JP2001115268A - Method for producing semiconductor system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a silicon semiconductor system deposited with an electroless nickel plating film with high uniformity and tight adhesion. SOLUTION: A silicon wafer is dipped into a pretreating solution containing hydrofluoric acid and an oxidizer, is subjected to surface activation, is water- washed and is immediately applied with electroless nickel plating. As the oxidizer, a ternary solution using hydrogen peroxide aqueous solution and nitric acid, and in which, as a third solution, phosphoric acid, water or acetic acid is added is prepared.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor device using a silicon wafer, and more particularly to a method for activating the surface of a substrate when electroless nickel (hereinafter referred to as Ni) plating is performed on the substrate surface.

[0002]

2. Description of the Related Art Conventional surface activation treatments of this type include physical means and chemical means. As physical means,
Forming treatment, that is, fine surface roughening, and as a chemical means, a chemical species that can become an activation nucleus such as palladium (hereinafter referred to as Pd) salt or a silicone coupling agent is adsorbed on the surface. Surface activation has been performed.

[0003]

In the forming process as a physical means, the substrate surface is formed by sandblasting in which fine particles such as silicon carbide and silicon are blown under pressure and pressure, or a grinding machine using a rotary blade and a grinding stone finish. Has been roughened. Due to the formed surface irregularities, an anchor effect is brought about, precipitation is easy,
Electroless Ni plating with high adhesion is obtained.

However, this method has a problem that processing damage such as processing distortion and micro cracks is generated on the surface layer, and it is difficult to form a uniform and uniform Ni alloy layer. FIG.
(A)-(e) is a schematic explanatory drawing of the Ni plating method to the surface which performed the surface forming by the sandblast method. The diode wafer 803 is vacuum-sucked on the rotating table 804 and rotated by the rotating shaft 805. Nozzle 8
Then, a sand 802 is pumped at a pressure of several kg / cm ² from 01 and sprayed onto the surface of the diode wafer 803 (FIG. 8A). At this time, the nozzle 801 reciprocates in the diameter direction so that uniform processing can be performed.

FIG. 8B is a sectional view of a diode wafer 803 having both surfaces processed. FIG. 8C is an enlarged view thereof. An uneven surface 806 having a depression 808 of about several μm on both surfaces is obtained. FIG. 8D is a cross-sectional view of the initial stage of Ni plating. Ni clusters 809 precipitated in the depressions 808 can be seen. This becomes the nucleus of the subsequent Ni film formation. FIG. 8E is a cross-sectional view showing a state where the plating films 810 have been formed on both surfaces.

Since the oxidation-reduction potential of Ni is located almost in the middle of the band gap of the silicon semiconductor, electrons are easily emitted from the n-type side having a higher potential, while that of the p-type side is (Fermi level) Difficult to release. Therefore, both surfaces are not chemically treated, and in the case of the silicon fabric itself, the plating is likely to be thick on the n-side and thin on the p-side. In some cases, the n-side becomes as thick as 50%, and fine plating and special plating solution are required in the process for uniform plating on both sides. However, the anchor effect occurs due to the physical shape of the surface, and the adhesion of the film is very high.

In the case of a silicone coupling agent, there is a problem that an organic substance (or its constituent atoms, such as carbon, hydrogen and oxygen, hereinafter referred to as C, H and O, respectively) is entangled in the electroless nickel film to be deposited. was there. FIG. 9 (a)
(D) is a schematic explanatory view of a Ni plating method on a surface subjected to a chemical treatment with a silicone coupling agent.

[0008] The rotating table 9
04, and while being rotated by a rotating shaft 905, a silicone coupling agent 902 is
Is dropped in an appropriate amount (FIG. 9A). FIG. 9B is a cross-sectional view showing a state after coating and drying on both surfaces. An extremely thin coupling agent layer 906 is formed on the surface.

FIG. 9C is an enlarged sectional view showing a coupling agent layer 906 on the surface of the diode wafer 903. In the figure, R is C and H, for example, methyl (CH ₃ )
And an organic sensitive group such as an ethyl (C ₂ H ₅ ) group. This process, active site O is negatively charged weakly to the surface (-Oσ ^-) but not to form, addition and C, organic constituent elements of the H or the like of the O also coexist lot, particularly, Si
A Ni cluster core layer exceeding several tens nm exists at the interface between the Ni plating film and the Ni plating film.
At the time of alloying with nitrogen (N ₂ / hydrogen H ₂ = 5/95 vol%) for 0 minute, C and O are particularly affected, and a uniform and uniform sinter layer cannot be obtained.

