JPH04271120A - Etching method - Google Patents

Abstract

PURPOSE:To obtain a sufficient etching selection ration of a gate insulating film and a semiconductor protective film and a low resistance semiconductor film, a drain electrode and a source electrode, by applying etching using plasma of specified mixed gas to an array manufacturing process of TFT-LCD. CONSTITUTION:Plasma of mixed gas is used, which contains at least the following; gas which forms fluorine ions or fluorine radicals in plasma, gas which contains chlorine in composition, and gas which contains NxOy in composition. In another case, plasma of mixed gas is used, which contains at least the following; fluorocarbon shown by CxHyFz or CxFy, gas which contains chlorine in composition, and gas which contains oxygen in composition. Etching is performed by using plasma of the above mixed gas.

Description

[Detailed description of the invention]

[Purpose of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an etching method used for manufacturing active matrix liquid crystal display elements using, for example, thin film transistors (TFTs).

0002

2. Description of the Related Art The active matrix method is a method in which switching elements connected to pixels are provided at the intersections of electrodes arranged in a matrix. Among the active matrix methods, the TFT type is particularly actively being researched and developed. An example of one substrate having a TFT disposed on a glass substrate is, for example, the IEEE Transaction on Electron Device (IEEE Tran
s. on Electron Devices, Vol. 20, pp. 995-1001 (1973).

[0003] For example, the steps for manufacturing such a TFT array substrate are as follows. First, an insulating substrate made of, for example, glass is used as a front glass substrate, a scanning electrode line and a gate electrode are simultaneously formed on this substrate, and a gate insulating film, a semiconductor film, and a semiconductor protective film are sequentially formed thereon. next,
After forming the semiconductor protective film, a low resistance semiconductor film is formed,
Molding a semiconductor film and a low-resistance semiconductor film at the same time. after that,
A pixel electrode is formed and the gate insulating film on the electrode pad is removed, and a signal electrode, source electrode, and drain electrode are formed. In this state, the source electrode and the drain electrode are short-circuited by the low resistance semiconductor film, so the low resistance semiconductor film on the semiconductor protective film is removed using the source electrode and the drain electrode as a mask. Finally, an insulating film is formed to protect the TFT array substrate.

[0004] Such a TFT array substrate is made of a front glass substrate, and the surface is exposed to transmitted light from non-pixel electrode portions and TFs.
A rear glass substrate is a glass substrate on which a light shielding film called a black matrix for shielding light incident on T and a transparent counter electrode made of, for example, an indium tin oxide film (ITO) is formed. After applying a liquid crystal alignment film to the TFT formation side of the front glass substrate and the counter electrode side of the rear glass substrate, an alignment treatment is performed, for example, by rubbing,
A front glass substrate and a rear glass substrate are bonded together facing each other in parallel with a distance of approximately 10 μm, with the surfaces subjected to the alignment treatment being placed on the inside, and a liquid crystal is filled in the gap to form a liquid crystal cell. Furthermore, after connecting an external circuit to the liquid crystal cell manufactured in this manner, it is housed in a case.

[0005]

[Problems to be Solved by the Invention] Active matrix liquid crystal display devices (hereinafter referred to as TFTs) using this type of TFT
In the TFT array manufacturing process for a TFT array (referred to as -LCD), the process of removing a low-resistance semiconductor on a semiconductor protective film has a large effect on the characteristics of the array. It is necessary to be able to selectively etch a low resistance semiconductor without impairing the performance of the semiconductor protective film. For the low resistance semiconductor film, an n-type semiconductor or a p-type semiconductor doped with P (phosphorus), B (boron), or the like is used. Here, as the semiconductor material, S
Poly-Si or a-Si with i as the base material is used. In addition, silicon nitride (SiN
x ) or silicon oxide (SiOx) is often used. As this etching method, a so-called plasma etching technique using plasma is used.

For example, as a low resistance semiconductor, n+ type a
- In the case of TFT-LCD using Si, n+ a-Si
If the selectivity between the semiconductor protective film and the semiconductor protective film is not sufficiently large, it is necessary to absorb fluctuations that normally occur in the thin film forming or pattern forming process, such as uneven etching rate and uneven film thickness. In particular, when the TFT-LCD is large, the substrate used is also large, so this requirement is essential in order to obtain a process margin that takes into account mass production.

[0007]Currently, the etching method uses CFC alone,
Combinations such as fluorocarbon + oxygen and SF6 + fluorocarbon are known, and the selectivity ratio obtained with these combinations is reported to be 3 to 6 at maximum in literature. TFT-LC
When using a particularly large substrate of D, this degree of selectivity is not sufficient to absorb process variations and obtain uniform image quality and satisfactory TFT characteristics, and the film formation process and
This places an excessive burden on improving the uniformity of the etching process and improving equipment. In a mass production process, a selection ratio of 10 or more is usually the standard.

