Abstract:
A method for detaching a first material layer from a second material layer includes following steps. Firstly, a high-magnetic-permeability material layer is formed on a first material layer. Secondly, a second material layer is formed on the high-magnetic-permeability material layer. Thirdly, the first and second material layers are cooled such that the first and second material layers shrink, wherein the first and second material layers are low-magnetic-permeability materials. Finally, the high-magnetic-permeability material layer is heated by applying a high-frequency radiofrequency electromagnetic wave thereto such that the high-magnetic-permeability material layer expands, thus detaching the first material layer from the second material layer.

Description:
BACKGROUND 
     1. Field of the Invention 
     The present disclosure relates generally to a method for detaching material layers, and more particularly, to a method for detaching material layers of a semiconductor device. 
     2. Description of Related Art 
     A building block of many electronic devices such as diodes, transistors, and lasers is usually made of semiconductor material that can be grown over a substrate. The semiconductor material is fabricated by growing an epitaxial layer of the semiconductor material upon a substrate. For example, a light emitting diode (hereafter LED) is fabricated by growing an epitaxial layer of III-Nitride semiconductor on a sapphire substrate using a method of metal-organic chemical vapor deposition. 
     However, the sapphire substrate has a weak thermal conductivity, such that heat can not be dissipated efficiently out of the LED. This will reduce the light emitting efficiency of the LED. On the other hand, the sapphire substrate has a lattice parameter different from the III-Nitride semiconductor, thereby having a different expansion coefficient from the III-Nitride semiconductor. The difference of expansion coefficients may result in distortion of the sapphire substrate or the III-Nitride semiconductor when a temperature of the LED is high. Thus, the sapphire substrate is required to be detached/separated from the LED after growing epitaxial layer of III-Nitride semiconductor. 
     Typically, the sapphire substrate is detached from the LED by applying a method of laser lift off melt the epitaxial layer at its interface with the substrate on which is grown. However, the laser has high energy, which is absorbed by the epitaxial layer. This may break a lattice structure of the epitaxial layer, thereby resulting in quality reduction of the LED. 
     Therefore, there is a need in the art for method for detaching layers, which overcomes the above-mentioned problems. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many aspects of the present embodiments can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present embodiments. Moreover, in the drawings, all the views are schematic, and like reference numerals designate corresponding parts throughout the several views. 
         FIG. 1  is a flow chart of a method for detaching a material layer from a multilayer structure in accordance with a first exemplary embodiment. 
         FIGS. 2(   a )- 2 ( e ) are cross-sectional views illustrating successive stages of the method for detaching a layer from a multilayer structure according to an alternative embodiment. 
         FIGS. 3(   a )-( b ) are cross-sectional views illustrating temperature gradients of the multilayer structure of  FIG. 2(   c ) without and with a cooling substance applied. 
         FIG. 4  is a flow chart of a method for detaching a material layer from a multilayer structure in accordance with a second exemplary embodiment. 
         FIGS. 5(   a )- 5 ( f ) are cross-sectional views illustrating successive stages of the method for detaching a material layer from a multilayer structure as shown in  FIG. 4 . 
         FIG. 6  is a cross-sectional view illustrating successive stages of a method for detaching a material layer from a multilayer structure in accordance with a third exemplary embodiment. 
         FIG. 7  is a cross-sectional view illustrating successive stages of a method for detaching a material layer from a multilayer structure in accordance with a fourth exemplary embodiment. 
         FIG. 8  is a cross-sectional view illustrating successive stages of a method for detaching a material layer from a multilayer structure in accordance with a fifth exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a method for detaching a material layer from a multilayer in accordance with a first exemplary embodiment is provided. In this embodiment, the method is used for detaching one semiconductor layer from another semiconductor layer, or one semiconductor layer from an insulating layer. Referring to  FIG. 2 , the method is described in detail as follows. 
     Step  12 : a high-magnetic-permeability material layer is formed on a first material layer. 
     Referring to  FIG. 2(   a ), a high-magnetic-permeability material layer  104  is formed on a surface of a first material layer  102  by sputtering or vapor plating. The first material layer  102  is made of a low-magnetic-permeability material. In this embodiment, the first material layer  102  can be a semiconductor material or an insulating material. 
     The high-magnetic-permeability material layer  104  can be selected from the group consisting of molybdenum-metal (Mo-metal), permalloy, electrical steel, Nickel zinc ferrite, manganese zinc ferrite, steel and nickel. Generally, a magnetic permeability of the high-magnetic-permeability material layer  104  is at least 10 2  times larger than that of the first material layer  102 . For example, when the first material layer  102  is sapphire having a magnetic permeability of 1.25 N/A 2 , the corresponding high-magnetic-permeability material layer  104  may have a magnetic permeability of equal to or more than 125N/A 2 . A table showing magnetic permeability values of some high-magnetic-permeability materials and the sapphire is illustrated below. 
     
