Method for thinning aluminum layer metal of directional control chip

Abstract

The invention relates to the field of integrated circuit failure analysis, and particularly discloses a directional control chip aluminum layer metal thinning method which comprises the following steps: S1, locally exposing an aluminum layer: removing a passivation layer, a dielectric layer and the exposed aluminum layer in a to-be-processed area of a chip through etching to form an electrolysis window; step S2, establishing an electrolysis system: immersing the chip into an electrolyte, using a probe as a working electrode to electrically contact with the chip, and configuring a power supply and a reference electrode to form a micro-area electrolytic corrosion system; s3, directional and fixed-point electrolytic thinning: under the action of an electric field, the aluminum layer in electrical contact with the probe is subjected to a dissolution reaction, the aluminum layer is thinned to an expected thickness range, and the aluminum layer which is not in electrical contact with the probe is subjected to a passivation reaction; and S4, post-treatment and detection: after electrolysis is completed, residual electrolyte on the surface of the chip is removed for subsequent detection, and the aluminum layer metal of the chip can be thinned in a directional and fixed-point mode on the premise that the overall performance of a device is not affected.

Description

Technical Field

[0001] This application relates to the field of integrated circuit failure analysis, and specifically discloses a method for thinning the aluminum layer of a directional control chip. Background Technology

[0002] In chip manufacturing, to achieve good electrical connections, heat dissipation, and reliability, a thick metal layer is often formed on the chip surface, especially in high-current areas or critical connection points. This type of thick metal layer is particularly common in semiconductor power devices such as MOSFETs, and the aluminum layer on top is widely used due to its excellent conductivity and stability.

[0003] However, while thick metal layers like aluminum offer performance advantages to chips, they also present significant challenges to chip failure analysis. Failure analysis often requires the use of techniques such as optical emission microscopy (EMMI) to inspect the chip under power. EMMI locates faults by detecting the weak photon radiation generated by defects within the chip. However, the thick aluminum layer on the chip surface strongly absorbs, reflects, and blocks these photons, causing severe attenuation or even complete shielding of the EMMI signal. This prevents analysts from accurately detecting the defect emission points beneath the metal layer, significantly reducing the accuracy and efficiency of fault location analysis.

[0004] To overcome the obstruction of defective light-emitting points by thick metal layers, existing technologies typically employ a method of overall thinning of the chip's aluminum layer, mainly including: Chemical mechanical polishing (CMP) thinning: This method performs global grinding and polishing of the metal layer on the chip surface. Its disadvantages are that the process is difficult to control precisely, which can easily cause uneven metal layer thickness, chip damage, and may even damage the fragile device structure under the metal layer (such as gate oxide layer, shallow junction, etc.), change the electrical parameters of the device, and lead to distorted failure analysis results.

[0005] Dry etching (such as reactive ion etching, RIE) thinning: This method uses plasma to etch the metal as a whole. Although it has good directionality, it is still a large-area process and lacks local selectivity. It is difficult to control the etching rate, uniformity and endpoint, and there is also a risk of over-etching and damaging the underlying structure, and post-processing damage may also occur.

[0006] It is evident that current technologies cannot achieve targeted, quantitative, and controllable thinning of specific metal regions. Therefore, this invention provides a method for directional control of aluminum layer metal thinning in chips to solve the aforementioned problems. Summary of the Invention

[0007] The purpose of this invention is to provide a process for directional and targeted thinning of aluminum layers, thereby improving detection sensitivity without affecting the overall performance of the device.

[0008] To achieve the above objectives, the basic solution of the present invention provides a method for thinning the aluminum layer of a directional control chip, comprising the following steps: Step S1, Local exposure of aluminum layer: The passivation layer and dielectric layer of the chip to be processed are removed by etching, and the aluminum layer is exposed to form an electrolytic window; Step S2, establish the electrolysis system: immerse the chip in the electrolyte, use a probe as the working electrode to make electrical contact with the electrolysis window, immerse the counter electrode in the electrolyte, and configure a power supply to form a micro-area electrolytic etching system; Step S3, directional and fixed-point electrolytic thinning: through the action of an electric field, the aluminum layer that is electrically in contact with the probe undergoes a dissolution reaction, and the aluminum layer is thinned to the desired thickness range, while the aluminum layer that is not electrically in contact with the probe undergoes a passivation reaction. Step S4, Post-processing and Inspection: After electrolysis, the residual electrolyte on the chip surface is removed before subsequent inspection.

