JP3819793B2 - Film-forming method and semiconductor device manufacturing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for forming a zinc oxide film by sputtering and a method for manufacturing a semiconductor device in which a zinc oxide film is stacked on a substrate by sputtering.
[0002]
[Prior art]
An electronic device such as a thin film transistor, a light-emitting element, or a piezoelectric body is formed by stacking thin films having different conductivities such as an insulating film, a semiconductor film, or a conductive film.
Zinc oxide is used to form an insulating film, a transparent electrode film, a semiconductor film, or the like. When an electronic device is configured using zinc oxide, the electronic device is formed by laminating a zinc oxide film and a film made of a substance having a conductivity different from that of zinc oxide, or a plurality of oxides each having different conductivity. It is configured by laminating zinc films. When a plurality of zinc oxide films having different conductivities are formed by sputtering, the amount of doped impurities (Al or Ga, etc.) is different for each zinc oxide film in order to adjust the carrier density in the film. Each zinc oxide film is formed using a zinc oxide target.
[0003]
[Problems to be solved by the invention]
However, when forming a thin film with different conductivity by the conventional film formation method, a plurality of substances (zinc oxide and zinc oxide having different conductivity) are prepared, or a plurality of oxidations having different impurity contents are prepared. Since it is necessary to prepare a zinc target, an increase in material cost or an increase in the number of manufacturing steps occurs, and there is a problem that the cost of the electronic device increases.
[0004]
FIG. 5 shows that when a 200 nm zinc oxide film is formed on a glass substrate using an RF sputtering apparatus, non-doped zinc oxide (99.99%) is used as a target, and Ar gas and oxygen gas are used as discharge gases. 5 is a graph showing the relationship between the oxygen flow rate ratio in the discharge gas and the conductivity of the zinc oxide film. The film formation conditions were a substrate temperature of 300 ° C., a pressure of 0.5 Pa, an RF power density of 10 W / cm ² , and the oxygen flow rate ratio was changed between 0% and 100%. In the figure, the horizontal axis represents the flow rate ratio (%) of oxygen gas in the discharge gas, and the vertical axis represents the conductivity (S / cm) of the zinc oxide film.
[0005]
When the oxygen flow ratio is 0% (when only Ar gas is used as the discharge gas), the conductivity of the zinc oxide film is the highest (over 1 × 10 ⁻² S / cm), and the oxygen flow ratio is 0% to 10%. The conductivity decreases rapidly from above 1 × 10 ⁻² S / cm to about 1 × 10 ⁻⁸ S / cm. Further, when it is increased to 25%, it decreases to about 1 × 10 ⁻⁹ S / cm, and when it is increased to 50%, it decreases to about 1 × 10 ⁻¹⁰ S / cm. When increasing from 50% to 100%, the conductivity gradually decreases and becomes the lowest at 100% (when only oxygen gas is used as the discharge gas).
From the graph, as the flow rate ratio of oxygen gas in the discharge gas increases (0% to 100%), the conductivity decreases (above 1 × 10 ⁻² S / cm to less than 1 × 10 ⁻¹⁰ S / cm). I understand that. This is presumably because when the zinc oxide film contains a large amount of oxygen, the number of donors due to oxygen defects decreases and the conductivity decreases.
[0006]
In addition, when zinc oxide doped with impurities is used as a target, the conductivity hardly changes even if the flow rate ratio of oxygen gas is changed.
From the above results, the inventors can easily increase the conductivity of the zinc oxide film by using a non-doped zinc oxide target and changing the partial pressure (here, the flow ratio) of the oxygen gas in the discharge gas. In addition, we have obtained knowledge that it can be changed over a wide range and with high accuracy.
[0007]
The present invention has been made on the basis of such knowledge. When a zinc oxide film is formed by a sputtering method using a non-doped zinc oxide target, the partial pressure of oxygen gas in the discharge gas is changed. Another object of the present invention is to provide a film forming method capable of reducing the material cost and easily forming a zinc oxide film having different conductivity.
Another object of the present invention is to provide a film forming method capable of easily forming a zinc oxide film whose conductivity continuously changes in the film thickness direction by continuously increasing or decreasing the partial pressure of oxygen gas in the discharge gas. It is to provide.
