Semiconductor device and manufacturing method thereof

A semiconductor device having a FET in an element forming region of a semiconductor substrate to which an impurity of a first conductive type is doped, comprising:

• a gate electrode of the FET which is formed on the semiconductor substrate;
• a side wall spacer located at each side of the gate electrode;
• a lightly doped source region and a drain region of the FET each lightly doped with an impurity of a second conductive type and formed at a region under the side wall spacer in the semiconductor substrate;
• a source region and a drain region of the FET each heavily doped with an impurity of a second conductive type and respectively formed at a region outside of and adjacent to the lightly doped source region and the lightly doped drain region;
• a main channel region of the FET which is provided under the gate electrode between the lightly doped source region and the lightly doped drain region in the semiconductor, said main channel region comparatively lightly doped with an impurity of the same conductive type as the substrate;
• an isolation formed around the element forming region on the semiconductor substrate so as to separate the element forming region from other regions;
• a channel stop region, comparatively heavily doped with an impurity of the first conductive type, formed under the isolation in the semiconductor substrate;
• a first buffer region formed between the channel stop region and at least a region to which a high voltage is applied of the heavily doped drain region and the heavily doped source region in the semiconductor substrate, the first buffer region being doped with an impurity of the opposite conductive type as said lightly doped source and drain regions having a density approximately equal to that of the lightly doped source region and the lightly doped drain region;
• and
• a second buffer region formed under the gate electrode in the semiconductor substrate and between the isolation and the main channel region, said second buffer region being doped with, an impurity of the same conductive type and the same density as that of the main channel region.

A method of manufacturing a semiconductor device having an isolation for isolating an element forming region from other regions and a FET composed of a gate electrode, a source region and a drain region in an element forming region of a semiconductor substrate to which an impurity of a first conductive type is doped, comprising the steps of:

• heavily doping an impurity of a first conductive type to a region where the isolation of the semiconductor substrate is to be formed to form a channel stop region;
• forming an insulating film to be the isolation at the isolation forming region on the semiconductor substrate;
• doping an impurity of the first conductive type to the substrate to a density of threshold adjusting level to the element forming region;
• forming the gate electrode of the FET on the element forming region;
• and
• forming the source region and the drain region of the FET by doping an impurity of a second conductive type to both sides of the gate electrode of the element forming region,
• wherein the step of forming the drain region and the source region is conducted so that at least a region to which a high voltage is applied of the drain region and the source region is formed a set-distance inside of the element forming region from an end part of the isolation, separating the drain region and source region from a channel stop region.

A method of manufacturing a semiconductor device having an isolation for isolating the element forming region from other regions and a FET composed of a gate electrode, a lightly doped source region, a lightly doped drain region, a heavily doped source region and heavily doped drain region in an element forming region of a semiconductor substrate to which an impurity of a first conductive type is doped, comprising the steps of:

• doping an impurity for forming a channel stop to a region where the isolation of the semiconductor substrate is to be formed;
• forming an insulating film to be the isolation at the isolation forming region on the semiconductor substrate;
• doping an impurity of the first conductive type to that of the semiconductor substrate to a density of threshold adjusting level to the element forming region;
• forming the gate electrode of the FET on the element forming region;
• doping lightly an impurity of a second conductive type to a region at both sides of the gate electrode of the element forming region;
• forming a side wall spacer on each side of the gate electrode of the FET;
• and
• forming the heavily doped source region and the heavily doped drain region by heavily doping an impurity of the second conductive type on the side of the side wall spacer of the element forming region after the formation of the side wall spacer of the gate electrode,
• wherein the step of forming the heavily doped source region and the heavily doped drain region is conducted so that a region to which a high voltage is applied of the heavily doped source region and the heavily doped drain region is formed a set-distance inside of the element forming region from the end part of the isolation, separating the drain region and the source region from the channel stop region.

A semiconductor device having a FET of the buried channel region type in an element forming region of a semiconductor substrate to which an impurity of a first conductive type is doped, comprising:

• a gate electrode of the FET which is formed on the semiconductor substrate;
• a source region and a drain region of the FET, doped with an impurity of a second conductive type, respectively provided under both sides of the gate electrode in the semiconductor substrate;
• a main channel region of the FET, comparatively lightly doped with an impurity of the opposite conductive type as the substrate, provided under the gate electrode between the source region and the drain region in the semiconductor;
• an isolation formed around the element forming region on the semiconductor substrate so as to isolate the element forming region from other regions;
• a channel stop region, comparatively heavily doped with an impurity of the first conductive type, formed under the isolation in the semiconductor substrate;
• a first buffer region, doped with an impurity of the same conductive type and the same density as that of the main channel region, formed between the channel stop region and at least a region to which a high voltage is applied of the drain region and source region in the semiconductor substrate;
• and
• a second buffer region, doped with an impurity of the same conductive type and the same density as the main channel, formed under the gate electrode in the semiconductor substrate between the isolation and the main channel region.