Abstract:
An SOI wafer and a method for forming the same, where the method for forming an SOI wafer includes: preparing a monocrystalline silicon wafer on which a mask layer is formed; etching the mask layer and the monocrystalline silicon wafer to form several trenches; forming a first insulating layer on the sidewalls and the bottoms of the trenches; etching and removing the first insulating layer on the bottoms of the trenches; etching along the trenches the monocrystalline silicon wafer beneath the trenches to form cavities; processing the inner walls of the cavities to form a second insulating layer; and filling up the trenches and the cavities with an insulating material layer. The process of the invention is easy to be implemented at a low manufacturing cost and an SOI wafer being formed is of high quality while being capable of being compatible with a standard process of manufacturing a bulk silicon CMOS.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority to 200910165230.2 filed Aug. 13, 2009 entitled “SOI WAFER AND METHOD FOR FORMING THE SAME”, incorporated by reference for all purposes. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to the field of semiconductor technologies and in particular to an SOI wafer and a method for forming the same. 
       BACKGROUND OF THE INVENTION 
       [0003]    At present, Silicon-On-Insulator (SOI) wafers, which are semiconductor substrates capable of providing semiconductor devices with high performance, have been highly regarded widely. An SOI wafer includes a silicon substrate, an insulating layer and a top silicon layer. Such a structure can be advantageous in that: (1) it can be used to manufacture a large scale integrated circuit with lines of less than 0.1 μm to thereby eliminate various parasitic effects due to manufacturing of such highly integrated devices in bulk silicon; (2) it can be used to manufacture high-speed and low-power-consumption semiconductor devices required for various mini apparatus; (3) it can be used to manufacture a semiconductor device against nuclear radiation; and (4) local isolation of MOS devices can be formed to boost an allowable operating voltage of the isolated devices. Therefore, the SOI material has been commonly recognized in the industry as a basic material for the future predominant industry of large scale integrated circuits. 
         [0004]    There are three existing methods for manufacturing an SOI material, the first of which is referred to as Separation by Implanted Oxygen, which is the main method currently adopted for manufacturing the SOI material. As illustrated in  FIG. 1 , this method generally includes preparing a monocrystalline silicon wafer  1 , implanting oxygen ions  2  into the monocrystalline silicon wafer and forming an insulating layer  3  in the monocrystalline silicon wafer  1  through annealing at a high temperature. Such an insulating layer separates the original monocrystalline silicon wafer  1  into two parts, i.e., a top silicon layer  4  and a silicon substrate  5 . 
         [0005]    The second method is referred to as “Bonding SOI”, which forms an SOI wafer of excellent quality. In this method as illustrated in  FIG. 2 , the surfaces of a first monocrystalline silicon wafer  10  and of a second monocrystalline silicon wafer  12  are bonded tightly to each other, wherein, an insulating layer  14  formed through oxidization, etc., on the surface of the first monocrystalline silicon wafer  11  or the second monocrystalline silicon wafer  12  is annealed to enhance adhesion at the bonding interface, and referring to  FIG. 3 , thereafter the non-bonded side of the second monocrystalline silicon wafer  12  is polished or etched to leave a relatively thin top silicon layer  12   a  on the insulating layer  14 . The most important point in this method lies in the step of thinning the substrate. 
         [0006]    The third method is referred to as “Smart Cut”, as mentioned in the solution disclosed in Chinese Patent Application No. 200710161139. As illustrated in  FIG. 4 , a first monocrystalline silicon wafer  20  is prepared; and an insulating layer  22  is formed on the bonded side of the first monocrystalline silicon wafer  20  through thermal oxidation, etc. Hydrogen ions  24  are implanted into the first monocrystalline silicon wafer  20  through the insulating layer  22  to form a uniform ion implanted layer  26 . After ion implantation, the first monocrystalline silicon wafer  20  is subject to a thermal process, which is a process prior to a stripping process for reducing in advance the mechanical strength of the “implantation interface” of the ion implanted layer  26  and also for preventing a roughness increase of the surface of an SOI film resulting from stripping the “implantation interface” in the subsequent process. As illustrated in  FIG. 5 , after the surfaces of the first monocrystalline silicon wafer  20  and a second monocrystalline silicon wafer  30  are subject to a cleaning process, the first monocrystalline silicon wafer  20  and a second monocrystalline silicon wafer  30  are bonded tightly; and then a thermal process is performed to enhance the bonding strength of the insulating layer  22  of the first monocrystalline silicon wafer  20  with first the monocrystalline silicon wafer. Referring to  FIG. 6 , the silicon substrate on the ion implanted layer  26  of the first monocrystalline silicon wafer  20  is stripped mechanically from the first monocrystalline silicon wafer  20  to form an SIO wafer. 
