Bipolar transistor with diffused layer between deep trench sidewall and collector diffused layer

A semiconductor device comprising:

• a semiconductor substrate of a first conductivity type;
• a first diffusion layer formed in the semiconductor substrate and doped with a dopant of a second conductivity type that is a conductivity type opposite to the first conductivity type;
• a first trench and a second trench which are formed in the semiconductor substrate to surround the first diffusion layer and which form an isolation region;
• a second diffusion layer formed below the first trench and doped with a dopant of the first conductivity type;
• and
• a third diffusion layer formed between a sidewall of the first trench and the first diffusion layer, and doped with a dopant of the second conductivity type,
• wherein the first trench is formed immediately under the second trench to connect to the second trench;
• the third diffusion layer is spaced apart from a surface of the semiconductor substrate by the second trench;
• a concentration of the dopant in the third diffusion layer is higher than a concentration of the dopant in the first diffusion layer, and
• in the third diffusion layer, a concentration of the dopant in a region in a vicinity of the first diffusion layer is higher than a concentration of the dopant in a region in a vicinity of the sidewall of the first trench.