Patent Publication Number: US-2021193475-A1

Title: Method of manufacturing semiconductor device, and etching gas

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2018-169983, filed on Sep. 11, 2018, and the prior International Patent Application No. PCT/JP2019/027316, filed on Jul. 10, 2019, the entire contents of which are incorporated herein by reference. 
    
    
     FIELD 
     Embodiments described herein relate to a method of manufacturing a semiconductor device, and etching gas. 
     BACKGROUND 
     When a semiconductor device such as a three-dimensional memory is manufactured, a concave portion is often formed in a process target film by etching with fluorohydrocarbon (C x H y F z ) gas. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A to 1C  are sectional views showing a method of manufacturing a semiconductor device of a first embodiment; 
         FIGS. 2A and 2B  are sectional views for explaining advantages of the method of manufacturing the semiconductor device of the first embodiment; 
         FIG. 3  is a schematic sectional view for explaining advantages of the method of manufacturing the semiconductor device of the first embodiment; 
         FIGS. 4A to 4C  are tables showing examples of etching gas of the first embodiment; 
         FIG. 5  is a graph for explaining characteristics of the etching gas of the first embodiment; and 
         FIG. 6  is a sectional view showing a structure of the semiconductor device of the first embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments will now be explained with reference to the accompanying drawings. In  FIGS. 1A to 6 , the same or similar components are given the same signs and their duplicated description is omitted. 
     In one embodiment, a method of manufacturing a semiconductor device includes etching a film with etching gas that includes a chain hydrocarbon compound expressed as C x H y F z  where C, H and F respectively denote carbon, hydrogen and fluorine, “x” denotes an integer of three or more, and “y” and “z” respectively denote integers of one or more. Furthermore, the C x H y F z  is the chain hydrocarbon compound in which each of terminal carbon atoms on a carbon chain of the chain hydrocarbon compound is bonded only to fluorine atoms out of hydrogen and fluorine atoms. 
     First Embodiment 
       FIGS. 1A to 1C  are sectional views showing a method of manufacturing a semiconductor device of a first embodiment. The semiconductor device of the present embodiment will be described by describing its example “three-dimensional memory.” 
     First, a lower layer  2  is formed on a substrate  1 , and a stacked film is formed which alternately includes a plurality of sacrificial layers  3  and a plurality of insulating layers  4 , on the lower layer  2  ( FIG. 1A ). The sacrificial layers  3  are examples of first films, and the insulating layers  4  are examples of second films. Next, an upper layer  5  is formed on this stacked film, and a mask layer  6  is formed on the upper layer  5  ( FIG. 1A ). 
     The substrate  1  is, for example, a semiconductor substrate such as a silicon (Si) substrate.  FIG. 1A  shows an X-direction and a Y-direction which are parallel to a surface of the substrate  1  and perpendicular to each other, and a Z-direction perpendicular to the surface of the substrate  1 . In the present specification, the +Z-direction is regarded as the upward direction, and the −Z-direction is regarded as the downward direction. The −Z-direction may coincide with the direction of gravity or may not coincide with the direction of gravity. 
     The lower layer  2  is, for example, an insulator such as a silicon oxide film (SiO 2 ) or a silicon nitride film (SiN), or a conducting layer formed between insulators. The sacrificial layers  3  are, for example, silicon nitride films, and the insulating layers  4  are, for example, silicon oxide films. The upper layer  5  is, for example, an insulator such as a silicon oxide film or a silicon nitride film, or a conducting layer formed between insulators. The mask layer  6  is, for example, an organic hard mask layer. 
     Next, an opening pattern for forming a memory hole M is formed in the mask layer  6  by lithography and dry etching ( FIG. 1B ). Next, the memory hole M penetrating the upper layer  5 , the plurality of insulating layers  4 , the plurality of sacrificial layers  3  and the lower layer  2  is formed by dry etching using the mask layer  6  ( FIG. 1B ). An aspect ratio of the memory hole M is, for example, 10 or more. The memory hole M is an example of a concave portion. 
