JP2000277496A - Etching method of metallic thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the etching-speed selecting ratio of a resist film to a metallic thin film present on an insulating substrate, by projecting alternately on the metallic thin film positive and negative ions in a parallel magnetic field with the electrode of a low-frequency oscillator, and by etching the metallic thin film. SOLUTION: A chamber 5 comprises a metallic container 1 subjected to aluminum anodizing and a quart window 2 for introducing into the chamber 5 an induced electric field, and is exhausted by a vacuum pump 6. A photomask 4 is put on an electrode 3 present in the chamber 5 to etch the photomask 4. By an one-turn induction coil antenna 7 present on the quartz window 2 and connected with an oscillator 8 of 13.56 MHz and a matching device 13, an inductively coupled plasma is generated in the chamber 5. On the other hand, an oscillator 9 of 100 kHz is connected with the electrode 3 as removing its DC voltage component by a transformer 10. As an etching gas, a chlorine gas is fed from a gas introducing port 12. In the plasma generated just below the quartz window 2 having the put-on antenna 7, the chlorine gas is ionized by electron impacts against atoms. Thereby, the etching-speed selecting ratio of a resist film to a chrome film which constitute jointly the photomask 4 is improved to mask obtainable a highly accurate chrome-mask.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a liquid crystal panel or
The present invention relates to a method for plasma etching a semiconductor photomask with high accuracy.

[0002]

2. Description of the Related Art A semiconductor photomask will be described as an example. The photomask is formed by sputter depositing chromium on a quartz substrate, coating a resist on the chromium thin film, drawing an integrated circuit IC pattern with an electron beam, developing it, and developing a plasma of a reactive gas containing fluorine and chlorine atoms. The chromium thin film is plasma-etched by using to form an integrated circuit pattern of the chromium thin film on a quartz substrate.

For example, a conventional parallel plate type plasma etching method is shown in FIG.
Since an insulating quartz substrate mask is placed and etched, the photomask is negatively charged due to the attachment of electrons with extremely high mobility in the plasma, and positive ions in the ionized etching gas are accelerated by the negative potential. The chromium thin film is etched by impacting the chromium thin film. As a result, the resist is physically and chemically sputtered by the high-energy ion bombardment, and the etching rate of the resist is increased, greatly exceeding the etching rate of the chromium thin film. , Ie, the selectivity is deteriorated.

Here, the parallel plate type is taken as an example, but the magnetron type, ECR (Electron Cyclotron Resonance), ICP
In (inductively coupled plasma), a similar deterioration of the selectivity occurs in the chromium mask etching on the negative bias application electrode.

If the etching selectivity is poor, the width of the resist recedes, and the pattern dimension at the time of drawing is lost, so that a highly accurate chromium mask pattern according to the pattern dimension cannot be obtained. There is a defect that causes serious trouble.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a ratio of the etching rate between a resist and a chromium thin film on a quartz substrate,
That is, an etching method having a high selectivity is provided.
An object of the present invention is to provide an etching method that enables high density and high integration of I.

[0007]

According to the present invention, an induction coil antenna is arranged in an upper quartz window, a substrate is mounted on an electrode coupled to a low frequency oscillator via a transformer, and a magnetic field parallel to the electrode is provided. It is characterized in that the metal thin film is alternately irradiated with positive ions and negative ions and etched.

[0008]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. FIG.
FIG. 2 is a vertical sectional view of the induction type plasma etching apparatus of the present invention, and FIG.

A photomask 4 is placed on an electrode 3 in a chamber 5 comprising an anodized metal container 1 and a quartz window 2 for introducing an induction electric field, and etching is performed. The chamber 5 is evacuated by a vacuum pump 6 and decompressed to about 30 mTorr.

A 13.56 MHz oscillator 8 connected to a single-turn induction coil antenna 7 on a quartz window 2 and a matching device 13 cause an inductively coupled plasma (IC
P) occurs. On the other hand, the 100 kHz oscillator 9 is connected to the electrode 3 after removing the DC component by the transformer 10.

[0011] Chlorine gas inlet 1 as an etching gas
Supply from 2. In plasma generated immediately below a quartz substrate on which an antenna is mounted, chlorine gas is ionized as follows by electron impact. ^{_{Cl 2 → Cl 2 + + e}} -

However, the electron energy decreases toward the downstream, and the electrons adhere to the Cl ₂ gas, generating chlorine negative ions as described below. Cl ₂ + e ⁻ → 2Cl ⁻

[0013] In the downstream region of the chlorine inductively coupled plasma,
There are still a lot of electrons. When chromium on the quartz substrate is etched in this state, electrons adhere to the insulating quartz substrate, and a negative potential (called a self-bias voltage) is generated. Due to this negative potential, the positive ions Cl ₂ ⁺ rapidly etch both the chromium and the resist on which the resist circuit pattern is formed.

On the other hand, a chromium mask is called a reticle for photolithography that requires high precision, and the generation of scratches and dust must be minimized.

Therefore, the mask is required to be separated from the electrode coupled with the low-frequency power by about 0.1 to 1 mm, so that non-contact is always required. As a result, a capacitance is generated between the mask substrate and the electrode substrate, and the negative self-bias voltage is further increased. In order to suppress the self-bias voltage, it is necessary to remove electrons in the plasma by some method.

Therefore, a self-bias voltage is reduced by applying a magnetic field from outside the chamber 5 to the magnet 3 in parallel with the electrode 3 to promote electrons in the plasma, thereby pulling negative ions Cl ⁻ into the chromium mask quartz substrate. It is possible to effectively irradiate the photomask 4 with Cl ⁻ ions.

