Semiconductor device and method of fabricating the same

Abstract

A semiconductor device includes a semiconductor substrate and first and second trenches. The first trench with a high aspect ratio is formed in a surface of the semiconductor substrate and has a bottom, two sidewalls and an open end. The first trench is formed so that at the bottom side, an inclination of each sidewall relative to the bottom has a first angle approximate to a right angle and at the bottom side, the inclination of each sidewall relative to the bottom has a second angle smaller than the first angle. The second trench has a lower aspect ratio than the first trench. The second trench has a bottom, two sidewalls and an open end and is formed so that an inclination of each sidewall relative to the bottom is substantially uniform from the bottom side to the open end side and has a third angle which is approximate to the second angle.

1 . A semiconductor device comprising: 
 a semiconductor substrate having a surface;    a first trench having a higher aspect ratio and formed in the surface of the semiconductor substrate, first trench having a bottom, two sidewalls and an open end, the first trench being formed so that at the bottom side thereof, an inclination of each sidewall relative to the bottom has a first angle approximate to a right angle and at the bottom side, the inclination of each sidewall relative to the bottom has a second angle smaller than the first angle; and    a second trench having a lower aspect ratio than the first trench, the second trench having a bottom, two sidewalls and an open end and being formed so that an inclination of each sidewall relative to the bottom thereof is substantially uniform from the bottom side to the open end side and has a third angle which is approximate to the second angle.    
   
   
       2 . The semiconductor device according to  claim 1 , wherein the first trench is formed as an element isolation region for a region where a memory cell is adapted to be formed, and the second trench is formed as an element isolation region for a region where a peripheral circuit is adapted to be formed.  
   
   
       3 . The semiconductor device according to  claim 2 , wherein the semiconductor substrate is formed with a gate insulating film and a gate electrode.  
   
   
       4 . A method of fabricating a semiconductor device, comprising: 
 patterning an etching mask material so that trenches having higher and lower aspect ratios and formed in a surface of a semiconductor substrate so as to be open at the surface, respectively; and    etching the semiconductor substrate with the patterned etching mask using an etching gas made by mixing a halogen gas, a fluorocarbon gas and oxygen so that the trenches are simultaneously formed.    
   
   
       5 . The method according to  claim 4 , further comprising, prior to the etching step, depositing a gate insulating film and a gate electrode material on the semiconductor substrate.  
   
   
       6 . A method of fabricating a semiconductor device, comprising: 
 forming a gate insulating film on a semiconductor substrate;    forming a polycrystalline silicon film;    forming a silicon nitride film;    forming a silicon oxide film;    etching the silicon oxide film, silicon nitride film, polycrystalline silicon film and gate insulating film all formed on the semiconductor substrate into a pattern corresponding to a first trench with a higher aspect ratio and a second trench with a lower aspect ratio, with a mask serving as a resist;    etching the semiconductor substrate using an etching gas made by mixing a halogen gas, a fluorocarbon gas and oxygen with the patterned silicon oxide film serving as a mask until a predetermined depth is reached, thereby forming a trench; and    filling the trench with an insulating film.