JP6082165B2 - Metal film and method for forming metal film - Google Patents

Description

  The present invention relates to a low resistivity metal film formed by sputtering and a film forming method thereof.

  Ta is often used as a stable and low electrical resistance material in lead wiring used for magnetic heads in semiconductors and storage. Ta is known to have either an α structure or a β structure as a crystal structure at room temperature. The α structure is a body-centered cubic (bcc) structure, and bulk Ta often has an α structure. On the other hand, a thin film usually tends to have a β structure, which is a tetragonal structure of a metastable phase. The specific resistance of an α-structure Ta film (also referred to as α-Ta) is as low as about 13 to 20 μΩ · cm, whereas the specific resistance of a β-structure Ta film (also referred to as β-Ta) is about 170 to 200 μΩ · cm. And high. Therefore, it is desirable to use α-Ta rather than β-Ta for lead wiring that requires low electrical resistance.

  Since general wiring is thin, a thin Ta film is likely to be β-Ta. Special treatment is required to make the thin Ta film α-Ta. Conventionally, for example, when a semiconductor wiring is manufactured, in order to form a Ta film (α-Ta) having an α structure, TaN is formed as a base layer, and a Ta film is formed thereon. For example, when producing a lead wiring for a magnetic head, a bcc material is deposited as an underlayer, and a Ta film is deposited thereon. Thus, α-Ta can be formed by forming a predetermined underlayer and then forming a Ta film.

  In addition, the use of α-Ta for an ink jet type thermal head (recording head) has been studied. In the thermal head, a heating resistor that generates bubbles in the ink and wirings that are electrically connected to the heating resistor are formed at a high density on the same substrate.

  The base of the thermal head is desired to have a structure capable of efficiently generating heat in the heating resistor and at the same time reducing mechanical damage caused by the heat generation and chemical damage caused by ink contact. . Therefore, in a general thermal head substrate, the heating resistor connected to the wiring pattern is covered with a protective film, and the heating resistor conducts heat to the ink through this protective film, and bubbles are formed in the ink. Give rise to

  The protective film covering the heating resistor is a film that can withstand mechanical or chemical damage, and is required to have insulating properties to protect the wiring. Therefore, the protective film used for conventional general thermal heads is a highly stable upper film that can withstand mechanical damage caused by heat generation and chemical damage caused by ink, and an insulating lower film that protects wiring. Often has a two-layer structure. Specifically, for example, β-Ta, which has high chemical and mechanical stability, is used for the upper layer film, and a SiN film or SiO film that can be formed relatively easily by an existing semiconductor manufacturing apparatus is used for the lower layer film. It is done.

  In recent years, there has been an increasing demand for high-speed output of high-quality digital images comparable to silver halide photographs in inkjet printers, and various recording technologies have been developed to further improve recording density and recording speed. Yes. In thermal heads as well, ink droplets are reduced, recording elements are densified, and drive frequencies are increased.

  Under such circumstances, a thermal head substrate using a conventional general two-layer protective film may not have sufficient thermal conductivity, residual stress characteristics, and structural stability. For example, in order to increase the driving frequency, an immediate heat generation response of the heating resistor is required. Therefore, it is desirable that the protective film used for the thermal head is formed thin with a material having high thermal conductivity. On the other hand, from the viewpoint of protecting the substrate itself, the protective film is preferably formed thick. That is, it has been difficult for the conventional protective film to meet these two conflicting requirements.

  As described above, the Ta film includes the Ta film (α-Ta) having the α structure and the Ta film (β-Ta) having the β structure. Although β-Ta is used in the conventional general two-layer protective film, it is more suitable to use α-Ta having an α structure having a low specific resistance, that is, a high thermal conductivity.

  Several methods have been proposed as α-Ta film forming methods. In the technique described in Patent Document 1, a TiW film is formed on the entire surface of the β-Ta film formed by sputtering in addition to a portion other than the part corresponding to the heat generating part. Thereafter, TiW and the mask are etched, and α-Ta is obtained by causing phase transition of at least part of β-Ta corresponding to the heat generating portion.

  In the technique described in Patent Document 2, α-Ta is formed by sputtering in a state where a small amount of nitrogen gas is introduced. In the technique described in Patent Document 3, α-Ta is formed by sputtering Ta on a base film made of at least one element selected from an element group having a bcc crystal structure.

