Reduction of defects in the lapping process of the silicon wafer manufacturing: the Six Sigma application
, oraz | 30 lip 2019
O artykule
Data publikacji: 30 lip 2019
Zakres stron: 87 - 105
Otrzymano: 05 gru 2018
Przyjęty: 05 cze 2019
DOI: https://doi.org/10.2478/emj-2019-0013
© 2019 Mithun Sharma, Sanjeev P. Sahni, Shilpi Sharma, published by Sciendo
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License.
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Overview of key quality management concepts
| C | O | A | F | M | C |
|---|---|---|---|---|---|
| Total Productive Maintenance | Japan (the 1950s) | Increase process capability by reduction of unplanned failures, accidents and defects | Preventive and predictive maintenance of processes | Gap analysis of historical records, cause‐effect analysis | Skilled workers required to implement, resource demanding and long‐term |
| Total Quality Control | Japan (the 1960s) | To coordinate quality maintenance and improvement from all groups to achieve the most economical process | To reduce rework and achieve maximum customer satisfaction | Methodology: Plan Do Study Act Tools: Statistical techniques | Vague and difficult to coordinate |
| Total Quality Management (TQM) | Japan (the 1990s) | Improve the quality and consistency of processes | Customer satisfaction | Methodology: Plan Do Study Act Tools: Statistical techniques | Vague and inconsistent conceptualisation, excessive resource consumption, unsatisfactory resu lts |
| Zero Defects | Denver Division of the Martin Marietta Corporation (the 1960s) | To enhance the quality of a process outcome through the elimination of any defects in the production process | Defect elimination | Extra attention and care devoted to each step of the production process ensuring no mistakes | Expensive |
| Reliability engineering | Shewart during the 1920s and the 1930s: cited in | To reduce failure modes | Longevity and dependability of parts, products and systems | Reliability‐Centred Maintenance, failure modes and effects, root cause analysis, condition‐ based maintenance | Technical and requires skilled staff. Expensive and demands long term commitment |
Critical to Quality metrics of the lapping process
| T | N | VOC | CTQ |
|---|---|---|---|
| External | Polishing | No sharp roll‐off at the edge of wafer | For Loose Spec TTV < 3.5 μm |
| For Tight Spec TTV < 2.0 μm | |||
| Internal | Lapping | Comparable yield to old active agent | TTV reject < 0.10 % |
| Good Flatness | For Tight Spec TTV < 2.0 μm |
Displaying the impact of improvements on TTV rejects
| B | A | ||||
|---|---|---|---|---|---|
| P | T | L | C | T | L |
| Wafer Qty | 5,623 | 28,120 | 33,743 | 19,677 | 50,666 70,343 |
| TTV Reject % | 9.82 | 3.35 | 4.43 | 0.02 | 0.01 0.01 |
| DPMO | 98,168 | 33,499 | 44,282 | 152 | 118 127 |
| Process Capability (Ppk) | 0.21 | 0.52 | ‐NA‐ | 3.87 | 1.30 ‐NA‐ |
Four key stages of silicon wafer manufacturing process
| P | D | P | P |
|---|---|---|---|
| Slicing | Silicon ingot is mounted on the slicing machine. A web of meatl wire along with cutting slurry passes through the ingot slowly to provide disc shaped silicon wafers | To generate wafer slice structure. To achieve correct wafer thickness, orientation and warp | Poor flatness High surface damage High contamination |
| Lapping | Sliced wafers held in carriers are placed in between two metal plates along with abrasive slurry falling on wafers. Rotation of plates and carriers causes mechnical removal of slicon therby reducing wafer | Reduce slicing damage. Establish optimum wafer flatness | Susceptible to surface and flatness rejects |
| Chemical Etching | Lapped wafers are subjeted to abrasive chemicals which disolves silicon into chemical thereby thinning wafers | Reduce Previous Process Damage Reduce surface contamination | Degrades flatness wafer staining |
| Polishing | Etched wafers are mounted on plates. With pressure applied on these plates, the wafers are rubbed against fine abrasive polishing pads along with polishing slurry to give a mirror like finish | Establish optimum flatness. Eliminate surface damage. Minimise contamination level | High rejection rate Rework cost |
Key results from process capability charts
| P | T | L | C |
|---|---|---|---|
| Wafer Qty | 5,623 | 28,120 | 33,743 |
| TTV Reject % | 9.82 | 3.35 | 4.43 |
| DPMO | 98,168 19,677 | 33,499 | 44,282 |
| Process Capability (Ppk) | 0.21 | 0.52 | ‐NA‐ |
Response Table for Means
| L | S | B | E | A | P | R | A | S | S |
|---|---|---|---|---|---|---|---|---|---|
| 1 | 1.2893 | 1.0338 | 1.0053 | 1.0092 | 1.1997 | 0.9940 | 1.0120 | 0.9957 | 1.0062 |
| 2 | 0.7123 | 0.9678 | 0.9963 | 0.9925 | 0.8020 | 1.0077 | 0.9897 | 1.0060 | 0.9955 |
| Delta | 0.5770 | 0.0660 | 0.0090 | 0.0167 | 0.3977 | 0.0137 | 0.0223 | 0.0103 | 0.0107 |
| Rank | 9 | 5 | 6 | 4 | 8 | 7 |
Selected success stories of the Six Sigma implementation in industries
| A | N | B |
|---|---|---|
| Citibank group | Numerous benefits have been reported across different organisations of this group. They successfully halved their credit processing time and reduced internal call‐back time by 80% and external by 85%. Reduced the time between a customer first placing an order till the actual service delivery and the credit decision cycle from 3 days to just 1 day. The time taken to process a statement was also decreased from 28 days to 15 days only | |
