JP5021538B2 - Method for forming metal structure - Google Patents

Description

  The present invention relates to a method for forming a structure such as a wiring, an electrode, or a MEMS (Micro-Electro-Mechanical Systems) device, and more particularly to a method for forming a metal structure for producing a structure by plating.

  In a highly integrated circuit mounting process, there is a technique called wire bonding in which substrates are electrically connected through pads provided on each substrate. As a material constituting the pad, gold (Au) is often used from the viewpoint of chemical stability and high conductivity. Since the reliability of connection by wire bonding depends on the cleanness of the pad surface, removal of contaminants on the pad surface is an important technique.

  A MEMS device, which is a micromachine created using semiconductor process technology, is configured by three-dimensionally arranging structures such as fine movable parts and control electrodes. One method for forming such a structure is a multilayer thickening technique by plating (see Patent Document 1). In the plating method, a structure is formed by growing a plating film on the surface where a resist pattern is opened on a seed layer that is a seed for plating growth or on a structure formed of a metal to be plated. Forming the body. In this plating, the same kind of metal is deposited on the surface of the seed layer by an electrochemical reaction with the plating solution on the surface of the seed layer on which the plating film is formed. In such plating, Au is often used as a material constituting the seed layer and the metal structure from the viewpoint of chemical stability and high conductivity.

  The uniformity and reproducibility of the shape of the structure formed by plating depends on the seed layer or the seed layer exposed in the opening of the resist pattern formed by patterning the resist on the metal structure, or Depends on the cleanliness of the surface of the metal structure. Therefore, also in this case, removal of contaminants on the surface of the seed layer and the metal structure is an important technique.

Conventionally, as a technique for removing contaminants on the surface, oxygen (O ₂ ) plasma, oxygen plasma of a mixed gas with an inert gas such as argon (Ar) or nitrogen (N ₂ ), or carbon tetrafluoride An irradiation treatment with a plasma of a mixed gas of fluorine-containing gas such as (CF ₄ ) and oxygen is generally used.

JP 2003-270554 A

However, nonuniformity occurs in the shape and height of the plating even after the seed layer in the resist pattern opening or the surface of Au constituting the metal structure is processed by irradiation with plasma containing O _2. There was a case. In addition, after the irradiation treatment with plasma containing O ₂ , even if the plating process is started, the deposition of the plating is not started immediately, and it is confirmed that the plating starts to be deposited after a dead time (incubation). Has been. This phenomenon, O ₂ or by CF ₄ / O _2, such as plasma species and the irradiation time, and also varies depending on the location in the wafer. Accordingly, when the seed layer in the opening of the resist pattern or the surface of the metal structure is plated after the irradiation treatment with the plasma containing O ₂ , there is a problem that the plating cannot be deposited with good controllability.

  The present invention has been made to solve the above-described problems, and a seed layer or a metal structure in which a resist pattern is opened even after an irradiation process including activated oxygen is performed. An object of the present invention is to make it possible to deposit the plating uniformly and with good controllability on the surface of the substrate.

  The metal structure forming method according to the present invention includes a first step in which a base layer made of gold is formed on a substrate, and a second step in which activated oxygen is applied to the surface of the base layer. And a third step of removing the gold oxide formed on the surface of the underlayer in the second step, and a fourth step of forming a metal structure by plating on the surface of the underlayer after the third step. And at least a process.

In the method for forming the metal structure, in the third step, by heating the underlying layer in an atmosphere of - reducing gas to remove oxides of gold. In this case, the temperature of the heating in the third step, the 110 ° C. or less.

