JP5417793B2 - Surface inspection method - Google Patents

Description

  The present invention relates to a surface inspection method, and more particularly, to a technique for detecting fine irregularities present on the surface of the silicon wafer or the surface of the silicon oxide film.

  Along with the high integration and miniaturization of semiconductor devices, there is a demand for the completeness of the crystal structure in which no defects exist in the surface layer of the silicon wafer that is the substrate of the semiconductor device, particularly the device active region. Examples of such defects include Grow-in defects such as COP (Crystal Originated Particle), FPD (Flow Pattern Defects), and LSTD (Laser Scattering Tomography Defects). These Grown-in defects appear as fine irregularities on the surface of the silicon wafer, and when the semiconductor device is formed, for example, the oxide film breakdown voltage characteristic is deteriorated.

  As a method of detecting defects present on the surface of such a silicon wafer, for example, a method of measuring fine irregularities on the surface of the silicon wafer using a laser scattering type surface inspection apparatus is known (for example, Patent Document 1). This surface inspection apparatus irradiates the surface of a silicon wafer with laser light. At this time, if the surface of the silicon wafer does not have fine irregularities due to defects or the like and is in a smooth state, the irradiated laser light is reflected as a regular reflection light that is reflected at a predetermined angle on the surface of the silicon wafer. Is output.

  On the other hand, in the case where fine irregularities due to defects or the like exist on the surface of the silicon wafer, when the irradiated laser light hits such fine irregularities, irregular reflection at an angle different from that of the regular reflection light occurs at that portion. By detecting such scattered light with a photodetector such as a light receiving element or a photomultiplier tube from an angle different from the specularly reflected light, the number of defects, density distribution, size, etc. present on the surface of the silicon wafer Can be detected.

  FIG. 16 is a waveform diagram showing an example of an output signal (light reception signal) when the surface of the silicon wafer is inspected using the laser scattering type surface inspection apparatus described above. According to this figure, a background noise (Haze component) in a certain range is always output from the surface inspection apparatus, and is larger than the background noise in a place where a foreign object, for example, a dent or contamination due to a defect exists. A wave of fluctuation width (scattering from a foreign object) is observed.

The amplitude of the wave generated by scattering from such a foreign object becomes smaller as the size of the fine irregularities present on the surface of the silicon wafer is smaller. That is, if a fine unevenness (defect) of a smaller size is to be detected with high accuracy, the ratio of the fluctuation width between the background noise (N) and the wave (S) caused by the scattered light generated on the surface of the silicon wafer. It is necessary to increase (S / N ratio).
US Pat. No. 6,201,601

  However, in the conventional surface inspection method using laser scattered light, a method of increasing the ratio (S / N ratio) between the background noise (N) and the wave (S) caused by the scattered light generated on the surface of the silicon wafer. There was a limit. For this reason, for example, in the fine unevenness of, for example, 0.05 μm or less existing on the surface of the silicon wafer, the signal from the scattered light generated by this fine unevenness is buried in the background noise, and such 0.05 μm or less There was a problem that it was difficult to detect fine irregularities (defects).

  The present invention has been made in order to solve the above-mentioned problems, and it is possible to increase the fine unevenness caused by defects or foreign matter existing on the surface of the silicon wafer or the surface of the silicon oxide film formed on one surface of the silicon wafer. A surface inspection method capable of detecting with high accuracy is provided.

