JP6619625B2 - Electrode cleaning method and integrated circuit device manufacturing method - Google Patents

Description

  The present invention relates to an electrode cleaning method and an integrated circuit device manufacturing method.

  Patent Document 1 discloses a technique related to a wire bonding apparatus. In the wire bonding apparatus described in this document, in order to remove dirt such as carbon and dust adhering to the electrode of the semiconductor bare chip, the laser light irradiation unit irradiates the electrode surface of the semiconductor bare chip with laser light.

JP-A-4-346236 JP 2010-44030 A Japanese Patent No. 3800802

  Wire bonding is widely used as a method for mounting a semiconductor integrated circuit element in a package. Wire bonding is performed by pressing and crimping one end of a metal wire (wire) against the surface of the metal electrode in a state where the end is held by a jig. At that time, if the surface of the metal electrode is dirty, the bonding strength between the one end portion of the wire and the metal electrode is lowered, which hinders improvement in reliability. Therefore, the surface of the metal electrode is cleaned before wire bonding. Examples of such cleaning methods include organic cleaning using an organic solvent as a cleaning liquid, and plasma cleaning in which an electrode is exposed to plasma. In organic cleaning, ultrasonic waves may be irradiated while the electrode is immersed in an organic solvent.

  However, these methods have the following problems. In organic cleaning (ultrasonic cleaning) and plasma cleaning, the entire package is exposed to a cleaning liquid or plasma. Therefore, when another semiconductor integrated circuit element mounted in the package by a method other than wire bonding already exists, the semiconductor integrated circuit element is also exposed to the cleaning liquid or plasma, and the influence on the semiconductor integrated circuit element is increased. Is concerned.

  With respect to the above problems, for example, cleaning by laser irradiation as described in Patent Document 1 can locally irradiate the surface of the electrode with laser light, so that the influence on other semiconductor integrated circuit elements can be avoided. It becomes. However, if the laser beam cleaning ability is weak, it takes a long time to clean the electrodes, and the working time of the manufacturing process becomes long. Further, if the energy of the laser beam is simply increased, other semiconductor integrated circuit elements may be damaged by heat generated by the laser beam.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a method for cleaning an electrode and a method for manufacturing an integrated circuit device, which can improve the cleaning capability of cleaning by laser irradiation. To do.

In order to solve the above-described problems, a method for cleaning an electrode according to the present invention includes a surface of an electrode surface layer including a base layer containing at least one of Ni and a Ni alloy, and a surface layer containing Au provided on the base layer. In contrast, by irradiating pulsed light emitted from a femtosecond laser or a picosecond laser, the surface of the surface layer is cleaned to remove precipitates containing at least one of Ni and Ni alloy deposited on the surface of the surface layer. It is characterized by performing.

  As an electrode structure, there may be a base layer containing at least one of Ni and Ni alloy (hereinafter referred to as Ni) and a surface layer containing Au provided on the base layer. In that case, for example, the water-soluble flux adhering during mounting of other semiconductor integrated circuit elements is washed with water, and / or due to thermal diffusion during heat treatment such as reflow, Ni or the like of the underlying layer It may be deposited on the surface of the surface layer. Precipitates such as Ni hinder the bonding between the end portion of the bonding wire and the surface layer, and are therefore desirably removed by cleaning.

  The present inventor has found through experiments that irradiation with pulsed light emitted from a femtosecond laser or a picosecond laser is extremely effective as a method for removing Ni or the like deposited on the surface layer containing Au. That is, such an extremely short time pulse light can increase the peak energy while suppressing the energy of the entire pulse light. Therefore, by irradiating the surface layer with pulsed light emitted from these lasers, it is possible to enhance the cleaning ability for precipitates such as Ni while suppressing heat generation due to the pulsed light. Thereby, since precipitates such as Ni can be removed in a short time, the time required for cleaning the electrode can be shortened, and the working time of the manufacturing process can be shortened.

  The cleaning method may be characterized in that the time width of the pulsed light is 100 picoseconds or less. According to the knowledge of the present inventor, Ni and the like deposited on the surface layer containing Au can be more effectively removed by irradiating such an extremely short time pulse light.

  The cleaning method may be characterized in that the wavelength of the pulsed light is a wavelength corresponding to the second harmonic of the YAG laser. According to the inventor's experiment, Ni and the like can be more effectively removed by irradiating pulsed light having such a wavelength.