As described above, according to the present invention, after removing the gold oxide formed on the surface of the underlayer by applying activated oxygen to the surface of the underlayer composed of gold, the underlayer Since the metal structure is formed by plating on the surface of the seed layer, even after the irradiation process including the activated O ₂ , the resist pattern has an opening on the seed layer or the surface of the metal structure. On the other hand, an excellent effect that the plating can be performed uniformly and with good controllability can be obtained.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[Embodiment 1]
First, the formation method of the metal structure in Embodiment 1 of this invention is demonstrated. First, as shown in FIG. 1A, the insulating layer 102 is formed on the semiconductor substrate 101 made of silicon by, for example, a thermal oxidation method or a CVD (Chemical Vapor Deposition) method. Further, a titanium (Ti) film and an Au film are sequentially formed by an evaporation method or the like, and the seed layer 103 is formed on the insulating layer 102.

Next, as shown in FIG. 1B, a resist pattern 104 having an opening region in a desired region is formed on the seed layer 103. The resist pattern 104 can be formed by, for example, forming a positive-type photosensitive polyimide film and exposing and developing a predetermined pattern by a known photolithography technique. After the resist pattern 104 is formed in this manner, for example, irradiation with O ₂ plasma (RF power: 100 W) is performed for 6 minutes, so that the resist pattern 104 is attached to the surface of the seed layer 103 in the opening region of the resist pattern 104. The organic substance (residue) is removed.

In this embodiment, irradiation treatment with O ₂ plasma is used. However, Ar / O ₂ mixed plasma or CF ₄ / O ₂ is used depending on the degree of contamination of the surface of the seed layer 103 in the opening region. An irradiation process using mixed plasma may be used.

In the above-described organic residue treatment, the surface layer 103 a made of gold oxide or the like constituting the seed layer 103 is formed on the seed layer 103. In the first embodiment, the surface layer 103a formed on the surface is removed by irradiation treatment with O ₂ plasma by performing immersion treatment (surface treatment) with an acid solution (pH 3 or lower) such as a hydrochloric acid solution for 1 minute. State. When the pH is higher than 3, it takes a long time to remove the surface layer 103a, and there may be a case where the surface layer 103a cannot be completely removed due to a change in pH. On the other hand, by setting the pH to 3 or less, the surface layer 103a can be removed in a practical treatment time (about 1 minute).

  Next, as shown in FIG. 1C, by depositing Au on the seed layer 103 exposed in the opening region of the resist pattern 104 by an electroplating method using a gold sodium sulfite solution as a plating solution, Assume that the structure 105 is formed. In the present embodiment, the clean surface of the seed layer 103 is exposed by the above-described surface treatment with an acid such as hydrochloric acid, so that the metal structure 105 is formed with a uniform height and good controllability. The

Next, as shown in FIG. 1D, the resist pattern 104 is removed by, for example, ashing (ashing) using O ₂ plasma.

  Next, using the metal structure 105 as a mask, Au on the seed layer 103 is removed by a wet etching method using an iodine / ammonium iodide solution, and then the seed layer 103 is formed by a wet etching method using a hydrofluoric acid solution. The lower Ti is removed. As a result, the fixed electrode 151 and the control electrode 152 are formed on the insulating layer 102. Although not shown in FIG. 1D, a seed layer is disposed below the fixed electrode 151 and the control electrode 152.

  Next, as shown in FIG. 1E, the fixed electrode 151 and the control electrode 152 are covered with the organic resin layer 106, and then the organic resin layer 106 is exposed so that a part of the fixed electrode 151 is exposed. It is assumed that the opening 106a is formed. The organic resin layer 106 can be formed by, for example, forming a positive-type polyimide film having photosensitivity and exposing and developing a predetermined pattern so that the opening 106a is opened. The opening 106a formed in the organic resin layer 106 penetrates to the fixed electrode 151 and is disposed in a region where a support 107 described later is formed.

Next, for example, an irradiation process using O ₂ plasma (RF power: 100 W) is performed for 6 minutes, so that organic substances (residues) attached to the surface of the fixed electrode 151 in the opening 106a are removed. In the above description, irradiation with O ₂ plasma is used. However, depending on the degree of contamination of the surface of the metal structure 105 in the opening region 106a, Ar / O ₂ mixed plasma or CF ₄ / O ₂ mixed is used. Plasma irradiation treatment may be used.

