JP2005340321A - Method of forming alignment mark - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of forming an alignment mark with little contamination. <P>SOLUTION: In forming the alignment mark, laser light is irradiated on a metal film formed on a silicon substrate to form a metal silicide, which is to be used as the alignment mark. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for forming an alignment mark, and more particularly to a method for forming an alignment mark with high accuracy and low contamination.

In recent years, with the miniaturization of semiconductor integrated circuits, the accuracy of overlaying circuit patterns required in a lithography process has become increasingly severe.
Conventionally, in a lithography process, a projection exposure apparatus (stepper) that divides an exposure area of a wafer into a number of shot areas and exposes a mask pattern on each shot area by a step-and-repeat method. Was used. On the other hand, recently, in order to expose a reticle pattern with a larger area without increasing the diameter of the projection optical system, each shot area on the wafer is positioned at the scanning start position by the stepping method, and then projected. There is also a so-called step-and-scan type projection exposure apparatus that performs exposure while scanning the reticle and wafer shot areas relatively synchronously with respect to the optical system.
In such a projection exposure apparatus, for example, an alignment mark for alignment provided as an uneven pattern in each shot area of the wafer is optically detected, and the position of the wafer stage is controlled.

FIG. 5 is a schematic diagram showing the structure of the alignment mark.
FIG. 5A shows a concave alignment mark provided on the silicon substrate 501. The mark is constituted by a recess 502 formed on the silicon substrate 501. This alignment mark is obtained by forming a resist pattern having a desired mark shape on a silicon substrate by exposure and etching the substrate using the resist pattern as a mask. As the etching, dry etching such as RIE (parallel plate type reactive ion etching) is employed.

  FIG. 5B shows a convex alignment mark provided on the silicon substrate 503. The mark is made of heavy metal 504 such as tungsten (W) or gold (Au) deposited on a silicon substrate 503.

  However, in a dry etching process such as RIE, adhesion of foreign matter on the silicon substrate often becomes a problem, which may affect the reliability of the alignment mark and further the reliability of the semiconductor device itself. Further, the alignment mark of FIG. 5B has a problem that impurities contained in the heavy metal are scattered and the substrate and the process apparatus are contaminated.

  The present invention has been made on the basis of recognition of such problems, and an object thereof is to provide a method for forming an alignment mark with less contamination.

  According to the method for forming an alignment mark of the present invention, a metal film formed on a silicon substrate is irradiated with laser light to form a metal silicide, which is used as an alignment mark.

That is, according to one aspect of the present invention,
Forming a metal film on the silicon layer;
A step of forming a metal silicon compound layer by irradiating a laser beam to a position mark formation scheduled region on the metal film;
A method for forming an alignment mark is provided.

  Here, the method may further include a step of removing a metal layer other than the metal silicon compound layer on the silicon layer.

  Further, the metal film may be irradiated with the laser beam in the form of interference fringes using a diffraction grating.

  Further, as the material of the metal film, titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), cobalt (Co), nickel (Ni), zirconium (Zr), zinc (Zn), niobium (Nb), ruthenium (Ru), rhodium (Rh), palladium (Pd), hafnium (Hf), tantalum (Ta), tungsten (W), osmium (Os), iridium (Ir), and platinum (Pt) Any selected from the group can be used.

  According to the method for forming an alignment mark of the present invention, a dry etching process is not required for processing the alignment mark, so that a method for forming an alignment mark with little contamination can be provided. In addition, since a desired mark shape can be obtained according to the cross-sectional shape of the laser beam, a highly accurate alignment mark can be formed relatively easily.

  Embodiments of the present invention will be described below.

FIG. 1 is a process diagram showing a method of forming an alignment mark according to the first embodiment of the present invention.
First, as shown in FIG. 1A, a molybdenum (Mo) film 102 is formed on a silicon substrate 101 by sputtering, MBE (molecular beam epitaxy), or the like.
Next, as shown in FIG. 1B, the alignment mark formation scheduled region 103 is irradiated with laser light 104.
As shown in FIG. 1C, the region irradiated with the laser light is heated, and molybdenum (Mo) and silicon combine to form molybdenum silicide (Mo _x Si _Y ) 105.
Through the above steps, a concave alignment mark is formed.

In the step of FIG. 1B, the formation of molybdenum silicide (Mo _X Si _Y ) can be controlled by adjusting the energy density of laser light, irradiation time, spot diameter, and laser wavelength. That is, it is possible to arbitrarily adjust the film thickness, line width, and dent amount on the substrate of the alignment mark.
Further, since dry etching is not performed in the processing step of the alignment mark, there is no need to worry about contamination of the substrate.

