A method for preparing a regular-shaped indium column array
A method for preparing indium columns with regular shape and improved adhesion addresses the issues of uneven morphology and connectivity defects by using photolithography and rotary evaporation, resulting in enhanced interconnection performance for infrared focal plane detectors.
Patent Information
- Application Number
- CN202411365742.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2024-09-29
- Publication Date
- 2024-12-20
- Estimated Expiration
- 2044-09-29
AI Technical Summary
Indium columns with low height and uneven morphology cause blind pixels and short-circuit defects in infrared focal plane detectors, especially in large-scale arrays with small-size pixels, due to lateral growth and uneven shape during the evaporation process, leading to poor connectivity and reduced interconnection qualification rates.
A method involving photolithography, surface modification, and rotary evaporation to form a uniform metal layer on the substrate, followed by indium layer growth, and subsequent stripping to achieve a regular indium column array with improved adhesion and morphology, using processes like argon plasma treatment and isosceles trapezoidal photolithography holes.
The method ensures consistent indium column height and regular shape, enhancing connectivity and reducing defects, thus improving interconnection quality and qualification rates, compatible with pixel pitches from 7.5 μm to 50 μm.
Smart Images
Figure CN118888564B_ABST
Abstract
Description
Technical Field
[0001] The invention provides a method for preparing an indium column array with a regular shape, and belongs to the technical field of infrared focal plane detectors. Background Art
[0002] Infrared focal plane detectors are currently developing in the direction of large-scale arrays and small-size pixels. The indium column plays the role of connecting the infrared focal plane array chip and the readout circuit to ensure good conduction between the two. However, indium columns with low height and uneven morphology are prone to cause blind pixels and increase short-circuit defects after reverse soldering interconnection. Therefore, it is necessary to grow indium columns with consistent height and regular shape to ensure the connectivity quality of the indium columns after reverse soldering interconnection.
[0003] The existing indium pillar growth process is to prepare the indium pillar array by evaporation after patterning with negative photoresist. The reason for using negative photoresist evaporation is that if the photolithography opening is in a "positive trapezoid", it is easier to peel off the film layer on it. During the growth process, since the sidewalls of the photolithography holes have high-density micropores and rough interface characteristics, as the evaporation process proceeds, the thicker indium layer gradually grows laterally on the sidewalls of the photolithography holes. As time goes by, the photolithography holes will be gradually blocked, and the diameter of the top layer of the indium pillar will become smaller and smaller, resulting in the low growth height and poor uniformity of the top layer of the indium pillar after peeling. The sharp cone characteristics. At the same time, the development direction of large-scale arrays and small-size pixels makes the growth conditions of indium pillars more and more harsh. Indium pillars with substandard growth height and uneven shapes increase the difficulty of the interconnection process, thereby reducing the interconnection qualification rate and making it difficult to ensure a good hybrid interconnection coupling effect between the chip and the circuit.
[0004] Although the existing indium column reflow process can improve the uniformity of indium column growth by melting, wetting and surface tension treatment of the indium column, for detector processes with a pixel pitch below 10μm, the overall indium content is low due to the influence of the lateral growth characteristics of the indium column. The growth height will be reduced after the indium column reflow process. Therefore, it is necessary to develop an indium column growth process with a large growth height and regular shape. Summary of the invention
[0005] In order to solve the problems of substandard growth height and uneven shape in the existing indium column growth and reflow processes, the present invention provides a method for preparing an indium column array with a regular shape.
[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for preparing an indium column array with a regular shape, comprising the following steps:
[0007] S1: forming a photolithography hole array after photolithography on the substrate surface;
[0008] S2: performing surface modification treatment on the substrate after the photolithography process is completed;
[0009] S3: forming a uniform metal layer on the surface of the surface-modified substrate by a coating process;
[0010] S4: forming a uniform indium layer on the surface of the substrate on which the metal growth is completed by using a coating process;
[0011] S5: The substrate after the indium layer is grown is processed by a stripping and cleaning process to remove the metal layer and photoresist on the side wall of the photolithography hole array and the metal layer and indium layer on the top of the photoresist, thereby obtaining an indium column array with a large growth height and regular shape.
[0012] In step S1, a photolithography hole array is formed on a substrate by a photolithography process using a coating machine and a photolithography machine.