[0008] In addition, when plasma etching is performed using Freon, the characteristics vary greatly. One of the causes of this variation is CnFm generated during plasma etching.
A compound residue represented by is considered. In fact, X-ray photoelectron spectroscopy shows that with fluorocarbons alone, fluorocarbons + oxygen, and combinations of SF6 + fluorocarbons, polymer residues represented by decomposition products such as CF4 or CHF3 are present on the surface after etching. It can be analyzed using methods such as or Auger electron spectroscopy. Furthermore, if a significant amount of residue is present, the surface can be observed using a technique such as a scanning electron microscope.

Furthermore, in the TFT array manufacturing process of TFT-LCD, Ta, Mo, W, or alloys of these metals are used alone or together with other metals as conductors, and plasma etching or wet etching is used to form them. It is used.

[0010] In TFT-LCD, it is necessary to lower the price and improve the quality, and it is desired to improve the productivity in each process. In forming a conductor made of the metal, it is necessary to improve productivity and quality by increasing the etching rate and increasing the selectivity of the etching rate with respect to the insulator on which the conductor is laminated.

For example, the gate electrode and the scanning electrode line are made of glass or a metal conductor made of an alloy of Mo and Ta laminated on glass with an insulating film such as SiOx interposed therebetween. For these etchings, for example, CF
It is known to use a gas mixture of 4 and O2. However, this mixed gas has the disadvantage that the etching rate is slow.

Furthermore, when forming the signal electrode line, it is necessary to consider the etching selectivity between the signal electrode line material and the insulating film material formed on the scanning electrode line. It is known that a Mo/Al two-layer structure is used as the signal electrode wire material, SiNx or SiOx is used as the insulating film material, and a mixed gas of CF4 and O2 or CCl4 is used as the etching gas for the signal electrode wire material. However, this method has the disadvantage of slow etching speed. If we focus only on the etching speed, CF4 + Freon 1
There are mixed gases such as No. 2 that are faster than the above gases, but the selection ratio is about 0.5 to 2, which is not suitable for practical use. [Structure of the invention]

[0013]

Means for Solving the Problems The invention according to claim 1 is suitable for etching a semiconductor film or a metal film, using a gas that forms fluorine ions or fluorine radicals in plasma, and a gas containing chlorine in its composition. A plasma of a mixed gas having at least a gas containing Nx Oy in its composition is used.

Further, the invention according to claim 2 uses Cx Hy as a gas that forms fluorine ions or fluorine radicals in plasma for etching processing of semiconductor films and metal films.
A plasma of a mixed gas containing at least a fluorocarbon represented by Fz or Cx Fy, a gas containing chlorine in its composition, and a gas containing oxygen in its composition is used.

[0015]

[Operation] In the present invention, SF is used as a gas that forms fluorine ions or fluorine radicals in plasma.
When using SF6, the etching rate of Si is 1000 to 2000 angstroms/min, which is close to that of SF6 alone or a mixture of the two (for example, SF6 + CFC).
to maintain high speed. On the other hand, the etching rate of SiNx is 10
00 angstroms/min, 100 angstroms/min
It decreases significantly around angstroms/min. As a result, a Si/SiNx selectivity ratio of 10 or more can be easily obtained.

Furthermore, in the present invention, when CF4 is used as a gas that forms fluorine ions or fluorine radicals in plasma, the etching rate of Si is 3 to 4 times faster than when CF4 is used alone, and the etching rate is 1200 nm.
~1500 angstroms/min. on the other hand,
The etching rate of SiNx is significantly reduced to about 100 angstroms/min, compared to about 1000 angstroms/min in the case of CF4 alone or a combination of the two (for example, CF4 + oxygen). As a result, a Si/SiNx selectivity ratio of 10 or more can be easily obtained. Further, after etching, there was no residue considered to be Cn Fm.

Furthermore, when the present invention is used, the etching rate of Mo, for example, can be obtained at 500 to 800 angstroms/min, which is comparable to the rate when chlorine-based gas is added to SF6 or CF4. This value is 5 to 10 times faster than the etching rate obtained under similar conditions using CF4, which is conventionally known as a Mo etching gas, or a gas in which O2 is added to CF4, using the same experimental equipment. twice as fast. On the other hand, when a chlorine-based gas is added to SF6 or CF4, the etching rate of SiNx is as fast as that of Mo, and the selectivity expressed by Mo/SiNx is less than 1, which is not practical. On the other hand, in this invention, the etching rate of SiNx is 10
It decreases significantly to around 0 angstroms/min. As a result, the selection ratio of Mo/SiNx was 7 to 10
is obtained. Among the three types of gases in this invention, the selection ratio of Mo/SiNx is 3 when used alone or in combination of two types.
is not easy to obtain.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be explained below with reference to the drawings.