In the treatment of the organic residue described above, a surface layer made of gold oxide or the like constituting the fixed electrode 151 is formed on the fixed electrode 151 in the opening 106a. In the first embodiment, the immersion treatment with a solution of an acid such as hydrochloric acid solution (pH 3 or less) (surface treatment) by performing one minute, the surface layer formed on the surface by irradiation treatment with O ₂ plasma is removed State.

  As shown in FIG. 1 (f), Au is deposited by electroplating using the surface of the fixed electrode 151 exposed in the opening 106a thus formed as a seed layer and using a sodium gold sulfite solution as a plating solution. In addition, a support portion (metal structure) 107 filling the opening 106 a of the organic resin layer 106 is formed. In the present embodiment, since the clean surface of the fixed electrode 151 is exposed by the surface treatment with the acid such as hydrochloric acid described above, the support portion 107 has a high flatness on the surface and is controlled. It is well formed.

  Next, the organic resin pattern 108 including the opening 108 a is formed on the organic resin layer 106. The upper surface of the support portion 107 is exposed at a part of the opening 108a. For example, a positive-type photosensitive polyimide film may be formed, and a predetermined pattern exposure and development may be performed by a known photolithography technique.

Next, for example, by performing an irradiation process with O ₂ plasma (RF power: 100 W) for 6 minutes, the organic matter (residue) attached to the surface (upper surface) of the support portion 107 in the opening portion 108a is removed. To do. In the above description, the irradiation process using O ₂ plasma is used. However, depending on the degree of contamination of the surface of the support 107 in the opening 108a, Ar / O ₂ mixed plasma or CF 4 / O ₂ mixed plasma is used. Irradiation treatment may be used.

In the above-described organic residue treatment, a surface layer made of a gold oxide or the like constituting the support portion 107 is formed on the upper surface of the support portion 107. In the first embodiment, the surface layer formed on the surface is removed by the irradiation treatment with O ₂ plasma by performing an immersion treatment with an acid solution (pH 3 or lower) such as a hydrochloric acid solution for 1 minute.

  By depositing Au by an electroplating method using the surface of the support 107 exposed in the region of the opening 108a thus formed as a seed layer and using a sodium gold sulfite solution as a plating solution, FIG. As shown in FIG. 5, the movable electrode (metal structure) 109 is formed in the opening 108a of the organic resin layer 108. In the present embodiment, since the clean surface of the support portion 107 is exposed by the surface treatment with the acid such as hydrochloric acid described above, the movable electrode 109 has a high flatness on the surface and has controllability. Well formed.

Thereafter, the organic resin layer 106 and the organic resin layer 108 are removed by, for example, an ashing (ashing) process using O ₂ plasma, so that an insulating layer is formed as shown in FIG. The movable electrode 109 supported by the support portion 107 on the fixed electrode 151 made of Au is formed on the control electrode 152 made of Au so as to be spaced apart from and opposed to the control electrode 152.

  In addition, although the manufacturing method which produces a MEMS device was demonstrated above, the structure produced by the manufacturing method using this invention is not restricted to a MEMS device. For example, the present invention can be used in a method for forming a metal structure formed by using a plating method such as an electrode pad or a fine electric wiring.

FIG. 2 shows the result of measuring the variation in plating height when there is no surface treatment with acid such as hydrochloric acid as the pretreatment for plating (a) and when the surface treatment is carried out (b), and the result is expressed as a frequency distribution. It is. In this investigation, first, a Ti film and an Au film are sequentially formed on a silicon wafer by a vapor deposition method or the like to form a seed layer, and then a positive resist film is formed with a resist pattern having a more open region. Then, irradiation with O ₂ plasma (RF power: 100 W) is performed for 6 minutes, so that organic substances (residues) adhering to the seed layer surface in the opening region are removed.

