JPH1062355A - Inspecting method and inspecting device for semiconductor wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inspecting method and inspecting device in which a defect inspection can be easily and precisely performed while discriminating surface layer, inner layer, and reverse layer. SOLUTION: The luminous flux from a wavelength variable laser 1 is halved to surface irradiating luminous flux and reverse irradiating luminous flux, the surface irradiating luminous flux changed in wavelength and the reverse irradiating luminous flux changed in wavelength are emitted to the surface and reverse sides of a semiconductor wafer, respectively, the reflected light on and around the surface of the semiconductor wafer by the surface irradiating luminous flux is mainly detected, and the transmitted light by the semiconductor wafer by the reverse irradiating luminous flux is also mainly detected, whereby the defect of the semiconductor wafer is detected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for inspecting a semiconductor wafer.

[0002]

2. Description of the Related Art In recent years, the semiconductor industry has made remarkable progress, and in particular, LSI circuit patterns have been miniaturized. Also,
Currently, development of manufacturing process equipment is being promoted every day in major technology countries such as the United States and Japan, centering on DRAMs for forming a large amount of LSI on an 8-inch silicon wafer. Under such circumstances, the specific gravity of quality inspection in each manufacturing process has been increasing. The present invention relates to an automatic inspection apparatus for crystal defects generated in an upstream process (for example, a process for performing epitaxial growth, a heat treatment process for a diffusion furnace).

[0003] In the LSI manufacturing process, either one of the heat treatment processes of the epitaxial process and the thermal diffusion process is necessarily passed. What is important here is that as the silicon wafer size increases, it is technically more difficult to maintain heat uniformity. Of particular importance in the defective quality generated in this process is a crystal defect called a slip. It is said that this defect is also caused by heat non-uniformity between the silicon wafer surface and the thickness direction and the shape of the silicon wafer. As a phenomenon, heat is applied to the silicon wafer, and in the process of cooling, a temperature gradient appears around the silicon wafer, and as a result, stress remains inside. As a result, the crystals that cannot withstand the stress generate cracks linearly along the crystal orientation, as in a fault seen in an earthquake, at an uneven portion. This is a phenomenon that appears from the periphery to the inside of the silicon wafer. At present, there is no inspection standard such as the width and depth of the crack. There is only the total length of the generated slip, which is about 300 mm. Conventionally, this quality inspection is mainly performed by a visual inspection by a silicon wafer maker, and a sampling inspection is performed by a device maker using a differential interference microscope or X-ray topography.

[0004]

However, in a visual inspection, a large diameter of 8 to 12 inches causes an increase in the visual field of view, causing a distraction of attention. And will lack reliability. If you are a very skilled person, the slip width is 5μ
m and a length of about 1 mm can be determined, but inspection cannot be performed continuously for one hour. In addition, it takes a long time to observe and inspect the entire circumference (5 to 10 mm) of an 8-inch silicon wafer using a differential interference microscope. From the viewpoint of performance, it is possible to inspect a slip having a width of about 1 μm at a high magnification using a differential interference microscope, but it is very difficult to determine the total length. Similarly, X-ray topography takes about three hours for one measurement. This is because it is necessary to perform an operation of irradiating soft X-rays from below the silicon wafer and printing transmitted light on a photographic dry plate. Also, the use of X-rays allows only a very limited number of people to use it. Further, this device is very expensive, and the device occupied area is as large as about 6 tatami mats, which is not practical. Further, in the case of X-ray topography, since inspection is performed by transmission, the surface layer, the inner layer, and the back surface layer are all photographed, so that it is impossible to extract only the surface layer.

The present invention has been made in view of the above-described problems, and provides an inspection method and an inspection apparatus that can easily and accurately perform a defect inspection while distinguishing a surface layer, an internal layer, and a rear surface layer. The purpose is to:

[0006]

First, the spectral characteristics of a silicon wafer will be described. The spectral characteristics show a characteristic behavior when the wavelength of incident light is changed. In other words, in the visible light range, the light is reflected only from the surface layer of the silicon wafer, and if it exceeds that range, transmitted light will appear if it exceeds about 1000 nm. The present invention has been made based on such knowledge.

