■ In Semiconductor Manufacturing, "Cooling" and "Heating" Exist at the Same Time
For example, the inside of a process chamber is hot.
Right outside it there are
● Sensors
● Seals
● Wiring
● Control components
In other words, the structure is:
You want the inside hot.
You do not want the outside hot.
So
● Thermal insulation
● Cooling
● Sealing
● Heat shielding
are combined.
Such technology that separates places where you want heat to pass from places where you do not becomes important.
■ Keeping the Heater's Heat from Escaping to the Surroundings
When heating the process area,
if the heater’s heat escapes throughout the equipment, problems arise such as
● Power consumption increases
● Surrounding components become hot
● Thermal expansion increases
● It takes time for the temperature to stabilize
That is why a structure is required that heats only the necessary place and does not let heat escape to the surroundings.
Here,
● Thermal insulation materials
● Reflective materials
● Air layers
● Thin-film thermal insulation components
become important.
■ On the Other Hand, There Are Also Places Where You Want to Release Heat Immediately
RF power supplies.
Motor drivers.
Laser power supplies.
Control boards.
For such components, you want to release the generated heat outside as quickly as possible.
In other words, within a single piece of semiconductor manufacturing equipment,
technology to confine heat and technology to release heat are needed at the same time.
■ In Plasma Equipment, Heat and Electricity Become Problems at the Same Time
Equipment that uses plasma uses high-frequency power.
That is why
● Heat generation
● High voltage
● Electromagnetic noise
● Insulation
exist at the same time.
For example, around the electrodes, you want to release heat.
But electrically, you want to insulate.
Furthermore, you want to maintain vacuum.
In other words, it becomes a combined challenge of
heat × insulation × vacuum × noise.
■ Heat Also Matters for Insulating Materials
Using insulating films or insulating sheets can block electricity.
However, making the insulating material thicker can make it harder for heat to escape.
Thinner is advantageous for heat.
But it becomes more susceptible to
● Dielectric breakdown
● Pinholes
● Burrs
● Foreign matter
In other words, in semiconductor manufacturing equipment too, the requirement arises that
heat should pass through.
Electricity should not pass through.
This has a strong connection with OTIS.
■ In Vacuum Equipment, "Not Leaking" Is the Top Priority
Many processes in semiconductor manufacturing use vacuum environments.
Deposition.
Etching.
Ion implantation.
Vacuum is used in many other processes as well.
To maintain vacuum, the quality of
● O-rings
● Gaskets
● Seal materials
● Joints
is important.
Even a tiny gap affects vacuum performance.
In other words, not only heat, but airtightness is also important.
■ The Combination of High Temperature and Vacuum Makes Seal Materials Difficult
Around vacuum chambers, temperatures can rise.
Seal materials may be subjected simultaneously to
high temperature,
compression,
vacuum,
and chemicals.
As a result,
● Hardening
● Deformation
● Compression set
● Gas release
● Degradation
become problems.
In other words, it is not enough for seal materials just not to leak.
They must maintain performance over long periods even under temperature changes.
■ In Vacuum, Outgassing Is Also a Problem
In vacuum environments, trace gases released from inside materials also become a problem.
This is generally called
outgassing.
For example, if volatile components come out of
● Adhesives
● Resins
● Rubber
● Bonding agents
they may contaminate the inside of the chamber.
Because semiconductor manufacturing requires extremely high cleanliness,
materials must be chosen considering even what will come out in vacuum.
In other words,
being heat-resistant,
being able to adhere,
and being able to insulate
are not enough.
■ Outgassing May Increase as Temperature Rises
When materials are heated, volatile components inside may come out more easily.
That is why
an adhesive that has no problem at room temperature may not be usable in high-temperature vacuum.
In other words, components for vacuum equipment must be evaluated by combining
operating temperature × degree of vacuum × material.
■ In Cleanrooms, Foreign Matter Is Also a Serious Problem
In semiconductor manufacturing, small foreign particles affect product yield.
That is why components inside equipment are required to
● Shed little powder
● Not peel easily
● Not wear easily
● Produce little debris
For example, graphite.
Foam.
Adhesives.
If powder or debris comes out during processing or use, it may become a source of contamination inside the equipment.
In other words, processing quality relates not only to dimensions, but even to particle generation.
■ Foreign Matter Can Also Come from Die-Cut Edges
When films and adhesives are die-cut,
if the edge condition is poor,
● Fine debris
● Stringing
● Peeled fragments
may be generated.
Even where this would only be an appearance problem in general products,
in semiconductor manufacturing equipment it may lead to foreign matter contamination.
That is why control of
● Blades
● Dies
● Processing conditions
● Scrap removal
is important.
■ The Accuracy of Temperature Sensors Is Also Important
To control temperature precisely, it must be measured accurately.
However, even if the sensor itself is correct,
measurement results change depending on where it is mounted.
For example, directly above the heater.
A metal plate a little away.
Near cooling pipes.
Each has a different temperature.
In other words, the position of the temperature sensor itself becomes control design.
■ Contact Between the Sensor and the Object Is Also Important
If a temperature sensor is lifting off the object, it may not be able to measure the correct temperature.
There is air between the sensor and the metal plate.
Adhesive thickness varies.
The application position differs.
Then differences appear in the measured values.
