Patent Publication Number: US-8975097-B2

Title: Method of manufacturing liquid discharge head

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This disclosure relates to a method of manufacturing a liquid discharge head. 
     2. Description of the Related Art 
     A liquid discharge head is used for a liquid discharge apparatus such as an ink jet recording apparatus, and includes a flow passage forming member and a substrate. The flow passage forming member is provided on the substrate, has a liquid flow passage formed therein and, in some cases, has a liquid discharge port. The substrate has a liquid supply port, and liquid supplied from the liquid supply port to the flow passage is discharged from the liquid discharge port and lands on a recording medium such as paper. 
     In general, such liquid discharge head (chip) as described above is manufactured in such a manner that a plurality of liquid discharge heads are manufactured simultaneously on one piece of wafer, and the wafer is cut off along a cut-off portion into small pieces of liquid discharge heads. 
     Japanese Patent Laid-Open No. 2010-162874 describes a procedure of forming a liquid supply port and a cut-off portion in the wafer by forming flow passage forming members on a front side of a wafer (substrate) and etching the wafer from a back side. 
     Japanese Patent Laid-Open No. 2002-25948 describes a procedure of forming a cut-off portion with holes by forming members on a front side of a wafer, forming a non-penetrating hole in the wafer between the members, and penetrating the non-penetrating hole by grinding the wafer from a back side. 
     SUMMARY OF THE INVENTION 
     According to the disclosure, a method of manufacturing a liquid discharge head is provided. The liquid discharge head includes a substrate having a liquid supply port and a flow passage forming member on a front side of the substrate and is configured to be manufactured by being cut off from a wafer at a cut-off portion. The method includes: forming a first hole which penetrates through a wafer and becomes at least part of the liquid supply port and a second hole which does not penetrate through the wafer and becomes at least part of the cut-off portion in the wafer from a front side of the wafer; arranging a dry film on the front side of the wafer so as to close the first hole and the second hole on the front side; forming the flow passage forming member from the dry film by heating and developing the dry film in a state in which the first hole penetrates through the wafer; and cutting off the liquid discharge head from the wafer by grinding the wafer from a back side which is a side opposite to the front side so that the second hole penetrates through the wafer. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a drawing illustrating an example of a liquid discharge head manufactured in accordance with this disclosure. 
         FIGS. 2A to 2G  are drawings illustrating an example of a method of manufacturing the liquid discharge head of this disclosure. 
         FIGS. 3A and 3B  are drawings illustrating an example of the method of manufacturing a liquid discharge head of this disclosure. 
         FIGS. 4A and 4B  are drawings illustrating an example of the method of manufacturing the liquid discharge head. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     According to the method described in Japanese Patent Laid-Open No. 2010-162874, since a process (etching) of causing the wafer to be penetrated from the front surface to the back surface is performed after the formation of the flow passage forming member, it takes a long time to process the wafer, and hence it is necessary to sufficiently protect the flow passage forming member. Therefore, longer manufacturing time and higher costs are required correspondingly. According to the method disclosed in Japanese Patent Laid-Open No. 2002-25948, since the holes are formed through the wafer between the members, high degree of accuracy is required in formation of the members and a high technology is required for forming holes. Furthermore, when forming the holes for the cut-off portion and the liquid supply port simultaneously, a higher technology is required for the formation of the members and the holes. 
     In order to solve the above-described problems, a method of forming holes for the liquid supply port and the cut-off portion from the front side of the wafer, and forming the flow passage forming member on the front side after the formation of the holes is conceivable. In this case, although the holes may be filled with a material in order to prevent the flow passage forming member from dropping into the formed holes, the filled material needs to be removed later. Therefore, it is preferable to arrange a dry film for closing the holes in order to prevent the flow passage forming member from dropping into the holes instead of filling the holes with the material, and utilize the dry film as a flow passage forming member. The dry film arranged thereon has a flow passage and a discharge port formed by, for example, a photolithography process. 
