Patent Publication Number: US-6663227-B2

Title: Semiconductor device and process for producing the same

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a semiconductor device and a process for producing the same. More particularly, it relates to the technology of semiconductor device fabrication for ensuring that elements formed in an integrated circuit on a semiconductor chip will not break down electrically due to processing steps such as sand blasting and dry etching. The semiconductor device contemplated by the invention is formed as the recording head of ink-jet printer. 
     A typical process for producing the recording head of a thermal ink-jet printer comprises the steps of preparing a semiconductor device by forming heaters (heat-generating resistors) and their drive circuit on a semiconductor chip (substrate), forming an ink channel and ink supply holes and forming a cavity on each heater that serves as an ink chamber, attaching an orifice plate to the entire surface of the semiconductor device, and opening ink ejection orifices (nozzles) in a position corresponding to each heater. 
     Conventionally, ink channels and ink supply holes are formed by anisotropic etching of a semiconductor chip with a liquid etchant such as hydrazine or potassium hydroxide (KOH), with the regions other than the ink channels and ink supply holes being masked with a photoresist. However, hydrazine is a very strong carcinogen and has a potential hazard of explosion; KOH is such a strong etchant that it can potentially strip the resist and damage the areas other than the ink channels and ink supply holes. 
     Alternative methods of forming ink channels and ink supply holes are laser ablation and sand blasting. In sand blasting, small-diameter particles of a blasting medium such as alumina are blown at high speed against a semiconductor device (substrate), with the regions other than ink channels and ink supply holes being masked, to form ink channels and ink supply holes simultaneously in a plurality of semiconductor chips formed on a semiconductor wafer. Sand blasting has the advantage of forming ink channels and ink supply holes in higher resolution with better efficiency than laser ablation. 
     However, the sand blasting process involving the blowing of small-diameter particles with dry air is not without problems. On account of the friction between the particles and the air, static electricity is generated and the resulting static buildup on the surface of the semiconductor chip can potentially break down the semiconductor device. In the case of the recording head of a thermal ink-jet printer, the drive circuit formed as an element of an integrated circuit on the semiconductor chip may break down due to static buildup during production. 
     Speaking further of the recording head of a thermal ink-jet printer, orifices are usually formed by dry etching an orifice plate while masking the regions other than those corresponding to the individual heaters. However, when orifices are opened by dry etching, molecules in the state of an ion plasma cause static buildup on the oxidized film formed on each heater and can potentially break down the drive circuit connected to each heater. 
     SUMMARY OF THE INVENTION 
     The present invention has been accomplished under these circumstances and has an object providing a semiconductor device furnished with a structure which ensures that elements that comprise a drive circuit for driving an ink ejection or delivery unit and which are formed in an integrated circuit on a semiconductor chip to comprise the recording head of an ink-jet printer will not break down electrically during fabrication due to processing steps such as sand blasting and dry etching. 
     Another object of the invention is to provide a process for producing the semiconductor device. 
     The first object of the invention can be attained by a semiconductor device according to its first aspect which is in the form of a semiconductor chip formed as a recording head of an ink-jet printer, the semiconductor chip comprising at least an ink ejection unit, an integrated circuit composed of a drive circuit for driving the ink ejection unit, bonding pads and a metal film covering at least part of an upper layer of the integrated circuit, the metal film being formed to extend from the integrated circuit to an edge of the semiconductor chip. 
     Preferably, the metal film also covers further an upper layer of at least one of the bonding pads in such a way as to extend from the bonding pad to an edge of the semiconductor chip. 
     According to its first aspect, the invention also provides a semiconductor device as a semiconductor wafer including at least two semiconductor chips of the structure described above and at least one grounding pad being formed of the metal film in a region peripheral to the semiconductor wafer and which is outside the semiconductor chips, wherein the metal film is also formed in a region between the semiconductor chips, and wherein the metal films formed to extend to edges of all the semiconductor chips are interconnected via the region between the semiconductor chips and also connected to the grounding pad. 
     Preferably, the region between the semiconductor chips is a scribing line. 
     In each of the embodiments described above, the ink ejection unit includes heat-generating resistors, the metal film is formed of the same material as the heat-generating resistors, and the recording head of the ink-jet printer is a recording head of a thermal ink-jet printer. 