         [0007]    The existing three methods for forming an SOI wafer suffer from respective drawbacks. In the method of Separation by Implanted Oxygen, crystal lattices of the monocrystalline silicon wafer may be destroyed after oxygen gas implantation and annealing processes to thereby reduce greatly the insulating performance of the insulating layer and further reduce the quality of the SOI material. 
         [0008]    In the method of “Bonding SOI”, the silicon substrate with a thickness up to approximately several hundreds of micrometers has to be polished or etched uniformly to several micrometers or even one micrometer or less, which may be technically of extremely difficulty in terms of controllability and uniformity and at a extremely high cost. Moreover, gaps may occur at the bonding interface during bonding for formation of an SOI wafer, for example, due to contamination on the bonding surface or unevenness of the bonding surface with poor evenness, to thereby influence the quality of the SOI wafer. 
         [0009]    The method of “Smart Cut” demands for high precision of the process, which may be difficult and expensive to be implemented. 
       SUMMARY OF THE INVENTION 
       [0010]    An problem solved by the invention is to provide an SOI wafer and a method for forming the same so as to avoid poor insulating performance of an insulating layer and poor quality of the SOI wafer as well as a high manufacture cost. 
         [0011]    To address the above problem, an embodiment of the invention provides a method for forming an SO wafer, which includes: preparing a monocrystalline silicon wafer on which a mask layer is formed; etching the mask layer and the monocrystalline silicon wafer to form several trenches; forming a first insulating layer on the sidewalls and the bottoms of the trenches; etching and removing the first insulating layer on the bottoms of the trenches; etching along the trenches the monocrystalline silicon wafer beneath the trenches to form cavities; processing the inner walls of the cavities to form a second insulating layer; and tilling up the trenches and the cavities with an insulating material layer. 
         [0012]    Optionally, the mask layer includes a first film layer and a second film layer on the first film layer. 
         [0013]    Optionally, the first film layer is made of silicon oxide, and the second film layer is made of silicon nitride. 
         [0014]    Optionally, the first insulating layer is formed through thermal oxidization, thermal nitrification or chemical vapor deposition. 
         [0015]    Optionally, the first insulating layer is made of silicon oxide or silicon nitride with a thickness of 1 nm to 10 μm. 
         [0016]    Optionally, the first insulating layer on the bottoms is etched and removed through plasma etching or ion beam etching using Gas of Argon. 
         [0017]    Optionally, the monocrystalline silicon wafer is etched through dry etching using gas of XeF 2  or mixed gas of HNO 3  and HF. 
         [0018]    Optionally, the second insulating layer is formed through thermal oxidation or thermal nitrification. 
         [0019]    Optionally, the second insulating layer is made of silicon oxide or silicon nitride. 
         [0020]    Optionally, the insulating material layer is filled through low-pressure chemical vapor disposition or spin coating. 
         [0021]    Optionally, the insulating material layer is made of silicon oxide or silicon oxide containing phosphor, boron, carbon, nitrogen or hydrogen. 
         [0022]    An SOI wafer includes: a monocrystalline silicon wafer; trenches arranged in the monocrystalline silicon wafer; cavities arranged in the monocrystalline silicon wafer and interconnected with the trenches; a first insulating layer arranged on the sidewalls of the trenches; a second insulating layer arranged on the inner walls of the cavities; and an insulating material layer filling up the trenches and the cavities. 
