CN102097303B - Photolithographic process for thick metal - Google Patents

Abstract

The invention relates to a photolithographic process for a thick metal. The photolithographic process comprises the following steps of: a, uniformly depositing a metal material on a substrate for many times till the thickness of a metal layer formed on the substrate is 3.9 to 4.1 microns; b, coating photoresist on the metal layer, etching a plurality of mark windows on the photoresist, and exposing the metal layer at the bottom of the mark windows; c, performing metallic corrosion on the metal layer at the bottom of the mark windows, and exposing alignment marks shaded by the metal layer; d, removing the photoresist from the metal layer; e, recoating the photoresist on the metal layer, wherein the photoresist is coated on the metal layer where the alignment marks are exposed; and f, selectively masking and etching the photoresist, performing photolithography on the metal layer by using the exposed alignment marks as alignment coordinates, and obtaining required metal graphs on the metal layer. The photolithographic process can reduce the surface roughness and reduce the interference of surface grains to alignment signals, and has high alignment precision, safety and reliability.

Description

A photolithography process for thick metals

technical field

The invention relates to a photolithography process, in particular to a photolithography process for thick metals, specifically a process for photoetching metals with a thickness of 4 μm, and belongs to the technical field of integrated circuit manufacturing.

Background technique

In power integrated circuits, in order to ensure that the device can pass a large current, the thickness of the metal layer of the circuit is often many times thicker than that of the conventional CMOS circuit. Generally, the thickness of the AL-SI-Cu alloy is 4um. The metal deposition of this thickness forms The metal grains of the metal are large, and the roughness of the metal surface increases sharply. These surface characteristics have a great impact on the alignment of metal lithography. It is difficult to achieve alignment of thick metal lithography by conventional alignment methods.

The conventional alignment method is to use the NIKON lithography machine to adopt the FIA (Field Image Alignment) alignment method or the manual alignment method to barely align, so that the alignment accuracy is difficult to control, and the circuit with high alignment requirements cannot meet the process at all. Require. FIA alignment is an alignment method specially designed by NIKON lithography machine for the film layer with rough surface, but when the grain on the metal surface is larger than or equal to the mark size, the FIA alignment method cannot achieve accurate alignment.

The process steps of conventional metal lithography are detailed as follows:

Metal deposition: complete 4um metal deposition at one time, as shown in Figure 1;

Metal lithography: adopt conventional alignment method to achieve barely alignment, and the overlay error is relatively large (one version is greater than 0.3um); metal etching and glue removal: due to the large grain size, metal etching is difficult, and a large number of Residues may cause device leakage.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies in the prior art and provide a photolithography process for thick metals, which can reduce surface roughness, reduce the interference of surface grains on alignment signals, and have high alignment accuracy and safety. reliable.

According to the technical solution provided by the present invention, the photolithography process for thick metal includes the following steps:

a. Deposit metal materials uniformly on the substrate multiple times, so that the thickness of the metal layer formed on the substrate is 3.9 μm to 4.1 μm; b. Coat photoresist on the above metal layer, selectively mask and engrave Etching the photoresist, etching a plurality of marking windows on the photoresist, exposing the metal layer at the bottom of the marking window; c, carrying out metal corrosion to the metal layer at the bottom of the marking window, removing the corresponding The metal layer exposes the alignment mark blocked by the metal layer; d, removes the photoresist on the metal layer; e, coats the photoresist again on the above metal layer, and the photoresist is coated on the exposed alignment mark On the outer metal layer; f, selectively mask and etch the photoresist, use the above-mentioned exposed alignment mark as the alignment coordinate, carry out photolithography to the metal layer, and obtain the required metal pattern on the metal layer .

The substrate includes silicon. The metal material is Al-Si-Cu alloy. In the step a, the metal material is uniformly deposited on the substrate three times. The metal material is deposited on the substrate by PVD sputtering.

