JP5923698B2 - Manufacturing method of semiconductor device using noble metal paste - Google Patents

Description

  The present invention relates to a method for manufacturing a semiconductor device in which a substrate and a semiconductor element are bonded using a noble metal paste.

  As a method for manufacturing a semiconductor device for bonding a substrate and a semiconductor element using a noble metal, a method using a brazing material is known. As the brazing material, an AuSn brazing material, which is a flux-less brazing material, is generally used. After arranging a pair of members to be joined via the brazing material, the melting point or higher (about 300 ° C. or higher) The method of fusing the brazing material by heating to a temperature of However, in the method of heating the bonding member to a high temperature as described above, there is a case where a problem of variation in electrical characteristics occurs in a member such as a semiconductor element due to a thermal stress applied after the bonding.

  For these reasons, it has been desired to join the members with heating as low as possible. Patent Document 1 describes a method using silver paste containing noble metal powder as silver powder and containing silver powder and an epoxy resin. When such silver paste is used, bonding is possible at a relatively low temperature of 100 to 200 ° C. It has become.

  In addition, the present inventors have proposed a manufacturing method using a gold paste containing a gold powder having a predetermined purity and particle size and an organic solvent instead of a brazing material as a bonding material (Patent Document 2). . In this document, when bonding semiconductor elements, a method is adopted in which a gold paste is applied to a bonding member, dried and sintered, the other member is then placed, and both members are bonded by heating and pressing. Therefore, it is possible to join at a relatively low temperature as compared with the joining using the conventional brazing material.

JP 2004-359830 A JP 2007-324523 A

  However, in the case of a joining method using a noble metal paste containing a resin as in Patent Document 1, there is a case where the resin is not completely decomposed by heating during joining and remains on the member after joining. For this reason, in a member such as a semiconductor chip, the remaining resin may be a cause of contamination and affect semiconductor performance and the like.

  On the other hand, in the joining method of Patent Document 2, the above-mentioned contamination problem can be solved by using a noble metal paste that does not contain a resin. On the other hand, when no resin is contained, after the paste is applied to the joining member, noble metal particles aggregate. In some cases, the organic solvent tended to progress relatively easily and the organic solvent oozed out from the applied paste. Further, the joining method of Patent Document 2 requires a relatively large number of processes, such as a drying process in order to improve the formability and handling of the precious metal paste after application.

  Therefore, the present invention provides a method for manufacturing a semiconductor device that can be joined without causing contamination of the member after joining, and aims to provide a technique that can be applied to the joining member uniformly and can be joined by a simple process. And

The present invention for solving the above-described problems is a method for manufacturing a semiconductor device in which a substrate and a semiconductor element are bonded as a bonding member, the method including the following steps.
(A) One joining member is composed of a noble metal powder having a purity of 99.9% by mass or more and an average particle size of 0.1 to 0.5 μm, and an organic solvent having a boiling point of 200 to 350 ° C. A step of applying a noble metal paste having a thixotropy index (TI) value of 6.0 or more calculated from a measured value of a viscosity of 4 / s with respect to a viscosity of a shear rate of 40 / s at 23 ° C.
(B) The process of arrange | positioning said one joining member and the other joining member through the said noble metal paste, and pressurizing and joining from one direction or both directions, heating at least a sintered compact at 80-350 degreeC.

  In this invention, after apply | coating a noble metal paste to a joining member, it can join by arrange | positioning a pair of joining member through a noble metal paste, and heating and pressurizing. That is, since a noble metal paste having an appropriate TI value (thixotropic property) is used, the moldability of the paste applied to the joining member is improved. For this reason, the drying process required in the conventional joining method can be omitted, and the manufacturing process can be simplified. Moreover, also about the pressurization at the time of joining a joining member, high joining strength is realizable by low pressure. Hereinafter, the semiconductor device manufacturing method of the present invention will be described in detail.

  Examples of semiconductor devices that can be bonded by the method of the present invention include so-called power devices such as LEDs, rectifier diodes, and power transistors. These semiconductor devices are manufactured by bonding various substrates such as silicon wafers and semiconductor elements as bonding members.

  As a method of applying the noble metal paste to these joining members, the size of the joining portion, such as a spin coating method, a screen printing method, an ink jet method, a method of spreading the paste with a spatula after dropping, or a method of mounting an object to be joined as it is, Various methods can be used depending on the situation.

