Semiconductor device and method of manufacturing the same

A semiconductor device includes a substrate, and a semiconductor thin film bonded to the substrate, wherein the semiconductor thin film includes a plurality of discrete operating regions and an element isolating region which isolates the plurality of discrete operating regions, and the element isolating region is etched to a shallower depth than a thickness of the semiconductor thin film, and is a thinner region than the plurality of discrete operating regions.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device formed by bonding a semiconductor thin film such as an LED epitaxial film to a substrate, to an LED print head using this semiconductor device, to an image-forming apparatus using this LED print head, and to a method of manufacturing the semiconductor device.

2. Description of the Related Art

In the conventional art, the electrical connection between an LED chip and a driver IC chip for driving and controlling the LED chip, was made by a bonding wire (e.g., Japanese Patent Laid-Open Publication No. 2001-244543).FIG. 13is a perspective view schematically showing a conventional semiconductor device wherein an LED chip and a driver IC chip are connected by bonding wires, andFIG. 14is a perspective view showing an enlargement of the LED chip ofFIG. 13. As shown inFIG. 13orFIG. 14, the semiconductor device includes a unit board301, an LED chip302, and a driver IC chip303. The LED chip302includes light-emitting parts304, discrete electrodes305, and electrode pads306. The electrode pads306of the LED chip302and the electrode pads307of the bonding IC chip303are connected by bonding wires308. Further, electrode pads309of the driver IC chip303and electrode pads310of the unit board301are connected by bonding wires311.

However, in the aforesaid conventional semiconductor device, a surface area of electrode pads306(e.g., of the order of 100 μm×100 μm) is larger than the surface area occupied by the light-emitting parts304on the LED chip302. Therefore, as long as the electrode pads306are provided, it is difficult to reduce the chip width of the LED chip302, and difficult to reduce the material cost of the LED chip302.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a semiconductor device which permits a major reduction of material cost, an LED print head using this semiconductor device, an image-forming apparatus using this LED print head, and a method of manufacturing the semiconductor device.

A semiconductor device according to the present invention includes a substrate, and a semiconductor thin film bonded to the substrate. The semiconductor thin film includes a plurality of discrete operating regions, each of which has an operating layer, and an element isolating region, which is a thinned region of said semiconductor thin film mutually isolating the operating layers of the plurality of discrete operating regions.

An LED print head according to the present invention includes the above semiconductor device and a holder for holding the semiconductor device.

An image-forming according to the present invention includes the above LED print head, and a photosensitive body installed facing the LED print head.

A method of manufacturing a semiconductor device according to the present invention includes forming a semiconductor thin film including a plurality of discrete operating regions, each of which has an operating layer, on a first substrate such that the semiconductor thin film can be separated from first substrate; bonding the semiconductor thin film which has been separated from the first substrate to a second substrate; and forming an element isolating region by etching a region other than the plurality of discrete operating regions of the semiconductor thin film bonded to the second substrate so as to mutually isolate the operating layers of the plurality of discrete operating regions.

DETAILED DESCRIPTION OF THE INVENTION

FIRST EMBODIMENT

FIG. 1is a perspective view schematically showing the construction of a semiconductor device according to a first embodiment of the present invention.FIG. 2is a perspective view showing a driver IC chip, metal layer, and LED epitaxial film of the semiconductor device ofFIG. 1, andFIG. 3is a cross-sectional view schematically showing a section through a line S3-S3in the semiconductor device ofFIG. 1.

As shown inFIG. 1,FIG. 2, orFIG. 3, the semiconductor device according to the first embodiment includes a unit board11, a driver IC chip12fixed on the unit board11, a metal layer13formed on the driver IC chip12, and an LED epitaxial film14which is a semiconductor thin film bonded on the metal layer13.

The driver IC chip12is an Si substrate in which an LED control driver IC is formed. Plural electrode terminals12aand plural electrode terminals12bconnected to the driver IC are provided on the surface of the driver IC chip12.

