JPH01230241A - Method for detecting defect in embedded diffused layer - Google Patents

Abstract

PURPOSE:To make it possible to check the rosette of a silicon substrate automatically and to improve productivity, by projecting ultraviolet rays and infrared rays having the different transmittances on a defective rosette and an oxide film on a wafer, and detecting the intensity of the reflected ultraviolet rays or the reflected infrared rays. CONSTITUTION:Light that is emitted from a Deep UV light source 12 in a defect checking device at an embedded diffused layer is made to be infrared rays in the wavelength range of 180-220nm through a bandpass filter 13. The Deep UV light having the central wavelength of 200nm that is reflected from a half mirror 14 is projected on the surface of a wafer 11. The reflected light from the wafer 11 is received with a Deep UV sensor 15 through the mirror 14. A sample stage 16 on which the wafer 11 is mounted is moved with a sample-stage moving system 17 in a two-dimensional pattern, and the entire surface of the wafer 11 is scanned. When a rosette 45 is present in the wafer 11, the intensities of the received reflected light are detected with the sensor 15 based on the difference in transmittances for the infrared rays having the wavelength of 200nm between the rosette 45 and an oxide film 42 on a silicon substrate 41. Thus, the automatic check of the rosette 45 can be performed.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for detecting defects occurring in a buried diffusion layer of a semiconductor integrated circuit, and in particular, a method for detecting defects occurring in a buried diffusion layer of a semiconductor integrated circuit. The present invention relates to a method for optically detecting defects using ultraviolet light or infrared light having different wavelengths, or using scanning infrared light having a wavelength that covers the absorption band of the defective rosette.

[Prior Art] Conventionally, in the manufacture of semiconductor integrated circuits, particularly integrated circuits using bipolar devices, N+ diffusion is performed in a buried diffusion layer to reduce collector series resistance. Defects may occur during the formation of this buried diffusion layer.
A rosette defect was reported in the Proceedings of the 46th Japan Society of Applied Physics Academic Conference 3a-W-7 (Noh Kobayashi, 1 person) held at Kyoto University in the fall of 2015. This is because defects called "rosettes" occur in the oxide film during spin-on diffusion, especially when SB or As is used as a dopant.
These rosettes may also reach the SiK and degrade the characteristics of the device.

FIG. 4 is a sectional view showing the formation of rosettes. Figure (a)
41 is a silicon substrate made of P-type silicon. 42 is an oxide film, which is patterned on a silicon substrate.

In the figure (b), 43 is a spion sb doped oxide film, which is formed on the surface of the silicon substrate 41 and the oxide film 42 by coating.

Figure (c) shows the element shown in figure (b) at 1200-1250°C.
It is a state diagram when heat treatment (Sb diffusion) is performed for 30 to 700 minutes. In the figure, 44 is an N+ buried diffusion layer formed by solid phase diffusion from a spin-on SB doped oxide film.

45 is a defect called a rosette, which is the crystallization of the oxide film 42. Further, 46 is an abnormal diffusion layer. Crystallized oxides generally include cristobalite (
It is said that there are two types: tetragonal system) and tridymite (hexagonal system).

FIG. 5 is a reproduction of a SEM photograph of a rosette, showing a rosette (5000x magnification) generated when a buried diffusion layer was formed by a spin-on SB doped oxide film. According to the same figure, s
The b rosette has a hexagonal crystal system and is presumed to be tridymite. These crystallized 5IO2 are more dense than oxide films, according to literature such as "Fundamentals of Silicon Integrated Device Technology" (Chijinshokan, edited by R.M., Berger, R.P., Tonofan, p. 121, Section 4.4). The boundary with the oxide film has porous properties. Therefore, the diffusion rate of impurities is fast, and the oxide film 42
It is considered that an anomalous diffusion layer 4B with N inversion is formed on the surface of the silicon substrate 41 below the rosette 45 where the crystallized rosette 45 is formed.

When these rosettes are formed, the device characteristics deteriorate and the manufacturing yield of integrated circuits is extremely reduced. Therefore, it is necessary to detect rosettes in order to manage buried diffusion. Therefore, after heat treatment, the silicon substrate 41 is generally light-etched with approximately 5% hydrofluoric acid, and the number of rosettes is detected using a metallurgical microscope or a scanning electron microscope, as one of the characteristics that can replace defects in the buried diffusion layer. Ta.

