Abstract:
A semiconductor element includes a super-lattice buffer layer including Al x N 1-x  layers and Al y O 1-y  layers (0&lt;x&lt;1, 0&lt;y&lt;1). The super-lattice buffer layer can mitigate corrosion to the side wall by chemical solution during chip fabrication, and improve chip yield. Fabrication the super-lattice buffer layer to achieve the effects can be realized, for example, using chemical vapor deposition (CVD).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a continuation of, and claims priority to, PCT/CN2016/097754 filed on Sep. 1, 2016, which claims priority to Chinese Patent Application No. 201510564961.X filed on Sep. 8, 2015. The disclosures of these applications are hereby incorporated by reference in their entirety. 
     
    
     BACKGROUND 
       [0002]    Semiconductor cutting technology is evolving from diamond tool cutting to ordinary laser cutting. In laser cutting, the wavelength is generally 355 nm or 266 nm, sufficient to scribe sapphire substrates and various film layers, such as GaN layers, Bragg reflective layers and metal layers. In cutting, a surface cutting channel can be formed by scribing the epitaxial wafer surface with laser. Or, an invisible cutting channel can be formed by focusing a laser inside the substrate to separate a single chip. 
         [0003]    In the first case, impurities from laser burning would adhere to the side wall of the cutting channel, which blocks light emission and affects external quantum efficiency (EQE) of the semiconductor element. Therefore, to avoid effects on luminance, after a laser cutting channel is formed, the side wall of the cutting channel is cleaned with immersion and corrosion of chemical solution to remove the laser burning impurities adhered thereto. 
         [0004]    Physical vapor deposition (PVD) is an easy-to-operate process that consumes little raw material and causes little environmental pollution. Moreover, the film formed via PVD is dense and even, and is tightly bonded to the base. With these advantages, PVD is increasingly applied in fabrication of semiconductor elements, in particular, to fabrication of bottom layers of epitaxial wafer. For example, by depositing an AlN layer as the buffer layer, defects from lattice mismatch and thermal mismatch between the substrate and the epitaxial layer can be minimized, and the stress caused therefrom can be eased, thus improving quality of the semiconductor element. 
         [0005]    However, the multi-lattice and anisotropic AN layer formed via PVD is vulnerable to corrosion by chemical solution. Therefore, if an epitaxial wafer comprises a buffer layer formed via PVD, when the epitaxial wafer surface is cut by a laser and then immersed in chemical solution, the contact surface between the buffer layer and the substrate is prone to over-corrosion, leading to abnormal electricity of chip and low production yield. 
       SUMMARY 
       [0006]    To solve the above problems, various embodiments of the present disclosure provide a semiconductor element comprising a super-lattice buffer layer composed of at least Al x N 1-x  layers and Al y O 1-y  layers (0&lt;x&lt;1, 0&lt;y&lt;1), wherein, the super-lattice buffer layer can mitigate corrosion to the side wall by chemical solution during chip fabrication and improve chip yield. The present invention also provides a method for fabricating the super-lattice buffer layer to achieve the effects of some embodiments disclosed herein. 
         [0007]    Technical approaches of various embodiments of the present disclosure can include: a semiconductor element, comprising: a substrate, a buffer layer, an N-type semiconductor layer, a light-emitting layer and a P-type semiconductor layer, wherein, the buffer layer is a super-lattice structure layer with cyclically (periodically) laminated Al x N 1-x  layers and Al y O 1-y  layers (0&lt;x&lt;1, 0&lt;y&lt;1); the super-lattice buffer layer can mitigate corrosion to the side wall by chemical solution during chip fabrication and improve chip yield. 
         [0008]    In some embodiments, in the first cyclically-laminated layer of the buffer layer, the Al x N 1-x  layer is between the Al y O 1-y  layer and the substrate. 
         [0009]    In some embodiments, thickness of the Al x N 1-x  layer is ≧ that of the Al y O 1-y  layer. 
         [0010]    In some embodiments, the Al x N 1-x  layer is 5-500 Å. 
         [0011]    In some embodiments, the Al y O 1-y  layer is 5-500 Å. 
         [0012]    In some embodiments, a non-doping semiconductor layer is provided between the buffer layer and the N-type semiconductor layer. 
         [0013]    In some embodiments, number of cycles (periods) in the super-lattice structure layer is ≧2. 
