JPH07294462A - Secondary ion mass spectrometry for oxygen in silicon - Google Patents

Abstract

PURPOSE:To provide a means which can accurately evaluate the concentration distribution in the depth direction or the surface direction of oxygen existing in a silicon and oxygen-containing sample used in an electronic device or the like in secondary ion mass spectrometry for oxygen in silicon. CONSTITUTION:A (s<+> ion is radiate to a sample containing silicon and oxygen, and a quantity of a three-atom composite ion CsOSi<+> composed of Cs, O and Si and a two-atom composite ion CsSi<+> composed of Cs and Si sputtered from this sample is detected, and an analytical curve to show the relationship between a ratio of CsOSi<+>/CsSi<+> and the oxygen concentration is created, and the concentration distribution in the depth direction and the surface direction of oxygen in the sample containing silicon and oxygen is quantitatively determined by using this analytical curve. When the analytical curve is created, a silicon oxide film having a thickness of 10nm or more is used as a high concentration sample, and the ratio of CsOSi<+>/CsSi<+> is found from a part separated in the surface direction by 10nm or more from an interface with backing of the silicon oxide film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention quantifies the concentration of oxygen contained in a sample containing silicon and oxygen such as single crystal silicon, polycrystalline silicon, amorphous silicon or silicon oxide used in electronic devices such as MOS ICs. It relates to secondary ion mass spectrometry of oxygen in silicon to be evaluated.

[0002]

2. Description of the Related Art Conventionally, in a MOS IC, an extremely thin silicon oxide film has been used as a gate oxide film, but there are many problems in the manufacture of devices related to the oxide film such as deterioration of the oxide film function due to heat treatment and breakthrough. Exists,
Information about the oxygen concentration in the oxide film is extremely important. It is also known that a slight amount of oxygen in silicon adversely affects the carrier concentration due to the formation of a donor or the like.

Conventionally, secondary ion mass spectrometry (Secon)
darry Ion Mass Spectrometer
y: SIMS) is a method for quantifying oxygen, in which O ⁻ and S sputtered from a sample using Cs ⁺ as primary ions.
This was a method of detecting the amount of i ⁻ and using the O ⁻ / Si ⁻ ratio.

[0004]

However, according to this method,
Then O^-The detection sensitivity of is severely affected by the matrix effect
However, even if it can be used for quantitative analysis at the ppm level,
It cannot be used for quantitative analysis of data. In addition,
, CsO as a quantitative analysis method of oxygen in silicon oxide film
⁺/ CsSi ⁺A method that uses a ratio has been proposed.
In the method of, the range from ppm order to% order
Markedly CsO⁺/ CsSi⁺Since the ratio is different, p
Uniform quantitative analysis ranging from pm order to% order
Can't be done.

The present invention accurately evaluates the concentration distribution of oxygen existing in a sample containing silicon and oxygen used in an electronic device in the depth direction or in the plane direction, and determines the characteristics of the electronic device by the oxygen concentration distribution. It is an object of the present invention to provide a secondary ion mass spectrometry method for oxygen in silicon characterized by evaluation.

[0006]

In the secondary ion mass spectrometry of oxygen in silicon according to the present invention, in order to solve the above problems, a sample containing silicon and oxygen is irradiated with Cs ⁺ ions, Cs sputtered from the sample,
Triatomic compound ion CsOSi ⁺ formed from O and Si
And a diatomic compound ion Cs formed from Cs and Si
A calibration curve showing the relationship between the CsOSi ⁺ / CsSi ⁺ ratio and the oxygen concentration is created by detecting the amount of Si ⁺ , and the concentration curve of oxygen in a sample containing silicon and oxygen in the depth direction and the plane direction is prepared using the calibration curve. The process of quantifying the distribution was adopted.

In this case, when preparing the calibration curve, a silicon oxide film having a thickness of 10 nm or more is used as the high-concentration sample, and in this case, 10 n from the interface between the silicon oxide film and the base.
CsOSi ⁺ / CsS from the part more than m away from the surface
By obtaining the i ⁺ ratio, CsOSi ⁺ / CsSi ⁺
The ratio can be accurately determined.

Further, in these cases, Cs ⁺ ions are applied to a sample containing silicon and oxygen in an amount of 55 to 55 with respect to the normal direction.
By irradiating in the range of 70 degrees, the amount of Cs accumulated on the surface of the sample can be reduced and the CsOSi ⁺ signal can be stabilized.

[0009]

As in the present invention, a sample containing silicon and oxygen is irradiated with Cs ⁺ ions, and C sputtered from this sample is irradiated.
Triatomic compound ion CsOS formed from s, O and Si
The amount of diatomic compound ion CsSi ⁺ formed from i ⁺ and Cs, Si is detected to obtain CsOSi ⁺ / CsSi ⁺
A calibration curve showing the relationship between the ratio and the oxygen concentration was created, and using this calibration curve, the concentration profiles of oxygen in the depth direction and the plane direction in a sample containing silicon and oxygen were quantified. The effect due to the matrix effect, which has been a problem in (3), can be eliminated, and the amount of oxygen in silicon in the range of ppm order to% order can be uniformly quantified.

[0010]

EXAMPLE An example of the present invention will be described below. In this example, a sample obtained by ion-implanting a Si substrate formed by the floating zone method with a different dose amount, and C pulled by the Czochralski method.
A calibration curve was prepared using a sample in which a silicon oxide film having a thickness of 50 nm was formed on a Z-Si substrate by thermal oxidation, and the amount of oxygen in silicon was quantified using this calibration curve.

In this embodiment, the oxygen ion implantation conditions for the FZ-Si substrate in which oxygen ( ¹⁶ O ⁺ ) was ion-implanted with the dose amount changed are as follows.

