JP5622900B2 - Manufacturing method of semiconductor device - Google Patents

Description

  The present invention relates to a method for manufacturing a semiconductor device, in which plating is formed on a Zn compound substrate.

  A compound containing Zn (zinc) such as ZnS is used as a sealing material and window material for optical components using a semiconductor device. For example, there is an optical component in which a semiconductor device is sealed by bonding a second substrate made of ZnS to a first substrate on which a semiconductor device as an optical element is formed.

  When a metal film is formed on a surface of a substrate made of ZnS by plating, electrolytic plating cannot be applied because ZnS is not a good conductor. Therefore, it is conceivable to perform electroless plating instead of electrolytic plating or as a base for electrolytic plating.

The general process of electroless plating on nonconductors such as plastics and forming a metal film on the surface of nonconductors is mainly degreasing, etching, pre-dip, catalyzing (catalyst, accelerator), It consists of a process of electroless plating (Non-Patent Document 1). More specifically, the material to be plated is first attached to a plating jig, and then degreased and cleaned to remove dirt such as fingerprints and oil. The next etching step is to impart an anchor effect to the material to be plated in order to improve adhesion, and chemically roughen the surface of the material to be plated by roughening the surface of the material to be plated with acid. . After neutralization, the catalyzing step is performed. This catalyzing process generally consists of a catalyst and an accelerator. The catalyst adsorbs the Sn ²⁺ -Pd ²⁺ complex to the surface of the material to be plated, and the accelerator dissolves Sn ions with sulfuric acid or hydrochloric acid to precipitate metallic palladium (Sn ²⁺ + Pd ^{2 +} → Sn ⁴⁺ + Pd). In this catalyzing step, metal catalyst nuclei are formed on the surface of the material to be plated, and a metal layer can be formed by electroless plating in a subsequent step. In the electroless plating process, electroless copper plating and electroless nickel plating are used properly according to the requirements of each product, and the metal layer is formed by immersing the material to be plated after the catalyzing process in the electroless plating bath Was formed on the surface of the material to be plated.

  As described above, before the electroless plating step, it is necessary to attach a catalytic metal nucleus such as palladium to the surface of the material to be plated. In the catalyzing process for that purpose, a treatment solution of a tin-palladium mixed solution and an acid, generally called a catalyst, is often used today.

Electroplating Study Group, “Electroless Plating Basics and Applications”, Nikkan Kogyo Shimbun, May 30, 1994, p132

  When the above-described general electroless plating method was applied to the ZnS substrate and the plating was actually performed, the adhesion of the plating film was very weak, and the adhesion was such that it could be peeled off in the tape test. This does not have plating adhesion required for regular use.

  In order to solve the above-described problems, the present invention immerses a substrate made of a compound containing Zn into a copper sulfate solution before forming an electroless plating film on the substrate on which the Cu thin film is formed. The gist is to form a Cu thin film.

According to the present invention, by immersing a substrate made of a compound containing Zn in a copper sulfate solution, Zn ⁺ of the substrate is dissolved, and the remaining elements are bonded to Cu to perform displacement plating. This forms a very thin film of Cu on the surface of the zinc compound. This makes it possible to form a film with high adhesion by electroless plating even with a compound that does not have autocatalytic properties such as ZnS.

It is sectional drawing explaining the concept of the manufacturing method of the plating substrate of this invention in time series. It is sectional drawing of the plating substrate obtained by the method of this invention. It is the schematic of an example of the jig | tool holding a board | substrate. It is the schematic of the jig | tool of FIG. It is a chart which shows the measurement result by the X-ray photoelectron spectroscopy of an Example. It is the schematic of an example of the jig | tool holding a board | substrate. It is the schematic which shows operation | movement of the jig | tool of FIG. It is sectional drawing of the jig | tool of FIG. It is the schematic of an example of the jig | tool which does not rock | fluctuate in a plating solution. It is explanatory drawing of an optical component. It is sectional drawing explaining the manufacturing method of an optical component in time series. It is sectional drawing explaining another manufacturing method of an optical component in time series. It is the schematic of the cross section and fracture interface of the adhesiveness measurement sample of Example 1. It is sectional drawing which shows the evaluation location of the film thickness uniformity in an Example. It is a microscope picture of the hole in an Example. It is a microscope picture of the hole in an Example.

(First Embodiment: Method for Manufacturing Electroless Plating Substrate)
Hereinafter, an embodiment of a method for producing a plated substrate of the present invention will be specifically described with reference to the drawings.

  FIG. 1 is a cross-sectional view illustrating the concept of the method for producing a plated substrate of the present invention in time series. In the illustrated embodiment, an example in which the electroless plating is Ni plating will be described.

  First, a substrate 11 that is a material to be plated is prepared (FIG. 1A). In the present embodiment, the substrate 11 can be made of, for example, ZnS. The substrate 11 is immersed in a copper sulfate solution to form a Cu thin film 12 on the substrate 11 (FIG. 1B). In the illustrated example, the Cu thin films 12 are scattered in an island shape on the substrate 11. Next, as an example of electroless plating, an electroless Ni plating film 13 is formed on the substrate 11 on which the Cu thin film 12 is formed (FIG. 1C). In the illustrated embodiment, an electrolytic Cu plating film 14 is further formed on the electroless Ni plating film 13 by electrolytic plating (FIG. 1D).

  Through the steps described above, a Cu thin film 12 is formed on the substrate 11, and an electroless Ni plating film 13 is formed covering the Cu thin film 12, as shown in a sectional view in FIG. A plated substrate having an electrolytic Cu plating film 14 formed on the electrolytic Ni plating film 13 is obtained.

  The inventors conducted research on the reason why the plating adhesion was poor when electroless plating was performed on a substrate made of ZnS by a conventional method. As a result, the following causes are considered.

