JP3210449B2 - Plasma etching method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma etching method for etching a substance to be etched by exciting an etching gas into a plasma state.

[0002]

2. Description of the Related Art For example, in the manufacturing process of a thin film transistor (TFT) in a liquid crystal device, fine processing plays an important role, and a plasma etching technique is used as the fine processing. That is, a metal film for forming a gate line is formed on a liquid crystal substrate by a film forming technique such as plasma CVD, and a part of the metal film is covered with a resist and etched to form the gate line. After formation, the thin film transistor is formed on the substrate by repeating formation and etching of an insulating film, a silicon film, a silicon nitride film, or the like on the substrate.

FIG. 4 shows a configuration of a general thin film transistor. In FIG. 1, reference numeral 1 denotes a liquid crystal substrate. On this liquid crystal substrate 1, a gate line 2 made of an alloy of molybdenum (Mo) -tantalum (Ta) is formed. The gate - DOO line 2 gate made of silicon Oki site (SiO _X) - is covered by the gate insulating film 3. On the gate insulating film 3, a first silicon nitride (SiN _x ) film 4, an amorphous silicon (a-Si) film 5, a second silicon nitride (SiN _x ) film 6, an n + amorphous silicon The films 7 are sequentially formed.

A plurality of signal lines 8 are formed on the n + amorphous silicon film 7. The plurality of signal lines 8 must be separately provided in contact with the n + amorphous silicon film 7. Therefore, n
After forming the signal line 8 on the amorphous silicon film 7, the portion indicated by 7a in FIG. 4 of the n + amorphous silicon film 7 must be removed by etching.

When the portion 7a of the n + amorphous silicon film 7 is removed by etching, the second silicon nitride film 6 underlying this film is also etched and reduced. When the silicon nitride film 6 is reduced, there occurs a problem that the switching characteristics of the thin film transistor are impaired.

Therefore, when the n + amorphous silicon film 7 is removed by etching, it has a high etching rate with respect to the n + amorphous silicon film 7 and a high etching rate with respect to the second silicon nitride film 6. It is required to perform selective etching in which etching is hardly performed.

Conventionally, the above-described selective etching has been performed by using a parallel plate type etching apparatus, applying a high frequency of 13.56 MHz to the anode side, and under the etching conditions shown in FIG. 6, for example. That is, the etching gas is SF ₆ which is a fluorine-based gas, and C which is a halogenated carbon which is a target of regulated Freon material.
A mixed gas of Cl ₄ and He is used, and SF ₆ / CC
The mixing ratio was set to l ₄ / He = 360/180/360 (SCCM).

However, in the conventional etching method, since the etching rate of the n + amorphous silicon film 7 is as low as about 2000 A / min, the selectivity with respect to the silicon nitride film 6 is only about 7 at the maximum. . Therefore, when the n + amorphous silicon film 7 is etched, the silicon nitride film 6 is also etched, and the loss may be increased.

On the other hand, when the gate line 2 is etched, in order to improve the coverage of the gate insulating film 3 made of silicon oxide laminated thereon, the gate line 2 is etched. As shown in FIG. 5B, it is required to attach tapes 2a to both ends in the width direction.

In order to attach a taper 2a to the gate line 2, the Mo film formed on the substrate 1 as shown in FIG.
When etching the Ta alloy film 8, the gate line 2
It is necessary to perform etching while receding the resist 9 covering the portion to be formed. That is, the tape 2a can be provided on the end face of the gate line 2 by suitably setting the selectivity of the etching rate between the Mo-Ta alloy film 8 and the resist 9.

[0011]

As described above, when plasma etching is performed, the etching rate of silicon nitride and silicon or a molybdenum-tantalum alloy film and a resist covering the alloy film as a material to be etched is used. It is necessary to increase the selectivity.

The present invention has been made based on the above circumstances, and an object of the present invention is to select an etching gas in accordance with the material of a substance to be etched so that the etching rate can be increased. It is an object of the present invention to provide an improved plasma etching method.

[0013]

According to a first aspect of the present invention, an etching gas is introduced into an etching chamber in which a substance to be etched is installed, and the etching gas is excited into a plasma state. In a plasma etching method for etching a substance to be etched,
The material to be etched is silicon nitride (SiN).
x) with amorphous silicon (a-Si) laminated on
There are, the etching gas is a fluorine-based gas, HCl,
At least one gas selected from BCl and HBr
A plasma etching method characterized in that the gas is a mixed gas containing a mixture of gases . According to a second aspect of the present invention, there is provided a plasma etching method in which an etching gas is introduced into an etching chamber in which a substance to be etched is installed, and the etching gas is excited into a plasma state to etch the substance to be etched. H for system gas
At least one selected from Cl, BCl, and HBr
A mixed gas of species of the gas, the etching target
Amorphous silicon (a-Si) is a silicon
Etchant selectively to nitrite (SiNx)
Plasma etching method characterized by graying. Third
Of the present invention relates to an etching chip on which a substance to be etched is installed.
An etching gas is introduced into the chamber, and the etching gas is
The material to be etched is excited by exciting the
In the plasma etching method for etching,
The etching gas is a fluorine-based gas, such as HCl, BCl, or HBr.
A mixture of at least one gas selected from
Molybdenum, which is a gas mixture and is the substance to be etched
(Mo) -tantalum (Ta) alloy film to resist
A plasma etching method characterized by selectively etching.

