KR102740966B1 - Method for analyzing contamination at surface of wafer - Google Patents

Abstract

The invention provides a method for analyzing contamination of a wafer surface, comprising the steps of forming an oxide film on a surface of a silicon wafer; injecting high-speed primary ions into the silicon wafer; and measuring the concentration of secondary ions emitted from the surface of the silicon wafer.

Description

{METHOD FOR ANALYZING CONTAMINATION AT SURFACE OF WAFER}

The present invention relates to a method for analyzing contamination on a wafer surface, and more specifically, to a method for accurately analyzing the concentration of boron on a silicon wafer surface.

Silicon wafers, which are used as materials for producing electronic components such as semiconductors and solar cells, are manufactured through a series of processes, starting with the growth of a silicon single crystal ingot using the Czochralski (CZ) method. Then, semiconductors are manufactured through processes such as injecting specific ions into the wafer and forming circuit patterns.

Silicon is used as a basic material for semiconductor devices, but impurities or defects within silicon can have a negative effect on the operating characteristics of the device during the semiconductor manufacturing process or in the finished product state. In particular, as can be seen from the increasingly fine design rules, the most desirable and safe way to control these impurities or defects is to prevent or remove them from the growth stage of the silicon single crystal ingot.

Organic substances from various chemicals and raw materials based on solutions such as acids, alkalis, slurries, solvents, and oils used in semiconductor and wafer manufacturing processes, or impurities such as boron contained in the air in the process room can contaminate wafers.

The analytical devices used to analyze these impurities include FT-IR (Fourier Transform-Infrared spectrophotometer), UV-visible spectrophotometer, SIMS (Secondary Ion-Mass spectrometer), GC-MS (Gas Chromatography-Mass Spectrometer), etc., and GC-MS is the only device that can perform qualitative and quantitative analysis.

However, due to the limitations of current analytical methods and analytical devices, there is a problem in that the organic components can only be identified in a limited manner for a few widely known raw materials.

In addition, when analyzing organic substances contained in raw materials, problems such as corrosion and contamination of the device and blockage of the sample movement path within the device occur, which limits the analysis of organic substances contained in raw materials.

In addition, in the case of D-SIMS (Dynamics-SIMS), which injects strong ions into the surface of a wafer and then measures the ions released again from the wafer, it may be advantageous for analysis in the bulk direction using strong ions, but there are limitations in analyzing the surface of the wafer.

The invention provides a method for analyzing contamination of a wafer surface, which accurately analyzes the concentration of boron on the surface of a silicon wafer.

The invention provides a method for analyzing contamination of a wafer surface, comprising the steps of forming an oxide film on a surface of a silicon wafer; injecting high-speed primary ions into the silicon wafer; and measuring the concentration of secondary ions emitted from the surface of the silicon wafer.

The oxide film may be a silicon oxide film.

The oxide film can be deposited by the CVD method.

An oxide film can be formed with a thickness of at least 100 nanometers.

The method for analyzing contamination of a wafer surface may further include a step of leaving the silicon wafer in a clean room prior to formation of an oxide film.

The neglect phase can last from one to three hours.

A method for analyzing contamination of a wafer surface according to an embodiment can accurately measure the concentration of boron on the surface and in some bulk regions of the wafer without boron being released to the outside before and after the injection of primary ions by performing the D-DIMS method after deposition of a silicon oxide film.

Figure 1 is a flow chart of a method for analyzing contamination of a wafer surface according to an embodiment.
Figure 2 is a schematic drawing of a device used for analyzing contamination of a wafer surface according to an embodiment.
Figure 3 is a diagram showing the principle of D-SIMS.
Figure 4 is a drawing showing the concentration of boron detected through the above-described method.
Figure 5 is a diagram showing the correlation between the concentration of boron detected in Figure 4 and the concentration of boron determined by another method.
Figure 6 is a drawing showing the concentration of boron detected through the method of Comparative Example 1.
Figure 7 is a drawing showing the concentration of boron detected through the method of Comparative Example 2.

Hereinafter, the present invention will be described in detail with reference to examples to specifically explain the invention, and in order to help understanding the invention, the invention will be described in detail with reference to the attached drawings.

However, the embodiments according to the present invention can be modified in various different forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to more completely explain the present invention to a person having average knowledge in the art.

Additionally, relational terms such as “first,” “second,” “upper,” and “lower,” as used hereinafter, may be used only to distinguish one entity or element from another, without necessarily requiring or implying any physical or logical relationship or order between such entities or elements.

FIG. 1 is a flow chart of a method for analyzing contamination of a wafer surface according to an embodiment, and FIG. 2 is a schematic diagram of a device used for analyzing contamination of a wafer surface according to an embodiment. Hereinafter, a method for analyzing contamination of a wafer surface will be described with reference to FIGS. 1 and 2.

