Test structure for charged particle beam inspection and method for defect determination using the same
A test structure and method thereof for determining a defect in a sample of semiconductor device includes at least one transistor rendered grounded. The grounded transistor is preferably located at at least one end of a test pattern designed to be included in the sample. When the test structure is inspected by charged particle beam inspection, the voltage contrast (VC) of the transistors in the test pattern including the grounded transistor is observed for determination of the presence of defect in the sample.
1. A method for determining a sub-threshold leakage defect in a sample of semiconductor device, comprising:
providing said sample with at least one test row of transistors, wherein at least one transistor in each said test row of transistor is rendered grounded;
obtaining a charged particle microscopic image of said sample; and
determining said sub-threshold leakage defect in said sample by monitoring the voltage contrast (VC) level of said test rows of transistors from said charged particle microscopic image.
2. The method of claim 1 , wherein if a predefined number of consecutive transistors in any said test row of transistors meet a predefined voltage contrast level, it is determined that a sub-threshold leakage defect exists in said sample.
3. The method of claim 2 , wherein said predefined voltage contrast level comprises the bright voltage contrast (BVC).
4. The method of claim 1 , wherein said grounded transistor is rendered grounded by allowing electrical conduction between a doped region of said grounded transistor and a substrate.
5. The method of claim 4 , wherein said allowing electrical conduction between said doped region and said substrate is achieved by adjusting the coverage area of an ion implantation mask for said doped region.
6. The method of claim 1 , wherein said sub-threshold leakage defect comprises an electrical leakage between the source/drain regions of a transistor.
7. The method of claim 1 , further comprising providing at least one normal row of transistors, all transistors in said normal row of transistors having source and drain regions with a dopant type opposite to that of said substrate, wherein said sub-threshold leakage defect is determined by comparing the voltage contrast (VC) level of said test and normal rows of transistors from said charged particle microscopic image.
8. The method of claim 7 , wherein said source and drain regions have an n-type dopant and said substrate has a p-type dopant.
9. The method of claim 1 , wherein said semiconductor device comprises static random access memory (SRAM).
10. A test structure for determining a sub-threshold leakage defect of a semiconductor device, comprising:
at least one test row of transistors, at least one transistor in each said test row of transistors being rendered grounded,
wherein said sub-threshold leakage defect is determined by monitoring the voltage contrast (VC) level of said test rows of transistors from a charged particle microscopic image of said sample.
11. The test structure of claim 10 , wherein said grounded transistor is located at the end of said test row of transistors.
12. The test structure of claim 10 , wherein said grounded transistor is rendered grounded by allowing electrical conduction between a doped region of said grounded transistor and a substrate.
13. The test structure of claim 12 , wherein said allowing electrical conduction between said doped region and said substrate is achieved by adjusting the coverage area of an ion implantation mask for said doped region.
14. The test structure of claim 10 , wherein at least a portion of the transistor gates in said test rows of transistors are virtually grounded by electrical connection to a capacitor of high volume capacitance.
15. The test structure of claim 14 , wherein at least a portion of the transistor gates in said test rows of transistors are virtually grounded by electrical connection to a doped region having the same type of dopant as a substrate.
16. The test structure of claim 15 , wherein said doped regions have a p-type dopant and said substrate has a p-type dopant.
17. The test structure of claim 10 , further comprising providing at least one normal row of transistors, all transistors in said normal row of transistors having source and drain regions with a dopant type opposite to that of said substrate, wherein said sub-threshold leakage defect is determined by comparing the voltage contrast (VC) level of said test and normal rows of transistors from said charged particle microscopic image.
18. The test structure of claim 17 , wherein said doped regions have an n-type dopant and said substrate has a p-type dopant.
19. The test structure of claim 17 , wherein the transistors in said test and normal rows of transistors are NMOSFET transistors.
20. The test structure of claim 10 , wherein said sub-threshold leakage defect comprises an electrical leakage between the source/drain regions of a transistor.