The LED epitaxial film14includes a plurality of discrete operating regions (light-emitting parts, i.e., LEDs)14aand an element isolating region14bwhich electrically isolates the plurality of discrete operating regions14afrom each other. The element isolating region14bis a region wherein the LED epitaxial film14is etched to a shallower depth than the thickness of the LED epitaxial film14, and is a thinner region than the plurality of discrete operating regions14a. The LED epitaxial film14, as shown inFIG. 3, has a multilayer semiconductor epitaxial structure wherein a lower contact layer21, a lower cladding layer22, an activation layer23as an operating layer, an upper cladding layer24, and an upper contact layer25are provided in that order from the side of the driver IC chip12. For example, the lower contact layer21is an n-GaAs layer, the lower cladding layer22is an n-AlzGa1−zAs layer, the activation layer23is an AlyGa1−yAs layer, the upper cladding layer24is a p-AlxGa1−xAs layer, and the upper contact layer25is a p-GaAs layer. Herein, the values of x, y, and z are respectively set within a range from zero to unity so as to obtain high light-emitting efficiency. The epitaxial layers forming the LED epitaxial film14are not limited to the aforesaid example.

The thickness T of the LED epitaxial film14may be selected from among various thicknesses, but the thickness T may be made as thin as about 2 μm. The etching depth required to isolate the light-emitting regions14amay be to immediately above the activation layer23(when the activation layer23is non-doped), or may be to below a top surface of the lower cladding layer22.FIG. 3shows the case where etching has been performed to below the top surface of the lower cladding layer22.

The metal layer13is formed, for example, in a region where the driver IC is formed, or a region adjacent to the region where the driver IC is formed, on the surface of the driver IC chip12, wherein the region where the driver IC is formed is a flat region. The metal layer13may, for example, be palladium, gold, or the like. The metal layer13may, for example, be formed by chemical vapor deposition or sputtering. The LED epitaxial film14is bonded to the surface of the metal layer13. The metal layer13has the function of fixing the LED epitaxial film14, which is stuck to the metal layer13, to the driver IC chip12, and the function of electrically connecting a common terminal region (lower contact layer21) on the lower surface of the LED epitaxial film14and a common terminal region of the driver IC chip12(not shown). Ohmic contacts are preferably formed between the metal layer13and the lower contact layer21in the LED epitaxial film14, and between the metal layer13and the common terminal region of the driver IC chip12. The bonding of the LED epitaxial film14to the metal layer13may, for example, be achieved by intermolecular forces between the epitaxial film and the metal layer, and by a reaction between the epitaxial film and the metal layer (atomic rearrangement of interface).

As shown inFIG. 1andFIG. 3, the semiconductor device according to the first embodiment further includes discrete interconnection layers (thin film interconnections)32extending from tops of the discrete operating regions14athrough the element isolating region14bto the driver IC chip12. As shown inFIG. 3, an interlayer insulating film31is provided between the LED epitaxial film14and the discrete interconnection layer32, the discrete interconnection layer32being connected to the upper contact layer25via openings31ain the interlayer insulating film31. The discrete interconnection layers32electrically connect the upper surfaces of the light-emitting part14aof the LED epitaxial film14, and the discrete terminal regions12aof the IC chip12. The discrete interconnection layer32is a thin film metal interconnection or the like, e.g., an Au layer, a Pd layer, a Pd/Au laminated layer, an Al layer, or a polysilicon layer. A plurality of discrete interconnection layers32may be formed all at once using a photolithography technique.

The unit board11has electrode pads11aon its surface. The electrode terminals12bof the driver IC chip12and the electrode pads11aof the unit board11are connected by bonding wires33.

Next, the method of manufacturing a semiconductor device according to the first embodiment will be described.FIG. 4andFIG. 5are cross-sectional views schematically showing process for manufacturing a semiconductor device according to the first embodiment. As shown inFIG. 4, first, a separation layer (sacrificial layer)112is formed on a manufacturing substrate (e.g., a GaAs substrate)111for forming the LED epitaxial layer114, and the LED epitaxial layer (semiconductor thin film)114including a plurality of discrete operating regions is formed on the sacrificial layer112. The LED epitaxial layer114can be manufactured by the metal oxide chemical vapor deposition method (MOVCD method), metal oxide vapor phase epitaxy method (MOVPE method), molecular beam epitaxy method (MBE method), or the like known in the art. The LED epitaxial layer114includes an n-GaAs layer121, an n-AlzGa1−zAs layer122, an AlyGa1−yAs layer123, a p-AlxGa1−xAs layer124, and a p-GaAs layer125, which correspond to the lower contact layer21, the lower cladding layer22, the activation layer23, the upper cladding layer24, and the upper contact layer25, respectively.

On the other hand, as shown inFIG. 1, the metal layer13is formed by chemical vapor deposition or sputtering on the driver IC chip (Si substrate)12. Next, the LED epitaxial film (the LED epitaxial layer114) is obtained by etching part of the LED epitaxial layer114and the sacrificial layer112as shown inFIG. 5and peeling (i.e., separating) the LED epitaxial layer114away from the GaAs substrate111by the chemical lift-off method, and the LED epitaxial film is bonded to the metal layer13of the driver IC chip12.

Next, as shown inFIG. 1, an element isolating region14bwhich electrically isolates the plurality of discrete operating regions14a, is formed by etching a region other than the plurality of discrete operating regions14aof the LED epitaxial film14bonded to the driver IC chip to a shallower depth than the thickness of the LED epitaxial film14. In the etching, a resist is used to prevent etching of the discrete operating regions14aand etch the element isolating region14b. The etching solution used may, for example, be a solution of phosphoric acid, and the etching temperature may, for example, be of the order of 30° C. The etching time is determined based on a pre-obtained etching rate and the desired etching depth. However, the etching conditions are not limited to these examples. Next, the interlayer insulating film31is formed, and the discrete interconnection layers32extending from the tops of the discrete operating regions14aover the element isolating region14bto the tops of the discrete electrode terminals12aof the driver IC chip12, are formed by a photolithography technique.

As described above, in the semiconductor device according to the first embodiment, the thin LED epitaxial film14which has a thickness of several micrometers is used as the light-emitting element device, so the light-emitting parts14aof the LED epitaxial film14and the discrete electrode terminals12aof the driver IC chip12can be connected by the discrete interconnection layers32. Therefore, it is unnecessary to provide electrode pads on the LED epitaxial film14, and due to the reduction in the surface area of the LED epitaxial film14, major material cost savings can be achieved.

In the semiconductor device according to the first embodiment, the element isolating region14bis formed so that there is no reduction in the contact area between the LED epitaxial film14and the driver IC chip12, hence the electrical properties of the discrete operating regions14acan be enhanced without reducing the adhesion strength of the LED epitaxial film14on the driver IC chip12.

Also, in the semiconductor device according to the first embodiment, the contact surface area of the LED epitaxial film14with the driver IC chip12is large, so contact resistance can be reduced. Herein, for reference purposes, a comparison will be made with the case where the elements are separated by completely etching a region other than the light-emitting part of the LED epitaxial film (comparative example).FIG. 6is a perspective view schematically showing the construction of the semiconductor device according to this comparative example.FIG. 7is a perspective view showing the driver IC chip, metal layer and LED epitaxial film of the semiconductor device ofFIG. 6, andFIG. 8is a cross-sectional view schematically showing a section through a line S8-S8in the semiconductor device ofFIG. 6. In the case of the comparative example shown inFIG. 6toFIG. 8, as the semiconductor thin film is only the light emitting parts14a, the contact area is extremely small, but the contact surface area of the LED epitaxial film14of the semiconductor device in the first embodiment is the sum of the surface areas of the light-emitting parts14aand the element isolating region14b, so the contact surface area is extremely large.

In the semiconductor device according to the first embodiment, the metal layer13is disposed on the undersurface of the LED epitaxial film14, so light emitted from the light-emitting parts14ain the direction of the undersurface (i.e., towards the driver IC chip12) can be extracted in the surface direction as light reflected by the metal layer13, and the power of the emitted light is thus increased.

Further, in the semiconductor device according to the first embodiment, part of the LED epitaxial film14remains on the element isolating region14bof the LED epitaxial film14, so steps on the LED epitaxial film14are reduced, and the occurrence of breaks in thin film interconnections such as the discrete interconnection layers can be reduced.

In the aforesaid description, the case was described where the semiconductor device was a light-emitting element array, but the present invention may be applied also to a semiconductor device other than a light-emitting element array.

