2nd Asian IM User Group Meeting in Japan

1. 2nd Asian IM User Group Meeting in Japan SAMSUNG 2001.09.13.

2. Short Summary This TRIZ application case was done by researchers of SAIT(Samsung Advanced Institute of Technology), not by TRIZ specialist, although there was help from TRIZ specialist. They had 40 hours TRIZ lesson at company, so they just knew the concept of Contradiction and could use Techoptimizer As in #9 slide, as soon as they encountered problem, they recognized it as physical contradiction. But with that contradiction expression they could not adopt 4 principles of solving physical contradiction. At that time, TRIZ specialist helped them and converted physical contradiction in another expression : TRIZ specialist thought earlier expression was the result of mental inertial of professional of specific area which had deep relationship with process of manufacturing, dry etching process. As soon as converting physical contradiction, they could solve it by "Separation by Space Principles". As in #15, 16, the typical process of solving problem could be shown. In generally, although they could solve one problem, frequently, another problem occur after solving one problem. As in this presentation, researchers regarded it as Technical Contradiction. So they used Contradiction Table in Techoptimizer. In this case, they could find exactly the same example of principle named "self-aligned process". Besides solving current loss problem by uniform shape of p-metal, they could additionally remove the most critical and difficult process, so they achieved quantum increase in yield. In this case, some guy could say they are too lucky. But it is the more difficult to deny the powerfulness of contradiction table and Principle module of Techoptimizer. In summary, from the first case, SAIT TRIZ specialist (Hyo June Kim, Nikolai Shpakovsky) learned the importance of expression of Contradiction and role of mental inertia at expression. From the second case, also learned how to formulate the technical contradiction from typical problem solving process.

3. Design Verify • Project definition - Technology Roadmap - Voice of customer • CTQ selecting - Threshold Current (Ith) - Variance of Ith • Process Mapping - Selecting Essential steps for CTQ • Ridge shape change by TRIZ • p-metal process Improvement by TRIZ • Oxidation Process optimization by DOE • Property evaluation • Verification of variance of Ith • Strategy - Reducing Ith by Ridge shape change - Reducing variance of Ith by p-metal process improvement and optimization of oxide process <Strategy> - Reducing IthRidge shape change  TRIZ - Reducing variance of Ithp-metal process improvement  TRIZ - Reducing variance of Ithoptimization of oxide process DOE Measure Analyze Define 6 s Process for GaN Laser Diode

4. D M A D V BeforeTRIZ in 6 sigma 40 mA, 6V 200mA, 6.7V

5. D M A D V Current (mA) Operating Current: 140mA Life time: 1.7 hr Time (min) Project Definition CTQ Selection • Problem Statement • - Life time of GaN Laser Diode • present : 1.7 hr (at CW 1mW, 20oC) • - Threshold Current (Ith) • present : 200 mA • variance of Ith : 105 mA • Objectives • - Life time of GaN Laser Diode > 1000 hr • - Reducing of Ith : Ith >200 mA → Ith ≤ 50 mA • - Improvement of Ith variance : s(Ith) = 105 mA →s(Ith)≤ 10 mA

6. D M A D V 1 8 Critical step for CTQ variance of Ith 2 9 Critical step for CTQ Ith 3 10 4 11 Critical step for CTQ variance of Ith 12 5 6 13 7 Process Mapping Fabrication Process

7. D M A D V Strategy for each critical process step • Ith • dry etching for ridge formation • - present : 0.2 mm etching depth • from active layer • Variance of Ith • p-metal layer deposition • - present : formation of 1.5 mm width • p-metal on the 2 mm ridge • passivation layer deposition • - present : BOE time < 40 sec TRIZ TRIZ DOE Preparing strategy

8. D M A D V Device Fabrication n Ridge wave guide Ridge wave guide etching w p-electrode SiO Facet Etching w 2 GaN / p-Al Ga N Passivation layer deposition p-Al Ga N w 0.14 0.86 p- GaN 0.2 0.8 MD-SLS w Formation of n-electrode Cladding layer InGaN / InGaN MQW n- GaN w Formation of p-electrode GaN / n-Al Ga N n-electrode 0.14 0.86 Bonding metal & mirror coating w n- GaN Ridge wave guide part : n (0001) Sapphire Substrate Critical effect to electric property of LD. Especially depending on depth of ridge. Dry Etching for Ridge Formation:TRIZ Initial situation

