JP2011181800A - Method of manufacturing igzo-based amorphous oxide insulating film and method of manufacturing field effect transistor using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To manufacture an IGZO-based amorphous oxide insulating film which has excellent stability against electrical stress and heat. <P>SOLUTION: A film of an IGZO-based amorphous oxide layer is formed under a back pressure of higher than 5×10<SP>-4</SP>Pa in a sputtering method, and then subjected to annealing processing at an annealing temperature of 100 to 300°C. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method of manufacturing an IGZO amorphous oxide insulating film and a method of manufacturing a field effect transistor using this manufacturing method.

  Field effect transistors are used for unit elements of semiconductor memory integrated circuits, high frequency signal amplifying elements, liquid crystal driving elements, and the like. Particularly, thinned transistors are used in a wide range of fields as thin film transistors (TFTs).

  As a semiconductor channel layer (active layer) for forming a field effect transistor, a silicon semiconductor or a compound thereof is often used. For a high-frequency amplifier element and an integrated circuit that require high-speed operation, single-crystal silicon or low-speed operation is used. Although it is sufficient, amorphous silicon is used for a liquid crystal driving device that is required to cope with a large area such as a display application.

  In the display field, in recent years, flexible displays that are lightweight and bendable have attracted attention. For such a flexible device, a highly flexible resin substrate is mainly used. However, the resin substrate has a heat-resistant temperature of usually 150 to 200 ° C., and even a polyimide resin having high heat resistance is about 300 ° C., such as a glass substrate. Low compared to inorganic substrates.

  Since amorphous silicon usually requires high-temperature heat treatment exceeding 300 ° C. in its production process, it is difficult to use it for a supporting substrate such as a flexible substrate in a current display having low heat resistance.

  On the other hand, an In-Ga-Zn-O-based (IGZO-based) oxide semiconductor that can be deposited at room temperature and can exhibit performance as a semiconductor even when amorphous is discovered by Tokyo Tech Hosono et al. It is regarded as a promising TFT material for next-generation displays (Non-Patent Documents 1 and 2). Further, it is known that an IGZO-based oxide can be an electric resistance value of not only a semiconductor but also a conductor or an insulator. For example, in FIG. 4 (FIG. 6 of the present specification) of Patent Document 1, when an annealing process (heat treatment) at 120 ° C. to 250 ° C. is performed on an amorphous IGZO film that was a semiconductor film after vacuum film formation at room temperature, 1 It is shown that the resistance is reduced by three to three digits.

  Patent Document 2 discloses a transistor having a semiconductor layer made of an IGZO-based amorphous oxide thin film and a gate insulating film, and the oxygen flow rate ratio in the sputtering gas during sputtering film formation is 10% or less. It is disclosed that a gate insulating film is formed with a film of 20% or more. In Patent Document 2, in a transistor using an IGZO-based amorphous oxide semiconductor film as an active layer, the gate insulating film is the same IGZO-based oxide film, thereby simplifying the manufacturing process and reducing the cost. From the viewpoint of simplification of the manufacturing process and cost reduction, it is preferable that the semiconductor film, the insulating film, and further the conductive film can be manufactured using the film made of the same element.

JP 2009-99847 A JP 2007-109918 A

K. Nomura et al, Science, 300 (2003) 1269. K. Nomura et al, Nature, 432 (2004) 488

  However, in Patent Document 2, all films formed at room temperature are used as they are without being subjected to annealing treatment. An IGZO amorphous oxide semiconductor that has not been subjected to stabilization treatment such as annealing after film formation at room temperature was used as a heat treatment performed in a later process (for example, a heating process required for patterning) or as an element. In some cases, the resistance value may change due to electrical stress applied during driving.

  The present invention has been made in view of the above circumstances, and a method for producing an IGZO-based amorphous oxide insulating film having good stability against electrical stress and heat, and excellent in device stability and simple. An object of the present invention is to provide a method of manufacturing an IGZO field effect transistor that can be manufactured at a low cost by a simple manufacturing process.

In the method for producing an IGZO amorphous oxide insulating film of the present invention, an IGZO amorphous oxide layer is formed by sputtering with a back pressure exceeding 5 × 10 ⁻⁴ Pa, and then annealed at 100 ° C. or higher and 300 ° C. or lower. An insulating film made of an IGZO-based amorphous oxide is manufactured by annealing at a temperature.

  In this specification, the IGZO-based amorphous oxide thin film means an amorphous oxide thin film containing In and Ga, and preferably means an amorphous oxide thin film containing Zn. In addition to these metal elements, other elements such as dopants and substitution elements may be included.

  In this specification, the annealing process includes all processes in which the thin film formed by sputtering is heated in addition to the annealing process after the sputtering film formation. For example, a patterning process such as photolithography or lamination is performed. It includes heat treatment in the film forming process.

Further, in this specification, the “insulating film” means a thin film having a specific resistance value of 10 ⁷ Ω · cm or more.

  Here, “back pressure in sputter film formation” is an ultimate vacuum in a vacuum container (film formation apparatus) in which a substrate is placed when performing sputter film formation, and before film formation starts, that is, a film formation apparatus. It means the degree of vacuum in the film forming apparatus before introducing the film forming gas into it.