[0013] After being formed, each photolithography hole in the photolithography hole array is in the shape of an isosceles trapezoid, and the inner angle of the long base of the isosceles trapezoid is 70-85°.
[0014] In step S1, NR9-6000PY negative photoresist is selected to form a photolithography hole array.
[0015] In step S2, a plasma degumming machine is used to perform argon plasma surface treatment on the substrate, or flame treatment, RIE plasma etching treatment, or corona discharge treatment is used to modify the surface of the substrate.
[0016] The metal layer coating process in step S3 and the indium layer coating process in step S4 are completed by ion beam evaporation, electron beam evaporation or magnetron sputtering evaporation.
[0017] In step S3, while metal evaporation is being performed, the substrate is rotated 180° in the vertical direction at a constant speed, so that a metal layer of a specified thickness is evaporated on the bottom and side wall of the photolithography hole.
[0018] The metal layer formed by evaporation in step S3 is a metal of a combination of Ti / Pt / Au, Cr / Au, Ti / Au or Ti / Ni / Au.
[0019] The thickness of the indium layer formed in step S4 is 6-8 μm.
[0020] The indium layer in step S4 can be replaced by an aluminum layer.
[0021] The beneficial effects of the present invention compared with the prior art are as follows:
[0022] 1. The present invention can increase the adhesion between the metal layer and the side wall of the photolithographic hole by performing argon plasma modification treatment on the surface of the photolithographic hole array; can increase the metal evaporation incident angle of the side wall of the photolithographic hole by uniformly rotating the metal-evaporated substrate in the vertical direction, and generate a relatively uniform, dense and smooth metal layer on the side wall of the photolithographic hole with high-density micropores and rough interfaces; thus, the interface contact of the indium column on the side wall of the photolithographic hole can be improved, and the lateral growth effect of the indium column can be inhibited, thereby greatly reducing the generation of indium columns with low growth height and poor morphology;
[0023] 2. The present invention can simultaneously complete the growth of the metal layer and the indium layer through one photolithography and two evaporation (metal, indium) processes. The metal layer at the bottom of the indium column serves as the UBM layer, wherein the UBM layer (Under Bump Metallurgy) is a metallization transition layer between the chip pad and the bump, which can provide better welding contact and conductive performance between the chip and the indium column. There is no overlay deviation between the indium column array and the UBM layer caused by secondary photolithography, and the metal layer on the side wall can be removed by stripping, which has no negative impact on subsequent processes. BRIEF DESCRIPTION OF THE DRAWINGS
[0024] The present invention will be further described below in conjunction with the accompanying drawings:
[0025] Figure 1 is a schematic diagram of the structure of the photolithography hole array after the photolithography in step S1 of the method of the present invention;
[0026] Figure 2 This is a schematic diagram of the structure of performing plasma treatment on the surface of the photolithography hole array in step S2 of the method of the present invention;
[0027] Figure 3 It is a rotational schematic diagram of the metal evaporation process in step S3 of the method of the present invention;
[0028] Figure 4 Schematic diagram of metal evaporation on the right side wall of the photolithography hole in step S3 of the method of the present invention;
[0029] Figure 5 Schematic diagram of metal evaporation on the left side wall of the photolithography hole in step S3 of the method of the present invention;
[0030] Figure 6 It is a structural schematic diagram of the substrate after metal evaporation is completed after step S3 of the method of the present invention;
[0031] Figure 7 It is a schematic diagram of the structure of the substrate after the step S4 of the method of the present invention has completed the indium evaporation;
[0032] Figure 8 A schematic diagram of the structure of an indium column array after the stripping and cleaning process is completed in step S5 of the method of the present invention;
[0033] In the figure: 1 is a substrate, 2 is a photolithography hole array, 3 is a photoresist, 4 is a metal evaporation source, 5 is a metal layer, 6 is an indium layer, and 7 is an indium column array. DETAILED DESCRIPTION
[0034] like Figures 1 to 8 As shown, the present invention provides a method for preparing an indium pillar array with a regular shape, by modifying the photoresist on the substrate 1 and performing a rotary evaporation metal deposition process, a dense and smooth metal layer 5 is uniformly grown on the side wall of the photolithography hole, and then an indium layer 6 is evaporated, and then the photoresist 3 and the metal layer are peeled off by a stripping process, and the smooth metal layer 5 on the side wall of the photolithography hole can inhibit the lateral growth of the indium pillar, thereby obtaining an indium pillar array 7 with uniform growth height and regular morphology. The specific implementation steps are as follows:
[0035] S1: forming a photolithography hole array 2 on the surface of a substrate 1 after photolithography;
[0036] S2: performing surface treatment on the substrate 1 after the photolithography process is completed;
[0037] S3: uniformly evaporating a metal layer 5 on the surface of the surface-treated substrate 1;
[0038] S4: uniformly evaporating an indium layer 6 on the surface of the substrate 1 on which the metal growth is completed;
[0039] S5: The substrate 1 after the indium layer 6 is grown is processed by a stripping and cleaning process to remove the metal layer 5 and the photoresist 3 on the side wall of the photolithography hole array 2 and the metal layer 5 and the indium layer 6 on the top of the photoresist 3, thereby obtaining an indium column array 7 with a large growth height and regular shape.
