JP2011142174A - Film forming method and semiconductor device - Google Patents

Abstract

When a thin film is formed on an oxide semiconductor film by sputtering, plasma damage of the oxide semiconductor film is suppressed with good in-plane uniformity.
An oxide semiconductor film including In and at least one element selected from the group consisting of Ga, Zn, Mg, Al, Sn, Sb, Cd, and Ge, formed on a substrate B. In the film forming method of forming the thin film 2 containing the constituent elements of the target T by sputtering using plasma with the substrate B and the target T facing each other, the plasma potential Vs in the plasma when forming the thin film 2 is formed. The potential difference between (V) and the substrate potential Vsub (V) of the substrate B is set to be more than 0V and 20V or less.
[Selection] Figure 1A

Description

  The present invention relates to a film forming method for forming a thin film on a base of an oxide semiconductor film such as IGZO by a sputtering method, and a semiconductor device obtained by using the method.

  In recent years, semiconductor devices such as thin film transistors (TFTs) have been widely used as drive elements for liquid crystal displays and organic electroluminescence (organic EL) displays. As a semiconductor film in a thin film transistor, amorphous silicon, low-temperature polysilicon, or the like is generally used. However, a high-temperature process is indispensable for the formation of these semiconductor films, and a flexible substrate with low heat resistance such as a resin substrate is used. It is difficult to form a film.

  Thus, an oxide semiconductor film such as IGZO has attracted attention as a semiconductor film that can be formed at a low temperature. Since an oxide semiconductor film can be formed even at a temperature lower than the heat resistant temperature of the resin substrate, it is expected as a semiconductor film such as a thin film transistor or a thin film sensor used for a flexible EL display or the like.

  When forming a thin film such as an insulating film on the oxide semiconductor film, a sputtering method (sputtering method) capable of forming a thin film without using high-temperature treatment is mainly used. In the sputtering method, plasma ions such as Ar ions generated by plasma discharge in a high vacuum are collided with a target, and the constituent atoms or particles (hereinafter referred to as sputtered particles) of the target knocked out by this are formed. In this method, the film is deposited on the surface of the substrate.

  When a thin film is formed on an oxide semiconductor film by a sputtering method, plasma ions collide not only with the target but also with the oxide semiconductor film formed on the substrate and cause plasma damage to the oxide semiconductor film. Is a problem. FIG. 2 (FIG. 8) shows the influence of the IGZO film on the electrical resistance with respect to the Ar plasma irradiation time to the IGZO film. FIG. 2 shows that the longer the time of irradiation with Ar ions, the lower the electrical resistivity of the IGZO film and the higher the carrier density.

  In paragraph [0022] of Patent Document 1, the electric conductivity and electron carrier density of an oxide semiconductor are usually controlled by the oxygen partial pressure during film formation, and mainly by controlling the amount of oxygen vacancies in the thin film. Controlling the density is described. Patent Document 1 discloses a method of flowing oxygen when forming a thin film by sputtering in order to suppress the above oxygen deficiency.

Further, Non-Patent Document 1 describes that the threshold voltage of the obtained thin film transistor is shifted depending on the oxygen condition when the SiO ₂ protective film is formed on the IGZO film, thereby affecting the electrical characteristics ( Non-Patent Document 1, FIG. 5).

JP 2008-218495 A

“Improvements in the device characteristics of amorphous indium gallium zinc oxide thin-film transistors by Ar plasma treatment”, Sumsung SDI Co. Ltd., Applied Physics Letters 90, 262106 2007. “World ’s Largest (15-inch) XGA AMLCD Panel Using IGZO Oxide TFT”, Sumsung Electronics Co. Ltd., SID08 DIGEST, p.625-628

  However, in the method of adjusting the oxygen flow rate in the film forming gas in Patent Document 1, the amount of oxygen in the film forming gas varies depending on the position of the surface of the oxide semiconductor film due to the uneven flow of oxygen, and the effect of oxygen introduction is uniform. Therefore, it is difficult to obtain a highly reliable film having a uniform carrier density in the film surface. The reliability of a semiconductor film greatly affects the element characteristics of a thin film element using the semiconductor film. For example, in a thin film transistor, when a semiconductor film with low carrier density is used, a drain current rises in Vg-Id characteristics. Patent Document 1 also describes that the gate application voltage and the threshold voltage are shifted to the negative side, which shows undesirable properties in terms of thin film transistor characteristics.

  Non-Patent Document 1 does not describe any method for controlling oxygen conditions, so the specific film forming conditions are unknown.

  The present invention has been made in view of the above problems. When a thin film is formed on an oxide semiconductor film by a sputtering method, the carrier density of an oxide semiconductor film such as IGZO as a base is uniform in the film plane. It is an object of the present invention to provide a film forming method capable of maintaining high performance.

  It is another object of the present invention to provide a semiconductor device having good element characteristics and reliability obtained by using the above film forming method.

The film forming method of the present invention includes an oxide formed on a substrate and containing In and at least one element selected from the group consisting of Ga, Zn, Mg, Al, Sn, Sb, Cd, and Ge. In a film formation method for forming a thin film containing a constituent element of the target on a semiconductor film by a sputtering method using plasma with the substrate and the target facing each other,
The potential difference is controlled so that the potential difference | Vs−Vsub | between the plasma potential Vs (V) in the plasma during the deposition of the thin film and the substrate potential Vsub (V) of the substrate satisfies the following formula (1). Then, the thin film is formed. In the film forming method of the present invention, the thin film is preferably formed by controlling the potential difference so as to satisfy the following formula (2).
0 <| Vs−Vsub | (V) ≦ 20 (1),
0 <| Vs−Vsub | (V) ≦ 16 (2)

Here, the plasma potential means the maximum absolute value of the potential of plasma ions ionized in the sputtering apparatus. For example, when Ar gas is used as the film forming gas, it means the maximum value of Ar ⁺ ion potential.