In another chemical means, Pd
The method using a salt has problems such as difficulty in managing the plating solution, short solution life, and high cost. In view of such a situation, an object of the present invention is to continuously and uniformly form a silicon surface,
An object is to form a uniform and high-quality electroless Ni plating film.

[0011]

In order to solve the above-mentioned problems, a method of the present invention is based on hydrofluoric acid (hereinafter referred to as HF), and is immersed in a pretreatment solution containing an oxidizing agent to activate the surface. Perform electroless nickel plating immediately after washing. Silicon is an HF solution containing an oxidizing ^{_{agent, Si + 6HF 2 - → SiF}} 6 2- + 6HF + 4e - (1) Si + O x → -Si-OH + HF 2 - → -Si-F + F - + H to ₂ O ₍₂₎ (1) formula It dissolves directly, albeit slightly, in the reaction shown.

Further, as shown in the formula (2), it is oxidized by an oxidizing agent. Here, since it is in an aqueous solution, it is represented as an OH group. Furthermore, HF ₂ which HF dissociates ^- by an active ionic species, and replacing O with F, actually Comprising believed SiF ₆ dissolved as ^2-. In fact, the reaction of equation (2) is dominant. When the reactive group of the formula (2) is reviewed in consideration of the electronegativity of each atom, -S
In i-OH, Si: 1.8, O: 3.5, H: 2.1
Because That is, O (oxygen) attracts electrons and is partially negatively charged. In -Si-F, since F is 4.0, F (fluorine) attracts electrons and is partially more negatively charged. In a solution in which Ni ²⁺ is present, Is easily replaced with H, and becomes -Si-O-Ni ^* .
on the other hand, Is likely to be chemically adsorbed also at the F site of -Si-F ... Ni
^* If you think a little more three-dimensional, A chemical structure such as

That is, in the pretreatment solution containing HF and the oxidizing agent of the present invention, while oxidizing silicon, a slight dissolution reaction occurs, and an electrically active site of O or F atoms is formed. Ni ²⁺ is attracted to the active site in the plating bath to first generate nuclei of Ni atom clusters. After the nucleation, an electroless Ni plating film is continuously generated as an active site.

Further, the precipitation of Ni is as follows:
It is considered that the reaction predominates during OH formation. In other words, the point of the present invention is to control and form an extremely thin oxide film (actually, a silicon-rich suboxide) on the silicon surface, and to utilize O atoms substantially the same as the background as active sites for Ni nucleation. The purpose is to continuously form a uniform, homogeneous and high-quality electroless Ni plating film. Actually ESCA (Electron Spectroscopy for
Chemical Analysis) has confirmed an oxide film having a thickness of several to several tens of nm.

As the oxidizing agent, for example, aqueous hydrogen peroxide (hereinafter referred to as H ₂ O ₂ ), nitric acid (hereinafter referred to as HNO ₃ )
Is mentioned. Further, in order to balance the oxidation rate and the dissolution rate, phosphoric acid (hereinafter referred to as H ₃ PO ₄ ), water,
A third diluent such as glacial acetic acid (hereinafter referred to as CH ₃ COOH) shall be added. As a result of a thorough experiment, an appropriate composition was determined so that a sufficient amount of Ni atom cluster nuclei were formed on the substrate surface in various ternary solutions, and a uniform and uniform electroless Ni plating film was easily formed. .

[0016]

Embodiments of the present invention will be described below based on examples. In the following, HF, H
₂ O ₂ , H ₃ PO ₄ , CH ₃ COOH, and HNO ₃ are respectively about 50%, 31%, 85%, 99.8%, 61% (all are wt%) which are most widely used in the semiconductor process. ) Was used. Their mixing ratio is shown by volume ratio (vol%).

[Embodiment 1] First, based on HF, H
_The ternary system of ₂ O ₂ and H ₃ PO ₄ will be described. The diode wafer has a surface impurity concentration of 2 × 10 ¹⁹ cm by phosphorus diffusion on one surface of an n-type silicon wafer having a specific resistance of 30 Ω · cm.
^-3 , an n ⁺ layer having a diffusion depth of 30 μm, and a p ⁺ layer having a surface impurity concentration of 1 × 10 ¹⁹ cm ^-3 and a diffusion depth of 30 μm formed on the other surface by boron diffusion.

