Method and apparatus for pattern inspection
Because a mirror electron imaging type inspection apparatus for obtaining an inspection object image with mirror electrons has been difficult to optimize inspection conditions, since the image forming principles of the apparatus are different from those of conventional SEM type inspection apparatuses. In order to solve the above conventional problem, the present invention has made it possible for the user to examine such conditions as inspection speed, inspection sensitivity, etc. intuitively by displaying the relationship among the values of inspection speed S, inspection object digital signal image pixel size D, inspection object image size L, and image signal acquisition cycle P with use of a time delay integration method as a graph on an operation screen. The user can thus determine a set of values of a pixel size, an inspection image width, and a TDI sensor operation cycle easily with reference to the displayed graph.
1. A wafer defect inspection method, comprising the steps of:
radiating an electron beam on a certain area of a wafer;
reflecting radiated electrons by applying a negative voltage to said wafer just before said radiated electrons reach a surface of said wafer;
forming an image of the reflected electrons;
moving said wafer at a certain speed with respect to said radiated electron beam;
obtaining a digital image with a time delay integration data acquisition synchronously with a moving speed of said wafer; and
extracting a defect of said wafer using an obtained image and displaying a position and an image of said defect,
wherein said method further includes a step of displaying on an operation screen a relationship among the values of S, D, L, and P when L is defined as a length in a direction perpendicular to a moving direction of said wafer of which image is being obtained in a range of an inspection object image in the region on which said electron beam is radiated, S is defined as an area of said wafer to be inspected per unit time, D is defined as a size on said wafer, corresponding to a unit pixel of said obtained digital image, and P is defined as an image signal acquisition frequency in said time delay integration formula, as well as a step of adjusting an electron optical system and a wafer moving speed on the basis of user determined S, D, L, and P values,
wherein a graph for S=D×L×P is displayed with respect to a plurality of L values and P values respectively by assuming the horizontal axis as D and the vertical axis as S, and
wherein said horizontal axis of said graph is displayed as a defect sensitivity obtained by multiplying said D value by a constant less than 1.
2. The method according to claim 1 , wherein the L value is 200 μm or under.
3. The method according to claim 1 , wherein the D value is 250 nm or under.
4. The method according to claim 1 , wherein a condition for operating an electron lens is determined to realize user determined values of D and L with reference to a numerical table that holds said condition for operating said electron lens corresponding to each of said D and L values beforehand.
5. The method according to claim 1 , wherein said constant is ⅓ or under.
6. The method according to claim 1 , wherein an Si wafer marked with an uneven pattern is used when said user selects said constant, thereby measuring beforehand a potential of said Si wafer and a focal point of an objective lens, as well as a ratio between the size of said marked pattern and the size of a mirror electron image so that said measurement results are set in said numerical table, then a wafer surface potential with respect to said constant is related to an objective lens focal condition according to said results in said numerical table.
7. A defect inspection apparatus, comprising:
means for radiating an electron beam on a certain area of a wafer;
means for reflecting radiated electrons by applying a negative voltage to said wafer just before said electrons reach a surface of said wafer;
means for forming an image of the reflected electrons;
means for moving said wafer at a certain speed with respect to said radiated electron beam;
means for obtaining a digital image with a time delay integration formula synchronously with a moving speed of said wafer; and
means for extracting a defect of said wafer using an obtained image and displaying a position and an image of said defect,
wherein said method further includes means for displaying a relationship among values of S, D, L, and P when L is defined as a length in a direction perpendicular to a moving direction of said wafer of which image is being obtained in a range of an inspection image in the region on which said electron beam is radiated, S is defined as an area of said wafer to be inspected per unit time, D is defined as a size on said wafer, corresponding to a unit pixel of said obtained digital image, and P is defined as an image signal acquisition frequency in said time delay integration formula, as well as means for adjusting an electron optical system and a wafer moving speed on the basis of user determined values of S, D, L, and P,
wherein said apparatus further includes means for displaying an graph for S=D×L×P with respect to a plurality of values of L and P respectively by assuming the horizontal axis as D and the vertical axis as S, and
wherein said apparatus further includes means for displaying the horizontal axis of said graph as a defect sensitivity obtained by multiplying a D value by a constant less than 1.
8. The apparatus according to claim 7 , wherein the L value is selected within 200 microns or under.
9. The method according to claim 7 , wherein the D value is displayed as 250 nm or under.
10. The apparatus according to claim 7 , wherein said apparatus further includes means for holding a numerical table in which a condition for operating an electron lens corresponding to each of D and L values is set beforehand and means for determining a condition for operating said electron lens to realize user determined values of D and L with reference to said numerical table.