  In this specification, “potential” is measured by a single probe method or a triple probe method using a Langmuir probe. Other methods may be used as long as they can be measured in principle.

  Further, the period for controlling the potential difference | Vs−Vsub | at the time of film formation to be 20 (V) or less is not necessarily the entire period in the step of forming the thin film over the oxide semiconductor film. The film thickness may be controlled until the influence of sputtering on the surface of the underlying oxide semiconductor film is negligible.

Further, the potential difference | Vs−Vsub | is only required to relatively change the difference between the plasma potential Vs and the substrate potential Vsub. However, the potential difference | Vs−Vsub | It is preferable to change by applying a bias. Either or both of the plasma potential Vs and the substrate potential Vsub may be changed as long as the film deposition rate is not significantly affected. When the plasma ions are positive ions and the plasma potential Vs is greater than 0V and 50V or less, it is preferable to control the potential difference | Vs−Vsub | by applying a positive voltage to the substrate. In addition, the film forming method of the present invention is suitably applied when the oxide semiconductor film is made of one or more kinds of oxides represented by the following general formula (P1) (may contain inevitable impurities). can do.
_{(In 2-x Ga x)} O 3 · (ZnO) m ··· (P1)
(Where 0 <x <2 and m is a natural number)

  In the film formation method of the present invention, the substrate temperature Ts during the film formation is 300 ° C. or less, the distance D between the substrate and the target is 40 mm or more and 150 mm or less, and the film formation pressure P is 0.1 Pa or more and 5 Pa. The film forming pressure P is preferably 0.1 Pa or more and 1.0 Pa or less.

  Moreover, the film forming method of the present invention can be suitably applied when the thin film is an insulator film.

  The thin film element of the present invention is an oxide semiconductor containing In and at least one element selected from the group consisting of Ga, Zn, Mg, Al, Sn, Sb, Cd and Ge, formed on a substrate. A film and a thin film formed by the film forming method of the present invention are provided. Examples of such a thin film element include a semiconductor device such as a thin film transistor provided with an active layer made of the oxide semiconductor film and a gate insulating film made of the thin film.

The thin film element of the present invention is provided with a substrate, and an oxidation containing In and at least one element selected from the group consisting of Ga, Zn, Mg, Al, Sn, Sb, Cd and Ge on the substrate. Forming a physical semiconductor film;
Forming an insulating film on the oxide semiconductor film by the film forming method of the present invention;
It can be manufactured by a method for manufacturing a thin film element including a step of applying a voltage to the oxide semiconductor film or forming an electrode for taking out current from the oxide semiconductor film.

  In the method for manufacturing a thin film element of the present invention, the electrode is preferably formed using the film forming method of the present invention.

  In the film formation method of the present invention, when a thin film is formed on an oxide semiconductor film such as IGZO formed on a substrate by a sputtering method using plasma, the plasma potential Vs ( V) and the substrate potential Vsub (V) are formed such that the potential difference | Vs−Vsub | is controlled to be 20 (V) or less. According to such a configuration, oxygen vacancies due to plasma damage of the oxide semiconductor film can be suppressed with high uniformity in the film plane. Therefore, according to the present invention, the carrier density of the underlying oxide semiconductor film such as IGZO can be maintained with high uniformity in the film plane.

  In the configuration in which the plasma potential Vs is positive and the potential difference is controlled by applying a positive voltage to the substrate, the potential difference | Vs−Vsub | can be controlled without significantly reducing the film formation rate.

Schematic sectional view of an RF sputtering film forming apparatus suitable for the film forming method of the present invention A diagram schematically showing the state during sputter deposition Schematic diagram showing the state of potential distribution between substrate and target in the Ar ⁺ plasma space in the RF sputtering system 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) Top view of thin film element sample of Example 1 A-A 'sectional view of FIG. 4A FIG. 11 is a graph showing the relationship between the potential difference | Vs−Vsub | and the carrier density of the oxide semiconductor film. Diagram showing the relationship between target input power and substrate potential Diagram showing the relationship between pressure and substrate potential FIG. 2

"Thin film deposition method"
A film forming method according to an embodiment of the present invention will be described with reference to the drawings. In the film formation method of the present invention, a thin film is formed on an oxide semiconductor film such as InGaZnO ₄ (IGZO) formed on a substrate by a sputtering method using plasma.

  A sputtering method using plasma is not particularly limited, but a bipolar sputtering method, a three-pole 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, and Examples include a pulse sputtering method.

  In this embodiment, an RF sputtering method will be described as an example. FIG. 1A is a cross-sectional view showing the overall configuration of the apparatus, and FIG. 1B is a view schematically showing a state during film formation. In order to facilitate visual recognition, the scale of each part is changed as appropriate. In the present embodiment, a high frequency sputtering apparatus (RF sputtering apparatus) will be described as an example.

