JPH11354469A - Thin film formation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique capable of reducing hillocks to be a problem especially at the time of using an Al thin film as a wiring material, in the manufacturing method of an Al or Al alloy wiring film. SOLUTION: When contamination for which the oxidative gas of oxygen or water or the like remains inside a processor at the time of sputtering for forming the Al thin film is generated, an oxidized film is formed at the grain boundary of the Al film, the growth of grains is obstructed and the hillock is generated on the surface of the Al thin film in a heating process thereafter. In order to prevent that, in this case, before growing the Al thin films 5a and 5c on a substrate 5, high frequency power weak enough not to sputter a target 3 is supplied to the target 3, plasma is generated, the surface of the target 3 and the surface of the substrate 5 are cleaned and the oxidative gas is removed. Thus, the oxidized film is prevented from being formed at the grain boundary, the growth of the grains is not obstructed and the generation of many hillocks on the surface is prevented even when a heating processing is performed after forming the thin film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a thin film wiring made of an Al thin film or an alloy thin film containing Al as a main component, which is used for a display device such as a liquid crystal device or a semiconductor device.
In particular, the present invention relates to a technique for reducing the amount of hillocks generated in thin film wiring.

[0002]

2. Description of the Related Art Conventionally, in a semiconductor device, pure Al or an alloy containing Al as a main component has been generally used as a material of a thin film wiring. Meanwhile, thin film transistor
(Hereinafter referred to as TFT) as a driving element in a liquid crystal display device (hereinafter referred to as LCD), a thin film wiring material such as Cr
And Mo have been used.

However, since the resistance of Cr, Mo, and the like is relatively high, the LCD is required to have a large size and high definition, and the problems of signal delay and insufficient writing to pixels due to the resistance component of the thin film wiring are remarkable. It has become.

Attempts have been made to use, as a material for thin film wiring, Al or an alloy containing Al as a main component, instead of Cr, Mo, or the like. By the way, Al or a thin film containing Al as a main component used in a semiconductor element or a TFT (in this specification, a thin film containing Al as a main component is referred to as A
1 called a thin film. ) Is generally manufactured by a direct current (DC) magnetron sputtering method, but when an Al thin film is formed on a glass substrate or a Si wafer substrate to form a thin film wiring, the heat treatment in a subsequent process is performed. Hillocks (protrusions) are generated on the Al thin film wiring, and if the insulating film on the Al thin film wiring is pierced, a short circuit occurs with the upper thin film wiring formed on the insulating film. .

In order to prevent the occurrence of such hillocks, there is a method in which a refractory metal such as Cu, Si, Ti, Ta, Nd, Mo, or Zr is added to the material of the Al thin film wiring. If the amount of the high melting point metal added is increased to enhance the effect, there is a problem that the resistance value of the thin film wiring increases.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in order to solve such problems of the prior art.
An object of the present invention is to provide a technique capable of reducing the amount of hillocks generated without increasing the resistance value of the Al thin film wiring.

[0007]

FIGS. 1A and 1B show the state of crystal grains of Al thin film wirings 10 and 20 formed by using a sputtering method. Symbols 11a to 11c and 21a to 21f are:
The crystal grains constituting the Al thin film wirings 10 and 20 are shown.

After the Al thin film wirings 10 and 20 are formed, an interlayer insulating film and an upper thin film wiring are further formed on the surface thereof. Since there is a difference in the coefficient of thermal expansion of the substrate serving as the base, if the low-temperature state and the high-temperature state are repeated by the heat treatment during the process after the formation of the Al thin-film wirings 10, 20, the Al thin-film wirings 10, 20 Compressive stress is generated inside, and at that time, Al atoms move along the grain boundaries of the crystal grains 11a to 11c and 21a to 21f, and hillocks are formed at intersections of the grain boundaries.

At this time, as shown in FIG. 1A, in the Al thin film wiring 10 in which the crystal grains 11a to 11c have a large grain size, hillocks are generated because the total area of the grain boundaries and the intersections of the grain boundaries are small. However, as shown in FIG.
In the Al thin film wiring 20 having small a to 21f, the total area of the grain boundaries is large, and there are many intersections 22a to 22d of the grain boundaries, so that hillocks are easily generated.