         [0023]    Optionally, the first insulating layer is made of silicon oxide or nitride silicon with a thickness of 1 nm to 10 μm. 
         [0024]    Optionally, the second insulating layer is made of silicon oxide or nitride silicon. 
         [0025]    Optionally, the insulating material layer is made of silicon oxide or silicon oxide containing phosphor, boron, carbon, nitrogen or hydrogen. 
         [0026]    The invention offers the following advantages over the prior art: the trenches and the cavities are formed in the monocrystalline silicon wafer, and then the insulating layers and the insulating material layer are formed in the trenches and the cavities as an insulating layer of an SIO wafer, where the insulating material layer in the cavities separates the monocrystalline silicon wafer into a silicon substrate and a top layer silicon. In this process, insulating silicon oxide is formed through deposition or spin coating to thereby address the problem in the method of Separation by Implanted Oxygen that crystal lattices of the monocrystalline silicon wafer may be destroyed due to the oxygen gas implantation and annealing processes to degrade the insulating performance of the insulating layer, also to obviate the problem in the method of “Bonding SOI” that gaps may occur at the bonding interface due to contamination on the bonding surface or unevenness of the bonding surface with poor evenness, and further achieve easiness of the process, a low manufacturing cost and the resulting SOI wafer of high quality as compared with the method of “Smart Cut” while being capable of being compatible with a standard process of manufacturing a bulk silicon CMOS. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]      FIG. 1  illustrates a schematic diagram of forming an SOI wafer in the method of Separation by Implanted Oxygen in the prior art; 
           [0028]      FIG. 2  to  FIG. 3  illustrate schematic diagrams of forming an SOI wafer in the method of “Bonding SOI” in the prior art; 
           [0029]      FIG. 4  to  FIG. 6  illustrate schematic diagrams of forming an SOI wafer in the method of “Smart Cut” in the prior art; 
           [0030]      FIG. 7 ,  FIG. 8 ,  FIG. 9   FIG. 10 ,  FIG. 11   a,    FIG. 11   b,    FIG. 12   a,    FIG. 12   b,    FIG. 13   a  and  FIG. 13   b  illustrate schematic diagrams of an embodiment of a process for forming an SOI wafer according to the invention; and 
           [0031]      FIG. 14  illustrates a flow chart of an embodiment of forming an SOI wafer according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0032]    The existing several method for forming an SOT wafer may destroy crystal lattices of a monocrystalline silicon wafer to thereby degrade the insulating performance of the SOI wafer or suffer from complex processes, a high manufacturing cost and degrading of the quality of the resulting SOI wafer. According to embodiments of the invention, trenches and cavities are formed in a monocrystalline silicon wafer, and then insulating layers and an insulating material layer are formed in the trenches and the cavities as an insulating layer of an SIO wafer, where the insulating material layer in the cavities separates the monocrystalline silicon wafer into a silicon substrate and a top layer silicon. In this process, insulating silicon oxide is formed through deposition or spin coating to thereby address the problem in the method of Separation by Implanted Oxygen that crystal lattices of the monocrystalline silicon wafer may be destroyed due to the oxygen gas implantation and annealing processes to degrade the insulating performance of the insulating layer, also obviate the problem in the method of “Bonding SOI” that gaps may occur at the bonding interface due to contamination on the bonding surface(s) or unevenness of the bonding surface(s) with poor flatness, and further achieve easiness of the procedure, a low manufacturing cost and the resulting SOT wafer of high quality as compared with the method of “Smart Cut”. 
         [0033]      FIG. 14  illustrates a flow chart of an embodiment of forming an SOI wafer according to the invention. As illustrated in  FIG. 14 , the step S 11  is performed to prepare a monocrystalline silicon wafer on which a mask layer is formed; the step S 12  is performed to etch the mask layer and the monocrystalline silicon wafer to form several trenches; the step S 13  is performed to form a first insulating layer on the sidewalls and the bottoms of the trenches; the step S 14  is performed to etch and thus remove the first insulating layer on the bottoms of the trenches; the step S 15  is performed to etch along the trenches the monocrystalline silicon wafer beneath the trenches to form cavities; the step S 16  is performed to process the inner walls of the cavities to form a second insulating layer; and the step S 17  is performed to fill up the trenches and the cavities with an insulating material layer. 