  A film forming apparatus 100 shown in FIG. 1A can have a substrate B mounted therein, a substrate holder 11 capable of heating the mounted substrate B to a predetermined temperature, and a target holder 12 capable of mounting a target T. The vacuum vessel 10 is provided with a schematic configuration. In the apparatus of this embodiment, the inside of the vacuum vessel 10 is a film forming chamber. Within the vacuum vessel 10, the substrate holder 11 and the target holder 12 are spaced apart so as to face each other. The vacuum vessel 10 is made of a conductor such as stainless steel and is grounded.

  The substrate B is not particularly limited, and can be appropriately selected depending on applications such as a Si substrate, an oxide substrate, a glass substrate, and various flexible substrates. The substrate B may be a substrate on which a film such as an electrode is formed. The composition of the target T is selected according to the composition of the film to be formed.

  In the film forming apparatus 100, the gas G introduced into the vacuum vessel 10 is discharged by the discharge of the plasma electrode (in this embodiment, the target holder 12 functions as a plasma electrode), and positive ions such as Ar ions are generated. Generate. The generated positive ions sputter the target T. The constituent elements of the target T sputtered by the positive ions are deposited on the substrate B in a neutral or ionized state released from the target. In the figure, the symbol P schematically shows the plasma space.

  The film forming apparatus 100 is provided with gas introduction means for introducing the gas G to be converted into plasma into the vacuum vessel 10. The gas introduction means includes a supply source (not shown) of the gas G to be converted into plasma and a gas introduction pipe 18 for introducing the gas G supplied from the supply source into the vacuum vessel 10.

The film forming apparatus 100 includes a gas discharge pipe 19 that is connected to an exhaust means (not shown) such as a vacuum pump and exhausts the gas V in the vacuum vessel 10. The connection location of the gas introduction pipe 18 and the gas exhaust pipe 19 with respect to the vacuum vessel 10 can be designed as appropriate, and the gas introduction pipe 18 and the gas exhaust pipe 19 are provided so that the gas concentration in the vacuum vessel 10 is as uniform as possible. It is preferable. There is not any specific restriction on the gas G, Ar, or Ar / _{O 2} mixed gas is used.

  As schematically shown in FIG. 1B, the deposition gas G introduced into the vacuum vessel 10 by the discharge of the plasma electrode 12 is turned into plasma, and positive ions Ip such as Ar ions are generated. The generated positive ions Ip sputter the target T. The constituent atoms or particles (sputtered particles) Tp of the target T sputtered by the positive ions Ip are already deposited on the deposition substrate B (or on the deposition substrate B) in a neutral or ionized state released from the target. On the surface of the thin film). In the figure, the symbol P indicates the plasma space.

  The potential of the plasma space P becomes the plasma potential Vs (V) in the plasma during film formation. The potential of the deposition substrate B becomes the substrate potential Vsub (V). Due to the acceleration voltage of the potential difference | Vs−Vsub | between the potential of the plasma space P and the potential of the film formation substrate B, the sputtered particles Tp between the target T and the film formation substrate B obtain kinetic energy and form a film. A thin film is deposited on the oxide semiconductor film 1 formed on the substrate B. Note that the oxide semiconductor film 1 and the deposition substrate B are considered to have substantially the same potential.

  The substrate holder 11 is schematically configured from a plate-shaped holder main body 11A on which the substrate B is placed, and a fixing member 11B attached to the holder main body 11A and fixing the end of the substrate B. The substrate holder 11 is held by a holding member 15 attached to the inner bottom surface of the vacuum vessel 10.

  The holder body 11A, the fixing member 11B, and the holding member 15 are all made of a conductor such as stainless steel, and the holding member 15 and the vacuum vessel 10 are insulated from each other via an insulating material (the insulating material is not shown). . The substrate holder 11 is electrically connected to a direct current application unit (potential adjusting means) 17 disposed outside the vacuum vessel 10, so that a potential can be applied to the substrate holder 11 and the potential can be adjusted. It is configured. The direct current application unit 17 is generally configured by a direct current power source 17A and a matching circuit 17B. The matching circuit 17B is provided as necessary, and by interposing the matching circuit 17B between the DC power source 17A and the substrate holder 11, it is easy to adjust the potential of the substrate holder 11, which is preferable.

  In the present embodiment, the holder main body 11A, the fixing member 11B, and the holding member 15 are at the same potential. In the present embodiment in which a DC bias current is applied to the substrate holder 11, it is preferable that the substrate itself is a conductor, or a conductor film such as an electrode is formed on the substrate surface even if the substrate is an insulator. Such a configuration is preferable because the substrate B and the substrate holder 11 can be effectively at the same potential. In the formation of a piezoelectric film or the like, since the lower electrode is usually formed on the base, the substrate potential and the substrate holder 11 can be set to the same potential.

  In the present embodiment, the size of the holder main body 11A of the substrate holder 11 is preferably designed to be larger by 10 mm or more from the outer periphery of the substrate B to the side of the substrate B.

  The target holder 12 includes a plate-shaped holder body on which the target T is placed, and is held by a holding member 16 attached to the vacuum vessel 10. The holding member 16 and the vacuum vessel 10 are insulated from each other via an insulating material. The holding member 16 is connected to a high frequency power source (RF power source) 13 disposed outside the vacuum vessel 10, and the target holder 12 serves as a plasma electrode (cathode electrode) for generating plasma. The side opposite to the target holder connection side of the high frequency power supply 13 is grounded.

  In the present embodiment, a high frequency power source 13 and a target holder 12 that functions as a plasma electrode (cathode electrode) are provided as plasma generating means 14 for generating plasma in the vacuum vessel 10.