FIG. 1 is a schematic sectional view showing a part of a TFT array substrate formed using an embodiment of the present invention, and will be explained according to the manufacturing process. First, a molybdenum-tantalum alloy thin film, for example, is deposited on a glass substrate 1 to a thickness of approximately 0.2 μm by sputtering or the like, and striped scanning electrode lines (not shown) are formed by photolithography. A pattern of gate electrode 2 electrically connected to the scanning electrode line is formed. Next, SF6, CCl4, N2
A mixed gas containing O and He is irradiated with microwaves to generate plasma, and the scanning electrode line and gate electrode 2 are formed by plasma etching. The ratio of gas used at this time is 0.1 to 0.1 to CCl4 to SF6.
0.5% by weight, N2O from 0.5 to 4% by weight, and He was added as a balance gas.

[0020] Next, for example, by plasma CVD method or the like,
The gate insulating film 3 is made of silicon nitride (SiNx) with a thickness of 0.3 μm, for example, and the semiconductor film 4 is made of silicon nitride (SiNx) with a thickness of 0.3 μm, for example.
1 μm amorphous silicon (a-Si) and semiconductor protective film 5
For example, SiNx with a film thickness of 0.3 μm is continuously deposited, and a semiconductor protective film 5 is formed on the gate electrode 2 by photolithography. Next, for example, plasma CVD
A low-resistance semiconductor film 6 made of, for example, n+ a-Si is deposited by a method, and the semiconductor film 4 and the low-resistance semiconductor film 6 are simultaneously formed by a photolithography method.

Subsequently, portions requiring electrical connection to the outside, such as the gate insulating film 3 on the electrode pads, are removed by photolithography. Next, for example, ITO is deposited to a thickness of 0.1 μm by sputtering, and the pixel electrode 7 is formed by photolithography.

[0022] Next, for example, Mo with a thickness of 0.05 μm,
Al with a thickness of 1.0 μm and Mo with a thickness of 0.05 μm are sequentially deposited by sputtering or the like, and a signal electrode line and a drain electrode 8 electrically connected to the signal electrode line are formed by photolithography. , the source electrode 9 is simultaneously formed by plasma etching. Here, the gas used for etching the Mo layer is a gas that forms fluorine ions or fluorine radicals in plasma, such as SF6, and a chlorine-based gas such as Freon 11, Freon 12, or Freon 13, which contains chlorine in its composition. , Freon 113, Freon 114, Freon 21, Freon 123, CCl4, etc., for example, in an amount of 0.1 to 0.5% by weight, and NO and N2 as gases having components represented by NxOy in the composition. 0.5 ~ selected from O etc.
4% by weight. Furthermore, the gas composition used for etching the Al layer was changed from that for the Mo layer, and CCl4 was used alone. At this time, a capacitively coupled device equipped with parallel plate electrodes was used for plasma etching, and a high frequency of 13.56 MHz was applied to the cathode electrode. Further, the substrate to be etched is held on the cathode electrode side. The etching rate for Mo and Al is 500 to 900 angstroms/min, respectively.
, 1000 to 2000 angstroms/min. In addition, as a result of measuring the etching rate of the SiNx film used as a monitor and Mo, the Mo/SiN
A selectivity ratio of 7 was obtained for x.

Next, plasma etching of the low resistance semiconductor film 6 is performed using the drain electrode 8 and source electrode 9 as masks. The gas used here is the same as the gas used for etching the Mo layer described above. In this plasma etching, the etching rate of the low resistance semiconductor film 6 made of n+a-Si was 1000 to 2000 angstroms/min. In addition, the etching rate of the SiNx film used as a monitor was 100 to 15
It was 0 angstrom/min. Next, an insulating film 10 made of, for example, SiNx is deposited on the glass substrate 1.
．． The insulating film 10 is deposited to a thickness of 1 to 1.0 μm, and the portions of the insulating film 10 that require electrical connection are removed by photolithography.

