JP2009249655A - METHOD FOR FORMING Zn-CONTAINING COMPOSITE OXIDE FILM - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for forming a Zn-containing composite oxide film, which solves the problem of Zn omission, and can form the Zn-containing composite oxide film of high quality, which has a desired composition ratio. <P>SOLUTION: The method for forming the Zn-containing composite oxide film is directed at forming the film on a substrate to be film-formed which is placed at a position separated from a target, by depositing a material composing the target placed on a target holder with the use of a sputtering technique using plasma includes controlling a potential difference Vs-Vf (V) between a plasma potential Vs (V) and a floating potential Vf (V) in the plasma generated for forming the film to a threshold value or less, at which Zn in the formed film is reversely sputtered. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for forming a Zn-containing composite oxide film by sputtering.

  A transparent conductive film having high visible light transmittance and low resistance is indispensable as a coating material having various displays such as organic EL displays and thin film solar cells, or an ultraviolet blocking property and an infrared reflection property. Currently, the most widely used transparent conductive film is a metal oxide film, tin oxide (SnO2) having high chemical stability, and tin-doped indium oxide with excellent electrical and optical characteristics. (SnO2-In2O3, so-called ITO), recently, transparent conductive films such as zinc oxide (ZnO) based on excellent electrical and optical properties comparable to ITO, low cost and abundant resources It has been.

  As a method for forming a transparent conductive film, various methods such as a sputtering method, a spray method, a normal pressure or reduced pressure CVD method, a vapor deposition method, and an electrodeposition method are known. In particular, in the sputtering method, high energy plasma 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 released thereby are formed on the film formation substrate. The film can be deposited by depositing on the surface of the film, can be formed with high adhesion, the film thickness can be controlled with high precision only by the film formation time, can be formed even with a high melting point material, and the composition of the target material It has the advantage that it can be formed without changing the ratio, and is widely used.

However, when forming a transparent conductive film made of a metal oxide film as described above, it is very difficult to control the composition. Therefore, a method for forming a high-quality transparent conductive film is desired. For example, Patent Documents 1 and 2 describe that a transparent conductive film having good conductivity, transparency, and smoothness can be obtained by well controlling the amount of oxygen vacancies in the transparent conductive film.
JP 2006-249554 A JP 2006-342371 A

  However, when a Zn-containing composite oxide film such as a ZnO-based transparent conductive film is formed by sputtering, the ratio of Zn that has a high vapor pressure and is easily sputtered out of the composition ratio of the formed film is the target. There is a peculiar problem that the composition ratio of the raw material is lowered (so-called Zn loss). This phenomenon is prominent when the temperature of the deposition substrate is high.

  This causes not only the variation of the structure of the Zn-containing composite oxide film but also the deterioration of the film quality when films are formed at different film formation substrate temperatures.

  The present invention has been made in view of the above problems, and can suppress the above-described Zn loss and can form a high-quality Zn-containing composite oxide film having a desired composition ratio. An object of the present invention is to provide a method for forming an oxide film.

  In the vapor phase growth sputtering method using plasma, the factors that influence the characteristics of the film to be formed include the substrate temperature, the type of substrate (influenced by the structure and surface energy of the substrate), and the film formed on the substrate first. If there is a film, the composition of the substrate, the deposition pressure, the amount of oxygen in the atmospheric gas, the input power, the substrate / target distance, the electron temperature and electron density in the plasma, the active species density in the plasma and the lifetime of the active species, etc. Conceivable. Among the many film formation factors, the inventor of the present invention has characteristics of a film to be formed such that the substrate temperature and the potential difference Vs−Vf (V) between the plasma potential Vs (V) and the floating potential Vf (V) are two. The inventors have found that it depends greatly on two factors, and by focusing on these factors, attention has been paid to the fact that a high-quality film can be formed, leading to the present invention.