In order to solve the above problems, the present invention provides the following surface inspection method.
That is, the surface inspection method of the present invention irradiates a laser beam toward the surface of a silicon wafer made of silicon single crystal or the surface of an SOI wafer in which a silicon oxide film is formed inside the silicon wafer. A surface inspection method for detecting fine irregularities present on the surface of the silicon wafer or the surface of the SOI wafer by detecting scattered light irregularly reflected on the surface or the surface of the SOI wafer with a photodetector. ,
The linearly polarized light whose vibration direction of the light electric vector is included in the incident plane is P-polarized light, and the vibration direction of the light electric vector is perpendicular to the plane including the normal of the incident surface and the normal of the wavefront of light. When the circularly polarized light whose polarization direction and the electric vector of light rotate in a circular shape with respect to the incident surface is C-polarized light, the laser light incident on the surface and the scattering incident on the photodetector PP mode in which both light is the P-polarized light, or the laser light that is incident on the surface is the C-polarized light, the CU mode that does not polarize scattered light that is incident on the photodetector, or the laser that is incident on the surface SS mode in which the scattered light both the S-polarized light incident on the light and the light detector, one of, and set to either one mode, by the PP mode and the CU mode, wavelength 355 detects the following crystal defects and foreign matter 30nm using a laser wavelength of m, it said by the SS mode, surface inspection method characterized by detecting a 30nm less crystal defects and foreign matter with a laser wavelength of 355 nm.

  When inspecting the surface of the silicon wafer, the PP mode, the CU mode, or the SS mode is preferably selected when inspecting the surface of the SOI wafer.

  According to the surface inspection method of the present invention, in the case of a silicon wafer in which no silicon oxide film is formed as an object to be inspected, both the laser light incident on the surface of the silicon wafer and the scattered light incident on the photodetector are both P-polarized light. The background noise during surface inspection is greatly reduced by using the PP mode or the CU mode in which the laser light incident on the surface of the silicon wafer is C-polarized and the scattered light incident on the photodetector is not polarized. It becomes possible to do.

  By reducing the background noise (N), the fluctuation width of the output signal wave (S) due to scattered light caused by fine irregularities (defects) existing on the surface of the silicon wafer is small, that is, the size of the irregularities is extremely large. Even if it is small, the S / N ratio can be increased, so that such fine irregularities can be detected with high accuracy.

  Further, in the case of an SOI wafer in which a silicon oxide film is formed inside a silicon wafer as an object to be inspected, an SS mode in which both laser light incident on the surface of the SOI wafer and scattered light incident on a photodetector are S-polarized light is used. By doing so, it becomes possible to greatly reduce the background noise during the surface inspection without depending on the thickness of the single crystal thin film existing on the silicon oxide film. This makes it possible to detect fine irregularities on the SOI wafer with high accuracy.

  Hereinafter, the best embodiment of the surface inspection method according to the present invention will be described with reference to the drawings. This embodiment is specifically described in order to make the gist of the invention better understood, and is not intended to limit the present invention unless otherwise specified. In addition, in the drawings used in the following description, in order to make the features of the present invention easier to understand, there is a case where a main part is shown in an enlarged manner for the sake of convenience. Not necessarily.

The fine irregularities in the present invention are those caused by foreign matters such as impurities and fine dust (contamination) existing on the surface of the silicon wafer, and those caused by crystal defects such as COP, FPD and LSTD. In particular, the irregularities exist locally in a narrow range on the surface of the silicon wafer.
On the other hand, unlike the above-described fine unevenness, the background noise is assumed to be caused by a gentle slope (microroughness) generated on the entire silicon wafer. In the present invention, fine unevenness means unevenness locally present in a narrow range due to foreign matters and crystal defects on the surface of the silicon wafer described above unless otherwise specified.

  FIG. 1 is a schematic diagram showing an example of a laser scattering type surface inspection apparatus used in the surface inspection method of the present invention. The surface inspection apparatus 10 includes a laser light source 11, a side collector mirror 12, and a photodetector 13. A first polarizing unit 14 and a second polarizing unit 15 are provided on the emission side of the laser light source 11 and the incident side of the photodetector 13, respectively.

  The laser light source 11 may be a laser irradiation device that can irradiate laser light L having a predetermined intensity and wavelength. The laser beam R to be irradiated may be, for example, a wavelength region of 200 to 700 nm and an intensity of 1 mW or more. The side collector mirror 12 only needs to be formed in a shape that reflects the scattered light generated on the surface 21 a of the silicon wafer 21 toward the photodetector 13 along the periphery of the inspection target, that is, the silicon wafer 21. . The photodetector 13 only needs to be composed of, for example, a light receiving element or a photomultiplier tube.

