JP2012229490A - Film-forming method - Google Patents

Abstract

Provided is a film forming method for forming a film having a desired composition ratio by suppressing a decrease in composition of an element that is easily reverse sputtered by a sputtering method using plasma.
All the constituent elements contained in the composite target T using the composite target T containing a plurality of metal elements on the substrate 20 by sputtering using plasma, and all the metals contained in the composite target T are solved. Among the elements, a film 40 in which the binding energy Emax of the element having the highest binding energy of each elemental element and the binding energy Emin of the element having the lowest binding energy of each elemental element satisfy the following formula (1): In which the potential difference between the plasma potential Vp (V) and the substrate potential Vsub (V) in the plasma during the film formation is reversely sputtered by the element having the lowest binding energy in the film 40. The film formation is controlled so as to be as follows. Emax / Emin ≧ 1.5 (1)
[Selection] Figure 1

Description

   The present invention relates to a method for forming a film by sputtering using a composite target.

   Currently, composite oxide films such as piezoelectric films used for ferroelectric elements, transparent conductive films used for touch panels, transparent semiconductor films, etc., wiring films for liquid crystal panel displays, and solar cells The sputtering method is widely used in the formation of various functional films.

   Sputtering is generally performed by placing a substrate and a target facing each other, causing an inert gas in a plasma state under reduced pressure to collide with the target, and using the energy to attach molecules and atoms that have jumped out of the target to the substrate. This is a method of forming a thin film, and is one of the film forming methods that can easily increase the area and obtain a high-performance film.

  In the sputtering method, the film composition to be formed is basically the same as the target composition. When forming a composite material such as the above-mentioned composite oxide or composite alloy, the target is formed using a composite target including those constituent materials. Among the constituent elements of the film to be formed, When there is an element having a high vapor pressure, a so-called reverse sputtering phenomenon is likely to occur where the element is sputtered on the film surface, and it is difficult to obtain a composition that is substantially the same as the target composition.

In addition, in recent years, in zinc oxide (ZnO) -based transparent conductive films (semiconductor films) such as InGaZnO ₄ (IGZO), which have excellent electrical and optical characteristics comparable to ITO, and are abundant in resources at low cost. However, similarly to Pb, Zn is more easily sputtered compared to other constituent elements, and the film composition tends to be a composition containing less Zn than the target composition.

  For this reason, it is difficult to control the film composition to be formed, and adjustments to the target composition, film formation conditions, and the like have been made to obtain a desired composition.

  In Patent Document 1, in the PZT film, the relationship between the film forming pressure and the Pb amount in the film and the relationship between the film forming temperature and the Pb amount in the film are required (FIGS. 1 and 2 of Patent Document 1). See). Patent Document 1 describes that the film forming pressure is preferably 1 to 100 mTorr, and the film forming temperature is preferably 600 to 700 ° C. (see claims 2 and 5 of Patent Document 1).

JP-A-6-49638

   As described in Patent Document 1, conventionally, a piezoelectric film made of a Pb-containing perovskite oxide such as PZT is preferably formed at a film forming temperature of 550 to 700 ° C. However, since the suitable film formation temperature differs depending on the material, it is difficult to apply the conditions described in Patent Document 1 as they are to a Zn-containing transparent conductive film having a suitable film formation temperature of 100 to 400 ° C.

   Also, in the method of adjusting the film composition to the desired composition by adjusting the target composition, since the rate of reverse sputtering varies depending on the film forming conditions, it is also necessary to change the target so that the optimum target composition is obtained according to the material. It is complicated.

   The present invention has been made in view of the above circumstances, and in a sputtering method using plasma, it is possible to form a film having a desired composition while suppressing a decrease in the composition of elements that are easily reverse sputtered. It is an object of the present invention to provide a film forming method that can be applied regardless of the type.

   In particular, an object of the present invention is to provide a method for forming a piezoelectric film capable of stably suppressing Zn loss in a method for forming a transparent conductive film made of a Zn-containing composite oxide. .