That is, the method for forming a Zn-containing composite oxide film of the present invention is as follows.
In a method for forming a Zn-containing composite oxide film, in which a constituent material of a target on a target holder is formed on a deposition substrate located at a position separated from the target by sputtering using plasma,
The potential difference Vs−Vf (V) between the plasma potential Vs (V) in the plasma during film formation and the floating potential Vf (V) is set to be equal to or less than a threshold value at which Zn in the formed film is reverse sputtered. The film is formed by controlling.

  Further, “plasma potential Vs” and “floating potential Vf” in the plasma during film formation mean those measured by a single probe method using a Langmuir probe. The floating potential Vf is measured in the shortest possible time by placing the tip of the probe in the vicinity of the film formation substrate (about 10 mm from the substrate) so as not to include an error due to the film being deposited on the probe. Shall. The potential difference Vs−Vf (V) between the plasma potential Vs and the floating potential Vf 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).

  Furthermore, in the method for forming a Zn-containing composite oxide film according to the present invention, it is preferable to form a film having substantially the same composition as the target, and the potential difference Vs−Vf is controlled by setting a gap for the passage of the film forming gas. It is preferable to surround the outer periphery of the target holder on the film formation substrate side with a shield composed of a plurality of shield layers that are stacked and change in number, and the number of the plurality of shield layers is changed.

  Here, “substantially the same composition” means that the difference between the composition ratio in the film of Zn with respect to the metal element other than Zn that is most difficult to be sputtered and the composition ratio in the target is within 3%. Means that.

  The potential difference Vs−Vf is preferably controlled to 30 V or less, and more preferably 20 V or less in this case.

  Further, the present invention can be applied even when the substrate temperature of the deposition substrate in forming the Zn-containing composite oxide film is 100 ° C. or higher and 500 ° C. or lower.

  Furthermore, the Zn-containing composite oxide film preferably contains In and / or Ga, and more preferably a transparent conductive film.

  Here, the “substrate temperature” means the surface temperature at the center of the film formation substrate.

  The “transparent conductive film” means a film having a light transmittance of 70% or more and a resistivity of 1 Ω · cm or less excluding the surface reflectance.

  Japanese Patent Application Laid-Open No. 2004-197178 discloses a transparent conductive film in which a transparent conductive 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 a sputtering method. A manufacturing method is disclosed, and a Zn-containing composite oxide film is cited as a transparent conductive film. Therefore, it is known to form a Zn composite oxide film by controlling the Vs−Vf value.

  However, Japanese Patent Application Laid-Open No. 2004-197178 aims to improve the wear resistance of a general transparent conductive film, and has found a Vs-Vf value that does not inhibit crystal growth in order to improve the wear resistance. is there. In contrast, according to the present invention, it is possible to form a Zn-containing composite oxide film having a desired composition with good reproducibility by suppressing Zn loss from the formed film. In JP-A-2004-197178, since a transparent conductive film other than a Zn-containing composite oxide film is targeted, suppression of Zn loss peculiar to a Zn-containing composite oxide film cannot exist as a problem, and is also described There is no suggestion. Therefore, the method for producing a Zn-containing composite oxide film of the present invention has not been easily invented from Japanese Patent Application Laid-Open No. 2004-197178.

  In the method for forming a Zn-containing composite oxide film according to the present invention, a potential difference Vs−Vf (V) between a plasma potential Vs (V) and a floating potential Vf (V) in plasma during film formation was formed. It is controlled below the threshold at which Zn in the film is reverse sputtered. Thereby, the kinetic energy of plasma ions and sputtered particles can be controlled, and reverse sputtering of Zn that has a high vapor pressure and is easily sputtered can be suppressed. As a result, it is possible to form a high-quality Zn-containing composite oxide film having a desired composition ratio while suppressing the loss of Zn.

  Hereinafter, although an embodiment of the present invention is described using a drawing, the present invention is not limited to this.

"Method for forming Zn-containing composite oxide film"
The Zn-containing composite oxide film forming method of the present invention is a Zn-containing composite oxide film in which a constituent material of a target on a target holder is formed on a deposition substrate at a position separated from the target by sputtering using plasma. In the method of forming a physical film,
The potential difference Vs−Vf (V) between the plasma potential Vs (V) in the plasma during film formation and the floating potential Vf (V) is controlled to be equal to or lower than the threshold value at which Zn in the formed film is reverse sputtered. A film is formed.

