CN110034016B - Method for welding aluminum layer on front surface of semiconductor chip - Google Patents
Method for welding aluminum layer on front surface of semiconductor chip Download PDFInfo
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- CN110034016B CN110034016B CN201910228034.9A CN201910228034A CN110034016B CN 110034016 B CN110034016 B CN 110034016B CN 201910228034 A CN201910228034 A CN 201910228034A CN 110034016 B CN110034016 B CN 110034016B
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
- C23C14/04—Coating on selected surface areas, e.g. using masks
- C23C14/042—Coating on selected surface areas, e.g. using masks using masks
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
- C23C14/06—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the coating material
- C23C14/14—Metallic material, boron or silicon
- C23C14/16—Metallic material, boron or silicon on metallic substrates or on substrates of boron or silicon
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
- C23C14/22—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the process of coating
- C23C14/24—Vacuum evaporation
- C23C14/28—Vacuum evaporation by wave energy or particle radiation
- C23C14/30—Vacuum evaporation by wave energy or particle radiation by electron bombardment
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer
- H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic System or AIIIBV compounds with or without impurities, e.g. doping materials
- H01L21/28—Manufacture of electrodes on semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/268
- H01L21/283—Deposition of conductive or insulating materials for electrodes conducting electric current
- H01L21/285—Deposition of conductive or insulating materials for electrodes conducting electric current from a gas or vapour, e.g. condensation
- H01L21/28506—Deposition of conductive or insulating materials for electrodes conducting electric current from a gas or vapour, e.g. condensation of conductive layers
Abstract
The invention belongs to the field of double-sided heat dissipation semiconductors, and particularly relates to a method for welding a front aluminum layer of a semiconductor chip, in particular to a process method for welding a front electrode of a wide-bandgap vertical power semiconductor device. The natural alumina layer with poor front adhesion of the chip is removed by wet etching, and then metal Ti, Ni and Ag are sequentially evaporated and plated.
Description
Technical Field
The invention belongs to the field of double-sided heat dissipation semiconductors, and particularly relates to a method for welding a front aluminum layer of a semiconductor chip, in particular to a process method for welding a front electrode of a wide-bandgap vertical power semiconductor device.
Background
With the continuous improvement of power density of semiconductor power modules, such as inverters and converters, the requirement of a system on heat dissipation is more and more strict, single-side heat dissipation gradually fails to meet the application requirement, and double-side heat dissipation is imperative. Most of commercial semiconductor bare chips in the current market are single-sided weldable: the top layer of the front electrode is made of metal Al, so that the weldability is poor, and Al can naturally form aluminum oxide in air, so that the weldability is poorer; and the metal of the top layer on the back is gold or silver, so that the welding is easy. Single-sided solderable semiconductor power modules cannot meet the ever-increasing practical heat dissipation requirements.
At present, few researches on the method for realizing the front face solderability of the semiconductor chip are made at home and abroad, and the industrial industry is rare. The university of Tianjin applied a patent to a method for metallizing an aluminum layer on the front surface of a chip in 2018, which mainly uses magnetron sputtering to metallize Ti/Ag to make the front surface of the chip solderable, and the method has the following defects: first, the aluminum pad surface on the power device usually generates a dense aluminum oxide layer due to exposure to air, the layer can significantly reduce the adhesion strength of the deposited metal layer, the aluminum layer is not removed before plating, and the aluminum oxide layer naturally oxidized on the surface of the aluminum layer. Secondly, only two layers of metal Ti/Ag are provided, and no intermediate buffer layer is provided, so that the corrosion of the solder in the packaging and welding process can not be well prevented.
Disclosure of Invention
Aiming at the defects or the improvement requirements of the prior art, the invention provides a semiconductor chip front aluminum layer solderability method, which removes a natural aluminum oxide layer with poor front adhesion of a chip by wet etching, and then sequentially evaporates and plates Ti, Ni and Ag.
