JP2023090154A - Detection method for crystal defect of silicon wafer surface - Google Patents

Abstract

To provide a detection method for crystal defect of a silicon wafer surface, the detection method enabling a minute defect of a few tens to be highly accurately and non-destructively detected, and being preferable to inspection of a silicon wafer for a semiconductor device.SOLUTION: A detection method for crystal defect of a silicon wafer surface is provided, comprising the steps of: growing a silicon single crystal formed under a condition of a vacancy dominant type by a Czochralski method; obtaining a silicon wafer W by slicing the silicon single crystal; performing on the silicon wafer W, heat treatment at a temperature of 1250°C or more and 1375°C or less under an oxygen-containing atmosphere, thereby forming an oxide film of 3 nm or more and 40 nm or less on a wafer surface; and inspecting the wafer surface by a laser light scattering particle counter.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for detecting crystal defects on the surface of a silicon wafer, and more particularly to a method for detecting crystal defects on the surface of a silicon wafer suitable for inspecting silicon wafers for semiconductor devices.

BACKGROUND ART Conventionally, single crystal silicon wafers grown by the Czochralski method have been widely used in the manufacture of memory devices and logic devices. In order to improve the quality of devices, it is particularly required to make the surface layer of the silicon wafer defect-free. Silicon wafers grown by the Czochralski method have various types of grown-in defects, such as void defects, related to the behavior of point defects (interstitial silicon, vacancies) during growth. , oxygen precipitates and dislocations are formed.

Conventionally, a technique has been established for minimizing the formation of grown-in defects by controlling the crystal growth rate (pulling rate) v and the temperature gradient G in the crystal axis direction near the solid-liquid interface.
However, the reduction of grown-in defects in silicon wafers is not necessarily sufficient for the recent miniaturization and high-quality integration of semiconductor devices. Therefore, there is a demand for a method of inspecting defects on the surface of a silicon wafer with high sensitivity.

Techniques for inspecting grown-in defects existing on the surface of a silicon wafer with high sensitivity are described in Patent Documents 1 and 2, for example.
In Patent Document 1, the substrate or a predetermined layer is etched by anisotropic etching with a high selectivity for crystal defects contained in the substrate or the predetermined layer, and the conical etching residue caused by the crystal defects is removed from the substrate. Alternatively, a crystal defect evaluation method is disclosed in which a layer surface is exposed and crystal defects are evaluated based on this conical etching residue.

Further, Patent Document 2 discloses a method for detecting defects introduced during growth on the surface of a semiconductor substrate.
Specifically, first, the surface of the semiconductor substrate is exposed to a first reducing atmosphere containing hydrogen at a first temperature of 900° C. to 1250° C. to create a state in which oxides are easily removed from the surface of the semiconductor substrate. do. Then, at a second temperature of 800° C. to 1100° C. lower than the first temperature, the surface of the semiconductor substrate is subjected to a Exposure to a second reducing atmosphere comprising gaseous etchant and hydrogen. This etches the surface of the semiconductor substrate to reveal the locations of growth-introduced defects contained in the semiconductor substrate. Then, the surface of the semiconductor substrate having the defects introduced during growth whose positions are indicated is scanned by an optical detection device.

According to the methods disclosed in Patent Documents 1 and 2, crystal defects existing on the wafer surface can be detected with high sensitivity.
However, since these methods require etching of the surface of the wafer, they are basically destructive inspections and have the problem that they cannot be applied to inspection methods for all manufactured wafers.

To address this problem, Patent Document 3 discloses a method of non-destructively inspecting for void defects (Crystal Originated Particles: COPs). In the method disclosed in Patent Document 3, after a silicon wafer is thermally oxidized to form an oxide film on the wafer surface, the wafer surface is inspected with a laser light scattering particle counter.