[0014]

When a mixed gas of a fluorine-based gas and a chlorine-based gas is used as the etching gas, the material to be etched can be etched at a predetermined etching rate by controlling the mixing ratio.

[0015]

1 and 2 show a first embodiment of the present invention.
This will be described with reference to FIG.

FIG. 2 shows a parallel plate type etching apparatus 11 for performing plasma etching according to the present invention. The etching apparatus 11 has an etching chamber 12 in which a cathode 13 is provided. Above the cathode 13, an anode 14 is disposed so as to face the cathode. The anode 14 is connected to a high frequency power supply 15. The high frequency power supply 15 applies a high frequency of 13.56 MHz to the anode 14.

A liquid crystal substrate 1 shown in FIG. 4 is mounted on the upper surface of the cathode 13, and a gate line 2, a gate insulating film 3 or a gate insulating film 3 formed on the liquid crystal substrate 1 as a substance to be etched. The n + amorphous silicon film 7 is plasma-etched as described later.

An etching gas introduction pipe 16 is connected to one side of the etching chamber 12, and an exhaust pipe 17 connected to an exhaust pump (not shown) is connected to the other side.
When an etching gas is supplied from the introduction pipe 16 into the etching chamber 12 and the etching gas is excited by a discharge generated between the cathode 13 and the anode 14 to be in a plasma state, an etching species generated from the etching gas is obtained. Thus, the material to be etched formed on the liquid crystal substrate 1 is etched.

When the n + amorphous silicon film 7 covering the second silicon nitride film 6 of the liquid crystal substrate 1 is etched, SF ₆ (sulfur hexafluoride), which is a fluorine-based gas, and chlorine H, the system gas
A mixed gas obtained by mixing He (helium) with Cl (hydrochloric acid) is used. When the mixed gas is excited to be in a plasma state, fluorine-based etching species and chlorine-based etching species can be generated at a ratio corresponding to the mixing ratio of SF ₆ and HCl. He is effective for stabilizing the plasma generated in the etching chamber 12 and improving the uniformity.

The above-mentioned fluorine-based etching species has an etching effect on both amorphous silicon and silicon nitride. On the other hand, the chlorine-based etching species etches amorphous silicon at a slower etching rate than the fluorine-based etching species, but has little etching effect on silicon nitride.

Therefore, if the etching is performed utilizing this phenomenon, the amorphous silicon is etched with the fluorine-based etching species while the etching of the chlorine-based silicon nitride is suppressed, so that only the amorphous silicon is selectively etched. Can be etched.

That is, the n + amorphous silicon film 7 of the thin film transistor formed on the liquid crystal substrate 1 can be etched at a high etching rate. Etching of the silicon nitride film 6 can be prevented from being reduced.

FIG. 1 shows the results of an experiment in which the relationship between the SF ₆ / HCl based gas composition ratio and the etching rate was measured. In the figure, curve A indicates that the flow rate of SF ₆ is constant at 360 SCCM,
The etching rate of amorphous silicon when Cl is changed in the range of 0 to 360 SCCM is shown, and the curve B also shows the etching rate of silicon nitride.
Curve C is the result of measuring the uniformity of the etching rate of amorphous silicon, and curve D is the result of measuring the uniformity of the etching rate of silicon nitride.
Curve E shows the selectivity of the etching rate between amorphous silicon and silicon nitride.

As is apparent from the experimental results, the etching rate of silicon nitride is 1000 A / min or less, which is almost the same as the conventional one shown in FIG. 6, but the etching rate of amorphous silicon is much larger than the conventional one. Improved. As a result, the selectivity of these etching rates was improved to about 15.

In the uniformity shown by the curves C and D, the variation is the smallest when (SF ₆ / HCl) = (360/90), and the etching rate and the selectivity are relatively small in the vicinity. It turns out that it is good.

That is, by using a gas in which HCl is mixed with SF ₆ as an etching gas, the selectivity of the etching rate between amorphous silicon and silicon nitride can be sufficiently increased as compared with the conventional case. Thereby, when the n + amorphous silicon layer 7 of the thin film transistor formed on the liquid crystal substrate 1 is etched, the second silicon nitride layer 6 under the n + amorphous silicon layer 7 can be prevented from being reduced by etching, so that the switching characteristics of the thin film transistor Is not caused.