   The present inventor has intensively studied to solve the above problems, and in the sputtering method using plasma, the reverse sputtering phenomenon in which a specific element escapes from the formed film is caused by the binding energy of each element constituting the film. It was found that it greatly depends on the difference, and found that an element having a low binding energy among the constituent elements is easily reverse sputtered. Therefore, by optimizing the film formation conditions so that an element having a low binding energy is not reverse sputtered, it is possible to form a film having a desired composition while suppressing a decrease in the composition of elements that are easily reverse sputtered.

According to a first film forming method of the present invention, a composite target including a plurality of metal elements is used on a substrate by a sputtering method using plasma, and includes all the constituent elements included in the composite target. Among all the metal elements included in the element, the bond energy Emax of the element having the highest bond energy of each elemental element and the bond energy Emin of the element having the lowest bond energy of each elemental element are represented by the following formula (1 The Zn-containing film that satisfies the above-mentioned conditions) is formed, wherein the potential difference between the plasma potential Vp (V) and the substrate potential Vsub (V) in the plasma during the film formation is determined by the bond energy in the film being the highest. It is characterized in that the film is formed by controlling so that a low element is equal to or lower than a threshold value for reverse sputtering.
Emax / Emin ≧ 1.5 (1)

In addition, the second film forming method of the present invention includes all the constituent elements contained in the composite target using a composite target containing a plurality of metal elements on a substrate by a sputtering method using plasma. Among all the metal elements contained in the target, the binding energy Emax of the element having the highest binding energy of each elemental element and the binding energy Emin of the element having the lowest binding energy of each elemental element are represented by the following formula ( 1) A method for forming a Zn-containing film satisfying 1), wherein the plasma potential Vp (V) and the substrate potential Vsub (V) in the plasma during film formation satisfy the following formula (2). It is characterized by forming a film.
Emax / Emin ≧ 1.5 (1),
Vp−Vsub (V) ≦ 20 (2)

In this specification, the “plasma potential Vp and substrate potential Vsub” are measured by a single probe method using a Langmuir probe. The measurement of the substrate potential Vf should be performed in the shortest possible time with the tip of the probe placed near the substrate (about 10 mm from the substrate) so as not to include errors due to the film being deposited on the probe. To do.
The potential difference Vp−Vsub (V) between the plasma potential Vp and the substrate potential Vsub can be directly converted into the electron temperature (eV). This corresponds to an electron temperature of 1 eV = 11600 K (K is an absolute temperature).

According to the film forming method of the present invention, a film having substantially the same composition as the composite target can be formed.
In this specification, “substantially the same composition” means the composition ratio of the metal element having the smallest binding energy of the elemental element to the metal element having the largest binding energy of the elemental element in the formed film, and the ratio in the target. This means that the difference from the composition ratio is within 5% of the composition ratio in the target.

   In the film forming method of the present invention, it is preferable to control the difference between the plasma potential Vp and the substrate potential Vsub so as to satisfy the formula (2) by applying a bias voltage to the substrate. It is preferable to form a film under the following pressure.

Further, the film forming method of the present invention can be preferably applied even when the film is a film containing Zn. Examples of such a film include a film containing an oxide represented by the following general formula (P2).
_{N x M y R z O (} x + 3y / 2 + 3z / 2) ··· (P2)
(Wherein R = In, M = In, Fe, Ga, Al, at least one element selected from the group consisting of N, Zn = xn, x, y, and z are real numbers greater than 0.)

   Japanese Patent Application Laid-Open No. 2004-197178 discloses a transparent conductive film in which a transparent conductive thin film is formed on a plastic film by controlling a potential difference between a plasma potential Vs and a floating potential Vf to more than 0 V and not more than 20 V by sputtering. And a Zn-containing composite oxide is mentioned as the transparent conductive thin film. Therefore, it is known to form a Zn-containing composite oxide by controlling the Vp-Vsub value.

     However, Japanese Patent Laid-Open No. 2004-197178 aims to improve the wear resistance of a general transparent conductive thin film, and has found a Vp-Vsub value that does not inhibit crystal growth in order to improve the wear resistance. It is. On the other hand, in the present invention, it is possible to form a film having a desired composition with high reproducibility by suppressing the reverse sputtering phenomenon of the formed film. In JP-A-2004-197178, since a transparent conductive thin film that does not require suppression of the reverse sputtering phenomenon is also targeted, suppression of the reverse sputtering phenomenon cannot exist as a problem, and there is no description or suggestion. Therefore, the film forming method of the present invention has not been easily invented from Japanese Patent Application Laid-Open No. 2004-197178.