Specifically, the surface of a mirror-finished silicon wafer has a large number of concave defects (crystal defects) such as void defects.
When this silicon wafer is heat-treated (for example, at 1000° C.) by the method disclosed in Patent Document 3 to form an oxide film on the wafer surface, the inner wall of the recessed defect is oxidized and the opening diameter of the recessed defect is enlarged. This is because when silicon (Si) is oxidized and becomes an oxide such as _SiO2 , the defect volume expands by about two times and becomes a detectable size as a light scatterer (LPD: Light Point Defect). . Since the laser beam used for defect detection passes through the oxide film, it is not necessary to remove the oxide film.
That is, according to the method disclosed in Patent Document 3, it is possible to detect minute defects with a size of 0.07 μm or more by enlarging the opening diameter of minute concave defects.

JP-A-2000-058509 Special Table 2015-50153 JP-A-2003-142544

As described above, the inspection method disclosed in Patent Document 3 can detect minute defects with an opening diameter of 0.07 μm or more, that is, 70 nm or more.
However, in the advanced logic area in recent years, mass production of nano-sized devices is progressing, and detection of minute defects with a size of several tens of nanometers smaller than 70 nm is required.
In other words, the detection method disclosed in Patent Document 3 has a problem that it is impossible to detect a minute defect of nm size smaller than 70 nm.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for detecting crystal defects on the surface of a silicon wafer, which is suitable for inspecting silicon wafers for semiconductor devices, and which can detect minute defects of several tens of nanometers in a non-destructive manner with high accuracy. .

A method for detecting crystal defects on the surface of a silicon wafer according to the present invention, which has been made to solve the above problems, is a method for detecting crystal defects on the surface of a silicon wafer, wherein the Czochralski method is used under vacancy-dominant conditions. growing the formed silicon single crystal; slicing the silicon single crystal to obtain a silicon wafer; and subjecting the silicon wafer to heat treatment at a temperature of 1250° C. or more and 1375° C. or less in an oxygen-containing atmosphere. forming an oxide film of 3 nm or more and 40 nm or less on the wafer surface; and inspecting the wafer surface with a laser light scattering particle counter.

In the step of growing a silicon single crystal formed under vacancy-dominant conditions by the Czochralski method, the silicon single crystal is desirably doped with 5×10 ¹³ /cm ³ or more of nitrogen.

According to this method, the inner wall of the recessed defect on the wafer surface is oxidized by the oxide film forming process on the silicon wafer, the volume of the defect itself increases, and the surface energy of the recessed inner wall is reduced by rapid high-temperature heating. is minimized, the shape of the concave defect is deformed into a spherical shape, and the opening diameter is greatly expanded. As a result, minute concave defects (void defects, pits) of several tens of nanometers in size, which have been undetectable in the past, can be detected non-destructively and with high accuracy by the laser light scattering particle counter.
In addition, according to the method for detecting crystal defects on the surface of a silicon wafer of the present invention, non-destructive inspection can be performed. wafers with 100 or more LPDs) can be sorted out.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a method for detecting crystal defects on a surface of a silicon wafer, which can detect minute defects of several tens of nanometers in a non-destructive and highly accurate manner, and which is suitable for inspection of silicon wafers for semiconductor devices. .

FIG. 1(a) is a cross-sectional view schematically showing part of a surface layer portion of a silicon wafer to be inspected by the crystal defect inspection method for a silicon wafer surface of the present invention, and FIG. FIG. 1(a) is a cross-sectional view schematically showing a part of a surface layer portion of the silicon wafer after the silicon wafer of FIG. FIG. 1B is a cross-sectional view schematically showing part of the surface layer of the silicon wafer after the silicon wafer has been subjected to oxidation heat treatment at a temperature lower than that in FIG. 1B. FIG. 2 is a cross-sectional view showing an outline of an example of a heat treatment apparatus used to form the silicon wafer of FIG. 1(b). FIG. 3 is a flow showing the steps of the method for detecting crystal defects on the surface of a silicon wafer according to the present invention. FIG. 4 is a graph showing the results of Example (Experiment 1) of the present invention. FIG. 5 is a graph showing the results of Example (Experiment 2) of the present invention.