  In the case of a silicon wafer 21 made of a silicon single crystal in which a silicon oxide film is not formed inside as an object to be inspected, the first polarizing means 14 formed on the emission side of the laser light source 11 is a laser emitted from the laser light source 11. The light L is polarized so that the vibration direction of the electric vector of the light becomes linearly polarized light included in the incident surface, that is, the surface 21a of the silicon wafer 21, that is, so-called P-polarized light Lp.

  On the other hand, in the case of a silicon wafer 21 made of a silicon single crystal that does not form a silicon oxide film as an object to be inspected, it is formed on the incident side of the photodetector 13 that detects scattered light Ld generated on the surface 21a of the silicon wafer 21. Similarly to the first polarizing means 14, the second polarizing means 15 is also polarized so as to become linearly polarized light included in the surface 21 a of the silicon wafer 21, so-called P-polarized light Lpd.

  When inspecting the surface 21 a of the silicon wafer 21 in which no silicon oxide film is formed, P-polarized light is incident on the surface 21 a of the silicon wafer 21 through the first polarizing means 14. At this time, as shown in FIG. 2, when the surface 21a of the silicon wafer 21 is smooth without any fine irregularities due to defects or foreign matter, the incident P-polarized light Lp is regularly reflected at an angle as it is. It is emitted as reflected light Lf.

  On the other hand, when the surface 21a of the silicon wafer 21 has protrusions (fine irregularities) 31 due to foreign matters or the like, and depressions (fine irregularities) 32 due to defects or the like, the incident P-polarized light Lp has these protrusions 31. The light is irregularly reflected by fine irregularities such as the dent 32 and the like, and is emitted as scattered light Ld at an angle other than the regular reflected light Lf.

  Referring to FIG. 1 again, such scattered light Ld is reflected by the side collector mirror 12 toward the photodetector 13. The scattered light Ld is converted to P-polarized light Lpd via the second polarizing means 15 and then enters the photodetector 13. The photodetector 13 outputs a predetermined signal (waveform signal) according to the intensity of the P-polarized light Lpd of the incident scattered light Ld.

  Such fine irregularities present on the surface 21a of the silicon wafer 21 are caused by foreign matters such as impurities and fine dust (contamination), and crystal defects such as COP, FPD, and LSTD. Examples are given.

  Further, the silicon wafer 21 may be subjected to surface inspection while moving so as to cover the inspection range. Further, the surface inspection may be performed by scanning the laser beam L in the inspection range without moving the silicon wafer 21.

  In the surface inspection method of the present invention, as described above, in the silicon wafer 21 in which no silicon oxide film is formed, the laser beam L incident on the silicon wafer 21 is P by the first polarizing means 14 as described above. The surface 21a of the silicon wafer 21 is converted into the polarized light Lp by using the PP mode in which the scattered light Ld diffusely reflected by the surface 21a of the silicon wafer 21 is incident on the photodetector 13 as the P-polarized light Lpd by the second polarizing means 15. Perform the inspection.

  Further, as shown in FIG. 3, in a silicon wafer 21 in which a silicon oxide film is not formed inside as an object to be inspected, a laser beam L incident on the silicon wafer 21 is converted into an electric vector of light by a third polarizing means 44. It is also preferable to polarize the light so that the vibration direction becomes circularly polarized light Lc that rotates in a circle with respect to the incident surface, that is, the surface 21 a of the silicon wafer 21. In this case, the scattered light Ld diffusely reflected by the surface 21a of the silicon wafer 21 is directly incident on the photodetector 13 without passing through the polarization means. The surface 21a of the silicon wafer 21 is inspected using such a CU mode.