  In the case of “Background Art”, when a Zn-containing composite oxide film is formed by sputtering, the proportion of Zn in the composition ratio of the formed film is lower than the composition ratio of the target. It has been stated that Zn loss is likely to occur. This is because Zn which has a high vapor pressure and is easily sputtered is sputtered on the surface of the formed film (reverse sputtering). When Zn is released on the film surface, the film composition and the film surface state change, so that it is difficult to obtain a good film, and therefore, it is difficult to obtain good film characteristics. In the present invention, by controlling Vs−Vf (V) to be equal to or less than a threshold value at which Zn in the formed film is reversely sputtered, a Zn-containing composite oxide film is formed while suppressing Zn loss.

  When the film is formed by the sputtering method, the threshold value for reverse sputtering varies depending on the substance, but is about 15V to 30V. Considering the potential difference Vs−Vf (V) at which the Zn-containing composite oxide film is reverse sputtered, Vs−Vf is preferably 30 V or less, and more preferably 20 V or less. When the Vs-Vf value is 20 V or less, a film having almost the same composition as the target with almost no Zn loss can be obtained.

  Further, in the film forming method of the present invention, the substrate temperature is not particularly limited, and Zn can be effectively suppressed even in film formation at a high temperature at which Zn is more easily released. For example, the present invention can be applied to high-temperature film formation where the substrate temperature is 100 ° C. or higher and 500 ° C. or lower. In consideration of the manufacturing process as a device, the substrate temperature is preferably close to the film formation temperature (temperature in the film formation furnace, substrate temperature, etc.) when forming another film. Therefore, for example, when a Zn composite oxide film is formed on a device that simultaneously includes a film that needs to be formed at a high temperature of about 300 ° C., it is possible to form the film while suppressing the loss of Zn.

Since the film-forming method of the present invention forms a high-quality film by suppressing the loss of Zn during film formation in the Zn-containing composite oxide film, all films made of composite oxide containing Zn ( (It may contain inevitable impurities). For example, examples of the Zn-containing composite oxide film include homologous compounds such as ZnIn ₂ O ₄ and InGaZnO ₄ (IGZO) represented by the following general formula.
General _{formula: Zn x M y In z O} (x + 3y / 2 + 3z / 2-d)
(Wherein M is at least one element selected from the group consisting of In, Fe, Ga, and Al, x, y, and z are real numbers greater than 0, d is the amount of oxygen deficiency, and 0 ≦ d ≦ (x + 3y / (2 + 3z / 2) / 10)

  The Zn-containing composite oxide film is preferably a transparent conductive film, which enables application to transparent electronic devices such as transparent thin film transistors.

  In the present invention, 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. However, Japanese Patent Application No. 2006-263881 filed earlier by the present applicant (not disclosed at the time of the present application). ), The plasma space potential can be adjusted by a simple method. This sputtering film forming apparatus includes a shield that surrounds the outer periphery of the target holder that holds the target on the film forming substrate side, and adjusts the potential state of the plasma space by the presence of the shield.

Hereinafter, an embodiment of a method for forming a Zn-containing composite oxide film according to the present invention will be described by taking as an example the case of using the film forming apparatus described in Japanese Patent Application No. 2006-263881.
FIG. 1A is a schematic cross-sectional view of a sputtering film forming apparatus used in the method for forming a Zn-containing composite oxide film of the present embodiment, and FIG. 1B is a diagram schematically showing a state during film formation.

  As shown in FIG. 1A, a sputter deposition apparatus 200 includes a substrate holder 11 such as an electrostatic chuck that can hold a deposition substrate B and heat the deposition substrate B to a predetermined temperature, and plasma that generates plasma. An electrode (cathode electrode) 12 is schematically constituted by a vacuum vessel 210 provided therein. The plasma electrode 12 corresponds to a target holder that holds the target T.