In this embodiment corresponding to claim 1, a Mo layer which is a component of the drain electrode 8 and the source electrode 9;
The low-resistance semiconductor film 6 is etched using plasma of a mixed gas containing at least a gas that forms fluorine ions or fluorine radicals, a gas that contains chlorine in its composition, and a gas that contains Nx Oy in its composition. By using the gate insulating film 3 and the semiconductor protective film 5,
The etching selectivity between the low resistance semiconductor film 6, the drain electrode 8, and the source electrode 9 was improved. Along with this, the results of measuring the TFT characteristics of the fabricated array showed that good transfer characteristics (drain current vs. gate voltage characteristics) were obtained, and furthermore, no characteristic deterioration due to damage during plasma etching was observed. Ta.

Next, another embodiment of the present invention will be explained using FIG. 1 as well. This embodiment differs from the previous embodiment in the plasma etching method of the semiconductor thin film 6 using the drain electrode 8 and source electrode 9 as masks. That is, the gas used here is CF4 as a fluorocarbon represented by Cx Hy Fz or Cx Fy.
, CHF3, CH2F2, CH3F and C2
Among F6, for example, for CF4, Freon 11, Freon 1, which contains chlorine in its composition as a chlorine-based gas,
2. 0.05 to 0.5% by weight of a material selected from Freon 13, Freon 113, Freon 114, Freon 21, Freon 123, CCl4, etc., as a gas having a component represented by oxygen in its composition. O2, NO and N2
A material selected from O, etc. was mixed in a proportion of 0.2 to 4% by weight. In this plasma etching, n+
The etching rate of the semiconductor thin film 6 made of a-Si is 1
000 to 1200 angstroms/min,
After etching, there was no residue believed to be Cn Fm. The etching rate of the SiNx film used as a monitor was 100 to 150 angstroms/min.
Met. At this time, a capacitively coupled device equipped with parallel plate electrodes was used for plasma etching, and a high frequency of 13.56 MHz was applied to the cathode electrode. Further, the substrate to be etched is held on the cathode electrode side.

In this embodiment corresponding to claim 2, the low resistance semiconductor film 6 is etched using fluorocarbon represented by Cx Hy Fz or Cx Fy, a gas containing chlorine in its composition, and a gas containing chlorine in its composition. By using a plasma of a mixed gas containing at least a gas containing oxygen, the etching selectivity of the semiconductor protective film 5 and the low-resistance semiconductor film 6 is improved. No compound residue represented by Fm was generated. Accordingly, in this example, as in the previous example, the results of measuring the TFT characteristics of the prepared array showed that good transfer characteristics (drain current vs. gate voltage characteristics) were obtained, and furthermore, Damages during plasma etching
No deterioration of characteristics due to the damage was observed.

FIG. 2 is a sectional view showing a liquid crystal display element manufactured using the array shown in FIG. In FIG. 2, a light shielding film 12 made of, for example, Al and a counter electrode 13 made of, for example, ITO are formed on a glass substrate 11 at positions facing the TFTs 12 of the TFT array substrate. Next, after coating the alignment film 14 on the TFT formation side of the glass substrate 1 and the counter electrode 13 side of the glass substrate 11, an alignment treatment is performed, for example, by rubbing. Subsequently, the two glass substrates 1 and 11 are bonded together so that they face each other in parallel with a distance of approximately 10 μm, with the surfaces subjected to the orientation treatment placed inside each other.
A liquid crystal 15 is sealed in the gap.

[0028] When we evaluated the image output of this liquid crystal display element, we found that the local characteristic unevenness, which was thought to be unique to the film forming process and etching equipment, was eliminated, and the image quality was significantly improved, resulting in good results. . Furthermore, defects caused by intersections between scanning electrode lines and signal electrode lines are almost eliminated.

[0029]

[Effects of the Invention] This invention makes it possible to obtain a sufficient etching selectivity between metal films and semiconductor films and other insulating films by performing etching using plasma of a mixed gas containing at least three predetermined gases. . By applying this etching method to the TFT-LCD array manufacturing process, local characteristic unevenness, which was thought to be unique to the film forming process and etching equipment, was eliminated, and the image quality was significantly improved.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing an example of a TFT array substrate produced using an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing an example of a liquid crystal display element manufactured using an embodiment of the present invention.

Claims (2)

[Claims] 1. Etching using a plasma of a mixed gas containing at least a gas that forms fluorine ions or fluorine radicals in the plasma, a gas containing chlorine in its composition, and a gas containing Nx Oy in its composition. An etching processing method characterized by: [Claim 2] Cx Hy Fz or Cx Fy
An etching method characterized by etching using a plasma of a mixed gas containing at least a fluorocarbon represented by: a gas containing chlorine in its composition and a gas containing oxygen in its composition.