JPH09105720A - Material evaluating method using laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a material evaluating method by which the size and the number of crystal defects are evaluated from scattering due to the crystal defects such as inclusions by using laser beams penetrating a certain material. SOLUTION: In the material evaluating method using a laser, laser beams, which are penetrable through a material to be measured, are converged by means of a lens so as to be incident on the material, and then, the size and the number of crystal defects in the material are measured by detecting scattering generated from the crystal defects such as inclusions in the material. In this method, only the scattering generated from the defects, which are positioned within a predetermined distance from a laser focal point, is distinguished from others so as to be taken in as a signal, so that the size and the number of the detects in the material can be measured precisely.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a material evaluation method for evaluating the size and number of crystals by scattering crystal defects such as inclusions using a laser that transmits a certain material.

[0002]

2. Description of the Related Art Defects having a refractive index different from that of the surroundings, for example, defects caused by fine particles such as dust in the air and inclusions in crystals, cause a scattering phenomenon when exposed to light. If the intensity of the scattering can be measured, it becomes possible to detect defects and the fine particles that cause the defects. In recent years, this technique has been used to detect so-called crystal defects such as inclusions present in crystals, and is an effective means for evaluating dislocations in GaAs and oxygen precipitates in silicon. .

Infrared interferometry (Optical Precipitate Profil
er, hereinafter referred to as OPP) is one of them. The infrared interferometry scans the measurement area while making the infrared laser focused on the diameter of about 1 μm by the lens enter from one side of the silicon wafer, and the phase shift of the infrared laser transmitted from the opposite side is taken as the signal intensity. By detecting, the crystal defect existing in an arbitrary region of the silicon wafer is detected. This phase shift represents the intensity of scattering due to the crystal defect, and the intensity of scattering is proportional to the cube of the size of the defect. That is, the signal intensity represents the intensity of scattering, and the defect size can be obtained from the signal intensity.

[0004]

When the intensity of incident light such as parallel rays is constant at any place, the intensity of scattering is theoretically proportional to the cube of the defect size. However, when a laser focused by a lens is used as the incident light, a steep intensity distribution is generated near the laser focus, so that the intensity of scattering does not always reflect the size. In other words, the defect is the maximum position of the laser intensity,
That is, the scattering intensity proportional to the cube of the size is obtained only when it exists at the laser focal point, and when it deviates from the laser focal point, the scattering intensity decreases according to the shift amount. Therefore, when the positional relationship between the defect and the laser focus when measuring the scattering intensity is not clear, there is a problem that the reliability of the measured value is significantly reduced. Also in OPP, which is a method for evaluating crystal defects in a silicon wafer, the signal obtained by measurement did not always reflect the size of the defect for the above reason. Further, as will be described later, in the current OPP, it is impossible to specify the size of the measurement region, and thus it is not possible to obtain an accurate defect density.

An object of the present invention is to provide a method for evaluating a material using a laser, which can eliminate the above-mentioned ambiguity in measurement and determine the exact size and density of defects from the scattering intensity.

[0006]

In order to solve the above-mentioned problems, the present invention separates only the scattering generated from crystal defects having a positional relationship such that the distance from the laser focal point is a certain value or less, from a certain distance or more. The present invention provides a method for evaluating a material that enables accurate size evaluation of defects by capturing as a signal in distinction from scattering from defects at different positions. As a method for that purpose, there is a method in which the maximum value of the scattering intensity is obtained by focusing on the same defect and measuring the scattering while continuously changing the positional relationship between the defect and the laser focus.

When the positional relationship between the defect and the laser focus cannot be clarified by any means, for example, when the moving device of the material can move only in a single direction or two directions perpendicular to each other, a plurality of defects in the measurement region can be detected. Multiple signals are obtained by measurement, a frequency distribution is created by dividing the signal intensity class by a geometrical series, and the contribution of scattering generated from defects distant from the laser focus by a certain distance is calculated to calculate each frequency. It becomes possible to measure accurate size and density without completely clarifying the positional relationship between the defect and the laser focus.

