Through-hole non-destructive inspection method and device

Abstract

The present invention aims to provide a non-destructive inspection method and device for inspecting the presence or absence of defects in through holes. [Solution] A heating laser 1 emits a periodic heating laser to a measurement section 12 directly above a through-hole 11 so that the intensity varies sinusoidally, a laser intensity detection means detects the intensity of the periodic heating laser in the measurement section 12, an infrared sensor 6 detects the intensity of the radiated infrared light that varies sinusoidally and is emitted from the measurement section 12, and a phase difference detection means takes in the detection signals from the laser intensity detection means and the infrared sensor 6 and detects the phase difference between the two, and the detected phase difference is regarded as the value of the thermal time constant (product of heat capacity and thermal resistance) in the through-hole 11, and if a decrease in heat capacity and an increase in temperature are observed it is determined that there is a void, and if an increase in thermal resistance is observed it is determined that there is a crack.

Description

[Technical Field]

[0001] The present invention relates to a method and apparatus for non-destructive through-hole inspection, and more particularly to a method and apparatus for non-destructively inspecting the electrical conductivity of through-holes densely filled with conductive material such as copper or gold provided in a substrate such as an interposer in chiplet mounting. [Background technology]

[0002] In recent years, semiconductor chips have been made more powerful, multifunctional, power-efficient, and cost-effective by miniaturizing the wiring width of their circuits. However, as semiconductor microfabrication technology becomes more advanced, the limits of this miniaturization are becoming apparent. Chips made using microfabrication technology have a certain probability of defects during the manufacturing process. These defects are primarily caused by variations in manufacturing conditions and the inclusion of impurities and debris, and the larger the chip area, the higher the frequency of defective chips, resulting in a lower yield. In other words, if a defect occurs in part of a chip, that chip is deemed defective, resulting in a lower yield.

[0003] Therefore, rather than forming large-scale circuits with large chip areas all at once, the trend is to use chips in which circuits are divided by function and their area is reduced, which contributes to improvements in yield, cost, and versatility. Chiplets are a technology in which large-scale circuits that were previously integrated on a single chip are separated into multiple small chips by function, and then mounted on a substrate called an interposer that connects the chips to increase the scale and fit them into a single package. When using this chip, only the separated good chips are selected to form large-scale circuits, which improves the yield of the entire semiconductor device.

[0004] In semiconductor packaging, an interposer is an intermediate layer substrate used to connect and position different chips or components, and is used to integrate multiple semiconductor chips into a single package. Interposers have multiple layers of through-holes densely filled with conductive materials such as copper or gold, and patterns that serve as connection paths between the through-holes. These through-holes and patterns establish electrical connections between chips and the package substrate, enabling high-speed, low-noise, stable signal transmission. They also effectively dissipate heat generated during semiconductor device operation, helping to manage temperature, thereby improving device performance and extending its lifespan.

[0005] As mentioned above, the through holes of the interposer are densely filled with conductive material such as copper or gold, but it goes without saying that there must be no defects such as voids or cracks inside the through holes in order to maintain good electrical conductivity between the upper and lower chips. Therefore, it is necessary to inspect the presence or absence of such defects in advance, but until now, no reliable inspection method or inspection device has been proposed for this purpose.

[0006] Meanwhile, various non-contact, non-destructive inspection methods have been proposed and put to practical use for quickly inspecting the quality of wire bonding in semiconductor wire bonding. For example, Japanese Patent Publication No. 6620499 discloses a non-contact, non-destructive instantaneous inspection method for metal bonding, in which cyclic heating with a laser is performed and temperature changes are measured by measuring the amount of radiated infrared light, based on the finding that when one of the bonded micro-metals is heated periodically with strong and weak waves (sine wave), the heated part undergoes a temperature change (temperature response) synchronized with the heating cycle, and the phase difference between the heating cycle and the temperature change cycle correlates with the area of ​​the bonded part.

[0007] The method according to this invention calculates the bonded area based on the phase difference on the premise that the phase difference between the heating laser, which varies in a sinusoidal wave, and the radiated infrared light, which also varies in a sinusoidal wave, correlates with the area of ​​the bonded portion, i.e., that the bonded area is similar when the phase difference is close. Until now, the idea that this phase difference correlates with the area of ​​the bonded portion has been accepted, and inspections have been carried out based on this idea.