         [0014]    Compared with conventional single AlN layer structure, the super-lattice buffer layer disclosed in the present invention is equivalent to divide the single AlN buffer layer into a multi-layer film structure and to insert an Al y O 1-y  layer in the multi-layer film. According to test results, the contact surface of the Al x N 1-x  layer and the Al y O 1-y  layer is better resistant to chemical solution corrosion than the Al x N 1-x  layer body. On this basis, a contact surface of the Al x N 1-x  layer and the Al y O 1-y  layer is added in this super-lattice structure to improve resistance to chemical solution corrosion of the buffer layer; moreover, as the Al y O 1-y  layer changes lattice stress of the buffer layer, the final super-lattice buffer layer has higher crystal quality over original AlN buffer layer; therefore, during side-wall corrosion process of subsequent chip fabrication, i.e., when impurities adhered to the side wall of the chip are removed through chemical solution corrosion, corrosion to the buffer layer is mitigated and the effect on chip electricity is reduced. Meanwhile, as the multi-layer film changes the light refraction angle, the super-lattice structure layer can increase light extraction efficiency and improve EQE of the semiconductor element. 
         [0015]    Some embodiments disclosed herein provide a method for fabricating the semiconductor bottom layer structure, comprising: S1: providing a substrate; S2: deposing a super-lattice buffer layer composed of Al x N 1-x  layers and Al y O 1-y  layers (0&lt;x&lt;1, 0&lt;y&lt;1) on the substrate surface via PVD, in which, the buffer layer can mitigate chemical solution corrosion in subsequent chip fabrication and improve chip yield; S3: depositing an epitaxial layer composed of an N-type semiconductor layer, a light-emitting layer and a P-type semiconductor layer on the buffer layer surface via chemical vapor deposition method (CVD), in which, the buffer layer fabricated under low temperature is annealed and re-crystallized in subsequent fabrication of the epitaxial layer under high-temperature to release stress during subsequent depositing process. 
         [0016]    As oxygen cannot be doped during depositing in conventional MOCVD, in this method, a super-lattice buffer layer is deposited via PVD and an Al y O 1-y  layer is introduced; with anti-corrosion feature of the Al y O 1-y  layer and its lattice difference from the Al x N 1-x  layer, the buffer layer characteristics of the semiconductor element are improved, thus releasing stress from subsequent depositing of an epitaxial layer and facilitating subsequent chip end fabrication. 
         [0017]    In some embodiments, in S2, an Al x N 1-x  layer is deposited on the substrate surface via PVD, and an Al y O 1-y  layer is deposited on the Al x N 1-x  layer surface, thus forming a super-lattice buffer layer through successive and cyclic lamination. 
         [0018]    In some embodiments, in S3 of both methods, at first, a non-doping semiconductor layer is deposited on the buffer layer surface and an N-type semiconductor layer is then deposited. 
         [0019]    In some embodiments, thickness of the Al x N 1-x  layer is ≧ that of the Al y O 1-y  layer. 
         [0020]    In some embodiments, the Al x N 1-x  layer is 5-500 Å. 
         [0021]    In some embodiments, the Al y O 1-y  layer is 5-500 Å. 
         [0022]    In some embodiments, number of cycles in the super-lattice structure layer is ≧2. 
         [0023]    In another aspect, a light-emitting system is provided including a plurality of the semiconductor elements described above. The light-emitting system can be used for lighting, signage, displays, etc. 
         [0024]    Various embodiments of the present disclosure can have one or more of the following advantages. 
         [0025]    1. In the semiconductor element according to some embodiments, the buffer layer is a super-lattice structure comprising Al x N 1-x  layers and Al y O 1-y  layers (0&lt;x&lt;1, 0&lt;y&lt;1). The contact surface of the Al x N 1-x  layer and the Al y O 1-y  layer is better resistant to chemical solution corrosion. Therefore, compared with single Al x N 1-x  layer, alternative arrangement of Al x N 1-x  layers and Al y O 1-y  layers enlarges the contact surface, and improves corrosion resistance of the entire buffer layer. Meanwhile, with corrosion resistance of the Al y O 1-y  layer material, the buffer layer is more resistant to corrosion to avoid over-corrosion during side-wall corrosion of chip fabrication. 
         [0026]    2. Compared MOCVD, oxygen can be doped in PVD depositing of film layers. Therefore, in this method, a super-lattice buffer layer comprising Al y O 1-y  layers is deposited via PVD. With anti-corrosion of the Al y O 1-y  layer and its lattice difference from the Al x N 1-x  layer, the buffer layer characteristics are improved and stress from subsequent epitaxial depositing is released. 