     The second object of the invention can be attained by a process according to its second aspect for producing a semiconductor device in a semiconductor wafer having at least two semiconductor chips formed thereon, each serving as a recording head of an ink-jet printer, which process comprises the steps of forming at least an ink ejection unit and an integrated circuit composed of a drive circuit for driving the ink ejection unit on a semiconductor substrate for each of the semiconductor chips, covering at least part of an upper layer of the integrated circuit on each of the semiconductor chips to form metal films that each extend from the integrated circuit to an edge of each of the corresponding semiconductor chips and which are also interconnected via a region between the semiconductor chips, and also forming at least one grounding pad from the metal film in a region peripheral to the semiconductor wafer and which is outside the semiconductor chips, the grounding pad being connected to the metal film via the region between the semiconductor chips, and applying a processing step with the metal films being grounded via the grounding pad. 
     Preferably, the ink ejection unit includes the heat-generating resistors, the recording head of the ink-jet printer is a recording head of a thermal ink-jet printer, and the metal films are formed of the same material as the heat-generating resistors simultaneously with formation of the heat-generating resistors after forming the drive circuit. 
     Preferably, not only the integrated circuit but also bonding pads are further formed on the semiconductor substrate for each of the semiconductor chips, and the metal film also covers further an upper layer of at least one of the bonding pads in such a way as to extend from the bonding pad to an edge of each of the semiconductor chips. 
     Preferably, the processing step is either a step of forming an ink channel for supplying ink to each of the ink ejection unit or a step of boring ink supply holes through each of the semiconductor substrate for supplying ink to the ink channel or both steps. 
     Preferably, the region between the semiconductor chips is a scribing line. 
     Preferably, the metal films are also further formed on a reverse side of the semiconductor wafer which is opposite a side where the integrated circuits for the semiconductor chips are formed. 
     Preferably, the metal films formed on the reverse side of the semiconductor wafer cover the entire surface of the reverse side of the semiconductor wafer. 
     Preferably, the metal films formed on the reverse side of the semiconductor wafer are removed after finishing of the processing step. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a structural outline for the recording head of a thermal ink-jet printer which is an embodiment of the semiconductor device according to the first aspect of the invention; 
     FIG. 2 is a cross-sectional layout of an embodiment of the recording head shown in FIG. 1; 
     FIG. 3 is a plan view showing in conceptual form an embodiment of the semiconductor device according to the first aspect of the invention; 
     FIG. 4 is a flowchart for exemplary steps in the process for producing the semiconductor device according to the second aspect of the invention; 
     FIG. 5A to FIG. 5D are sections A—A of the semiconductor device in the process of fabrication according to the invention; 
     FIG.  6 A and FIG. 6B are sections B—B of the semiconductor device in the process of fabrication according to the invention; and 
     FIG. 7 is a section of the semiconductor device in the process of fabrication by another example of the invention process. 
    
    
     PREFERRED EMBODIMENT OF THE INVENTION 
     The semiconductor device of the invention and the process for producing it are described below in detail with reference to the preferred embodiments shown in the accompanying drawings. 
     The recording head of a thermal ink-jet printer as an embodiment of the semiconductor device which is formed as the recording head of an ink-jet printer according to the first aspect of the invention is described below. 
     FIG. 1 shows a structural outline for an embodiment of the recording head of a thermal ink-jet printer according to the first aspect of the invention. As shown, the recording head generally indicated by  10  comprises heat-generating resistors  11  (R 1 , R 2 , . . . , Rn) associated with individual orifices (nozzles) and their drive circuit  12 . The orifices are recording elements that perform printing. The drive circuit  12  comprises driver transistors T 1 , T 2 , . . . Tn respectively associated with the heat-generating resistors R 1 , R 2 , . . . Rn and their control circuit  14 . 
     The heat-generating resistors R 1 , R 2 , . . . Rn are connected at one end to a common ground GND and are connected at the other end to the sources of the associated driver transistors T 1 , T 2 , . . . Tn. The drains of the driver transistors T 1 , T 2 , . . . Tn are connected to a common power supply VDD and their gates are each supplied with a control signal from the control circuit  14 . The number of the heat-generating resistors R 1 , R 2 , . . . Rn is not limited to any particular value. 