It is known that the occurrence of a short circuit due to a hillock is not determined only by the size of crystal grains, but is also affected by the orientation of crystal grains. If there is, compared to the case where the crystal grains are uneven,
Since a large compressive stress rarely occurs locally in the Al thin film wiring, even if a hillock occurs, its size is small. Therefore, the hillock does not break through the interlayer insulating film, and a short circuit is less likely to occur.

The inventors of the present invention have determined that these crystal grain sizes,
It has been found that the residual gas at the time of sputter deposition and the gas adsorbed on the target surface and the substrate surface greatly affect the crystal grain orientation.

In particular, when sputtering is performed in a state where an oxidizing gas such as oxygen or water is adsorbed on a target surface or a substrate surface, an oxide film is formed at a crystal grain boundary of an Al film, and crystal grains grow. Is considered to be hindered, and the orientation is considered to be non-uniform.

[0013] The present invention has been made based on the above findings. As in the first aspect of the present invention, a substrate is placed in a processing chamber, and a sputtering gas is introduced in a vacuum atmosphere to introduce Al. A thin film formed on the substrate by sputtering a target including: applying a weak high-frequency power to the target such that the target is not sputtered before growing the thin film on the substrate. A pre-processing step is provided.

With this configuration, it is possible to clean the substrate surface and the target surface by generating plasma before growing the thin film (this is referred to as plasma cleaning in this specification), and the substrate surface is cleaned. And the adsorbed gas can be removed from the target surface.

Therefore, it is possible to suppress that a gas such as an oxidizing gas is adsorbed on the substrate surface or the target surface to form an oxide film at the crystal grain boundary, and the crystal grain size is large and the orientation is uniform. Film can be obtained. as a result,
Even after the heat treatment step, generation of hillocks on the Al film can be significantly reduced.

By the way, depending on the magnitude of the high-frequency power supplied to the target, the target is sputtered at the time of plasma cleaning, and film formation is started. At this time, since the film formation is started before the adsorbed gas is removed from the substrate surface or the target surface, a partially oxidized Al film is formed on the substrate, and then formed by applying a DC voltage. The crystallinity of the Al thin film deteriorates.

The inventors of the present invention have reported that A at a pressure of 0.3 Pa
In a r gas atmosphere, a 13.56 MHz high frequency power of 50 W to a target of 3400 cm ^{2 made} of Al is applied.
Plasma was generated by supplying a predetermined value in the range of 500 W, and the deposition rate of Al was measured. The measurement results are shown in the graph of FIG. In FIG. 2, the horizontal axis represents high-frequency power, and the vertical axis represents the deposition rate of Al.

From the graph of FIG. 2, the high frequency power is 250 W
In the following, the deposition rate of Al is 0 ° / min and the target 3 is not sputtered at all.
It can be seen that the deposition rate of Al is further increased when the rate becomes Å / min and becomes 300 W or more.

As described above, in the thin film forming method according to the first aspect, as in the second aspect, the target is sputtered by applying a high frequency power of less than 300 W in the pretreatment step. Without generating plasma.

Further, as described in claim 3, in the thin film forming method according to claim 1 or 2, in the pretreatment step, a reducing gas may be added to the sputtering gas.

With this configuration, even if gas molecules of the oxidizing gas cannot be completely removed by plasma alone during plasma cleaning, the gas molecules can be reduced by the reducing gas. The amount of the oxidizing gas adsorbed on the surface can be further reduced.

In order to alleviate the compressive stress applied to the Al thin film, first, a metal thin film having a thermal expansion coefficient close to that of the Al thin film is formed on the substrate surface, and the Al thin film is formed on the metal thin film. And its orientation can be further improved.

Therefore, according to the thin film forming method according to any one of the first to third aspects, after the Ti thin film is formed on the substrate, the T
Preferably, the thin film is formed on the i thin film.

The thin film forming method according to any one of the first to fourth aspects is particularly useful when the substrate is a glass substrate or a silicon substrate as in the fifth aspect of the invention. is there.

