Submount for Semiconductor Laser Device

FIG. 1 shows how a laser chip secured to a metal block with a conventional semiconductor laser deviCe submount,

FIG. 2 shows how a laser chip secured to a metal block with a semiconductor laser device submount according to the present invention;

FIG. 3 shows variations in resistance values in the thickness direction of the submount of FIG. 2 after each bonding step; and

FIG. 4 shows variations in resistance values in the thickness direction of the submount of FIG. 1 after each bonding step.

Now, the present invention is described, referring to an embodiment of a semiconductor laser device submount shown in FIG. 2. The submount 10 of FIG. 2 is an Si submount, which comprises an Si submount body 2 doped with Sb, and a multi-layered metallization structure comprising a sputtered Au layer 11, an AuSb layer 12 and a plated Au layer 13 sequentially formed in the named order on each of opposing surfaces of the submount body 2. As in conventional devices, the laser chip 6 is bonded to the metal block 7 by means of the submount 10. The metal block 7 is a block which can efficiently dissipate heat, such as, for example, a Cu block having a surface plated with Au, and an Ag block.

For a laser chip 6 having a thickness of 100 .mu. and a height and a width of about 300 .mu. and about 200 .mu., the thickness, the height and the width of the Si submount body 2 used are about 270 .mu. about 400 .mu. and about 300 .mu.. The Si submount body 2 is doped with from 0.11 to 0.21 weight percent, preferably 0.16 weight percent, of Sb, which results in a resistivity .rho. of the Si submount body 2 of 0.005-0.017 .OMEGA..cm. The sputtered Au layer 11 is formed to a thickness of 0.2.+-.0.04 .mu.. and the AuSb layer 12 is formed by vapor deposition or sputtering to a thickness of 0.2.+-.0.04 .mu.. The plated Au layer 13 is formed to a thickness of 5.+-.1 .mu.. The metal block 13 has a thickness of about 1400 .mu., and has a height of about 1600 .mu. and a width of about 1600 .mu.. As explained with respect to the conventional submount shown in FIG. 1, the reason why the Au layer 11 is formed by sputtering is that a sputtered Au layer has good adhesion to the Si submount body 2, and the reason why the Au layer 13 is formed by plating is that an Au layer when plated, can be formed to a desired thickness in a short time.

The laser chip 6, the submount 10 and the metal block 7 stacked as shown in FIG. 2 are placed in a heating apparatus (not shown). and the positional relationship between these three components is adjusted. Then, a weight of, for example, about 20 g is placed on the top surface of the laser chip 6, and current is applied to flow through a heater of the heating apparatus so that the assembly comprising the three components is heated to 400.degree. C. or higher. This heat treatment results in the formation of an AuSi eutectic solder layer on each of the opposing surfaces of the Si submount body 2. Sb in the Sb-doped Si submount body 2 and Sb in the AuSb layer 12 are diffused into the AuSi eutectic solder layer, and AuSiSb eutectic solder layers comprising a highly homogeneous mixture of Au, Si and Sb are formed. The thus formed AuSiSb eutectic solder layers bond the laser chip 6 to the Si submount 10 and at the same time the Si submount 10 to the metal block 7.

Semiconductor laser devices were made using the Si submounts of the present invention, and the resistance values R in the thickness direction of the Si submounts were measured after the heat treatment of each of the bonding steps. It has been found that variations in the resistance values R are significantly smaller than those of conventional Si submounts, such as the one shown in FIG. 1, and that almost all of the submounts have resistance values within the allowable range. This is shown in FIG. 3. As shown in FIG. 3, the resistance values R measured after the respective bonding steps, namely, the die bonding step (D/B). the block bonding step (B/B) and the wire bonding step (W/B), are all within a range of from 5 .OMEGA. to 9 .OMEGA.. It has been revealed that the percent defective is less than 1%.

The present invention has advantages over the invention disclosed in the aforementioned Japanese UM Published application No. SHO 62-10461 that the number of steps for manufacturing the semiconductor laser devices of the present invention is less that no troublesome surface treatment is required and that the devices of the present invention are more reliable and have a longer life.

The values, such as the sizes of various parts, the Sb concentrations etc. used in the description of the illustrated embodiment are only examples, and they may be varied as occasion demands within the scope of the present invention.