  Thereafter, using the presence or absence of surface treatment as a parameter, Au is deposited by an electroplating method using a sodium gold sulfite solution as a plating solution (Tanaka Kikinzoku Co., Ltd.), and finally, the positive resist film is removed to prepare a sample. . However, a hydrochloric acid solution having a pH of 3 is used as the hydrochloric acid solution, and the immersion time is 1 minute. Further, in the plating for sample preparation in this investigation, constant current application was performed with the wafer as the positive electrode and the counter electrode made of platinum (Pt) as the negative electrode, and Au plating was performed on the opening area on the wafer, and the height was 40 μm. The quadrangular prism structure is formed. At this time, the amount of deviation of the height of the quadrangular prism structure from 40 μm is defined as the variation in plating height.

As shown in FIG. 2, it can be seen that the variation in the height of the quadrangular columnar structure is suppressed as the surface immersion is performed as the plating pretreatment. This result proves that the variation in the plating height was reduced because the gold surface (gold oxide film) modified by the O ₂ plasma irradiation was removed by immersion in a hydrochloric acid solution. Therefore, by manufacturing the structure using the present invention, plating can be formed with good controllability.

[Embodiment 2]
Next, the formation method of the metal structure in Embodiment 2 of this invention is demonstrated. In the second embodiment, the surface treatment with hydrochloric acid described with reference to FIG. 1B, FIG. 1E, and FIG. It is replaced with a surface treatment by heating in a vacuum or an inert gas atmosphere.

The second embodiment will be described. By performing irradiation treatment with O ₂ plasma (RF power: 100 W) or the like on the seed layer, organic substances (residues) attached to the surface of the seed layer 103 in the opening region are removed. After the state, the surface of the seed layer 103 is heated (surface treatment) in a vacuum or in an atmosphere of an inert gas such as Ar or N ₂ .

As heating conditions for the surface treatment, a heating temperature of 260 ° C. or higher is desirable. This is because the complete decomposition temperature of gold oxide formed by irradiation treatment with plasma containing O ₂ is 260 ° C. The heating time may be about 1 minute. Needless to say, this heating time varies depending on the irradiation conditions (for example, RF power and irradiation time) of plasma containing O ₂ .

  As a result of measuring the height variation of the structure created according to the second embodiment, it was proved that the height variation of the quadrangular prism structure was suppressed as in the demonstration experiment shown in the first embodiment.

[Embodiment 3]
Next, the formation method of the metal structure in Embodiment 3 of this invention is demonstrated. In the third embodiment, the gold oxide removal method (surface treatment method) used in FIGS. 1B, 1E, and 1F in the structure forming method in the first embodiment is used. The following method has been changed.

In the third embodiment, the organic layer (residue) attached to the surface of the seed layer 103 in the opening region is removed by performing irradiation treatment with O ₂ plasma (RF power: 100 W) or the like on the seed layer. After that, the surface of the seed layer 103 is heated at 110 ° C. for 1 minute in an atmosphere of molecular hydrogen (H ₂ ), a so-called reducing gas such as hydrogen gas, and the seed layer 103 is irradiated by O ₂ plasma. It is assumed that the Au oxide formed on the surface is removed.

In the third embodiment, as a method for removing Au oxide, heat treatment is performed in a molecular hydrogen (H ₂ ) atmosphere, but a reducing gas containing at least activated molecular or atomic hydrogen is used. Needless to say, the atmosphere is good. Examples of reducing gas species that generate atomic hydrogen include saturated hydrocarbons such as methane (CH ₄ ), ethane (C ₂ H ₆ ), and propane (C ₃ H ₈ ), or ethylene (C ₂ H _4). If it is a person skilled in the art, it is an unsaturated hydrocarbon such as hydrogen) (H ₂ ), ammonia (NH ₃ ), hydrogen sulfide (H ₂ S), etc. Easy to analogize.

In the third embodiment, in the method for removing Au oxide, a heat treatment is performed at 110 ° C. for 1 minute. This heating condition is a condition for irradiating plasma containing O ₂ (for example, RF power or irradiation). Needless to say, it varies depending on the time).