  As described in the background art, when the thin film 2 is formed on the oxide semiconductor film 1 such as IGZO by the sputtering method using plasma, the carrier density of the oxide semiconductor film 1 is increased due to plasma damage, and the electric It has been stated that the properties are degraded and that the carrier density is usually controlled by the amount of oxygen vacancies in the film.

  According to Patent Document 1 and Non-Patent Documents 1 and 2, the increase in carrier density due to plasma damage in the sputtering method is caused by oxygen in the oxide semiconductor film being sputtered by collision of plasma ions with the oxide semiconductor film 1 in the film. This is thought to be due to oxygen deficiency.

The inventor has also confirmed that the carrier density varies depending on the amount of oxygen in the film. The inventor examined the relationship between the amount of oxygen in the film and the carrier density by changing the amount of oxygen in the film forming gas during sputtering of the IGZO film. As a result, the carrier density decreases as the amount of oxygen increases, and the volume fraction of oxygen in the film forming gas is set to about 0.8%. It has been confirmed that a carrier density (1 × 10 ¹⁴ to 1 × 10 ¹⁵ (pieces / cm ³ )) having good characteristics to rise can be obtained.

  As a method for compensating for oxygen deficiency, Patent Document 1 discloses a method in which oxygen is allowed to flow into a vacuum vessel and oxygen element is positively injected into the film. Since the defect suppressing effect cannot be obtained uniformly in the film plane, the film quality becomes non-uniform and the reliability as an oxide semiconductor film becomes low. Furthermore, when oxygen is allowed to flow into the vacuum vessel, the film formation rate is greatly affected, and it is difficult to maintain good productivity.

  The inventor has intensively studied a method for compensating for oxygen vacancies while maintaining in-plane uniformity of carrier density of an oxide semiconductor film serving as a base.

  As described above, oxygen deficiency (plasma damage) to the oxide semiconductor film 1 is a phenomenon that occurs when the oxide semiconductor film 1 is sputtered. The plasma ions obtain energy from the potential difference between their own potential and the target or substrate to be sputtered to sputter the target or substrate.

FIG. 2 is a schematic diagram showing a state of potential distribution between the substrate and the target when the substrate is grounded in the Ar ⁺ plasma space in the RF sputtering apparatus. As shown in FIG. 2, Ar gas is ionized into Ar ⁺ and electrons by plasma, and the target side has a negative potential (about −100 to −150 V) due to self-bias due to the difference in the reaction rate of RF between Ar ⁺ and electrons. ). The plasma potential is Ar + potential (maximum potential) in the plasma space between the substrate and the target, and is 0 V in the grounded substrate.

Since Ar ⁺ plasma ions are positive ions, they accelerate to the negative potential target side and collide with the target. However, when the energy exceeds the sputtering threshold of the constituent elements of the target, the element is knocked out ( The film is formed on the opposite substrate side. The energy of plasma increases as the potential difference between the plasma ions and the sputtered side increases.

  On the other hand, as shown in the figure, since there is a potential difference between the substrate potential Vsub and the plasma potential Vs, the surface on the substrate side is sputtered with energy corresponding to the potential difference, which is considered to cause plasma damage. Therefore, in order to suppress the plasma damage of the oxide semiconductor film, by reducing the potential of the oxide semiconductor film, that is, the potential difference | Vs−Vsub | (V) between the substrate potential Vsub and the plasma potential Vs, It is considered that plasma energy colliding with the surface of the oxide semiconductor film is reduced, and oxygen sputtering can be suppressed. In such a method, oxygen vacancies due to plasma damage of the oxide semiconductor film can be suppressed with high uniformity in the film surface. Note that | Vs−Vsub | (V) can be directly converted into an electron temperature (eV). This corresponds to an electron temperature of 1 eV = 11600 K (K is an absolute temperature).

  The present inventor has found a suitable range for the potential difference | Vs−Vsub | that can suppress oxygen vacancies due to plasma damage of the oxide semiconductor film with high uniformity on the film surface.

That is, the film forming method of the present invention includes In and at least one element selected from the group consisting of Ga, Zn, Mg, Al, Sn, Sb, Cd, and Ge formed on the substrate B. A film forming method for forming a thin film 2 containing a constituent element of a target T by a sputtering method using plasma with a substrate B and a target T facing each other over the oxide semiconductor film 1 including the plasma. The thin film 2 is formed by controlling this potential difference so that the potential difference | Vs−Vsub | between the plasma potential Vs (V) in the substrate and the substrate potential Vsub (V) of the substrate B satisfies the following formula (1). It is characterized by this.
0 <| Vs−Vsub | (V) ≦ 20 (1)

FIG. 5 of an example described later shows a relationship between | Vs−Vsub | found by the present inventor and the carrier density of the oxide semiconductor film. Generally, the carrier density of the semiconductor film is preferably about 1 × 10 ^{14 to} 1 × 10 ¹⁵ (pieces / cm ³ ). FIG. 5 shows the carrier density of the oxide semiconductor film 1 when the potential difference | Vs−Vsub | is within the range satisfying the above formula (1) when the film is formed on the oxide semiconductor film 1 by the sputtering method. It has been shown that the thin film 2 can be formed on the oxide semiconductor film while maintaining a range suitable for a semiconductor film used for a semiconductor device or the like.

