JPS63148629A - Method of forming position detection mark - Google Patents

Abstract

PURPOSE:To improve the accuracy of position detection by a method wherein apertures are drilled in an insulating film covering the surface of a semiconductor substrate so as to correspond to a pattern for a semiconductor element and a metal layer which is different from ohmic metal layers is applied so as to cover one of the apertures to form a mark. CONSTITUTION:Apertures 5 which are drilled in an insulating film 3 covering the surface of a semiconductor substrate 1 are covered with ohmic metal layers 6 and the metal layers 6 are contacted with the semiconductor substrate 1 in the apertures 5. A mark pattern composed of one of the apertures 5 formed in the insulating film 3 is not deformed even if it is subjected to a heat treatment at about 450 deg.C which is necessary to ensure the ohmic contacts between the ohmic metals 6 and the semiconductor substrate 1. Further, the mark-shape aperture 5 in the insulating film and the surroundings of the aperture 5 are covered with a metal layer 10 which is different from the ohmic metal layer 6. By the contact between the metal layer 10 and the semiconductor substrate 1, charging of the insulating film 3 can be avoided and the lowering of alignment accuracy can be avoided.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a method for forming a position detection mark, and in particular to a method for forming a position detection mark, particularly for position detection used when drawing using a charged particle beam such as an electron beam. It is suitable for marks.

(Prior Art) Recent semiconductor devices have become highly integrated and highly functional, even in integrated circuits such as VLSIs and individual semiconductor devices such as high-frequency semiconductor devices.

Therefore, many attempts have been made to miniaturize the dimensions of the elements. The direct writing method, which uses an electron beam as a link, is more advantageous in forming fine patterns than photolithography, which uses a photomask and ultraviolet light exposure, and has already been widely adopted due to its high alignment accuracy. is the current situation.

By the way, in order to form a pattern by electron beam writing on the electron beam sensitive resist covering the surface of a semiconductor substrate, it is necessary to align the drawn pattern with the pattern already created on the semiconductor substrate. A common method is to provide a position detection mark (hereinafter abbreviated as "mark") on the image, and scan this mark with an electron beam to detect the position immediately before drawing.

This mark is known to have many shapes, with a convex or concave cross-sectional shape, an L-shape or a cross shape as the top surface, and the material is difficult to charge due to electron beam irradiation, so it is reliable. Metals are often used to obtain accurate mark detection signals.

The mark is formed before this electron beam lithography process, and is made of the same material as the reference electrode, and the surface of the mark and its surroundings are made as flat as possible to improve position detection accuracy. be considerate.

Now, to briefly explain the mark formation process using FIG. 0 forming
Next, after depositing the electrode metal on this pattern, the photoresist layer 21 is dissolved and the excess electrode metal is removed, and the openings are filled with the metal layer and the electrodes 23 and Mark 24 is installed.

(Problems to be Solved by the Invention) When the above-mentioned mark formation method is applied to a magnetized gallium field effect transistor (hereinafter abbreviated as GaAsFET) in which the positional relationship of the gate electrode with respect to the source and drain electrodes greatly contributes to the characteristics, the following will occur. A problem arises.

For GaAsFETs, Si is introduced from the surface of the GaAs semiconductor substrate toward the inside to provide an active layer, and source and drain electrodes that serve as a reference are formed on 2N at the same time as marks, and the gate pattern is drawn using an electron beam. Then, the position of this mark is detected and alignment is performed.

The source electrode, drain electrode, and mark are formed of the same material, AuGe/Ni, as described above.

Further, in order to ensure ohmic contact between the source and drain electrodes, heat treatment is performed at 450° C. in a hydrogen atmosphere before forming the gate pattern. However, due to this heat treatment, Mark 2
It has been found that the upper surface and the cross section of the sensor 4 are deformed as shown in FIGS.

There is also a method of forming the mark with an insulating film in order to prevent the mark from deforming, but there is a problem in that when drawing the gate pattern with an electron beam, the insulating film is charged and the position detection accuracy is reduced.

It is an object of the present invention to provide a novel method for forming position detection marks that eliminates this difficulty.