  In this specification, the ultimate vacuum (back pressure) is a value obtained by reading the value of an ion gauge (ionization vacuum gauge) installed in the sputter deposition apparatus. Since the ultimate vacuum (back pressure) in the film forming apparatus is almost equivalent to the amount of water (water pressure) in the film forming apparatus, it is measured using a mass spectrometer (for example, ULVAC's Qulee CGM series). It is good also as a value calculated from the measured water pressure.

  In the method for manufacturing an IGZO amorphous oxide insulating film of the present invention, it is preferable that the film forming pressure in the sputter film forming is 10 Pa or less.

In the method of the IGZO-based amorphous oxide insulating film of the present invention, the film forming gas in the sputtering deposition is intended to include the Ar and O _2, the flow ratio of Ar and O ₂ of the film forming gas It is preferable that O ₂ / Ar ≦ 1/15.

  A method for producing a field effect transistor according to the present invention is a method for manufacturing a field effect transistor comprising an IGZO amorphous oxide semiconductor layer, a source electrode, a drain electrode, a gate electrode, and a gate insulating film on a substrate. In the manufacturing method, the gate insulating film is formed by using the insulating film manufacturing method.

  In the method for manufacturing a field effect transistor of the present invention, the substrate can be a flexible substrate.

When the present inventors sputter-deposited an IGZO-based amorphous oxide thin film on a substrate, the present inventors have optimized thermal stability by optimizing the back pressure during sputter deposition and the annealing temperature after sputter deposition. It was found that an excellent IGZO-based amorphous oxide insulator thin film can be manufactured. In the present invention, an IGZO-based amorphous oxide layer is formed by sputtering with a back pressure exceeding 5 × 10 ⁻⁴ Pa, and then annealed at an annealing temperature of 100 ° C. or higher and 300 ° C. or lower. Thus, an IGZO amorphous oxide insulator thin film having good stability against electrical stress and heat can be manufactured.

  Therefore, in the method for manufacturing an IGZO field effect transistor, by manufacturing an insulating layer such as a gate insulating film or an interlayer insulating film by the method for manufacturing an IGZO amorphous oxide insulating film according to the present invention, it is possible to prevent electrical stress and heat. An IGZO field-effect transistor having an IGZO amorphous oxide insulating layer with good stability and excellent in element stability can be manufactured at a low cost by a simple manufacturing process.

The figure which shows typically the relationship between the moisture content in the film-forming apparatus at the time of changing back pressure at the time of sputtering film-forming, and the moisture content in the IGZO type amorphous oxide thin film formed into a film Sectional drawing which shows the manufacturing process of the semiconductor device (thin film element) of one Embodiment which concerns on this invention (the 1) Sectional drawing which shows the manufacturing process of the semiconductor device of one Embodiment which concerns on this invention (the 2) Sectional drawing which shows the manufacturing process of the semiconductor device of one Embodiment which concerns on this invention (the 3) Sectional drawing which shows the manufacturing process of the semiconductor device of one Embodiment which concerns on this invention (the 4) The figure which shows the relationship between the electrical resistance value of the IGZO type amorphous oxide thin film sputter-deposited by different back pressure in Example 1, and annealing treatment temperature The figure which shows IR spectrum near the peak wavelength of OH group on the surface of the IGZO amorphous oxide thin film after sputter film formation shown in FIG. The figure which shows the relationship between the electrical resistance value of the IGZO type amorphous oxide thin film sputter-deposited by different oxygen flow volume in the comparative example 1, and annealing treatment temperature FIG. 4 of Patent Document 1

"Method of manufacturing IGZO amorphous oxide insulating film"
The inventor has intensively studied a method of manufacturing an IGZO-based amorphous oxide thin film having good stability against electrical stress and heat. As a result, the electrical resistance value of the IGZO-based amorphous oxide thin film formed changes depending on the amount of water in the film forming apparatus, and further, the value changes depending on the annealing temperature after the sputtering film formation. By optimizing the combination of the moisture content in the film forming apparatus and the annealing temperature after the sputter film formation, it has an arbitrary electric resistance value within the range from the conductor region to the insulator region, and is electrically It has been found that an IGZO-based amorphous oxide thin film having good stability against stress and heat can also be produced. (See Example 1 and FIG. 3 below).

In this specification, the “conductor” means one having a specific resistance value of 100 Ω · cm or less. Further, “semiconductor” means a semiconductor having a specific resistance value in the range of 10 ³ to 10 ⁶ Ω · cm. Further, in this specification, “insulator” means a material having a specific resistance value of 10 ⁷ Ω · cm or more.

  In sputter deposition, it is known that the water content (moisture pressure) in the deposition apparatus has a correlation with the back pressure in sputter deposition, and the lower the back pressure, that is, the higher the vacuum, It is known to be lower. The present inventor conducted composition analysis by FT-IR measurement for each IGZO-based amorphous oxide thin film with different electrical resistance values formed by changing the back pressure at the time of sputtering film formation, and as a result, in each film It was confirmed that the peak area of OH groups was different and the amount of OH groups was increased when the back pressure was increased, that is, the water content was increased (see Examples, FIG. 4 to be described later).