[0025]

Embodiments of the present invention will be described below with reference to the drawings. Referring to FIG. 3A, reference numeral 1 denotes a sputtering film forming apparatus used in the thin film forming method of the present invention. This sputtering film forming apparatus 1 has a chamber 2 that can be evacuated, a mounting table 4 is provided at the bottom of the chamber 2, and an area of 3400 cm on the ceiling side.
^Two targets 3 are provided.

The chamber 2 is provided with a gas inlet 6 and an exhaust port 7. The gas inlet 6 is connected to a gas introducing system (not shown), and the exhaust port 7 is connected to a vacuum pump (not shown). ing.

A DC power source 8 and a high-frequency power source 9 are provided outside the chamber 2. The DC power source 8 is directly connected to the target 3 and the RF filter 13
The high frequency power supply 9 is connected via the.

A substrate (300 × 400 × 1.1 mm # 70 manufactured by Corning Incorporated) is used by using such a sputtering film forming apparatus 1.
The case where an Al thin film is formed directly on the (59 glass substrate) 5 will be described below.

First, after the inside of the chamber 2 is evacuated by a vacuum pump (not shown) in advance, the substrate 5 whose glass surface is exposed is loaded into the chamber 2 while maintaining the vacuum state, and the film forming surface is And was placed on the mounting table 4.

Next, a sputtering gas is introduced into the chamber 2.
(Ar gas) was introduced from the gas inlet 6, and when the inside of the chamber 2 was stabilized at a pressure of 0.3 Pa, the high frequency power
Was started, and a high frequency power of 13.56 MHz and 50 W was supplied to the target 3 to generate plasma in the chamber 2.

After the supply of high frequency power was stopped 20 seconds after the start of supply, a DC voltage was continuously applied to the target 3 and sputtering was performed by a DC magnetron sputtering method. At the time of sputtering, the temperature of the substrate 5 was set to 100 ° C., and an Al thin film was formed on the surface of the substrate 5 in that state.

When the thickness of the Al thin film reached 3000 ° C., the application of the DC voltage and the introduction of the sputtering gas were terminated, and the substrate 5 was carried out of the chamber 2. FIG. 3B is a sectional view of the substrate 5. On the surface of the substrate 5, an Al thin film 5a is directly formed.

Next, the substrate 5 is placed in an oven at atmospheric pressure.
Heating was performed in a nitrogen gas atmosphere, and heat treatment was performed at 350 ° C. for 1 hour. The surface of the Al thin film 5a is SEM (Scanning ele
The number of hillocks was counted by observation with a ctron microscope (scanning electron microscope).

The reason for setting the temperature of the heat treatment to 350 ° C. is that the CVD method for forming the gate insulating film after forming the gate bus line of the TFT is performed at the same temperature.

After that, other conditions are not changed from the above conditions,
The high frequency power is set to a predetermined value in the range of 50 W to 500 W,
After forming a 3000 ° Al thin film 5a on the substrate 5, heat treatment was performed under the same conditions as above, and the number of hillocks was counted. The relationship between hillock density and high frequency power is shown in the graph of FIG. In FIG. 4, the horizontal axis represents high-frequency power, and the vertical axis represents hillock density.

From this graph, it can be seen that the area of the target 3 is 3
When the sputtering atmosphere is 0.3 Pa at 400 cm ² ,
It can be seen that the hillock density can be reduced to 0.01 / μm ² or less (the minimum value is taken at 150 W) when the high frequency power is in the range of 50 W to ²⁰⁰ W.

The specific resistance of the Al thin film 5a is 5
As long as high-frequency power in the range of 0 W to 200 W was supplied, the resistivity was not increased, and a relatively low specific resistance value of 3.1 μΩcm could be obtained. Thus, the amount of hillocks can be reduced without increasing the resistance value.

In the above-described formation of the Al thin film 5a, only Ar gas was used as a sputtering gas. However, as described below, plasma cleaning is performed by adding a reducing gas such as hydrogen gas to the sputtering gas. And the amount of hillocks generated can be further reduced.

