JPH08203969A - Crystal defect measuring method of semiconductor substrate - Google Patents

Abstract

PURPOSE: To provide a measuring method of crystal defect which can define the position of crystal defect in a semiconductor substrate by a simple and inexpensive method. CONSTITUTION: A magnetic field (Hz) 14 is applied to a semiconductor substrate 11 vertically to the substrate surface. A specified current (Jx) is made to flow in the semiconductor substrate 11 in the direction intersecting the magnetic field (Hz). Thus a Hall voltage (Ey) generated in the semiconductor substrate 11 is measured. After the Hall voltage (Ey) is measured, the surface of a semiconductor substrate 11 is oxidized, and an oxide film is formed. A new surface of the semiconductor substrate is exposed by selectively etching the oxide film, and the Hall voltage (Ey) is again measured. When crystal defect exists in the film eliminated by etching, the Hall voltage (Ey) changes largely before and after the etching, so that the depth of crystal defect can be accurately recognized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring crystal defects in a semiconductor having a crystal structure, and more particularly to a method for measuring the position of crystal defects in a semiconductor substrate.

[0002]

2. Description of the Related Art In recent years, the miniaturization of semiconductor elements has advanced, and if crystal defects exist in a semiconductor substrate, the performance of the semiconductor element deteriorates. For example, crystal defects are introduced into the semiconductor substrate during the ion implantation process or the like during the manufacturing process of the semiconductor 2 element. If the crystal defects remain as minute crystal defects in the vicinity of the semiconductor element, current leakage or the like may occur at the pn junction, the element characteristics may not be sufficient, and the reliability of the semiconductor element may deteriorate. There's a problem.

Therefore, the performance of these semiconductor elements is maintained.
In order to improve, it is necessary to reduce crystal defects in the semiconductor substrate. On the other hand, crystal defects in each semiconductor substrate (for example, a silicon wafer) that have undergone the same element formation process often occur for the same reason, and therefore exist at substantially the same position (depth) in each substrate. . For this reason, for one semiconductor substrate that is selectively taken out, the presence or absence of the crystal defect and the position thereof are measured to elucidate, for example, which step of the manufacturing process causes the crystal defect. be able to. Therefore, the measurement of the presence or absence and the position of this crystal defect has become an important subject in the semiconductor device manufacturing technology.

Conventionally, as a method of measuring crystal defects in a semiconductor substrate, for example, an X-ray topography, a direct observation method of selectively observing crystal defects by etching with an etching solution,
The thermal wave method, the fluorine concentration observation by SIMS (secondary ion mass spectrometer), etc. were used.

Here, the X-ray topograph is a crystal defect measuring method that utilizes the fact that X-ray diffraction changes depending on the presence or absence of crystal defects, and is widely used for measuring the in-plane distribution of relatively macro crystal defects. Has been.

In the direct observation method, for example, a semiconductor substrate is processed by using a selective etching solution such as a Sirtl etching solution or a Secco etching solution (when the substrate is silicon) to expose crystal defects in the substrate on the surface. This is a method of directly observing with a general optical microscope or the like. This method is also used as a comparatively macroscopic measuring method for crystal defects.

The thermal wave method is a defect evaluation method utilizing the photothermal displacement generated on the substrate surface by irradiating the semiconductor substrate surface with laser light. This method is used for evaluation of crystal defects introduced in the ion implantation process and the like.

Further, the fluorine concentration observation using SIMS is a method of BF ₂ ion implantation into a semiconductor substrate and observing the distribution of the fluorine concentration in the substrate. In this method, when BF ₂ is injected into a semiconductor substrate and a predetermined heat treatment is performed, if a crystal defect exists in the substrate, fluorine that normally diffuses outside the substrate is gettered to the crystal defect. The phenomenon is used. Then, the distribution of the fluorine concentration in the semiconductor substrate in the depth direction is measured by using SIMS to specify the position of the crystal defect from the peak position.

[0009]

However, the X-ray topography method and the direct observation method by selective etching described above are suitable for measuring relatively large crystal defects that can be observed with the naked eye or an optical microscope. However, there is a problem that it is difficult to measure minute crystal defects.

