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Oxide Etch Application Notes
OVERVIEW
To accurately understand the abatement issues for any given process, it is necessary to understand the process in the tool, the chemicals that are put in, and how the process modifies them. The following overview represents our understanding of this process and is the basis of this recommendation.
The removal of thin films from the surface of a wafer is an important step in the manufacture of today's semiconductor devices. One of the most important removal steps is the patterning of silicon dioxide (often simply called oxide) layers which serve as transistor gates, and as insulation between layers of a microchip. The wafer is first patterned by photolithography, and then the etching process removes the exposed areas, transferring the pattern to the oxide layer. Oxide etch processes operate using reactive ion etching, RIE. In this process, the etch gases are introduced into an electrical field. This field ionizes the gases, creating a plasma full of energetic ions. This plasma etches the wafer through several mechanisms. The first involves actual physical etching. This occurs when the highly excited ions smash into the wafer, breaking off a part of the surface. The second mechanism utilizes the high reactivity of the ionic species present in the plasma. The reactive ionic species diffuse to the wafer surface where they react with the exposed layer to form a volatile by-product that is swept away in the effluent gas stream. Applied Materials (AMAT) offers oxide etch on their versatile Centura plasma platform. Their Induced Plasma Source (IPS) has been well proven for this application. Also available from AMAT is the Precision 5000. Along with IPS chamber, AMAT offers the eMxP+ chamber. These chambers can operate alone or with other chambers on a single Centura platform, offering a wide range of flexibility for customers. The actual chemistry of the plasma involves many complex reactions. The exact reactions are difficult to quantify, and many of the by-products only last a few fleeting moments. However, we expect that a majority of the effluent will be mineral acids like HF, halogen gases, like F2, and etch by-products, like SiF4. The amount of fluorine compounds created will depend on the efficiency of the plasma. There could also be some CO2 present from plasma reactions involving organic compounds. Different ratios of process gases are used to affect the exact etch rate and selectivity
PROCESS RECIPE
Although there are many different layers which can be etched using a metal etch process, the basic recipe features Cl2 and BCl3. SF6 is often added when etching tungsten layers. Some newer applications feature recipes which include even more fluorinated hydrocarbons. However, these recipes are still in the minority to the gases shown below.
ABATEMENT CONSIDERATIONS
As with most semiconductor processes, there are many abatement considerations for an oxide etch process. To illustrate the dangerous nature of oxide etch processes, the following chart of exposure limits has been prepared. TLV is the Threshold Limit Value for a gas. This is the maximum time weighted average exposure for an 8 hour period. IDLH is the level which is an Immediate Danger to Life and Health. This is the concentration which represents a danger after 15 minutes of exposure. This table includes all the gases which might be present in this process, including process byproducts.
It is easy to see the dangers that the effluent of oxide etch processes presents to worker health. Point of use scrubbing protects fab personnel by removing toxic and dangerous acid gases at the earliest possible point. This greatly reduces the dangers associated with a leak in the exhaust system.
Another abatement consideration is environmental protection. All of the precursor gases used in this process have been identified as contributing to global warming. Some facilities regulate the amount of these gases which are allowed to escape into the atmosphere. At these facilities, PFC destruction is the main goal of abatement. At other facilities, the removal of acid gas by-products is the goal. Another concern with oxide etch is the removal of etch by-products, like SiF4. This condensable solid can deposit out in exhaust piping, and can eventually clog the pipes.
BAZM SOLUTION: Vector
Depending upon the abatement objections, either a water scrubber such as the Vector or GST SDS or if PFC gas abatement is desired a Durian Plasma or Dragon Fuel based system can be used. The Vector water scrubber has evolved over many years, and now showcases many features which make it an excellent choice for the abatement of poly etch processes. The Vector Ultra is capable of handling up to four process inlets, allowing a single Vector Ultra scrubber to abate one furnace with up to four processing tubes.
BAZM recommends that each process chamber be plumbed to a separate inlet on the Vector Ultra. The Vector also allows for multiple tools to be abated by a single scrubber, if the number of chambers does not exceed four. The effluent gases from the Etch chamber first enter the Vector scrubber through the entry device. The entry lay out is specially designed to prevent clogging, by introducing a co-annular flow of nitrogen with the process gas. This flow is designed to shield the process gas from back-streaming water vapors. This keeps solid forming reactions within the main body of the scrubber, and out of the entry pipe. Furthermore, the inner walls of the lower entry area are continually washed with water, which sweeps away any solids which might try to form in that area. In a typical poly etch application, the entry should require simple, routine cleaning about once every month.