  According to the present invention, after applying a noble metal paste, a bonding object such as a semiconductor element is mounted (mounted) on the applied paste without performing a drying process, and the bonding member is bonded by heating and pressing. it can. By this heat treatment, evaporation of the organic solvent in the paste and sintering of the noble metal powder proceed. According to the present invention, evaporation and sintering can proceed uniformly without forming voids and the like at this time, and a densely joined portion can be formed. The heating temperature is preferably 80 to 350 ° C. If the temperature is less than 80 ° C., bonding may be insufficient. If the temperature exceeds 350 ° C., the influence of thermal strain during cooling increases.

  Moreover, in the manufacturing method of this invention, in the above-mentioned joining process, it becomes possible to join on low-pressure conditions than before. Specifically, even under pressure conditions of 1 MPa or less per sintered body, bonding can be performed with sufficient strength. On the other hand, in the conventional joining method using the noble metal paste, it was necessary to pressurize at about several tens of MPa per sintered body in order to obtain sufficient joining strength. In the conventional method, vacuum drying or the like is performed after applying the noble metal paste, and unevenness is generated on the paste surface in this drying step. Therefore, it is considered that higher pressure conditions than those of the present invention were necessary.

  Moreover, in this invention, you may perform arbitrary sintering processes before joining after paste application | coating (between (a) process and (b) process). When importance is attached to the simplification of the process, not only the drying step but also the sintering step can be omitted. On the other hand, when the sintering step is performed, the noble metal particles and the joining surface of the joining member ( It can be set as the sintered compact which formed the proximity state which carried out point contact mutually between the paste application surface) and the noble metal particle. For this reason, in the joining process after sintering, a plastic deformation is generated at the contact portion between the particles by heating and pressurization, and a bond between noble metal atoms is generated at the deformation interface, thereby realizing a precise bonding.

  When the sintering step is performed before joining (between the steps (a) and (b)), the sintering temperature is preferably 80 to 350 ° C. If it is less than 80 degreeC, the above point contacts will not arise easily. On the other hand, if it exceeds 350 ° C., the sintering proceeds excessively, the necking between the metal powders proceeds and bonds firmly, and even after pressing, it does not become a dense joint, This is because distortion tends to remain at the time. More preferably, the sintering temperature is 300 ° C. or lower. This is because the present invention aims at joining at 300 ° C. or lower from the viewpoint of protecting the joining member in the first place. The heating time during sintering is preferably 5 to 120 minutes. This is because in a short time, the temperature of the sintering furnace is not stable and sufficient sintering cannot be performed, and if the time is too long, productivity is impaired. In addition, this sintering is preferably performed in a state where no pressure is applied. The sintering temperature may be the same temperature from the start to the end of sintering, or may be increased or decreased after the start of sintering, as long as it is within the above-described preferred range.

  Next, the noble metal paste used in the present invention will be described in detail. In the present invention, it consists of a noble metal powder having a purity of 99.9% by mass or more and an average particle size of 0.1 to 0.5 μm, and an organic solvent having a boiling point of 200 to 350 ° C. A noble metal paste having a thixotropy index (TI) value calculated from a measured value of the viscosity of 4 / s with respect to the viscosity of s of 6.0 or more is used. Such noble metal paste can be uniformly applied to the joining member without including various resins that may cause contamination of the joining member. Even after being applied to the material, the dispersibility of the precious metal particles can be maintained uniformly, and even during heating during bonding, generation of voids due to non-uniform evaporation of organic solvents and non-uniform sintering of precious metal powder is suppressed. it can.

  Here, the “TI (thixotropic index) value” will be described. In pastes such as noble metals, the viscosity tends to decrease as the shear rate applied to the paste during measurement increases. Under such a background, the TI value is calculated as the ratio of the two viscosities using the values of the viscosities measured at two rotational speeds having different shear rates. For this reason, the TI value is a value indicating a change in viscosity with respect to the rotation speed, that is, an index representing the high thixotropic property.