[0009] Furthermore, in step S1, the chip is processed using FIB to expose its aluminum layer.

[0010] Furthermore, in step S2, the probe contacts the chip's pins or the surface of the electrolytic window.

[0011] Furthermore, in step S2, the distance between the probe and the counter electrode is shortened to accelerate the aluminum layer dissolution reaction in step S3.

[0012] Furthermore, based on 100ml of electrolyte, the component ratios in the electrolyte are as follows: Sodium silicate 10±1g, sodium hydroxide 2.5±0.25g, sodium chloride 5±0.5g, glacial acetic acid 10±1ml; The pH of the electrolyte is 10-11.

[0013] Furthermore, the probe is made of tungsten, and the counter electrode is made of copper.

[0014] Furthermore, in step S3, the morphology, color, or thickness changes of the aluminum layer surface are observed in real time using a microscope, and the electrolysis time, voltage, and current are dynamically adjusted to precisely control the local thickness of the aluminum layer.

[0015] Furthermore, in step S3, electrolysis is performed until the aluminum layer thickness in the target area is sufficient to allow the defect luminescent points beneath the metal layer to completely penetrate.

[0016] Furthermore, in step S4, the chip surface is gently rinsed several times with deionized water and then dried with nitrogen before being used for subsequent detection processing.

[0017] The principle and effect of this solution are as follows: 1. This invention targets the reaction characteristics of aluminum layer metal on chip surface. After etching to expose the aluminum layer, electrolysis is used to thin the aluminum layer in a directional and targeted manner. The aluminum layer metal in contact with the probe acts as the anode and continuously undergoes a dissolution reaction, while the aluminum layer metal surface not in contact with the probe is passivated, thus slowing down the corrosion rate.

[0018] 2. During operation, this invention will not adversely affect the non-aluminum layer, dielectric layer, or the underlying circuitry, which helps protect the valuable bonding points and test points on the chip and provides the possibility for before-and-after comparison testing in failure analysis.

[0019] 3. The present invention uses electrolysis to thin the aluminum layer, which can also form a relatively flat thinned surface in the vertical direction, and there is no mechanical stress introduced, thus avoiding scratches and stress damage that may be caused by chemical mechanical polishing.

[0020] 4. In summary, the present invention has the advantages of precise positioning and strong controllability, near non-destructive to devices, high processing flatness, clear processing boundaries, good compatibility and flexibility, and improved analysis success rate and accuracy. It can reduce the aluminum layer of the chip in a directional and precise manner without affecting the overall performance of the device, thereby improving the sensitivity of detection. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 A process flow diagram of an aluminum layer thinning method for a directional control chip according to an embodiment of this application is shown; Figure 2 This paper shows an overall comparison of the chip before and after processing using a method for thinning the aluminum layer of a directional control chip according to an embodiment of this application. Figure 3 This paper shows a detailed diagram of a chip portion processed by a method for thinning the aluminum layer of a directional control chip according to an embodiment of this application. Figure 4 This paper shows a detailed diagram of a chip portion processed by a method for thinning the aluminum layer of a directional control chip according to an embodiment of this application. Figure 5 This paper shows a detailed diagram of a chip portion processed by a method for thinning the aluminum layer of a directional control chip according to an embodiment of this application. Figure 6The illustration shows a detailed view of a portion of the chip processed by a method for thinning the aluminum layer of a directional control chip according to an embodiment of this application. Detailed Implementation

[0023] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0024] A method for thinning the aluminum layer of a directional control chip, implementing, for example... Figure 1 As shown: Includes the following steps: Step S1, partially expose the aluminum layer The chip is processed using focused ion beam (FIB) technology, which involves focusing a high-energy ion beam to bombard the sample surface and using physical sputtering to peel off the material layer by layer. This selectively removes the passivation layer and dielectric layer above the target area, exposing the target aluminum layer locally and forming the initial aluminum layer electrolysis window for the electrolysis reaction. After etching stops, the aluminum layer surface of the target area is cleanly exposed, forming the electrolysis window.