First, the ZnS substrate is easily soluble in acid, and particularly vigorously dissolved in hydrochloric acid. As for this, when the ZnS substrate was actually immersed in 0.5 M hydrochloric acid for 5 minutes, the surface was etched, and it was confirmed that the surface was roughened. ZnS does not dissolve in sulfuric acid but dissolves in hydrochloric acid. As a result, the ZnS substrate has priority over the action of chloride ions (Cl ions) binding to Zn ²⁺ to form complex ions, rather than the action of H ⁺ dissolution, which promotes dissolution of the ZnS substrate. It is thought that. When the ZnS substrate is dissolved, the metal catalyst that is the base of the electroless plating is not in close contact, so that even if the subsequent electroless plating is performed, the adhesion cannot be ensured.

  However, hydrochloric acid is indispensable for the conventional electroless plating method. That is, in the catalyst process catalyst, the mixed catalyst solution is generally a mixed solution of stannous chloride and palladium chloride and hydrochloric acid, and is usually a commercially available concentration of stannous chloride and palladium chloride. Dilute the solution with a large amount of hydrochloric acid solution. At this time, hydrochloric acid plays a role of adsorbing Cl ions on the substrate surface and facilitating the formation of a subsequent catalyst.

  Also, in the pre-dip process, which is a pre-process of the catalyst, a solution containing Cl ions may be used to roughen or clean the substrate. Furthermore, when making a bath, the product solution and hydrochloric acid are mixed. There are many cases that must be made.

  Further, in the electroless plating solution, a surfactant containing Cl ions may be used as an additive.

  For these reasons, it has been considered difficult to carry out catalysis without using Cl ions in the conventional method.

In this regard, in this embodiment, the ZnS substrate is immersed in a copper sulfate solution. By this immersion, Zn ⁺ of the substrate is dissolved, and the remaining elements are combined with Cu, and displacement plating is performed. A Cu thin film is deposited on the ZnS substrate surface with a thickness of several atoms. As a result, a catalyst layer called Cu is formed on the ZnS surface that does not have autocatalytic properties, and a plated film can be formed on the ZnS substrate by electroless plating in a later step.

  Further, hydrochloric acid is not added to the copper sulfate solution in which the ZnS substrate is immersed, but sulfuric acid is added. Since this solution does not dissolve the ZnS substrate, the Cu thin film deposited on the surface of the ZnS substrate has high adhesion. Therefore, the electroless plating film formed on this Cu thin film has high adhesion.

  The substrate made of a compound containing Zn is not limited to a ZnS substrate, and a ZnSe substrate, a ZnO substrate, and a ZnTe substrate can be used. A ZnSe substrate, a ZnO substrate, and a ZnTe substrate are compounds having characteristics similar to those of a ZnS substrate.

  The electroless plating is not limited to electroless Ni plating, and may be electroless Cu plating, and is not particularly limited.

[Adhesion improvement]
Regarding the adhesion improvement obtained by immersing a substrate made of a compound containing Zn in a copper sulfate solution to form a Cu thin film on this substrate, after actually treating the ZnS substrate with copper sulfate, the surface was plated with 4 μm of Ni plating After the thickness was formed, a tensile test was performed in the thickness direction of the Ni plating film, and a tensile strength of 6.6 MPa or more was obtained. This value is based on the tensile strength of the adhesive used in the tensile test, and the adhesion strength between the actual ZnS interface and the plating film is considered to be higher than this value. On the other hand, when Ni plating was formed by applying the conventional method to a ZnS substrate, that is, when an HCl-based catalyst was used in the catalyzing process, the plating film was peeled off by the tape test. In this case, the adhesion strength between the ZnS interface and the plating film is 0.1 MPa or less from the tape standard. Therefore, it was confirmed that the plating substrate manufacturing method of this embodiment improved the strength by 160 times or more compared with the conventional method.

[About cost]
In the conventional method, the formation process of the catalyst layer performed before the Ni plating film formation process consists of three steps of neutralization, catalyst, and accelerator, compared to the case where a water washing step is inserted between each of these steps. In the method of the form, it is only necessary to immerse in a copper sulfate solution and wash with water, and the number of steps is greatly reduced. In addition, the Pd catalyst in the conventional method needs to be formed with a thickness of μm, and when a liquid containing catalyst is repeatedly used, the concentration of Pd in the liquid decreases. Therefore, the number of liquids that can be processed is limited to some extent. On the other hand, in the method of the present embodiment, the thickness of the Cu catalyst formed on the substrate is 1 nm or less. It is thought that there are few. In addition, even if the cost and liquid composition of Pd, which is the catalyst of the conventional method, and Cu, which is the catalyst of the method of the present embodiment, are compared, the present embodiment has a simpler structure, which greatly reduces the cost. It seems possible.

  The copper sulfate solution is preferably contained at a concentration of sulfuric acid: 0.1 to 2.0 mol / liter and copper sulfate: 0.1 to 1.0 mol / liter. By using copper sulfate as the metal salt of the catalyst raw material and copper sulfate aqueous solution as the solution, the catalyst layer can be formed on the substrate surface while suppressing dissolution of the substrate made of a compound containing zinc such as ZnS. Here, when copper sulfate is 0.1 mol / liter or more, abnormal precipitation does not occur, and when it is 1.0 mol / liter or less, copper sulfate crystals do not precipitate in the solution when stored at room temperature. Therefore, the range of 0.1 to 2.0 mol / liter is preferable. Sulfuric acid has an action of suppressing excessive dissolution of the base material, and is preferably in the range of 0.1 to 2.0 mol / liter as a range in which the effect is sufficiently exhibited and other harmful effects are not caused.