  FIG. 1 shows the relationship between the amount of water in the film forming apparatus and the amount of water in the formed IGZO amorphous oxide thin film when the back pressure (the ultimate vacuum in the film forming apparatus) is changed. It is an image figure shown. As shown in the figure, the higher the back pressure, the greater the amount of moisture in the film forming apparatus. Accordingly, it is considered that the amount of moisture taken into the film increases and affects the electric resistance value of the thin film.

  From FIG. 1 and Example 4 described later, it can be confirmed that the amount of water (OH group amount) in the IGZO amorphous oxide thin film immediately after the sputter deposition changes depending on the back pressure during the sputter deposition. FIG. 3 shows that an IGZO-based amorphous oxide thin film having various electrical resistance values in the region from the conductor region to the insulator region can be manufactured due to the difference in back pressure during sputter deposition and the subsequent annealing temperature. It is shown.

  The method for controlling the amount of moisture in the film forming apparatus is not limited to the control by the back pressure in the above-described sputtering film formation, and can be controlled by, for example, a method of directly introducing moisture during film formation. is there. As described in the section “Means for Solving the Problems”, the back pressure is the degree of vacuum in the film forming apparatus before introducing the film forming gas, and is a factor that can be easily changed. Therefore, it is preferable to control the amount of water in the oxide thin film by back pressure. Hereinafter, a method for controlling the water pressure by controlling the back pressure will be described as an example.

  FIG. 3 shows that an IGZO amorphous oxide thin film having different electrical resistance values can be formed even in an IGZO amorphous oxide thin film immediately after sputter deposition without annealing. However, as described in the section “Problems to be Solved by the Invention”, an insulating film that is only sputtered without any stabilization treatment has problems with stability against electrical stress and heat. is there. Therefore, in the manufacturing method of the IGZO amorphous oxide insulating film of the present invention, after the sputter film formation, an annealing process is performed as a stabilization process.

That is, in the method for producing an IGZO amorphous oxide insulating film according to the present invention, an IGZO amorphous oxide layer is formed by sputtering with a back pressure exceeding 5 × 10 ⁻⁴ Pa, and then 100 ° C. or more and 300 ° C. or less. Annealing treatment is performed at the annealing temperature.

  The method for the annealing treatment is not particularly limited, but annealing at normal pressure is sufficient, so that the heat treatment using a hot plate or the like is easy. In addition, a clean oven or a vacuum chamber may be used.

  As described above, in the method for manufacturing an IGZO-based amorphous oxide insulator film of the present invention, the back pressure is only changed in the sputtering film formation, and the moisture content in the film formation apparatus can Even if the membrane method is used, it varies depending on the back pressure. Therefore, in the manufacturing method of the IGZO amorphous oxide insulating film of the present invention, the sputtering film forming method is not particularly limited, and any method can be applied.

  Examples of the sputtering film forming method include a bipolar sputtering method, a tripolar sputtering method, a direct current sputtering method, a high frequency sputtering method (RF sputtering method), an ECR sputtering method, a magnetron sputtering method, a counter target sputtering method, a pulse sputtering method, and Examples thereof include an ion beam sputtering method.

  Further, the substrate on which the film is formed is not particularly limited, and in the present embodiment, the substrate is not particularly limited, and may be selected according to the use, such as a Si substrate, a glass substrate, and various flexible substrates. Since the manufacturing method of the IGZO type amorphous oxide insulating film of this invention can be implemented by the low temperature process of 300 degrees C or less, it can be applied suitably also to a resin substrate with low heat resistance. Therefore, the method for producing an IGZO-based amorphous oxide insulating film of the present invention can be applied to the production of a thin film transistor (TFT) used for a flexible display or the like.

As flexible substrates, polyvinyl alcohol resins, polycarbonate derivatives (Teijin Limited: WRF), cellulose derivatives (cellulose triacetate, cellulose diacetate), polyolefin resins (Nippon Zeon Co., Ltd .: ZEONOR, ZEONEX), polysulfone resins (Polyethersulfone, polysulfone), norbornene resin (JSR Corporation: Arton), polyester resin (PET, PEN, cross-linked fumaric acid diester) polyimide resin, polyamide resin, polyamideimide resin, polyarylate resin Resin, acrylic resin, epoxy resin, episulfide resin, fluorine resin, silicone resin film, polybenzazole resin, cyanate resin, aromatic ether resin (polyether ketone), Imide - a resin substrate such as an olefin-based resin, liquid crystal polymer substrate,
In these resin substrates, silicon oxide particles, metal nanoparticles, inorganic oxide nanoparticles, inorganic nitride nanoparticles, Metal / inorganic nanofibers or microfibers, carbon fibers, carbon nanotubes, glass ferkes, glass fibers, glass beads, clay minerals, composite resin substrates containing mica-derived crystal structures,
At least once by laminating plastic layers, inorganic layers (ex.SiO2, Al2O3, SiOxNy) and organic layers (above) that have at least one bonding interface between thin glass and the above single organic material. A composite material having the above-mentioned bonding interface and barrier performance,
Stainless steel substrate, metal multilayer substrate in which different metals are laminated with stainless steel, aluminum substrate, or aluminum with an oxide film whose surface insulation is improved by subjecting the surface to oxidation treatment (eg anodizing treatment) A substrate etc. can be mentioned.