An embodiment of the method for inspecting crystal defects on the surface of a silicon wafer according to the present invention will be described below with reference to the drawings.
FIG. 1(a) is a cross-sectional view schematically showing a part of the surface layer portion of a silicon wafer W to be inspected by the crystal defect inspection method for the surface of a silicon wafer according to the present invention. The illustrated silicon wafer W is obtained by slicing a silicon single crystal formed in the Nv region, which is a vacancy-dominant neutral region, and mirror-polishing the surface. In the surface layer portion of this silicon wafer W, a plurality of minute concave defects 1 (where X is the opening diameter), which are crystal defects, are present. This concave defect 1 is a void defect, a pit, or the like.

FIG. 1(b) is a cross-sectional view schematically showing part of the surface layer portion of the silicon wafer W1 after the silicon wafer W of FIG. 1(a) has been subjected to a predetermined oxidation heat treatment. As shown in FIG. 1B, an oxide film 2 having a thickness t, specifically 3 nm or more and 40 nm or less, is formed on the wafer surface.
Further, the opening diameter of the recessed defect 1 is expanded from the opening diameter X before the oxidation heat treatment to the opening diameter Z. As shown in FIG. This is because the inner wall of the concave defect 1 is oxidized by heat treatment in an oxygen-containing atmosphere, the volume of the defect itself increases, and the surface energy of the inner wall of the concave is minimized by rapid high-temperature heating. This is because the shape of the defect 1 is deformed into a spherical shape and the opening diameter is greatly enlarged.

When the temperature of the oxidation heat treatment for the silicon wafer W is set to a temperature lower than 1250° C., the surface energy of the inner wall of the concave portion of the concave defect 1 is not minimized, and the concave defect 1 becomes spherical as shown in FIG. 1(c). It does not deform (Patent Document 3 discloses heat treatment at 1000°C). In that case, the defect volume increases due to oxidation, and the opening diameter expands from the opening diameter X before the oxidation heat treatment to the opening diameter Y. Stays smaller than caliber Z).
In the crystal defect inspection method of the present invention, concave defects are detected with a laser light scattering particle counter on the surface of the silicon wafer W1 shown in FIG. 1(b).

FIG. 2 is a cross-sectional view showing an outline of an example of a heat treatment apparatus used to form the silicon wafer W1 of FIG. 1(b). As shown, the heat treatment apparatus 10 includes a chamber (reaction tube) 20 having an atmospheric gas inlet 20a and an atmospheric gas outlet 20b, a plurality of lamps 30 spaced apart above the chamber 20, and a substrate supporting part 40 for supporting the silicon wafer W in the reaction space 25 within 20 . Further, although not shown, there is provided rotating means for rotating the silicon wafer W around its central axis at a predetermined speed.

The substrate support section 40 includes an annular susceptor 40a that supports the outer peripheral portion of the silicon wafer W, and a stage 40b that supports the susceptor 40a. The chamber 20 is made of quartz, for example. The lamp 30 is composed of, for example, a halogen lamp. The susceptor 40a is made of silicon, for example. The stage 40b is made of quartz, for example.

When heat-treating a silicon wafer W using the heat-treating apparatus 10 shown in FIG. A silicon wafer W is supported on the susceptor 40a. Then, an oxygen-containing gas is introduced from the ambient gas inlet 20a, and the substrate surface is irradiated with lamps 30 while the silicon wafer W is rotated by a rotating means (not shown).

The temperature control in the reaction space 25 in the heat treatment apparatus 10 is performed by a plurality of radiation thermometers 50 embedded in the stage 40b of the substrate supporting part 40, which is used to control the substrate surface at multiple points in the substrate radial direction below the silicon wafer W ( For example, the average temperature of 9 points) is measured, and based on the measured temperature, a plurality of halogen lamps 30 are controlled (individual ON-OFF control of each lamp, control of the emission intensity of emitted light, etc.) .

