JP2005314802A - Film-forming method, base plate and liquid discharge head - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for forming a film on a substrate, which is hardly peeled off and has improved durability and reliability. <P>SOLUTION: This film-forming method comprises: forming a sacrificial layer 12 on the substrate 10; depositing a material of a metallic film 11 thereon; and then removing the above material together with the sacrificial layer 12 to form the metallic film 11. The film-forming method employs a liftoff film-forming technique, and prepares an overhang formed into a shape of a reverse taper part 12a on a side face of the sacrificial layer 12, so that the formed metallic film 11 acquires a circumferential edge part having a thickness distribution in which the film thickness gradually decreases to substantially zero at the film edge from a predetermined thickness in a central part. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a film forming method used for a substrate such as an element substrate of a liquid discharge head, a semiconductor element, or an electronic element, a substrate having a substrate on which the film is formed, and a liquid discharge head.

  Generally, a vacuum deposition method, a sputtering method, or the like is used as a method for forming a thin film. However, depending on the film-forming material, in particular, a chemically stable and excellent corrosion-resistant material, for example, a metal film such as a noble metal, has a weak adhesive force with a counterpart material such as SiN, Si, or SiO serving as a film-forming substrate. There is a problem that it is easy to peel off.

  Therefore, in order to increase the adhesion strength of the film, we aim at anchor effects such as optimization of substrate pretreatment, use of contact metal, improvement of diffusion due to film formation conditions such as heating temperature, reduction of stress, increase of surface roughness, etc. Physical improvements were made.

  However, in practice, there are many cases where this is not sufficient, and film peeling from the edge of the pattern opening is likely to occur, and thus further improvement in adhesion strength has been demanded.

  FIG. 11A shows a conventional method of forming a pattern opening in the metal film 101 on the substrate 100 by wet etching. A resist 102 is applied on the metal film 101 formed on the substrate 100 and patterned. The metal film 101 is etched by dipping in the etchant from the resist opening thus formed to form a pattern opening. Since wet etching is isotropic etching, the end surface 101a of the pattern opening of the metal film 101 is a surface connecting points at equal distances from the edge 102a of the resist opening.

  FIG. 11B illustrates a case where patterning is performed by conventional dry etching. A metal film 111 is formed on the entire surface of the substrate 110 by sputtering or the like, and then a photoresist pattern 112 is formed. Pattern openings are formed by ion sputtering (RIE) or sputtering / etching with Ar gas. In reactive ion sputtering, a reaction gas (chlorine gas, phosgene, or the like) that combines with the metal to be etched is introduced, and etching is performed by reaction. Therefore, the end surface 111a of the pattern opening of the metal film 111 is formed as shown in FIG. Although a certain degree of smoothness can be obtained as compared with a), since the metal material of the film and the selection ratio (the etching rate of the metal film 111 / the etching rate of the base 110) are finite values, the base 110 is slightly etched. As a result, a recess 110a is formed. This tendency is particularly noticeable with noble metals that have a low selectivity.

  Also, as shown in FIG. 12A, when the adhesion layer 121 is interposed between the base 110 and the metal film 111, the end surface 121a of the adhesion layer 121 is exposed on the end surface 111a of the pattern opening in the dry etching described above. To do. Since the so-called reactive material such as Ti, Cr, Ni, and Ta is used for the adhesion layer 121, the adhesion layer 121 dissolves in various chemicals from the exposed portion, and also causes a reaction such as oxidation to the inside. It may penetrate and damage the adhesion layer 121.

  FIG. 12B shows a metal film 131 formed by pattern formation by conventional mask film formation. In the mask film formation, the film is formed in a state in which a mask 132 having a finite thickness having an opening at a portion to be formed is in close contact with the substrate 130. The amount of sputtered particles flying by sputtering is the largest at an incident angle of 0 ° according to a so-called cosine law proportional to cos θ with respect to the emitted angle θ, and gradually decreases as the angle increases. Accordingly, when the side surface of the mask 132 is vertical, the film thickness gradually decreases at the end portion 131a of the metal film 131, but at the film end, the film is in contact with the side surface of the mask 132, so Thickness remains.

