Abstract:
A method of manufacturing an array type semiconductor laser device. The method includes forming first and second electrodes on lower and upper surfaces of a wafer comprising a plurality of semiconductor laser arrays having a plurality of laser emission regions, and forming a metal bonding layer on the second electrode of the wafer. The method also includes dicing the wafer into the semiconductor laser arrays and mounting each of the individually separated semiconductor laser arrays on a base with the surface of the metal bonding layer in contact with the base. The method further includes melting the metal bonding layer to fix the mounted semiconductor laser array on the base.

Description:
CLAIM OF PRIORITY 
     This application claims the benefit of Korean Patent Application No. 2006-0017420 filed on Feb. 22, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a high power semiconductor laser device and, more particularly, to a method of manufacturing a semiconductor laser device which includes an efficiently improved metal bonding process of a high power semiconductor laser array. 
     2. Description of the Related Art 
     Recently, high power semiconductor laser devices are extensively used in various applications such as industrial and medical fields including optical communication, optical recording devices, welding and dicing, and are also beginning to be applied to visible ray lasers for display, and thus expected to have further expanded applications. 
     In general, it is impossible to manufacture a laser apparatus of more than tens of watts with a single semiconductor laser device. Thus, in order to obtain a high power laser, an array type semiconductor laser device is used with several laser diodes arranged in the form of a bar. 
     In order to obtain light output of tens of watts, high current exceeding tens of amperes is applied, causing a considerable amount of heat in the laser array itself. If the heat is not appropriately discharged, the light output is degraded and the lifetime of the chip is shortened. 
     To overcome such problematic conditions, the array type laser device in general is provided in a package in which a laser array (or a laser bar)  10  is mounted on a base  21  of high heat conductivity using a metal bonding layer  29  such as solder. 
     In order to manufacture the conventional array type semiconductor laser device  20  into a package as shown in  FIG. 1   b , the bar-shaped laser array  10  is mounted on an upper surface of the base  21  with the metal bonding layer  29  deposited thereon as shown in  FIG. 1   a.    
     The laser array  10  includes a semiconductor laser stack structure  10 ′ formed on a conductive substrate  11  and first and second electrodes  17  and  18  formed on upper and lower surfaces thereof. The laser array  10  requires a heat-treating process after the first and second electrodes  17  and  18  are formed, and thus has the metal bonding layer  29 , which tends to be relatively easily melted at high temperature, formed on an upper surface of the base  21 . 
     However, the base is usually manufactured for each unit package, and thus requires an individual deposition process of the metal bonding layer, which adversely affects the efficiency of the manufacturing process and a yield. 
     Further, as shown in  FIG. 1   b , when the laser array is heat-pressed on an upper surface of the base with the metal bonding layer provided thereon, the metal bonding material being melted for bonding may spread along the surface of the semiconductor laser array as denoted by the reference sign S, potentially causing short circuit of the laser. 
     SUMMARY OF THE INVENTION 
     The present invention has been made to solve the foregoing problems of the prior art and therefore an aspect of the present invention is to provide a method of manufacturing an array type semiconductor laser device which efficiently improves a metal bonding process of a semiconductor laser array to a base, thereby preventing short circuit due to metal bonding material melted during the bonding process. 
     According to an aspect of the invention, the invention provides a method of manufacturing a high power array type semiconductor laser device. The method includes: 
     forming first and second electrodes on lower and upper surfaces of a wafer comprising a plurality of semiconductor laser arrays having a plurality of laser emission regions; 
     forming a metal bonding layer on the second electrode of the wafer; 
     dicing the wafer into the semiconductor laser arrays; 
     mounting each of the individually separated semiconductor laser arrays on a base with the surface of the metal bonding layer in contact with the base; and 
     melting the metal bonding layer to fix the mounted semiconductor laser array on the base. 
     According to the present invention, the step of forming the first and second electrodes includes: depositing the first and second electrodes on lower and upper surfaces of the wafer, respectively; and heat-treating the deposited first and second electrodes. 
