JPH095251A - Defect-inspecting equipment - Google Patents

Abstract

PURPOSE: To obtain a defect-inspecting equipment which can detect the respective densities of an oxygen deposit, a line defect and a stacking fault separately by one measurement and also has high measuring accuracy. CONSTITUTION: This equipment is constructed of a laser light emitting device 12, three polarizers 16a, 16b and 16c, three light-receiving lenses 14a, 14b and 14c, three TV cameras 15a, 15b and 15c and three image processing devices 17a, 17b and 17c. The polarizers 16a, 16b and 16c, the light-receiving lenses 14a, 14b and 14c and the TV cameras 15a, 15b and 15c are disposed respectively in three directions corresponding to scattered light (polarized light) caused by an oxygen deposit, a line defect and a stacking fault in an Si wafer 11 being a sample.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a defect inspection apparatus, and more particularly to a defect inspection apparatus capable of inspecting the density of oxygen precipitates, dislocations and stacking faults existing in crystals such as Si.

[0002]

2. Description of the Related Art In most cases, Si crystals used as substrates for semiconductor devices such as LSI are manufactured by a single crystal manufacturing method called Czochralski method (hereinafter referred to as CZ method). Therefore, first, a method for producing a single crystal by the CZ method will be described.

FIG. 2 is a sectional view schematically showing a single crystal growth apparatus used for the CZ method, and 21 in the drawing shows a crucible.

This crucible 21 is composed of a bottomed cylindrical quartz inner layer holding container 21a and a bottomed cylindrical outer layer holding container 21b made of graphite and also fitted to the outside of the inner layer holding container 21a. The crucible 21 is supported by a support shaft 28 that rotates at a predetermined speed in the direction of the arrow in the drawing. A resistance heating type heater 22 is provided outside the crucible 21.
However, heat insulating cylinders 27 are arranged concentrically outside the heater 22, and the heater 22 is provided inside the crucible 21.
The melt 23 of the crystal raw material melted by the above is filled. A pulling shaft 24 made of a pulling rod, a wire, or the like is hung on the center axis of the crucible 21. When manufacturing a single crystal, the pulling shaft 24 is attached to the tip of the pulling shaft 24 via a seed chuck 24a. The obtained seed crystal 25 is brought into contact with the surface of the melt 23, and the pulling shaft 24 is pulled up while rotating at the same speed as the supporting shaft 28 in the same direction or in the opposite direction at a predetermined speed. By such an operation, the melt 23 is solidified and crystallized to grow the single crystal 26.

In the Si single crystal produced as described above, oxygen atoms mixed in from the quartz inner layer holding vessel 21a during pulling up are about 10 × 10 ¹⁷ atoms / cm 3.
There are a large amount of ³ and therefore oxygen atoms existing in the interstitial space are usually in a supersaturated state.

Oxygen atoms contained in this supersaturation do not form a solid solution in the Si single crystal, and form oxygen precipitates (SiO ₂ ) in the heat treatment process when manufacturing LSI or the like.

When this oxygen precipitate is formed, it takes various forms depending on the conditions of the heat treatment. That is, when the heat treatment temperature is about 650 to 850 ° C., only oxygen precipitates are deposited without dislocation and stacking fault, and the heat treatment temperature is 85.
When the temperature is about 0 to 1000 ° C, oxygen precipitates accompanied by dislocations are formed, and when the heat treatment temperature is about 1000 to 1150 ° C, oxygen precipitates accompanied by stacking faults are formed.

S generated by such supersaturated oxygen
When a defect in the i-single crystal exists deep in the wafer surface, that is, deeper than the active region of the device, the dislocations generated in the wafer are fixed, the strength of the wafer is increased, and the wafer This has the advantage of growing oxygen precipitates in the heat treatment process and generating strain around them, trapping impurities that enter the surface region of the wafer in the device manufacturing process, and preventing contamination of the active region of the device.

However, when defects such as dislocations and stacking faults occur in a so-called device active region within a few μm from the wafer surface, it causes an increase in leak current and deteriorates device characteristics. .
In particular, when thermally oxidizing a wafer, stacking faults (oxidation-induced stacking faults (OS) that grow due to agglomeration of interstitial Si atoms released from an oxide film growing from the wafer surface during thermal oxidation.
F)) is generated on the wafer surface, which is a problem.