First, an oxide film (SiOx) is formed on the surface of a silicon wafer (S100). The oxide film can be deposited on the surface of the wafer, for example, by a CVD (chemical vapor deposition) method. If the oxide film is formed using liquid oxygen or ozone (O ₃ ), the silicon on the surface of the silicon wafer may be used, which may affect the surface characteristics such as the thickness of the wafer. However, if the oxide film is deposited by the CVD method, silicon (Si) atoms and oxygen (O) atoms are supplied separately, so that the silicon on the surface of the wafer is not used, thereby preventing the above-mentioned problem. Another type of oxide film can be formed instead of the silicon oxide film, but it is preferable that it be an oxide film that is less reactive with silicon in the bulk region.

At this time, considering sputtering in the D-SIMS method described later, the oxide film (SiOx) can be deposited with a thickness of at least 100 nanometers. That is, if the thickness of the oxide film is less than 100 nanometers, the entire oxide film may be damaged by the primary ion, exposing the bulk area of the wafer, and thus the boron concentration measurement may not be performed properly.

Additionally, the D-SIMS method can be used to analyze the impurity contamination on the surface of the wafer, especially the concentration of boron (B).

Figure 3 is a diagram showing the principle of D-SIMS.

D-SIMS (Dynamics-Secondary Ion Mass Spectroscopy) collides high-speed primary ions with the surface of a solid sample, and the generated collision energy is transmitted to the particles inside the sample, and some of the particles break bonds and are released from the sample. Since it can penetrate a solid sample by several nanometers per second, it can be used to measure the contamination concentration in the bulk direction of a wafer. However, due to the strong primary ions, it may be difficult to accurately analyze only the surface of the wafer, and the surface of the wafer here can refer to a natural oxide film with a thickness of less than 10 angstroms (Å).

Referring to Fig. 2, a method for analyzing impurity contamination on the surface of a wafer, particularly the concentration of boron (B), using the D-SIMS method is described in detail.

In FIG. 2, the D-SIMS device (100) includes a chamber (200) in which a wafer is placed, a primary ion source (300) that emits primary ions for sputtering the surface of the wafer, a primary ion gun column (400) that converges the primary ions emitted from the primary ion source (300), a secondary ion lens (500) that extracts secondary ions emitted from the wafer, a mass analyzer (600) that analyzes the secondary ions transmitted from the secondary ion lens (500), a detector (700) that detects the mass-separated secondary ions, a vacuum pump (800) that maintains the vacuum state of the devices, and a substrate (900) that carries a wafer and moves and rotates it to adjust the angular position of the primary ions irradiated onto the wafer, and the like. The primary ion gun column (400) may be equipped with electrodes (1000) for injecting primary ions.

When high-speed primary ions are injected into the surface of the wafer through the above-described D-SIMS device (100) as a primary ion source (300), bonds between elements within the silicon oxide film deposited on the surface of the silicon wafer in the above-described S100 process are broken and can be released to the outside, and at this time, secondary ions released from the silicon wafer can be collected through the above-described secondary ion lens and analyzed in a mass spectrometer.

Figure 4 is a drawing showing the concentration of boron (B) detected through the above-described method.

As a result of performing the same method described above on two silicon wafer samples (sample 1, sample 2), the concentration of boron (B) in each sample was strongly measured at a depth of approximately 500 to 1,300 nanometers, and the boron concentrations showed similar patterns.

At this time, before depositing a silicon oxide film on the surface of the silicon wafer, the silicon wafer may be left in the clean room for 1 to 3 hours, for example, 2 hours. 1 to 3 hours may be the time for boron to adhere to the surface of the wafer in the clean room. If the leaving time is too short, the concentration of boron may be too small to detect, and if the leaving time is too long, the increase in the concentration of boron may be minimal, which may cause a problem in that the process time increases. Boron may be introduced from the outside air or discharged from a filter, etc. in the clean room, and thus exist in the clean room. Therefore, boron may adhere to the surface of the bulk area of the silicon wafer. In addition, when depositing a silicon oxide film using the CVD method described above, it may be performed at a temperature of less than 500°C in order to minimize the movement of boron due to high temperature.

When boron is partially attached to the surface of a silicon wafer using the above-described method and a silicon oxide film is deposited using the CVD method, the boron cannot penetrate to the outside, so the boron concentration can be measured without loss of boron.

And, when the above-described primary ions are injected into the silicon oxide film of the silicon wafer, some of the boron can diffuse in the bulk direction of the silicon wafer, and thus the boron concentration in the shape shown in Fig. 4 can be measured.

