Oxide-nitride-oxide stack having multiple oxynitride layers

Abstract

A semiconductor device including an oxide-nitride-oxide (ONO) structure having a multi-layer charge storing layer and methods of forming the same are provided. Generally, the method involves: (i) forming a first oxide layer of the ONO structure; (ii) forming a multi-layer charge storing layer comprising nitride on a surface of the first oxide layer; and (iii) forming a second oxide layer of the ONO structure on a surface of the multi-layer charge storing layer. Preferably, the charge storing layer comprises at least two silicon oxynitride layers having differing stoichiometric compositions of Oxygen, Nitrogen and/or Silicon. More preferably, the ONO structure is part of a silicon-oxide-nitride-oxide-silicon (SONOS) structure and the semiconductor device is a SONOS memory transistor. Other embodiments are also disclosed.

1 . A method of forming a charge storing layer of a semiconductor device, the method comprising steps of:
 depositing on a substrate a silicon-rich nitride; and   oxidizing the silicon-rich nitride to form a silicon-rich, oxygen-rich first oxynitride layer.   
   
   
       2 . A method according to  claim 1 , further comprising the step of forming over a surface of the first oxynitride layer at least one additional layer to form a multi-layer charge storing layer. 
   
   
       3 . A method according to  claim 2 , wherein the step of forming at least a one additional layer comprises the step of forming a second oxynitride layer. 
   
   
       4 . A method according to  claim 3 , wherein the first oxynitride layer and second oxynitride layer have differing stoichiometric compositions of oxygen, nitrogen and/or silicon. 
   
   
       5 . A method according to  claim 3 , wherein the step of forming the second oxynitride layer comprises the step of forming a second oxynitride layer under conditions selected to form a silicon-rich, oxygen-lean oxynitride layer. 
   
   
       6 . A method according to  claim 5 , wherein the first oxynitride layer is formed in a chemical vapor deposition (CVD) process using a process gas comprising a dichlorosilane (SiH 2 Cl 2 )/ammonia (NH 3 ) mixture and a nitrous oxide (N 2 O)/NH 3  mixture at a ratio of about 8:1, and wherein the second oxynitride layer is formed in a CVD process using a process gas comprising a N 2 O/NH 3  mixture and a SiH 2 Cl 2 /NH 3  mixture at a ratio of about 5:1. 
   
   
       7 . A method according to  claim 6 , wherein the steps of forming the first oxynitride layer and the second oxynitride layer are performed sequentially in a single CVD tool by changing the ratio of the N 2 O/NH 3  and SiH 2 Cl 2 /NH 3  mixtures. 
   
   
       8 . A method according to  claim 6 , wherein at least one of the first oxynitride layer and the second oxynitride layer is formed at temperature of at least about 780° C. 
   
   
       9 . A method of forming a semiconductor device including an oxide-nitride-oxide (ONO) structure, the method comprising steps of:
 forming a first oxide layer of the ONO structure;   forming a multi-layer charge storing layer comprising nitride on a surface of the first oxide layer; and   forming a second oxide layer of the ONO structure on a surface of the multi-layer charge storing layer.   
   
   
       10 . A method according to  claim 9 , wherein, the multi-layer charge storing layer comprises at least two silicon oxynitride (Si 2 N 2 O) layers. 
   
   
       11 . A method according to  claim 10 , wherein the at least two oxynitride layers have differing stoichiometric compositions of oxygen, nitrogen and/or silicon. 
   
   
       12 . A method according to  claim 11 , wherein the at least two oxynitride layers include a top oxynitride layer and a bottom oxynitride layer, and wherein the top oxynitride layer is formed under conditions selected to form a silicon-rich, oxygen-lean oxynitride layer, and the bottom oxynitride layer is formed under conditions selected to form a silicon-rich, oxygen-rich oxynitride layer. 
   
   
       13 . A method according to  claim 12 , wherein the top oxynitride layer is nitrogen-rich oxynitride layer. 
   
   
       14 . A method according to  claim 12 , wherein the step of forming the first oxide layer comprises the step of forming the first oxide layer using a steam anneal, and wherein a ratio of thicknesses between the top oxynitride layer and the bottom oxynitride layer is selected to facilitate forming the multi-layer memory layer following the step of forming the tunnel oxide layer using a steam anneal. 
   
   
       15 . A method according to  claim 12 , wherein the top oxynitride layer is formed using a process gas comprising a dichlorosilane (SiH 2 Cl 2 )/ammonia (NH 3 ) mixture and a nitrous oxide (N 2 O)/NH 3  mixture at a ratio of about 5:1, and the bottom oxynitride layer is formed using a process gas comprising a N 2 O/NH 3  mixture and a SiH 2 Cl 2 /NH 3  mixture at a ratio of about 8:1. 
   
   
       16 . A method according to  claim 10 , wherein the at least two oxynitride layers are formed at temperature of at least about 780° C. 
   
   
       17 . A semiconductor device including an oxide-nitride-oxide (ONO) structure comprising a multilayer memory layer between a first oxide layer and a second oxide layer, wherein the multilayer memory layer comprises at least two silicon oxynitride layers. 
   
   
       18 . A semiconductor device according to  claim 17 , wherein the at least two oxynitride layers have differing stoichiometric compositions of oxygen, nitrogen and/or silicon. 
   
   
       19 . A semiconductor device according to  claim 17 , wherein oxygen, nitrogen and silicon profiles across the at least two oxynitride layers are selected to meet a predetermined data retention specification at an operating temperature of at least 125° C. 
   
   
       20 . A semiconductor device according to  claim 17 , wherein the at least two oxynitride layers include a top oxynitride layer and a bottom oxynitride layer, and wherein a ratio of thickness between the top oxynitride layer and the bottom oxynitride layer is from 1 to 5.