Abstract:
A method for growing an epitaxial layer includes obtaining a semiconductor substrate having a plurality of insulating and conductive surfaces, adsorbing a first source gas into the plurality of conductive surfaces to grow a first epitaxial layer thereon, such that the first epitaxial layer has lateral portions overhanging the insulating surfaces, etching the first epitaxial layer to form an etched epitaxial layer, such that the etched epitaxial layer has curved surfaces, and supplying a second source gas to trigger additional epitaxial growth in the etched epitaxial layer.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a method of forming a selective epitaxial growth in semiconductor devices. More particularly, the present invention relates to a method of forming a selective epitaxial growth having reduced width relative to its thickness.  
         [0003]     2. Description of the Related Art  
         [0004]     Selective epitaxial growth refers to a method of forming a thin crystalline layer on selected portions of a substrate. In the field of semiconductor devices, for example, portions of a silicon substrate may be exposed, such that a silicon crystalline layer may be grown on the exposed portions thereof. Such selective growth may provide a capability of varying doping concentration, forming elevated source/drain regions, or forming source/drain pads in a dynamic random access memory (DRAM).  
         [0005]     In a conventional selective epitaxial growth method, a semiconductor substrate may be coated with a patterned insulation layer, such that portions of the substrate may be exposed through the patterned insulation layer to form a plurality of seed holes or conductive portions. A three-dimensional epitaxial layer portions may be grown in each of the seed holes or conductive portions of the substrate to form various patterns, e.g., layer portions having a plurality of facets and edges, having predetermined thickness and width values.  
         [0006]     However, growing an epitaxial layer to a predetermined thickness may trigger overextended width thereof, i.e., lateral portions in a horizontal direction of each of the epitaxial layer portions may overhang the insulation layer. Extensive width of the epitaxial layer portions may result in bridging between facets and/or edges of adjacent lateral portions, thereby restricting further horizontal growth thereof. Limited horizontal growth may inhibit vertical growth, thereby resulting in epitaxial layers having insufficient overall thickness and uniformity.  
         [0007]     Accordingly, there exists a need for a method for selectively forming an epitaxial layer on a semiconductor substrate having sufficient thickness.  
       SUMMARY OF THE INVENTION  
       [0008]     The present invention is therefore directed to a method for selectively growing epitaxial layers in semiconductor devices which substantially overcomes one or more of the disadvantages of the related art.  
         [0009]     It is therefore a feature of an embodiment of the present invention to provide a method for selectively growing an epitaxial layer having a sufficient thickness by controlling a width thereof.  
         [0010]     At least one of the above and other features and advantages of the present invention may be realized by providing a method for growing an epitaxial layer, including obtaining a semiconductor substrate having a plurality of insulating and conductive surfaces, adsorbing a first source gas into the plurality of conductive surfaces to grow a first epitaxial layer thereon, such that the first epitaxial layer may have lateral portions overhanging the insulating surfaces, etching the first epitaxial layer to form an etched epitaxial layer, such that the etched epitaxial layer may have curved surfaces, and supplying a second source gas to trigger additional epitaxial growth in the etched epitaxial layer. The adsorbing, etching, and supplying may be performed by an in-situ process.  
         [0011]     Etching the first epitaxial layer may include employing an etching gas containing a hydrochloric acid gas (HCl). Etching the first epitaxial layer may also include employing an etching gas containing dichlorosilane (DCS), disilane (Si 2 H 6 ), silane (SiH 4 ), or germane (GeH 4 ) in an amount of about 5% to about 15% by volume of the etching gas.  
         [0012]     Adsorbing and supplying the source gas may include employing dichlorosilane (DCS), disilane (Si 2 H 6 ), silane (SiH 4 ), or germane (GeH 4 ). Adsorbing and supplying the source gas may also include use of hydrochloric acid gas (HCl). The first and second source gases may be the same.  
         [0013]     Adsorbing a first source gas into the plurality of conductive surfaces to grow a first epitaxial layer may include forming a plurality of epitaxial layer portions, each epitaxial layer portion having lateral portions overhanging the insulating surfaces. Additionally, etching the first epitaxial layer may further include reducing a width of each epitaxial layer portion, such that a thickness to width ratio of each epitaxial layer portion is reduced as compared to a thickness to width ratio of an un-etched epitaxial layer portion.  