   Japanese Patent Application Laid-Open No. 2004-119703 proposes that a bias is applied to the substrate in order to relieve the tensile stress applied to the piezoelectric film when the piezoelectric film is formed by sputtering. In Japanese Patent Application Laid-Open No. 2004-119703, by applying a bias to the substrate, the energy amount of the constituent element of the target entering the substrate is increased, and the tensile stress applied to the piezoelectric film is relaxed by the peening effect. Therefore, Japanese Patent Laid-Open No. 2004-119703 has no description or suggestion about the plasma potential Vp and Vp−Vsub which is the difference between the plasma potential Vp and the substrate potential Vsub.

   In the present invention, when a film is formed by a sputtering method using plasma using a composite target, the binding energy of the element having the highest binding energy of each individual metal element among all the metal elements contained in the film. When forming a film having a composition in which the ratio of Emax to the lowest element binding energy -Emin exceeds 1.5, the film forming conditions should be optimized so that the element having the binding energy Emin is not reverse sputtered. Thus, it is possible to form a film having a desired composition ratio while suppressing a decrease in the composition of elements that are easily reverse sputtered. In the present invention, it is possible to identify a metal element that is easily reverse sputtered based on the ratio of the binding energy between the metal elements contained in the film, and to form the film under conditions that make it difficult for the metal element to be reverse sputtered. Therefore, according to the present invention, it is possible to form a film having a desired composition ratio while suppressing a decrease in the composition of elements that are easily sputtered regardless of the type of film to be formed.

(A) is a schematic sectional view of an RF sputtering apparatus, (b) is a diagram schematically showing a state during film formation. Explanatory drawing which shows the measuring method of plasma potential Vs and floating potential Vf Sectional drawing which shows the structure and manufacturing process of the semiconductor device of embodiment which concern on this invention The figure which shows the relationship of the composition ratio of Zn with respect to In with respect to the substrate temperature of the IGZO film obtained in Example 2

  “Film Formation Method” The film formation method of the present invention includes a composite target including all the constituent elements included in a composite target using a composite target including a plurality of metal elements by sputtering on a substrate. Among all the metal elements included in the above, the bond energy Emax of the element having the highest bond energy of each elemental element and the bond energy Emin of the element having the lowest bond energy of each elemental element are expressed by the following formula (1). A method of forming a satisfactory film,

The potential difference between the plasma potential Vp (V) and the substrate potential Vsub (V) in the plasma during film formation is controlled so as to be equal to or lower than the threshold value at which the element having the lowest binding energy is reverse sputtered. It is characterized by forming a film.
Emax / Emin ≧ 1.5 (1)

  The present inventor has found that the reverse sputtering phenomenon in which a specific element escapes from the formed film depends greatly on the difference in the binding energy of each of the constituent elements of the film, and satisfies the above formula (1). It has been found that when a film is formed, at least a metal element having a binding energy of Emin is easily reverse sputtered. Therefore, by optimizing the film formation conditions so that an element having a low binding energy is not reverse-sputtered, that is, the potential difference between the plasma potential Vp (V) and the substrate potential Vsub (V) is determined by the binding energy in the film. By forming the film so that the lowest element is less than or equal to the threshold value for reverse sputtering, it is possible to form a film having a desired composition ratio while suppressing a decrease in the composition of elements that are easily reverse sputtered.

The reverse sputtering phenomenon is almost the same without preferentially sputtering only elements that are easily sputtered on the target when there is a large difference in the sputtering efficiency (sputtering rate) among the constituent elements in the sputtering method. In spite of being sputtered by the composition, on the deposition substrate, constituent elements that are easily sputtered are preferentially sputtered by sputtered particles on the film surface and knocked out of the film. is there. In this target, even if an element is preferentially sputtered at a certain moment in the target, the element is deficient on the target surface, so that another target composition is sputtered at the next moment. However, on the film surface, film deposition and reverse sputtering released from the target can occur at the same time.
The film forming method of the present invention will be described below with reference to the drawings.