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
               
               
                   
                 Coefficient of 
                 Magnetic 
                   
               
               
                 material 
                 magnetization 
                 (×10 −6  N/A e ) 
                 Magnetic field 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Mo-metal 
                 20,000 
                 25000 
                 at 0.002T 
               
               
                 permalloy 
                   8000 
                 10000 
                 at 0.002T 
               
               
                 electrical steel  
                   4000 
                 5000 
                 at 0.002T 
               
               
                 (ρ = 0.01 μΩ · m) 
                   
                   
                   
               
               
                 nickel zinc ferrite 
                   
                 20-800 
                   
               
               
                 manganese zinc 
                   
                 &gt;800 
                   
               
               
                 ferrite 
                   
                   
                   
               
               
                 steel 
                   700 
                 875 
                 at 0.002T 
               
               
                 nickel 
                   100 
                 125 
                 at 0.002T 
               
               
                 sapphire 
                 −2.1 × 10 −7   
                 1.2566368 
               
               
                   
               
             
          
         
       
     
     Step  14 : a second material layer is formed on the high-magnetic-permeability material layer. 
     Referring to  FIG. 2(   b ), a second material layer  106  is formed on the high-magnetic-permeability material layer  104 . The second material layer  106  is made of a low-magnetic-permeability material. The first material layer  102 , the high-magnetic-permeability material layer  104  and the second material layer  106  cooperatively form a multilayer structure  100 . Generally, a magnetic permeability of the high-magnetic-permeability material layer  104  is at least 102 times larger than that of the second material layer  106 . In this embodiment, the second material layer  106  can be a semiconductor material or an insulating material. In an alternative embodiment, the second material layer  106  can be the same to the first material layer  102 , such that the first and second material layers  102  and  106  are gallium nitride. In another alternative embodiment, the second material layer  106  can be different from the first material layer  102 , such that the first material layer  102  is sapphire and the second material layer  106  is gallium nitride. 
     Step  16 : the first and second material layers are cooled and the high-magnetic-permeability material layer is heated by applying a radio frequency electromagnetic wave having a high radio frequency thereto. Thus, the first and second material layers shrink and the high-magnetic-permeability material layer expands, such that a stress force is generated between the first material layer and the high-magnetic-permeability material layer and between the second material layer and the high-magnetic-permeability material layer. The first material layer or the second material layer is detached from the high-magnetic-permeability material layer. That is, the first and second material layers are detached from each other. 
     Referring to  FIG. 2(   c ), the first material layer  102  and the second material layer  106  are cooled by applying a cooling substance  108 . In an alternative embodiment, the cooling substance  108  can be cooling fluid, such as liquid nitrogen, dry ice, low temperature air, low temperature water and etc. A cooling process for the first and second material layers  102  and  106  is described in detail as follows. The multilayer  100  is placed in a vacuum cavity (not shown). Then the cooling substance  108  is introduced into the vacuum cavity to cool the first and second material layers  102  and  106 . Meanwhile, the high-magnetic-permeability material layer  104  is also cooled. In an alternatively embodiment, the first and second material layers  102  and  106  can also be cooled by applying a cooling device, such as one or more thermoelectric coolers. At this moment, the first material layer  102  contacts a cold end of a thermoelectric cooler, and the second material layer  106  contacts a cold end of another thermoelectric cooler. 