SECOND EMBODIMENT

FIG. 9is a perspective view schematically showing the construction of a semiconductor device according to a second embodiment of the present invention.FIG. 10is a cross-sectional view schematically showing a section through a line S10-S10in the semiconductor device ofFIG. 9.

As shown inFIG. 9orFIG. 10, the semiconductor device according to the second embodiment includes a unit board51, a driver IC chip52fixed to the unit board51, and an LED epitaxial film54which is a semiconductor thin film bonded to the driver IC chip52. The driver IC chip52and the LED epitaxial film54are bonded by an adhesive53.

The LED epitaxial film54includes a plurality of discrete operating regions (light-emitting regions, i.e., LEDs)54a, and an element isolating region54bwhich electrically isolates the plurality of discrete operating regions54afrom each other. The element isolating region54bis a region wherein the LED epitaxial film54has been etched to a shallower depth than the thickness of the LED epitaxial film54, and is a thinner region than the plurality of discrete operating regions54a. The LED epitaxial film54, as shown inFIG. 10, has a multilayer semiconductor epitaxial structure including, in order from the side of the driver IC chip52, a lower contact layer61, a lower cladding layer62, an activation layer63, an upper cladding layer64, and an upper contact layer65. For example, the lower contact layer61is an n-GaAs layer, the lower cladding layer62is an n-AlzGa1−zAs layer, the activation layer63is an AlyGa1−yAs layer, the upper cladding layer64is a p-AlxGa1−xAs layer, and the upper contact layer65is a p-GaAs layer. Herein, the values of x, y, and z are respectively set within a range from zero to unity so as to obtain high light-emitting efficiency. The epitaxial layers forming the LED epitaxial film54are not limited to the aforesaid example.

The thickness T of the LED epitaxial film54may be selected from among various thicknesses, but the thickness T may be made as thin as about 2 μm. Further, in the second embodiment, the element isolating region54bis formed from part of the lower contact layer61. Here, the case is shown where the etching depth to electrically isolate the light-emitting parts54extends to midway in the lower contact layer61. As a result, the thickness of the lower contact layer61is made larger than that of the contact layer21in the first embodiment. The thickness of the lower contact layer61may be set within a range in which etching can be stopped midway in the lower contact layer61.

As shown inFIG. 9andFIG. 10, the semiconductor device according to the second embodiment further includes discrete interconnection layers (thin film interconnections)72which extend from the tops of the discrete operating regions54aover the element isolating region54bto the tops of the driver IC chip52. As shown inFIG. 10, an interlayer insulating film71is provided between the LED epitaxial film54and the discrete interconnection layer72, the discrete interconnection layer72being connected to the upper contact layer65via openings71ain the interlayer insulating film71. The discrete interconnection layers72electrically connect the upper surfaces of the light-emitting parts of the LED epitaxial film54with discrete terminal regions52aof the driver IC chip52.

The unit board51has electrode pads51aon its surface. The electrode terminals52bof the driver IC chip52and the electrode pads51aof the unit board51are connected by bonding wires73.

As shown inFIG. 9andFIG. 10, an electrode pad74is provided on the lower contact layer61, the electrode pad74, and a common electrode terminal52cof the driver IC chip52being connected by a common interconnection layer (thin film interconnection)75. The discrete interconnection layers72and the common interconnection layer75may, for example, be thin film metal interconnections, and may be formed all at once by a photolithography technique. Hence, in the second embodiment, both the discrete interconnection layers72and the common interconnection layer75are provided on the upper side of the LED epitaxial film54, so the contact resistance of the underside of the LED epitaxial film54does not have to be taken into account. As a result, there is more freedom of choice in the adhesive53used to improve the bonding strength of the LED epitaxial film54, and the adhesion strength can be enhanced. Also, as the whole of the LED epitaxial film54is connected by the lower contact layer61, it can be widened by the common electrode pad74and the contact resistance can be reduced compared to the first embodiment.

In the semiconductor device according to the second embodiment, in the same way as in the first embodiment, major material cost reductions, improved adhesion strength of the LED epitaxial film54and improved electrical properties of the discrete operating regions can be obtained. Except for the above-mentioned points, the semiconductor device of the second embodiment is the same as that of the first embodiment.