To achieve the above object, according to one aspect of the present invention, there is provided a method for solderable front aluminum layer of a semiconductor chip, including the steps of:
(1) covering photoresist on a non-electrode area on the front surface of the cleaned chip by a photoetching method to obtain the front surface of the chip protected by the photoresist;
(2) wet etching treatment is carried out on the front surface of the chip protected by the photoresist to remove the alumina layer on the surface of the aluminum layer on the front surface of the chip, and the residual corrosive agent on the surface is cleaned after etching is finished to obtain the front surface of the chip with the surface alumina layer removed;
(3) sequentially evaporating metal titanium, metal nickel and metal silver on the front surface of the chip with the surface alumina layer removed to obtain the front surface of the chip with evaporated metal;
(4) and carrying out photoresist stripping treatment on the front surface of the metal-evaporated chip to obtain the semiconductor chip with the front aluminum layer capable of being welded.
Preferably, the cleaning in the step (1) is specifically: and carrying out plasma cleaning on the front surface of the chip to be processed, and removing dust and impurities on the surface of the aluminum layer on the front surface of the chip to obtain the cleaned front surface of the chip.
Preferably, when the photoresist is applied by the photolithography method, the spin coating is performed at a rotation speed of 500-.
Preferably, in the mask layer used in the photolithography of step (1), the width of the mask region corresponding to the region between the gate pad and the source pad on the front side of the chip is not less than the actual distance between the gate pad and the source pad.
Preferably, a width of a region of the mask layer corresponding to a region between the gate pad and the source pad is at least 0.08mm greater than a distance between the gate pad and the source pad.
Preferably, the etchant used in the wet etching is hot phosphoric acid with the temperature ranging from 70 ℃ to 80 ℃, and the wet etching time is 3-4 minutes.
Preferably, step (3) is performed within 1 minute after step (2) is completed, to avoid re-oxidation of the front surface of the chip in air.
Preferably, the evaporation comprises the following specific steps:
(4-1) putting the chip with the surface aluminum oxide layer removed into an evaporation table, and coating the chip at high altitude by using an electron beam evaporation source with the vacuum degree of not less than 9.0 x 10-4Pa, starting to thermally bake the chip, and keeping the temperature at 80-150 ℃ for 4-10 minutes;
(4-2) when the vacuum degree is not less than 8.0 x 10-4And (3) beginning evaporation when Pa, sequentially adopting titanium, nickel and silver in the evaporation sequence, and taking the chip after the evaporation is finished and the cooling is finished to obtain the front surface of the evaporated metal chip.
Preferably, the thickness of the evaporated metal titanium is 100nm-300nm, the thickness of the metal nickel is 200nm-1000nm, and the thickness of the metal silver is 200-1000 nm.
Preferably, the semiconductor chip is a wide bandgap vertical power semiconductor chip.
Preferably, the semiconductor chip is a MOSFET, an IGBT chip or a power diode chip, and the semiconductor chip is a Si material or a SiC material.
In general, compared with the prior art, the above technical solution contemplated by the present invention can achieve the following beneficial effects:
(1) the method for welding the aluminum layer on the front surface of the semiconductor chip adopts wet corrosion combined with one-time evaporation of the metal titanium nickel silver, so that the chip can be welded from only the back surface to double-surface welding, the process is simple and reliable, and the development of double-surface heat dissipation is greatly promoted.
(2) The invention adopts a method for plating the metal titanium nickel silver by one-time evaporation, Ti is used as a contact layer, the thermal expansion coefficient of the Ti is close to that of Si/SiC, the adhesiveness is strong, and the ohmic contact characteristic is good; ni is used as an intermediate buffer layer, the layer is in good contact with the upper layer and the lower layer of metal, and can well prevent the corrosion of solder in the process of packaging and welding; ag is used as a conductive layer, and has low resistivity, strong electromigration resistance, stable performance and good weldability.
(3) According to the invention, a photoetching method is adopted to protect the non-electrode area of the chip before wet etching, and the short circuit between electrodes caused by metal evaporation is avoided by controlling the treatment of the grinding layer at the narrow size of the chip.
