JP2732294B2 - Thin film formation method - Google Patents

Description

The present invention relates to a method for forming a thin film such as a semiconductor thin film and an insulator thin film.

[Conventional technology]

Generally, as a method of forming an amorphous semiconductor thin film such as a-Si or an insulating thin film such as SiN or SiO ₂ , a plasma CVD method using a parallel plate RF glow discharge is well known.
Since there is a problem with the film formation rate, the so-called magnetron discharge method that uses a magnetic field in combination with the RF glow discharge method
It has been considered to improve the film forming speed.

By the way, the method of forming a thin film by the magnetron discharge method will be briefly described. A cathode electrode and an anode electrode are disposed in parallel in a reaction chamber, a thin film forming substrate is attached to the anode electrode, and RF power is applied between the two electrodes. And
The plasma of the reaction gas introduced into the reaction chamber is generated by RF glow discharge, and the plasma is confined between the two electrodes by the magnetic field formed by the magnet provided outside the cathode electrode, thereby increasing the density of the plasma. This makes it possible to improve the film formation speed on the substrate.

On the other hand, in such a magnetron discharge method, various methods have been considered in order to improve the film quality. One of them is to form a film forming gas and hydrogen [H], helium [He], neon [ There is a method of alternately introducing a gas for high quality treatment comprising a non-film-forming rare gas such as Ne] to alternately repeat film formation and high quality treatment up to a predetermined film thickness.

At this time, when shifting from film formation to high quality processing,
Alternatively, in the opposite case, in order to eliminate the influence of the residual gas in the previous step, the discharge is temporarily stopped and the gas is replaced.

[Problems to be solved by the invention]

In the conventional case, the discharge must be stopped and restarted repeatedly, and it takes a long time to reach a predetermined film thickness. In addition, due to the instability of the discharge state immediately after the discharge is restarted, the previous film forming process is performed. Between the film formed in step 1 and the film formed in the next film forming step, an interface with many defects is generated, and the film quality is improved compared to the case where high quality processing is not performed, but the film quality is significantly improved There is a problem that it cannot be aimed at.

The present invention has been made in consideration of the above points, and has as its object to significantly reduce defects and improve the film quality.

[Means for solving the problem]

In order to achieve the above object, a flat cathode electrode and an anode electrode are disposed in parallel in a reaction chamber, a thin film forming substrate is attached to the anode electrode, and a high-frequency electric field is formed between the two electrodes to form the high-frequency electric field. A method for forming a thin film on the substrate by generating a plasma of a reaction gas introduced into the reaction chamber by an electric field, confining the plasma between the two electrodes by a magnetic field formed by a magnet provided outside the cathode electrode, and forming a thin film on the substrate In the above, the magnet is constituted by an electromagnet, and the current to the electromagnet is periodically changed to be large or small, and the type of the reaction gas introduced into the reaction chamber is switched between a large current and a small current. Features.

[Action]

In the above-described configuration, the current to the electromagnet is periodically changed to be large or small, so that when the current is large, the magnetic field strength is increased and the plasma is drawn to the cathode electrode side, and the plasma is attached to the anode electrode. At a small current, the strength of the magnetic field is weakened, the plasma bulges toward the anode electrode side, and the plasma approaches the substrate.

At this time, the type of radical generated by changing the type of reactive gas at the time of a large current and at the time of a small current where the distance between the plasma and the substrate is different changes. Reactive radicals are generated to efficiently form a film, and when a high-quality processing gas is introduced at a small current, high-quality processing radicals are generated to perform a high-quality film processing, that is, a surface treatment. During this time, the film formation and the quality improvement process can be repeated without stopping the discharge between the two electrodes, so that the occurrence of defects due to the unstable discharge as in the conventional case is greatly reduced.

〔Example〕

An embodiment will be described with reference to FIG. 1 to FIG.

In FIG. 1 schematically showing a forming apparatus, (1),
(2) is a flat cathode electrode and an anode electrode (hereinafter simply referred to as a cathode (1) and an anode (2)) disposed in parallel with the reaction chamber into which the reaction gas has been introduced, and (3) is an anode (2) The substrate for thin film formation attached to (4)
An RF power source, one output terminal of which is grounded together with the anode (2), and the other output terminal of which is connected to the cathode (1).

Reference numeral (5) denotes an electromagnet, which is provided below the cathode (1), and a large current and a small current are alternately and repeatedly passed periodically by a power source having an output current variable (not shown). The plasma of the reaction gas is confined between the cathode (1) and the anode (2) by the magnetic field formed as shown by the one-dot chain line in FIG. Note that the reaction chamber is evacuated by the exhaust device.

At this time, the flowing direction of the current to the electromagnet (5) is constant, and the current value changes between large and small, so that the magnetic field intensity becomes strong at the time of a large current, and the plasma is reduced as indicated by the broken line in FIG. The plasma is strongly attracted to the (1) side, and the plasma moves away from the anode (2). At a small current, the magnetic field strength is weakened and the confinement force of the plasma is reduced. To the side, the plasma approaches the substrate (3).