         [0014]     In another aspect of the present invention, there is provided a method for preparing epitaxial layers, including applying an insulating layer to a semiconductor substrate, such that a plurality of active regions at a predetermined angle may be formed therein, disposing a plurality of gate patterns on the insulating layer, such that the gate patterns may intersect with the plurality of active regions, adsorbing a first source gas into the plurality of active regions to grow a first epitaxial layer thereon, such that the first epitaxial layer may have lateral portions overhanging the insulating layer, etching the first epitaxial layer to form an etched epitaxial layer, such that the etched epitaxial layer may have curved surfaces, and supplying a second source gas to trigger additional epitaxial growth in the etched epitaxial layer. The epitaxial layer may be formed to fill a gap between adjacent gate patterns. The adsorbing, etching, and supplying may be performed by an in-situ process.  
         [0015]     Etching the first epitaxial layer may include employing an etching gas containing a hydrochloric acid gas (HCl). Etching the first epitaxial layer may also include employing an etching gas containing dichlorosilane (DCS), disilane (Si 2 H 6 ), silane (SiH 4 ), or germane (GeH 4 ) in an amount of about 5% to about 15% by volume of the etching gas.  
         [0016]     Adsorbing and supplying the source gas may include employing dichlorosilane (DCS), disilane (Si 2 H 6 ), silane (SiH 4 ), or germane (GeH 4 ). Adsorbing and supplying the source gas may also include use of hydrochloric acid gas (HCl). The first and second source gases may be the same.  
         [0017]     Disposing a plurality of gate patterns may include intersecting each active region with two gate patterns. Intersecting each active region with two gate patterns may include forming two electrode gates and three active portions, such that the each electrode gate is disposed between two active portions. Additionally, adsorbing the first source gas into the plurality of active regions may include growing a first epitaxial layer on the three active portions. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]     The above and other features and advantages of the present invention will become more apparent to those of ordinary skill in the art by describing in detail exemplary embodiments thereof with reference to the attached drawings, in which:  
         [0019]      FIG. 1  illustrates a partial plane view of a semiconductor device in accordance with an embodiment of the present invention;  
         [0020]      FIG. 2  illustrates a flow chart of a method of preparing an epitaxial layer in accordance with an embodiment of the present invention; and  
         [0021]      FIGS. 3-5  illustrate sequential sectional views corresponding to processing steps of the method illustrated in  FIG. 2 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]     Korean Patent Application 2005-123314 filed on Dec. 14, 2005, in the Korean Intellectual Property Office, and entitled: “Method for Epitaxial Growth with Selectivity,” is incorporated by reference herein in its entirety.  
         [0023]     The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are illustrated. The invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.  
         [0024]     It will further be understood that when an element or layer is referred to as being “on” another element, layer or substrate, it can be directly on the other element, layer or substrate, or intervening elements/layers may also be present. Further, it will be understood that when an element or layer is referred to as being “under” another element or layer, it can be directly under, or one or more intervening elements or layers may also be present. In addition, it will also be understood that when an element or layer is referred to as being “between” two elements or layer, it can be the only element or layer between the two elements or layers, or one or more intervening elements or layers may also be present. Like reference numerals refer to like elements throughout.  
         [0025]     An exemplary embodiment of a semiconductor device according to the present invention is more fully described below with reference to  FIG. 1 . As illustrated in  FIG. 1 , a semiconductor device, e.g., a DRAM, in accordance with an embodiment of the present invention may include a substrate (not shown), an insulation layer  12  formed on the substrate, a plurality of active regions  14 , and a plurality of gate patterns  16 .  
         [0026]     The insulation layer  12  may be a patterned insulating film, such that a plurality of gaps may be formed therein to define the plurality of active regions  14 . The plurality of active regions  14  may be in communication with the substrate and arranged in various patterns to provide a higher integration degree. For example, the plurality of active regions  14  may be formed as a plurality of sequential discontinuous segments arranged in parallel rows and at a predetermined angle, as illustrated in  FIG. 1 . With respect to the present invention “a predetermined angle” refers to any angle other than 0° or 90° formed between the active regions  14  and an x-axis, as illustrated in  FIG. 1 .  
         [0027]     Each gate pattern  16  may include a gate insulation film (not shown), at least one gate electrode (not shown) having sidewalls and formed on the gate insulation film, spacers (not shown) disposed on the sidewalls of the gate electrode, and a capping insulation film (not shown) disposed on the gate electrode. The at least one gate electrode may intersect with the active region  14 .  