[Problems to be Solved by the Invention] In rosette detection using the conventional metallurgical microscope as described above, the number of rosettes generated is usually as small as 0.1 to 10/c4. Visual inspection is required, and one point is that both the oxide film and the rosette are basically transparent materials in visible light, and their optical clarity is low, with little difference in interference color caused by slight differences in refractive index. Due to the lack of reproducibility in interference colors, it was difficult to introduce automatic detection equipment, and detection with the naked eye was necessary.

On the other hand, when detecting rosettes using a scanning electron microscope, the contrast of the image is good, but since the sample surface is covered with an insulating film such as an oxide film, a gold coating is required to prevent charge-up phenomenon, which leads to damage. Since it requires inspection, it was difficult to introduce it into the production line. Therefore, in any of the above methods, it takes a long time to inspect a large number of silicon substrates on a production line, and these methods are not technically satisfactory.

This invention was made to solve these problems, and it enables rosette inspection of a large number of silicon substrates on a production line, prevents defects in buried diffusion layers, and improves yield in the manufacturing process. The purpose is to obtain an excellent inspection method.

[Means for resolving the problem] In the method for detecting defects in a buried diffusion layer according to the present invention, ultraviolet light having different transmittances is applied to the defective rosette and the oxide film on the wafer, respectively, as the first and second methods. A method for detecting rosettes in the embedded diffusion layer by irradiating the wafer with light and infrared light and detecting the intensity of reflected ultraviolet light or detecting the intensity of transmitted infrared light. It is.

A third method is to irradiate the wafer with wavelength-scanning infrared rays that cover the absorption band (wavelength 2.5 μm to 3.0 μm) contributed by defective rosettes, and transmit the wafer and the oxide film thereon. A method is implemented in which the wavelength-scanned transmitted light is detected in synchronization with the wavelength scanning, and the presence or absence of an absorption band for the defective rosette is determined to detect the rosette of the buried diffusion layer.

[Function] In this invention, as a defect detection method of a buried diffusion layer,
Utilizing the fact that the hexagonal crystalline quartz forming the rosette and the normal oxide film have different d excesses in the ultraviolet light region and the infrared light region, irradiating the wafer with the ultraviolet light or infrared light; Rosettes are detected based on the intensity of ultraviolet reflected light or infrared transmitted light from the wafer.

There is also an absorption band (wavelength 2.5 μm to 3.0 μm) that has a rosette.
A wafer is irradiated with wavelength scanning infrared light in a range that covers IJm), and the wavelength scanning transmitted light transmitted from the wafer is received by an infrared light sensor in synchronization with the wavelength scanning, and the received light wavelength and signal intensity are A rosette is detected by determining the hm of the absorption band from .

[Example] FIG. 1 is a structural diagram showing a first example of the present invention.
1 is a wafer, 12 is a deep UV light source, 13 is a bandpass filter with a wavelength band of 200 nm±20 nm, 1
4 is a half mirror, 115 is a Decp UV sensor, 16 is a sample stage, and 17 is a sample stage moving system.

The operation shown in FIG. 1 will be explained. Deep U V destination FAI2
Dcep UV light from wavelength band 20Onm±20nm
Through the interference type band pass filter 13, the half mirror
The surface of the wafer 11 is irradiated with the deep UV light having a center wavelength of 200 nm reflected by the wafer 14 . The reflected light from the wafer 11 passes through the half mirror 14 and is sent to the deep UV sensor 15.
The light is received by The Doep UV sensor 15 photoelectrically converts the received light signal and outputs an electric signal. Since the sample stage IB is moved two-dimensionally by the sample stage moving system 17, the entire surface of the wafer 11 can be scanned with the deep UV light.

