WO2020199236A1 - Metal deposition method combining microelectromachinery and casting - Google Patents

Abstract

Disclosed in the present invention is a metal deposition method combining microelectromachinery and casting, comprising: S1, providing a silicon micro-mold, a hole trough structure being provided in the silicon micro-mold; S2, clamping the silicon micro-mold, which needs to be filled, between an upper cover panel and a lower cover panel to form a sandwich structure, a nozzle hole in the lower cover panel perpendicularly corresponding to the hole trough structure; S3, filling the hole trough structure with a high temperature, melted liquid metal; S4, cutting and separating the liquid metal in the nozzle hole and the hole trough structure; S5, evenly curing the liquid metal in the hole trough structure; and S6; separating the upper cover panel and the lower cover panel from the silicon micro-mold. The present invention combines new MEMS technology with millennia-old casting technology, creating a completely new metal deposition method for the field of microelectronics.

Description

A metal deposition method combining microelectronic machinery and casting Technical field

The invention belongs to the field of semiconductor or microelectronic manufacturing, and in particular relates to a metal deposition method combining microelectronic machinery and casting.

Background technique

There is currently no strict definition of thick metal layers. Generally, the thickness is less than 1um, and evaporation or sputtering can be used. When the thickness is from a few microns to tens or even hundreds of microns, electroplating is required.

Thick metal layers are widely used in microelectronic devices. In advanced packaging fields, such as flip chip soldering, bumping is used, or TSV (Through-silicon via) and TGV (Through glass via), filter structures are used in integrated passive devices, delayers are all thick metal structures, and in the field of MEMS devices, spiral inductors are used.

At present, the deposition of thick metals mainly depends on electroplating. The electroplating filling can be divided into four steps. The first step is the deposition of the seed layer, which generally adopts sputtering or evaporation. The thickness of the seed layer is generally less than 1 micron. The second step is to conduct electroplating deposition in the electroplating solution by adding a field. The electroplating process is a very complex electrochemical process. The uniformity and yield of electroplating are related to the electric field distribution, the ratio of the electrolyte, and the concentration of inhibitors and accelerators in the electrolyte. After the filling is completed, if it is the filling of the via interconnection, because the seed layer is in the hole and the surface, there will be metal plating deposition on the hole and the surface during electroplating. The metal plating on the surface needs to pass the third step of chemical mechanical polishing ( CMP). The fourth step is to go to the seed layer. Some areas on the electroplated surface do not require electroplating, so they will be covered with glue or other non-conductive materials before electroplating. After the electroplating is completed, the covering and the underlying seed layer also need to be removed.

Electroplating has the following defects:

1. The electroplating filling process is complicated, because the electroplating needs to be realized on the conductive surface, so for silicon wafers, glass wafers and other materials, a seed layer must be deposited in advance, and the seed layer needs to be removed after filling;

2. The electroplating solution used in electroplating is very toxic and easy to pollute the environment. With the rise of environmental protection awareness, the government now has stricter and stricter control on electroplating production;

3. The filling speed of electroplating is not fast, especially for via filling, which usually takes several or even dozens of hours.

In addition to electroplating, electroless plating is also a method of thick metal deposition. However, the precision of electroless plating is difficult to control, and it also has high selectivity to materials.

Humans have used casting for thousands of years. Metal casting is a widely used method of metal manufacturing. Humans have used casting for more than 5,000 years. The basic principle of casting is to melt the metal or alloy and inject it into a prefabricated mold. After it is solidified, the mold is removed to take out the molded casting. The combination of MEMS technology and casting is due to one thing in common: Both are manufacturing technologies for mechanical parts, and the difference lies in the scale of several orders of magnitude. Compared with other machining methods, such as turning, washing, polishing, etc., the advantage of casting is that it can form mechanical parts with complex structures. And MEMS technology is a micro-processing technology developed from microelectronics technology in recent decades. By manufacturing micron-scale mechanical parts on silicon wafers or other substrates, functions such as sensing, energy harvesting, and execution can be realized. The basic concept of the combination of MEMS and casting is to create a micro-mold that needs to be formed on a silicon wafer (or other material substrate) through a bulk silicon etching process, and then melt the metal to fill it and solidify it.

