Waferless automated cleaning method for image sensor manufacturing processes
Patent Information
- Application Number
- CN202510332829.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-19
- Publication Date
- 2026-09-25
AI Technical Summary
这些聚合物可能随机脱落并沉积在晶圆表面，造成颗粒缺陷(Particle Defect)，严重影响芯片良率
[0022]本发明采用Cl2和BCl3的组合气体作为清洁气体，用于铝垫刻蚀工艺的片与片之间的无晶圆清洗，能有效刻蚀清除铝垫刻蚀腔的内壁残留的含铝或钨的副产物，避免了在后续的铝垫刻蚀工艺中可能引入的颗粒污染，可以使得后续的钨层刻蚀工艺良率提升。
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Figure CN122825547A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of semiconductor manufacturing technology and relates to a fabless automated cleaning method for image sensor manufacturing processes. Specifically, it relates to a fabless automated cleaning process after aluminum pad (AlPad) etching during the manufacturing of back-illuminated CMOS image sensor (CIS) chips, particularly a highly efficient cleaning method for mixed byproducts generated during dry etching of aluminum and / or tungsten metal layers. Background Technology
[0002] In all stages of semiconductor manufacturing, especially after processes such as thin film deposition and etching, various chemicals and tiny particles often remain on the wafer surface. If these contaminants are not cleaned in time, they will seriously affect the results of subsequent processes and the final performance of the product.
[0003] In the manufacturing process of back-illuminated CIS (CMOS Image Sensor) chips, cleaning after aluminum pad etching is one of the key steps. Due to over-etching during the etching process, the tungsten metal layer beneath the aluminum metal layer is partially etched simultaneously, resulting in etching byproducts containing compounds or polymers of both aluminum (Al) and tungsten (W). Currently, the industry commonly uses fabless automated cleaning processes with chlorine gas (Cl2) as the cleaning gas. Under the action of a plasma source, chlorine dissociates into plasma, which reacts with the etching byproducts. The resulting volatile substances are then extracted from the chamber by a vacuum pump. The mechanism is as follows: 1) Plasma dissociation: Under the action of a power source (such as an RF power supply), chlorine gas dissociates into chlorine free radicals (Cl2). ● ) and chloride ions (Cl + );2) Oxide layer removal: Cl + Driven by bias power, the oxide layer (such as Al2O3, WO3, etc.) on the surface of aluminum and tungsten metals is bombarded, breaking the covalent bonds between the metal and oxygen atoms, i.e., opening the covalent bonds. 3) Chemical reaction: Cl ● It then reacts with the exposed metals (Al, W) to generate volatile byproducts AlCl3 and WCl6, which are eventually discharged from the chamber through a vacuum system.
[0004] Although the above methods are widely used, they have the following drawbacks in practical applications:
[0005] 1) Byproduct residues and defect formation: Due to Cl + The bombardment capability is relatively weak, making it difficult to completely destroy the covalent bonds in the metal oxide layer. This results in the oxide layer on the aluminum and tungsten metal surfaces not being fully removed, leading to subsequent Cl... ●The reaction efficiency with metals decreases. On the other hand, unreacted AlCl3 and WCl6 gradually accumulate on the inner wall of the chamber, forming non-volatile polymers. These polymers may randomly detach and deposit on the wafer surface, causing particle defects and severely affecting chip yield.
[0006] 2) Insufficient process stability: Cleaning efficiency decreases as the cavity is used for a longer period of time, requiring frequent shutdowns for maintenance, which increases production costs. Summary of the Invention
[0007] The purpose of this invention is to solve the cleaning problem of aluminum pad etching chamber. In the waferless cleaning process, a mixed gas of Cl2 and BCl3 is introduced as a cleaning gas. Under the action of plasma electric field, BCl3 helps to open the covalent bonds of metal contaminants and promotes the generation of volatile metal chlorides, thereby achieving the purpose of deep cleaning.
[0008] To achieve the above objectives, the present invention provides a fabless automated cleaning method for image sensor manufacturing processes, comprising:
[0009] After the working wafer is removed from the aluminum pad etching cavity, a cleaning gas is introduced into the aluminum pad etching cavity, and under the action of a plasma radio frequency source, the residual by-products in the aluminum pad etching cavity are etched away.
