Abstract:
A semiconductor laser diode includes a mesa having a width on a semiconductor substrate and aligned with a direction of resonance, a current blocking layer formed by selective growth on both sides of the mesa and having a first embedded layer and a second embedded layer covering the first embedded layer.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method of producing a semiconductor laser diode used mainly in optical communications and particularly an embedded double junction semiconductor laser diode based on InP and that has a current blocking layer. 
     2. Description of the Related Art 
     Semiconductor laser diodes that have embedded layers based on InP on both sides of a mesa have been used as the light source for optical communications. FIGS. 26A-26D are schematic diagrams for explaining the respective steps in the production of the semiconductor laser diode of a conventional example (hereinafter referred to as a first conventional example). The semiconductor laser diode of the conventional example has been produced by forming an n cladding layer  2  made of n-InP, an active layer  3  and a p cladding layer  4  made of p-InP successively on a substrate  1  made of n-InP as shown in FIG.  26 A. Thereafter, as shown in FIG. 26B, an oxide film  205  is formed on a portion where a mesa is to be formed, and the other portion is etched away thereby forming the mesa. During this etching step, so-called undercut occurs below both edges of the oxide film  205 , causing the edges of the oxide film  205  to project in a manner of overhang on both sides. 
     Then a p-InP layer  206  and an n-InP layer  207  are grown on both sides of the mesa as shown in FIG. 26C, and the oxide film  205  is removed while forming a p contact layer  8  and a contact layer  9  as shown in FIG.  26 D. The semiconductor laser diode of the first conventional example thus produced has a problem of a current leakage path  210  being formed as shown in FIG. 26D that allows current leakage. A method of producing a semiconductor laser diode (hereinafter referred to as a second conventional example) that minimizes the current leakage is disclosed, for example, in the Japanese Patent No. 2828628. The production method disclosed in the Japanese Patent No. 2828628 comprises forming the n cladding layer  2  made of n-InP, the active layer  3  and the p cladding layer  4  made of p-InP successively on the substrate  1  made of n-InP as shown in FIG. 27A, followed by the formation of a nitride film  211  and an oxide film  212  on the p cladding layer  4  that is made of p-InP. 
     Then as shown in FIG. 27B, a photosensitive film  213  is formed on a portion where a mesa is to be formed, and the nitride film  211  and the oxide film  212  are etched away by using the photosensitive film  213  as a mask in a wet etching step using hydrofluoric acid, thereby forming a nitride film  211   a  and an oxide film  212   a . In this wet etching step, since the etching rate is higher for the oxide film than for the nitride film, the oxide film  211   a  becomes smaller than the nitride film  212   a  as shown in FIG.  27 B. Then as shown in FIG. 27C, the photosensitive film  213  is removed and the mesa is formed by etching with the nitride film  211   a  and the oxide film  212   a  as the mask. During this etching step, undercut occurs below both edges of the nitride film  211   a , making the nitride film  211   a  wider than the width of the mesa as shown in FIG. 27A, and therefore protruding edges are formed similarly to the first conventional example. 
     Then as shown in FIG. 28A, the protruding edges of the nitride film  211   a  are removed through dry etching by making use of the fact that the etching rate is higher for the nitride  211   a  film than for the oxide film  212   a  in dry etching. Thereafter, as shown in FIG. 28B, a p-InP layer  214  and an n-InP layer  215  are grown on both sides of the mesa, followed by removal of the oxide film  212   a  and the nitride film  211   a  thereby to form a p contact layer  216  and a contact layer  217  as shown in FIG.  28 C. In the semiconductor laser diode of the second conventional example thus produced, leakage current is less than that in the semiconductor laser diode of the first conventional example. 
     However, the semiconductor laser diode of the first conventional example had such a problem that the leakage current cannot be reduced as described above. 
     There was also a problem that an active layer is exposed on side faces of the mesa during dry etching of the protruding edges of the nitride film, resulting in a possibility of lowering the reliability of the active layer  3 . 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a method of producing the semiconductor laser diode that has high reliability with minimized leakage current. 
     In order to achieve the object described above, the present invention provides a method of producing the first semiconductor laser diode having a mesa of a predetermined width formed on the semiconductor substrate with the longitudinal direction thereof being aligned with the direction of resonance and the current block layer formed by selective growth on both sides of the mesa, which comprises: 
     forming a two-stage mask comprising a first mask of SiO 2  in contacting with the top semiconductor layer of semiconductor layers formed on a semiconductor substrate and a second mask of SiN with width different from that of the first mask, 
     forming said mesa by etching said semiconductor layers positioned at both sides of said two-stage mask, 
     forming a selective growth mask by etching said two-stage mask to make the width equal to the smaller width of said first mask and said second mask, and 
     selectively growing said current block layer on both sides of said selective growth mask. 
     With this method, optimum mask can be used in the etching step to form the mesa and in the selective growth step, and therefore it is made possible to form the current block layer having sufficient width in the vicinity of the mesa. As a consequence, according to the method of producing the first semiconductor laser diode of the present invention, the semiconductor laser diode with less leakage current can be produced. 
     In the method of producing the first semiconductor laser diode according to the present invention, width of the first mask may be made larger than that of the second mask. 
     In the method of producing the first semiconductor laser diode according to the present invention, width of the first mask may also be made smaller than that of the second mask. 
     The present invention provides a method of producing the fourth semiconductor laser diode having a mesa of a predetermined width formed on a semiconductor substrate with a longitudinal direction thereof being aligned with the direction of resonance and a current block layer formed by selective growth on both sides of the mesa, 
     wherein a selective growth mask comprising a first mask and a portion made of a different material is made by forming the portion of different material, having thermal expansion coefficient different from that of the first mask, on at least part of the first mask that is formed in contact with the mesa. 
     This makes it possible to prevent the shape of the selective growth mask from deforming thus accelerating the selective growth in the vicinity of the mesa during selective growth, and prevent the selective growth mask from deforming thus impeding the selective growth in the vicinity of the mesa. 
     The different material mentioned in this specification refers not only to those of different composition but also to those having the same composition but different crystalline structure or internal deformation. 
     Therefore it is made possible to prevent such a deformation of the selective growth mask that accelerates the selective growth in the vicinity of the mesa during selective growth, or prevent such a deformation of the selective growth mask that impedes the selective growth in the vicinity of the mesa, and it is made possible to form the current block layer having sufficient thickness in the vicinity of the mesa. As a consequence, the semiconductor laser diode with less leakage current can be produced. 
     In the method of producing the fourth semiconductor laser diode according to the present invention, it is preferable to select the different material from those having thermal expansion coefficient lower than that of the first mask material and form the different material layer over substantially the entire surface of the first mask. This configuration makes it possible to warp the selective growth mask so that the space between the substrate and the selective growth mask is enlarged at a high temperature during the selective growth step, thus causing a stock material gas to be supplied sufficiently to the portion where selective growth is desired. 