The thickness of the photoresist in step b and step d is 8 μm. In the step b, 5 marking windows are obtained on the metal layer.

Advantages of the present invention: in order to avoid depositing a metal layer on the substrate to form larger crystal grains, the metal material is uniformly deposited on the substrate in 3 times, and by selectively masking and etching photoresist, on the metal layer Form a plurality of marking windows, and after corroding the metal layer at the bottom of the marking window, the alignment mark blocked by the metal layer can be exposed, and the alignment mark can be used as the alignment coordinate to etch the desired pattern on the metal layer as the alignment , realizes precise alignment of metal photolithography, improves registration accuracy, reduces grain size after metal deposition, reduces metal surface roughness, and is safe and reliable.

Description of drawings

FIG. 1 is a schematic diagram of a structure after depositing a metal layer on an existing substrate.

Fig. 2 is a schematic diagram of the structure after depositing a metal layer on the substrate of the present invention.

Figure 3-1 to Figure 3-3 are schematic diagrams of specific process steps of the photolithography process of the present invention, wherein:

Figure 3-1 is a schematic diagram of the structure after the marked window is obtained;

Figure 3-2 is a schematic diagram of the structure after etching the corresponding metal layer at the bottom of the marking window;

Figure 3-3 is a schematic diagram of the structure after obtaining the desired image after photolithography of the metal layer.

FIG. 4 is a schematic structural diagram of an alignment mark being blocked by a metal layer.

FIG. 5 is a schematic diagram of the structure after corroding the metal layer and exposing the alignment marks.

Detailed ways

The present invention will be further described below in conjunction with specific drawings and embodiments.

As shown in FIGS. 1 to 5 , the present invention includes a substrate 1 , a metal layer 2 , an alignment mark 3 , a mark window 4 , a metal pattern 5 and a photoresist 6 .

In order to solve the current situation that the grains of the metal layer are large, metal etching is difficult, and a large amount of residue occurs, which may cause device leakage, the thick metal photolithography process of the present invention includes the following steps:

a. The metal material is uniformly deposited on the substrate 1 multiple times, so that the thickness of the metal layer 2 formed on the substrate 1 is 3.9 μm to 4.1 μm, as shown in FIG. 2 ;

The substrate 1 comprises silicon, and the thickness of the metal layer 2 is generally 4 μm; the metal material is a conventional Al-Si-Cu alloy; the metal material is deposited by PVD (Physical Vapor Deposition) sputtering method Above the substrate 1; in order to avoid the formation of larger crystal grains, the entire deposition process is divided into three times to complete, the entire deposition process is in a vacuum state, and the substrate 1 does not see the atmosphere; after the metal layer 2 is deposited three times, the metal The cross-sectional structure of layer 2 is significantly different from that of conventional metal layer 2;

b. Coating photoresist 6 on the metal layer 2, selectively masking and etching the photoresist 6, etching a plurality of marking windows 4 on the photoresist 6, exposing the marking windows 4 Metal layer 2 at the bottom, as shown in Figure 3-1;

The thickness of the photoresist 6 is 8 μm, and there are five marking windows 4 in this embodiment; the photoresist 6 is used as a shielding layer etched by the metal layer 2;

c. Perform metal corrosion on the metal layer 2 at the bottom of the marking window 4, remove the corresponding metal layer 2 at the bottom of the marking window 4, and expose the alignment mark 3 covered by the metal layer 2, as shown in Figure 3-2;