[0010] The cleaning gas contains Cl2 and BCl3.
[0011] Optionally, the volume ratio of Cl2 to BCl3 in the cleaning gas is 1:1 to 3:1.
[0012] Optionally, the pressure inside the etching chamber of the aluminum pad is 5 mtorr to 10 mtorr.
[0013] Optionally, the plasma radio frequency source includes HF radio frequency with a power of 800W to 1500W.
[0014] Optionally, the process temperature inside the aluminum pad etching chamber is 60℃~400℃.
[0015] Optionally, it also includes a purging step: switching the flow of purging gas into the aluminum pad etching chamber.
[0016] Optionally, the purging gas contains at least one of N2 or Ar.
[0017] Optionally, the flow rate of the purging gas is greater than the flow rate of the cleaning gas.
[0018] Optionally, during the purging step, the pressure in the aluminum etching chamber is 10 mtorr to 30 mtorr.
[0019] Optionally, the byproducts include aluminum byproducts and / or tungsten byproducts.
[0020] Optionally, in the aluminum pad etching process, after each working wafer completes plasma etching and is removed from the aluminum pad etching cavity, a cleaning gas is introduced into the aluminum pad etching cavity to clean it.
[0021] Compared with the prior art, the technical solution of the present invention has at least the following beneficial effects:
[0022] This invention uses a combination of Cl2 and BCl3 gases as cleaning gases for wafer-free cleaning between wafers in the aluminum pad etching process. It can effectively etch away aluminum or tungsten-containing byproducts remaining on the inner wall of the aluminum pad etching cavity, avoiding particulate contamination that may be introduced in the subsequent aluminum pad etching process, and improving the yield of the subsequent tungsten layer etching process.
[0023] Furthermore, the present invention selects a dosage ratio of Cl2 and BCl3 such that Cl2 is moderately excessive. For example, the volume ratio of Cl2 to BCl3 is 1:1 to 3:1. Under this dosage ratio, by setting the power of the plasma radio frequency source, the pressure inside the cavity, the temperature, and other conditions, the purpose of quickly and thoroughly cleaning the aluminum pad etching cavity can be achieved. Attached Figure Description
[0024] Figure 1 This is a schematic diagram of the reaction mechanism for waferless cleaning according to the present invention, wherein a represents a schematic diagram of the reaction mechanism for cleaning alumina impurities, and b represents a schematic diagram of the reaction mechanism for cleaning tungsten oxide impurities.
[0025] Figure 2 This is a flowchart of a fabless automated cleaning method for image sensor manufacturing processes according to the present invention.
[0026] Figure 3 To provide a comparative example, the schematic diagrams show the state of the aluminum pad etched wafer before and after etching the W stop layer after cleaning the aluminum pad etching cavity. In the diagram, a represents a partial state of the aluminum pad etched wafer (before etching the W stop layer), and b represents a partial state of the wafer after etching the W stop layer.
[0027] Figure 4 This is an example of a schematic diagram showing the state of the aluminum pad etched wafer before and after etching the W stop layer after cleaning the aluminum pad etching cavity. In this diagram, a represents a partial state of the aluminum pad etched wafer (before etching the W stop layer), and b represents a partial state of the wafer after etching the W stop layer.
[0028] Attached image labels:
[0029] 10 on the surface of the chamber
[0030] Alumina impurity 11
[0031] Tungsten oxide impurity 12
[0032] Aluminum pads 31, 41
[0033] W Stop Layer 32, 42
[0034] Residue 33
[0035] Abnormal contour 35
[0036] Normal outlines 34, 43. Detailed Implementation
[0037] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0038] In the description of this invention, it should be noted that the terms "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.
[0039] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.
[0040] As described in the background section, existing fabless automated cleaning processes between wafers typically use chlorine gas as the cleaning gas. However, this gas is often insufficient for cleaning byproducts containing aluminum or tungsten, which affects the yield of subsequent processes.
