Patent Publication Number: US-2011049554-A1

Title: Package base structure and manufacturing method thereof

Description:
FIELD OF THE INVENTION 
     The present invention relates to a package base structure, and more particularly to a package base structure for packaging a light emitting diode. The present invention also relates to a method of manufacturing such a package base structure. 
     BACKGROUND OF THE INVENTION 
     For most optoelectronic systems, the mechanism for changing the optical path is very important.  FIG. 1  is a schematic perspective view illustrating a package base structure according to the prior art. The package base structure has a reflective surface  120  for deflecting the light emitted by the light-emitting element  11  to the out-of-plane direction with respect to the substrate  10 . As shown in  FIG. 1 , a glass block  12  having a 45-degree reflective surface  120  is bonded on a substrate  10 . In addition, a micro lens  13  is mounted on the upper edge of the 45-degree reflective surface  120 . As such, the light beam emitted by the light-emitting element  11  is reflected by the reflective surface  120  and then focused and collimated by the micro lens  13 . The conventional package base structure, however, still has some drawbacks. For example, since the light-emitting element  11 , the glass block  12  and the micro lens  13  are discrete elements, the package base structure is very costly. Since the light-emitting element  11 , the glass block  12  and the micro lens  13  need to be precisely aligned with each other, the process of manufacturing the package base structure is not cost-effective, and the mass production of the package base structure is difficult. 
     Therefore, there is a need of providing a package base structure and a manufacturing method thereof in order to obviate the drawbacks encountered from the prior art. 
     SUMMARY OF THE INVENTION 
     In accordance with an aspect of the present invention, there is provided a manufacturing process of a package base structure. Firstly, a semiconductor substrate having a top surface is provided. Then, a first etching mask with a first etching window is formed on the top surface of the semiconductor substrate. The etching window has a sidewall oriented at a bias angle with respect to a specific equivalent crystallographic orientation of the semiconductor substrate. The bias angle ranges from 0 degree to 90 degrees except 45 degrees. Then, a selective anisotropic etching procedure is performed through the first etching window to form a slant surface on the semiconductor substrate. Then, a second etching mask with a plurality of second etching windows is formed on the slant surface. Afterwards, an etching process is performed through the second etching windows to form a micro diffractive optical element with a plurality of trenches on the slant surface. 
     In accordance with another aspect of the present invention, there is provided a package base structure for packaging a light-emitting element. The package base structure includes a semiconductor substrate, a receiving space and a micro diffractive optical element. The semiconductor substrate has a top surface. The receiving space is disposed in the tope surface of the semiconductor substrate and defined by a plurality of slant surfaces. A specified slant surface of the plurality of slant surfaces is oriented at a bias angle with respect to a specific equivalent crystallographic orientation of the semiconductor substrate. The bias angle ranges from 0 degree to 90 degrees except 45 degrees. The micro diffractive optical element is formed on the specified slant surface and having a plurality of trenches for collimating or focusing a light beam that is emitted by the light-emitting element. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above contents of the present invention will become more readily apparent to those ordinarily skilled in the art after reviewing the following detailed description and accompanying drawings, in which: 
         FIG. 1  is a schematic perspective view illustrating a package base structure according to the prior art; 
         FIG. 2A  is a schematic top perspective view illustrating a package base structure according to an embodiment of the present invention; 
         FIG. 2B  is a cross-sectional view illustrating the package base structure of  FIG. 2A  taken along line D-D′; 
         FIG. 2C  is a cross-sectional view illustrating the package base structure of  FIG. 2A  taken along line E-E′; 
         FIGS. 3A˜3J  are schematic cross-sectional views illustrating a process for manufacturing a package base structure according to the present invention; 
         FIG. 4  is a schematic perspective view illustrating an exemplary micro diffractive optical element of the package base structure according to an embodiment of the present invention; and 
         FIG. 5  is a schematic perspective view illustrating another exemplary micro diffractive optical element of the package base structure according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention will now be described more specifically with reference to the following embodiments. It is to be noted that the following descriptions of preferred embodiments of this invention are presented herein for purpose of illustration and description only. It is not intended to be exhaustive or to be limited to the precise form disclosed. 
       FIG. 2A  is a schematic top perspective view illustrating a package base structure according to an embodiment of the present invention.  FIG. 2B  is a cross-sectional view illustrating the package base structure of  FIG. 2A  taken along line D-D′.  FIG. 2C  is a cross-sectional view illustrating the package base structure of  FIG. 2A  taken along line E-E′. Please refer to  FIGS. 2A ,  2 B and  2 C. The package base structure  2  is used for packaging a semiconducting light-emitting element  200 . An example of the semiconducting light-emitting element  200  includes but is not limited to an optical pickup head of an optical storage device, a light emitting diode (LED) or a laser diode for use in edge-emitting laser or vertical-cavity surface-emitting laser. 