The supplied high frequency power is fixed at 150 W,
1 × 10 in Ar gas^-Four~ 2 × 10 ^-2Place within the range of Pa
Plasma cleaning is performed by adding a fixed value of hydrogen gas.
Target 3 is sputtered directly on the substrate 5
An Al thin film is formed, and the same heat treatment as in the above embodiment is performed.
The number of hillocks was counted.

The measurement results are shown in the graph of FIG. In FIG. 5, the horizontal axis represents the partial pressure of the added hydrogen gas (hereinafter, this partial pressure is referred to as hydrogen addition partial pressure), and the vertical axis represents the hillock density. From this graph, it can be seen that the hillock density decreases as the hydrogen-added partial pressure increases, and the hillock generation amount can be further reduced as compared with the case where plasma is generated using only Ar gas. In particular, the hydrogenation partial pressure is 1 ×
The hillock density is 0 within the range of 10 ^{−4 to} 5 × 10 ⁻³ Pa.
Particles / μm ² , and no hillocks were generated.

This is because, when plasma is generated in a hydrogen gas atmosphere as a reducing gas, gas molecules of an oxidizing gas such as water or oxygen that cannot be removed by the plasma are reduced by the hydrogen gas. It is considered that this is because the effect of preventing the oxidizing gas from adhering to the surface of the substrate 5 or the substrate 5 has increased.

As described above, when the Al thin film 5a is formed directly on the substrate 5, it has been found that the amount of hillocks can be reduced by performing plasma cleaning before the start of the growth of the Al thin film 5a. But T on the substrate 5
When an i film is formed and then an Al thin film is formed, the amount of hillocks can be further reduced. Hereinafter, this case will be described.

First, using Ar as a sputtering gas,
After forming a Ti thin film having a thickness of 500 ° on the substrate 5 in advance by a sputtering method under a pressure of 0.3 Pa, the chamber 2
The inside of the chamber 2 is evacuated and the vacuum state is maintained, the substrate 5 is carried into the chamber 2, Ar gas is introduced from the gas inlet 6, and 13.56 MHz when the inside of the chamber 2 is stabilized at a pressure of 0.3 Pa. , 50 W of high frequency power was supplied to the target 3 to generate plasma in the chamber 2.

After 20 seconds from the start of the supply, the supply of the high-frequency power was stopped. Subsequently, a DC voltage was applied to the target 3 to perform sputtering to form an Al thin film on the surface of the Ti thin film. Thereafter, when the thickness of the Al thin film reaches 3000 °, the application of the DC voltage and the introduction of the sputtering gas are terminated, and the substrate 5
Was carried out of the chamber 2.

FIG. 3C shows a sectional view of the substrate 5 at that time. On the surface of the substrate 5, a Ti film 5b and an Al thin film 5a are sequentially formed. Next, the substrate 5 was heated in an oven under atmospheric pressure and nitrogen gas atmosphere, and heat treatment was performed at 350 ° C. for 1 hour. The surface of the Al thin film 5a was observed by SEM, and the number of hillocks was counted.

FIG. 6 is a graph showing the relationship between the high-frequency power and the hillock density in this case. Comparing this graph with the graph of FIG. 4, it can be seen that the hillock density is reduced as a whole. In particular, high frequency power of 100 to 20
In the range of 0 W, the hillock density is 0 / μm ² ,
It can be seen that hillocks were not generated at all.

The above Al thin films 5a and 5c are made of pure Al.
Although the present invention is a thin film, the present invention is not limited thereto, and can be widely applied to an Al thin film containing Al as a main component. For example, Al, Cu, Si, Ti, Ta, N
A using a target alloyed with d, Mo, Zr, etc.
It is also applicable when forming a thin film.

Although the pressure of the sputtering gas is set to 0.3 Pa, the present invention is not limited to this, and the pressure of the sputtering gas may be increased or decreased within a range of about 0.2 to 2 Pa.

Furthermore, although a glass substrate is used as the substrate 5, the present invention is not limited to this, and can be applied to a case where a semiconductor wafer such as silicon is used as the substrate.