First, according to the inspection method of the present invention, the light beam from the wavelength tunable laser is divided into a front irradiation light beam and a back irradiation light beam, and the front surface irradiation light beam having a changed wavelength is applied to the surface of the semiconductor wafer. While applying the backside illuminating light beam having a changed wavelength to the back surface of the semiconductor wafer, while mainly detecting reflected light near the front surface and the front surface of the semiconductor wafer by the front surface irradiating light beam, the backside irradiating light beam A defect in the semiconductor wafer is detected mainly by detecting light transmitted through the semiconductor wafer. Here, the wavelength tunable laser used for the defect inspection of the silicon wafer is wavelength 7
It is preferable to use a laser that can be continuously changed from 00 nm to 1100 nm. According to this inspection method, the detection result of the reflected light on the front surface and near the surface of the semiconductor wafer by the surface irradiation light beam with the changed wavelength, and the detection of the transmitted light of the semiconductor wafer by the back surface irradiation light beam with the changed wavelength From the result, the position and size of the surface defect and the internal defect of the semiconductor wafer can be easily detected.

According to a second aspect of the present invention, there is provided an inspection apparatus, comprising: a tunable laser; a surface irradiation optical system for irradiating a light beam from the tunable laser to a surface of the semiconductor wafer; A backside irradiating optical system for irradiating the backside, first light detecting means for mainly detecting light reflected on the front surface and near the surface of the semiconductor wafer by the frontside irradiating light beam, and transmission of the semiconductor wafer by the backside irradiating light beam And a second light detecting means for mainly detecting light. According to this inspection device, the detection result of the reflected light on the surface and near the surface of the semiconductor wafer by the surface irradiation light beam having a changed wavelength,
From the detection result of the transmitted light of the semiconductor wafer by the back-side irradiation light beam having the changed wavelength, the planar position, depth, size, and the like of the surface defect and the internal defect of the semiconductor wafer can be easily detected.

According to a third aspect of the present invention, in the inspection apparatus of the second aspect, the front-side illumination optical system and the back-side illumination optical system are provided with a light beam shaping lens system and a condensing projection lens, respectively. The light beam shaping lens systems provided in the front-side illuminating optical system and the back-side illuminating optical system are used to form a perfect circular beam shape at the front and back convergence points of the semiconductor wafer. According to this inspection apparatus, since the beam profile shows a perfect Gaussian distribution in all directions, the detection sensitivity can be improved.

According to a fourth aspect of the present invention, in the inspection apparatus of the second or third aspect, the object side telecentric lens and a variable spatial filter installed between the object side telecentric lens and the imaging surface. A variable circular knife edge, irradiating a light beam from a metal halide lamp as a parallel light beam to the surface of the semiconductor wafer with a collimating lens, and minute angle components of a reflected light beam from the semiconductor wafer are reflected by the variable circular knife edge. It is characterized by being configured to shut off. According to this inspection apparatus, when a defect exists on the surface of the semiconductor wafer, the angle component of the reflection component from the defect is cut off, so that the contrast between the defect and the background can be improved.

[0011]

FIG. 1 shows an inspection apparatus according to the present invention. In this inspection apparatus, the light beam from the wavelength tunable laser 1 is divided into a front surface irradiation light beam and a back surface irradiation light beam, and the front surface irradiation light beam is applied to the front surface of the semiconductor wafer W, and the back surface irradiation light beam is applied to the back surface of the semiconductor wafer W. It has become. Further, in this inspection apparatus, a light beam from the metal halide lamp 21 is applied to the surface of the semiconductor wafer W. First,
These irradiation systems will be described.

(Irradiation System) The semiconductor laser 1 in this case is not particularly limited, but is 700 nm to 1100 nm.
A semiconductor laser whose wavelength can be changed in the range of nm is used. If the wavelength can be changed within this range, it is sufficient for a defect inspection of a silicon wafer.

A half mirror 3 is used to divide the light beam 2 into a front surface irradiation light beam and a back surface irradiation light beam.

Further, the surface irradiation light beam is transmitted to the semiconductor wafer W
The surface irradiating optical system 4 for applying light to the surface of the optical system comprises a light beam shaping lens system 5, a polarizing plate 6, a λ / 2 wavelength plate 7, and a condensing projection lens 8.

