JP5522662B2 - Microstructure formation method - Google Patents

Description

  The present invention relates to a method for forming a fine structure such as a metal bump using a gas deposition method.

  With the development of semiconductor LSI chips, downsizing and increasing the density of electronic components are simultaneously progressing downsizing and improving the performance of various devices equipped with them. One of the most important technologies for mounting small electronic components at high density is an electrical connection technology between the electronic components and the wiring board.

  Conventionally, it has been practiced to improve the mounting density of electronic components by mounting a solder processed into a ball shape of, for example, about 0.1 mm on an electrode and melting it in a reflow furnace. At present, the connection pitch obtained using solder balls is about 0.1 mm. However, with the miniaturization of solder balls, technical difficulties related to the production and placement of balls have increased, and a new finer alternative to this method has become available. There is a need for an electrode connection method.

  One of them is a method called flip-chip connection, in which fine protruding metal bumps are formed on metal electrodes and pressed against the opposing electrodes to physically and mechanically connect them by heat or ultrasonic vibration. .

  In this method, how fine and high-precision metal bumps are produced, and the bumps that are produced do not spread around when the bumps are crushed to cope with the fine electrode pitch, or bonding by the produced bumps. It is necessary to ensure that the device has a mechanically and electrically stable connection.

International Publication Number WO2007-114314

  In view of the above circumstances, an object of the present invention is to provide a method for forming a microstructure such as a metal bump capable of realizing mechanically and electrically stable interelectrode connection.

  In order to solve the above-mentioned problems, the present invention is a method of spraying metal nanoparticles from above an opening provided in a photoresist by a gas deposition method to form a protruding microstructure in the opening. Thus, there is provided a fine structure forming method characterized by displacing the flow path direction from the spray nozzle so as to incline the fine structure in one direction.

  Here, the opening is a hole or a groove, for example, the protrusion is a cone or an edge, and the microstructure is a bump, for example.

  The present invention also provides a metal bump characterized by having a vertex shifted from the center in a desired direction, and a semiconductor chip provided with the metal bump.

(A) is the figure which showed the example of the bump by the conventional gas deposition method, (b) The bump by this invention. (A) is a figure for demonstrating the bump by the conventional gas deposition method, (b) The bump by this invention. (A) is a figure for demonstrating the bump by the conventional gas deposition method, (b) The bump by this invention. (A) (b) is a figure for demonstrating the bump and chip | tip by this invention. It is a figure which shows an example of the bump formation method by this invention. It is a figure which shows another example of the bump formation method by this invention. It is a figure which shows another example of the bump formation method by this invention. (A) and (b) are figures which show another example of the bump formation method by this invention. It is a figure which shows the conical metal bump | vamp actually produced by this invention. It is a figure which shows the hole pattern for conical metal bump formation of FIG. It is a figure explaining the experimental conditions of FIG. It is another figure explaining the experimental conditions of FIG. It is a figure which shows the chip | tip attachment jig as a block body at the time of the gas deposition used for the conical metal bump formation of FIG. It is a figure for demonstrating the relationship between a nozzle scan and bump formation. It is a figure for demonstrating evaluation of a bump formation process. It is a figure for demonstrating the resist hole shape in calculation of a bump growth rate and bump formation time. It is a figure for demonstrating the cone bump shape in calculation of a bump growth rate and bump formation time. It is a figure for demonstrating the resist hole shape, cone bump shape, and eaves shape in calculation of eaves growth rate.

