TWI518787B - Fabricating method of igzo amorphous oxide semiconductor film and fabricating method of field effect transistor using the method - Google Patents

Description

Method for producing IGZO-based amorphous oxide semiconductor film and method for producing field effect transistor using the same

The present invention relates to a method for producing an IGZO (InGaGaN Indium Oxide, InGaZnO)-based amorphous oxide semiconductor film, and a method for producing a field effect transistor using the same.

The field effect transistor can be used as a unit element of a semiconductor memory integrated circuit, a high frequency signal amplifying element, a liquid crystal driving element, etc., in particular, a thinned field effect transistor is being used as a thin film transistor (thin-film transistor, TFT) is used in a wide range of fields.

The semiconductor channel layer (active layer) forming the field effect transistor mostly uses a germanium semiconductor or a compound thereof, and a high frequency amplifying element, an integrated circuit or the like which requires high speed operation is a single crystal germanium, and although it is sufficient at a low speed, it is required. Amorphous germanium is used for the use of a liquid crystal driving device having a large area such as a display use.

In the field of displays, lightweight and flexible flexible displays have attracted attention in recent years. The flexible device mainly uses a resin substrate having high flexibility. However, the heat resistance temperature of the resin substrate is usually 150 to 200 ° C, and the polyimide resin having high heat resistance is only about 300 ° C, which is lower than inorganic materials such as glass substrates. Substrate. In the process of the amorphous germanium, a high-temperature heat treatment of more than 300 ° C is usually required. Therefore, since the amorphous germanium has low heat resistance, it is difficult to be used for a support substrate such as a flexible substrate in the conventional display.

On the other hand, Hirano et al. of the Tokyo Institute of Technology found that an In-Ga-Zn-O-based (IGZO-based) oxide semiconductor can form a film at room temperature and exhibits semiconductor performance even in an amorphous state. It is expected to be used as a TFT material for next-generation displays (Non-Patent Documents 1 and 2).

However, it is known that an IGZO-based amorphous oxide semiconductor which is not subjected to a stabilization treatment such as annealing treatment after being formed at room temperature can function as an active layer of a TFT, but the threshold voltage is likely to be driven during driving. There is a problem in electrical stability due to electrical stress.

As an active layer which is excellent in element stability, as described in Non-Patent Document 3 or Non-Patent Document 4, an IGZO-based amorphous oxide semiconductor which is annealed at 350 ° C to 400 ° C after film formation is preferred. FIG. 4 of Patent Document 1 (FIG. 7 of the present specification) shows that an amorphous IGZO film as a semiconductor film is subjected to annealing treatment (heat treatment) at 120 ° C to 250 ° C after vacuum deposition at room temperature. The carrier density is increased to reduce the resistance to 1 digit to more than 3 digits. In other words, in the annealing treatment in the heat resistant temperature range of the resin substrate, it is difficult to obtain a semiconductor layer having a carrier density (1 × 10 ¹³ to 1 × 10 ¹⁶ /cm ³ ) exhibiting good semiconductor characteristics as the active layer of the transistor. . The inventors of the present invention have also confirmed the above tendency (see Fig. 6 of the following example).

Patent Document 2 discloses a transistor including a semiconductor layer including an IGZO-based amorphous oxide film and a gate insulating film, and discloses that an oxygen flow rate ratio in a sputtering gas when sputtering is formed into a film is 10% or less. On the other hand, a semiconductor film is formed, and the oxygen flow rate ratio is set to 20% or more to form a gate insulating film. However, any of the films of Patent Document 2 is a film which is formed by directly forming a film at room temperature without performing an annealing treatment, and it is considered that the heat treatment in the subsequent step may cause a change in the resistance value, and in terms of element stability as described above. There is a problem.

Further, Patent Document 3 discloses that a field effect transistor including an amorphous oxide film as a semiconductor layer is provided with hydrogen or germanium to the electrode portion and the semiconductor layer in order to improve the element stability.

[Previous Technical Literature]

[Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2009-99847

[Patent Document 2] Japanese Patent Laid-Open Publication No. 2007-109918

[Patent Document 3] Japanese Patent No. 4332545

[Non-patent literature]

[Non-Patent Document 1] K. Nomura et al, Science, 300 (2003) 1269.

[Non-Patent Document 2] K. Nomura et al, Nature, 432 (2004) 488

[Non-Patent Document 3] K. Nomura et al, Applied Physics Letters 93 (2008) 192107

[Non-Patent Document 4] D. Kang et al, Applied Physics Letters 90 (2008) 192101

However, since the introduction of hydrogen or helium requires new equipment and processes, there are problems in terms of process simplicity and cost.

The present invention has been made in view of the above circumstances, and an object of the invention is to provide a method for producing an IGZO-based amorphous oxide semiconductor film, which is a method for producing an IGZO-based amorphous oxide semiconductor film which can be produced on a resin substrate. An IGZO-based amorphous oxide semiconductor film having a carrier density suitable as an active layer of a TFT and having good electrical stress and heat stability by a simple and low-cost process; and manufacturing of the device using the method A method of IGZO-based field effect transistor having excellent stability.

The present inventors have found that when an IGZO-based amorphous oxide film is sputter-deposited on a substrate, it is possible to manufacture an arbitrary resistance value by optimizing the back pressure at the time of sputtering film formation and the annealing treatment temperature after sputtering deposition. An IGZO-based amorphous oxide insulator film having good thermal stability.

