Method for judging etching end point in thick aluminum wet etching process

Abstract

The invention discloses a method for judging an etching end point in a thick aluminum wet etching process, which optimizes a process result judgment process of wet etching of an aluminum layer by improving a chip manufacturing process flow. According to the specific technical scheme, the method comprises the following steps: calculating the relation between the velocity and clear ratio in the vertical and horizontal directions of aluminum-silicon-copper corrosion, calculating the time required for corrosion to the bottom of aluminum-silicon-copper, obtaining the time required for corrosion addition according to the distance between aluminum wires, and finally determining the total time. According to the method, the time required for corroding to the bottom of the aluminum-silicon-copper can be accurately calculated, and the total corrosion time is determined according to the time. According to the method, the accuracy and consistency of corrosion time are greatly improved, and subjectivity and uncertainty caused by depending on manual observation of color change in a traditional method are avoided. By accurately controlling the corrosion time, the problem that the aluminum wire is broken due to too long corrosion time is effectively avoided, and the stability and reliability of a semiconductor product are ensured.

Description

Technical Field

[0001] The invention belongs to the field of semiconductor chip manufacturing technology, and in particular relates to a method for judging an etching endpoint in a thick aluminum wet etching process. Background Art

[0002] The silicon in aluminum-silicon-copper (AlSiCo) materials can significantly suppress resistance increases, while the copper prevents localized narrowing of the aluminum due to charge transfer, leading to their widespread use in power semiconductors. AlSiCo is grown entirely on the wafer surface, and wet etching is required to partially remove the AlSiCo to form the aluminum wires required for the semiconductor. However, due to varying corrosion rates at different locations on the wafer and varying exposed aluminum areas across different products, the time required for complete corrosion cannot be directly calculated. Simply increasing the etching time can lead to excessive corrosion of the aluminum wires, potentially breaking them.

[0003] The current solution is to start timing after the wafer enters the etching tank. During the etching process, the wafer will be pulled out of the liquid surface at regular intervals. The operator needs to observe whether there is any color change in the corroded area. When a color change is observed, the etching time T1 is recorded. Then, the etching time T2 is increased by a proportion X based on the etching time T1. The total etching time T=T1+T2=T1(1+X). However, this improvement has many shortcomings. First, the operator must stay at the machine at all times and cannot take care of other work. More importantly, different people have different standards for judging color changes, which will result in product results that do not meet the requirements. This requires certain changes to the judgment of the chip production process. Summary of the Invention

[0004] In response to the above-mentioned shortcomings, the present invention provides a method for determining the etching endpoint in the thick aluminum wet etching process. By improving the chip manufacturing process flow, the process for determining the process results of wet etching of the aluminum layer is optimized to free up manpower and produce different products that meet the requirements.

[0005] In order to achieve the above-mentioned purpose, the technical solution provided by the present invention is as follows.

[0006] A method for determining the etching endpoint in a thick aluminum wet etching process calculates the relationship between the vertical and horizontal etching rates and the clear ratio of aluminum-silicon-copper, calculates the time required to etch to the bottom of the aluminum-silicon-copper, and obtains the time required for additional etching based on the distance between aluminum lines, ultimately determining the total etching time.

[0007] The specific steps include: Step 1: Deposit 0.2 μm of undoped silicate glass (USG) and 0.8 μm of borophosphosilicate glass (BPSG) on a silicon substrate. Then sputter 4 μm of aluminum-silicon-copper (AlSiCu) above the BPSG. Corrode the prepared wafer using an aluminum etchant, and calculate the average rate V1 of the aluminum etchant on AlSiCu. Step 2: Deposit 0.2 μm of undoped silicate glass (USG) and 0.8 μm of borophosphosilicate glass (BPSG) on a silicon substrate. Then sputter 4 μm of aluminum-silicon-copper (AlSiCu) above the BPSG. Deposit a 2.4-μm layer of photoresist above the aluminum layer. After exposure and development using photolithography plates with different clear ratios, corrode the prepared wafer using an aluminum etchant, and calculate the average longitudinal rate Vy and the lateral corrosion rate Vx of the aluminum etchant on AlSiCu. Then obtain the relationships between the clear ratio and the corrosion rates Vy and Vx, i.e., Vy = f1(clear ratio & V1) and Vx = f2(clear ratio & V1).

[0008] Step 3: According to Vx and Vy, the shortest time 4 / Vx required to etch 4 μm of aluminum can be calculated. The maximum time L / 2Vy required for corrosion can be calculated based on the width L of the aluminum wire before corrosion. Therefore, the corrosion time T of the aluminum layer should follow 4 / Vx < T < L / 2Vy. According to the measured values, take T as (L / 2Vy - 4 / Vx) / 2 + 4 / Vx.

