Abstract:
A liquid ejecting head including a coating resin layer including a plurality of ejection outlets for ejecting liquid and flow paths which are in fluid communication with the ejection outlets, respectively; an energy generating element for generating energy for ejecting liquid; and an adhesion improving layer provided between the coating resin layer and the substrate, wherein the coating resin layer further includes a first resin material layer closest to the substrate and at least one second resin material layer, and the first resin material layer provides at least one stepped portion continuing from a periphery of the second resin material layer.

Description:
FIELD OF THE INVENTION AND RELATED ART 
       [0001]    The present invention relates to a liquid jet head which records by ejecting liquid toward recording medium. In particular, it relates to an ink jet recording head which records by ejecting ink. Further, it relates to a method for forming microscopic structural components usable for manufacturing semiconductors or the like. 
         [0002]    There have been disclosed various liquid jet heads of the so-called side shooter type, that is, liquid jet heads which jet ink droplets in the direction perpendicular to the substrate of a liquid jet head (Japanese Laid-open Patent Application 2007-261169). 
         [0003]      FIG. 6  is a schematic perspective view of an example of liquid jet head of the conventional side-shooter type. Incidentally, for simplification,  FIG. 6  schematically shows a substantially smaller numbers of liquid ejection outlets  106  and energy generating elements  101  that the actual number of liquid ejection outlets  106  and energy generating elements  101  of the liquid jet head. 
         [0004]    As for the structure of this liquid jet head, this liquid jet head is made up of a substrate  102  and a resinous plate  103  having multiple liquid ejection outlets  106 . The resinous plate  103  is bonded to the substrate  102 . The substrate  102  has an ink distribution hole  107 . The liquid jet head is also provided with multiple energy generating elements  101 , which are disposed on the surface of the substrate  102 , to which the resinous plate  103  is adhered, in such a manner that the energy generating elements align with the liquid ejection outlets  106 , one for one. Bonding of the resin plate  103  to the substrate  102  creates multiple ink passages which extend from the ink distribution hole  107  to the ink ejection outlets  106 , which are above the abovementioned energy generating elements, one for one. Ink is supplied to each ink passage  108  through the ink distribution hole  107 , is jetted out of the ink ejection outlet  106  by the bubble generated by the function of the energy generating element, and adheres to recording medium. 
         [0005]    In the case of a liquid jet head structured like the liquid jet head described above, the resinous plate  103 , that is, a resin layer formed in a manner to cover the substrate  102 , its inward portion is provided with liquid ejection outlets  106  and ink passages  108 . Therefore, the inward portion of the resinous plate  103 , in terms of the direction parallel to the primary surfaces of the substrate  102 , is less in physical volume than its outward portion. That is, the outward portion of the resinous plate  103  is greater in physical volume than the inward portion of the resinous plate  103 . 
         [0006]    In comparison, in the case of the liquid jet head disclosed in Japanese Laid-open Patent Application 2003-080717, its peripheral portion (outward portion) of the resin plate (layer) is made thinner than its center portion (inward portion), and therefore, the outward portion of the resinous layer is less in physical volume than its inward portion. Further, the thin peripheral portion of the resin layer of the ink jet head disclosed in the second patent document is provided with grooves. That is, these thin portions are separated by the grooves, and have vacant portions. 
         [0007]    In recent years, demand has been increasing for ink jet printers which are substantially faster in printing speed than conventional ink jet printers. This demand for the increase speed seems to come from the fact that there has been a significant increase in the processing speed of a computer, and also, that ink jet printers have been further reduced in the size of their already minutes ink droplets, being therefore required to be higher in ink dot density (ink droplet density). 
         [0008]    Further, in the field of printers capable of outputting a print of a large size, or printers connected to a network, the desire to increase the printers in output speed is even greater. There are two ways to increase a printer in output speed. One is to increase a printer in the number of ink droplets it can jet per unit length of time, that is, to increase a printer in the frequency with which it can jet ink droplets per unit length of time. The other is to increase a printer in the number of ink ejection outlets. Usually, both of the two methods are employed to increase a printer in output speed. However, increasing a printer in the number of ink ejection outlets results in the increase in the length of the liquid jet head of the printer. 
         [0009]    In recent years, however, it has become evident, through various tests, that the longer the liquid jet head, the more likely the peripheral portions of the resin layer, of which the liquid passage plate of the liquid jet head is made, to separate from the substrate. More specifically, the portions of the resin layers, which are on the outward side relative to the liquid ejection outlets and ink passages, that is, the portions which are greater in volume, are greater in the amount of the stress to which they are subjected, than the portions of the resin layer, which have the liquid ejection outlets and liquid passages. Thus, the frequency and extent with which the outward portions separate from the substrate is greater than those with which the inward portions separate from the substrate. It also became evident that the thicker the liquid passage plate (resin layer) of a liquid jet head, the greater the amount of the stress to which the liquid passage plate (resin layer) is subjected, and therefore, the higher the frequency with which it separates from the substrate. 
         [0010]    On the other hand, in the case of the liquid jet head disclosed in Japanese Laid-open Patent Application 2003-080717, the peripheral portions of the liquid passage plate (resin layer) are formed thinner than the other portions. However, it is rather difficult to control the manufacturing process for a liquid jet head so that the peripheral portions will have a specified thickness. Thus, under certain conditions, it was rather difficult to make liquid jet heads, the liquid passage plate (resin layer) of which is sufficiently thin across its peripheral portions. Therefore, even in the case of the liquid jet head made in accordance with this patent application, the separation of the liquid passage plate (resin layer) from the substrate sometimes occurred. 
       SUMMARY OF THE INVENTION 
       [0011]    One of the objects of the present invention is to solve the above-described problem of a conventional liquid jet recording head. Thus, the primary object of the present invention is to provide a highly reliable liquid jet head by solving the problems which a conventional liquid jet recording head suffers, more specifically, the problem that the liquid passage plate (resin layer) of a liquid jet head separates from the substrate of the liquid jet head. 
         [0012]    According to an aspect of the present invention, there is provided a liquid ejecting head and a structure therefor, a manufacturing method therefor, wherein said liquid ejecting head comprises a coating resin layer including a plurality of ejection outlets for ejecting liquid and flow paths which are in fluid communication with the ejection outlets, respectively; an energy generating element for generating energy for ejecting liquid; and an adhesion improving layer provided between said coating resin layer and said substrate, wherein said coating resin layer further includes a first resin material layer closest to said substrate and at least one second resin material layer, and said first resin material layer provides at least one stepped portion continuing from a periphery of said second resin material layer. 