     Preferably, the second electrode is closer to an active region of the laser than the first electrode so as to facilitate heat radiation through the base. In a specific embodiment of the present invention, the second electrode can be the p-electrode. 
     According to an embodiment of the present invention, the step of forming a metal bonding layer includes: 
     forming a photoresist pattern having open regions formed apart from the edges of the upper surface of the second electrode; 
     depositing a metal bonding layer in the photoresist pattern; and 
     removing the photoresist pattern by a lift-off process to form a metal bonding layer apart from the edges of the upper surface of the second electrode. 
     More preferably, the photoresist pattern can be formed with a plurality of the open regions spaced apart in a predetermined interval. 
     The metal bonding layer can be made of one selected from the group consisting of In, Pb, Sn, Au, Ag and alloys thereof. In addition, preferably, the base may be a ceramic substrate of AIN or SiC or a metal substrate of Cu or CuW with excellent heat conductivity so as to be utilized as an effective heat sink. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIGS. 1   a  and  1   b  are perspective views illustrating a conventional manufacturing process of an array type semiconductor laser device; 
         FIG. 2(   a ) to  2 ( c ) are perspective views illustrating the procedures of fabricating a semiconductor laser array in the process of manufacturing an array type semiconductor laser device according to the present invention; and 
         FIG. 3(   a ) and  3 ( b ) are sectional views illustrating the bonding procedures in the process of manufacturing the array type laser device according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. 
       FIG. 2(   a ) to  2 ( c ) are perspective views illustrating the procedures of fabricating a semiconductor laser array in a method of manufacturing an array type semiconductor laser device according to an embodiment of the present invention. 
     For the sake of convenience, the drawing exemplifies only one semiconductor laser array, but in actuality, the method is conducted at wafer level, and the semiconductor laser array should be understood as a wafer composed of a plurality of semiconductor laser arrays similar to the one shown in the drawing. 
     First, as shown in  FIG. 2   a , the semiconductor laser array  30  is fabricated. The method of fabricating the semiconductor laser array  30  can entail forming a first conductivity clad layer  32 , an active layer  33 , a second conductivity clad layer  34  and a second conductivity contact layer  35  on a first conductivity semiconductor substrate  31  and selectively depositing a current blocking layer  36 , which is an insulation material, to define beam emitting regions B where beams are generated. Then, a first electrode  37  is formed on a lower surface of the semiconductor substrate  31  and a second electrode  38  is formed on the second conductivity contact layer  35  with the insulation layer  36  formed thereon. The electrodes can be formed by a typical deposition process and a heat-treating process. Before forming the first electrode  37 , there may be adopted a lapping process to decrease the thickness of the substrate to 100 to 300 nm. As described above, the semiconductor laser array  30  shown in  FIG. 2   a  can be understood as a wafer composed of a plurality of semiconductor laser arrays similar to the one shown in  FIG. 2   a.    
     Next, a metal bonding layer  39  ( FIG. 2(   c )) is formed on an upper surface of the second electrode  38  of the semiconductor laser array  30 . The procedure for forming the metal bonding layer adopted in the present invention can be more effectively implemented at wafer level together with a series of semiconductor processes of for example growing an epitaxial layer and forming the electrodes for the laser. In particular, a photoresist process is readily carried out to enhance the accuracy of the process while improving a yield. In addition, selective formation of the metal bonding layer allows effective prevention of short circuit due to the metal bonding material melted in the metal bonding process. 
     Now, a process of forming the metal bonding layer according to an embodiment of the present invention will be explained with reference to  FIGS. 2(   b ) and  2 ( c ). 
