JPH0430530A - Forming method of thin film for wiring - Google Patents

Abstract

PURPOSE:To improve heat resistance by using an aluminum target containing at least boron of 0.1 to 2 wt.% in deposition of an aluminum wiring layer by a sputtering method. CONSTITUTION:Boron is a heat-resistant material in itself, being in the same group with aluminum on a periodic table and being compounded with an amorphous metal, and it is an element obstructing a shift of a defect of a grain boundary and the like and being effective for making a crystal minute. By adding the boron to the aluminum, accordingly, a recrystallization temperature is raised and heat resistance is improved. Therefore, an aluminum target containing the boron is prepared and a thin film is prepared by a sputtering method. The boron content of the aluminum is preferably 0.1 to 2 wt.%. Addition of a hydrogen gas to a sputter gas, i.e. an argon gas, produces a remarkable effect on suppression of formation of a hillock. The amount of hydrogen added to the sputter gas is preferably 1 to 20 wt.%.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for forming wiring used in electronic components such as display panels, sensors, and ICs manufactured using thin film formation technology.

(Conventional technology) Various wiring materials are used in electronic components manufactured using thin film formation technology depending on their purpose and manufacturing process. For example, for ICs, aluminum, tungsten, various silicides, etc. are used, while for display panels, Chromium, tantalum, titanium, etc. are used. These materials suit the application and manufacturing process from various viewpoints such as low electrical resistance as wiring materials, adhesion to silicon oxide films and glass, ease of etching, heat resistance, and oxidation resistance. Material is selected.

Among the above materials, aluminum is the wiring material most commonly used in ICs because it has excellent adhesive properties, low electrical resistance, and can be easily etched. Although vacuum evaporation and CVD are known as methods for depositing this aluminum film, currently sputtering is mainly used. As is well known, the sputtering method usually uses argon gas as the sputtering gas, collides argon ions generated in a plasma state with the target, and causes the ejected target material to adhere to the opposing sample. Since it is possible to deposit a film while maintaining the alloy composition relatively, it is often used in aluminum film deposition where silicon or the like is often added.

(Problem to be solved by the invention) However, this aluminum also has the disadvantage of being heat resistant.

In Ic, along with the miniaturization of wiring, it has been pointed out that aluminum wiring has limitations in terms of heat resistance. That is, hillocks or voids occur due to heat treatment after wiring processing, leading to breakage of fine wiring. For this reason, aluminum wiring is currently being reconsidered.

On the other hand, in display panels, especially active matrix liquid crystal display panels, which are considered to be the mainstream of future high-resolution flat displays, it is essential to significantly reduce the resistance of the lotus line in order to increase the screen size, and the full application of aluminum wiring is considered. However, the heat resistance of aluminum is also considered a problem here.

Usually, the width of the lot line of an active matrix is not as fine as that of an IC. However, in the currently used active matrix, amorphous silicon TPT is formed on the pass line with an insulating film interposed therebetween. Therefore, the pieline surface is required to be as smooth as possible. However, when aluminum wiring is used here, it lacks heat resistance, resulting in a significantly rough surface and even several hundred nanometers.
Hillocks up to m in length are formed.

When the surface is roughened in this way, it is impossible to flatten the surface even if an insulating film is deposited thereon in a low-temperature process such as an actite matrix manufacturing process, and the structure of the insulating film becomes rough. For this reason, the amorphous silicon TPT formed thereon suffers significant characteristic deterioration and even insulation failure. Therefore, it is not possible to use aluminum wiring in the active matrix without any ingenuity.

Also in ICs, aluminum alloys containing 1 to 4% copper are sometimes used to improve the heat resistance of aluminum. However, even with such a material, surface roughness and the occurrence of hillocks cannot be prevented, and the material has drawbacks that impede the formation of active matrix TPT.

The present invention was proposed in order to improve the above-mentioned drawbacks, and its purpose is to provide a method for forming a thin film for wiring, which improves the heat resistance of aluminum wiring.

(Means for Solving the Problems) In order to achieve the above object, the present invention is characterized in that an aluminum target containing at least 0.1 to 2% by weight of boron is used in depositing an aluminum wiring layer by sputtering. The gist of the invention is a method for forming a thin film for wiring.