Further, the thermal wave method has a high measurement accuracy when a large number of crystal defects are present in the substrate or when the crystal defects are locally distributed in a minute area. It is known that there are many problems.

Furthermore, in the fluorine concentration observation method by SIMS, when fluorine is not introduced into the semiconductor substrate, a step of separately introducing fluorine into the semiconductor substrate for observation is required. For example, when the semiconductor substrate to be measured is an n-type semiconductor substrate in which P (phosphorus), As (arsenic), etc. are implanted, it is necessary to introduce fluorine into the substrate separately from the impurity implantation step. Further, since an appropriate heat treatment step is required thereafter, there are many processing steps for measurement and there is a problem that the measurement takes time. Further, when fluorine is introduced later into the semiconductor substrate into which the impurities have been implanted, there is a problem that the distribution of the impurity concentration in the substrate changes. Then, the heat treatment after the introduction of fluorine must be performed under the condition that fluorine ions having a large diffusion coefficient can remain in the substrate,
There were many restrictions on the defect observation conditions, and the measurement stability was low. Further, there is a problem that the measurement by SIMS is expensive.

The present invention has been made in order to solve the above problems, and provides a crystal defect measuring method capable of measuring the position of a minute crystal defect existing in a semiconductor substrate with high accuracy, easily and at low cost. It is intended to be provided.

[0013]

In order to achieve the above object, the semiconductor substrate crystal defect measuring method according to the present invention has the following features.

A Hall effect measuring step of measuring a Hall effect generated in the semiconductor substrate by applying a current in a predetermined direction to the semiconductor substrate while applying a magnetic field in the predetermined direction to the semiconductor substrate; An etching step for etching and a Hall effect measuring step are provided, and the depth of crystal defects in the semiconductor substrate is measured by alternately performing the etching step.

In the etching step, the surface of the semiconductor substrate is oxidized to form an oxide film, and the oxide film is etched to expose a new surface of the semiconductor substrate.

The oxide film is formed by anodizing the surface of the semiconductor substrate.

[0017]

In the crystal defect measuring method of the present invention, the measurement of the Hall effect of the semiconductor substrate and the etching of the surface of the semiconductor substrate are alternately executed, and the crystal defect in the semiconductor substrate is determined based on the change of the Hall effect before and after the etching. Measure the depth of.

As shown in FIG. 1, the Hall effect is obtained by applying a magnetic field (H) in a predetermined direction to a semiconductor material (for example, the semiconductor substrate 11).
z) 14 is applied, and when a predetermined direct current (Jx) is applied in the direction orthogonal to the magnetic field 14, the applied magnetic field Hz
And a predetermined Hall voltage (E
This is a phenomenon in which y) occurs.

The Hall coefficient represented by (Ey / JxHz) depends on the carrier type, mobility and carrier concentration in the semiconductor substrate. And when an electric field is applied,
When crystal defects are present in the semiconductor substrate, electron-hole pairs are generated around the crystal defects. Therefore, if crystal defects are present in the substrate, the carrier concentration in the semiconductor substrate appears to be higher than the electrically activated impurity concentration. Therefore, when the crystal defect portion in the semiconductor substrate is removed by etching, the Hall coefficient changes before and after the etching. Therefore, it can be estimated that a crystal defect exists in the film etched when the Hall coefficient changes, and the position (depth) of the defect can be easily and accurately specified from the etching amount of the semiconductor substrate surface. .

As described above, according to the present invention, a crystal defect locally distributed in the semiconductor substrate can be measured at low cost without requiring a large-scale measuring device as compared with the conventional method.
Furthermore, since there are few restrictions on the size of the measurement sample (semiconductor substrate), the degree of freedom in measuring the crystal defects is high, and the measurement can be easily performed.

Further, according to the method for measuring crystal defects of the present invention,
In the step of etching a semiconductor substrate, the surface of the semiconductor substrate is oxidized to form an oxide film, and then the oxide film is selectively removed by etching. Therefore, the measurement of the crystal defect position can be stably performed in a short time.

Furthermore, by using the anodic oxidation method as the method for oxidizing the semiconductor substrate, the film thickness of the oxide film can be controlled extremely accurately, and the resolution for measuring the position of crystal defects can be improved.

