Insulating film and method of forming the same

Details Insulating film and method of forming the same Insulating film and method of forming the same

1999-05-19

2002-04-09

Wille, Douglas (Department: 2814)

Semiconductor device manufacturing: process

Coating of substrate containing semiconductor region or of...

By reaction with substrate

C438S776000, C438S787000

Reexamination Certificate

active

06368984

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an insulating film used as a tunnel oxide film of a flash memory, a gate oxide film of a transistor or the like, and to a method of forming such a film.
2. Description of the Related Art
Apart from the memory for general use, such as DRAM, SRAM or the like, recently there has been an increasing demand of EEPROM (flash memory), in which data remains if the power is turned off, data can be rewritten for 10
6
times or more, and which is suitable for a large increase in capacity. The reliably of such a flash memory is deeply correlated with the reliability of the silicon oxide film (insulating film) having a thickness of 10 nm or less, which is called a tunnel oxide film. Thus, the reliability of the flash memory is greatly influenced by three different electrical characteristics: (1) dielectric breakdown life, (2) charge trap amount and (3) stress leak amount, which are items of evaluating the reliability of a silicon oxide film. If at least one of these characteristics is deteriorated, the device cannot function sufficiently.
As described above, it is necessary for a flash memory to keep up the above three reliabilities at the same time; however, with a conventional thermal oxide film, all of the reliabilities cannot be satisfied. For example, as to the conventional thermal oxide film, there has been a report of achieving the prolongation of the dielectric breakdown life and the reduction of the charge trap amount; however, there has been no report of achieving a significant reduction in the stress leak amount.
Further, in the case of the gate oxide film of a transistor, for example, the variance of the element characteristics occurs due to hot carrier implantation. The hot carrier implantation is a phenomenon in which electrons in a channel of a transistor becomes hot as energy being supplied from an electric field in the direction along the channel, and the electrons are implanted into the gate oxide film. This phenomenon generates a charge trap in an oxide film, or an interface state at an interface between the oxide film and the substrates, which causes a variation in the threshold value of the transistor or a gm deterioration.
Meanwhile, with regard to the method of forming a tunnel oxide film, in the case where an oxide film having a thickness of about 5 to 10 nm is formed by a conventional vertical diffusion furnace, it has been reported that an oxide film, which was oxidized in a water vapor atmosphere, in a so-called wet oxidizing atmosphere, has an insulation breakage life longer than an oxide film, which was oxidized at a temperature of 850°, in a so-called dry oxidizing atmosphere (dry oxidizing atmosphere). Further, with regard to the amount of stress leak generated, it has been reported that the amount of the stress leak of an oxide film formed in a water vapor oxidizing atmosphere is suppressed more (lower) than the case of an oxide film formed in a dry oxygen atmosphere. Meanwhile, it has been reported that the density of the charge trap is reduced more in an oxide film formed in a dry oxygen atmosphere than in an oxide film formed in a water vapor atmosphere. However, there has been no report on a silicon thermal oxide film or a method of forming such a film, which satisfies all of the above-described three reliabilities at the same time.
As described, with a silicon thermal oxide film, by itself, it is not possible to satisfy the three reliabilities at the same time, and therefore a silicon oxynitride film in which nitrogen is introduced into a silicon thermal oxide film, is presently used as a tunnel oxide film. The silicon oxynitride film is able to decrease the stress leak amount, and further satisfies the conditions of a dielectric breakage life which the silicon thermal oxide film itself possesses and a decrease in the charge trap amount. Thus, the silicon oxynitride film satisfies the above-described reliabilities at the same time.
However, the silicon oxynitride film has current-voltage (I-V) characteristics different from those of a silicon oxide film which does not contain nitrogen, since nitrogen is introduced to a silicon thermal oxide film. Also, the device operation characteristics are varied along with the amount of nitrogen introduced, which creates a problem. As typically exemplified in the thinning of a thermal oxide film at an element separation edge, the three reliabilities are very much influenced by the reliability of the silicon thermal oxide film itself, which serves as an underlayer. In reality, it is necessary to improve the film quality of the silicon thermal oxide film must be further improved in terms of all of the three reliabilities, from those of the present status.
SUMMARY OF THE INVENTION
The present invention has been proposed in consideration of the above-described drawback of the prior art technique, and the object thereof is to provide an insulating film having a long dielectric breakage life, capable of reducing the amount of the interface state and the amount of charge trap generated, and capable of remarkably reducing the amount of stress leak generated when a high electrical field stress is applied, as well as a method of manufacturing such a film.
According to an aspect of the present invention, there is provided an insulating film formed on a surface of a substrate and made of a material containing oxygen, wherein a charge correction is carried out at a
1
s
peak position of a carbon adsorbed on a surface of said insulating film, and relative amounts between first to fourth peaks obtained when an oxygen
1
s
peak of said insulating film is decomposed by a same half width of 1.208 eV into a first peak at the oxygen
1
s
peak position obtained from an &agr;-quartz crystal charge corrected similarly, and second to fourth peaks at positions of +0.87 eV, −0.35 eV and −0.83 eV, respectively from the oxygen is first peak position, have relationship of that the third peak is higher than the second and fourth peaks, and the first peak is higher than the third peak, when a portion about 1 nm thick from the surface of the substrate of the insulating film is analyzed by a photoelectronic spectral method for an photoelectron extracting angle of 15° or less. With this structure, it becomes possible to form an insulating film having excellent electrical characteristics, even if the thickness thereof is only 3 nm or more and 10 nm or less.
With regard to the insulating film of the present invention, the insulating film made of a material containing oxygen, is meant to be a silicon oxide film, silicon oxynitride film or the like.
Further, with the insulating film of the present invention, the portion about 1 nm thick (deep) from the surface of the substrate is analyzed by a photoelectronic spectral method while setting the photoelectron extracting angle at 15° or less. This is because the difference from a conventional insulating film can be observed only in a region very close to the surface of the substrate, as the matter of the sensitivity of the analysis. Therefore, for example, at a section 10 nm-deep from the surface of the substrate, a fine difference between the insulating film of the present invention and a conventional one cannot be observed due to a low sensitivity of the analyzing device. Further, the reason why the photoelectron extracting angle is set at 15° or less in the photoelectronic spectral method, is to analyze the insulating film mainly. When the angle exceeds 15°, for example, when the angle is 90°, the amount of photoelectrons from the substrate increases, and therefore the sensitivity for analyzing the insulating film is relatively decreased.
In the insulating film of the present invention, it is preferable that the relative amount of the first peak should be 40% or more of an area of the oxygen
1
s
peak, the relative amount of the third peak should be 30% or less of the area of the oxygen
1
s
peak, and the relative amounts of the second and fourth peaks should be 20% or less of the area of the oxyg

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