Method of preparing a substrate for ink jet head and method of preparing an ink jet head

Abstract: A method of preparing an ink jet head comprises a support (1); an electrothermal transducer formed on said support and having a heat-generating resistor (2) and a pair of electrodes (3) connected electrically to said heat-generating resistor; and a liquid path (6) formed on said support corresponding to the heat-generating portion of said electrothermal transducer formed between said pair of electrodes, and communicating with a discharge opening for discharging liquid, which comprises the step of dry etching to pattern the material for said heat-generating resistor provided on said support in the form of a layer.

Description: This invention relates to a method of preparing a substrate for a recording head according to the preamble of claim 1, wherein said recording head is to be used in an ink jet recording device which performs recording by forming droplets of ink by discharging ink and attaching the droplets onto a recording medium such as paper, etc., and to a method of preparing an ink jet head. Principal structure of a recording head of the type utilizing heat energy as the ink discharging energy are exemplarily shown in Figs. 1A and 1B. The recording head has a structure formed by bonding a substrate comprising an electrothermal transducer as heat generating means provided for converting electrical energy to heat energy to be utilized for ink discharge arranged on the surface exhibiting insulating property of a support 1, and further, if necessary, an upper layer 4 as the protective layer provided at least on the heat-generating resistor 2 and electrodes 3 to be positioned finally below a liquid path 6 and a liquid chamber 10 having an ink supply opening 9, to a covering member 5 having a recession for the liquid path 6 and the liquid chamber 10, etc. formed thereon. The discharging energy for ink discharge in this recording head is imparted by the electrothermal transducer having a pair of electrodes 3 and a heat-generating resistor 2 connected electrically to these electrodes. That is, when current is applied on the electrodes 3 to generate heat from the heat generating portion 8 of the heat-generating resistor 2, the ink in the liquid path 6 near the heat-generating portion 8 is momentarily heated to generate bubbles thereat, and through volume change by momentary volume expansion and shrinkage by generation of the bubbles, ink are discharged as a droplet from a discharge opening. As the representative method for preparing the electrothermal transducer of the substrate in such constitution of the recording head as described above, there has been known the method as disclosed in Japanese Laid-open Patent Publication No. 59-194859 according to the steps, in which at first a heat-generating resistor layer comprising HfB₂, etc. and an electrode layer comprising Al, etc. are successively laminated on an appropriate support, next the electrode layer is etched to a predetermined shape by use of an etchant, and then the heat-generating resistor layer is further etched to a predetermined shape with the use of an etchant. Whereas, according to such method, during etching of the heat-generating resistor layer, the etchant will attack the side face of the electrode layer already subjected to patterning, whereby curling or defect will sometimes occur on the side surface of the electrode layer. Also, as shown in Fig. 2, if the heat-generating resistor layer 2 may be overetched to have the side surface of the electrode layer 3 exposed, when a protective layer 4 is further provided, its coverage capacity will become extremely poor, giving rise to defective results such as dissolution of electrodes by penetration of ink when assembled in the recording head. According to document US-A-4 412 885 there is known a method of the fabrication of semiconductors, wherein electrodes, i.e. conductors of an aluminium layer are etched by means of dry etching technology in order to avoid that exposed sections of the aluminium layer are attacked by a chemical used in a wet chemical etching process. Thus, this method is applied to products and has purposes which are different from the purpose of the substrate and the purpose of the above-mentioned method. According to the document DE-A-3 414 792 there is disclosed a method according to the preamble of claim 1, namely a generic method of subjecting previously the width of the electrode layer 3 to patterning smaller than the width of the heat-generating resistor layer 2 as shown in Fig. 3. However, such method cannot be said necessarily satisfactory in practical application or in the point of its effect. More specifically, during patterning of the heat-generating resistor layer 2 after patterning of the electrode layer 3, it is necessary to provide a resist mask for patterning by registration with good precision on the electrode pattern 3. Particularly, when higher densification is effected by making smaller the arrangement pitch of the heat-generating portion 8 of the heat-generating resistor 2, the difference in width (W) between the electrode layer 3 and the heat-generating resistor layer 2 must be formed on the order of, for example, 1 µm or less, and registration of the resist mask with good precision in such case is technically difficult, whereby generation of defective registration will occur remarkably to often result in lowering of yield inevitably. Also, since patterning of the heat-generating resistor layer is effected in the wet step by use of an etchant, defective patterning of the heat-generating