     Therefore it possible to form the current block layer having sufficient thickness in the vicinity of the mesa. As a consequence, the semiconductor laser diode with less leakage current can be produced. 
     In the method of producing the fourth semiconductor laser diode according to the present invention, the different material portion may also be formed in the form of a plurality of strips that are parallel to each other and are at right angles with the direction of resonance. 
     This configuration makes it possible to prevent the selective growth mask from deforming thus impeding the selective growth in the vicinity of the mesa during the selective growth step and to prevent the stock material gas supply to the portion where selective growth is to be carried out from being impeded. 
     Therefore selective growth can be carried out while preventing the current block layer from being thinned in the vicinity of the mesa. As a consequence, the semiconductor laser diode with less leakage current can be produced. 
     The present invention provides a method of producing the sixth semiconductor laser diode having a mesa of a predetermined width formed on a semiconductor substrate with a longitudinal direction thereof being aligned with the direction of resonance and a current block layer formed by selective growth on both sides of the mesa, which comprises the steps of: 
     forming a first embedded layer on both sides of said mesa by using a selective growth mask; 
     removing said selective growth mask after forming said first embedded layer; 
     growing a second semiconductor layer to such a thickness as the surface becomes substantially flat, on the mesa and on the first embedded layer on both sides of said mesa after removing the selective growth mask; and 
     forming a second embedded layer on said first embedded layer on both sides of said mesa by etching said second semiconductor layer until the surface of said mesa is exposed. 
     This construction makes it possible to form the second embedded layer having relatively large thickness. 
     Therefore it is made possible to form the second embedded layer having relatively large thickness and the semiconductor laser diode with less leakage current can be produced. 
     In the method of producing the sixth semiconductor laser diode according to the present invention, it is preferable to further form an etching stopper layer on the mesa before forming the first embedded layer. 
     In the method of producing the sixth semiconductor laser diode according to the present invention, it is made possible to easily control the etching of the second embedded layer and control the thickness of the second embedded layer accurately, and the semiconductor laser diode with less leakage current can be produced. 
     In the method of producing the sixth semiconductor laser diode according to the present invention, an etching accelerating layer may also be formed on the mesa before forming the first embedded layer. 
     In the method of producing the sixth semiconductor laser diode, it is made possible to easily control the etching of the second embedded layer and control the thickness of the second embedded layer accurately, and the semiconductor laser diode with less leakage current can be produced. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic diagram showing a two-stage mask used in mesa etching during the production process of the semiconductor aer diode according to the first embodiment of the present invention. 
     FIG. 2 is a schematic sectional view showing the semiconductor layer configuration of the semiconductor laser diode according to the first embodiment of the present invention. 
     FIG. 3A is a schematic sectional view after growing a p-cladding layer during the production process of the semiconductor laser diode according to the first embodiment of the present invention. 
     FIG. 3B is a schematic sectional view after forming a oxide film mask during the production process of the semiconductor laser diode according to the first embodiment of the present invention. 
     FIG. 3C is a schematic sectional view after forming a nitride mask during the production process of the semiconductor laser diode according to the first embodiment of the present invention. 
     FIG. 4A is a schematic sectional view after etching to form the mesa during the production process of the semiconductor laser diode according to the first embodiment of the present invention. 
     FIG. 4B is a schematic sectional view after re moving protruding portions of an oxide mask during the production process of the semiconductor laser diode according to the first embodiment of the present invention. 
     FIG. 4C is a schematic sectional view after growing the embedded layer during the production process of the semiconductor laser diode according to the first embodiment of the present invention. 
     FIG. 5A is a schematic sectional view after growing the cladding layer during the production process of the semiconductor laser diode according to the second embodiment of the present invention. 
     FIG. 5B is a schematic sectional view after forming the oxide film mask during the production process of the semiconductor laser diode according to the second embodiment of the present invention. 
     FIG. 5C is a schematic sectional view after forming the nitride film during the production process of the semiconductor laser diode according to the second embodiment of the present invention. 
     FIG. 6A is a schematic sectional view after etching to form the mesa during the production process of the semiconductor laser diode according to the second embodiment of the present invention. 
     FIG. 6B is a schematic sectional view after removing protruding portions of oxide mask during the production process of the semiconductor laser diode according to the second embodiment of the present invention. 
     FIG. 6C is a schematic sectional view after growing the embedded layer during the production process of the semiconductor laser diode according to the second embodiment of the present invention. 
     FIG. 7A is a schematic sectional view after growing the cladding layer during the production process of the semiconductor laser diode according to the third embodiment of the present invention 
     FIG. 7B is a schematic sectional view after forming the nitride film mask during the production process of the semiconductor laser diode according to the third embodiment of the present invention 
     FIG. 7C is a schematic sectional view after forming oxide mask during the production process of the semiconductor laser diode according to the third embodiment of the present invention 
     FIG. 8A is a schematic sectional view after etching to form the mesa during the production process of the semiconductor laser diode according to the third embodiment of the present invention. 
     FIG. 8B is a schematic sectional view after removing protruding portions of nitride mask during the production process of the semiconductor laser diode according to the third embodiment of the present invention. 
     FIG. 8C is a schematic sectional view after growing the embedded layer during the production process of the semiconductor laser diode according to the third embodiment of the present invention. 
     FIG. 9A is a schematic sectional view after growing the cladding layer during the production process of the semiconductor laser diode according to the fourth embodiment of the present invention. 
     FIG. 9B is a schematic sectional view after forming the insulating film during the production process of the semiconductor laser diode according to the fourth embodiment of the present invention. 
     FIG. 9C is a schematic sectional view after removing the insulating film on both sides of the resist film during the production process of the semiconductor laser diode according to the fourth embodiment of the present invention. 
     FIG. 10A is a schematic sectional view after etching to form the mesa during the production process of the semiconductor laser diode according to the fourth embodiment of the present invention. 
     FIG. 10B is a schematic sectional view after removing protruding portions of insulating film during the production process of the semiconductor laser diode according to the fourth embodiment of the present invention. 
     FIG. 10C is a schematic sectional view after growing the embedded layer during the production process of the semiconductor laser diode according to the fourth embodiment of the present invention. 
     FIG. 11A is a schematic sectional view after growing the cladding layer during the production process of the semiconductor laser diode according to the fifth embodiment of the present invention. 
     FIG. 11B is a schematic sectional view after forming the insulating film during the production process of the semiconductor laser diode according to the fifth embodiment of the present invention. 
     FIG. 11C is a schematic sectional view after forming an insulating film during the production process of the semiconductor laser diode according to the fifth embodiment of the present invention. 
     FIG. 12A is a schematic sectional view after etching to form the mesa during the production process of the semiconductor laser diode according to the fifth embodiment of the present invention. 
     FIG. 12B is a schematic sectional view after removing protruding portions of insulating film during the production process of the semiconductor laser diode according to the fifth emembodiment of the present invention. 
