JPH029129A - Semiconductor device - Google Patents

Abstract

PURPOSE:To obtain an a-Si TFT stable for a long period of time of 600 times as long as a conventional one by employing an SiNX film having specific value of electron spin density of the SiNX film. CONSTITUTION:A conductor is selectively formed as a gate electrode 2 on a glass board 1. An SiNX is deposited as a gate insulating film 3, and a-Si films are continuously deposited as a semiconductor film 4 by the same plasma chemical vapor depositing method as that of the SiNX film. The a-Si film is selectively removed, and an insular a-Si film pattern 4 is formed. The pattern 4 and an N<+> type a-Si film 5 containing phosphorus as an impurity selectively remain between a source electrode 6 and a drain electrode 7 selectively covered and made of conductors to form an a-Si TFT. The electron spin density of the SiNX is small value of 2.4X10<17>cm<-3> or less. Thus, a stable a-Si TFT endurable for a long period of time of 600 times a conventional one is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a semiconductor device having a silicon nitride film used as a passivation film, an interlayer insulating film, or the like.

Conventional technology: A silicon nitride film (hereinafter referred to as StN film) and an amorphous silicon film (hereinafter referred to as A-8T film) are formed using plasma chemical vapor deposition method (hereinafter referred to as plasma CVD method), respectively. Thin film field effect transistor (hereinafter referred to as a-5iTFT) formed continuously as a gate insulating film and a semiconductor film
Because it has excellent on-resistance and off-resistance, it has been put into practical use as a switching element for liquid crystal image display devices.

Problems to be Solved by the Invention However, there are large differences in characteristic deterioration depending on the manufacturing method and manufacturing conditions, and some inferior products have a lifespan of only about 100 minutes (Reference Nikkei Electronics 1982.12) .20P146-14 ``Special feature on amorphous silicon'').

Therefore, an object of the present invention is to improve the film quality of the SiNx film and provide an a-8i TFT with excellent reliability.

Means for Solving the Problems In order to achieve the above objects, the present invention provides an SiNx film manufactured by plasma CVD with an electron spin density of 2.4×10
(It uses a SiN film having a small value of m or less.

Function The present invention improves the film quality of the SiNx film, thereby improving the film quality of the SiNx film.
This provides a-8iTPT that is stable for a longer period of time than 0 times. Furthermore, the SiNx film according to the present invention has excellent film quality especially near the interface and has few trap levels, so it can provide an a-3i TFT with excellent characteristics. Therefore, other applied semiconductor devices using the 5iNX film of the present invention can also have excellent characteristics.

Embodiment FIG. 2 shows a cross-sectional view of the main structure of an embodiment of an a-3i TFT. KCr, MoS 12 on glass substrate 1
A conductor such as the like is selectively formed as the gate electrode 2. 1
A SiNx film with a thickness of about 5eooA was formed as the gate insulating film 3 using a parallel plate plasma CVD method using a glow discharge of 3.56 MHz, and a SiNx film with a thickness of about 5eooA was formed as the semiconductor film 4 using the same plasma chemical vapor deposition method as the SiN film. Hitoshika's a-3L
A film is continuously deposited, and the a-5i film is selectively removed by etching or the like to form an island-like pattern 4 of the a-3i film.

An n+ type a-9i film 5 containing phosphorus as an impurity is interposed between the a-3i film pattern 4 and a selectively deposited source electrode 6 and drain electrode 7 made of a conductor such as Al or MOS 12. A-3 with a film thickness of about 500 continuous speed selectively left
iTFT is manufactured. According to our research, the characteristics of a-3i TFTs, especially the on-characteristics and reliability, are greatly influenced by the quality of the SiNx film used as the gate insulating film.

Furthermore, it has been found that among the film qualities of these SiNx films, the electron spin density is a major parameter that indicates an optimal SiN film.

The electron spin density of the SiNx film in this example is a
-St T F A SiNx film was deposited on a double-sided polished single crystal silicon substrate with a resistivity of 200 to 240 Ω (7) under the same conditions as for fabricating the T F T, and the substrate temperature was 26°C.
q using an electron spin resonance device at Q±3.0℃
The electron spin number of silicon with fM of 2.006 to 2.006 is measured, and the electron spin number of the SiN film is obtained by subtracting the electron spin number of the silicon substrate alone. It appears as a voltage V, and depending on whether the sign of the applied gate voltage is positive or negative, a shift of V with the same sign occurs.

The gate threshold voltage (■) in this example is determined by using an a-3i TFT shown in FIG. 2 with a channel width W and a channel length W/L ratio of 66.7, and a substrate temperature of 25.0. When the source is connected and a constant drain voltage of 15V is applied in a dark environment at ±3℃, the drain current is l.
I worked as a gate electrician when it became X10A. The shift amount V is obtained by subtracting the gate threshold voltage V immediately after fabricating the a-3i TFT from the threshold voltage t when the a-StTFT has been operated for a long time.