  After forming the Cu thin film, before forming the electroless plating film, it is preferable that a metal having a higher ionization tendency than Cu is brought into contact with the substrate and the formation of the electroless plating film is started while keeping the contact. By passing a small amount of current through a temporary contact of a metal (base metal) that has a higher ionization tendency than Cu with a Cu thin film attached to the surface of a substrate made of a Zn-containing compound such as ZnS, and making the material to be plated a base metal. The plating reaction can be started. Therefore, in addition to the effect that a highly adhesive film can be formed by electroless plating on a substrate made of a compound containing Zn as described above, electroless plating can also be started for a smooth substrate. Therefore, there is an effect that electroless plating can be easily performed.

  An example of such a metal (base metal) having a higher ionization tendency than Cu is Ni. Materials other than Ni include Fe, Co, Cr and the like. In addition, even if it is a base metal rather than Cu, the metal which melt | dissolves easily in the plating solution of a post process cannot be used. Therefore, the metal that is easily dissolved in the plating solution is excluded from the metal that contacts the substrate.

  As a specific method of bringing a metal having a higher ionization tendency than Cu into contact with the substrate, the substrate may be held by a jig including a metal having a higher ionization tendency than Cu. By giving the effect of initiating the plating reaction to the jig itself that holds the substrate immersed in the plating solution during the electroless plating process, the process for contacting the base metal can be omitted. Cost can be reduced.

  FIG. 3 schematically shows an example of the jig 31 that holds the substrate 21 during the electroless plating process. 3A is a plan view, FIG. 3B is a perspective view, and FIG. 3C is a cross-sectional view. The illustrated jig 31 has a substantially U-shaped cross-sectional shape, and sandwiches both surfaces of the substrate 21 on which a Cu thin film is formed. At least a portion in contact with the substrate 21 of the jig 31 is made of a metal having a higher ionization tendency than Cu. By using such a jig, a Cu thin film formed on the surface of the substrate 21 can be made from Cu without preparing a material for contacting the base metal separately or performing a contact process. In addition, a metal (base metal) having a large ionization tendency can be temporarily brought into contact.

  At the time of electroless plating, as shown in a perspective view in FIG. 4, a wire 32 is fixed to the jig 31, and the jig 31 and the substrate 21 are suspended in the plating bath by the wire 32. The wire can be, for example, an iron wire protected with an insulating tape.

  Electroless Ni plating bath for forming Ni plating as electroless plating is 0.1 to 1.0 mol / liter of sodium succinate and DL malic acid and nickel chloride or sulfide, or sulfamine oxide, sodium phosphinate, respectively. In a concentration of 0.1 to 1.0 mol / liter. Concerning the upper and lower limits of the concentration of these components, the concentration is within a range where both electroless plating can be normally deposited (the plating solution does not decompose and electroless plating occurs due to the oxidation-reduction reaction of the reagent). It was decided as. By using a plating bath containing these components, it is possible to activate the Cu catalyst formed on the ZnS substrate and form an electroless Ni plating film having excellent adhesion. Therefore, it is possible to further enhance the effect that a film having high adhesion can be formed by electroless plating on a substrate made of a compound containing Zn as described above.

  In the case of forming Ni plating as electroless plating, the electroless Ni plating bath may be a plating bath obtained by adding 0.001 to 0.010 mol / liter of saccharin sodium in addition to the above-described components. The upper and lower limits of the saccharin sodium concentration described above are defined as concentrations within which electroless plating can be normally deposited (the plating solution does not decompose and electroless plating occurs due to the oxidation-reduction reaction of the reagent). It was. By adding saccharin to the electroless Ni plating bath, the internal stress of the plating film can be suppressed. Therefore, it is possible to further improve the effect that a film having high adhesion can be formed by electroless plating on a substrate made of a compound containing Zn as described above.

FIGS. 5A to 5D are charts showing the results of X-ray photoelectron spectroscopy (XPS) analysis of the substrate surface after electroless Ni plating according to Example 1 described in detail later. The vertical axis represents the intensity of X-ray photoelectrons at each binding energy, and the horizontal axis represents the atom binding energy. As can be seen from these figures, as a result of analysis, zinc is in the chemical state of ZnS, copper is in the chemical state of Cu ₂ O, nickel is in the chemical state of nickel oxide (III) Ni ₂ O ₃ and nickel sulfide NiS, Existing.

  The reaction in which the copper catalyst is formed on the substrate surface is considered to be shown in the following formula.

  The following reactions occur when immersed in a copper sulfate solution.

ZnS + Cu ²⁺ → CuS + Zn ²⁺
ZnS + 2Cu ²⁺ → Cu ₂ S + Zn ²⁺
Next, the following reaction occurs in the process of washing and drying the substrate after immersion.

2CuS + 7 / 2O ₂ → Cu ₂ O + 2SO ₃ (solid)
2Cu ₂ S + 4O ₂ → 2Cu ₂ O + 2SO ₃ (solid)
2CuS + 5 / 2O ₂ → Cu ₂ O + 2SO ₂ (ki)
Cu ₂ S + 3/2 O ₂ → Cu ₂ O + SO ₂ (ki)
The reaction in which the electroless Ni-P plating film is formed on the base material on which the copper catalyst is formed is considered to be represented by the following formula.

  The following reactions occur when immersed in an electroless Ni-P plating solution.

First, due to the action of the reducing agent,
Cu ₂ O + 2H ⁺ → 2Cu + H ₂ O (Cu ₂ O is reduced to Cu)
The following reaction occurs when metal Cu is not formed by the above reaction.