         [0028]     In particular, the plurality of gate patterns  16  may be formed in a stripe pattern on the substrate, such that a plurality of longitudinal members may be disposed in parallel and at equal intervals on the substrate. More specifically, the insulation layer  12  and the active regions  14  may be disposed between the substrate and the plurality of gate patterns  16 , such that each active region  14  may intersect with two gate patterns  16 , i.e., each active region  14  may have two intersection regions with the gate patterns  16 . The two intersection regions of the active regions  14  may divide each active region  14  into a first, second, and third active portion  14   a,    14   b,  and  14   c,  respectively, each portion separated from the other portion by the intersection region, as illustrated in  FIG. 1 . Each intersection region may include the gate electrode of a respective gate pattern  16 .  
         [0029]     The three active portions  14   a,    14   b  and  14   c  may be treated to operate as source and drain regions. In particular, the substrate may be treated with ionic impurities at predetermined regions, such that the second active portion  14   b  of each active region  14  may be a drain region and the first and third active portions  14   a  and  14   c  of each active region  14  may be source regions. More specifically, as illustrated in  FIG. 1 , the drain region, i.e., the second active portion  14   b,  may be formed in a center of the active region  14  between two gate electrodes of the gate pattern  16 , and the source regions, i.e., the first and third active portions  14   a  and  14   c,  may be formed in peripheral portions of the active region  14 . Accordingly, each gate electrode of the gate pattern  16  may be positioned between one drain region and one source region.  
         [0030]     An epitaxial layer according to an embodiment of the present invention may be selectively formed on the source and drain regions, i.e., first, second and third active portions  14   a,    14   b  and  14   c,  respectively, of the active region  14 . The epitaxial layer may form, for example, elevated source/drain regions or source/drain pads for connecting the source/drain regions with contact plugs to be formed later. In this respect, it should be noted that the epitaxial layer may be isolated from the gate electrodes of the gate patterns  16  by the spacers thereof. Alternatively, the epitaxial layers may be formed on the gate electrodes of the gate patterns  16 .  
         [0031]     According to another aspect of the present invention, an exemplary method of forming a selective epitaxial layer according to an embodiment of the present invention will be more fully described with respect to  FIGS. 2-5 .  
         [0032]     First, i.e., in step S 1 , a semiconductor substrate  50  may be coated with the insulation layer  12 , such that the active regions  14  may be defined therein, as illustrated in  FIGS. 1 and 3 . In particular, the insulation layer  12  may be formed such that the active regions  14  may be defined at a predetermined angle. Next, gate patterns  16  may be disposed on the semiconductor substrate  50  as previously described with respect to  FIG. 1 . Subsequently, the semiconductor substrate  50  may be placed inside a temperature-controlled reaction chamber, where epitaxial layer portions  58   a  may be grown thereon. In this respect, it should be noted that “epitaxial layer portions” refer to discrete portions grown on separate active regions  14  or portions thereof of the semiconductor substrate  50 . On the other hand, an “epitaxial layer” refers cumulatively to a plurality of epitaxial layer portions formed on a semiconductor substrate.  
         [0033]     Without intending to be bound by theory, it is believed that formation of the insulation layer  12  and the active regions  14  according to an embodiment of the present invention illustrated in  FIGS. 1 and 3 , i.e., formation of the active regions  14  at the predetermined angle may be advantageous in preventing bridging between adjacent facets and/or edges of the epitaxial layer portions  58   a.  In particular, the geometric configuration of the active regions  14  illustrated in  FIG. 1  may trigger different growth rates thereon with respect to the crystalline orientation of the semiconductor substrate  50 , such that adjacent epitaxial layer portions  58   a  disposed on a, same active region  14  may have different thickness and width values. As a result, adjacent epitaxial layer portions  58   a  may have different structures and increased gaps therebetween, thereby exhibiting minimized contact between facets and/or edges thereof.  
         [0034]     In more detail, growth of the epitaxial layer portions  58   a  may first include supplying a source gas into a reaction chamber having the semiconductor substrate  50 , i.e., step S 2 , as illustrated in  FIG. 2 . The source gas may be any precursor gas containing silicon or germanium, e.g., dichlorosilane (DCS), disilane (Si 2 H 6 ), silane (SiH 4 ), germane (GeH 4 ), and so forth, to trigger growth of a silicon or germanium epitaxial layer. Additionally, small amounts of chlorine containing gas, e.g., hydrochloric acid gas (HCl), may be added to the source gas to limit formation of an epitaxial layer on the insulation layer  12 , i.e., interaction of the HCL gas with an oxide or nitride film employed as the insulation layer  12  may inhibit adsorption of the source gas therein, thereby minimizing growth of an epitaxial layer in the insulation layer  12 .  