  The substrate holder 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 to be formed on the plasma electrode 12 is mounted. The plasma electrode 12 is connected to a high frequency power supply 13. The plasma electrode 12 and the high-frequency power source 13 are referred to as a plasma generation unit. The sputter deposition apparatus in this embodiment includes a shield 250 that surrounds the outer periphery of the target T on the deposition substrate B side. In addition, this structure can also be said to include the shield 250 surrounding the outer periphery of the plasma electrode 12 holding the target T, that is, the target holder on the film formation substrate side.

  In the present embodiment, the film formation substrate B is not particularly limited, and may be selected according to applications such as a Si substrate, a glass substrate, and various flexible substrates. In the case of a flexible substrate, the film forming temperature needs to be lower than the heat resistant temperature of the substrate. For example, as a flexible substrate, polyvinyl alcohol resin, polycarbonate derivative (Teijin Limited: WRF), cellulose derivative (cellulose triacetate, cellulose diacetate), polyolefin resin (Nippon Zeon Co., Ltd .: ZEONOR, ZEONEX), polysulfone resin (Polyethersulfone) Norbornene resin (JSR Co., Ltd .: Arton), polyester resin (PET, PEN), polyimide resin, polyamide resin, polyarylate tree, polyether ketone and the like.

The target T is not particularly limited as long as it includes all the constituent elements of the Zn-containing composite oxide film to be formed. If a target obtained by mixing and firing each oxide constituting the composite oxide is used. Good. For example, in the case of forming an IGZO film, ZnO, Ga ₂ O ₃ , In ₂ O ₃ powder mixed and baked at 1250 ° C. can be used.

  The vacuum vessel 210 is provided with a gas introduction pipe 214 for introducing a film forming gas G necessary for film formation into the vacuum container 210 and a gas exhaust pipe 15 for exhausting the film forming gas G in the vacuum container 210. It has been. The gas inlet 214 for introducing the film forming gas G is provided at the same height as the shield 250 on the side opposite to the gas exhaust pipe 15.

As the film forming gas G, Ar, Ar / O ₂ mixed gas, or the like is used. As schematically shown in FIG. 1B, the film-forming gas G introduced into the vacuum vessel 210 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 emitted from the target and deposited on the deposition substrate B 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 Vs (V) in the plasma during film formation. Usually, the film formation substrate B is an insulator and is electrically insulated from the ground. Therefore, the film formation substrate B is in a floating state, and the potential thereof is a floating potential Vf (V). Due to the acceleration voltage of the potential difference Vs−Vf (V) between the potential of the plasma space P and the film formation substrate B, the sputtered particles Tp between the target T and the film formation substrate B obtain kinetic energy and form. It collides with the film formation substrate B in the film, and is deposited as a Zn-containing composite oxide film. Since the kinetic energy E is generally expressed as a function of the temperature T as shown in the following equation, Vs−Vf is considered to have the same effect as the temperature on the film formation substrate B.
E = 1 / 2mv ² = 3 / 2kT
(Where m is mass, v is velocity, k is a constant, and T is absolute temperature.)
Further, Vs−Vf is considered to have effects such as the effect of promoting surface migration and the effect of etching weakly bonded portions in addition to the same effect as temperature.

  The plasma potential Vs and the floating potential Vf 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. 3 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 value is 0 is the floating potential Vf. This state is that the ion current and the electron current flow into the probe surface become equal. The surface of the metal in an insulating state and the surface of the film formation substrate B are at this potential. As the probe voltage is made higher than the floating potential Vf, the ionic current gradually decreases, and only the electron current reaches the probe. The voltage at this boundary is the plasma potential Vs.

  1A is further provided with a shield 250 that surrounds the outer periphery of the target T on the film formation substrate B side.

  The shield 250 is disposed on the bottom surface 210a of the vacuum vessel 210 so as to surround the outer periphery of the target T on the film-forming substrate B side on an earth shield, that is, a grounding member 202 erected so as to surround the plasma electrode 12. Yes. Thereby, the shield 250 is electrically connected to the ground member 202 and grounded, and a ground potential is formed.