[0041] Through experimental verification and mechanism research, it was found that the defects of the existing technology are mainly caused by the following factors:
[0042] 1)Cl + Insufficient bombardment energy: The bias power setting limits Cl +The kinetic energy of the material prevents it from effectively breaking the high-strength chemical bonds in the aluminum and tungsten oxide layers (e.g., the Al-O bond energy is about 501 kJ / mol, and the WO bond energy is about 650 kJ / mol).
[0043] 2) Differences in the volatility of byproducts: AlCl3 has higher volatility (boiling point: 180℃), while WCl6 has relatively lower volatility (boiling point: 347℃), making it easier for tungsten-containing compounds to remain in the cavity. Therefore, relying solely on Cl... ● The chemical etching mechanism cannot simultaneously and efficiently remove aluminum and tungsten oxides, and the difference in reaction kinetics between the two further exacerbates the accumulation of byproducts.
[0044] This invention improves the cleaning gas by selecting a combination of Cl2 and BCl3 as the cleaning gas to remove byproducts containing Al and / or W. For example... Figure 1 As shown, BCl3 dissociates into BCl3 under the action of the source power generator. + And electrons. BCl3 + mass relative to Cl + The larger the concentration, the stronger the bombardment capability under the bias power. This allows the covalent bonds between metal atoms and oxygen atoms to be more easily broken, facilitating the dissociation of Cl2 and the formation of Cl... ● It reacts readily with metals, thereby generating volatile byproducts (AlCl3, WCl6).
[0045] See Figure 1 a, Alumina (Al2O3) impurities 11 on the surface of chamber 10 in BCl3 + Under bombardment, the Al-O covalent bond breaks, and the resulting Al radical readily reacts with Cl radicals (Cl... ● This combination forms volatile AlCl3, which can be easily pumped out of the aluminum pad etching chamber, thus cleaning the chamber. (See also...) Figure 1 b, tungsten oxide (WO3) impurity 12 on chamber surface 10 in BCl3 + Under bombardment, the covalent bonds of WO break, and the resulting W radical readily reacts with Cl radicals (Cl... ● The two molecules combine to form volatile WCl6, which can be easily pumped out of the aluminum pad etching chamber, thus achieving the purpose of cleaning the aluminum pad etching chamber.
[0046] like Figure 2 The diagram shown is a process flow chart of a fabless automated cleaning method for image sensor manufacturing provided by the present invention. The cleaning method includes:
[0047] Step S1: Remove the working wafer from the aluminum pad etching cavity;
[0048] Step S2: A cleaning gas is introduced into the aluminum pad etching chamber, and under the action of a plasma radio frequency source, the residual by-products in the aluminum pad etching chamber are etched away; wherein, the cleaning gas contains Cl2 and BCl3.
[0049] The "aluminum pad etching chamber" mentioned herein refers to a processing chamber used in the etching process of aluminum pads. When etching forms an aluminum pad, the etching gas may come into contact with the W stop layer beneath the aluminum pad. Therefore, in addition to aluminum-containing impurities (aluminum-containing compounds and / or polymers), the etching process may also generate tungsten-containing impurities (tungsten-containing compounds and / or polymers), and aluminum- or tungsten-containing impurities may remain on the inner wall of the chamber. This invention is not limited thereto; according to the technical concept of this invention, the method of this invention is applicable to scenarios where the processing chamber contains polymeric impurities of aluminum or tungsten. The "byproducts" mentioned herein include aluminum byproducts and / or tungsten byproducts.
[0050] In some embodiments, the volume ratio of Cl2 to BCl3 in the cleaning gas is 1:1 to 3:1. This application has unexpectedly discovered that a moderate excess of Cl2 in the cleaning gas can achieve better cleaning results; for example, the volume ratio of Cl2 to BCl3 is 1.1:1 to 2:1.
[0051] This invention can directly introduce a mixture of Cl2 and BCl3, or it can first introduce BCl3, and after the BCl3 is fully ionized, then introduce Cl2. In other embodiments, BCl3 is introduced first, and after the BCl3 is fully ionized, a mixture of Cl2 and BCl3 is introduced. When BCl3 is introduced first, for example, after 2 to 5 seconds, Cl2 or a mixture of Cl2 and BCl3 is introduced, saving time and gas consumption. In some embodiments, Cl2 and BCl3 can be introduced alternately.
