JP6414779B2 - Micro bump manufacturing method - Google Patents

Description

  The present invention relates to a method for manufacturing a microbump that can stably mass-produce solder bumps (hereinafter referred to as “microbumps”) having a height on the order of microns.

  Conventionally, examples of the solder bump forming method include a plating method, a solder ball mounting method, a printing method, a sputtering method, and the like, and the sputtering method is considered promising from the viewpoint of miniaturization (Patent Document 1). Each of these four methods is known to have the following advantages and disadvantages.

  The plating method has the advantage that a fine pattern is possible, but requires precise composition control, and has disadvantages such as narrow material selectivity, low throughput, and large bump height variation. Therefore, the size / pitch of the bump is limited to about 40 μm / 50 μm.

  The solder ball mounting method is advantageous in that the variation in bump height is small, but a fine pattern is difficult. Therefore, the current size / pitch of the bump is about 80 μm / 150 μm.

  The printing method has the advantages that it can be manufactured at low cost, has a high throughput, and the bump height can be increased. However, the bump method has a large variation in bump height, and voids (defects) easily occur inside the bump. is there. For this reason, the size / pitch of the bump is limited to about 80 μm / 100 μm.

The sputtering method has the advantages that fine patterning is possible, the bump composition is easily controlled, the material selectivity is wide, and the bump height variation is small, but the throughput is low. Since it has such many advantages, according to the sputtering method, the size / pitch of the bumps can be set to 40 μm or less / 50 μm or less.
Therefore, since the sputtering method is more promising than other methods in realizing a fine bump size / pitch, development of a high-speed film formation technique has been expected.

However, in order to increase the height of the bump, it is first necessary to prepare a resist structure having an internal space larger than the height of the bump formed by the sputtering method.
However, in reality, the resist shape as shown in the photos of FIGS. 10A and 10B is the limit due to the steps shown in FIGS. 9A to 9C. In other words, the distance between the resist-shaped roof (histicle) and the object to be processed is about 0.5 μm in the case of FIG. 10A and about 1.4 μm in the case of FIG. It was difficult.

  FIG. 11 is a schematic cross-sectional view showing the relationship between the bump size and various substrates (package substrate, interposer, device chip). In the present invention, the target micro-bump is disposed between the package substrate and the interposer or between the interposer and the device chip. Although the height is lower (3 to 8 μm) than conventional solder balls and solder bumps, micro bumps are required to have excellent uniformity in height variation.

  However, conventionally, since the resist shape as shown in the photographs of FIGS. 10A and 10B is the limit, only solder bumps as shown in FIGS. 12 and 13 can be formed. There wasn't. FIG. 12 is a solder bump having a low height of 1 μm or less, and FIG. 13 is about 3 μm in height, but is in contact with the resist structure and cannot be lifted off (cannot be patterned). . Any solder bump is unsuitable as a solder bump.

Accordingly, the present inventors have developed a method capable of stably producing a resist structure having a larger internal space than the height of the bump in order to form a microbump having a small variation in height.
When this resist structure was used to study the formation of micro bumps by sputtering, it was found that the outer shape of the deposited adherend tends to have a shape in which the peripheral edge rises upward from below. Since this shape is inappropriate as a micro bump, the development of a method for improving this was expected.

Japanese Patent Laid-Open No. 08-018333

  The present invention has been devised in view of such a conventional situation, and provides a method for producing a microbump capable of forming an adherend formed by a sputtering method into a shape suitable as a bump. The purpose is to provide.

According to a first aspect of the present invention, there is provided a method for manufacturing a microbump, comprising: a resist structure having a predetermined opening and an internal space having a height on the order of microns; Used as a method of manufacturing a micro bump by a sputtering method on a specific region of one surface of the object facing the internal space, and depositing sputter particles that have passed through the opening in the specific region, A process X for forming a desired adherend (Adherend), a process Y for removing the resist structure and leaving the adherend on one surface of the object to be treated, and a heat treatment for the adherend and a step Z to perform, only including,
The heat treatment in the step Z is performed in a formic acid (HCOOH) atmosphere, and the heat treatment in the step Z includes a preheating time zone and a main heating time zone that is set to a higher temperature condition than the preheating. The temperature is 160 ° C. to 200 ° C. and the time is 280 to 360 seconds, and the main heating is 230 to 300 ° C. and the time is 100 to 140 seconds. It is characterized by .