  The ground member 202 is for preventing discharge to the vacuum vessel 210 from the plasma electrode 12 to the side or downward.

  As an example, the shield 250 is composed of a plurality of annular metal plates or rings (shield layers) 250a as shown in FIGS. 1A and 2. Four of these rings 250a are used in the illustrated example, and conductive spacers 250b are disposed between the rings 250a (FIG. 2).

  Since the rings 250a are stacked as a shield layer simply through the spacers 250b, the number of the rings 250a can be changed by removing the rings 250a. Further, the lowermost ring 250a of the shield 250 is separated from the outer periphery of the target T. However, if the distance between the target T and the shield 250 is zero, no discharge occurs, and the far distance is long. If it is too large, the effect of the shield is reduced. Therefore, in order to obtain the effect efficiently, it is desirable that the distance is about 1 mm to 30 mm.

  A plurality of spacers 250b are arranged at intervals in the circumferential direction of the ring 250a, and a gap 204 is formed between the spacers 250b so that the deposition gas G can easily flow. From this point of view, the spacer 250b is preferably disposed between the grounding member 202 and the ring 250a placed immediately above the grounding member 202.

  The material of the ring 250a and the spacer 250b is not particularly limited, and SUS (stainless steel) or the like is preferable.

  It is good also as a structure which attaches the conduction | electrical_connection member which electrically connects the some ring 250a to the outer peripheral side of the shield 250. FIG. The rings 250a of the shield 250 are electrically connected to each other by the conductive spacer 250b and can be grounded by itself. However, by separately attaching a conductive member to the outer peripheral side, it becomes easy to ground the plurality of rings 250a. .

  The shield 250 is composed of a plurality of rings 250a arranged in the vertical direction so that the gap 204 is formed by the spacer 250b. This has the following two advantages.

  One is that the shield function of the shield 250 can be maintained for a long time.

  The sputtered particles Tp emitted from the target T adhere to the deposition substrate B and also to the ring 250a of the shield 250 around the target T. The most adhering amount is the inner peripheral edge 251 facing the target T of the ring 250a and its vicinity. This state is shown in FIG. As shown in FIG. 2, the sputtered particles Tp adhere to the inner edge 251 of the ring 250a and the upper and lower surfaces of the ring 250a in the vicinity thereof to form a film 253. If the film 253 is formed on the entire surface of each ring 250a, the function of the shield 250 as the ground potential is impaired. Therefore, the shield 250 is preferably configured so that the film 253 is not attached as much as possible.

  Therefore, by forming the gap 204 in the shield 250, it is possible to prevent the sputtered particles Tp from adhering to the entire shield 250 and changing its potential state. Therefore, the shield 250 functions stably even when repeated film formation is performed, and the potential difference Vs−Vf between the plasma potential Vs and the floating potential Vf is stably maintained.

  In particular, the width of each ring 250a that is a shield layer (that is, the length obtained by subtracting the inner diameter from the outer diameter of the ring 250a, which is the thickness of the wall material of the shield 250 orthogonal to the stacking direction) L, and the shield The distance between the layers (that is, the distance between the rings 250a adjacent to each other in the stacking direction) S is preferably in a relationship of L> S. Accordingly, there is an effect that the thickness L is expanded within a predetermined range with respect to the distance S between the rings 250a, and the film 253 is difficult to adhere to the entire ring 250a. That is, by increasing the depth of the ring 250a, it is possible to prevent the sputtered particles Tp from entering the outer periphery of the gap 204 and prevent the shield 250 from functioning in a short period of time.

  The other is that the gap 204 serves as a passage for the deposition gas G. As a result, the deposition gas G easily passes through the gap 204 of the shield 250 and reaches the plasma space P near the target T. Accordingly, gas ions converted into plasma in the vicinity of the target T can easily reach the target T, and the sputtered particles Tp can be effectively released. As a result, a high-quality film having desired characteristics can be stably formed.