Another object of the present invention is to make it possible to easily and alternately stack a low-conductivity zinc oxide film and a high-conductivity zinc oxide film by repeatedly increasing and decreasing the partial pressure of oxygen gas in the discharge gas. It is to provide a membrane method.
Still another object of the present invention is to form a zinc oxide film by continuously reducing the partial pressure of oxygen gas in the discharge gas, thereby reducing the material cost and improving the conductivity from the substrate side. An object of the present invention is to provide a method of manufacturing a semiconductor device that can easily form a semiconductor device including a zinc oxide film continuously increasing in the pressure direction.
[0008]
[Means for Solving the Problems]
According to a first aspect of the present invention, there is provided a film forming method for forming a zinc oxide film by a sputtering method, wherein non-doped zinc oxide is used as a target, and an inert gas, an oxygen gas, or an inert gas and an oxygen gas are used as a discharge gas. And a step of increasing the partial pressure of the oxygen gas at least once during the film formation and a step of decreasing the partial pressure of the oxygen gas at least once during the film formation. And
[0009]
In the first invention, since the conductivity of the formed zinc oxide film changes according to the partial pressure of the oxygen gas in the discharge gas when forming the zinc oxide film, non-doped oxidation The conductivity in the zinc oxide film can be adjusted by using only zinc as a target material and changing the partial pressure of the oxygen gas in the discharge gas. In other words, since only zinc oxide is used, the material cost can be reduced, the number of manufacturing steps can be reduced because there is no need to replace the target, and the conductivity can be adjusted by changing the partial pressure of oxygen gas. Therefore, zinc oxide films having different electrical conductivities can be easily formed. As described above, an electronic device using a zinc oxide film can prevent an increase in cost, and the degree of freedom in designing the electronic device can be improved.
When the partial pressure of oxygen gas in the discharge gas is 100%, the discharge gas is composed only of oxygen gas, and when the partial pressure of oxygen gas is 0%, the discharge gas is composed only of inert gas. The
[0010]
The film forming method according to the second invention is characterized in that the partial pressure is continuously increased or decreased.
In the second invention, when the partial pressure of the oxygen gas in the discharge gas during the formation of the zinc oxide film is continuously increased, the conductivity of the formed zinc oxide film is continuous. When the partial pressure is decreased continuously, the conductivity increases continuously, so that a zinc oxide film whose conductivity continuously changes in the film thickness direction can be easily formed. . For this reason, for example, a laminated film having an LDD (Lightly Doped Drain) / semiconductor film (active layer) structure can be easily formed at low cost.
[0011]
A film forming method according to a third invention is characterized in that the partial pressure is alternately increased / decreased.
In the third aspect of the invention, for example, the first zinc oxide film is formed by increasing the partial pressure of oxygen gas in the discharge gas, and then the partial pressure is decreased and formed on the first zinc oxide film. A second zinc oxide film is formed. In this case, the first zinc oxide film has a lower conductivity than the second zinc oxide film. In this manner, since a zinc oxide film having a high conductivity and a zinc oxide film having a low conductivity can be alternately stacked, a stacked structure of zinc oxide films having different conductivity can be easily formed at low cost. be able to.
[0012]
According to a fourth aspect of the present invention, there is provided a method for manufacturing a semiconductor device, comprising: stacking a zinc oxide film on a substrate by a sputtering method; and providing a source electrode, a drain electrode, and a gate electrode. The first zinc oxide film is formed by sputtering using an inert gas, an oxygen gas, or a mixed gas of an inert gas and an oxygen gas as a discharge gas. First, the oxygen gas or the mixed gas is used as a discharge gas. Then, the second zinc oxide film is formed by sputtering while continuously reducing the partial pressure of oxygen in the discharge gas. Next, a groove for dividing the second zinc oxide film is formed. Next, a gate electrode is provided on the groove via an insulating layer, and a source electrode and a drain electrode are provided on the second zinc oxide film so as to sandwich the groove. It is characterized in.
[0013]
In the fourth invention, after the first zinc oxide film is formed, the second zinc oxide film is formed while continuously reducing the oxygen partial pressure in the discharge gas by using the film forming method of the second invention. Therefore, when the semiconductor device is formed, the effect of the second invention can be obtained. That is, it is possible to easily form a semiconductor device including a zinc oxide film whose material cost is reduced and whose conductivity continuously increases in the film pressure direction from the substrate side.