Examples of the IGZO-based amorphous oxide include a homologous compound such as InGaZnO ₄ (IGZO) represented by the following general formula (P1).
_{(In 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 becomes slow and the productivity deteriorates, and therefore it is preferably 10 Pa or less, and more preferably 5 Pa or less. More preferably, it is 1 Pa or less.

The film formation gas at the time of sputtering film formation is not particularly limited, and examples thereof include those containing Ar and O ₂ .
As described in the section of “Background Art”, the electric resistance value of the film formed by sputtering changes depending on the flow rate ratio of Ar and O ₂ in the film forming gas. Therefore, in the film forming method of the present invention, In addition to the back pressure, this flow rate ratio may be changed to control the electric resistance value. However, the film forming rate tends to decrease by increasing the oxygen partial pressure, as shown in FIG. As described above, depending on the back pressure and the annealing temperature, the influence of the oxygen partial pressure during film formation on the electrical resistance value may be almost eliminated. In the present invention, an IGZO-based amorphous oxide thin film having an electrical resistance value in the insulator region can be manufactured only by optimizing the back pressure and the annealing temperature, so that the oxygen partial pressure O ₂ / Ar is 1 / A constant value of 15 or less is preferable.

In Example 1 described later, an IGZO system showing various electric resistance values by changing the back pressure and the annealing temperature under the conditions of a film forming pressure of 0.8 Pa, an input power of DC 50 W, Ar: 30 sccm, and O ₂ : 0.25 sccm. An amorphous oxide thin film was produced. As shown in FIG. 3, the manner in which the electrical resistance value (specific resistance value) changes with respect to the annealing temperature differs between the range in which the back pressure is high, the range in which it is low, and the intermediate region.

The plots of ○ and ● in FIG. 3 (back pressure 5 × 10 ⁻⁴ Pa, 5 × 10 ⁻³ Pa) have a maximum value in the annealing temperature range of 100 ° C. to 300 ° C., and then 1 × 10 ⁻ around 400 ° C. There is a tendency to decrease to an electric resistance value near ^{6 and} to show a substantially constant value. Since the electric resistance value near the maximum value is that of the insulator region (electric resistance value of 10 ⁷ Ω or more), a suitable temperature within the range of 100 ° C. to 300 ° C. with a back pressure exceeding 5 × 10 ⁻⁴ Pa. IGZO-based amorphous oxide thin film having the electrical resistance value of the insulator region can be manufactured by performing the annealing process.

  Since the IGZO amorphous oxide insulating film thus manufactured is annealed after the film formation, the IGZO amorphous oxide insulating film has good stability against electrical stress and heat. Accordingly, the back pressure and the temperature of the annealing process during the sputtering film formation can be selected within such a range so as to obtain a desired insulating property (electric resistance value).

  In FIG. 3, 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 electric resistance value is reduced. Even if there is a temperature distribution in the film surface of the thin film during the annealing process, such as when the annealing process is performed with a hot plate, if the effect of the in-plane uniformity of the annealing process temperature on the electrical resistance value is small The influence on the uniformity of the electrical resistance value in the film surface can be reduced. Since the upper limit of the annealing temperature is determined by the heat resistance temperature of the substrate to be used, the annealing temperature is determined according to the heat resistance of the substrate, and the back pressure has a maximum value near the annealing temperature. Thus, an insulating film with high uniformity of conductivity within the film surface and excellent reliability can be manufactured.

It is considered that the annealing temperature showing the maximum value varies depending on the back pressure as shown in FIG. Therefore, in the case of a back pressure condition in which the annealing temperature showing the maximum value is unknown, the sputter film is formed with the back pressure exceeding 5 × 10 ⁻⁴ Pa, and then the annealing treatment is performed in the range of 100 ° C. or more and 300 ° C. or less. In this case, it is preferable to obtain the annealing temperature dependency of the electrical resistance value of the IGZO-based amorphous oxide layer in advance and to perform the annealing treatment at a temperature around (± 5 ° C.) where the change rate of the electrical resistance value becomes zero. . By determining the annealing temperature according to the heat resistance of the substrate and setting the back pressure to have a maximum value in the vicinity of the annealing temperature, the uniformity of insulation within the film surface is high and the reliability is excellent. Insulating films can be manufactured.

As described above, according to the method for manufacturing an IGZO amorphous oxide insulating film of the present invention, an IGZO amorphous oxide layer is formed by sputtering with a back pressure exceeding 5 × 10 ⁻⁴ Pa, and then 100 An IGZO amorphous oxide insulator thin film having good stability against electrical stress and heat can be manufactured by a simple method in which annealing is performed at an annealing temperature of not lower than 300 ° C. and not higher than 300 ° C.