     As shown in  FIG. 2A , the package base structure  2  comprises a semiconductor substrate  20 , a receiving space  21  and a micro diffractive optical element  22 . The semiconductor substrate  20  is a silicon substrate with a diamond crystalline structure. The semiconductor substrate  20  has a top surface  201 , which is a {100} equivalent crystallographic surface. The receiving space  21  is defined by a plurality of slant surfaces  211 . These slant surfaces  211  are extended in the direction D-D′ and the direction E-E′, respectively. The slant surface  211  in the direction D-D′ is oriented at a bias angle α with respect to the &lt;100&gt; equivalent crystallographic orientation of the semiconductor substrate  20 . The bias angle α is greater than or equal to 0 degree and smaller than 45 degrees, or greater than 45 degrees and smaller than or equal to 90 degrees. For obtaining an optimum effect, the bias angle is 22 degrees in this embodiment. 
     As shown in  FIG. 2B , the slant surface  211  is on a {110} equivalent crystallographic plane of the semiconductor substrate  20 . In addition, the slant surface  211  is a 45-degree slant surface with respect to the {100} equivalent crystallographic surface  201 . As shown in  FIG. 2B , the slant surface  211  is also on the {110} equivalent crystallographic plane of the semiconductor substrate  20 . In addition, the slant surface  211  is a 45-degree slant surface with respect to the {100} equivalent crystallographic surface  201 . In accordance with a key feature of the present invention, the micro diffractive optical element  22  is formed on the slant surface  211  in the direction D-D′. When the light beam emitted by the light-emitting element  200  is projected on the micro diffractive optical element  22  formed on the slant surface  211 , the light beam will be successfully deflected to the out-of-plane direction. In addition, the light beam could be collimated or focused by the micro diffractive optical element  22 . The monolithic package base structure  2  of the present invention has the functions of deflecting the light beam to the out-of-plane direction and collimating or focusing the light beam. 
       FIGS. 3A˜3J  are schematic cross-sectional views illustrating a process for manufacturing a package base structure according to the present invention. The process for manufacturing the package base structure is applied to a semiconductor fabricating process. Firstly, as shown in  FIG. 3A , a semiconductor substrate  20  having a {100} equivalent crystallographic top surface  201  is provided. Then, as shown in  FIG. 3B , a mask layer  2011  made of silicon nitride is formed on the top surface  201  of the semiconductor substrate  20 . Then, as shown in  FIG. 3C , a photoresist layer  2012  is formed on the mask layer  2011 . Then, as shown in  FIG. 3D , a photoresist pattern  2001  is defined in the photoresist layer  2012  by means of a photomask (not shown). Then, according to the photoresist pattern  2001 , the mask layer  2011  is etched by a reactive ion etching (RIE) process to form an etching window  2013  (see  FIG. 3E ). As shown in  FIG. 3F , the photoresist pattern  2001  is removed, and then a wet etching process is performed to partially etch off the semiconductor substrate  20  through the etching window  2013 , thereby forming a receiving space  21  defined by a plurality of slant surfaces  212 . In this embodiment, the wet etching process is a selective anisotropic etching procedure. The etchant solution used in the selective anisotropic etching procedure can be a mixture of potassium hydroxide, water and isopropanol. The proportions of the components in the mixture depend on the desired etching rate. The temperature of the etchant solution ranges from 60° C. to 95° C. during the selective anisotropic etching procedure. In addition, during the selective anisotropic etching procedure, the etchant solution should be continuously stirred to remove bubbles, which are possibly adhered onto the slant surfaces to adversely affect the surface smoothness. 
     After the residual mask layer  2011  is removed (see  FIG. 3G ), an e-beam writing process is performed on one of the plurality of slant surfaces  212 . By the way, the slant surface  212  (i.e. the reflective surface) needs to be perpendicular to the electron beam before the E-beam writing process is performed. As shown in  FIG. 3G , the semiconductor substrate  20  is tilted at a tilt angle such that the slant surface  212  is perpendicular to the electron beam. Then, as shown in  FIG. 3H , a mask layer  2014  is formed on the slant surface  212  (i.e. the reflective surface). For clarification, only the circled portion of  FIG. 3G  is shown in  FIGS. 3H˜3J . Then, as shown in  FIG. 3H , the mask layer  2014  is etched by an E-beam writing process to form a plurality of etching windows  2015 . Then, as shown in  FIG. 3J , a reactive ion etching (RIE) process is performed to partially etch off the semiconductor substrate  20  through the etching windows  2015 , thereby forming a micro diffractive optical element  22  with a plurality of trenches  221  on the slant surface  212 . Afterwards, the remaining mask layer  2014  is removed. The resulted package base structure  2  is shown in  FIGS. 2A ,  2 B and  2 C. 