(4) The method for welding the aluminum layer on the front surface of the semiconductor chip sequentially carries out welding treatment on the front surface of the chip through photoetching protection, wet etching and one-time evaporation, and is not only suitable for a general semiconductor chip with the aluminum layer on the front surface, but also suitable for a silicon carbide vertical semiconductor chip with high voltage, thinness and small size.
(5) In the invention, wet etching is adopted to remove the aluminum oxide, so that the subsequent evaporated metal can be more compact and firmer. Compared with the technology without removing the aluminum oxide layer, the metal of the scheme for removing the aluminum oxide layer is combined more firmly, is less prone to falling off in subsequent packaging, and is higher in reliability.
Drawings
Fig. 1 is a schematic diagram of the chip size of a SiC MOSFET of embodiment 1 of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
The invention provides a method for welding an aluminum layer on the front surface of a semiconductor chip, which comprises the following steps:
(1) carrying out plasma cleaning on the front surface of the chip to be processed, and removing dust and impurities on the surface of an aluminum layer on the front surface of the chip to obtain the cleaned front surface of the chip;
(2) covering photoresist on the non-electrode area on the front surface of the chip by a photoetching method to obtain the front surface of the chip protected by the photoresist;
(3) wet etching treatment is carried out on the front surface of the chip protected by the photoresist to remove the alumina layer on the surface of the aluminum layer on the front surface of the chip, and the residual corrosive agent on the surface is cleaned after etching is finished to obtain the front surface of the chip with the surface alumina layer removed;
(4) sequentially evaporating metal titanium, metal nickel and metal silver on the front surface of the chip with the surface alumina layer removed to obtain the front surface of the chip with evaporated metal;
(5) and carrying out photoresist stripping treatment on the front surface of the metal-evaporated chip to obtain the semiconductor chip with the front aluminum layer capable of being welded.
And (2) covering photoresist on the non-electrode area on the front surface of the chip by a photoetching method, wherein the photoresist can be positive photoresist or negative photoresist. The rotation speed and the spin time determine whether the photoresist is uniformly spin-coated. In order to ensure uniform photoresist spin coating, in some embodiments, the photoresist is spin coated at a rotation speed of 500-.
In some chip front-side structures, part of the non-electrode area is narrow, for example, the distance between the gate pad and the source pad of the MOSFET is very limited, only 0.08mm, so that before depositing metal, photoresist is needed to accurately control the mask layer to prevent short circuit between the source pad and the gate pad when plating the metal film. In some embodiments, in order to avoid short circuit, in the mask layer used in the step (2) of photolithography, the width of the mask region corresponding to the region between the gate pad and the source pad on the front surface of the chip is not less than the actual distance between the gate pad and the source pad, and preferably, the width of the mask region corresponding to the region between the gate pad and the source pad in the mask layer is at least 0.08mm greater than the distance between the gate pad and the source pad.
Under natural conditions, Al of the aluminum layer on the front surface of the chip can be oxidized to form aluminum oxide, the adhesion of the aluminum oxide is poor, and the aluminum oxide layer naturally formed on the aluminum layer needs to be removed before subsequent metallization. In some embodiments of the present invention, the etchant used in the wet etching is hot phosphoric acid with a temperature ranging from 70 ℃ to 80 ℃, and the wet etching time is 3 minutes to 4 minutes. For SiC MOSFET chips, the back side is Ni/Ag metal and will not be corroded by hot phosphoric acid. The height of the grid bonding pad and the height of the source bonding pad on the front side of the chip are different, the area of the grid bonding pad is smaller, and the source bonding pad can be observed to react faster and more fiercely in the corrosion process.