[0009] Compared with the prior art, the beneficial effects of the present invention are as follows: First, by scientifically calculating the relationships between the vertical and horizontal corrosion rates of aluminum-silicon-copper and the Clear ratio (the proportion of the developed area), the present invention can accurately calculate the time required to corrode to the bottom of the aluminum-silicon-copper, and determine the total corrosion time based on this. This method greatly improves the accuracy and consistency of the corrosion time, avoiding the subjectivity and uncertainty brought by relying on manual observation of color changes in traditional methods. At the same time, it releases human resources, enabling the operator to not need to continuously monitor the corrosion process and be able to attend to other tasks, thereby improving the overall production efficiency.

[0010] Second, by precisely controlling the corrosion time, the present invention effectively avoids the problem of the aluminum wire being corroded and broken due to excessive corrosion time, ensuring the stability and reliability of semiconductor products. In addition, it also reduces the product rejection rate caused by differences in human judgment, improves the product yield and consistency, and further reduces the production cost. This precise control of the corrosion process not only optimizes the product quality but also enhances the controllability and predictability of the process.

[0011] Finally, the proposal and application of this invention not only solves the technical difficulties in current wet etching processes but also provides important insights and references for the further optimization and upgrading of subsequent semiconductor chip manufacturing processes. It promotes technological progress and industrial upgrading in the semiconductor chip manufacturing industry, with significant economic and social benefits. In summary, this invention demonstrates significant benefits in improving production efficiency, optimizing product quality, enhancing process controllability, and promoting technological advancement, possessing significant application value and promotional prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a schematic diagram of the film structure before the wet aluminum etching process described in the present invention. DETAILED DESCRIPTION

[0013] The present invention will be described in further detail below with reference to specific examples, but the embodiments of the present invention include but are not limited to the scope represented by the following examples.

[0014] This invention discloses a method for improving the determination of the etching endpoint in the thick aluminum wet etching process. During the etching process, the relationship between the vertical and horizontal etching rates of aluminum-silicon-copper and the clear ratio (the proportion of the clear area) is collected. The time required to etch to the bottom of the aluminum-silicon-copper is calculated. The time required for further etching is calculated based on the distance between the aluminum lines, and the total etching time is finally determined. The specific method is as follows: Step 1: Dep 0.2um USG and 0.8um BPSG on the silicon substrate, sputter 4um AlSiCu on top of BPSG, use aluminum etching solution to etch the prepared wafer, and collect the average rate V1 of aluminum etching solution on AlSiCu.

[0015] Step 2: Dep 0.2um USG and 0.8um BPSG on the silicon substrate, sputter 4um AlSiCu on top of BPSG, and dep a 2.4um photoresist on the aluminum layer. After exposure and development using photomasks with different clear ratios, use aluminum etching solution to etch the prepared wafer, collect the average longitudinal rate Vy and lateral etching rate Vx of the aluminum etching solution on AlSiCu, and then obtain the relationship between the clear ratio and the etching rate Vy or Vx, that is, Vy=f1(clear ratio & V1) and Vx=y2(clear ratio & V1). See the structure. Figure 1 .

[0016] Step 3: Based on Vx and Vy, the shortest time required to etch 4um aluminum can be calculated as 4 / Vx. According to the width L of the aluminum wire before corrosion, the longest time required for corrosion can be calculated as L / 2Vy. Therefore, the aluminum layer corrosion time T should follow 4 / Vx < T < L / 2Vy. According to the measured values, T is taken as (L / 2Vy - 4 / Vx) / 2 + 4 / Vx. The measured results meet the product requirements and there is no need for human observation anymore.

[0017] Clear ratio = (2*d2) / (2*d1 + 2*d2 + L), which is the ratio of the developed area to the total area.

[0018] The above d1 is the photoresist coverage area, and d2 is the lithography CD. Embodiment

[0019] (1) During one acid replacement cycle, the average corrosion rate of the aluminum etchant on AlSiCu was collected as V1 = 3000 ± 300 A. (2) For product P1 with a clear ratio of 15%, according to the relationship between the corrosion rate and the clear ratio model, the corresponding Vx = 3600 ± 360 A / min and Vy = 5000 ± 500 A / min can be obtained.

[0020] (3) It is known that the aluminum wire L to be etched by the PR barrier is 15um, and the thickness of the aluminum silicon copper is 4um.

[0021] (4) Therefore, the shortest corrosion time is 40000 / (3600 ± 360) = 10.1 - 12.3 min, and the longest corrosion time is 150000 / (5000 ± 500) / 2 = 13.6 - 16.6 min.