     FIG. 12C is a schematic sectional view after growing the embedded layer during the production process of the semiconductor laser diode according to the fifth embodiment of the present invention. 
     FIG. 13A is a schematic sectional view after growing the cladding layer during the production process of the semiconductor laser diode according to the sixth embodiment of the present invention. 
     FIG. 13B is a schematic sectional view after forming insulating film  20 ,  21  during the production process of the semiconductor laser diode according to the sixth embodiment of the present invention. 
     FIG. 13C is a schematic sectional view after forming insulating film  22  during the production process of the semiconductor laser diode according to the sixth embodiment of the present invention. 
     FIG. 14A is a schematic sectional view after etching to form the mesa during the production process of the semiconductor laser diode according to the sixth embodiment of the present invention. 
     FIG. 14B is a schematic sectional view after removing protruding portions of insulating film during the production process of the semiconductor laser diode according to the sixth embodiment of the present invention. 
     FIG. 14C is a schematic sectional view after growing the embedded layer during the production process of the semiconductor laser diode according to the sixth embodiment of the present invention. 
     FIG. 15 is a schematic sectional view after forming the selective growth mask during the production process of the semiconductor laser diode according to the seventh embodiment of the present invention. 
     FIG. 16 is a schematic sectional view when the embedded layer is growing during the production process of the semiconductor laser diode according to the seventh embodiment of the present invention. 
     FIG. 17A is a schematic sectional view after growing a p-InP first cladding layer during the production process of the semiconductor laser diode according to the seventh embodiment of the present invention. 
     FIG. 17B is a schematic sectional view after forming insulating films during the production process of the semiconductor laser diode according to the seventh embodiment of the present invention. 
     FIG. 17C is a schematic sectional view after etching to form the mesa during the production process of the semiconductor laser diode according to the seventh embodiment of the present invention. 
     FIG. 18A is a schematic sectional view when the embedded layer is growing during the production process of the semiconductor laser diode according to the seventh embodiment of the present invention. 
     FIG. 18B is a schematic sectional view after growing a contact layer during the production process of the semiconductor laser diode according to the seventh embodiment of the present invention. 
     FIG. 18C is a schematic sectional view after forming the electrode during the production process of the semiconductor laser diode according to the seventh embodiment of the present invention. 
     FIG. 19 is a perspective view showing a selective growth mask during the production process of the semiconductor laser diode according to the eighth embodiment of the present invention. 
     FIG. 20 is a perspective view showing a selective growth mask in selective growth during the production process of the semiconductor laser diode according to the eighth embodiment of the present invention. 
     FIG. 21 is a perspective view showing a selective growth mask during the production process of the semiconductor laser diode according to the ninth embodiment of the present invention. 
     FIG. 22A is a schematic sectional view after forming an insulating film during the production process of the semiconductor laser diode according to the tenth embodiment of the present invention. 
     FIG. 22B is a schematic sectional view after growing the second embedded layer during the production process of the semiconductor laser diode according to the tenth embodiment of the present invention. 
     FIG. 23A is a schematic sectional view after etching the second embedded layer during the production process of the semiconductor laser diode according to the tenth embodiment of the present invention. 
     FIG. 23B is a schematic sectional view after removing an etching stopper layer during the production process of the semiconductor laser diode according to the tenth embodiment of the present invention. 
     FIG. 24 is a schematic sectional view showing major steps during the production process of the semiconductor laser diode according to the eleventh embodiment of the present invention. 
     FIG. 25 is a schematic sectional view showing the construction of the semiconductor laser diode according to the present invention. 
     FIG. 26A is a schematic sectional view after growing p-cladding layer during the production process of the semiconductor laser diode according to the first conventional example. 
     FIG. 26B is a schematic sectional view after forming the mesa during the production process of the semiconductor laser diode according to the first conventional example. 
     FIG. 26C is a schematic sectional view after growing the embedded layer during the production process of the semiconductor laser diode according to the first conventional example. 
     FIG. 26D is a schematic sectional view after growing contact layer during the production process of the semiconductor laser diode according to the first conventional example. 
     FIG. 27A is a schematic sectional view after forming an oxide film during the production process of the semiconductor laser diode according to the second conventional example. 
     FIG. 27B is a schematic sectional view after forming a photosensitive film  213  during the production process of the semiconductor laser diode according to the second conventional example. 
     FIG. 27C is a schematic sectional view after removing the photosensitive film during the production process of the semiconductor-laser diode according to the second conventional example. 
     FIG. 27D is a schematic sectional view after forming the mesa during the production process of the semiconductor laser diode according to the second conventional example. 
     FIG. 28A is a schematic sectional view after removing protruding portions during the production process of the latter half of the semiconductor laser diode according to the second conventional example. 
     FIG. 28B is a schematic sectional view after growing the embedded layer during the production process of the latter half of the semiconductor laser diode according to the second conventional example. 
     FIG. 28C is a schematic sectional view after growing contact layer during the production process of the latter half of the semiconductor laser diode according to the second conventional example. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. 
     Embodiment 1 
     A semiconductor laser diode of the first embodiment according to the present invention is produced by, after forming a mesa  5  by using a double-layer mask comprising a f irst mask (oxide mask)  12  formed from SiO 2  in constant with a semiconductor layer and a second mask (nitride mask)  11  formed from SiN on the first mask with width smaller than that of the first mask  12 , etching the two-stage mask to make the width thereof equal to the width of the second mask (nitride mask)  11  to form a selective growth mask, and growing a first embedded layer  14  and a second embedded layer  15  by using the selective growth mask, thereby to form a current block layer  7  comprising the first embedded layer  14  and the second embedded layer  15 . 
     In the first embodiment, in case the mesa  5  with top surface width of about 1 μm is to be formed, for example, width W 1  of the oxide mask  12  is set to 5 to 7 μm and width W 2  of the nitride mask  11  is set to 3 to 4 μm. 
     In the semiconductor laser diode of the first embodiment produced by using the double-layer mask as described above, the current block layer  7  comprising the first embedded layer  14  and the second embedded layer  15  that are formed on both sides of the mesa  5  can be formed so that the second embedded layer  15  covers the entire top surface of the first embedded layer  14  as shown in FIG.  2 . Consequently, formation of leakage current path can be prevented with minimized leakage current in the semiconductor laser diode of the first embodiment. 
     A method of producing the semiconductor laser diode according to the first embodiment of the present invention will be described in detail below. 
     In the method of producing the semiconductor laser diode according to the first embodiment, first, an n cladding layer  2  made of n-InP, an active layer  3  and a p cladding layer  4  made of p-InP are formed successively on a substrate  1  made of n-InP as shown in FIG.  3 A. Then after forming an oxide film made of SiO 2  on the p cladding layer  4 , the oxide film is etched to leave the oxide film on a portion where a mesa is to be formed, thereby forming an oxide mask  12  made of silicon oxide, as shown in FIG.  3 B. 