[0025] Step S2, Establish a fixed-point electrolysis system The chip is immersed in the electrolyte, and a probe is used as the working electrode to make electrical contact with the electrolytic window. The counter electrode is immersed in the electrolyte, and a power supply is configured to form a micro-area electrolytic etching system. The chip is transferred to a precision probe stage equipped with a high-magnification optical microscope. Under the microscope, a tungsten probe is manipulated to precisely press its tip against the surface of the exposed aluminum layer window or the corresponding pin of the chip, establishing electrical conductivity between the probe and the aluminum layer window. After immersing the chip in the electrolyte, the probe is connected to the working terminals of a potentiometer. Simultaneously, a copper counter electrode is placed in the electrolyte, forming a micro-area electrolytic etching system.

[0026] The composition ratio of each component in 100ml of electrolyte is as follows: Sodium silicate 10±1g, sodium hydroxide 2.5±0.25g, sodium chloride 5±0.5g, glacial acetic acid 10±1ml; Furthermore, the components fluctuate to maintain the pH of the electrolyte at 10-11.

[0027] In this electrolyte, chloride ions in sodium chloride promote the dissolution of the aluminum layer; silicate ions in sodium silicate promote the passivation of the aluminum layer; glacial acetic acid acts as a corrosion inhibitor to stabilize the galvanometer; and sodium hydroxide maintains a high pH environment in the electrolyte to achieve a dynamic balance of electrochemical polarization regulation.

[0028] Step S3, directional and targeted electrolytic thinning Under the influence of an electric field, the aluminum layer that forms a current loop with the probe, counter electrode, and power supply undergoes an anodic dissolution reaction, thinning the aluminum layer to a predetermined thickness or completely penetrating it to expose the underlying structure. Simultaneously, the aluminum layer that is not in electrical contact with the probe undergoes a passivation reaction, as detailed below: An anodic potential of 1-2 V and 5-8 μA is applied using a potentiometer. However, the voltage and current are not limited to these values ​​and will vary depending on the specific device being tested. Refer to the device's datasheet for details. After the potential is turned on, the aluminum layer near the probe contact point, or the aluminum layer in electrical contact with the probe, begins to undergo an oxidation and dissolution reaction. During this process, copper and aluminum form a macroscopic cell upon electrical contact, with aluminum acting as the anode and continuously dissolving. Specifically, the aluminum layer in electrical contact with the probe through the chip pins, or directly in contact with the probe, acts as the anode and continuously undergoes a dissolution reaction. Meanwhile, the aluminum layer not in contact with the probe undergoes the following reaction in the high-pH silicate system: That is, passivation of the aluminum layer surface that is not in contact with the probe slows down the corrosion rate.

[0029] By observing the morphology, color, or thickness changes of the aluminum layer surface in real time using a microscope, the electrolysis time, voltage, and current are dynamically adjusted to precisely control the local thickness of the aluminum layer. For example, through real-time microscopic observation, centered on the probe contact point, the color of the aluminum layer gradually changes from silvery-white to darker, and gradually becomes brown as the thickness decreases. Of course, for different devices, the color of the aluminum layer area as it thins may vary, and the above color change should not be considered a specific example limiting this embodiment to those skilled in the art. By monitoring the current-time curve, it is found that the current tends to a stable value after the initial rise. When the aluminum layer is observed to become sufficiently thin and the current curve shows slight fluctuations, the applied voltage is immediately stopped.

[0030] In this step, the distance between the probe and the counter electrode directly affects the reaction rate on the aluminum layer surface. The dissolution of the aluminum layer can be accelerated by shortening the distance between the probe and the counter electrode.

[0031] Step S4, Post-processing and Detection After electrolysis, the power is disconnected, and the chip surface is cleaned with solvent to remove residual electrolyte before subsequent testing. Remove the probe, gently rinse the chip surface several times with deionized water, and then dry it with nitrogen. After treatment, the aluminum layer in the target area of ​​the chip is thinned to allow the defect emission points beneath the metal layer to completely penetrate. Place the chip in the corresponding detection system and perform detection under normal operating bias.