(Function) Boron itself is a heat-resistant material and is in the same group as aluminum on the periodic table, and when added to amorphous metals, it prevents the movement of defects such as grain boundaries and helps refine crystals. It is a valid element. Therefore, it is thought that adding boron to aluminum increases the recrystallization temperature and improves heat resistance.

Therefore, a boron-containing aluminum target was prepared, a thin film was formed using a sputtering method, and the heat resistance was evaluated. The results revealed that boron alloying is effective in preventing surface roughness. Also regarding hillocks 20
A clearly strong suppressive effect was observed when combined with substrate heating at about 0°C. Furthermore, this system is characterized by a relatively small increase in specific resistance even when the additive concentration is increased. Therefore, it has become possible to significantly improve heat resistance compared to conventionally used copper-aluminum alloys.

However, in heat treatment at 300°C or higher, hillocks occur although both hillock density and hillock size are small, and depending on the process conditions such as the heating process for active matrix fabrication, heat resistance may still not be sufficient. understood.

Therefore, we conducted various further studies based on this alloy. We have found that adding hydrogen gas to the sputtering gas, ie, argon gas, has a remarkable effect on suppressing the formation of hillocks. Films deposited with a combination of a boron-containing aluminum target and a hydrogenated sputtering gas were
Even after the 'C heat treatment, the surface remained mirror-like without being roughened at all, and no hillocks were detected when examined using a dark-field microscope. The details of this hydrogen action are currently unknown. However, even if hydrogenated argon was used as the sputtering gas, it was found that when ordinary pure aluminum was used as the target, the surface of the deposited film was rather roughened, and hillocks were not suppressed at all. ing.

Furthermore, when a hydrogen-containing sputtering gas is used, the resistivity of the film increases. Therefore, hydrogen cooperates with boron to suppress the diffusion of aluminum atoms incorporated into the film.
It is also possible that non-uniformity in the film structure, which could become a nucleus for hillock growth during film formation, is eliminated.

In any case, the action of boron and hydrogen suppresses surface roughness and hillock density caused by recrystallization.

The phenomena associated with the addition of the above elements will be described below. When only boron is added to aluminum, a glossy surface can be stably obtained even with a target boron addition amount of 0.1% by weight, and as the amount of boron increases, the hillock density and its size gradually decrease. In particular, by heating the substrate during deposition, the frequency of occurrence of spots and etch can be significantly reduced. Further, the increase in electrical resistivity is gradual and maintains a value of 1OμΩ·1 or less even when the content is 2% by weight or more. However, at the same time, the workability of wet etching using a phosphoric acid-based aluminum etching solution deteriorates in terms of batten dimensional accuracy and etching uniformity. As a result of the above, the content of boron relative to aluminum is preferably 0.1 to 2% by weight.

On the other hand, with the addition of hydrogen gas, a hillock suppression effect clearly appears with a hydrogen flow rate of 1% or more in a boron 0.5% by weight target, and as the hydrogen flow rate is further increased, the suppression effect becomes more pronounced. 3 for % or more
No hillocks appear even after heat treatment at 50°C. At this time, unlike the case of boron alone, the specific resistance also increases,
At a flow rate of 20% or more, it becomes 20 μΩ·1 or more. Further, as the hydrogen content increases, the film deposition rate also decreases, and at a flow rate of 20% or more, the decrease is 15% or more. At the same time, excessive hydrogen is taken into the film from the flow rate in this vicinity, causing bubbles to be generated during the subsequent heat treatment process and causing the wiring to swell. Note that the addition of hydrogen gas does not affect etching processability using a phosphoric acid-based aluminum etching solution. From the above results, the amount of hydrogen added is preferably 1 to 20% by flow rate.

An example in which the aluminum wiring of the present invention is applied to an actitus matrix will be shown below.

(Example) Next, examples of the present invention will be described.

It should be noted that the embodiments are merely illustrative, and it goes without saying that various changes and improvements may be made without departing from the spirit of the present invention.

An active matrix for a liquid crystal panel was formed using so-called reverse staggered TPT on a glass substrate. That TPT
A schematic cross-sectional view of the completed section is shown in Figure 1.