     In the recording head  10 , the driver transistors T 1 , T 2 , . . . Tn are turned on and off under the control of the control circuit  14 . If the driver transistors T 1 , T 2 , . . . Tn are turned on, an electric current flows to the associated heat-generating resistors R 1 , R 2 , . . . Rn which then generate heat. If the driver transistors T 1 , T 2 , . . . Tn are turned off, no current flows to the heat-generating resistors R 1 , R 2 , . . . Rn and they do not generate heat. 
     We now describe a layout of the recording head of a thermal ink-jet printer. 
     FIG. 2 is a cross-sectional layout for an embodiment of the recording head shown in FIG.  1 . 
     The recording head generally indicated by  10  in FIG. 2 is an embodiment of the semiconductor device according to the first aspect of the invention that has been produced by the semiconductor fabrication technology using the process according to the second aspect of the invention and which is used as the recording head of a thermal ink-jet printer. In the center of the region of a semiconductor chip  16  on a semiconductor substrate  15  such as a silicon substrate, an ink channel  18  through which ink is supplied to orifices is made by excavating the surface of the semiconductor substrate  15  and it extends perpendicular to the paper on which FIG. 2 is drawn. 
     In order to supply ink to the ink channel  18 , a plurality of ink supply holes (through-holes)  20  providing communication between the back side of the semiconductor substrate  15  for the semiconductor chip  16  and the ink channel  18  are opened (bored) at given spacings in the direction in which the ink channel  18  extends. A support frame  22  is provided as a support member for proper placement of the semiconductor chip  16 . Ink channels (or ink supply holes)  24  are formed in the support frame  22  to ensure that ink supplied from an ink tank (not shown) are fed via the ink supply holes  20  into the ink channel  18  formed in the obverse side of the semiconductor substrate  15  for the semiconductor chip  16 . 
     On opposite sides of the ink channel  18 , two orifice rows are formed in symmetrical positions, with each row consisting of a plurality of orifices  26  that are arranged at equal spacings along the ink channel  18 . Each orifice  18  is in a hollow cylindrical form and made in an orifice plate  28  that is formed of polyimide or the like and placed on top of the semiconductor chip  16 . For a resolution of 360 npi (nozzles per inch), orifices  26  are arranged perpendicular to the paper on a pitch of about 71 μm per row so that an overall resolution of 720 npi can be realized by two rows. 
     On top of the semiconductor substrate  15  for the semiconductor chip  16  but below the orifice rows, heat-generating resistors  11  are formed to control ink ejection or delivery from the individual orifices  26 . A drive circuit  12  for driving the individual heat-generating resistors  11  is formed on the surface of the semiconductor chip  16  (semiconductor substrate  15 ) in areas, with the ink channel  18  lying in between, which are outside the orifice rows. Between the surface of the semiconductor chip  16  and the orifice plate  28 , there are formed partitions  30  that define an ink flow path through which ink is supplied from the ink channel  18  to each orifice  26 . 
     Ink from the ink tank flows through the ink channel  24  in the support frame  22  to be supplied into the ink channel  18  in the surface of the semiconductor chip  16  (semiconductor substrate  15 ) via the ink supply holes  20  opened in the semiconductor chip  16  (semiconductor substrate  15 ); from the ink channel  18 , the ink flows through the ink flow path defined by the partitions  30  and is distributed to the orifice rows formed on opposite sides of the ink channel  18 . The individual heat-generating resistors  11  (R 1 , R 2 , . . . , Rn) are controlled by the drive circuit  12  in accordance with image data and a predetermined amount of ink is ejected or delivered from the associated orifices  26 . 
     The semiconductor device of the invention which is to be used as the recording head of an ink-jet printer is described in greater detail with reference to FIG.  3 . 
     FIG. 3 is a plan view showing in conceptual form an embodiment of the semiconductor device according to the first aspect of the invention. 
     Shown conceptually in FIG. 3 is a semiconductor wafer  34  on which a plurality of semiconductor chips are formed so that each of them serves as the recording head  10  (see FIG. 2) of a thermal ink-jet printer. In FIG. 2, the recording head  10  is shown to have two orifice rows but in FIG. 3, in order to provide ease in explanation, the provision of only one orifice row is assumed as in the case of the recording head  10  shown in FIG.  1 . 