     The oxide mask  12  is made wider than the mesa  5  to allow the mesa  5  of desired width to be formed. In case the mesa with top surface width of about 1 μm is to be formed, for example, width of the oxide mask is set to 5 to 7 μm. 
     Then a nitride film made of SiN is formed on the oxide mask  12 , and a nitride mask  11  having width smaller than that of the oxide mask  12  is formed over the portion where a mesa is to be formed as shown in FIG.  3 C. 
     Width of the nitride mask  11  is set so that the flow of stock material gas will not be impeded when growing the first embedded layer  14  made of semi-insulating InP (Fe-doped InP or the like) or p-InP and the second embedded layer  15  made of n-InP. 
     In case the mesa  5  with top surface width of about 1 μm is to be formed, for example, width of the nitride mask  11  is set to 3 to 4 μm. 
     Next, the two-stage mask comprising the nitride mask  11  and the oxide mask  12  is used as a mask in etching to form the mesa  5  shown in FIG.  4 A. Thus the mesa that corresponds to the width of the oxide mask  12  is formed. 
     Then as shown in FIG. 4B, protruding portions  12   b  of the oxide film  12  protruding beyond the nitride film  11  are removed by selective etching in a wet etching process using hydrofluoric acid or the like. 
     The insulating film mask, comprising the oxide mask  12   a  with the protruding portions  12   b  removed and the nitride mask  11  laminated on one another, is used as a selective growth mask for growing the first embedded layer  14  made of semi-insulating InP (Fe-doped InP or the like) or p-InP and the second embedded layer  15  on both sides of the mesa. 
     Then after removing the oxide mask  12   a  and the nitride mask  11  located on the mesa by wet etching step using hydrofluoric acid or the like, a p-InP layer  16  and a contact layer  17  are formed as shown in FIG.  2 . 
     Last, apelectrode (notshown) andanelectrode (notshown) are formed thereby making the semiconductor laser diode of the first embodiment. 
     In the semiconductor laser diode of the first embodiment produced as described above, the mesa is formed by etching with the two-stage insulating film mask comprising the nitride mask  11  and the oxide mask  12  that is formed under the nitride mask  11  and has the protruding portions  12   a  protruding beyond the nitride mask  11 , then the protruding portions  12   a  are removed by selective etching of the oxide mask  12  and the first embedded layer  14  and the second embedded layer  15  are formed. Thus since the protruding portions  12   a  that impede the growth of the second embedded layer  15  in the vicinity of the mesa are removed in the semiconductor laser diode of the first embodiment, the second embedded layer  15  can be grown up to near the mesa, thereby substantially eliminating the leakage current path. 
     Also according to the first embodiment, since two types of insulation mask, the nitride mask  11  and the oxide mask  12 , are formed separately, the insulation masks can be formed with high precision and, as a result, the mesa can be formed with high precision. 
     Also according to the first embodiment, it is preferable to form the nitride mask  11  and the oxide mask  12  by dry etching, which makes it possible to formed the insulating film masks with even higher precision and, as a result, form the mesa more precisely. 
     Also because the oxide film  12  is removed by wet etching after forming the mesa, reliability of the element can be improved without causing damage to the side face of the active layer  3  of the mesa unlike in the case of dry etching. 
     According to the present invention, however, removal of the oxide film  12  is not limited to wet etching. 
     Also because the oxide film  12  is formed in contact with the top surface of the semiconductor layer (top surface of the mesa) in the first embodiment, the mesa  5  can be precisely etched. That is, according to the present invention, while a nitride mask made of SiN may be formed in contact with the semiconductor layer as described later for the third embodiment, in this case, bonding strength of the nitride mask and the semiconductor layer that is excessively high causes such a problem that the narrowest portion of the mesa does not agree with the top surface of the mesa, resulting in a bottle neck to be formed below the top of the mesa. According to the first embodiment, since the oxide mask is formed in contact with the semiconductor layer, such a problem can be eliminated. 
     Embodiment 2 
     FIGS. 5A-6C are schematic sectional views showing the steps of the method of producing the semiconductor laser diode according to the second embodiment of the present invention. 
     In the method of producing the semiconductor laser diode according to the third embodiment, first, the n cladding layer  2  made of n-InP, the active layer  3  and the p cladding layer  4  made of p-InP are formed successively on the substrate  1  made of n-InP as shown in FIG. 5A similarly to the first embodiment. Then an oxide film mask  12   d  made of silicon oxide is formed on the p cladding layer  4  in a portion where the mesa is to be formed, as shown in FIG.  5 B. This is followed by the formation of a nitride film llf made of SiN to cover the oxide mask  12   d  as shown in FIG.  5 C. Width of the oxide mask  12   d  is set so that the flow of stock material gas will not be impeded when growing the first embedded layer  14  made of semi-insulating InP (Fe-doped InP or the like) or p-InP and the second embedded layer  15  made of n-InP. Width of the wider nitride mask  11   f  is set so as to enable the formation of the mesa having a desired shape, for example, in case the mesa with top surface width of about 1 μm is to be formed, width of the nitride mask  11   f  is set to 5 to 7 μm. 
     Next, the two-stage mask comprising the oxide film mask  12   d  and the nitride film mask  11   f  formed to cover the oxide film mask  12   d  is used in etching to form the mesa shown in FIG.  6 A. 
     Then as shown in FIG. 6B, the nitride film  11   f  is removed by selective etching in a dry etching step such as CF 4  plasma etching. 
     The oxide mask  12   d  is used as a selective growth mask for growing the first embedded layer  14  made of semi-insulating InP (Fe-doped InP or the like) or p-InP and the second embedded layer  15  made of n-InP on both sides of the mesa as shown in FIG.  6 C. 
     Thereafter, similar steps as those of the first embodiment are carried out thereby to produce the semiconductor laser diode of the second embodiment. 
     In the semiconductor laser diode of the second embodiment produced as described above, the mesa is formed by etching with the two-stage mask comprising the oxide mask  12   d  and the nitride mask  11   f  that is formed to cover the oxide mask  12   d  and has the protruding portions  11   e  protruding beyond the oxide mask  12   d , then after the nitride mask  11   f  is removed by selective etching, the first embedded layer  14  and the second embedded layer  15  are grown. Thus since the protruding portions  11   e  that impede the growth of the second embedded layer  15  in the vicinity of the mesa are removed, the second embedded layer  15  can be grown up to near the mesa, thereby substantially eliminating the leakage current path. 
     Also according to the second embodiment, since two types of insulating film mask, the nitride mask  11   f  and the oxide mask  12   d , are formed separately, the insulating film masks can be formed with high precision and, as a result, the mesa can be formed with high precision. According to the second embodiment, accuracy of forming the mesa can be improved further by forming the nitride mask  11   f  and the oxide mask  12   d  by dry etching. 