Next, the crystal defect inspection method for the silicon wafer surface according to the present invention will be described along the flow of FIG.
In the crystal defect inspection method according to the present invention, the surface of a silicon wafer sliced from a silicon single crystal ingot grown by, for example, the Czochralski method is subjected to oxidation heat treatment under predetermined manufacturing conditions.

First, a silicon single crystal ingot is grown by the Czochralski method by a well-known method (step S1 in FIG. 3).
Specifically, polycrystalline silicon filled in a quartz crucible is heated to form a silicon melt, a seed crystal is brought into contact with the silicon melt from above the surface of the silicon melt, and the seed crystal and the quartz crucible are rotated while being pulled up. A silicon single crystal ingot is manufactured by expanding the diameter to a diameter of 100 mm and growing a straight body portion. In the growth of this silicon single crystal, it is desirable to dope the single crystal ingot to be pulled with 5×10 ¹³ /cm ^{3 or} more of nitrogen. This is for the following reasons.

That is, when the single crystal is grown, the shape of the void defect is octahedral in the case of the nitrogen-undoped crystal. In the case of an octahedron, even if the shape is changed to a sphere by oxidation heat treatment, the opening diameter does not change greatly. On the other hand, it is known that if nitrogen is doped at a concentration of 5×10 ¹³ /cm ³ or more during crystal growth, the shape of void defects changes into a plate-like shape. In the case of a plate shape, when it is changed into a sphere by an oxidizing heat treatment at 1250° C. or more and 1375° C. or less, the diameter expansion width from the opening diameter in the plate shape is very large, so it is possible to detect with higher sensitivity. .
In pulling the single crystal, the ratio v/G between the pulling speed v and the temperature gradient G at the solid-liquid interface is controlled to obtain a silicon single crystal formed in the Nv region, which is a vacancy-dominant neutral region. Cultivate.

The silicon single crystal ingot thus obtained is processed into silicon wafers by a well-known method (step S2 in FIG. 3).
That is, after slicing a silicon single crystal ingot into wafers with an inner peripheral blade or a wire saw, silicon substrates are manufactured through processing steps such as chamfering of the outer peripheral portion, lapping, etching, and mirror polishing. It should be noted that the processing steps described here are exemplary, and the present invention is not limited to only these processing steps.

Next, heat treatment is performed on the surface of the manufactured silicon substrate under predetermined manufacturing conditions. Specifically, in the heat treatment apparatus 10 as shown in FIG. 2, the manufactured silicon wafer W is placed in the chamber 20 maintained at a desired initial temperature (step S3 in FIG. 3).
After the wafer is placed, an oxygen-containing gas (oxygen gas, water vapor, mixed combustion gas of oxygen gas and hydrogen gas, etc.) is introduced into the chamber 20 from the atmosphere gas inlet 20a at a predetermined flow rate (step S4 in FIG. 3). .

Then, the interior of the chamber 20 is rapidly heated by the halogen lamps 30, and heat treatment is performed at a wafer temperature of 1250° C. or more and 1375° C. or less for a predetermined time (for example, 30 seconds) (step S5).
By this heat treatment, an oxide film 2 having a thickness t (3 nm or more and 40 nm or less) is formed on the surface of the silicon wafer W (the silicon wafer W on which the oxide film 2 is formed is called a silicon wafer W1). By this oxide film forming process, the silicon (Si) on the inner wall of the recessed defect 1 is oxidized to become an oxide such as SiO ₂ , thereby increasing the volume of the defect. In addition, the opening diameter of the recessed defect 1 increases accordingly.
If the oxide film thickness t is less than 3 nm, the opening diameter of the recessed defect 1 is not widened, and an improvement in detection power cannot be expected. On the other hand, when the oxide film thickness t is larger than 40 nm, the surface roughness of the silicon wafer W becomes rough, which is not preferable.