  Based on FIG. 1, a configuration example of a film forming apparatus using plasma will be described by taking a sputtering apparatus as an example. FIG. 1A is a schematic cross-sectional view of an RF sputtering apparatus, and FIG. 1B is a diagram schematically showing a state during film formation.

  The RF sputtering apparatus 1 includes a heater 11 capable of heating the mounted substrate 20 to a predetermined temperature and a plasma electrode (cathode electrode) 12 for generating plasma. The vacuum vessel 10 is generally configured. The heater 11 and the plasma electrode 12 are spaced apart so as to face each other, and a target T having a composition corresponding to the composition of the film formed on the plasma electrode 12 is mounted. The plasma electrode 12 is connected to a high frequency power supply 13.

A gas introduction pipe 14 for introducing a gas G required for film formation into the vacuum container 10 and a gas discharge pipe 15 for exhausting the gas V in the vacuum container 10 are attached to the vacuum container 10. As the gas G, Ar, Ar / O ₂ mixed gas, or the like is used. As schematically shown in FIG. 1B, the 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 element Tp of the target T sputtered by the positive ions Ip is emitted from the target and deposited on the substrate 20 in a neutral or ionized state. In the figure, the symbol P indicates the plasma space.

  The potential of the plasma space P becomes the plasma potential Vp (V). Usually, the substrate 20 is an insulator and is electrically insulated from the ground. Therefore, the substrate 20 is in a floating state, and its potential is set to the substrate potential Vsub (V) (floating potential). The constituent element Tp of the target between the target T and the substrate 20 has a kinetic energy corresponding to an acceleration voltage of a potential difference Vp−Vsub between the potential of the plasma space P and the potential of the substrate 20, and the substrate 20 during film formation. It is thought that it will collide with.

The plasma potential Vp and the substrate potential Vsub can be measured using a Langmuir probe. When the tip of a Langmuir probe is inserted into the plasma P and the voltage applied to the probe is changed, for example, current-voltage characteristics as shown in FIG. 2 can be obtained (Mitsuharu Onuma, “Plasma and Film Formation Fundamentals” p. 90, published by Nikkan Kogyo Shimbun). In this figure, the probe potential at which the current becomes 0 is the floating potential, that is, Vsub. This state is that the ion current and the electron current flow into the probe surface become equal. The surface of the metal in the insulating state and the surface of the substrate are at this potential. As the probe voltage is made higher than the floating potential, the ionic current gradually decreases, and only the electron current reaches the probe. The voltage at this boundary is the plasma potential Vp.
Vp-Vsub can be changed by installing a ground between the substrate and the target.

  On the other hand, the film forming method of the present invention can also be implemented by a bias sputtering method in which a film is formed by applying a voltage to the substrate 20. In the case of using the bias sputtering method, the value of the voltage Vb applied to the substrate 20 does not become Vp−Vsub as it is, but the value of Vp−Vsub can also be controlled by Vb (see the examples described later). .

In the sputtering method using plasma, in addition to the Vp-Vsub value, the factors that influence the characteristics of the film to be formed include the film forming temperature, the type of the substrate, and the film previously formed on the substrate. Composition of substrate, surface energy of substrate, deposition pressure, oxygen content in ambient gas, input electrode, substrate / target distance, electron temperature in plasma, ion temperature and density, ion density, active species density in plasma In addition, the lifetime of the active species can be considered. However, regarding the sputtering rate, it is considered that the positive ion Ip colliding with the target T and the substrate 20 and the Vp-Vsub value that directly affects the kinetic energy of the target constituent element Tp are the factors that have the greatest influence. The present inventor has found that by optimizing the Vp-Vsub value, reverse sputtering can be suppressed and a film having desired characteristics can be formed.
Therefore, when forming a film that is likely to cause reverse sputtering, the present inventor has formed a film under plasma conditions in which reverse sputtering is unlikely to occur, that is, under plasma conditions in which the Vp-Vsub value is equal to or lower than the reverse sputtering threshold. Thus, even an element having a high sputtering rate can be formed without reverse sputtering. The element that is easily reverse sputtered may be one type or a plurality of types, but the Vp-Vsub value that is the threshold for reverse sputtering varies depending on the material, but most metal elements are 15 V to 30 V. It is a value within the range, most of which is 20V or less. Therefore, the film may be formed under the condition of the reverse sputtering threshold of all the elements that are easily reverse sputtered. However, the composition by reverse sputtering is sufficient if the element has the lowest binding energy and the threshold of reverse sputtering. It is possible to form a film having a desired composition and characteristics. Furthermore, if the Vp-Vsub value is 20 V or less, many metal elements are almost below the threshold value. Therefore, by reducing the composition due to reverse sputtering, the film is formed under the condition that satisfies the above formula (2). Thus, a film having a desired composition and characteristics can be formed.