After leaving the entry, the process gas contacts the water in the main scrubber barrel. The water is introduced at the top of the packed column through a rotating spray bar, which helps provide a uniform flow of water through the packed bed of the column. The main barrel is a fused column construction. This eliminates corners where gas can escape scrubbing, and the fused construction eliminates glued joints which can leak. The packing material used inside the column provides a high surface area, allowing for excellent mass transfer from the gas phase to the liquid phase. This helps the Vector scrubbers to achieve such high efficiency.
After absorbing process gases, the liquid exits the packing and flows into a sump at the bottom of the unit. A pump at the bottom of the unit removes water from the sump. Most of this flow from the sump is circulated through the system via the spray bar. The remainder of the flow is pumped to the drain. The pressurized drain system is an integral design of the Vector unit and not an externally attached option. This enables the unit to be placed in the subfab below the waste drain level. Level switches in the sump of the scrubber regulate the sump level. Fresh water is metered in to replenish the water in the sump of the scrubber.
The processes gases are then sent through a final packed column. The secondary polishing column is a standard part of the Vector Ultra. The polishing scrubber bed fits directly into the exhaust pipe of the unit. With this feature, incoming fresh water for the Vector is introduced at the top of the polishing scrubber column. From there, it flows counter-currently to the exiting gas, providing additional scrubbing capacity. This polishing scrubber provides excellent increases in overall adsorption efficiency for ammonia and other water soluble and acid gases. This helps the Vector scrubbers to achieve such high efficiency.
ABATEMENT CHEMISTRY
HF(g) à HF(aq)
F2 (g) + H2O à HF(aq)
SiF4 (g) + 2 H2O à 4 HF(aq) + SiO2
Any PFC gases, like CF4, C2F6, or SF6 which survive the plasma will not be abated by a Vector scrubber. Any CO2 which might form in the plasma will pass through the water scrubber as well.
EFFICIENCY
Process Gases:
CHF3, CH2F2, CF4,
C2F6, C4F8, SF6,
O2
Process By-products:
HF, SiF4, F2
For any addition questions, please contact BAZM Solution - your gas abatement expert.
To accurately understand the abatement issues for any given process, it is necessary to understand the process in the tool, the chemicals that are put in, and how the process modifies them. The following overview represents our understanding of this process and is the basis of this recommendation.
The removal of thin films from the surface of a wafer is an important step in the manufacture of today's semiconductor devices. One of the most important removal steps is the patterning of silicon dioxide (often simply called oxide) layers which serve as transistor gates, and as insulation between layers of a microchip. The wafer is first patterned by photolithography, and then the etching process removes the exposed areas, transferring the pattern to the oxide layer. Oxide etch processes operate using reactive ion etching, RIE. In this process, the etch gases are introduced into an electrical field. This field ionizes the gases, creating a plasma full of energetic ions. This plasma etches the wafer through several mechanisms. The first involves actual physical etching. This occurs when the highly excited ions smash into the wafer, breaking off a part of the surface. The second mechanism utilizes the high reactivity of the ionic species present in the plasma. The reactive ionic species diffuse to the wafer surface where they react with the exposed layer to form a volatile by-product that is swept away in the effluent gas stream. Applied Materials (AMAT) offers oxide etch on their versatile Centura plasma platform. Their Induced Plasma Source (IPS) has been well proven for this application. Also available from AMAT is the Precision 5000. Along with IPS chamber, AMAT offers the eMxP+ chamber. These chambers can operate alone or with other chambers on a single Centura platform, offering a wide range of flexibility for customers. The actual chemistry of the plasma involves many complex reactions. The exact reactions are difficult to quantify, and many of the by-products only last a few fleeting moments. However, we expect that a majority of the effluent will be mineral acids like HF, halogen gases, like F2, and etch by-products, like SiF4. The amount of fluorine compounds created will depend on the efficiency of the plasma. There could also be some CO2 present from plasma reactions involving organic compounds. Different ratios of process gases are used to affect the exact etch rate and selectivity
PROCESS RECIPE
Although there are many different layers which can be etched using a metal etch process, the basic recipe features Cl2 and BCl3. SF6 is often added when etching tungsten layers. Some newer applications feature recipes which include even more fluorinated hydrocarbons. However, these recipes are still in the minority to the gases shown below.
| Process Gas | Flow Rate |
|---|---|
| CHF3 | 100 sccm |
| C5F8 | 30 sccm |
| CH2F2 | 30 sccm |
| CF4 | 100 sccm |
| C4F8 | 30 sccm |
| SF6 | 100 sccm |
| CO | 500 sccm |
| O2 | 50 sccm |
| N2 | 100 sccm |
| Ar | 100 sccm |
ABATEMENT CONSIDERATIONS
As with most semiconductor processes, there are many abatement considerations for an oxide etch process. To illustrate the dangerous nature of oxide etch processes, the following chart of exposure limits has been prepared. TLV is the Threshold Limit Value for a gas. This is the maximum time weighted average exposure for an 8 hour period. IDLH is the level which is an Immediate Danger to Life and Health. This is the concentration which represents a danger after 15 minutes of exposure. This table includes all the gases which might be present in this process, including process byproducts.