         [0034]    The SOI wafer formed based upon the above embodiment includes: the monocrystalline silicon wafer; the trenches arranged in the monocrystalline silicon wafer; the cavities arranged in the monocrystalline silicon wafer and interconnected with the trenches; the first insulating layer arranged on the sidewalls of the trenches; the second insulating layer arranged on the inner walls of the cavities; and the insulating material layer filling up the trenches and the cavities. 
         [0035]    An embodiment of the invention will be detailed below with reference to the drawings. 
         [0036]      FIG. 7 ,  FIG. 8 ,  FIG. 9 ,  FIG. 10 ,  FIG. 11   a,    FIG. 11   b,    FIG. 12   a,    FIG. 12   b,    FIG. 13   a  and  FIG. 13   b  illustrate schematic diagrams of the embodiment of a process for forming an SOI wafer according to the invention. As illustrated in  FIG. 7 , a monocrystalline silicon wafer  100  with a thickness or 500 μm to 1500 μm is prepared; a first film layer  102   a  made of silicon oxide with a thickness of 1 nm to 1 μm is formed on the monocrystalline silicon wafer  100  through thermal oxidization; and a second film layer  102   b  made of Silicon Nitride with a thickness of 1 nm to 1 μm is formed on the first film layer  102   a  through chemical vapor disposition, where the first film layer  102   a  and the second film layer  102   b  constitute a mask layer  102  which functions to prevent the monocrystalline silicon wafer  100  from being damaged during subsequent etching and grinding. 
         [0037]    Referring to  FIG. 8 , several trenches  103  are formed in the monocrystalline silicon wafer  100 . A specific formation process is as follows: a photoresist layer (not illustrated) is formed on the mask layer  102  through spin coating and is exposed and developed to define several trench photoresist patterns on the photoresist layer; the mask layer  102  is etched along the trench photoresist patterns using the photoresist layer as a mask to form trench patterns; and the photoresist layer is removed and then the monocrystalline silicon wafer  100  is etched along the trench patterns using the mask layer  102  as a mask to form the trenches  103 . 
         [0038]    In this embodiment, the trenches  103  have a width of 10 nm to 50 μm, a depth of 50 nm to 50 μm and the number of the trenches  103  is dependent upon whether the cavities to be formed subsequently beneath the trenches  103  can be interconnected to separate the monocrystalline silicon wafer  100  into a silicon substrate and a top layer silicon. 
         [0039]    As illustrated in  FIG. 9 , a first insulating layer  104  with a thickness of 1 nm to 10 μm is formed on the mask layer  102  and the sidewalls of the trenches and the first insulating layer  104  is made of silicon oxide or silicon nitride for the purpose of isolation to prevent any material to be filled subsequently into the trenches from being diffused into the monocrystalline silicon wafer  100 , where if the first insulating layer  104  is made of silicon oxide, it can be formed through thermal oxidation, and if the first insulating layer  104  is made of silicon nitride, it can be formed through thermal nitrification or chemical vapor deposition. 
         [0040]    Referring to  FIG. 10 , the first insulating layer  104  on the mask layer  102  and the bottoms of the trenches is removed through dry etching using Gas of Argon. 
         [0041]    As illustrated in  FIG. 11   a  and  FIG. 11   b,  isotropic etching is performed along the trenches on the monocrystalline silicon wafer  100  beneath the trenches through wet etching using a solution of XeF 2  or a mixed solution of HNO 3  and HF to form cavities. 
         [0042]    In this embodiment, the cavities  106  have a depth of 50 nm to 50 μm. 
         [0043]    If one cavity  106  were sufficient to separate the monocrystalline silicon wafer  100 , then it would be sufficient to form one trench in the monocrystalline silicon wafer  100 . 
