Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
1998-07-14
2001-02-20
Hardy, David (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S410000
Reexamination Certificate
active
06191463
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor device and a method of manufacturing the same and, more particularly, to a semiconductor device and a method of manufacturing the same, which can improve the reliability and the like of the gate insulating film of a MOS semiconductor device.
Recently, in a device using a gate oxide film as a tunnel oxide film, represented by an electrically programmable and erasable nonvolatile semiconductor memory (EEPROM), a high electric field of 10 MV/cm or more has been applied to the gate oxide film to write and erase data. Higher electric fields tend to be applied to the gate oxide film of a logic operation device to maintain high performance with advances in micropatterning. When the above high electric field is applied to the gate oxide film, electrons gaining high energy from the electric field pass through the gate oxide film. For this reason, high dielectric breakdown strength is required for the gate oxide film.
An empirical method of setting conditions has been used. More specifically, various oxide films are formed first while parameters such as a film formation temperature and a film formation atmosphere are variously changed. The electrical characteristics of the formed films are then evaluated to use conditions that meet the required specifications. With the current trend toward thinner gate oxide films, however, it is difficult to meet the above specifications. In addition, with the current trend toward a larger number of types of products and faster change of generations, the above empirical method of setting conditions is very inefficient. This leads to a serious problem of an increase in product cost.
As described above, although high dielectric breakdown strength is required for the tunnel insulating film of a nonvolatile memory and the gate insulating film of a logic operation device, it is very difficult to meet satisfactory specifications, resulting in a deterioration of the reliability of the device.
A gate oxide film having a thickness of 5 nm or less is required for a transistor used for a logic operation device to attain a reduction in power consumption.
To meet such requirements, i.e., to improve the reliability of a gate oxide film, e.g., to increase the dielectric breakdown strength, it is taken for granted that introduction of fluorine (F) atoms into the gate oxide film is effective. If, however, F atoms are excessively implanted into the gate oxide film, the number of electron traps increases, resulting in a deterioration in the reliability of the device.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to provide a semiconductor device and a method of manufacturing the same, which can improve the reliability of a gate insulating film, e.g., increasing the dielectric breakdown strength, thus improving the reliability of the device.
In order to achieve the above object, according to the first aspect of the present invention, there is provided a semiconductor device comprising:
a semiconductor substrate;
a first insulating film formed on the semiconductor substrate; and
an electrode formed on the first insulating film
wherein the first insulating film contains a halogen element and any one of a combination of silicon and nitrogen and a combination of silicon, oxygen, and nitrogen, and a maximum concentration of the halogen element in the first insulating film ranges from 10
20
atoms/cm
3
to 10
21
atoms/cm
3
inclusive.
The halogen element is preferably fluorine.
The semiconductor device further comprises a pair of impurity diffusion layers formed on the semiconductor substrate to extend along two ends of the electrode, and the electrode is interposed between the pair of impurity diffusion layers.
In the above semiconductor device, the semiconductor substrate, the insulating film, and the electrode can constitute a capacitor.
A method of manufacturing the semiconductor device according to the first aspect comprises the steps of:
forming a gate insulating film containing any one of a combination of silicon and oxygen and a combination of silicon, oxygen, and nitrogen on a semiconductor substrate; and
introducing a halogen element into the gate insulating film with a maximum concentration ranging from 10
20
atoms/cm
3
to 10
21
atoms/cm
3
inclusive.
Note that the maximum concentration is the maximum concentration of the halogen element in the gate insulating film in the direction of thickness.
In a region near the interface between the gate insulating film and the silicon substrate, Si—F bonds with high bonding energy can be formed by terminating the dangling bonds of silicon with fluorine or substituting fluorine atoms for the hydrogen atoms of Si—H bonds with low bonding energy. In addition, fluorine may be reacted with a distorted Si—O—Si bond to separate it into an Si—O bond and an Si—F bond, thereby reducing the stress. By introducing fluorine into the gate insulating film in this manner, characteristics associated with the reliability of the gate insulating film, e.g., the TDDB (Time-Dependence-Dielectric-Breakdown) characteristics, can be improved when a high electric field is applied to the gate insulating film for a long period of time.
FIG. 1
shows the effects obtained when fluorine is introduced into a gate oxide film. Referring to
FIG. 1
, the abscissa represents the amount of charge (Charge-to-Breakdown: Qbd) injected into the gate oxide :film when a constant electric field is kept applied to the film until dielectric breakdown occurs, and the ordinate represents an accumulated failure rate P due to dielectric breakdown as ln(−ln(1−P)). Without fluorine, the shape of the distribution indicates that many breakdowns occur at a low Qbd. With fluorine, the distribution exhibits a sharp shape, indicating that MOS semiconductor devices having oxide film quality made uniform by introducing fluorine into the films can be obtained.
FIG. 2
shows the 50% Qbd (average value of Qbd) and the Qbd
ex
failure rate (the ratio of the number of chips undergoing dielectric breakdown within short periods of time to the total number of chips) with respect to the maximum fluorine concentration in a gate oxide film. As is obvious from
FIG. 2
, when the maximum fluorine concentration exceeds 10
21
atoms/cm
3
, the 50% Qbd abruptly decreases, whereas when the maximum fluorine concentration becomes lower than 10
20
atoms/cm
3
, the Qbd
ex
failure rate abruptly increases to 10% or more.
FIG. 3
shows SiF/Si (i.e., the ratio of Si—F bonds) and SiF
2
/Si (i.e., the ratio of Si—F
2
bonds) with respect to the maximum fluorine concentration in a gate oxide film. As is obvious from
FIG. 3
, when the maximum fluorine concentration in the gate oxide film exceeds 10
21
atoms/cm
3
, the number of Si—F
2
bonds that degrade the reliability of the gate oxide film abruptly increases.
The above description is associated with the case in which a silicon oxide film is used as a gate insulating film. The same applies to a case in which a silicon nitride film or an oxynitride film containing silicon, oxygen, and nitrogen is used.
As described above, to obtain a highly reliable gate insulating film, the maximum fluorine concentration in the gate insulating film is preferably set to 10
20
atoms/cm
3
to 10
21
atoms/cm
3
. With this setting, even if a gate insulating film is thin (e.g., 8 nm or less), the dielectric breakdown characteristics, low-electric-field leakage current characteristics, and the like of the gate insulating film can be improved, and hence the reliability of the gate insulating film can be improved. This leads to an improvement in the reliability of the device.
The step of introducing a halogen element such as fluorine into the gate insulating film and the subsequent steps are preferably free from the annealing step at 850° C. or more for 30 min or more. If such annealing steps are performed, the halogen element is further implanted from the halogen element source into the gate insulating film. As a result, the gate insulating film may contain the ha
Mitani Yuichiro
Satake Hideki
Toriumi Akira
Hardy David
Kabushiki Kaisha Toshiba
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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