In the present invention, a resist structure having a predetermined opening and an internal space having a height on the order of microns is used as a mask, and the sputtered particles that have passed through the opening are deposited on the specific region to obtain a desired structure. By the step X of forming the adherend (Adherend), for example, sputtered particles can be deposited so as to cover a specific region where the conductive portion is disposed on one surface of the object 10 to be processed. At this time, the situation (area, thickness (height), three-dimensional shape, etc.) where the sputtered particles are deposited is roughly determined by the opening of the resist structure and the height of the internal space. In the present invention, since the height of the internal space is set to the micron order, the height of the adherend can be set to the micron order.
After the formation of the adherend, the resist structure is removed, and the adherend is exposed on the surface of the object to be processed by the process Y left on the surface of the object to be processed. It can be.
Next, the adherend is heated uniformly from its periphery by the step Z of heat-treating the adherend that is exposed on one surface of the treatment. Thereby, the site | part which makes the abnormal shape in the external shape (especially peripheral part) of a to-be-adhered body moves so that it may be taken in by the center part, and it can shape | mold in the "bowl shape" suitable for a solder bump.
Therefore, the present invention provides a method for manufacturing a microbump that can form an adherend formed by a sputtering method into a shape suitable as a bump.

Sectional drawing which shows an example of the manufacturing method of the resist structure used with the manufacturing method of the microbump which concerns on this invention. Sectional drawing which shows an example of the manufacturing method of the microbump which concerns on this invention. The cross-sectional SEM photograph which shows an example of the resist structure produced by this invention. The cross-sectional SEM photograph which shows another example of the resist structure produced by this invention. The cross-sectional SEM photograph which shows an example of the microbump produced by this invention. The cross-sectional SEM photograph which shows another example of the microbump produced by this invention. The graph which shows the temperature profile of the heat processing which concerns on this invention. The cross-sectional SEM photograph which shows before and after heat processing of the micro bump produced by this invention. Sectional drawing which shows an example of the manufacturing method of the resist structure which concerns on a prior art example. The cross-sectional SEM photograph which shows an example of the resist structure produced in the prior art example. Sectional drawing explaining the application example of bump size. The cross-sectional SEM photograph which shows an example which formed the bump using the resist structure of a prior art example. The cross-sectional SEM photograph which shows another example which formed the bump using the resist structure of a prior art example.

  Below, one Embodiment of the manufacturing method of the microbump based on this invention is described based on drawing.

FIG. 1 is a cross-sectional view showing an example of a resist structure manufacturing method used in the microbump manufacturing method according to the present invention in the order of steps.
Here, an example in which a resist structure is formed by the manufacturing method (steps RA to RD) described below is introduced, but the present invention is not limited to this.

<Processing object 10>
FIG. 1A shows an object to be processed 10 used for forming a resist structure. The object to be processed 10 is disposed inside the insulating base 11, the first conductive portion 12, the insulating portion 13, and the insulating portion 13, and the second conductive portion 14 that is in electrical contact with the first conductive portion 12. , Including. The upper surface of the second conductive portion 14 is flush with the upper surface of the first conductive portion 12, and the upper surface of the second conductive portion 14 and the upper surface of the first conductive portion 12 are both exposed. .

<Step RA for Forming Thick Film A of First Resist>
FIG. 1B to FIG. 1D show step RA for forming the thick film A made of the first resist. The thick film A made of the first resist in the present invention is not formed at a time, but is laminated by a technique in which the film is divided into many times.

