JP2689565B2 - Silicon crystal evaluation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Overview] Regarding a method for evaluating impurity oxygen in silicon crystals that is widely used as a semiconductor substrate, in addition to the conventional information on the oxygen concentration in the isolated interstitial type where absorption appears at a wave number of 1106 cm ⁻¹ , For the purpose of obtaining information on the concentration of oxygen in the aggregated state, infrared light was transmitted through a silicon crystal and the wave number of the transmitted light was 740.
The infrared absorption peak intensity appearing in the wave number region of ˜810 cm ⁻¹ is measured to determine the relative concentration of oxygen atoms in the aggregated state.

[Industrial applications]

The present invention relates to a method for evaluating a silicon crystal, and more particularly to a method for evaluating impurity oxygen in a silicon crystal.

Silicon (Si) widely used as a semiconductor substrate
Czochralski method (czochralski method (CZ method);
Although it is produced as a high-purity crystal by the pulling method), it actually contains about 10 ¹⁸ / cm ³ of oxygen, and this oxygen is intrinsic gettering (intrinsic gettering).
plays an important role such as performing actions.
Therefore, it is extremely important to accurately grasp the amount of impurity oxygen in the silicon crystal.

[Problems to be solved by conventional technology and invention]

Impurity oxygen in a silicon crystal exists in the crystal in various forms due to differences in the thermal history during crystal production. These oxygen forms precipitates by heat treatment during the device manufacturing process and has a significant effect on the debasing characteristics, but the behavior of oxygen during heat treatment depends on the existing form of oxygen before the device process is introduced. Therefore, it is important to control the behavior of oxygen with respect to the silicon crystal used as the semiconductor substrate and to select a crystal with an appropriate amount of oxygen. For that purpose, it is necessary to clarify the existence form of oxygen in the crystal. Need to In particular, some of the oxygen in the aggregated state is likely to form precipitates in the subsequent heat treatment, so it is important to estimate the amount of oxygen in the aggregated state.

Now, as a conventional method for measuring oxygen in silicon crystals,
An infrared absorption method (IR method) utilizing the lattice vibration of impurities in oxygen crystals is known. It is a method of transmitting infrared light through a silicon crystal to be measured. As shown in FIG. 4, an infrared light of intensity I ₀ (wave number 180 to 300 cm ^{−1) is} applied to a silicon crystal W having a thickness t = 1 to 2 mm. ) Is irradiated, I ₀ (1-R) ² e ^-t where R is the reflection coefficient and α is the absorption coefficient. The impurity concentration can be specified from the absorption intensity of the wavelength. The specific wavelength of this specific impurity is 1106 cm ^-1 (wavelength 9 μm in the case of oxygen in the silicon crystal).
Absorption appears at a certain level, and the content concentration can be determined from the absorption intensity (ASTM F121-80, ASTM F123
See −81).

However, the reason why the absorption peak intensity appears at the wave number of 1106 cm ^-1 is due to the vibration of the isolated interstitial oxygen atom, and the wave number of 1106 cm ^-1 for the oxygen atoms in the above-mentioned precipitation or aggregation state.
Absorption does not appear.

Therefore, at present, in order to obtain the amount of precipitated oxygen, the concentration of isolated interstitial oxygen contained in the crystal is measured before precipitation, and then the isolated interstitial oxygen is heat treated and then isolated interstitial oxygen is again measured. A method is adopted in which the concentration of oxygen is measured and the amount of precipitated oxygen is determined from the difference. That is, it is a method of quantifying the concentration difference of isolated interstitial oxygen before and after precipitation by using an infrared absorption method. However, in this method, the total oxygen concentration other than the isolated interstitial oxygen is only indirectly known, but it is not a direct measurement of the precipitated or aggregated form. Further, this method cannot be quantified when the interstitial oxygen concentration before precipitation is unknown.

Therefore, at present, a method for directly obtaining information on oxygen in an aggregated state has not been known so far, and therefore, it is extremely insufficient to control the behavior of oxygen during heat treatment.

The present invention solves such a problem, and the conventional wavenumber 11
In addition to the information on the isolated interstitial oxygen concentration at which absorption appears at 06 cm ^-1 , as a new factor to know the existing form of oxygen, a silicon crystal for the purpose of obtaining information on the concentration of oxygen in the aggregated state The evaluation method is proposed.

[Means for solving the problem]

The task is to transmit the infrared light through the silicon crystal and measure the infrared absorption peak intensity that appears in the wave number region of the transmitted light wave number of 740 to 810 cm ^-1 to determine the relative concentration of oxygen atoms in the aggregated state. It is solved by the evaluation method of the silicon crystal.

(Operation)

That is, in the present invention, the infrared absorption due to the lattice vibration of the isolated interstitial oxygen atom (mainly the vibration of the oxygen atom itself) is the wave number
It appears as the absorption peak intensity at 1106 cm ^-1 ,
The vibrations that occur around the aggregated oxygen (mainly due to the silicon atoms linked to oxygen atoms) are 740-810 cm ^-1.
In order to appear in the wave number region of, the peak intensity in the wave number region is relatively investigated to evaluate the aggregation state of oxygen in the silicon crystal.