[0008] However, the present applicant subsequently proposed a method and apparatus for evaluating the quality of a semiconductor wire bond bonded portion using a laser cyclic heating method (Patent Publication No. 7565642) based on the idea that the phase difference is strongly correlated with the thermal resistance of the bonded portion, instead of the conventional non-destructive inspection method for metal bonds based on the idea that the phase difference is correlated with the bonded area. However, this method is only intended to evaluate the quality of the bonded portion of a semiconductor wire bond, and cannot be used to inspect for defects such as voids and cracks in through holes. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Patent No. 6620499 [Patent Document 2] Patent No. 7565642 Summary of the Invention [Problem to be solved by the invention]

[0010] As described above, no reliable inspection method and inspection device have been proposed to date for inspecting the presence or absence of defects such as voids and cracks in through holes of interposers, etc., and the appearance of such a method and inspection device has been eagerly awaited. The present invention has been made to meet such a demand, and an object of the present invention is to provide a non-destructive through-hole inspection method and device that can inspect the presence or absence of defects such as voids and cracks in through holes of interposers, etc., with sufficient reliability and high accuracy. [Means for solving the problem]

[0011] The invention according to claim 1 to solve the above problem is: basis In through holes in a board that are densely packed with conductive material Lack of A method for non-destructively inspecting for the presence or absence of defects, comprising: a heating step of heating the measurement portion directly above the through-hole from above by irradiating the measurement portion with a periodic heating laser beam that changes in a sinusoidal waveform; an intensity measuring step of detecting the intensity of the periodic heating laser, which varies sinusoidally, and the intensity of the radiant infrared light, which varies sinusoidally and is radiated from the heated measurement portion; a phase difference detection step of detecting a phase difference between the periodic heating laser and the radiated infrared light; The phase difference is It is calculated from the product of heat capacity and thermal resistance a defect determination step for determining whether or not there is a defect in the through-hole by regarding the defect as a thermal time constant; The non-destructive through-hole inspection method comprises:

[0012] In one embodiment, the determination of the presence or absence of a defect in the through hole in the defect determination step includes: Subject to inspection The product of the thermal capacity and thermal resistance of the through-hole is Subject to inspection Measure the thermal time constant of the through-hole The measured thermal time constant of the through-hole to be inspected is compared with upper and lower thresholds of the thermal time constant of a through-hole having a good thermal structure, which have been measured and set in advance. This is done by:

[0014] In one embodiment, the step of determining the presence or absence of a defect in the through-hole further comprises: Warm the level of the temperature response signal is also compared with upper and lower thresholds of the temperature response signal level of the through-hole of a good thermal structure that have been previously measured and set;

[0015] In one embodiment, the heating of the measuring part in the heating step is performed using a sine wave modulated blue laser that has good absorption rate for copper and gold.

[0016] Claims to solve the above problem 5 The invention relates to: basisIn through holes in a board Lack of A device for non-destructively inspecting for the presence or absence of defects, a laser irradiation means for emitting the periodic heating laser to a measurement portion directly above the through-hole so that the periodic heating laser intensity varies sinusoidally; a laser intensity detection means for detecting the intensity of the periodic heating laser in the measurement unit; an infrared intensity detection means for detecting the intensity of the radiated infrared light radiated from the measuring unit and varying in a sinusoidal manner; a phase difference detection means for receiving a detection signal from the laser intensity detection means and a detection signal from the infrared intensity detection means, and detecting a phase difference between the sinusoidally changing periodic heating laser and the sinusoidally changing radiated infrared light; The phase difference detected by the phase difference detection means is It is calculated from the product of heat capacity and thermal resistance a defect determination means for determining the presence or absence of a defect in the through-hole by regarding the defect as a thermal time constant; The non-destructive through-hole inspection device is characterized by comprising:

[0017] In one embodiment, the defect determination means determines whether or not the through-hole has a defect by: Subject to inspection The product of the thermal capacity and thermal resistance of the through-hole is Subject to inspection Measure the thermal time constant of the through-hole The measured thermal time constant of the through-hole to be inspected is compared with upper and lower thresholds of the thermal time constant of a through-hole having a good thermal structure that has been measured in advance. This is done by:

[0018] In one embodiment, the defect determination means determines whether or not the through-hole has a defect. Furthermore, the measured temperature response signal level is compared with upper and lower thresholds of the temperature response signal level of the through-hole of a good thermal structure, which have been measured and set in advance. . [Effects of the Invention]

