CN112563246A

CN112563246A - Photoetching overlay mark and preparation method thereof

Info

Publication number: CN112563246A
Application number: CN202011500287.6A
Authority: CN
Inventors: 李国强
Original assignee: Heyuan Choicore Photoelectric Technology Co ltd
Current assignee: Heyuan Choicore Photoelectric Technology Co ltd
Priority date: 2020-12-18
Filing date: 2020-12-18
Publication date: 2021-03-26
Anticipated expiration: 2040-12-18
Also published as: CN112563246B

Abstract

The invention relates to the technical field of semiconductors, in particular to a photoetching overlay mark and a preparation method thereof. The preparation method comprises the following steps: step S1: making a marking point pattern, and transferring the marking point pattern to a chip to expose the epitaxial layer; step S2: etching the epitaxial layer; step S3: evaporating metal mark points, wherein the metal structure is CrAlTiPtAu; the CrAlTiPtAu metal structure sequentially comprises a metal Cr layer, an Al layer, a Ti layer, a Pt layer and an Au layer from bottom to top; step S4: stripping and removing the photoresist. The photoetching overlay mark prepared by the method provided by the invention has strong abrasion resistance and high resolution, is not easy to corrode, and is slightly influenced by physical bombardment of ions and corrosion of chemical solution; meanwhile, the metal marking points can reflect light, so that the metal marking points are clearer, and the alignment accuracy is improved.

Description

Photoetching overlay mark and preparation method thereof

Technical Field

The invention relates to the technical field of semiconductors, in particular to a photoetching overlay mark and a preparation method thereof.

Background

The semiconductor refers to a material having a conductivity between a conductor and an insulator at normal temperature. With the progress of science and technology and the development of society, semiconductors are widely applied to various fields such as integrated circuits, consumer electronics, communication systems, photovoltaic power generation, illumination, high-power conversion and the like. Most electronic products, such as computers, mobile phones or digital audio recorders, have a core unit closely related to a semiconductor. In the semiconductor manufacturing process, the photolithography process is used as a core technology, and the precision of the overlay will directly affect the appearance and performance of the product.

In the conventional alignment process, a power semiconductor device pattern is formed on a silicon wafer through first photoetching and etching, and an alignment mark is also formed for subsequent photoetching alignment. Starting with the second lithography, each lithography requires alignment with the previous layer. After the alignment and lithography overlay marks are formed, the alignment and lithography overlay marks are subjected to ion implantation and annealing processes. In this process, the photolithographic overlay marks are worn due to physical bombardment of ions and chemical reaction during annealing, and problems such as dimensional change of alignment marks, reduction of pattern resolution, reduction of step difference, reduction of contrast, and disappearance of the pattern of the flues can occur. Therefore, photoetching alignment photoetching overlay marks are influenced, the precision of a subsequent preparation process of the power semiconductor device is reduced, and the rejection rate and the production cost of the power semiconductor device are increased.

Therefore, further improvements to the prior art are needed.

Disclosure of Invention

In view of the above, it is desirable to provide a lithographic overlay mark and a method for making the same, which can improve the precision of the overlay.

In order to achieve the purpose, the invention adopts the following technical scheme:

a method for preparing a photoetching overlay mark comprises the following steps:

step S1: making a marking point pattern, and transferring the marking point pattern to a chip to expose the epitaxial layer;

step S2: etching the epitaxial layer;

step S3: evaporating metal mark points, wherein the metal structure is CrAlTiPtAu; the CrAlTiPtAu metal structure sequentially comprises a metal Cr layer, an Al layer, a Ti layer, a Pt layer and an Au layer from bottom to top;

step S4: stripping and removing the photoresist.

The first layer Cr of the metallic structure has adhesion and light efficiency. The second layer of Al has good reflectivity, because the mark points are arranged below the epitaxial layer, ultraviolet rays need to penetrate through the epitaxial layer and carry out alignment exposure with the mark points, the Al can reflect partial light rays, good exposure conditions are provided for a photoetching process after bonding, the mark points are clearer, and the alignment accuracy is further improved. The third layer of Ti and the fourth layer of Pt are used as barrier layers, and the Ti prevents the second layer of Al from alloying with the fifth layer of Au, so that stability is influenced. Pt prevents Au from diffusing, thereby maintaining stable ohmic contact characteristics.

Further, in the above method for preparing the lithographic overlay mark, the mark dot pattern in step S1 is a vertically and horizontally symmetrical pattern.

Preferably, in the above method for preparing a lithographic overlay mark, the mark dot patterns include, but are not limited to, a "back" character, an "H" character, and a "cross" character.

Preferably, in the above method for preparing a lithographic overlay mark, the size of the mark point pattern is 200 μm × 200 μm, and the distance between adjacent mark points is 600 μm.

Further, in the above method for preparing the photoetching overlay mark, the mark dot pattern is transferred to the chip by means of spin coating, exposure and development; the uniform glue uses positive photoresist, and the glue thickness is 3-4 μm.