Further, based on the above findings, the inventors have found that a simple and low-cost production of an IGZO system which can be produced on a resin substrate and has a carrier density suitable as an active layer of a TFT and which is excellent in electrical stress and heat stability. A method of crystal oxide semiconductor film.

In other words, the present invention provides a method for producing an IGZO-based amorphous oxide semiconductor film by sputtering an IGZO-based amorphous oxide layer into a film and then performing annealing treatment to produce a semiconductor film containing an IGZO-based amorphous oxide. The method is characterized in that a film is formed under the conditions satisfying the following formulas (1) and (2). In the method for producing an IGZO-based amorphous oxide semiconductor film of the present invention, it is preferred to form a film under conditions satisfying the following formula (3).

1×10 ^-5 ≦P(Pa)≦5×10 ^-4 (1),

100≦T(°C)≦300 (2),

2×10 ^-5 ≦P(Pa)≦1×10 ^-4 (3)

(wherein P is the back pressure in the above-described sputtering film formation, and T is the annealing temperature in the above annealing treatment)

Here, the "back pressure in the sputtering film formation" is the ultimate vacuum in the vacuum container (film forming apparatus) in which the substrate is provided during the sputtering film formation, and means the film forming apparatus before the film formation starts. The degree of vacuum in the film forming apparatus before introducing the film forming gas.

In the present specification, the ultimate vacuum (back pressure) is a value for reading an ion gauge provided in a sputtering film forming apparatus. The ultimate vacuum (back pressure) in the film forming apparatus is roughly equivalent to the water content (water pressure) in the film forming apparatus, and thus the moisture measured by using a mass spectrometer (for example, ULVAC company's Qulee CGM series, etc.) can also be used. Press the value obtained.

In the present specification, the IGZO-based amorphous oxide film refers to an amorphous oxide film containing In and Ga, and preferably an amorphous oxide film further containing Zn. In addition to these metal elements, other elements such as dopants or substitution elements may be contained.

In the present specification, the annealing treatment includes not only the annealing treatment after the sputtering film formation but also the entire processing of heating the film which is sputter-deposited, for example, a patterning step including photolithography or a film of the laminated layer. Heat treatment or the like in the film forming step.

In the present specification, "conductor" means a resistivity of 100 Ω‧cm or less.

In addition, "semiconductor" means a resistivity in the range of 10 ³ to 10 ⁶ Ω ‧ cm. In addition, "insulator" means a resistivity of 10 ⁷ Ω ‧ cm or more.

The annealing temperature is preferably 150 ° C or higher and 250 ° C or lower.

The method for producing an IGZO-based amorphous oxide semiconductor film of the present invention preferably satisfies the conditions of the following formulas (4) and (5), or satisfies the conditions of (6) and (7), or satisfies ( Film formation under conditions of 8) and (9) or under the conditions of (10) and (11).

P(Pa)=2×10 ^-5 (4),

200≦T(°C)≦300 (5),

P(Pa)=5×10 ^-5 (6),

120≦T(°C)≦270 (7),

P(Pa)=6.5×10 ^-5 (8),

100≦T(°C)≦240 (9),

P(Pa)=1×10 ^-4 (10),

100≦T(°C)≦195 (11)

Further, the values of the back pressure P of the above formulas (4), (6), (8), and (10) have a magnitude of ±10%.

In the method for producing an IGZO-based amorphous oxide semiconductor film of the present invention, the film formation pressure of the sputtering film formation is preferably 10 Pa or less.

Further, it is preferable that the film forming gas to be sputtered into a film is a gas containing Ar and O ₂ , and the flow rate ratio of Ar to O ₂ in the film forming gas is set to O ₂ /Ar≦1/15.

The present invention provides a method for producing a field effect transistor, which is characterized in that a thin film transistor including a semiconductor layer including an IGZO-based amorphous oxide, a source electrode, a germanium electrode, a gate electrode, and a gate insulating film is provided on a substrate. The method of forming the semiconductor layer by the method for producing an IGZO-based amorphous oxide semiconductor film of the present invention.

In the method for producing a field effect transistor of the present invention, it is preferred to use a flexible substrate as the substrate.

In the ambient gas at the time of film formation, water is contained in a partial pressure of 5.0 × 10 ⁵ Pa to 10 Pa, and it is described that the normally-off type TFT can be stably produced. However, the inventors of the present invention have confirmed that the IGZO-based oxide thin film formed in the above-described water-pressure range is subjected to annealing treatment at a temperature lower than the heat-resistant temperature of the resin substrate, and the electric resistance value varies depending on the difference in water-pressure at the time of film formation. Since the value range extends from the insulator region to the conductor region, the TFT cannot be stably produced under the above-described water pressure. See below for details.

In the case of the back pressure (normal high vacuum) and the water pressure described in Japanese Laid-Open Patent Publication No. 2007-73697, the inventors of the present invention have not described the annealing process. In the obtained active layer, the test of the operating characteristics of the TFT was carried out, and as a result, the operation of the TFT was not confirmed. In view of the above, it is considered that the annealing treatment is performed at a temperature of 400 ° C or higher in Japanese Patent Laid-Open Publication No. 2007-73697.