  Further, patterning by lift-off is known as a deformation of mask film formation. In the mask film formation, the mask is mechanically attached and detached, whereas in the lift-off method, a sacrificial layer pattern is provided on a substrate, a metal film is formed thereon, and then the sacrificial layer pattern is dissolved. In general, a sacrificial layer pattern is formed with a photoresist, and a metal film of a desired material is formed on the sacrificial layer pattern to be thinner than the sacrificial layer pattern. By utilizing the step between the sacrificial layer pattern and the metal film, By etching the sacrificial layer from the gap, the metal film adhering to the sacrificial layer pattern is also removed.

  However, for example, when a noble metal film is formed, the temperature during the film formation is high, and a resin-based resist cannot be used for the sacrificial layer pattern. In addition, it has been pointed out that the resist pattern is partially broken by sputtered particles, resulting in poor pattern accuracy. In order to solve such a problem, Patent Document 1 proposes lift-off using an inorganic sacrificial layer pattern of Al, which is a metal that can be easily etched.

  However, in the method disclosed in Patent Document 1, since the cross-sectional shape of the Al sacrificial layer pattern is rectangular and has a side surface perpendicular to the substrate, the film formation on the Al sacrificial layer pattern is similar to the mask film formation described above. In addition, the film edge of the metal film is ½ of the maximum film thickness. Moreover, even if the sputtered particles adhere to the side surface of the sacrificial layer pattern of Al and the etchant penetrates from the thin part of the metal film and dissolves Al, the metal film is not sufficiently cut between the base and the upper surface of the sacrificial layer pattern. Therefore, it is necessary to forcibly peel off unnecessary metal films.

Conventionally, an element substrate of a liquid discharge head mounted on a recording apparatus that discharges a liquid such as ink using thermal energy has a heating resistor (heater) having a heat acting portion, and serves as a protective film thereof. For example, it is necessary to have insulation that electrically insulates the ink from the heating resistor, corrosion resistance that can withstand high-temperature ink, and cavitation that can withstand the impact of cavitation when bubbles disappear. In addition, an insulating protective film made of, for example, SiO ₂ , SiC, SiN, etc. is provided, and a cavitation / corrosion-resistant protective film made of Ta etc. is further provided thereon to generate heat from the use environment. It is common to protect the resistor.

In particular, as a material having high corrosion resistance, for example, Patent Document 2 discloses that a mechanical film has a conventional mechanical strength by adopting a protective film made of a noble metal such as Ir (iridium), Pt (platinum), or Ru (ruthenium). It is disclosed that the durability against ink is about 2 to 3 times that of Ta (tantalum), so that it is possible to achieve a lifespan 2 to 3 times longer than conventional ones. However, at present, it is difficult to form a noble metal film in a predetermined pattern, and commercialization at a low cost has not been realized.
JP 7-273280 A JP-A-5-254122

  The above-described conventional technique has an unresolved problem that film peeling from the film end of the formed film is likely to occur, and patterning is difficult for a noble metal film suitable for a protective film of a liquid discharge head.

  The present invention has been made in view of the above-mentioned unsolved problems of the prior art, and includes a film forming method, a substrate, and a liquid discharge head capable of manufacturing a film that hardly causes film peeling and has excellent durability. It is intended to provide.

  In order to achieve the above object, the film forming method of the present invention includes a step of depositing a material of the film on a substrate on which a sacrificial layer having an overhang is formed, and removing the sacrificial layer to thereby form the sacrificial layer. And removing the material of the film deposited on the sacrificial layer.