  Furthermore, when the following formula (2) is satisfied, the carrier density of the oxide semiconductor film 1 after the formation of the thin film 2 is suppressed within 10 times that before the formation of the thin film 2, and the carrier of the oxide semiconductor film 1 is reduced. The change in density can be suppressed more favorably, which is preferable. The value of | Vs−Vsub | may be set according to the required carrier density of the semiconductor film. That is, | Vs−Vsub | may be set to be equal to or less than a threshold value at which the required carrier density of the semiconductor film is obtained.

0 <| Vs−Vsub | (V) ≦ 16 (2)
According to the method of forming the thin film 2 on the oxide semiconductor film 1 of this embodiment, the plasma is obtained by optimizing the potential difference | Vs−Vsub | when forming the thin film 2 on the oxide semiconductor film 1. Compared with the method of mixing oxygen in the film forming gas shown in Patent Document 1 to suppress damage, the in-film uniformity of the oxygen deficiency suppressing effect obtained in the oxide semiconductor film 1 is high, and as a result The thin film 2 can be formed while maintaining the carrier density of the oxide semiconductor uniformly and satisfactorily.

  The potential difference | Vs−Vsub | is only required to relatively change the difference between the plasma potential Vs and the substrate potential Vsub. For example, either the plasma potential Vs or the substrate potential Vsub may be changed. May be.

  In the film forming apparatus 100 of the present embodiment, a direct current application unit (potential adjusting means) 17 is electrically connected to the substrate holder 11 so that a potential can be applied to the substrate holder 11 and the potential can be adjusted. It is configured. In such a configuration, it is preferable to control the potential difference | Vs−Vsub | by applying a voltage to the substrate B and controlling the substrate potential Vsub. When the plasma potential Vs is a positive potential, a positive voltage is biased to the substrate B as Vsub to control the potential difference | Vs−Vsub |.

  In the configuration in which the potential difference | Vs−Vsub | is controlled by applying a bias to the substrate B, the film formation rate and the plasma potential affecting the film quality are not changed, and the reaction rate such as oxygen is used as the film formation gas. Since the gas to be reduced is not mixed, the film formation rate can be suppressed and the film formation can be performed with high production efficiency.

  Further, as described above, the period for controlling | Vs−Vsub | so as to satisfy the above formula (1) may be the entire period in the step of forming a thin film over the oxide semiconductor film. The thin film thickness may be a part of the period until the influence of sputtering on the surface of the underlying oxide semiconductor film is negligible. For example, in the period in which the thin film 2 is formed over the oxide semiconductor film 1, the potential difference | Vs−Vsub | is controlled to 20 (V) or less until the film 2 has a predetermined thickness, for example, about several nm. Thereafter, the potential difference | Vs−Vsub | may be returned to a value of 20 (V) or more (potential difference depending on the conventional deposition conditions) to form the thin film 2.

  Further, the potential difference | Vs−Vsub | may be kept constant during the period of control within the range satisfying the expression (1), and the potential difference | Vs−Vsub | It may be changed intermittently. Note that by changing the potential difference | Vs−Vsub | during film formation, depending on the type of the thin film 2, the film characteristics may be affected. Therefore, it is preferable that the configuration in which the potential difference | Vs−Vsub | is changed halfway is performed in a range in which the influence on the film characteristics can be ignored.

  Control of the potential difference | Vs−Vsub | is not limited to the method of changing the substrate potential by bias application, and various methods can be applied as long as the method can control the potential difference | Vs−Vsub |.

  For example, as shown in Example 2 described later, it is also possible to control by target input power and film formation pressure. However, as shown in FIGS. 6 and 7 of Example 2 described later, it is possible to change the plasma potential Vs by changing the film formation pressure and the target input power, but the change is made as shown in the figure. For example, when Ar ions are used, it is difficult to set | Vs−Vsub | to 20 V or less due to target input power, and to make | Vs−Vsub | A pressure of 10 Pa or more is required, and the film formation rate becomes very slow, which is not preferable in terms of productivity.

  In general, in sputtering, it is not practical in terms of productivity unless film formation is performed at a target input power of 4 W or more and a film formation pressure of 0.1 Pa to 5 Pa, more preferably 1 Pa or less. The value of the film formation pressure varies depending on the type of element, but if it is too large, the rate at which the particles knocked out from the target T reach the substrate B due to the influence of scattering or the like decreases and film formation becomes difficult. Moreover, even if it is too small, a stable plasma space cannot be obtained.

Therefore, the control by the deposition pressure and the target input power is controlled by a configuration using plasma ion species capable of maintaining good productivity, a configuration combined with substrate bias application, or a thin film thickness of the underlying oxide. A configuration in which the shortest period of time until the influence of sputtering on the surface of the semiconductor film 1 is in a negligible range is considered preferable.
The film forming conditions other than | Vs−Vsub | for the thin film 2 are not particularly limited as long as the plasma in the film forming apparatus can be stably generated. However, the film forming conditions can be performed with good productivity. Is preferred. Since the said oxide semiconductor film 1 is suitable as a flexible device, it is preferable to set it as the conditions which can form into a film suitably at the temperature below the heat-resistant temperature of the board | substrate to be used. In general, since the heat resistance temperature of the resin substrate is about 300 ° C. with high heat resistance such as polyimide, the film formation temperature Ts is preferably 300 ° C. or less.

The longer the substrate-target distance D, the slower the film formation speed, but the better the uniformity of the film formed. Moreover, since the stability of plasma will be impaired when too short, it is preferable that the substrate-target distance D is 40 mm or more and 150 mm or less.
Hereinafter, a material configuration suitable for applying the film forming method of the present invention will be described.