Although hydrogen gas is used as a reducing gas to be added to the sputtering gas, another reducing gas such as methane gas or ethane gas may be used. In this experiment,
Although a high frequency of 13.56 MHz was used as the plasma cleaning, the frequency in the plasma cleaning of the present invention is not limited to 13.56 MHz. For example, even if a medium frequency of about 100 kHz is used, the same plasma cleaning effect can be obtained. Obtained.

[0051]

As described above, according to the present invention, the generation of hillocks on the Al or Al alloy thin film after the heat treatment step can be greatly reduced. As a result, problems such as short-circuiting due to hillocks can be suppressed, and T
Inexpensive and low-resistance Al in FT and semiconductor manufacturing processes
Wiring can be used with high reliability.

[Brief description of the drawings]

FIG. 1 is a view showing a state of crystal grains on a substrate at the time of film formation;
(A): A diagram showing the state of crystal grains when the crystal grain size is large. (B): A diagram showing the state of crystal grains when the crystal grain size is small.

FIG. 2 is a graph showing the relationship between high-frequency power applied to a target and the deposition rate of Al in the present invention.

3A and 3B are diagrams illustrating an experiment according to an embodiment of the present invention. FIG. 3A is a cross-sectional view illustrating a configuration of a sputtering film forming apparatus used in the experiment performed in the embodiment. FIG. Sectional view for explaining the state of a glass substrate on which a surface is formed (c): Cross-sectional view for explaining the state of a glass substrate on which a Ti film and an Al film are sequentially formed on the surface by experiments

FIG. 4 is a graph showing the relationship between high-frequency power and hillock density when only an Al film is formed on a glass substrate in an embodiment of the present invention.

FIG. 5 is a graph showing a relationship between a hydrogen addition amount and a hillock density when a hydrogen gas is added to a sputtering gas in the embodiment of the present invention.

FIG. 6 shows a Ti film, A on a glass substrate in an embodiment of the present invention.
Graph showing the relationship between high-frequency power and hillock density when l films are sequentially formed

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Sputter film-forming apparatus 2 ... Chamber (processing chamber) 3
... Target 4 ... Placement table 5 ... Substrate 5a, 5c ... A
1 thin film 5b ... Ti film 10, 20 ... Al thin film wiring 1
1a, 11b, 11c,..., Crystal grains 21a, 21b, 2
1c, 21d, 21e, 21f ... crystal grains 22a, 22
b, 22c, 22d ... intersection of grain boundaries

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Isao Sugiura, 523 Yokota, Yamatake-cho, Yamatake-gun, Chiba Prefecture Inside the Chiba Super Materials Research Laboratory, Japan Sky Technology Co., Ltd. (72) Shigenori Hayashi, 523 Yokota, Yamatake-cho, Yamatake-gun, Chiba No. 523, Japan Vapor Technology Co., Ltd.Chiba Super Materials Research Laboratories (72) Inventor Hajime Nakamura 523, Yamatake-cho, Yamatake-gun, Chiba Prefecture Japan Vacuum Technologies Co., Ltd.Chiba Super Materials Research Laboratories (72) Inventor Takahide Hori 523 Yokota Takemachi Japan Chiku Technology Co., Ltd.Chiba Super Materials Research Institute (72) Inventor Kafumi Ota 523 Yamatake Town Yokota Sanmu-gun Chiba Prefecture Japan Chiku Technology Co., Ltd.

Claims (5)

[Claims] 1. A method for forming a thin film on a substrate, wherein a substrate is placed in a processing chamber, a sputtering gas is introduced in a vacuum atmosphere, and a target containing Al is sputtered to form a thin film on the substrate. A method of forming a thin film, comprising: before growing a thin film on a substrate, a pretreatment step of applying a high-frequency power weak enough to not sputter the target to the target. 2. The thin film forming method according to claim 1, wherein high frequency power of less than 300 W is applied in said pretreatment step. 3. The thin film forming method according to claim 1, wherein in the pretreatment step, a reducing gas is added to the sputtering gas. 4. The method according to claim 1, wherein the thin film is formed after a Ti film is formed on the substrate.
The method for forming a thin film according to any one of the preceding claims. 5. The thin film forming method according to claim 1, wherein the thin film is formed on a glass substrate or a silicon substrate.