| JP Morgan Chase (Global Investment Banking) | Improved customer experience in using bank's services such as account opening, balance enquiry, making transfers and payments via online or cheque mode; leading to increased customer satisfaction and a reduction in process cycle time by more than 30% | |
| British Telecom wholesale | Financial benefits of over $100 million, greater customer satisfaction, error reduction | |
| Bank of America | 24% reduction in customer complaints and a 10.4% increase in customer satisfaction | |
| Sun Trust Banks | Significant improvement in customer satisfaction | |
| American Express | Improved the external vendor related processes and reduced the numbers of non‐received renewal cards | |
| Motorola (1992 and 1999) | 1992: Achieved dramatic reduction in the defect levels of their process by about 150 times | |
| 1999: Huge financial gains of about $15 billion over 11 years | ||
| Honeywell | Profit of $1.2 billion | |
| Texas Instruments | Achieved a financial gain of over $ 600 million | |
| Johnson and Johnson | The financial gain of about $500 million | |
| Telefonica de Espana (2001) | Whooping increase in revenue by about 30 million in the first 10 months and gain in savings too | |
| Dow chemical/rail delivery project | Reported substantial savings in capital expenditures: of over $2.4 million | |
| AlliedSignal/ Bendix IQ brake pads | The cycle time of their production‐shipment process decreased by 10 months (18 to 8 months) | |
| AlliedSignal/ Laminates plant in South Carolina | Reaped a range of benefits: their capacity almost doubled, and punctuality in delivering goods reached 100% threshold level. Their cycle time and inventory had a reduction of 50% each | |
| DuPont/Yerkes plant in New York (2000) | Increase in yearly savings of over $25 million | |
| Seagate Technology | Gained financial profits of about £132 million in just 2 years | |
| General Electric | Increase in yearly financial savings by about $2 billion | |
| Hughes Aircraft's Missiles Systems Group / Wave soldering op. | The quality of their yields improved by about 1000% and productivity by 500% | |
| Raytheon/ Aircraft Integration Systems | Achieved a significant reduction (approx. 88%) in the inspection time spent on the depot maintenance process | |
| GE/ Railcar leasing business | Achieved a 62% reduction in the time spent at repair stops | |
| Radiology film library, Anderson cancer centre | Service quality improved | |
| Outpatient CT exam lab at the University of Texas | Preparation and waiting times for patients reduced from 45 min to 5 min Dramatic increase by 45% in daily numbers of examinations without an increase in workforce/ equipment | |
| Engineering and Construction sector | ||
| General Electric | 1997: made a profit of $320 million which was more than double their goal of $150 million, further in 1999, annual savings of 2 billion | |
| Volvo cars (Sweden) | Profit of over 55 million euro in the years 2000 and 2002 | |
| Anderson et al. (2006) | Business Unit of Transmission and Transportation Networks at Ericsson | Savings of over 200 million euro between the years 1997‐2003 |
Data collection plan
| I | W | W | W | H | W | W |
|---|---|---|---|---|---|---|
| 1 | Wafer Traceability | To with correlate differentpoor TTV | Every Lot | Data applicationcapture | Central BrowserDatabase | ‐ Lapping Op |
| 2 | TTV | KPOV, CTQ | Every wafer | Lapping upload ADE, Data | Central Database | CW Insp. Op |
| 3 | Slurry Mixing Time | KPIV | Every time fresh slurry prepared | Machine Setting (SOP) | Slurry Sheet | Lapping Op |
| 4 | Slurry Density | KPIV | Every slurry time prepared fresh | Manual Measurement | Control Charts | Lapping Op |
| 5 | Machine flowrate | KPIV | Every was changedtime loop | Manual Measurement | Control Charts | Lapping Op |
| 6 | Plate Shape | KPIV shape) (can affect wafer | Every Opertion 40 hr Time of | Using dial gauge | Plate Shape Sheet | Lapping Op |
| 7 | Recycle StatusSlurry | To different evaluate slurryimpact of | Every 5 mins | Data application capture | BMS Database | PSE Op |
| 8 | Active Agent Volume | KPIV (can affect slurry viscosity) | Every time fresh slurry prepared | Machine Setting (SOP) | Slurry Sheet | Lapping Op |
| 9 | Sun Gear Ratio | KPIV (can affect wafer rotation) | Any by engineertime changed | Machine Setting (SOP) | QA Records | Engineer |
| 10 | Bottom Plate Speed | KPIV (can affect wafer rotation) | Any by engineertime changed | Machine Setting (SOP) | QA Records | Engineer |
| 11 | Exhaust Timer | KPIV rotation)(can affect wafer | Any by engineertime changed | Machine Setting (SOP) | QA Records | Engineer |
| 12 | Acceleration Timer | KPIV rotation)(can affect wafer | Any by engineertime changed | Machine Setting (SOP) | QA Records | Engineer |
| 13 | Slurry Temperature | KPIV viscosity)(can affect slurry | Every slurry time preparedfresh | Machine Setting (SOP) | Slurry Sheet | Lapping Op |
| 14 | Plate Temperature | KPIV viscosity)(can affect slurry | At the start of shift | Digital thermometer | Lot SheetProcessing | Lapping Op |