JPH0533306B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for manufacturing an insulating film used as a gate insulating film in MIS transistors, a passivation insulating film often used in various devices, or a coating thin film. It is something.

Conventional Structures and Problems Capacitively coupled high-frequency glow discharge is often used as a method for forming silicon nitride films or silicon nitride films at relatively low temperatures (around 300° C.).

FIG. 1 is a simplified cross-sectional view of a capacitively coupled high frequency glow discharge device. Here, a high frequency electrode b and a substrate holder c are placed facing each other in a glow discharge chamber a.
The distance d between the two electrodes can be changed. In such devices, the distance d between the high-frequency electrode and the substrate holder has conventionally been adjusted according to the high-frequency power supply as an additional parameter to obtain uniformity of the plasma discharge state and the resulting uniformity of the deposited film thickness. I was changing it. Therefore, this inter-electrode distance d is 30~30 as a general vapor deposition condition.
At around 35mm, an insulating film with poor electrical properties was generally formed. The narrowest electrode distance in the conventional example is reported to be 20 mm in the Institute of Electronics and Communication Engineers SSD _82-148 Shunan Sei et al.

Purpose of the Invention The present invention optimizes the manufacturing conditions of an insulating film using capacitively coupled high-frequency glow discharge, and in particular, a-Si:H
The purpose of this study is to provide a manufacturing method for forming a high-performance gate insulating film with excellent electrical properties for TFT using .

Structure of the Invention The present invention provides a capacitively coupled high frequency glow discharge device in which the distance between electrodes is less than 20 mm.

Description of Examples The present inventors have determined that the inter-electrode distance d in the capacitively coupled high-frequency glow discharge device shown in FIG.
It was discovered that this parameter has a great influence on the film quality of silicon nitride films and silicon nitride oxide films. Particularly when using it as a high-performance insulating film, we first focus on the distance d between the electrodes, and while keeping this at less than 20 mm, we change other parameters to obtain various properties such as uniformity of the insulating film. It is important to optimize manufacturing conditions.

Here, a silicon nitride film will be described as an example of the insulating film 3. Note that in the case of a silicon nitride oxide film, it can be manufactured by simply adding a small amount of N ₂ O or the like to various mixed gases for manufacturing the silicon nitride film, so the same can be said as described below.

First, a method for evaluating the film quality of silicon nitride films will be described. Figure 2 shows a cross-sectional view of the MIS transistor used for this film quality evaluation. A gate electrode 2 made of _M0 is selectively deposited on a glass substrate 1, and three layers of a gate insulating film 3 to be evaluated, hydrogenated amorphous silicon 4, and P-doped n ⁺ hydrogenated amorphous silicon 5 are deposited. After that, a source 6 and a drain electrode 7 made of Al are selectively deposited, and a part of the P-doped n ⁺ hydrogenated amorphous silicon 5 exposed in the channel part is covered with HF. :HNO ₃ =1:30 mixture.

To evaluate the gate insulating film 3 of this MIS type transistor, voltage (10, 20, 30, 40, 50, 60 volts) was sequentially applied to both the gate and drain electrodes for 30 minutes, and the transistor characteristics were measured each time. By doing so, it is possible to determine the shift in threshold voltage, that is, the magnitude of the number of electrons forcibly injected into the gate insulating film (the insulating film to be evaluated). A decrease in the saturation drain current I _D (in this case, the gate voltage
12V, drain voltage 12V, drain current value _ID (decrease in source common) was measured, and the quality of the insulating film was evaluated. In addition, the dielectric breakdown field strength was measured using a single layer of insulating film, and the withstand voltage was also evaluated.

For the semiconductor layer 4 (active region of the transistor) of this MIS type transistor, hydrogenated crystalline silicon manufactured under the same conditions was used. It has also been confirmed that the cause of deterioration of the transistor due to this voltage application is due to the gate insulating film, and is far greater than the deterioration of the hydrogenated amorphous silicon that forms the active region.

As shown in FIG. 1, the manufacturing apparatus has a glow discharge chamber a, a high frequency electrode b and a substrate holder c disposed facing each other in the chamber, and a distance d between the two electrodes.
This is a capacitively coupled high-frequency glow discharge device configured so that gas can be changed and gas is supplied into the chamber.

Example 1 A case will be described in which a gas containing silicon atoms such as SiH ₄ and a gas containing nitrogen atoms such as NH ₃ (excluding N ₂ ) are used as source gases and H ₂ is used as a carrier gas.

The insulating film 3 made of silicon nitride by the present inventors is
It is formed under the following conditions obtained as a result of optimization of manufacturing conditions. The mixed gas component ratio is SiH ₄ :NH ₃ :H ₂ =
1:6:12, substrate temperature 300℃, 13.56MHz high frequency power supply power per unit area of high frequency electrode 0.2W/cm ²
A gate insulating film 3 having a thickness of about 4000 Å is formed.

Here, as shown in Fig. 1, the distance between the electrodes d
The optical properties of the insulating film when only the
Figures 3 and 4 show the use of these insulators.
FIG. 5 shows the current value deterioration due to voltage application of the MIS type transistor (see FIG. 2). The definition of the energy gap E ^opt/g in Figure 3 is the absorption relationship α=
The energy of the wavelength of light that is 5×10 ⁴ is E ^opt/g .

Furthermore, data obtained from Augier electron spectroscopy shows that the elemental ratio Si/N is approximately 3/4 in all films. Therefore, as the refractive index determined from optical interference (Figure 4) increases, it is thought that the packing density increases, approaching the silicon nitride film produced by high-temperature thermal CVD, which is an excellent insulating film.