FIG. 3 shows the case where the Au surface formed by the vapor deposition method is irradiated with O ₂ plasma (RF power: 100 W) for 6 minutes (the upper part of FIG. 3), and subsequently at 110 ° C. in an H ₂ atmosphere. It is an XPS (X-ray photoelectron spectroscopy) spectrum in the 4f region of Au when the above heating is processed for 1 minute (the lower part of FIG. 3).

As shown in the lower part of FIG. 3, it can be seen that the spectrum of gold oxide seen in the vicinity of 86 eV and 90 eV disappears with the heat treatment at 110 ° C. in the hydrogen molecule (H ₂ ) atmosphere. Similarly, in the heat treatment at 110 ° C. (110 ° C. or lower) in a hydrogen plasma (H ₂ ^* , H ^* ) atmosphere, the same result as in the lower part of FIG. 3 is obtained. This is 110 ° C. when the gold surface (gold oxide film) modified by O ₂ plasma irradiation is placed in an atmosphere of a reducing gas such as hydrogen molecules or hydrogen plasma (H ₂ ^* , H ^* ). It shows that reduction and disappearance can be achieved even by heat treatment at low temperatures. In addition, the spectrum which exists in 84 eV and 88 eV vicinity seen in the lower stage of FIG. 3 is a spectrum of gold | metal | money which is a structure.

When removing gold oxide in a vacuum or an inert gas atmosphere, heat treatment at a high temperature of 260 ° C. or higher is required because of the use of heat self-decomposition reaction, but hydrogen molecules or hydrogen plasma ( When removing gold oxide in a reducing gas atmosphere of H ₂ ^* , H ^* ), a reduction reaction is used, and the activation energy at this time can be reduced, so that heat treatment is performed at a low temperature of 110 ° C. or lower. It seems to have improved.

  As a result, by using the invention according to the third embodiment, an organic resin having lower heat resistance can be used as an organic resin used for forming a resist pattern or the like. Further, since the treatment can be performed at a low temperature of 110 ° C., for example, the mutual diffusion between the lower layer Ti and the upper layer Au in each seed layer can be suppressed to a level that hardly occurs. The adhesion is obtained by disposing Ti in the lower layer, but this adhesion is lowered by mutual diffusion. This interdiffusion is more likely to occur as the temperature applied by each process increases. On the other hand, as described above, if treatment can be performed at a low temperature of 110 ° C., interdiffusion between Ti and Au can be suppressed, and deterioration of adhesion can be prevented. In addition, since the process can be performed at a low temperature, the cost of the process can be further reduced.

It is process drawing for demonstrating the surface treatment method in Embodiment 1 of this invention. It is a frequency distribution figure which shows the result of having measured the height dispersion | variation and its frequency by making the presence or absence of hydrochloric acid immersion into a parameter. The Au surface formed by vapor deposition is irradiated with O ₂ plasma (RF power: 100 W) for 6 minutes, and then heated at 110 ° C. in a hydrogen molecule atmosphere for 1 minute. It is an XPS (X-ray photoelectron spectroscopy) spectrum in a region.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 101 ... Semiconductor substrate, 102 ... Insulating layer, 103 ... Seed layer, 103a ... Surface layer, 104 ... Resist pattern, 105 ... Metal structure, 106 ... Organic resin layer, 106a ... Opening, 107 ... Supporting part, 108 ... Organic Resin pattern, 108a ... opening, 109 ... movable electrode, 151 ... fixed electrode, 152 ... control electrode.

Claims (1)

A first step in which a base layer made of gold is formed on a substrate;
A second step of allowing activated oxygen to act on the surface of the underlayer;
A third step of removing gold oxide formed on the surface of the underlayer in the second step;
After the third step, at least a fourth step of forming a metal structure on the surface of the base layer by plating ,
Wherein in the third step, the method of forming the metal structure characterized Rukoto for removing oxides of the gold by heating the underlying layer in an atmosphere of reducing gas at a temperature of 110 ° C. or less.

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