         [0027]    3. With the light refraction angle changed by the super-lattice and multi-film structure, both light extraction efficiency and EQE of the semiconductor element are improved. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0028]    The accompanying drawings, which are included to provide a further understanding of the invention and constitute a part of this specification, together with the embodiments, are therefore to be considered in all respects as illustrative and not restrictive. In addition, the drawings are merely illustrative, which are not drawn to scale. 
           [0029]      FIG. 1  is a structural diagram of the semiconductor element of Embodiment 1. 
           [0030]      FIG. 2  is a structural diagram of the buffer layer of Embodiment 1. 
           [0031]      FIG. 3  is a structural diagram of the semiconductor element of Embodiment 2. 
           [0032]      FIG. 4  is a structural diagram of the semiconductor element of Embodiment 3. 
       
    
    
       [0033]    In the drawings:  10 . substrate;  20 . buffer layer;  21 . Al x N 1-x  layer;  22 . Al y O 1-y  layer;  30 . N-type semiconductor layer;  40 . light-emitting layer;  50 . P-type semiconductor layer;  60 . non-doping semiconductor layer; a. Al x N 1-x  layer body; b. contact surface of Al x N 1-x  layer  21  and Al y O 1-y  layer  22 . 
       DETAILED DESCRIPTION 
       [0034]    Various embodiments of the present disclosure will be described in detail with reference to the accompanying drawings and embodiments. 
       Embodiment 1 
       [0035]    Referring to  FIGS. 1 and 2 , a semiconductor element according to the present invention is provided, comprising a substrate  10 , a buffer layer  20 , an N-type semiconductor layer  30 , a light-emitting layer  40  and a P-type semiconductor layer  50 , wherein, the buffer layer  20  is a super-lattice structure layer composed of at least of 5-500 Å Al x N 1-x  layers  21  and 5-500 Å Al y O 1-y  layers  22  (0&lt;x&lt;1, 0&lt;y&lt;1) with number of cycles≧2, and Al x N 1-x  layer  21  thickness≧Al y O 1-y  layer  22  thickness. As test results shown, when thickness ratio of the Al x N 1-x  layer  21  and the Al y O 1-y  layer  22  is higher, the better lattice quality is the buffer layer  20 . In this structure, by forming a buffer layer  20  through the super-lattice structure composed of Al x N 1-x  layers  21  and Al y O 1-y  layers  22 , corrosion to the side wall by chemical solution during subsequent chip fabrication is mitigated and chip yield is improved. 
         [0036]    With further reference to  FIGS. 1 and 2 , compared with the Al x N 1-x  layer  21  body a, the contact surface b of the Al x N 1-x  layer  21  and the Al y O 1-y  layer  22  is better resistant to chemical solution corrosion. Therefore, compared with single AlN layer in conventional structure, alternative arrangement of Al x N 1-x  layers  21  and Al y O 1-y  layers  22  enlarges the contact surface b, and improves anti-corrosion of the entire buffer layer  20 ; meanwhile, with corrosion resistance of the Al y O 1-y  layer  22  material, the buffer layer  20  is more resistant to corrosion to avoid over-corrosion during side-wall corrosion of chip fabrication. In addition, due to large lattice difference between the Al x N 1-x  layer  21  and the Al y O 1-y  layer  22 , the contact surface of the Al x N 1-x  layer  21  and the Al y O 1-y  layer  22  in the super-lattice structure is compressed and deformed, thus increasing the release stress ability of the buffer layer  20 , easing lattice stress of the subsequently-deposited epitaxial layer, and reducing wrap from stress. Meanwhile, when the buffer layer  20  is a laminated structure with multi-layer films, as different material layers have various refractive indices, the refraction angle of the buffer layer  20  for light emitted by the light-emitting layer  40  is changed, thus increasing light extraction efficiency and improving EQE of the semiconductor element. 
         [0037]    To achieve the above structure and function, some embodiments disclosed herein provide a method for fabricating the semiconductor element: 
         [0038]    S1. provide a substrate  10 , wherein, the substrate is made of sapphire, SiC (6H—SiC or 4H—SiC), Si, GaAs, GaN or single crystal oxide with lattice constant approximate to that of nitride semiconductor. In this invention, a sapphire substrate is preferred. 