JP 2008-302625 A JP-T-2006-517614 JP-A-11-120525

  In the technique described in Patent Document 1, there is some variation in the accuracy of arrangement of the formed mask. If the difference between the position of the formed mask and the position of the heat generating portion is large, there is a problem that the high thermal conductivity of α-Ta cannot function effectively.

  The technique described in Patent Document 2 has a problem that process management is difficult because it is necessary to control a small amount of nitrogen gas pressure. Moreover, since not only α-Ta but also β-Ta is partially generated, or nitrogen gas and Ta react to generate TaN, the specific resistance of the obtained film may not be as expected. is there.

  In the technique described in Patent Document 3, since the specific resistance of the material of the base film formed under α-Ta is added, the specific resistance cannot be lowered sufficiently. Moreover, there is anxiety from the viewpoint of performance stability due to heat from the heat generating part.

  In order to form a protective film used for a thermal head, a method of directly forming α-Ta without forming a mask or a base film that can deteriorate the characteristics of the protective film is required. There is also a need for a method of forming α-Ta by reducing impurities such as nitrogen gas.

  The present invention has been made in view of the above-described technical problems, and has high thermal conductivity and structural stability that can be easily formed at a high yield at a low yield by a manufacturing process that is simplified compared to the prior art. An object of the present invention is to provide a metal film having the same and a film forming method thereof.

  A first aspect of the present invention is a film forming method for forming a Ta film on a substrate by sputtering, wherein VHF power and a first DC voltage are applied to the Ta target, and the Ta target is sputtered. 1 and Ta atoms sputtered from the Ta target in the first step are deposited on the substrate maintained at a first temperature to form a Ta film having a specific resistance of 60 μΩ · cm or less. And a second step of forming a film.

  A second aspect of the present invention is a Ta film, in which a VHF power and a first DC voltage are applied to a Ta target, the Ta target is sputtered, and the Ta step is performed in the first step. And having a specific resistance of 60 μΩ · cm or less formed by the second step of depositing Ta atoms sputtered from the target on the substrate maintained at the first temperature.

  According to the present invention, a Ta film having a low specific resistance of 60 μΩ · cm or less is formed by applying VHF power and a first DC voltage to a Ta target and performing sputtering, without forming a mask or an underlayer. (Α-Ta) can be formed.

It is a schematic block diagram of the film-forming apparatus which concerns on one Embodiment of this invention. It is a figure which shows the XRD measurement result of an Example and a comparative example. It is a figure which shows the XRD measurement result of an Example and a comparative example. It is a figure which shows the orientation and the change of FWHM with respect to VHF electric power. It is a figure which shows the change of the specific resistance with respect to VHF electric power, and the film-forming speed | rate. It is a figure which shows the relationship between a film thickness, temperature, and DC voltage. It is a figure which shows the relationship between a film thickness, temperature, and DC voltage. It is a figure which shows the change of the specific resistance with respect to Ta film thickness. It is sectional drawing of the thermal head manufactured by the manufacturing method which concerns on one Embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the embodiments. In the drawings described below, components having the same function are denoted by the same reference numerals, and repeated description thereof may be omitted.

(First embodiment)
FIG. 1 is a schematic configuration diagram of a film forming apparatus 100 according to the present embodiment. The film forming apparatus 100 includes a vacuum container 101 (chamber) to which an exhaust unit 102 such as a vacuum pump and a gas introduction unit 103 such as a mass flow controller (MFC) are connected. A gate valve 101a is provided on the side wall of the vacuum vessel 101. The vacuum vessel 101 can be sealed by closing the gate valve 101a, and the substrate S is opened via the gate valve 101a by opening the gate valve 101a. Can be carried in and out. In the vacuum vessel 101, a cathode 104 (cathode electrode) on which a Ta target T can be mounted and a substrate stage 105 on which a substrate S can be placed at a position facing the cathode 104 are provided.

  The cathode 104 is connected to a VHF power source 107 via a matching unit 106 and also connected to a superimposing DC power source 108. In this embodiment, the frequency of the VHF power source 107 is 60 MHz. The frequency of the VHF power source 107 is not limited to this value, and may be any high frequency from 20 MHz to 450 MHz.