FIGS. 7A to 7D are schematic explanatory views of the nickel plating method on the surface subjected to the activation treatment of the present invention. Pretreatment solution 70 having a predetermined composition containing HF and an oxidizing agent
2 in a processing tank 701 containing 2
(FIG. 7A). Then, a very thin (about several to several tens of nm) silicon-rich suboxide 707 is generated on the surface [FIG.

As described in the section of operation, the suboxide 7
In -Si-O-H 07, the relationship between electronegativity, O atoms are attracted around the electronic locally charged active sites on the negative ^- has a (-Si-O ^* σ) . After washing thoroughly with water, immerse in the following plating bath for 5 minutes,
Plating while gently rocking. As the electroless Ni plating bath, an alkaline bath was used. The plating bath composition and plating conditions are as follows.

Nickel sulfate (NiSO ₄ ) 0.1 M Sodium dihydrogen phosphate (NaH ₂ PO ₄ ) 0.35 M Sodium borophosphate (Na ₂ H ₂ P ₂ O ₇ ) 0.2 M Ammonium hydroxide (NH ₄ OH) PH 9.0 temperature 83 ° C. Precipitate Ni / 8% P FIG. 7 (c) is a schematic diagram showing the Ni cluster nucleation process.

In the plating bath, sub-force is generated by Coulomb force.
Ni on the active site of the oxide 707 ²⁺Ions are attracted
And chemically adsorbed, the Ni cluster nucleus 708 becomes uniform
It is formed. Further, with the Ni cluster nucleus 708 as a nucleus,
Ni deposition progresses, on both n and p surfaces of diode wafer
It is possible to apply a uniform Ni plating film 710 almost uniformly.
(FIG. 7D).

The O atoms in the suboxide 707 react with H in the atmosphere and P in the plating film at the time of sintering in a later step, and thus do not adversely affect the characteristics of the plating film. FIG. 1 shows HF and H ₂ O used in the first embodiment of the present invention.
₂ is a characteristic diagram showing the composition of the ternary pretreatment solution of H ₃ PO ₄ and the plating results thereof. The circles indicate that the silicon wafer was subjected to electroless Ni plating after pretreatment with a solution of the composition. The unit is vol%.

The white circles indicate that the turning, surface condition, adhesion, and film thickness distribution (± 5%) were good. In the above system, good results were obtained at almost all composition points. HF
In a system in which silicon and an oxidizing agent coexist, dissolution of silicon and oxidation of silicon occur as a competitive reaction, and as described above, the silicon oxidation reaction is considered to be dominant.

At this time, H ₃ PO ₄ lowers the overvoltage of hydrogen generation, acts also as a reducing agent, and acts as a good controlling agent for forming an extremely thin oxide film desired by us. In the Ni plating by this method, not only a uniform and uniform plating film can be easily formed, but also there is no problem of impurity contamination when a conventional coupling agent is used. It was also confirmed that there was no problem when applied to the formation of electrodes in an actual semiconductor device.

[Embodiment 2] In the same manner as in Embodiment 1, H
Immediately after treatment with a ternary solution of F, H ₂ O ₂ and water, electroless nickel plating was performed. FIG. 2 shows HF, H ₂
O _2, the composition of the water ternary solutions, and is a characteristic diagram showing the plating result. The circles indicate that the silicon wafer was electrolessly plated at each composition point.

The white circles indicate that the rotation, surface condition, adhesion, and film thickness (± 5%) were good. The black circle is p,
n indicates defective portions such as no plating on both sides, only one side of p and n, a small hole, and peeling. The area along the axis connecting HF and water is generally good, but the area where H ₂ O ₂ is 70% or more is poor. This is because the formation rate is higher than the dissolution rate of the oxide film.

[Embodiment 3] Similarly, HF and H
Immediately after treatment with a ternary solution of ₂ O ₂ and CH ₃ COOH, electroless Ni plating was performed. FIG. 3 shows HF, H
FIG. 3 is a characteristic diagram showing the composition of a ternary solution of ₂ O ₂ and CH ₃ COOH, and the plating results thereof. The circles indicate each composition point.
Indicates that the silicon wafer was electrolessly plated.