         [0039]    S2. put the substrate  10  into a PVD chamber. Deposit a super-lattice buffer layer  20  composed of at least 5-500 Å Al x N 1-x  layers  21  and 5-500 Å Al y O 1-y  layers  22  (0&lt;x&lt;1, 0&lt;y&lt;1) on the surface of the substrate  10  via PVD with number of cycles≧2, and Al x N 1-x  layer  21  thickness≧Al y O 1-y  layer  22  thickness. The buffer layer  20  can mitigate chemical solution corrosion to the side wall in subsequent chip fabrication, and improve chip yield; as an Al y O 1-y  layer  22  with oxygen cannot be deposited in conventional MOCVD method, in this method, an Al y O 1-y  layer  22  is introduced with PVD to realize the structure feature of the present invention. 
         [0040]    S3. put the wafer deposited with the buffer layer  20  to the MOCVD chamber, and deposit an epitaxial layer composed of an N-type semiconductor layer  30 , a light-emitting layer  40  and a P-type semiconductor layer  50  on the surface of the buffer layer  20  via MOCVD, wherein, in subsequent fabrication of the epitaxial layer, the buffer layer  20  grown via low-temperature PVD is annealed and re-crystallized under high temperature; annealing for the buffer layer helps release stress in subsequent depositing process and improve crystal quality of the semiconductor element. 
         [0041]    According to some embodiments, a semiconductor element is fabricated with a combination of PVD and MOCVD. At first, deposit a buffer layer  20  with oxygen via PVD buffer layer  20 . In this way, chemical solution corrosion to the buffer layer  20  is mitigated without affecting formation of the buffer layer on the AlN layer via PVD, thus improving electricity performance of the element after chemical solution treatment. Then, deposit an epitaxial layer composed of an N-type semiconductor layer  30 , a light-emitting layer  40  and a P-type semiconductor layer  50  on the surface of the buffer layer  20  via MOCVD to finally form a semiconductor element. 
       Embodiment 2 
       [0042]    Referring to  FIG. 3 , difference between this embodiment and Embodiment 1 is that, in this embodiment, the buffer layer  20  is a super-lattice structure layer composed of 5-500 Å Al x N 1-x  layers  21  and 5-500 Å Al y O 1-y  layers  22  (0&lt;x&lt;1, 0&lt;y&lt;1), in which, in the first cyclic laminated layer, the Al x N 1-x  layer  21  is between the Al y O 1-y  layer  22  and the substrate  10 , with number of cycles in the super-lattice structure layer≧2 and Al x N 1-x  layer  21  thickness≧Al y O 1-y  layer  22  thickness. 
         [0043]    Difference between the fabrication method of this embodiment and that of Embodiment 1 is that: S2, put the substrate  10  into a PVD chamber. Deposit a super-lattice buffer layer  20  composed of 5-500 Å Al x N 1-x  layers  21  and 5-500 Å Al y O 1-y  layers  22  (0&lt;x&lt;1, 0&lt;y&lt;1) on the surface of the substrate  10  via PVD. In this step, at first, deposit an Al x N 1-x  layer  21  on the surface of the substrate  10 , and deposit the Al y O 1-y  layer  22  on the surface of the Al x N 1-x  layer  21  to form a super-lattice structure through successive and cyclic lamination; number of cycles in the super-lattice structure is at least 2. As the test results shown, on the surface of the substrate  10 , either an Al x N 1-x  layer  21  or an Al y O 1-y  layer  22  can be deposited at first. In this embodiment, it is preferred to deposit an Al x N 1-x  layer  21  on the surface of the substrate  10  at first. In this embodiment, the buffer layer  20  can also mitigate chemical solution corrosion to the side wall in subsequent chip fabrication, and improve chip yield. 
       Embodiment 3 
       [0044]    Referring to  FIG. 4 , difference between this embodiment and Embodiment 1 is that, a non-doping semiconductor layer  60  is deposited between the buffer layer  20  and the N-type semiconductor layer  30  to further improve crystal quality of the subsequent epitaxial layer and photoelectric property of the semiconductor element. 
         [0045]    All references referred to in the present disclosure are incorporated by reference in their entirety. Although specific embodiments have been described above in detail, the description is merely for purposes of illustration. It should be appreciated, therefore, that many aspects described above are not intended as required or essential elements unless explicitly stated otherwise. Various modifications of, and equivalent acts corresponding to, the disclosed aspects of the exemplary embodiments, in addition to those described above, can be made by a person of ordinary skill in the art, having the benefit of the present disclosure, without departing from the spirit and scope of the disclosure defined in the following claims, the scope of which is to be accorded the broadest interpretation so as to encompass such modifications and equivalent structures.