Documents such as “Charts of basic physical properties focusing on spectroscopic properties”
According to (Keiko Kudo, Kyoritsu Publishing Co., Ltd.), wafer 1
The transmittance of quartz crystal (molten), which has the same properties as the normal oxide film formed on the surface of 1, at a wavelength of 200 ni is 85% at a thickness of 6.4G. However, the transmittance at the same wavelength of quartz (crystal), which has the same properties as the hexagonal crystalline quartz that is the rosette, is 29% at a thickness of 2.0 mm, and the reflectance of silicon at a wavelength of 200 nm is 65%, and the amount of surface reflection on the oxide film surface is 45%. Therefore, if there is a rosette on the wafer 11, the rosette 45 and the oxide film 42 on the silicon substrate 41 will have a wavelength of 2
Dec
The reflected light received by the pUV sensor 15 has different strengths, so a detection signal with high contrast is obtained, and the rosette is easily detected. Usually, the main purpose of detecting these rosettes is the number of rosettes generated per 111 area, rather than their shape or size. A method of generating a rosette FA output when the value falls below a threshold value may be used.

FIG. 2 is a structural diagram showing a second embodiment of the present invention, and 1
1 and 17 are exactly the same as the equipment shown in FIG. 2
2 is an infrared light source, 23 is a wavelength band of 4 μm ± 0.1 LII
n bandpass filter, 24 a sapphire sample stand,
25 is an infrared light sensor.

The operation shown in FIG. 2 will be explained. The infrared light from the infrared light source 22 is passed through a bandpass filter 23 with a wavelength band of 4-±0.1 μm.
The infrared light with a center wavelength of 4- is transmitted through the sample stage 24 made of sapphire and irradiated onto the back side of the wafer 11. The transmitted light from the wafer 11 is received by the infrared light sensor 25. The infrared light sensor 25 photoelectrically converts the received light signal and outputs an electric signal. In addition, the sample stage 24 is moved between two locations by the sample stage moving system 17.
Since it is moved dimensionally, the entire surface of the wafer 11 can be scanned. According to the literature cited in the explanation of Figure 1,
The transmittance at a wavelength of 4 μm of crystal (molten), which has the same properties as the normal oxide film formed on the surface of the wafer 11, is at a thickness of 6
．． It is 70% at 46 mm. However, the transmittance of quartz (crystal), which has the same properties as the hexagonal crystalline quartz that is the rosette, at the same wavelength is 20% at a thickness of 2.0 mm, and the transmittance of silicon is 20% at a thickness of 2.0 mm. It is 55% in 5th order. The thickness of silicon Ml used in semiconductor integrated circuits is usually 0.4
~0.7 m11, and infrared light with a wavelength of 41JII+ can be sufficiently transmitted. Therefore, due to the difference in transmittance of the rosette 45, the silicon substrate 41, and the oxide film 42 to the infrared light having the wavelength 4IJI11, the infrared light sensor 25 detects the wafer 11.
Rosettes can be easily detected by detecting the intensity of infrared light transmitted through the rosette. The detection method of the infrared light sensor 25 is De
Similar to the rosette detection method of the ep UV sensor 15, level detection may be performed by setting a threshold value.

Fig. 1 is a structural diagram showing a third embodiment of the present invention;
11.17.22.24.25 are exactly the same as the equipment shown in FIG. 33 is a diffraction grating, and 34 is a diffraction grating scanning system.

The operation shown in FIG. 3 will be explained. The infrared light from the infrared light source 22 is converted into infrared light that is scanned at high speed in a wavelength range of 2 to 3 μm by a diffraction grating 33 and a diffraction grating scanning system 34. The back side of the wafer IT is irradiated through the wafer IT. The wavelength-scanned transmitted light from the wafer 11 is subjected to photoelectric conversion of the received light intensity for the wavelength of the transmitted light by an infrared light sensor 25 in synchronization with the scanning system of the diffraction grating, and is output as an electrical signal. In addition, since the sample stage 24 is moved two-dimensionally by the sample stage moving system 17,
The entire surface of the wafer 11 can be scanned with the infrared light of 3-. According to the literature cited in the explanation of FIG. , 46 m11 and 90 to 85%, which is a flat characteristic. However, crystals with the same properties as the hexagonal crystalline quartz that is the rosette have a wavelength of 2.5 to 3 μm.
Since there is an absorption band in the wavelength range of 2.0 to 3.0 μm, the transmittance of infrared light is reduced. Further, the transmittance of silicon is 55% at a thickness of 2.5 mm, and the characteristics are flat between wavelengths of 2 and 31JIn. Generally, the thickness of silicon substrate used in integrated circuits is 0.4 to 0.7, and the wavelength is 2 to 3.
Infrared light of μm is sufficiently transmitted.