Therefore, the present invention can be stabilized for the first time by annealing at a temperature lower than the heat resistant temperature of the resin substrate, has a carrier density of 1 × 10 ¹³ to 1 × 10 ¹⁶ /cm ³ , and is suitable as a TFT. An IGZO-based amorphous oxide semiconductor film of an active layer. According to the present invention, it is easy to control the back pressure of the sputtering film formation in the range of 1 × 10 ^-5 or more and 5 × 10 ^-4 or less only by the annealing treatment temperature (below the heat-resistant temperature of the resin substrate). In the method, the IGZO-based amorphous oxide semiconductor film can be easily and inexpensively manufactured without requiring a new device or the like.

In the present invention, the IGZO-based amorphous oxide layer is sputter-deposited by a back pressure of 1 × 10 ^-5 or more and 5 × 10 ^-4 or less, and then annealed at a temperature of 100 ° C or more and 300 ° C or less. A semiconductor film containing an IGZO-based amorphous oxide was produced. According to this method, it is possible to easily and inexpensively produce an IGZO-based amorphous oxide having a carrier density suitable as an active layer of a TFT and having good electrical stress and heat stability at a temperature lower than the heat-resistant temperature of the resin substrate. Semiconductor film.

Therefore, in the method for producing an IGZO-based field effect transistor, the active layer (semiconductor layer) can be produced by the method for producing an IGZO-based amorphous oxide semiconductor film of the present invention, and it can be manufactured at a low cost by a simple process. An IGZO-based field effect transistor having an IGZO-based amorphous oxide insulating layer having excellent electrical stress and thermal stability and excellent element stability.

"Method for producing IGZO amorphous oxide semiconductor film"

The present inventors conducted intensive studies on a method of producing an IGZO-based amorphous oxide film having good electrical stress or heat stability. As a result, it was found that the resistance value of the formed IGZO-based amorphous oxide film changes depending on the water content in the film forming apparatus, and the resistance value changes depending on the annealing treatment temperature after the sputtering film formation, that is, by optimizing the film forming apparatus. The combination of the water content in the inside and the annealing treatment temperature after the sputtering film formation can produce an IGZO-based amorphous oxide having an arbitrary resistance value in the range from the conductor region to the insulator region and having good electrical stress and heat stability. Film (refer to Example 1, Figure 4 below).

In the present specification, "conductor" means a resistivity of 100 Ω‧cm or less.

In addition, "semiconductor" means a resistivity of 10 ³ to 10 ⁶ Ω ‧ cm. In addition, in the present specification, the term "insulator" means a resistivity of 10 ⁷ Ω ‧ cm or more.

It is known that the water content (water pressure) in the film formation apparatus in the sputtering film formation is related to the back pressure of the sputtering film formation, and it is known that the lower the back pressure, the higher the vacuum, and the lower the water pressure. The present inventors changed the back pressure at the time of sputtering film formation, and analyzed the composition of each IGZO-based amorphous oxide film having different resistance values by FT-IR (fourier transform infrared spectroscopy) measurement. As a result, it was confirmed that the peak area of the OH group differs in each of the amorphous oxide films, and when the back pressure is increased, the amount of the OH group increases, that is, the water content increases (see the following example, FIG. 5).

FIG. 1 is a schematic view showing the relationship between the water content in the film forming apparatus and the water content in the formed IGZO-based amorphous oxide film when the back pressure (the ultimate vacuum degree in the film forming apparatus) is changed. As shown, the higher the back pressure, the greater the water content in the film forming apparatus. Therefore, it is considered that an increase in the amount of moisture permeating into the film affects the resistance value of the film.

From FIG. 1 and FIG. 5 of the following example, it was confirmed that the water content (the amount of OH groups) in the IGZO-based amorphous oxide film immediately after the sputtering film formation changes depending on the back pressure at the time of sputtering film formation. Further, FIG. 4 shows that an IGZO-based amorphous oxide having various resistance values in a region from a conductor region to an insulator region can be produced according to the difference in back pressure at the time of sputtering film formation and the annealing temperature after sputtering deposition. film.

The method of controlling the water content in the film forming apparatus is not limited to being controlled by the back pressure in the sputtering film formation, and may be controlled, for example, by a method of directly introducing moisture during film formation. As described in the "Technical means for solving the problem", the back pressure is a factor that can be easily changed in the degree of vacuum in the film forming apparatus before the film forming gas is introduced. Therefore, it is preferable to control the oxide film by back pressure. The water content in the water. Hereinafter, a method of controlling the back pressure to control the water content will be exemplified.

4 shows that an IGZO-based amorphous oxide film having a different resistance value depending on the difference in back pressure can be formed for the IGZO-based amorphous oxide film which has not been subjected to the annealing treatment. As described in the "Prior Art", the insulating film which is not subjected to any stabilization treatment and is only subjected to sputtering film formation has problems in terms of stability against electrical stress or heat. Therefore, in the method for producing an IGZO-based amorphous oxide semiconductor film of the present invention, an annealing treatment is performed as a stabilization treatment after sputtering and film formation.

In the method for producing an IGZO-based amorphous oxide semiconductor film of the present invention, the IGZO-based amorphous oxide layer is sputter-deposited under a back pressure of 1 × 10 ^-5 or more and 5 × 10 ^-4 or less, and then The annealing treatment is performed at a temperature of 100 ° C or more and 300 ° C or less.

The annealing treatment method is not particularly limited, and annealing at normal pressure is sufficient, so that it is easy to heat-treat using a hot plate or the like. In addition to this, a clean oven or a vacuum chamber can also be used.