In the step RA for forming the thick film A, the first resist layer formed by the step A1 [FIG. 1 (b)] in which the first resist layer is formed on the object to be processed by the spin coating method and the first step A1. Step A2 [FIG. 1C] for baking the resist layer is provided, and the thick film A is set to a predetermined thickness [FIG. 1D] by repeating Step A1 and Step A2.
As the first resist, a resist which is melted by an alkaline developer and does not have photosensitivity is suitably used. For example, SF-7 series (manufactured by Nippon Kayaku Co., Ltd.), LOR series (manufactured by Nippon Kayaku Co., Ltd.). ) And the like.

  FIG. 1B shows that the first resist layer 15a (15α) is applied by spin coating (R1 is covered) so as to cover one surface of the object 10 to be processed, that is, the insulating portion 13 and the second conductive portion. The film is formed by [representing rotation of the processing body 10] [step A1]. The application conditions (application amount per unit time, rotation speed R1, etc.) may be adjusted as appropriate.

  Next, as shown in FIG. 1C, the first resist layer 15a (15α) formed in the step A1 is baked using the heating means H1. Thereby, the baked first resist layer 15aB (15β) is obtained [Step A2]. The firing conditions (treatment temperature, treatment time, etc.) may be adjusted as appropriate.

FIG. 1D shows a state in which the thick film A having a predetermined thickness is formed by repeating the steps A1 and A2 a plurality of times. FIG. 1 (d) shows a configuration example [15aB, 15bB, 15cB (15β)] in which the steps A1 and A2 are repeated three times, but the present invention is not limited to three times. It does not matter if it is more than once. Moreover, there is no restriction | limiting in particular in the thickness of the film | membrane formed in process A1, The same thickness may be repeated and you may make it different thickness. That is, the number of repetitions and the thickness of each film are appropriately selected.
However, the total thickness of the thick film A is preferably at least 2 μm and not more than 15 μm in order to form a micron-order space in a subsequent process.

<Step RB of Forming Thick Film B of Second Resist>
FIG.1 (e)-FIG.1 (g) have shown step RB which forms the thick film B which consists of a 2nd resist. For the thick film B made of the second resist in the present invention, a method of laminating a single film at a time and a method of laminating in multiple times are used according to the film thickness.

The step RB for forming the thick film B is formed by the step B1 [FIG. 1 (e)] of forming a second resist layer on the thick film A (15β) by the spin coating method and the step B1. Step B2 [FIG. 1 (f)] for firing the second resist layer, and by repeating Step B1 and Step B2, the thick film B has a predetermined thickness [FIG. 1 (g)]. To do.
As the second resist, a resist etched by photolithography is preferably used. For example, OFPR series (manufactured by Tokyo Ohka Kogyo Co., Ltd.), KMPR1000 series (manufactured by Nippon Kayaku Co., Ltd.), TZNR series (Tokyo Ohka Kogyo Co., Ltd.) Co., Ltd.), SU-8 series (Nippon Kayaku Co., Ltd.), PMER series (Tokyo Ohka Kogyo Co., Ltd.), ZPN series (Nihon Zeon Co., Ltd.), and the like.

  In FIG. 1E, the second resist layer 16a (16α) is formed by spin coating (R2 represents the rotation of the workpiece 10) so as to cover the upper surface of the thick film A (15β). Step B1]. Application conditions (application amount per unit time, rotation speed R2, etc.) may be adjusted as appropriate.

  Next, as shown in FIG. 1 (f), the second resist layer 16a (16α) formed in the step B1 is baked using the heating means H2. Thereby, the baked second resist layer 16aB (16β) is obtained [Step B2]. The firing conditions (treatment temperature, treatment time, etc.) may be adjusted as appropriate.

  FIG. 1G shows a state in which the thick film B having a predetermined thickness is formed by repeating the steps B1 and B2 a plurality of times. FIG. 1G shows a configuration example [16aB, 16bB (16β)] in which the process B1 and the process B2 are repeated twice. However, the present invention is not limited to two times, but three times or more. It doesn't matter. Moreover, there is no restriction | limiting in particular in the thickness of the film | membrane formed at process B1, The same thickness may be repeated and you may make it different thickness. That is, the number of repetitions and the thickness of each film are appropriately selected.