That is, the present invention is constructed as follows for each of the above-mentioned claims. First, the present invention according to claim 1 squeezes a laser capable of transmitting a material to be measured with a lens and makes it enter the material, and detects scattering generated from a defect existing in the material and having a refractive index different from that of the surroundings. In a method of evaluating a material using a laser for measuring the size and number of defects in the material, only the scattering generated from the defect having a positional relationship such that the distance from the laser focus is a certain value or less The method for evaluating a material is characterized in that the accurate size and number of defects in the material are measured by distinguishing and capturing as a signal.

The present invention according to claim 2 is characterized in that a laser capable of transmitting a material to be measured is focused on the material by a lens and incident on the material, and scattering generated from a defect existing in the material and having a refractive index different from that of the surroundings. In a method of evaluating a material using a laser, which detects the size and number of defects in the material by detecting the presence of the laser in the material while continuously changing the focal position of the laser for irradiating the material. A method for evaluating a material, characterized by detecting the scattering from a defect, obtaining the maximum value of the scattering intensity, and incorporating it as a signal to measure the exact size and number of defects in the material. .

Further, in the present invention according to claim 3, a laser capable of transmitting a material to be measured is focused by a lens and made incident on the material, and scattering generated from a defect existing in the material and having a refractive index different from that of the surrounding is present. In a method of evaluating a material using a laser for detecting and measuring the size and density of defects in the material, the material or the laser is moved to move in a measurement area of length Xo × width Yo in the X direction and Y perpendicular thereto. Obtaining a plurality of signals by performing continuous scanning in a direction and capturing the maximum value of the scattering intensity in one of the defects as a signal for the plurality of defects detected in the measurement region, and A step of obtaining a frequency distribution of signal intensities obtained by dividing a class from a plurality of signals by geometric progressions, and further, X direction and Y
The contribution of the signal generated from the crystal defect located at the position Z1 or more away from the laser focus in the Z direction perpendicular to the direction is calculated, and the contribution is subtracted from the frequency of each class, and the obtained frequency is measured. Volume of Xo × Yo ×
It is a method of evaluating a material, characterized by comprising a step of obtaining a defect density by dividing by Z1 × 2.

The present invention according to claim 4 is characterized in that a laser capable of transmitting a material to be measured is focused by a lens and made incident on the material, and scattering generated from a defect existing in the material and having a refractive index different from that of the surrounding is present. In a method for evaluating a material using a laser for detecting and measuring the size and density of defects in the material, the material or the laser is moved to continuously scan in the X direction in the measurement area of the vertical Xo to obtain one. Taking in the maximum value of the scattering intensity in a defect as a signal is performed for a plurality of defects detected in the measurement region, and a step of obtaining a plurality of signals and a class are divided into geometrical series from the obtained plurality of signals. The step of obtaining the frequency distribution of the signal intensity, and further, the defect at a position separated from the laser focus by a distance Y1 or more in the Y direction perpendicular to the X direction and a distance Z1 or more in the Z direction perpendicular to the X and Y directions. Determined by calculating the contribution of the signal generated from, Xo × Y1 × the steps of subtracting it from the frequency of each class, the volume of the measurement region resulting frequency
And a step of obtaining the density of defects by dividing by 2 × Z1 × 2.

Further, in the present invention according to claim 5, a laser capable of transmitting the material to be measured is focused by a lens and made incident on the material, and is generated from a defect existing in the material and having a refractive index different from that of the surroundings. A method for evaluating a material using a laser that detects scattering to measure the size and density of defects in the material is characterized by using an infrared interferometry (OPP) crystal defect evaluation apparatus.

According to the present invention of claim 6,
The material is a silicon wafer.

According to the present invention of claim 7,
The material is a compound semiconductor wafer.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. The laser intensity at a point near the focus is X = Y = when the laser focus is the origin on the three-dimensional coordinates and the relative position of the point is (X, Y, Z).
The maximum change is taken at Z = 0. The scattering intensity of a defect existing at a position (X, Y, Z) relative to the laser focus is uniquely determined by the laser intensity at the position (X, Y, Z) and the size of the defect. Therefore, if the values of X, Y, and Z are always constant, the size of the defect can be uniquely obtained from the scattering intensity.