  As described above, when inspecting the silicon wafer 21 made of silicon single crystal, in which no silicon oxide film is formed, the above-described PP mode or CU mode is used to measure the background noise (N ) Can be reduced. If the background noise (N) can be reduced, the S / N ratio is increased even if the amplitude of the wave (S) caused by the scattered light caused by the fine irregularities (defects) is small, that is, the size of the fine irregularities is extremely small. Therefore, it is possible to detect such fine irregularities with high accuracy.

  4 shows background noise (Haze) when inspecting a silicon wafer made of a silicon single crystal without forming a silicon oxide film in various polarization modes, and fine irregularities using five kinds of particle samples. It is the graph which showed the average of the fluctuation width of the output waveform at the time of forming. In FIG. 4, each polarization mode on the horizontal axis is indicated by a two-letter alphabet. That is, the left alphabet indicating each polarization mode is the polarization state of the light incident on the surface of the silicon wafer, and the right alphabet indicating each polarization mode is the light detector of scattered light irregularly reflected on the surface of the silicon wafer. The polarization state of the light when it enters into is shown. Each alphabet indicates a state in which P is P-polarized light, S is S-polarized light, C is circularly polarized light, and U is not changed by polarizing means.

  In addition, PSL (Polystyrene Latex) particles, which are standard particles used for producing a standard wafer for measuring dust particles, were used as particle samples for forming fine irregularities. PSL particles are particles that are very close to a single fraction, and five types of particles having particle diameters of 0.499 μm, 0.300 μm, 0.240 μm, 0.204 μm, and 0.126 μm are used, and FIG. As shown in FIG. 2, the silicon wafer 21 was formed on the surface 21a. Note that FIG. 5B shows a measurement example of a silicon wafer on which such five kinds of PSL particles having a particle diameter are formed.

  As shown in FIG. 4, when inspecting a silicon wafer made of a silicon single crystal, in which no silicon oxide film is formed, the PP mode, that is, the light incident on the surface of the silicon wafer and the light detector. When measured in a mode in which both scattered light is P-polarized or in CU mode, that is, in which light incident on the surface of the silicon wafer is C-polarized and scattered light incident on the photodetector is not polarized, background noise ( Haze) can be significantly reduced.

  By reducing the background noise (Haze), even if weak scattered light, that is, the fine unevenness size existing on the surface of the silicon wafer is extremely small, the output waveform caused by the fine unevenness is accurately detected. be able to. When the surface of a silicon wafer is inspected in such a PP mode or CU mode, for example, if a laser wavelength of 355 nm is used, extremely fine crystal defects and foreign matters of 30 nm or less, preferably 20 nm or less can be reliably detected. Is possible.

  On the other hand, in the case of an SOI wafer in which a silicon oxide film is formed inside the silicon wafer, the laser light incident on the silicon single crystal thin film existing on the silicon oxide film is made S-polarized light and is irregularly reflected on the surface of the single crystal thin film. It is preferable to inspect the surface of the SOI wafer using the SS mode in which the scattered light is also incident on the photodetector as S-polarized light.

  6 to 15 show a background noise (Haze) when a surface is inspected in various polarization modes using an SOI wafer in which a silicon oxide film is formed inside a silicon wafer, and fineness using five kinds of particle samples. It is the graph which showed the average of the fluctuation width of the output waveform at the time of forming unevenness.

  An SOI wafer was prepared in which the thickness of the silicon single crystal thin film existing on the silicon oxide film was changed to 10 levels of 36 nm, 45 nm, 48 nm, 50 nm, 52 nm, 54 nm, 57 nm, 60 nm, 65 nm, and 70 nm. The thickness of the silicon oxide film was all 140 nm. As the PSL particle sample for forming fine irregularities, five kinds of particles having particle diameters of 0.499 μm, 0.300 μm, 0.240 μm, 0.152 μm, and 0.126 μm were used.

  As in the graph shown in FIG. 4, the polarization mode is indicated by a two-letter alphabet. That is, the left alphabet indicating each mode is the polarization state of the light incident on the surface of the SOI wafer, and the right alphabet indicating each mode is the scattered light that is irregularly reflected on the surface of the SOI wafer entering the photodetector. It shows the polarization state of the light. Each alphabet indicates a state in which P is P-polarized light, S is S-polarized light, C is circularly polarized light, and U is not changed by polarizing means.