[0019] The non-destructive testing method and device for detecting defects in through holes according to the present invention are as described above, and have a relatively simple configuration, and are effective in quickly, reliably, and highly accurately testing for defects such as voids and cracks in through holes in interposers, etc. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a conceptual diagram of an optical measurement system of a through-hole nondestructive inspection device according to the present invention. [Figure 2] 1 is a cross-sectional image diagram showing a defect in a through-hole that is the subject of inspection by a non-destructive through-hole inspection method and apparatus according to the present invention; [Figure 3] 4 is a graph showing the phase difference between a reference signal (laser modulated signal) and a temperature response signal (sensor output signal) in the nondestructive through-hole inspection method according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0021] The nondestructive through-hole inspection method and apparatus according to the present invention will be described below with reference to the accompanying drawings. The nondestructive through-hole inspection method and apparatus according to the present invention are used to nondestructively inspect through-holes, i.e., through-holes 11 in chiplet interposers 10 and the like, which are densely filled with conductive material such as copper or gold, for defects such as voids and cracks. Although the term "through-hole" generally refers to through-holes in printed electronic circuit boards, the through-holes inspected by the method and apparatus according to the present invention are those densely filled with conductive material.

[0022] The method according to the present invention includes a heating step of heating the measurement portion 12 directly above the through-hole from above by irradiating the measurement portion 12 with a periodic heating laser beam that changes in a sinusoidal waveform; an intensity detection step of detecting the intensity of the periodic heating laser, which varies in a sinusoidal manner, and the intensity of the radiated infrared light, which varies in a sinusoidal manner and is radiated from the heated measurement unit 12; a phase difference detection step of detecting a phase difference between the periodic heating laser and the radiated infrared light; and a defect determination step for determining whether or not there is a defect in the through-hole by regarding the phase difference as a thermal time constant of the through-hole.

[0023] The present invention also provides an apparatus for carrying out the above method, comprising: a laser irradiation means for emitting a periodic heating laser to a measurement portion 12 directly above the through-hole 11 so that the periodic heating laser intensity at the heated measurement portion 12 varies sinusoidally; a laser intensity detection means for detecting the intensity of the periodic heating laser in the measurement unit 12; an infrared intensity detection means for detecting the intensity of the infrared radiation radiated from the measurement unit 12 and varying in a sinusoidal waveform; a phase difference detection means for receiving a detection signal from the laser intensity detection means and a detection signal from the infrared intensity detection means, and detecting a phase difference between the heating laser that varies sinusoidally and the radiated infrared light that varies sinusoidally; The phase difference detected by the phase difference detection means is regarded as a thermal time constant in the through hole 11, i.e., the product of the heat capacity and the thermal resistance, and thereby the defect determination means determines whether or not there is a defect in the through hole 11.

[0024] The nondestructive through-hole inspection device according to the present invention will be described in more detail below with reference to the conceptual diagram of the optical measurement system shown in FIG. 1. This device is equipped with a laser irradiation means comprising a heating laser 1, which is a semiconductor laser light source, a collimating lens 2, and a modulation signal output means (not shown). The modulation signal output means is, for example, an oscillator, and generates a laser modulation signal, which serves as a reference signal, whose voltage varies sinusoidally at a predetermined frequency and a predetermined amplitude, based on a control signal from a defect presence / absence determination means (not shown). The heating laser 1 emits a heating laser whose intensity varies sinusoidally based on the modulation signal from the modulation signal output means.

[0025] The heating laser emitted from heating laser 1 is converted into parallel light by collimating lens 2, hits optical filter 3, which is a heating laser selective reflection means, and is polarized toward measurement unit 12. Objective lens 4, which is a focusing means, is located between optical filter 3 and measurement unit 12. Objective lens 4 focuses the parallel light incident from above through optical filter 3 along its optical axis and emits it toward measurement unit 12. Therefore, the intensity of the heating laser focused on measurement unit 12 varies sinusoidally, and its frequency is synchronized with the frequency of the modulation signal. It goes without saying that the output of heating laser 1 is adjusted to an output that can heat through-hole 11 without damaging it.

[0026] The objective lens 4 also converts the measurement light emitted from and reflected by the measurement unit 12 and incident from below into parallel light along its optical axis, and emits it toward the optical filter 3. The measurement light converted into parallel light by the objective lens 4 contains infrared light of a predetermined wavelength emitted from the measurement unit 12 (infrared light whose intensity varies sinusoidally). This infrared light of a predetermined wavelength is collected by an infrared lens 5 arranged above the optical filter 3 and input to an infrared sensor 6, which is an infrared intensity detection means. The detection signal from the infrared sensor 6, whose intensity varies sinusoidally, is then amplified by a sensor amplifier or the like and input as a temperature response signal (sensor output signal) to a phase difference detection device (not shown), such as a lock-in amplifier.