According to another aspect of the present invention, there is provided a method of manufacturing an integrated circuit device comprising: an electrode in a package provided with an electrode having a base layer including at least one of Ni and Ni alloy; and a surface layer including Au provided on the base layer The first mounting step of surface-mounting the first semiconductor integrated circuit element in another region, and irradiating the electrodes in the package with pulsed light emitted from a femtosecond laser or picosecond laser , A cleaning process for cleaning the surface of the surface layer for removing precipitates including at least one of Ni and Ni alloy deposited on the surface, and the electrode and the second semiconductor integrated circuit element are electrically connected by wire bonding. And a second mounting step. According to this manufacturing method, the cleaning capability with respect to precipitates such as Ni can be enhanced by including the cleaning step using the above-described cleaning method.

  The manufacturing method may further include a step of washing the flux with water and / or a heating step after the first mounting step and before the cleaning step. According to the knowledge of the present inventor, when the flux remaining after the first mounting process is washed with water, a battery effect due to the moisture remaining after that occurs, and Ni or the like of the underlayer easily deposits on the surface layer containing Au. Become. In addition, precipitation of Ni or the like similarly occurs due to thermal diffusion of Ni in a heating process such as heat treatment during reflow. Even in such a case, according to the above manufacturing method, precipitates such as Ni can be effectively removed.

  According to the method for cleaning an electrode and the method for manufacturing an integrated circuit device according to the present invention, it is possible to improve the cleaning capability of cleaning by laser irradiation.

It is sectional drawing which illustrates notionally the cleaning method of the electrode by one Embodiment of this invention. It is a block diagram which shows the structural example of the cleaning apparatus for enforcing the cleaning method of an electrode. It is a flowchart which shows the manufacturing method of the integrated circuit device containing an electrode cleaning method. (A) It is a top view for demonstrating a 1st mounting process. (B) It is a top view for demonstrating a 2nd mounting process. It is a graph which shows the irradiation conditions of the cleaning apparatus used in the Example and the comparative example. It is a graph which shows the Auger analysis result of the electrode surface. It is an image which expands and shows the electrode surface before cleaning, and the electrode surface after cleaning by the Example (picosecond laser, wavelength 515nm). It is an image which expands and shows the electrode surface before cleaning, and the electrode surface after cleaning by an Example (picosecond laser, wavelength 343 nm). It is an image which expands and shows the electrode surface before cleaning, and the electrode surface after cleaning by the comparative example (nanosecond laser, wavelength 532nm). It is a graph which shows the result of the strength test of the bonding wire joined to the electrode surface after implementing the cleaning method by an Example.

  Embodiments of an electrode cleaning method and an integrated circuit device manufacturing method according to the present invention will be described below in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

FIG. 1 is a cross-sectional view conceptually illustrating an electrode cleaning method according to an embodiment of the present invention. This method is a method for cleaning an electrode (wire bonding pad) 30 having a base layer 31 containing at least one of Ni and Ni alloy and a surface layer 32 containing Au provided on the base layer 31. In this method, the surface 32a of the surface layer 32 is cleaned by irradiating pulsed light L emitted from a femtosecond laser or a picosecond laser. The time width of the pulsed light L is, for example, 100 femtoseconds or more, and more preferably, 540 femtoseconds or more. Further, the time width of the pulsed light L is, for example, 100 picoseconds or less, and more preferably 10.9 picoseconds or less. The peak power of the pulsed light L is, for example, 1 MW or more, for example, 40 MW or less. The fluence (irradiation energy per unit area) of the pulsed light L is, for example, 10 mJ / cm ² or more, for example, 300 mJ / cm ² or less. The wavelength of the pulsed light L is, for example, a wavelength corresponding to the second harmonic of a YAG laser (in the example, 515 nm), a wavelength corresponding to the third harmonic (in the example, 343 nm), or a wavelength corresponding to the fourth harmonic (an example). 258 nm).

  FIG. 2 is a block diagram illustrating a configuration example of a cleaning device for performing the electrode cleaning method according to the present embodiment. As shown in FIG. 2, the cleaning device 1 </ b> A includes a main body unit 3, a display unit (display) 5, and an input unit 7. The display unit 5 displays an image of the electrode surface that has been cleaned inside the main body unit 3. The input unit 7 is used when an operator inputs various setting information to the main body unit 3. The input unit 7 is configured by a keyboard or the like, for example.