After photoetching, the areas of the front surface of the chip, which are not needed to be metallized, are protected by photoresist. And the front surface of the semiconductor chip is sequentially evaporated with metal Ti, Ni and Ag. In order to avoid the phenomenon of layering or falling off of the metal after metallization as much as possible and facilitate subsequent packaging and sintering, the thickness of the vapor plating metal titanium is 100nm-300nm, the thickness of the metal nickel is 200nm-1000nm, and the thickness of the metal silver is 200nm-1000 nm. The specific numerical value is determined according to specific conditions. The structure of the multilayer metal takes the adhesion between the metal and the chip into consideration and the requirements of the packaging process on the metal layer into consideration. The full-automatic control operation mode is adopted, the efficiency is high, the stability is high, the thickness of each evaporated metal layer is uniform under the high vacuum environment, and the compactness of each metal layer is high.
It is particularly noted that evaporation metallization needs to be performed quickly after wet etching of the alumina to minimize the possibility of re-oxidation of the Al layer in air. For example, step (4) is preferably performed within 1 minute after step (3) is completed, so as to prevent the front surface of the chip from being oxidized again in the air.
In some embodiments, the metal deposition step is:
(4-1) putting the chip with the surface aluminum oxide layer removed into an evaporation table, and coating the chip at high altitude by using an electron beam evaporation source with the vacuum degree of not less than 9.0 x 10-4Pa, starting to thermally bake the chip, and keeping the temperature at 80-150 ℃ for 4-10 minutes;
(4-2) when the vacuum degree is not less than 8.0 x 10-4And (3) beginning evaporation when Pa, sequentially adopting titanium, nickel and silver in the evaporation sequence, taking the chip after the evaporation is finished and cooling for not less than 10 minutes, and obtaining the front surface of the evaporated metal chip.
And (3) carrying out photoresist stripping treatment on the front surface of the metal evaporated chip, wherein a conventional photoresist stripping method can be adopted, such as stripping by adopting an organic stripping liquid, and ultrasound can also be assisted to remove metals evaporated in other areas except the grid electrode and the source electrode bonding pad.
The method for welding the aluminum layer on the front surface of the semiconductor chip is not only suitable for common semiconductor chips with the aluminum layer on the front surface, such as power MOSFET, IGBT chips or power diode chips, Si materials or SiC materials. But also for higher voltage, thinner, and smaller size SiC devices, such as SiC vertical semiconductor chips.
For the double-sided heat dissipation structure, the front surface of the chip is necessary to be metallized, and after metallization, the chip can be welded from the back surface single-sided to the front surface and the back surface both-sided. The front side metallization treatment mainly comprises two key steps: firstly, Al on the surface of Al layer needs to be removed before metal coating2O3And the second is the metal coating itself.
The invention adopts hot phosphoric acid wet etching to remove the alumina, and has simple and reliable process and low cost. For the metallization process, the following requirements are mainly made: the adhesiveness between the silicon chip and the surface of the Si or SiC chip is good; ohmic contact is good, and the conductivity is good; and subsequent welding and packaging are easy. The invention adopts a method for plating the metal titanium nickel silver by one-time evaporation, Ti is used as a contact layer, the thermal expansion coefficient of the Ti is close to that of Si/SiC, the adhesiveness is strong, and the ohmic contact characteristic is good; ni is used as an intermediate buffer layer, the layer is in good contact with the upper layer and the lower layer of metal, and can well prevent the corrosion of solder in the process of packaging and welding; ag is used as a conductive layer, and has low resistivity, strong electromigration resistance, stable performance and good weldability. The invention has the advantages that the aluminum oxide is removed by phosphoric acid wet etching, the titanium nickel silver is plated by one-time evaporation, the back surface of the chip can be welded into double-sided weldable, the process is simple and reliable, and the development of double-sided heat dissipation is greatly promoted.
The following are examples:
the embodiment aims to provide a solderable structure and a process for a front aluminum layer of a wide bandgap vertical power semiconductor chip. The metallization method has good conductivity, and the commercial semiconductor chip is improved from single-side welding to double-side welding, so that double-side heat dissipation is facilitated, the power density of the semiconductor module is improved, and the reliability of semiconductor packaging can be improved.
