JP2018182193A - Semiconductor device, and method for manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor device improved about plating omission and surface roughening in an electroless plating step to form UBM (Under Bump Metallurgy).SOLUTION: A semiconductor device comprises: an electrode film formed on a semiconductor substrate; and UBM formed on the electrode film, and composed of an electroless Ni plating film/an electroless Au plating film, or an electroless Ni plating film/an electroless Pd plating film/an electroless Au plating film. The surface roughness Ra of a surface of the electroless Au plating film is 0.050 μm or less. The coverage of the electrode film by the plating film is 99% or more.SELECTED DRAWING: None

Description

  The present invention relates to a semiconductor device and a method of manufacturing the semiconductor device.

  With the miniaturization and high integration of semiconductor packaging technology, the transition from wire bonding to flip chip bonding is expanding as a method of bonding chips such as LSIs and ICs. In the flip chip method, metal pads and solder are used. The formation of UBM (Under Bump Metallurgy) for bonding purposes is required.

  As a method of forming a UBM, forming by electroless plating, which is expected to be low cost, is increasing. As a method of forming a UBM by electroless plating, a degreasing process or a soft etching process is performed in order to first clean a portion to be plated (pad or wiring) on a semiconductor wafer. Next, a catalyst application step is performed. Zincate treatment is applied to the aluminum-based metal surface, and palladium treatment is applied to the copper-based metal surface. Then, the method of forming UBM of Ni / Au film | membrane by electroless nickel (Ni) plating and substitution type electroless gold (Au) plating is common. When the plated wafer is exposed to high temperature or high humidity, Ni diffuses into the Au film and precipitates on the surface to form Ni oxide, which adversely affects solder wettability and wire bondability. . In this case, it is general to perform Ni / Pd / Au film by performing electroless palladium (Pd) plating which is a barrier layer of Ni diffusion between electroless nickel plating and substitution type electroless gold plating. . In the present invention, the symbol “/” means the structure of a plurality of plating films formed in each plating process, and the order of plating of each plating film is determined by the order of plating from the substrate side.

  Electroless plating, which is one of UBM formation methods, has attracted attention in terms of cost and short processing time. However, even in the case of non-electrolytic plating, plating defects and surface roughening of the plating film occur even in the case of non-electrolytic plating, even if the contamination on the surface to be plated and the pre-process residue do not pose a problem in the electroplating method. The poor plating and the surface roughness of the plating film are one of the causes for the deterioration of the wettability with solder balls, wires and the like.

In the step of removing the contamination on the electrode surface and the pre-process residue, a plasma cleaning method is used as a method of cleaning the electrode surface.
For example, Patent Document 1 states that cleaning using only argon is insufficient as a plasma cleaning method for cleaning the surface of the electrode portion before plating, and argon + forming gas (for example, nitrogen + 2% hydrogen) And the like, and a method of plasma cleaning using an inert gas containing hydrogen, etc.) is disclosed.
Patent documents 2 and 3 disclose that the surface of the electrode is plasma cleaned with argon and oxygen gas.
However, in Patent Documents 1 to 3 above, conditions such as specific power, time, and the like at the time of plasma cleaning are not disclosed.
In addition, Patent Document 4 discloses that oxygen gas (100 cc / min), 800 W, 2 to 5 minutes, and a vacuum degree of 10 Pa are used as the conditions for plasma cleaning the electrode.
Further, in Patent Document 5, an aluminum-based electrode film can be obtained only by sequentially performing plasma cleaning treatment using argon, degreasing treatment, acid washing treatment, zincate treatment, electroless nickel plating treatment, and electroless gold plating treatment. An air gap may be formed at the interface with the nickel film, and when the air gap is formed, the electrical reliability of the semiconductor device is reduced, which causes the operation of the element to be impaired. An oxide film is formed by artificially oxidizing and a nickel film is formed on the surface of the formed oxide film. Plasma cleaning is performed using argon at 100 cc / min, 800 W, 2 minutes, at a vacuum degree of 10 Pa, before or after forming the oxide film.

Unexamined-Japanese-Patent No. 2000-252313 JP 2008-085368 A JP, 2011-193007, A JP, 2013-194291, A JP, 2015-220408, A

Contamination on the electrode surface, some residues in the previous process are difficult to remove, or if the amount is too large, they can not be removed sufficiently in the removal process, and plating omission, surface roughness, etc. in the subsequent electroless plating process There was a problem that plating formation defects occur.
The present invention relates to a plating omission in an electroless plating process in a semiconductor device having a UBM comprising an electroless Ni plating film / electroless Au plating film or an electroless Ni plating film / electroless Pd plating film / electroless Au plating film. -It aims at providing the semiconductor device which improved surface coarseness.