As described above, in the method for producing an IGZO-based amorphous oxide semiconductor film of the present invention, only the back pressure is changed at the time of sputtering, and the water content in the film forming apparatus is used when any of the sputtering film forming methods is used. Both change according to back pressure. Therefore, in the method for producing an IGZO-based amorphous oxide semiconductor film of the present invention, the method of sputtering the film formation is not particularly limited, and any method can be applied.

Examples of the sputtering film formation method include a two-pole sputtering method, a three-pole sputtering method, a DC sputtering method, a radio frequency sputtering method, and an electron cyclotron resonance ion beam sputtering method (electron). Coupling resonance sputtering, magnetron sputtering, facing target sputtering, pulse sputtering, and ion beam sputtering.

In addition, the substrate to be formed is not particularly limited. In the present embodiment, the substrate is not particularly limited, and a Si substrate, a glass substrate, various flexible substrates, and the like may be appropriately selected depending on the application. The method for producing an IGZO-based amorphous oxide insulating film of the present invention can be carried out by a low-temperature process of 300 ° C or lower. Therefore, a resin substrate having low heat resistance is also applicable. Therefore, the method for producing an IGZO-based amorphous oxide semiconductor film of the present invention can also be applied to the production of a thin film transistor (TFT) used for a flexible display or the like.

Examples of the flexible substrate include a polyvinyl alcohol-based resin, a polycarbonate derivative (Teijin: WRF), a cellulose derivative (cellulose triacetate, cellulose diacetate), and a polyolefin. Resin (Nippon Zeon: ZEONOR, ZEONEX), polyfluorene-based resin (polyether oxime, polyfluorene), norbornene-based resin (JSR (stock): ARTON), polyester resin (PET (poly) Ethylene terephthalate, PEN (polyethylene naphthalene), cross-linked fumaric acid diester, polyimide resin, polyamine resin, poly Amidoxime resin, polyarylate resin, acrylic resin, epoxy resin, episulfide resin, fluorine resin, polyoxyn resin film, polybenzoxazole resin, cyanate ester system a resin substrate such as a resin, an aromatic ether resin (polyether ketone) or a maleimide-olefin resin, or a liquid crystal polymer substrate; and the resin substrate contains cerium oxide particles or a metal nanoparticle. Particles, inorganic oxide nanoparticles, inorganic nitride nanoparticles, metal/inorganic nanofibers a composite resin substrate of microfibers, carbon fibers, carbon nanotubes, glass cullet, glass fiber, glass beads, clay mineral, mica-derived crystal structure; and a laminate having at least one joint interface between the thin glass and the above-mentioned individual organic material a plastic material, a composite material having barrier properties having at least one bonding interface by alternately laminating inorganic layers (ex. SiO ₂ , Al ₂ O ₃ , SiO _x N _y ) and an organic layer (described above); stainless steel substrate A metal multilayer substrate in which stainless steel is laminated with different kinds of metals, an aluminum substrate, or an aluminum substrate with an oxide film which is provided with an oxidation treatment (for example, anodizing treatment) to enhance the surface insulation property.

An example of the IGZO-based amorphous oxide is an InGaZnO ₄ (IGZO) equivalent compound represented by the following formula (P1).

_{(ln 2-x Ga x)} O 3 ‧ (ZnO) m (P1)

(where 0≦x≦2 and m is a natural number)

The film formation pressure at the time of film formation is not particularly limited. However, if the film formation pressure is too high, the film formation rate is lowered and the productivity is deteriorated. Therefore, the film formation pressure is preferably 10 Pa or less, more preferably 5 Pa or less, and still more preferably 1 Pa below.

The film forming gas at the time of sputtering film formation is not particularly limited, and examples thereof include Ar and O ₂ .

As described in the "Prior Art", the resistance value of the film formed by sputtering changes according to the flow ratio of Ar to O ₂ in the film forming gas, and in the film forming method of the present invention, not only the back pressure can be changed to control The resistance value may also change the flow ratio of the film forming gas to control the resistance value, but there is a tendency to increase the partial pressure of oxygen to cause a decrease in the film forming speed, as shown in Fig. 6 of Comparative Example 1 below, and also in some back pressure. At the annealing treatment temperature, the partial pressure of oxygen at the time of film formation hardly affects the resistance value. According to the present invention, the IGZO-based amorphous oxide film having the electric resistance value of the insulator region can be produced by optimizing only the back pressure and the annealing treatment temperature. Therefore, the oxygen partial pressure O ₂ /Ar is preferably set to be 1/15 or less. value.

The inventors confirmed that the resistance value is related to the carrier density (Fig. 2). In general, the active layer of a transistor which can obtain good switching characteristics has a carrier density of 1 × 10 ¹³ to 1 × 10 ¹⁶ /cm ³ , so that the resistance value of the semiconductor region in which good switching characteristics can be obtained is the value of FIG. The value in the range of resistance values in the dotted line frame (range of 10 ³ to 10 ⁶ Ω‧cm). Therefore, by setting the above-described back pressure conditions and the annealing treatment temperature range, it is possible to produce an IGZO-based amorphous oxide semiconductor film having high uniformity of carrier density in the film surface, excellent switching characteristics, and excellent reliability.

In the following Example 1, an IGZO system exhibiting various resistance values was produced under conditions of a film formation pressure of 0.8 Pa, an input power of DC 50 W, Ar: 30 sccm, and O ₂ : 0.25 sccm by changing the back pressure and the annealing treatment temperature. Amorphous oxide film. As shown in FIG. 4, in a range in which the back pressure is high, a lower range, and a middle portion thereof, the resistance value (resistivity) varies depending on the annealing treatment temperature.