     However, according to the study of the inventors of this disclosure, it is found that when heating is performed in a post exposure bake (PEB) process after the exposure in the photolithography process, air in the hole (cavity portion), which is sealed by the dry film, expands and hence affects the shape of the flow passage forming member. This phenomenon will be described with reference to  FIGS. 4A and 4B . First, as illustrated in  FIG. 4A , a hole  2  and a hole  3  are formed from a front side of a wafer  1 , and a dry film  4  is arranged so as to close the holes. The hole  2  becomes at least part of the cut-off portion, and the hole  3  becomes at least part of the liquid supply port. The hole  2  and the hole  3  form the sealed spaces by the arrangement of the dry film. Subsequently, when the PEB process is performed, parts of the dry film on the sealed spaces are deformed by the air expanded in the sealed spaces, whereby deformed portions  5  are formed in the dry film  4 . In particular, since the deformed portion on the hole  3  serves as parts of the flow passage, the shape of the flow passage forming member is deformed as a consequence. The heating process may also be needed in processes other than the photolithography process, and the heating process may cause deformation as described above. 
     Accordingly, this disclosure aims to form a flow passage forming member with high degree of accuracy even in the case of forming the hole for the supply port and the hole for the cut-off portion from the front side of the wafer, then forming the flow passage forming member on the front side of the wafer by using a dry film, and heating and developing the wafer. 
     Embodiments of this disclosure will be described below.  FIG. 1  is a drawing illustrating an example of a liquid discharge head manufactured in accordance with this disclosure. The liquid discharge head includes a substrate  7  having a liquid supply port  6  and a flow passage forming member  8 . The flow passage forming member  8  is formed on a front surface  7   a  side of the substrate  7 . The liquid supply port  6  penetrates through the substrate from the front surface  7   a  to a back surface  7   b , which is a surface opposite to the front surface. The substrate  7  is cut off from one piece of wafer into individual substrates. The substrate  7  includes an energy-generating element  9 . Examples of the energy-generating element  9  include an electrothermal conversion element and a piezoelectric transducer. A control signal input electrode configured to drive an energy-generating element is electrically connected to the energy-generating element  9 . The flow passage forming member  8  is formed on the front side of the substrate  7  and the flow passage forming member  8  forms a liquid flow passage  10 . The flow passage forming member  8  also forms a liquid discharge port  11 . Liquid supplied from the liquid supply port  6  to the flow passage  10  receives energy from the energy-generating element  9 , and is discharged from the liquid discharge port  11 . 
     A method of manufacturing the liquid discharge head will be described with reference to  FIGS. 2A to 2G .  FIGS. 2A to 2G  are drawings illustrating cross-sectional views of a wafer including a II-II cross section of the liquid discharge head in  FIG. 1 . 
     First, as illustrated in  FIG. 2A , the substrate  7  provided with the energy-generating element  9  on the front surface  7   a  side is prepared. At this moment, the substrate is not cut off from the wafer, and hence the substrate  7  is part of the wafer. The substrate  7  is preferably a silicon substrate formed of silicon. In this case, the wafer is a so-called silicon wafer. The silicon substrate preferably has a crystal orientation of (100) on the surface thereof. Alternatively, a silicon substrate having a crystal orientation of (110) on the surface thereof. 
     Subsequently, as illustrated in  FIG. 2B , an etching mask layer  12  is formed on the front side of the wafer. The etching mask layer may be formed of any material as long as it is hardly disappeared by etching in comparison with the wafer and, for example, is formed of SiN, SiC, SiCN, SiO 2 , or the like. The etching mask layer is provided with an opening  12   a  and an opening  12   b . The etching mask layer may be used as a protective layer or an insulative layer that covers the energy generating element. In this manner, the necessity of removing the etching mask layer is eliminated. The protective layer and the insulative layer need not to be provided separately. The opening  12   a  and the opening  12   b  are formed, for example, by photolithography or reactive ion etching. 
     Subsequently, as illustrated in  FIG. 2C , the wafer is processed from the opening  12   a  and the opening  12   b , and a first hole  13  and a second hole  14  are formed from the front side of the wafer. The first hole  13  is formed from the opening  12   a  so as to penetrate through the wafer from the front surface  7   a  to the back surface  7   b . The first hole  13  forms at least part of the liquid supply port. The second hole  14  is formed from the opening  12   b  and is not penetrated through the wafer. The second hole  14  forms at least part of a cut-off portion. The cut-off portion is a portion at a boundary along which the respective liquid discharge heads are cut off from the wafer. Examples of the method of forming the first hole and the second hole include reactive ion etching, wet etching, and a mechanical process. The first hole and the second hole may be formed using a combination of above-described methods. If the second hole  14  is formed to be a hole penetrating through the wafer at this time point, the liquid discharging head is easily separated from the wafer in the process of forming the flow passage forming member or in other processes, so that manufacture of the liquid discharge head with high degree of accuracy becomes difficult. 
