JPH04296025A - Reactive ion etching method - Google Patents

Abstract

PURPOSE:To perform the title reactive ion etching step with excellent dimensional precision leaving no excessive etching residue on the base stepped part when an amorphous silicon film on a glass substrate is etched away using a reactive gas. CONSTITUTION:A part of the thickness of an amorphous silicon film 14 (in the film thickness of t1, t2) partly covered with a photoresist mask 15 is reactive ion etched away using SF6 gas 16 or NF3 gas on a glass substrate 10 so that the etching residue on the base stepped part may be avoided by making the etching step in the lateral direction feasible. Next, the remaining film thickness part of the film 4 is etched away using CCl2F3 gas 17 containing N2 capable of advancing the etching step in the vertical direction. Through these procedures, the amorphous silicon film having the stepped part can be etched away with excellent dimensional precision leaving no excessive etching residue.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a reactive ion etching method for etching an amorphous silicon film using a reactive gas, and more particularly to a reactive ion etching method for etching an amorphous silicon film with steps. .

0002

2. Description of the Related Art Conventionally, in the manufacturing method of thin film transistor devices, a reactive ion etching method using parallel plate electrodes has been used in order to form fine patterns with good reproducibility. FIG. 2 is a diagram schematically showing an etching apparatus that carries out the conventional reactive ion etching method described above. This apparatus is configured such that a pair of parallel plate electrodes 2 and 3 are arranged in an etching chamber 1, and an object to be etched 4 is placed on one of the electrodes 3 via a glass substrate. Introducing a reaction gas into the etching chamber 1 through the gas introduction hole 1a and exhausting it through the exhaust hole 1b,
In this state, a high frequency voltage is applied between the electrodes 2 and 3 using the high frequency power source 5 to cause discharge, and plasma is generated to etch the object 4 to be etched.

When etching an amorphous silicon film on a glass substrate using such a reactive ion etching method, a gas containing chlorine, such as CCl4 gas, has conventionally been used as a reactive gas. Here, the related process of patterning the amorphous silicon film in the gate electrode portion will be described next. First, a gate chrome film is patterned on a glass substrate, then an oxide film is formed as a gate insulating film by sputter deposition, and a nitride film is formed by plasma CVD. Furthermore, an amorphous silicon film is formed as a conductive film by plasma CVD. Next, the amorphous silicon film is etched with CCl4 gas using the etching apparatus shown in FIG. Through this process, the amorphous silicon film other than under the photoresist is completely removed, and etching can be performed with a sufficient selectivity to the underlying nitride film. Etching using CCl4 gas progresses uniformly only in the vertical direction, so that good etching without constrictions or overhangs on the etched surface can be obtained.

0004

[Problems to be Solved by the Invention] The conventional reactive ion etching method described above has problems in the above manufacturing process, especially when applied to an amorphous silicon film with steps.
A problem arises in that amorphous silicon remains at the step portion. This situation will be explained based on FIG. Note that FIG. 3 is a diagram for explaining a situation in which when an amorphous silicon film with a step is etched using conventional CCl4 gas as a reactive gas, amorphous silicon remains at the step. Figure 3
Figures a to c are process longitudinal cross-sectional views showing the etching process step by step.

In FIG. 3A, a gate electrode made of a chromium film 11, an oxide film 12, a nitride film 13, and an amorphous silicon film 14 as a conductor are formed on a glass substrate 10. The amorphous silicon film 14 is deposited almost uniformly even in the step portion, and for example, the thickness t1 of the amorphous silicon film 14 in the step portion is larger than the film thickness t2 in other portions. Note that 15 is a photoresist mask for etching the amorphous silicon film 14. 3b shows that the amorphous silicon film 14, which is the material to be etched, is etched from the surface by the CCl4 gas 18 for reactive etching, and the broken line shows the progress of etching over time. There is.

Etching by the CCl4 gas 18 proceeds uniformly only in the vertical direction, and the step portion, unlike other planar portions, is not etched at the same distance from the surface. Therefore, as shown in FIG. 3C, an accurate pattern 14a is formed on the lower surface of the mask 15, but the stepped portion is
A remaining portion 14b of amorphous silicon ends up being formed. That is, in the conventional etching method described above, the pattern 14a of the amorphous silicon film should be left only on the lower surface of the mask 15, but an extra portion 14b remains, and as a result, the electricity inside the thin film transistor cell is It has a drawback that causes poor characteristics. As a countermeasure against this problem, a method has conventionally been used in which the remaining portion 14b of the amorphous silicon film is further etched and cut. However, this adds an extra etching process, which increases the manufacturing time and manufacturing cost of the thin film transistor device. This has the problem of resulting in an increase in

The main technical object of the present invention is to solve the above drawbacks and problems, and for example, etching an amorphous silicon film with steps so that no amorphous silicon remains in the steps. An object of the present invention is to provide a reactive ion etching method that allows

[0008]

[Means for Solving the Problems] The present invention first etches a part of the amorphous silicon film using SF6 gas or NF3 gas, and then etches the remaining film thickness using N2. The etching is performed using gas containing CCl2F2, thereby achieving the above object.

That is, the present invention comprises parallel plate electrodes placed opposite to each other and to which high frequency power is applied, a reactive gas is introduced to generate plasma between the electrodes, and one of the electrodes is In a reactive ion etching method for etching an amorphous silicon film placed on top, a part of the thickness of the amorphous silicon film is etched by SF6.
This is a reactive ion etching method characterized by comprising a step of etching using gas or NF3 gas and a step of etching the remaining film thickness part using CCl2F2 gas containing N2, and as the amorphous silicon film, This is a reactive ion etching method suitable for amorphous silicon films with steps.