[0032] After processing, the aluminum layer in the target area of ​​the chip has been thinned or removed at specific points, and optical obstructions have been eliminated. It can be immediately used for subsequent inspection processes, such as EMMI inspection, to accurately locate the defective light-emitting points underneath. Because this method can perform microprocessing on only a very small local area, the overall chip structure, especially the bonding points and circuit functions in the unprocessed areas, are well preserved, allowing for continued electrical parameter testing and functional verification.

[0033] In this embodiment, the original overall photograph of the chip to be processed is as follows: Figure 2 As shown in (a), the overall image of the chip after processing by the method of the above embodiment is as follows. Figure 2 As shown in (b), the brown area represents the area where the aluminum layer has been thinned; specific details are shown below. Figure 3 (a)(b) Figure 4 (a)(b) Figure 5 (a) (b) and Figure 6 As shown in (a) and (b), the color of the processed area after thinning the aluminum layer may vary depending on the device, and the processed area after thinning may also be other colors. The brown area in this embodiment cannot be regarded as a special case of this embodiment.

[0034] As can be seen, the chip processed according to this embodiment can be almost non-destructive, and the functional test remains basically unchanged. After directional and point-to-point electrolytic thinning or removal, functional testing or defect detection can still be performed. At the same time, the thinning or removal has a high degree of flatness and there is no drift or extension, which fully demonstrates the superiority of this process.

[0035] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any indirect modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for thinning the aluminum layer of a directional control chip, characterized in that, Includes the following steps: Step S1, Local exposure of aluminum layer: The passivation layer and dielectric layer of the chip to be processed are removed by etching, and the aluminum layer is exposed to form an electrolytic window; Step S2, establish the electrolysis system: immerse the chip in the electrolyte, use a probe as the working electrode to make electrical contact with the electrolysis window, immerse the counter electrode in the electrolyte, and configure a power supply to form a micro-area electrolytic etching system; Step S3, directional and fixed-point electrolytic thinning: through the action of an electric field, the aluminum layer that is electrically in contact with the probe undergoes a dissolution reaction, and the aluminum layer is thinned to the desired thickness range, while the aluminum layer that is not electrically in contact with the probe undergoes a passivation reaction. Step S4, Post-processing and Inspection: After electrolysis, the residual electrolyte on the chip surface is removed before subsequent inspection.

2. The method for thinning the aluminum layer of a directional control chip according to claim 1, characterized in that, In step S1, the chip is processed using FIB to expose its aluminum layer.

3. The method for thinning the aluminum layer of a directional control chip according to claim 1, characterized in that, In step S2, the probe is brought into contact with the chip pins or the surface of the electrolytic window.

4. The method for thinning the aluminum layer of a directional control chip according to claim 3, characterized in that, In step S2, the distance between the probe and the counter electrode is shortened to accelerate the aluminum layer dissolution reaction in step S3.

5. A method for thinning the aluminum layer of a directional control chip according to claim 3 or 4, characterized in that, Based on 100ml of electrolyte, the component ratios in the electrolyte are as follows: Sodium silicate 10±1g, sodium hydroxide 2.5±0.25g, sodium chloride 5±0.5g, glacial acetic acid 10±1ml; The pH value of the electrolyte is 10-11.

6. The method for thinning the aluminum layer of a directional control chip according to claim 1, characterized in that, The probe is made of tungsten, and the counter electrode is made of copper.

7. The method for thinning the aluminum layer of a directional control chip according to claim 1, characterized in that, In step S3, the morphology, color, or thickness changes of the aluminum layer surface are observed in real time using a microscope, and the electrolysis time, voltage, and current are dynamically adjusted to precisely control the local thickness of the aluminum layer.

8. The method for thinning the aluminum layer of a directional control chip according to claim 1, characterized in that, In step S3, electrolysis is performed until the aluminum layer thickness in the target area is sufficient to allow the defect luminescent points beneath the metal layer to completely penetrate.

9. The method for thinning the aluminum layer of a directional control chip according to claim 1, characterized in that, In step S4, the chip surface is gently rinsed several times with deionized water and then dried with nitrogen before being used for subsequent detection and processing.

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