The above problems are solved by the invention of the following (1).
(1) An electrode film formed on a semiconductor substrate,
UBM formed of electroless Ni plating film / electroless Au plating film or electroless Ni plating film / electroless Pd plating film / electroless Au plating film formed on the electrode film,
A semiconductor device having
The surface roughness Ra of the surface of the electroless Au plating film is 0.050 μm or less, and the electroless Ni plating film / electroless Au plating film or the electroless Ni plating film / electroless Pd plating film / electroless Au plating The semiconductor device whose coverage of the electrode film by a film is 99% or more.

  According to the present invention, it is possible to provide a semiconductor device with improved plating loss and surface roughness in the electroless plating step.

It is an optical microscope image of the electroless Au plating film surface of Example 2 and Comparative Example 1. 7 is a height profile of a plated surface of Example 2. 7 is a height profile of a plated surface of Comparative Example 1; It is a microscope image which shows the solder wet spread of the electroless Au plating film surface of Example 2 and Comparative Example 1. FIG.

Hereinafter, the present invention (1) will be described in detail, but since the following (2) to (5) are also included in the embodiment, these are also described together.
(2) The semiconductor device according to (1), wherein the amount of wetting and spreading of the solder ball obtained by the following formula is 1.90 or more.
Amount of wetting spread = post-heating solder diameter ÷ solder ball initial diameter Heating condition: 245 ° C, 60 seconds (3) Plasma cleaning the surface of the electrode film formed on the semiconductor substrate, electroless Ni plating film / electroless Au plating A method of manufacturing a semiconductor device, comprising the steps of: forming a film or electroless Ni plating film / electroless Pd plating film / electroless Au plating film,
The method of manufacturing a semiconductor device, wherein the step of performing the plasma cleaning uses argon as a cleaning gas, and has a power of 400 W or more and a processing time of 600 seconds or more.
(4) The method for manufacturing a semiconductor device according to (3), wherein a gas pressure in the step of plasma cleaning is 1 Pa to 30 Pa.
(5) The method of manufacturing a semiconductor device according to (3) or (4), wherein the electrode film is aluminum-based, copper-based, or gold-based.

The semiconductor device of the present invention is
An electrode film formed on a semiconductor substrate;
UBM formed of electroless Ni plating film / electroless Au plating film or electroless Ni plating film / electroless Pd plating film / electroless Au plating film formed on the electrode film,
A semiconductor device having
The surface roughness Ra of the surface of the electroless Au plating film is 0.050 μm or less, and the electroless Ni plating film / electroless Au plating film or the electroless Ni plating film / electroless Pd plating film / electroless Au plating The coverage of the electrode film by the film is 99% or more.

  When the surface roughness Ra of the surface of the electroless Au plating film is 0.050 μm or less, it can be seen that there is no plating formation defect such as plating loss or surface roughness, and the Au plating film having a gloss is formed. . In addition, when the surface roughness Ra of the surface of the electroless Au plating film is 0.050 μm or less, solder wettability is improved.

The surface roughness Ra is a parameter in the height direction called "arithmetic mean roughness", and a part of the roughness curve measured by the roughness meter is extracted at a reference length, and the unevenness state of the section is an average value And was measured in accordance with JIS B 0601-2001.
Specifically, measurement can be performed using a laser microscope (VK-9700, manufactured by Keyence Corporation) or the like.

In the semiconductor device of the present invention, the coverage of the electrode film by the electroless Ni plating film / electroless Au plating film or the electroless Ni plating film / electroless Pd plating film / electroless Au plating film is 99% or more And preferably 100%. When the coverage is 99% or more, there is almost no plating loss and it can be used as a product.
The coverage was determined from the peak area of the height profile.
For the height profile, data of the numerical value in the height direction of each pixel is obtained from the optical microscope image of the Au plated surface, and the peak top of the height of the plated surface is taken as the relative height “0”. The frequency is shown on the vertical axis on the horizontal axis.
When there is no plating loss, there is one peak, but when there is plating loss, the number of peaks is two or more. When there is one peak, the coverage is 100%, and when there are two or more peaks, the total area of the peaks is taken as 100, and the percentage of the area of the peak without plating omission is determined as the coverage .