Because there is no photoresist 6 at the mark window 4 as protection, the metal layer 2 at the bottom of the mark window 4 can be photolithographically removed to remove the metal layer 2 at the bottom of the mark window 4; For the alignment mark 3, the subsequent etching and alignment of the metal layer 2 cannot achieve accurate positioning; when the metal layer 2 is etched, the alignment mark 3 covered by the metal layer 2 is exposed, and the subsequent alignment can use the exposed Alignment marks 3 are used as alignment coordinates to achieve precise alignment;

d, removing the photoresist 6 on the metal layer 2;

e. Coating photoresist 6 again on the above-mentioned metal layer 2, the photoresist 6 is coated on the metal layer 2 exposed outside the alignment mark 3, and the photoresist 6 is not coated on the alignment mark 3, The exposed alignment marks 3 can be used as alignment coordinates for subsequent alignment to achieve precise alignment; the thickness of the photoresist 6 is 8 μm;

f. Selectively mask and etch the photoresist 6, use the exposed alignment mark 3 as the alignment coordinates, perform photolithography on the metal layer 2, and obtain the required metal pattern 5 on the metal layer 2, As shown in Figure 3-3; photolithography is carried out on the metal layer 2 through a photolithography plate. Due to the alignment effect of the alignment mark 3, the required metal image 5 can be accurately realized on the metal layer 2 without causing damage to the device. leakage.

As shown in Figure 4 and Figure 5: the thickness of the metal layer 2 reaches 4 μm and becomes a thick metal. The metal layer 2 blocks the alignment mark 3. Due to the difference in the deposition process of the metal layer 2, subsequent etching The security of the metal pattern 5 and the device requires precise positioning of the etching of the metal layer 2 . Fig. 5 shows the structural diagram after etching the metal layer 2 at the bottom of the marking window 4, exposing the alignment mark 3 covered by the metal layer 2; When the required metal pattern is 5, it can realize the precise alignment of thick metal photolithography, and the registration accuracy can reach within 0.15 μm.

In the present invention, in order to avoid depositing the metal layer 2 on the substrate 1 to form larger crystal grains, the metal material is uniformly deposited on the substrate 1 in three times, thereby reducing the surface roughness of the metal layer 2, by selectively masking and Etching the photoresist 6, forming a plurality of marking windows 4 on the metal layer 2, after corroding the metal layer 2 at the bottom of the marking windows 4, the alignment marks 3 covered by the metal layer 2 can be exposed, through which the alignment marks 2 As the alignment coordinate, it can be used as the alignment to etch the required pattern 5 on the metal layer 2, which realizes the precise alignment of metal lithography, improves the alignment accuracy, reduces the size of the grain after metal deposition, and makes the metal surface Reduced roughness, safe and reliable.

Claims (6)

1. a photolithography process for thick metal, it is characterized in that, the photolithography process of described thick metal comprises the steps: (a) The metal material is uniformly deposited on the substrate multiple times, so that the thickness of the metal layer formed on the substrate is 3.9 μm to 4.1 μm; (b) Coating photoresist on the above metal layer, selectively masking and etching the photoresist, etching a plurality of marking windows on the photoresist, exposing the metal layer at the bottom of the marking window ; (c) Carry out metal corrosion on the metal layer at the bottom of the marking window, remove the corresponding metal layer at the bottom of the marking window, and expose the alignment mark blocked by the metal layer; (d), removing the photoresist on the metal layer; (e) Coating photoresist again on the above metal layer, the photoresist is coated on the metal layer exposed outside the alignment mark; (f), selectively masking and etching the photoresist, using the above-mentioned exposed alignment marks as alignment coordinates, performing photolithography on the metal layer, and obtaining the desired metal pattern on the metal layer; In the step (a), the metal material is uniformly deposited on the substrate three times. 2. The photolithography process for thick metals according to claim 1, wherein said substrate comprises silicon. 3. The photolithography process for thick metal according to claim 1, characterized in that: the metal material is an alloy of Al-Si-Cu. 4. The photolithography process for thick metal according to claim 1, wherein the metal material is deposited on the substrate by PVD sputtering. 5. The photolithography process for thick metal according to claim 1, characterized in that: the thickness of the photoresist in the step (b) and step (d) is 8 μm. 6. The photolithography process for thick metal according to claim 1, characterized in that: in the step (b), five marking windows are obtained on the metal layer.

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