     In the embodiment of the present invention, the semiconductor substrate  20  having the {100} equivalent crystallographic top surface  201  is provided. Generally, the {111} equivalent crystallographic surface is more stable. The bias angle of 45 degrees is not suitable because a great amount of {111} equivalent crystallographic micro-planes are possibly induced. In this situation, the surface smoothness of the slant surface  212  (i.e. the reflective surface) is deteriorated. It is found that the bias angle close to 0 degree or 90 degrees will result in a better surface smoothness of the slant surface  212  (i.e. the reflective surface), but the deviation of the formed slant surface  212  from the perfect 45-degree slant surface is increased. On the other hand, if the bias angle is close to 45 degrees, the deviation of the formed slant surface  212  from the perfect 45-degree slant surface is decreased, but the surface smoothness of the slant surface  212  (i.e. the reflective surface) is impaired. The selection is up to the manufacturer depending on practical requirements. For example, when it is required to obtain a 45-degree angle between the top surface  201  of the semiconductor substrate  20  and the slant surface  212  with an acceptable deviation ±1 degree, the bias angle should be controlled in the range between 22 degrees to 68 degrees except 45 degrees. 
     In the foregoing, the present invention is illustrated by referring to the semiconductor substrate  20  having a {100} equivalent crystallographic surface  201 . Nevertheless, the present invention can also be applied to a semiconductor substrate having a {110} equivalent crystallographic surface or &lt;110&gt; equivalent crystallographic orientation. Thus, the plurality of slant surfaces produced by the selective anisotropic etching procedure are on the {100} equivalent crystallographic plane. 
       FIG. 4  is a schematic perspective view illustrating an exemplary micro diffractive optical element of the package base structure according to an embodiment of the present invention. As shown in  FIG. 4 , the micro diffractive optical element  22  has a circular profile. In addition, the micro diffractive optical element  22  comprises a plurality of trenches  221 . When the light beam  2000  emitted by the light-emitting element  200  is projected on the slant surface  211  of the micro diffractive optical element  22 , the light beam  2000  will be successfully deflected to the out-of-plane direction. In addition, the light beam  2000  could be collimated or focused by the micro diffractive optical element  22 . 
       FIG. 5  is a schematic perspective view illustrating another exemplary micro diffractive optical element of the package base structure according to an embodiment of the present invention. As shown in  FIG. 5 , the micro diffractive optical element  32  has an elliptical profile. Since the micro diffractive optical element makes the light beam deflect by a large angle, serious off-axis aberration (e.g. astigmatic aberration) will be resulted from different refraction power in the sagittal-plane direction and the tangential-plane direction. The elliptical profile of the micro diffractive optical element  32  could provide different refraction power in two dimensions in order to correct off-axis aberration of the 45-degree slant surface  311  (i.e. the reflective surface). 
     From the above discussion, it is fount that the micro diffractive optical element has a function of the general reflective concave mirror. A radius of curvature and an aspheric coefficient of the concave mirror are important parameters for determining focal length, aberration control and tolerance. After the parameters of the concave mirror are decided, equiphase surfaces of the concave mirror are defined according to the wavelength. The neighboring equiphase surface has an optical path difference for a single wavelength. After the equiphase surfaces corresponding to the integer part are eliminated, the micro diffractive optical element  22  or  32  perfectly equivalent to the concave mirror is obtained. The distance between the adjacent trenches  221  or  321  of the micro diffractive optical element  22  or  32  (see  FIGS. 4 and 5 ) is varied according to the wavelength and the optical imaging design. 
     It is noted that the micro diffractive optical elements used in the package base structure of  FIGS. 4 and 5  may be modified while retaining the teachings of the invention. For example, other micro diffractive optical element such as an optical grating could be used to split and diffract light. 
     In the above embodiments, the micro diffractive optical element is formed on the slant surface by a reactive ion etching (RIE) process. It is noted that, however, those skilled in the art will readily observe that numerous modifications and alterations may be made while retaining the teachings of the invention. For example, in some embodiments, the micro diffractive optical element is firstly formed on a plastic polymeric film, and then the micro diffractive optical element is attached on the slant surface of the semiconductor substrate by a hybrid integration process. In this situation, the package base structure still has the functions of deflecting the light beam to the out-of-plane direction and collimating or focusing the light beam. 
     As previously described, since the light-emitting element, the glass block and the micro lens of the conventional package base structure are discrete elements, the conventional process of manufacturing the package base structure is costly and fails to be mass produced. From the above description, the package base structure of the present invention has the functions of deflecting the light beam to the out-of-plane direction and collimating or focusing the light beam by means of monolithic integration. In other words, the process for manufacturing the package base structure is very cost-effective and the mass production of the package base structure is feasible. 
     While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention needs not to be limited to the disclosed embodiment. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.