         [0035]     The source gas may dissociate in the reaction chamber as a result of the temperature therein, thereby triggering silicon or germanium adsorption into the active regions  14  of the semiconductor substrate  50  and facilitating growth of the epitaxial layer portions  58   a  therein. The growth of the epitaxial layer portions  58   a  may be monitored to achieve a predetermined thickness thereof, as measured in a vertical direction, i.e., along a y-axis. In this respect, it should be noted that the growth rate of the epitaxial layer portions  58   a  may depend on a crystalline orientation thereof, such that the epitaxial layer portions  58   a  may grow to have three-dimensional crystalline structures having a plurality of surfaces and boundaries capable of filling gaps or spaces between the gate patterns  16  and, subsequently, extending laterally, i.e., along a horizontal direction along a z-axis, as illustrated in  FIGS. 3-5 , to overhang the insulation layer  12 .  
         [0036]     Next, in step S 3 , the supply of the source gas may be paused, and an etching gas may be supplied to etch the epitaxial layers  58   a,  as illustrated in  FIG. 2 . In particular, the etching gas may be any etching gas employed in the art in similar processes, e.g., wet etching process, and having an etch selectivity with respect to silicon and germanium. The etching gas may include HCl gas with a small amount, e.g., from about 2% to about 10% by volume of the total etching gas, of DCS, Si 2 H 6 , SiH 4 , or GeH 4  in order to enhance the etch rate.  
         [0037]     The etching gas may etch the edges of the epitaxial layer portions  58   a  to form etched epitaxial layer portions  58   b  having curved surfaces, as illustrated in  FIG. 4 . In other words, the etching gas may round the edges of each epitaxial layer portions  58   a  and minimize the width thereof, i.e., as measured along the z-axis, such that a horizontal distance between adjacent etched epitaxial layer portions  58   b  along the z-axis may be maximized, while contact therebetween may be minimized. Accordingly, the width of the etched epitaxial layer portions  58   b  may be significantly reduced, such that a thickness/width ratio of each etched epitaxial layer portion  58   b  may be increased as compared to a thickness/width ratio of each epitaxial layer portion  58   a,  i.e., thickness/width ratio prior to etching.  
         [0038]     Once the edges of the etched epitaxial layer portions  58   b  are etched to have curved surfaces, the etching gas may be paused and the source gas may be supplied again into the reaction chamber in step S 4 . In particular, the source gas may dissociate again in the reaction chamber and trigger further silicon and/or germanium adsorption into the active regions  14 , thereby advancing further epitaxial growth of etched epitaxial layer portions  58   b.  The etched epitaxial layer portions  58   b  may grow into three-dimensional epitaxial layers  58 . Without intending to be bound by theory, it is believed that because the etched epitaxial layer portions  58   b  may be formed to have curved surfaces with reduced width in step S 3 , the etched epitaxial layer portions  58  in step S 4  may continue growing vertically and horizontally according to the crystalline orientation thereof without horizontal bridging therebetween. In particular, because the thickness/width ratio of the etched epitaxial layer portions  58   b  is smaller as compared to the thickness/width ratio of the epitaxial layer portions  58   a,  the etched epitaxial layer portions  58   b  may grow vertically into epitaxial layers  58  and achieve a desired thickness without intersecting horizontally with adjacent etched epitaxial layer portions  58   b.    
         [0039]     Steps S 1  through S 3  may be performed by an in-situ process, i.e., varying the supply time and components of the source and etching gases into the reaction chamber without removing the semiconductor substrate from the reaction chamber. Further, the epitaxial layers  58  may contain different layers, e.g., a first epitaxial layer and a second epitaxial layer may include alternating layers of silicon and germanium epitaxial layers.  
         [0040]     Exemplary embodiments of the present invention have been disclosed herein, and although specific terms are employed, they are used and are to be interpreted in a generic and descriptive sense only and not for purpose of limitation. Accordingly, it will be understood by those of ordinary skill in the art that various changes in form and details may be made without departing from the spirit and scope of the present invention as set forth in the following claims.