^{_{H 2 PO 2 - + H 2}} O → H 2 PO 3 - + 2H + + 2e -
Ni ²⁺ + ZnS → NiS + Zn ²⁺ (bonding at the interface)
^{Ni 2+ + 2e - → Ni (} Ni film deposition)
Next, the following reaction occurs on the surface of the plating film in the process of washing and drying the substrate after immersion.

4Ni + 3O ₂ → 2Ni ₂ O ₃ (Surface natural oxidation)
In general, the oxidation reaction of Cu and Ni in the atmosphere is considered to occur in the surface from several atomic layers to several tens of atomic layers. The thickness of the plating film of the measurement sample used in this analysis was several nm. From these facts, it is considered that oxides of Cu and Ni were observed.

  From the above reaction / measurement results, the process of forming the electroless plating film on the base material is considered as follows.

By immersing the base material in an aqueous copper sulfate solution, CuS or Cu ₂ S is formed on the base material, and they change to Cu ₂ O during the water washing and drying process.

Next, by immersing the base material on which Cu ₂ O is formed in an electroless plating bath, Cu ₂ O is reduced by the reducing agent contained in the plating solution to change to metal Cu.

  Next, with a metal Cu as a catalyst, a minute current flows by contact of the plating jig, electroless plating is started, and an electroless plated film is formed on the substrate.

  Next, in the process of washing and drying them, an oxide film of about several nm is formed on the electroless plating film surface.

  The formation of NiS in the process of electroless Ni-P plating indicates that a layer having a chemical bond with strong adhesion to the substrate was formed on the plating film. Thereby, it is considered that strong adhesion was obtained between the electroless Ni-P plating film formed according to the present invention and the substrate.

(Second Embodiment: Method for Manufacturing Electroplating Substrate)
After the step of forming an electroless plating film made of a compound containing Zn, a step of forming an electrolytic Cu plating film on the electroless plating film can be performed. A substrate made of a compound containing Zn and subjected to electroless plating can be used as a plated substrate as a product, but a product obtained by performing electrolytic plating on this electroless plating can also be used as a plated substrate as a product. it can.

  By forming an electrolytic Cu plating film on the electroless plating film, the film thickness of the entire plating can be increased. In addition, since the thickness of the entire plating can be increased, a through-hole that ensures airtightness is formed by providing a through-hole in the ZnS substrate and filling the through-hole with electroless plating electrolytic Cu plating. It becomes possible.

  The electrolytic Cu plating solution may be contained at a concentration of 0.1 to 2.0 mol / liter of sulfuric acid, 0.1 to 1.0 mol / liter of copper sulfate, and 0.001 to 0.1 mol / liter of chloride ions. By making the copper sulfate 0.1 mol / liter or more, abnormal precipitation does not occur, and by making it 1.0 mol / liter or less, copper sulfate crystals do not precipitate in the solution when stored at room temperature, It is preferable to be in the range of -2.0 mol / liter. Since sulfuric acid has an action of suppressing excessive dissolution, it is preferably in a range of 0.1 to 2.0 mol / liter as a range that exhibits a sufficient effect and does not cause other harmful effects. The upper limit of the chloride ion concentration is the limit concentration at which crystal grains are not coarsened by the chloride ion, and the lower limit is the range of 0.001 to 0.1 mol / liter as the minimum concentration at which the plating precipitation promotion effect by the chloride ion can be obtained. It is preferable to do this.

  By adjusting the electrolytic Cu plating solution to the concentration of each component described above, it is possible to form a plating film while suppressing defects in voids and holes in the material to be plated. Polyethylene glycol and various organic compounds having a disulfide bond can be added to the plating solution to control the surface form and film thickness.

  In the step of forming the electrolytic Cu plating, it is preferable to swing the substrate immersed in the electrolytic Cu plating solution by the flow of the plating solution. By swinging the object to be plated, an irregular flow is generated in the plating solution around the material to be plated, thereby promoting the diffusion of metal ions. Due to this effect, there is an effect of suppressing the film thickness non-uniformity generated in the plating film and the generation of voids and defects. Further, since the flow of the plating solution is used, a power device that is generally used for rocking is not required, so that the cost can be reduced.

  Note that the substrate immersed in the plating solution as described above can be swung not only during the electrolytic Cu plating step but also during the electroless plating step prior to the electrolytic Cu plating step. Even if it is performed during the electroless plating process, swinging the object to be plated generates an irregular flow in the plating solution around the material to be plated, thereby promoting the diffusion of metal ions. is there. Due to this effect, there is an effect of suppressing the film thickness non-uniformity generated in the plating film and the generation of voids and defects. Further, since the flow of the plating solution is used, a power device that is generally used for rocking is not required, so that the cost can be reduced.

(Third embodiment: jig for plating)
An example of a jig suitable for swinging the substrate immersed in the plating solution by the flow of the plating solution is shown in FIGS. 6-8, the same code | symbol is attached | subjected about the same member. 6A is a top view of the jig 50, FIG. 6B is a front view of the jig 50, and FIG. 6C is a perspective view of the jig 50. The jig 50 is a jig for holding the substrate 41 on which the electroless plating is formed. The jig 50 is made of an insulating material and is in contact with the substrate 41. The cylinder 50 has flexibility due to the flow of the plating solution. And a conductor 53 that is inserted into the cylindrical portion 52 and is electrically connected to the substrate 41 through the substrate holding portion 51 and connected to a power source (not shown). As shown in a cross section in FIG. 8, the substrate carrier 51 and the conductor 53 have a shape that sandwiches a part of the substrate 41, and both surfaces of the substrate 41 can come into contact with the plating solution. By using such a jig 50, there is an effect of causing the substrate 41 to swing.

  In electro Cu plating, the plating solution is agitated by a stirrer such as a magnetic stirrer or propeller mixer, or the plating solution is fluidized using a feed pump, or bubbles using an air pump This is performed with stirring of the plating solution.

