JPS63181317A - Alignment mark - Google Patents

Abstract

PURPOSE:To enable the alignment to be performed with a high precision by forming grooves in a substrate, and filling the surrounding thereof with a material of a different refractive index. CONSTITUTION:In a substrate 16, there are provided trenches 15 and buried layers 11 filling the trenches 15, and the buried layers 11 are formed so as to have a height same as that of the surrounding part of the trenches 15 and have a refractive index different from that of the substrate 16 forming the surrounding of the trenches 15. For example, it the substrate 16 is Si, the buried layers 11 are silicon dioxide SiO2 or silicon nitride Si3N4, and the refractive indices of these layers 16, 11 are 3.55 for Si, 1.47 for SiO2 and 1.8 2.0 for Si3N4. And a resist film 13 is formed on these buried layers 11 and the substrate 16, and in this condition the alignment with a photomask is performed. With this, the precision of the alignment can be maintained high.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for forming a photomask on a wafer used for alignment between a photomask and a wafer in a photolithography process of a semiconductor device manufacturing process. Regarding alignment marks.

[Conventional technology]

An example of a conventional alignment mark is shown in FIG. This alignment mark is suitable when a monochromatic light source is used for illumination, and as shown in the figure, a step forming film 1 is arranged on a substrate 6, and a resist 3 is applied thereon. As a result, a step portion 5 is also formed on the surface of the resist 3.

When scanning is performed in the direction shown by the arrow 4 and the reflected light is converted into a signal, the intensity of the signal changes at the stepped portion 5. By differentiating this, a pulse-like signal is obtained and the position of the alignment mark can be determined. We are planning to detect it.

[Problem that the invention seeks to solve]

In the above alignment mark, as shown in Fig. 3, the resist film thicknesses a and b at the step portion are different on the left and right sides, and as shown in Fig. 4, the slope angles α and β of the step portion are different on the left and right sides. As a result, the detection signal becomes as shown in Fig. 5, and the original center position S of the alignment mark is
1 and the detected position S2 by signal processing, which caused a problem that the accuracy of alignment decreased.

An object of the present invention is to provide an alignment mark that can maintain high alignment accuracy.

[Means for solving problems]

The alignment mark of the present invention includes a trench formed on a wafer surface and a buried layer that fills the trench, and the buried layer has a reflectance different from the layers surrounding the trench.

[Effect]

When an alignment mark like the one described above is used, when the wafer is scanned, the reflectance of light differs between the buried layer of the trench and the surrounding area, so if a signal based on the reflected light is used, the position of the alignment mark can be determined. can be known. Since the alignment mark of the present invention does not use a step-forming film, there is no problem that the accuracy of alignment mark detection is reduced due to differences in the thickness of the resist or differences in the slope angle of the step-forming film.

〔Example〕

FIG. 1(a) is a plan view of an alignment mark according to an embodiment of the present invention, and FIG. 1(b) is a sectional view thereof.

As shown in the figure, the alignment marks 1 to 1 are on the substrate 16.
It has a trench 15 provided in the range 1 to 15, and a buried layer 11 filling the ranges 1 to 15. Buried layer 11 is formed to have the same height as the surrounding portion of trench 15 . The buried layer 11 has a different reflectivity, for example a lower reflectivity, than the layer forming the periphery of the trench 15, for example the substrate 16.

For example, if the substrate 16 is made of silicon (S i ),
The buried layer 11 is silicon oxide (Si02) or silicon nitride (Si3N4).The refractive index of these layers is S: 3.55, Si02 1.47, and Si3N.
4 is between 1.8 and 2.0.

In the illustrated example, a resist film 13 is formed on the buried layer 11 and the substrate 16, and in this state alignments 1 to 1 with a photomask are performed.

In FIG. 1(a), when scanning is performed in the direction indicated by arrow 14, the reflectance changes along the scanning line as shown in FIG. 1(c), and the intensity of reflected light is proportional to the reflectance. Therefore, by differentiating the signal 1q caused by scanning, a signal that rises in a pulse-like manner at the interface between the buried layer 11 and its adjacent portion is obtained, as shown in FIG. 1(d).

Since the buried layer 11 is formed at the same height as the portion adjacent to it, the thickness of the resist 13 formed thereon is approximately constant. Therefore, alignment errors due to differences in film thickness do not occur as in the prior art. Further, since a step forming film is not used as in the conventional method, errors in alignment 1 to 1 due to differences in slope angles do not occur.

FIG. 6 shows another embodiment of the invention. In this embodiment, the buried material 11 is formed only in the groove and is formed as a thin film over the entire surface. If this is done, multiple interference will occur in the thin film portion 11a, and the overall reflectance will be different from that in the groove portion. Therefore, in this case as well, the groove portion can be used as an alignment mark.

FIG. 7 roughly shows another embodiment of the present invention. In this example, after filling the trench, the BPSG
An insulating film 17 as shown in FIG. Even in this case, the same effect as the embodiment shown in FIG. 6 can be obtained.

〔Effect of the invention〕

As described above, according to the present invention, a groove is formed in the substrate and the surrounding area is filled with a material having a different refractive index.
No step occurs in the alignment mark section. Therefore, alignment 1~ can be performed with high precision without causing errors in alignment 1~ due to differences in the film thickness of the resist applied to the step portion or differences in the slope angle of the step forming film as in the conventional method. can.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an embodiment of the present invention, Fig. 2 is a plan view and a sectional view showing an example of a conventional alignment mark, and Figs. 3 and 4 are alignment errors in the alignment mark of Fig. 2. 5 is a cross-sectional view showing the difference in the resist film thickness and the difference in the slope angle of the step forming film, which cause the difference in thickness. FIG. 5 is a diagram showing the signal waveform generated in the case of FIGS. 3 and 4. The figure is a sectional view showing another embodiment of the present invention. 11... Buried layer, 15... Groove, 16... Substrate. Patent applicant: Oki Electric Industry Co., Ltd. Patent attorney: Toshiaki Suzuki (Soudaisemi 15: IL (C) (ct) l: Stage I-type FX Pus 2: Mask Le 3: L Cyst 4: Sori 1J Jukata 5: Keisatsu 6: Board Conventional Ryo 2 Inment Mark Tea 2 Tomiton Strike 94 Doors Fu-Kamu 3 In 44ffi Corner O Lamb Match Sheep 4 Nagi Oki Moxibustion rA Go Sheep 5th

Claims (1)

[Claims] An alignment mark formed on a wafer and used for alignment between a photomask and a wafer in a photolithography step of a semiconductor device manufacturing process, comprising: a trench formed on a surface of the wafer; and the trench. and a buried layer filling the trench, the buried layer having a reflectance different from that of layers surrounding the trench.