     The memory hole M of the present embodiment is formed by dry etching using etching gas including C x H y F z  (fluorohydrocarbon) gas. Note that C, H and F respectively denote carbon, hydrogen and fluorine, and “x”, “y” and “z” respectively denote integers of one or more. Consequently, a protecting film  7  is formed on side faces (lateral faces) of the insulating layers  4  and the sacrificial layers  3  in the memory hole M during the dry etching, and the side faces of the insulating layers  4  and the sacrificial layers  3  are protected by the protecting film  7 . The protecting film  7  of the present embodiment is a C m F n  (fluorocarbon) film. Note that “m” and “n” respectively denote integers of one or more. The C x H y F z  of the present embodiment is, for example, a chain hydrocarbon compound in which “x” is an integer of three or more and “y” and “z” are respectively integers of one or more. 
     In the present embodiment, each of terminal carbon (C) atoms on a carbon chain of C x H y F z  gas is bonded only to fluorine atoms out of hydrogen atoms (H atoms) and fluorine atoms (F atoms). In other words, none of H atoms are bonded to the terminal C atoms on the carbon chain. For example, when the C x H y F z  molecule is a linear chain-type chain C 4 H 4 F 6  molecule, the C 4 H 4 F 6  molecule includes two terminal C atoms and two non-terminal C atoms. The two terminal C atoms are bonded only to F atoms out of H atoms and F atoms and are not bonded to H atoms. All the four H atoms are bonded to the non-terminal C atoms. The C x H y F z  molecule of the present embodiment may be other than a linear chain-type chain C x H y F z  molecule as long as it includes terminal C atoms, and may be, for example, a side chain-type chain C x H y F z  molecule. The side chain-type chain C x H y F z  molecule includes three or more terminal C atoms. 
     The present embodiment makes it possible to form the memory hole M while preferably protecting the side faces of the insulating layers  4  and the sacrificial layers  3  in the memory hole M with the protecting film  7 , by performing dry etching using the etching gas as above. Details of such an effect of the present embodiment are mentioned later. 
     Next, the protecting film  7  and the mask layer  6  are removed, and a block insulator  11 , a charge storage capacitor  12  and a tunnel insulator  13  are sequentially formed in the memory hole M ( FIG. 1C ). Next, the block insulator  11 , the charge storage capacitor  12  and the tunnel insulator  13  are removed from a bottom part of the memory hole M, and a channel semiconductor layer  14  and a core insulator  15  are sequentially formed in the memory hole M ( FIG. 1C ). The charge storage capacitor  12  is, for example, a silicon nitride film. The channel semiconductor layer  14  is, for example, a polysilicon layer. The block insulator  11 , the tunnel insulator  13  and the core insulator  15  are, for example, silicon oxide films or metal insulators. 
     After that, the sacrificial layers  3  are removed via a slit or a hole formed at a different position from that of the memory hole M to form a plurality of hollows between the insulating layers  4 , and a plurality of electrode layers are formed in these hollows. Moreover, various plugs, lines and inter layer dielectrics and the like are formed on the substrate  1 . As above, the semiconductor device of the present embodiment is manufactured. 
       FIGS. 2A and 2B  are sectional views for explaining advantages of the method of manufacturing the semiconductor device of the first embodiment. 
       FIG. 2A  shows the protecting film  7  that is formed down to a deep place in the memory hole M. In this case, since the side faces of the insulating layers  4  and the sacrificial layers  3  are sufficiently protected by the protecting film  7 , the side faces of the insulating layers  4  and the sacrificial layers  3  are scarcely shaved during etching. 
     On the other hand,  FIG. 2B  shows the protecting film  7  that is formed only at a shallow place in the memory hole M. In this case, since the side faces of the insulating layers  4  and the sacrificial layers  3  are not sufficiently protected by the protecting film  7 , the side faces of the insulating layers  4  and the sacrificial layers  3  are shaved during etching by a larger value than a predetermined one. This results in a depression called bowing in these side faces (refer to sign B). This problem is more remarkable with a higher aspect ratio of the memory hole M. 