  When the substrate 41 attached to the jig 50 shown in FIG. 6 is immersed in the stirred liquid, the cylindrical portion 52 is made of a flexible material, and is inserted into the cylindrical portion 52. Since the portion of the conductor 53 is also flexible, as shown in FIG. 7, the cylindrical portion 52 is bent by the flow of the plating solution generated by stirring, and the substrate 41 and the substrate carrying portion 51 are swung. In such a state where the substrate 41 is swung, electric current is applied and electroplating is performed. Thus, in addition to the stirring of the plating solution, the substrate 41 is swung, so that a flow of the plating solution is formed on the surface and inside of the substrate 41 and the diffusion of metal ions is promoted. It is considered that this effect can be obtained when the jig 50 is applied to electroless plating.

  Thus, the plating film thickness, shape, and film thickness are uniform depending on the shape of the plating jig so that the substrate can be swung by the flexibility of the jig holding the substrate immersed in the plating solution. Gender can be controlled. By changing the shape of the jig, the plating solution flow state, ion diffusion, and the flow of minute current are controlled, and the local plating speed of the object to be plated is changed, so that the plating film thickness There is an effect of controlling the shape and film thickness uniformity.

  For comparison, FIG. 9 is a front view (FIG. 9A), a side view (FIG. 9B), and a top view (FIG. 9C) of an example of a jig that does not swing in the plating solution. Show. The jig shown in FIG. 9 is provided with a substrate carrying portion 61 made of a rigid insulating material, and a conductor that is provided inside the substrate carrying portion 61 and is exposed at one end of the substrate carrying portion and connected to a power source (not shown). 62. The jig shown in FIG. 9 shows a cross section of the material. Since the substrate holding part 61 has rigidity, it is not bent even by the flow of the plating solution generated by stirring during the electrolytic plating.

Fourth Embodiment: Semiconductor Device Manufacturing Method
Next, a manufacturing method of a semiconductor device to which the plating substrate manufacturing method of the present invention is applied will be described.

  In an optical component manufacturing process, an optical component in which a semiconductor device is sealed by bonding a second substrate made of ZnS to a first substrate on which a semiconductor device as an optical element is formed is manufactured at low cost. Considering the application of wafer level packaging, it is desirable to form a through electrode on the second substrate made of ZnS and connect to the optical element through the through electrode. Therefore, it is required to fill the through hole formed in the second substrate with a conductive metal for the through electrode. In addition, in order to join the first substrate on which the semiconductor device is formed and the second substrate made of ZnS by a surface activated joining method or a solder joining method, a metal film is formed on the joining portion of the second substrate. It is required to keep. However, since ZnS is not a good conductor, the filling of the metal into the through hole of the second substrate and the formation of the metal film at the joint cannot be performed directly by electroplating.

  Therefore, a semiconductor device is manufactured by applying the plating substrate manufacturing method of the present invention to the formation of the through electrode and the formation of the metal film at the joint portion of the second substrate. More specifically, when manufacturing a semiconductor device in which a second substrate made of a compound containing Zn is bonded to a first substrate having an element region, after forming a through hole in the second substrate, Two substrates are immersed in a copper sulfate solution to form a Cu thin film on the surface of the substrate including the through holes, and then an electroless plating film is formed on the surface of the substrate on which the Cu thin film is formed. Then, the through hole of the second substrate is filled with Cu.

  This manufacturing method will be described with reference to FIGS.

  FIG. 10 is a schematic cross-sectional view (FIG. 10A) and top view (FIG. 10B) of an optical component as an example of a semiconductor device obtained by applying the semiconductor device manufacturing method of the present invention. is there. The illustrated optical component is composed of a window substrate 110 and an element substrate 100, and is joined to circulate the outer frame of the element substrate 100 through a metal layer 180 as shown in the top view of FIG. A space region 150 is provided between the window substrate 110 and the element substrate 100.

  Further, a plurality of through electrodes 120 are arranged in a plane on the window substrate 110 as shown in the top view of FIG. 10B in order to extract signals from the elements. The periphery of the through electrode 120 is insulated from at least another bonding metal layer 180 by the window substrate 110. A surface electrode 140 connected to the through electrode 120 is formed on the surface of the window substrate 110. Further, the through electrode 120 and the electrode of the element substrate 100 are connected via the electrode 130. In addition, in order to join the window substrate 110 and the element substrate 100, the metal layer 180 respectively formed on the opposing surfaces of the two are the one formed on the window substrate 110 and the one formed on the element substrate 100. It is desirable that they are metals such as Au, Cu, Al, and the same material. In addition, the electrode 130 that connects the through electrode 120 of the window substrate 110 and the electrode of the element substrate 100 is also formed of the window substrate 110 and the element substrate 100 such as Au, Cu, and Al. It is desirable that they are metal and are the same material.

  An example of a manufacturing process of the optical component shown in FIG. 10 will be described using a time-series schematic cross-sectional view shown in FIG.

  First, the window substrate 210 is prepared. This window substrate 210 has a concave portion to be a space region at a position corresponding to an element area of an element substrate to be bonded later, in the central portion on the back surface side. It is filled with a protective resin or the like (FIG. 11A). In the illustrated embodiment, an example in which the window substrate 210 is provided with a recess in the central portion on the back side in order to manufacture an optical sensor as an optical component is shown. However, depending on the type of the optical sensor and other semiconductors Depending on the configuration of the apparatus, this recess may be omitted.

  Next, the through-hole 225 is provided in the window substrate 210 (FIG. 11B). As a drilling method for forming the through hole 225, a processing method such as drilling, blasting, laser, or etching may be used.