Therefore, determining whether or not the oxygen precipitates are accompanied by dislocations and stacking faults and measuring the density of these produce a wafer used for a high performance semiconductor device. In this case, it is a very important issue, and various methods have been proposed.

As one method for detecting the density of oxygen precipitates, dislocations and stacking faults in a Si wafer, there is a method of measuring the above-mentioned defects using a transmission electron microscope.

However, in the above method, the field of view to be observed is narrow and shallow (depth: about 0.3 μm, vertical and horizontal: about 100 μm).
Therefore, the measurement results are apt to vary, and the measurement method is not sufficiently reliable.

Therefore, in recent years, a defect measuring method called a laser tomography method (or infrared tomography method) using a laser beam has been widely used.

The laser tomography method is a method of irradiating a sample with laser light, receiving 90 ° scattered light generated by a defect or the like, and measuring the density of the defect from the shadow thereof.

FIG. 3 is a conceptual diagram schematically showing a defect detecting device by the laser tomography method.
Is a laser light irradiation device of a YAG laser.

A laser beam 13 (wavelength: 1.06 μm) having a beam diameter of several μm is emitted from the laser beam irradiation device 12 as S
The i-wafer 11 is irradiated with scattered light 39 generated by various defects 38 existing in the Si wafer 11, and the scattered light 39 is generated.
6 and 37, the light is received by a light receiving lens 34 provided in a direction that is at a right angle (90 °) to the irradiation direction of the laser beam 13 ([001] direction of the Si wafer), and magnified. The polarizing element 36 allows only polarized light oriented in a direction perpendicular to the plane formed by the laser light 13 and the scattered light 39 (V direction) to pass, and the polarizing element 37 is parallel to the direction (H direction).
Only polarized light directed to In this way, the polarizing element 3
6, or after passing only polarized light in a specific direction through the polarizing element 37, this polarized light is received by the light receiving lens 34, enlarged, and imaged by the infrared television camera 35. The density of the defects 38 is measured by analyzing the shadow of the captured image with the image processing device 40.

At this time, the direction in which the scattered light 39 is received is changed by rotating the Si wafer 11 while keeping the positional relationship between the irradiation direction of the laser beam 13 and the lens 34, and V
By combining with the polarization element 36 that transmits only the polarized light in the directional direction or the polarization element 37 that transmits only the polarized light in the H direction, only the scattered light 39 in the specific polarization direction (electric field direction) can be detected.

As shown in Table 1 below, when the defect is an oxygen precipitate, the defect is a dislocation, and the defect is a stacking fault, the polarization direction of the scattered light and the kind of polarization ( Since V and H) are different, oxygen precipitates, dislocations, and stacking faults can be detected separately by the above method. In the case of expressing the direction of the crystal, usually, when the coordinate is negative, a line is drawn over the number, but in the online application, such an expression method cannot be adopted. Therefore, in the specification and tables of the present invention, a line is drawn below the numeral.

[0019]

[Table 1]

According to the above method, wide area observation is possible (depth: about 7 μm, vertical and horizontal: 200 μm) and 50 n
Since it is possible to detect a very small defect 38 of m or more, it is possible to measure the density of the defect quite accurately.

[0021]

However, when the density of defects 38 (oxygen precipitates, dislocations and stacking faults) is measured by the laser tomography method, as shown in Table 1 above, at least three directions are required. Therefore, there is a problem that a long measurement time is required if such a measurement is attempted.

In addition, the intensity of the laser beam to be applied may fluctuate during the sequential measurement in the three directions, and the intensity of the scattered light 39 also changes accordingly.
There was also a problem that the accuracy of the measurement results was not very high.

The present invention has been made in view of the above problems, and the density of oxygen precipitates, dislocations and stacking faults can be detected separately in one measurement, and the defect inspection is highly accurate. The purpose is to provide a device.