     As shown in FIG. 3, the semiconductor device of the invention, if it is in the form of a discrete semiconductor chip, has a metal film  36  applied to an upper layer in the region of the drive circuit  12  in such a way that it extends to an edge of the semiconductor chip  16 . In other words, the metal film  36  is composed of two regions  36   a  and  36   b ; the first region  36   a  covers an upper layer of the drive circuit  12  and the second region  36   b  is an extension of the region  36   a . In the illustrated case, a metal film  36  is also applied to an upper layer of a bonding pad  38  and it similarly extends to an edge of the semiconductor chip  16 . In other words, the metal film  36  also is composed of two regions  36   c  and  36   d , the first region  36   c  covering an upper layer of the bonding pad  38  and the second region  36   d  being an extension of the region  36   c . The metal film  36  composed of the region  36   c  which covers an upper layer of the bonding pad  38  and the region  36   d  which is extension to an edge of the semiconductor chip  16  is an optional element and more than one such metal film may be provided depending on the case. 
     If a plurality of semiconductor devices are to be fabricated from a semiconductor wafer  34 , a metal film  36  is also applied along the region (scribing line)  40  between individual semiconductor chips  16  to form a line region  36   e  and two regions  36   b  and  36   d  of a metal film  36  which extend to an edge of every semiconductor chip  16  are interconnected by the line region  36   e  of the metal film  36  formed on each scribing line  40 . A grounding pad  42 , made of the same metal film, is formed in a region that is peripheral to the semiconductor wafer  34  and which is outside the individual semiconductor chips  16  and this grounding pad  42  is connected to the metal film  36  applied along the scribing lines  40 . 
     After finishing of the fabrication process, the semiconductor chips  16  formed on the semiconductor wafer  34  are separated apart on the scribing lines  40 , yielding discrete semiconductor chips  16 . The metal film  36  in the line regions  36   e  formed on the scribing lines  40  in the semiconductor wafer  34  is removed when the latter is scribed into discrete semiconductor chips  16 ; as a result, the only metal film  36  that is left intact on each discrete semiconductor chip  16  is composed of four regions  36   a - 36   d , the first region  36   a  covering an upper layer of the drive circuit  12 , the second region  36   b  extending to an edge of the semiconductor chip  16 , the third region  36   c  covering an upper layer of the bonding pad  38 , and the fourth region  36   d  extending to an edge of the semiconductor chip  16 . 
     The metal film  36  may be applied to cover the entire surface of the drive circuit  12  as indicated by  36   a  in FIG.  3 . If desired, the surface of the drive circuit  12  may partly be left uncoated with the metal film  36 ; in this case, the drive circuit  12  is covered with the metal film  36  except in regions that are electrically sensitive to external effects such as static capacity. In each of the semiconductor chips  16 , the metal film  36  covering an upper layer of the drive circuit  12  (to define the region  36   a ) and the metal film  36  covering an upper layer of the bonding pad  38  (to define the region  36   c ) may each extend to the metal film  36  formed on the scribing lines  40  (to define the line region  36   e ). Alternatively, these metal films  36  may be connected on the semiconductor chip  16  and one or more of such connected metal films may extend to the metal film  36  on the scribing lines  40 . 
     In order to provide ease in the process to be described below for fabricating the semiconductor device, the metal film  36  may be formed of known metal compounds such as TaSiO for making the heat-generating resistors  11  with known metals such as Ni for making conductive wires with that connect the heat-generating resistors  11  to the drive circuit  12 . In addition, metals such as Al, W, Ti, Mo, Ta, Pt and Au that are used in the conventional semiconductor fabrication processes and their alloys can all be employed. These metals may be used either individually or in combination; in the latter case, layers of different metals may be placed one on top of another. 
     In the invention, the thickness of the metal film  36  is not limited to any particular value; however, the preferred range is from 10 nm (100 Å) to 10 μm and the more preferred range is from 0.1 μm (100 nm) to 1 μm. 
     Needless to say, at least a certain insulation film is provided between the metal film  36  and each of the drive circuit  12  and the bonding pad  38 . The insulation film may be formed of any electrical insulator and examples include those which are commonly used in semiconductor devices, such as SiO 2 , SiN, borosilicate glass and polyimides. 