         [0013]    The present invention can prevent the liquid passage plate (resin layer) of a liquid jet head from separating from the substrate of the liquid jet head, and therefore, it can improve a liquid jet head in reliability. Further, the liquid jet head manufacturing method in accordance with the present invention can even more precisely form a liquid jet head which is highly reliable in that its liquid passage plate is unlikely to separate from its substrate. 
         [0014]    These and other objects, features, and advantages of the present invention will become more apparent upon consideration of the following description of the preferred embodiments of the present invention, taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a schematic perspective view of the liquid jet head in the first embodiment of the present invention. 
           [0016]      FIG. 2(   a ) is a plan view of the recording chip, which is a part of the liquid jet head in the first embodiment of the present invention, and  FIG. 2(   b ) is a sectional view of the recording head. 
           [0017]      FIGS. 3(   a )- 3 ( f ) are schematic drawings for describing the steps in a typical method for manufacturing the liquid jet head in accordance with the present invention. 
           [0018]      FIG. 4(   a ) is a plan view of the recording chip, which is a part of the liquid jet head in the second embodiment of the present invention, and  FIG. 4(   b ) is a sectional view of the recording chip. 
           [0019]      FIG. 5(   a ) is a plan view of the recording chip, which is a part of the liquid jet head in the third embodiment of the present invention, and  FIG. 5(   b ) is a sectional view of the recording chip. 
           [0020]      FIG. 6  is a schematic perspective view of an example of a typical conventional liquid jet head. 
           [0021]      FIG. 7  is a schematic sectional view of an example of a liquid jet head in accordance with the present invention. 
           [0022]      FIGS. 8(   a   1 )- 8 ( e   1 ) are schematic sectional views of the recording chip, in various stages of its manufacture, one for one, for describing a typical method for manufacturing the liquid jet head in accordance with the present invention, and  FIGS. 8(   a   2 )- 8 ( e   2 ) are schematic plan views of the recording chip, in various stages of its manufacture, one for one, also for describing the typical method for manufacturing the liquid jet head in accordance with the present invention. 
           [0023]      FIGS. 9(   a )- 9 ( e ) are also schematic sectional views of the recording chip, in various stages of its manufacture, one for one, for describing the typical method for manufacturing the liquid jet head in accordance with the present invention. 
           [0024]      FIGS. 10(   a ) and  10 ( b ) are schematic drawing of a couple of examples of a liquid jet head in accordance with the present invention. 
           [0025]      FIG. 11  is a schematic sectional view of a precursor of a liquid jet head in accordance with the present invention, for showing an example of a liquid jet head manufacturing method in accordance with the present invention. 
           [0026]      FIG. 12  is a schematic sectional view of a precursor of the liquid jet head in accordance with the present invention, for showing another example of a liquid jet head manufacturing method in accordance with the present invention. 
           [0027]      FIG. 13  is a schematic sectional view of a precursor of the liquid jet head in accordance with the present invention, for showing another example of a liquid jet head manufacturing method in accordance with the present invention. 
           [0028]      FIG. 14  is a schematic sectional view of a precursor of the liquid jet head in accordance with the present invention, for showing another example of a liquid jet head manufacturing method in accordance with the present invention. 
           [0029]      FIG. 15  is a schematic sectional view of a precursor of the liquid jet head in accordance with the present invention, for showing another example of a liquid jet head manufacturing method in accordance with the present invention. 
           [0030]      FIG. 16  is a schematic sectional view of a precursor of the liquid jet head in accordance with the present invention, for showing another example of a liquid jet head manufacturing method in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0031]    Hereinafter, the present invention will be concretely described with reference to the appended drawings. It should be noted here that if a given component of the liquid jet head in any of the following embodiments of the present invention is the same in structure as any of the previously described component, the second component will be given the same referential number, and may not be described. 
         [0032]    A liquid jet head in accordance with the present invention is mountable in a printer, a copying machine, a facsimile machine with a communication system, a word processor or the like apparatus with a printer portion, and also, an industrial recording apparatus which is in combination with various processing apparatuses. Further, a liquid jet head in accordance with the present invention can be used as an ink jet recording head to record on various recording media, for example, paper, thread, fiber, cloth, leather, metal, plastic, glass, lumber, ceramic, etc. Incidentally, not only does “recording” mean to form a meaningful image, such as a letter, a pattern having a specific meaning, but also, to form a meaningless image on recording medium. 
         [0033]    Further, the present invention is compatible with a recording head of the so-called full-line type, which is wide enough to cover the entire recordable range of a sheet of recording medium, in terms of the direction perpendicular to the direction in which the sheet of recording medium is conveyed. Moreover, it is compatible with a large recording head made up of an integral combination of small recording heads, a color recording head made up of a combination of multiple, individually manufactured small recording heads. 
         [0034]    Hereafter, the preferred embodiment of the present invention will be described with reference to the appended drawings. 
       Embodiment 1 
       [0035]      FIG. 1  is a schematic perspective view of the liquid jet head in this embodiment. 
         [0036]    This liquid jet head is made up of a substrate  2 , an ink passage plate  3 , energy generating elements  1 , contact pad  13 . The energy generating elements  1  are disposed in two columns on the substrate  2 , at a preset pitch. The contact pad  13  is for establishing electrical connection between the liquid jet head and the other devices, and is formed also on the substrate  2 . The substrate  2  has an ink distribution hole  7 , the top opening of which is between the two columns of energy generating elements. The ink passage plate  3  has two columns of ink ejection outlets  6 , and multiple ink passages  8  which extend from the ink distribution hole  7  to the ink ejection outlets  6 , one for one. The ink passage plate  3  hereafter may be referred to as a substrate covering resin layer  3 , or simply as a resin layer  3 . The ink passage plate  3  is bonded to the substrate  2  with the placement of an adhesion enhancement layer  5  between the ink passage plate  3  and substrate  2 , in such a manner that the ink ejection outlets  6  align with the energy generating elements one for one. 
         [0037]      FIG. 2(   a ) is a top plan view of the recording chip which is a part of the liquid jet head in this embodiment.  FIG. 2(   b ) is a sectional view of the recording chip at a line A-A in  FIG. 2(   a ). 
         [0038]    As described above, the stress generated in the substrate covering resin layer  3  is affected by the thickness of the resin layer  3 . That is, the greater the thickness of the resin layer  3 , the greater the amount by which stress is generated in the resin layer  3 . This stress sometimes causes the resin layer  3  to separate from the adhesion enhancement layer  5 , and the separation adversely affects the liquid jet head in terms reliability. 
