JP3775861B2 - Semiconductor wafer inspection method and inspection apparatus - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a semiconductor wafer inspection method and inspection apparatus.
[0002]
[Prior art]
In recent years, progress in the semiconductor industry has been remarkable, and in particular, miniaturization of LSI circuit patterns has progressed. Currently, development of manufacturing process equipment is being promoted every day in major technical countries including the United States and Japan, centering on DRAM which forms a large amount of LSI on an 8-inch silicon wafer. Under such circumstances, the specific gravity of quality inspection in each manufacturing process is increasing. The present invention relates to an automatic inspection apparatus for crystal defects generated in an upstream process (for example, a process for epitaxial growth or a heat treatment process for a diffusion furnace).
[0003]
In the LSI manufacturing process, either an epitaxial process or a thermal diffusion process, which is a thermal diffusion process, always passes. What is important here is that it is technically difficult to maintain heat uniformity as the silicon wafer size increases. A crystal defect called slip is particularly important in the quality of defects generated in this process. This defect is said to be caused by the non-uniformity of the silicon wafer surface and the thickness direction and the shape of the silicon wafer. As a phenomenon, in the process where heat is applied to the silicon wafer and it is cooled, a temperature gradient appears in the periphery, and as a result, stress remains inside. As a result, the crystal that cannot withstand the stress has a non-uniform portion that is cracked in a straight line along the crystal orientation like a fault seen in an earthquake. This is a phenomenon that appears from the periphery to the inside of the silicon wafer. There are currently no inspection standards 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 visual inspection in silicon wafer manufacturers, and device manufacturers perform sampling inspection using a differential interference microscope or X-ray topography.
[0004]
[Problems to be solved by the invention]
However, in the visual inspection, the enlargement of the visual field due to the large diameter of 8 to 12 inches causes a distraction of attention, and the inspection contents vary by humans. A very skilled person can discriminate a slip width of about 5 μm and a length of about 1 mm, but cannot inspect continuously for one hour.
In addition, it takes a long time to observe and inspect the periphery (5 to 10 mm) of an 8-inch silicon wafer using a differential interference microscope. From the viewpoint of performance, a differential interference microscope can be used to inspect a slip having a width of about 1 μm at a high magnification, but it is very difficult to obtain the total length.
Similarly, X-ray topography takes about 3 hours for one measurement. This is because an operation of irradiating soft X-rays from the lower part of the silicon wafer and baking the transmitted light on the dry plate of the photograph is necessary. Also, by using X-rays, only a very limited number of people can use it. Furthermore, this apparatus is very expensive, and the area occupied by the apparatus is as large as about 6 tatami mats and lacks practicality. Furthermore, in the case of X-ray topography, since inspection is performed by transmission, the surface layer, the inner layer, and the back layer are all photographed, so that it is impossible to extract only the surface layer.
[0005]
The present invention has been made in view of such problems, and it is an object of the present invention to provide an inspection method and an inspection apparatus that can easily and accurately perform a defect inspection by distinguishing a surface layer, an inner layer, and a back layer. And
[0006]
[Means for Solving the Problems]
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, reflection is only from the surface layer of the silicon wafer, and beyond that range, transmitted light appears when it exceeds about 1000 nm. The present invention has been made based on such knowledge.
[0007]
First, the inspection method according to claim 1 divides the light beam from the wavelength tunable laser into a front surface irradiation light beam and a back surface irradiation light beam, changes the wavelength, and changes the surface irradiation light beam to the first condensing projection lens. To the surface of the semiconductor wafer via the second condensing projection lens, and to the back surface of the semiconductor wafer via the second condensing projection lens. While the light from the semiconductor wafer is detected by a photodiode located at a position slightly away from the reflection component, the light is above the surface of the semiconductor wafer and on an extension line of the optical axis of the second condenser projection lens. by detecting the light from the semiconductor wafer by existing photomultiplier or image intensifier, the slip defects of the semiconductor wafer Characterized in that it was to be out. Here, as the wavelength tunable laser used for defect inspection of the silicon wafer, it is preferable to use a laser that can be continuously changed from a wavelength of 700 nm to 1100 nm.
According to this inspection method, the detection result of the reflected light near the surface and the surface of the semiconductor wafer by the surface irradiation light beam with the wavelength changed, and the detection of the transmitted light of the semiconductor wafer by the back surface irradiation light beam with the wavelength changed From the results, it is possible to easily detect the surface defect of the semiconductor wafer caused by the slip, the position and size of the internal defect, and the like.
