Semiconductor memory device and manufacturing method thereof

A method of manufacturing a semiconductor memory device, comprising:

• forming a transistor on a semiconductor substrate;
• forming a contact plug connected to a diffusion layer of the transistor;
• depositing a material of a lower electrode on the contact plug;
• forming a magnetic tunnel junction element on a material of the lower electrode;
• depositing a material of a first protection film on a top surface and a side surface of the magnetic tunnel junction element;
• polishing a material of the first protection film until the top surface of the magnetic tunnel junction element is exposed;
• depositing a material of an upper electrode on the magnetic tunnel junction element and the first protection film;
• forming the upper electrode and the first protection film by processing a material of the upper electrode and a material of the first protection film;
• attaching a material of the lower electrode to side surfaces of the upper electrode and the first protection film while removing the material of the lower electrode by using the upper electrode and the first protection film as a mask;
• and
• forming a second protection film by oxidizing the material of the lower electrode attached on the side surfaces of the upper electrode and the first protection film.