US 4,998,021 AGranted

Method of detecting an end point of surface treatment

AssigneeDainippon Screen Mfg. Co., Ltd.

InventorMasahiro Mimasaka

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Abstract

A method of detecting an end point of surface treatment of a wafer includes the steps of: projecting coherent light onto an upper surface of the wafer provided with a layer to be treated; receiving superposed light caused by interference of light reflected on a surface of the layer to be treated and on the other surface thereof and converting it to a photoelectric signal; sampling the photoelectric signal; detecting a first point where a variation range caused by the interference in the sampled data becomes smaller than a predetermined value; detecting a second point where an extreme value of the variation of the photoelectric signal caused by the interference occurs prior to the first point; and determining the end point of treatment by prescribed calculation using the second point as a reference point. The detection of the first point may be incorrect depending on the detection conditions. However, the second point prior to the first point is detected in a relatively stable manner irrespective of the detecting conditions. Thus, since the end point of treatment is determined by the prescribed calculation using the second point as a reference point, the end point of treatment is detected correctly and with good repeatability.

Claims15

Dependent claims

A method of accurately determining an end point of treatment, comprising the steps of:

(A) holding a wafer, said wafer having a main surface and a layer to be treated, said lever being formed in advance on said main surface;
(B) supplying treatment solution on said layer and thereby decreasing the thickness of said layer;
(C) projecting coherent light on said lever, a part of said coherent light being reflected on a surface of said layer, another part of said coherent light being reflected on said main surface, and said parts of said coherent light interfering with each other to form superposed light, the intensity of said superposed light having a variation which is cyclical between extreme values as the thickness of said lever decreases and which then becomes smaller than a certain value;
(D) receiving said superposed light and outputting a photoelectric signal, the photoelectric signal being representative of the intensity of said superposed light such that said photoelectric signal has a variation which is cyclical between extreme values and which then becomes smaller than a predetermined value;
(E) sampling said photoelectric signal and thereby obtaining sampled data;
(F) detecting a first point of time at which the variation of said photoelectric signal becomes smaller than said predetermined value;
(G) thereafter determining a second point of time corresponding to the occurrence of the last of said extreme values of said photoelectric signal;
and
(H) determining said end point of treatment by prescribed calculation using said second point as a reference point.

6 more elements

Dependencies are inferred from the claim text.