Therefore, the wafer 11 is irradiated with infrared light having a wavelength of 2 to 3-3 as the rosette detection light without scanning the wavelength at high speed.
The infrared light sensor 25 detects the received light wavelength and the received light intensity from the transmitted light of 1, and detects the wavelength 2.5 to 3 that the rosette has.
．． Rosettes can be detected by determining the presence or absence of a 0 um absorption band. This rosette detection method is a detection method that is resistant to external disturbances and eliminates the effects of movement of the absorption band due to the state of the rosette, dust on the sample, uneven scanning of infrared light, and the like.

[Effects of the Invention] As described above, according to the present invention, as a defect detection method for a buried diffusion layer, the defective rosette and the oxide film on the wafer 1 are
A method of detecting the intensity of reflected light or transmitted light by irradiation with ultraviolet light or infrared light, each having a different transmittance, or a method of detecting the intensity of reflected light or transmitted light by irradiation with wavelength-scanning infrared light that covers the absorption band of the defective rosette. Since a method of detecting the presence of rosettes is adopted, it is possible to automatically inspect rosettes of a large amount of silicon substrates on a production line, which is effective in improving productivity.

Furthermore, the automatic rosette inspection described above improves the yield in the manufacturing process and has an economical effect.

[Brief explanation of the drawing]

FIG. 1 is a structural diagram of a first embodiment of the present invention, FIG. 2 is a structural diagram of a second embodiment of the present invention, FIG. 3 is a structural diagram of a third embodiment of the present invention, and FIG. The figure is a cross-sectional view showing the generation of rosettes, and FIG. 5 is a reproduction of an SEM photograph of the rosette. In the figure, 11 is a wafer, 12 is a deep UV light source, 13 is a band pass filter, and 14 is a half mirror 1.
15 is DC! 0pUV sensor, 16 is a sample stage, 17 is a sample stage moving system, 22 is an infrared light source, 23 is a band pass filter, 24 is a sapphire sample stage, 25 is an infrared light sensor, 33 is a diffraction grating, 34 is a diffraction 41 is a silicon substrate, 42 is an oxide film, 43 is a spion sb doped oxide film, 44 is a buried diffusion layer, 45 is a rosette, and 4B is an anomalous diffusion layer. Mouth e-6t h conversion'! c % wrWJ12g 4th
figure

Claims (3)

[Claims] (1) In a method for detecting defective rosettes that occur in a buried diffusion layer of a semiconductor integrated circuit, light emitted from a deep UV light source is passed through a bandpass filter to a wavelength range of 180 nm to 220 nm. The ultraviolet light is applied to the surface of the wafer on which the buried diffusion layer is formed, and the reflected light transmitted through and reflected by the oxide film and the rosette on the wafer is received. A method for detecting defects in an embedded diffusion layer, characterized in that the rosette is detected by detecting the intensity of reflected light caused by a difference in transmittance to ultraviolet light. (2) In a method for detecting defective rosettes occurring in a buried diffusion layer of a semiconductor integrated circuit, light emitted from an infrared light source is passed through a bandpass filter with a wavelength ranging from 3.5 μm to 4.5 μm. The infrared light is applied to the wafer on which the buried diffusion layer is formed, and the transmitted light transmitted through the wafer, the oxide film, and the rosette is received, and the oxide film and the rosette respond to the infrared light. A method for detecting defects in a buried diffusion layer, characterized in that the rosette is detected by detecting the intensity of transmitted light due to a difference in transmittance. (3) In a method for detecting defective rosettes occurring in a buried diffusion layer of a semiconductor integrated circuit, light emitted from an infrared light source is passed through a diffraction grating and a diffraction grating scanning system to a wavelength of 2.0 μm to 3.0 μm. The scanning infrared light is applied to the wafer on which the buried diffusion layer is formed, and the scanning transmitted light that has passed through the wafer, the oxide film, and the rosette is received, and the transmitted infrared light is The wavelength and signal intensity of light are detected in synchronization with the diffraction grating scanning system, and the wavelength 2. that the rosette has in the infrared light region is detected.
A method for detecting defects in a buried diffusion layer, comprising determining the presence or absence of an absorption band in a range from 5 μm to 3.0 μm, and detecting the rosette.