  FIG. 2 is a process diagram showing a method of forming an alignment mark according to the second embodiment of the present invention. 2A to 2C are the same as FIGS. 1A to 1C described above, and FIG. 2D is added as a new process.

In the step of FIG. 2D, etching is performed using an etching solution in which sulfuric acid (H ₂ SO ₄ ), nitric acid (HNO ₃ ), and water (H ₂ O) are mixed at a mixing ratio of 1: 1: 3. Thereby, only metal molybdenum (Mo) can be selectively removed, and only molybdenum silicide (Mo _x Si _Y ) 202 is formed on the silicon substrate 201. Through the above steps, a convex alignment mark is formed. Since the etching at this time is wet etching, the mark shape does not deteriorate as when dry etching is used.

  By adding the step of removing the metal molybdenum (Mo) film, the influence of contamination by the metal molybdenum (Mo) in the subsequent process can be eliminated. Further, compared with the alignment mark shown in FIG. 1C, the alignment mark shown in FIG. 2D has advantages such as improved detection sensitivity.

  Which alignment mark is used may be determined according to the application. For example, when used as an alignment mark for a mask for charged particle beam exposure, there is no concern about contamination, so the molybdenum film does not have to be removed.

FIG. 3 is a schematic view showing only element parts in the exposure apparatus for forming the alignment mark according to the embodiment of the present invention.
The laser light 302 emitted from the laser light source 301 is irradiated on the wafer W fixed on the stage 305 through the illumination optical system 303 and the projection optical system 304. Broadly speaking, the laser beam 302 is processed into a desired shape in the illumination optical system 303 and exposed to a desired position on the wafer by the projection optical system 304. That is, the mark shape can be adjusted by operating the illumination optical system 303.

For example, a laser beam can be processed into an interference fringe pattern using a diffraction grating and exposed to form a more accurate alignment mark.
FIG. 4 is a top view showing the shape of the alignment mark processed using the interference fringe laser beam. The alignment mark has a two-dimensional equally spaced pattern shape, and the accuracy of alignment using this is improved. The two-dimensional pattern intervals x and y can be optically adjusted by the parameters of the diffraction grating.
As described above, by using the diffraction grating, it is possible to irradiate the laser at the equally spaced positions with high accuracy. By applying this laser beam to the method for forming an alignment mark of the present invention, it is possible to form an alignment mark with high accuracy without using an expensive positioning mechanism.

  In addition, the formation method of the alignment mark of this invention is not limited to embodiment described so far. For example, as a metal silicide material, titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), cobalt (Co), nickel (Ni), zirconium (Zr), zinc (Zn), niobium ( Metals such as Nb), ruthenium (Ru), rhodium (Rh), palladium (Pd), hafnium (Hf), tantalum (Ta), tungsten (W), osmium (Os), iridium (Ir), platinum (Pt) It is also possible to use silicide.

It is process drawing showing the formation method of the alignment mark concerning the 1st Embodiment of this invention. It is process drawing showing the formation method of the alignment mark concerning the 2nd Embodiment of this invention. It is the schematic diagram showing only the element part in the exposure apparatus for forming the alignment mark concerning embodiment of this invention. It is a top view showing the shape of the alignment mark processed using the interference fringe laser beam. It is a schematic diagram showing the structure of the alignment mark.

Explanation of symbols

101, 201, 501 and 503 Silicon substrate 102 Molybdenum film 103 Mark formation scheduled areas 104 and 302 Laser light 105 and 202 Molybdenum silicide 301 Laser light source 303 Illumination optical system 304 Projection optical system 305 Stage 501 Silicon substrate 502 Indentation 504 Heavy metal W Wafer

Claims (4)

Forming a metal film on the silicon layer;
A step of forming a metal silicon compound layer by irradiating a laser beam to a position mark formation scheduled region on the metal film;
A method of forming an alignment mark, comprising:   2. The method for forming an alignment mark according to claim 1, further comprising a step of removing a metal layer other than the metal silicon compound layer on the silicon layer.   3. The method of forming an alignment mark according to claim 1, wherein the laser beam is irradiated onto the metal film in an interference fringe pattern using a diffraction grating. As the material of the metal film, titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), cobalt (Co), nickel (Ni), zirconium (Zr), zinc (Zn), niobium (Nb) ), Ruthenium (Ru), rhodium (Rh), palladium (Pd), hafnium (Hf), tantalum (Ta), tungsten (W), osmium (Os), iridium (Ir) and platinum (Pt). 4. The method of forming an alignment mark according to claim 1, wherein any one of the selected ones is used.

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