     The process for producing the above-described semiconductor device according to the second aspect of the invention is described below with reference to the flowchart in FIG. 4 which shows the process of producing the semiconductor device as the recording head of an inkjet printer, as well as FIGS. 5A to  5 D and FIGS. 6A and 6B which show steps involved in the production process. FIGS. 5A,  5 B,  5 C and  5 D are sections A—A of the semiconductor device in the process of fabrication in steps S 1 , S 4 , S 6  and S 8 , respectively (see the flowchart in FIG.  4 ), and FIGS. 6A and 6B are sections B—B of the semiconductor device in the process of fabrication in steps S 1  and S 3 , respectively (see the flowchart in FIG.  4 ). 
     First, consider a plurality of semiconductor devices on a semiconductor wafer  34  and apply the semiconductor fabrication technology to form the drive circuit  12  in a region of each semiconductor chip  16  on the semiconductor substrate  15  as shown in FIG.  5 A and FIG. 6A (step S 1 ). 
     Thereafter, a protective layer  44  such as a TEOS layer for the drive circuit  12  is formed over the drive circuit  12  and its peripheral area as shown in FIG.  5 A. On both sides of the drive circuit  12 , a conductor such as an Al conductor  46  is formed to provide electrical connection from the drive circuit  12 . 
     In the next step S 2 , heat-generating resistors  11  are formed. For instance, a two-layer metal film  36  is applied to the entire surface of the semiconductor wafer  34 . This metal film is composed of a metal layer  37   a , typically formed of TaSiO, which serves as the constituent material of the heat-generating resistors  11  and a metal layer  37   b , typically formed of Ni, which serves as the constituent material of the conductive wire for connecting the heat-generating resistors  11  and the drive circuit  12 . Then, using a heat-generating resistor forming mask, the two layers of the metal film  36  are photoetched to provide the region of heat-generating resistors  11  in which the two-layer metal film  36  has been stripped of the Ni layer  37   b  (see FIG.  5 B). 
     In the embodiment under consideration, the double-layered metal film  36  is etched with a different mask pattern than has been used to form the heat-generating resistors  11 . As a result, an upper layer of the drive circuit  12  is also covered with a two-layer metal film  36  which is made of a TaSiO layer  37   a  and a Ni layer  37   b  as in the case of the heat-generating resistors  11  but in a region independent thereof (step S 3 ). The protective layer  44  on the topmost part of the drive circuit  12  is not shown in FIG.  6 B. The metal film  36  covering an upper layer of the drive circuit  12  extends to an edge of each semiconductor chip  16  and the resulting extensions  36   b  permit all semiconductor chips  16  on the semiconductor wafer  34  to be interconnected via the scribing lines  40 . 
     Simultaneously with the formation of the heat-generating resistors  11 , an upper layer of the bonding pads  38  (Al conductors  46 ) formed on each semiconductor chip  16  is also covered with a double-layered metal film  36  (particularly the region  36   c ) by the same photoetching step (see FIG.  5 B). In this case, at least the metal film  36  (particularly the region  36   c ) which is applied to an upper layer of the bonding pad  36  that corresponds to the ground terminal extends to an edge of the semiconductor chip  16  and the resulting extension  36   d  connects to the metal film  36  (particularly the line region  36   e ) which is applied to the scribing line  40 . 
     In the same photoetching step, a grounding pad  42  (see FIG. 3) is formed in a region that is peripheral to the semiconductor wafer  34  and which is outside the semiconductor chips  16 . The grounding pad  42  is also connected to the two-layered metal film  36  covering the scribing lines  40 . The number of grounding pads  42  is not limited to any particular value as long as at least one such grounding pad is used. 
     Thus, by using the metal film  36  applied to form heat-generating resistors and conductors, an upper layer of the drive circuit  12 , an upper layer of the bonding pads  38  and the like can be covered with the metal film  36  without increasing the number of fabrication steps involved. The constituent materials for the heat-generating resistors and conductors are not limited to those used in the embodiment described above and other materials may of course be used. If desired, the step of forming the heat-generating resistors  11  and conductors may be separate from the step of forming the metal film  36  on an upper layer of the drive circuit  12 . An advantage in this case is that the heat-generating resistors and conductors can be formed of different materials from the metal film  36  on an upper layer of the drive circuit  12 . 