  The main body 3 includes an ultrashort pulse laser 11, a pulse picker 12, a wavelength conversion unit 13, and an exit shutter 14 as elements constituting a femtosecond laser or a picosecond laser that generates the pulsed light LB. The ultrashort pulse laser 11 periodically outputs ultrashort pulse light LA having a wavelength of, for example, 1030 nm. The pulse width of the ultrashort pulse light LA is, for example, 100 femtoseconds to 100 picoseconds. As the ultrashort pulse laser 11, for example, MOIL-ps manufactured by Hamamatsu Photonics, which is an LD direct excitation type Yb: YAG picosecond pulse laser (pulse width of 0.54 to 10.9 picoseconds at the second harmonic, repetitive) Frequency 1 kHz to 200 kHz). The excitation source of MOIL-ps is a laser diode (wavelength 940 nm).

  The pulse picker 12 extracts one pulsed light LA2 from the ultrashort pulsed light LA periodically output from the ultrashort pulse laser 11. The pulsed light LA2 taken out by the pulse picker 12 is wavelength-converted by the wavelength conversion unit 13 to become pulsed light LB. At this time, the wavelength of the pulsed light LB becomes a harmonic (second harmonic, third harmonic, etc.) of the output wavelength of the ultrashort pulse laser 11. When the output wavelength of the ultrashort pulse laser 11 is 1030 nm, the wavelength conversion unit 13 outputs 515 nm (second harmonic) or 343 nm (third harmonic) pulsed light LB. The pulsed light LB is output to the subsequent optical component via the emission shutter 14. Further, the pulsed light LA 1 removed by the pulse picker 12 is input to the power meter 22. The power meter 22 detects the light intensity of the pulsed light LA1 and sends a signal related to the detection result to the control unit 24.

  The main body 3 includes a beam expander 18 and a galvano scanner 19 as subsequent optical components. The beam expander 18 parallelizes the pulsed light LB with high accuracy and adjusts the beam diameter of the pulsed light LB. The adjusted pulsed light LC is input to the galvano scanner 19. The galvano scanner 19 irradiates the stage 20 with the pulsed light LC as the pulsed light L shown in FIG. An object such as a package having the electrode 30 shown in FIG. The galvano scanner 19 scans the surface of the electrode 30 with the pulsed light LC. The stage 20 is provided on the moving / rotating stage 21, and the angle and position of the stage 20 are variable by the moving / rotating stage 21. Thereby, the pulsed light LC can be irradiated over a wider range together with the galvano scanner 19. The object on the stage 20 is photographed by the camera 23. The video data is sent from the camera 23 to the control unit 24.

  The control unit 24 gives an instruction to the laser control unit 25 based on the setting information input from the input unit 7, the detection result from the power meter 22, and the like. The laser control unit 25 controls the peak power, pulse time width, repetition period, and the like of the ultrashort pulsed light LA output from the ultrashort pulse laser 11. Further, the control unit 24 controls operations of the pulse picker 12, the emission shutter 14, and the galvano scanner 19.

  The main body 3 is further provided with an exhaust system A1 and an intake system A2. The exhaust system A1 performs vacuum suction of the space in which the stage 20 is provided. The intake system A2 introduces assist gas into the space.

  FIG. 3 is a flowchart showing a manufacturing method of the integrated circuit device including the electrode cleaning method according to the present embodiment. This manufacturing method includes a first mounting step S11, a cleaning step S12, a cleaning step S13, and a second mounting step S14. FIGS. 4A and 4B are plan views for explaining the first mounting step S11 and the second mounting step S14.

  In the first mounting step S11, as shown in FIG. 4A, the surface mounting of the first semiconductor integrated circuit element 37 is performed in a region 36 different from the electrode 30 in the package 35 provided with the electrode 30. Do. The package 35 is a ceramic package, for example. The first semiconductor integrated circuit element 37 is, for example, an ASIC (application specific integrated circuit). The first semiconductor integrated circuit element 37 is mounted by, for example, flip chip bonding (FCB). Further, this step S11 includes a heating step (specifically, heat treatment during reflow).