FIG. 1 is an explanatory diagram of a calibration curve according to an embodiment of the present invention. In this figure, the horizontal axis represents oxygen concentration and the vertical axis represents CsOSi ⁺ / CsSi ⁺ intensity ratio. According to this figure, the secondary ion intensity ratio (◯) shows linearity with respect to the oxygen concentration up to 1 × 10 ^{17 to} 5 × 10 ²² cm ⁻³ . In this case, 1 × 10 ¹⁷ cm ^-3 is equivalent to 2 ppm,
5 × 10 ²² cm ⁻³ corresponds to the oxygen concentration in silicon oxide.

Therefore, according to this embodiment, ppm
A calibration curve from order to% order can be created, and quantitative oxygen analysis can be performed uniformly over the range of ppm order to% order. On the other hand, the CsO ⁺ / CsSi ⁺ intensity ratio (□) according to the conventional method written in this figure sharply increases when the oxygen concentration exceeds 5 × 10 ²¹ cm ⁻³ , and deviates greatly from the straight line in the low concentration region. . Therefore, with the conventional method, it is impossible to uniformly perform quantitative oxygen analysis in the range of ppm order to% order.

FIG. 2 is an explanatory diagram of the analysis result of the oxygen amount in the depth direction of the silicon oxide film when the incident angle of the primary ions is 60 degrees. In this figure, the horizontal axis represents the depth of the silicon oxide film, and the vertical axis represents the intensity (number of ions). This figure shows the results of analyzing the oxygen amount in the depth direction of a sample in which a silicon oxide film having a thickness of 50 nm was formed on a silicon substrate. In the 10 nm region near the interface, CsO
Abnormality is seen in the signal of Si ⁺ . It is considered that this is because the surface primary ion concentration changes near the interface. Therefore, when preparing a calibration curve for quantitative analysis of oxygen, a silicon oxide film having a thickness of 10 nm or more is used on the silicon substrate, and further, the interface 1 between the silicon substrate and the silicon oxide film is used.
It is desirable to use the signal in the region outside the 0 nm region.

FIG. 3 is an explanatory diagram of the analysis result of the oxygen amount in the depth direction of the silicon oxide film when the incident angle of the primary ions is 50 degrees. In this figure, the horizontal axis represents the depth of the silicon oxide film, and the vertical axis represents the intensity (number of ions). According to this figure, compared to the signal of CsSi ⁺ , CsOS
It can be seen that the i ⁺ signal is unstable.

[0016] In addition, CsOSi ⁺ of the signal is affected by the Cs ⁺ of the signal, the Cs ⁺ signal shows the opposite behavior. Alkali metal in the insulator is easy to move, and it is impossible to accumulate Cs on the sample surface more than necessary.
It is considered to lead the signal of Si ⁺ to an unstable state.

FIG. 4 is a diagram for explaining the relationship between the incident angle with respect to the normal line of Cs ⁺ ions and the sputtering yield. As shown in this figure, when the incident angle of the primary ion with respect to the normal line is 55 to 70 degrees, the sputtering yield is large. Therefore, it is desirable to keep the Cs ⁺ primary ion incident angle at 55 to 70 degrees, which has a large sputtering yield, and minimize the surface Cs concentration.

In this embodiment, an example using a silicon substrate into which oxygen is ion-implanted and a sample in which a silicon oxide film is formed on the silicon substrate has been described.
It can be applied to the case of quantifying oxygen in a sample containing silicon and oxygen, such as the case of quantifying oxygen in a wiring made of an Al-Cu alloy to which i is added.

[0019]

As described above, the method for quantitative analysis of oxygen in a sample containing silicon and oxygen according to the present invention is pp.
Oxygen can be uniformly quantified in the order of m to%, which greatly contributes to the improvement of the evaluation technology for the characteristics of electronic devices.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a calibration curve according to an example of the present invention.

FIG. 2 is an explanatory diagram of an analysis result of an oxygen amount in a depth direction of a silicon oxide film when an incident angle of primary ions is 60 degrees.

FIG. 3 is an explanatory diagram of an analysis result of an oxygen amount in a depth direction of a silicon oxide film when an incident angle of primary ions is 50 degrees.

FIG. 4 is an explanatory diagram of a relationship between an incident angle with respect to a normal line of Cs ⁺ ions and a sputtering yield.

Claims (4)

[Claims] 1. Cs⁺Ions containing silicon and oxygen
Cs, O, Si sputtered from the sample by irradiating the sample
Triatomic compound ion CsOSi formed from ⁺And C
diatomic compound ion CsSi formed from s and Si⁺of
Amount of CsOSi⁺/ CsSi⁺Ratio of oxygen concentration
Create a calibration curve that shows the relationship, and use the calibration curve to
And Oxygen Concentrations in Samples Containing Oxygen and Oxygen
The distribution of oxygen in silicon characterized by quantifying the distribution.
Secondary ion mass spectrometry. 2. The secondary ion mass spectrometry method for oxygen in silicon according to claim 1, wherein a silicon oxide film having a thickness of 10 nm or more is used as the high-concentration sample when the calibration curve is prepared. 3. A CsOSi ⁺ / CsSi ⁺ ratio is obtained from a portion distant by 10 nm or more from the interface between the silicon oxide film and the base in the surface direction when the calibration curve is formed using the silicon oxide film. Item 2. The secondary ion mass spectrometry method for oxygen in silicon according to item 1 or 2. 4. The amount of CsOSi ⁺ and CsSi ⁺ is determined by irradiating a sample containing silicon and oxygen with Cs ⁺ ions in the range of 55 to 70 degrees with respect to the normal direction. The secondary ion mass spectrometry method for oxygen in silicon according to claim 2 or 3.