What is important in the surface irradiation optical system 4 is to create a perfect circular shape as a shape at a focusing point and to create a perfect Gaussian distribution as a beam profile. Moreover, it must be achieved in the entire wavelength range of 700 nm to 1100 nm. Therefore, it is particularly preferable to combine an aspherical lens, a cylindrical lens, a spatial filter, and the like in an elliptical molded lens. In this way, the beam shape is elliptical immediately before the irradiation, but can be completely circular at the focal point, and the beam profile also shows a perfect Gaussian distribution in all directions. The polarizing plate 6 functions to decompose the surface irradiation light beam that has passed through the light beam shaping lens 5 into two linearly polarized light components that vibrate in directions perpendicular to each other in a plane perpendicular to the traveling direction. The λ / 2 wave plate 7 has a function of giving a phase difference of λ / 2 to two linearly polarized lights vibrating at right angles to each other. The condensing projection lens 8 is for converging the light beam emitted from the λ / 2 wavelength plate 7 and projecting the light beam on the surface of the semiconductor wafer W.

On the other hand, the backside illuminating optical system 9 for applying the backside illuminating light beam to the front surface of the semiconductor wafer W is a fiber 1
0, illuminance distribution correction optical system 11, optical molded lens system 12,
It comprises a total reflection mirror 13 and a condensing projection lens 14. Here, the illuminance distribution correction optical system 11 functions to make the illuminance distribution of the light beam emitted from the fiber 10 uniform. The light beam shaping lens system 12 is used to create a perfect circular shape as a shape at a focusing point, and to create a perfect Gaussian distribution as a beam profile. The total reflection mirror 13 is for changing the traveling direction of the light beam. The condensing projection lens 14 is for converging the light beam reflected by the total reflection mirror 13 and projecting the light beam on the back surface of the semiconductor wafer W.

(Detection Optical System) Next, the detection optical system in this inspection apparatus will be described. This detection optical system includes a first detection optical system 30 for detecting light from the semiconductor wafer W by the photomultiplier tube 31 and a second detection optical system 40 for detecting light from the semiconductor wafer W by the photodiode 41.
It is composed of

The photomultiplier tube 31 of the first detection optical system 30
Exists on the semiconductor wafer W and on an extension of the optical axis of the condenser projection lens 14, and detects light from the semiconductor wafer W via the condenser lens 32. The first detection optical system 30 detects the reflected / transmitted scattered intensity by converting a weak intensity change into an electric quantity using a photomultiplier 31 (or an image intensifier). This intensity change is detected by the maximum entropy method or by the fast Fourier transform method.

The photodiode 41 of the second detection optical system 40 exists at a position slightly away from the regular reflection component of the light from the condensing projection lens 8, and transmits the light from the semiconductor wafer W via the condensing lens 42. It is designed to detect.

(Image optical system) This image optical system is an illumination system 2
0 and an image detection system 50. Lighting system 20
Is for irradiating the light beam from the metal halide lamp 21 to the semiconductor wafer W, and includes a pinhole 22, a wavelength selection filter 23, a collimating lens 24, and a shutter 2.
5. The half mirror 26 is provided.

The pinhole 22 is for producing a point light source, the wavelength selection filter 23 is for selecting the wavelength of the light beam 3 emitted by the metal halide lamp 21, and the collimating lens 24 is for controlling the light beam 3. The shutter 25 is for blocking light from the metal halide lamp 21, and the half mirror 26 is for directing the light beam 3 toward the semiconductor wafer W.

The image detection system 50 includes a half mirror 52 for splitting light traveling from the semiconductor wafer W to the photomultiplier tube 31. The light split by the half mirror 52 is reflected by a total reflection mirror 53. After that, the CCD is passed through a telecentric optical system 54 with a built-in spatial filter.
This is detected at 51.