Further, in the preparation method of the photoetching overlay mark, the developing and the baking are carried out by a hot plate, the baking temperature is 90-100 ℃, and the baking time is 60-90 s.

Further, in the above method for preparing the lithography overlay mark, the epitaxial layer is etched by using an inductively coupled plasma etching method in step S2; the etching gas is Cl₂And BCl₃(ii) a The etching depth is 6000A-8000A; the etching angle is 70-80 degrees. The etching angle is 70-80 degrees, so that subsequent metal stripping is more convenient, and meanwhile, the number of welting metal wires is reduced in the angle range, so that the outline of the marked point pattern is clearer and smoother. When the etching depth is 6000A-8000A, the stripping of the evaporated metal is further facilitated.

Further, in the above method for preparing the lithographic overlay mark, the metal mark points are evaporated by an electron beam evaporation method in step S3.

Further, in the above method for preparing the photoetching overlay mark, before evaporating the metal mark points in step S3, the residual organic matter in the etched groove is removed, and then the etched groove is dried by a rotary dryer and hot nitrogen blow-drying.

Further, in the preparation method of the photoetching overlay mark, the thickness of the first Cr layer of the metal structure is 20-50A; the thickness of the second layer of Al is 1000-3000A; the thickness of the third layer of Ti is 500-2000A; the thickness of the fourth layer of Pt is 200-500A; the thickness of the fifth layer of Au is 1000-3000A.

Further, in the above method for preparing the lithography overlay mark, step S4 employs a blue film stripping and organic photoresist removing solution to clean the photoresist.

Preferably, in the above method for preparing the photolithographic overlay mark, the photoresist is soaked in acetone for 5min before being stripped.

A photoetching overlay mark is prepared by the preparation method of the photoetching overlay mark.

The invention has the beneficial effects that:

(1) the invention provides a preparation method of a photoetching overlay mark, wherein a metal structure of a vapor plating metal mark point is CrAlTiPtAu, and the metal structure of the CrAlTiPtAu is a metal Cr layer, an Al layer, a Ti layer, a Pt layer and an Au layer from bottom to top in sequence; the coating has the advantages of strong abrasion resistance, high resolution, difficult corrosion and the like, and is slightly influenced by physical bombardment of ions and corrosion of chemical solution.

(2) According to the preparation method of the photoetching overlay mark, the metal mark points of the vapor plating can reflect light, so that the metal mark points are clearer, and the alignment accuracy is improved.

(3) According to the preparation method of the photoetching overlay mark, provided by the invention, the edge pasting metal wires are reduced by limiting the etching angle, so that the contour lines of the metal mark points are clearer and smoother, and the alignment accuracy is further improved. Meanwhile, the etching angle limited by the invention is more convenient for metal stripping, the difficulty of the subsequent metal stripping process is reduced, and the abrasion strength of the chip is correspondingly reduced.

Drawings

FIG. 1 is a process flow diagram of the present invention;

FIG. 2 is a diagram of two marker points;

FIG. 3 is a schematic view after spin-coating;

FIG. 4 is a schematic view after etching the epitaxial layer;

FIG. 5 is a schematic view after stripping and stripping;

FIG. 6 is a comparative wear resistance plot of different metal structures;

FIG. 7 is a comparison graph of the topography of metal marker points at different etching angles.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be further clearly and completely described below with reference to the embodiments of the present invention. It should be noted that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Example 1

A photoetching overlay mark is prepared by the following method:

step S1: making a marking point pattern which is a 'hui' character; transferring the mark point pattern onto the chip by adopting glue homogenizing, exposing and developing modes to expose the epitaxial layer; the uniform glue uses positive photoresist, and the glue thickness is 4 μm;

step S2: etching the epitaxial layer; etching epitaxial layer by inductively coupled plasma etching with Cl as etching gas₂And BCl₃The etching depth is 8000A, and the etching angle is 80 degrees;

step S3: evaporating metal mark points, wherein the metal structure is CrAlTiPtAu; the thickness of the first Cr layer of the metal structure is 50A; the thickness of the second layer of Al is 3000A; the thickness of the third layer of Ti is 2000A; the thickness of the fourth layer Pt is 500A; the fifth layer was Au 1000A thick.

Step S4: stripping and removing the photoresist; after soaking in acetone for 5min, the photoresist is cleaned by adopting blue film stripping and organic photoresist removing solution.

Example 2

A photoetching overlay mark is prepared by the following method:

step S1: making a marking point pattern which is a cross character; transferring the mark point pattern onto the chip by adopting glue homogenizing, exposing and developing modes to expose the epitaxial layer; the uniform glue uses positive photoresist, and the glue thickness is 3 μm;

step S2: etching the epitaxial layer; etching epitaxial layer by inductively coupled plasma etching with Cl as etching gas₂And BCl₃The etching depth is 6000A, and the etching angle is 70 degrees;

step S3: evaporating metal mark points, wherein the metal structure is CrAlTiPtAu; the thickness of the first Cr layer of the metal structure is 20A; the thickness of the second layer of Al is 1000A; the thickness of the third layer of Ti is 500A; the fourth layer Pt was 200A thick. Fifth layer Au thickness 3000A.