  Moreover, in the manufacturing method of the said IGZO type amorphous oxide insulating film of this invention, annealing treatment temperature is 100 to 300 degreeC. Therefore, the method for manufacturing an IGZO amorphous oxide insulating film of the present invention can be applied to a flexible substrate having low heat resistance such as a resin substrate.

"Field Effect Transistor (Thin Film Transistor: TFT)"
With reference to FIGS. 2A to 2D, a field effect transistor including an IGZO amorphous oxide insulating film manufactured by the method of manufacturing an IGZO amorphous oxide insulating film of the present invention and a method for manufacturing the field effect transistor will be described. In the present embodiment, a bottom gate type will be described as an example. 2A to 2D are manufacturing process diagrams (cross-sectional views in the thickness direction of the substrate) of a field effect transistor (TFT). In order to facilitate visual recognition, the scale of the constituent elements is appropriately changed from the actual one.

  As shown in FIG. 2D, the field effect transistor (TFT) 2 of this embodiment includes an active layer (semiconductor layer) 11 made of an IGZO amorphous oxide thin film 1 on the substrate B and the IGZO system of the present invention. A gate insulating film 31 manufactured by the method for manufacturing an amorphous oxide insulating film is provided.

As shown in FIG. 3, in the manufacturing method of the IGZO-based amorphous oxide insulating film of the present invention, if the back pressure exceeds 5 × 10 ⁻⁴ Pa and the annealing temperature is in the range of 100 ° C. or more and 300 ° C. or less, Since an IGZO insulating film having good stability against electrical stress and heat can be manufactured, the annealing temperature is selected according to the annealing conditions of other layers in a thin film element such as a semiconductor device and the like. It is possible to select a back pressure that gives a desired insulating property (electric resistance value) at the annealing temperature.

Therefore, according to the present invention, an IGZO field effect transistor having a gate insulating film 31 having excellent stability against electrical stress and heat and having excellent element stability can be manufactured at a low cost by a simple manufacturing process. Can do.
Below, the detail of the manufacturing method of TFT2 is demonstrated.

First, as shown in FIG. 2A, after preparing the substrate B and forming the gate electrode 21 made of n ⁺ Si or the like, the IGZO amorphous oxide is manufactured by the method for manufacturing an IGZO amorphous oxide insulating film of the present invention. A gate insulating film 31 made of the thin film 1 (may contain inevitable impurities) is formed. The method for forming the gate insulating film 31 is as described in the above embodiment. For example, when the substrate B is a resin substrate having a glass transition temperature of around 220 ° C., the back pressure is 5 × 10 ⁻⁴ Pa. By performing the annealing process at 200 ° C., the gate insulating film 31 with good insulation can be formed. As the substrate B, the same substrate as described in the above embodiment can be used.

  Next, as shown in FIG. 2B, a semiconductor layer 11 (active layer 11) made of the IGZO-based amorphous oxide thin film 1 (which may include inevitable impurities) is formed. The method for forming the semiconductor layer 11 (active layer 11) is not particularly limited, but it is preferable that the semiconductor layer 1 is also formed by the same apparatus (film formation method) as the gate insulating film 31 so that the process becomes easier. .

  Next, as illustrated in FIG. 2C, the source electrode 22 and the drain electrode 23 are formed on the active layer 11.

Finally, as shown in FIG. 2D, a protective film (insulating film) 32 is formed on the active layer 11, the source electrode 22, and the drain electrode 23.
Through the above steps, the TFT 2 of the present embodiment is manufactured.

  In the above embodiment, the gate insulating film 31 is formed by the method for manufacturing an IGZO amorphous oxide insulating film of the present invention. However, other insulating layers such as an interlayer insulating film are formed of the IGZO amorphous oxide insulating film of the present invention. You may manufacture by the manufacturing method of a film | membrane.

  The field effect transistor (TFT) 2 of this embodiment manufactures an insulating layer such as a gate insulating film 31 and an interlayer insulating film using the method for manufacturing the IGZO amorphous oxide thin film 1 of the present invention. Therefore, according to the manufacturing method of the IGZO field effect transistor, an IGZO field effect transistor having an IGZO amorphous oxide insulating layer having excellent stability against electrical stress and heat and having excellent element stability can be easily obtained. It can be manufactured at low cost by the manufacturing process.

  As described above, FIG. 3 also shows that the conductive film and the semiconductor film have an arbitrary electric resistance value by optimizing the combination of the back pressure during the sputtering film formation and the temperature of the annealing treatment. In addition, it has been shown that an IGZO-based amorphous oxide thin film having good stability against electrical stress and heat can be manufactured.