     A high-frequency radiofrequency electromagnetic wave  110  is provided. Then the multilayer structure  100  is placed in the high-frequency radiofrequency electromagnetic wave  110 . A frequency of the high-frequency radiofrequency electromagnetic wave  110  is in a range from 3 gigahertz (GHz) to 300 GHz. It is well known that a high magnetic-permeability material  104  in a high-frequency radiofrequency radio field will generate a high temperature by absorbing the high-frequency radiofrequency electromagnetic wave  110 . In an alternative embodiment, the high-frequency radiofrequency electromagnetic wave  110  can be generated by a wire winding, which is arranged around the multilayer  100 . At this moment, temperatures of the first and second material layers  102  and  106  almost remain unchanged for the magnetic-permeability thereof is low. 
     In this case, the high-magnetic-permeability material layer  104  expands according to increase in temperature, and the first and second material layers  102  and  106  shrink according to cooling by the cooling substance  108 . A first stress force is generated between the first material layer  102  and the high-magnetic-permeability material layer  104 , and a second stress force is generated between the second material layer  106  and the high-magnetic-permeability material layer  104 . As the temperature of the high-magnetic-permeability material layer  104  increases gradually, the stress force increases correspondingly. Referring to  FIG. 2(   d ), when the temperature of the high-magnetic-permeability material layer  104  reaches a certain value, the first stress force becomes larger than a bonding force between the first material layer  102  and the high-magnetic-permeability material layer  104 . At this moment, the first material layer  102  is detached from the high-magnetic-permeability material layer  104 . Alternatively, referring to  FIG. 2(   e ), when the temperature of the high-magnetic-permeability material layer  104  reaches a certain value, the second stress force becomes larger than a bonding force between the second material layer  106  and the high-magnetic-permeability material layer  104 . Thus the first and second material layers  102  and  106  are detached from each other. 
     After the first and second material layers  102  and  106  are detached from each other, a cleaning step is provided. The cleaning step including removing the high-magnetic-permeability material on the first and second material layers  102  and  106  by chemical mechanical polishing, chemical wet etching or dry etching. 
       FIG. 3  illustrates temperature gradients of the multilayer structure  100  in  FIG. 2(   c ) with and without the cooling substance  108  applied. In this embodiment, the temperature gradients distribute along a direction perpendicular to the first material layer  102 , the second material layer  106  and the high-magnetic-permeability material layer  104 . As shown in  FIG. 3(   a ), a temperature gradient of the multilayer structure  100  without the cooling substance  108  applied is shown at the right hand of the multilayer structure  100 . As shown in  FIG. 3(   b ), a temperature gradient of the multilayer structure  100  with the cooling substance  108  applied is shown at the right hand of the multilayer structure  100 . From the two temperature gradients as shown in  FIGS. 3(   a ) and  3 ( b ), it is seen that the temperature of the multilayer structure  100  decreases gradually from a middle of the high-magnetic-permeability material layer  104  to the first and second material layers  102  and  106  respectively. The difference between  FIGS. 3(   a ) and  3 ( b ) is that, the temperature gradient in  FIG. 3(   a ) shows two straight lines and the  FIG. 3(   b ) shows two arc lines. That is, difference in temperature between the high-magnetic-permeability material layer  104  and the first and second material layer  102  and  106  with the cooling substance  108  is larger than that without the cooling substance  108 . Thus, the stress force between the high-magnetic-permeability material layer  104  and the first and second material layer  102  and  106  with the cooling substance  108  is larger than that without the cooling substance  108 . 
     Referring to  FIG. 4 , a method for detaching a material layer from a multilayer of a second exemplary embodiment is provided. In this embodiment, the method is used for detaching one semiconductor layer from another semiconductor layer, or one semiconductor layer from an insulating layer. Referring to  FIG. 5 , the method is described in detail as follows. 
     Step  22 : a high-permeability material layer is formed on a first material layer. 