In Figure 4, the horizontal axis represents the depth from the surface of the wafer toward the inside of the bulk region, and the vertical axis represents the concentration of boron in terms of the number of boron atoms per cubic centimeter (cm ³ ).

In Fig. 4, the high concentration of boron near the surface of the wafer can be regarded as a numerical value caused by signal interference of the measuring device, and the region where the concentration of boron peaks at a depth of about 650 nanometers can be estimated to be the interface (surface) between the silicon oxide film and the silicon wafer, so the thickness of the silicon oxide film can be estimated to be about 650 nanometers, and the section where the concentration of boron increases at a depth of about 500 to 1,300 nanometers is estimated to be the section where boron diffuses and is distributed to the bulk region by the injection of the aforementioned primary ions.

Figure 5 is a diagram showing the correlation between the concentration of boron detected in Figure 4 and the concentration of boron determined by another method.

The vertical axis represents the concentration of boron detected in FIG. 4, i.e., the concentration of boron detected by the method according to the present invention, and the horizontal axis represents the number per unit area of boron (atoms/cm ² ) measured by Surface B for the same wafer. Surface B is a method whose accuracy has been verified in the past, and as shown, the concentration of boron detected by the method according to the present invention and the number per unit area of boron measured by Surface B show a very large correlation of 0.9983, so it can be seen that the concentration of boron detected by the method according to the present invention is very accurate.

As described above, when measuring the boron concentration on the wafer surface using the D-SIMS method, it is difficult to accurately analyze the surface of the wafer because the energy of the primary ion is large. However, if the D-DIMS method is performed after deposition of the silicon oxide film, the boron concentration on the surface of the wafer and some bulk regions can be accurately measured without boron being released to the outside before the injection of the primary ion and after the injection of the primary ion.

Figure 6 is a drawing showing the concentration of boron detected through the method of Comparative Example 1.

Figure 6 shows the results of measuring the boron concentration by the D-SIMS method after leaving two silicon wafer samples (sample 1, sample 2) in a clean room for 12 hours to allow boron to adhere to the surface of the wafer. As described above, the boron concentration in the region of 0 to 20 nanometers on the surface of the wafer is very unreliable data due to the characteristics of the device, and very small concentrations of boron are detected in other regions as well. This is because the boron adheres to the surface of the silicon wafer and then falls off again, and is also dispersed from the surface of the wafer to some bulk region by strong primary ions, so the pattern of boron concentration cannot be properly confirmed.

Figure 7 is a drawing showing the concentration of boron detected through the method of Comparative Example 2.

In this example, the boron concentration was measured by the D-SIMS method after gold (Au) was coated on the surface of the wafer with a thickness of about 200 nanometers, which is the same as the method of Fig. 6. That is, in order to prevent boron from being released and to prevent damage to the bulk region of the wafer by D-SIMS, a gold coating was used instead of the silicon oxide film in this invention.

In Fig. 7, theoretically, boron should be measured after a thickness of 200 nanometers, which is a gold coating layer, but in reality, a boron concentration like the red graph was measured. This is because the gold coating layer is softer than the silicon oxide film, so the gold coating layer is greatly damaged by primary ions, and boron quickly flows out, resulting in an unreliable accuracy of the boron concentration, such as a peak in the boron concentration appearing at a depth of about 20 nanometers.

Although the embodiments have been described above by way of limited examples and drawings, the present invention is not limited to the above embodiments, and those skilled in the art to which the present invention pertains can make various modifications and variations from this description.

Therefore, the scope of the present invention should not be limited to the described embodiments, but should be defined not only by the claims described below but also by equivalents of the claims.

100: D-SIMS device 200: Chamber
300: Primary ion source 400: Primary ion gun column
500: Secondary ion lens 600: Mass spectrometer
700: Detector 800: Vacuum pump
900: substrate 1000: electrode

Claims (6)

A step of leaving the silicon wafer in a clean room for 1 to 3 hours;
A step of forming an oxide film with a thickness of at least 100 nanometers on the surface of the silicon wafer;
A step of implanting primary ions into the above silicon wafer; and
Comprising a step of measuring the concentration of secondary ions emitted from the surface of the silicon wafer,
The above injection and measuring steps use a D-SIMS (Dynamics-SIMS) device,
In the above measuring step, the secondary ions emitted from the secondary ion lens are extracted, and the secondary ions transmitted from the secondary ion lens are analyzed in the mass spectrometer.
A method for analyzing contamination of a wafer surface, wherein the secondary ion is a boron ion and the formation of the oxide film is performed at a temperature of less than 500°C. In the first paragraph,
The above oxide film is a method for analyzing contamination on the wafer surface, which is a silicon oxide film. In the first paragraph,
A method for analyzing contamination on a wafer surface on which the above oxide film is deposited by a CVD method. delete delete delete