The following takes 1200V SiC MOSFET bare chip of CREE corporation as an example, and the invention is described more fully with reference to the specific embodiments and the drawings in the examples. It is obvious that the described embodiments are only a part of all embodiments of the invention. Other embodiments, which are not the inventor or which the applicant can obtain without making any inventive contribution, are within the scope of protection of the present patent.
In this embodiment, the front surface of the SiC MOSFET has 1 Gate Pad (Gate Pad) and 3 Source pads (Source Pad), and the surface metal of these 4 electrodes is a metal aluminum layer with a thickness of 4 μm, and the chip is schematically shown in fig. 1.
And (3) a front aluminum layer solderability process:
(1) cleaning: firstly, plasma cleaning is carried out on the SiC MOSFET chip to be processed, and dust and impurities on the surface of the chip are removed, so that the SiC MOSFET chip meets the requirements of the subsequent process.
(2) Photoetching a mask: the photolithographic masking is performed prior to the evaporation of the multi-layer metal film by protecting all other regions except the gate pad and the source pad, especially the termination structure, with photoresist. Secondly, because the distance between the MOSFET grid bonding pad and the source bonding pad is very limited and is only 0.08mm, before metal deposition, photoresist is needed to accurately control the mask layer so as to prevent short circuit between the source bonding pad and the grid bonding pad when metal coating is carried out. Here, the mask layer is set to have a width of 0.35mm corresponding to the distance between the gate pad and the source pad, and a photoresist is first spin-coated, which in this embodiment is a negative photoresist, at a rotation speed of 600 rotations for 5 seconds, and then at a high speed of 1200 rotations for 10 seconds. The rotation speed and the spin-coating time determine whether the photoresist is uniformly spin-coated. Prebaking at 143 ℃ for 8 minutes. The exposure was carried out for 60 seconds and the intensity was 3.6 x 1000. mu.W/cm 2. Development for 150 seconds and fixation for 120 seconds. Hardening the film at 143 ℃ for 40 minutes.
(3) Wet etching of Al2O3In air, under natural conditions, Al oxidizes to form alumina, which has poor adhesion and requires removal of the naturally formed alumina layer prior to subsequent metallization. The corrosive liquid is hot phosphoric acid, the temperature is 70-80 ℃, and the soaking time is 3-4 minutes. The back surface of the SiC MOSFET chip is made of Ni/Ag metal and cannot be corroded by hot phosphoric acid. The height of the grid bonding pad and the height of the source bonding pad on the front side of the chip are different, the area of the grid bonding pad is smaller, and the source bonding pad can be observed to react faster and more fiercely in the corrosion process.
(4) Cleaning: and (4) cleaning the residual phosphoric acid on the chip to prepare for the next evaporation coating.
(5)Evaporation and metal plating: after photoetching, the areas of the front surface of the chip, which are not needed to be metallized, are protected by photoresist. And the front surface of the semiconductor chip is sequentially evaporated with metal Ti, Ni and Ag. In order to avoid the phenomenon of layering or falling off of the metal after metallization as much as possible and facilitate subsequent packaging and sintering, the thickness ranges of the metal of each layer are 100nm-300nm of Ti, 200nm-1000nm of Ni and 200nm-1000nm of Ag, and the specific numerical value is determined according to specific conditions. The structure of the multilayer metal takes the adhesion between the metal and the chip into consideration and the requirements of the packaging process on the metal layer into consideration. It is particularly noted that evaporation metallization needs to be performed quickly after wet etching of the alumina to minimize the possibility of re-oxidation of the Al layer in air. Loading the cleaned chip into an evaporation table, and coating at high altitude by using an electron beam evaporation source until the vacuum degree reaches 9.0 x 10-4Pa starts to bake thermally, and the temperature is kept constant at 100 ℃ for 5 minutes. When the vacuum degree reaches 8.0 x 10-4And (4) beginning to evaporate when Pa, sequentially adopting titanium, nickel and silver in the evaporation sequence, cooling for 10 minutes after evaporation is finished, and taking the slices. The full-automatic control operation mode is adopted, the efficiency is high, the stability is high, the film thickness of each metal layer evaporated under the high vacuum environment is uniform, the compactness of each metal layer is high, the combination is good, and the surface of the silver layer is bright. After the film coating is finished, the alloy is subjected to high vacuum, and the vacuum degree is 3 x 10-3Pa, and keeping the temperature at 500 ℃ for 40 minutes. After the alloy is alloyed, the ohmic contact between the chip and each metal layer is tighter, and the weldability is enhanced.