Further, the heat treatment at a temperature of 1250° C. or more and 1375° C. or less works to minimize the surface energy of the inner wall of the recessed defect 1 on the wafer surface, and the recessed defect 1 is easily deformed into a spherical shape. As a result, the opening diameter is expanded to a greater extent. If the heat treatment temperature is lower than 1250° C., it is difficult to deform the shape of the concave defect 1, and if it is higher than 1375° C., the surface of the wafer rises, which is not preferred.
In addition, in order to control a constant gas flow and oxygen concentration in the heat treatment space 25, the atmosphere in the chamber 20 is exhausted at a predetermined flow rate from the exhaust port 20b.

Next, the heat-treated silicon wafer W1 is inspected by a laser light scattering particle counter (not shown) (step S6 in FIG. 3).
As a laser light scattering particle counter, for example, Surfscan SP7 manufactured by KLA-Tencor can be used. This inspection system has a laser penetration depth of about 5 nm and a minimum detectable defect size of 14 nm (nominal value).
The inspection of the silicon wafer W1 by the laser light scattering particle counter irradiates the wafer surface with laser light, detects concave defects, and measures their positions, sizes and numbers.
The oxide film 2 on the surface of the silicon wafer W1 to be inspected may remain. This is because the laser light passes through the oxide film 2 . Alternatively, after removing the oxide film 2, the inspection may be performed using a laser light scattering particle counter.

As described above, according to the embodiment of the present invention, the silicon wafer W is subjected to heat treatment at 1250° C. or more and 1375° C. or less in an oxygen-containing atmosphere, so that the surface of the silicon wafer W has a thickness of 3 nm or more and 40 nm or less. oxide film 2 is formed.
In addition, this oxide film forming process oxidizes the inner wall of the concave defect 1 on the wafer surface, increasing the volume of the defect itself and rapidly heating to a high temperature, thereby minimizing the surface energy of the inner wall of the concave. , the shape of the concave defect 1 is deformed into a spherical shape, and the opening diameter is greatly expanded. As a result, minute concave defects (void defects, pits) of several tens of nanometers in size, which have been undetectable in the past, can be detected non-destructively and with high accuracy by the laser light scattering particle counter.

In addition, according to the method for detecting crystal defects on the surface of a silicon wafer of the present invention, non-destructive inspection can be performed. wafers with 100 or more LPDs) can be sorted out.

In the above-described embodiment, defects are detected by a laser light scattering particle counter in the state where the oxide film 2 is formed on the surface of the silicon wafer W, but the present invention is limited to this form. not to be
For example, after removing the oxide film 2 formed on the surface of the silicon wafer W, the defects may be detected by a laser light scattering particle counter.

In addition, the present invention is not limited to the detection of void defects, but can be widely applied to concave defects such as pits caused by metal impurities and minute scratches caused by processing, and it is possible to detect them with high sensitivity. .

The method for detecting crystal defects on the surface of a silicon wafer according to the present invention will be further described based on examples. In this example, the following experiments were conducted based on the above embodiment.

(Experiment 1)
In Experiment 1, a preferable temperature range for heat treatment of silicon wafers was verified.
First, a single crystal was grown by the Czochralski method. In pulling this single crystal, the ratio v/G between the pulling speed v and the temperature gradient G at the solid-liquid interface was controlled to grow a silicon single crystal formed in the Nv region, which is the neutral region of the vacancy dominant type. .
Then, the grown silicon single crystal was sliced and the surface was polished to obtain a silicon wafer to be inspected.

Next, an oxygen-containing gas was introduced into the chamber using the heat treatment apparatus configured as shown in FIG. 2, and heat treatment was performed for 30 seconds under a plurality of temperature conditions. Specifically, the heating temperature is 1250° C. in Example 1, 1300° C. in Example 2, 1350° C. in Example 3, 1375° C. in Example 4, no heat treatment in Comparative Example 1, and 1200° C. in Comparative Example 2. , 1220° C. in Comparative Example 3, and 1390° C. in Comparative Example 4. At this time, the oxygen content in the introduced gas (diluted with argon gas) and the heat treatment time were adjusted so that the thickness of the oxide film formed on the wafer surface was 5 nm.

