Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
1999-01-13
2001-03-27
Thomas, Tom (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S408000, C257S382000
Reexamination Certificate
active
06208002
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a field effect transistor having a gate oxynitride film containing heavy hydrogen atoms, and a manufacturing method thereof.
In an element such as an electrically writable, erasable, and programmable read only memory (EEPROM), an electric field of 10 MV/cm or higher is applied to a gate oxide film in reading/erasing the information stored in the memory, and the gate oxide film is used as a tunnel oxide film. When the gate oxide film is applied with so high electric field, electrons energized by the high electric field pass through the gate oxide film. Accordingly, the gate insulating film is required to have high voltage withstand capability. If the gate insulating film is not formed to withstand such a high electric field, the impurity such as boron in the gate electrode is introduced into the gate insulating film to reach the substrate surface though the gate insulating film. The impurity concentration of the substrate surface is deviated from the desired level thereby, and thus the normal transistor characteristics may not be obtained.
Conventionally, the manufacturing condition of the gate oxide film has been determined empirically: various oxide films are formed by varying parameters such as a forming temperature and the concentration of the oxygen contained in the atmosphere; the electric characteristics of the formed films are evaluated thereafter; and then the oxide film satisfying the desired specification is selected from the films. As the types of products are varied and the speed of the alternation of product generations increases, however, the above-mentioned empirical determination method of the forming condition of the oxide film becomes not so effective, and is beginning to increase the manufacturing cost.
It has been reported that the post-annealing process (for 30 minutes at 900° C.) performed in a D
2
atmosphere containing heavy hydrogen (DV), i.e., “deuterium” is effective to suppress the generation of the interface state at the interface of the gate oxide film and the substrate (N. S. Saks and R. W. Rendell, IEEE Trans. Vol. NS-39, pp. 2220-2229, 1992). The method disclosed by the report, however, relates to the gate oxide film alone.
BRIEF SUMMARY OF THE INVENTION
The object of the present invention is to provide a gate insulating film structure for obtaining a gate insulating film having high electric reliability and a small thickness, and the forming method of the gate insulating film, which enables the gate insulating film structure to be realized.
According to the first aspect of the present invention, the above-mentioned objects of the present invention are attained by a manufacturing method of a field effect transistor having a gate electrode formed on a semiconductor layer to hold a gate insulating film therebetween, comprises the steps of forming the gate insulating film into which heavy hydrogen atoms are implanted by exposing a main surface of the semiconductor layer to an atmosphere containing oxygen atoms and nitrogen atoms such that a concentration of the heavy hydrogen atoms in an interface between the gate insulating film and the gate electrode is higher than that of a middle portion of the gate insulating film located in the middle of the gate insulating film in a direction of a thickness of the gate insulating film, forming the gate electrode on the gate insulating film, and forming a pair source and drain regions on the main surface of the semiconductor layer so as to sandwich the gate electrode therebetween.
It is preferable that the gate insulating film forming step includes the steps of forming a silicon oxide film on the semiconductor layer, and implanting the heavy hydrogen atoms and the nitrogen atoms into the silicon oxide film by exposing the silicon oxide film to gas containing a compound of the heavy hydrogen atoms and the nitrogen atoms after the silicon oxide film forming step.
The silicon oxide film forming step may include a step of exposing the semiconductor layer to a dry oxygen atmosphere in a heated atmosphere under an atmospheric pressure.
The silicon oxide film forming step may include the steps of bubbling liquid D
2
O, introducing mixed gas of a gas generated by the bubbling step, D
2
gas, and O
2
gas into a reactive chamber in which the semiconductor layer is located, and forming a silicon thermal oxide film containing the heavy hydrogen atoms on the semiconductor layer in a heated atmosphere.
The silicon oxide film forming step may include the steps of bubbling liquid D
2
O, introducing mixed gas of a gas generated by the bubbling step and D
2
O gas into a reactive chamber in which the semiconductor layer is located, and forming a silicon thermal oxide film containing the heavy hydrogen atoms on the semiconductor substrate in a heated atmosphere.
The silicon oxide film forming step may include a step of exposing the semiconductor substrate to an atmosphere containing activated oxygen in a heated atmosphere under a reduced pressure.
It is also preferable that the heavy hydrogen atoms and the nitrogen atoms introducing step includes a step of exposing the main surface of the semiconductor layer on which the silicon oxide film is formed to ND
3
gas in a heated atmosphere under a reduced pressure.
It is further preferable to perform an ion implantation step of implanting D
+
ion into the silicon oxide film after the introducing the heavy hydrogen atoms and the nitrogen atoms into the silicon oxide film.
It is further preferable that the forming step of the gate electrode includes a step of forming the gate electrode by using SiD
4
gas and HD
3
gas as source gases in a heated atmosphere under a reduced pressure by means of a CVD method.
It is still further preferable to perform a step of forming an interlayer insulating film on the semiconductor layer after the forming step of the source and drain regions, the interlayer insulating film forming step including the steps of forming a silicon oxide film containing D atoms by exposing the semiconductor layer to a gas containing SiD
4
gas and oxygen gas, and forming a silicon oxide film containing D atoms in a heated atmosphere under a reduced pressure with use of one of SiD
4
gas and Si
2
D
6
gas by means of a CVD method.
Before the forming step of the gate insulating film to which the heavy hydrogen atoms are implanted, a step of forming a region containing high concentration of D atoms in the semiconductor layer may be performed by exposing the semiconductor layer to a D
2
gas atmosphere in a heated atmosphere under an atmospheric pressure.
According to the present invention, a serious problem of the conventional technique, such as the deterioration of the transistor characteristics and the property of the insulating film, and bad efficiency of the insulating film selection process, which have never been solved by the conventionally known technique, can be surely solved.
More specifically, an Si—D bonding more stabilized than an Si—H bonding is formed in an interface of the gate electrode to have sufficiently high concentration, at first. Thereby the dangling bond generated in the interface of the gate electrode and the gate oxynitride film can be terminated by D atoms in the Si—D bonding. By forming the Si—D bonding in this manner, the unevenness which may be generated in the interface between the gate electrode and the insulating film can be suppressed even after performing the subsequent processes such as a heating process. The unevenness in the interface is remarkable on a silicon thermal nitride film in comparing with on a silicon oxide film. Accordingly, it is very useful to implant D atoms in a silicon thermal nitride film to stabilize the interface structure.
As described above, according to the above-mentioned first aspect of the present invention, the withstand capability of the insulating film can be improved, and the gate insulating film on the side of the gate electrode is formed to be structurally stabilized and dense, by implanting high concentration of Si—D bonding in the interface of
Satake Hideki
Toriumi Akira
Kabushiki Kaisha Toshiba
Nguyen Cuong Q
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Thomas Tom
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