The present invention discloses a method for making alignment mark, comprising: 1)
etching an alignment mark on the back side of a
silicon chip; and 2) deposing a layer of
oxide-film on the alignmentmark. The invention also discloses an alignment mark made by the method, which is arranged on the back side of a
silicon chip. In addition, the invention further discloses a detection device for alignment mark, which comprises a
light source, the light emitted by the
light source passes through a half transparent and half reflecting mirror, is focused by a first convex lens, passes through a holeon a carrier corresponding to the alignment mark on the back side of a
silicon chip, is focused to the alignment mark on the back side of the
silicon chip, and is reflected by the alignment mark,
signal light sent by the alignment mark passes through the half transparent and half reflecting mirror, and is focused by a second convex lens, and finally an imaged is formed on the plane of the detection device. An alignment mark made by the method is on the back side of a
silicon chip, occupying no use area of the front side of the
silicon chip, and the method for detecting an alignment mark can beused for detecting the alignment mark.