     As shown in  FIG. 2(   b ), a photoresist pattern M is formed on an upper surface of the second electrode  38  of the semiconductor laser array  30 . It is preferable that the photoresist pattern M is formed such that open regions are spaced apart at a predetermined interval d 1  from the edges of the wafer (the photoresist pattern can be formed in a width of d 1 ×2), and that a plurality of open regions are spaced apart from each other in a predetermined interval d 2 . Such intervals d 1  and d 2  are provided to ensure a buffer region for preventing the melted metal bonding material from being pushed up and spread when the laser array is compressed on the base in a subsequent metal bonding process. Such a photoresist process can be effectively implemented together with a series of wafer-level semiconductor processes for forming the laser array  30  as mentioned above. In addition, the photoresist process is implemented after a lapping procedure for decreasing the thickness of the wafer. Optionally, the lapping procedure is implemented on the wafer while the wafer is fixed on a separate support substrate such as a glass substrate. However, if a high power laser is designed in such a fashion that an appropriate thickness is obtained after the lapping procedure, the photoresist process can be implemented without a separate support substrate. 
     As shown in  FIG. 2(   c ), the metal bonding layer  39  is deposited on the semiconductor laser array  30  with the photoresist pattern M formed thereon and then the photoresist pattern M can be removed by a lift-off process to obtain a desired pattern of the metal bonding layer  39 . The metal bonding layer  39  can be made of one selected from the group consisting of In, Pb, Sn, Au, Ag and alloys thereof. For example, the metal bonding layer  39  can be a typical solder material made of Au—Sn, Sn, In, Au—Ag or Pb—Sn. As in this embodiment, in order to more effectively radiate heat through the base to be bonded in a subsequent process, it is preferable that the metal bonding layer  39  is formed on the second electrode  38  which is closer to the active region than the first electrode  37 . 
     The semiconductor laser array with the metal bonding layer formed thereon as shown in  FIG. 2(   c ), is diced into the bar-shaped individual chip units. Then, each unit semiconductor laser array is mounted on the base by the metal bonding process shown in  FIGS. 3   a  and  3   b.    
     As shown in  FIG. 3(   a ), the semiconductor laser array is mounted on the base  41  with the surface of the metal bonding layer  37  as the bonding surface. As explained above, the metal bonding layer  39  is formed on the second electrode  38  which is closer to the active region than the first electrode  37  and the semiconductor laser array  30  is mounted with a semiconductor stack structure  30 ′, in particular, with the active layer thereof facing the base  41 . The base  41  can be a ceramic substrate or a metal substrate with excellent heat radiation characteristics. Of course, if an insulation ceramic substrate is adopted for the base  41 , it can be electrically connected to the second electrode of the semiconductor laser array by a separate wire structure. 
     In the present invention, the metal bonding layer  39  can be formed in a pattern shape through a precise photoresist process, thereby preventing potential short circuit of the laser by the metal bonding layer  39 . This will be explained in detail with reference to  FIG. 3   b.    
     As shown in  FIG. 3   b , the metal bonding layer  39  is melted to fix the semiconductor laser array  30  on the base  41 . When the metal bonding layer  39  such as solder is melted, the melted metal bonding layer  39  is pressed by the semiconductor laser array  30  and spread in sideward directions (denoted by arrows), but the melted metal bonding layer  30  is prevented, by the buffer region A ( FIG. 3   a ) secured beforehand, from overflowing to the side surface of the laser  30 . This solves the problem of short circuit leading to a chip defect, caused by the melted metal bonding material being spread along the edges of the semiconductor laser array  30 . 
     Therefore, according to the present invention, the patterning process of the metal bonding layer is implemented together with a series of semiconductor processes including the photoresist process for fabricating the semiconductor laser array, thereby allowing a more efficient manufacturing process of the semiconductor laser device. 
     As set forth above, according to the present invention, a metal bonding layer is formed before a semiconductor laser array is diced into individual units at wafer-level, significantly improving efficiency in the manufacturing process and in particular, efficiency in a metal bonding process. Furthermore, a photoresist process is continuously implemented together with a series of semiconductor processes to form the metal bonding layer in a pattern with a buffer region, thereby effectively preventing short circuit due to the metal bonding layer melted during the bonding process. 
     While the present invention has been shown and described in connection with the exemplary embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims.