Active solid-state devices (e.g. – transistors – solid-state diode – Conductivity modulation device
Reexamination Certificate
2001-06-06
2003-03-25
Nelms, David (Department: 2818)
Active solid-state devices (e.g., transistors, solid-state diode
Conductivity modulation device
C438S234000, C438S381000, C438S393000, C438S394000, C257S213000
Reexamination Certificate
active
06538271
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor device using a silicon nitride film as an insulating film, and a method of manufacturing the same.
A semiconductor memory device has been widely used as a memory device for use in an information processing apparatus in recent years. The semiconductor memory device is highly resistive to mechanical shock due to the absence of a mechanical driving mechanism. In addition, it is possible for the semiconductor memory to gain high-speed access since a reading-out operation is electrically performed.
However, the tendency toward miniaturization of memory cells, that is, high integration of the semiconductor memory device, has been accelerated by recent progress in semiconductor technologies, particularly in miniaturization technologies. With the high integration of the semiconductor memory device, problems are raised regarding memory cell storage characteristics.
For example, in a DRAM having a memory cell consisting of a MOS transistor and a capacitor connected in series, capacitance is inclined to decrease with reduction in capacitor area due to the high integration. As a result, problems called “soft error” occur. The soft errors are phenomena where a different memory is mistakenly read out, and where a stored memory data is broken by an &agr;ray.
To solve the soft error problems, it is important that the capacitance is maintained even if the memory cell is reduced in size. To attain this, it is necessary to increase a capacitor area as well as to reduce thickness of a capacitor insulating film.
As the capacitor insulating film, a silicon nitride film, which has a higher dielectric constant than a silicon oxide film, has been widely used. The silicon nitride film of this type has hitherto been formed by a low pressure CVD method. However, the silicon nitride film thus formed has a drawback in that a leakage current is likely to increase.
BRIEF SUMMARY OF THE INVENTION
An object of the present invention is to provide a semiconductor device using a silicon nitride film with a low leakage current.
To attain the object, a semiconductor device according to a first aspect of the present invention comprises:
a semiconductor substrate; and
a silicon nitride film formed on the semiconductor substrate, the silicon nitride film being substantially free from an Si—H bond.
The density of Si—H contained in a unit area of the silicon nitride film is 1×10
15
cm
−2
or less.
It is preferable that the silicon nitride film have a film thickness within 4 nm to 8 nm.
The silicon nitride film may have a stacked structure having unit layers of 2 nm or less in thickness stacked one upon another.
The silicon nitride film may be used in at least one of a capacitor insulating film and a gate insulating film.
The silicon nitride film is substantially free from an N—H bond.
A method of manufacturing a semiconductor device according to a second aspect of the present invention comprises the steps of:
loading a substrate in a low pressure CVD apparatus; and
forming a silicon nitride film substantially free from an Si—H bond by introducing a predetermined silicon source gas into the low pressure CVD apparatus.
The step of forming the silicon nitride film includes a step of forming a silicon nitride film having an Si—H density per unit area of 1×10
15
cm
−2
or less.
A silicon source gas free from an Si—H bond is used as the predetermined silicon source gas.
The predetermined silicon source gas desirably contains silicon whose bonds are entirely bonded to at least one element selected from the group consisting of silicon, nitrogen, and halogen.
The predetermined silicon source gas is preferably one of tetrachlorosilane, hexachlorodisilane, tetrakisdimethylaminosilane and trichlorosilylazide.
The step of forming a silicon nitride film can further comprise the steps of:
forming the silicon nitride film by using the predetermined silicon source gas having an Si—H bond;
reducing hydrogen contained in the silicon nitride film by a heat treatment; and
forming a silicon nitride film having an Si—H density per unit area of 1×10
15
cm
−2
or less.
It is preferable that the heat treatment be performed at a temperature within a range of 900° C. to 1100° C.
A method of manufacturing a semiconductor device according to a third aspect of the present invention comprises:
a step of loading a semiconductor substrate into a chamber;
a first step of introducing a silicon-containing gas into a chamber;
a second step of performing a first annealing of the semiconductor substrate in the silicon-containing gas at a temperature within 600 to 900° C. and a pressure within 0.1 Torr to 10 Torr;
a third step of exhausting the silicon-containing gas after the first annealing;
a fourth step of introducing a nitrogen-containing gas after the third step;
a fifth step of performing a second annealing of the semiconductor substrate in the nitrogen-containing gas at a temperature within 600 to 1000° C. and a pressure within 0.5 Torr to 100 Torr;
a sixth step of exhausting the nitrogen-containing gas after the fifth step; and
a step of repeating the first to sixth-steps a plurality of times.
It is desirable that the silicon-containing gas include at least one of tetrachlorosilane, trichlorosilane, and dichlorosilane.
It is desirable that the nitrogen-containing gas include at least one of ammonia, nitrogen trifluoride, hydrazine, dimethylhydrazine and monomethylhydrazine.
A step of thermally nitriding the semiconductor substrate can be included before the first step.
Furthermore, before the first step, it is possible to further include the steps of:
forming a native oxide film on a surface of a semiconductor substrate; and
removing the native oxide film.
Moreover, before the first step, it is possible to comprise the steps of:
forming a native oxide film on a surface of the semiconductor substrate; and
annealing the native oxide film in hexachlorodisilane.
It is desirable that the temperature of the annealing performed in hexachlorodisilane is 400° C. or less.
It is preferable that the third and sixth steps include the step of replacing anyone of the silicon containing gas and the nitrogen containing gas with anyone of an inert gas, a hydrogen chloride gas and a hydrogen gas.
It is preferable that an Si—H density per unit area of the silicon nitride film formed in the fifth step is 1×10
15
cm
−2
or less.
The silicon nitride film formed in the fifth step may have a film thickness of 2 nm or less.
The present invention is made based on the following findings.
The silicon nitride film for use in the capacitor insulating film is formed conventionally by a low-pressure CVD method. The silicon nitride film formed by this method contains a large amount of hydrogen (3×10
21
cm
−3
or more).
In this case, hydrogen contained in the silicon nitride film forms an Si—H bond and an N—H bond. However, since the binding ability of the Si—H bond is especially weak, there are a large number of silicon dangling bonds present in the silicon nitride film. The silicon dangling bond will serve as an electron and hole trap. This means that if the silicon nitride film has a number of silicon dangling bonds, the leakage current will increase.
The leakage current may be reduced by decreasing Si—H concentration so that the number of silicon dangling bonds may decrease. It is found that the Si—H density per unit area of 1×10
15
cm
−2
or less is good enough to reduce the leakage current sufficiently.
According to a semiconductor device of a first aspect of the present invention, the silicon nitride film has an Si—H density per unit area of 1×10
15
cm
−2
or less. Therefore, the silicon nitride film with a low leakage current can be realized.
In the present invention, the thickness of the silicon nitride film is set at 4 nm or more. If the silicon nitride film is formed within the thickness range, it can be formed in a well-controlled thickness.
Furthermore, to reduce the Si—H density per unit area, it is effect
Saida Shigehiko
Tsunashima Yoshitaka
Berry Renee R
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Kabushiki Kaisha Toshiba
Nelms David
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