[0024]

In order to achieve the above object, a defect inspection apparatus according to the present invention is a light beam irradiating means for irradiating a sample with a light beam, and the light beam irradiates a defect in the sample. Of the 90 ° scattered light generated by
Polarization selecting means for passing only polarized light in a specific direction, light receiving means for enlarging and receiving polarized light in a specific direction that has passed through the polarization selecting means, imaging means for imaging a light-receiving image received by the light receiving means, and the imaging In a defect inspection apparatus equipped with an image processing means for measuring the density of defects by image-processing the electric signal from the means, three types of scattered light generated by oxygen precipitates, dislocations, or stacking faults in the sample are detected. The polarization selecting means, the light receiving means, and the imaging means are arranged in each direction.

In the defect inspection apparatus according to the present invention, as the light beam irradiation means, for example, an irradiation apparatus using a laser beam as a light source which has been conventionally used can be mentioned. Among them, in terms of wavelength, beam diameter and the like. , For example Si
It is preferable to use YAG laser light for _x GaAs and Ar laser light for Al ₂ O ₃ depending on the composition of the sample.

As the polarization selecting means, the light receiving means, the image pickup means, and the image processing means, it is possible to use objects and devices conventionally used for laser tomography. It is possible to use an element, a lens for detecting infrared rays as a light receiving means, a television camera for infrared rays as an imaging means, and an image processor as an image processing means. Further, the lens and the television camera may be integrated.

[0027]

As an example of the defect inspection apparatus according to the present invention, the direction of irradiating the sample with the laser beam using the light beam irradiating means is the [001] direction of the Si crystal. the light receiving lens, perpendicular to the irradiation direction of the laser beam, and an angle of each of 45 ° around the sample, the Si crystal [110], [1 10], [01
[0] and are used to detect scattered light (polarized light) generated by oxygen precipitates, dislocations, and stacking faults, respectively.

A polarizing element is disposed as a polarized light selecting means between the light receiving lens and the sample so that only polarized light in a specific direction is transmitted. In the [110] direction, the V direction and [ 1 Only the polarized light in the H direction is transmitted in the [10] direction, and only the polarized light in the H direction is transmitted in the [010] direction.

As shown in Table 1 above, it has been revealed by the analysis of Moriya that oxygen precipitates, dislocations, and stacking faults can be detected by disposing the lens in the above-mentioned direction ( Proceeding of International Con
conference on the Science and Technology of Defect Con
trol in Semiconductors 1989 pp. 1-6).

That is, according to the above analysis, when the defect is an oxygen precipitate and the light-receiving lens is installed in the [110] direction, the scattered light is polarized in the V direction, and this polarization can be detected. Thus, the density of oxygen precipitates can be measured. When the defect is a dislocation, the length of the Burgers vector of the complete dislocation in the Si single crystal is (√2) a / 2, and the direction thereof is <110>. Here, a is the lattice constant of Si, (√2)
Represents the square root of 2. For √, the same applies hereinafter. This scattering vector is maximum when it is perpendicular to the Burgers vector, and the scattered light is polarized in the H direction. Irradiation direction of the laser beam is [001] direction, the light receiving lens are arranged in [1 10] direction, the direction of the scattering vector in this case is [1 11]. Vectors equivalent to the Burgers vector are [110], [1 1 0], [101], [ 1
There are 6 dislocations of [01], [011], and [01 1 ], and among them, three dislocations of [110], [101], and [01 1 ] can be detected by the light receiving lens. Therefore, S
The dislocation density in the i crystal can be obtained by doubling the result obtained by this measurement.

Further, when the defect is a stacking fault, the Burgers vector of the partial dislocation around the stacking fault in the Si single crystal has a length of a / 3 (√3) and its direction is <111>. is there. The scattering vector becomes maximum when it is perpendicular to the Burgers vector, and the scattered light is polarized in the H direction. The direction of laser light irradiation is [0
Since the light receiving lens is arranged in the [010] direction, the direction of the scattering vector at this time is [0]
11]. Vectors equivalent to the Burgers vector are [111], [ 1 11], [1 1 1], [11 1 ]
The stacking faults in which the Burgers vectors of partial dislocations are [1 1 1] and [11 1 ] can be detected. Therefore, the density of stacking faults in the Si crystal can be obtained by doubling the result obtained by this measurement.