Then, two reaction gas introduction systems are provided, and the reaction gas is alternately reacted from the two introduction systems when the current to the electromagnet (5) is large or small under the control of a control device including an electromagnetic valve and the like. Change the type of reaction gas at high current and low current.

For example, when a film forming gas is introduced at the time of a large current, and a high-quality processing gas such as H, He, and Ne is introduced at a low current, a reactive radical and a quality-enhancing radical are efficiently generated, respectively.

Now, when an a-Si thin film is formed, a monosilane gas [SiH ₄ ] is used as a film-forming gas, a hydrogen gas [H ₂ ] is used as a high-quality processing gas, and an electromagnet is formed as shown in FIG. The current to (5) flows periodically in a sinusoidal shape with the maximum value I (A) and the minimum value 0, and the period at this time is λ, and as shown in FIG. / 4 period H ₂
To introduce SiH ₄ for a period of λ / 4 at a large current, and to exhaust residual gas in the reaction chamber when switching between introduction of H ₂ and SiH ₄ , as shown in FIG. A gas introduction suspension period of λ / 4 is provided.

Thus, when SiH ₄ is introduced at the time of a large current, a long-lived reactive radical such as a SiH ₃ radical is efficiently generated, and a film is formed by a reaction between the reactive radical and the substrate (3), When H ₂ is introduced at a small current, H radicals, which are high quality treatment radicals, are efficiently generated, and the H radicals are used to perform high quality treatment of the thin film. The quality treatment can be repeated, and an a-Si thin film having good film quality can be obtained.

By the way, the relationship between the frequency and the photoconductivity of the a-Si thin film was examined to find the optimum range of the frequency of the current to the electromagnet (5).
^{When the} frequency is higher than ^-1 Hz, the switching of the introduced gas in the reaction chamber is not completely performed, and the reaction gas is in a mixed state. As a result, the photoconductivity of the formed a-Si thin film rapidly decreases. It can be seen that the frequency of the current to (5) should be 10 ^-1 Hz or less.

An a-Si thin film (I) was formed under the conditions shown in Table 1 under the current conditions and the switching conditions of the gas to be introduced, and the characteristics were examined. It has become.

For comparison, the current to the electromagnet (5) was 10
Fixed (A), the and the a-Si thin film formed without introducing H ₂ (II), without flowing current, and the a-Si thin film formed without introducing H ₂ (III), Apply 10 current to the electromagnet (5).
Similar characteristics were examined for the a-Si thin film (IV) fixed to (A) and formed by introducing H ₂ , and the respective forming conditions are shown in Table 1 and the characteristics are also shown in Table 2.

Thus, as is clear from Table 2, the electromagnet (5)
The SiH ₄ and H ₂ flow into the reaction chamber at high current and low current.
The a-Si thin film (I) formed by alternately introducing and improving the photoconductivity by one digit, the dark conductivity is reduced, and the spin density and space, which are indicators of defects in the film. This indicates that the charge density is significantly reduced and the defects are significantly reduced, indicating that the film quality is improved as compared with the conventional case.

〔The invention's effect〕

Since the present invention is configured as described above,
The following effects are obtained.

By changing the type of reactant gas between when the current to the electromagnet is large and when the current is small, the type of radicals generated according to the distance between the plasma and the substrate changes. By doing so, reactive radicals are generated and a film can be formed, and by introducing a high quality processing gas at a small current, a high quality processing radical is generated, and the film is subjected to a high quality processing, that is, Surface treatment can be performed, and during this time, film formation and quality improvement processing can be repeated without stopping discharge between both electrodes as in the conventional case, and defects such as those caused by unstable discharge as in the conventional case can be eliminated. Generation can be significantly reduced, and the quality of the formed thin film can be improved.

[Brief description of the drawings]

The drawing shows one embodiment of the thin film forming method of the present invention,
2A to 2C are timing charts for explaining the operation, and FIG. 3 is a diagram showing the relationship between frequency and photoconductivity. (1) Cathode, (2) Anode, (3) Thin film forming substrate, (4) RF power supply, (5) Electromagnet.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Shoichi Nakano 2-18-18 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (56) References JP-A-58-132920 (JP, A) JP-A-Hei 1-130533 (JP, A) JP-A-1-130531 (JP, A)

Claims (1)

(57) [Claims] 1. A flat plate-like cathode electrode and an anode electrode are disposed in parallel in a reaction chamber, a thin film forming substrate is attached to the anode electrode, and a high-frequency electric field is formed between the two electrodes. A thin film forming method for generating a plasma of a reaction gas introduced into a reaction chamber, confining the plasma between the two electrodes by a forming magnetic field of a magnet provided outside the cathode electrode, and forming a thin film on the substrate, The magnet is constituted by an electromagnet, and the current to the electromagnet is periodically changed to be large or small, and the type of the reaction gas introduced into the reaction chamber is switched between a large current and a small current. Thin film formation method.