Further, by continuously decreasing the oxygen partial pressure in the discharge gas, the conductivity of the second zinc oxide film continuously increases in the film pressure direction from the substrate side. For this reason, the regions on the source electrode side and the drain electrode side of the second zinc oxide film having a high conductivity can act as the source region and the drain region, and the second zinc oxide film having a lower conductivity than the region can be used. The region on the first zinc oxide film side can act as an LDD region.
When the partial pressure of oxygen gas in the discharge gas is 100%, the discharge gas is composed only of oxygen gas, and when the partial pressure of oxygen gas is 0%, the discharge gas is composed only of inert gas. The
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the drawings illustrating embodiments thereof.
In this embodiment, a zinc oxide film is formed on a glass substrate using a known RF sputtering apparatus. Non-doped zinc oxide (99.99%) is used as the target, and oxygen gas and Ar gas are used as the discharge gas. The film forming conditions are a substrate temperature of 300 ° C., a pressure of 0.5 Pa, and an RF power density of 10 W / cm ² . Moreover, the partial pressure of oxygen gas is adjusted by changing the flow rate ratio between Ar gas and oxygen gas.
[0015]
Embodiment 1.
1 and 2 are explanatory diagrams for forming an FET having an LDD / semiconductor film laminated film by using the film forming method according to the first embodiment of the present invention.
A flow rate ratio of oxygen gas in the discharge gas is set to 3%, and a zinc oxide semiconductor film 11 having a film thickness of 200 nm is formed on one surface of the glass substrate 10 (FIG. 1A). Subsequently, the flow rate ratio of the oxygen gas is continuously decreased from 3% to 0% (that is, the discharge gas is only Ar gas) without turning off the discharge, and the film thickness of 10 nm is formed on the zinc oxide semiconductor film 11. An LDD / source / drain film 12 is formed (FIG. 1B).
Next, etching is performed using dilute hydrochloric acid to remove a part of the LDD / source / drain film 12, thereby forming a groove 12a (FIG. 1C).
[0016]
On the LDD / source / drain film 12 and in the trench 12a, SiN is deposited by plasma CVD to form an insulating film 130 having a thickness of 500 nm (FIG. 2A). Only the insulating film 130 is removed by etching to form the insulating layer 13 having the groove 12a as the bottom (FIG. 2B).
Finally, an Al film is formed on the LDD / source / drain film 12 and the insulating layer 13 to form a source electrode 141 and a drain electrode 143 on the LDD / source / drain film 12, and on the insulating layer 13. A gate electrode 142 is formed (FIG. 2C).
[0017]
According to the film formation method as described above, the zinc oxide semiconductor film is formed on the n ⁻ -type zinc oxide semiconductor film 11 by continuously reducing the flow rate ratio of oxygen gas from 3% to 0%. Thus, the LDD / source / drain film 12 that continuously changes from the n ⁻ -type to the n ⁺ -type can be easily stacked.
Further, since the film is formed by continuously reducing the flow ratio of oxygen gas, the conductivity of the LDD / source / drain film 12 continuously increases in the film pressure direction from the substrate side. For this reason, the regions on the source electrode 141 side and the drain electrode 143 side of the LDD / source / drain film 12 have high conductivity and act as the source region and the drain region, and the zinc oxide semiconductor film 11 of the LDD / source / drain film 12 The side region has lower conductivity than the source region and the drain region, and acts as an LDD region. That is, an FET having a laminated film having an LDD / semiconductor film structure can be easily formed at low cost.
[0018]
The FET formed as described above can relax the electric field in the vicinity of the drain electrode by the LDD / semiconductor film structure, and the FET performance degradation due to hot electrons (high-speed accelerated carriers are injected into the insulating layer 13). And a fixed charge) can be prevented.
[0019]
Embodiment 2. FIG.
FIG. 3 is an explanatory diagram in the case of forming a multilayer film of zinc oxide films having different conductivities using the film forming method according to the second embodiment of the present invention.
A flow rate ratio of oxygen gas is set to 100% (that is, only oxygen gas is used as a discharge gas), and a first zinc oxide film 21 having a thickness of 100 mm is formed on one surface of the glass substrate 20 (FIG. 3A). ). Subsequently, the discharge is turned off, the flow rate ratio of the oxygen gas is reduced to 0% (that is, only Ar gas is used as the discharge gas), the discharge is restarted, and a film thickness of 100 mm is formed on the first zinc oxide film 21. The second zinc oxide film 22 is laminated (FIG. 3B). Similarly, the first zinc oxide film 21 and the second zinc oxide film 22 are alternately stacked (FIG. 3C).