  A magnet mechanism 104a is provided in the cathode. In the present embodiment, the magnet mechanism 104a is a PCM (Point Cusp Magnet). The PCM includes a large number of magnet pieces provided on a plate-like support, and each magnet piece has the same shape and the same magnetic flux density. The magnet pieces are arranged in a grid pattern at substantially the same intervals. Any two adjacent magnet pieces have opposite polarities when viewed from the target T side. On the other hand, in the quadrangle formed of any four adjacent magnet pieces, the polarities of the two magnet pieces along the diagonal direction viewed from the target T side are the same. With such an arrangement, a point cusp magnetic field is formed by any four adjacent magnet pieces.

  When PCM is used as the magnet mechanism 104a, the magnetic field strength on the surface of the target T is increased, and thereby the discharge impedance can be kept low. In addition, the magnetic field strength greatly decreases with distance from the target T, and a sufficiently weak magnetic field is formed in the vicinity of the substrate S, so that the influence of Ar ions on the substrate can be reduced. The magnet mechanism 104a is not limited to PCM, and an arbitrary shape such as a flat plate shape or a rod shape and an arbitrary number of magnets may be used.

  The substrate stage 105 includes a heating mechanism (not shown) connected to the heating power source 109 and a high temperature ESC (electrostatic adsorption) device (not shown) connected to the ESC power source 110. The substrate stage 105 is further connected to a bias power source 111 via a matching unit (not shown). In the present embodiment, the frequency of the bias power supply 111 is 13.56 MHz.

  Around a space between the cathode 104 and the substrate stage 105 (hereinafter referred to as a discharge space), a grounded shield 112 surrounding the cathode 104 on which the target T is mounted and the substrate stage 105 on which the substrate S is disposed. Is arranged. The shield 112 is configured so that part or all of the side walls can be driven. When the substrate S is taken in and out of the vacuum vessel 101 via the gate valve 101a, the substrate S is placed inside the shield 112 (that is, the discharge space). An opening 112a for introduction can be formed.

  In the film forming method executed using the film forming apparatus 100 according to this embodiment, first, a predetermined VHF power from the VHF power source 107 and a predetermined DC voltage from the DC power source 108 are made of Ta via the cathode 104. Applied to the target T, the target T is sputtered. Then, Ta atoms sputtered from the target T are deposited on the substrate S held at a predetermined temperature on the substrate stage 105 to form a Ta film.

  In the film forming method according to the present embodiment, the film forming process was performed under various conditions as described below, and various measurements were performed on the formed film.

Example 1
As Example 1 according to this embodiment, a film forming process was performed under the following conditions. First, the Ta target T was fixed to the cathode 104 by bonding, and the substrate S was placed on the substrate stage 105. As the substrate S, a 300 mm thermal oxide film substrate was used. The thermal oxide film of the substrate S is 100 nm, and its surface is an insulator.

  Next, the substrate S on the substrate stage 105 was heated to 370 ° C., Ar gas for processing was introduced from the gas introduction unit 103 at a flow rate of 100 sccm, and the pressure in the vacuum vessel 101 was set to 5 Pa. In this state, 500 W of 60 MHz VHF power was applied to the cathode 104 to start discharging. The discharge voltage at this time is −10 V or less, and is a potential at which sputtering hardly occurs.

  After ignition, the pressure in the vacuum vessel 101 is increased to 0.4 Pa below the ignition limit by adjusting the conductance valve of the exhaust unit 102 and increasing the exhaust speed without changing the Ar gas flow rate in a state where discharge is continued. Lowered. Thereafter, the VHF power applied to the cathode 104 was set to 1500 W, and a DC voltage of −50 V was superimposed on the cathode 104 to form a film for a predetermined time.

  During the film forming process, in order to keep the temperature of the substrate S at the set temperature, an ESC voltage of −600 V was applied to the substrate stage 105, and Ar gas for heat conduction was introduced to the back surface of the substrate S. In this embodiment, no bias voltage is applied to the substrate stage 105.

(Comparative Example 1)
As Comparative Example 1, a film forming process was performed under the following conditions. The temperature of the substrate S was room temperature (20 ° C.), the pressure in the vacuum vessel 101 was the same 2 Pa before and after discharge, the VHF power was 2000 W, and the DC voltage was −300 V. The other conditions were the same as those in Example 1 for film formation.