         [0039]    In this embodiment, therefore, the substrate covering resin layer  3  is separated into two sublayers, that is, a first resin layer  10  and a second resin layer  11 , with the presence of a step  12 . Next, this structural setup will be described in detail. 
         [0040]    Referring to  FIGS. 2(   a ) and  2 ( b ), the liquid jet head in this embodiment has the substrate  2 , first resin layer  10  formed on the substrate  2 , and second resin layer  11  formed on the first resin layer  10 . In other words, the second resin layer  11  is above the substrate  2  with the presence of the first resin layer  10  between the second resin layer  11  and substrate  2 . 
         [0041]    Further, the second resin layer  11  is made smaller than the first resin layer  10 , creating therefore the step  12  between the top surface of the second resin layer  10  and the top surface of the first resin layer  11 . That is, the location of the step  12  coincides with those of the bottom edges of the second resin layer  11 . Referring to  FIG. 2(   b ), the hatched portion  12 , that is, a portion of the first resin layer  10 , which horizontally extends beyond the bottom edges of the second resin layer  11 , is solid. That is, the step portion  12  does not have grooves or the like. Further, the step portion  12  and second resin layer  11  are integral parts of the ink passage plate  3 , that is, the substrate covering resin layer  3 . 
         [0042]    The amount by which stress is generated in the step portion  12  of the substrate covering resin layer  3  can be reduced by reducing the step portion  12  in thickness. Further, the step portion  12  is the portion of the first resin layer  10 , which horizontally extends beyond the edge of the second resin layer  11 , as described above. That is, there is a step between the first and second resin layers  10  and  11 . In other words, the substrate covering resin layer  3  is provided with a pliant portions, that is, the boundaries between the bottom edges of the second resin layer  11  and the first resin layer  10 . Therefore, the stress generated in the peripheral portion of the substrate covering resin layer  3  can be dispersed into the abovementioned boundaries, and the boundary between the first resin layer  10  and adhesion enhancement layer  5 . That is, the above-described structural arrangement can reduce the stress generated in the substrate covering resin layer  3 . In other words, the present invention can afford more latitude in designing a liquid jet head in terms of the thickness of the first resin layer  10 . 
         [0043]    Further, the liquid jet head in this embodiment is structured so that the height h (thickness) of the step portion  12  from the interface between the adhesion enhancement layer  5  and substrate covering resin layer  3  is less than the half of the thickness t of the thickest portion of the substrate covering resin layer  3 . The first resin layer  10  is in direct contact with the adhesion enhancement layer  5 , and therefore, the volume of the first resin layer  10  significantly affects whether or not the first resin layer separates from the substrate  2  (adhesion enhancement layer  5 ). Thus, in order to minimize the amount by which stress is generated in the first resin layer  10  by reducing the first resin layer  10  in volume, the liquid jet head in this embodiment is structured so that the thickness tl of the first resin layer  10  is no more than one half the thickness t of the substrate covering resin layer  3 . Further, even though the liquid jet head is structured so that the step portion  12  is thin, the step portion  12  does not have grooves or the like; it is solid. Thus, the step portion  12  is satisfactorily strong. 
         [0044]    As for the thickness t of the substrate covering resin layer  3  having the step portion  12 , the thickness t is the sum of the thickness t 1  of the first resin layer  10  and the thickness t 2  of the second resin layer  11 . That is, the provision of the step portion  12  divides the substrate covering resin layer  3 , the thickness of which is t, into the portion which is t 1  in thickness, and the portion which is t 2  in thickness. Thus, the stress generated in the substrate covering resin layer  3  is distributed into the portion with the thickness of t 1  and the portion with the thickness of t 2 , in proportion to the their thickness. Therefore, the amount by which stress is generated in the step portion  12 , that is, the peripheral portion of the first resin layer  10 , which is in contact with the adhesion enhancement layer  5 , is relatively small because the step portion  12  is thin (t 1  in thickness). Therefore, the step portion  12  is unlikely to separate from the substrate  2 . 
         [0045]    In this embodiment, the liquid jet head is structured so that the first resin layer  10  is thinner (t 1  in thickness) than the second resin layer  11 , as described above. Thus, the second resin layer  11  is relatively thick (t 2  in thickness) compared to the first resin layer  10  (t 1  in thickness). In order for an ink jet head to be satisfactory in ink ejecting performance, the distance between each of its liquid ejection outlets  6  and the corresponding energy generating element  1 , that is, the thickness t of the substrate covering resin layer  3 , has to be set to a specific value. In this embodiment, the thickness t of the substrate covering resin layer  3  is roughly 75 μm. Structuring a liquid jet head so that the thickness t 2  of the second resin layer  11  is greater than the thickness t 1  of the first resin layer  10  makes the second resin layer  11  greater than the first resin layer  10  in the amount by which stress is generated in them. If the amount of stress in the second resin layer  11  exceeds a certain value, the second resin layer  11  cracks. However, the cracks which occur in the second resin layer  11  are different from the cracks which occur at the interface between the substrate covering resin layer  3  and adhesion enhancement layer  5  as the substrate covering resin layer  3  separates from the substrate  2 . That is, unlike the cracks which occur at the interface between the substrate covering resin layer  3  and adhesion enhancement layer  5 , the cracks which occur in the substrate covering resin layer  3  are attributable to the cohesive failure of the substrate covering resin layer  3  itself. 
         [0046]    Thus, in this embodiment, in order to prevent the occurrences of the cracking of the substrate covering resin layer  3 , which is attributable to cohesive failure, the corner portions  11   b  of the second resin layer  11  are rounded to reduce the amount of the stress which concentrates to these portions. 
         [0047]    However, the corner portions  11   a  of the first resin layer  10  are not rounded; a vertical surface of the first resin layer  10  (relative to substrate  2 ) perpendicularly intersects with its adjacent vertical surfaces. That is, in this embodiment, the four corners  11   a  of the first resin layer  10  have an angle 90°; the vertical surfaces of the first resin layer  10  perpendicularly intersect with the adjacent vertical surfaces. If the corner portions  11   a  of the first resin layer  10  are rounded, the point to which stress concentrates is likely to shift from the first resin layer  10  to the adhesion enhancement layer  5 , and therefore, the adhesion enhancement layer  5  and substrate  2  may separate from each other, or cohesive failure may occur to the adhesion enhancement layer  5 . If the adhesion enhancement layer  5  separates from the substrate  2  or becomes damaged due to cohesive failure, the adhesion enhancement layer  5  fails to protect the surface of the substrate. This is why the corner portions  11   a  of the first resin layer  10  are angled at 90° to prevent the point to which stress concentrates, from shifting from the first resin layer  10  to the adhesion enhancement layer  5 . 
         [0048]    In this embodiment, the overall thickness t of the resin layer  3  is roughly 75 μm, and the thickness t 1  of the first resin layer  10 , which is a part of the substrate covering resin layer  3  is roughly 20 μm, whereas the width w of the step portion  12  is roughly 80 μm. Thus, even if the substrate covering resin layer  3  is changed in thickness, the same effects as those described above can be obtained by changing the second resin layer  11  in thickness (t 2 ) and/or the step portion  12  in width w, as necessary. 