  The noble metal paste of the present invention has a TI value of 6.0 or more, and has a reasonably high thixotropic property. For this reason, the moldability of the noble metal paste can be maintained in the coating step of the present invention, and the sintering of the noble metal can be uniformly progressed during the joining, so that the joined portion can be in a dense state. For this reason, the present invention is particularly suitable for die bond bonding with a large application area of the noble metal paste. When the TI value of the noble metal paste is less than 6.0, the solvent may ooze out (bleed out) when the noble metal paste is applied to the joining member. Further, the upper limit of the TI value is preferably 20 or less. When it exceeds 20, it tends to be difficult to handle at the time of kneading before applying the noble metal paste.

  Moreover, it is preferable that it is 100-1000 Pa.s about the viscosity of the share rate 4 / s used as the premise which calculates TI value. If it is less than 100 Pa · s, the precious metal powder tends to settle and easily separate from the solvent, and if it exceeds 1000 Pa · s, the handling property tends to deteriorate.

  The organic solvent constituting the noble metal paste has a boiling point of 200 to 350 ° C. (under atmospheric pressure). When the boiling point of the organic solvent is less than 200 ° C., the evaporation rate of the organic solvent is high at the time of bonding, and it becomes difficult to control the aggregation of the noble metal particles. In some cases, the organic solvent evaporates even at room temperature, so in the coating process. Handling becomes difficult. On the other hand, when the boiling point of the organic solvent exceeds 350 ° C., the organic solvent may remain in the joined member. If it is in the range of this boiling point, the organic solvent can contain 1 type, or 2 or more types. Here, regarding the organic solvent of the present invention, “boiling point 200 to 350 ° C.” means that when two or more organic solvents are included, all kinds of organic solvents contained have boiling points 200 to 350, respectively. It means being within the range of ° C.

  Specific examples of usable organic solvents include branched saturated aliphatic dihydric alcohols and monoterpene alcohols. Examples of branched saturated aliphatic dihydric alcohols include propylene glycol and 1,2-butane. Diol, 1,3-butanediol, 1,2-pentanediol, 1,3-pentanediol, 1,4-pentanediol, 1,5-pentanediol, 2,3-pentanediol, 2,4-pentanediol 1,2-hexanediol, 1,3-hexanediol, 1,4-hexanediol, 1,5-hexanediol, 1,6-hexanediol, or derivatives thereof, and the monoterpene alcohol is citronellol. , Geraniol, Nellore, Menthol, Terpiol, Carveol, Twill alcohol Pinot Kang Fe ol, beta-Fen chill alcohol, dimethyl octanol, hydroxy citronellol, or a derivative thereof is used.

  Considering the boiling point of the solvent, the carbon number is preferably 5-20. In particular, in the case of consisting of only one organic solvent, it is preferable to use a saturated aliphatic dihydric alcohol having 5 to 20 carbon atoms, 2,4-diethyl-1,5-pentanediol (product name: Nippon Mars; Nippon Perfume Pharmaceutical Co., Ltd., hereinafter referred to as MARS) is particularly suitable. In the case of comprising two kinds of organic solvents, it is preferable to use a mixture of monocyclic monoterpene alcohol having 5 to 20 carbon atoms and bicyclic monoterpene alcohol. Isobornylcyclohexanol (product name: Tersolve MTPH; Japan A mixture of Terpen Chemical Co., Ltd. (hereinafter referred to as MTPH) and α-terpineol at a mass ratio of 1/1 to 3/1 is particularly suitable.

  Next, as the noble metal powder constituting the noble metal paste, gold powder, silver powder, or a mixed powder thereof is suitable. In consideration of electrical and thermal conductivity, it is particularly preferable to use only gold powder.

  The purity of the precious metal powder that requires a high purity of 99.9% by mass or more is that if the purity is low, the sintering behavior of Au particles becomes unstable and the stability of the bonding strength decreases, or the bonding after bonding This is because the member becomes hard and cracks easily occur due to thermal shock or the like. The average particle diameter of the noble metal powder is 0.1 to 0.5 μm. If it exceeds 0.5 μm, it will be difficult to maintain the dispersed state in the paste, and the precious metal powder will easily settle. In addition, when the noble metal powder is sintered by heating at the time of joining, it is difficult to express a preferable proximity state. On the other hand, when the thickness is less than 0.1 μm, aggregation of the noble metal powder may occur.