This image optical system is for judging whether or not a slip appears on the surface layer. The feature is that a variable spatial filter can be installed between the ultra-high resolution telecentric lens and the imaging surface (CCD 51), and the surface state can be imaged as a grayscale image corresponding to the minute angle component of the surface. It is. That is, the telecentric optical system 54 includes a perfect object side telecentric lens and a variable circular knife edge which is a variable spatial filter. Then, using a perfectly parallel light beam as the irradiation light beam, a minute angle component of the reflected light beam is cut off by a variable circular knife edge. According to the telecentric optical system 54, when a slip exists on the surface of the silicon wafer, the angle component of the reflected component from the slip is cut off, so that there is an effect that the contrast between the slip and the background can be obtained. Further, by converting the density of the image captured by the CCD 51 into multiple gradations and repeating calculus, the amount of the slip difference can be analyzed and detected in real time with a resolution of about 100 Å.

A metal halide lamp 21 is used as a light source for the image optical system.
Since there is a bright line spectrum at 6 nm, the wavelength is used to irradiate the surface of the semiconductor wafer W as a parallel light beam by the collimating lens 24. By using this wavelength, detection at the surface layer can be reliably performed.

When this image optical system is used, the luminous flux of the tunable laser 1 is blocked by a shutter (not shown).

(Inspection Stage System) The stage for holding the silicon wafer must have a structure that is strong against external factors such as particles. In particular, since the back surface is irradiated with a laser beam, the transmittance must be high in a wavelength range of about 400 to 1300 nm, and a quartz glass material is used as the stage material. Further, it is necessary to reduce the contact area between the silicon wafer and the stage to about 2% in order to reduce the influence of particles and the like. Rotational accuracy (runout etc.) is also 0.2
It is necessary to use a rotating means such as an air bearing or a rotary laser encoder because it is necessary to set the diameter to μm or less.

(Inspection Method) Next, an inspection method using the optical inspection apparatus will be described.

When inspecting, for example, a silicon wafer with this optical inspection apparatus, first, the light source wavelengths of the wavelength lasers are classified into three types according to the spectral characteristics of the silicon wafer. That is, a wavelength range of 700 to 800
nm (wavelength first group), 800 to 1000 nm (wavelength second group), 1000 to 1100 nm (wavelength third group)
Group). Then, the first wavelength group is used for the surface layer, the second wavelength group is used for the inner layer, and the third wavelength group is used for detecting slip of the surface layer, the inner layer, and the back layer. At the time of inspection, the silicon wafer is taken out of the cassette in which the silicon wafer is stored while being aligned by a robot, and the silicon wafer is automatically set on a quartz-based transparent stage. Then, the silicon wafer is rotated with the crystal orientation reference (notch) as the rotation origin, and is moved inward from the outermost periphery for each focused beam point diameter for detection. The representative values of the three wavelength groups are determined by the difference in the crystal orientation of the silicon wafer. (The optimal wavelength is 1n from 700 to 1100nm.
It is found to be variable in m steps. )

Next, a specific inspection method will be described. In the first wavelength group, there is no transmission of the irradiation light beam from the back surface of the silicon wafer, and therefore, can be ignored. Therefore, the change in the intensity of the detection light from the photomultiplier tube 31 and the photodiode 41 is all a change in the intensity of light from the surface layer (even though the surface layer is actually penetrated by several μm from the surface into the internal layer). is there. When the intensity of light detected by the photomultiplier tube 31 or the photodiode 41 changes,
At that time, the shutter 23 is opened, the image near the change is captured by the CCD 51, and image analysis is performed in real time. Then, the result is stored in the memory together with the detected position information. In this case, when a change in intensity is detected by the photodiode 41, it is confirmed from the image analysis that a slip has occurred in the surface layer. On the other hand, when the intensity change is detected only in the photomultiplier tube 31 (for example, when the slip defect is minute), the presence of the slip may not always be confirmed in the image analysis. However, if a change is detected by the photodiode 41 in the second wavelength group as well, it is determined that a slip exists at the boundary between the inner layer and the surface layer. (A detailed analysis of the silicon wafer gives a rough correlation between the wavelength and the amount of light penetration.
A rough numerical representation of the occurrence depth can also be made. )

