG.
205b, surface uneven specular light 206 and diffracted light 207 are all integrating spheres
Since it mixes with 301b and reaches the detector 302b, it is impossible to distinguish irregularities from foreign matter.

Next, the Brewster angle illumination detection method will be described.

FIG. 7 shows the configuration of the X-ray mask 1 on which the organic protective film 104 is formed and the illumination and detection method. As shown in the figure, the X-ray mask 1 includes a support material 101, a base material 102, a circuit pattern 103,
And an organic protective film 104.

Here, on the support material 101 side, since the thickness of the base material 102 is sufficiently large, there is no surface irregularity of the base material. Therefore, the base material side is the epi-illumination unit 2
It suffices to detect foreign matter by using.

On the other hand, on the organic protective film side, since the organic protective film is thin, unevenness occurs on the surface of the organic film due to the step of the circuit pattern.

However, if the illumination is detected at the P-polarized Brewster angle of the present invention, the specularly reflected light due to the surface irregularities can be made almost zero, and only the scattered light of the foreign matter can be detected. The principle will be described below.

As shown in FIG. 8, when polarized light is incident on a substance having a different refractive index, the intensity R _p of the reflected light 8 depends on the incident angle 9 (i ₁ ). If the intensity E _p of the incident light 6 of P-polarized light, the refraction angle 7i ₂ , the refractive index of the medium 4 are n, and the refractive index of the medium 5 is n ′, then E _p
And the ratio of R _p is from Fresnel's equation, However, n <n '. Details are described in "Applied Optics" P146-P149.

Therefore, when P-polarized illumination is performed, the refractive index n '= 1.8 of the organic protective film 109, and therefore the ratio of E _p and R _p is calculated using the equation (1), and FIG. 9 is obtained. From the figure, when i ₁ = 61 °, the ratio of E _p becomes zero. Also, within the range of 61 ° ± 5 °, E _p
And the ratio of R _p can be suppressed to 0.5% or less.

Therefore, when the refractive index of n ′ = 1.8 is used, if the irradiation angle of the P-polarized illumination is set to 61 °, the foreign substance scattered light can be detected without being affected by the unevenness of the organic protective film 104.

7 and 10 show an embodiment of the present invention. The mask 1 having the organic protective film formed thereon is supported by a holder portion 11 and is scanned in the direction of an arrow 13 by a uniaxial stage 12 capable of double-sided inspection. On the other hand, as the illumination light, the light 18 having a wavelength of 380 nm or less from the laser oscillator 14 is used, the beam diameter is expanded by the beam expander 15b, and the Brewster angle 304 is passed through the condenser lens 16b and the Brewster angle illumination mirror 22. In the following, the P-polarized laser light 203c is focused on the point 20. In the meantime galvo mirror
17b is provided, and the point 20 is swung in the direction perpendicular to the arrow 13. As a result, since the point 20 scans the entire surface of the mask, if the scattered light 306 is detected by the condenser 301c and the detector 302c in synchronization with the scanning, a device capable of detecting minute foreign matter without being affected by the surface irregularities of the organic protective film. Can be realized. In short, the Brewster angle illumination detection optical system 3a can detect minute foreign matters on the organic protective film 104 having irregularities.

On the other hand, when the Brewster angle illumination detection method shown in FIG. 7 is used, when P-polarized illumination is not eliminated on the surface of the organic protective film,
It is possible to detect only the foreign substance scattered light 306 by this technique, but as shown in FIG. 11, if the P-polarized light of the illumination light 203c is disturbed even a little, specular reflected light 206 and diffracted light 207 are generated, which are also It is impossible to distinguish between foreign matter and unevenness.

However, as shown in FIGS. 1 and 4, if the integrating sphere detection system 3 in which the cylindrical light shielding plate 441 that separates the specular reflection light is inserted is used, the light shielding plate 441 causes the specular reflection light 206 and the diffraction that causes an erroneous detection. Since the light 207 is blocked, these lights are hardly mixed in the integrating sphere, and the foreign substance scattered light 5 can be emphasized and detected. The principle is shown below.

When light is incident on the minute surface 221 that is inclined as shown in FIG. 12, specular reflection light is generated due to the inclination angle α of the surface. Also,
Diffracted light 207 is generated by the interference with the reflected light from the inclined minute surface 222 adjacent thereto. Here, the angle θ ₁ of the regular reflection light is geometrically determined as θ = 2a. On the other hand, the angle a'of the m-th order diffracted light is calculated by Required by. For details, see Physical optics (Kyoritsu Publishing) PP.101-
Please refer to 113.

Here, _{what matters is} the magnitude relation between the intensity I _{par of the} scattered light of the foreign matter, the intensity I _ref of the specular reflection light, and the intensity I _def.m of the m-th order diffracted light. If the intensity of the incident light is I _in and the component absorbed is I _T , The relationship is established. As for I _ref , since it is twice the inclination angle α of the unevenness as described above, it is easy to set up a light blocking plate that blocks this, so by inserting the light blocking plate I _ref that is mixed into the integrating sphere Can be zero. On the other hand, regarding I _fef.m , according to the equation (2), the generation angle has a dispersion value, and most of the energy of the diffracted light is concentrated in the ± 1st to ± 2nd order diffracted light (physical optics). reference)
Focusing on, all the diffracted light below a certain k-th order is blocked and I
_{If ref.} = 0 Can be If "3" on the right side of the above equation has such a ratio, if it is electrically binarized after detection
It is a guideline that only I _par. Can be determined.

Therefore, as shown in FIG. 13, if the light-shielding angle θ ₂ of the light-shielding plate 441 is set so that the generation angle a ′ _k of the diffracted light 267 of the kth order and the angle 2a of the regular reflection light can be shielded, the surface irregularities of the organic protective film and the foreign matter are prevented. Can be discriminated and detected.