Figure 3 shows that the electron 7 pin density of the SiNx film is 1.7X101.
The V of the 8/7ff' a-3i TFT shows the shift pattern.

The characteristics of a-3i TFT immediately after fabrication are curves, and ■, -
vt1z5.9■ Tea Tsuta. a-8iT F T In a dry nitrogen gas atmosphere in complete darkness 25. After operating for 30 minutes in an environment of o±3.0°C with a common source, a constant drain voltage of 12 V, and a constant gate voltage of 30 V (DC operating conditions) (7) Characteristic force B Curve tear, Vt = Vt2 = 9. The drain current when the gate voltage is 15 V is initially ID1=17 μA, but after operation, it has been halved to ID2=8 μA.

Figure 1 shows SiNx films produced under various plasma CVD conditions such as the flow rate ratio of S I H4 gas and NH3 gas, discharge power, degree of vacuum, etc. in a dry nitrogen gas atmosphere in the dark at 26.0±3. In an environment of 0℃, source common, drain voltage 12■, gate voltage constant 3oV (DC operating conditions)
SiN
It is a diagram in which the electron spin density of the x film is plotted on the horizontal axis.

In FIG. 1, even when films are subjected to various plasma CVD conditions, by using the electron spin density as a parameter, the vt shift amount of the a-8i TFT is aligned on two straight lines. And the electron spin density is about 2.4XIQ
It has become clear that when the value becomes larger than c7R, the amount of v7 shift increases as the electron spin density increases.

Figure 4 shows an a-8i TFT placed on the glass substrate of Figure 2, illuminated with a fluorescent lamp so that the illumination intensity is 8000/rex on the surface on which the a-SiTPT is not formed, and placed in a dry nitrogen gas atmosphere. In an environment of 80.0±3'C, a pulse voltage of 21V between peaks of 60°C with a pulse width of 60μ is applied to the gate electrode with the source grounded, and the drain voltage is 3V.
V when applying AC rectangular e (AC operating condition) with 4V peak-to-peak at 01-it and operating for 1000 hours,
It is a diagram in which the shift amount is plotted on the vertical axis and the electron spin density of the SiN film is plotted on the horizontal axis. Similar to the previous figure 1, SiNx
When the electron spin density of the film becomes larger than 2.4 × 10 , the v1 amplitude of the a-3i TFT becomes S I
It can be seen that it increases as the Nx film increases. Also, SiN
.

It has become clear that when the electron spin density of the film becomes less than 2.4×10ff, the η shift becomes below the measurement limit.

From the above, in order to obtain a highly reliable a-3i TFT, the electron spin density of the SiNx film must be 2.4
It can be seen that it is necessary to be as small as 10 3 or less.

Effects of the Invention The 5iN3c film produced by the plasma CVD method with a small electron spin density of 2.4×10ff or less according to the present invention has the following properties:
As mentioned above, the level density near the interface is low, and it is considered to be excellent as an interlayer insulating film or a passivation film for semiconductor devices. Furthermore, an a-3iTFT using the 5INx film of the present invention as a gate insulating film in combination with an a-Si film
has a lifespan that is 00 times longer than that previously reported.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of the main part structure of an a-SiTFT in one embodiment of the present invention, and Figure 2 is the electron spin density of the SiNx film and the gate threshold voltage of the a-3iTFT when DC operation is performed for 30 minutes. ■, Characteristic diagram showing the relationship with the shift amount, Figure 3 plots the drain current on the vertical axis and gate voltage on the horizontal axis, ■, Characteristic diagram showing the state of shift, Figure 4 shows the 5i
FIG. 3 is a characteristic diagram showing the relationship between the spin density of the NX film and the gate threshold voltage vt shift amount of a-5iTPT when AC operation is performed for 1000 hours. 1...Glass substrate, 2...Gate electrode,
3...SiNx film, 4-...-a-Si film,
5-...n+ type a-3i film, 6...source electrode, end...tosine electrode. Name of agent: Patent attorney Toshio Nakao and 1 other person 1st
Figure glass base 1 trap - 1 electric switch SiNx field Q-9i film n? Pear α-5iW gastric source electrode train Vt shift t<V) Fig. Gate voltage (v)

Claims (5)

[Claims] (1) A semiconductor layer and an insulating film that are in contact with each other on one main surface of a substrate are included as part of the structure, and the insulating film is 2.4×
A semiconductor device characterized in that it is a silicon nitride film having an electron spin density of 10^1^7 cm^-^3 or less. (2) Claim 1, wherein the insulating film is a silicon nitride film produced by plasma chemical vapor deposition.
The semiconductor device described. (3) The semiconductor device according to claim 1, wherein the insulating film is a gate insulating film of a field effect transistor. (4) The semiconductor device according to claim 1, wherein the semiconductor layer is an amorphous silicon film. (5) The semiconductor device according to claim 1 or 4, wherein the semiconductor layer is an amorphous silicon film produced by plasma chemical vapor deposition.