However, the total thickness of the thick film B is preferably at least 2 μm and not more than 10 μm in order to form a micron-order space in a subsequent process.
In the “step RC for forming the second space in the thick film B using the photolithography method”, which will be described later, a film thickness that is easy to produce the second space is required for the total thickness of the thick film B.

<Step RC Forming Second Space in Thick Film B>
FIG. 1 (h) shows the second space so that the thick film B (16β) is penetrated through the thick film B and the upper surface of the thick film A (15β) is exposed using the photolithography method. 16H is formed.
When performing the photolithography method, the second space 16H is formed by irradiating the thick film B (16β) with light of the wavelength hν (λ) through the opening using a mask M1 having an aperture of 16W. Is formed. In FIG. 1 (h), reference numeral 16HS is the inner surface of the thick film B (16β) that defines the second space 16H, and reference numeral 16HB is the exposure of the thick film A (15β) that defines the second space 16H. This is the top surface.

  In that case, the occupied area SA of the first space 15H is wider than the occupied area SB of the second space 16H when viewed from the overlapping direction of the first space 15H and the second space 16H formed in the next step, and The photolithography is performed on the thick film B (16β) so that the occupied area SB is included in the occupied area SA. Thereby, in the next step, it is possible to form the second space 16H that functions as an opening of the mask when forming the first space 15H with respect to the thick film A (15β).

<Step RD for Forming First Space in Thick Film A>
In FIG. 1 (i), the thick film A (15β) is penetrated through the thick film A (15β) by using a wet etching method, and the upper surfaces (13, 14) of the object to be processed 10 are exposed. The first space 15H is formed.

  When performing the wet etching method, by appropriately selecting factors (such as the type and pressure of the gas and the temperature of the object to be processed) that control the temperature of the chemical solution, the first space 15H and the second space 16H The first space 15H is formed so that the occupied area SA of the first space 15H is wider than the occupied area SB of the second space 16H when viewed from the overlapping direction. In FIG. 1I, reference numeral 15HS denotes an inner surface of the thick film A (15β) that defines the first space 15H. Reference numeral 15HB is an exposed upper surface of the target object 10 (insulating portion 13 and second conductive portion 14) that defines the first space 15H. Reference numeral 15HT denotes a portion extending like a roof when viewed from the overlapping direction of the first space 15H and the second space 16H.

  In step RD, it is important to form the first space 15H so that the upper surface (insulating portion 13 and second conductive portion 14) of the workpiece 10 is exposed on the bottom surface 15HB of the first space 15H. . Thereby, it can be set as the structure by which the solder bump formed using a sputtering method was electrically connected with the 2nd electroconductive part 14 reliably in the subsequent process.

  Further, in the direction of cross-sectional view of each layer shown in FIG. 1 (i), “(width of second conductive portion 14) <(opening diameter 16W of second space 16H) <(opening diameter 15W of first space 15H). It is also important to adjust the dimension of the portion 15HT extending like a roof so as to satisfy the relational expression " Thereby, in a later step, when the solder bump is formed by using the sputtering method, the solder bump covers the second conductive portion 14 and is provided by controlling the size (diameter, height) of the solder bump. Is possible.

<Resist structure>
3 and 4 are cross-sectional SEM photographs showing the resist structure produced by the above-described steps RA to RD. FIG. 3 shows a resist structure in which the width (inner diameter) of the first space 15H formed in the thick film A is 30 μm and the width (inner diameter) of the second space 16H formed in the thick film B is 20 μm. The total film thickness of A and thick film B is 12 μm. FIG. 4 shows a resist structure in which the width (inner diameter) of the first space 15H formed in the thick film A is 60 μm and the width (inner diameter) of the second space 16H formed in the thick film B is 50 μm. The total film thickness of A and thick film B is 12 μm.

The microbump manufacturing method according to the present invention sequentially performs steps X to Z described below using the resist structure [FIG. 1 (i)] prepared in this way.
As shown in FIG. 2 (j), a resist structure provided on one surface of the object to be processed 10 and having a predetermined opening and an internal space having a micron-order height is used as a mask. Thereby, micro bumps are manufactured by a sputtering method in a specific region on one surface of the object to be processed facing the internal space.