(Comparative Example 2)
As Comparative Example 2, the film was formed under the same conditions as in Example 1 except that the DC voltage was -200V.

(Measuring method)
The film thickness was measured by the X-ray reflectivity measurement method (XRR), and the sheet resistance was measured by a sheet resistance measuring instrument using a direct current 4-probe method, and the specific resistance value of the formed film was calculated. The crystal structure of the formed film was examined using an out-of-plane measurement by X-ray diffraction (XRD). The crystal grain size was observed with a planar TEM, and the grain size in the formed film was analyzed.

  From the measurement results of Example 1, it was confirmed that the film thickness was 80 nm and the specific resistance was 16 μΩ · cm, which is as low as the bulk. The crystal grain size (average equivalent circle diameter or average particle size) at this time was φ257 nm. On the other hand, in the measurement result of Comparative Example 1, the specific resistance was 170 μΩ · cm at a film thickness of 32 nm, which was about 10 times higher than that of Example 1. The crystal grain size at this time was φ8 nm. In the measurement result of Comparative Example 2, the specific resistance was 143 μΩ · cm, and the specific resistance was also about 10 times higher than Example 1.

  2A and 2B are diagrams showing the XRD measurement results of Example 1 and Comparative Examples 1 and 2. FIG. In FIG. 2A, the horizontal axis is the angle, and the vertical axis is the intensity. 2A, the graph of E1 shows the measurement result of Example 1, the graph of C1 shows the measurement result of Comparative Example 1, and the graph of C2 shows the measurement result of Comparative Example 2. FIG. 2B is a diagram showing the peak position with respect to the angle for Example 1 (E1) and Comparative Example 1 (C1) of FIG. 2A.

  In the XRD measurement result of Example 1 (E1) in FIG. 2A, a peak indicating the (110) plane of α-Ta having a bcc structure was strongly observed around 38.5 degrees. That is, it was confirmed that an α-Ta film can be formed by the film forming method according to the present embodiment.

  On the other hand, in the XRD measurement results of Comparative Example 1 (C1) and Comparative Example 2 (C2) in FIG. 2A, β-Ta peaks having a tetragonal structure (for example, (002) plane, (410) plane, etc.) are present. Many were seen.

  Next, the relationship between VHF power and various characteristics of the formed film was investigated. FIG. 3 is a diagram showing changes in orientation and half width (FWHM) when measurement is performed while changing only the VHF power among the conditions of Example 1. The horizontal axis in FIG. 3 is the VHF power, and the vertical axis is the orientation and the full width at half maximum (FWHM). FIG. 4 is a diagram showing changes in specific resistance and film formation rate when measurement is performed by changing only the VHF power among the conditions of Example 1. FIG. The horizontal axis in FIG. 4 is the VHF power, and the vertical axis is the specific resistance (Resistability) and the deposition rate (Deposition Rate). 3 and FIG. 4, an arrow attached to each graph indicates which vertical axis the graph corresponds to.

  The orientation in FIG. 3 represents the ratio of the peak intensity of the (110) plane to the peak intensity of the (200) plane of the XRD measurement result. A large value of this orientation indicates that the content of α-Ta which is a bcc structure in the Ta film is high. In FIG. 3, since the value of Ta (110) / Ta (200) is improved as the VHF power is increased, it was found that the orientation of Ta (110) can be improved by increasing the VHF power. The half width in FIG. 3 is calculated from the peak width of the XRD measurement result, and indicates the degree of variation in crystal spacing (lattice spacing). It is known that the larger the half width, the smaller the crystal grain size, and the smaller the crystal grain size, the greater the specific resistance. In FIG. 3, the full width at half maximum tends to decrease as the VHF power increases, and it was found that increasing the VHF power increases the crystal grain size.

  Furthermore, as shown in FIG. 4, it was found that by increasing the VHF power, the deposition rate can be increased while keeping the specific resistance low. That is, when the VHF power is increased, Ar ions increase and the cathode current increases. As a result, the cathode power increases even when the absolute value of the cathode voltage is kept low, so that the deposition rate can be increased.