     The insulating layers  4  and the sacrificial layers  3  of the present embodiment are etched using plasma generated from the C x H y F z  gas in the step of  FIG. 1B . Specifically, the protecting film  7  is formed with radicals included in the plasma, and the side faces of the insulating layers  4  and the sacrificial layers  3  are etched with ions included in the plasma. It is therefore considered that the protecting film  7  as shown in  FIG. 2A  is formed when radicals can reach a deep place in the memory hole M. On the other hand, it is considered that the protecting film  7  as shown in  FIG. 2B  is formed when radicals cannot reach a deep place in the memory hole M. 
       FIG. 3  is a schematic sectional view for explaining advantages of the method of manufacturing the semiconductor device of the first embodiment. 
     Sign P1 denotes a radical generated by eliminating an H atom from a C 4 HF 5  molecule in which a terminal C atom is bonded to the H atom. Etching gas including this C 4 HF 5  molecule (CF 2 ═CF—CF═CHF) is, for example, etching gas of a comparative example of the present embodiment. 
     On the other hand, sign P2 denotes a radical generated by eliminating an H atom from a C 4 HF 5  molecule in which a non-terminal C atom is bonded to the H atom (namely, the terminal C atoms are not bonded to the H atom). Etching gas including this C 4 HF 5  molecule (CF 2 ═CF—CH═CF 2 ) is an example of etching gas of the present embodiment. 
     In a C x H y F z  molecule, the bond energy of a C—H bond is smaller than the bond energy of a C—F bond, and the C—H bond is more easily cleaved than the C—F bond. Therefore, when the C x H y F z  molecule is made into plasma, a C—H bond is often cleaved to leave an unpaired electron at the place of the C—H bond. Sign P1 denotes the radical that has an unpaired electron at the terminal C atom, and sign P2 denotes the radical that has an unpaired electron at the non-terminal C atom. 
     Unpaired electrons have high reactivity and this causes radicals to stick onto the side faces of the insulating layers  4  and the sacrificial layers  3 . In this case, when a radical has an unpaired electron at a non-terminal C atom as denoted by sign P2, the radical scarcely sticks onto the side faces of the insulating layers  4  and the sacrificial layers  3  because of large steric hindrance around the unpaired electron. In other words, F atoms around the unpaired electron disturb the reaction of the unpaired electron with the side faces of the insulating layers  4  and the sacrificial layers  3 . On the other hand, when a radical has an unpaired electron at a terminal C atom as denoted by sign P1, the radical easily sticks onto the side faces of the insulating layers  4  and the sacrificial layers  3  because of small steric hindrance around the unpaired electron. 
     It is consequently considered that the radical with sign P1 scarcely reach the deep place in the memory hole M since it has a high sticking possibility onto the side faces of the insulating layers  4  and the sacrificial layers  3 . On the other hand, it is considered that the radical with sign P2 easily reaches the deep place in the memory hole M since it has a low sticking possibility onto the side faces of the insulating layers  4  and the sacrificial layers  3 . The present embodiment therefore makes it possible to form the protecting film  7  down to a deep place in the memory hole M by using radicals as denoted by sign P2 (see  FIG. 2A ). 
       FIGS. 4A to 4C  are tables showing examples of the etching gas of the first embodiment. 
       FIGS. 4A to 4C  show various kinds of C x H y F z  gas where the value of “x” is an integer from 3 to 5 and y≤z. The reason why the value of “x” is 3 to 5 is that C x H y F z  with the value of “x” being 6 or more has low vapor pressure and is hard to feed as gas at the normal temperature.  FIG. 4A  shows examples with four C atoms (x=4),  FIG. 4B  shows an example with three C atoms (x=3), and  FIG. 4C  shows an example with five C atoms (x=5). Each value of “D.B.” in the tables represents the number of double bond(s) in a C x H y F z  molecule.  FIG. 4A  also shows cyclic C 4 F 8  for reference. 
       FIG. 5  is a graph for explaining characteristics of the etching gas of the first embodiment. 