  Next, in the washing step S12, the water-soluble flux contained in the solder material used in the previous surface mounting is washed with water. Subsequently, in the cleaning step S13, the surface 30a (see FIG. 1) of the surface layer 32 of the electrode 30 is cleaned by irradiating the electrode 30 in the package 35 with the pulsed light LC (see FIG. 2). I do. Subsequently, in the second mounting step S <b> 14, as shown in FIG. 4B, the electrode 30 and the second semiconductor integrated circuit element 38 are electrically connected using a bonding wire 39. Thereafter, other electrical elements are mounted, the package 35 is sealed, and the integrated circuit device is completed.

  The effects obtained by the electrode cleaning method and integrated circuit device manufacturing method according to the present embodiment described above will be described. When the base layer 31 including at least one of Ni and Ni alloy (hereinafter referred to as Ni) and the surface layer 32 including Au provided on the base layer 31 are present as the structure of the electrode 30, for example, other semiconductor integration The surface layer 32a of the surface layer 32 is caused by Ni or the like in the underlayer 31 due to thermal diffusion during the heat treatment such as step S12 in which the water-soluble flux attached when the circuit element 37 is mounted is washed with water and / or reflow. May precipitate. Specifically, the battery effect is generated by the moisture remaining after the cleaning step S12, and Ni or the like of the underlayer is easily deposited on the surface layer 32 containing Au. In addition, precipitation of Ni or the like similarly occurs due to thermal diffusion of Ni in a heating process such as a heat treatment during reflow in the first mounting process S11. Precipitates such as Ni hinder the bonding between the end portion of the bonding wire 39 and the surface layer 32, and therefore it is desirable to remove them by cleaning.

  As shown in Examples described later, the inventor irradiates pulsed light L emitted from a femtosecond laser or a picosecond laser as a method for removing Ni or the like deposited on the surface layer 32 containing Au. Was found to be extremely effective. That is, such an extremely short-time pulsed light L has a high peak power because the pulse width is short. In other words, the peak energy can be increased while suppressing the energy of the entire pulsed light L. The electrode can be cleaned with energy that greatly exceeds the processing threshold due to the high peak power. Therefore, by irradiating the surface layer 32 with the pulsed light L emitted from these lasers, the heat generation due to the pulsed light L is suppressed and damage to other semiconductor integrated circuit elements 37 is suppressed, while precipitation of Ni or the like is performed. It is possible to improve the cleaning ability for objects. Thereby, since precipitates such as Ni can be removed in a short time, the time required for cleaning the electrode 30 can be shortened and the working time of the manufacturing process can be shortened.

  Further, as in the present embodiment, the time width of the pulsed light L may be 100 picoseconds or less. According to the knowledge of the present inventor, Ni or the like deposited on the surface layer 32 containing Au can be more effectively removed by irradiating the pulsed light L for such an extremely short time.

  Further, as shown in the examples described later, the wavelength of the pulsed light L is preferably a wavelength corresponding to the second harmonic of the YAG laser (for example, 515 nm). By irradiating the pulsed light L having such a wavelength, Ni or the like can be more effectively removed.

(Example)
Here, an example and a comparative example of the electrode cleaning method according to the embodiment will be described. FIG. 5 is a chart showing the irradiation conditions (wavelength, repetition frequency, irradiation power or energy, scanning speed, scanning line interval, and beam diameter) of the cleaning device used in this example and the comparative example. As shown in the figure, in this example, the electrodes were cleaned under three irradiation conditions (No. 1, No. 2, and No. 3). In addition, irradiation condition No. which concerns on the said Example. 1 has a pulse time width of 0.8 picoseconds and irradiation condition no. The pulse time width of 2 was 0.8 picoseconds. In addition, the irradiation condition no. The pulse time width of 3 was 1 nanosecond.

  FIG. 6 is a chart showing the results of Auger analysis of the electrode surface. The detection depth was 1 nm. The electrode underlayer was an electroless Ni plating layer (thickness 1.27 to 8.89 μm), and the surface layer was an electroless Au plating layer (thickness 0.50 μm). Further, the lowermost stage (REF) in FIG. 6 shows the Auger analysis result before the first mounting step S11. As shown in FIG. 6, in two unirradiated samples that have not been cleaned, Au is not detected at all on the electrode surface, and a lot of Ni, O, and Cl are detected. This is considered to be caused by precipitated Ni-based oxides or flux residues. In contrast, No. 1 irradiated with pulsed light from a picosecond laser was used. 1 and no. In each of the two samples of 2, the detection amount of these elements is greatly reduced, and the detection amount of Au is increased. In particular, Ni is not detected at all. No. In the sample 1, the surface state equivalent to that before the first mounting step S11 (REF) is obtained by the cleaning of the above embodiment. From this, it can be seen that the cleaning method of the above embodiment is extremely effective for cleaning the electrode surface (in particular, removal of Ni and the like). It should be noted that No. 1 in the comparative example irradiated with the pulsed light from the nanosecond laser. In the two samples of No. 3, although a certain degree of cleaning effect was obtained, the amount of decrease in Ni, O, and Cl was No. 3. 1 and no. Compared to 2, the amount of Ni is detected with a small amount. Therefore, no. 1 and no. According to the irradiation condition No. 2, Compared with 3, an extremely high cleaning effect can be obtained.