As described above, according to the defect inspection apparatus of the present invention, the polarization selecting means, the light receiving means, and the light receiving means are respectively provided in three directions corresponding to scattered light generated by oxygen precipitates, dislocations, or stacking faults in the sample. Since the image pickup means is provided, the density of oxygen precipitates, dislocations, and stacking faults in the Si wafer can be detected separately in one measurement, and the intensity of the laser beam irradiated during measurement can be increased. The measurement accuracy is high.

[0033]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the defect inspection apparatus according to the present invention will be described below with reference to the drawings.

FIG. 1 is a conceptual diagram schematically showing the defect inspection apparatus according to the embodiment.

The defect inspection apparatus according to the embodiment includes a laser light irradiation device 12 of a YAG laser used as a light beam irradiation means, and three polarization elements 16a and 16b as polarization selection means for passing only polarized light in a specific direction. , 16c,
Three light-receiving lenses 14a, 14b, 14c as light-receiving means for enlarging and receiving the polarized light, and three television cameras 15a, 15b, 15c as image-taking means for picking up a light-receiving image received by the light-receiving means, And three image processing devices 17 as image processing means for measuring the density of the defects by performing image processing on the electric signal from the imaging means.
It is composed of a, 17b and 17c. Then, when the laser light 13 is applied to the Si single crystal forming the Si wafer 11 in the [001] direction, scattered light generated due to oxygen precipitates, dislocations, and stacking faults in the sample Si wafer 11 Polarizing elements 16a, 16b, 16c and the light-receiving lens 14 are respectively arranged in three directions corresponding to (polarized light).
a, 14b, 14c, TV cameras 15a, 15b, 1
5c is provided.

[0036] Specifically, the direction of the lens 14a relative to the Si wafer 11 (Si single crystals) is [110] direction, the direction of the light receiving lens 14b is the direction of the [1 10], the light receiving lens 14c The direction is the [010] direction, and the directions of these light receiving lenses 14a ...
It makes an angle of 5 °. Further, the polarizing element 16a is configured to pass only polarized light in the V direction, the polarizing element 16b in the H direction, and the polarizing element 16c is configured to pass in the H direction, whereby oxygen precipitates, dislocations, and stacking faults in the Si wafer 11 are transmitted. The scattered light (polarized light) generated as a result of can be detected separately.

When the defects 18 in the Si wafer 11 are measured using the defect inspection apparatus having the above-described structure, first, as in the conventional case, the laser beam irradiation apparatus 12 is used.
Laser beam 13 with a beam diameter of several μm (wavelength: 1.0
6 μm) is applied to the Si wafer 11.

At this time, as described above, in the direction perpendicular to the irradiation direction of the laser beam 13 (90 °),
And each should make an angle of 45 ° with each other [11
0], [1 10], and [010] direction are receiving lens 14a · · · it is arranged, and also the light receiving lens 14a · ·
Between the Si wafer 11 and the
a is provided.

Therefore, by the irradiation of the laser beam 13 described above, the scattered light (polarized light) 19a, 19b, 19c caused by oxygen precipitates, dislocations, and stacking faults is received.
4a ... Can receive and expand the light.

Next, the scattered light (polarized light) 19a ... Received and expanded by the light receiving lenses 14a ... Is received and imaged by the television camera 15a. Each image is processed by the image processing device 17a.
The density of three types of defects 18 of oxygen precipitates, dislocations, and stacking faults is calculated by performing analysis with.

In this embodiment, the three image processing devices 17a ... Are connected to the respective television cameras 15a ... For image processing, but in another embodiment,
One image processing device may be a device connected to three television cameras 15a. In this case, the signals sent from the three TV cameras 15a ...

Next, the defect 18 in the Si wafer 11 was actually measured using this defect inspection apparatus. At the time of measurement, it is necessary to adjust the optical axis, focus the defect, etc., but even if these are included, the measurement time is 30 minutes. On the other hand, in the case of the conventional defect inspection apparatus shown in FIG. 3, it took about 90 minutes.