resistor layer due to the peeling of the etching resist or the battery reaction between the heat-generating resistor layer and the electrode layer will sometimes be inevitably generated. The present invention has been accomplished in view of the aforementioned problems in the prior art, and its object is to provide a method which can prepare an electrothermal transducer with good precision and good yield, and yet can prepare a substrate for ink jet recording head and a head having the substrate of good quality. This object is achieved by the features defined in the characterizing part of claim 1. According to these features the etching of the layers is effected with the same resist pattern, and the etching of the second step is dry etching. Thus, according to the present invention, since the dry etching method which can easily control the state of etching is used for patterning of heat-generating resistor layer, etching of the electrode layer and the heat-generating resistor layer can be effected with the same resist pattern, whereby no registration working of mask as in the prior art is required and also there occurs no such problem as described above involved in the wet step because it is the dry step. Particularly, in the dry etching method, strength of etching or its speed can be easily controlled, and overetching of the heat-generating resistor or side etching of the electrode can be easily prevented or reduced. Preferable embodiments of the invention are defined in the claims 2 to 18. In the following the invention is further illustrated by embodiments with reference to the enclosed figures. Figs. 1A and 1B are schematic illustrations showing an example of the principal structure of the ink jet recording head, Fig. 1A showing a partical sectional view of the substrate constituting the recording head, and Fig. 1B an exploded view showing the positional relationship between the substrate and the covering member. Fig. 2 is a partial sectional view showing the state of overetching in the method of the prior art, Figs. 3A and 3B diagrammatic views showing the relationship between the electrode and the heat-generating resistor in the prior art, Fig. 3A being a plan view of the substrate and Fig. 3B being a sectional view at the line X-Y in Fig. 3A. Figs. 4A-4F are process diagrams showing the principal steps in the method of the present invention as schematic sectional views of the substrate. Fig. 5 is a schematic perspective view showing the appearance of an ink jet device equipped with an ink jet head obtained according to the present invention. In the following, an embodiment of the method of the present invention is described by referring to the drawings. First, as shown in Figs. 4A and 4B, a heat-generating resistor layer 2 comprising HfB₂, etc. and an electrode layer 3 comprising Al, etc. are successively laminated on a support 1 as conventionally practiced. Next, an etching resist 11 is provided as shown in Fig. 4C. As the etching resist, one comprising a material which is effective for both etching of the electrode layer and dry etching of the heat-generating resistor layer is suitable because these can be etched with the same resist. As the material for formation of resist, for example, OFPR 800 (Tokyo Oka), AZ 130 (Hoechst), microposit 1400 (Shipley), etc. may be included, and it may be provided to a predetermined shape on the electrode layer 3 according to the patterning method by use of photolithographic steps, etc. After the etching resist 11 is thus provided, first the electrode layer 3 is etched as shown in Fig. 4D. The etching may be also effected by the wet step by use of an etchant, provided that etching with good precision is possible, which may be suitably selected depending on the material for forming the electrode layer. As the material for formation of the electrode layer, a material which is not attacked by subsequent dry etching of the heat-generating resistor layer is preferred. On completion of etching of the electrode layer 3, the heat-generating resistor layer 2 is subjected to dry etching as shown in Fig. 4E. The operating conditions of dry etching in this case may be suitably selected depending on these materials so that no damage may be given the electrode layer and the heat-generating resistor layer may be formed with good precision and without overetching or with as little overetching as possible. For exmaple, when a boride of such a metal as hafnium, lanthanum, zirconium, titanium, tantalum, tungsten, molybdenum, niobium, chromium, vanadium, etc. is used, halogenic gases including, for example, chlorine-type gases such as Cl₂, BCl₃, CCl₄, SiCl₄, etc. and fluorine-type gases such as CF₄, CHF₃, C₂F₆, NF₃, etc. are preferable as an etching gas. After the electrode layer 3 and the heat-generating resistor layer 2 are thus patterned to desired shapes, the resist 11 is removed from the support I as shown in Fig. 4F, and further the predetermined portion of the heat-generating resistor layer is exposed according to the etching step of the electrode layer by use of photolithographic steps to form a heat-generating portion of heat-generating resistor, thus providing an electrothermal transducer on the support. Further, if desired, a protective film comprising SiO₂, polyimide, etc. is provided to form a substrate for ink jet recording head. The substrate obtained can be bonded to, for example, a covering member as shown in Fig. 1B to form a recording head. The present invention is described in more detail below by referring to Examples. Example 1 First, on a silicon wafer (A4 size) as the support having a SiO₂ film (5 µm) formed on its surface by heat oxidation, HfB₂ was laminated with a layer thickness of 2000 Å as the heat-generating resistor layer by RF Magnetron sputtering, and further Al was laminated with a thickness of 5000 Å as the electrode layer by the EB vapor deposition method. Next, an etching resist comprising OFPR 800 (produced by Tokyo Oka) was formed on the obtained electrode layer by the method according to photolithographic technique. By use of the resist thus formed as the mask, first the Al layer was etched with a phosphoric acid-nitric acid type etchant. Next, the heat-generating resistor layer was etched with the use of RIE using CCl₄ as the reactive gas under the conditions of a gas pressure of 3 Pa, a power of 300 W and an etching speed of 300 Å/min. In the etching operations, no peeling of resist or defective etching was recognized. Further, as the result of SEM observation after etching, the product had a good sectional shape without large overetching or side etching of the electrode layer. Next, the resist was peeled off, and further for the purpose of having a heat-generating resistor exposed at the predetermined portion, a resist (OFPR 800, produced by Tokyo Oka) film was formed at the portion except for the portion corresponding to the portion to be exposed, and this was treated with a phosphoric acid-nitric acid type etchant for Al to etch Al where no resist was provided to complete formation of an electrothermal transducer having a heat-generating portion of heat-generating resistor provided between a pair of electrodes on the support. The arrangement pitch of the heat-generating resistor was 70 µm, and the uniformity of its dimension over the whole formation surface was examined to be good. Finally, on the electrothermal transducer was provided SiO₂ layer as the protective layer and further the polyimide layer at the portion except for the heat-generating portion to complete the substrate for ink jet head. The substrate thus prepared was bonded to a covering member 5 made of glass having a recession for forming the liquid path 6 and the liquid chamber 10, etc. as shown in Fig. 1B to prepare an ink jet recording head, and recording test therefor was performed. As the result, good recording could be practiced, with durability being also good. Example 2 A substrate for ink jet head and an ink jet head using the substrate were prepared according to the present invention in the same manner as in Example 1 except for employing BCl₃ as the reactive gas for etching. Etching speed was 120 Å/min. Also in this example, a substrate for ink jet head and an ink jet head using the substrate were prepared with high precision and high quality. Example 3 A substrate for ink jet head and an ink jet head using the substrate were prepared according to the present invention in the same manner as in Example 1 except for employing BCl₃ + Cl₂ (flow rate ratio 1:1) as the reactive gas for etching. Etching speed was 260 Å/min. Also in this example, a substrate for ink jet head and an ink jet head using the substrate were prepared with high precision and high quality. Example 4 A substrate for ink jet head and an ink jet head using the substrate were prepared according to the present invention in the same manner as in Example 1 except for employing CF₄ as the reactive gas for etching. Etching speed was 31 Å/min. Also in this example, a substrate for ink jet head and an ink jet head using the substrate were prepared with high precision and high quality. Example 5 A substrate for ink jet head and an ink jet head using the substrate were prepared according to the present invention in the same manner as in Example 1 except for employing C₂F₆ as the reactive gas for etching. Etching speed was 32 Å/min. Also in this example, a substrate for ink jet head and an ink jet using the substrate were prepared with high precision and high quality. Example 6 A substrate for ink jet head and an ink jet head using the substrate were prepared according to the present invention in the same manner as in Example 1 except for employing CHF₃ as the reactive gas for etching. Etching speed was 21 Å/min. Also in this example, a substrate for ink jet head and an ink jet head using the substrate were prepared with high precision and high quality. Example 7 A substrate for ink jet head and an ink jet head using the same were prepared according to the present invention in the same manner as in Example 1 except for employing ZrB₂ as the material for forming a heat-generating resistor. Etching speed was 320 Å/min. Also in this example, a substrate for ink jet head and an ink jet head using the substrate were prepared with high precision and high quality. Example 8 A substrate for ink jet head and an ink jet head using the same were prepared according to the present invention in the same manner as in Example 1 except for employing ZrB₂ as the material for forming a heat-generating resistor and employing CF₄ as the reactive gas for etching. Etching speed was 31 Å/min. Also in this example, a substrate for ink jet head and an ink jet head using the substrate were prepared with high precision and high quality. Example 9 A substrate for ink jet head and an ink jet head using the same were prepared according to the present invention in the same manner as in Example 1 except for employing TiB₄ as the material for forming a heat-generating resistor. Etching speed was 290 Å/min. Also in this example, a substrate for ink jet head and an ink jet head using the substrate were prepared with high precision and high quality. Example 10 A substrate for ink jet head and an ink jet head using