[0023]

Embodiments of the present invention will be described below with reference to the drawings.

First, FIG. 1 is a conceptual diagram for measuring the Hall effect in this embodiment.

In FIG. 1, the semiconductor substrate 11 is a silicon substrate, and a magnetic field (Hz) 14 is applied in a direction perpendicular to the surface of the semiconductor substrate 11 and an electrode 12 connected to a power supply 15 is used to form the semiconductor substrate 11. A direct current (Jx) in the direction perpendicular to the magnetic field (Hz) 14 is passed through 11. And
At this time, the Hall voltage (Ey) generated in the semiconductor substrate 11 is measured using the electrode 13 to obtain the Hall coefficient (Ey).
y / JxHz) can be obtained.

The etching process for the semiconductor substrate 11 of FIG. 1 is performed in the procedure as shown in FIG.

First, as shown in FIG. 2A, the semiconductor substrate 11 is
The surface of is oxidized by the anodic oxidation method. As a result, the oxide film 2 is formed on the surface of the semiconductor substrate 11 as shown in FIG.
2 is formed.

Next, the oxide film 22 is selectively removed using a hydrofluoric acid solution or the like to expose a new semiconductor substrate surface 23 as shown in FIG. 2C.

The oxide film formed on the surface of the semiconductor substrate 11 by the anodic oxidation method can accurately control the film thickness of the oxide film depending on the oxidation time and the applied voltage. Therefore, if the anodic oxide film 22 is selectively etched. The etching amount on the surface of the semiconductor substrate can be controlled easily and with high accuracy.

When the etching is finished, the new surface 23
The Hall effect (Hall coefficient) is measured again for the semiconductor substrate 11 with the exposed portion, and the difference in the Hall coefficient before and after the etching process is obtained.

By alternately executing the etching step of FIG. 2 and the Hall effect measuring step of FIG. 1 and sequentially obtaining the Hall coefficient difference, the variation distribution of the Hall coefficient difference in the depth direction of the semiconductor substrate is obtained. .

The Hall coefficient difference changes depending on the state in the silicon layer removed in the etching process. Therefore,
When crystal defects 24 are present in the surface portion of the semiconductor substrate 11 as shown in FIG. 2A, when the crystal defects 24 are removed by etching, the difference in the Hall coefficient before and after the etching, that is, the Hall effect changes significantly. Will be done. Therefore, it can be detected that the crystal defect exists at the depth where the difference in the Hall coefficient difference occurs.

Next, the actual measurement results will be described.

FIG. 3 shows the results of measurement of the concentration distribution of fluorine in the depth direction by SIMS, which has been conventionally used. The vertical axis shows the fluorine concentration (cm ^-3 ) and the horizontal axis shows the depth of the sample (semiconductor substrate). (Nm) is shown. The sample used was one in which BF ₂ ⁺ ions were implanted into a silicon single crystal substrate at an energy of 40 keV and 2 × 10 ¹⁵ cm ⁻² , and then heat treatment was performed at 900 ° C. for 20 seconds.

When the surface of the silicon single crystal substrate becomes amorphous by the ion implantation, the fluorine implanted into the semiconductor substrate by the ion implantation remains in the vicinity of the interface between the amorphized layer and the crystal layer during the subsequent heat treatment. The defects getter and aggregate.

In the fluorine concentration distribution of FIG. 3, a fluorine concentration peak 31 due to fluorine aggregation appears near the depth of 65 nm of the silicon single crystal substrate. Therefore, the residual crystal defects are
It can be seen that this substrate exists just below the depth of 65 nm.

On the other hand, the measurement result of the Hall coefficient difference for the sample prepared under the same conditions as in FIG. 3 using the method of this embodiment is as shown in FIG. In FIG. 4, the vertical axis represents the difference between the Hall coefficient measured before the nth etching and the Hall coefficient measured after the nth etching on the arbitrary axis of the silicon single crystal substrate, and the horizontal axis represents
Depth of sample (nm) corresponding to the amount of etching on the sample surface
Is shown.

According to FIG. 4, the conventional SIM shown in FIG.
It can be seen that the hole coefficient difference greatly changes at the same depth (65 nm) as the crystal defect position (65 nm) obtained by the fluorine concentration measurement by S. This change in the Hall coefficient difference indicates that there was a crystal defect 24 in the layer removed in the etching process when the change occurred, as shown in FIG.

