Patent Publication Number: US-9852912-B1

Title: Method of manufacturing semiconductor device for reducing grain size of polysilicon

Description:
BACKGROUND 
     Technical Field 
     The disclosure relates in general to a method of manufacturing a semiconductor device, and more particularly to a method of manufacturing a semiconductor device for reducing grain size of polysilicon. 
     Description of the Related Art 
     Reduction of feature size, improvements of the rate, the efficiency, the density and the cost per integrated circuit unit are the important goals in the semiconductor technology. The electrical properties of the device have to be maintained even improved (ex: with the decrease of the size) to meet the requirements of the commercial products in applications. Also, the layers and components with defects would have considerable effects on the electrical performance of the device. For example, the conventional method for manufacturing the semiconductor device comprises many thermal processes, which induces growth of grain size of polysilicon. Since large grain size polysilicon induces implant penetration through channel to the silicon substrate, a silicon substrate with a polysilicon having large grain size formed thereon could cause considerable deterioration on the electrical properties of the devices. 
     SUMMARY 
     The disclosure is directed to a method of manufacturing a semiconductor device. The proposed method of the present embodiment provides a way for effectively reducing grain size of polysilicon, thereby improving the properties of the semiconductor device. 
     According to one aspect of the present disclosure, a method of manufacturing a semiconductor device is provided, including providing a silicon substrate with multiple layers formed on a front side and a backside, wherein at least a dielectric layer is formed on the backside of the silicon substrate; defining isolation regions and active regions at the front side of the silicon substrate, wherein the active regions are separated by the isolation regions; treating the multiple layers formed at the front side and the backside of the silicon substrate, so as to remain the dielectric layer as an outermost layer exposed at the backside of the silicon substrate; and depositing a polysilicon layer on the isolation regions and the active regions at the front side of the silicon substrate. 
     According to another aspect of the present disclosure, a method of manufacturing a semiconductor device is provided, including providing a silicon substrate having a front side and a backside, and isolation portions and polysilicon portions being formed and exposed at the front side of the silicon substrate, and at least a dielectric layer remained as an outermost layer exposed at the backside of the silicon substrate, wherein the polysilicon portions are separated by the isolation portions; depositing a polysilicon layer on the isolation portions and the polysilicon portions at the front side of the silicon substrate when the dielectric layer is exposed at the backside of the silicon substrate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simple illustration showing manufacture of the semiconductor devices according to the present disclosure. 
         FIG. 2  is a flow diagram of a method of manufacturing a semiconductor device according to the embodiment of the disclosure. 
         FIG. 3A - FIG. 3H  illustrate a method of manufacturing a semiconductor device according to one embodiment of the disclosure. 
         FIG. 4  shows effects on grain size of polysilicon grown in different configurations of the semiconductor devices. 
         FIG. 5  shows the macro leakage of the semiconductor devices with conventional and embodied configurations. 
         FIG. 6  shows the yields of the semiconductor devices with conventional and embodied configurations. 
     
    
    
     In the following detailed description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the disclosed embodiments. It will be apparent, however, that one or more embodiments may be practiced without these specific details. In other instances, well-known structures and devices are schematically shown in order to simplify the drawing. 
     DETAILED DESCRIPTION 
     In the embodiment of the present disclosure, a method of manufacturing a semiconductor device for reducing grain size of polysilicon is provided. According to the method of the embodiment, the grain size of polysilicon can be reduced, and the conventional problem of implant dopant penetration into the substrate through channel can be effectively solved. Also, no thermal budge change in the embodied method. Therefore, the electrical properties of the semiconductor device manufactured by applying the embodied method can be significantly improved. 
     The embodiment of the present invention (i.e. the substrate with a backside dielectric film during polysilicon deposition) can be applied to manufacture a semiconductor device with different types of flash memory cells. Embodiments are provided hereinafter with reference to the accompanying drawings for describing the related procedures and configurations. However, the present disclosure is not limited thereto. It is noted that not all embodiments of the invention are shown. The identical and/or similar elements of the embodiments are designated with the same and/or similar reference numerals. Also, it is noted that there may be other embodiments of the present disclosure which are not specifically illustrated. Modifications and variations can be made without departing from the spirit of the disclosure to meet the requirements of the practical applications. It is also important to point out that the illustrations may not be necessarily be drawn to scale. Thus, the specification and the drawings are to be regard as an illustrative sense rather than a restrictive sense. 
     Moreover, use of ordinal terms such as “first”, “second”, “third” etc., in the specification and claims to describe an element does not by itself connote any priority, precedence, or order of one claim element over another or the temporal order in which acts of a method are performed, but are used merely as labels to distinguish one claim element having a certain name from another element having the same name (but for use of the ordinal term) to distinguish the claim elements. 