  In addition, the liquid discharge head of the present invention includes an energy generator that generates energy used to discharge a liquid provided on a substrate, wiring connected to the energy generator, the energy generator, and the energy generator. An insulating protective film covering the wiring; an adhesive layer provided on the insulating protective film; and a durable protective film provided on the adhesive layer, wherein the durable protective film has a predetermined thickness. And an edge portion having a film thickness distribution that gradually decreases from the predetermined film thickness until the film thickness becomes substantially zero at the film edge, and the edge portion covers the edge of the adhesion layer. It is characterized by.

  In forming the film, by providing an overhang on the side surface of the sacrificial layer, a film having an edge portion having a film thickness distribution gradually decreasing until the film thickness becomes substantially zero at the film end is formed. As a result, film peeling at the film edge of the formed film can be reduced, and the durability and reliability of the film can be greatly improved.

  The mechanism when the thin film was peeled off was examined. The film was peeled off because the force more than the adhesive force works. In mechanical parts, the action by external force can be considered. In most cases, the film stress that acts relatively between the film and the substrate was found to be the source.

  A film formed by a method such as sputtering or vapor deposition retains compressive and tensile film stress depending on the material and conditions. The film stress varies depending on the material, the temperature during film formation, and the heat treatment after film formation. However, each parameter is limited, and the quality of the film such as packing density and crystallinity of the film is also affected.

  When tensile stress is acting as film stress at the film interface with a finite size and uniform film thickness and film stress, the shear tensile force at the film-substrate interface is the film stress direction. Multiplied by the cross-sectional area. Since the tensile force is applied equally from all directions to the central part of the film, the interface does not peel off from the central part unless the initial strain is present. However, the tensile force increases as the distance from the center of the membrane increases, and the shearing force is maximized because the membrane edge is pulled only from the inside. Therefore, it is considered that film peeling is likely to occur from the film edge. In addition, when peeling begins, the tensile force in the shear direction increases at the edge interface, and depending on the shape of the peeled film, a tensile force in the vertical direction is also applied to the interface, and the peeling progresses in a chained manner. The entire surface will be peeled off.

  In view of the above, in order to eliminate film peeling without changing parameters related to film quality such as sputtering conditions, it is important to first eliminate peeling at the film edge. As a measure for this, even if the film stress is the same, by providing an edge that gradually decreases toward the edge of the film, the tensile force in the shear direction at the interface of the edge is gradually reduced. By gradually reducing the film thickness until the film thickness becomes zero, the tensile force in the shearing direction at the film edge becomes zero.

  Embodiments of the present invention will be described with reference to the drawings.

  An example in which the present invention is suitably used is the formation of a metal film that requires a strong adhesive force or a noble metal film such as Pt, Ir, Os, Ru, or Ni.

  FIG. 1 shows a state in which a metal film, which is a thin film, is formed on a substrate by lift-off using the film forming method according to one embodiment, and FIG. 1 (a) is a schematic view seen from the upper surface of the substrate. b) is a schematic cross-sectional view taken along the line AA ′ in FIG. 1A, and FIG. 1C is a schematic cross-sectional view taken along the line BB ′ in FIG. 1 (d) is a schematic cross-sectional view taken along the line CC ′ in FIG.

  As can be seen from the schematic cross-sectional views shown in FIGS. 1B to 1D, the metal film in the present embodiment has a shape in which the film thickness gradually decreases toward the end on the entire circumference of the metal film 11. Details will be described in the description of FIG. Furthermore, if the formed metal film has corners, the corners are easily peeled off. Therefore, in the present embodiment, as shown in FIG. 1A, the metal film 11 on the formation surface on which the metal film is formed on the base is formed so that the corners are rounded. ing. That is, when the metal film 11 is viewed from the upper surface of the substrate 10, the shape has no corners. This can be dealt with by rounding the corners of the Al pattern which is a sacrificial layer in lift-off film formation.

  As described above, in the present embodiment, since the entire metal film 11 is structured not to be peeled off, a highly reliable metal film can be formed.