     The first hole and the second hole may be formed in the same process. When the first hole and the second hole are formed by reactive ion etching, the opening area of the opening  12   a  is preferably larger than the opening area of the opening  12   b  in terms of the opening area of the opening in the direction parallel to the front surface of the substrate. With such a configuration, the processing speed in the opening  12   a  is increased when the reactive ion etching is performed simultaneously, and hence a relationship that the first hole  13  penetrates through the wafer and the second hole  14  does not penetrate through the wafer is easily achieved. 
     Although the second hole does not penetrate through the wafer, the depth thereof is preferably at least 50% of the thickness of the wafer, that is, the depth of the first hole. If the depth of the second hole is smaller than 50% of the thickness of the wafer, the amount of time required for grinding the wafer increases in later processes, and the manufacture of the liquid discharge head is affected. More preferably, the depth of the second hole is at least 60%, further preferably, at least 70% of the thickness of the wafer. In order to maintain the strength of the wafer at the time of the process, the depth of the second hole is preferably not larger than 95% of the depth of the first hole. If the depth of the second hole exceeds 95% of the depth of the first hole, the thickness of the remaining part of the wafer at the bottom of the second hole becomes extremely thin, and hence the strength of the wafer is lowered, and the substrate probably separates from the wafer. More preferably, the depth of the second hole is not larger than 90%, further preferably, not larger than 80%. 
     The first hole and the second hole each may be formed continuously, for example, in the longitudinal direction like a groove. Alternately, the first holes and the second holes may be formed discontinuously in the longitudinal direction. The same applies to the width direction. If holes are formed discontinuously, the holes may be connected later by etching. 
     Subsequently, as illustrated in  FIG. 2D , a dry film is arranged on the front side of the wafer where the first hole  13  and the second hole  14  are formed on the front side of the wafer so as to close the first hole  13  and the second hole  14 . Furthermore, the dry film is exposed by using a mask  15  and is heated (in the PEB process), a latent image pattern is formed on the dry film. In other words, heating of the dry film is performed in a state in which the first hole  13  has penetrated through the wafer. The dry film used here is a film in a dry state that is formed on a base material such as polyester. After the dry film has transferred to the wafer, the base material is removed. The dry film is preferably a photosensitive dry film. In particular, the dry film is preferably a dry film formed of a negative photosensitive resin. Examples of the material of the dry film include an epoxy resin. 
     A latent image pattern  4   a  on the dry film is a part that closes the first hole  13 , and is a part finally removed to form the flow passage. A latent image pattern  4   b  is a part that closes the second hole  14 , and is a part removed finally and located above the cut-off portion. A latent image pattern  4   c  is a part that becomes part of the flow passage forming member  8 . When the dry film is heated in the PEB process, the latent image pattern  4   b  deforms as illustrated in  FIG. 2D . This is caused by expansion of air in the second hole  14 , which is a sealed space, located below the latent image pattern  4   b . However, that part is located above the cut-off portion, and hence the expansion affects little on the shape of the flow passage forming member. In contrast, deformation occurs little on the latent image pattern  4   a . This is because the first hole  13  located below the latent image pattern  4   a  penetrates through the wafer, and hence is not a sealed space, so that air may be released therefrom. Since a hole is substantially not formed below the latent image pattern  4   c , the latent image pattern  4   c  is little subjected to deformation. 
     Part of the latent image pattern  4   b , in other words, part of the dry film which closes the second hole  14  is preferably not cured by exposure. In the case where the dry film is a dry film of negative type, the part of the dry film that closes the second hole  14  is preferably masked so as not to be exposed. If the part of the dry film that closes the second hole  14  is cured, deformation may affect the flow passage forming member in some cases. 