  Next, the film forming conditions for obtaining α-Ta were investigated. Here, the measurement result of the Ta structure formed when the conditions are variously changed on the basis of the film formation conditions of the above-described Example 1 will be described. First, with respect to the film thickness, the specific resistance increased with decreasing thickness from 80 nm, and the specific resistance of the 20 nm film became equivalent to the specific resistance of β-Ta. Further, when the DC voltage superimposed on the 1500 W VHF power is decreased (that is, when the absolute value is increased), the ratio of β-Ta tends to increase, and at −300 V, the formed film is β−. It became Ta single phase. When the pressure in the vacuum vessel 101 was increased from 5 Pa, the ratio of β-Ta increased, and the film formed at a pressure of 10 Pa became a β-Ta single phase. When bias power was applied to the substrate stage 105, the ratio of β-Ta increased, and a β-Ta single phase was obtained at 300W. Moreover, it became difficult to become α-Ta when the substrate temperature (film formation temperature) was lowered, and became a β-Ta single phase at room temperature (20 ° C.). That is, by changing the film forming conditions, the crystal structure of Ta can be controlled between α-Ta and β-Ta.

  5 and 6 are diagrams showing whether α-Ta can be obtained for each combination of film thickness, DC voltage, and substrate temperature. FIG. 5 shows the results of measurement performed by forming a Ta film having a thickness of 70 nm, and FIG. 6 shows the results of measurement performed by forming a Ta film having a thickness of 30 nm. A Ta film having a low specific resistance of 60 μΩ · cm or less is considered to be a phase having a high α-Ta content. In FIGS. 5 and 6, a circle indicates a combination with a specific resistance of 60 μΩ · cm or less, and a triangle indicates a specific resistance of 60 μΩ · cm or less due to film formation pressure, bias voltage conditions, or adjustment of the stage configuration. The x mark is a combination having a specific resistance larger than 60 μΩ · cm.

  First, from FIG. 5 (range surrounded by a broken line), the conditions for α-Ta at a film thickness of 70 nm are that the film forming temperature is 300 ° C. or higher and the DC voltage is −150 V or higher. Further, from FIG. 6 (range surrounded by a broken line), the conditions for α-Ta at a film thickness of 30 nm are a film formation temperature of 370 ° C. or higher and a DC voltage of −100 V or higher. Further, it is common in FIGS. 5 and 6 that the higher the temperature and the larger the DC voltage (that is, the smaller the absolute value), the more likely α-Ta is obtained. From the above, it was found that α-Ta having a low resistance can be obtained by increasing the thickness of the film under the film formation conditions of a film formation temperature of 300 ° C. or higher and a DC voltage of −150 V or higher.

  Under general sputtering conditions, positively charged Ar ions are accelerated by cathode fall (Vdc) on the target side during the discharge, and the target is sputtered. Neutral Ar that has no electric charge due to sputtering is reflected by the surface of the target and reaches the substrate at high speed. This Ar is called recoil Ar. When the recoil Ar collides with the substrate at a high speed, Ar may be trapped in the film formed on the substrate. If the film contains a large amount of Ar, it tends to be β-Ta having a tetragonal structure and a large specific resistance.

  On the other hand, in the film forming method according to the present embodiment, the absolute value of the DC voltage (cathode voltage) on the target side is kept smaller than the general sputtering condition, so that Ar ions are used as a target in a state where acceleration due to cathode fall is low. Incident. For this reason, it is considered that the recoil Ar reflected from the target surface has a low speed and is less likely to enter the film formed on the substrate. As a result, it is considered that Ar entering the film is reduced and α-Ta having a bcc structure and a small specific resistance is easily generated.

  In addition, the effect of making Ar difficult to enter the film by reducing the absolute value of the DC voltage (cathode voltage) and slowing the recoil Ar is not limited to Ta, but has a large content of Ar such as W or Au. It is considered that the wiring material having a relatively large mass number appears similarly. That is, even with these materials, it is considered that a film having a low specific resistance can be obtained by the film forming conditions for slowing the recoil Ar as in the case of Ta. A specific resistance film could be obtained. The phenomenon that when Ar enters the film, a β structure (tetragonal crystal) having a relatively large specific resistance is likely to occur even with an atom having a large mass number as the energy of recoil Ar increases. It is done. Examples of elements that have a large Ar content and are expected to have an effect of the film forming method according to this embodiment include Ta, W, Au, Pt, Cu, Ru, and Ir.