[Structure of the invention]

(Means for solving the problem) In order to achieve this object, in the present invention, holes are formed in the insulating film covering the surface of the semiconductor substrate in accordance with the semiconductor element pattern, and ohmic metal is used to cover the holes. The mark is formed by depositing a metal layer different from the mark.

(Function) The mark pattern formed by the openings in the insulating film is approximately
The present invention was completed based on the knowledge that no deformation occurs even after heat treatment at 50°C, and furthermore, the mark pattern-shaped insulating film opening and the vicinity of the opening are made of a metal different from the ohmic metal. Since it is covered with a layer, the connection between the metal layer and the semiconductor substrate makes it possible to prevent the insulating film from being charged, thereby preventing a decrease in alignment accuracy.

(Example) Embodiments according to the present invention will be described in detail with reference to FIGS.

This example shows an example in which the method of the present invention is applied to a GaAs FET. After introducing Si or the like into the inside of a GaAs semiconductor substrate 1 from the surface thereof to form an n-type active layer 2,
ooo After coating the silicon oxide film 3, photoresist layer 4
The cross-sectional structure shown in FIG. Next, holes are simultaneously formed at the positions where the source electrode, drain electrode, and mark of the FET are to be formed by known photolithography, and the silicon oxide film 3 is subsequently exposed to the holes.
is etched through the openings to form openings 5 . . . to expose the active layer 2 and the GaAs semiconductor substrate. (
(Figure 1) After depositing 2,000 layers of AuGe and 500 layers of Ni as the ohmic metal 6 necessary for the FET in this order, dissolve this photoresist layer with acetone and remove the areas other than the openings. The ohmic metal layer adhering to the photoresist layer is removed, and the source electrode 7 and drain electrode 8 necessary for the FET are provided as shown in FIG. Ru.

Next, the photoresist layer 9 is coated on the entire surface again, and then the photoresist layer 9 is coated by the photolithography process as described above.
A hole is opened at the position where the mark is to be formed, and the exposed ohmic metal 6 is dissolved away to create a new hole 11 with the cross-sectional structure shown in FIG. 12. The thickness will continue to be around 1,000 people.
After depositing 7i1O by vapor deposition, a photoresist layer 9 is formed.
By dissolving the Ti layer, the Ti layer deposited on the second layer is removed, and as shown in Figure 1E, the openings in the silicon oxide film are filled with Ti.
A mark with a concave cross-sectional structure covered with layers is completed.

In the above embodiment, silicon oxide is used as the insulating film 3, but silicon nitride, aluminum nitride, etc. can also be used.

To complete a GaAsFET device, as mentioned above, approximately 45
Of course, steps such as heat treatment and gate electrode formation are performed to ensure ohmic contact between the ohmic metal layer, the source electrode 7, and the drain electrode in a hydrogen atmosphere maintained at 0°C.

〔Effect of the invention〕

As described above, in the method for forming a position detection mark according to the present invention, the mark has a structure in which an opening formed in an insulating film covering the surface of a semiconductor substrate is covered with a metal layer, and this metal layer is connected to the semiconductor substrate at the opening. Since they are connected, charging of the insulating film caused by electron beam irradiation can be prevented. Therefore, the position detection accuracy is improved, which in turn brings about an effect on mass production.

[Brief explanation of the drawing]

FIGS. 1A to 1E are cross-sectional views showing the process of the present invention, and FIG. 2I is a cross-sectional view showing the conventional process. DESCRIPTION OF SYMBOLS 1... Semiconductor substrate, 3... Insulating film 4... Photoresist layer, 5... Opening 6... Ohmic,
9... Photoresist layer 10... Ti layer

Claims (1)

[Claims] A step of forming an insulating film on the surface of the semiconductor substrate, a step of coating the insulating film with a photoresist layer, and a step of opening holes in the photoresist layer corresponding to the positions where detection marks and elements are to be formed on the semiconductor substrate. a step of forming a pattern by removing the insulating film exposed in the opening; a step of depositing an ohmic metal on the photoresist pattern; a step of dissolving the photoresist layer; and a step of forming a mark at a planned position. A method for forming a position detection mark, comprising the steps of: removing the ohmic metal from the insulating film pattern; and depositing another metal to cover the insulating film opening.