The electroless Au plating film preferably has a wetting and spreading amount of 1.90 or more as determined from the following equation.
Amount of wetting spread = Post-heating solder diameter ÷ Solder ball initial diameter Heating condition: 245 ° C, 60 seconds Measurement of wetting spread amount is
-Solder ball: SnAg (3%) Cu (0.5%) Senju metal (0.2 mmφ)
-Flux: TSF-6502 A rosin-based flux, manufactured by Kester Co., was used according to the following procedure.
Evaluation procedure-Apply flux to the target pad.
Place the solder ball on the flux.
Heat at 245 ° C. for 60 seconds on a hot plate.
・ Check the solder wetting spread.
The wet spread amount is obtained from the above equation.
The initial diameter of the solder ball is the diameter of the used solder ball, and the diameter of the solder after heating can be measured by optical microscope observation. The longest diameter of the solder spread by heating was taken as the solder diameter after heating.

The semiconductor device of the present invention can be manufactured by the method of manufacturing a semiconductor device of the present invention.
The method for manufacturing a semiconductor device according to the present invention comprises the steps of plasma cleaning the surface of an electrode film formed on a semiconductor substrate, electroless Ni plating film / electroless Au plating film, or electroless Ni plating film / electroless Pd plating A method of manufacturing a semiconductor device, comprising the steps of: forming a film / electroless Au plating film;
The plasma cleaning process is performed using argon as a cleaning gas, at a power of 400 W or more, and for a processing time of 600 seconds or more.

On the surface of the electrode film formed on the semiconductor substrate, depending on the wafer manufacturing process, electrode oxides, electrode fluorides (for example, Al ₂ O ₃ , AlF ₃ etc. if Al electrodes), residue of protective film material There are contamination and pre-process residues such as polyimide (PI), Si compounds (SiO ₂ and Si ₃ N ₄ etc.), Ti, etc. In order to remove these, a plasma cleaning process is performed using argon as a cleaning gas.
If the power for plasma cleaning is less than 400 W, even if the processing time is longer than 600 seconds, the contamination / previous process residue can not be sufficiently removed, plating omission occurs, and the coverage of the electroless Au plated surface is It can not be 99%, and the surface roughness Ra exceeds 0.050 μm. In addition, when the power is 400 W or more, the contamination / previous process residue can be removed, and the coverage may be 99% or more. However, if the processing time is less than 600 seconds, plating can be performed. The surface of the film becomes rough, the surface roughness Ra exceeds 0.050 μm, and a shiny plating surface can not be obtained.
It was found that the surface roughness Ra of the surface of the Au plating film was improved to a power of 400 W or more, a treatment time of 600 seconds or more, a high power and a long treatment time of 0.050 μm or less. It is considered that the contamination on the electrode and the pre-process residue also affect the roughness of the Au plating film surface. The power for plasma cleaning is preferably 800 W or more and 600 seconds or more.

In addition, the gas pressure in plasma cleaning is preferably low, and 1 Pa to 30 Pa is preferable, since the low pressure discharge generally reduces the reattachment probability of the removed particles.
Although the gas flow rate in plasma cleaning depends on the chamber size of the discharge device, the exhaust condition of the vacuum pump, the pressure of the process gas, etc., for example, 10 to 300 sccm can be mentioned as a preferable range.

The discharge device used for plasma cleaning preferably has stable discharge in continuous discharge such as electric power for performing plasma cleaning and treatment time.
In the present invention, the plasma cleaning conditions are high power and long processing time. The continuous dischargeable time depends on the cooling fan capacity of the RF power supply, and depending on the device, a power supply failure may occur in the continuous discharge. In that case, the measures against heat radiation around the power supply should be implemented to ensure stable continuous discharge. In addition, there are cases where heating of the sample by discharge can not be neglected due to high power and long processing time. In that case, it is preferable to increase the cooling efficiency by changing the method of setting the sample.

As a semiconductor substrate, the board | substrate provided with the electrode used for a semiconductor wafer, a flexible substrate, etc. are mentioned, for example.
The electrode film formed on the semiconductor substrate is preferably aluminum-based, copper-based, or gold-based.

As a wafer of a semiconductor wafer, a silicon wafer can be used, an electrode is formed by a normal process, the outermost surface of the electrode surface is made a copper-based or aluminum-based surface, and after plasma cleaning according to the present invention It is preferable to carry out electrolytic Ni plating.
Also, a GaAs substrate can be used as the wafer. In this case, it is preferable to perform electroless Ni plating after the outermost surface of the electrode surface is a gold-based surface and plasma cleaning according to the present invention is performed.