<Process X>
Step X deposits the sputtered particles SP that have passed through the opening so as to cover a specific region of the insulating portion 13 including the second conductive portion 14, thereby forming a desired adherend 20 </ b> A (20). Form [FIG. 2 (j)].

  An internal space in which the resist structure R is composed of a thick film A (15β) and a thick film B (16β) and has predetermined openings 15W and 16W and a micron-order height (corresponding to a thickness of 15β). 15H is provided, the thickness at the center of the desired adherend 20A (20) can be on the order of microns. However, it has been found that the above-mentioned adherend (Adherend) 20A (20) tends to have a shape in which the peripheral edge rises away from the insulating portion 13.

Therefore, in the next step Y, in order to remove the resist structure R and leave the adherend 20A (20) on one surface of the object to be processed 10, the resist structure R [thick film A (15β) and The sample 1J (1) is immersed in a desired etching solution capable of removing all of the thick film B (16β)].
As a result, a sample 1K (1) is obtained in which the adherend 20A (20) remains on one surface of the object 10 [FIG. 2 (k)].

  Next, heat treatment is performed on the sample 1L (1) in which the entire adherend 20A (20) is exposed on one surface of the object 10 at a temperature of, for example, 180 ° C. to 340 ° C. [FIG. 2 (l)]. By this heat treatment, the adherend 20A (20) is uniformly heated from its surroundings.

  By performing the heat treatment described above, the abnormally shaped portion of the outer shape (particularly the peripheral portion) of the adherend 20B (20) moves so as to be taken into the central portion, and is suitable for solder bumps. It can be formed into an adherend 20C (20) having the outer shape [FIG. 2 (m)].

  When performing such heat treatment, the atmosphere G in which the adherend 20B (20) is placed is preferably composed of air flux (normal air atmosphere), nitrogen, or formic acid (HCOOH). In particular, when the atmosphere G is made of formic acid, the adherend 20C (20) having a “bowl-like” shape suitable for solder bumps has various characteristics such as resist opening and heat treatment temperature and time. Regarding conditions, it is more preferable because it can be stably formed in a wide range of condition settings.

  FIG. 5 is a cross-sectional SEM photograph showing an example of a microbump produced according to the present invention, and shows the bump shape produced by changing the resist opening diameter during sputtering film formation and the atmosphere during heat treatment. Show. At that time, the resist opening diameter was tested for three levels of 10, 20, and 30 [μm], and the atmosphere was tested for three types of atmospheric flux, nitrogen, and formic acid.

The mark shown at the upper left of each photo shows the following contents.
○: Both ends of the cross-sectional photograph have a “bowl-like” outer shape suitable for bumps.
Δ: In the cross-sectional photograph, one end has a “bowl-like” outer shape suitable for bumps, but the other end has a portion having an abnormal shape in the peripheral portion.
X mark: The site | part which makes an abnormal shape remains in a peripheral part with both ends in a cross-sectional photograph.

  In an atmosphere composed of atmospheric flux, an adherend 20C (20) having a “bowl-like” outer shape suitable for solder bumps was obtained only when the resist opening diameter was 20 [μm] (marked with a circle). When the resist opening diameter was set to 10, 30 [μm], a portion having an abnormal shape remained in the peripheral portion (Δ mark, X mark). From this result, when atmospheric flux is used as the atmosphere, it is possible to form a “bowl-like” outer shape suitable for solder bumps, but the solution of the resist opening diameter to be realized is 20 [μm It seems to be in a narrow range before and after.

In an atmosphere composed of nitrogen (N ₂ ), the adherend 20C (20) having a “bowl-like” outer shape suitable for a solder bump is used in the investigated resist opening diameter range (10 to 30 μm). It was not possible to obtain (× mark to Δ mark). Under any condition, a portion having an abnormal shape remained in the peripheral portion.