[0040] The substrate 1 is a chip of an infrared focal plane array having a metal layer 5 (UBM layer) and an indium column array 7 to be prepared.
[0041] In the specific step S1, a photolithography hole array 2 is formed on the substrate 1 by a photolithography process using a coating machine and photolithography, and the implementation steps are as follows:
[0042] NR9-6000PY negative photoresist is selected to form the photolithography hole array 2, and the NR9-6000PY negative photoresist is evenly dropped on the center of the substrate 1, and then the rotation speed is 300-800 rpm for 3-5 seconds, and then the rotation speed is 1000-1500 rpm for 30 seconds to spread the photoresist, and the substrate 1 after the spread is placed on a heating plate, and baked at a temperature of 120°C for 300 seconds to evaporate the solvent of the photoresist; the contact mode (Hard) of the ultraviolet lithography machine is used to partially expose the photoresist with an exposure dose of 400-800 mj to define a pattern (the pattern is an isosceles trapezoid shape), and the partially exposed substrate 1 is placed on a heating plate and baked at a temperature of 100-120°C for 90-180 seconds to cure the primer. Then, the exposed substrate 1 is placed in a tetramethylammonium hydroxide (2.38% TMAH) solution diluted with deionized water, developed for 40 to 80 seconds, taken out and fixed in deionized water for 30 to 60 seconds, and then the substrate 1 is taken out and blown dry with nitrogen, at which time an isosceles hole array 2 is formed on the substrate 1. Each of the lithographic holes in the lithographic hole array 2 is in the shape of an isosceles trapezoid, and the inner angle of the long base of the isosceles trapezoid is between 70 and 85 degrees.
[0043] Specifically, in step S2, a plasma stripper can be used to perform argon plasma surface treatment on the substrate 1. The implementation steps are as follows: the substrate 1 after the photolithography process is placed in the plasma stripper, and the surface of the substrate 1 is treated with argon plasma at a flow rate of 300 sccm and a power of 70 W for 30 to 45 seconds. Figure 2 As shown, the purpose is to modify the surface of the side wall of the photolithography hole and increase the adhesion of the metal layer 5 when it grows on the side wall of the photolithography hole in step S3.
[0044] In step S2 , the surface treatment of the substrate 1 may also be performed by flame treatment, RIE (Reactive Ion Etching) plasma etching treatment, or corona discharge treatment.
[0045] The specific step S3 is: fix the substrate 1 after the photolithography process on the stage of the evaporation machine, rotate the substrate 1 uniformly in the vertical direction, and evaporate a metal layer 5 of a specified thickness on the bottom and side wall of the photolithography hole, that is, evaporate Ti / Pt / Au in sequence through the metal evaporation source 4, and the thickness of the three is 50 / 50 / 300nm respectively. During the evaporation process, the substrate 1 is controlled to rotate in the vertical direction at a uniform speed, such as Figure 3 The rotating arrow shown is the direction of rotation. The process of rotary evaporation is as follows: Figure 4-5 As shown, the purpose is to increase the evaporation incident angle of the metal particles emitted by the metal evaporation source 4 on the side wall of the photolithography hole, thereby further ensuring the adhesion and density of the metal layer 5 grown on the side wall of the photolithography hole in different directions.
[0046] The specific step S4 is: fixing the substrate 1 after metal evaporation on the stage of the evaporation machine to evaporate an indium layer 6 with a thickness of 6 to 8 μm, the purpose of which is to grow an indium column array 7 in the photolithography hole array 2.