(6) Stripping: and stripping and removing the metal evaporated on the other areas except the grid electrode and the source electrode bonding pad by adopting an organic stripping liquid and ultrasonic method. The organic stripping solution is a conventional stripping solution for stripping photoresist, such as JB-1133 (Strepper-1133).
Through the steps, the SiC MOSFET chip is changed from back welding only to front welding and back welding, necessary conditions are provided for double-side welding packaging and manufacturing of a double-side heat dissipation semiconductor module, and heat dissipation performance and power density of the semiconductor module can be improved.
The parameters related to the above embodiments can be adjusted within a certain range according to actual requirements, and the adjusted range also belongs to the protection scope of the present invention.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (5)
1. A method for welding an aluminum layer on the front surface of a semiconductor chip is characterized by comprising the following steps:
(1) covering photoresist on a cleaned non-electrode area on the front surface of the chip by a photoetching method aiming at the chip with the back electrode metal of Ni/Ag to obtain the front surface of the chip protected by the photoresist;
(2) wet etching treatment is carried out on the front surface of the chip protected by the photoresist to remove the alumina layer on the surface of the aluminum layer on the front surface of the chip, and the residual corrosive agent on the surface is cleaned after etching is finished to obtain the front surface of the chip with the surface alumina layer removed;
(3) sequentially evaporating metal titanium, metal nickel and metal silver on the front surface of the chip with the surface alumina layer removed to obtain the front surface of the chip with evaporated metal; the thickness of the vapor plating metal titanium is 100nm-300nm, the thickness of the metal nickel is 200nm-1000nm, and the thickness of the metal silver is 200-1000 nm; the evaporation plating comprises the following specific steps:
(3-1) putting the chip with the surface aluminum oxide layer removed into an evaporation table, and coating the chip at high altitude by using an electron beam evaporation source with the vacuum degree of not less than 9.0 x 10-4Pa, starting to thermally bake the chip, and keeping the temperature at 80-150 ℃ for 4-10 minutes;
(3-2) when the vacuum degree is not less than 8.0 x 10-4When Pa, evaporation is started, the evaporation sequence is titanium, nickel and silver in sequence, and after evaporation is finished and cooling is carried out, a chip is taken out, so that the front surface of the metal-evaporated chip is obtained;
(4) carrying out photoresist stripping treatment on the front surface of the metal-evaporated chip to obtain a semiconductor chip with a weldable front aluminum layer;
in the step (2), the etchant adopted by the wet etching is hot phosphoric acid with the temperature ranging from 70 ℃ to 80 ℃, and the wet etching time is 3-4 minutes;
in addition, the step (3) is carried out within 1 minute after the step (2) is completed, so that the front surface of the chip is prevented from being oxidized again in the air;
in the mask layer adopted in the photoetching in the step (1), the width of a mask region corresponding to a region between a gate bonding pad and a source bonding pad on the front side of the chip is not less than the actual distance between the gate bonding pad and the source bonding pad.
2. The solderable method of claim 1, wherein a width of an area of the mask layer corresponding to an area between the gate pad and the source pad is at least 0.08mm greater than a distance between the gate pad and the source pad.
3. The solderable method of claim 1 wherein the cleaning of step (1) is specifically: and carrying out plasma cleaning on the front surface of the chip to be processed, and removing dust and impurities on the surface of the aluminum layer on the front surface of the chip to obtain the cleaned front surface of the chip.
4. The solderable method of claim 1 wherein the photolithography is performed with a paste at 500-.
5. The solderable method of claim 1, wherein the semiconductor chip is a wide bandgap vertical power semiconductor chip.
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