  The volume content of the noble metal powder in the noble metal paste (the volume of the noble metal powder / the volume of the entire noble metal paste) is preferably 26 to 66% by volume (v / v). With such a volume content, a noble metal paste having a TI value of 6.0 or more tends to be obtained. In addition, the sintered body after joining is also likely to be in a dense state, and joining with high adhesion can be realized. When the content of the metal powder is less than 26% by volume, it is difficult to obtain the effect of improving adhesion, and the paste is also difficult to knead. On the other hand, when the content of the metal powder exceeds 66% by volume, the noble metal powder may be aggregated. The precious metal content is more preferably 35 to 55% by volume (v / v).

  The noble metal paste may further contain 0.05 to 1% by mass of a surfactant. When the surfactant is included, it is easy to maintain a state in which the noble metal powder is uniformly diffused in the noble metal paste. When the surfactant is less than 0.05% by mass, the effect of suppressing the aggregation of the noble metal powder is low, and when it exceeds 1% by mass, the surfactant may remain on the member after joining. As the surfactant, a cationic surfactant is preferable. For example, dodecyltrimethylammonium salt, hexadecyltrimethylammonium salt, octadecyltrimethylammonium salt, dodecyldimethylammonium salt, octadecenyldimethylethylammonium salt, dodecyldimethylbenzylammonium salt Quaternary ammonium salts such as salt, hexadecyldimethylbenzylammonium salt, octadecyldimethylbenzylammonium salt, trimethylbenzylammonium salt, triethylbenzylammonium salt, alkyl such as octadecylamine salt, stearylamine salt, N-alkylalkylenediamine salt Pyridinium salt systems such as amine salt systems, hexadecyl pyridinium salts, dodecyl pyridinium salts are used. Among them, alkyl (C8-C18) amine acetate (product name: Armac C) and N-alkyl (C14-C18) trimethylenediamine oleate (product name: duomin TDO) are particularly suitable. In addition, since a polymer type surfactant requires high temperature for decomposition | disassembly, it is not suitable for this invention.

  As described above, the present invention is a technique that can uniformly apply a paste to various joining members and can progress sintering uniformly upon heating during joining. In addition, high-strength bonding can be performed by a simple process without causing contamination of members after bonding.

Cross-sectional observation results by external X-ray fluoroscopic observation and cross-sectional electron microscope (SEM) of the joint. The figure which shows the test method of joining strength.

  Hereinafter, preferred embodiments of the present invention will be described.

[Example 1]
95% by mass of gold powder (average particle size: 0.3 μm) having a purity of 99.99% by mass produced by a wet reduction method, 3.75% by mass of isobornylcyclohexanol (MTPH) as an organic solvent, α- A gold paste was prepared by mixing terpineol with 1.25% by mass. The volume content of the gold powder in this gold paste was 49.6% by volume. The following physical properties were measured for the organic solvent used and the gold paste obtained.

Physical Properties Measurement The viscosity of the organic solvent and the gold paste was measured at a measurement temperature of 23 ° C. with a cone-type rotational viscometer (HAAKE, Rheoless RS75, cone plate: titanium, 35 mm, φ1 °, measured with a gap of 0.050 mm). After holding at a share rate of 0 / s for 30 seconds, the share rates of 4 / s, 20 / s, and 40 / s were held for 30 seconds, respectively, and measurement was continuously performed. The boiling point of the organic solvent was measured at a temperature increase rate of 10 ° C./min in the atmosphere by TG-DTA (thermal weight / differential thermal simultaneous analysis: TG8101D manufactured by Rigaku). Further, the thixotropy index (TI) value was calculated by the following formula from the viscosity measurement values of the share rates of 4 / s and 40 / s. Moreover, about the gold paste of Example 1, TG-DTA (thermal weight / differential thermal simultaneous analysis) was performed.
TI = (viscosity at a share rate of 4 / s) / (viscosity at a share rate of 40 / s)

  As a result, the viscosity of the gold paste of Example 1 at a shear rate of 4 / s was 256 Pa · s. From TG-DTA, it was confirmed that in the gold paste of Example 1, the evaporation of the organic solvent started at 70 ° C. and the organic component completely disappeared at 190 ° C.

[Examples 2 to 4, Comparative Examples 1 to 6]
Using the same gold powder as in Example 1, a gold paste was prepared using the organic solvent shown in Table 1. In Comparative Example 6, bisalkenyl succinimide (manufactured by King Industries, trade name: KX1223C) was used as the organic solvent. For each example and comparative example, the results of the viscosity and boiling point of the organic solvent and the viscosity and TI value of the gold paste were measured in the same manner as in Example 1. The results are shown in Table 1.