Combining emerging MEMS technology with thousands of years of casting technology has created a new metal deposition method for the microelectronics field, but this combination faces huge technical challenges. First of all, for macroscopic castings, the problem is that bubbles or cavities are easily generated inside the castings. The size of these bubbles or cavities can reach the millimeter level, which has far exceeded the size of the MEMS structure. Secondly, casting is usually used in the manufacture of mechanical parts rather than electronic components. Whether MEMS castings can meet the requirements of devices in terms of electrical properties also needs to be studied. Finally, the combination of MEMS and casting is not just as simple as replacing the macroscopic mold with the silicon micromold etched by bulk silicon, because the surface effect and temperature effect caused by the shrinking of the casting size by several orders of magnitude, etc., in the silicon micromold Manufacturing, mold clamping, microfluidic filling of molten alloys, volume shrinkage during solidification and demolding cannot be solved by macro casting. Only by introducing related micro-nano effects can the combination of MEMS and casting be realized in a true sense.

Summary of the invention

In order to solve the problems in the prior art, the present invention proposes a metal deposition method combining microelectronic machinery and casting.

The technical scheme adopted by the present invention is:

A metal deposition method combining microelectronic machinery and casting includes:

S1, providing a silicon micro-mold with a slot structure provided on the silicon micro-mold;

S2, sandwiching the silicon micro-mold to be filled between the upper cover plate and the lower cover plate to form a sandwich structure, and the nozzle holes on the lower cover plate correspond vertically to the hole and groove structure;

S3, filling the hole structure with liquid metal melted at high temperature;

S4, cutting and separating the hole and groove structure and the liquid metal of the nozzle hole;

S5, rapid cooling and uniform solidification of the liquid metal in the hole structure;

S6, separating the upper cover plate and the lower cover plate from the silicon micro mold.

Preferably, after step S6, it further includes:

S7, performing chemical mechanical polishing on the silicon micromold.

Preferably, in step S2, an air gap is left between the lower cover plate and/or the upper cover plate and the silicon micro-mold.

Preferably, the surface of the lower cover plate and/or the upper cover plate is provided with convex points or strip-shaped grooves forming the ventilation gap.

Preferably, in step S3, the entire sandwich structure is placed on the surface of the molten metal pool.

Preferably, assuming that the nozzle hole, the air pressure in the pore structure and the ventilation groove communicating gap space is P _i, the metal surface of the pool to the pressure P _0, the pressure difference Δp = P ₀ -P _i, then: Step S3 In the above, the liquid metal is filled into the hole and groove structure through the nozzle hole by increasing the pressure difference Δp.

Preferably, in step S4, the liquid metal in the nozzle hole is cut by reducing the pressure difference Δp.

Preferably, in step S3, the hole and groove structure is evacuated, and the liquid metal is filled from the nozzle hole into the hole and groove structure in a vacuum environment under the action of external air pressure.

Preferably, in step S5, cold air is blown to the upper cover plate exposed to the outside.

Preferably, in step S6, for low-temperature alloys, nano-molecular layer materials that can reduce the surface energy are deposited on the surfaces of the upper and lower cover plates; for high-temperature alloys, deposited on the surfaces of the upper and lower cover plates A layer of release material.

Compared with the prior art, the beneficial effects of the present invention are:

The invention realizes the combination of microelectronic machinery and casting, and provides a brand-new metal layering method for thick metal deposition. It utilizes capillary phenomenon and liquid bridge pinch-off phenomenon to realize filling of liquid metal in the hole and groove structure through the nozzle hole. The technology avoids the seed layer deposition and chemical mechanical polishing required by the commonly used electroplating filling methods, and uses rapid cooling to increase the number of nuclei during the solidification process to achieve a uniform solidification effect.

Of course, any product implementing the present invention does not necessarily need to achieve all the advantages described above at the same time.

Description of the drawings

Figure 1 is a flow chart of the thick metal deposition process combining microelectronic machinery and casting of the present invention;

2 is a schematic structural diagram of a filling method according to an embodiment of the present invention.

detailed description

In order to make the objectives, technical solutions, and advantages of the present invention clearer, the various embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

Please refer to Figure 1 and Figure 2 comprehensively. A metal deposition method combining microelectronics and casting includes the following steps:

S1, a silicon micro-mold 1 is provided, and a hole structure 5 is provided on the silicon micro-mold 1;

The silicon micro-mold 1 adopts silicon body processing technology, and there are two main types: deep silicon etching and KOH etching. Among them, deep silicon etching can achieve a higher aspect ratio. Generally, the pattern is determined by photolithography, and the accuracy can be controlled within 1 micron.

Compared with macroscopic casting, in addition to replacing the mold with a silicon micro mold 1, the present invention also changes the silicon micro mold 1 into a flat shape. This thick metal deposition method can reduce the size of traditional casting to several microns.