  In the film forming method according to the present embodiment, although the absolute value of the DC voltage is reduced in order to suppress recoil Ar, the film forming speed is impaired because high-density plasma is generated by the VHF power. In addition, a low specific resistance α-Ta film can be formed. More specifically, since the film forming method according to the present embodiment uses 60 MHz VHF power rather than 13.56 MHz RF, the number of oscillations of electrons in the plasma increases. Since the electrons collide with Ar gas in the gas phase and Ar ions are generated, more Ar ions can be generated at a high frequency, and high-density plasma can be obtained. The deposition rate is proportional to the product of the DC voltage (cathode voltage) and the cathode current (cathode power). In the film forming method according to the present embodiment, although the absolute value of the DC voltage is reduced in order to suppress recoil Ar, a large amount of Ar ions are generated because the discharge is performed with VHF having a higher frequency than in the past. A lot of cathode current flows. Therefore, it is possible to form α-Ta without preventing the cathode power from decreasing and without deteriorating the deposition rate.

  It should be noted that even if RF power of 13.56 MHz is used instead of VHF power of 60 MHz, Vdc is generated, so it seems that the specific resistance is low to some extent. However, when Vdc is generated with RF power of 13.56 MHz, the absolute value of Vdc is larger than when VHF power of 60 MHz is applied. Therefore, in the formed Ta film, α-Ta and β It is considered difficult to obtain a film in which -Ta is mixed and the resistivity is sufficiently low. Of course, a general DC cathode generates a discharge voltage of minus several hundred volts, so it is considered that a film having a low specific resistance cannot be obtained. On the other hand, in the film forming method according to this embodiment, the absolute value of Vdc generated at the cathode can be kept low by using the VHF power source.

  According to the film forming method according to the present embodiment, since it is possible to directly form α-Ta without forming a mask or an underlayer as in the prior art, it is possible to form a film at a lower cost than in the past. it can. In addition, since the film formation process can be simplified, the yield can be improved. In addition, a Ta film having better thermal conductivity, residual stress characteristics, structural stability, and the like can be formed.

  In another experiment, as a result of comparing the specific resistance between α-Ta formed on TaN as the underlayer and α-Ta formed under the conditions of this embodiment (Example 1), the conditions of Example 1 were compared. The specific resistance of α-Ta formed in (1) was lower. It is considered that α-Ta formed on TaN has a crystal grain size smaller than that of α-Ta formed in Example 1. Therefore, according to the film forming method according to the present embodiment, α-Ta having better characteristics than the conventional technique of forming a Ta film on an underlayer made of TaN can be obtained.

  Examples of the substrate on which α-Ta can be formed by the film forming method according to the present embodiment include a silicon substrate on which a silicon oxide film is formed, a substrate on which an SiN insulating protective layer is formed, and a silicon substrate. The α-Ta film forming method according to the present embodiment is suitably used for forming a Ta film required in a thermal head for an ink jet printer or a semiconductor wiring process in which a low specific resistance film is required. It can also be used to form a lead wiring for a magnetic head.

  In addition, when the temperature is high for wiring use, the film forming method according to the present embodiment is useful. Α-Ta formed by the film forming method according to the present embodiment is more stable with respect to temperature because it does not require a TaN layer and does not need to contain nitrogen as compared with the conventional method. Therefore, durability becomes high.

(Second Embodiment)
By setting the vacuum vessel 101 to a low pressure, Vdc, which is a DC voltage, is generated as a self-bias voltage at the cathode 104 without applying a DC voltage only by applying VHF power to the cathode 104. Of the conditions of Example 1 according to the first embodiment, as a result of film formation with no DC voltage applied from the DC power supply 108, α-Ta having a low specific resistance can be obtained as the film formed. did it. Vdc during film formation was −20 V, and the specific resistance was 16.3 μΩ · cm. Therefore, it has been found that α-Ta can also be obtained by generating Vdc at the cathode 104 with VHF power without supplying a DC voltage from the external power source to the cathode 104.