  In this embodiment, the board | substrate B is not restrict | limited in particular, What is necessary is just to select according to uses, such as a Si substrate, a glass substrate, and various flexible substrates. In the present invention, an oxide semiconductor film that can be formed at a temperature lower than the heat resistant temperature of the resin substrate is provided. Therefore, a flexible substrate such as a resin substrate can be used as the film formation substrate B.

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,
A laminated plastic material having at least one bonding interface between a thin glass and the single organic material, an inorganic layer (ex. SiO ₂ , Al ₂ O ₃ , SiO _x N _y ) and an organic layer (above) alternately A composite material having a barrier performance having at least one bonding interface by laminating,
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.

The oxide semiconductor film 1 is made of an oxide semiconductor containing In and at least one element selected from the group consisting of Ga, Zn, Mg, Al, Sn, Sb, Cd, and Ge (including inevitable impurities). However, a homologous compound such as InGaZnO ₄ (IGZO) represented by the following general formula (P1) can be given as an example.
_{(In 2-x Ga x)} O 3 · (ZnO) m ··· (P1)
(Where 0 <x <2 and m> 0)

  The method for forming the oxide semiconductor film 1 is not particularly limited, and a suitable film forming method such as a vapor phase method or a liquid phase method may be used depending on the type of the substrate and the oxide semiconductor to be used.

  The thin film 2 formed over the oxide semiconductor film 1 is not particularly limited, and can be applied to film formation of any composition such as a conductor film, a semiconductor film, an insulator film, and a dielectric film. . In the case where the oxide semiconductor film 1 is used as a semiconductor layer of a thin film transistor, a protective film, a gate insulating film, an insulating film such as an interlayer insulating film, a source / drain electrode, and the like can be given.

These insulating films of the thin film transistor are made of an oxide such as Ga ₂ O ₃ , SiO ₂ , Al ₂ O ₃ , SiON, SiN, HfO ₂ , Y ₂ O ₃ , Ta ₂ O ₅ , MgO (inevitable impurities). An insulating film may be used.

  Further, as source / drain electrodes, metals such as Pt, Au, Pd, Cr, Ni, Mo, Ag, W, Cu, Ti, In, Sn, alloys thereof, tin oxide, indium oxide, indium tin oxide are used. A thing (ITO) etc. are mentioned.

  In an oxide semiconductor containing In and at least one element selected from the group consisting of Ga, Zn, Mg, Al, Sn, Sb, Cd and Ge, the easiness of sputtering of the constituent elements (sputtering rate) is Oxygen is much higher (agrees that the sputter threshold is much lower). Therefore, in the above oxide semiconductor film, when the film to be formed thereon is sputtered, an element that escapes from the surface of the film and has a defect has a remarkably large proportion of oxygen, and the oxygen defect greatly affects the carrier density. It will be a factor. The sputtering rate of Ga, Zn, Mg, Al, Sn, Sb, Cd, and Ge is large in Zn, but various films (protective films, insulating films, electrodes, etc.) formed on the oxide semiconductor film this time are used. Under the film forming conditions, these elements may be considered to be almost the same, and the influence of oxygen vacancies may be considered. Here, the “sputter rate” is defined by the ratio between the number of incident ions and the number of atoms sputtered thereby, and its unit is (atoms / ion). For example, Table 8.1.7 of “Vacuum Handbook” (published by ULVAC, Inc., issued by Ohm) describes the sputtering rate under the condition of Ar ion of 300 eV.

  In the film forming method of the present invention, when the thin film 2 is formed on the oxide semiconductor film 1 such as IGZO formed on the substrate B by the sputtering method using plasma, the plasma in the plasma during the film forming is formed. The film is formed by controlling the potential difference | Vs−Vsub | between the potential Vs (V) and the substrate potential Vsub (V) to be 20 (V) or less. According to such a configuration, oxygen vacancies due to plasma damage of the oxide semiconductor film 1 can be suppressed with high uniformity in the film plane. Therefore, according to the present invention, the thin film 2 can be formed while maintaining the carrier density of the underlying oxide semiconductor film 1 such as IGZO with high uniformity in the film plane.

  Further, the configuration in which the plasma potential Vs is positive and the potential difference | Vs−Vsub | is controlled by applying a positive voltage to the substrate B is preferable because the potential difference can be controlled without greatly reducing the film formation rate. .

"Semiconductor devices (thin film elements)"
With reference to FIGS. 3A to 3D, a semiconductor device (thin film element) 3 using the oxide semiconductor film 1 and the thin film 2 of the above embodiment and a method for manufacturing the same will be described. In the present embodiment, a bottom gate type will be described as an example. 3A to 3D are manufacturing process diagrams (cross-sectional views in the thickness direction of the substrate) of the thin film transistor (TFT). In order to facilitate visual recognition, the scale of the constituent elements is appropriately changed from the actual one.

  The semiconductor device (thin film transistor: TFT) 3 of this embodiment is formed on the substrate B by the active layer 32 obtained by using the oxide semiconductor film 1 of the above embodiment and the film forming method of the above embodiment. A protective film (insulating film) 2 and an electrode.

First, as shown in FIG. 3A, a substrate B is prepared, and a gate electrode 30 and a gate insulating film 31 made of n ⁺ Si or the like are formed. Examples of the gate insulating film 31 include the insulator material described above. As the substrate B, the same substrate as described in the above embodiment can be used.