     Subsequently, as illustrated in  FIG. 2E , a discharge port forming member is formed on the dry film. The discharge port forming member forms part of the flow passage, that is, an upper wall of the flow passage in  FIG. 2E . In other words, the discharge port forming member in  FIG. 2E  is part of the flow passage forming member. In  FIG. 2E , the latent image pattern  4   a  remains without being developed (removed), and the discharge port forming member is formed thereon. However, the discharge port forming member may be formed after the latent image pattern  4   a  is developed. A latent image pattern  11   a  is formed on the discharge port forming member by, for example, exposure. The latent image pattern  11   a  is a part where a latent image of the shape of the discharge port is formed. 
     The discharge port forming member is preferably formed of a resin, and more preferably, formed of a photosensitive resin. The discharge port forming member may be formed by spin coating or direct coating, or may be stacked as a dry film on the dry film located below. When exposing the discharge port forming member, the sensitivity of the dry film located below and that of the discharge port forming member need to be differentiated. In this case, the discharge port forming member is preferably formed of a dry film. Although the mode in which a discharge port forming member is further formed has been described, a flow passage forming member having a flow passage and a discharge port formed only with a single dry film is also applicable. 
     When the discharge port forming member is heated, a deformed portion  11   b  is formed. The deformed portion  11   b  is located above the second hole  14 , and is formed with deformation due to the expansion of air in the second hole  14  or deformation of the latent image pattern  4   b . The deformed portion  11   b  is located above the cut-off portion, and hence affects little the shape of the flow passage forming member. 
     Subsequently, as illustrated in  FIG. 2F , the latent image pattern  4   a , the latent image pattern  4   b , the latent image pattern  11   a , and the deformed portion  11   b  are removed. Accordingly, the flow passage  10  and the liquid discharge port  11  are formed on the flow passage forming member  8 . Here, the example in which the latent image pattern  4   a , the latent image pattern  4   b , the latent image pattern  11   a , and the deformed portion  11   b  are removed simultaneously has been described. However, the latent image pattern  4   a , the latent image pattern  4   b , the latent image pattern  11   a , and the deformed portion  11   b  may be removed separately. Alternatively, when the liquid discharge port  11  is formed not by exposure or development, but by reactive ion etching or laser irradiation, removal of the discharge port pattern is not necessary. 
     In this stage as well, the first hole  13  penetrates through the wafer, but the second hole  14  does not penetrate through the wafer. Subsequently, as illustrated in  FIG. 2G , the wafer is ground from the back side so as to cause the second hole  14  to penetrate through the wafer. Examples of a method of grinding include mechanical grinding (CMP) or reactive ion etching. 
     When the second hole  14  penetrates through the wafer, a portion including the second hole becomes the cut-off portion, so that the liquid discharge head is allowed to be cut off from the wafer at this portion. Simultaneously, the first hole  13  becomes the liquid supply port  6 . In  FIG. 2G , the state in which two liquid discharge heads are formed is illustrated. 
     As described above, according to this disclosure, deformation of the flow passage forming member due to the expansion of air in the sealed space is restricted, and the liquid discharge head having the flow passage forming member with high degree of accuracy is manufactured. 
     EXAMPLES 
     This disclosure will be described below further in detail by using the examples. 
     Example 1 
     First, as illustrated in  FIG. 2A , the substrate (wafer)  7  provided with the energy-generating element  9  on the front surface  7   a  side was prepared. The energy-generating element was made of TaSiN, and a substrate, which was a silicon substrate, having a crystal orientation of (100) was used as the substrate. The thickness of the substrate was 700 m. Films of SiO 2  and SiN were formed on the energy-generating element by plasma CVD, and the formed film was used as an insulating protection layer. 
     Subsequently, as illustrated in  FIG. 2B , the etching mask layer  12  was formed. The etching mask layer  12  was formed by using a resin (product name: THMR-iP5700 HP, manufactured by TOKYO OHKA KOGYO CO., LTD), so as to have a thickness of 10 m. Subsequently, the opening  12   a  and the opening  12   b  were formed by photolithography process. The opening width of the opening  12   a  was 100 m, and the opening width of the opening  12   b  was 40 m in terms of the direction parallel to the front surface of the substrate. The opening area of the opening  12   a  was 10000 m 2 , and the opening area of the opening  12   b  was 1600 m 2  in terms of the direction parallel to the front surface of the substrate. 