[Gas deposition method]
The gas deposition method has already been disclosed in many patents, and a method for forming a fine metal bump in one of them has already been filed by the present applicant (Patent Document 1). According to this already-applied method, a fine hole is provided in a photoresist film covering a metal electrode on a substrate by using a photolithography technique used in a normal semiconductor manufacturing process, and a nano-hole is formed from above by a gas deposition method. By spraying metal particles of a size with a gas under reduced pressure conditions, metal deposition occurs in the hole, and at the same time, metal deposition from the periphery of the hole, that is, an eaves that covers the hole, As the opening diameter of the hole is reduced, a metal protrusion-like bump having a conical shape can be finally formed in the hole by self-alignment. The features of this method are that the size of bumps can be controlled at the 0.1 micron level by using photolithography technology, and the hole of the photoresist is self-closed, so that the protrusion structure of the same shape is formed by the gas deposition method. It can be automatically formed only by metal deposition. Moreover, a plurality of bumps can be produced uniformly by scanning the gas spray region with respect to the hole portion of the photoresist.

[Control of bump protrusion direction]
When nano metal particles are sprayed onto the fine holes formed in the photoresist as described above by the gas deposition method, the size of the spray nozzle is larger than the hole diameter (usually, the bump size is several tens of μm or less, the nozzle diameter: The bumps to be created are isotropic, if the shape of the hole is a square, a quadrangular pyramid, if it is a circle, it will be a cone, and the protrusion is formed at the center of the hole. FIG. 1A shows an example of a conical bump 1 having a vertex at the center of a circle.

  By the way, in recent LSI chips and the like, it is required to reduce the thickness of the chip at the same time as increasing the density by reducing the pitch of the metal electrodes to be connected. On the other hand, the deformation (warp) of the chip at the time of connection is a problem. . With respect to this warpage, when using a flip chip method in which fine bumps 1 are formed on a metal electrode and pressed against a counter electrode and connected, for example, as shown in FIG. By equalizing the stress radially from the center of the chip 2, the strain into the chip 2 can be made isotropic.

  However, for example, as shown in FIG. 3A, when the bump diameter d and the bump pitch p are in the relationship of a sandwiching pitch of p <2d, a short circuit may occur due to the deformation of the bump 1 at the time of flip chip pressing. .

  Therefore, in the present invention, for example, as shown in FIG. 1B, the protrusion direction of the bump 1 formed around the chip 2 is inclined in one direction of the chip 2, that is, the entire bump 1 is inclined in one direction. By removing the vertex from the center of the circle, as shown in FIG. 2B, a tensile stress in the direction opposite to the tilt direction is applied to the chip 2 body during the flip chip pressing, while the substrate 3 is pulled in the tilt direction. Stress is applied, that is, pressure is applied so that the chip 2 and the substrate 3 slide sideways, and short-circuiting can be prevented even at a pinching pitch as shown in FIG.

  In the example of FIGS. 4A and 4B, the apexes of the bumps 1 are inclined inwardly or outwardly, so that in the case of inclining inwardly (FIG. When an inward pulling force or an outward pulling force is applied to the substrate 3, and when the outer side is inclined (FIG. 4B), an outward pulling force is applied to the chip 2 and an inward pulling force is applied to the substrate 3. In addition, as a result, the deformation of the chip 2 can be effectively suppressed or prevented.

  Further, in a flip chip that applies ultrasonic vibration, the positional deviation of the chip due to ultrasonic vibration is usually a problem, but by displacing the protrusion direction (or apex direction) of the bump 1 in the above-described direction, The effect of absorbing the displacement due to vibration can also be obtained.

  The displacement in the protruding direction can be realized by shifting the gas deposition spray nozzle 6 from the center of the hole 5 of the photoresist 4 as shown in FIG. More specifically, as an example, when metal nanoparticles are sprayed by gas deposition to the hole 5 formed in the film-like photoresist 4, the position of the spray nozzle 6 is set to the spray scan direction y (perpendicular to the paper surface). To the axial direction x orthogonal to Thereby, at least a part of the metal particles riding on the gas flow from the nozzle 6, that is, the metal particle flow collides with the photoresist 4 around the opening of the hole 5, and the flow path direction to the hole 5 is displaced. 5, the deposition rate of the metal particles in a certain direction as viewed from the center position becomes slower or faster relative to the other direction, and the bump 1 formed in the hole 5 is inclined in a certain direction. The apex has a shape displaced in one direction from the projection central axis.