  FIG. 7 is an enlarged image showing the electrode surface E1 before cleaning and the electrode surface E2 after performing the cleaning method according to this example (No. 1). FIG. 8 is an enlarged image of the electrode surface E3 before cleaning and the electrode surface E4 after performing the cleaning method according to this example (No. 2). 7 and 8, it can be seen that the electrode surfaces E2 and E4 are sufficiently cleaned compared to the electrode surfaces E1 and E3. In contrast, FIG. 9 is an enlarged image of the electrode surface E5 before cleaning and the electrode surface E6 after performing the cleaning method according to the comparative example (No. 3). Referring to FIG. 9, it can be seen that the electrode surface E6 is insufficiently cleaned as compared with the electrode surface E5.

  FIG. 10 is a graph showing the results of the strength test (pull test and shear test) of the bonding wire bonded to the electrode surface after performing the cleaning method according to this example. FIG. 10 shows the pull intensity and the shear intensity when the peak power of the pulsed light is changed from 99.0 mW to 694.2 mW and when it is not irradiated. In each pull strength and each shear strength, the left graph is an average value, and the right graph is a minimum value. Moreover, the broken line F1 in a figure is a pass value of pull strength, and the broken line F2 is a pass value of shear strength. Referring to FIG. 10, it can be seen that the pull strength and the shear strength are improved as the peak power of the pulse light is increased.

  DESCRIPTION OF SYMBOLS 1A ... Cleaning apparatus, 3 ... Main-body part, 5 ... Display part, 7 ... Input part, 11 ... Ultra-short pulse laser, 12 ... Pulse picker, 13 ... Wavelength conversion unit, 14 ... Output shutter, 18 ... Beam expander, 19 DESCRIPTION OF SYMBOLS ... Galvano scanner, 20 ... Mounting stage, 21 ... Moving / rotating stage, 22 ... Power meter, 23 ... Camera, 24 ... Control part, 25 ... Laser control part, 30 ... Electrode, 31 ... Underlayer, 32 ... Surface layer, 32a ... surface, 35 ... package, 37 ... first semiconductor integrated circuit element, 38 ... second semiconductor integrated circuit element, 39 ... bonding wire, A1 ... exhaust system, A2 ... intake system, L, LA, LA1, LA2 , LB, LC: Pulse light.

Claims (5)

Pulse light emitted from a femtosecond laser or picosecond laser to the surface of the surface layer of an electrode having a base layer containing at least one of Ni and Ni alloy and a surface layer containing Au provided on the base layer Cleaning the surface of the surface layer to remove precipitates containing at least one of Ni and Ni alloy deposited on the surface of the surface layer by irradiating the surface of the electrode.   2. The electrode cleaning method according to claim 1, wherein a time width of the pulsed light is 100 picoseconds or less.   2. The electrode cleaning method according to claim 1, wherein the pulsed light has a wavelength corresponding to a second harmonic of a YAG laser. A first semiconductor integrated circuit in a region different from the electrode in the package provided with an electrode having a base layer containing at least one of Ni and Ni alloy and a surface layer containing Au provided on the base layer A first mounting step for surface mounting the element;
In order to remove precipitates containing at least one of Ni and Ni alloy deposited on the surface of the surface layer by irradiating the electrodes in the package with pulsed light emitted from a femtosecond laser or picosecond laser. A cleaning step of cleaning the surface of the surface layer,
A second mounting step of electrically connecting the electrode and the second semiconductor integrated circuit element by wire bonding;
A method for manufacturing an integrated circuit device, comprising:   5. The method of manufacturing an integrated circuit device according to claim 4, further comprising a step of cleaning the flux with water and / or a heating step after the first mounting step and before the cleaning step.