Electricity: measuring and testing – Determining nonelectric properties by measuring electric... – Semiconductors for nonelectrical property
Reexamination Certificate
1998-08-14
2001-08-21
Brown, Glenn W. (Department: 2858)
Electricity: measuring and testing
Determining nonelectric properties by measuring electric...
Semiconductors for nonelectrical property
C324S501000, C324S551000, C324S754120, C324S765010
Reexamination Certificate
active
06278267
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a technique that determines the amount of impurities present in the vicinity of an insulating film formed on surface of a substrate.
2. Description of the Related Art
An insulating film formed on a surface of a substrate, such as a semiconductor wafer, is often contaminated with mobile ions including alkali metal ions (hereinafter referred to as ‘intra-film impurity ions’) in the course of wafer processing. These intra-film impurity ions readily move under the influence of an electric field and thereby lower the stability of electric characteristics of the surface of the semiconductor wafer.
The amount of intra-film impurity ions in the insulating film is generally measured by C-V characteristic measurement with the aid of BT (bias temperature) treatment. In the BT treatment, a direct current bias is applied to a gate electrode on the insulating film at high temperatures.
The BT treatment heats up the semiconductor wafer to high temperatures and thereby requires a relatively long treatment time.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a technique that determines the amount of impurity ions present in the vicinity of an insulating film formed on surface of a substrate, such as a semiconductor wafer, without heating the substrate.
The above and other objects of the invention are attained at least partly by a method of determining an amount of impurities in the vicinity of an insulating film formed on a surface of a substrate. The method comprises the steps of: (a) obtaining a first measurement value of a predetermined electrical property, which relates to an amount of intra-film impurity ions in the insulating film; (b) irradiating the surface of the substrate with light of a first wavelength range, so as to electrically neutralize the intra-film impurity ions; (c) obtaining a second measurement value of the predetermined electrical property in the state that the intra-film impurity ions are neutralized; and (d) determining the amount of the intra-film impurity ion in a state prior to the irradiation with the light of the first wavelength range, based on the first measurement value and the second measurement value.
Irradiation of the surface of the substrate with light of the specified first wavelength range electrically neutralizes the intra-film impurity ions in the insulating film. The method can determine the amount of the intra-film impurity ions in the state prior to the irradiation with the light, based on the measurement values of the predetermined electrical property, which relates to the amount of the intra-film impurity ion in the insulating film, obtained before and after the irradiation with the light.
In a preferred embodiment of the invention, the insulating film contains plural kinds of intra-film impurity ions, and the first wavelength range comprises a specific wavelength range that electrically neutralize one specific kind of intra-film impurity ions among the plural kinds of different intra-film impurity ions and does not electrically neutralize the other kinds of the intra-film impurity ions.
This structure enables the amount of one specific intra-film impurity ion in the insulating film to be determined separately from the other intra-film impurity ions.
In a preferred embodiment of the invention, the first wavelength range is at least part of a range of about 100 nm to about 500 nm.
Irradiation with the light of this wavelength range can effectively neutralize the intra-film impurity ions in the step (b).
In a preferred embodiment of the invention, the light of first wavelength range does not ionize impurities adsorbed to the surface of the insulating film.
If the adsorbed impurities are present on the surface of the insulating film, inappropriate irradiation would ionize the adsorbed impurities while neutralizing the intra-film impurity ion in the insulating film. This would make it difficult to accurately determine the amount of the intra-film impurity ions in the step (d). In such cases, appropriate irradiation with light of the specific wavelength range, which neutralizes only the intra-film impurity ions but does not ionize the adsorbed impurities, enables accurate determination of the amount of the intra-film impurity ions.
In a preferred embodiment of the invention, the method further comprises the steps of: (e) irradiating the surface of the substrate with light of a second wavelength range, which includes a range different from the first wavelength range, so as to ionize the adsorbed impurities; (f) obtaining a third measurement value of the predetermined electrical property in the state that the adsorbed impurities are ionized; and (g) determining an amount of the adsorbed impurities in a state prior to the irradiation with the light of the second wavelength range, based on the second measurement value and the third measurement value.
The adsorbed impurities on the surface of the insulating film are ionized in the step (e), while the intra-film impurity ions are neutralized in the step (b). The amount of the adsorbed impurities is then determined in the step (g).
In a preferred embodiment of the invention, the first wavelength range is at least part of a range of about 270 nm to about 300 nm, and the second wavelength range is at least part of a range of about 250 nm to about 270 nm.
Irradiation with the light of the first wavelength range in the step (b) effectively neutralizes only the intra-film impurity ions when adsorbed impurities are present on the surface of the insulating film. This enables the amount of the intra-film impurity ions to be determined accurately in the step (d). Irradiation with the light of the second wavelength range in the step (e) effectively ionizes the adsorbed impurities. This enables the amount of the adsorbed impurities to be determined accurately in the step (g).
The present invention is also directed to an impurity content determination apparatus for determining an amount of impurities in the vicinity of an insulating film formed on surface of a substrate. The impurity content determination apparatus comprises: an electrical property measurement unit that specifies a measurement value of a predetermined electrical property, which relates to the amount of impurities in the vicinity of the insulating film; a first irradiation unit that irradiates the surface of the substrate with light of a first wavelength range, which electrically neutralizes intra-film impurity ions included in the insulating film; and an intra-film impurity ion content determination unit that determines an amount of the intra-film impurity ions in a state prior to the irradiation with the light of the first wavelength range, based on a first measurement value of the predetermined electrical property in the state prior to the irradiation with the light of the first wavelength range and a second measurement value of the predetermined electrical property in a state after the irradiation with the light of the first wavelength range.
These and other objects, features, aspects, and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with the accompanying drawings.
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M. Itsumi, et al., “Effect of UV Light Irradiation on Passivation of Nobile Ions in MOS Devices”,The Institute Of Electronics, Information And Communication Engineers, SDM97-94 (Aug. 1997), pp. 13-20.
R. Williams, “Photoemission of Electronics from Silicon into Silicon Dioxide”, Physical Review, vol. 140, number 2A, Oct. 1965, pp. A 569-575.
Hirae Sadao
Kono Motohiro
Okada Hiroshi
Brown Glenn W.
Dainippon Screen Mfg. Co,. Ltd.
Ostrolenk Faber Gerb & Soffen, LLP
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