[0008]
The inspection apparatus according to claim 2 is an inspection apparatus for a semiconductor wafer for detecting slip defects, and a wavelength tunable laser and a light beam from the wavelength tunable laser through a first condensing projection lens. A front surface irradiation optical system for irradiating the front surface, a back surface irradiation optical system for irradiating the rear surface of the semiconductor wafer with a light flux from the wavelength tunable laser through a second condenser projection lens, and a position on the front surface side of the semiconductor wafer. And a photodiode that detects light from the semiconductor wafer present at a position slightly away from the specular reflection component of the surface irradiation light beam, and an optical axis extension of the second condenser lens above the surface of the semiconductor wafer. And a photomultiplier tube or an image intensifier for detecting light from the semiconductor wafer existing on the line.
According to this inspection apparatus, the detection result of the reflected light near and on the surface of the semiconductor wafer by the surface irradiation light beam with the wavelength changed, and the detection of the transmitted light of the semiconductor wafer by the back surface irradiation light beam with the wavelength changed. From the result, it is possible to easily detect the surface defect of the semiconductor wafer caused by the slip, the planar position, depth, size, etc. of the internal defect.
[0009]
The inspection apparatus according to claim 3 is the inspection apparatus according to claim 2, wherein a beam shape is formed at a focusing point on the front and back surfaces of the semiconductor wafer by the light beam shaping lens system provided in the front surface irradiation optical system and the back surface irradiation optical system. Is characterized by having a perfect circle shape. According to this inspection apparatus, since the beam profile shows a complete Gaussian distribution in all directions, the detection sensitivity of slip defects can be improved.
[0010]
The inspection device according to claim 4 is the inspection device according to claim 2 or 3, wherein the variable telescope is an object-side telecentric lens and a variable spatial filter installed between the object-side telecentric lens and the imaging surface. A knife edge, and irradiates the surface of the semiconductor wafer with a light beam from a metal halide lamp as a parallel light beam by a collimating lens, and blocks a minute angle component of the reflected light beam from the semiconductor wafer with the variable circular knife edge. It is characterized by being configured.
According to this inspection apparatus, if there is a defect on the surface of the semiconductor wafer, the angle component of the reflection component from the defect is blocked, so that the contrast between the defect and the background can be improved.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
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, 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 is like that. Further, in this inspection apparatus, the 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.
[0012]
(Irradiation system)
The semiconductor laser 1 in this case is not particularly limited, but a semiconductor laser capable of changing the wavelength in the range of 700 nm to 1100 nm is used. If the wavelength can be changed within this range, it is sufficient for defect inspection of silicon wafers.
[0013]
Further, the half mirror 3 is used to divide the light beam 2 into a front surface light beam and a back surface light beam.
[0014]
Further, the surface irradiation optical system 4 for applying the surface irradiation light beam to the surface of the semiconductor wafer W includes a light beam shaping lens system 5, a polarizing plate 6, a λ / 2 wavelength plate 7, and a condensing projection lens 8.
[0015]
What is important in the surface irradiation optical system 4 is that a perfect circular shape is created as a shape at a focusing point, and a complete Gaussian distribution is created as a beam profile. In addition, this must be achieved in the entire wavelength range of 700 nm to 1100 nm. For this reason, 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 an ellipse just before irradiation, but it can be a perfect circle at the focusing point, and the beam profile also shows a perfect Gaussian distribution in all directions.
The polarizing plate 6 functions to decompose the surface-illuminated 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 within a plane orthogonal to the traveling direction thereof. The λ / 2 wave plate 7 functions to give a phase difference of λ / 2 to two linearly polarized light that vibrate in a direction perpendicular to each other.
The condensing projection lens 8 is for focusing the light beam emitted from the λ / 2 wavelength plate 7 and projecting it on the surface of the semiconductor wafer W.
[0016]
On the other hand, the back side illumination optical system 9 for applying the back side illumination light beam to the surface of the semiconductor wafer W is composed of a fiber 10, an illuminance distribution correction optical system 11, an optical molding lens system 12, a total reflection mirror 13, and a condensing projection lens 14. ing.
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 for creating a perfect circular shape as a shape at a focusing point and for creating a complete 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 it on the back surface of the semiconductor wafer W.
[0017]
(Detection optics)
Next, a detection optical system in this inspection apparatus will be described.
This detection optical system includes a first detection optical system 30 that detects light from the semiconductor wafer W by the photomultiplier tube 31 and a second detection optical system 40 that detects light from the semiconductor wafer W by the photodiode 41. It consists of and.
[0018]
The photomultiplier tube 31 of the first detection optical system 30 exists on the semiconductor wafer W and on the extension line of the optical axis of the condensing projection lens 14, and collects light from the semiconductor wafer W through the condensing lens 32. It is supposed to detect through. The first detection optical system 30 detects the reflection / transmission scattering 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.