  FIG. 2A shows an enlarged cross-sectional shape of the edge portion of the metal film 11 in the present embodiment. The metal film 11 has an edge portion 11a that gradually decreases in thickness according to a known cosine law until the film thickness becomes substantially zero from the target film thickness in the central portion to the film edge. As shown in FIG. 2B, when the adhesion layer 21 is interposed between the base 10 and the metal film 11, the edge portion 11 a is formed so as to cover the film end 21 a of the adhesion layer 21. For the adhesion layer 21, a so-called reactive material such as Ti, Cr, Ni, or Ta is preferably used. In this embodiment, the edge of the adhesion layer is covered with the edge 11 a of the metal film 11. Therefore, it is possible to prevent the adhesion layer from being damaged by dissolving in various drugs or causing a reaction such as oxidation.

  As shown in FIG. 2C, the metal film 11 having the edge portion 11a whose film thickness gradually decreases as described above uses an Al pattern 12 which is a sacrificial layer having an overhang due to the reverse tapered portion 12a on the side surface. The film is formed by the lift-off film formation.

  That is, in the sputtering, there is an angle distribution in the direction in which the film forming particles are incident on the substrate, and in order to form the edge portion 11a, the side surface is in the incident direction so that the film forming particles do not adhere to the side surface of the Al pattern 12. A cross-sectional shape having a reverse taper portion 12a that is shaded with respect to the shape may be used. Instead of lift-off film formation, mask film formation using a mask having the same cross-sectional shape as the Al pattern 12 may be employed.

  The taper angle of the reverse taper portion 12a of the Al pattern 12 is set to be larger than the maximum value of the incident angle of the film forming particles indicated by the broken line. The distribution of the amount of sputtered particles depending on the incident angle varies depending on the apparatus and film forming conditions such as the distance from the target, collimator, and film forming power.

  Since the taper angle of the Al pattern 12 whose side surface is reversely tapered with respect to the substrate 10 such as a Si wafer is larger than the maximum value of the incident angle of the film formation particles, the film formation particles incident from the openings of the Al pattern 12 The outer end of the region that hits the substrate 10, that is, the film formation end (film end) is outside the opening end of the Al pattern 12, and immediately after sputtering, as shown in FIG. A metal film 13 is deposited on the metal film 11 and the Al pattern 12.

  Here, FIG. 5 shows a schematic diagram of the process of forming the metal film. The metal film 11-1, the metal film 11-2, and the metal film 11-3 show how the metal film is formed over time. Thus, since the film in the middle of formation also has a shape in which the film thickness gradually decreases in accordance with cosine law, stress in the film hardly occurs even during film formation.

  As the sacrificial layer, as shown in FIG. 3B, an Al pattern 22 having an overhang due to a step 22a may be used instead of an inversely tapered shape. The metal film 13 on the Al patterns 12 and 22 is removed by etching the Al patterns 12 and 22. In this way, it is possible to form the metal film 11 having the edge portion 11a that gradually decreases until the film thickness becomes substantially zero toward the film end.

  When the adhesive layer 21 is provided as shown in FIG. 2B, a material for improving adhesiveness such as Ti and Cr is previously sputtered on the substrate 10 having the Al pattern 12 shown in FIG. By forming the adhesion layer 21 and subsequently sputtering the film material to be the metal film 11 thicker on the upper layer, a two-layer film having a structure in which the metal film 11 having a film thickness distribution by cosine law covers the adhesion layer 21 is obtained. be able to.

  FIG. 7 shows a schematic diagram of a sacrificial layer for forming the above metal film. 7A is a schematic view seen from the top surface of the substrate, FIG. 7B is a schematic cross-sectional view taken along line AA ′ of FIG. 7A, and FIG. 7C is FIG. ) Is a schematic cross-sectional view taken along line BB ′ of FIG.

  As described above, the sacrificial layer is provided with the overhang 12a so that the film thickness gradually decreases in accordance with cosine law at the entire periphery of the metal film to be formed. By attaching, as shown in FIG. 1A, the corners of the metal film 11 are also rounded, and the metal film 11 as a whole can be prevented from peeling off.