  That is, in order to form the bump 1 having an arbitrary inclination, the ejection flow path from the spray nozzle 6 may be displaced so that the flow is biased in a desired direction. An example of this specific method is the axis shift of the spray nozzle 6 illustrated in FIG. As other methods, for example, those shown in FIGS.

  In FIG. 5, by shifting the position of the nozzle 6, the photoresist 4 around the hole 5 becomes the wall of the gas flow or the metal particle flow directly, but in FIG. 6 and FIG. In order to promote the flow, the flow path block body 7 is provided around the hole 5. The flow path block body 7 in FIG. 6 is a convex body formed on the photoresist 4 in the vicinity of the outside of the hole 5, and the flow path block body 7 in FIG. 7 is partially located above the hole 5. A plate-like body provided between the photoresist 4 and the nozzle 6. When at least part of the ejection flow path from the nozzle 6 hits or is blocked by these flow path block bodies 7, the flow path is displaced, and the metal nanoparticles reaching the holes 5 are deposited in a certain direction. As a result, the formed bumps have a generally inclined shape. The flow path block body 7 may be provided at a position shifted from the center position of the hole 5 in a direction parallel to the scanning direction y, or may be provided at a position shifted in a direction x orthogonal to the scanning direction y.

  As yet another example, as shown in FIGS. 8A and 8B, the nozzle 6 or the substrate 3 or the hole 5 or the like is placed in a direction parallel to or perpendicular to the scanning direction y. The angle θ is inclined. As a result, the ejection flow path from the nozzle 6 as viewed from the center of the hole 5 is displaced with an inclination of the inclination angle θ, and a bump having an inclined protrusion direction can be formed. The inclination angle θ is set so that a desired bump inclination displacement direction and displacement amount can be obtained.

  The above-described axis shift of the nozzle 6, the installation of the block body 7, and the inclination of the nozzle 6, etc. are performed with a position, shape and size that can be changed by biasing the ejection flow path in a certain direction, or with an inclination angle θ. 5, the deposition rate of the metal particles can be relatively lowered or increased only in a desired direction, and a projection shape inclined with a desired displacement direction and displacement amount can be realized. Of course, the means for displacing the ejection flow path is not limited to these, and at least a part of the gas flow or metal particle flow from the nozzle 6 is blocked or caused to collide, thereby directly or indirectly causing the flow path to move in a certain direction. It is only necessary that the flow is biased to the right. Further, as a structure to be formed, not only conical bumps but also fine protrusion structures that can be formed by gas deposition in openings such as holes and grooves such as line-shaped protrusions can be considered. For example, the line-shaped protrusion can be used as a line-shaped bump for groove connection, a line-shaped sealant for a chip, or the like.

[Example of bump production]
Here, the cone-shaped metal bump actually produced according to the present invention will be described. FIG. 9 is an electron microscopic image of the produced conical Au bump, and FIG. 10 is an electron microscopic image of a hole pattern for forming this bump.

  In this experiment, a hole array was formed on a resist having a film thickness of 30.5 μm with a diameter of 34.5 μm and a pitch of 60.0 μm by UV lithography according to the detailed specifications of the chip and resist pattern shown in FIG. These were produced by the gas deposition method under the film forming conditions shown in FIG. At the time of gas deposition, a chip mounting jig having a height of 3 mm and an inclined surface angle of 45 ° shown in FIG. 13 was used as the block body 7 described above. A space of 510 μm was provided between the chip mounting jig and the center of the outermost hole (bump) in the hole array (bump array), and the height position of the nozzle was 4 mm.

  As a result, as shown in FIG. 9, a conical bump having a vertex displaced 6.7 μm from the central axis could be obtained.