         [0049]    Also in this embodiment, the substrate covering resin layer  3  is structured so that there is only one step between the main portion of the substrate covering resin layer  3  and the peripheral portion of the substrate covering resin layer  3 . However, the substrate covering resin layer  3  may be structured so that there are two or more steps between the main portion of the substrate covering resin layer  3  and the peripheral portion of the substrate covering resin layer  3 . That is, the substrate covering resin layer  3  may be structured so that there are two or more second resin layers  11  on the first resin layer  10 . In a case where the substrate covering resin layer  3  is structured so that two or more second resin layers  11  are on the first resin layer  10 , the main portion of the substrate covering resin layer  3  is surrounded by two or more step portions  12 , which are different in thickness. For example, if the substrate covering resin layer  3  is structured so that there are two second resin layers  11  stacked on the first resin layer  10 , the bottom second resin layer  11  is formed on the first resin layer  10  in such a manner that the peripheral area of the first resin layer  10  remains exposed from the bottom resin layer  11 , and the top second resin layer  11  is formed on the bottom second resin layer  11  in such a manner that the peripheral area of the bottom second resin layer  11  remains exposed from the top second resin layer  11 . 
         [0050]    By structuring the substrate covering resin layer  3  so that there are two or more steps between the main portion (center portion in term of plane parallel to substrate  2 ) of the substrate covering resin layer  3  and the outermost edge of the substrate covering resin layer  3 , the stress generated at the step portions  12 , that is, the peripheral portions of the resin layer  3 , can be dispersed in steps into the two or more step portions  12 ; the stress can be further dispersed. 
         [0051]    Next, referring to  FIG. 3 , a typical method for manufacturing the liquid jet head in accordance with the present invention will be described. 
         [0052]    First, referring to  FIG. 3(   a ), a layer  4  is formed of dissolvable resin on the substrate  2  which already has the energy generating elements  1 . The dissolvable resin layer  4  is formed in the pattern of the multiple ink passages  8 . More concretely, first, a dry sheet of dissolvable resin is laminated to the substrate  2 , and resist is coated on the laminated sheet of dissolvable resin by spin-coating or the like method. Then, the resist layer is exposed to ultraviolet rays (Deep-UV light), and developed. Even more concretely, polymethyl isopropenyl ketone (ODUR-1010: product of Tokyo Ohka Kogyo Co., Ltd.) is spin-coated on the substrate  2 , and dried. Then, the dried polymethyl isopropenyl ketone is patterned by being exposed with the use of Deep-UV light, and developed. 
         [0053]    Next, referring to  FIG. 3(   b ), the first resin layer  10  is formed on the dissolvable resin layer  4 . 
         [0054]    Next, referring to  FIG. 3(   c ), the first resin layer  10  is exposed with ultraviolet rays (Deep-UV light), for example. Then, the portion of the first resin layer  10 , which will become the step portion  12 , is heated to create the pattern of the step portion  12 . 
         [0055]    Then, the material for the second resin layer  11  is coated as shown in  FIG. 3(   d ). 
         [0056]    Next, the coated material for the second resin layer  11  is exposed with ultraviolet rays (Deep-UV light), for example, as shown in  FIG. 3(   e ). 
         [0057]    Lastly, the precursor of the liquid jet head formed through the above described steps is developed to form the first and second resin layers  10  and  11  as shown in  FIG. 3(   f ). 
         [0058]    As described above, the liquid jet head in this embodiment is provided with the step portion  12 , that is, the portion of the first resin layer  10 , which extends outward beyond the second resin layer  11 . Therefore, it is unlikely to suffer from the problem that the peripheral portion of the substrate covering resin layer  3  separates from the substrate  2 . Further, the step portion  12  is solid, being therefore satisfactorily strong. 
       Embodiment 2 
       [0059]    Next, referring to  FIGS. 4(   a ) and  4 ( b ), the second preferred embodiment of the present invention will be described.  FIG. 4(   a ) is a top plan view of the recording chip, which is a part of the liquid jet head in this embodiment, and  FIG. 4(   b ) is a sectional view of the recording chip, at a line A-A in  FIG. 4(   a ). 
         [0060]    In this embodiment, the second resin layer  11  is provided with a groove  9 , which surrounds the ink passage portion having the liquid ejection outlets  6  and ink passages  8 . The groove  9  is shaped so that the surface  9   a  of each of its two lateral walls is jagged; the cross section of the surface  9   a  of each of its lateral walls, at a plane perpendicular to the substrate  2 , looks like saw teeth. 
         [0061]    The structure of the liquid jet head in this embodiment is the same as that of the liquid jet head in the first embodiment, except that the second resin layer  11  of the latter has the groove  9 . Thus, the features of the liquid jet head in this embodiment, which are the same as those of the liquid jet head in the first embodiment will not be described in detail. Further, the structural components of the liquid jet head in this embodiment, which are the same as the counterparts in the first embodiment will be given the same referential codes to describe them. 
         [0062]    If the surface  9   a  of each of the lateral walls of the groove  9  is flat, the stress generated in the second resin layer  11  works in the same direction across a large area, and therefore, the separation of the substrate covering resin layer  3  from the adhesion enhancement layer  5  occurs across a large area of the interface between the substrate covering resin layer  3  and adhesion enhancement layer  5 . In this embodiment, however, the surface  9   a  of each of the lateral surfaces of the groove  9  of the substrate covering resin layer  3  is made jagged so that its cross section, at a plane parallel to the substrate  3 , looks like the teeth portion of a saw. Therefore, the stresses different in direction are generated in the same area of the interface between the second resin layer  11  and adhesion enhancement layer  5 . Thus, some of the stresses cancel with each other, reducing therefore the stress which acts on the substrate covering resin layer  3 . Further, since the second resin layer  11  of the liquid jet head in this embodiment is provided with the groove  9 , the substrate covering resin layer  3  of the liquid jet head in this embodiment is smaller in overall volume than the liquid jet head in the first embodiment. That is, the amount by which stress is generated in the substrate covering resin layer  3  of the liquid jet head in this embodiment is smaller, by an amount equivalent to its overall volume reduction, than the amount by which stress is generated in the substrate covering resin layer  3  of the liquid jet head in the first embodiment. That is, not only can this embodiment reduce the amount by which stress is generated in the peripheral portion of the substrate covering resin layer  3  of the liquid jet head to prevent the substrate covering resin layer  3  from separating from the substrate  2 , but also, can prevent the problem that the portions of the substrate covering resin layer  3 , which surrounds its area having the ink passages  8 , separate from the substrate  2 . 
         [0063]    The groove  9  is not located in the step portion  12 . Therefore, the liquid jet head in this embodiment is satisfactorily strong in spite of the presence of the groove  9 . 
       Embodiment 3 