9. D M A D V Shallow ridge etching depth n Current spreading problem w GaN / n-Al Ga N 0.14 0.86 Increase Threshold current w n- GaN Sapphire Substrate Physical Contradiction : Ridge etching depth must deep and must not deep Optical loss GaN / n-Al Ga N 0.14 0.86 Deep ridge etching depth n n- GaN w Optical Loss w Threshold current Increase Sapphire Substrate Dry Etching for Ridge Formation:TRIZ Problem refinement

10. D M A D V Must Deep Must Not Deep Physical Contradiction : Ridge etching depth must deep and must not deep Separation by Time Separation by Space … Dry Etching for Ridge Formation:TRIZ Solution of Contradiction

11. D M A D V Physical Contradiction : Ridge etching depth must wide and must not wide Physical Contradiction : Ridge etching depth must deep and must not deep Must Wide Must Not Wide Dry Etching for Ridge Formation:TRIZ Solution of Contradiction

12. D M A D V Principle of Separation by Space Physical Contradiction : Ridge etching depth must wide and must not wide Upper part : narrow ridge prevent current spreading Lower part : wide ridge prevent optical loss Dry Etching for Ridge Formation:TRIZ Solution of Contradiction

13. D M A D V Dry Etching for Ridge Formation:TRIZ Solution of Contradiction

14. D M A D V Result Previous Ridge Ith > 200 mA Improved Ridge Ith < 50 mA Breakthrough ! Dry Etching for Ridge Formation:TRIZ

15. D M A D V Initial Situation Old structure of P-metal : Narrow P-metal Demerit : 1. Not enough removal of heat generated in GaN. Critical effect to life time 2. Too narrow P-metal make process difficult P-metal Layer Deposition : TRIZ

16. D M A D V Initial Situation New structure of P-metal : Wide P-metal Merit : Enough removal of heat generated in GaN. Good effect to life time Another problem appear : Loss of current Typical process of Problem solving. P-metal Layer Deposition : TRIZ

17. D M A D V Device Fabrication n m 2 m (Ridge Width) Ridge & Mesa Etching w m 1.5 m (Contact hole width) Passivation layer deposition w p-electrode SiO 2 Formation of n-electrode w GaN / p-Al Ga N p-Al Ga N 0.14 0.86 p- GaN 0.2 0.8 Formation of contact hole w MD-SLS Cladding layer Formation of p-electrode InGaN / InGaN MQW w n- GaN GaN / n-Al Ga N n-electrode Bonding metal & mirror coating w 0.14 0.86 n- GaN 1 Fine contact hole patterning (1.5mm x 500mm) Too fine 1.5mm width etching unstable process large variance of Ith Loss of current appear (0001) Sapphire Substrate 2 P-metal Layer Deposition : TRIZ Initial Situation

18. D M A D V Length of stationary objectLoss of energy 6. Multifunctionality 28.Mechanical interaction substitution Improving feature : increase P-metal width. Worsening feature : current loss at P-metal at outside of ridge Technical Contradiction P-metal Layer Deposition : TRIZ Problem refinement

19. D M A D V Reused PR mask (Multifunction) Oxide passivation layer Self-aligned Contact hole PR SiO 2 GaN / n-Al Ga N GaN / n-Al Ga N GaN / n-Al Ga N 0.14 0.86 0.14 0.86 0.14 0.86 n- GaN n- GaN n- GaN Sapphire Substrate Sapphire Substrate Sapphire Substrate Ridge Etching with PR/SiO mask 2 Reused SiO2 mask (Multifunction) 1.5mm width etching, contact hole patterning process was disappeared. Oxidation of etching surface P-metal Layer Deposition : TRIZ Solution of Contradiction

20. D M A D V Solution of Contradiction Contact hole formation with self-aligned process. Removing of most difficult process. No current loss by uniform shape of p-metal. 않고 Saving of process time. Improved reliability of process (yield) Improved reliability of product (variance of Ith) P-metal Layer Deposition : TRIZ

21. D M A D V Needs of DOE Not enough PECVD condition for SiO2 passivation layer. Optimization need n Results of DOE 1st DOE : 2(4) + 2 , selecting meaning factor : N2Ogas and Temperature. No corelationship between factors.2nd DOE : 2(2) + 1.3rd DOE : 2(2) + 2(2) + center point, another meaning factor SiH4/N2O ratio. 4th Response Surface Analysis n n n n Passivation Layer Deposition : DOE

22. D M A D V Variance of Ith : From 105mA to 16mA After Before 산포 105 mA  16 mA 임계전류 (Ith) 260 mA 42 mA AfterTRIZ in 6 sigma

23. D M A D V AfterTRIZ in 6 sigma 45 mA, 5V, 5mW 30 mA, 5.8V, 3mW