In the line diagram of ■, □, ◆, △ of Fig. 4 (back pressure 1 × 10 ^-4 Pa, 6.5 × 10 ^-5 Pa, 5 × 10 ^-5 Pa, 2 × 10 ^-5 Pa), by lifting The annealing temperature and the resistance value continue to increase in the region below 300 °C. Further, regarding the graph of ◆, in the annealing treatment temperature range of 150 ° C to 250 ° C, the slope becomes very gentle and becomes a shape having a substantially constant value in the range of 10 ⁴ to 10 ⁵ Ω ‧ cm.

4 shows that by selecting a suitable combination of back pressure and annealing temperature at a back pressure of 1×10 ⁻⁵ Pa or more and 5×10 ⁻⁴ Pa or less, and an annealing treatment temperature of 100° C. to 300° C. A semiconductor film having good switching characteristics in a range of resistance values of 10 ³ to 10 ⁶ Ω ‧ cm can be obtained.

In addition, when the back pressure is set to 5×10 ^-5 Pa, the in-plane uniformity of the annealing treatment temperature has less influence on the resistance value in the annealing treatment temperature range of 150 ° C to 250 ° C, and can be reduced. The influence of the temperature distribution in the film surface of the film in the small annealing treatment on the uniformity of the resistance value in the film surface.

Further, in Fig. 4, when the annealing treatment temperature is 400 ° C or higher, the resistance value of the semiconductor region having good switching characteristics can be produced regardless of the back pressure at the time of sputtering film formation, and the film surface can be loaded. An IGZO-based amorphous oxide film having high sub-density uniformity and excellent reliability.

As shown in FIG. 4, it is not preferable to obtain a resistance value in the range of 10 ³ to 10 ⁶ Ω ‧cm in all the ranges satisfying the following formulas (1) and (2), or (3) and (2) A semiconductor film with switching characteristics. 4 shows a tendency that the annealing temperature at which the semiconductor film which can obtain good switching characteristics can be manufactured to satisfy the following formula (2), the lower the back pressure (close to the high vacuum) in the range satisfying the following formula (1) The higher the range becomes.

For example, as conditions for forming the semiconductor film, conditions satisfying the following formulas (4) and (5), conditions satisfying (6) and (7), or (8) and (9) are satisfied. The conditions or the conditions of (10) and (11) are satisfied (P is the above-mentioned back pressure, and T is the temperature of the above annealing treatment). Further, the values of the back pressure P of the following formulas (4), (6), (8), and (10) have an amplitude of ±10%.

In other words, it is found that it is easy to investigate the relationship between the annealing temperature and the resistance value satisfying the formula (2) at any back pressure satisfying the following formula (1), except for the range represented by the following formulas (4) to (11). The combination of back pressure and annealing temperature can also produce a semiconductor film that can achieve good switching characteristics.

P(Pa)=2×10 ^-5 (4),

200≦T(°C)≦300 (5),

P(Pa)=5×10 ^-5 (6),

120≦T(°C)≦270 (7),

P(Pa)=6.5×10 ^-5 (8),

100≦T(°C)≦240 (9),

P(Pa)=1×10 ^-4 (10),

100≦T(°C)≦195 (11)

Further, in the method for producing an IGZO-based amorphous oxide semiconductor film of the present invention, the annealing treatment temperature is 100 to 300 °C. Therefore, the method for producing an IGZO-based amorphous oxide semiconductor film of the present invention is also applicable to a flexible substrate having low heat resistance such as a resin substrate.

As described above, according to the method for producing an IGZO-based amorphous oxide insulating film of the present invention, the carrier density suitable for the active layer of the TFT can be easily and inexpensively produced at a temperature lower than the heat-resistant temperature of the resin substrate. An IGZO-based amorphous oxide semiconductor film having excellent electrical stress and thermal stability.

"Field Effect Transistor (Thin Film Transistor: TFT)"

A method of manufacturing the field effect transistor of the present invention will be described with reference to Figs. 3A to 3D. In the present embodiment, the bottom gate type will be described as an example. 3A to 3D are process diagrams of a field effect transistor (TFT) (a cross-sectional view in the thickness direction of the substrate). In order to make it easy to visually confirm, the scale of the constituent elements is appropriately different from the actual one.

In the field effect transistor (TFT) 2 of the present embodiment, the active layer of the IGZO-based amorphous oxide semiconductor film 1 produced by the method for producing an IGZO-based amorphous oxide semiconductor film of the present invention is provided on the substrate B. 11.

As shown in FIG. 4, in the method for producing an IGZO-based amorphous oxide semiconductor film of the present invention, the annealing temperature is 100° C. or more as long as the back pressure is 1×10 ⁻⁵ Pa or more and 5×10 ⁻⁴ Pa or less. In the range of 300 ° C or lower, an IGZO-based semiconductor film having a carrier density with good switching characteristics and excellent electrical stress and thermal stability can be produced. Therefore, the field effect transistor can be combined with annealing treatment conditions of other layers. The annealing treatment temperature is selected, and the back pressure of the carrier concentration having a good switching characteristic is selected at the annealing treatment temperature.

Therefore, according to the present invention, the IGZO-based TFT 2 having the active layer 11 excellent in electrical stress and heat stability and having excellent element stability can be manufactured at a low cost by a simple process.

Hereinafter, a method of manufacturing the TFT 2 will be described in detail.

First, as shown in FIG. 3A, the substrate B is prepared, and after forming the gate electrode 21 including n ⁺ Si or the like, the gate insulating film 31 is formed.