For example, the plots of ▲ and ◇ in FIG. 3 (back pressure 6 × 10 ⁻⁶ Pa, 1 × 10 ⁻⁵ Pa: low back pressure region (high vacuum)) are minimum values in the annealing temperature range of 100 ° C. to 300 ° C. After that, in the vicinity of 400 ° C., there is a tendency to increase to an electric resistance value of about 1 × 10 ^{6 and} to show a substantially constant value. Here, since the electric resistance value near the minimum value is that of the conductor region (electric resistance value of 100 Ω · cm or less, preferably 10 Ω · cm or less), it is 100 ° C. with a back pressure of 1 × 10 ⁻⁵ Pa or less. By performing an annealing process at a suitable temperature within a range of ˜300 ° C., an IGZO-based amorphous oxide thin film having an electric resistance value in the conductor region can be manufactured.

  Further, as in the case of the maximum value, annealing at a temperature near the minimum value is preferable because the effect on the electrical resistance value exerted by the in-plane uniformity of the annealing temperature is reduced, and the same effect as described above is obtained.

It is considered that the annealing temperature showing the minimum value varies depending on the back pressure as shown in FIG. Therefore, when the annealing temperature showing the minimum value is an unknown back pressure condition, an IGZO amorphous oxide layer is formed by sputtering with a back pressure of a predetermined value of 1 × 10 ⁻⁵ Pa or less, and 100 ° C. or higher. In the case where annealing is performed in the range of 300 ° C. or lower, the annealing temperature dependency of the electrical resistance value of the IGZO-based amorphous oxide layer is acquired in advance, and around the temperature at which the change rate of the electrical resistance value becomes 0 (± 5 ° C.) It is preferable to perform an annealing process.

In the plots of ■, □, ◆, and Δ in FIG. 3 (back pressure 1 × 10 ⁻⁴ Pa, 6.5 × 10 ⁻⁵ Pa, 5 × 10 ⁻⁵ Pa, 2 × 10 ⁻⁵ Pa), By increasing, the electric resistance value continuously increases in the region up to 300 ° C. Further, the plot of ◆ shows a form in which the slope becomes very gentle in the annealing temperature range of 150 ° C. to 250 ° C. and shows a substantially constant value in the range of 10 ⁴ to 10 ⁵ Ω · cm. .

The electrical resistance value of 10 ⁴ to 10 ⁵ Ω · cm is a value within the range of electrical resistance values of 10 ³ to 10 ⁶ Ω · cm of a semiconductor region in which generally good ON-OFF characteristics are obtained. Furthermore, the present inventor has confirmed that there is a correlation between the electric resistance value and the carrier density. Therefore, by setting the back pressure condition and the annealing temperature range, an IGZO-based amorphous oxide semiconductor film having high uniformity of carrier density in the film surface and good ON-OFF characteristics and excellent reliability is manufactured. be able to.

In FIG. 3, a suitable combination of back pressure and annealing temperature is selected in the range of back pressure 1 × 10 ⁻⁵ Pa to 5 × 10 ⁻⁴ Pa and annealing treatment temperature 100 ° C. to 300 ° C. Thus, it is shown that a semiconductor film capable of obtaining good ON-OFF characteristics within a range of electric resistance values of 10 ³ to 10 ⁶ Ω · cm can be manufactured.

Further, when the back pressure is 5 × 10 ⁻⁵ Pa, in the annealing temperature range of 150 ° C. to 250 ° C., the in-plane uniformity of the annealing temperature has little influence on the electrical resistance value, It is also shown that the influence on the uniformity of the electrical resistance value in the film surface due to the temperature distribution in the film surface of the thin film can be reduced.

  Furthermore, FIG. 3 shows that when the annealing temperature is 400 ° C. or higher, the electrical resistance value of the semiconductor region can be obtained with good ON-OFF characteristics regardless of the back pressure at the time of sputtering film formation. It is shown that an IGZO-based amorphous oxide thin film having high uniformity of carrier density and excellent reliability can be produced.

As shown in FIG. 3, in the case of a back pressure of 5 × 10 ⁻⁵ Pa, a good semiconductor layer 1 (active layer 11) is manufactured in an annealing process at 150 ° C. to 220 ° C. (because heat resistance is 220 ° C.). can do. Further, the sputter film formation is performed under the same conditions as the gate insulating film, and then the annealing process is performed at about 100 ° C., whereby the semiconductor layer 1 can be formed by a simpler process.

  Summarizing the above-mentioned conditions of suitable back pressure and annealing temperature when manufacturing the semiconductor film, the insulating film, and the conductive film, the semiconductor film is formed under the conditions satisfying the following formulas (1) and (2). It is preferable that the conductive film is produced under the conditions satisfying the following formulas (2) and (3), and the conductive film is produced under the conditions satisfying the following formulas (2) and (4). Further, it is more preferable that the semiconductor film is manufactured under conditions that satisfy the following formula (5).

  As shown by the following formula, the manufacturing method of the IGZO amorphous oxide insulating film of the present invention can be carried out by a low-temperature process of 300 ° C. or less, and is therefore suitably applied to a flexible substrate having low heat resistance. can do. That is, the field effect transistor manufacturing method of the present invention can be applied to the manufacture of thin film transistors (TFTs) used in flexible displays and the like.