     Referring to  FIG. 5(   a ), a high-permeability material layer  204  is formed on a surface of a first material layer  202  by sputtering or vapor plating. The first material layer  202  is a low-magnetic-permeability material. In an alternative embodiment, the first material layer  202  can be a semiconductor material, such as an element semiconductor or a compound semiconductor. The element semiconductor can be silicon or germanium. The compound semiconductor can be selected from the group consisting of IV-IV semiconductor, III-V semiconductor, and II-VI semiconductor. The III-V semiconductor is one of a material for forming an LED. The III-V semiconductor material can be selected from the group consisting of an AlGaInP-based material, an AlGaInN-based material, and an AlGaAs-based material. The AlGaInN-based material can be selected from the group consisting of AlN, GaN, InN, AlGaN, GalnN, AlInN, and AlGaInN. In this alternative embodiment, the first material layer  202  can be formed by liquid-phase epitaxy (LPE), vapor-phase epitaxy (VPE), metal organic chemical vapor deposition, (MOCVD) and molecular beam epitaxy (MBE). In another alternative embodiment, the first material layer  202  can also be an insulating material, such as sapphire. The high-magnetic-permeability material layer  204  has a same material to the high-magnetic-permeability material layer  104  of the first exemplary embodiment. 
     Step  24 : a portion of the high-magnetic-permeability material layer is removed to expose a portion of the first material layer. 
     Referring to  FIG. 5(   b ), a portion of the high-magnetic-permeability material layer  204  is removed by applying a photolithography method, such that a portion of the first material layer  202  is exposed. In the illustrated embodiment, the exposed portion of the first material layer  202  forms a patterned structure as lattice structure. A reason for exposing the first material layer  202  is that the high-magnetic-permeability material layer  204  is a material not capable of epitaxial growth of a second material layer  206  in a latter step  26 . Thus the second material layer  206  can be epitaxially grown on the exposed first material layer  202 . 
     Step  26 : a second material layer is epitaxially grown on the exposed portion of the first material layer, and covers the high-magnetic-permeability material layer. 
     Referring to  FIGS. 5(   c ) and  5 ( d ), the second material layer  206  is epitaxially grown on the exposed portion of the first material layer  202  and covers the entire surface of the high-magnetic-permeability material layer  204 . The second material layer  206  can be a semiconductor material or an insulating material. A material of the second material layer  206  can be same to the first material layer  202 , for example they both are GaN. The material of the second material layer  206  can also be different from that of the first material layer  202 , for example the first material layer  202  is sapphire and the second material layer is GaN. 
     Step  28 : the first and second material layers are cooled and the high-magnetic-permeability material layer is heated by applying a radio frequency electromagnetic wave having a high radio frequency thereto. Thus the first and second material layers shrink and the high-magnetic-permeability material layer expands, such that a stress force is generated between the first material layer and the high-magnetic-permeability material layer and between the second material layer and the high-magnetic-permeability material layer. The first material layer or the second material layer is detached from the high-magnetic-permeability material layer. That is, the first and second material layers are detached from each other. 
     Referring to  FIGS. 5(   e ) and  5 ( f ), a cooling method for the first and second material layers  202  and  206  is similar to the cooling method as described in the first exemplary embodiment, and the heating method for the high-magnetic-permeability material layer  204  by applying high-frequency radiofrequency electromagnetic wave  108  is similar to the heating method of the first exemplary embodiment. For the same reason to the first exemplary embodiment, the first material layer  202  or the second material layer  206  is detached from the high-magnetic-permeability material layer  204 . As shown in  FIG. 5(   f ), in this embodiment, the first material layer  202  is detached form the high-magnetic-permeability material layer  204 . 
     After the first and second material layers  202  and  206  are detached from each other, a cleaning step is provided. The cleaning step including removing the high-magnetic-permeability material on the first and second material layers  202  and  206  by chemical mechanical polishing, chemical wet etching or dry etching. 