  In this way, the metal film having the edge portion that gradually decreases until the film thickness becomes substantially zero as it goes to the film end can be obtained by mask film formation using a mask having an inverse taper portion or an overhang due to a step. However, even if the alignment between the mask and the substrate, distortion during heating film formation, or misalignment due to differences in thermal expansion is compensated by optimizing the mask material and process, the mask itself is thick, so the edge position accuracy of the film formation In this respect, lift-off using an inorganic resist such as an Al pattern is superior.

  Formation of a sacrificial layer of an inorganic resist such as a metal used for lift-off film formation is performed according to the following procedure. The sacrificial layer has an overhang due to a reverse tapered shape or the like, and is formed by the following procedure.

(1) A multilayer structure having a lower layer made of a material having a high etching rate and an upper layer made of a material slower than the same etchant is formed on the substrate.
(2) A resist resisting the above etchant is patterned thereon.
(3) Etching is performed with the above etchant. Since etching is faster in the lower layer, an overhang due to an inverted taper shape or the like is formed.

  First, with respect to a mixed acid (phosphoric acid: acetic acid: nitric acid: water = 15: 1: 1: 1, 40 ° C.) of an aluminum oxide film reactively sputtered while introducing oxygen into an Ar sputtering gas using an Al target. The results of measuring the etching rate are shown in the graph of FIG. From this graph, it can be seen that the etching rate increases as the amount of oxygen introduced increases, and reaches a maximum value at about 10%.

  Therefore, as shown in FIG. 8A, an aluminum oxide layer 12b is formed to a thickness of about 300 nm by introducing 10% oxygen into the lower layer using a Si wafer as a base. Subsequently, as shown in FIG. 8B, the upper Al layer 12c was formed to a thickness of about 300 nm using only the Ar sputtering gas. Next, as shown in FIG.8 (c), the photoresist pattern 16 was formed by apply | coating 1 to 2 micrometers of photoresist on it, and patterning. Further, etching was performed with the above mixed acid, and over-etching was performed for 30 seconds after the Al layer disappeared visually and the substrate surface of the Si wafer was seen.

  When the cross section of this sample FIG. 8D was observed with an SEM, it was confirmed that the Al pattern 12 had a reverse taper shape. It was also confirmed that the taper angle can be adjusted by changing the overetching time.

  Through the above steps, an Al pattern was formed on a substrate made of a Si wafer, a Ti film was formed to a thickness of 10 nm as an adhesion layer, and an Ir film as a metal film was formed to a thickness of 200 nm thereon.

  When the cross section was observed with an SEM, the film did not adhere to the side surface of the Al pattern, which is the sacrificial layer, and gradually decreased as shown in FIG. It was confirmed that an edge portion was formed.

  The product thus prepared was etched by mixed acid immersion for a time determined by the size of the Al pattern and the etching rate, washed with pure water, and then washed and dried with a rinse shower dryer.

  When observed in that state, there was an Al pattern that should be removed and an unnecessary Ir layer that probably did not separate from the substrate due to water adsorption, so an adhesive tape (ELEP Holder V-8M (trade name, manufactured by Nitto Denko Corporation) It was confirmed that it could be removed by other means such as ultrasonic cleaning, but peeling by adhesion with less force applied to the Si wafer was superior.

  Moreover, the following things were understood about the suitable amount of reverse taper. If the over-etching is too small, the reverse taper angle becomes small, and the deposited particles start to adhere to the side surface of the Al pattern that is the sacrificial layer. If lift-off is performed in this state, the film on the sacrificial layer and the film formed on the substrate are connected and difficult to remove, and since the film edge has a thickness, the tensile force cannot be sufficiently relaxed. Further, it is a Ti film. The adhesion layer is exposed on the surface, causing problems such as poor corrosion resistance. Conversely, if the overetching is too much, the overhang of the sacrificial layer pattern becomes thin and long, so that the tip of the overhang hangs down on the substrate, and the deposited film connects the sacrificial layer pattern and the substrate. Disappear.