As shown in FIG. 3, a semiconductor film capable of obtaining good ON-OFF characteristics within the range of electric resistance values of 10 ³ to 10 ⁶ Ω · cm is expressed by the following formulas (1) and (2) or (3 ) And (2) are not necessarily obtained in the entire range. In FIG. 3, the annealing temperature at which a semiconductor film with good ON-OFF characteristics can be manufactured as the back pressure is lower (closer to high vacuum) in the range satisfying the following formula (1) It shows a tendency to increase in the range satisfying 2).

  For example, the conditions under which such a semiconductor film can be formed include, for example, conditions that satisfy the following formulas (6) and (7), conditions that satisfy the following formulas (8) and (9), formulas (10) and Conditions that satisfy (11) and conditions that satisfy the following expressions (12) and (13) are mentioned (P is the back pressure, and T is the annealing temperature). In addition, the value of the back pressure P in the following formulas (6), (8), (10), and (12) is assumed to have a width of ± 10%.

  Even if it is outside the range shown in the following formulas (6) to (13), the relationship between the annealing temperature and the electrical resistance value satisfying the formula (2) at an arbitrary back pressure satisfying the following formula (1) If the combination of the back pressure and the annealing temperature found as a result of the investigation is found, a semiconductor film capable of obtaining good ON-OFF characteristics can be manufactured.

1 × 10 ⁻⁵ ≦ P (Pa) ≦ 5 × 10 ⁻⁴ (1),
100 ≦ T (° C.) ≦ 300 (2),
5 × 10 ⁻⁴ ≦ P (Pa) (3),
P (Pa) ≦ 1 × 10 ⁻⁵ (4),
2 × 10 ⁻⁵ ≦ P (Pa) ≦ 1 × 10 ⁻⁴ (5),
P (Pa) = 2 × 10 ⁻⁵ (6),
200 ≦ T (° C.) ≦ 300 (7),
P (Pa) = 5 × 10 ⁻⁵ (8),
120 ≦ T (° C.) ≦ 270 (9),
P (Pa) = 6.5 × 10 ⁻⁵ (10),
100 ≦ T (° C.) ≦ 240 (11),
P (Pa) = 1 × 10 ⁻⁴ (12),
100 ≦ T (° C.) ≦ 195 (13)

The plots of ▲ and ◇ in FIG. 3 (back pressure 6.0 × 10 ⁻⁶ Pa, 1 × 10 ⁻⁵ Pa) are the back pressure in a high vacuum state in which normal sputtering film formation is performed. According to Example 1, an IGZO amorphous oxide thin film having an arbitrary electric resistance value from the conductor region to the insulator region is manufactured by optimizing the combination of the back pressure at the time of sputtering film formation and the annealing temperature. Can be.

Furthermore, in the normal high-vacuum film formation, if the annealing temperature is in the range of 100 ° C. to 300 ° C., the resistance is lowered, and if the annealing treatment is not performed at a temperature of 400 ° C. or higher, it has good ON-OFF characteristics. It has been shown that a semiconductor film cannot be obtained. This is apparent from FIG. 5 of Comparative Example 1, but it is possible to narrow the region to be a conductive film by controlling the oxygen flow rate during film formation and changing the resistance value of as-depo. is there. For example, as shown in FIG. 5 of Comparative Example 1, when the O ₂ flow rate during film formation is 0.25 sccm, the region is 300 ° C. or lower, but when 0.33 sccm and 0.4 sccm, the temperature is 200 ° C. or higher and 300 or lower. It becomes an area. In other words, the annealing temperature region of the film obtained as the semiconductor region can be expanded.

  As described above, there is no example reported so far that the method of changing the electric resistance value with respect to the annealing temperature varies depending on the back pressure at the time of sputtering film formation.

  According to the above findings of the present inventors, by changing the combination of the back pressure and the annealing temperature, in addition to the IGZO amorphous oxide thin film having the resistance value of the insulator region, the range from the conductor region to the semiconductor region IGZO-based amorphous oxide thin film having an arbitrary electrical resistance value can be manufactured together, so that not only the IGZO-based amorphous oxide insulating film but also the predetermined electrical properties of the semiconductor region and the conductor region are formed on the substrate. A field effect transistor can be manufactured by forming a plurality of IGZO-based amorphous oxide thin films having a resistance value by a simple method in which the back pressure is changed during sputtering film formation, which is preferable.

  For example, after manufacturing an IGZO-based amorphous oxide thin film having a predetermined electrical resistance value of an insulator region on a substrate by the manufacturing method of the present invention, the back pressure in sputter deposition is lowered and the manufacturing method of the present invention An IGZO-based amorphous oxide thin film having a predetermined electric resistance value in the region can be manufactured. In this case, it is preferable that the annealing temperature is the same for all layers, or the annealing temperature for the upper layer is lower than the annealing temperature for the lower layer.

  In terms of simplification of the manufacturing process, it is preferable to manufacture as many layers as possible by the above-described method for manufacturing an IGZO-based amorphous oxide thin film.

  Although the bottom gate field effect transistor has been described in the above embodiment, the present invention can also be suitably applied to a top gate field effect transistor.