[Bump formation process evaluation method]
The metal bump according to the present invention is automatically formed into a conical shape by self-alignment by depositing metal nanoparticles such as Au in the hole formed in the photoresist and closing the hole by the eaves growing on the metal nanoparticle. Is done. At this time, stabilization of formation conditions during film formation is important.

  Thus, when the actual conical Au bump described above was observed in detail, it was found that a step structure was observed on the surface as apparent from FIG. On the surface of the bump shown in FIG. 9, a stripe pattern of contour lines constituting the step structure can be confirmed. As illustrated in FIG. 14, this step structure is generated like an annual ring by scanning the spray nozzle 6 over the hole 5 of the photoresist 4. It is related to time and eaves growth rate.

  First, when the number of steps appearing on the actual bump surface in FIG. 9 is counted from the bump bottom surface to the apex, there are 28 steps. That is, it can be seen that bumps were formed in 28 scans. From the three-dimensional shape measurement with a laser microscope, it is known that the height of the bump apex is 38.0 μm, so that the average film thickness for each scan is as high as 1.4 μm. As film formation conditions at this time, the scanning speed of the stage is 2 mm / s, the stroke is 20 mm, and 105 resist holes arranged in a line on one side of a 7.5 mm square chip are scanned in 10 seconds. As a result, the film formation rate was calculated to be 0.14 μm / s, and 105 bumps 1 row were produced at a pitch of 60 μm in just 4 minutes 40 seconds (bump formation time). The scanning stroke of the stage is 20 mm for a 7.5 mm square chip size, and an extra film is formed by 12.5 mm. Therefore, if this amount is excluded, the formation time can be further shortened, and if the scan stroke is the same as the 7.5 mm square of the chip size, it can be calculated that it can be produced in 1 minute 45 seconds.

  Further, not only the film formation speed and the formation time but also the eaves growth speed during bump formation can be calculated as follows. Since the apex height of the conical bump is 1.25 times higher than the height of the resist hole, it can be seen that the vertical film formation rate was 1.25 times faster than the eaves growth rate. From this speed ratio, the growth speed of the eaves can be calculated as 0.112 μm / s.

  Thus, by measuring the three-dimensional shape of resist holes and bumps and the number of steps, it is possible to calculate the average film formation rate, formation time, and eaves growth rate.

  Furthermore, not only the average film deposition rate, but also the step shape and interval are measured more precisely as shown in FIG. 15 to obtain even the three-dimensional shape of the bump surface. Information such as the film speed and growth direction can be obtained, and stable bump formation can be performed by feeding back the formation conditions to various parameters of the gas deposition method based on this data. The measurement of the step shape and the interval can be obtained from, for example, an electron microscope image or an optical microscope image, and growth direction information such as an inclination + −α ° from the central axis can be calculated from this data.

  Here, the film formation rate, the formation time, and the eaves growth rate will be described more specifically.

By counting the number of steps n _scan appearing on the surface of the conical bump produced by the gas deposition method as described above,
1. Average deposition rate per scan (= conical bump growth rate) v _scan (= v _bump )
2. Bump formation time T _bump
3. Average eaves growth rate per scan v _visor
Can be calculated.

  In the case of the resist hole shape and the conical bump shape as shown in FIGS. 16 and 17, the bump growth rate and the bump formation time can be calculated as follows.

There is a stripe pattern on the surface of the conical bump, and this step represents the film thickness to be formed in one scan when the nozzle (or stage) is scanned back and forth during the gas deposition film formation. Therefore, the average film thickness h _{scan for} each _scan can be calculated from the height h _bump of the cone bump apex and the number of steps n _scan .

Since the film is formed by reciprocating and scanning the nozzle (or stage), if the time taken for one scan is t _scan [s / scan], the film thickness per second, that is, the film formation speed v _bump is It can be calculated by the following formula using h _scan .