[0020]
The multilayer film formed by the film forming method as described above is formed by laminating a high-resistance first zinc oxide film 21 and a low-resistance second zinc oxide film 22. For this reason, the second zinc oxide films 22, 22,... Are insulated by the first zinc oxide films 21, 21,.
[0021]
FIG. 4 is a schematic diagram of a multilayer film formed by the film forming method.
In the figure, 2 is an electron contributing to electrical conduction. The electrons 2 move inside the second zinc oxide film 22 where the electrons 2 are located, do not pass through the first zinc oxide film 21 and move to other second zinc oxide films 22. That is, the electrons 2, 2,... Can be confined in each second zinc oxide film 22, and a decrease in mobility due to impurity scattering can be prevented. For this reason, the multilayer film has a high electron mobility.
That is, since the film formation method of this embodiment includes a multilayer film having different conductivity, an electronic device (eg, TFT) having high electron mobility can be easily formed at low cost.
[0022]
In Embodiments 1 and 2, an RF sputtering apparatus is used and oxygen gas and Ar gas are used as the discharge gas. However, a DC sputtering apparatus, an ECR sputtering apparatus, a helicon plasma wave sputtering apparatus, or the like is used, and the discharge gas is used. As an alternative, oxygen gas and rare gas such as He gas, Ne gas, or Kr gas may be used.
Further, the film forming method of the present invention may be used when an electronic device such as a light-transmitting thin film transistor, a photosensor, or a piezoelectric body is formed.
[0023]
【The invention's effect】
According to the film forming method of the present invention, it is possible to easily form a zinc oxide film having different electrical conductivity while reducing the material cost. In addition, a zinc oxide film whose conductivity continuously changes in the film thickness direction can be formed. Furthermore, a zinc oxide film having a low conductivity and a zinc oxide film having a high conductivity can be alternately stacked.
In addition, according to the method for manufacturing a semiconductor device of the present invention, the present invention can reduce the material cost and easily form a semiconductor device including a zinc oxide film whose conductivity continuously changes in the film thickness direction. Excellent effect.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a film forming method according to a first embodiment of the present invention.
FIG. 2 is an explanatory diagram of a film forming method according to Embodiment 1 of the present invention.
FIG. 3 is an explanatory diagram of a film forming method according to a second embodiment of the present invention.
FIG. 4 is a schematic diagram of a multilayer film formed by a film forming method according to Embodiment 2 of the present invention.
FIG. 5 is a graph showing the relationship between the oxygen flow rate ratio in the discharge gas and the conductivity of the zinc oxide film.
[Explanation of symbols]
11 zinc oxide semiconductor film 12 LDD / source / drain film 21 first zinc oxide film 22 second zinc oxide film

Claims (4)

In a film forming method for forming a zinc oxide film by sputtering,
A step of increasing the partial pressure of oxygen gas at least once during film formation using non-doped zinc oxide as a target, an inert gas, oxygen gas, or a mixed gas of inert gas and oxygen gas as a discharge gas And a step of reducing the partial pressure of the oxygen gas at least once during the film formation. The film forming method according to claim 1, wherein the partial pressure is continuously increased or decreased. The film forming method according to claim 1, wherein the partial pressure is alternately increased / decreased. In a method for manufacturing a semiconductor device in which a zinc oxide film is stacked on a substrate by a sputtering method, and a source electrode, a drain electrode, and a gate electrode are provided,
Non-doped zinc oxide is used as a target, inert gas, oxygen gas, or a mixed gas of inert gas and oxygen gas is used as a discharge gas, and first, sputtering is performed using oxygen gas or the mixed gas as a discharge gas. The formation of the first zinc oxide film is started, and then the second zinc oxide film is formed by sputtering while continuously reducing the partial pressure of oxygen in the discharge gas. A groove part for dividing the zinc film is formed, then a gate electrode is provided on the groove part via an insulating layer, and a source electrode and a drain electrode are provided on the second zinc oxide film so as to sandwich the groove part. A method for manufacturing a semiconductor device.

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