     Referring to  FIG. 6 , a method for detaching two layers of a multilayer structure in accordance with a third exemplary embodiment is provided. The method is similar to the method of second exemplary embodiment. The method of this embodiment differs from the method of second exemplary embodiment is described as follows. A multilayer  300  of this embodiment includes three semiconductor layers  302 ,  306  and  310  stacked one after another in the above order. A first high-magnetic-permeability material layer  304  is arranged between the semiconductor layers  302  and  306 , and a second high-magnetic-permeability material layer  308  is arranged between the semiconductor layers  306  and  310 . The first and second high-magnetic-permeability material layers  304  and  308  each have a patterned structure to exposed semiconductors  302  and  306 , such that the semiconductor layer  306  epitaxially grown on an exposed portion of the semiconductor layer  302  and the semiconductor layer  310  epitaxially grown on a exposed portion of the semiconductor layer  306 . Similar to the second exemplary embodiment, the semiconductor layers  302 ,  306  and  310  are cooled by the cooling substance  108 , and the high-magnetic-permeability material layers  304  and  310  are heated by the high-frequency radiofrequency electromagnetic wave  110 , such that the semiconductor layers  302 ,  306  and  310  are detached from each other. 
     After the semiconductor layers  302 ,  306  and  310  are detached from each other, a cleaning step is provided. The cleaning step including removing the high-magnetic-permeability materials on the semiconductor layers  302 ,  306  and  310  by chemical mechanical polishing, chemical wet etching or dry etching. 
     Referring to  FIG. 7 , a method for detaching a layer from a multilayer structure in accordance with a fourth exemplary embodiment is provided. In this embodiment, the method is used for detaching two layers with a same material. This method is similar to the method of the second exemplary embodiment. A multilayer structure of this embodiment is an LED  40 . This method is used for detaching a sapphire substrate  42  from the LED  40 . The LED  40  includes the sapphire substrate  42 , a GaN buffer layer  44 , a functional structure  46  and a metal substrate  48  stacked one after another in the above order. The functional structure  46  includes an N-type GaN layer  462 , a multi-quantum well layer  464  and a P-type GaN layer  466 . A high-magnetic-permeability material layer  442  is formed in the GaN buffer layer  44 . The high-magnetic-permeability material layer  442  includes a patterned structure, such that the GaN buffer layer  44  includes two layers partly partitioned by the high-magnetic-permeability material layer  442  and forming a single body. 
     The cooling method for the GaN buffer layer  44  is similar to the cooling method as described in the first exemplary embodiment, and the heating method for the high-magnetic-permeability material layer  442  by applying high-frequency radiofrequency electromagnetic wave  108  is similar to the heating method of the first exemplary embodiment. For the same reason to the first exemplary embodiment, the two layers of the GaN buffer layer  44  are detached from each other. That is, the sapphire substrate  42  is detached from the LED  40 . 
     Referring to  FIG. 8 , a method for detaching a layer from a multilayer structure in accordance with a fifth exemplary embodiment is provided. In this embodiment, materials of the two detached layers are different. In the illustrated embodiment, the method is used for detaching a sapphire substrate  52  from an LED  50 . The LED  50  is similar to the LED  40  of the fourth embodiment and the difference is that a high-magnetic-permeability material layer  542  is arranged between the substrate  52  and a GaN buffer layer  54 . Similar to the method of the fourth exemplary embodiment, a cooling method for the GaN buffer layer  54  and the sapphire substrate  52  and a heating method for the high-magnetic-permeability material layer  542  are applied, such that the sapphire substrate  52  is detached form the LED  50 . 
     The above methods for detaching a layer from a multilayer structure apply a cooling substance to cool the low-magnetic-permeability material layers and apply a high-frequency radio frequency electromagnetic wave to heat the high-magnetic-permeability material layer sandwiched between the low-magnetic-permeability material layers, and thus the low-magnetic-permeability material layers are detached from each other because of the stress force. This can prevent from breaking the lattice structure of the low-magnetic-permeability material layers. 
     It can be understood that the above-described embodiment are intended to illustrate rather than limit the disclosure. Variations may be made to the embodiments and methods without departing from the spirit of the disclosure. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the disclosure.