After that, the number of concave defects on the wafer surface was detected by a laser light scattering particle counter. Surfscan SP7 from KLA-Tencor was used as a laser light scattering particle counter. Since this inspection apparatus has a laser penetration depth of about 5 nm and a detectable minimum defect size of 14 nm (nominal value), the detected concave defects are defects with an opening diameter of 14 nm or more.

The results of Experiment 1 are shown in the graph of FIG. As shown in the graph of FIG. 4, in Example 1, 572 concave defects were detected. In Example 2, 604 concave defects were detected. In Example 3, 620 concave defects were detected. In Example 4, 569 concave defects were detected. On the other hand, in Comparative Example 1 in which no heat treatment was performed, 20 recessed defects were detected. Further, in Comparative Example 2, 57 concave defects were detected, and in Comparative Example 3, 118 concave defects were detected.
Further, as a result of observing the surface of the silicon wafer inspected in Experiment 1 using a scanning electron microscope (SEM), it was confirmed that the detected defects were void defects.
As a result of Experiment 1, it was confirmed that the preferred temperature range for heat treatment of silicon wafers is 1250° C. or higher and 1375° C. or lower.

(Experiment 2)
In Experiment 2, the preferred thickness range of the oxide film formed on the surface of the silicon wafer was verified. First, a silicon wafer to be inspected was obtained under the same conditions as in Experiment 1.
Next, an oxygen-containing gas was introduced into the chamber using the heat treatment apparatus configured as shown in FIG. 2, and heat treatment was performed at a temperature of 1350° C. for 30 seconds.
At this time, the oxygen content in the introduced gas (diluted with argon gas) and the heat treatment time were adjusted, and the thickness of the oxide film formed on the wafer surface was changed for each wafer as experimental conditions. Specifically, the oxide film thickness was 3 nm in Example 5, 40 nm in Example 6, 0 nm in Comparative Example 5 (no oxide film formed), 1 nm in Comparative Example 6, 45 nm in Comparative Example 7, and 50 nm in Comparative Example 8. and
After that, as in Experiment 1, the number of concave defects on the wafer surface was detected by a laser light scattering particle counter.

The results of Experiment 2 are shown in the graph of FIG. As shown in the graph of FIG. 5, in Example 5, 610 concave defects were detected. In Example 6, 572 concave defects were detected. On the other hand, in Comparative Example 5 in which no oxide film was formed, 18 recessed defects were detected. In Comparative Example 6, 174 concave defects were detected. In Comparative Example 7, the number of detected defects was 1304, which was considered to include the number of false defects detected due to deterioration of roughness. In Comparative Example 8, 2472 defects were detected, and it was considered that this also included the detection of false defects.
As a result of Experiment 2, it was confirmed that the preferable thickness range of the oxide film formed on the surface of the silicon wafer is 3 nm or more and 40 nm or less.

As a result of the above examples, it was confirmed that according to the crystal defect detection method according to the present invention, it is possible to perform an inspection with much higher precision than the conventional one.

1 concave defect (crystal defect)
2 oxide film 10 heat treatment apparatus W silicon wafer W1 silicon wafer (on which oxide film is formed)

Claims (2)

A method for detecting crystal defects on a silicon wafer surface, comprising:
growing a silicon single crystal formed under vacancy-dominant conditions by the Czochralski method;
obtaining a silicon wafer by slicing the silicon single crystal;
a step of heat-treating the silicon wafer at a temperature of 1250° C. or more and 1375° C. or less in an oxygen-containing atmosphere to form an oxide film of 3 nm or more and 40 nm or less on the wafer surface;
inspecting the wafer surface with a laser light scattering particle counter;
A method for detecting crystal defects on the surface of a silicon wafer, comprising: In the step of growing a silicon single crystal formed under vacancy-dominant conditions by the Czochralski method,
2. The method for detecting crystal defects on the surface of a silicon wafer according to claim 1, wherein the silicon single crystal is doped with nitrogen at a concentration of 5*10< ^{13 >} /cm< ^{3 >} or more.

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