Top Down Method

1. Top Down Method Plasma Etch and the MATEC Plasma Etcher Simulation

2. Plasma (dry) Etch Advantages • No need for immersion • More precise control of etch feature sizes • More rapid than chemical etch without plasma assist • Plasma can create reactive species in gases • Plasma can be used to perform physical etch as the chemical etch proceeds

3. Examples of species to be etched • Aluminum • Silicon • Silicon Dioxide • Silicon Nitride • Tungsten • Polysilicon

4. Etch chemistry/method depends on • Surface deposition to be etched • What is immediately below the deposition • High selectivity will minimize damage to the layer below • Low selectivity can result in damage to the layer below • Etch Profile Required • Isotropic Etch (equal etch in both planes) • Anisotropic Etch (for tall, vertical sidewalls)

5. Dry Etch Materials and Etchants Source: MATEC Module 47 (M047NR01)

6. Etch Mechanisms • Damaging Mechanism • Ion bombardment breaks chemical bonds between the atoms on the surface • Increased RF energy and plasma etch • Dangling bonds are more attacked by free radicals • Surface atoms bond with radicals to form volatiles that are swept away • Anisotropic profile due to plasma etch • Normally used with oxides and nitride

7. Etch Mechanisms • Damaging Mechanism (2) • Plasma is also used to dissociate gases used plasma CF4 → CF3 + F plasma F + Si3N 4 → SiF4 + N (SF6 may also be used to provide fluorine) • Silicon tetrafluoride is volatile (from Xaio (2001) Introduction to Semiconductor Manufacturing Technology, Prentice-Hall, NJ)

8. Etch Mechanisms • Blocking Mechanism • Additional gaseous species added to process provides a passivation layer on the sidewall • Creates a boundary on sidewall to minimize etch to provide anisotropic etch profile • Commonly used in metal etch • Chlorine (Cl2) is commonly used for metal etch • Plasma breaks up Cl2 into Cl radicals that react with metals such as aluminum to form volatile by-products.

9. Etch Mechanisms • Blocking Mechanism (2) • Additional gaseous species added to process provides a passivation layer on the sidewall • BCl3 is commonly used for sidewall passivation • N2 and CF4 can also be used to improve passivation • More chemical etch and less plasma (physical) etch • The “recipe” includes several species

10. Plasma Etch Processes • Generally include several steps • Preparation of chamber • Temperature/Low Pressure • Cleaning (Nitrogen or other gas) • Concentration of vapors • Main Etch Process • Removal of volatile residues • Secondary Etch Process • Clearing Chamber/Return to initial conditions

11. Example Etch Recipe

12. Practice Questions Click once for each question. 1. What are the advantages of plasma aided etch? Anisotropic profiles, higher etch rates, and sidewall passivation 2. What must be considered in choosing dry etch chemical agents? Selectivity, the surface layer and the layer below 3. What are the two anisotropic mechanisms? Damaging and Blocking

13. MATEC Etch Simulator Guide (2) • Process the lot • Enter the concentration, power level, and other parameters for each processing step • The process is real time, so start and stop as indicated in the recipe • When complete, the simulator will verify if the process was successful • If unsuccessful, the simulator will show what needs to be changed • Print a copy and re-process until successful!

14. MATEC Dry Etch Simulator Guide • Select a “Lot Traveler” • A process document that indicates what processes a wafer undergoes and who • Start the MATEC Dry Etch training program • Enter your name and the information on the substrate to be etched, underlying layer, and thickness. Refer to MATEC tech manual • Select a recipe based on the species • Copy down etch parameters