Here, n _s t _s in Equation 2 represents a time T _bump until the eaves are completely blocked and a conical bump is formed. That is, the conical bump formation time T _bump can be easily calculated by counting the number of steps n _scan . Since one scan time t _scan is related to the moving speed v _scan of the nozzle (or stage) and the scan distance d _scan , the following equation 3 holds. From this, it can be seen that the conical bump formation time T _bump changes in proportion to d _scan under the same film forming conditions with constant v _scan .

  If Equation 3 is used, Equation 2 can be expressed as Write Number 4.

  Next, the growth rate of the eaves can be calculated as follows in the case of the resist hole shape, conical bump shape, and eaves shape as shown in FIG.

First, it is assumed that the growth rates v _bump and v _visor of the bumps and the eaves are constant regardless of the shape of the holes, and the average growth rate of each is expressed by the following equation. Here, it should be noted that the time for completely covering the eaves and the time for forming the bumps are the same.

From _Equation 6, the v _visor can be easily calculated by counting n _scans .

From Equations 5 and 6, the relationship between v _bump and v _visor is given by the following equation.

From _Expression 7, the aspect ratio AR _bump of the conical _bump is determined by the ratio of v _bump and v _visor . That is, the taper angle of the conical bump can be changed by changing v _bump and v _visor according to the film deposition conditions of the gas deposition method.

For example, if the aspect ratio AR _hole = 1 (h _hole = d _hole ) of the resist hole shape and the height h _bump of the conical bump coincides with the resist film thickness h _hole , the v _visor is just v _bump Halved.

1 Bump 2 Chip 3 Substrate 4 Photoresist 5 Hole 6 Nozzle 7 Flow path block body

Claims (16)

A method in which metal nanoparticles are sprayed from above an opening provided in a photoresist by a gas deposition method to form a protruding fine structure in the opening,
A fine structure forming method, wherein the flow path direction from the spray nozzle is displaced so that the fine structure is inclined in one direction.   The method according to claim 1, wherein the spray nozzle is shifted from the center of the opening to displace the flow direction from the spray nozzle.   The method of Claim 1 using the flow-path block body which displaces the flow-path direction from a spray nozzle.   The method according to claim 3, wherein at least a part of the flow path from the spray nozzle is blocked by the flow path block body.   The method according to claim 3, wherein the flow path from the spray nozzle is applied to the flow path block body.   The method according to claim 2, wherein the flow path block body is provided in the vicinity of the opening or the spray nozzle.   The method according to claim 1, wherein the spray nozzle or the object to be formed is inclined to displace the flow direction from the spray nozzle as viewed from the opening.   The method according to claim 1, wherein the opening is a hole or a groove.   The method according to claim 1, wherein the protruding shape is a cone shape or an edge shape.   The method according to claim 1, wherein the microstructure is a bump.   The method according to claim 1, wherein the microstructure is a line-shaped protrusion. A method for evaluating a formation process of a fine structure formed by the method according to any one of claims 1 to 11, wherein the step appears on the surface of the fine structure formed in the opening by a gas deposition method. A method for evaluating a fine structure forming process, which obtains at least one of a film formation speed of the fine structure, a formation time of the fine structure, and a growth speed of the eaves on the opening based on the number . The method according to claim 12, wherein the shape and interval of steps appearing on the surface of the microstructure are obtained, and the growth direction of the microstructure is obtained based on the shape and interval . A method for evaluating a formation process of a fine structure formed by the method according to any one of claims 1 to 11, wherein the step appears on the surface of the fine structure formed in the opening by a gas deposition method. A method for evaluating a formation process of a fine structure, which obtains a shape and a distance and obtains a growth direction of the fine structure based on the shape and the distance. A metal bump formed by the method according to any one of claims 1 to 11, Chi lifting vertices shifted in the desired direction from the center, has a step of a plurality of stages to form a striped pattern of contours on the surface Metal bumps characterized by that. A semiconductor chip comprising the metal bump of claim 15 .