[0027] The optical filter 3 selectively reflects the heating laser emitted from the heating laser 1 toward the measurement unit 12, but a portion (a few percent) of the heating laser passes through the optical filter 3 and reaches a laser intensity detection means (e.g., a photosensor) beyond. The heating laser, whose intensity varies sinusoidally, detected there is appropriately amplified and input to a phase difference detection device, and this detection signal is the intensity of the irradiated light, which is the heating laser irradiated to the measurement unit 12, and is a reference signal (laser modulation signal) corresponding to the intensity of the irradiated light that varies sinusoidally.

[0028] In this way, the phase difference detection device receives as input a temperature response signal (sensor output signal) from the infrared sensor 6, whose intensity varies in a sinusoidal manner, and a reference signal (laser modulation signal) from the laser intensity detection means, whose intensity varies in a sinusoidal manner. The phase difference between the temperature response signal and the reference signal is measured, and the measured phase difference is output to a determination device, which is a means for determining whether or not there is a defect.

[0029] The non-destructive through-hole inspection method using the above-described device will be described in more detail below, step by step.

[0030] Heating step First, a measurement section 12 directly above a through-hole 11 to be inspected is irradiated with a periodic heating laser from a heating laser 1 to heat the measurement section 12. The periodic heating laser is emitted from the heating laser 1 so that its intensity varies sinusoidally. For example, if the through-hole 11 is filled with copper or gold, the laser to be irradiated here is a blue laser that has good absorption by copper or gold and is sinusoidally modulated.

[0031] Reference signal and temperature response signal detection step Next, a laser intensity detection means, such as a photosensor, detects a reference signal (laser modulation signal) of the periodic heating laser emitted from the heating laser 1, in which the periodic heating laser intensity changes in a sinusoidal manner, and an infrared sensor 6 detects a temperature response signal (sensor output signal) of the radiated infrared light emitted from the heated measurement section 12, which changes in a sinusoidal manner, and each of these is input to a phase difference detection device.

[0032] Phase difference detection step The phase difference detection device detects the phase difference between the temperature response signal (sensor output signal) whose intensity changes sinusoidally from the infrared sensor 6 input and the reference signal (laser modulation signal) whose intensity changes sinusoidally from the laser intensity detection means.

[0033] Defect detection step The defect determination means determines, from the phase difference, whether or not there is a defect in the inspected through-hole 11. The presence or absence of a defect is determined by regarding the phase difference as the thermal time constant of the through-hole 11, i.e., the product of the heat capacity and the thermal resistance, and comparing the measured value of the thermal time constant with upper and lower threshold values ​​of the thermal time constant of a through-hole with a good thermal structure that have been measured and set in advance.

[0034] The thermal time constant is calculated using the following formula 1. τ=C×Rt...Equation 1 (τ[s]: Thermal time constant C[J / K]: Heat capacity Rt[K / W]: Thermal resistance)

[0035] The heat capacity is calculated using the following formula 2. C=αQ / T=m·c···Equation 2 (C[J / K]: Heat capacity, α: Absorption rate, Q[J]: Calorific value, T[K]: Temperature, m[Kg]: Mass, c[J / Kg K]: Specific heat Mass m decreases in the presence of voids.

[0036] The thermal resistance is calculated using the following formula 3. Rt=1 / λ×d / A...Equation 3 (Rt [K / W]: thermal resistance, λ [W / m K]: thermal conductivity, d [m]: thickness, A [m 2 ]:area) *Source of Formula 3: University of Tokyo Press University of Tokyo Mechanical Engineering 6 Heat Transfer Engineering by Masahiro Shoji If cracks are present, A decreases.

[0037] If there is a void (cavity) inside the through hole 11, the volume of the through hole 11 will decrease, so the heat capacity (product of mass and specific heat) of the through hole 11 will be smaller, and the thermal time constant will be measured to be smaller than that of a through hole with a good thermal structure, and the temperature of the measurement part 12 will also be higher, indicating the presence of a void.