     Subsequently, as illustrated in  FIG. 2C , the wafer was processed by reactive ion etching from the opening  12   a  and the opening  12   b , and the first hole  13  and the second hole  14  were formed from the front side of the wafer. Bosch process was employed as the reactive ion etching, and the difference in etching rate depending on the opening area was utilized, whereby the first hole  13  penetrating through the wafer and the second hole  14  which does not penetrate through the wafer were formed simultaneously. The depth of the first hole  13  was 700 m, which was the same as the thickness of the wafer, and the depth of the second hole was 560 m. 
     Subsequently, as illustrated in  FIG. 2D , a dry film was arranged on the front side of the wafer where the first hole  13  and the second hole  14  were formed so as to close the first hole  13  and the second hole  14  on the front side of the wafer. A negative photosensitive dry film containing an epoxy resin was used as the dry film. Furthermore, by exposing the dry film by using the mask  15  and heating (PEB process) the same, a latent image pattern was formed on the dry film. The exposure was conducted under the conditions of an amount of exposure of 6000 J/m 2 , and heating at 50° C. for 5 minutes. 
     Subsequently, as illustrated in  FIG. 2E , the discharge port forming member was formed on the dry film. A negative photosensitive dry film containing an epoxy resin was used as the discharge port forming member. The discharge port forming member was exposed and heated (PEB process), so that the latent image pattern  11   a  was formed on the dry film. The exposure was conducted under the conditions of an amount of exposure of 2000 J/m 2 , and heating at 90° C. for 4 minutes. At the time of heating (PEB), the first hole  13  was in the state of penetrating through the wafer. 
     Subsequently, as illustrated in  FIG. 2F , the latent image pattern  4   a , the latent image pattern  4   b , the latent image pattern  11   a , and the deformed portion  11   b  were removed by melting with propyleneglycol monomethylether acetate to form the flow passage  10  and the liquid discharge port  11  in the flow passage forming member  8 . 
     Finally, as illustrated in  FIG. 2G , the wafer is ground by 150 m from the back side by CMP so as to cause the second hole  14  to penetrate through the wafer. The portion including the portion in which the second hole  14  penetrates through the wafer was used as the cut-off portion, and the liquid discharge head was cut off from the wafer at this portion. 
     The liquid discharge head was manufactured in the manner described above. The manufactured liquid discharge head was provided with the flow passage forming member formed with high degree of accuracy. 
     Example 2 
     In Example 1, the first hole  13  and the second hole  14  were formed by reactive ion etching as illustrated in  FIG. 2C . In Example 2, the first hole  13  and the second hole  14  were formed by laser irradiation and wet etching instead of the procedure illustrated in  FIG. 2C . Description on parts which are the same as those of Example 1 were herein omitted. 
     As illustrated in  FIG. 3A , the substrate  7  was irradiated with a laser from the opening  12   a  and the opening  12   b , and the first hole  13  and the second hole  14  were formed in the substrate  7 . The irradiation with laser was performed using a third harmonic (wavelength: 355 nm) of YAG laser at an output of 10 W and a frequency of 100 KHz. The first hole  13  was caused to penetrate through the wafer, and the second hole  14  was not caused to penetrate through the wafer. A plurality of the first holes  13  were formed within the openings  12   a , and one second hole  14  was formed in the opening  12   b.    
     Subsequently, as illustrated in  FIG. 3B , the wafer was subjected to wet etching with tetra-methyl-ammonium-hydride (TMAH) having 22 mass % solution. The etching conditions were as follows; an etching temperature of 83° C., and an etching time of 2 hours. Even after the wet etching, the first holes  13  penetrated through the wafer, and the second hole  14  did not penetrated through the wafer. 
     In the same manner as Example 1 except for the points described above, the liquid discharge head was manufactured. The manufactured liquid discharge head was provided with the flow passage forming member formed with high degree of accuracy. 
     According to this disclosure, even when the hole for the supply port and the hole for the cut-off portion are formed from the front side of the wafer, and then the flow passage forming member is formed on the front side of the wafer by the dry film to heat and develop the same, the flow passage forming member may be formed with high degree of accuracy. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2013-136151, filed Jun. 28, 2013, which is hereby incorporated by reference herein in its entirety.