     Further according to the second embodiment, because the oxide film  12  is formed in contact with the top surface of the semiconductor layer (top surface of the mesa), the mesa  5  can be formed with high precision by etching, similarly to the first embodiment. 
     Embodiment 3 
     FIGS. 7A-8C are schematic sectional views showing the steps of the method of producing the semiconductor laser diode according to the third embodiment of the present invention. 
     In the method of producing the semiconductor laser diode according to the third embodiment, first, the n cladding layer  2  made of n-InP, the active layer  3  and the p cladding layer  4  made of p-InP are formed successively on the substrate  1  made of n-InP as shown in FIG. 7A similarly to the first and the second embodiments. Then a nitride film  11   c  made of silicon nitride is formed on the p cladding layer  4  that is made of p-InP in a portion where the mesa is to be formed, as shown in FIG.  7 B. This is followed by the formation of an oxide film  12   c  made of SiO 2  having width smaller than that of the nitride mask  11   c  on the nitride mask  11   c  at the position right above the mesa to be formed as shown in FIG.  7 C. 
     Width of the oxide mask  12   c  is set so that the flow of stock material gas will not be impeded when growing the first embedded layer  14  made of semi-insulating InP (Fe-doped InP or the like) or p-InP and the second embedded layer  15  made of n-InP. Width of the wider nitride mask  11   c  is set so as to enable the formation of the mesa having the desired shape, for example, in case the mesa with top surface width of about 1 μm is to be formed, width of the nitride mask  11   c  is set to 5 to 7 μm. 
     Next, the two-stage mask comprising the nitride mask  11   c  and the oxide mask  12   c  formed on the nitride mask  11   c  is used in etching to form the mesa  5  shown in FIG.  8 A. 
     Then protruding portions  11   b  of the nitride mask  11   c  protruding beyond the oxide mask  12   c  are removed as shown in FIG. 8B, by selective etching in a dry etching step such as CF 4  plasma etching. 
     The nitride mask  11   a  with the protruding portions  11   b  removed and the oxide mask  12   c  are used as selective growth mask for growing the first embedded layer  14  made of semi-insulating InP (Fe-doped InP or the like) or p-InP and the second embedded layer  15  made of n-InP on both sides of the mesa as shown in FIG.  8 C. 
     Thereafter similar steps as those of the first and the second embodiments are carried out to produce the semiconductor laser diode of the third embodiment. 
     In the semiconductor laser diode of the third embodiment produced as described above, the mesa is formed by etching with the two-stage mask comprising the oxide mask  12   c  and the nitride mask  11   c  that has the protruding portions  11   b  protruding beyond the oxide mask  12   c , then after the protruding portions  11   b  of the nitride mask  11   c  are removed by selective etching, the first embedded layer  14  and the second embedded layer  15  are grown. Thus since the protruding portions  11   b  that impede the growth of the second embedded layer  15  in the vicinity of the mesa are removed, the second embedded layer  15  can be grown up to near the mesa, thereby substantially eliminating the leakage current path. 
     Also according to the third embodiment, since two types of insulating film mask, the nitride mask  11   c  and the oxide mask  12   c , are formed separately, the insulating film masks can be formed with high precision and, as a result, the mesa can be formed with high precision. According to the third embodiment, it is preferable to form both the nitride mask  11   c  and the oxide mask  12   c  by dry etching, which improves the accuracy. 
     Embodiment 4 
     FIGS. 9A-10C are schematic sectional views showing the steps of the method of producing the semiconductor laser diode according to the fourth embodiment of the present invention. 
     In the method of producing the semiconductor laser diode according to the fourth embodiment, first, the n cladding layer  2  made of n-InP, the active layer  3  and the p cladding layer  4  made of p-InP are formed successively on the substrate  1  made of n-InP as shown in FIG.  9 A. Then an insulating film made of SiO 2  or SiN, for example, is formed on the p cladding layer  4  that is made of p-InP in a portion where the mesa is to be formed, as shown in FIG.  9 B. The insulating film  18  is formed so that the width thereof is larger than that of the mesa that is to be formed and the insulating film protrudes substantially evenly to the right and left beyond the edges of the mesa. 
     Then a resist film is formed on the insulating film  18  right above the mesa to be formed, and the insulating film on both sides of the resist film are removed by etching, thereby shaping the insulating film  18   a  to have stepped cross section having raised central portion as shown in FIG.  9 C. That is, the insulating film  18   a  consists of a thick portion  18   c  at the center and thin portions  18   b  extending therefrom over substantially the same distances on both sides. 
     Width of the insulating film  18   a  is made larger than that of the mesa  5  to enable the formation of the mesa  5  having desired oshape. In case the mesa with top surface width of about 1 μm is to be formed, for example, width of the insulating film  18   a  is set to 5 to 7 μm. 
     Width of the thick portion  18   c , on the other hand, is set so that the flow of stock material gas will not be impeded when growing the first embedded layer  14  made of semi-insulating InP (Fe-doped InP or the like) or p-InP and the second embedded layer  15  made of n-InP. 
     In case the mesa  5  with top surface width of about 1 μm is to be formed, for example, width of the nitride mask  11  is set to 3 to 4 μm. 
     Then as shown in FIG. 10A, the mesa is formed by etching with the insulating film  18   a , having stepped cross section with the raised central portion, being used as a mask. Thereafter, the thin portions  18   b  of the insulating film mask  18   a  are removed by wet etching or dry etching as shown in FIG. 10B, then the first embedded layer  14  made of semi-insulating InP (Fe-doped InP or the like) or p-InP and the second embedded layer  15  made of n-InP are grown on both sides of the mesa by using the insulating film, that consists of the thick portion  18   c  with the thin portions  18   b  being removed, as the selective growth mask, as shown in FIG.  10 C. 
     The thick portion  18   c  of the mask on the mesa is then removed by wet etching using hydrofluoric acid or the like, the p-InP layer and the contact layer  17  are formed similarly to the first through the third embodiments and, last, the p electrode is formed thereby making the semiconductor laser diode of the fourth embodiment. 
     The semiconductor laser diode according to the fourth embodiment produced as described above can be made by using one type of insulating film with effects similar to those of the first and the second embodiments. 
     Embodiment 5 
     FIGS. 11A-12C are schematic sectional views showing the steps of the method of producing the semiconductor laser diode according to the fifth embodiment of the present invention. 
     In the method of producing the semiconductor laser diode according to the fifth embodiment, first, the n cladding layer  2  made of n-InP, the active layer  3  and the p cladding layer  4  made of p-InP are formed successively on the substrate  1  made of n-InP as shown in FIG.  11 A. Then an insulating film  19  made of SiO 2 , SiN or the like is formed on the p cladding layer  4  that is made of p-InP in a portion where the mesa is to be formed, as shown in FIG.  11 B. This is followed by the formation of an insulating film  19   a  made of the same material as that of the insulating film  19  to cover the insulating film  19 . The insulating film  19   a  is formed so that the width thereof is larger than that of the mesa that is to be formed and the insulating film protrudes substantially evenly to the right and left from the edges of the mesa. 