[0022] (5) So the corrosion time should be selected between 12.3 - 13.6 min. Take the actual process as 13 min. The actual width of the aluminum wire after corrosion is measured to be 2um, meeting the product requirements (2.5 ± 1.5um).

[0023] From the above embodiments, it can be seen that the present invention has the following beneficial effects: 1. Significantly improve production efficiency: The core of the present invention is to achieve precise prediction and control of the etching end point in the wet etching process through scientific data analysis and mathematical modeling. This innovative method greatly reduces the dependence on manual observation in the traditional process, enabling operators to free up human resources and focus on other production links without continuously monitoring the corrosion process. In addition, due to the precise calculation of the corrosion time, repeated operations caused by over-corrosion or under-corrosion are avoided, further improving the overall production efficiency.

[0024] 2. Improved product quality stability: By deeply analyzing the physical and chemical mechanisms of the corrosion process, this invention establishes a mathematical relationship model between the corrosion rate and various influencing factors. This model accurately reflects the actual conditions during the corrosion process and provides a scientific basis for setting and optimizing process parameters. As a result, in actual production, it can ensure that every wafer achieves the ideal corrosion effect during the corrosion process, avoiding quality issues such as aluminum wire breakage and short circuits caused by uneven or excessive corrosion, significantly improving product stability and reliability.

[0025] 3. Enhanced process controllability: The implementation of this invention relies not only on the collection and analysis of experimental data but also on mathematical modeling to simplify the complex corrosion process into a predictable and controllable mathematical model. This model provides clear guidance for adjusting and optimizing process parameters, making the process more controllable and repeatable. Furthermore, the precise calculation of corrosion time results in more consistent and stable process results, reducing process fluctuations and errors caused by human factors.

[0026] 4. Promoting Technological Innovation and Development: The development and application of this invention not only resolves the technical challenges of current wet etching processes but also provides new ideas and methods for further optimizing and upgrading semiconductor chip manufacturing processes. By introducing data-driven and intelligent control concepts, this technology propels the semiconductor manufacturing industry towards greater efficiency, precision, and sustainability. Furthermore, the successful implementation of this invention provides valuable insights and references for optimizing other similar processes, helping to promote technological advancement and industrial upgrading across the industry.

[0027] In summary, the beneficial effects of the present invention are not only reflected in the improvement of production efficiency and the stabilization of product quality, but also in its enhancement of process controllability and promotion of technological innovation. These effects together constitute the important value and significance of the present invention in the semiconductor chip manufacturing process.

Claims

1. A method for judging the etching end point in a thick aluminum wet etching process, characterized in that: Calculate the relationship between the etching rates in the vertical and horizontal directions and the clarity ratio of aluminum-silicon-copper corrosion, calculate the time required to etch to the bottom of the aluminum-silicon-copper, and obtain the additional etching time based on the distance between aluminum wires, and finally determine the total time.

2. The method for judging the etching end point in a thick aluminum wet etching process according to claim 1, characterized in that: Specifically, it includes the following steps: The first step: Deposit 0.2 microns of undoped silicate glass (USG) and 0.8 microns of borophosphosilicate glass (BPSG) on a silicon substrate, sputter 4 microns of aluminum-silicon-copper (AlSiCu) on top of the BPSG, and use an aluminum etching solution to etch the prepared wafer, and calculate the average rate V1 of the aluminum etching solution on AlSiCu. The second step: Deposit 0.2 microns of undoped silicate glass (USG) and 0.8 microns of borophosphosilicate glass (BPSG) on a silicon substrate, sputter 4 microns of aluminum-silicon-copper (AlSiCu) on top of the BPSG, deposit a 2.4-micron photoresist layer on top of the aluminum layer, perform exposure and development using photomasks with different clarity ratios, and then use an aluminum etching solution to etch the prepared wafer, calculate the average longitudinal rate Vy and the lateral etching rate Vx of the aluminum etching solution on AlSiCu, and then obtain the relationship between the clarity ratio and the etching rates Vy and Vx, that is, Vy = f1(clarity ratio & V1) and Vx = f2(clarity ratio & V1). The third step: According to Vx and Vy, the shortest time 4 / Vx required to etch 4 microns of aluminum can be calculated. According to the width L of the area covered by the aluminum wire, the longest time L / 2Vy required for etching can be calculated. Therefore, the aluminum layer etching time T should satisfy 4 / Vx < T < L / 2Vy, and take T as (L / 2Vy - 4 / Vx) / 2 + 4 / Vx.

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