  Next, according to the plating substrate method of the present invention, the window substrate 210 is immersed in a copper sulfate solution to perform the displacement plating shown in Example 1, and the entire surface of the window substrate 210 and the inner surface of the through hole are formed. Cu thin film 226 adheres to (FIG. 11 (c)). At this time, the Cu thin film 226 does not adhere to the resist 215.

  Next, by performing Ni electroless plating as described in the first embodiment, an electroless Ni film 227 is generated in all areas to which the Cu thin film 226 is attached (FIG. 11D). At this time, the electroless Ni film 227 is not formed on the resist 215.

  By generating the electroless Ni film 227, the window substrate 210 after plating becomes a conductor, and electrolytic plating becomes possible. Then, next, the electrolytic Cu film 228 is formed on the surface of the window substrate 210 by performing electrolytic plating of Cu as shown in the second embodiment on the window substrate 210 after plating. The inside of the through hole 225 is filled with Cu (FIG. 11E).

  After filling the inside of the through-hole 225 with Cu, the upper and lower surfaces of the window substrate 210 are lapped and polished to remove excess Cu plating film formed on the upper and lower surfaces of the window substrate 210 made of ZnS. The surface is exposed (FIG. 11 (f)).

  Further, an electrode pad 230 and a sealing metal layer 280 are formed on the lower surface side of the window substrate 210 (the bonding side with the element substrate 260). Similarly, the electrode pad 231 is patterned on the upper surface side of the window substrate 210 (FIG. 11G). At this time, the electrode pad 230, the sealing metal layer 280, and the electrode pad 231 may be formed selectively using a mask using sputtering, vapor deposition, plating, or the like.

  Next, the resist in the concave portion 250 corresponding to the light transmission portion of the window substrate 210 is removed (FIG. 11H).

  Finally, the window substrate 210 and the element substrate 260 are bonded ((FIG. 11 (i)), thereby enabling packaging of the element substrate 260. At this time, a method of bonding the window substrate 210 and the element substrate 260 In this case, a bonding method such as surface activation bonding, solder bonding, resistance heating, or diffusion bonding may be used.

  According to the method for manufacturing a semiconductor device of the present embodiment, the plating method of the present invention can be applied as a through electrode of an optical sensor using a ZnS substrate as a window material. For this reason, high durability and high airtightness can be obtained, and the reliability of the sensor can be improved.

  The semiconductor device manufactured by the semiconductor device manufacturing method of this embodiment can use this Ni layer as wiring by providing a non-conductive ZnS substrate with an Ni layer by electroless plating. Further, the Ni layer can be used as a conductive layer for electrolytic plating, and a through electrode can be formed on a ZnS substrate serving as an optical member by subsequent electrolytic Cu plating. Further, ZnS and Ni of the substrate form a compound called NiS and has a strong bonding force with the ZnS substrate, so that a plating film with high adhesion is obtained.

  Furthermore, considering the application of ZnS substrates to optical device window substrates, the Cu thin film formed by immersion in a copper sulfate solution is very thin and cannot be completely removed in the post-deposition process. Can be estimated to have little effect on the transmittance of the substrate itself.

  FIG. 12 illustrates another example of the optical component manufacturing process using time-series schematic cross-sectional views. In FIG. 12, the same members as those in FIG. 11 are denoted by the same reference numerals, and redundant description is omitted in the following description.

  The difference between the manufacturing process shown in FIG. 12 and the manufacturing process shown in FIG. 11 is that a sealing metal is generated by the electrolytic Cu plating film 228.

  As shown in FIG. 12B, a notch 240 is provided in advance near the end of the back surface of the window substrate 210. Thereafter, through the same manufacturing process as described above with reference to FIG. 11, the electroless Ni film 227 and the electrolytic Cu plating film 228 are also formed in the notch 240 (FIG. 12E). .

This is lapped and polished in the same manner as shown in FIG. 11, so that the electrolytic Cu plating film 228 remains in the sealing area even if the surface of the window substrate 210 made of ZnS is exposed. Thus, unlike the manufacturing process shown in FIG. 11, the sealing metal layer 280 is formed in the notch 240 of the window substrate 210 without providing a process for forming the sealing metal layer 280 by a film forming method such as sputtering. Since the electrolytic Cu plating film 228 directly becomes a sealing metal layer, it can be joined to the element substrate 260 side. As a result, the number of processes can be reduced, leading to cost reduction.

  Thus, in the manufacturing process shown in FIG. 12, the metal layer for sealing is formed by a sputtering process of metal or the like by applying the plating method of the present invention not only to the through electrode but also to the joint portion with the element substrate. Doing so is unnecessary, leading to cost reduction. Furthermore, since the electrolytic Cu plating film as the metal layer for sealing has high adhesion, it leads to improvement in the reliability of the joint.

Next, the present invention will be specifically described with reference to examples.

Example 1
In Example 1, a ZnS substrate was immersed in a copper sulfate solution to form a Cu thin film on the substrate, and then an electroless plating film was formed on the substrate on which the Cu thin film was formed.

A copper sulfate aqueous solution having the following composition was prepared using copper sulfate (CuSO ₄ .5H ₂ O) and sulfuric acid (H ₂ SO ₄ ) as main components. In addition, sulfuric acid shows the effect | action which suppresses the excessive melt | dissolution of a board | substrate.

■ Composition of aqueous copper sulfate solution:
CuSO ₄ · 5H ₂ O: 0.6 mol / liter
H ₂ SO ₄ : 1.8 mol / liter Then, the substrate was immersed in the above aqueous solution, and an immersion treatment was performed at an aqueous solution temperature of 25 ° C. for 80 minutes to form a Cu thin film 12 as a copper catalyst on the substrate 11 (FIG. 1B). )reference).