The substrate B is not particularly limited, and the same substrate as the substrate described in the above embodiment can be used. In the method for producing a TFT of the present invention, the active layer 11 is produced by the method for producing an IGZO-based amorphous oxide semiconductor film of the present invention. Therefore, the active layer can be produced at a temperature lower than the heat-resistant temperature of the resin substrate B. 11. Therefore, a resin-made flexible substrate can be applied as the substrate B.

The gate insulating film 31 is not particularly limited. When the substrate B is a resin substrate, it is necessary to form a gate insulating film which can be formed at a temperature lower than the heat resistant temperature of the resin substrate B.

Next, as shown in FIG. 3B, the active layer 11 containing the IGZO-based amorphous oxide film 1 (which may contain unavoidable impurities) is formed. The method of forming the active layer 11 is as described in the above embodiment. For example, in the case where the back pressure is 5 × 10 ^-5 Pa, a good active layer 11 can be produced by an annealing treatment at 150 ° C to 220 ° C (heat resistance of 220 ° C).

Then, as shown in FIG. 3C, the source electrode 22 and the germanium electrode 23 are formed on the active layer 11.

Finally, as shown in FIG. 3D, a protective film (insulating film) 32 is formed on the active layer 11, the source electrode 22, and the germanium electrode 23.

Through the above steps, the TFT 2 of the present embodiment can be manufactured.

In the field effect transistor (TFT) 2 of the present embodiment, the active layer 11 is produced by using the above-described method for producing an IGZO-based amorphous oxide semiconductor film of the present invention. Therefore, according to the method for producing an IGZO-based TFT, an IGZO-based field effect transistor having an IGZO-based active layer excellent in electrical stress and heat stability and excellent in element stability can be manufactured at a low cost by a simple process.

As described above, FIG. 4 shows that, for the conductive film and the insulating film, it is also possible to manufacture an arbitrary resistance value and electrical stress as well by optimizing the combination of the back pressure at the time of sputtering film formation and the temperature of the annealing treatment. An IGZO-based amorphous oxide film having good thermal stability.

For example, the line diagram of ▲ and ◇ in Fig. 4 (back pressure 6 × 10 ^-6 Pa, 1 × 10 ^-5 Pa: area with low back pressure (high vacuum)) has the following tendency: at an annealing temperature of 100 ° C to 300 There is a minimum value in the range of °C, and thereafter the resistance value rises to around 1 × 10 ⁶ at around 400 ° C, showing a substantially fixed value. Here, the resistance value near the minimum value is in the conductor region (the resistance value is 100 Ω ‧ cm or less, preferably 10 Ω ‧ cm or less), and therefore, the back pressure is less than 1 × 10 ^-5 Pa (described below) In the formula (12)), an annealing treatment is carried out at a suitable temperature (the following formula (2)) in the range of 100 ° C to 300 ° C to produce an IGZO-based amorphous oxide film having a resistance value of a conductor region.

100≦T(°C)≦300(2),

P(Pa)<1×10 ^-5 (12)

Further, similarly to the maximum value, the annealing treatment at a temperature near the minimum value is less affected by the in-plane uniformity of the annealing treatment temperature, so that the same effect as described above can be obtained, which is preferable.

As shown in FIG. 4, it can be considered that the annealing treatment temperature showing the minimum value differs depending on the back pressure. Therefore, under the back pressure condition in which the annealing temperature at which the minimum value is displayed is not clear, it is preferable to sputter the IGZO-based amorphous oxide layer into a film by setting the back pressure to a specific value of less than 1 × 10 ^-5 Pa. When the annealing treatment is performed in the range of 100 ° C or more and 300 ° C or less, the resistance value of the IGZO-based amorphous oxide layer depends on the annealing treatment temperature, and the temperature change rate of the resistance value becomes 0 (±5). °C) Annealing treatment.

Contrary to the above, the pattern of ○ and ● in FIG. 4 (back pressure 5×10 ⁻⁴ Pa, 2×10 ⁻³ Pa) has a tendency to have a maximum value in the range of annealing temperature of 100° C. to 300° C. After that, the resistance value was reduced to around 1 × 10 ^-6 at around 400 ° C, showing a substantially fixed value. Since the resistance value in the vicinity of the maximum value is in the insulator region (resistance value is 107 Ω or more), it is in the range of 100 ° C to 300 ° C by a back pressure of 5 × 10 ^-4 Pa or more (the following formula (13)). The annealing treatment is carried out at a suitable temperature (the following formula (2)) to produce an IGZO-based amorphous oxide film having a resistance value of an insulator region.

100≦T(°C)≦300 (2),

5×10 ^-4 ≦P(Pa) (13)

Similarly to the minimum value, the annealing treatment at a temperature near the maximum value is preferable because the influence of the in-plane uniformity of the annealing treatment temperature on the resistance value is small. The annealing treatment temperature is determined in accordance with the heat resistance of the substrate, and a back pressure having a maximum value in the vicinity of the annealing treatment temperature is employed, whereby an insulating film having high insulation uniformity in the film surface and excellent reliability can be produced.

Heretofore, there has been no report on how the resistance value changes with respect to the annealing treatment temperature in accordance with the back pressure at the time of sputtering film formation.