  In the case of using the sputter deposition apparatus 200 described above, the Zn-containing composite oxide film deposition method of the present invention introduces the deposition gas G after evacuating the interior of the vacuum vessel 210, Plasma is generated by supplying high-frequency power, and a potential difference Vs−Vf (V) between the plasma potential Vs (V) and the floating potential Vf (V) in the plasma at the time of film formation is determined as Zn in the formed film. Is controlled so as to be equal to or lower than the threshold value for reverse sputtering, and the target T is sputtered by accelerating the film-forming gas G (plasma ions) ionized by plasma with a high voltage of potential difference Vs−Vf. The sputtered particles Tp that have been knocked out are deposited on the film formation substrate B to form a film.

  In the present embodiment, the plasma potential Vs (V) and the floating potential Vf (V) are surrounded by the shield 250 having the above-described configuration surrounding the outer periphery of the target holder 12 on the film formation substrate B side and having the gap 204 through which the film formation gas G passes. Vs−Vf (V), which is a potential difference with respect to (), is adjusted and optimized. This utilizes the fact that the potential difference Vs−Vf tends to decrease as the number of the rings 250a increases and the height of the entire shield 250 increases.

  Although details will be described later, FIG. 4 shows the tendency (see Example 1 described later). This shows that the potential difference Vs−Vf decreases as the number of rings 250a increases. This is presumably because the potential difference Vs−Vf decreases because the discharge between the shield 250 and the target T becomes stronger as the overall height of the shield 250 increases. Furthermore, it is considered that since the shield 250 is grounded, the spread of plasma is suppressed by the shield 250, and as a result, the potential difference Vs−Vf between the plasma potential Vs and the floating potential Vf can be reduced.

  FIG. 4 shows that the potential difference Vs−Vf can be controlled between about 45 and 20 V by changing the number of rings 250a between 0 and 8. As described above, in the present invention, the Vs−Vf value is controlled to be equal to or lower than the threshold value at which Zn is reversely sputtered. Therefore, the number of rings 250a may be changed so that the Vs-Vf value is equal to or less than the threshold value for reverse sputtering of Zn.

  When a voltage of the high frequency power supply 13 is applied to the plasma electrode 12 to form a film on the film formation substrate B, plasma is generated above the target T and discharge is also generated between the shield 250 and the target T. It is considered that the plasma is confined in the shield 250 by this discharge, the plasma potential Vs is lowered, and the potential difference Vs−Vf (V) is lowered.

  And according to said result, Zn omission can be suppressed by reducing potential difference Vs-Vf.

  For example, consider a case where an IGZO film is formed. The sputtering rate of In and Zn under certain conditions is 0.8 for In and 2.0 for Zn. 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). In other words, Zn is more likely to be sputtered twice or more than In.

When InZnGaO ₄ is used as a target when depositing IGZO, if the target is a homogeneous target, only Zn is sputtered with substantially the same composition without being preferentially sputtered on the target. This is because even if Zn is preferentially sputtered at a certain moment, Zn is deficient on the target surface at this time, and the other target composition is sputtered at the next moment. On the other hand, on the film surface, film deposition and reverse sputtering of constituent materials in the already deposited film can occur simultaneously. At this time, if the potential difference Vs−Vf is high, that is, if the kinetic energy of the sputtered particles colliding with the film formation substrate is large, Zn having a high sputtering rate is reverse sputtered by the collision of the sputtered particles and knocked out from the surface of the film formation substrate. . That is, this becomes a factor of Zn loss. Therefore, by reducing the potential difference Vs−Vf, the kinetic energy when the sputtered particles collide with the film formation substrate is reduced, and by suppressing the reverse sputtering of Zn on the film formation substrate surface, Zn escape is suppressed. Can do it.