  Next, as shown in FIG. 3B, an oxide semiconductor film 1 (active layer 32) containing In and at least one element selected from the group consisting of Ga, Zn, Mg, Al, Sn, Sb, Cd, and Ge. ). The film forming method is as described in the embodiment of the film forming method.

  Further, as shown in FIG. 3C, the source electrode 33 and the drain electrode 34 are formed on the active layer 32. The source electrode 33 and the drain electrode 34 can be formed by a manufacturing method in which gas phase film formation such as sputtering or vapor deposition and patterning by photolithography are combined, an inkjet method, or the like.

Finally, as shown in FIG. 3D, the protective film (insulating film) 2 is formed on the active layer 32, the source electrode 33, and the drain electrode 34 by the film forming method of the above embodiment.
Through the above steps, the semiconductor device (TFT) 3 of the present embodiment is manufactured.

  The semiconductor device (TFT) 3 of this embodiment includes a protective film 2 formed by the film forming method of the present invention on an active layer 32 obtained using the oxide semiconductor film 1. Therefore, the same effect as the film forming method of the present invention is achieved. Since the semiconductor device 3 according to the present embodiment includes the oxide semiconductor film 1 with high reliability and stable carrier density, the ON-OFF characteristic is good and the stability is high.

  In this embodiment, in the method for manufacturing a semiconductor device, since film formation in all steps can be performed at a film formation temperature of 300 ° C. or less, good semiconductor characteristics can be obtained even on a flexible substrate having low heat resistance. The semiconductor device 3 shown can be obtained. Therefore, according to the method for manufacturing a semiconductor device of the present invention, it is possible to provide a high-quality semiconductor device that can be suitably used for various electric products such as a flexible large-screen organic EL display.

In the case of the bottom gate type as in this embodiment, when the source electrode 33 and the drain electrode 34 are formed by a sputtering method with high productivity, the film is formed by the above-described sputtering method of the present invention. It is preferable. Plasma damage received when the source electrode 33 and the drain electrode 34 are formed by sputtering is good in terms of ohmic contact. However, when the carrier density of the oxide semiconductor film is increased, the resistance between the source and the drain is increased. As a result, the ON-OFF characteristics of the semiconductor device deteriorate. Therefore, by forming the source electrode 33 and the drain electrode 34 by the film forming method of the present invention, a semiconductor device with better ON-OFF characteristics can be manufactured.

"Design changes"
In the above embodiment, the RF sputtering film forming apparatus is used as the sputtering film forming apparatus, but the sputtering apparatus is not particularly limited as long as the plasma space potential can be adjusted so as to satisfy the above film forming conditions.

  Although this embodiment is an example in which the plasma potential Vs is higher than the substrate potential Vsub, the potential difference | Vs−Vsub | is controlled to be equal to or less than the above value even when the substrate potential Vsub is higher than the plasma potential Vs. If it does, the same effect can be acquired.

  Further, the semiconductor device including the oxide semiconductor film 1 has been described, but the present invention can also be applied to a semiconductor device such as a sensor or an actuator other than the semiconductor device.

Examples and comparative examples according to the present invention will be described.
Example 1
Insulation formed on an about 1 cm ² square commercially available synthetic quartz substrate (1 mm thick, T-4040 synthetic quartz substrate manufactured by Irie Co., Ltd.) by the IGZO semiconductor film, the electrode, and the film forming method of the present invention. A plurality of thin film element samples provided with a film (protective film) were prepared as follows. 4A is a top view of the thin film element sample, and FIG. 4B is a cross-sectional view taken along line AA ′ of FIG. 4A. In FIG. 4A, the size of the vertical and horizontal sides of the substrate is W1 = 10 (mm), the size of the vertical and horizontal sides of the IGZO film is W2 = 8 (mm), and the distance between the electrodes is W3 = 6 (mm). It is.

First, an IGZO film having a film thickness of 50 nm was formed on a substrate using a multi-sputter apparatus manufactured by Pascal. The film forming conditions are as follows: substrate temperature Ts = normal temperature, ultimate vacuum 6.0 × 10 ⁻⁶ Pa, Ar / O ₂ mixed atmosphere (O ₂ volume fraction 0.8%), film forming pressure 0.8 Pa, target InGaZnO ₄ and ZnO (both 4N target), substrate-target distance 150 mm, target input power DC50W (IGZO), DC10W (ZnO), and film formation time 30 minutes.

  Next, Ti / Au electrodes (thickness 50 nm / 200 nm) were formed on the four corner regions on the IGZO film by vacuum deposition.

When the carrier density of the formed IGZO film was measured using an AC Hall measuring system (RESITEST 8300) manufactured by Toyo Technica, the carrier density was about 2 × 10 ¹⁴ (pieces / cm ³ ).

For each of the plurality of thin film element samples, a bias is applied to the substrate in the range of ground potential (0 V) to 26 V so as to have different potential differences | Vs−Vsub | An insulating film, Ga ₂ O _3, was formed using a metal mask so that the electrode surface was partially exposed. When the plasma potential in the vicinity of the substrate position C shown in FIG. 1A was measured using a Japan High Frequency Triple Probe Monitor (TPM-2000), the plasma potential Vs was 26 (V).

The film formation conditions are: substrate temperature Ts = normal temperature, ultimate vacuum 7.0 × 10 ⁻⁶ Pa, Ar atmosphere, film formation pressure 0.4 Pa, target Ga ₂ O ₃ (4N target), substrate-target distance 150 mm, target input The power was RF50W and the film formation time was 30 minutes.