  At this time, the copper catalyst is in the form of a very thin thin film, and the film thickness is only a few atoms attached, and the appearance is almost the same as before the copper catalyst was applied.

Next, nickel sulfate (NiSO ₄ · 6H ₂ O) and sodium hypophosphite _{(H 2 NaO 2 P · H} 2 O), sodium succinate _{(NaOOCCH 2 CH 2 COONa · 6H} 2 O), DL- malic acid Adjust the pH to 4.8 with sodium hydroxide to an electroless Ni-P plating bath containing (HOOCCHOHCH ₂ COOH) and saccharin (C ₇ H ₄ NNaO ₃ S · 2H ₂ O) Prepared.

■ Composition of electroless Ni-P plating bath:
NiSO ₄ · 6H ₂ O: 0.1 mol / liter
H ₂ NaO ₂ P · H ₂ O: 0.3 mol / liter
NaOOCCH ₂ CH ₂ COONa ・ 6H ₂ O: 0.1 mol / liter
HOOCCHOHCH ₂ COOH: 0.1 mol / liter
C ₇ H ₄ NNaO ₃ S · 2H ₂ O: 0.006 mol / liter
pH: 4.8
As shown in FIG. 3, the substrate 21 on which the copper catalyst is formed is held by a jig 31 having a nickel film having a thickness of 10 μm or more formed on the surface. The jig 31 shown in FIG. 3 has a shape in which a part of the substrate 21 is sandwiched from both sides. The jig 31 is brought into direct contact with the substrate 21 and nickel, which is a dissimilar metal having a higher ionization tendency than Cu together with the support of the substrate 21. Contacted with a copper catalyst.

  As shown in FIG. 4, a wire 32 made of an iron wire protected with an insulating tape is attached to a jig 31 so that the substrate 21 can be suspended and held in the plating bath.

  Then, the substrate 21 on which the copper catalyst is formed is immersed in the above plating bath together with the jig 31, and electroless plating is performed for 210 minutes at a bath temperature of 70 ° C. to form an electroless Ni—P plating film 13 having an average film thickness of 15 μm. (See FIG. 1 (c)).

5A to 5D are charts showing the results of analysis by X-ray photoelectron spectroscopy (XPS) of the substrate surface after electroless Ni plating according to Example 1. FIG. The vertical axis represents the intensity of X-ray photoelectrons at each binding energy, and the horizontal axis represents the atom binding energy. As can be seen from these figures, as a result of analysis, zinc is in the chemical state of ZnS, copper is in the chemical state of Cu ₂ O, nickel is in the chemical state of nickel oxide (III) Ni ₂ O ₃ and nickel sulfide NiS, Existing.

  The formation of NiS in the process of electroless Ni-P plating indicates that a layer having a chemical bond with strong adhesion to the substrate was formed on the plating film. Thereby, it is considered that strong adhesion was obtained between the electroless Ni-P plating film formed according to the present invention and the substrate.

(Example 2)
In Example 2, electrolytic copper plating was performed on the ZnS substrate on which the electroless Ni—P plating film 13 was formed according to Example 1 described above.

Hydrochloric acid (HCl) was added to an electrolytic copper plating bath mainly composed of sulfuric acid steel (CuSO ₄ .5H ₂ O) and sulfuric acid (H ₂ SO ₄ ) to prepare a plating bath having the following composition. Bisdisulfide (SPS) acts as a plating accelerator, and polyethylene glycol (PEG) acts as a plating inhibitor.

■ Composition of electrolytic copper plating bath:
CuSO ₄ · 5H ₂ O: 0.6 mol / liter
H ₂ SO ₄ : 1.8 mol / liter
HCl: 100ppm
Bis (3-sulfopropyl) disulfide (SPS): 5ppm
Polyethylene glycol (PEG4000): 600ppm
As shown in FIG. 6, the substrate 41 on which the copper catalyst and the electroless Ni—P plating film are formed is held by a jig 50. As shown in FIG. 6, the jig 50 has a substrate holding portion 51 that is an insulating material and a conductor 53 that is copper, and electrical conduction to the substrate 41 is ensured by the conductor 53. Further, the cylindrical portion 52 of the jig 50 has flexibility to be deformed by the flow of the plating solution. As shown in FIG. 8, the substrate holding part 51 and the conductor 53 of the jig 50 are shaped so as to sandwich a part of the substrate 41 so that both surfaces of the substrate 41 are in contact with the plating solution.

Then, the substrate 41 is immersed in the above plating bath, and the substrate 41 on which the electroless Ni—P plating film is formed is used as a cathode and the copper plate is used as an anode, and the plating bath temperature is 25 ° C. and the cathode current density is 5 mA / cm ² . Electroplating was performed for a minute, and an electric Cu plating film 14 was formed on the electroless Ni-P plating film (see FIG. 1D).

  In this electroplating process, the plating solution is stirred by the stirrer, and the jig 50 is bent by the flow of the plating solution generated by the stirring, and the substrate holding portion 51 and the substrate 41 are swung (see FIG. 7). In such a state where the substrate 41 is swung, an electric current is applied to perform electroplating.

Example 3
In Example 3, electroplating was performed in the same manner as in Example 2 except that the conditions for electro Cu plating in Example 2 were 10 mA / cm ² and the plating time was 90 minutes.

(Comparative Example 1)
In Comparative Example 1, the same copper sulfate aqueous solution as in Example 1 was used, except that the substrate was changed from ZnS to glass, and immersion treatment was performed in the same manner as in Example 1.

(Comparative Example 2)
In Comparative Example 2, the same electroless plating bath as in Example 1 was used except that the jig used in electroless Ni-P plating in Example 1 was changed to a non-metallic plastic. Then, electroless Ni-P plating was performed.