[0052] In some embodiments, in step S2, the pressure inside the aluminum pad etching chamber is 5 mtorr to 10 mtorr. The process temperature inside the aluminum pad etching chamber is 60°C to 400°C; for example, it can be 100°C to 200°C, 200°C to 300°C, or 300°C to 400°C. The chamber temperature of the cleaning process can be selected according to the different impurities. For example, when there are only aluminum impurities, the process temperature can be lower because AlCl3 has a low boiling point; when there are only W impurities, the process temperature is preferably higher than 350°C to ensure sufficient and rapid removal of WCl6 because WCl6 has a high boiling point. When aluminum impurities and tungsten impurities may coexist, a higher process temperature can be used, or the temperature can be gradually increased, first heating to near the boiling point of AlCl3, and then heating to near the boiling point of WCl6.
[0053] In some embodiments, the plasma radio frequency source includes HF (high frequency, e.g., 60 MHz) radio frequency and has a power of 800 W to 1500 W. Under the electric field of the plasma radio frequency source, the cleaning gas dissociates into BCl3. ﹢ Cl - And active particles such as electrons. Under the bombardment of heavier plasma, the Al-O covalent bonds and WO covalent bonds are more easily broken, thereby promoting the combination of Cl- with Al and / or W, and the generated AlCl3 and / or WCl5 are easily sublimated and discharged from the aluminum pad etching cavity at the process temperature, thus achieving the cleaning of the aluminum pad etching cavity.
[0054] In some embodiments, a purge gas is introduced in step S2 to promote the removal of byproducts (impurities). The purge gas is an inert gas, such as helium (He), argon (Ar), or nitrogen (N2). The purge gas can be introduced in a pulsed or continuous manner. The flow rate of the purge gas can be greater than that of the cleaning gas. The purge gas not only carries away gaseous impurities or small particles, but also exerts a physical impact on the impurities, promoting their removal. During the purge step, the pressure in the aluminum etching chamber is 10 mtorr to 30 mtorr.
[0055] In some embodiments, after step S2, a purging step is further included: switching the flow of purging gas into the aluminum pad etching chamber.
[0056] In some embodiments, during the aluminum pad etching process, after each working wafer completes plasma etching and is removed from the aluminum pad etching cavity, a cleaning gas is introduced into the aluminum pad etching cavity to clean it.
[0057] In other embodiments, based on practical experience, multiple wafers can be processed continuously as much as possible while ensuring product yield, for example, after 30 to 200 wafers, the aluminum pad etching cavity can be cleaned using the method of the present invention. Then, the aluminum pad etching process continues.
[0058] The following comparative examples and embodiments verify the beneficial effects of the present invention.
[0059] Comparative Example
[0060] After the first wafer is removed from the aluminum pad etching chamber, Cl2 (flow rate 1000 sccm) is introduced to perform fabless cleaning of the aluminum pad etching chamber. The plasma RF source includes HF RF (60MHz) with a power of 1000W. The pressure inside the aluminum pad etching chamber is 5 mtorr to 10 mtorr. The cleaning process temperature inside the aluminum pad etching chamber is 300℃ to 400℃, and the processing time is 120s. Then, the next wafer is introduced into the aluminum pad etching chamber for the aluminum pad etching process. After etching, a partial cross-sectional view of the wafer is shown below. Figure 3 As shown in Figure a, it includes an aluminum pad 31 and a W stop layer 32. Several residues 33 are visible on the W stop layer 32. The residues 33 are compounds containing Al and / or W, such as aluminum oxide, tungsten oxide, etc.
[0061] The wafer is etched with a stop layer 32 (W) to form a grid structure, such as... Figure 3 As shown in b. Due to the obstruction of the residue 33, an abnormal profile 35 is formed, while the portion not covered by the residue 33 is etched to form a normal profile 34.
[0062] Example
[0063] After the first wafer is removed from the aluminum pad etching chamber, a combination of Cl2 and BCl3 gas is introduced to perform fabless cleaning of the aluminum pad etching chamber. The volume ratio of Cl2 to BCl3 is 2:1 (total flow rate 1000 sccm), and the plasma radio frequency source includes HF radio frequency (60MHz) with a power of 1000W. The pressure inside the aluminum pad etching chamber is 5 mtorr to 10 mtorr. The process temperature inside the aluminum pad etching chamber is 300℃ to 350℃, and the processing time is 80 seconds. Then, the next wafer is introduced into the aluminum pad etching chamber for the aluminum pad etching process. After etching, a partial cross-sectional view of the wafer is shown below. Figure 4 As shown in figure a, it includes an aluminum pad 41 and a W stop layer 42. No residue was found on the W stop layer 42.
[0064] The wafer is etched with a stop layer 42 to form a grid structure, such as... Figure 4 As shown in b. Due to the absence of residue, the etching forms a normal contour 43.
[0065] Through comparative experiments with comparative examples, it can be seen that the method of the embodiments of the present invention for waferless automatic cleaning can efficiently and thoroughly remove residual impurities on the inner wall of the aluminum pad etching cavity, especially impurities containing aluminum or tungsten, avoiding the introduction of impurities on the aluminum pad etching wafer, which is beneficial to improving the product yield of subsequent W stop layer etching.
[0066] In summary, this invention uses a combination of Cl2 and BCl3 gases as cleaning gases for wafer-to-wafer cleaning in aluminum pad etching processes. This effectively etches away residual aluminum or tungsten-containing byproducts on the inner wall of the aluminum pad etching cavity, avoiding potential particulate contamination in subsequent aluminum pad etching processes and improving wafer yield in subsequent tungsten layer etching. Furthermore, this invention selects the optimal ratio of Cl2 and BCl3 and sets the power of the plasma RF source, the pressure within the cavity, and the temperature, achieving rapid and thorough cleaning of the aluminum pad etching cavity.
[0067] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.
Claims
1. A fabless automated cleaning method for image sensor manufacturing processes, characterized in that, Include: After the working wafer is removed from the aluminum pad etching cavity, a cleaning gas is introduced into the aluminum pad etching cavity, and under the action of a plasma radio frequency source, the residual by-products in the aluminum pad etching cavity are etched away. The cleaning gas contains Cl2 and BCl3.
2. The fabless automated cleaning method for image sensor manufacturing processes as described in claim 1, characterized in that, In the clean gas, the volume ratio of Cl2 to BCl3 is 1:1 to 3:
1.
3. The fabless automated cleaning method for image sensor manufacturing processes as described in claim 1, characterized in that, The pressure inside the etching chamber of the aluminum pad is 5 mtorr to 10 mtorr.
4. The fabless automated cleaning method for image sensor manufacturing processes as described in claim 1, characterized in that, The plasma radio frequency source includes HF radio frequency and has a power of 800W to 1500W.
5. The fabless automated cleaning method for image sensor manufacturing processes as described in claim 1, characterized in that, The process temperature inside the etching chamber of the aluminum pad is 60℃~400℃.
6. The fabless automated cleaning method for image sensor manufacturing processes as described in claim 1, characterized in that, It also includes a purging step: switching the flow of purging gas into the etching chamber of the aluminum pad.
7. The fabless automated cleaning method for image sensor manufacturing processes as described in claim 6, characterized in that, The purging gas contains at least one of N2 or Ar.
8. The fabless automated cleaning method for image sensor manufacturing processes as described in claim 6, characterized in that, The flow rate of the purging gas is greater than the flow rate of the cleaning gas.
9. The fabless automated cleaning method for image sensor manufacturing processes as described in claim 6, characterized in that, During the purging process, the pressure in the aluminum etching chamber is 10 mtorr to 30 mtorr.
10. The fabless automated cleaning method for image sensor manufacturing processes as described in claim 1, characterized in that, The byproducts include aluminum byproducts and / or tungsten byproducts.
11. The fabless automated cleaning method for image sensor manufacturing processes as described in any one of claims 1-10, characterized in that, In the aluminum pad etching process, after each working wafer completes plasma etching and is removed from the aluminum pad etching cavity, a cleaning gas is introduced into the aluminum pad etching cavity to clean it.