According to the findings of the inventors of the present invention, by changing the combination of the back pressure and the annealing temperature, it is possible to manufacture not only an IGZO-based amorphous oxide film having a resistance value of a semiconductor region but also a conductor region and an insulator region. An IGZO-based amorphous oxide film having any resistance value in the range, so that an IGZO-based amorphous oxide semiconductor film can be formed on the substrate and an insulator region can be formed by a simple method of changing only the back pressure in the sputtering film formation. A variety of IGZO-based amorphous oxide thin films having specific resistance values in the conductor region are preferred, and field effect transistors are preferred.

For example, after the IGZO-based amorphous oxide film having a specific resistance value of the insulator region is formed on the substrate by the above-described manufacturing method, the back pressure in the sputtering film formation can be reduced, and the IGZO-based amorphous film of the present invention described above can be used. The semiconductor layer 1 is produced by the method for producing a germanium semiconductor film, and the back electrode is further reduced to produce the source electrode 22 and the germanium electrode 23, or the contact layers thereof. At this time, the annealing temperature is preferably such that the same temperature is used for all the layers, or the annealing temperature of the upper layer is smaller than the annealing temperature of the lower layer.

In terms of simplifying the process, it is preferred to manufacture as many layers as possible by the above-described method for producing an IGZO-based amorphous oxide film.

As described above, the method for producing the IGZO-based amorphous oxide semiconductor film of the present invention can be carried out by a low-temperature process of 300 ° C or lower. Therefore, a flexible substrate having low heat resistance is also applicable. Therefore, in the method of manufacturing the field effect transistor of the present invention, the other layers constituting the TFT 2 can be manufactured by a low temperature process of 300 ° C or lower, which is also applicable to a thin film transistor (TFT) used for a flexible display or the like. Manufacturing.

In the above embodiment, the bottom gate type field effect transistor is described, but it can also be applied to a high gate type field effect transistor.

[Example]

Examples of the invention and comparative examples will be described.

(Example 1)

An InGaZnO ₄ (at ratio) polycrystalline target was used to form an IGZO film having a thickness of 50 nm on a commercially available synthetic quartz substrate (thickness 1 mm, T-4040 synthetic quartz substrate) of about 1 cm ² square.

In order to investigate the influence of the back pressure and the annealing temperature on the resistance value of the IGZO film, the back pressure (the ultimate vacuum before film formation) was set to 6 × 10 ^-6 Pa, 1 × 10 ^-5 Pa, 2 ×, respectively. Samples were prepared for 10 ^-5 Pa, 5 × 10 ^-5 Pa, 6.5 × 10 ^-5 Pa, 1 × 10 ^-4 Pa, 5 × 10 ^-4 Pa, and 2 × 10 ^-3 Pa, respectively. At this time, the back pressure is set in such a manner that the film forming chamber of the sputtering apparatus is evacuated after the atmosphere is opened, and the ion vacuum gauge provided in the sputtering apparatus is used to confirm that the desired back pressure condition is reached. Film formation. Other film formation conditions were: substrate temperature Ts = normal temperature, Ar/O ₂ mixed environment (Ar flow rate: 30 sccm, O ₂ flow rate 0.25 sccm), film formation pressure 0.8 Pa, substrate-target spacing 150 mm, target input The power is DC 50 W (IGZO) and the film formation time is about 19 minutes.

After sputter deposition, the film thickness and composition of the five samples before annealing were measured by XRF (X-ray Fluorescent Analyzer), and it was confirmed that any of the samples was In:Ga:Zn=1. : 0.9:0.7, film thickness is about 50 nm.

Then, using a hot plate, the above samples were subjected to 5 minutes at various annealing treatment temperatures (100 ° C, 150 ° C, 200 ° C, 250 ° C, 300 ° C, 350 ° C, 400 ° C, 450 ° C, 500 ° C, 600 ° C). Annealing, resistance value (resistivity) was measured using Hiresta (manufactured by Mitsubishi Chemical Corporation, MCP-HT450 (probe type URS)). The result is shown in Fig. 4.

Fig. 4 shows that, for example, when the annealing treatment temperature is 250 ° C, the resistance value has a change of about 9 digits depending on the back pressure condition. It is confirmed from Fig. 4 that an IGZO-based amorphous oxide film having any resistance value in the conductor region to the insulator region can be produced by optimizing the back pressure at the time of sputtering film formation and the annealing treatment temperature.

In order to investigate the influence of the back pressure on the film characteristics during the film formation by sputtering, the ATR method (attenuated total reflectance method) was used to treat the five samples which were not annealed after sputtering and used as a reference. The quartz substrate was subjected to FT-IR measurement of the surface (Nicolet 4700 manufactured by ThermoFisher). The result is shown in Fig. 5. As shown in Fig. 5, it was confirmed that the peak of the stretching vibration from the OH group (the broad peak in the range of 2500 cm ^-1 to 4000 cm ^-1 ) was observed in any of the samples, and the peak area increased as the back pressure became higher.

Further, it was confirmed that the above tendency is the same even when co-sputtering using a plurality of kinds of targets.

(Comparative Example 1)

An IGZO amorphous oxide film was produced in the same manner as in Example 1 except that the back pressure was set to a fixed condition of 1 × 10 ^-6 Pa, and the oxygen flow rate of the film forming gas was changed to 0.25 sccm, 0.33 sccm, and 0.4 sccm. The samples were annealed under the same annealing conditions as in Example 1, and the respective resistance values were measured. The result is shown in Fig. 6.