  An example in which the present invention is applied to a durable protective film of a liquid discharge head used in a liquid discharge recording method in which a liquid such as ink is discharged from a discharge port to form pixels on a print material will be described.

  FIG. 9 is a schematic view having a partial cross-section of the liquid discharge head 70.

  A heater 74, which is a heating element, is disposed as an energy generator on a substrate such as Si. An ink chamber 73 and a discharge port 76 are provided in the top plate 79 on the Si substrate corresponding to the heater 74, respectively. Ink is supplied to the ink chamber 73 from an elongated ink supply port 75 provided on the Si substrate, and is discharged from the discharge port 76 by the heater 74.

  The durable protective film of the liquid discharge head needs to have excellent corrosion resistance and adhesion. The durability of the liquid discharge head having the film structure as shown in FIG. 10 was evaluated.

  FIG. 10 shows a film configuration of an element substrate having a discharge energy generator of a liquid discharge head, and shows a cross-sectional view of the element substrate. The manufacturing process of this substrate is as follows. A heating resistor 52 made of a TaN film and a wiring conductor 53 made of an Al film are sequentially sputtered on a base 51 made of a Si wafer having an underlying heat storage layer. Next, a wiring pattern that is wiring and a heating resistor pattern that is an energy generating part are formed by photolithography and etching, and then a SiN film 54 that is a first protective film that is an insulating protective film is formed by CVD. The adhesion layer 21 was formed of Ti, and an Ir metal film 55 serving as a second protective film as a durable protective film was formed by lift-off. That is, an Ir metal film 55 was formed as a pattern as a second protective film covering only the energy generating portion that requires cavitation resistance and the like. The end of the adhesion layer 21 is covered with an edge that gradually decreases until the thickness of the metal film 55 becomes substantially zero, so that the adhesion layer dissolves in various chemicals or reacts such as oxidation. It is possible to prevent the damage from occurring.

  When a Ta film is used as the second protective film as in the conventional example, dry etching using a chlorine-based gas is performed. Then, the insulating layer of the Al pad portion used as the external lead terminal of the electrical wiring and the second protective film are removed by dry etching. Thus, when Ta is used for the second protective film, it can be chemically etched using a chlorine-based gas. However, etching is difficult because noble metals such as Ir are chemically stable. Therefore, in the liquid discharge head having the film configuration shown in FIG. 10, the Ir film as the metal film 55 was formed by the following method.

Ten liquid discharge heads were manufactured for each of Samples A, B, and C. First, on the SiN film which is the first protective film, an aluminum oxide layer introduced with 10% oxygen as a lower layer of a sacrificial layer is formed to about 300 nm, and subsequently an upper layer of Al is formed to about 300 nm using only Ar sputtering gas. A photoresist was applied by 1-2 μm and patterned to form a resist pattern. Further, etching is performed with a mixed acid (phosphoric acid: acetic acid: nitric acid: water = 15: 1: 1: 1, 40 ° C.), sample A is 30 seconds, sample B is 60 seconds, and sample C is 90 seconds. Then, Al patterns having different cross-sectional shapes were formed. After stripping the photoresist with a resist stripper, the adhesion layer is formed by first reverse sputtering the substrate, and then depositing a 10 nm Ti film at a deposition pressure of 5 × 10 ⁻¹ Pa, a substrate temperature of 300 ° C., and a power of 300 W. As a second protective layer, which is a durable protective layer, an Ir film having a thickness of 200 nm was formed at a film forming pressure of 7 × 10 ⁻¹ Pa, a substrate temperature of 300 ° C., and a power of 1000 W. Then, lift-off with mixed acid, pure water cleaning, shower rinse drying, adhesive tape (ELEP Holder V-8M (trade name, manufactured by Nitto Denko Corporation) is pasted, and Ir that sticks to the substrate surface after lift-off. Thereafter, an ink chamber, which is a known ejection means, a top plate on which ejection ports are formed, and the like were formed, and 10 liquid ejection heads were prepared for each sample.