     Width of the insulating film  19  is set so that flow of stock material gas will not be impeded when growing the first embedded layer  14  made of semi-insulating InP (Fe-doped InP or the like) or p-InP and the second embedded layer  15  made of n-InP. Width of the wider insulating film  19  is set so as to enable the formation of the mesa having desired shape, for example, in case the mesa with top surface width of about 1 μm is to be formed, width of the insulating film  19  is set to 5 to about 7 μm. 
     Then as shown in FIG. 12A, the mesa is formed by etching with the two-stage mask comprising the insulating film  19  and the insulating film  19   a  as the mask. Thereafter, the insulating film  19   a  is removed by wet etching or dry etching as shown in FIG. 12B, then the first embedded layer  14  made of semi-insulating InP (Fe-doped InP or the like) or p-InP and the second embedded layer  15  made of n-InP are grown on both sides of the mesa by using the insulating film  19  as the selective growth mask, as shown in FIG.  12 C. 
     The insulating film  19  on the mesa is then removed, the p-InP layer and the contact layer  17  are formed similarly to the first through the fourth embodiments and, last, the p electrode is formed thereby making the semiconductor laser diode of the fifth embodiment. 
     The semiconductor laser diode according to the fifth embodiment produced as described above can be made by using one type of insulating film with effects similar to those of the first and the second embodiments. 
     Since the insulating film  19  and the insulating film  19   a  are formed separately, width and thickness of the insulating films can be controlled accurately, thereby forming the mesa with high precision. 
     Embodiment 6 
     FIGS. 13A-14C are schematic sectional views showing the steps of the method of producing the semiconductor laser diode according to the sixth embodiment of the present invention. 
     The production method according to the sixth embodiment is a variation of the production method according to the fourth embodiment wherein an etching stopper layer is provided in the insulating film thereby making it possible to improve the processing accuracy. 
     In the method of producing the semiconductor laser diode according to the sixth embodiment, first, the n cladding layer  2  made of n-InP, the active layer  3  and the p cladding layer  4  made of p-InP are formed successively on the substrate  1  made of n-InP as shown in FIG.  13 A. Then two insulating films having different etching rates with regard to dry etching are formed on the p cladding layer  4  that is made of p-InP, and a predetermined resist pattern is formed thereby to form an insulating film  20  and an insulating film  21  that are laminated one on another, as shown in FIG.  13 B. The insulating films  20 ,  21  are formed to be wider than the mesa that is to be formed and protrude to the right and left from the edges of the mesa. 
     Widths of the insulating films  20 ,  21  are set so as to enable the formation of the mesa having a desired shape, for example, in case the mesa with top surface width of about 1 μm is to be formed, width of the oxide film mask  12  is set to 5 to about 7 μm. 
     Then an insulating film different from the insulating film  21  is formed on the insulating film  21  and dry etching is carried out using the resist pattern, to form an insulating film  22  that is narrower than the insulating films  20 ,  21  over the mesa to be formed. In order for the insulating film  21  to function as an etching stopper layer, a material having a lower etching rate than the insulating film  22  with regard to dry etching is used for the insulating film  21 . Width of the insulating film  22  is set so that the flow of stock material gas will not be impeded when growing the first embedded layer  14  made of semi-insulating InP (Fe-doped InP or the like) or p-InP and the second embedded layer  15  made of n-InP. 
     Then the mesa is formed by etching with a stepped triple-layer insulating film comprising the insulating films  20 ,  21 ,  22  used as a mask as shown in FIG.  14 A. 
     Next, the insulating films  20 ,  21  located on both sides of the insulating film  22  and the insulating film  22  are removed by wet etching or dry etching. Then the insulating film comprising the remainder of the insulating film  20   a  and insulating film  21   a  are used as a selective growth mask, as shown in FIG. 14C, to grow the first embedded layer  14  made of semi-insulating InP (Fe-doped InP or the like) or p-InP and the second embedded layer  15  made of n-InP on both sides of the mesa. The insulating films  20   a ,  21   a  on the mesa are then removed, the p-InP layer and the contact layer  17  are formed similarly to the foregoing embodiments and, last, the p electrode is formed thereby making the semiconductor laser diode of the sixth embodiment. 
     The semiconductor laser diode according to the sixth embodiment produced as described above has effects similar to those of the first through the fifth embodiments. Also since the semiconductor laser diode according to the sixth embodiment employs the etching stopper layer, the insulating film  20  can be protected from being etched when etching the insulating film  22  into a desired shape, thus maintaining the shape (particularly the width) of the insulating film  20 . This makes it possible to form the insulating films more precisely and, in turn, to form the mesa with high accuracy. 
     In the method of producing the semiconductor laser diode according to the sixth embodiment, it is preferable to use SiN for the insulating film  20 , 22  and SiO 2  for the insulating film  21 . Use of SiO 2  for the insulating film  20  that is in contact with the semiconductor layer allows it to prevent a bottle neck described in conjunction with the first embodiment from being formed in the mesa, thus forming the mesa of the desired configuration with high accuracy. Also with the insulating film  21  that serves as the etching stopper layer being formed from SiN, it functions effectively as the etching stopper layer for the insulating layer  20  made of SiO 2 . 
     Embodiment 7 
     The semiconductor laser diode according to the seventh embodiment is produced by, after etching to form a mask with a selective growth mask  100  of double-layer structure made by laminating an insulating film  106  and an insulating film  107  having thermal expansion coefficient lower than that of the insulating film  106  as shown in FIG. 15, the selective growth mask  100  is used to form the first embedded layer  108  made of p-InP and the second embedded layer  109  made of n-InP on both sides of the mesa as shown in FIG.  16 . Since this configuration causes the first embedded layer  108  made of p-InP and the second embedded layer  109  to grow at a high temperature, the selective growth mask  100  of double-layer structure warps to expand the space of the embedding portion around the mesa as shown in FIG. 16 thus allowing the stock material gas to be supplied sufficiently to the space around the mesa. This makes it possible, in the semiconductor laser diode according to the seventh embodiment, to grow the first and second embedded layers, particularly the second embedded layer  109 , to a sufficient thickness of 0.3 μm or greater in the vicinity of the mesa, thus minimizing the leakage current. 
     In case the first embedded layer  108  made of p-InP and the second embedded layer  109  made of n-InP are grown by metal organic chemical vapor deposition (MOCVD) technique, the growing temperature is set to 600 to 700° C. In the seventh embodiment, for example, SiO 2  (thermal expansion coefficient 5×10 −7 ° C. −1 ) can be used for the insulating film  106 , and Si 2 N 3  (thermal expansion coefficient 4×10 −7 ° C. −1 ) can be used for the insulating film  107 . 