  According to FIGS. 6 to 15, when the thickness of the silicon single crystal thin film on the silicon oxide film is changed stepwise, all the single crystal thin films are incident on the SS mode, that is, the surface of the SOI wafer. It can be seen that the background noise (Haze) can be reduced by making the laser light to be S-polarized and the scattered light irregularly reflected on the surface of the SOI wafer incident on the photodetector as S-polarized light. By inspecting the surface of the SOI wafer in this SS mode, for example, when a laser wavelength of 355 nm is used, for example, 30 nm or less, preferably 20 nm, regardless of the thickness of the silicon single crystal thin film on the silicon oxide film. The following extremely fine crystal defects and foreign matters can be reliably detected.

It is the schematic which showed an example of the surface inspection apparatus used for the surface inspection method of this invention. It is explanatory drawing which showed the mode of reflection of the incident light on the silicon wafer surface. It is the schematic which showed another example of the surface inspection apparatus used for the surface inspection method of this invention. It is the graph which showed the reduction effect of the background noise in the silicon wafer which does not form an oxide film. It is explanatory drawing which shows an example of the standard particle used in the case of the verification shown in FIG. It is the graph which showed the reduction effect of the background noise in an SOI wafer. It is the graph which showed the reduction effect of the background noise in an SOI wafer. It is the graph which showed the reduction effect of the background noise in an SOI wafer. It is the graph which showed the reduction effect of the background noise in an SOI wafer. It is the graph which showed the reduction effect of the background noise in an SOI wafer. It is the graph which showed the reduction effect of the background noise in an SOI wafer. It is the graph which showed the reduction effect of the background noise in an SOI wafer. It is the graph which showed the reduction effect of the background noise in an SOI wafer. It is the graph which showed the reduction effect of the background noise in an SOI wafer. It is the graph which showed the reduction effect of the background noise in an SOI wafer. It is the wave form diagram which showed the relationship between the signal resulting from the fine unevenness | corrugation of a wafer surface, and background noise.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Surface inspection apparatus, 11 Laser light source, 12 Side condensing mirror, 13 Photo detector, 14 1st polarizing means, 15 2nd polarizing means

Claims (2)

Irradiate a laser beam toward the surface of a silicon wafer made of silicon single crystal or the surface of an SOI wafer in which a silicon oxide film is formed inside the silicon wafer, and diffusely reflect on the surface of the silicon wafer or the surface of the SOI wafer. A surface inspection method for detecting fine irregularities present on the surface of the silicon wafer or the surface of the SOI wafer by detecting the scattered light with a photodetector,
Linearly polarized light whose vibration direction of the electric vector of light is included in the incident surface is P-polarized light,
S-polarized light is a linearly polarized light whose vibration direction of the electric vector of light is perpendicular to the plane including the normal of the incident surface and the normal of the wavefront of the light,
Circularly polarized light whose vibration direction of the electric vector of light rotates circularly with respect to the incident surface is C-polarized light,
And when
PP mode in which both the laser light incident on the surface and the scattered light incident on the photodetector are P-polarized light,
Alternatively, the laser light incident on the surface is C-polarized light, and the CU mode that does not polarize scattered light incident on the photodetector,
Alternatively, an SS mode in which the laser light incident on the surface and the scattered light incident on the photodetector are both S-polarized light,
Set one of the modes ,
With the PP mode and the CU mode, while detecting a crystal defect or foreign matter of 30 nm or less using a laser wavelength of 355 nm,
A surface inspection method for detecting crystal defects and foreign matters of 30 nm or less using a laser wavelength of 355 nm by the SS mode . When inspecting the surface of the silicon wafer, the PP mode, or the CU mode,
The surface inspection method according to claim 1, wherein the SS mode is selected when inspecting the surface of the SOI wafer.

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