A region where HF is as high as 20% or more is generally good, but a region where HF is as thin as 10% or less and H ₂ O ₂ is as high as 40% or more is defective. This is also because the dissolution rate of the oxide film is low and the balance between the dissolution rate and the formation rate is poor. Even in a region where CH ₃ COOH is as high as 80% or more, it is defective. This is because neither oxidation nor dissolution proceeds sufficiently in this region.

Example 4 Using HNO ₃ as an oxidizing agent, similarly, after treating with a ternary solution of HF, HNO ₃ and H ₃ PO ₄ , electroless nickel plating was immediately performed. FIG. 4 is a characteristic diagram showing the composition of a ternary solution of HF, HNO ₃ and H ₃ PO ₄ and the plating results.
The circles indicate that the silicon wafer was electrolessly plated at each composition point.

A region with a high HF of 30% or more is generally good, but a region with a low HF of 20% or less is defective. Since H ₃ PO ₄ acts as a weak oxidizing agent, the dissolution rate of the oxide film is low, and the balance between the dissolution rate and the formation rate is poor. Example 5 Similarly, after treatment with a ternary solution of HF, HNO ₃ and water, electroless nickel plating was immediately performed.

FIG. 5 is a characteristic diagram showing the composition of a ternary solution of HF, HNO ₃ and water, and the plating results. The circles indicate that the silicon wafer was electrolessly plated at each composition point. A region along the axis connecting HF and water is only slightly good, and a region with a large amount of HNO ₃ (60% or more) and a region with a large amount of water (60% or more) are defective. This is also because the balance between the dissolution rate and the formation rate is poor.

Embodiment 6 Similarly, HF, HNO ₃ , C
Immediately after the treatment with the ternary solution of H ₃ COOH, electroless nickel plating was performed. FIG. 6 shows HF, HN
O _3, CH ₃ composition ternary solution of COOH, and it is a characteristic diagram showing the plating result. The circles indicate that the silicon wafer was electrolessly plated at each composition point.

A region along the axis connecting HF and CH ₃ COOH is only slightly good, but a large amount of HNO ₃ (30% or more) and a small region of HF (50% or less) are defective. This is also because the balance between the dissolution rate and the formation rate is poor. In the above embodiment, if the film thickness distribution is ± 5.
% Or more is regarded as defective, but it is not an absolute reference of an actual semiconductor device, so that the good / defective boundary in FIGS.

[0034]

As described above, according to the present invention, a silicon wafer is immersed in a pretreatment solution containing hydrofluoric acid and an oxidizing agent to activate the surface, and immediately after washing with water, electroless nickel plating is performed. This makes it possible to easily manufacture a semiconductor device having a uniform and uniform Ni plating film without containing impurities.

The growth of an oxidized layer on the silicon surface is controlled by using a hydrogen peroxide solution or nitric acid as an oxidizing agent and a ternary solution containing phosphoric acid, water or acetic acid as a third solution. Thus, the degree of freedom of the process is increased, and a uniform Ni plating film can be surely formed. All are easily available chemicals, the process is simple, and the cost is not high, so that they can be widely applied to various semiconductor devices.

[Brief description of the drawings]

FIG. 1 shows HF—H ₂ O ₂ —H ₃ PO of Example 1 of the present invention.
₄ Plating characteristics at each composition point when pre-treatment with ternary solution

FIG. 2 is a plating characteristic diagram at each composition point when pretreatment is performed with an HF-H ₂ O ₂ —H ₂ O ternary solution of Example 2.

FIG. 3 is a plating characteristic diagram at each composition point when pretreatment is performed with an HF-H ₂ O ₂ —CH ₃ COOH ternary solution of Example 3.

FIG. 4 is a plating characteristic diagram at each composition point when pretreatment is performed with the HF-HNO ₃ —H ₃ PO ₄ ternary solution of Example 4.

FIG. 5 is a plating characteristic diagram at each composition point when pretreatment is performed with an HF-HNO ₃ —H ₂ O ternary solution of Example 5.

FIG. 6 is a plating characteristic diagram at each composition point when pretreatment is performed with a HF-HNO ₃ —CH ₃ COOH ternary solution of Example 6.