     In FIG.  15  and FIG. 16, numeral  1  denotes a substrate made of n-InP,  102  denotes an n-InGaAsP light confinement layer,  103  denotes an InGaAsP-MQW quantum well active layer,  104  denotes an undoped InGaAsP light confinement layer and  105  denotes a p-InP first cladding layer. 
     The method of producing the semiconductor laser diode according to the seventh embodiment will be described below with reference to FIGS. 17A-18C in the sequential order of the steps. 
     According to this production method, the n-InGaAsP light confinement layer  102 , the InGaAsP-MQW quantum well active layer  103 , the undoped InGaAsP light confinement layer  104  and the p-InP first cladding layer  105  are formed on the substrate  1  as shown in FIG.  17 A. 
     Next, after forming an insulating film of SiO 2  and an insulating film Si 2 N 3  on the p-InP first cladding layer  105  by sputtering or CVD process, the insulating films are etched into a predetermined shape by wet etching or dry etching thereby to form the selective growth mask  100  comprising the first insulating film  106  made of SiO 2 , and the second insulating film  107  made of Si 2 N 3  laminated on one on another. 
     Then wet etching is carried out by using HBr to form a mesa  90  that serves as an optical waveguide as shown in FIG.  17 C. 
     The selective growth mask  100  of double-layer structure comprising the first insulating film  106  and the second insulating film  107  being laminated one on another is used to grow the first embedded layer  108  made of p-InP and the second embedded layer  109  made of n-InP by metal organic chemical vapor deposition (MOCVD) technique as shown in FIG.  18 A. Since the growing temperature with the MOCVD process is set to 500 to 700° C., the selective growth mask  100  warps during growth due to the difference in the thermal expansion coefficient between the first insulating film  106  and the second insulating film  107 , so that the space between the substrate  1  and the protruding portions  100   a  of the selective growth mask  100  is expanded. Since this makes it possible to supply the stock material gas sufficiently to around the mesa for forming the first embedded layer  108  and the second embedded layer  109 , the first embedded layer  108  and the second embedded layer  109  can be formed with a sufficient thickness of 0.3 μm or larger up to the vicinity of the mesa. According to the present invention, thickness of each of the first insulating film  106  and the second insulating film  107  that constitute the selective growth mask  100  of double-layer structure is preferably set to 500 to 2000 Å in order to effectively achieve the operation/working effect of the selective growth mask and the effects of the present invention. 
     After growing the layers, the selective growth mask  100  is removed by wet etching or dry etching and, as shown in FIG. 18B, a p-InP second cladding layer  110  and a p + -InGaAs contact layer  111  are formed successively by MOCVD process. 
     After forming an insulating film  112  made of SiO 2  or SiN on the p + -InGaAs contact layer  111  by sputtering or CVD process, the insulating film is removed from over the mesa which should be connected with an electrode. 
     Then as shown in FIG. 18C, a Ti/Au-deposited electrode  113  m that makes contact with the p + -InGaAs contact layer  111  is formed in an aperture formed in the insulating film and an Au-plated electrode  114  to serve as a surface electrode (p electrode) is formed on the deposited electrode  113 , followed by the formation of an AuGe/Ni/Ti/Pt/Au-deposited electrode  115  and an Au-plated electrode  116  as n electrodes. 
     In the semiconductor laser diode according to the seventh embodiment produced by the method described above, since the p-InP embedded layer  108  and the n-InP embedded layer  109  can be formed with a sufficient thickness of 0.3 μm or greater up to near the mesa, leakage current path can be prevented from being formed thus minimizing the leakage current. 
     In the semiconductor laser diode according to the seventh embodiment, since the selective growth mask  100  comprising the insulating film  106  and the insulating film  107  having different thermal expansion coefficients is used, the selective growth mask  100  warps so that the space between the substrate  1  and the protruding portions  100   a  of the selective growth mask  100  expands when growing the p-InP embedded layer  108  and the n-InP embedded layer  109  by MOCVD process. Consequently, the stock material gas for forming the p-InP embedded layer  108  and the n-InP embedded layer  109  can be supplied sufficiently to around the mesa, thus making it possible to form the p-InP embedded layer  108  and the n-InP embedded layer  109  with a sufficient thickness of 0.3 μm or larger up to the vicinity of the mesa. 
     Materials having different thermal expansion coefficients  1 are used to form the insulating film  106  and the insulating film  107  in the seventh embodiment, but the present invention is not limited to this configuration, and such a selective growth mask of double-layer structure may be used that consists of two films formed from an identical material but are made to have different amounts of deformation produced in the films when growing the crystal thereby giving different thermal expansion coefficients. 
     When forming a selective growth mask from SiN, for example, the first insulation mask may be formed from SiN by plasma CVD process and the second insulation mask may be formed from SiN by high-temperature thermal CVD process. This configuration makes it possible to differentiate the amount of deformation produced in the first insulation mask formed from SiN by plasma CVD process and the amount of deformation produced in the second insulation mask formed from SiN by high-temperature thermal CVD process, thus achieving effects similar to those of the seventh embodiment. 
     Embodiment 8 
     The semiconductor laser diode according to the eighth embodiment is produced similarly to the seventh embodiment except that a selective growth mask  150  is used instead of the selective growth mask  100  in the production method of the seventh embodiment. 
     Specifically, according to the method of producing the semiconductor laser diode of the eighth embodiment, the selective growth mask  150  is made by forming a plurality of insulating films  117  spaced at predetermined intervals with the longitudinal direction thereof arranged at right angles with the longitudinal direction of the mesa on the insulating film  106 . In case the thermal expansion coefficient is made different between the insulating film  106  and the insulating film  107  in the selective growth mask  150  that is made as described above, the selective growth mask  150  is deformed in an undulating configuration as shown in FIG. 20 due to the difference in the thermal expansion coefficient between the insulating film  106  and the insulating film  107  at the growth temperature when forming the p-InP embedded layer  108  and the n-InP embedded layer  109  by the MOCVD process. 
     This deformation makes it possible to prevent the protruding portions  150   a  from sagging toward the substrate  1  in the selective growth mask  150  when forming the first embedded layer  108  and the second embedded layer  109 , thereby preventing the space between the substrate  1  and the protruding portions  150   a  of the selective growth mask  150  from decreasing. This makes it possible to supply the stock material gas for forming the first embedded layer  108  and the second embedded layer  109  sufficiently to around the mesa, thus making it possible to form the first embedded layer  108  and the second embedded layer  109  with a sufficient thickness of 0.3 μm or larger up to the vicinity of the mesa. 
     According to the eighth embodiment, the insulating film  106  may be made of SiO 2  and the insulating film  117  may be made of Si 2 N 3 . However, accordingtothepresent invention, acombination of insulation materials having different thermal expansion coefficients may be used, or alternatively the insulating films may also be made of the same material with the thermal expansion coefficients differentiated by producing different amounts of internal deformation during growth. 