       [0064]    Next, the third preferred embodiment of the present invention will be described with reference to  FIG. 5(   a ), which is a top plan view of the recording chip, that is, a part of the liquid jet head in this embodiment, and  FIG. 5(   b ), which is a sectional view of the recording chip at a line A-A in  FIG. 5(   a ). 
         [0065]    Except that the liquid jet head in this embodiment is provided with a groove  19  and multiple connective portions  14 , the liquid jet head in this embodiment is the same as that in the first embodiment. Thus, the features of the liquid jet head in this embodiment, which are the same as those of the liquid jet head in the first embodiment will not be described in detail. Further, the structural components of the liquid jet head in this embodiment, which are the same as the counterparts in the first embodiment, will be given the same referential codes as those given to the counterparts in the first embodiment, one for one, instead of directly describing them. 
         [0066]    The liquid jet head in this embodiment is provided with a groove  19 , which surrounds the portion of the substrate covering resin layer  3 , which has the liquid ejection outlets  6  and ink passages  8 . The groove  19  in this embodiment is different from that in the second embodiment in that the surface  19   a  of each of the lateral walls of the groove  19  in this embodiment is flat. Further, the portion  3   a  of the substrate covering resin layer  3 , which is on the outward side of the groove  19 , is connected to the portion  3   b  of the substrate covering resin layer  3 , which is on the inward side of the groove  19 , by the multiple connective portions  14 , which are separated from the adjacent ones by a present distance. 
         [0067]    In this embodiment, the internal surfaces  19   a  are flat. Therefore, the effects provided by the first embodiment, that is, the effects obtained by the jagged surfaces  9   a,  the cross section of which at a plane parallel to the substrate  2  looks like the teeth portion of a saw, cannot be obtained. However, the portion  3   a  of the substrate covering resin layer  3 , which is on the outward side of the groove  9 , and the portion  3   b  of the substrate covering resin layer  3 , which is on the inward side of the groove  9 , are supported by the connective portions  14 . Therefore, the separation of the substrate covering resin layer  3  can be prevented. 
         [0068]    Further, the present invention may be embodied in the combination of the second and third preferred embodiments. That is, not only may the surface of each of the lateral walls of the abovementioned groove be made jagged, but also, the substrate covering resin layer  3  may be provided with multiple connective portions, which connect the portion  3   a  of the substrate covering resin layer  3 , which is on the outward side of the groove, and the portion  3   b  of the substrate covering resin layer  3 , which is on the inward side of the groove. 
         [0069]    Incidentally, the numerical values or the like quoted in the description of the preceding preferred embodiment are nothing but examples. That is, these values are not intended to limit the present invention in scope. 
         [0070]    Next, a typical method for manufacturing the liquid jet head in this embodiment will be described. 
         [0071]    First, referring to  FIG. 8 , an example of a method for manufacturing the liquid jet head in this embodiment will be roughly described. 
         [0072]      FIGS. 8(   a   1 )- 8 ( e   1 ) are schematic sectional views of the precursors of the liquid jet head in the various stages of the manufacturing of the liquid jet head in this embodiment, as seen at a plane equivalent to the sectional plane in  FIG. 7 .  FIG. 8(   a   2 )- 8 ( e   2 ) are top plan views of the same precursors as those shown in  FIGS. 8(   a   1 )- 8 ( e   1 ), one for one. 
         [0073]    First, energy generating elements  1  are formed on a substrate  2  as shown in  FIGS. 8(   a   1 ) and  8 ( a   2 ). 
         [0074]    Next, a pattern  21  for the formation of the liquid passages is formed of dissolvable resin. More concretely, a sheet of dry film of resist is laminated on the surface of the substrate  2 , or the top surface of the substrate is coated with resist by spin-coating or the like method. Then, the resist layer is exposed with ultraviolet rays (Deep-UV light), and developed. As the material for the resist, polymethyl isopropenyl ketone (ODUR-1010: product of Tokyo Ohka Kogyo Co., Ltd.) can be listed. Incidentally, if necessary, an adhesion improvement layer may be formed on the substrate before the formation of the pattern  21 , in order to better adhere the liquid passage formation plate to the substrate  2 . As the material for the adhesion improvement layer, polyether amide can be listed, for example. 
         [0075]    Next, a cover layer  22 , which is for forming the liquid passage formation plate, is formed on the pattern  21 . Then, liquid ejection outlets  6  are formed through the cover layer  22 , obtaining the precursor shown in  FIGS. 8(   c   1 ) and  8 ( c   2 ). It is in this step that the step portion  12  is formed in a manner to surround the primary portion of the cover layer  22 . From the standpoint of reducing the amount by which stress is generated in the substrate covering resin layer  3 , the step portion  12  is formed in such a manner to entirely surround the primary portion of the cover layer  22 . 
         [0076]    Next, referring to  FIGS. 8(   d   1 ) and  8 ( d   2 ), the liquid distribution hole  7  is formed through the substrate  2  by etching or the like method. More specifically, in a case where a silicon wafer is used as the material for the substrate  2 , the ink distribution hole  7  is formed by anisotropic etching, with the use of strong alkaline solution, such as KOH, NaOH, and TMAH. More concretely, the bottom surface of the substrate (silicon wafer) is thermally oxidized, and the pattern for the liquid distribution hole  7  is formed on the oxidized bottom surface of the substrate  2 . Then, the substrate  2  is etched with TMH solution for ten hours plus several hours, while keeping the temperature of the TMH solution at 80° to form the ink distribution hole  7 . 
         [0077]    Next, referring to  FIGS. 8(   e   1 ) and  8 ( e   2 ), the pattern  21  is removed to form the liquid passages  8 . More concretely, the pattern  21  is exposed in entirety with Deep-UV light through the cover layer  22 , and then, is dissolved away. Then, the remainder is dried. Incidentally, subjecting the precursor to ultrasonic waves while dissolving the pattern  21  can definitely reduce the time necessary for dissolving away the pattern  21 . 
         [0078]    After the completion of the above described steps, the precursor is provided with electrical contacts necessary for electrical connection. This is the last step in the manufacturing of the liquid jet head in this embodiment. 
         [0079]    Next, the step shown in  FIGS. 8(   b   1 ) and  8 ( b   2 ), and the step shown in  FIGS. 8(   c ) and  8 ( c   2 ), that is, the steps for forming the step portion  12  will be described in detail with reference to  FIG. 9 . 
         [0080]      FIG. 9  is a sectional view of the precursor of the liquid jet head in this embodiment, which is equivalent to the precursor shown in  FIG. 8(   a   1 ). 
         [0081]    Referring to  FIG. 9(   a ), in order to form a liquid passage formation plate  24  on the pattern  21  on the substrate, a first cover layer  25 , which is the bottom portion of the cover layer  22 , is formed in a manner to cover the pattern  21  and the substrate  2 . More specifically, the first cover layer  25  is formed by spin-coating the pattern  21  and the top surface of the substrate  2  with photosensitive resinous compound of the negative type. The photosensitive resinous compound used in this embodiment contains polymeric resin and polymerization initiator. As the polymeric resins usable as the material for the first cover layer  25  in this embodiment, there are resins obtainable by radical polymerization, resins obtainable by cationic polymerization, resins obtainable by anionic polymerization, and the like. There is no requirement regarding the choice of the polymeric resin. As for the initiator, in the case of a resin obtainable by cationic polymerization, a cation polymerization initiator is appropriate. As the cationic polymerization initiator, a substance which generates acid as it is exposed to light can be used. As the substance which generates acid as it is exposed to light, aromatic sulfonate or aromatic iodonium salt can be used. The abovementioned resin and initiator can be used by dissolving them in an appropriate solvent. Sometimes, an additive or additives may be added to form a liquid jet head which is superior in various properties, such as, mechanical strength. In particular, a photosensitive resin of the negative type, the polymeric resin of which is an epoxy resin, and the initiator of which is a substance which generates acid as it is exposed to light, is desirable as the material usable for the photolithography used for the formation of a liquid jet head in accordance with the present invention. 