FIG. 5 (FIG. 9 is similar) shows an MIS type transistor having the structure shown in FIG. 2, with 12 volts applied to both the gate voltage (V _G ) and the drain voltage (V _D ), The initial value (I D initial value) of the drain current (I _D ) under the condition (V _S =0) is measured and used as a reference. The voltage application method is to first ground the source electrode, apply 10 volts to both the gate and drain electrodes, leave it for 30 minutes, and then measure the drain current ( _ID10 ) under the same conditions as the initial ID value. Take the ratio with the initial ID value. Next, after applying V _G =V _D =20 volts for 30 minutes with the source grounded, I _D20 is measured under the same conditions as the initial _ID value, and the ratio with the initial ID value is calculated. In this way, apply 30, 40, 50, and 60 volts to the gate voltage and drain voltage in sequence for 30 minutes each, measure _ID under the same conditions as the initial ID value, and calculate the ratio with the initial ID value. , is a plotted graph.

Electric field strength within 4000Å of gate insulating film is approximately 1×
Looking at the _ID deterioration characteristics when a voltage of 40 volts (10 ⁶ V/m) is applied, the shorter the distance between the electrodes, the smaller the deterioration. Also, when looking at the dielectric breakdown field strength, the shorter the distance d between the electrodes, the greater the value.

On the other hand, when looking at the distance between the electrodes from the viewpoint of uniformity of the deposited film thickness, if the distance between the electrodes is too close, the plasma discharge will concentrate at the center of the electrode or near the outer periphery of the electrode, resulting in an uneven state. The minimum electrode distance varies depending on the nature and area of the electrode, but it is generally desirable to be around 15 mm. Note that a diluent gas is used in addition to the raw material gas, and the minimum electrode distance can be further reduced by optimizing the type and mixing ratio of this diluent gas.

Example 2 A case where N ₂ is mainly used as a carrier gas in addition to the raw material gas will be described. The mixed gas component ratio is SiH ₄ :NH ₃ :N ₂ = 2:9:25, substrate temperature is 320°C, 13.56 MHz high frequency power source per unit area of high frequency electrode, effective power 0.2 W/cm ² , insulation film thickness approximately 4500 Å.
Form a gate insulating film. Results obtained by the same measuring method as in Example 1 are shown in FIGS. 7 to 10. As shown in FIGS. 7 and 8, both E ^opt/g and the refractive index have the same tendency as in Example 1, which explains that the shorter the inter-electrode distance d, the better the film quality. Further, as in Example 1, a voltage was applied to both the gate and drain electrodes, electrons were forcibly injected into the gate insulating film, and saturation current value deterioration was measured. The results are shown in FIG.
For the same reason as in Example 1, the gate insulating film
Looking at the _ID deterioration characteristics when a voltage of around 45 volts is applied, where the electric field strength within 4500 Å is approximately 1 × 10 ⁶ V/m,
The electrical characteristics begin to deteriorate when the distance between the electrodes is around 20 mm, and the deterioration is significant at 28 mm.

Further, as shown in FIG. 10, for the same reason as in Example 1, the shorter the distance between the electrodes, the better the breakdown voltage in terms of dielectric breakdown field strength.

On the other hand, when looking at the interelectrode distance from the perspective of uniformity of the deposited film thickness, if the distance is less than 12 mm, the plasma discharge will concentrate at the center of the electrode or near the outer periphery of the electrode, resulting in an uneven state; desirable.

From the above, the limit on the distance between the electrodes, which has a large effect on the quality of the insulating film, is 20 mm or less. When N ₂ and H ₂ are mainly used as the carrier gas, the film quality and plasma discharge state are intermediate between the measurement results of Example 1 using H ₂ and the measurement results of Example 2 using N ₂ . The measurement results showed that

Furthermore, almost the same results were obtained when a smaller amount of gas such as He or Ar was added.

Effects of the Invention As explained above, by setting the distance between the electrodes of the manufacturing apparatus using capacitively coupled high-frequency glow discharge to 20 mm or less, a high-performance insulating film with excellent electrical characteristics and high breakdown voltage can be formed.

[Brief explanation of the drawing]

Figure 1 is a simplified cross-sectional view of the capacitively coupled high-frequency glow discharge device, and Figure 2 is the one used in the voltage application experiment.
The cross-sectional views of MIS type transistors, FIGS. 3 and 7, show that the distance between the electrodes in FIG.
Figures 4 and 8 show the energy gap of the insulating film when the distance is changed to 28 mm, and the energy gap of the insulating film is shown when the inter-electrode distance d in Fig. 1 is changed to 16, 20, 24, and 28 mm. The graphs showing the refractive index, Figures 5 and 9, are graphs plotting the amount of decrease in drain current after voltage is applied to both the gate and drain electrodes in the MIS type transistor having the structure shown in Figure 2. FIG. 6 and FIG. 10 are diagrams showing the dielectric breakdown electric field strength of a single layer of an insulating film to be evaluated. a... Glow discharge chamber, b... High frequency electrode, c...
...Substrate holder, 1...Glass substrate, 2...Gate electrode, 3...Gate insulating film, 4...Hydrogenated amorphous silicon.

Claims (1)

[Scope of Claims] 1. A capacitively coupled type comprising a glow discharge chamber, a high frequency electrode and a substrate holder disposed facing each other in the glow discharge chamber, and configured such that gas is supplied into the glow discharge chamber. A method for producing an insulating film, characterized in that when forming a silicon nitride film or a silicon oxynitride film using a high-frequency glow discharge device, the distance between the high-frequency electrode and a substrate holder is less than 20 mm. 2. When forming a silicon nitride film using a gas containing silicon atoms and a gas containing nitrogen atoms (excluding N ₂ ), or a silicon nitride oxide film using the above two gases and a gas containing oxygen atoms such as N ₂ O. 2. The method of manufacturing an insulating film according to claim 1, wherein H ₂ is mainly used in addition to the two types of gases.