[0019]
The photodiode 41 of the second detection optical system 40 is located at a position slightly away from the regular reflection component of the light from the condensing projection lens 8 so as to detect the light from the semiconductor wafer W via the condensing lens 42. It has become.
[0020]
(Image optics)
This image optical system includes an illumination system 20 and an image detection system 50. The illumination system 20 is for applying 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, a shutter 25, and a half mirror 26.
[0021]
Among them, the pinhole 22 is for making 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 makes the light beam 3 parallel. The shutter 25 is for blocking the light from the metal halide lamp 21, and the half mirror 26 is for directing the light beam 3 toward the semiconductor wafer W side.
[0022]
The image detection system 50 is configured to include a half mirror 52 for branching light from the semiconductor wafer W toward the photomultiplier tube 31. After the light branched by the half mirror 52 is reflected by the total reflection mirror 53, a space is formed. It is detected by the CCD 51 through a telecentric optical system 54 with a built-in filter.
[0023]
This image optical system is for judging whether or not slip has appeared on the surface layer. As a feature, 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 formed as a grayscale image corresponding to a minute angle component of the surface. It is.
That is, the telecentric optical system 54 includes a complete object side telecentric lens and a variable circular knife edge that is a variable spatial filter. Then, a completely parallel light beam is used as the irradiation light beam, and a minute angle component of the reflected light beam is blocked by the variable circular knife edge. According to the telecentric optical system 54, if there is a slip on the surface of the silicon wafer, the angle component of the reflected component from the slip is cut off, so that the contrast between the slip and the background can be obtained.
Further, by converting the gray level of the image captured by the CCD 51 into multiple gradations and repeating the calculus, it is possible to analyze and detect the slip level difference in real time with a resolution of about 100 angstroms.
[0024]
Further, a metal halide lamp 21 is used as a light source used for the image optical system. Since this has a bright line spectrum at a wavelength of 436 nm, the collimator lens 24 irradiates the surface of the semiconductor wafer W as a parallel light beam using the wavelength. By using this wavelength, it is possible to reliably detect the surface layer.
[0025]
When this image optical system is used, the light beam of the wavelength tunable laser 1 is blocked by a shutter (not shown).
[0026]
(Inspection stage system)
The stage holding the silicon wafer needs to 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 the wavelength range of about 400 to 1300 nm, and a quartz glass material is used as the stage material. In order to make it less susceptible to particles and the like, the contact area between the silicon wafer and the stage needs to be about 2%. Since the rotational accuracy (such as surface runout) needs to be 0.2 μm or less, it is desirable to use a rotating means such as an air bearing or a rotary laser encoder.
[0027]
(Inspection method)
Next, an inspection method using this optical inspection apparatus will be described.
[0028]
When inspecting, for example, a silicon wafer with this optical inspection apparatus, first, the light source wavelength of the wavelength laser is classified into three groups based on the spectral characteristics of the silicon wafer. That is, the wavelength range is classified into 700 to 800 nm (wavelength first group), 800 to 1000 nm (wavelength second group), and 1000 to 1100 nm (wavelength third 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 slippage of the front surface layer / inner layer / back surface layer.
In the inspection, the silicon wafer is taken out from the cassette in which the silicon wafer is stored and aligned by the robot, and the silicon wafer is automatically set on the quartz transparent stage. Then, the silicon wafer is rotated with the crystal orientation reference (notch) as the rotation origin, and is detected by moving inward from the outermost periphery for each focused beam point diameter. The representative values of the three wavelength groups are determined by the difference in crystal orientation of the silicon wafer. (The optimum wavelength is found to be varied in 1 nm steps from 700 to 1100 nm.)
[0029]
Next, a specific inspection method will be described. In the first wavelength group, since there is no transmission of the irradiation light beam from the back surface of the silicon wafer, it can be ignored. Therefore, all of the intensity changes of the detection light of the photomultiplier tube 31 and the photodiode 41 are changes in the intensity of light from the surface layer (although the surface layer is actually several μm from the surface to the inner layer). is there.
When the intensity of light detected by the photomultiplier tube 31 or the photodiode 41 changes, the shutter 23 is opened at that time, and the image near the change is captured by the CCD 51, and image analysis is performed in real time. . 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 as a result of image analysis that slip has occurred in the surface layer. On the other hand, when an intensity change is detected only in the photomultiplier tube 31 (such as when the slip defect is very small), the presence of slip may not always be confirmed in the image analysis. However, even in the second wavelength group, when a change is detected in the portion by the photodiode 41, it is determined that slip exists at the boundary between the inner layer and the surface layer. (If a silicon wafer is analyzed in detail, a rough correlation between the wavelength and the amount of light trapped can be obtained, so the generation depth can be roughly quantified.)