When the Mo—Ta alloy film formed on the liquid crystal substrate 1 is etched to form the gate line 2, a mixed gas of SF ₆ , HCl and O ₂ is used as an etching gas. By controlling each gas ratio, the above Mo
An etching rate between the Ta alloy film and the resist is set. As a result, the alloy film can be etched while the resist is receded.
Can be formed.

FIGS. 3A and 3B show experimental results obtained by measuring the relationship between the etching rate of the Mo—Ta alloy film 8 and the resist 9 with respect to the mixing ratio of each component of the etching gas. FIG. 3A shows that SF ₆ / O ₂ is 360/120 (SC
When the CM), etching rate of varying the flow rate of the HCl - indicates the door, FIG. (B) The SF ₆ / O ₂ 360
The etching rate when the amount of HCl is changed at / 40 (SCCM) is shown.

From the experimental results, it has been found that by controlling the etching rates of the alloy film 8 and the resist 9, the angle of the taper 2a of the gate line 2 cut out from the alloy film 8 can be controlled. For example, the mixing ratio of each component of the etching gas is SF ₆ / HCl / O ₂ = 360/60/12
When the etching was performed at 0 (SCCM), the etching speed of the alloy film 8 was 1800 A / min, and 4
A taper angle of 0 degree could be obtained.

That is, by controlling the mixture ratio of each component of the etching gas, the selectivity of the etching rate between the alloy film 8 and the resist 9 can be set.
Then, the alloy film 8 is etched, thereby forming a taper 2a on the gate line 2 at a predetermined angle for improving the coverage of the gate insulating film 3.

The present invention is not limited to the above embodiment, but can be variously modified. For example, silicon as a material to be etched may be polysilicon. As the chlorine-based gas, BCl ₃ ,
It is considered that a similar effect can be expected even if a gas such as HBr or BCl ₃ is used. Further, the etching apparatus may be of a downflow type or another type instead of the parallel plate type.

[0032]

As described above, according to the present invention, when etching a substance to be etched in an etching chamber, a mixed gas of a fluorine-based gas and a chlorine-based gas is used as an etching gas.

Therefore, when etching silicon coated with silicon nitride as a substance to be etched, the selectivity of these etching rates can be increased by controlling the mixture ratio of the above-mentioned mixed gas. Silicon can be reliably etched without reducing the thickness of the silicon nitride.

When the material to be etched is a molybdenum-tantalum alloy film coated with a resist, the mixture ratio of the mixed gas is controlled and the selectivity of these etching rates is set. The edge of the molybdenum-tantalum alloy film can be etched in a tape shape while the resist is receded.

[Brief description of the drawings]

FIG. 1 is a graph showing measurement results of etching rates of amorphous silicon and silicon nitride with respect to a mixing ratio of an etching gas according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of a parallel plate type etching apparatus.

FIGS. 3A and 3B are graphs showing measurement results of etching rates of a molybdenum-tantalum alloy film and a resist when a flow rate of hydrochloric acid is changed, showing another embodiment of the present invention.

FIG. 4 is an enlarged cross-sectional view illustrating a configuration of a general thin film transistor.

FIGS. 5A and 5B are explanatory diagrams of a step of forming a gate line.

FIG. 6 is a graph showing etching rates of conventional amorphous silicon and silicon nitride.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Liquid crystal substrate, 2 ... Gate line, 3 ... Gate insulating film, 4 ...
1st silicon nitride film, 5 ... amorphous silicon film, 6 ... second silicon nitride film, 7 ... n +
Amorphous silicon film, 8 ... alloy film, 9 ... resist,
12 ... Etching chamber.

Continuation of front page (56) References JP-A-4-96223 (JP, A) JP-A-3-222417 (JP, A) JP-A-4-271120 (JP, A)

Claims (3)

(57) [Claims] 2. A plasma etching method comprising: introducing an etching gas into an etching chamber in which a substance to be etched is installed; exciting the etching gas into a plasma state to etch the substance to be etched; Nitride (SiN
x) with amorphous silicon (a-Si) laminated on
There are, the etching gas is a fluorine-based gas, HCl, BCl,
Mix at least one gas selected from HBr
A plasma etching method characterized in that the mixed gas is a mixed gas . 2. A introducing an etching gas in the etching object material placed etch chamber, the plasma etching method for etching the material to be etched by exciting the etching gas to a plasma state, the etching gas is a fluorine-based HCl, BCl,
Mix at least one gas selected from HBr
Is a mixed gas , and the amorphous silicon (a
-Si) to silicon nitride (SiNx)
A plasma etching method characterized by selectively etching. 3. An etchant provided with a substance to be etched.
Introducing an etching gas into the etching chamber
The gas to be etched is excited by exciting the gas into a plasma state.
In the plasma etching method of etching, the etching gas is a fluorine-based gas, HCl, BCl,
Mix at least one gas selected from HBr
A mixed gas, molybdenum is the material to be etched (Mo) - Tan
Selective etching of tantalum (Ta) alloy film with respect to resist
Plasma etching method which is characterized in that ring.