       FIG. 5  shows deposition rates of the protecting film  7  as bars and uniformities (evennesses) of the protecting film  7  as points for the various kinds of C x H y F z  gas. The molecular structures of the C x H y F z  gas are as shown in  FIGS. 4A to 4C . 
     From experiments of etching for the various kinds of C x H y F z  gas, the results shown in  FIG. 5  were obtained. The uniformities of the protecting film  7  were evaluated with the protecting film  7  in the case using the cyclic C 4 F 8  gas, which was often used in processing insulators, being as a reference. The uniformity was evaluated to be better as a change in film thickness of the protecting film  7  in the depth direction (Z-direction) was smaller, and specifically, the uniformity was evaluated to be better as the value of uniformity was lower. 
     Consequently, it was found that the uniformity of the protecting film  7  was better in the cases using C 4 HF 5  gas, C 4 H 2 F 4  gas, C 4 H 2 F 6  gas, C 4 H 4 F 6  gas, C 3 HF 5  gas and C 5 H 2 F 10  gas shown in  FIG. 5  than in the case using the cyclic C 4 F 8  gas. The etching gas of the present embodiment therefore desirably includes at least any of these kinds of gas as the C x H y F z  gas. Moreover, the C 4 HF 5  gas, the C 4 H 2 F 4  gas or the C 4 H 2 F 6  gas is desirably used when it is desirable to make the deposition rate of the protecting film  7  high while making the uniformity of the protecting film  7  good. 
     Referring to  FIGS. 4A to 4C , it is clear that the terminal C atoms of the C 4 HF 5  gas, the C 4 H 2 F 4  gas, the C 4 H 2 F 6  gas, the C 4 H 4 F 6  gas, the C 3 HF 5  gas and the C 5 H 2 F 10  gas shown in  FIG. 5  are bonded only to F atoms. The dry etching of the present embodiment is therefore desirably performed using the C x H y F z  gas in which the terminal C atoms are bonded only to F atoms. 
     In  FIGS. 4A to 4C , a molecular structure of C 4 HF 5  is expressed as CF 2 ═CF—CH═CF 2 , a molecular structure of C 4 H 2 F 4  is expressed as CF 2 ═CH—CH═CF 2 , and a molecular structure of C 4 H 2 F 6  is expressed as CF 3 —CH═CH—CF 3 . Moreover, a molecular structure of C 4 H 4 F 6  is expressed as CF 3 —CH 2 —CH 2 —CF 3 , a molecular structure of C 3 HF 5  is expressed as CF 2 ═CH—CF 3 , and a molecular structure of C 5 H 2 F 10  is expressed as CF 3 —CHF—CHF—CF 2 —CF 3 . 
     Examples of the C x H y F z  gas of the present embodiment are not limited to these. Other examples of the C x H y F z  gas of the present embodiment include C 4 H 4 F 6  (CF 3 —CH 2 —CH 2 —CF 3 ) gas, C 4 H 3 F 7  (CF 3 —CHF—CH 2 —CF 3 ) gas, C 4 H 2 F 8  (CF 3 —CHF—CHF—CF 3  or CF 3 —CF 2 —CH 2 —CF 3 ) gas, C 4 HF 9  (CF 3 —CHF—CF 2 —CF 3 ) gas and C 5 H 6 F 6  (CF 3 —CH 2 —CH 2 —CH 2 —CF 3 ) gas. Still other examples of the C x H y F z  gas of the present embodiment include some kinds of isomers of C 5 H 5 F 7  gas, C 5 H 4 F 8  gas, C 5 H 3 F 9  gas, C 5 H 2 F 10  gas, C 5 HF 11  gas and the like, the terminal C atoms in these isomers being bonded only to F atoms. 
     The etching gas of the present embodiment may be mixture gas including the C x H y F z  gas and other gas or may be mixture gas including two or more kinds of C x H y F z  gas. For example, the etching gas of the present embodiment may include oxygen gas, rare gas or C a F b  (fluorocarbon (fluorocarbon compound)) gas along with the C x H y F z  gas. Note that “a” and “b” denote integers of one or more. Examples of the C a F b  gas include CF 4  gas, C 2 F 4  gas, C 3 F 6  gas, C 4 F 6  gas and C 4 F 8  gas. 