         [0082]    Next, referring to  FIG. 9(   b ), a part of the first cover layer  25  is exposed with ultraviolet rays or the like. As the part of the first cover layer  25  is exposed, the acid generating substance in the exposed part reacts to light acid, producing acid in the exposed portion. More specifically, at least the area of the first cover layer  25 , which is on the outward side of the pattern, and the area of the first cover layer  25 , which is not in the adjacencies of the pattern, are exposed, as shown in  FIG. 10  (which is top plan view of precursor, which are equivalent to  FIGS. 8(   a   2 )- 8 ( e   2 )). The area of the first cover layer  25 , which is on the outward side of the pattern, is exposed. As a result, an exposed portion  23  is formed. Referring to  FIG. 10(   a ), the exposed portion  23  is formed in a manner to surround the pattern  21  like a frame. However, the area of the first cover layer  25 , which is on the outward side of the pattern  21 , may be exposed in such a manner that the exposed portion  23  will result on each side of the pattern  21  as shown in  FIG. 10(   b ). 
         [0083]    Next, referring to  FIG. 9(   c ), the second cover layer  26  for forming the liquid passage plate is formed on the first cover layer  25 . The second cover layer  26  is formed also on the exposed portion  23 . The material for the second cover layer  26 , which is to be formed on the first cover layer  1  can be selected from among the aforementioned photosensitive resin of the negative type. However, the polymerization initiator for the material for the second cover layer  26  is desired to be the same as that for the material for the first cover layer  25 . Further it is desired that the base resin for the material for the second cover layer  26  and the polymerization initiator for the material for the second cover layer  26  are the same as those for the material for the first cover layer  25 . In particular, it is desired that the two photosensitive resinous compounds of the negative type are the same in the chemical compound seed. Although it is desired that the two materials are the same in chemical compound seed, it is not necessary that the two are the same in the ratio of the chemical compound seed. Further, the two materials may be different in density, or the like, relative to the solvent for spin-coating. 
         [0084]    Next, referring to  FIG. 9(   d ), the portions of the surface of the second cover layer  25 , which will be turned into the liquid ejection outlets  6 , are masked. Then, the first cover layer  25  is exposed together with the second cover layer  26 . More concretely, the portions of the first cover layer  25 , which are on the pattern  21 , are exposed from above (through) the portion  23   a  (portions closer to pattern  21 ) of the exposed portion  23  of the second cover layer  26  formed on the exposed portions. Then, the portions of the first cover layer  25 , which are below the part of the exposed part  23  of the first cover layer  25 , is exposed through the portion of the second cover layer  26 , which is above the pattern  21 . As for the first cover layer  25 , the exposed portion  23  to the area on the pattern  21  are exposed. The other portion  23   b  (portion away from pattern  21 ) of the exposed portion  23  is left unexposed portion  23  with the use of a mask. Then, the precursor is heated to harden the exposed portions of the first and second cover layers  25  and  26 . 
         [0085]    Next, the precursor is developed to remove the unexposed portions of the first and second cover layers  25  and  26 , obtaining thereby the precursor, the cover layer  22  of which has the liquid ejection outlets  6  and the step portion  12  as shown in  FIG. 9(   e ). The precursor shown in  FIG. 9(   e ) is equivalent to the precursor of the liquid jet head in the first embodiment, which is shown in  FIG. 8(   c   1 ). 
         [0086]    It is preferable to harden the exposed portion  23  of the first cover layer  25  by heating the precursor, as shown in  FIG. 11 , after the completion of the steps described with reference to  FIG. 9(   b ). The hardening of the exposed portion  23  prevents the acid from dispersing. That is, it can prevent the acid from moving from the exposed portion  23  into the second cover layer  26  as the second cover layer  26  is painted on the exposed portion  23  ( FIG. 9  ( c )). The exposed portion  23  has only to be heated to harden the exposed portion  23  enough to prevent the acid movement. As for the temperature level for the heating, it is thought that a temperature range of 80° C.-90° C. is appropriate, although it depends on the ingredients of the photosensitive resin of the negative type. The hardening of the exposed portion  23  can provide a distinct contrast between the portion  23   b  of the exposed portion  23 , that is, the portion to be hardened, and the portion  11   a  of the second cover layer  26 , which is on the portion  23   b  of the exposed portion  23 , which is not to be hardened, respectively. Thus, the hardening ensures that the flange-like portion  12   a  of the step portion  12 , which corresponds to the top surface of the exposed portion  23 , is precisely formed in shape. 
         [0087]    Further, described above is the case where the cover layer  10  is not developed after a portion of the first cover layer  25  is developed to create the exposed portion  23 . The case where the cover layer  10  is developed after the hardening of the exposed portion  23  will be described later. 
         [0088]    The steps which follow the step shown in  FIG. 9(   b ) are the same as the steps shown in  FIGS. 8(   d   1 ) and  8 ( d   2 ). 
         [0089]    In a case where the first and second cover layers  25  and  26  are created by painting, it is not necessary that each cover layer is created by a single stroke of painting means. That is, they may be exposed after they are created by applying the material for each cover layer several times. 
         [0090]    Going through the above described steps when manufacturing the liquid jet head in this embodiment ensures that the resultant liquid jet head will have even more precisely formed step portion (flange-like portion) around its liquid passage plate, and therefore, the liquid passage plate does not separated from the substrate, because the precisely formed step portion (flange-like portion) can reduce the amount of stress to which the liquid passage plate is subjected. 
         [0091]    Next, referring to  FIG. 13 , the method for manufacturing the liquid jet head in another preferred embodiment will be described.  FIGS. 13(   a )- 13 ( h ) are schematic sectional views of the precursors of the liquid jet head, in this embodiment, which are in various manufacturing steps for the head, one for one, as are the  FIGS. 8(   a   1 )- 8 ( e   1 ). 
         [0092]    First, referring to  FIG. 13(   a ), energy generating elements  1  are formed on a substrate  2 . 
         [0093]    Next, referring to  FIG. 13(   b ), a first pattern  21  for liquid passages and a second pattern  30  for forming a moat-like portion are formed on the substrate  2 . The provision of the second pattern  30  causes the material for the first cover layer  25  to better fill the corner portion between the vertical edge of the first pattern  21  and the substrate  2 . The second pattern  30  is formed in a manner to surround the first pattern  21 . 