In the wave number region of 740 to 810 cm ^-1 , the absorption peak due to the isolated interstitial oxygen atom does not appear, but the absorption due to the aggregation of two or more oxygen atoms appears. Quantum mechanical calculations by the molecular orbital method using the cluster model show that localized interstitial oxygen exists in the localized interstitial oxygen and its energy is about 610 cm ^-1 wavenumber, which is confirmed experimentally. Has been.

[References] (1) C. Kaneda et al, International Conference on D
efects in Semiconductors, Budapest (1988) (2) Kaneda et al., The 49th Japan Society for Applied Physics (3) B.Pajot et al, Material Research Society Symp
osia Proceedings Vol.49 (1985) This energy mode itself is Raman activity (causing Raman scattering) and not infrared activity (causing infrared absorption), but interstitial oxygen is more than two When gathered, the symmetry of the atomic arrangement around oxygen changes and it becomes infrared active. Further, at this time, since the compressive force acts due to the aggregation of oxygen around oxygen, the frequency shifts to the high frequency side, and the infrared absorption peak appears in the wave number region of 740 to 810 cm ^-1. Will occur. On the other hand, on the other hand, since the atomic arrangement of oxygen and silicon changes greatly in the state where the precipitation proceeds, such an absorption peak does not occur. Therefore, only the oxygen in the polymerized state appears in this wavenumber region. .

Therefore, if the absorption peak intensity in this region is measured, it is possible to evaluate oxygen in silicon based on the difference in oxygen concentration in the aggregated state.

〔Example〕

Explaining in detail below with reference to the drawings, FIG. 1 is a diagram showing a localized lattice excitation due to isolated interstitial oxygen.
Is an oxygen atom, and ○ is a silicon atom. This oxygen atom
The vibration of the silicon atom ○ bound to is excited (indicated by the arrow)) and becomes Raman active. This is because quantum mechanical calculations show that absorbed energy appears at a wave number of 610 cm ^-1 , but when two or more such oxygen atoms are aggregated, the frequency is high due to the influence of the compressive force of oxygen in the aggregation state in the vicinity. It shifts to the side and also becomes infrared active due to a change in the symmetry of the atomic arrangement around oxygen, and an infrared-class final peak occurs in the wave number region of 740 to 810 cm ^-1 . On the other hand, no absorption peak appears in such a wave number region for oxygen that has become a precipitate.
Further, in the case of isolated interstitial oxygen in which oxygen is not in an aggregated state and exists only in one atom, the localized lattice excitation as shown in FIG. 1 does not become infrared active, and the isolated interstitial oxygen is mainly used. The vibration type that vibrates itself has a strong infrared activity and produces an absorption peak at 1106 cm ^-1 .

Next, the results of the measured examples will be described. FIG. 2 shows an infrared absorption spectrum (I) of a silicon crystal containing an oxygen concentration of 33.5 ppm and having a known oxygen content, measured at a temperature of 10K. The vertical axis is the absorption coefficient, and the horizontal axis is the wave number. A clear absorption peak appears at the wave number positions indicated by the arrows and at the positions of 770 cm ^-1 and 786 cm ^-1 . This is the red color generated by oxygen in the aggregated state. It is a result of external absorption.

FIG. 3 shows an infrared absorption spectrum (II) of a silicon crystal having an oxygen concentration of 29 ppm and a known oxygen content, measured at a temperature of 10K. Similar to Fig. 3, the vertical axis is the absorption coefficient and the horizontal axis is the wave number, but no absorption peak appears in the wave number region of 740 to 810 cm ^-1 because almost no oxygen in the aggregated state exists. Is.

Similar to such data, if you create and classify infrared absorption spectrum data from many silicon crystals with known oxygen concentrations, you can compare and evaluate the amount of oxygen in the aggregated state. It is possible to clarify the unclear oxygen concentration of the aggregated state in the crystal.

〔The invention's effect〕

As can be seen from the above description, the oxygen concentration evaluation method according to the present invention clarifies the amount of oxygen in the aggregated state, and as a result, controls the oxygen behavior in the silicon crystal and silicon having an appropriate amount of oxygen concentration. It is very useful for crystal selection and contributes to the improvement of performance and quality of semiconductor devices such as IC and LSI.

[Brief description of the drawings]

FIG. 1 is a diagram showing localized lattice excitation due to isolated interstitial oxygen, FIG. 2 is an infrared absorption spectrum (I) diagram, FIG. 3 is an infrared absorption spectrum (II) diagram, and FIG. 4 is It is a figure explaining an infrared absorption method. In the figure, W indicates a silicon crystal, ○ indicates a silicon atom, and ● indicates an oxygen atom.

Claims (1)

(57) [Claims] 1. A relative concentration of oxygen atoms in an aggregated state is determined by transmitting infrared light through a silicon crystal and measuring an infrared absorption peak intensity appearing in a wave number region of transmitted light having a wave number of 740 to 810 cm ^−1. A method for evaluating a silicon crystal characterized by the above.