  In an atmosphere composed of formic acid (HCOOH), an adherend 20C (20) having a “bowl-like” shape suitable for solder bumps is obtained even in the investigated resist opening diameter range (10 to 30 [μm]). (○ mark). By using formic acid (HCOOH) as the atmosphere, it is possible to stably manufacture the adherend 20C (20) having an outer shape suitable for solder bumps in a wide range of resist opening diameters.

  From the above results, it was confirmed that the most preferable atmosphere was formic acid. Air fluxes can also be used by narrowing down the conditions.

  FIG. 6 is a cross-sectional SEM photograph showing another example of the micro-bump manufactured according to the present invention, which is a result of examining dependence on heat treatment conditions (temperature and time of preheating, temperature and time of main heating). Here, the preliminary heating and the main heating under the heat treatment conditions are defined by, for example, a temperature profile shown in FIG. As shown in FIG. 7, the main heating temperature is set higher than the preheating temperature. Moreover, the time of preheating and this heating means the time which kept desired temperature constant.

  In FIG. 6, in the A group, a part having an abnormal shape remained in the peripheral portion. Group B was able to obtain adherend 20C (20) having a “bowl-shaped” shape suitable for solder bumps. The C group has a “bowl-like” outer shape suitable for solder bumps at the peripheral portion, but the central portion has a concave shape that is not preferable as a bump.

  From the above results, it is preferable that the group B, that is, “the preheating temperature is 180 ° C. and the time is 180 to 360 seconds and the main heating temperature is 280 ° C. and the time is 100 to 140 seconds” is preferable. I understood. Further, when the preheating temperature was set to 160 to 200 ° C. and the main heating temperature was set to 230 to 300 ° C. in the same processing time, the “bowl-like” outer shape suitable for the solder bump similar to the B group was obtained. An adherend 20C (20) was obtained. The present invention contributes to stable production of the adherend 20C (20) having a “bowl-like” outer shape suitable for solder bumps.

FIG. 8 is a cross-sectional SEM photograph showing before and after the heat treatment of the microbump produced according to the present invention. Thus, the action and effect of the heat treatment in the present invention can be confirmed from the cross-sectional SEM photograph. That is,
According to the present invention, when a desired adherend (Adherend) 20A (20) having a thickness on the order of microns is formed, there exists a portion that forms an abnormal shape in the outer shape (particularly the peripheral portion) of the adherend. Even so, by applying the heat treatment according to the present invention, the abnormal shape of the peripheral edge moves so as to be taken into the center of the adherend, and can be formed into a “bowl shape” suitable for solder bumps. It can be confirmed by observation of a cross-sectional SEM photograph.

Therefore, the microbump manufacturing method according to the present invention contributes to mass production of microbumps having a height on the order of microns.
The method for manufacturing the microbump of the present invention has been described above, but the present invention is not limited to this, and can be appropriately changed without departing from the spirit of the invention.

  The present invention can be widely applied to a method for manufacturing a microbump.

  R resist structure, 1 sample, 10 object, 11 substrate, 12 first conductive part, 13 insulating part, 14 second conductive part, 15β thick film A, 15H first space, 16β thick film B, 16H second Space, 20 adherend.

Claims (1)

A resist structure provided on one surface of the object to be processed and having a predetermined opening and an internal space having a micron-order height is used as a mask, and the surface of the object to be processed facing the internal space A method of manufacturing micro bumps in a specific area by sputtering,
A step X of depositing sputtered particles that have passed through the opening in the specific region to form a desired adherend;
Removing the resist structure and leaving the adherend on one surface of the object to be processed; and
See containing and a step Z performing heat treatment on the adherend,
The heat treatment in step Z is performed in a formic acid (HCOOH) atmosphere, and
In the heat treatment in the step Z, a preheating time zone and a main heating time zone set to a higher temperature condition than the preheating are set in order,
In the preheating, the temperature is 160 ° C. to 200 ° C., the time is 280 to 360 seconds,
The main heating has a temperature of 230 to 300 ° C. and a time of 100 to 140 seconds.
A method for producing a microbump characterized by the above.