         [0094]    Next, referring to  FIG. 13(   c ), the photosensitive resin compound of the negative type is applied to the top side of the substrate  2  to form a first cover layer  25  in a manner to cover both patterns  21  and  30 . 
         [0095]    Next, referring to  FIG. 13(   d ), the first cover layer  25  is exposed in such a manner that the resultant exposed portion  23  will surround the first and second patterns  21  and  30 . 
         [0096]    Next, referring to  FIG. 13(   e ), the second cover layer  26  is formed on the first cover layer  25  to form a liquid passage plate. The material for the second cover layer  26  may be selected from among the abovementioned photosensitive resin compounds of the negative type. 
         [0097]    Next, referring to  FIG. 13(   f ), the portions of the second cover layer  26 , which will become the liquid ejection outlets  6 , and the portions of the second cover layer  26 , which corresponds in position to the moat-like portion, are masked. Then, the first cover layer  25  is exposed together with the second cover layer  26 . During this exposing step, the second cover layer  26  is exposed across the portion which corresponds in position to a portion  23   a  (portion away from pattern  21 ), and the portion which corresponds in position to the exposed portion  21 , leaving exposed the portion which corresponds in position to the other portion  23   b  (portion closer to pattern  21 ), with the use of a mask. Then, the precursor is heated to harden the exposed portions of the first and second cover layers  25  and  26  to obtain a cover layer  22 , which is an integration of the first and second cover layers  25  and  26 . 
         [0098]    Next, referring to  FIG. 13(   g ), the liquid passages  8  and moat-like portion  20  are formed by removing the first and second patterns  21  and  30 . 
         [0099]    Next, referring to  FIG. 15 , the method for manufacturing the liquid jet head in another preferred embodiment of the present invention will be described.  FIGS. 15(   a )- 15 ( f ) are sectional views of the precursors of the liquid jet head, in this embodiment, which are similar to  FIGS. 9(   a )- 9 ( e ). 
         [0100]    Referring to  FIG. 15(   a ), lateral wall forming members  30  for forming the lateral walls of the liquid passages are formed on the substrate  2 , on which energy generating elements have been formed. The lateral wall forming members  30  are formed by hardening the patterned photosensitive resin compound of the negative type. 
         [0101]    Next, referring to  FIG. 15(   b ), the space between the lateral wall forming members  30 , which will become the liquid passages, is filled with dissolvable resin. More specifically, the dissolvable resin is poured into the space by the amount large enough to cover even the top surface of the lateral wall forming wall  30 . Then, the dissolvable resin is hardened to form a solid dissolvable resin layer  17 . 
         [0102]    Next, the solid layer  17  is filed until the top surface of the lateral wall forming member  30  is exposed, that is, until the top surface of the lateral wall forming member  30  becomes level with the top surface of the filed solid layer  17 , as shown in  FIG. 15(   c ). As the method for filing (polishing) the solidified dissolved resin layer  17 , it is possible to use one of the CMP (chemical-and-mechanical polishing) methods, for example. 
         [0103]    Next, referring to  FIG. 15(   d ), the material for a cover layer  18  is coated across the combination of the top surface of the lateral wall forming member  30  and the top surface of the solidified dissolvable resin layer  17 . The material for the cover layer  18  is a photosensitive resin compound of the negative type. It is desired to be the same as the material for the lateral wall forming member  30 . The examples of the photosensitive resin compound of the negative type for the cover layer  18  are the same as those mentioned as the examples of the material for the first cover layer  25 . 
         [0104]    Next, referring to  FIG. 15(   e ), the portions of the cover layer  18 , which will become the liquid ejection outlets  6  are masked, and also, the outward edge portion of the cover layer  18 , which corresponds in position to the outward edge portion  30   b  of the lateral wall forming member  30 , is masked. Then, the cover layer  18  is exposed. In other words, the cover layer  18  is exposed except for the portions which correspond in position to the liquid ejection outlets  6  and the outward edge portion  30   b  of the lateral wall forming member  30 . 
         [0105]    Next, the exposed cover layer  18  is hardened by the application of heat, and then, is developed. Then, the liquid distribution hole  7  is formed, and the solidified dissolvable layer  17  is removed. It is through this step that the liquid ejection outlets  16  are formed, and the outward edge portion of the lateral wall forming member  30  is removed in a manner to create a step between the lateral wall forming member  30  and liquid ejection outlet forming member  19 . 
         [0106]    At this time, another method for forming a structural component having a step, using the above described method, will be described referring to  FIGS. 14(   a )- 14 ( e ). 
         [0107]    First, referring to  FIG. 14(   a ), a first layer  27  is formed of a photosensitive resin compound of the negative type, on the substrate  2 . As the photosensitive resin compound of the negative type for the first layer  27 , one of those described as the examples of the photosensitive resin compounds of the negative type, which can be used as the material for the cover layers, can be used. 
         [0108]    Next, referring to  FIG. 14(   b ), the portions of the first layer  27  are selectively exposed to form an exposed portion  23 . Then, the first layer  27  is heated to harden the exposed portion  23  to prevent the polymerization initiation seeds from dispersing. 
         [0109]    Next, referring to  FIG. 14(   c ), a second layer  28  is formed of a photosensitive resin compound of the negative type, on the first layer  27  in such a manner as to cover the exposed portion  23  as well. It is desired that the second layer  28  is the same in composition as the first layer  27 . 
         [0110]    Next, the second layer  28  and first layer  27  are partially exposed so that a portion  23   a  of the exposed portion  23  of the first layer  27  is exposed. More specifically, the portion of the second layer  28 , which corresponds in position to the unexposed portion of the first layer is exposed from above the portion  23   a.  As for the first layer  27 , the portion, which was not exposed in the preceding exposing step, is exposed. In this step, the portion of the second layer  28 , which is above the other portion  23   b  of the exposed portion  23 , is left unexposed. Then the exposed portions of the first and second layers  27  and  28  are hardened by the application of heat. 
         [0111]    Next, the precursor was developed to remove the unexposed portions of the first and second layers  27  and  28 , obtaining thereby a structure  29  having a step portion  12 . 
         [0112]    Next, an embodiment of the present invention, which is related to a method for manufacturing a liquid jet head in accordance with the present invention, will be concretely described. 
       Embodiment 6 
       [0113]    First, a substrate  2 , which is a piece of wafer made of silicon crystal with a crystal axis of 100 is masked (unshown) across the portion which corresponds in position to the ink distribution hole. Then, electro-thermal transducers  2  are formed, as energy generating elements, on the substrate  2 . Then, a protective layer and a cavitation prevention layer (unshown) are formed ( FIG. 8(   a )). Each of the electro-thermal transducers is in connection to a control signal input electrode (unshown) for activating the element. 
         [0114]    Next, a liquid passage pattern  21  is formed of positive resist formed of acrylic resin (ODUR1010A: product of Tokyo Ohka Kogyo Co., Ltd.), on the substrate  2  ( FIG. 8(   b   1 )). Then, the following compound A is spin-coated on the pattern  21 , and the precursor is baked for nine minutes at 90° C, to form the first cover layer  25 , which is 20 μm in thickness ( FIG. 9(   a )). 
         [0000]    
       