For example, in the currently used X-ray mask, the maximum value of the slope of the unevenness is a = 7 °, and therefore 2a = 14 °
When the wavelength of the illumination light is λ = 0.325 μm at 4 μm (it has been experimentally clarified that the surface roughness of the organic protective film does not occur at L4 μm), m satisfying the formula (3) is satisfied.
Is m = 6. Further, since a'at that time is a '= 26 °, if the light blocking angle θ ₂ of the light blocking plate 441 is set to θ26 ° and detected, foreign matter having a target detection specification of 0.15 μm is detected. It is possible to detect with.

1 and 4 show an embodiment of the present invention. In the above, the organic protective film 10 described for the detection method of only the integrating sphere
The X-ray mask 1 coated with 4 is supported by a holder unit 11 and scanned in the direction of arrow 13 by a uniaxial stage 12 capable of double-sided inspection. On the other hand, the illumination light 203b is the wavelength from the laser oscillator 14.
The light 18 having a wavelength of 380 nm or less is used, the beam diameter is expanded by the beam expander 15b, and then the light is condensed at a point 20 via the condenser lens 16b. A carbano mirror 17b is provided between them, and the point 20 is swung in the direction perpendicular to the arrow 13. As a result, the point 20 scans the entire circuit pattern area of the mask 1. Therefore, the scattered light may be detected by the integrating sphere 301b and the detector 302b in synchronization with the scanning. Here, the m-th order diffracted light from the surface unevenness is not mixed into the integrating sphere 301b by the cylindrical light shielding plate 441 having the light shielding angle θ.

As described above, it is possible to realize an apparatus capable of detecting minute foreign matter on a mask without being affected by surface irregularities.

In addition, it is desirable that the outer surface of the cylindrical light shielding plate 441 has a mirror surface state with good reflectance.

〔The invention's effect〕

As described above, according to the present invention, the influence of the circuit pattern and the influence of the unevenness of the surface organic protective film are not affected by 0.15
It is possible to detect minute foreign matter having a size of μm or less. Therefore, when the sample is a mask, it is possible to significantly reduce the occurrence of pattern defects due to the transfer of foreign matter on the mask during exposure, which is a great effect in improving the yield of LSI products.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the basic structure of two embodiments of the present invention, FIG. 2 is a view showing a case where laser light is irradiated on the organic protective film side of an X-ray mask, and FIG. FIG. 4 is a diagram showing the spectral transmittance of the organic protective film, FIG. 4 is a perspective view showing two embodiments of the apparatus constructed based on the principle shown in FIG. 1, and FIG. 5 is another X-ray mask. FIG. 6 is a diagram for explaining the problems of the embodiment, FIG. 7 is a sectional view showing the basic structure of another embodiment of the present invention, and FIG. 8 is a P-polarization Brewster angle. Fig. 9 shows the reflection characteristics when illuminated with light, Fig. 9 shows the relationship between incident angle i ₁ and Rp / Ep, and Fig. 10 shows 7
FIG. 11 is a perspective view showing an embodiment of an apparatus configured based on the principle shown in the figure, FIG. 11 is a diagram for explaining the problems of the embodiment,
FIG. 12 is a diagram showing the reflection characteristics when the organic protective film is irradiated with laser light perpendicularly, and FIG. 13 is a conceptual diagram showing the best embodiment of the present invention. 101: Support material, 102: Base material, 103: Circuit pattern, 1
04 …… organic protective film, 302a, 302b, 302c …… detector, 203a, 2
03b …… Illumination light, 205a, 205b …… Foreign matter scattered light, 301a, 301b,
301c …… Integrating sphere, 441 …… Cylinder shading plate.

Claims (12)

[Claims] 1. A sample having a protective film on a circuit pattern is irradiated with light that is absorbed by the protective film, and scattered light generated on the surface of the protective film by the irradiated light is detected. A foreign matter detection method, comprising detecting foreign matter existing on a protective film. 2. The foreign matter detecting method according to claim 1, wherein the light absorbed by the protective film is light having a wavelength of 380 nm or less. 3. The foreign matter inspection method according to claim 1, wherein the light absorbed by the protective film is light emitted at a Brewster angle. 4. The foreign matter inspection method according to claim 3, wherein the light emitted at the Brewster's angle is polarized light. 5. The foreign matter inspection method according to claim 1, wherein the scattered light to be detected is high-order diffracted light. 6. The foreign matter on both sides of the sample is detected by irradiating the both sides of the sample with the light.
Foreign matter inspection method described. 7. A holding means for holding a sample having a protective film on a circuit pattern, an irradiating means for irradiating the sample held by the holding means with light that is absorbed by the protective film, Condensing means for condensing scattered light generated on the surface of the protective film by the light emitted by the irradiating means, and photoelectric conversion of the condensed scattered light to detect foreign matter existing on the protective film A foreign matter detection device comprising: a detection unit. 8. The foreign matter detecting device according to claim 7, wherein the light irradiated by the irradiation means and absorbed by the protective film is light having a wavelength of 380 nm or less. 9. The irradiating means irradiates the light onto the sample at a Brewster's angle.
The foreign matter detection device described. 10. The foreign matter detecting apparatus according to claim 7, wherein the light condensing unit has an integrating sphere that condenses the scattered light. 11. The light condensing means has a light-shielding portion that blocks low-order diffracted light of the scattered light and condenses high-order diffracted light by the integrating sphere. The foreign matter detection device described. 12. The foreign matter detecting apparatus according to claim 7, wherein the irradiation means, the light condensing means, and the detection means are provided on both sides of the sample, respectively.