The types of the slot structure 5 include through hole, blind hole and cavity structure. The slot structure 5 in FIG. 1 is composed of a plurality of through holes connected together, and the slot structure 5 in FIG. 2 is composed of a single through hole.

Preferably, the hole and groove structures 5 are arranged in an array on the silicon micro mold.

S2, sandwich the silicon micromold 1 to be filled between the upper cover plate 2 and the lower cover plate 3 to form a sandwich structure, and the nozzle hole 4 on the lower cover plate 3 corresponds to the hole structure 5 vertically;

As shown in FIG. 2, a plurality of nozzle holes 4 are provided on the lower cover plate 3, and the plurality of nozzle holes 4 correspond to a plurality of hole groove structures 5 one by one; further, as shown in FIG. 1, the lower cover plate 3 A nozzle hole 4 is provided, and the metal liquid flows into each interconnected through hole of the silicon micro-mold 1 through the entrance of the hole structure 5.

An air gap 7 is left between the lower cover plate 3 and/or the upper cover plate 2 and the silicon micro mold 1. Since the ventilation gap 7 is small enough, liquid metal will not overflow from the gap.

Optionally, the surface of the lower cover plate 3 and/or the upper cover plate 2 is provided with bumps 8 or strip-shaped grooves forming the ventilation gap 7.

Optionally, both the upper cover 2 and the lower cover 3 may be silicon wafers or glass wafers.

S3, filling the hole structure 5 with liquid metal melted at high temperature;

Flowing and filling of high-temperature molten metal in micro-scale microgrooves is similar to microfluidics, but due to the surface tension of the alloy, viscosity coefficient, and wettability with silicon micromold 1, compared to traditional microfluidics The aqueous solution is different, so it has a special flow filling mechanism.

In one embodiment, the entire sandwich structure is placed on the surface of the molten liquid metal pool 6 so that the liquid metal is pressed into the hole structure 5. This filling method has the advantages of fast speed and low cost, so it is very practical.

Suppose the nozzle holes 4, 5 and the pressure vent hole groove structure 7 communicating gap space pressure P _i, 6 of the surface of the metal pool P _0, the pressure difference Δp = P ₀ -P _i. Among them, the liquid metal does not wet the surfaces of the nozzle hole 4 and the hole structure 5. In this step, the liquid metal is filled into the slot structure 5 through the nozzle hole 4 by increasing the pressure difference Δp. Δp is increased can be obtained by reducing the P _i. If P _i when the vacuum drops to zero, Delta] p is also sufficient to overcome the capillary pressure of the nozzle holes 4, it can be considered to increase the value of P _0.

In another embodiment, the hole structure 5 is evacuated, and the liquid metal is filled from the nozzle hole 4 into the hole structure 5 in a vacuum environment under the action of external air pressure. Since the liquid metal generates filling pressure when filling the hole structure 5, it is necessary to apply a certain pressure on the upper cover plate 2 and the lower cover plate 3 to clamp the silicon micromold 1 at this time.

S4, cutting and separating the liquid metal of the hole structure 5 and the nozzle hole 4;

After the liquid metal fills the slot structure 5 through the nozzle hole 4, the liquid metal in the slot structure 5 and the metal pool 6 are connected through the nozzle hole 4. The liquid metal forms a liquid bridge in the nozzle hole 4. The liquid bridge needs a certain pressure to maintain. When the pressure of the liquid bridge is lower than its breaking pressure, the liquid bridge will be pinched off due to surface tension.

In one embodiment, by reducing the pressure differential Δp liquid metal to the cutting nozzle hole 4, and Δp is reduced can be obtained by increasing the P _i and / or decreasing P _0. In step S3 and step S4, the hole and groove structure 5 is filled with liquid metal and the cutting and separation (liquid bridge pinch off) of the liquid metal in the nozzle hole 4 is realized based on the huge surface tension on the micrometer scale.

In another embodiment, since the hole structure 5 is in a vacuum environment, the liquid bridge pinching effect can be achieved by reducing the filling pressure of the liquid metal, that is, the liquid metal in the hole structure 5 and the nozzle hole 4 Cutting separation.

S5, uniformly solidify the liquid metal in the hole structure 5;

Most metals undergo a volume shrinkage during the solidification process from liquid to solid phase, and the shrinkage is about 2% to 7%. In macro casting, the problem of volume shrinkage is achieved by means of compensation. That is, by controlling the casting to cool from bottom to top, the metal at the top riser finally melts, so that the solidification and shrinkage of the alloy below it can be compensated during the cooling process. However, in this embodiment, because of the flat structure of the wafer and the high thermal conductivity of the silicon material itself, the temperature gradient required for compensation cannot be achieved.

