1. A method of manufacturing a semiconductor memory device, the method comprising:
forming a tunnel insulation layer on a substrate;
forming a preliminary charge trapping layer on the tunnel insulation layer;
forming an etch stop layer on the preliminary charge trapping layer, wherein a portion of the preliminary charge trapping layer is not covered by the etch stop layer;
removing the exposed portion of the preliminary charge trapping layer to form a charge trapping layer having a uniform thickness;
forming a dielectric layer on the charge trapping layer; and
forming a gate electrode on the dielectric layer.
2. The method as claimed in claim 1, wherein forming the preliminary charge trapping layer includes performing an isotropic etching process on the preliminary charge trapping layer.
3. The method as claimed in claim 2, further comprising removing the etch stop layer after removing the exposed portion of the preliminary charge trapping layer.
4. The method as claimed in claim 1, further comprising, prior to forming the tunnel insulation layer:
sequentially forming a pad layer pattern and a mask on the substrate;
partially removing the substrate using the mask and the pad layer pattern as an etching mask to form a trench defining an active region in the substrate;
forming an isolation layer in the trench; and
removing the mask and the pad layer pattern to form an opening exposing the active region,
wherein the tunnel insulation layer is formed on the exposed active region.
5. The method as claimed in claim 4, wherein removing the mask and the pad layer pattern to form the opening includes performing a wet etching process, and a portion of the isolation layer is removed in the wet etching process.
6. The method as claimed in claim 5, wherein the preliminary charge trapping layer is formed on a bottom and a sidewall of the opening.
7. The method as claimed in claim 6, further comprising, after forming the etch stop layer:
removing an upper portion of the isolation layer so that a portion of the preliminary charge trapping layer is exposed.
8. The method as claimed in claim 7, wherein removing the upper portion of the isolation layer includes removing the upper portion of the isolation layer until a top surface of the isolation layer has a height substantially the same as a height of a lowermost portion of the etch stop layer.
9. The method as claimed in claim 7, wherein removing the upper portion of the isolation layer includes removing the upper portion of the isolation layer until a top surface of the isolation layer has a height substantially the same as, or higher than, that of a lowermost point of the preliminary charge trapping layer.
10. A method of manufacturing a semiconductor memory device, the method comprising:
forming a mask on a substrate;
partially removing the substrate using the mask as an etching mask to form a trench defining an active region in the substrate;
forming an isolation layer in the trench;
removing the mask to form an opening exposing the active region;
forming a preliminary charge trapping layer on a bottom and a sidewall of the trench and on the isolation layer;
forming an etch stop layer on the preliminary charge trapping layer;
removing an upper portion of the etch stop layer and an upper portion of the preliminary charge trapping layer on the isolation layer;
removing a portion of the isolation layer;
partially removing the preliminary charge trapping layer to form a charge trapping layer having a substantially uniform thickness;
forming a dielectric layer on the charge trapping layer; and
forming a gate electrode on the dielectric layer.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A zoom lens system comprising a negative first lens group, a positive second lens group, and a positive third lens group, in this order from an object,
wherein upon zooming from the short focal length extremity to the long focal length extremity, a distance between said negative first lens group and said positive second lens group decreases, and a distance between said positive second lens group and said positive third lens group increases;
wherein when zooming is being performed, said negative first lens group remains stationary, and said positive second lens group and said positive third lens group are moveable along the optical axis of said zoom lens system; and
wherein said zoom lens system satisfies the following conditions:
1.5<f3f2<2.5
0.8<f2(fw*ft)12<1.3
wherein
f2 designates the focal length of said positive second lens group;
f3 designates the focal length of said positive third lens group;
fw designates the focal length of the entire zoom lens system at the short focal length extremity; and
ft designates the focal length of the entire zoom lens system at the long focal length extremity.
2. The zoom lens system according to claim 1, further satisfying the following condition:
1.0<T2ymax<2.0
wherein
T2 designates a distance from the most object-side surface to the most image-side surface of said positive second lens group; and
ymax designates the maximum image height.
3. The zoom lens system according to claim 1, wherein said negative first lens group comprises a negative single lens element having the concave surface facing toward an image.
4. The zoom lens system according to claim 1, wherein said positive second lens group comprises a positive lens element and a negative lens element, in this order from said object.
5. The zoom lens system according to claim 1, wherein said positive third lens group comprises a positive single lens element.
6. The zoom lens system according to claim 1, wherein a position of said positive third lens group at the short focal length extremity is arranged to be identical to the position thereof at the long focal length extremity.
7. A zoom lens system comprising a negative first lens group, a positive second lens group, and a positive third lens group, in this order from an object,
wherein upon zooming from the short focal length extremity to the long focal length extremity, a distance between said negative first lens group and said positive second lens group decreases, and a distance between said positive second lens group and said positive third lens group increases;
wherein when zooming is being performed, said negative first lens group remains stationary, and said positive second lens group and said positive third lens group are moveable along the optical axis of said zoom lens system; and
wherein said zoom lens system satisfies the following condition:
1.0<T2ymax<2.0
wherein
T2 designates a distance from the most object-side surface to the most image-side surface of said positive second lens group; and
ymax designates the maximum image height.