(Third embodiment)
Under the conditions of Example 1 according to the first embodiment, the pressure in the vacuum vessel 101 was changed from 5 Pa to 0.4 Pa before and after the discharge, but this change was not made and the measurement was performed at 5 Pa before and after the discharge. At this time, VHF power was set to 2000 W, bias power of 100 W was applied to the substrate S from the bias power supply 111, and other conditions were the same as the film forming conditions of Example 1. As a result, α-Ta was obtained in the same manner as in Example 1. Therefore, it has been found that α-Ta can be obtained by applying a DC voltage having a small absolute value at a predetermined temperature or higher, regardless of the conditions of pressure and bias power.

(Fourth embodiment)
In the film forming conditions of Example 1 according to the first embodiment, it was found that when the Ta film exceeds a predetermined thickness, α-Ta is obtained. FIG. 7 is a diagram showing the relationship between film thickness and specific resistance. The horizontal axis in FIG. 7 is the film thickness of the formed Ta film, and the vertical axis is the specific resistance. FIG. 7 shows experimental results when the film forming temperatures are 360 ° C. and 400 ° C. From FIG. 7, at both 360 ° C. and 400 ° C., a decrease in specific resistance is observed at a film thickness of 20 nm or more, and α-Ta crystallinity can be obtained. More preferably, when the film thickness is 30 nm or more, it is found that the specific resistance is sufficiently low (that is, 60 μΩ · cm or less), and α-Ta.

  When a film is formed on a Ta film having a film thickness of α-Ta under the condition that is normally only β-Ta (in other words, a condition that β-Ta is formed when a Ta film is directly formed on the substrate) It was found that due to the crystallinity of α-Ta, a Ta film formed later also becomes α-Ta.

  Therefore, in the film formation method according to the present embodiment, the first film is formed under the film formation conditions of Example 1 at a predetermined thickness where an α-Ta film is formed, and then the film formation rate is high. By changing the conditions (usually β-Ta conditions, here, the conditions of Comparative Example 1) to form the second film, α-Ta is formed at a high film formation rate. More specifically, after the first film is formed under the film formation conditions of the DC voltage of −150 V or more and the film formation temperature of 300 ° C. or more, the DC voltage is less than −150 V and the film formation temperature on the first film. A second film is formed under film formation conditions of less than 300 ° C. As a result, the laminated Ta film of the first film and the second film formed as a whole has an α-Ta structure.

  Since the absolute value of the DC power is low in the α-Ta film formation condition, the film formation rate is lower than the β-Ta film formation condition. On the other hand, according to the film forming method according to the present embodiment, the α-Ta film forming condition that cannot provide a sufficient film forming speed is combined with the β-Ta film forming condition having a high film forming speed. -Put can be improved. The Ta film formed as the second film may be formed using a film formation method different from that in Example 1 and Comparative Examples 1 and 2, and in a separate processing chamber in consideration of productivity. It may be done.

  The internal stress (residual stress near the surface) of α-Ta produced in Example 1 according to the first embodiment was tensile stress. On the other hand, the internal stress of the laminated Ta film produced by the film forming method according to the present embodiment was a compressive stress. Therefore, by forming a laminated Ta film by the film forming method according to this embodiment, it is possible to control the internal stress of the film while maintaining the α-Ta crystallinity. In general, it is more advantageous in terms of corrosion resistance, fatigue strength, etc. that the stress on the surface of the film is a compressive stress. Therefore, α-Ta formed by the film forming method according to the present embodiment has a low specific resistance and a compressive stress on the surface, and thus functions such as corrosion resistance and life are further improved.

(Fifth embodiment)
This embodiment is a method for manufacturing an inkjet thermal head to which the α-Ta film forming method according to any one of the first to fourth embodiments is applied. A thermal head (recording head) is a component that ejects ink of an inkjet printer toward a sheet, an ink chamber that stores ink, an ink supply chamber that supplies ink to the ink chamber, and an ejection port that ejects ink from the ink chamber. A bubble generating unit that heats the ink in the ink chamber to generate bubbles in the ink. The thermal head is configured to extrude ink by bubbles generated by heating a part of the ink at a bubble generation unit in the ink chamber, and to discharge the ink from the discharge port toward the paper.