In this step, it is preferable to increase the number of nuclei in the solidification process by means of rapid cooling to achieve the goal of uniform solidification. Specifically, the upper cover plate 2 may be exposed to the outside, and the upper cover plate 2 may be rapidly cooled by blowing cold air. The cold air may be liquefied low-temperature nitrogen, which is not limited here.

S6, separating the upper cover plate 2 and the lower cover plate 3 from the silicon micro mold 1;

Because the alloy is filled after being melted, the upper cover plate 2 and the lower cover plate 3 are likely to be stuck by the alloy and cannot be separated after solidification. For low-temperature alloys, in this embodiment, it is preferable to deposit a special nano-molecular layer material on the surface of the cover plate to reduce its surface energy, thereby realizing easy slicing. For high-temperature alloys, because the nano-molecular layer decomposes at high temperatures, in this embodiment, it is preferable to deposit a layer of mold release material on the surfaces of the upper cover plate 2 and the lower cover plate 3 by physical or chemical deposition to assist the demolding.

S7, chemical mechanical polishing is performed on the silicon micro-mold 1.

Step S7 is not a necessary step. Depending on the actual situation, chemical mechanical polishing (CMP) may be required after demolding to level, or thin-layer electroplating on the surface of the casting may be required to meet specific application requirements.

The thick metal deposition method provided by the present invention can be applied to the following three microelectronic fields: 1) Silicon via interconnection TSV/glass via interconnection TGV for semiconductor advanced packaging; 2) MEMS devices, such as MEMS flux gates, electromagnetic Type energy harvester, etc.; 3) Three-dimensional stacked microwave components and integrated passive device IPD.

The above are only preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or changes within the technical scope disclosed by the present invention. All replacements shall be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims (10)

1. A metal deposition method combining microelectronic machinery and casting is characterized in that it comprises:

   S1, providing a silicon micro-mold with a slot structure provided on the silicon micro-mold;

   S2, sandwiching the silicon micro-mold to be filled between the upper cover plate and the lower cover plate to form a sandwich structure, and the nozzle holes on the lower cover plate correspond vertically to the hole and groove structure;

   S3, filling the hole structure with liquid metal melted at high temperature;

   S4, cutting and separating the hole and groove structure and the liquid metal of the nozzle hole;

   S5, uniformly solidify the liquid metal in the hole structure;

   S6, separating the upper cover plate and the lower cover plate from the silicon micro mold.
2. A metal deposition method combining microelectronic machinery and casting according to claim 1, characterized in that, after step S6, it further comprises:

   S7, performing chemical mechanical polishing on the silicon micromold.
3. The method for metal deposition combining microelectronic machinery and casting according to claim 1, wherein in step S2, there is a gap between the lower cover plate and/or the upper cover plate and the silicon micromold There is a ventilation gap.
4. The method of metal deposition combining microelectronic machinery and casting according to claim 3, wherein the surface of the lower cover plate and/or the upper cover plate is provided with bumps or bumps forming the ventilation gap. Strip groove.
5. A metal deposition method combining microelectronic machinery and casting according to claim 3, wherein in step S3, the entire sandwich structure is placed on the surface of the molten metal pool.
6. According to one of claim 5 in conjunction with the metal deposition process and MEMS foundry, characterized in that, assuming the nozzle hole, the pressure within the pore structure and the ventilation groove communicating gap space is P _i, metal pool surface The pressure of is P ₀ , and the pressure difference Δp=P ₀ -P _i , then: in step S3, the pressure difference Δp is increased so that the liquid metal is filled into the hole structure through the nozzle hole.
7. The metal deposition method combining microelectronic machinery and casting according to claim 6, characterized in that, in step S4, the liquid metal in the nozzle hole is cut by reducing the pressure difference Δp.
8. A metal deposition method combining microelectronic machinery and casting according to claim 1, wherein in step S3, the hole and groove structure is evacuated, and liquid metal is removed from the nozzle hole under the action of external air pressure. Filling into the hole structure in a vacuum environment.
9. A metal deposition method combining microelectronic machinery and casting according to claim 1, wherein in step S5, cold air is blown to the upper cover plate exposed to the outside.
10. A metal deposition method combining microelectronic machinery and casting according to claim 1, characterized in that, in step S6: for low-temperature alloys, deposition on the surface of the upper cover plate and the lower cover plate can reduce the surface energy Nano-molecular layer material; for high-temperature alloys, a layer of release material is deposited on the surface of the upper cover and the lower cover.

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