Examples and comparative examples according to the present invention will be described.
Example 1
On a commercially available synthetic quartz substrate (1 mm thick, T-4040 synthetic quartz substrate) of about 1 cm ² , an IGZO film with a film thickness of 50 nm is formed on the substrate using an InGaZnO ₄ (at ratio) polycrystalline target. did.

In order to investigate the influence of the back pressure and the annealing temperature on the electrical resistance value of the IGZO film, the back pressure (the ultimate vacuum before film formation) was 6 × 10 ⁻⁶ Pa, 1 × 10 ⁻⁵ Pa, and 2 respectively. Samples were prepared as × 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 was set by starting evacuation after releasing the film formation chamber of the sputtering apparatus to the atmosphere, and starting film formation after confirming that the desired back pressure condition was reached with an ion gauge equipped with the sputtering apparatus. . Other film formation conditions are: substrate temperature Ts = room temperature, Ar / O ₂ mixed atmosphere (Ar flow rate 30 sccm, O ₂ flow rate 0.25 sccm), film formation pressure 0.8 Pa, substrate-target distance 150 mm, target input power DC 50 W (IGZO), the film formation time was about 19 minutes.

  As a result of measuring film thickness and composition by XRF for five types of samples after sputtering film formation and before annealing treatment, all samples had In: Ga: Zn = 1: 0.9: 0.7, film thickness. It was confirmed that the thickness was about 50 nm.

  Next, the sample is subjected to various annealing temperatures (100 ° C, 150 ° C, 200 ° C, 250 ° C, 300 ° C, 350 ° C, 400 ° C, 450 ° C, 500 ° C, 600 ° C) using a hot plate. Then, annealing was performed for 5 minutes, and an electric resistance value (specific resistance) was measured using Hiresta (MCP-HT450 (probe type URS) manufactured by Mitsubishi Chemical). The result is shown in FIG.

  FIG. 3 shows that, for example, when the annealing temperature is 250 ° C., the electrical resistance value changes by about 9 digits depending on the back pressure condition. From FIG. 3, it is confirmed that an IGZO amorphous oxide thin film having an arbitrary electric resistance value can be produced in the conductor region to the insulator region by optimizing the back pressure and the annealing temperature during sputtering film formation. It was.

In order to investigate the factors that the back pressure at the time of sputter deposition gives to the film characteristics, surface FT-IR measurement (Nicolet 4700 from ThermoFisher) is performed on five types of samples that have not been annealed after sputter deposition and a quartz substrate used as a reference. Performed by ATR method. The result is shown in FIG. As shown in FIG. 4, any sample the peak derived from stretching vibration of OH groups ^(broad peak ranging 2500cm ^-1 ~4000cm -1) are observed, the peak area as the back pressure increases Was confirmed to be large.

  The above tendency has been confirmed to be the same in co-sputtering using a plurality of targets as targets.

(Comparative Example 1)
The IGZO amorphous oxide thin film was formed in the same manner as in Example 1 except that the back pressure was set to a constant condition of 1 × 10 ⁻⁶ Pa and the oxygen flow rate of the deposition gas was changed to 0.25 sccm, 0.33 sccm, and 0.4 sccm. Samples were prepared and annealed under the same annealing conditions as in Example 1, and the respective electrical resistance values were measured. The result is shown in FIG.

  As shown in FIG. 5, by increasing the oxygen flow rate, the electrical resistance value of the IGZO thin film after sputter deposition is increased, but both are minimized by the annealing process at 250 ° C. and reduced to the conductor region. It was confirmed that it was resisting.

  The present invention can be preferably applied to the manufacture of field effect transistors, X-ray sensors, and actuators mounted on liquid crystal displays and organic EL displays.

1 IGZO amorphous oxide thin film (IGZO amorphous oxide thin film)
2 Field effect transistor (Thin film transistor: TFT)
11 Active layer (semiconductor layer)
21 Gate electrode 22 Source electrode 23 Drain electrode 31 Gate insulating film 32 Protective film B Film formation substrate

Claims (5)

IGZO-based amorphous oxide layer was sputtered with a back pressure exceeding 5 × 10 ⁻⁴ Pa,
Then, an insulating film made of an IGZO amorphous oxide is manufactured by annealing at an annealing temperature of 100 ° C. or higher and 300 ° C. or lower. A method for manufacturing an IGZO amorphous oxide insulating film, comprising:   The method for producing an IGZO-based amorphous oxide insulating film according to claim 1, wherein a film forming pressure in the sputter film forming is set to 10 Pa or less. The deposition gas in the sputtering deposition includes Ar and O ₂ ,
The method for producing an IGZO-based amorphous oxide insulating film according to claim 1 or 2, wherein a flow rate ratio of Ar to O ₂ in the film forming gas is O ₂ / Ar ≦ 1/15. In a method of manufacturing a field effect transistor comprising an IGZO-based amorphous oxide semiconductor layer, a source electrode, a drain electrode, a gate electrode, and a gate insulating film on a substrate,
A method for manufacturing a field effect transistor, wherein the gate insulating film is formed using the method for manufacturing an insulating film according to claim 1.   5. The method of manufacturing a field effect transistor according to claim 4, wherein the substrate is a flexible substrate.

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