[0030]
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, the change can be detected again in the vicinity of the wavelength of 1000 nm). Further, when a change is detected for the first time by the photodiode 41 in this group, there is surely slip 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 occurs in the photomultiplier tube 31. When the change appears for the first time here, it means that slip occurs only in the back layer, but this probability is small. Mostly it will be slip of the inner layer. That is, since it is said that the occurrence of slip has a deep relationship with the internal stress, it is expected that the stress remains around the slip generated inside. Since the transmission scattering intensity change is emphasized due to the birefringence around the slip due to the stress, it is expected to be larger than the change amount detection in the second wavelength group. However, if it is the same as the detection position in the second wavelength group, the result in the second group is judged. What is important in the third wavelength group is that the second wavelength group naturally absorbs light, so that it is possible to detect minute slips, but it is possible to reliably detect slip in the inner layer in the third group. it can. As an additional effect, the stress distribution 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 or not slips appear on an important surface layer but also the numerical value of the length.
[0031]
As mentioned above, although the Example of the invention made | formed by this inventor was demonstrated, this invention is not limited to this Example, A various deformation | transformation is possible in the range which does not deviate from the summary.
[0032]
For example, in the above-described embodiment, the inspection of the silicon wafer is mainly described. However, in the case of the inspection of the compound semiconductor wafer, the inspection of the thin plate such as the liquid crystal glass substrate and the DVD (digital video disk) substrate is general. Applicable.
[0033]
In the above embodiment, the case of the slip inspection has been mainly described, but the present invention can also be applied to the case of inspecting the internal stress distribution of the thin plate.
[0034]
【The invention's effect】
The effect of the representative one of the present invention will be described. The detection result of the reflected light near the surface of the semiconductor wafer by the surface irradiation light beam with the wavelength changed, and the semiconductor by the back surface irradiation light beam with the wavelength changed. From the detection result of the transmitted light of the wafer, it is possible to easily detect the surface defect and the position and size of the internal defect of the semiconductor wafer.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an inspection apparatus according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Wavelength variable laser 4 Front surface irradiation system 9 Back surface irradiation system 30 1st detection system 40 2nd detection system

Claims (4)

The light beam from the wavelength tunable laser is divided into the front surface irradiation light beam and the back surface irradiation light beam, the wavelength is changed, and the front surface irradiation light beam is applied to the surface of the semiconductor wafer via the first condensing projection lens, A back-illuminated light beam is applied to the back surface of the semiconductor wafer via a second condensing projection lens, and is present at a position on the front surface side of the semiconductor wafer and at a position slightly away from the regular reflection component of the front-surface irradiated light beam. While detecting light from the semiconductor wafer by a diode, a photomultiplier tube or image intensifier exists above the surface of the semiconductor wafer and on the extension of the optical axis of the second condensing projection lens by detecting the light from the semiconductor wafer by, it is characterized in that to detect the slip defects of the semiconductor wafer A method of inspecting a semiconductor wafer. A semiconductor wafer inspection apparatus for detecting slip defects , comprising: a wavelength tunable laser; and a surface irradiation optical system that irradiates the surface of the semiconductor wafer with a light beam from the wavelength tunable laser via a first condensing projection lens; A backside illumination optical system for irradiating the backside surface of the semiconductor wafer with a light beam from the wavelength tunable laser via a second condensing projection lens; A photodiode for detecting light from the semiconductor wafer present at a position slightly away from the semiconductor wafer, and from the semiconductor wafer present above the surface of the semiconductor wafer and on an extension of the optical axis of the second condenser projection lens. A semiconductor wafer inspection apparatus comprising a photomultiplier tube or an image intensifier for detecting the light of.   3. The semiconductor wafer according to claim 2, wherein the beam shape is made into a perfect circle at the focusing points on the front and back sides of the semiconductor wafer by the light beam shaping lens system provided in the front surface irradiation optical system and the back surface irradiation optical system. Inspection equipment.   The semiconductor includes: an object-side telecentric lens; and a variable circular knife edge that is a variable spatial filter disposed between the object-side telecentric lens and the imaging surface, and the light beam from the metal halide lamp is converted into a parallel beam by a collimator lens. 4. The semiconductor wafer inspection according to claim 2, wherein the wafer surface is irradiated and a minute angle component of a reflected light beam from the semiconductor wafer is blocked by the variable circular knife edge. apparatus.

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