  As a sample D for comparison, after forming a SiN film, a Ti film was formed to a thickness of 10 nm and an Ir film was formed to a thickness of 200 nm under the same conditions as the samples A to C without a sacrificial layer. After that, a pattern was formed with a photoresist, sputter etching was performed with a milling apparatus, and 10 liquid ejection heads were formed through various processes such as formation of ink chambers and ejection openings.

  Further, as a sample E for comparison, after forming a SiN film, an adhesion mask was manufactured with 42 Ni having a thickness of 0.2 mm, and a mask film was formed. Since the mask was manufactured by etching from both sides due to the problem of accuracy, a reverse taper could not be formed.

  After the mask contact, a Ti film of 10 nm and an Ir film of 200 nm were formed under the same conditions as Samples A to C. Thereafter, ten liquid discharge heads were formed through various processes such as formation of ink chambers and discharge ports.

It is assumed that defects in film quality and adhesiveness are reflected in durability, and a heating resistor as a heater is subjected to foaming voltage measurement, a driving frequency of 10 kHz, a pulse width of 1 μsec, and a driving voltage of 5 under a driving condition of foaming voltage × 1.3. As a result of conducting a foaming endurance test of × 10 ⁸ pulses, all the samples A to C created by lift-off cleared the endurance test, but four of the samples D by sputter etching and the sample E created by mask film formation Two of them no longer foamed.

  Of the four samples that no longer foamed in the sample D by sputter etching, the heater was not cut and the cross section was observed, and peeling occurred between the first protective film and the second protective film. I found out. Further, the Ti film of the adhesion layer could not be identified. The remaining two were accompanied by breakage of the heater, and part of the second protective film was also lost. In addition, two of the samples E in which the mask was formed no longer foamed were accompanied by breakage of the heater, and part of the second protective film was also lost.

  The reason is presumably that the second protective film was peeled off because the Ti film was eroded and the adhesion was weak or the tensile force was large. In addition, since the sputter etching has no selectivity, the first protective film was also etched to some extent, and it is considered that ink penetrated from the first protective film and damaged the heater.

  In both mask deposition and sputter etching, the lift-off process was more durable because the shape factor at the edge was larger, and the superiority of lift-off using a sacrificial layer could be confirmed. It was.

  As described above, an Ir film having good adhesion can be obtained by forming the film by lift-off using an Al pattern having a multilayer film structure with different etching rates. By using such a noble metal film such as Ir as a protective layer of the element substrate, a liquid discharge head with good durability can be realized.

  In forming Al multilayer films having different etching rates, nitrogen reactive sputtering may be used instead of Al oxygen reactive sputtering. Further, the metal is not limited to Al, and a similar effect can be obtained by selecting an etchant as long as it is a metal material that can form oxides and nitrides such as Cr, Cu, and Mo. In addition, since a sacrificial layer of an inorganic material such as Al can withstand high-temperature film formation, it can be applied to pattern film formation of noble metals other than Ir, such as Pt (platinum), Os (osmium), Ru (ruthenium), or Ni (nickel). . In addition, since these materials often require close contact, a configuration in which the close contact layer is entirely covered with the edge portion having the above shape is particularly effective.

  In this embodiment, a heating resistor is used as an energy generator that generates energy used to discharge liquid, and bubbles are generated by applying thermal energy to a liquid such as ink, thereby forming the bubbles. Although an example of a method of discharging a liquid by the above is shown, it is also applicable to a method using a piezoelectric element as an energy generator.