the same were prepared according to the present invention in the same manner as in Example 1 except for employing TiB₄ as the material for forming a heat-generating resistor and employing CF₄ as the reactive gas for etching. Etching speed was 27 Å/min. Also in this example, a substrate for ink jet had and an ink jet head using the substrate were prepared with high precision and high quality. In the present invention, the liquid path of the ink jet head may be formed by initially forming the wall-forming member of the liquid path with a photosensitive resin and then bonding the top plate to the wall-forming member. In an ink jet head obtained according to the present invention, the direction of ink supply to the heat generating portion within the liquid path and the direction of ink discharge from the discharge opening may be substantially same or different from each other (for example, forming generally right angle). Further, the ink jet head obtained according to the present invention may be of the so-called full line type having discharge openings arranged over the whole recording width of a recording medium. Fig. 5 is a schematic perspective view showing the appearance of an ink jet device equipped with an ink jet head obtained according to the present invention. There are shown a main body 1000, a power switch 1100 and an operation panel 1200. According to the method of the present invention, since the dry etching method which can control easily the state of etching is used for patterning of the heat-generating resistor layer, no registration working of the mask as in the prior art is required and there is no lowering in yield due to registration mistake of mask. Also, since etching of the heat-generating resistor layer is effected in the dry step, there is no generation of defective etching in the wet step as in the prior art. Further, even with, for examdple, A4 size width (210 mm), a substrate with excellent dimensional precision can be provided.

Claims: A method of preparing a substrate (1, 2, 3) for an ink jet head comprising a support (1) and an electrothermal transducer (2, 3) formed on said support and having a heat generating resistor (2) and a pair of electrodes (3) connected electrically to said heat generating resistor, said method comprising a first step of etching to pattern a layer of said electrodes (3) provided on a layer of said heat generating resistor (2), and a second step of etching to pattern the layer of said heat generating resistor (2), characterized in that the etching of said layers (2; 3) is effected with the same resist pattern (11), and the etching of said second step is dry etching. A method according to claim 1, characterized in that said dry etching is carried out using a halogenic etching gas. A method according to claim 2, characterized in that said halogenic etching gas is a chlorine-type gas. A method according to claim 3, characterized in that said chlorine-type gas is selected from CCl₄, Cl₂, BCl₃ and SiCl₄. A method according to claim 2, characterized in that said halogenic gas is a fluorine-type gas. A method according to claim 5, characterized in that said fluorine-type gas is selected from CF₄, CHF₃, CF₆ and NF₃. A method according to claim 1, characterized in that said heat-generating resistor (2) is formed using a metal boride. A method according to claim 7, characterized in that said metal boride is selected from hafnium boride, lanthanum boride, zirconium boride, titanium boride, tantalum boride, tungsten boride, molybdenum boride, niobium boride, chromium boride and vanadium boride. A method according to claim 1, characterized in that the etching of said first step is dry etching. A method according to claim 1, characterized in that the etching of said first step is wet etching. A method according to claim 1, characterized in that subsequently to said second step, an additional step of forming a protective layer on said electrothermal transducer (2, 3) is performed. A method according to claim 11, characterized in that said protective layer is formed of SiO₂. A method according to claim 11, characterized in that said protective layer is formed of a polyimide. A method of preparing an ink jet head comprising a liquid path (6) and a substrate (1, 2, 3) having an electrothermal transducer (2, 3) formed by a heat-generating resistor (2) and a pair of electrodes (3) connected electrically to said heat-generating resistor on a support (1), wherein said liquid path (6) is formed on said support (1) corresponding to a heat-generating portion (8) of said electrothermal transducer (2, 3) formed between said pair of electrodes (3) and communicates with a discharge opening (7) for discharging liquid, characterized in that said substrate (1, 2, 3) is prepared by a method according to one of claims 1 to 13. A method according to claim 14 , characterized in that said electrothermal transducer (2, 3) generates heat utilized for discharging liquid. A method according to claim 14, characterized in that said liquid path (6) is formed by bonding said support (1) to a covering member (5) having a recession for forming said liquid path. A method according to claim 14, characterized in that said liquid path (6) is formed by forming a wall-forming member for forming a wall of said liquid path and then bonding said wall-forming member to a top plate. A method according to claim 17, characterized in that said wall-forming member is formed of a photosensitive resin.

Inventors: KOMURO HIROKAZU, KOMURO, HIROKAZU
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1988
Main classification: B41J2
IPC codes: B41J2