     Also according to the eighth embodiment, the insulating film  106  and the insulating film  117  may be made of the same material having the same thermal expansion coefficient. That is, in such a configuration as the film thickness varies periodically, less deformation due to thermal expansion is caused in thick portions and larger deformation due to thermal expansion is caused in thin portions, resulting in the undulating configuration as shown in FIG. 20 thereby achieving effects similar to those of the eighth embodiment. 
     Embodiment 9 
     The semiconductor laser diode according to the ninth embodiment is produced similarly to the seventh embodiment except that a selective growth mask  160  is used instead of the selective growth mask  100  in the production method of the seventh embodiment. 
     Specifically, according to the method of producing the semiconductor laser diode of the ninth embodiment, the selective growth mask  160  is made by forming an insulating film  127  having a pattern of grating or mesh on the insulating film  106 . In the selective growth mask  160  that is made as described above, since the thickness is greater in the portions where the insulating film  127  is formed on the insulating film  106 , the selective growth mask  160  can be prevented from deforming at the growth temperature when growing the first embedded layer  108  and the second embedded layer  109  by the MOCVD process. 
     Thus it is made possible to prevent the protruding portions  160   a  from sagging toward the substrate  1  in the selective growth mask  160  when forming the first embedded layer  108  and the second embedded layer  109 , thereby preventing the space between the substrate  1  and the protruding portions  160   a  of the selective growth mask from decreasing. This makes it possible to supply the stock material gas for forming the first embedded layer  108  and the second embedded layer  109  sufficiently to around the mesa, thus making it possible to form the first embedded layer  108  and the second embedded layer  109  with a sufficient thickness of 0.3 μm or larger up to the vicinity of the mesa. 
     According to the ninth embodiment, the insulating film  106  may be made of SiO 2  and the insulating film  127  may be made of Si 2 N 3 , although the insulating films may also be made of the same material having the same thermal expansion coefficient. That is, it suffices to form the insulating films in such a configuration that the thicker portions are prevented from deforming due to heat such as grating or mesh. 
     Embodiment 10 
     The semiconductor laser diode according to the tenth embodiment is produced by, after growing the first embedded layer  108  using a selective growth mask, removing the selective growth mask, growing a second embedded layer on the top surface and etching the entire surface uniformly, thereby forming the second embedded layer  109  of a desired thickness. 
     Specifically, similarly to the seventh embodiment, the n-InGaAsP light confinement layer  102 , the InGaAsP-MQW quantum well active layer  103 , the undoped InGaAsP light confinement layer  104  and the p-InP first cladding layer  105  are formed on the substrate  1  made of n-InP. 
     Then, in the tenth embodiment, an additional layer made of, for example, InAlAs that will become an etching stopper layer  137  is formed as shown in FIG.  22 A. 
     Next, after forming an insulating film of SiO 2  on the InAlAs layer by sputtering or CVD process, the insulating film is etched into a predetermined shape by wet etching or dry etching thereby to form the insulating film  106  made of SiO 2 , which is used as a mask for etching the mesa. 
     After forming the mesa by etching, the insulating film  106  is used as a selective growth mask to grow the first embedded layer  108  by the MOCVD process as shown in FIG.  22 A. 
     The insulating film  106  used as the selective growth mask is then removed and a second embedded layer  109   a  is grown to such a thickness as the entire top surface becomes substantially flat as shown in FIG.  22 B. 
     Then as shown in FIG. 23A, the second embedded layer  109   a  is etched with a uniform etching rate from above until the top surface of the etching stopper layer  137  is exposed. 
     In case n-InP is used for the second embedded layer in the present invention, dry etching with a mixture gas of CH 4 , O 2  and H 2  can be employed in the etching of the second embedded layer  109   a  from above. With this etching step, uniform etching rate in the direction of thickness can be achieved relatively easily. 
     Then as shown in FIG. 23B, the etching stopper layer  137  is removed by using HF, for example, and similar processes as those of the eighth embodiment are carried out to complete the semiconductor laser diode of the tenth embodiment. 
     In the production method according to the tenth embodiment, since the second embedded layer  109  is formed by growing the n-InP embedded layer  109   a  and etching it from above after removing the selective growth mask, the second embedded layer  109  can be formed with a sufficient thickness of 0.3 μm or greater up to near the mesa. 
     The production method according to the tenth embodiment may be applied not only to the case of double-layer structure of the first embedded layer and the second embedded layer, but also to an embedded layer of single-layer or triple-layer structure. 
     While the etching stopper layer  137  is formed in the tenth embodiment, the present invention is not limited to this, and the semiconductor laser diode may be produced without forming the etching stopper layer  137 . 
     Embodiment 11 
     While the etching of the second embedded layer  109   a  is controlled by means of the etching stopper layer  137  that has a slow etching rate in the tenth embodiment, an etching accelerating layer of higher etching rate is used instead of the etching stopper layer  137  as shown in FIG. 24 in the eleventh embodiment. 
     That is, in the eleventh embodiment, when etching the p-InP embedded layer  109   a , etching of the layer  147  proceeds rapidly when the etching step reaches the layer  147  that has a higher etching rate and the etching rate decreases when the surface of the cladding layer  105  is reached, upon which the etching step is terminated. 
     Thereafter, similar steps as those of the tenth embodiment are carried out to complete the semiconductor laser diode of the eleventh embodiment. 
     In the eleventh embodiment, HBr or HCl can be used to etch the p-InP embedded layer  109   a . In this case, InGaAsP or InGaAs may be used for the layer  147  of high etching rate. 
     Width of the selective growth mask in the seventh through eleventh. embodiments is set so that the mesa of the desired shape can be formed. In case the mesa with top surface width of about 1 μm is to be formed, for example, width of the selective growth mask is set to 5 to 7 μm. 
     In the semiconductor laser diode according to the embodiments described above, since the second embedded layers  15 ,  109  can be formed on the first embedded layers  14 ,  108  to make contact with the entire surface of the first embedded layers  14 ,  108  as described above, leakage current path can be prevented from being formed thus minimizing the leakage current. Also when the distance L from the side face of the mesa is 1 μm, for example, thickness of the second embedded layer can be made 0.3 μm or greater. Thus in the semiconductor laser diode according to the embodiments described above, since the relatively thick second embedded layer is formed, leakage current can be decreased further. 
     While the preferred embodiments described above involve the formation of the current block layer comprising the first embedded layer and the second embedded layer, the present invention is not limited to a semiconductor laser diode having a current block layer comprising two embedded layers, and may be applied to a semiconductor laser diode having three or more embedded layers. Also the preferred embodiments except for the tenth embodiment and the eleventh embodiment can be applied to a case of current block layer comprising a single embedded layer. 
     While the preferred embodiments have been described with regard to the semiconductor layers such as the substrate  1 , the first embedded layer and the second embedded layer taking reference to specific compositions, the present invention is not limited to these embodiments and can be applied to any semiconductor laser diode that has a mesa formed from one or more semiconductor layers on a substrate and is made by growing embedded layers on both sides of the mesa.