(Comparative Example 3)
Comparative Example 3 uses an electroless plating bath similar to that of Example 1 except that contact is made with an iron wire covered with a Ni film, and uses a jig made of plastic as in Comparative Example 2 to perform electroless Ni. -P plating was performed.

(Comparative Example 4)
Comparative Example 4 uses the same electroless plating bath as in Example 1 except that the substrate was not immersed in the copper sulfate solution, and thus the copper catalyst was not formed. Ni-P plating was performed.

(Comparative Example 5)
In Comparative Example 5, electro-Cu plating was performed in the same manner as in Example 2 using the same electroplating bath as in Example 2 except that electroless Ni-P plating was not performed.

(Comparative Example 6)
In Comparative Example 6, an electroless plating film was formed by a conventional method (water washing was performed between the three steps of neutralization, catalyst, and accelerator).

Example 4
Example 4 uses the same plating bath as in Example 3 except that electro Cu plating is performed using a jig that does not swing the substrate shown in FIG. went.

For Example 1 and Example 2 described above and Comparative Examples 1 to 4 and 6, the electroless Ni—P plating on the substrate was observed and the uniformity of the plating film was visually observed. The results are shown in Table 1.

  From Table 1, it is clear that Example 1 is most excellent in uniformity. Further, since the electro Cu plating could not be performed in the comparative example 5, it is clear that the electroless Ni-P plating film is necessary for performing the electro Cu plating.

  Next, the adhesion of the plating substrates of Example 1 and Comparative Example 6 was evaluated. The adhesion test was performed using an adhesive tape compliant with JIS-Z1522 by the method specified in JIS-H8504. As a result, in Example 1, the plating film did not peel off, but in Comparative Example 6, the electroless plating film peeled off. From this, it is clear that Example 1 is excellent in adhesion.

  Furthermore, in order to measure the adhesion of Example 1, the following adhesion test was performed.

  This adhesion test was performed according to the following procedure (see FIG. 13).

(1) Fix jig 74 (□ 12mm) and ZnS substrate sample 71 (□ 12mm) with adhesive 73 (3M Scotch-weld DP-460 off-white) and cure at room temperature.

(2) After bonding to the jig 74, the surface of the ZnS substrate sample 71 (all four surfaces) is polished with sandpaper, and the adhesive residue on the side surface is removed.

(3) Conduct a tensile test (n = 1). The tensile speed is 1.0 mm / min (load cell 5kN).

  As a result, the adhesive 73 was broken and the ZnS substrate sample 71 was broken, but the plating film 72 was not peeled off. From this, it was found that the adhesion of the plating film 72 was 16.6 MPa or more.

  Next, about Example 3 and Example 4, about the electrolytic Cu plating film 14 obtained by carrying out electrolytic Cu plating, the film thickness uniformity and the shape were measured and evaluated.

  As shown in the cross-sectional view of FIG. 14, this film thickness uniformity is evaluated by cutting the vicinity of the hole 82 of the ZnS substrate 81 subjected to electrolytic Cu plating in the thickness direction, and observing the cut cross section with a microscope. The film thickness of the formed electrolytic Cu plating film and the film thickness of the plating film in the hole 82 were measured and evaluated.

  FIGS. 15A and 15B are micrographs thereof, FIG. 15A shows Example 3, and FIG. 15B shows Example 4. FIG. In Example 3 shown in FIG. 15A, a thick Cu plating film is formed inside the hole. On the other hand, in Example 4 shown in FIG. 15A, it was observed that the Cu plating film inside the hole was thinner than Example 3 and was more non-uniform than Example 3.

  Next, Example 2 and Example 3 were similarly evaluated by measuring the film thickness uniformity and shape of the electrolytic Cu plating film obtained by electrolytic Cu plating.

  FIG. 16 is a photomicrograph of a portion where the hole of the substrate is cut in the thickness direction. FIG. 16 (a) shows Example 2 and FIG. 16 (b) shows Example 3. In Example 2 of FIG. 16A, the inside of the hole is almost filled with a Cu plating film. On the other hand, in Example 3 of FIG. 16B, it was observed that the Cu plating film was not sufficiently filled as in Example 2.

  In each of the embodiments described above, the substrates 11, 21, and 41 correspond to substrates made of a compound containing Zn of the present invention. The element substrates 100 and 260 correspond to the first substrate of the present invention. Window substrates 110 and 210 correspond to the second substrate of the present invention.

  As mentioned above, although the embodiment to which the invention made by the present inventors was applied has been described, the present invention is not limited by the description and the drawings that form part of the disclosure of the present invention according to this embodiment. That is, it should be added that other embodiments, examples, operation techniques, and the like made by those skilled in the art based on the above embodiments are all included in the scope of the present invention.

DESCRIPTION OF SYMBOLS 11 Board | substrate 12 Cu thin film 13 Electroless Ni plating film 14 Electrolytic Cu plating film 50 Jig 52 Cylindrical part 52 (flexible member)
100, 260 Element substrate (first substrate)
110, 210 Window substrate (second substrate)
225 Through hole

Claims (1)

A method of manufacturing a semiconductor device in which a second substrate made of a compound containing Zn is bonded to a first substrate having an element region,
After forming a through hole in the second substrate, the second substrate is immersed in a copper sulfate solution to form a Cu thin film on the surface of the substrate including the through hole, and then a metal having a higher ionization tendency than Cu. By holding a substrate with a jig provided with, a metal having a higher ionization tendency than Cu is brought into contact with the substrate, and formation of an electroless plating film is started while being in contact with the substrate, on which the Cu thin film is formed. A method of manufacturing a semiconductor device, comprising: forming an electroless plating film, and performing electrolytic Cu plating to fill the through hole of the second substrate with Cu.