Therefore, by utilizing the property that the laser intensity becomes maximum at X = Y = Z = 0, for example, the scattering is measured while continuously moving the material in the X direction by a certain distance, and then in the Y direction. When the maximum value of the scattering intensity is taken by focusing on the same defect, the operation of moving by a constant value and continuously moving in the X direction again for measurement is performed while moving by a constant value in each of the Y direction and the Z direction. It becomes the scattering intensity when the position of the defect is X = Y = Z = 0, and it is possible to distinguish the signal from the defect at a certain point of interest and the signal from other defects.

If all of the defects for which such a measurement is performed are carried out with the scattering intensity when X = Y = Z = 0, it is possible to compare the sizes of the defects from the scattering intensity. . In principle, such a method is applicable not only to OPP but also to any apparatus as long as it is an apparatus for evaluating the scattering of crystal defects with a laser passing through a lens.

Such a method is effective when the sample or laser can be moved in any of the X, Y, and Z directions, but in the case of OPP, for example, the vertical and horizontal directions, or the vertical and height directions. Since it can only be moved in two directions, the above method cannot be used. That is, the distance X in the X direction
When the scattering is measured while moving the material by the distance Yo in the o and Y directions and the maximum value is obtained, the defect position is X = Y = 0, but the Z value cannot be specified, so the scattering intensity Cannot uniquely determine the size from

However, assuming that the defects are randomly distributed in the Z direction and the laser intensity in the Z direction near the laser focus is known, it is possible to obtain a plurality of defects by the above method. By creating a special frequency distribution table that divides the classes by geometric series from the multiple signals,
(A) The number of defects located within a certain distance ± Z1 from the laser focus, and (B) ± Z1 from the laser focus.
It is possible to obtain the ratio of the number of defects located at positions separated as described above. Therefore, by removing the signal caused by the above (B) from the frequency distribution, the scattering intensity when the defect exists near the focal region of the laser can be obtained, and the size of the defect can be compared. At this time, Z1 is uniquely determined depending on how the class is divided when the frequency distribution is created. The number of defects obtained is Xo × Yo × Z.
Since it represents the number of defects existing in a region having a volume of 1 × 2, the defect density can be obtained by dividing the number of defects by this volume. Note that Xo is the distance of the measurement region in the X direction, and Yo is the distance of the measurement region in the Y direction.

Here, the procedure of a more specific evaluation method will be described with reference to FIG. The evaluation method to which the present invention is applied is
As shown in the figure, first, based on a plurality of signals obtained by the measurement, a frequency distribution table in which the classes are divided into geometric series is created (S
1). That is, each class n (where n = 1, 2, 3,... ⁾ Is defined as the number N _n ⁽⁰⁾ of signals whose obtained signal strength is larger than the class range _{Sn-1 and equal to} or smaller than Sn. Ask for each). At this time, the range of each class is S _n-1 = S _0.
r ⁿ⁻¹ and S _n = S ₀ · r ⁿ (where r is a common ratio that defines the width of the class and takes an arbitrary value).

Next, the contribution of the laser intensity distribution in the vicinity of the laser focus in the Z direction in which the laser focus cannot be moved is determined for each class n (S2). That is, as shown in the drawing, when the laser intensity distribution near the laser focus is P (Z) = Po × f (Z): (where Po is the laser intensity at the laser focus), f (Z ₁ )
= 1 / r, f (Z ₂ ) = 1 / r ² ,... F (Z _n ) = 1 /
Z ₁ such that r ^n, Z _2, seek ... Z _n.

Next, the operation of subtracting the Z-direction contributions Z ₁ , Z ₂ , ... Z _n for each class obtained from the number of classes for each class when there are n classes (n-1) )
By repeating this, the number of true defects in each class is obtained (S3, S4, S5, S6, S7).