  From the results of the above physical property measurements, it was shown that the noble metal pastes of Examples 1 to 4 have a TI value of 6.0 or more. On the other hand, in Comparative Examples 1, 2, 4, and 6, the TI value was less than 6.0. Further, in Comparative Examples 3 and 5, even when gold powder and an organic solvent are mixed, the noble metal powder immediately settles and separates from the solvent or becomes difficult to handle, both of which can be pasted. could not.

[Average particle size of gold powder]
In addition to the above Examples and Comparative Examples, a gold paste was prepared in the same manner as in Example 1 using gold powder having an average particle size of 0.7 μm and 0.05 μm. As a result, when the average particle size of the gold powder was 0.7 μm, the dispersion of the gold powder could not be maintained in the paste, causing sedimentation, and when it was 0.05 μm, partial aggregation was confirmed in the paste.

[Silver paste]
Moreover, the silver paste was created similarly to Example 1 using silver powder (86 weight%; 37 volume%) instead of gold powder, and the physical-property measurement was performed. As a result, the obtained silver paste had a viscosity at a share rate of 4 / s of 176 Pa · s, a viscosity at a share rate of 40 / s of 19 Pa · s, and a TI value of 9.3.

Application Test on Substrate Next, the gold pastes of Examples 1 to 4 and Comparative Examples 1, 2, and 4 were applied to the center of a 100 mm ² semiconductor substrate (Si) so as to have an area of 25 mm ² . The coating performance was evaluated. In addition, the board | substrate used what formed Ti (50 nm) and Au (200 nm) on the surface by sputtering beforehand.

  As a result, the gold pastes of Examples 1 to 4 had moderate wettability and were easy to apply to the substrate, and the gold paste after application maintained sufficient moldability. On the other hand, the gold paste of Comparative Example 2 had a tendency for the solvent to ooze out from the applied gold paste, and some of the paste after application was deformed.

Joining Test After applying the paste as described above, the following joining test was conducted without drying and sintering. In the joining test, an Si chip (Ti (20 nm), Au (200 nm) formed in advance) having an area of 4 mm ² was placed on the paste after coating, and joined by heating and pressing. The pressure at the time of joining was 20 N (5 MPa) per chip, the heating was 230 ° C. by heat transfer from the tool, and the heating and pressing time was 10 minutes.

About the junction part joined by the above, the structure | tissue observation was performed by the external appearance X-ray fluoroscopic image (made by a Uniheight system company), and the joining rate was computed based on the following formula. The results of the bonding rate are shown in Table 2. Moreover, the X-ray transmission image of Example 1 and Comparative Example 1 and the cross-sectional SEM observation result of Example 1 are shown in FIG. In the X-ray fluoroscopic image, a void is generated and a void is generated in the bonded portion, and the portion where the bonded portion is in close contact is observed as white (gray).
Joining rate = {Area of the closely attached part (gray part in the X-ray transmission image)} ÷ {Area of the whole joining part (total of gray part and white part in the X-ray transmission image)}

  In Example 1, from the external X-ray fluoroscopic image of FIG. 1, almost no white portion derived from voids due to the generation of voids is observed at the joint, and even in the cross-sectional SEM image, the metal powder is close to a point contact state. Was. Moreover, the joining rate of Table 2 was 90% or more. From the above, in Example 1, it was confirmed that the sintering of the gold powder by heating at the time of joining proceeded uniformly. Therefore, as in Example 1, it was shown that good bonding can be realized even as a manufacturing method in which drying and sintering after application to the substrate are omitted.

  In Examples 2 to 4, the joining rate was 90% or more from Table 2, and as in Example 1, almost no voids were observed, and it was confirmed that the sintering proceeded uniformly. Moreover, also when using a silver paste, generation | occurrence | production of a void was hardly observed from the external appearance X-ray fluoroscope image, and it has confirmed that sintering of silver powder progressed uniformly.

  On the other hand, in Comparative Example 1, the joining rate was less than 90% from Table 2, and many white portions derived from voids due to void generation were observed in the external X-ray fluoroscopic image of FIG. For this reason, in comparative example 1, it is thought that many voids were generated by the out (release) gas derived from the organic component, and the sintering of the gold powder at the time of joining did not proceed uniformly.

