JP3295867B2 - Secondary ion mass spectrometry of oxygen in silicon. - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for quantifying the concentration of oxygen contained in a sample containing silicon and oxygen such as single crystal silicon, polycrystal silicon, amorphous silicon or silicon oxide used in an electronic device such as a MOS IC. The present invention relates to secondary ion mass spectrometry of oxygen in silicon to be evaluated.

[0002]

2. Description of the Related Art Conventionally, in MOS ICs, an extremely thin silicon oxide film is used as a gate oxide film. However, there are many problems in manufacturing an oxide film related device such as deterioration of 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 small amount of oxygen in silicon has an adverse effect on the carrier concentration due to donor formation or the like.

Conventionally, secondary ion mass spectrometry (Secon
dary Ion Mass Spectrometer
y: SIMS) is a method for quantifying oxygen by using O 2 and S ⁻ sputtered from a sample using Cs ⁺ as a primary ion.
i ^- amount detecting a, O ^- / Si ^- was a method of using the ratio.

[0004]

However, according to this method,
Then, O^-Detection sensitivity is strongly affected by the matrix effect
Can be used for quantitative analysis at the ppm level,
It cannot be used for quantitative analysis of radar. Also nearby
Year, CsO as a quantitative analysis method of oxygen in silicon oxide film
⁺/ CsSi ⁺A method using the ratio has been proposed.
In the above method, the range from ppm order to% order is
Surrounded by CsO⁺/ CsSi⁺Because the ratios are different, p
Uniform quantitative analysis ranging from pm order to% order
Can not be done.

The present invention accurately evaluates the concentration distribution of oxygen present in a sample containing silicon and oxygen used in an electronic device in a depth direction or a plane direction, and furthermore, the characteristics of the electronic device are determined by the oxygen concentration distribution. An object of the present invention is to provide a secondary ion mass spectrometry for oxygen in silicon, which is characterized by being evaluated.

[0006]

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

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

In these cases, Cs ⁺ ions are added to a sample containing silicon and oxygen by 55 to 55
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]

According to the present invention, a sample containing silicon and oxygen is irradiated with Cs ⁺ ions, and Cs ⁺
Trisomic complex ion CsOS formed from s, O, Si
By detecting the amount of the diatomic complex ion CsSi ⁺ formed from i ⁺ and Cs, Si, CsOSi ⁺ / CsSi ⁺
When a calibration curve showing the relationship between the ratio and the oxygen concentration is created, and the depth and surface concentration distributions of oxygen in a sample containing silicon and oxygen are quantified using the calibration curve, the conventional secondary ion mass spectrometry In this method, the influence of the matrix effect, which has been a problem, can be removed, and the amount of oxygen in silicon ranging from the order of ppm to the order of% can be uniformly determined.

[0010]

An embodiment of the present invention will be described below. In this embodiment, a sample obtained by ion-implanting a Si substrate formed by the floating zone method at a different dose and C pulled up by the Czochralski method were used.
A calibration curve was created using a sample in which a 50-nm-thick silicon oxide film was formed on a Z-Si substrate by thermal oxidation, and the amount of oxygen in silicon was quantified using the calibration curve.

[0011] In this embodiment, oxygen ion implantation conditions of FZ-Si substrate by changing the dose amount of oxygen ⁽¹⁶ O ⁺⁾ is ion-implanted are as follows.

FIG. 1 is an explanatory diagram of a calibration curve according to one embodiment of the present invention. In this figure, the horizontal axis indicates the oxygen concentration, and the vertical axis indicates the CsOSi ⁺ / CsSi ⁺ intensity ratio. According to this figure, the secondary ion intensity ratio (○) shows a linearity from 1 × 10 ^{17 to} 5 × 10 ²² cm ^{−3 with} respect to the oxygen concentration. 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,
A calibration curve from order to% order can be made, and oxygen quantitative analysis can be uniformly performed over a range from ppm order to% order. On the other hand, the CsO ⁺ / CsSi ⁺ intensity ratio (□) according to the conventional method written in this figure rapidly increases when the oxygen concentration exceeds 5 × 10 ²¹ cm ^-3 and largely deviates from the straight line in the low concentration region. . Therefore, in the conventional method, it is impossible to uniformly perform the oxygen quantitative analysis in the order of ppm to%.

FIG. 2 is an explanatory view 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 indicates the depth of the silicon oxide film, and the vertical axis indicates the intensity (number of ions). This figure shows the result of analyzing the oxygen amount in the depth direction of a sample in which a silicon oxide film having a thickness of 50 nm is formed on a silicon substrate. In a 10 nm region near the interface, CsO
Abnormalities are seen in the Si ⁺ signal. This is considered 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 a silicon substrate, and further, an interface 1 between the silicon substrate and the silicon oxide film is used.
It is desirable to use a signal in a 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 indicates the depth of the silicon oxide film, and the vertical axis indicates the intensity (number of ions). According to this figure, CSOS compared to signals CsSi ⁺
It can be seen that the signal of i ⁺ 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 metals in insulators are easy to move, and storing Cs on the sample surface more than necessary is
It is considered that the Si ⁺ signal leads to an unstable state.

FIG. 4 is a diagram illustrating the relationship between the incident angle of the Cs ⁺ ion with respect to the normal line and the sputtering yield. As shown in this figure, when the incident angle of the primary ions 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 where the sputtering yield is large and to minimize the surface Cs concentration.

In this embodiment, an example using a silicon substrate into which oxygen has been ion-implanted and a sample having a silicon oxide film formed on the silicon substrate has been described.
The present invention can be applied to a case where oxygen in a sample containing silicon and oxygen is determined, such as a case where oxygen in an Al-Cu alloy to which i is added is determined.

[0019]

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

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a calibration curve according to one embodiment 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 a primary ion 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 a primary ion is 50 degrees.

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

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01N 23/225 G01N 27/62 H01L 21/66

Claims (4)

(57) [Claims] 1. Cs⁺Ions containing silicon and oxygen
Cs, O, Si sputtered from the sample
Complex ion CsOSi formed from ⁺And C
Diatomic complex ion CsSi formed from s, Si⁺of
The amount of CsOSi⁺/ CsSi⁺Ratio and oxygen concentration
Create a calibration curve showing the relationship and use the calibration curve to
And planar concentrations of oxygen in samples containing oxygen and oxygen
Characterizing oxygen distribution in silicon characterized by quantifying distribution
Secondary ion mass spectrometry. 2. The secondary ion mass spectrometry of 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 preparing the calibration curve. 3. The method according to claim 1, wherein when the calibration curve is formed using the silicon oxide film, the CsOSi ⁺ / CsSi ⁺ ratio is obtained from a portion separated from the interface between the silicon oxide film and the base by 10 nm or more in the surface direction. The secondary ion mass spectrometry of oxygen in silicon according to claim 1 or 2. 4. The method according to claim 1, wherein the sample containing silicon and oxygen is irradiated with Cs ⁺ ions in a range of 55 to 70 degrees with respect to the normal direction of the sample to obtain the amounts of CsOSi ⁺ and CsSi ^+. The secondary ion mass spectrometry of oxygen in silicon according to claim 2 or 3.