First, a boron-containing aluminum lamella of 0.2 μm was deposited on a cleaned glass substrate by DC magnetron sputtering. At this time, an aluminum target containing 0.5% by weight of boron was used. In addition, the sputtering gas has a flow rate of 5%.
It is argon which is made by cooling hydrogen. No particular substrate heating was performed. The deposited film had better specularity than pure aluminum. Also, the sheet resistance of the membrane is 0.45Ω/
It was the mouth. After the resist batten was formed, batten processing was performed using a normal aluminum etching solution, that is, a phosphoric acid solution containing about 10% nitric acid, and gate electrodes and gate buses 1 were fabricated. The side of the formed batan is about 45
It was found that the etching was approximately isotropic, with an inclination of . This is thought to be due to the grains becoming finer due to the addition of boron and hydrogen. The slope of the side surface of the wiring batten has an advantageous property t7 that can avoid coarsening of the structure at the step of the layer deposited thereon.
do. Next, a silicon nitride film of 0.00% is used as a gate insulating film.
2 μm2, amorphous silicon 0.05 as active layer
μm3, and a silicon nitride film as an active layer protective film 0.
A thickness of 3 μm4 was continuously deposited by plasma CVD. The maximum temperature at this time is 3.
00'C. When the deposited film was observed using a dark field microscope, no hillocks were observed on the aluminum wiring, and it remained smooth. After defining the active region, source/drain contacts are opened in the active layer protective film, phosphorus-doped amorphous silicon 5 is deposited and patterned as the source/drain electrode, and ITO is deposited to form the pixel electrode 6. Formed. Further, chromium was deposited to a thickness of 0.1 μm by sputtering, and then aluminum was deposited to a thickness of 0.4 μm using an aluminum target containing 0.5% by weight of poron. Here, the chromium layer has the function of avoiding direct contact between ITO and aluminum and stabilizing the contact. During aluminum deposition, the sputtering gas was argon only and no hydrogen was added.

Further, the substrate was heated to 200°C. The sheet resistance of the deposited film was 0.12Ω/hole.

After forming the resist batten, this laminated film was etched to produce a data bus 7. Finally, a silicon nitride film 8 2 was deposited as a protective film by plasma CVD. At this time, the substrate was heated to 280° C., and although the data bus did not contain hydrogen, no hillocks, which were poron-containing aluminum deposited while the substrate was heated, were observed. Finally, the external connection terminal parts were opened to complete the production of the active matrix board.

As a result of measurement using a test element placed inside this board, the specific resistance of aluminum in the data bus layer was 6.8 μΩ·l.
The data bus layer showed a value of 3.9 μΩ·C1N. This is lower than the value immediately after deposition, and is thought to be due to recovery or crystal grain growth occurring due to the thermal process. In this way, the resistance is 1.5 to 2 times higher than that of pure aluminum wiring, but compared to the chromium or tantalum wiring used in conventional active matrices, a nearly one-digit reduction in resistance has been achieved. .

In the above embodiment, an active matrix manufacturing process using inverted staggered TPTs was illustrated, but it is of course applicable to active matrices using staggered TPTs. Furthermore, aluminum wiring is not limited to display panels, but can also be used for electronic components such as ICs. I
In the case of application to C, it may be necessary to further add silicon to the aluminum, as is well known, to prevent penetration of the diffusion layer.

(Effects of the Invention) As described above, the present invention provides a method for improving the heat resistance of aluminum wiring. By using an aluminum target containing at least 0.1 to 2% by weight of boron in the deposition of aluminum wiring layers by sputtering, high-definition panels of 20 inches or more can be realized without color unevenness, and in binary drive, Panels larger than 1 inch (approximately 100 CI) can also be easily realized. Furthermore, it can be applied to various electronic components such as sensors and fax reading devices, and even ICs as reliable wiring by taking advantage of its heat resistance.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of a TFT portion of an inverted staggered TPT active matrix manufactured by applying the method of the present invention. 1... Boron-containing aluminum gate electrode and gate lotus that can be applied to the method of the present invention, 2... Gate insulating film, 3... Amorphous silicon active layer, 4... Active layer protective film, 5... Source. Drain, 6... Pixel electrode, 7... Aluminum source/drain electrode and data bus to which the method of the present invention is applied, 8... Protective film. Patent applicant Nippon Telegraph and Telephone Corporation

Claims (2)

[Claims] (1) A method for forming a thin film for wiring, characterized in that an aluminum target containing at least 0.1 to 2% by weight of boron is used in depositing an aluminum wiring layer by sputtering. (2) The method for forming a thin film for wiring according to claim 1, characterized in that in depositing the aluminum wiring layer by sputtering, a sputtering gas containing at least 1 to 20% hydrogen in a flow rate is used.