Wide and narrow trench formation in high aspect ratio MEMS

A method of forming a wide trench and a narrow trench on a substrate including an active layer disposed over a first sacrificial layer, the active layer having a surface, the method comprising the steps of:

• etching a first trench and a second trench through the active layer to expose a surface of the first sacrificial layer, each trench having an opening, sidewalls defining a first trench width, and substantially equal and uniform first trench widths;
• oxidizing the surface of the active layer and the sidewalls of the first trench and second trench;
• depositing a sacrificial material over the oxidized surfaces to form a second sacrificial layer;
• sealing the openings of the trenches with at least a portion of the second sacrificial layer;
• etching a hole through a portion of the second sacrificial layer and the oxidized surface to expose a portion of the active layer;
• removing material from the active layer between the first trench and the second trench to form a cavity having sidewalls;
• depositing another sacrificial material over the second sacrificial layer and the sidewalls of the cavity to form a third sacrificial layer;
• sealing the cavity with at least a portion of the third sacrificial layer;
• and
• removing the second sacrificial layer, the third sacrificial layer, and material from the oxidized surface of the active layer to form a third trench in the active layer from the first and the second trenches, the third trench having sidewalls defining a second trench width that is greater than the first trench width.

A method of forming a wide trench and a narrow trench on a substrate including an active layer disposed over a first sacrificial layer, the active layer having a surface, the method comprising the steps of:

• forming a first trench, a second trench, and a third trench in the active layer, each trench having an opening and sidewalls defining substantially equal first trench widths;
• oxidizing the surface of the active layer and the sidewalls of the first trench, the second trench, and the third trench to form a second sacrificial layer;
• depositing a sacrificial material over the second sacrificial layer to form a third sacrificial layer;
• sealing the openings of the trenches with at least a portion of the third sacrificial layer;
• etching a hole through a portion of the second sacrificial layer and the third sacrificial layer to expose a portion of the active layer;
• removing material from the active layer between the first trench and the second trench to form a cavity having sidewalls;
• depositing another sacrificial material over the third sacrificial layer and the sidewalls of the cavity to form a fourth sacrificial layer;
• sealing the cavity with at least a portion of the fourth sacrificial layer;
• and
• removing the second sacrificial layer, the third sacrificial layer, and fourth sacrificial layer to expose the third trench and form a fourth trench in the active layer from the first and the second trenches, the fourth trench having sidewalls defining a second trench width that is greater than the first trench width.