As described above, in the present embodiment, the measurement of the Hall coefficient difference of the semiconductor substrate and the etching process of the surface of the semiconductor substrate are alternately performed, and the surface of the semiconductor substrate is sequentially etched to measure the Hall coefficient difference. By measuring the change in the Hall coefficient difference, the position (depth) of the crystal defect in the semiconductor substrate can be accurately measured. Therefore, according to the method of the present embodiment, it is possible to measure crystal defects in a short time with a very simple procedure and at low cost, as compared with the conventional fluorine concentration measurement by SIMS, for example.

Further, by reducing the amount of anodic oxidation performed once on the surface of the semiconductor substrate to reduce the amount of etching in one etching step, it is possible to more accurately know the depth of crystal defects in the substrate. Become. Note that the etching method is not limited to the method of anodic oxidation and removal of the oxide film, and, for example, mechanical or chemical polishing or physical sputtering method may be used as the etching method.

Further, in the present embodiment, the difference in the Hall coefficient is obtained in order to emphasize the change in the Hall coefficient, but it is not always necessary to obtain the difference, and the depth of the crystal defect in the semiconductor substrate is directly calculated from the Hall coefficient. May be specified.

[0042]

According to the present invention, the Hall effect measurement of the semiconductor substrate and the etching of the semiconductor substrate surface are alternately performed,
The position (depth) of the crystal defect in the semiconductor substrate is measured from the change in the Hall effect before and after etching. When the crystal defect portion in the semiconductor substrate is removed by etching, the Hall effect, that is, the Hall coefficient changes before and after this etching. Therefore, it can be estimated that the crystal defects exist in the film removed by etching when the Hall coefficient changes, and the position (depth) of the crystal defects can be easily and accurately specified from the etching amount of the semiconductor substrate surface. You can

Therefore, according to the present invention, it is possible to measure crystal defects locally unevenly distributed in the semiconductor substrate at low cost without requiring a large-scale measuring device as compared with the conventional method. Further, since the size of the sample to be measured is not limited, the degree of freedom in measuring the crystal defect is high, and the measurement can be easily performed.

In the crystal defect measuring method of the present invention, in the step of etching the semiconductor substrate, the surface of the semiconductor substrate is oxidized to form an oxide film, and then the oxide film is selectively etched and removed. Therefore, the position of the crystal defect can be stably measured in a short time.

Furthermore, since the thickness of the oxide film can be controlled extremely accurately by using the anodic oxidation method as the method for oxidizing the semiconductor substrate, it is possible to improve the resolution of the position measurement of crystal defects.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of Hall effect measurement in an example of the present invention.

FIG. 2 is a diagram showing an etching process of a semiconductor substrate in an example of the present invention.

FIG. 3 is a diagram showing measurement results of crystal defects in a semiconductor substrate using conventional SIMS.

FIG. 4 is a diagram showing a measurement result of crystal defects in a semiconductor substrate in an example of the present invention.

[Explanation of reference numerals] 11 semiconductor substrate, 12 electrode, 13 electrode, 14 magnetic field, 15 power supply, 22 oxide film, 24 crystal defect.

Claims (3)

[Claims] 1. A Hall effect measuring step of measuring a Hall effect generated in the semiconductor substrate by applying a current in a predetermined direction to the semiconductor substrate while applying a magnetic field in the predetermined direction to the semiconductor substrate; An etching step of etching a predetermined amount, wherein the Hall effect measuring step and the etching step are alternately performed to measure the depth of crystal defects in the semiconductor substrate. Method for measuring crystal defects. 2. The method of measuring a crystal defect of a semiconductor substrate according to claim 1, wherein in the etching step, a surface of the semiconductor substrate is oxidized to form an oxide film, and the oxide film is etched to obtain a new semiconductor substrate surface. A method for measuring a crystal defect in a semiconductor substrate, which comprises exposing the crystal. 3. The method for measuring a crystal defect of a semiconductor substrate according to claim 2, wherein the oxide film is formed by anodizing the surface of the semiconductor substrate.