  The potential difference Vs−Vf can also be adjusted by changing the target input power, the film forming pressure, and the like. However, when the potential difference Vs−Vf is controlled by changing the target input power, the film forming pressure, or the like, other parameters such as the film forming speed may change, and the desired film quality may not be obtained. When the present inventor conducted an experiment under certain conditions, the potential difference Vs−Vf can be reduced from 38 V to 25 V when the target input power is changed from 700 W to 300 W, but the film formation speed is reduced from 4 μm / h to 2 μm / h. have done. In the sputter deposition apparatus 200 of the present embodiment, the potential difference Vs−Vf can be adjusted without changing other parameters such as the deposition rate. Therefore, it is easy to optimize the deposition conditions, and stable high-quality films can be obtained. It can be formed into a film.

  As described above, the potential difference Vs−Vf (V) between the plasma potential Vs (V) in the plasma at the time of film formation and the floating potential Vf (V) is set to be equal to or lower than the threshold value at which Zn in the formed film is reverse sputtered. By controlling so that the kinetic energy of plasma ions and sputtered particles is controlled, reverse sputtering of Zn having a high sputtering rate can be suppressed. As a result, it is possible to form a high-quality Zn-containing composite oxide film having a desired composition ratio while suppressing the loss of Zn.

<Example 1>
As shown in FIG. 1A, a commercially available sputter deposition apparatus 200 is prepared, and a stainless steel (SUS) ring 250 a having an inner diameter of 130 mmφ, an outer diameter of 180 mmφ, and a thickness of 1 mm is placed on the sides of a 120 mmφ target T. 2, 5 and 8 were installed at ground potential, and the value of the potential difference Vs−Vf (V) between the plasma potential Vs (V) and the floating potential Vf (V) for each number of rings 250a was measured.

  Each ring 250a was laminated via a columnar conductive spacer 250b having a diameter of 10 mmφ and a thickness of 5 mm. Since the spacer 250b is sufficiently smaller than the size of the ring 250a, the film forming gas G introduced into the vacuum vessel 210 passes through the gap 204 of the ring 250a and becomes the target T without being affected by the spacer 250b. Can be reached easily.

  An oxide sintered body of In: Zn: Ga (molar ratio) = 1.0: 1.0: 1.0 was used as the target T, and a Si wafer with a thermal oxide film was used as the deposition substrate B. The distance between the film formation substrate B and the target T was 12 mm, and 700 W was applied to the high-frequency power source under the conditions of a vacuum degree of 0.4 Pa and an Ar / O 2 mixed atmosphere (O 2 volume fraction 2.5%). When the potential difference Vs−Vf was measured under the above conditions, it was as shown in FIG.

  In the state without the ring 250a, the potential difference Vs−Vf = 43V. However, as the number of rings 250a is increased from one to two, the potential difference decreases, with Vs−Vf = 33V for two, Vs−Vf = 22V for five, and Vs−Vf = 20V for eight. . As described above, when the number of the rings 250a is increased, the potential difference Vs−Vf is decreased, and it is shown that the potential difference Vs−Vf can be controlled by changing the number of the rings 250a.

Therefore, the composition of the Zn-containing composite oxide film obtained when the number of rings 250a is 8 and the potential difference is Vs−Vf = 20V, the substrate temperature is changed from room temperature to 300 ° C., and the film is formed at each substrate temperature. The ratio was examined. The result is shown in FIG. 5, and the composition ratio is represented by the ratio of ZnO to In ₂ O ₃ . The composition ratio is measured by a fluorescent X-ray analysis (XRF) apparatus.

From FIG. 5, since 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, there is almost no loss of Zn, that is, almost the same composition as the target. It can be seen that a Zn-containing composite oxide film is formed.

  In addition, data in the case of Vs−Vf = 43V without using a ring is also shown. At this time, the composition ratio of Ga was constant.

<Example 2>
Measurement was performed under the same conditions as in Example 1 except that the number of rings 250a was two and Vs−Vf = 33V. The result is shown in FIG. 6, and the composition ratio is represented by the ratio of ZnO to In ₂ O ₃ . In addition, data in the case of Vs−Vf = 43V without using a ring is also shown. At this time, the composition ratio of Ga was constant.