         
               
             
               
               
               
             
           
               
                   
               
               
                 (Compound A) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Epoxy resin: 
                 94 parts by weight 
               
               
                   
                 EHPE3150 (Daicel Chemical Industry Ltd.) 
               
               
                   
                 Silane coupling agent: 
                  4 parts by weight 
               
               
                   
                 A-187 (Nippon Unicar (Co., Ltd)) 
               
               
                   
                 Optical acid generating agent: 
                  2 parts by weight 
               
               
                   
                 SP-172 (Adeka Corp.) 
               
               
                   
                 Solvent: xylene 
               
               
                   
                   
               
             
          
         
       
     
         [0115]    Next, the portion  23  of the first cover layer  25  is partially exposed at a 120 mJ/cm 2  ( FIG. 9(   b )). Then, the precursor was heated three minutes at 90° C. 
         [0116]    Then, the second layer  26 , which is 60 μm in thickness, was formed on the first cover layer  25  by coating the compound A on the first cover layer  25  ( FIG. 9(   c )). 
         [0117]    Next, the first and second cover layers  25  and  26  were exposed at 50 mJ/cm 2 . More specifically, the exposed portion  23  was exposed in such a pattern that the portion  23   a  was exposed while leaving the portion  23   b  unexposed ( FIG. 9(   d )). 
         [0118]    Then, the precursor was developed with xylene to form the liquid ejection outlets  6  and the step portion  12   a  (flange-like portion) ( FIG. 9(   e )). 
         [0119]    Next, the liquid distribution hole  7  was formed, and the pattern  21  was removed, to complete the liquid passage formation plate ( FIG. 8(   e   1 )). 
         [0120]    The liquid jet head in accordance with the present invention was obtained through the above described steps. 
       Embodiment 5 
       [0121]    This embodiment of the present invention, which is related to the manufacturing of a liquid jet head in accordance with the present invention, is the same as the fourth embodiment, except that in this embodiment, the precursor was not baked after the exposure of the portion  23  in  FIG. 9(   b ). 
       Embodiment 6 
       [0122]    Up to the step shown in  FIG. 9(   b ), this embodiment is the same as the fourth embodiment. 
         [0123]    Then, the first cover layer  25  was heated to harden the exposed portion  23 . Then, the precursor was developed to remove the portions of the first cover layer  25  other than the exposed portion  23 , obtaining the precursor shown in  FIG. 12(   a ). 
         [0124]    Next, the second cover layer  26  was formed in a manner to cover the exposed portion  23  ( FIG. 12(   b )). 
         [0125]    Then, the first and second cover layers  25  and  26  were exposed so that the portion  23   a  of the exposed portion  23  was exposed while the portion  23   b  remains unexposed. 
         [0126]    The steps which were carried out hereafter to obtain a liquid jet head in accordance with the present invention, were the same as those in the fourth embodiment, which were described with reference to  FIG. 9(   e ). 
       COMPARATIVE EXAMPLE 1 
       [0127]    Next, referring to  FIG. 16 , the method for manufacturing a comparative liquid jet head will be described.  FIGS. 16(   a )- 16 ( c ) are sectional views of a conventional liquid jet head (comparative liquid jet head), which are equivalent to  FIGS. 8(   a   1 )- 8 ( e   1 ). 
         [0128]    This liquid jet head manufacturing method is the same as the liquid jet head manufacturing method in the fourth embodiment up to its step which is the same as the step in fourth embodiment, shown in  FIG. 9(   b ) Then, the second cover layer  26  is formed on the first cover layer  25  without exposing the first cover layer  25 , obtaining the precursor shown in  FIG. 9(   a ) The method used for forming the second cover layer  26  is this embodiment is the same as that used in fourth embodiment. The first and second layers of this conventional liquid jet head are the same in thickness as the counterparts of the liquid jet head in the fourth embodiment. 
         [0129]    Next, the first and second cover layers  25  and  26  were exposed at 500 mJ/cm 2  ( FIG. 16(   b )). The portion X of the first cover layer  25  of this liquid jet head, which is shown in  FIG. 16(   b ), and is the outward end portion of the first cover layer  25 , is comparable to the exposed portion  23   a  in the fourth embodiment. 
         [0130]    The steps which were carried out thereafter to obtain the conventional liquid jet head shown in  FIG. 16(   c ) were the same as those carried in fourth embodiment. The comparative example of a liquid jet head, that is, the liquid jet head manufactured through this method for manufacturing a liquid jet head does not have the step portion  12   a  (flange-like portion). 
       (Evaluation) 
       [0131]    The liquid jet head in the first to third preferred embodiments, and the liquid jet head made with the use of the comparative example 1 of a liquid jet head were subjected to pressure-temperature tests. 
         [0132]    A certain number of each of the liquid jet heads in the first to third preferred embodiments of the present invention, and the comparative example of a liquid jet head (conventional liquid jet head) were prepared, and were dipped in ink. Then, they are left under twice the normal pressure at 121° for ten hours. Then the liquid jet heads were examined to find if separation occurred between the substrate  2  and liquid passage formation plate of any of the liquid jet head. 
         [0133]    In the case of the liquid jet heads in accordance with the present invention, virtually no separations were found between the liquid passage formation plate  24  and substrate  2 . Further, even in the case of a liquid jet head whose liquid passage formation plate  24  and substrate  2  separated from each other, the extent of separation is at a level which is not problematic in practical terms. 
         [0134]    On the other hand, in the case of the comparative liquid jet heads (conventional liquid jet heads), the ratio of the liquid jet heads whose liquid passage formation plate and substrate  2  had separated from each other was greater than in the case of the liquid jet heads in accordance with present invention. Further, the former was greater in the extent of separation than the latter. 
         [0135]    It is reasonable to think, based on the above described result, that because the liquid jet heads in the above described preferred embodiments of the present invention were provided the step portion  12  (flange-like portion), the stress which occurs in the liquid passage formation plate  24 , formed of the photosensitive resin of the negative type, that is, the material for the liquid passage formation plate  24 , shrinks when it hardens, or the like stress, is reduced by the step portion  12  (flange-like portion). 
         [0136]    Further, the flange-like portion  12   a  of the step portion  12  in the fourth preferred embodiment of the present invention, which corresponds in position to the top surface of the exposed portion  23  was flatter than the counterpart in the fifth preferred embodiment. It is reasonable to think that this occurred because in the case of the fourth embodiment, the exposed portion  23  is hardened by the application of heat after the formation of the exposed portion  23 , and therefore, the exposed portion  23  remained intact in the shape of its top surface as it was formed as a part of the first cover layer. That is, it is reasonable to think that the hardening reduced the movement of the acid generated by the exposure, and therefore, in the case of the fourth embodiment, the acid did not disperse into the second cover layer  26  as much as it did in the case of the fifth embodiment. 
         [0137]    Moreover, the surface of the liquid jet head in the fourth embodiment, which has the opening of each of the liquid ejection outlets  6 , was flatter than the counterpart in the sixth embodiment. It is reasonable to think that this occurred because in the case of the liquid jet head in the fourth embodiment, the second cover layer  26  was formed on the first cover layer  25  without carrying out the developing process after the exposure of the portion  23 , that is, while keeping flat the top surface of the first cover layer  25 . 
         [0138]    While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth, and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or the scope of the following claims. 
         [0139]    This application claims priority from Japanese Patent Applications Nos. 016369/2008 and 244196/2008 filed Jan. 28, 2008 and Sep. 24, 2008, respectively, which are hereby incorporated by reference.