Finally, the number of defects in each class is divided by the volume of the measurement area to obtain its density (S8).

From the above, the sizes of the true defects Sn-1 to Sn
And its density Dn are obtained. Table 1 summarizes this.

[0025]

[Table 1]

In principle, such a method is O if it is an apparatus for evaluating the scattering of crystal defects with a laser passing through a lens.
Not limited to PP, it can be applied to all things.

As described above, the sample is not in two directions,
Even when it can be moved only in one direction, the same method can be applied by changing the calculation formula. Specifically, as shown in FIG. 2, first, based on a plurality of signals obtained by the measurement, a frequency distribution table in which classes are divided by geometric series is created (S11). That is, each class n (where n = 1, 2, 3,... ⁾ Is defined as the number N _n ⁽⁰⁾ of signals whose obtained signal strength is larger than the class range _{Sn-1 and equal to} or smaller than Sn. Ask for each). At this time, the range of each class is S _n-1 = S ₀ · r ^n-1
And S _n = S ₀ · r ⁿ (where r is a common ratio that defines the width of the class and takes an arbitrary value).

Next, the contribution of the laser intensity distribution in the vicinity of the laser focus in the Y and Z directions in which the laser focus cannot be moved is determined for each class n (S1).
2). That is, as shown in the figure, the laser intensity distribution near the laser focus is P (Z) = Po × f (Y, Z):
(However, Po is the laser intensity of the laser focus), f (0, Z ₁ ) = 1 / r, f (0, Z ₂ ) =
1 / r ² , ... f (0, Z _n ) = 1 / r ⁿ , and f (Y
₁ , 0) = 1 / r, f (Y ₂ , 0) = 1 / r ² , ... f
Y ₁ , Y ₂ , ... Y such that (Y _n , 0) = 1 / r ⁿ
_{Find n} , Z ₁ , Z ₂ , ... Z _n .

Next, the Y-direction and Z-direction contributions Y ₁ , Y ₂ , ... Y _n , Z ₁ , Z ₂ , ...
_For each class, subtract n from the number N of that class,
When there are n classes, by repeating (n-1) times,
Find the number of true defects for each class (S13, S1)
4, S15, S16, S17).

Finally, the density is obtained by dividing the number of defects in each class by the volume of the measurement area (S18). From the above, the true defect size and its density can be obtained.

[0031]

Embodiments of the present invention will be described below.

Initial oxygen concentration 10.0 × 10 ¹⁷ atoms
/ Cc p-type 5-inch silicon wafer, which was heat-treated at 1100 ° C. for 4 hours in a nitrogen atmosphere, and heat-treated at 1100 ° C. for 16 hours in a nitrogen atmosphere, were prepared in three types. The crystal defects of the silicon wafer were evaluated by OPP.

The OPP has a device configuration in which the infrared laser has a wavelength of 1.3 μm and a laser intensity of 25 mW.
The diameter of the laser spot is reduced to 1 μm using a lens with a numerical aperture of 0.85.

EXAMPLE 1 As an example using the present invention, the laser focus is set to a thickness of 650.
The depth is set to 300 μm from the surface of the silicon wafer of μm, and the laser scanning is set to 20000 μm in length and 650 μ in width.
The frequency distribution of the signal intensity obtained by taking the maximum value of the signal intensity in a three-dimensional manner in a region of m × 40 μm in height is shown in Table 2 (a silicon wafer heat-treated at 1100 ° C. for 4 hours) and Table 3. A histogram created based on the (heat treated silicon wafer at 1100 ° C. for 16 hours) is shown in FIG. 3 (silicon wafer subjected to heat treatment at 1100 ° C. for 4 hours) and FIG. 4 (heat treated at 1100 ° C. for 16 hours). The applied silicon wafer).