Comparative example 1

A photoetching overlay mark is characterized in that a metal structure is CrAlTiPtTi, and the CrAlTiPtTi metal structure sequentially comprises a metal Cr layer, an Al layer, a Ti layer, a Pt layer and a Ti layer from bottom to top; the rest of the preparation method is the same as example 1.

Comparative example 2

A photoetching overlay mark is characterized in that a metal structure is CrPtTi, and the CrPtTi metal structure sequentially comprises a metal Cr layer, a Pt layer and a Ti layer from bottom to top; the rest of the preparation method is the same as example 1.

Comparative example 3

A photolithographic overlay mark with an etching angle of 30 ° was prepared in the same manner as in example 2.

Comparative example 4

A lithographic overlay mark with an etch angle of 50 ° was prepared as in example 2.

Comparative example 5

In a lithographic overlay mark, the thickness of the metal Cr was 5A, and the other conditions were the same as in example 1.

Comparative example 6

In a lithographic overlay mark, the thickness of metal Cr was 200A, and the other conditions were the same as in example 1.

Comparative example 7

A photolithographic overlay mark was made with metal Al at a thickness of 8000A, under the same conditions as in example 1.

First, wear resistance test

The metal mark points of the photoetching overlay marks prepared in the example 1, the comparative example 1 and the comparative example 2 are etched by using BOE solution, the BOE concentration is 1:7, the etching time is 240s, and the etching result is shown in FIG. 6. Fig. 6a is a metal mark dot in example 1, fig. 6b is a metal mark dot in comparative example 1, and fig. 6c is a metal mark dot in comparative example 2. BOE and Ti metal are subjected to chemical reaction, Ti is corroded and cannot play a role in protecting Al metal, Au metal has strong corrosion resistance and plays a certain role in protecting lower-layer metal. The comparison shows that the metal marking points of the CrAlTiPtAu metal structure in the embodiment 1 have better abrasion resistance and higher pattern resolution.

Second, influence of etching angle

The etched metal mark points of example 2, comparative example 3 and comparative example 4 were compared, and the results are shown in fig. 7. Fig. 7a is a metal mark of example 2, fig. 7b is a metal mark of comparative example 3, and fig. 7c is a metal mark of comparative example 4. As can be seen by comparison, when the etching angle is 70 degrees in the embodiment 2, the metal mark points are clearer, and the contour lines are smoother.

Third, influence of the thickness of the Metal layer

The lithographic overlay marks prepared in example 1 and comparative examples 5, 6 and 7 were compared. The comparative example 5 has poor metal adhesion, and the prepared mark points have metal falling; comparative example 6 the metal reflectivity is low, and the mark point is difficult to identify during exposure; comparative example 7 metallic Al has poor coating properties and the chemical solution corrodes metallic Al.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims

1. A method for preparing a photoetching overlay mark is characterized by comprising the following steps:

step S2: etching the epitaxial layer; step S3: evaporating metal mark points, wherein the metal structure is CrAlTiPtAu; the CrAlTiPtAu metal structure sequentially comprises a metal Cr layer, an Al layer, a Ti layer, a Pt layer and an Au layer from bottom to top; step S4: stripping and removing the photoresist.

2. The method for producing a lithographic overlay mark according to claim 1, wherein the mark dot pattern in step S1 is a vertically and horizontally symmetrical pattern.

3. The method for producing a lithographic overlay mark according to claim 1, wherein the mark dot pattern is transferred onto the chip by means of spin coating, exposure, and development; the uniform glue uses positive photoresist, and the glue thickness is 3-4 μm.

4. The method for preparing a photolithographic overlay mark according to claim 3, wherein the developed image is baked by a hot plate at a baking temperature of 90 ℃ to 100 ℃ for 60s to 90 s.

5. The method for preparing a lithographic overlay mark according to claim 1, wherein in step S2, the epitaxial layer is etched by using an inductively coupled plasma etching method; the etching gas is Cl₂And BCl₃(ii) a The etching depth is 6000A-8000A; the etching angle is 70-80 degrees.

6. The method for preparing a lithographic overlay mark according to claim 1, wherein the metal mark points are evaporated by electron beam evaporation in step S3.

7. The method for preparing a lithographic overlay mark according to claim 1, wherein before the metal mark is evaporated in step S3, the residual organic matter in the etched groove is removed, and then the metal mark is dried by a rotary dryer and hot nitrogen blow drying.

8. The method for preparing a lithographic overlay mark according to claim 1, wherein the thickness of the first layer of Cr of the metal structure is 20 to 50A; the thickness of the second layer of Al is 1000-3000A; the thickness of the third layer of Ti is 500-2000A; the thickness of the fourth layer of Pt is 200-500A; the thickness of the fifth layer of Au is 1000-3000A.

9. The method for preparing a lithographic overlay mark according to claim 1, wherein step S4 is performed by stripping a blue film and cleaning the photoresist with an organic photoresist removing solution.

10. A lithographic overlay mark prepared by the method of any one of claims 1 to 9.