From these examples, it can be seen that in the case of Vs−Vf = 20V, the ratio of ZnO to In ₂ O ₃ does not change compared to the case of Vs−Vf = 43V, and Zn loss is suppressed. Furthermore, since the ratio is almost stably 1.0, it can be seen that the film can be formed without changing the composition ratio of the target raw material. FIG. 7 shows the relationship between the substrate temperature and the surface resistance of the Zn-containing composite oxide film in this case. From this, it can be seen that variations in film characteristics can be suppressed by controlling the potential difference Vs−Vf using the ring 250a.

On the other hand, in the case of Vs−Vf = 33V, the ratio of ZnO to In ₂ O ₃ is hardly changed although it is not as much as in Example 1, and it can be seen that Zn loss is suppressed.

  As described above, by controlling the potential difference Vs−Vf (V) between the plasma potential Vs (V) and the floating potential Vf (V) in the plasma during film formation, Zn loss can be suppressed and a desired composition ratio can be obtained. It was proved that it was possible to form a Zn-containing composite oxide film.

(A) Schematic cross-sectional view of an RF sputtering film forming apparatus used in an embodiment of the present invention, (B) Schematic cross-sectional view showing a state during film formation Enlarged view of the shield and its vicinity Explanatory drawing showing the measurement method of plasma potential and floating potential Diagram showing the relationship between the number of rings and the potential difference between plasma potential and floating potential The figure which shows the relationship (Vs-Vf = 20V) of the composition ratio of Zn with respect to substrate temperature and In. The figure which shows the relationship (Vs-Vf = 30V) of the composition ratio of Zn with respect to substrate temperature and In. The figure which shows the relationship (Vs-Vf = 20V) of a substrate temperature and the surface resistance of Zn containing complex oxide film.

Explanation of symbols

11 Substrate holder 12 Plasma electrode (target holder)
13 High-frequency power supply 15 Gas exhaust pipe 200 Sputter deposition apparatus 202 Grounding member 204 Gap 210 Vacuum vessel 210a Vacuum vessel bottom surface 214 Gas inlet 250 Shield 250a Ring (shield layer)
250b Spacer 330 Control power source B Film formation substrate G Film formation gas Ip Plus ion L Thickness P Plasma space T Target Tp Sputtered particle Vf Floating potential Vs Plasma potential V Gas exhaust S Distance

Claims (8)

In a method for forming a Zn-containing composite oxide film, in which a constituent material of a target on a target holder is formed on a deposition substrate at a position separated from the target by sputtering using plasma,
The potential difference Vs−Vf (V) between the plasma potential Vs (V) in the plasma during film formation and the floating potential Vf (V) is set to be equal to or less than a threshold value at which Zn in the formed film is reverse sputtered. A method for forming a Zn-containing composite oxide film, comprising forming a film under control.   The method for forming a Zn-containing composite oxide film according to claim 1, wherein a film having substantially the same composition as the target is formed.   The control of the potential difference Vs−Vf is performed on the film formation substrate side of the target holder by a shield composed of a plurality of shield layers that are stacked with a gap for passage of film formation gas and can be changed in number. The method for forming a Zn-containing composite oxide film according to claim 1, wherein the method is performed by surrounding the outer periphery and changing the number of the plurality of shield layers.   4. The method for forming a Zn-containing composite oxide film according to claim 1, wherein the potential difference Vs−Vf is controlled to 30 V or less. 5.   The method for forming a Zn-containing composite oxide film according to claim 4, wherein the potential difference Vs−Vf is controlled to 20 V or less.   6. The Zn-containing composite oxide according to claim 1, wherein a substrate temperature of the deposition substrate when forming the Zn-containing composite oxide film is 100 ° C. or more and 500 ° C. or less. A film forming method.   The method for forming a Zn-containing composite oxide film according to claim 1, wherein the Zn-containing composite oxide film contains In and / or Ga.   The method for forming a Zn-containing composite oxide film according to claim 1, wherein the Zn-containing composite oxide film is a transparent conductive film.

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