[0047] In the specific step S5, the substrate 1 on which the indium layer 6 has been grown is subjected to a stripping and cleaning process, the purpose of which is to strip off and remove the metal layer 5 and the photoresist 3 on the side wall of the photolithographic hole array 2 and the metal layer 5 and the indium layer 6 on the top of the photoresist 3, thereby obtaining an indium column array 7 with a large growth height (height of 6-8 μm), good morphology, and regular shape, such as Figure 8 shown.
[0048] The metal evaporation and indium evaporation methods in steps S3 and S4 can adopt ion beam evaporation, electron beam evaporation or magnetron sputtering and other processes, and the evaporated metal can also be a combination of Cr / Au, Ti / Au or Ti / Ni / Au.
[0049] The preparation method of the present invention is also applicable to the preparation of aluminum welding spots.
[0050] In summary, the indium column array prepared by the method of the present invention has the following advantages:
[0051] 1. By modifying the sidewall of the photolithography hole and using a spin evaporation metal deposition process, a dense and smooth metal layer 5 can be uniformly grown on the sidewall of the photolithography hole, thereby greatly improving the morphology of the indium pillar array 7 without the need for a reflow process and enhancing subsequent interconnection performance;
[0052] 2. The pressure to be overcome for stripping is changed from the adhesion between the indium layer 6 and the photoresist 3 to the adhesion between the metal layer 5 and the photoresist 3, thereby increasing the efficiency of the stripping process and reducing the thickness of the photoresist grown by conventional indium pillars from more than twice the target indium pillar height to 1.2 to 1.5 times the target indium pillar height, thereby saving the amount of photoresist used;
[0053] 3. Only one photolithography is required to simultaneously grow the UBM layer and the indium layer 6 structure;
[0054] 4. The present invention is compatible with the chip-side process and circuit-side process of infrared detection devices with a pixel pitch of 7.5 μm to 50 μm.
[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.
Claims
1. A method for preparing a regular-shaped indium column array, characterized in that: The following steps are involved: S1: forming a photolithography hole array after photolithography on the surface of the substrate; each photolithography hole in the photolithography hole array is in an isosceles trapezoidal shape after being formed, and the internal angle of the long base of the isosceles trapezoid is 70-85°; S2: performing surface modification treatment on the substrate after the photolithography process is completed; S3: forming a uniform metal layer on the surface of the substrate after surface modification by a coating process; in step S3, while performing metal evaporation, the substrate is rotated 180° in the vertical direction at a constant speed, so as to evaporate a metal layer of a specified thickness on the bottom and side wall of the photolithographic hole; The metal layer formed by evaporation in step S3 is a metal of a combination of Ti / Pt / Au, Cr / Au, Ti / Au or Ti / Ni / Au; S4: forming a uniform indium layer on the surface of the substrate on which the metal growth is completed by using a coating process; S5: The substrate after the indium layer is grown is processed by a stripping and cleaning process to remove the metal layer and photoresist on the side wall of the photolithography hole array and the metal layer and indium layer on the top of the photoresist, thereby obtaining an indium column array with a large growth height and regular shape.
2. The method for preparing a regular-shaped indium column array according to claim 1, characterized in that: In step S1, a photolithography hole array is formed on a substrate by a photolithography process using a coating machine and a photolithography machine.
3. The method for preparing a regular-shaped indium column array according to claim 2, characterized in that: In step S1, NR9-6000PY negative photoresist is used to form a photolithography hole array.
4. The method for preparing a regular-shaped indium column array according to claim 1, characterized in that: In step S2, a plasma degumming machine is used to perform argon plasma surface treatment on the substrate, or flame treatment, RIE plasma etching treatment, or corona discharge treatment is used to modify the surface of the substrate.
5. The method for preparing a regularly shaped indium column array according to claim 1, characterized in that: The metal layer coating process in step S3 and the indium layer coating process in step S4 are completed by ion beam evaporation, electron beam evaporation or magnetron sputtering evaporation.
6. The method for preparing a regularly shaped indium column array according to claim 1, characterized in that: The thickness of the indium layer formed in step S4 is 6-8 μm.
7. A method for preparing a regular-shaped indium column array according to any one of claims 1 to 6, characterized in that: The indium layer in step S4 can be replaced by an aluminum layer.