  Further, the film formation temperature is also a factor affecting the easiness of sputtering, and the higher the film formation temperature, the higher the sputtering rate tends to be, but the present invention is not affected by the film formation temperature, Reverse sputtering can be suppressed (see Example 3 and FIG. 4 described later). Therefore, in the present invention, the film forming temperature is not limited.

  In the film forming method of the present invention, the other film forming conditions are such that the Vp-Vsub value is equal to or less than a threshold value at which the element having the lowest binding energy in the film is reverse sputtered, or the above formula (2) is satisfied. If it does, it will not restrict | limit in particular, However, It is preferable that the film-forming pressure is 10 Pa or less. When the film forming pressure is higher than 10 Pa, the rate at which particles knocked out of the target reach due to the influence of scattering or the like may decrease depending on the type of element. When such a phenomenon occurs, the composition shifts when reaching the substrate. Therefore, the film forming pressure is preferably 10 Pa or less. When the film forming pressure is 10 Pa or less, the plasma space becomes a condition between an intermediate flow and a molecular flow, which is an intermediate between the molecular flow and the viscous flow, so that the particles knocked out from the target are scattered before reaching the substrate. The possibility is negligible regardless of the type of element.

The sputtering method to which the film forming method of the present invention can be applied is not particularly limited as long as it is a sputtering method using plasma. For example, a bipolar sputtering method, a three-pole sputtering method, a direct current sputtering method, a high frequency sputtering method, an ECR sputtering method. , Magnetron sputtering, counter target sputtering, and pulse sputtering.
The substrate 20 is not particularly limited, and may be selected according to applications such as a Si substrate, an oxide substrate, a glass substrate, and various flexible substrates.

  The target T is not particularly limited as long as it includes all the constituent elements of the film to be formed. For example, in the case where the film to be formed is a complex oxide, a target or the like obtained by mixing and baking the respective oxides constituting the complex oxide may be used.

  The film forming method of the present invention can be applied to any film as long as it can be formed by a sputtering method using plasma. Whatever the type of film, if at least one metal element among the plurality of metal elements constituting the film is likely to be sputtered, reverse sputtering is likely to occur. The film forming method of the present invention can be applied regardless of film characteristics and film composition.

  The easiness of being sputtered is often expressed by the above-described sputtering rate, and the higher the sputtering rate, the easier it is to be sputtered. Here, the sputtering rate is defined by the ratio of the number of incident ions and the number of atoms sputtered thereby, and the unit is (atoms / ion).

  The inventor has focused on the correlation between the sputtering rate of metal elements and the binding energy. The bond energy means the total dissociation energy of all bonds of the molecule. Therefore, the smaller the single bond energy, the lower the dissociation, that is, the easier it is to be sputtered by the energy of collision of incident ions. become. Therefore, it is possible to determine whether or not the film is likely to cause the reverse sputtering phenomenon based on the value of the binding energy ratio of the constituent elements. That is, when the constituent elements of the film satisfy the above formula (1), at least a metal element whose binding energy is Emin is reverse-sputtered, and the composition in the film tends to decrease.

Table 1 shows the binding energy of the main metal simple substance. In the metal elements shown in Table 1, the binding energy of Zn, Pb, Bi, Ba, Se is particularly low. Like these elements, it is considered that a single element having a low binding energy is likely to be reverse sputtered. Therefore, when a film containing such an element is formed, the ratio with the binding energy of other metal elements contained in the film is calculated, and when the above formula (1) is satisfied, reverse sputtering is performed. By forming the film under conditions that are unlikely to occur, that is, conditions that satisfy the above formula (2), it is possible to form a film having substantially the same film composition as the target composition.