THIRD EMBODIMENT

FIG. 11is a cross-sectional view schematically showing the construction of an LED print head according to a third embodiment of the present invention.

As shown inFIG. 11, an LED print head100of the third embodiment includes a base member101, an LED unit102fixed to the base member101, a rod lens array103containing an alignment of plural rod-shaped optical elements, a holder104which holds the rod lens array103, and a clamp105which grips and fixes these components101-104. In the figure,101aand104aare openings through which the clamp105penetrates. The LED unit102includes an LED array chip102a. The LED array chip102aincludes one or more of the semiconductor devices of the first or second embodiment. Light generated by the LED array chip102apasses through the rod lens array103and is emitted to the outside. The LED print head100is used as an exposure device for forming an electrostatic latent image in an electrophotographic printer or electrophotographic copier. The construction of the LED print head including the semiconductor device of the first or second embodiment is not limited to that shown inFIG. 11.

In the LED print head of the third embodiment, the LED unit102uses the semiconductor device of the first or second embodiment, so excellent light emission properties, device compactness and major material cost reductions can be achieved.

FOURTH EMBODIMENT

FIG. 12is a cross-sectional view schematically showing the construction of an image-forming apparatus according to a fourth embodiment of the present invention.

As shown inFIG. 12, an image-forming apparatus200of the fourth embodiment includes four process units201-204which form yellow (Y), magenta (M), cyan (C) and black (K) images by an electrophotographic technique. The process units201-204are tandemly arranged in the transport path of a recording medium205. The process units201-204each include a photosensitive drum203awhich functions as an image carrier, a charging device203bwhich is disposed near the photosensitive drum203aand charges the surface of the photosensitive drum203a, and an exposure device203cwhich forms an electrostatic latent image by selectively irradiating the surface of the charged photosensitive drum203awith light. The exposure device203cis used for the LED print head100described in the third embodiment, and contains the semiconductor device described in the first or second embodiment.

The image-forming apparatus200also includes developing devices203dwhich transport toner to the surface of the photosensitive drums203on which the electrostatic latent image is formed, and cleaning devices203ewhich removes toner remaining on the surfaces of the photosensitive drums203a. The photosensitive drums203aeach are rotated in the direction of the arrow by a drive mechanism including a power source, not shown, and gears. The image-forming apparatus200further includes a paper cassette206which houses the recording medium205such as paper or the like, and a hopping roller207which separates and transports the recording medium205one sheet at a time. Pinch rollers208,209, and resist rollers210,211which correct the skew of the recording medium205together with the pinch rollers208,209and transport it to the process units201-204, are installed downstream of the hopping roller207in the transport direction of the recording medium205. The hopping roller207and resist rollers210,211rotate in synchronism with the power source, not shown.

The image-forming apparatus200further includes transfer rollers212disposed facing the photosensitive drums203a. The transfer rollers212each are formed of semi-electrically conducting rubber or the like. The potentials of the photosensitive drum203aand transfer roller212are set so that the toner image on the photosensitive drum203ais transferred to the recording medium205. Also, the image-forming apparatus is provided with a fixing device213which heats and pressurizes the toner image on the recording medium205, and rollers214,216and215,217for ejecting the recording medium205which has passed through the fixing device213.

The recording medium205stacked in the paper cassette206is separated and transported one sheet at a time by the hopping roller207. The recording medium205passes through the resist rollers210,211and pinch rollers208,209, and through the process units201-204in that order. In the process units201-204, the recording medium205passes between the photosensitive drums203aand the transfer rollers212, whereupon color toner images are transferred in sequence, and heated/pressurized by the fixing device213so that the color toner images are fixed on the recording medium205. Subsequently, the recording medium205is ejected to a stacker218by the ejecting rollers. The construction of the image-forming apparatus including the semiconductor device of the first or second embodiment or the LED print head of the third embodiment, is not limited to that shown inFIG. 12.

In the image-forming apparatus200of the fourth embodiment, the LED print head100of the third embodiment is used, so a high-quality image can be formed by the excellent light-emitting properties of the exposure device. Also, space is saved due to the compactness of the exposure device, and major material cost reductions can be achieved. The present invention may also be applied to a monochrome printer, but a particularly large advantage is obtained in the case of a full color printer having plural exposure units.