As shown in Fig. 6, it was confirmed that the resistance value of the IGZO thin film after sputtering deposition was increased by increasing the oxygen flow rate, but the annealing value at 250 ° C caused the resistance value of any of the samples to be extremely small, and the resistance was lowered. To the conductor area.

1‧‧‧IGZO-based amorphous oxide semiconductor film (semiconductor film)

2‧‧‧ Field Effect Transistor (Thin Film Transistor: TFT)

11‧‧‧Active layer

21‧‧‧ gate electrode

22‧‧‧ source electrode

23‧‧‧汲 electrode

31‧‧‧Gate insulation film

32‧‧‧Protective film

B‧‧‧ film forming substrate

FIG. 1 is a view schematically showing the relationship between the water content in the film forming apparatus when the back pressure is changed at the time of sputtering film formation and the water content in the formed IGZO-based amorphous oxide film.

2 is a view showing a relationship between a carrier density of a semiconductor film and a specific resistance.

3A is a cross-sectional view (1) showing a process of a semiconductor device (thin film element) according to an embodiment of the present invention.

3B is a cross-sectional view (2) showing a process of a semiconductor device according to an embodiment of the present invention.

3C is a cross-sectional view (3) showing a process of a semiconductor device according to an embodiment of the present invention.

3D is a cross-sectional view (4) showing a process of a semiconductor device according to an embodiment of the present invention.

4 is a graph showing the relationship between the electric resistance value and the annealing treatment temperature of the IGZO-based amorphous oxide film sputter-deposited under different back pressures in Example 1. FIG.

FIG. 5 is a view showing an IR spectrum in the vicinity of the peak wavelength of the OH group on the surface of the IGZO-based amorphous oxide film after the sputtering deposition shown in FIG. 4 .

6 is a graph showing the relationship between the electric resistance value and the annealing treatment temperature of an IGZO-based amorphous oxide thin film which is sputter-deposited at different oxygen flow rates in Comparative Example 1. FIG.

FIG. 7 is a diagram 4 of Patent Document 1.

2. . . Field effect transistor (thin film transistor: TFT)

11(1). . . Active layer

twenty one. . . Gate electrode

twenty two. . . Source electrode

twenty three. . . Helium electrode

31. . . Gate insulating film

32. . . Protective film

B. . . Film forming substrate

Claims (12)

A method for producing an IGZO-based amorphous oxide semiconductor film, which is obtained by sputtering an IGZO-based amorphous oxide layer and then performing annealing treatment to produce a semiconductor film including an IGZO-based amorphous oxide. characterized in that: in the film formation conditions satisfying the following formula (1) and ^{(2), 2 × 10 -5 ≦ P (} Pa) ≦ 5 × 10 -4 (1), 100 ≦ T (℃) ≦ 300 ( 2) (wherein P is the back pressure in the above-described sputtering film formation, and T is the annealing temperature in the above annealing treatment). The method for producing an IGZO-based amorphous oxide semiconductor film according to the first aspect of the invention, wherein the film is formed under the condition that the following formula (3) is satisfied, 2 × 10 ^-5 ≦ P (Pa) ≦ 1 × 10 ^-4 (3). The method for producing an IGZO-based amorphous oxide semiconductor film according to the first aspect of the invention, wherein the annealing temperature is 150° C. or higher and 250° C. or lower. The method for producing an IGZO-based amorphous oxide semiconductor film according to the second aspect of the invention, wherein the film is formed under the conditions satisfying the following formulas (4) and (5), and P(Pa) = 2 × 10 ^{- 5} (4), 200 ≦T (°C) ≦ 300 (5). The method for producing an IGZO-based amorphous oxide semiconductor film according to the second aspect of the invention, wherein the film is formed under the conditions satisfying the following formulas (6) and (7), and P(Pa) = 5 × 10 ^{- 5} (6), 120≦T (°C) ≦ 270 (7). The method for producing an IGZO-based amorphous oxide semiconductor film according to the second aspect of the invention, wherein the film is formed under the conditions satisfying the following formulas (8) and (9), and P(Pa) = 6.5 × 10 ^{- 5} (8), 100 ≦T (°C) ≦ 240 (9). The method for producing an IGZO-based amorphous oxide semiconductor film according to the second aspect of the invention, wherein the film is formed under the conditions of the following formulas (10) and (11), and P(Pa) = 1 × 10 ^{- 4} (10), 100 ≦T (°C) ≦ 195 (11). The method for producing an IGZO-based amorphous oxide semiconductor film according to any one of the first to seventh aspect, wherein the film formation pressure in the sputtering film formation is 10 Pa or less. The method for producing an IGZO-based amorphous oxide semiconductor film according to any one of the preceding claims, wherein the film-forming gas in the sputtering film formation contains Ar and O ₂ , and the film formation is performed. The flow ratio of Ar to O ₂ in the gas is O ₂ /Ar≦1/15. The application method of producing an amorphous IGZO-based oxide semiconductor film of the patentable scope of item 8, wherein the film forming gas in the sputtering deposition contains O ₂ and Ar, the deposition gas of Ar and O ₂ The flow ratio is O ₂ /Ar≦1/15. A method for producing a field effect transistor, which is a method for producing a thin film transistor comprising a semiconductor layer including an IGZO-based amorphous oxide, a source electrode, a germanium electrode, a gate electrode, and a gate insulating film on a substrate, The semiconductor layer is formed by the method for producing an amorphous oxide semiconductor film according to any one of claims 1 to 10. A method of producing a field effect transistor according to claim 11, wherein a flexible substrate is used as the substrate.