Among the elements with low binding energy exemplified above, Zn has the lowest binding energy. Zn is currently used as a constituent element of a transparent conductive film (semiconductor film) such as IGZO (InGaZnO ₄ ), and as already described, during the sputtering deposition of the Zn-containing transparent conductive film and the Zn-containing transparent semiconductor film. Similarly, there is a problem of Zn loss. Therefore, the film forming method of the present invention can be preferably applied to such a Zn-containing film.

Examples of the Zn-containing film include an oxide film containing a homologous compound represented by the following general formula (P2).
_{N x M y R z O (} x + 3y / 2 + 3z / 2) ··· (P2)
(Wherein R = In, M = In, Fe, Ga, Al, at least one element selected from the group consisting of N, Zn = xn, x, y, and z are real numbers greater than 0.)

Examples of the Zn-containing oxide film represented by the above formula (P2) include ZnIn ₂ O _{4 in} addition to InGaZnO ₄ (IGZO) already mentioned. For example, for IGZO, when the value of Emax / Emin is determined from the binding energy shown in Table 1, Emax / Emin = E _Ga / E _Zn = 2.1> 1.5, and the reverse sputtering phenomenon is likely to occur.

  When forming a Zn-containing oxide film represented by the above general formula (P2), the present inventor has a Zn composition lower than the target composition under film formation conditions that do not satisfy the above formula (2). It has been found that a film is formed (see Comparative Example 1 below).

As already described, the film forming method of the present invention can be applied to any film as long as it can be formed by a sputtering method using plasma. It is not restricted to the illustrated film. Although it is difficult to illustrate everything,
For example, a CuInCe film (Emax / Emin = E _Cu / E _In ≈1.54) used for an active layer of a solar cell, BaTiO ₃ (1.48 and 4.89, E _Ti / E _Ba ≈3) which is a piezoelectric material .30), BiFeO ₃ (E _Fe / E _Bi = 4.34 / 2.17≈, 2.00), Zn _1-x Al _x O (E _Al / E _Zn = 3.36 /) which is an optical functional material 1.35≈2.49), SrTiO ₃ (E _Ti / E _Sr = 4.89 / 1.70≈2.88), Ti _1-x Nb _x O ₂ (E _Nb / E _Ti = 7.59 / 4.89≈1.55).

   In the present invention, when a film is formed by a sputtering method using plasma using a composite target, the binding energy of the element having the highest binding energy of each individual metal element among all the metal elements contained in the film. When forming a film having a composition in which the ratio of Emax to the lowest element binding energy -Emin exceeds 1.5, the film forming conditions should be optimized so that the element having the binding energy Emin is not reverse sputtered. Thus, it is possible to form a film having a desired composition while suppressing a decrease in the composition of elements that are easily reverse sputtered. In the present invention, it is possible to identify a metal element that is easily reverse sputtered based on the ratio of the binding energy between the metal elements contained in the film, and to form the film under conditions that make it difficult for the metal element to be reverse sputtered. Therefore, according to the present invention, it is possible to form a film having a desired composition while suppressing a decrease in the composition of elements that are easily sputtered regardless of the type of film to be formed.

"Semiconductor device"
With reference to FIG. 3, a semiconductor device obtained by using a Zn-containing semiconductor film formed by the film forming method of the present invention and a manufacturing method thereof will be described. In the present embodiment, a bottom gate type will be described as an example. FIG. 3 is a manufacturing process diagram of a TFT (cross-sectional view in the thickness direction of the substrate). In order to facilitate visual recognition, the scale of the constituent elements is appropriately changed from the actual one.

   The semiconductor device (TFT) 4 of this embodiment includes an active layer 81 and electrodes (91, 93, 94) obtained by using a Zn-containing semiconductor film formed on a substrate 80 by the film forming method of the present invention. ).