  The copper on the surface of the electrode may be a known copper used as an electrode of a semiconductor wafer. For example, copper such as pure copper and phosphor bronze and copper alloys can be used. The aluminum system may be a known aluminum system used as an electrode of a semiconductor wafer, and for example, aluminum alloys such as pure aluminum, AlCu (0.5%), AlSi (1%) and the like can be used. The gold base may be a known gold base used as an electrode of a semiconductor wafer, and examples thereof include Ti / Pt / Au.

For example, in the case where the electrode is a copper-based surface and electroless Ni plating is performed, the following process is performed.
Plasma cleaning → Degreasing → Acid immersion → Activation (catalyst applied)
→ Electroless Ni plating In addition, when electroless Ni plating is performed on an aluminum-based electrode, the process is as follows.
Plasma cleaning → Degreasing → Acid immersion → Primary zincate → Acid immersion → Secondary zincate → Electroless Ni plating When electroless Ni plating is performed on the gold-based surface of the electrode, the process is as follows.
Plasma cleaning → Degreasing → Activation → Activation (catalyst applied)
→ Electroless Ni plating The steps of “Degreasing”, “Acid immersion”, “Activation (catalyst application)”, “Primary zincate”, “Secondary zincate” and “Activation” should be performed according to existing methods and conditions. Can. The zincate solution used for the primary zincate and secondary zincate treatment is preferably one that does not roughen the surface.

In addition, after the electroless Ni plating film is formed, an electroless plating film of Au or Pd / Au is formed.
A coating of Au or Pd / Au can be formed on the electroless Ni plating film by a general electroless plating process using a commercially available pretreatment or plating chemical.

As the plating solution used for the electroless Ni plating, the electroless Au plating, the electroless Pd plating, and the plating method, known plating solutions and plating methods used for forming UBM of a semiconductor wafer can be used.
In order to obtain the semiconductor device of the present invention, as the plating solution used for the electroless Ni plating, a medium phosphorus type electroless Ni plating solution using sodium hypophosphite as a reducing agent is preferable, and the electroless Pd is preferable. As the plating solution, an electroless Pd plating solution using sodium hypophosphite as a reducing agent is preferable, and as the electroless Au plating solution, a sulfite-based Au-based no cyanide-based substituted Au plating solution is preferable.

  The film thickness of the plating film of each plating changes depending on the application of the wafer and the required characteristics, but the film thickness of the Ni plating film needs to be 1.5 μm or more from the viewpoint of preventing the diffusion of solder at the time of solder bonding. And preferably 1.5 to 10 μm. Also, the Au film needs a film thickness of 0.01 μm or more from the viewpoint of wettability in the solder joint and 0.10 μm or more in the case of performing wire bonding, and preferably 0.01 in the solder joint from the viewpoint of wettability. In the case of performing wire bonding, it is 0.10 to 0.50 μm. Further, the film thickness of the Pd film of Ni / Pd / Au specification is required to be 0.02 μm or more from the viewpoint of preventing the diffusion of Ni, and preferably 0.02 to 0.20 μm.

  Hereinafter, the present invention will be described in more detail by way of examples.

Examples 1-2, comparative examples 1-7
(Used semiconductor wafer)
A semiconductor wafer having an Al alloy (Al-Cu) electrode and a protective film PI was used as a semiconductor substrate. An electrode oxide, an electrode fluoride, a residue PI of a protective film material, a Si compound (SiO or SiN), Ti, and the like were detected on the electrode by ToF-SIMS.

(Plasma cleaning)
The semiconductor wafer was set on an electrode of a vacuum plasma processing apparatus using a vacuum plasma processing apparatus (PC-S350RIE manufactured by Electronic Giken Co., Ltd.), and the surface of the electrode film was described under the following gas conditions and Table 2 Plasma cleaning was performed under the following conditions.
Gas condition-gas type: Ar
Gas pressure (Pa): 10
Gas flow rate (sccm): 100
※ Gas conditions were unified above.
In order to increase the cooling efficiency of the cooling water flowing to the electrode, the use of the wafer setting jig was abolished and the sample was set.

After the discharge treatment (plasma cleaning) was performed, formation of electroless Ni plating film / electroless Pd plating film / electroless Au plating film was performed according to the process described in Table 1.

The solutions used in the plating process are as follows.
Degreasing solution: UAC-100, JX Nippon Mining & Metals, Inc. Acid pickling: 50% nitric acid, Kanto Chemical Primary zincate solution: UAZ100, JX, Nippon Mining & Minerals Co., Ltd. Electrolytic Ni plating solution:
Medium phosphorus type electroless Ni plating solution using sodium hypophosphite as reducing agent (P concentration in Ni film: 7%)
Electroless Pd plating solution:
Electroless Pd plating solution using sodium hypophosphite as reducing agent (P concentration in Pd film: 5%)
Electroless Au plating solution: Sulfurous acid Au-based non-cyanide substitution Au plating solution The film thickness of the obtained UBM is Ni / Pd / Au = 2.54 / 0.065 / 0.067 (μm), and the normal value Met.