[0038] Furthermore, if there is a crack or the like inside the through hole, the cross-sectional area A of that location will decrease, so the thermal resistance (inversely proportional to the effective area) of the through hole 11 will increase, and the thermal time constant will be measured to be larger than that of a through hole 11 with a good thermal structure. Thus, by setting upper and lower thresholds for the thermal time constant and temperature response signal level, which are the measured values ​​for a through hole with a good thermal structure, it is possible to determine whether or not there is a crack by comparing them.

[0039] The method of the present invention was developed primarily for inspecting for defects such as voids and cracks in through holes that are densely filled with conductive material in substrates such as interposers, but it can also be used to determine the presence or absence of defects in components that have a structure similar to that of the through holes. [Industrial Applicability]

[0040] The non-destructive testing method and device for detecting defects in through holes according to the present invention are as described above, and have a relatively simple configuration, and are effective in quickly, reliably, and highly accurately testing for defects such as voids and cracks in through holes in interposers, etc., and have extremely high industrial applicability. [Explanation of symbols]

[0041] 1. Heating laser 2 Collimating lenses 3 Optical Filters 4 Objective Lenses 5. Infrared lens 6 Infrared Sensor 10 Interposer 11 through holes 12 Measuring part

Claims

1. A method for non-destructively inspecting a through-hole in a substrate that is densely filled with a conductive material for the presence or absence of defects, comprising: a heating step of heating the measurement portion directly above the through-hole from above by irradiating the measurement portion with a periodic heating laser beam that changes in a sinusoidal waveform; an intensity measuring step of detecting the intensity of the periodic heating laser, which varies sinusoidally, and the intensity of the radiated infrared light, which varies sinusoidally and is radiated from the heated measurement portion; a phase difference detection step of detecting a phase difference between the periodic heating laser and the radiated infrared light; a defect determination step of determining whether or not a defect exists in the through-hole by regarding the phase difference as a thermal time constant obtained from the product of the thermal capacity and thermal resistance of the through-hole; A through-hole non-destructive inspection method comprising:

2. 2. The non-destructive through-hole inspection method of claim 1, wherein the determination of the presence or absence of a defect in the through-hole in the defect determination step is performed by measuring the thermal time constant of the through-hole to be inspected from the product of the heat capacity and thermal resistance of the through-hole to be inspected, and comparing the measured thermal time constant of the through-hole to upper and lower threshold values ​​of the thermal time constant of a through-hole with a good thermal structure that have been measured and set in advance.

3. 3. A non-destructive through-hole inspection method as described in claim 2, wherein in the defect determination step, the level of the measured temperature response signal is further compared with upper and lower thresholds of the temperature response signal level of a through-hole of a good thermal structure that have been measured and set in advance.

4. 2. The non-destructive through-hole inspection method according to claim 1, wherein the heating of the measuring portion in the heating step is performed using a sinusoidally modulated blue laser having a good absorption rate for copper or gold.

5. An apparatus for non-destructively inspecting a through-hole in a substrate for defects, comprising: a laser irradiation means for emitting the periodic heating laser to a measurement portion directly above the through-hole so that the periodic heating laser intensity varies in a sinusoidal waveform; a laser intensity detection means for detecting the intensity of the periodic heating laser in the measurement unit; an infrared intensity detection means for detecting the intensity of the radiated infrared light radiated from the measuring unit and varying in a sinusoidal manner; a phase difference detection means for receiving a detection signal from the laser intensity detection means and a detection signal from the infrared intensity detection means, and detecting a phase difference between the sinusoidally changing periodic heating laser and the sinusoidally changing radiated infrared light; a defect determination means for determining the presence or absence of a defect in the through-hole by regarding the phase difference detected by the phase difference detection means as a thermal time constant calculated from the product of the thermal capacity and thermal resistance of the through-hole; A through-hole non-destructive inspection device comprising:

6. 6. A non-destructive through-hole inspection device as described in claim 5, wherein the defect determination means determines whether or not a defect is present in the through-hole by measuring the thermal time constant of the through-hole to be inspected from the product of the heat capacity and thermal resistance of the through-hole to be inspected, and comparing the measured thermal time constant of the through-hole to upper and lower threshold values ​​of the thermal time constant of a through-hole with a good thermal structure that has been measured in advance.

7. A non-destructive through-hole inspection method as described in Claim 6, wherein the defect determination means further compares the level of the measured temperature response signal with upper and lower threshold values ​​of the temperature response signal level of a through-hole with a good thermal structure that have been measured and set in advance when determining whether or not there is a defect in the through-hole.

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