  The bubble generating unit includes a heating unit having a heating element, and the surface of the heating unit is covered with a protective layer provided on the inner wall of the ink chamber. Since the bubble generating part is in direct contact with the ink, it may be corroded by the ink. Therefore, the protective layer covering the heating part surface of the bubble generating part is exposed to chemical stability (corrosion resistance), high thermal conductivity (low specific resistance), heat resistance, and repeated thermal expansion and contraction. It is required to have high fatigue strength (mechanical stability). As a protective layer having these properties, α-Ta having a low specific resistance is suitable.

FIG. 8 is a cross-sectional view of the periphery of the bubble generating portion of the thermal head 900 manufactured by the manufacturing method according to the present embodiment. The thermal head 900 includes a heat storage layer 902 made of SiO ₂ , a heating resistor layer 903 made of TaN, an electrode layer 904 made of Al, an insulating protective layer 905 made of SiN, and a substrate 901 made of Si. A protective layer 906 made of -Ta is sequentially formed. The material of each layer is an example, and any material may be used as long as the function of the thermal head can be ensured.

In the thermal head manufacturing method according to this embodiment, first, a SiO ₂ film as a heat storage layer 902 as a base of a heating resistor is formed on a substrate 901 by a thermal oxidation method, a sputtering method, a CVD method, or the like. Next, a TaN film as the heating resistor layer 903 is formed on the heat storage layer 902 by a sputtering method. Further, an Al film as an electrode layer 904 is formed on the heating resistor layer 903 by a sputtering method.

  Thereafter, a predetermined portion of the heating resistor layer 903 and the electrode layer 904 is etched to partition an electrode pattern and a heating area having a predetermined shape. The heating region can be heated by passing a current through the heating region (heating resistor layer 903) through the electrode pattern (electrode layer 904) thus formed.

  After the etching step, a SiN film as an insulating protective layer 905 is formed by a thermal oxidation method, a sputtering method, a CVD method, or the like. Thereafter, α-Ta as the protective layer 906 is formed on the insulating protective layer 905 by the film forming method according to any of the first to fourth embodiments.

  According to the manufacturing method of the thermal head according to the present embodiment, α-Ta is directly formed without the need to form a mask or a base film before forming α-Ta as in the prior art. Can do. Therefore, it is possible to manufacture a thermal head having a protective film with a low specific resistance at a lower cost than before. Since the manufacturing process can be simplified, the yield can be improved. In addition, it is possible to provide a thermal head substrate that has higher performance than conventional ones, and to realize a thermal head capable of maintaining a high-frequency discharge operation in a stable state for a long period of time.

The present invention is not limited to the above-described embodiment, and can be appropriately changed without departing from the spirit of the present invention.

Claims (4)

A film forming method for forming a Ta film on a substrate by sputtering,
Applying a VHF power and a first DC voltage to the Ta target, and sputtering the Ta target;
In the first step, Ta atoms sputtered from the Ta target are deposited on the substrate maintained at a first temperature to form a Ta film having a specific resistance of 60 μΩ · cm or less. A process ,
The film formation method , wherein the first DC voltage is −150 V or more, and the first temperature is 300 ° C. or more . A third step of applying a VHF power and a second DC voltage to the Ta target after the second step, and sputtering the Ta target;
In the third step, Ta atoms sputtered from the Ta target are deposited on the substrate maintained at the second temperature to form a Ta film having a specific resistance of 60 μΩ · cm or less. Process,
Further comprising
2. The film forming method according to claim 1 , wherein the second DC voltage is less than −150 V, and the second temperature is less than 300 ° C. 3.   The film forming method according to claim 1, wherein the frequency of the VHF power is 20 MHz to 450 MHz. Forming a heat storage layer made of SiO ₂ on a substrate made of Si;
Forming a heating resistor layer made of TaN on the heat storage layer;
Forming an electrode layer made of Al on the heating resistor layer;
Etching a predetermined portion of the electrode layer to form an electrode pattern and partitioning a part of the heating resistor layer as a heating region;
Forming an insulating protective layer made of SiN after the step of the etching,
Forming a protective layer made of Ta on the insulating protective layer, and
The said protective layer is formed using the film-forming method of any one of Claims 1 thru | or 3 , The manufacturing method of the thermal head for inkjets characterized by the above-mentioned.

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