     If the heat-generating resistors and conductors are to be formed of different materials than the metal film  36  on an upper layer of the drive circuit  12 , the metals used in ordinary semiconductor fabrication processes such as Al, W, Ti, Mo, Ta and Pt and their alloys can all be used to make the metal film  36  covering an upper layer of the drive circuit  12  and the like. The metal film  36  may be applied to cover the entire surface of an upper layer in the drive circuit  12  or, depending on the need, its coverage may be partial. 
     The metal film  36  except the one applied to form the heat-generating resistors, namely, the metal film  36  which is applied to an upper layer of the drive circuit  12  and the bonding pads  38  (particularly, regions  36   a  and  36   c ), to top of the scribing lines  40  (line regions  36   e ) and to the areas spanning each of the drive circuit  12  and the bonding pads  38  and the scribing lines  40  to form extensions (regions  36   b  and  36   d ), is not limited to a double-layered film; it may be formed of a single layer or it may be formed of three or more layers. For example, the metal film  36  except the one applied to form the heat-generating resistors, namely, the metal film  36  which is applied to an upper layer of the drive circuit  12  and the bonding pads  38 , to top of the scribing lines  40  and to the areas spanning each of the drive circuit  12  and the bonding pads  38  and the scribing lines  40  may be a single-layered film solely formed of TaSiO. 
     Subsequently, as shown in FIG. 5B, the bonding pads  38  and the grounding pad  42  for each semiconductor chip  16  are plated with gold by either electroplating or electroless plating (S 4 ). This ensures that the bonding pads  38  and the grounding pad  42  will not be oxidized in the next thermal oxidation step but retain their conductivity. Preferably, the bonding pads  38  and the grounding pad  42  for each semiconductor chip  16  are plated with gold after masking the other regions. 
     If no such masking is done before gold plating, not only the metal film  36  on the bonding pads  38  and the grounding pad  42  but those on the drive circuit  12  and the scribing lines  40  also plated with gold, leading to a dramatic increase in the use of the gold plating solution. By performing the aforementioned masking, the use of the gold plating solution can be considerably reduced. If desired, the Ni conductive wire ( 37   b ) connecting each of the heat-generating resistors  11  and the drive circuit  12  may be plated with gold. This contributes to lowering the resistance of the conductive wire. 
     Subsequently, the surface of each heat-generating resistor  11  is subjected to thermal oxidation treatment (S 5 ). As a result, an electrical insulating coat  11   a  is formed on the surface of each heat-generating resistor  11 . The formed insulating coat  11   a  has very high strength and is resistant to the corrosive action of ink. Hence, the protective film which is required by the recording head of the conventional thermal ink-jet printer in order to provide resistance against cavitation and corrosion can be dispensed with, reducing the energy input and the like and realizing a recording head that is compact and which still has high thermal efficiency. 
     Subsequently, as shown in FIG. 5C, those regions of the semiconductor substrate  15  for the semiconductor chip  16  in which ink supply holes  20  are to be formed are excavated by sand blasting the obverse and/or reverse side of the semiconductor wafer  34  (particularly, the semiconductor substrate  15 ) not only to form an ink channel  18  but also to open (bore) ink supply holes  20  through each semiconductor chip  16  (particularly, its semiconductor substrate  15 ) (S 6 ). 
     After these processing steps, as shown in FIG. 5D, partitions  30  are formed on the surface of the semiconductor chip  16  to define cavities over the heat-generating resistors  11  that serve as ink chambers  31 ; then, the orifice plate  28  is attached to the surface of the semiconductor wafer  34  (or the semiconductor chip  16 ) (S 7 ) and orifices  26  are opened (bored) by dry etching (S 8 ). 
     In the invention, when processing steps are performed as by sand blasting to form the ink channel  18  and open the ink supply holes  20  and by dry etching to open the orifices  26 , the metal film  36  applied to cover an upper layer in each of the drive circuits  12 , bonding pads  38  and the grounding pads  42  is grounded electrically via the grounding pad  42  on the semiconductor wafer  34  so as to guide electric charges into the ground. This is effective in preventing electrical breakdown of the drive circuits  12  in the invention. 