         [0044]    However the monocrystalline silicon wafer  100  typically has a relatively large area, and more than one trench has to be formed as restricted in the process, so that isotropic etching is performed on the monocrystalline silicon wafer  100  to thereby form the cavities  106  separating the monocrystalline silicon wafer  100 . Therefore there are relatively large number of trenches formed in the monocrystalline silicon wafer  100 , and after isotropic etching,  FIG. 11   a  illustrates a case where the cavities  106  are spaced at an interval of approximately 10 nm to 1000 nm, and  FIG. 11   b  illustrates another case where the cavities  106  are interconnected completely. 
         [0045]    Referring to  FIG. 12   a  and  FIG. 12   b,  the inner walls of the cavities  106  are processed to form a second insulating layer  108  with a thickness of 10 nm to 1000 nm, where the second insulating layer  108  is made of silicon oxide or silicon nitride for the purpose of isolation to prevent any material to be filled subsequently into the cavities from being diffused into the monocrystalline silicon wafer  100 , where if the second insulating layer  108  is made of silicon oxide. it can be formed through thermal oxidation, and if the second insulating layer  108  is made of silicon nitride, it can be formed through thermal nitrification. 
         [0046]    Referring to  FIG. 12   a  again, the cavities  106  are spaced at an interval during formation thereof and are interconnected through oxidization of the inner walls thereof to thereby separate the monocrystalline silicon wafer  100 . 
         [0047]    Referring to  FIG. 12   b,  the cavities  106  have been interconnected completely during formation thereof in this case to thereby separate the monocrystalline silicon wafer  100 . Therefore, it is sufficient for the purpose of isolation to form the second insulating layer  108  on the inner walls of the cavities  106 . 
         [0048]    As illustrated in  FIG. 13   a  and  FIG. 13   b,  the trenches and the cavities  106  are filled up with an insulating material layer  110 . A specified process is as follows: the insulating material layer  110  is formed on the monocrystalline silicon wafer  100  through low-pressure chemical vapor disposition; the trenches and the cavities  106  are filled up with the insulating material layer  110 ; and the insulating material layer  110  is planarized through chemical mechanical polishing until the mask layer  102  is exposed. 
         [0049]    In this embodiment, the insulating material layer  110  is made of Tetraethyl Orthosilicate, Polysilicon, Silicon Glass, etc. 
         [0050]    The first insulating layer  104 , the second insulating layer  108  and the insulating material layer  110  constitute the insulating layer of the SOI wafer and separate the monocrystalline silicon wafer into the silicon substrate  100   b  and the top layer silicon  100   a.    
         [0051]    The SOI wafer formed based upon the above embodiment includes: the monocrystalline silicon wafer  100 ; the trenches  103  with a depth of 50 nm to 50 μm arranged in the monocrystalline silicon wafer  100 ; the cavities  106  with a depth of 50 nm to 50 μm arranged in the monocrystalline silicon wafer  100  and interconnected with the trenches  103 ; the first insulating layer  104  arranged on the sidewalls of the trenches  103 ; the second insulating layer  108  arranged on the inner walls of the cavities  106 , each of the cavities  106  being interconnected directly or through the second insulating layer  108 ; and the insulating material layer  110  filling up the trenches  103  and the cavities  106 . 
         [0052]    Particularly, the first insulating layer  104  and the second insulating layer  108  function to prevent the insulating material layer  110  filled into the trenches  103  and the cavities  106  from being diffused into the monocrystalline silicon wafer  100 . 
         [0053]    Particularly, the first insulating layer  104 , the second insulating layer  108  and the insulating material layer  110  separate the monocrystalline silicon wafer into the silicon substrate  100   b  and the top layer silicon  100   a.    
         [0054]    Although the invention has been disclosed as above in connection with the preferred embodiments thereof, the scope of the invention will not be limited thereto, and any skilled in the art can make various variations and modifications without departing from the spirit and scope of the invention. Accordingly, the protection scope of the invention shall be as defined in the appended claims.