First, as shown in FIG. 3A, a substrate 80 is prepared, and a gate electrode 91 made of n ⁺ Si or the like and a gate insulating film 92 made of SiO ₂ or the like are formed. Next, as shown in FIG. 3B, after the Zn-containing semiconductor film 81 is formed by the film-forming method of the present invention, the carrier concentration of the region that becomes the source region and the drain region of the Zn-containing semiconductor film 81 is adjusted. Thus, the active layer 81 of the TFT is formed. A region between the source region and the drain region becomes a channel region. Finally, as shown in FIG. 3D, the source electrode 93 and the drain electrode 94 are formed on the active layer 81 to manufacture the semiconductor device (TFT) 4 of this embodiment.

   The substrate 80 is not particularly limited, such as a glass substrate or a flexible substrate. Examples of flexible substrates include polyvinyl alcohol resins, polycarbonate derivatives (Teijin Limited: WRF), cellulose derivatives (cellulose triacetate, cellulose diacetate), polyolefin resins (Nippon ZEON Co., Ltd .: ZEONOR, ZEONEX), polysulfone series. Resin (polyethersulfone) norbornene resin (JSR Co., Ltd .: Arton), polyester resin (PET, PEN), polyimide resin, polyamide resin, polyarylate tree, polyether ketone, and the like. When a flexible substrate is used, the film formation temperature is determined in consideration of the heat resistance of the substrate 80.

The Zn-containing semiconductor film (active layer) 81 is formed by the film forming method of the present invention, and examples thereof include ZnIn ₂ O ₄ and InGaZnO ₄ (IGZO).

   The gate electrode 91 is preferably excellent in conductivity, and for example, Al, Cu, Ag, Au, Pt, and alloys thereof are preferably used. Further, it may be a non-metallic film having conductivity such as ITO (indium tin oxide).

The gate insulating film 92 is made of, for example, silicon oxide or silicon nitride such as SiO ₂ , SiNx, or SiOxNy, Al ₂ O ₃ , TiO ₂ , ZrO ₂ , Y ₂ O ₃ or the like from the viewpoints of insulation and dielectric properties. It is desirable to use a metal oxide, particularly silicon oxide or silicon nitride. The thickness of the gate insulating film 92 can be appropriately selected according to various conditions, and is preferably about 50 to 500 nm.

   Since the active layer 81 of the semiconductor device 4 is made of the Zn-containing semiconductor film manufactured by the film forming method of the present invention, Zn loss is suppressed and the composition is substantially the same as the target composition. Therefore, the semiconductor device 4 of the present embodiment includes the active layer 81 having good film characteristics, and has excellent element characteristics (such as carrier mobility).

(Design changes)
The present invention is not limited to the above-described embodiment, and the design can be changed as appropriate without departing from the spirit of the present invention.

Examples and comparative examples according to the present invention will be described.
Example 1
Using the sputtering apparatus shown in FIG. 1, using an InGaZnO ₄ target having a size of 120 mmφ under the conditions of a vacuum degree of 0.5 Pa and an Ar / O ₂ mixed atmosphere (O ₂ volume fraction 1.0%), IGZO A semiconductor film made of was formed. As described above, E _Ga / E _Zn = 2.1.

   A PEN substrate was used as the deposition substrate, the substrate temperature was set to room temperature (about 25 ° C.), the RF power was 200 W, the substrate / target distance was 60 mm, and a 20 V bias was applied to the substrate for deposition. When the state of the plasma in the vicinity of the substrate at this time (= about 10 mm from the substrate) was measured with a single probe, Vp = about 35 V, and thus Vp−Vsub (V) = about 10.

   When the composition of the obtained film was measured by X-ray fluorescence analysis (XRF), it was In: Ga: Zn = 1: 0.98: 0.98, and the film had substantially the same composition as the target composition. confirmed.

(Comparative Example 1)
An IGZO film was formed in the same manner as in Example 1 except that the substrate was set at a floating potential. At this time, the state of plasma in the vicinity of the substrate (= about 10 mm from the substrate) was measured with a single probe, and Vp−Vsub (V) = about 35V. The composition of the obtained film was measured in the same manner as in Example 1. As a result, In: Ga: Zn = 1: 0.91: 0.66, and the Zn composition decreased as compared with the target composition. It was confirmed that Here, although the composition of Ga is also slightly reduced, this is not due to reverse sputtering, but is thought to be due to evaporation caused by the low melting point of Ga, about 30 ° C.

