Semiconductor device structure and methods of forming the same

A method, comprising:

• forming a first fin structure and a second fin structure from a substrate;
• depositing a first conformal layer over the first and second fin structures and between the first and second fin structures;
• depositing a second conformal layer on the first conformal layer;
• depositing a third conformal layer on the second conformal layer;
• depositing a fourth conformal layer on the third conformal layer;
• depositing a first insulating material on the fourth conformal layer between the first and second fin structures;
• performing a first anneal process, wherein the fourth conformal layer expands during the first anneal process and causes densities of the first, second, and third conformal layers to increase;
• depositing a second insulating material on the first insulating material, wherein the first and second fin structures are embedded by the second insulating material;
• removing portions of the second insulating material and the first, second, third, and fourth conformal layers to expose tops of the first and second fin structures;
• performing a second anneal process;
• and
• recessing the second insulating material and the first, second, third, and fourth conformal layers.

A semiconductor device structure, comprising:

• a first source/drain region disposed over a substrate;
• a first well portion disposed below the first source/drain region;
• a second source/drain region disposed over the substrate;
• a second well portion disposed below the second source/drain region;
• and
• an insulating structure disposed between the first and second well portions, the insulating structure comprising:
• an insulating material having a first height;
• a first conformal layer in contact with the insulating material, wherein the first conformal layer has a second height different from the first height;
• a second conformal layer in contact with the first conformal layer, wherein the second conformal layer has a third height different from the second height;
• and
• a third conformal layer in contact with the second conformal layer, wherein the third conformal layer has a fourth height different from the third height.