  In Comparative Examples 2 and 4, the bonding rate was less than 90% from Table 2, and many white portions derived from voids due to void generation were observed. In Comparative Example 6, many white portions derived from voids generated by voids were observed from the external X-ray fluoroscopic image.

Bonding strength test Next, with respect to the bonding was performed at above was subjected to bonding strength test in accordance with FIG. The bonding strength is that the semiconductor chip (heat-resistant Si chip) 30 bonded to the semiconductor substrate 10 via the sintered body 20 is brought into contact with the chip at a constant speed from the lateral direction and advanced to break (chip). The average value (unit: N) of the stress at the time of occurrence of peeling was measured. From this measured value and the joint area after fracture, the average value (unit: MPa) of the joint strength per unit area was calculated. The results are shown in Table 3.

  From Table 3, in Examples 1-4, it has confirmed that a junction part became joining strength (20 Mpa or more) sufficient for joining etc. of an electronic component. Even in Comparative Example 1, the bonding strength in Table 3 was similar to that in each Example, but as described above, the bonding rate was low (Table 2), and numerous voids were observed (FIG. 1). Therefore, it was not suitable for joining electronic components.

[Examination of bonding temperature]
Next, the bonding strength of the bonded portion was measured in the case where the bonding temperature when the semiconductor chip (heat-resistant Si chip) was bonded to the paste after coating was changed. The members were joined in the same manner as in Example 1 except that the joining temperature was changed to the temperature shown in Table 4, and the joining rate and joining strength test methods were also conducted in the same manner as in Example 1. The results are shown in Table 4.

  As a result, when the bonding temperature was set to 80 to 350 ° C. as in Examples 1, 5, and 6, the bonding portion had sufficient bonding strength for bonding electronic components and the like. On the other hand, as in Comparative Example 7, when the bonding temperature was less than 80 ° C., a bonded portion having sufficient bonding strength could not be realized. Further, according to the current measurement using a heat-resistant Si chip as the bonding member, even when the bonding temperature is higher than 350 ° C. as in Comparative Example 8, the bonding portion having a strength suitable for bonding electronic components However, when joining a joining member having no heat resistance, it is considered that deformation or breakage occurs and it becomes difficult to obtain sufficient joining strength. In the first place, when the temperature is higher than 350 ° C. as in Comparative Example 8, it is considered that the electrical characteristics of the electronic component are affected.

  According to the manufacturing method of the present invention, various joining members can be joined at a low temperature, which is useful for joining semiconductor elements and the like that are concerned about the influence of thermal stress.

Claims (5)

In the manufacturing method of the semiconductor device which joins a board | substrate and a semiconductor element as a joining member, the following process is included, The method characterized by the above-mentioned.
(A) One joining member consists of a noble metal powder having a purity of 99.9% by mass or more and an average particle size of 0.1 to 0.5 μm, and an organic solvent having a boiling point of 200 to 350 ° C.
The organic solvent is a mixture of one kind of saturated aliphatic dihydric alcohol or monocyclic monoterpene alcohol and bicyclic monoterpene alcohol,
A thixotropy index (TI) value calculated from a viscosity measured at 4 / s with respect to a viscosity of 40 / s at a shear rate of 23 / ° C. by a rotational viscometer is 6.0 or more, and a precious metal paste containing no resin is applied. Process.
(B) A step of arranging the one joining member and the other joining member via the noble metal paste and joining them by applying pressure in one direction or both directions while heating at least 80 to 350 ° C. 2. The bonding rate calculated from the ratio of the area of the bonded portion of the bonded portion with respect to the total area of the bonded portion in the X-ray fluoroscopic image is 90% or more in the bonded portion bonded in (b). The manufacturing method of the semiconductor device of description. The method for manufacturing a semiconductor device according to claim 1 or 2, wherein the noble metal powder of the noble metal paste is composed of at least one of gold powder and silver powder. The method for manufacturing a semiconductor device according to claim 1, wherein a volume content of the noble metal in the noble metal paste is 26 to 66% by volume (v / v). The manufacturing method of the semiconductor device in any one of Claims 1-4 in which a noble metal paste contains 0.05-1 mass% surfactant.