       FIG. 1  is a simple illustration showing manufacture of the semiconductor devices according to the present disclosure. In the typical manufacturing method, several silicon substrates are placed in a furnace with a silane or disilane ambient, and arranged by facing the polysilicon layers (ex: the polysilicon layer as an outermost layer exposed at the backside of the silicon substrate) to each other of adjacent silicon substrates. However, polysilicon consumes lots of silane (or disilane) and has short incubation time, thereby growing polysilicon with large grain size. According to the embodied method, as shown in  FIG. 1 , a dielectric layer  13  as an outermost layer exposed at the backside  10   b  of the silicon substrate  10  is provided before deposition of a polysilicon layer (ex: known as “Poly2”)  18  on the isolation regions (ex: STI) and the active regions (ex: known as “Poly1”) at the front side  10   f  of the silicon substrate  10 . 
     During the manufacturing method, silane (or disilane) flows from wafer edge to wafer center, and dielectric material has longer incubation time than polysilicon. In one embodiment, the dielectric layer  13  comprises oxides, nitrides or a combination thereof. Examples of the dielectric layer  13  include a silicon oxide (SiO 2 ) layer, a silicon nitride (SiN) layer and a silicon oxynitride (SiON) layer. 
     According to the embodied method, the isolation regions and conductive regions have been defined at the front side  10   f  of the silicon substrate  10  before the deposition of the polysilicon layer  18 , and the dielectric layer  13  formed as an outermost layer is exposed at the backside  10   b  of the silicon substrate  10  during the polysilicon growing.  FIG. 2  is a flow diagram of a method of manufacturing a semiconductor device according to the embodiment of the disclosure. First, a silicon substrate with multiple layers formed on a front side and a backside is provided, wherein at least a dielectric layer is formed on the backside of the silicon substrate (step S 1 ). Then, isolation regions (ex: comprising STI oxides) and active regions (ex: comprising polysilicon portions) are defined at the front side of the silicon substrate, wherein the active regions are separated by the isolation regions (step S 2 ). The multiple layers formed at the front side and the backside of the silicon substrate are treated (ex: removing both pad nitride layers and the front pad oxide layer), so as to remain the dielectric layer (ex:  13  in  FIG. 1 ) as an outermost layer exposed at the backside of the silicon substrate (step S 3 ). Afterward, a polysilicon layer (ex: Poly2) is deposited on the isolation regions and the active regions at the front side of the silicon substrate (step S 4 ). 
       FIG. 3A - FIG. 3H  illustrate a method of manufacturing a semiconductor device according to one embodiment of the disclosure. It is noted that the drawings and illustrations are provided for describing the disclosure, and the present disclosure is not limited to the details shown in the drawings. First, a silicon substrate  10  with multiple layers formed on a front side  10   b  and a backside  10   f  is provided. As shown in  FIG. 3A , a silicon substrate  10  with the gate oxide layers  11   b  and  11   f  respectively formed on the front side  10   b  and the backside  10   f  of the silicon substrate  10  is provided. 
     Then, other related layers are formed on the silicon substrate  10 , wherein the material of the related layer can be deposited or grown on the front and back sides of the silicon substrate simultaneously. For example, a first conductive layer  12   f  (ex: comprising polysilicon, and can be referred as “Poly1”), a first pad oxide layer  13   f  and a first pad nitride layer  14   f  are formed on the front side  10   f  of the silicon substrate  10 , wherein the first pad nitride layer  14   f  is formed on the first pad oxide layer  13   f  and the first conductive layer  12   f  is formed on the gate oxide layer  11   f , as shown in  FIG. 3B . Also, a second conductive layer  12   b , a second pad oxide layer  13   b  and a second pad nitride layer  14   b  are formed on the backside  10   b  of the silicon substrate  10 , wherein the second pad nitride layer  14   b  is formed on the second pad oxide  13   b  layer and the second conductive layer  12   b  is formed on the gate oxide layer  11   b , as shown in  FIG. 3B . In one example, the first pad oxide layer  13   f  and the second pad oxide layer  13   b  may be made of silicon oxide. In one example, the first pad nitride layer  14   f  and the second pad nitride layer  14   b  can be made of silicon nitride. Noted that those numerical values of related layers are provided only for illustration, not for limitation. 
     Next, a photo-resist layer PR is formed on the first pad nitride layer  14   f , as shown in  FIG. 3C , for defining isolation regions and active regions at the front side of the silicon substrate  10  in the subsequent steps. 
     Afterwards, as shown in  FIG. 3D , the first pad nitride layer  14   f , the first pad oxide layer  13   f , the first conductive layer  12   f , the gate oxide layer  11   f  and the silicon substrate  10  are patterned according to the photo-resist layer PR so as to form the trenches  103  and the patterned stacks  105 , thereby respectively defining the isolation regions (corresponding to the trenches  103 ) and the active regions (corresponding to the patterned stacks  105 ) at the front side of the silicon substrate  10 . 
     Afterwards, an insulation layer  16  is formed on the trenches  103  and the patterned stacks  105 , wherein the insulation layer  16  fills up the trenches  103  and covers the patterned stacks  105 , as shown in  FIG. 3E . Optionally, steps of trench liner pre-clean and trench liner oxidation can be performed before formation of the insulation layer  16 . In one embodiment, the insulation layer  16  can be a high-density plasma (HDP) chemical vapor deposition (CVD) oxide. 