| Gas | TLV | IDLH |
|---|---|---|
| HF | 3 ppm | 30 ppm |
| F2 | 0.1 ppm | 25 ppm |
| C5F8 | 2 ppm | -- |
| SiF4 | 25 ppm | 100 ppm |
| CHF3 | 1000 ppm | -- |
| CH2F2 | 1000 ppm | -- |
| CF4 | 1000 ppm | -- |
| C4F8 | 1000 ppm | -- |
| SF6 | 1000 ppm | -- |
It is easy to see the dangers that the effluent of oxide etch processes presents to worker health. Point of use scrubbing protects fab personnel by removing toxic and dangerous acid gases at the earliest possible point. This greatly reduces the dangers associated with a leak in the exhaust system.
Another abatement consideration is environmental protection. All of the precursor gases used in this process have been identified as contributing to global warming. Some facilities regulate the amount of these gases which are allowed to escape into the atmosphere. At these facilities, PFC destruction is the main goal of abatement. At other facilities, the removal of acid gas by-products is the goal. Another concern with oxide etch is the removal of etch by-products, like SiF4. This condensable solid can deposit out in exhaust piping, and can eventually clog the pipes.
BAZM SOLUTION: Vector
Depending upon the abatement objections, either a water scrubber such as the Vector or GST SDS or if PFC gas abatement is desired a Durian Plasma or Dragon Fuel based system can be used. The Vector water scrubber has evolved over many years, and now showcases many features which make it an excellent choice for the abatement of poly etch processes. The Vector Ultra is capable of handling up to four process inlets, allowing a single Vector Ultra scrubber to abate one furnace with up to four processing tubes.
BAZM recommends that each process chamber be plumbed to a separate inlet on the Vector Ultra. The Vector also allows for multiple tools to be abated by a single scrubber, if the number of chambers does not exceed four. The effluent gases from the Etch chamber first enter the Vector scrubber through the entry device. The entry lay out is specially designed to prevent clogging, by introducing a co-annular flow of nitrogen with the process gas. This flow is designed to shield the process gas from back-streaming water vapors. This keeps solid forming reactions within the main body of the scrubber, and out of the entry pipe. Furthermore, the inner walls of the lower entry area are continually washed with water, which sweeps away any solids which might try to form in that area. In a typical poly etch application, the entry should require simple, routine cleaning about once every month.
After leaving the entry, the process gas contacts the water in the main scrubber barrel. The water is introduced at the top of the packed column through a rotating spray bar, which helps provide a uniform flow of water through the packed bed of the column. The main barrel is a fused column construction. This eliminates corners where gas can escape scrubbing, and the fused construction eliminates glued joints which can leak. The packing material used inside the column provides a high surface area, allowing for excellent mass transfer from the gas phase to the liquid phase. This helps the Vector scrubbers to achieve such high efficiency.
After absorbing process gases, the liquid exits the packing and flows into a sump at the bottom of the unit. A pump at the bottom of the unit removes water from the sump. Most of this flow from the sump is circulated through the system via the spray bar. The remainder of the flow is pumped to the drain. The pressurized drain system is an integral design of the Vector unit and not an externally attached option. This enables the unit to be placed in the subfab below the waste drain level. Level switches in the sump of the scrubber regulate the sump level. Fresh water is metered in to replenish the water in the sump of the scrubber.
The processes gases are then sent through a final packed column. The secondary polishing column is a standard part of the Vector Ultra. The polishing scrubber bed fits directly into the exhaust pipe of the unit. With this feature, incoming fresh water for the Vector is introduced at the top of the polishing scrubber column. From there, it flows counter-currently to the exiting gas, providing additional scrubbing capacity. This polishing scrubber provides excellent increases in overall adsorption efficiency for ammonia and other water soluble and acid gases. This helps the Vector scrubbers to achieve such high efficiency.
ABATEMENT CHEMISTRY
HF(g) à HF(aq)
F2 (g) + H2O à HF(aq)
SiF4 (g) + 2 H2O à 4 HF(aq) + SiO2
Any PFC gases, like CF4, C2F6, or SF6 which survive the plasma will not be abated by a Vector scrubber. Any CO2 which might form in the plasma will pass through the water scrubber as well.
EFFICIENCY
| Gas | DRE |
|---|---|
| F2 | 99% |
| HF | >99% |
| SiF4 | >99% |
Process Gases:
CHF3, CH2F2, CF4,
C2F6, C4F8, SF6,
O2
Process By-products:
HF, SiF4, F2
For any addition questions, please contact BAZM Solution - your gas abatement expert.
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