7A is an explanatory view of a immersion state of a processing solution according to an embodiment of the present invention, FIG. 7B is a sectional view of a diode wafer after pretreatment,
(C) is a schematic view of a surface after immersion in a plating bath, and (d) is a cross-sectional view of a diode wafer after Ni plating.

FIG. 8 (a) is an explanatory view of a conventional sand blast situation,
(B) is a sectional view of the diode wafer after sandblasting,
(C) is an enlarged sectional view of the surface, (d) is a schematic view of the surface after immersion in the plating bath, and (e) is a sectional view of the diode wafer after Ni plating.

9A is an explanatory view of a state of application of a conventional coupling agent, FIG. 9B is a cross-sectional view of a diode wafer after application of the coupling agent, FIG. 9C is a schematic surface view after immersion in a plating bath, and FIG.
Is a cross-sectional view of the diode wafer after Ni plating

[Explanation of symbols]

 701 Processing tank 702 Processing solution 703, 803, 903 Diode wafer 707 Suboxide 709, 809 Ni cluster nucleus 710, 810, 910 Ni plating film 801, 901 Nozzle 802 Sand 804, 904 Rotary table 805, 904 Rotating axis 806 Uneven surface 808 Depression 902 Coupling agent 907 Coupling agent layer

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Masaki Ichinose 1-1, Tanabe Nitta, Kawasaki-ku, Kawasaki, Kanagawa Prefecture Inside Fuji Electric Co., Ltd. (72) Inventor Shigeyuki Nakayama 1st Tanabe Nitta, Kawasaki-ku, Kawasaki, Kawasaki, Kanagawa No.1 Fuji Electric Co., Ltd. F term (reference) 4K022 AA05 BA14 CA04 CA15 CA23 DA01 DB02 DB08 5F043 AA02 BB27 DD02 GG10

Claims (11)

[Claims] 1. A method for manufacturing a semiconductor device, comprising: immersing a silicon wafer in a pretreatment solution containing hydrofluoric acid and an oxidizing agent to activate the surface; and performing electroless nickel plating immediately after washing with water. 2. A semiconductor according to claim 1, wherein a pretreatment solution comprising a mixture of hydrofluoric acid (50 wt%), aqueous hydrogen peroxide (31 wt%) and phosphoric acid (85 wt%) is used. Device manufacturing method. 3. A pretreatment solution comprising a mixture of hydrofluoric acid (50 wt%), aqueous hydrogen peroxide (31 wt%) and water,
2. The method according to claim 1, wherein the amount of hydrogen peroxide is less than 70 vol%. 4. A pretreatment solution comprising a mixture of hydrofluoric acid (50 wt%), aqueous hydrogen peroxide (31 wt%), and glacial acetic acid (99.8 wt%), and the glacial acetic acid content is reduced to 80 vol% or less. The method for manufacturing a semiconductor device according to claim 1, wherein: 5. The method according to claim 4, wherein the content of hydrofluoric acid is 10 vol% or more. 6. Hydrofluoric acid (50 wt%), nitric acid (61 wt%)
2. The method according to claim 1, wherein a hydrofluoric acid is used in an amount of 30 vol% or more using a pretreatment solution comprising a mixed solution of phosphoric acid (85 wt%). 7. Hydrofluoric acid (50 wt%), (concentration: 61 wt%)
2. The method according to claim 1, wherein a hydrofluoric acid is used in an amount of 40 vol% or more by using a pretreatment solution comprising a mixture of water and water. 8. The method according to claim 7, wherein the amount of water is 10 vol% or more. 9. Hydrofluoric acid (50 wt%), nitric acid (61 wt%)
2. The method according to claim 1, wherein a pretreatment solution comprising a mixture of glacial acetic acid (99.8 wt%) and a hydrofluoric acid content of 50 vol% or more is used. 10. Hydrofluoric acid (50 wt%), nitric acid (61%)
wt%) and glacial acetic acid (99.8 wt%), using a pretreatment solution containing 10 vol% or less of nitric acid and 2 vol. of hydrofluoric acid.
2. The method for manufacturing a semiconductor device according to claim 1, wherein the concentration is 0 vol% or more. 11. The method for manufacturing a semiconductor device according to claim 1, wherein electroless nickel plating is performed using an alkaline bath having a pH of 9.0.