(Example 2)
An IGZO film was formed on the Si substrate using the same target as in Example 1 under the conditions of a vacuum degree of 0.4 Pa and an Ar / O ₂ mixed atmosphere (O ₂ volume fraction of 2.5%). At this time, the RF power is 700 W, the distance between the substrate and the target is 120 mm, the substrate is in a floating state, and a ground is disposed at a position apart from the substrate that is not between the target and the substrate. The film was formed by changing the thickness. The plasma state in the vicinity of the substrate (= about 10 mm from the substrate) at this time was measured with a single probe, and Vp−Vsub (V) = about 20.

The composition ratio of the Zn-containing composite oxide film obtained when the film was formed at each substrate temperature was examined by XRF. The result is shown in FIG. In FIG. 4, the composition ratio is represented by the ratio of ZnO to In ₂ O ₃ . FIG. 4 shows that the composition of ZnO with respect to In ₂ O ₃ in the obtained film is in the range of 1.00 to 1.03 regardless of the substrate temperature. Therefore, it was confirmed that under the condition of Vp−Vsub (V) = about 20, a film having almost the same composition as the target and having almost no missing of Zn can be formed.

(Comparative Example 2)
In the same manner as in Example 1, using the sputtering apparatus shown in FIG. 1, ITO (100 mmφ in size) under the conditions of a vacuum degree of 0.5 Pa and an Ar / O ₂ mixed atmosphere (O ₂ volume fraction 1.0%). Using an indium tin oxide, composition (molar ratio) In: Sn = 0.95: 0.05) target, a piezoelectric film made of IGZO was formed. E _In / E _Sn = 1.4.

   A Si wafer is used as the deposition substrate, the substrate temperature is set to room temperature (about 25 ° C.), the RF power is 200 W, the substrate / target distance is 100 mm, the substrate is floated, and the substrate is not between the target and the substrate. The film was formed by arranging a ground at a remote location. When the plasma state in the vicinity of the substrate (= about 10 mm from the substrate) at this time was measured with a single probe, Vp−Vsub (V) = about 30.

   The composition of the obtained film was measured by X-ray fluorescence analysis (XRF). As a result, In: Sn = 0.95: 0.05 and substantially the same as the target composition even when the Vp-Vsub value was 20 V or more. It was confirmed that a film having the composition was formed.

20, 80 Substrate 40 Film T Composite target

Claims (6)

On a substrate, by using a composite target containing a plurality of metal elements by a sputtering method using plasma, including all the constituent elements included in the composite target, among all the metal elements included in the composite target, A Zn-containing film is formed in which the binding energy Emax of the element having the highest binding energy of the element and the binding energy Emin of the element having the lowest binding energy of the individual element satisfy the following formula (1). A method,
The potential difference between the plasma potential Vp (V) and the substrate potential Vsub (V) in the plasma during film formation is controlled to be equal to or lower than the threshold value at which the element having the lowest binding energy in the film is reverse sputtered. A film forming method characterized by forming a film.
Emax / Emin ≧ 1.5 (1) On a substrate, by using a composite target containing a plurality of metal elements by a sputtering method using plasma, including all the constituent elements included in the composite target, among all the metal elements included in the composite target, A Zn-containing film is formed in which the binding energy Emax of the element having the highest binding energy of the element and the binding energy Emin of the element having the lowest binding energy of the individual element satisfy the following formula (1). A method,
A film forming method characterized in that a film is formed under a condition that a plasma potential Vp (V) and a substrate potential Vsub (V) in plasma during film formation satisfy the following formula (2).
Emax / Emin ≧ 1.5 (1)
Vp−Vsub (V) ≦ 20 (2)    The film forming method according to claim 1, wherein a film having substantially the same composition as the composite target is formed.    The film forming method according to claim 1, wherein a potential voltage is controlled by applying a bias voltage to the substrate.    The film forming method according to claim 1, wherein the film is formed under a pressure of 10 Pa or less. The film forming method according to claim 1, wherein the film contains an oxide represented by the following general formula (P2).
_{N x M y R z O (} x + 3y / 2 + 3z / 2) ··· (P2)
(Wherein R = In, M = In, Fe, Ga, Al, at least one element selected from the group consisting of N, Zn = xn, x, y, and z are real numbers greater than 0.)