     Herein, plasma generated from the C x H y F z  gas is described. 
     The insulating layers  4  and the sacrificial layers  3  of the present embodiment are etched using plasma generated from the C x H y F z  gas in the step of  FIG. 1B . Specifically, the protecting film  7  is formed with radicals included in the plasma, and the side faces of the insulating layers  4  and the sacrificial layers  3  are etched with ions included in the plasma. An average density (concentration) of the plasma in the etching treatment process chamber in this stage is, for example, 5.0×10 9  to 3.0×10 11  quantity/cm 3 . 
     The plasma of the present embodiment can include first to third radicals below. The first radical is generated by eliminating only H atom(s) out of H and F atoms from a C x H y F z  molecule. The second radical is generated by eliminating only F atom(s) out of H and F atoms from a C x H y F z  molecule. The third radical is generated by eliminating both of H and F atoms from a C x H y F z  molecule. The radical denoted by sign P2 in  FIG. 3  is an example of the first radical. 
     In the present embodiment, the C x H y F z  gas is desirably made into the plasma such that many first radicals are generated and not so many second and third radicals are generated. Specifically, the C x H y F z  gas is desirably made into the plasma such that a concentration of first radicals in the plasma is larger than a total concentration of second and third radicals in the plasma. The reason is that the steric hindrances around unpaired electrons of the second and third radicals are smaller than the steric hindrance around an unpaired electron of the first radical in many cases, which makes sticking possibilities of the second and third radicals higher than a sticking possibility of the first radical. 
       FIG. 6  is a sectional view showing a structure of a semiconductor device of the first embodiment. 
       FIG. 6  shows an example of the semiconductor device manufactured by the method of the present embodiment.  FIG. 6  shows a memory cell part and a step-like contact part of a three-dimensional memory. In  FIG. 6 , the lower layer  2  is constituted of a first insulator  2   a , a source-side conducting layer  2   b  and a second insulator  2   c , and the upper layer  5  is constituted of a cover insulator  5   a , a drain-side conducting layer  5   b , a first inter layer dielectric  5   c  and a second inter layer dielectric  5   d . The channel semiconductor layers  14  are electrically connected to a diffusion layer L in the substrate  1 . The sacrificial layers  3  are replaced by electrode layers  3 ′ including tungsten (W) layers or the like. The electrode layers  3 ′ are examples of the first films. 
       FIG. 6  further shows contact plugs  16  formed in contact holes H of the upper layer  5 . The contact plugs  16  are formed so as to be electrically connected to the corresponding electrode layers  3 ′. 
     As above, the memory holes M of the present embodiment are formed using the etching gas including the C x H y F z  gas, and each of terminal C atoms on a carbon chain of the C x H y F z  gas is bonded only to F atoms out of H atoms and F atoms. The present embodiment therefore makes it possible to form the protecting films  7  down to deep places in the memory holes M and to preferably protect the side faces of the insulating layers  4  and the sacrificial layers  3  in the memory holes M with the protecting films  7 . The present embodiment therefore makes it possible to preferably etch the insulating layers  4  and the sacrificial layers  3  to form the memory holes M. The present embodiment makes it possible to form even the memory holes M having a high aspect ratio, for example, of 10 or more into preferable shapes. 
     In the step of  FIG. 1A , the plurality of electrode layers  3 ′ and the plurality of insulating layers  4  may be alternately formed on the lower layer  2  instead of alternately forming the plurality of sacrificial layers  3  and the plurality of insulating layers  4  on the lower layer  2 . In this case, the step is unnecessary in which the sacrificial layers  3  are replaced by the electrode layers  3 ′. 
     Moreover, the dry etching of the present embodiment can be applied to a step other than the processing of the memory holes M, for example, can be applied to a step of processing concave portions other than the memory holes M. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel methods and gases described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and gases described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.