In the second wavelength group, it is considered that there is almost no change in the photomultiplier tube 31 in the case of a small slip (however, a change can be detected near the wavelength of 1000 nm). Furthermore, if a change is detected by the photodiode 41 for the first time in this group, a slip is definitely present in the inner layer. In the third wavelength group, in the case of a small slip, no change appears in the photodiode 41, and only a change appears in the photomultiplier tube 31. If a change appears here for the first time, it means that slip has occurred only in the back layer, but this probability is small. Mostly, it is considered that the inner layer slips. That is, since it is said that the occurrence of slip has a deep relationship with the internal stress, it is expected that stress remains around the slip generated inside. Since the transmitted scattering intensity change is emphasized due to the birefringence around the slip due to the stress, it is expected that the change amount will be larger than the change amount detection in the second wavelength group. However, if the detection position is the same as the detection position in the second wavelength group, the result of the second group is determined. What is important in the third wavelength group is that although the second wavelength group naturally absorbs light, there is a possibility that a minute slip may be detected. it can. Further, as an additional effect, the distribution of stress is also known. Furthermore, since the image is also taken and analyzed when the reflection / transmission scattering intensity changes, it is possible to measure not only whether a slip has appeared on an important surface layer but also a numerical value of the length.

Although the embodiments of the present invention made by the present inventor have been described above, the present invention is not limited to such embodiments, and various modifications can be made without departing from the gist of the present invention.

For example, in the above embodiment, the inspection of a silicon wafer has been mainly described. However, not only the inspection of a compound semiconductor wafer but also a general thin plate such as a liquid crystal glass substrate or a DVD (digital video disk) substrate. Applicable to inspection.

In the above-described embodiment, the case of the slip inspection has been mainly described. However, the present invention can also be applied to the case of inspecting the internal stress distribution of a thin plate.

[0034]

The effect of the typical one of the present invention will be described. The detection result of the light reflected on the surface and near the surface of the semiconductor wafer by the surface irradiation light beam of which the wavelength is changed,
From the detection result of the transmitted light of the semiconductor wafer by the back-side irradiation light beam having the changed wavelength, the position and size of the surface defect and the internal defect of the semiconductor wafer can be easily detected.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an inspection apparatus according to the present invention.

[Explanation of symbols]

 Reference Signs List 1 wavelength variable laser 4 front irradiation system 9 back irradiation system 30 first detection system 40 second detection system

Claims (4)

[Claims] 1. A light beam from a wavelength tunable laser is divided into a front surface irradiation light beam and a back surface irradiation light beam, and the front surface irradiation light beam having a changed wavelength is applied to the front surface of a semiconductor wafer, and the rear surface irradiation light beam having a changed wavelength. To the back surface of the semiconductor wafer, and mainly detects the reflected light on the front surface and near the front surface of the semiconductor wafer due to the front irradiation light beam, while mainly detecting the transmitted light of the semiconductor wafer due to the back irradiation light beam. A method of inspecting a semiconductor wafer, wherein a defect of the semiconductor wafer is detected. 2. A wavelength tunable laser, a surface irradiation optical system for irradiating a light beam from the wavelength tunable laser to a surface of a semiconductor wafer, and a back surface irradiation optics for irradiating a light beam from the wavelength tunable laser to a back surface of the semiconductor wafer. A first light detecting means for mainly detecting light reflected on the front surface and near the surface of the semiconductor wafer by the front irradiation light beam; and a second light detection device for mainly detecting transmitted light of the semiconductor wafer by the back irradiation light beam. An inspection apparatus for a semiconductor wafer, comprising: two light detection means. 3. The front-side irradiation optical system and the back-side irradiation optical system are provided with a light beam shaping lens system and a condensing projection lens, respectively, and are provided in the front-side irradiation optical system and the back-side irradiation optical system, respectively. 3. The semiconductor wafer inspection apparatus according to claim 2, wherein the light beam shaping lens system makes the beam shape a perfect circle at the focusing points on the front and back of the semiconductor wafer. 4. An object side telecentric lens, and a variable circular knife edge which is a variable spatial filter provided between the object side telecentric lens and the imaging surface, and uses a collimating lens to convert a light beam from a metal halide lamp by a collimating lens. 4. The device according to claim 2, wherein the surface of the semiconductor wafer is irradiated as a parallel light beam, and a minute angle component of the light beam reflected from the semiconductor wafer is cut off by the variable circular knife edge. Semiconductor wafer inspection equipment.