First, regarding the measurement result by the defect inspection apparatus according to the embodiment, when the measurement is performed three times at the same place on the same wafer, the measurement result is the same for all three times, and the precipitate density = 5 × 10. ⁹ / cm ³ , dislocation density = 1 × 10 ⁹ / cm
³ , stacking fault density = 2 × 10 ⁶ / cm ³ . On the other hand, when the same measurement was performed in the conventional defect inspection apparatus, the measurement result was as follows: precipitate density = 8 × 10 ⁹ / c
m ³ , 3 × 10 ⁹ / cm ³ , 5 × 10 ⁹ / cm ³ , dislocation density = 1.6 × 10 ⁹ / cm ³ , 0.6 × 10 ⁹ / cm ³
1 × 10 ⁹ / cm ³ , stacking fault density = 3.2 × 10 ⁶
/ Cm ³ , 1.2 × 10 ⁶ / cm ³ , 2 × 10 ⁶ / c
The results were different for m ³ and 3 times. It is considered that the variation of the measurement result by the conventional defect inspection apparatus described above is caused by the variation of the intensity of the laser irradiated during the measurement.

As is clear from this result, the defect inspection apparatus according to the embodiment is provided with the laser beam irradiation device 12, the three polarizing elements 16a, 16b, 16c, and the three light receiving lenses 14.
a, 14b, 14c, three TV cameras 15a, 15
b, 15c, and three image processing devices 17a, 17b,
17c, the polarizing element 1 is provided in each of three directions corresponding to scattered light (polarized light) generated due to oxygen precipitates, dislocations, and stacking faults in the sample Si wafer 11.
6a, 16b, 16c, light receiving lenses 14a, 14b, 1
4c and the television cameras 15a, 15b, and 15c are provided, so that the density of defects 18 (oxygen precipitates, dislocations, and stacking faults) can be measured separately in one measurement, and irradiation during the measurement can be performed. It is also possible to prevent fluctuations in the intensity of the laser light to be emitted. Therefore, three types of defects can be measured in a short time, and a defect inspection apparatus with high measurement accuracy can be provided.

[0045]

As described above in detail, in the defect inspection apparatus according to the present invention, the light beam irradiating means for irradiating the sample with the light beam, the light beam irradiating the defect in the sample Of the generated 90 ° scattered light, polarized light selecting means for passing only polarized light in a specific direction, light receiving means for expanding and receiving polarized light in a specific direction that has passed through the polarized light selecting means,
In a defect inspection apparatus comprising image pickup means for picking up a received light image received by the light receiving means, and image processing means for measuring the density of the defects by image processing an electric signal from the image pickup means, Since the polarization selecting means, the light receiving means, and the imaging means are respectively arranged in three directions corresponding to scattered light generated by oxygen precipitates, dislocations, or stacking faults, the oxygen precipitates can be measured by one measurement. The densities of dislocations and stacking faults can be detected separately, and fluctuations in the intensity of laser light irradiated during measurement can be prevented. Therefore, according to the present invention, it is possible to measure three types of defects in a short time, and it is possible to provide a defect inspection apparatus having high measurement accuracy.

[Brief description of drawings]

FIG. 1 is a conceptual diagram schematically showing a defect inspection apparatus according to an embodiment of the present invention.

FIG. 2 is a sectional view schematically showing a single crystal growth apparatus used for the CZ method.

FIG. 3 is a conceptual diagram schematically showing a conventional defect inspection apparatus using a laser tomography method.

[Explanation of symbols]

 11 Si wafer 12 Laser light irradiation device 14a, 14b, 14 Light receiving lens 15a, 15b, 15c Television camera 16a, 16b, 16c Polarizing element 17a, 17b, 17c Image processing device 19a, 19b, 19c Scattered light

Claims (1)

[Claims] 1. A light beam irradiating means for irradiating a sample with a light beam, and polarization selection for allowing only polarized light in a specific direction to pass among 90 ° scattered light generated by irradiating a defect in the sample with the light beam. Means, a light receiving means for magnifying and receiving the polarized light in a specific direction that has passed through the polarization selecting means, an image pickup means for picking up a received light image received by the light receiving means, and an image processing of an electric signal from the image pickup means. In the defect inspection device equipped with the image processing means for measuring the density of the defects by means of the polarization selection means and the received light in three directions corresponding to scattered light generated by oxygen precipitates, dislocations or stacking faults in the sample, respectively. A defect inspecting apparatus, which is provided with a means and the image pickup means.