[0035]

[Table 2]

[0036]

[Table 3]

EXAMPLE 2 As another example of using the present invention, the laser focus is set to a thickness of 6
The depth is set to 300 μm from the surface of the silicon wafer of 50 μm, and the laser scanning is performed in parallel with the surface of the wafer in the vertical direction 2.
The frequency distribution obtained by processing the signal intensities of a plurality of defects obtained two-dimensionally in a region of 0000 μm × width 650 μm according to the procedure of the evaluation method shown in FIG. 1 is shown in Table 4 (1100 ° C.). A histogram created based on the silicon wafer that has been subjected to heat treatment for 4 hours) and Table 5 (silicon wafer that has been subjected to heat treatment at 1100 ° C. for 16 hours) is shown in FIG. 5 (silicon subjected to heat treatment at 1100 ° C. for 4 hours). Wafer) and FIG. 6 (silicon wafer subjected to heat treatment at 1100 ° C. for 16 hours). However, in performing the process, S ₀ is 0.1 and r is 10 ^0.1
= 1.259 was used. The reason for using this value is 0.1
This is because V to 1V, 1V to 10V, and 10V to 100V can be divided into 10 sections, which makes it easy to see when logarithmic display is performed. Further, 1 / {1 as f (Z)
+ Using ^{(Z 2/4 2)}} . This equation is obtained as an equation that represents the change in the signal strength in the Z direction actually measured by OPP with the most error. In this case, Z1 is calculated to be about 2 μm.

[0038]

[Table 4]

[0039]

[Table 5]

Comparative Example As an example in which the present invention was not used, the laser focus was set to a depth of 300 μm from the surface of a silicon wafer having a thickness of 650 μm, and laser scanning was performed in parallel with the surface of the wafer at a length of 20000 μm × width of 650 μm. Table 6 (1100) shows the frequency distribution of the signal intensity obtained by two-dimensionally performing the region of
Silicon wafer that has been heat-treated at 4 ° C. for 4 hours) and Table 7
Fig. 7 shows a histogram created based on the silicon wafer (heat treated at 1100 ° C for 16 hours).
(Silicon wafer heat-treated at 1100 ° C for 4 hours)
8 and FIG. 8 (silicon wafer subjected to heat treatment at 1100 ° C. for 16 hours).

[0041]

[Table 6]

[0042]

[Table 7]

As shown in the above Tables 2 to 7 and FIGS. 3 to 8, the results of Examples 1 and 2 using the present invention show that the true defect size distribution is larger than that of the Comparative Example not using the present invention. It was found that it reflects. In addition, the total density of defects obtained in Examples 1 and 2 according to the present invention can be determined by another method, for example, by etching the surface of a silicon wafer and observing the exposed defects with a microscope to determine the size and number of defects. It showed good agreement with the result of the density obtained by the evaluation method.

Although the above-described embodiments are examples in which the present invention is applied to evaluate a silicon wafer by OPP, the present invention is not limited to the silicon wafer and can be suitably used for a compound semiconductor wafer. It is suitable for use in, for example, a wafer made of GaAs, AlGaAs, InP and other compound single crystals, a wafer obtained by laminating these compound semiconductors, and a wafer obtained by crystal growth of a layer of these compound semiconductors on a silicon wafer. be able to.

[0045]

EFFECTS OF THE INVENTION By using the evaluation method of the present invention, the scattering caused by a defect generated when a laser is incident on a material is evaluated, so that the signal intensity reflecting the size of the defect which cannot be evaluated by the conventional method. Since it is possible to obtain the frequency distribution of, it is possible to accurately evaluate the size of the defect. Also,
In the case of measurement by OPP, since the accurate volume of the measurement area can be calculated at the same time, the accurate volume density of defects can be obtained.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a procedure of an evaluation method of the present invention.

FIG. 2 is a flowchart showing a procedure of another evaluation method of the present invention.

FIG. 3 is a drawing showing a histogram created based on the evaluation according to the first embodiment.

FIG. 4 is a drawing showing a histogram created based on the evaluation according to the first embodiment.

5 is a drawing showing a histogram created based on an evaluation according to Example 2. FIG.

FIG. 6 is a drawing showing a histogram created based on an evaluation according to a third embodiment.