Table 1 and FIG. 5 show the results of measuring the carrier density of the thin film element after forming the insulating film in the same manner as described above. Table 1 and FIG. 5 show that when the substrate potential is the ground potential (0 V) (| Vs−Vsub | ≈26 V), the carrier density increases to about 1 × 10 ¹⁷ (pieces / cm ³ ). Then, if | Vs−Vsub | is set to 20 V or less by applying a bias to the substrate, the increase in carrier density can be suppressed within one digit, and further, within 16 V or less, good semiconductor characteristics can be obtained. It is shown that it can be maintained at a carrier density of 1 × 10 ¹⁴ to 1 × 10 ¹⁵ (pieces / cm ³ ).

Thus, the plasma ion is controlled by controlling the potential difference | Vs−Vsub | between the plasma potential Vs (V) and the substrate potential Vsub (V) in the plasma during film formation to 20 (V) or less, preferably 16 V or less. It has been demonstrated that it is possible to form a thin film on an oxide semiconductor film by suppressing oxygen vacancies due to collisions with the oxide semiconductor film due to, and suppressing an increase in carrier density in the oxide semiconductor film. .

(Example 2)
The film forming conditions under which | Vs−Vsub | could be controlled to 20 V or less by a method other than bias application to the substrate were examined. As the film formation conditions, the film formation pressure (depot pressure) and the target input power are selected, the substrate potential is set to the ground potential, and the plasma potential near the substrate position C shown in FIG. 1A when these film formation conditions are changed is shown. The state of the change was examined using a triple probe monitor (TPM-2000) manufactured by Nippon High Frequency in the same manner as in Example 1. The film forming conditions other than the changed film forming conditions were the same as those in Example 1.

  The results obtained are shown in FIGS. FIG. 6 is a diagram showing the relationship between the target input power and the substrate potential, and FIG. 7 is a diagram showing the relationship between the deposition pressure and the substrate potential.

  As shown in FIG. 6, it was confirmed that the plasma potential Vs22V to 30V, that is, the potential difference | Vs−Vsub | could be controlled to 22V to 30V when the target input power was changed between 25W and 100W.

  Further, as shown in FIG. 7, it is confirmed that the plasma potential Vs18V to 26V, that is, the potential difference | Vs−Vsub | can be controlled to 18V to 26V when the film forming pressure is changed from 0.4 Pa to 20 Pa. It was.

  The present invention can be applied to film formation having an arbitrary composition by sputtering using plasma. The present invention can be preferably applied to the manufacture of thin film transistors, X-ray sensors, and actuators mounted on liquid crystal displays and organic EL displays.

1 Oxide semiconductor film 2 Thin film (insulating film, protective film)
3 Semiconductor devices (thin film elements, thin film transistors)
10 Vacuum vessel 11 Substrate holder 12 Plasma electrode (target holder)
13 High frequency power supply 14 Plasma generating means 17 DC current applying unit (potential adjusting means)
18 Gas introduction pipe 19 Gas exhaust pipe 21, 22, 30, 33, 34 Electrode 100 Sputter deposition apparatus B Deposition substrate G Deposition gas Ip Plus ion P Plasma space T Target Tp Sputtered particle Vsub Substrate potential Vs Plasma potential

Claims (10)

On the oxide semiconductor film formed on the substrate and containing In and at least one element selected from the group consisting of Ga, Zn, Mg, Al, Sn, Sb, Cd, and Ge, In a film forming method for forming a thin film containing a constituent element of the target by sputtering using a plasma facing the target,
The potential difference is controlled so that the potential difference | Vs−Vsub | between the plasma potential Vs (V) in the plasma during the deposition of the thin film and the substrate potential Vsub (V) of the substrate satisfies the following formula (1). And forming the thin film.
0 <| Vs−Vsub | (V) ≦ 20 (1) The film forming method according to claim 1, wherein the thin film is formed by controlling the potential difference so as to satisfy the following formula (2).
0 <| Vs−Vsub | (V) ≦ 16 (2)   3. The film forming method according to claim 1, wherein the plasma potential Vs is greater than 0 V and equal to or less than 50 V, and a positive voltage is biased to the substrate to control the potential difference. The oxide semiconductor film is made of one or more kinds of oxides represented by the following general formula (P1) (may contain inevitable impurities). The film-forming method of description.
_{(In 2-x Ga x)} O 3 · (ZnO) m ··· (P1)
(Where 0 <x <2 and m> 0)   The substrate temperature Ts during the film formation is 300 ° C. or less, the distance D between the substrate and the target is 40 mm or more and 150 mm or less, and the film formation pressure P is 0.1 Pa or more and 5 Pa or less. The film-forming method in any one of Claims 1-4.   6. The film forming method according to claim 5, wherein the film forming pressure P is 0.1 Pa or more and 1 Pa or less.   The film forming method according to claim 1, wherein the thin film is an insulator film. Step of preparing a substrate and forming an oxide semiconductor film containing In and at least one element selected from the group consisting of Ga, Zn, Mg, Al, Sn, Sb, Cd and Ge on the substrate When,
A step of forming an insulating film on the oxide semiconductor film by the film forming method according to claim 1;
And a step of applying a voltage to the oxide semiconductor film or forming an electrode for extracting a current from the oxide semiconductor film.   The said electrode is formed using the film-forming method in any one of Claims 1-7, The manufacturing method of the thin film element of Claim 8 characterized by the above-mentioned. The method of manufacturing a thin film element according to claim 9, wherein the thin film element is a semiconductor device.

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