[0010] The present invention will be described in detail below, using a film with steps as an example of an amorphous silicon film. For an amorphous silicon film with a step, first, a part of the film thickness is etched with SF6 gas or NF3 gas, and thereby, in addition to the vertical etching, lateral etching progresses, and the step part is etched. Prevent etching residue (amorphous silicon residue). next,
C containing N2 whose etching progresses mainly in the vertical direction
Etching is performed using Cl2F2 gas. The N2 content is preferably about 5 to 30%. By employing this two-step etching method, even an amorphous silicon film with steps can be etched with excellent dimensional accuracy.

[0011]

[Embodiment] Next, an embodiment of the present invention will be explained in detail based on FIG. FIG. 1 is a diagram for explaining an embodiment of the present invention, and FIGS. 1A to 1C are longitudinal cross-sectional views showing each step of an etching process for manufacturing a thin film transistor device.

Embodiment 1 In FIG.
2. A nitride film 13 and an amorphous silicon film 14 as a conductor (a film with steps having thicknesses t1 and t2) are formed, and a photoresist mask 15 for etching is also formed. The thin film transistor device thus formed is placed on one electrode 3 of the parallel plate electrodes 2 and 3 of the reactive ion etching apparatus shown in FIG.

[0013] First, SF for reactive etching
6 gas 16 at flow rate 60 sccm, pressure 20 Pa, output 7
When used under the condition of 00W, the amorphous silicon film 14
Perform etching. Etching of the amorphous silicon film 14 by the SF6 gas 16 tends to proceed somewhat laterally, so as shown in FIG.
A small constriction is formed on the side surface of the amorphous silicon film 14 on the lower surface, but on the other hand, the etching of the amorphous silicon film 14 also progresses in the lateral direction at the stepped portion. In this case, since the SF6 gas 16 has a high etching rate for the amorphous silicon film 14, the etching is stopped before the nitride film 13 under the amorphous silicon film 14 is exposed.

Next, as a reactive etching gas, N2
CCl2F2 gas 17 containing about 5 to 30% of
The remaining amorphous silicon film 14 is etched under the conditions of ml/min, pressure of 16 Pa, and output of 600 W. As a result, as shown in FIG. 1C, the pattern 14a of the amorphous silicon film on the lower surface of the mask 15 is
Except for , the other amorphous silicon films were completely removed, and an etched shape with a small amount of undercut at the base of the amorphous silicon film was obtained. This is because the amorphous silicon film 14 is formed by the first SF6 gas 16.
Compared to etching, CCl2F2 gas containing N217
Although the etching rate of the film 14 is slow, the etching progresses mainly in the vertical direction.

(Example 2) In Example 1, first, SF6
Although this is an example in which an amorphous silicon film was etched with a gas, this second example is an example in which NF3 gas is used instead of SF6 gas, and is the same as Example 1 except for this point.

Since the etching rate of an amorphous silicon film by NF3 gas is more than twice as high as the etching rate by SF6 gas, there is an advantage that the etching time is greatly shortened and the loss of the resist is reduced. However, although high-speed etching can be performed, NF3
Since gas has a stronger tendency to etch laterally than SF6 gas, it also has the disadvantage of producing considerable constrictions on the etched side surfaces of amorphous silicon. Therefore, in order to remove all the amorphous silicon film by etching with NF3 gas and avoid causing a large undercut, the etching with NF3 gas was replaced with C containing N2.
It is important to be more careful when switching to Cl2F2 gas etching.

[0017]

Effects of the Invention As detailed above, the present invention, for example, first uses SF6 or NF3 gas as an etching gas for an amorphous silicon film with steps, and allows etching to proceed in the lateral direction as well. In the manufacturing process of the conductive part, a remarkable effect is produced in that it is possible to prevent the amorphous silicon film from remaining in the step part. Furthermore, by using CCl2F2 gas containing N2 as an etching gas for the remaining amorphous silicon film, etching proceeds mainly in the vertical direction.
Compared to the case where SF6 or NF3 gas is used alone, the effect is that etching with excellent dimensional accuracy can be obtained.

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining an embodiment of the present invention, and FIGS. 1 a to 1 c are process longitudinal cross-sectional views showing each step of an etching process for manufacturing a thin film transistor device. It is.

FIG. 2 is a schematic diagram of a reactive ion etching apparatus.

[Figure 3] Figure 3 shows conventional CCl4 as a reactive gas.
FIG. 3 is a diagram illustrating a situation in which amorphous silicon remains in the step portion when an amorphous silicon film with a step is etched using a method shown in FIGS.
These are process longitudinal cross-sectional views showing each step of the etching process.

[Explanation of symbols]

1 Etching chamber 1a Gas introduction hole 1b Exhaust hole 2, 3 Parallel plate electrode 4 Glass substrate 5 High frequency power supply 10 Glass substrate 11 Chromium film 12 Oxide film 13 Nitride film 14 Amorphous silicon film 14a
Pattern 14b Remaining part 15 Mask 16 SF6 gas 17 CCl2F2 gas 18 containing N2
CCl4

Claims (3)

[Claims] [Claim 1] Parallel plate electrodes to which high frequency power is applied are arranged opposite to each other, a reactive gas is introduced to generate plasma between the electrodes, and the plasma is placed on one of the electrodes. In a reactive ion etching method for etching an amorphous silicon film, a part of the thickness of the amorphous silicon film is etched with SF6 gas or NF.
1. A reactive ion etching method comprising the steps of: etching using 3 gases; and etching the remaining film thickness using CCl2F2 gas containing N2. 2. The reactive ion etching method according to claim 1, wherein the amorphous silicon film is an amorphous silicon film with steps. 3. The reactive ion etching method according to claim 1, wherein a CCl2F2 gas containing 5 to 30% N2 is used as the CCl2F2 gas containing N2.