The purpose of introducing the negative ion Cl ⁻ is Cl ⁻
Is an electron attached to Cl atom, so Cl atom easily reacts with metal to generate volatile reactant and has high reactivity, but positive ion Cl ₂ ⁺ reacts with metal after dissociating into Cl atom. So low reactivity. Accordingly, Cl ⁻ ions promote the etching of chromium, so that the etching selectivity with respect to the resist is increased, and high-precision etching becomes possible.

[0018] Figure 3, the electrode 3 with respect to the change in the gap G between the antenna 7, the probe ten current and I ₊ when a positive voltage is applied, when a negative voltage is applied - current I _- ratio I ₊
/ I _- it is the result of the measurement of the. Therefore, I ₊ represents a sum of negative ion current and the electron current, I _- is a positive ion current. When the gap was 18 cm, I ₊ = I ₋ . In other words, as a result of electrons have been removed in the I ₊ current, I ₊ current,
Only negative ions are present and have a value equal to the positive ion current due to the neutral condition of the charge of the plasma.

FIG. 4 shows the experimental results of the etching selectivity. At a gap of 18 cm, the selectivity became the maximum, which coincided with the result of FIG. This indicates that the maximum selectivity can be obtained at the electrode position where the current ratio of the positive ion to the negative ion is minimum.

The result is considered as follows. First, Cl ₂ , which is a heavy ion species, is located upstream of 15 cm.
^{Since +} ions are the main ion species, chromium is also etched, but the impact on the resist is large and the selectivity deteriorates.

On the downstream side of 20 cm, the amount of both positive and negative ions is reduced, and the etching rate is reduced, so that the etching time is shortened. Therefore, it is considered that the temperature of the resist increased and the selectivity also decreased. When the gap between the quartz window 2 and the electrode 3 is 15 to 20 cm, the selectivity is good and high-precision etching is possible.

FIG. 5 is a waveform with respect to the ground potential for explaining the irradiation of positive ions and negative ions. (A) before applying a magnetic field,
(B) is a diagram after a magnetic field is applied. The output of the low-frequency oscillator 9 is connected to the electrode 3 via the transformer 10, and the positive ions flow into the substrate in the positive cycle 15 and the negative ions in the negative cycle 16. As a low-frequency oscillator, 100 kHz
To 800 kHz. If the promotion of electrons by the magnetic field parallel to the electrode 3 increases, the irradiation amount of positive and negative ions is balanced, and the maximum etching selectivity can be obtained.

FIG. 6 is a sectional view of the photomask 4 before etching. The photomask 4 is 1000 mm on a quartz substrate 17 having a square of 152 mm on a side and a thickness of 6.25 mm.
Of chrome 18 and patterned resist 19.

In the above description, the case of etching chromium of a semiconductor photomask has been described. However, it is clear that the present invention can be realized in exactly the same manner for etching a metal thin film of a liquid crystal panel or a photomask for a liquid crystal panel.

In the above description, the case where the metal thin film is chromium has been described. However, it is clear that the present invention can be realized in exactly the same manner with other metal thin films such as molybdenum silicide or aluminum.

[0026]

As described above, the present invention has the following effects.

The etching selectivity between resist and chromium is high, and a high-precision chromium mask is realized.
Enables high integration.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of an induction type plasma etching apparatus of the present invention.

FIG. 2 is a plan view of the device of the present invention.

FIG. 3 shows the result of measuring the current ratio I ₊ / I _{− to} the electrode height.

FIG. 4 is an experimental result of an etching selectivity.

FIG. 5 is an explanatory diagram of positive / negative ion irradiation.

FIG. 6 is a sectional view of a photomask before etching.

FIG. 7 is a sectional view of a conventional capacitively coupled plasma etching apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Metal container, 2 ... Quartz window, 3 ... Electrode, 4 ... Photomask, 7 ... Induction coil antenna, 8, 9 ... Oscillator, 10 ...
Transformer, 11 magnet, 13 matching device, 17 quartz substrate, 18 chrome, 19 resist, 20 oscillator, 21 capacitor, 23 lower electrode, 24 upper electrode.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4K057 DA13 DB01 DB02 DB05 DB08 DD05 DE01 DG16 DM01 DM24 DM31 DM33 DM40 DN01 5F004 AA02 BA20 BB13 BB18 DA04 DB08 DB09 DB16 DB18 EB07

Claims (5)

[Claims] In a method of etching a metal thin film on an insulating substrate having an integrated circuit pattern formed of a resist by using a plasma of a gas containing a halogen element, an induction coil antenna is arranged on an upper quartz window, and is passed through a transformer. Etching the metal thin film in a magnetic field parallel to the electrode by placing the substrate on an electrode coupled to a low-frequency oscillator. 2. The method according to claim 1, wherein positive ions and negative ions in said halogen-containing gas plasma are accelerated by a negative voltage and a positive voltage, respectively, and bombard the metal thin film to perform etching. Item 4. The etching method according to Item 1. 3. The etching method according to claim 1, wherein the metal thin film is etched at an electrode position where a current ratio between positive ions and negative ions in the gas plasma containing the halogen element is minimized. 4. The etching method according to claim 1, wherein the magnetic field parallel to the substrate is 200 gauss or less. 5. The gap between the quartz window and the electrode is 15 to 2
2. The etching method according to claim 1, wherein the distance is 0 cm.