     Described above are the basic construction of the semiconductor device of the invention and the process for producing the same. 
     In the process of the invention for producing the semiconductor device, the metal film  36  is provided on the surface of the semiconductor wafer  34  where the drive circuit  12  is formed on each semiconductor chip  16  and its provision is effected prior to processing steps such as sand blasting to form the ink channel  18  and open the ink supply holes  20  and dry etching to open the orifices  26 . This is not the sole case of the invention and, as shown in FIG. 7, a metal film  50  is preferably provided on the reverse side of the semiconductor wafer  34  (particularly, its semiconductor substrate  15 ) in addition to the metal film  36  on the obverse side. The metal film  50  to be provided on the reverse side of the semiconductor wafer  34  may be of the same or different composition than the metal film  36 . 
     If the metal film  50  is to be provided, it preferably covers the entire surface of the reverse side of the semiconductor wafer  34  (semiconductor substrate  15 ). 
     After the metal films  36  and  50  are thusly formed on the obverse and reverse sides, respectively, of the semiconductor wafer  34  with drive circuits  12  on it, processing steps are conducted as by sand blasting to form the ink channels  18  and bore the ink supply holes  20  and by dry etching to open the orifices  26 . Even if static electricity is generated during these processing steps, the resulting electric charges can be flowed into the ground more effectively than when only one surface of the semiconductor wafer  34  is covered with the metal film  36  and, hence, the drive circuit  12  can more positively be protected against breakdown due to static charge-up. 
     After forming the ink channels  18 , ink supply holes  20  and orifices  26  by the processing steps, the metal film  50  formed on the reverse side of the semiconductor wafer  34  is preferably removed by a suitable method such as dry or wet etching. Needless to say, the unwanted areas of the metal film  36  on the obverse side of the semiconductor wafer  34  may also be etched away or otherwise removed after the processing steps. 
     To perform processing steps such as excavation and boring of the semiconductor substrate  15  for the semiconductor chip  16 , holes may be opened through it from one side, i.e., either the obverse or reverse side. If desired, holes may be opened simultaneously from both sides of the semiconductor chip  16 ; alternatively, holes may first be opened from either one side of the semiconductor chip  16  to an intermediate depth and then holes are opened into the other side of the semiconductor chip  16  until it is tunneled through. 
     The invention is applicable to the recording heads of both monochromatic and full-color thermal ink-jet printers which employ semiconductor devices. While various constructions are known for the recording heads including the top shooter type (face ink-jet) and the side shooter type (edge ink-jet), all of them can be used in the invention. Orifices can be arranged in any desired number of rows and there is no limitation on the number of recording elements that can be provided. 
     In the embodiments described above, the semiconductor device of the invention is used with the recording head of a thermal ink-jet printer which ejects ink upon heating. However, this is not the sole case of the invention and the claimed semiconductor device is applicable to all other known types of ink-jet printer including the pressure type which ejects ink by vibrating the diaphragm with the aid of a piezoelectric device or under static electric force. In the invention, the heat-generating resistors used in the thermal type as well as the piezoelectric device and the like that are used in the pressure type are collectively referred to as the ink ejection or delivery unit. 
     It should also be noted that the applicability of the invention is not limited to the recording head of a thermal ink-jet printer but that it is also applicable to semiconductor devices of such a type that the elements of an IC circuit formed on a semiconductor chip may potentially experience electrical breakdown due to processing steps performed in the fabrication process. 
     While the semiconductor device of the invention and the process for its production have been described above in detail with reference to various embodiments, it goes without saying that the invention is by no means limited to the foregoing embodiments and various improvements and modifications can be made without departing from the spirit and scope of the invention. 
     As described above in detail, the invention is characterized in that the metal film formed on an upper layer of each of the IC circuits and bonding pads is grounded via the grounding pad formed on the semiconductor wafer before the latter is processed to fabricate semiconductor devices. 
     As a result, the elements of the IC circuit in each semiconductor device can be prevented from undergoing electric breakdown due to processing steps such as sand blasting and dry etching and this offers the advantage of improving the production yield for semiconductor devices.