     Then, a planarization step is conducted, as shown in  FIG. 3F . In one embodiment, the insulation layer  16  is chemical-mechanical polished and stop on the first pad nitride layer  14   f  to form an insulation layer  16 ′. 
     Afterwards, removal of the nitride layers at the backside  10   b  and front side  10   f  of the silicon substrate  10 , followed by removing the oxide layer at the front side  10   f  of the silicon substrate  10  are conducted. In the embodiment, the first pad nitride layer  14   f  and the second pad nitride layer  14   b  are removed (ex: by hot H 3 PO 4 ), and then the first pad oxide layer  13   f  is removed (such as by single wafer clean; ex: dry oxide etching), so that the second pad oxide layer  13   b  (i.e. the dielectric layer) is remained as the outermost layer exposed at the backside  10   b  of the silicon substrate  10 , as shown in  FIG. 3G . In  FIG. 3G , after removal steps, several isolation portions  162  (ex: STI) and polysilicon portions  122  are formed and exposed at the front side  10   f  of the silicon substrate  10 , wherein the isolation portions  162  and the polysilicon portions  122  are separated from each other. 
     Next, in the presence of the second pad oxide layer  13   b  (i.e. the dielectric layer) as the outermost layer exposed at the backside  10   b  of the silicon substrate  10 , deposition of a polysilicon layer  18  (can be referred as “Poly2”) is conducted. As shown in  FIG. 3H , the polysilicon layer  18  is deposited on the isolation portions  162  and the polysilicon portions  122  at the front side of the silicon substrate  10  when a dielectric layer (ex: the second pad oxide layer  13   b ) is exposed at the backside of the silicon substrate  10 . In one embodiment, the polysilicon layer  18  is deposited in a furnace at 600° C.-660° C., with a thickness of about 1200 Å. 
     In this exemplified process, after forming the polysilicon layer  18 , the polysilicon layer  18  directly contacts the polysilicon portions  122 . The embodiment of the present invention can be applied to manufacture a semiconductor device with flash memory cells. In one application, the floating gate of the flash memory cell comprises the polysilicon portions  122  and configuration patterned from the polysilicon layer  18 . 
     &lt;Experimental Results&gt; 
     Some of experiments are conducted for investigating the effects of the method of the embodiment. In  FIG. 4 - FIG. 6 , the curve or the region labeled as “BS poly film” represents the result of conventional device with a polysilicon layer as the outmost layer on the backside of the silicon substrate, and the curve or the region labeled as “Embodiment” represents the result of embodied device with a dielectric layer as the outmost layer on the backside of the silicon substrate. 
       FIG. 4  shows effects on grain size of polysilicon grown in different configurations of the semiconductor devices. Compared to the results of the conventional method (ex: Poly1 on the backside) and the embodied method (dielectric film (ex:  13   b ) on the backside), the grain size formed by the embodied method does reduced from about 129 Å to 123 Å. Also, the wafers are monitored to investigate the extinction coefficient (k), and k of the wafer formed by the embodied method does increase, which means the grain size is reduced. 
       FIG. 5  shows the macro leakage of the semiconductor devices with conventional and embodied configurations. Compared to the results of the conventional method (ex: Poly1 on the backside) and the embodied method (dielectric film on the backside), the macro leakage of the structure manufactured by the embodied method has been eliminated (with much better distribution) since the polysilicon grain size is reduced. 
     Also,  FIG. 6  shows the yields of the semiconductor devices with conventional and embodied configurations. According to the results, the yield of the embodied semiconductor device does improve 6% to 15%. 
     According to the aforementioned descriptions, a dielectric layer is formed in the embodied method as an outermost layer exposed at the backside of the silicon substrate during deposition of polysilicon (ex: the polysilicon layer  18 ). According to the method of the embodiment, the grain size of polysilicon (ex: the polysilicon layer  18 ) does reduced, thereby effectively solving the conventional problem of implant dopant penetration into the substrate through channel. Also, no thermal budge change in the embodied method. Accordingly, the semiconductor device manufactured by applying the embodied method has significantly improved properties such as elimination of macro leakage of the cells, yield of production and electrical performance. 
     Other embodiments with different configurations of known elements in the semiconductor devices or flash memory cells can be applicable, and the arrangement of layers and components depends on the actual needs of the practical applications. It is, of course, noted that the configurations of figures are depicted only for demonstration, not for limitation. It is known by people skilled in the art that the shapes or positional relationship of the constituting elements and the procedure details could be adjusted according to the requirements and/or manufacturing steps of the practical applications without departing from the spirit of the disclosure. Moreover, although a dielectric material having longer incubation time than polysilicon is provided in the embodiment as described above for reducing grain size of polysilicon, other material having shorter incubation time than polysilicon (i.e. consumes less silane than polysilicon) can be applied as an outermost layer exposed at the backside  10   b  of the silicon substrate  10  for growing polysilicon with large grain size in other practical applications. 
     While the disclosure has been described by way of example and in terms of the exemplary embodiment(s), it is to be understood that the disclosure is not limited thereto. On the contrary, it is intended to cover various modifications and similar arrangements and procedures, and the scope of the appended claims therefore should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements and procedures.