Table 2 shows the results of determination of the discharge treatment conditions and the surface roughness Ra, the coverage, and the amount of spread of the surface of the electroless Au plating film.
Moreover, the optical microscope image of the electroless Au plating surface of Example 2 and Comparative Example 1 is shown in FIG. 1, the height profile of the plated surface of Example 2 is shown in FIG. 2, and the height profile of the plated surface of Comparative Example 1 is shown. It is shown in FIG.
The “surface shape” in FIG. 1 is an image of higher magnification than the “optical microscope image”, and is an image obtained by a laser microscope (Keyence KV-9700).
The height profiles in FIG. 2 and FIG. 3 are obtained by obtaining numerical value data in the height direction of each pixel in the range of 90 μm × 67 μm (number of pixels: 2048 × 1536 pixels) of the electroless Au plated surface, and the height of the plated surface The top of the peak was taken as the relative height "0", the relative height was taken on the horizontal axis, and the frequency on the vertical axis.
In Example 2, the height profile had one peak and the coverage was 100%. In Comparative Example 1, there were two peaks, and the total of the peak areas was set to 100, and the ratio of the area of the peak in the portion without plating omission was determined as the coverage. As a result, the coverage was 94.6%. In FIG. 2 and FIG. 3, the relative height of the height profile indicates the height (depth) in the substrate direction from the plating surface as +.
FIG. 4 shows the initial diameter of the solder ball after mounting the solder ball and the diameter of the solder after heating when measuring the solder wet spread amount in Example 2 and Comparative Example 1. As shown in FIG. The pattern of 400 μm × 1000 μm was formed on the target pad, and in Example 2, the solder wetted and reached the pattern of 200 μm, so the longest diameter in the long side (1000 μm) direction was heated after heating The solder diameter of

  From Table 2, in Examples 1-2, there is no plating omission or surface roughening, and it is possible to obtain a good plating surface having a luster whose surface roughness Ra of the Au plating film surface is 0.050 μm or less. I understand. In particular, in Example 2 (power: 800 W, processing time: 600 sec), the surface roughness Ra is 0.027 μm, and a glossy and good plated surface is obtained. In addition, the plating defects were also improved in Comparative Example 2 (power 300 W, processing time 600 sec), Comparative Example 3 (power 400 W, processing time 180 sec) and Comparative Example 4 (power 800 W, processing time 60 sec), which are relatively weak treatments. Was not confirmed. On the other hand, in Comparative Examples 2 to 7, the plating film surface was rough and the surface was cloudy. In Comparative Examples 4 to 7, there was no significant difference in the surface roughness Ra. In Comparative Example 1, the surface roughness Ra was 0.286 μm, and plating omission occurred.

Claims (5)

An electrode film formed on a semiconductor substrate;
UBM formed of electroless Ni plating film / electroless Au plating film or electroless Ni plating film / electroless Pd plating film / electroless Au plating film formed on the electrode film,
A semiconductor device having
The surface roughness Ra of the surface of the electroless Au plating film is 0.050 μm or less, and the electroless Ni plating film / electroless Au plating film or the electroless Ni plating film / electroless Pd plating film / electroless Au plating The semiconductor device whose coverage of the electrode film by a film is 99% or more. The semiconductor device according to claim 1, wherein the amount of wetting and spreading of the solder ball obtained by the following formula is 1.90 or more.
Amount of wetting spread = Post solder diameter / Solder ball initial diameter Heating condition: 245 ° C, 60 seconds Plasma cleaning the surface of the electrode film formed on the semiconductor substrate, and forming electroless Ni plating film / electroless Au plating film or electroless Ni plating film / electroless Pd plating film / electroless Au plating film A method of manufacturing a semiconductor device comprising the steps of
The method of manufacturing a semiconductor device, wherein the step of performing the plasma cleaning uses argon as a cleaning gas, and has a power of 400 W or more and a processing time of 600 seconds or more.   4. The method of manufacturing a semiconductor device according to claim 3, wherein a gas pressure in the step of performing plasma cleaning is 1 Pa to 30 Pa.   The method for manufacturing a semiconductor device according to claim 3, wherein the electrode film is aluminum-based, copper-based, or gold-based.