  Furthermore, in the present invention, not only when the metal film is formed in the concave portion as described above, but also when the metal film 11 is formed on the convex portion 15 of the base 10 as shown in FIG. By forming the metal film so that the film thickness is gradually reduced and the corners are rounded as described above, it is possible to form a highly reliable metal film that is difficult to peel off. As described above, the film forming method of the present invention is not limited to the thin film on the element substrate of the liquid discharge head, but can be applied to the thin film on the substrate of various semiconductor elements and electronic elements.

It is explanatory drawing which shows the metal film formed into a film by the lift-off using the film-forming method by one Embodiment. 4A and 4B are partial cross-sectional views illustrating a shape of an edge portion of the metal film, and FIG. 4C is a partial cross-sectional view illustrating a cross-sectional shape of a sacrificial layer for lift-off. . The edge part shape of a metal film is shown, (a) is a partial sectional view when a film is formed with a sacrificial layer having an overhang due to a reverse taper shape, and (b) is formed with a sacrificial layer having an overhang due to a step. It is a fragmentary sectional view in the case. It is a graph which shows the change of the etching rate with respect to mixed acid at the time of introduce | transducing oxygen at the time of Al film-forming. In one Embodiment, it is explanatory drawing of the process in which a metal film is formed. In other embodiment, it is a schematic cross section which shows the state which formed the metal film by the lift-off on the base | substrate which has a convex part. It is explanatory drawing which shows a sacrificial layer in one Embodiment. 6 is a process diagram showing a method for forming a sacrificial layer of an inorganic resist in Example 1. FIG. 6 is a schematic diagram of a liquid discharge head according to Embodiment 2. FIG. 3 is a schematic partial cross-sectional view illustrating a configuration of an element substrate of a liquid discharge head. FIG. It is explanatory drawing which shows two conventional examples. It is explanatory drawing which shows another two conventional examples.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10, 51 Base | substrate 11, 55 Metal film 11a Edge part 12, 22 Al pattern 12a Reverse taper part 21 Adhesion layer 22a Step 52 Heating resistor 53 Wiring conductor 54 SiN film

Claims (8)

A film forming method for forming a film on a substrate,
Depositing the material of the film on a substrate on which a sacrificial layer having an overhang is formed;
Removing the sacrificial layer to remove the sacrificial layer and the material of the film deposited on the sacrificial layer. The sacrificial layer is
From the base side, a lower layer of a metal compound containing at least one of oxygen and nitrogen,
The film forming method according to claim 1, further comprising a metal compound or metal upper layer including at least one of oxygen and nitrogen having a lower concentration than the lower layer on the lower layer. A substrate comprising a film and a substrate formed by the film forming method according to claim 1 or 2,
The film includes a central portion having a predetermined film thickness, and an edge portion having a film thickness distribution that gradually decreases from the predetermined film thickness until the film thickness becomes substantially zero at the film edge. substrate.   The substrate according to claim 3, wherein the shape of the film on the formation surface on which the film is formed on the substrate has no corners.   The substrate according to claim 3 or 4, wherein the material of the film is a metal material mainly composed of Pt, Ir, Os, Ni, or Ru. Having an adhesion layer between the substrate and the film;
The substrate according to claim 3, wherein an end portion of the adhesion layer is covered with the edge portion of the film. An energy generator that generates energy used to discharge the liquid;
Wiring connected to the energy generator;
An insulating protective film covering the energy generator and the wiring;
A durable protective film selectively provided on the insulating protective film,
The liquid discharge head according to claim 1, wherein the durable protective film is a film formed by the film forming method according to claim 1. An energy generator that generates energy used to discharge the liquid provided on the substrate;
Wiring connected to the energy generator;
An insulating protective film covering the energy generator and the wiring;
An adhesion layer provided on the insulating protective film;
A durable protective film provided on the adhesion layer,
The durable protective film comprises a central portion having a predetermined film thickness, and an edge portion having a film thickness distribution that gradually decreases from the predetermined film thickness until the film thickness is substantially zero at the film end,
An end portion of the adhesion layer is covered with the end edge portion.

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