FIG. 7 is a drawing showing a histogram created based on an evaluation according to a comparative example.

FIG. 8 is a drawing showing a histogram created based on an evaluation according to a comparative example.

Front page continued (72) Inventor Kazuto Kawakami 3434 Shimada, Hikari City, Yamaguchi Prefecture Nippon Steel Corporation Hikari Steel Works

Claims (7)

[Claims] 1. A laser which is capable of passing through a material to be measured is squeezed by a lens to enter the material, and the laser is present in the material.
In a material evaluation method using a laser that detects the size and number of defects in the material by detecting scattering generated from defects having different refractive indexes from the surroundings, the distance from the laser focus may be a certain value or less. A method for evaluating a material, characterized in that only the scattering generated from a defect having a different positional relationship is taken as a signal so as to be distinguished from others and the accurate size and number of the defect in the material are measured. 2. A laser which is capable of transmitting a material to be measured is focused on the lens and made incident on the material, and is present in the material.
In a method of evaluating a material using a laser, which measures the size and the number of defects in the material by detecting scattering generated from a defect having a refractive index different from that of the surroundings, the focal position of the laser irradiated to the material is continuously measured. By detecting the scattering from the defects existing in the material while changing to, and obtaining the maximum value of the scattering intensity and incorporating it as a signal, the accurate size and number of the defects in the material are measured. A material evaluation method characterized by the above. 3. A laser capable of transmitting a material to be measured is focused by a lens and incident on the material, and scattering generated from a defect existing in the material and having a refractive index different from that of the surrounding is detected to detect a defect in the material. In a method for evaluating a material using a laser for measuring size and density, the material or the laser is moved to continuously scan the measurement area of vertical Xo × horizontal Yo in the X direction and the Y direction perpendicular thereto. The maximum value of the scattering intensity of the one defect is captured as a signal for a plurality of the defects detected in the measurement region, and a plurality of signals are obtained, and a class is calculated from the obtained plurality of signals. The step of obtaining the frequency distribution of the signal intensity separated by, and the contribution of the signal generated from the crystal defect located at the position Z1 or more away from the laser focus in the Z direction perpendicular to the X direction and the Y direction. The determined by calculation, Xo × Yo × Z1 and steps of subtracting it from the frequency of each class, the volume of the measurement region resulting frequency
A method of evaluating a material, characterized by comprising a step of obtaining a defect density by dividing by × 2. 4. A laser capable of transmitting a material to be measured is focused by a lens and made incident on the material, and scattering generated from a defect existing in the material and having a refractive index different from that of the surrounding is detected to detect a defect in the material. In a method of evaluating a material using a laser for measuring size and density, the material or the laser is moved to move X within a measurement area of vertical Xo.
The maximum value of the scattered intensity in one defect is captured as a signal by continuously scanning in the direction for a plurality of defects detected in the measurement region, and a plurality of signals are obtained. A step of obtaining a frequency distribution of signal intensities obtained by dividing a class by a geometrical series from the signal, and further, a distance Y1 or more in the Y direction perpendicular to the X direction and a Z direction perpendicular to the X direction and the Y direction from the laser focus. Z
The step of subtracting it from the frequency of each class by calculating the contribution of the signal generated from a defect located at a distance of 1 or more, and the obtained frequency is Xo × Y1 × 2 × which is the volume of the measurement area.
Determining the density of defects by dividing by Z1 × 2,
A method for evaluating a material, comprising: 5. A defect in the material is detected by squeezing a laser capable of transmitting the material to be measured with a lens and making the laser incident on the material, and detecting the scattering generated from a defect existing in the material and having a refractive index different from that of the surroundings. The method for evaluating a material using a laser for measuring the size and the density of a material according to claim 1, wherein an infrared interferometry crystal defect evaluation apparatus is used.
4. The material evaluation method according to any one of 4 above. 6. The material evaluation method according to claim 1, wherein the material is a silicon wafer. 7. The method of evaluating a material according to claim 1, wherein the material is a compound semiconductor wafer.