In other words, temperature measurement also has the problem of
the contact interface.
Here too,
thin-film adhesives,
thermally conductive materials,
and high-precision application
may be important.
■ To Control Temperature, Also Consider "Heat Capacity"
In temperature control, there are requirements of
wanting to heat quickly
and wanting to cool quickly.
However, large metal parts have large heat capacity.
It takes time to change their temperature.
On the other hand, small, thin parts change temperature quickly.
In other words, there is the relationship that
the larger the heat capacity, the easier it is to stabilize, but the slower the response.
The smaller the heat capacity, the faster the response, but the more easily it fluctuates.
■ Higher Speed Also Makes Thermal Fluctuations Faster
In semiconductor manufacturing equipment, to improve productivity,
● High-speed transport
● High-speed positioning
● High-speed processing
● Higher output
are advancing.
Then heat generation from motors and power supplies also fluctuates more easily.
The faster the equipment becomes, the more easily temperature also moves.
In other words, it is necessary to achieve both improved productivity and temperature stability.
■ Motor Heat Affects Accuracy
Wafer transport.
Stage movement.
Robot arms.
These use motors.
Motors generate heat when they move.
The heat causes metal parts around the motor to expand.
As a result,
● Axis position
● Stage height
● Alignment position
may change.
In other words, it is necessary to consider drive performance and thermal accuracy at the same time.
■ Cooling Pipes Also Affect Equipment Accuracy
Using water cooling can efficiently remove heat inside the equipment.
However, cooling pipes have problems such as
● Water temperature fluctuation
● Flow fluctuation
● Pipe vibration
● Condensation
If the cooling water temperature changes, the temperature of equipment components also changes.
If the flow rate changes, the cooling capacity also changes.
In other words,
it is not necessarily the case that adding water cooling stabilizes temperature.
The cooling side must also be stable.
■ Overcooling Causes Condensation
When equipment components are lowered well below the ambient temperature, moisture in the air may condense.
In semiconductor manufacturing equipment, moisture and foreign matter are major problems.
That is why it is not the case that the lower the temperature, the better.
It is necessary to cool while considering
temperature,
humidity,
and dew point.
■ The Interface with Heat Exchangers and Cooling Plates Is Also Important
When attaching a cooling plate to equipment components,
materials such as
● TIM
● Thermally conductive sheets
● Grease
may be used in between.
Here, if
● The surface is warped
● Contact pressure is insufficient
● There are air bubbles
● The material is too thick
heat cannot be sufficiently transferred to the cooling plate.
In other words, in semiconductor manufacturing equipment too,
the interface can become the bottleneck before the performance of the cooling equipment.
■ In High-Precision Equipment, "Making Temperature Uniform" Is Also Important
When cooling a component,
if only one part is cooled strongly, only that part contracts.
Then the component warps.
In other words,
even if the average temperature is lowered, accuracy deteriorates if temperature differences are created.
That is why there are cases where making the temperature distribution uniform is more important than lowering temperature.
■ Thermal Insulation Materials Do Not Just Stop Heat
Using thermal insulation materials
can suppress heat transfer from hot parts to the surroundings.
However, inserting insulation materials also changes
● Temperature distribution
● Thermal response
● Surrounding dimensions
● Equipment start-up time
In other words, thermal insulation materials are not only materials that reduce heat loss,
but also materials that create the temperature distribution of the equipment.
■ Around Heaters, the Heat Resistance of Adhesives Becomes Important
Thin-film heaters.
Sensors.
Insulating materials.
Adhesives are sometimes used to fix these.
However, at high temperatures,
● Reduced adhesive strength
● Softening
● Creep
● Outgassing
● Peeling
may occur.
That is why it is necessary to choose not materials that can adhere,
but materials that are stable over the long term at the operating temperature.
■ With Thermal Cycling, Components Expand and Contract Many Times
The equipment operates.
The temperature rises.
It stops.
The temperature falls.
Through this repetition,
● Metals
● Films
● Adhesives
● Seal materials
expand and contract repeatedly.
When dissimilar materials are laminated, stress arises from differences in thermal expansion.
As a result,
● Peeling
● Warping
● Cracks
● Misalignment
may occur.
In other words, in semiconductor manufacturing equipment, it is necessary to look not only at the initial state,
but at the state after temperature cycling.
■ Summary
Heating and cooling exist at the same time.
The combined conditions of vacuum, sealing, outgassing and clean environments.
The position and contact state of temperature sensors governing measurement accuracy itself.
The possibility that cooling itself creates new problems, such as cooling pipes and condensation.
And components fatiguing little by little through repeated temperature cycles.
All of these are “invisible changes” inside the equipment.
Each may look like a small phenomenon.
However, as they accumulate, the temperature distribution and positional accuracy of the equipment quietly break down.
In Part 3, we look at why such tiny changes in heat and dimensions extend all the way to the accuracy of an ultra-fine product: the semiconductor.
Column Supervisor: Koji Kakumoto (President, OTIS Co., Ltd.)
After studying abroad and working in planning and development at a trading company, he joined OTIS Co., Ltd. in 2011. While primarily working in the Corporate Planning Department, he has also served concurrently in manufacturing and technical divisions, and since 2018 has served as President, working to drive business growth and strengthen the organization.
This article is a general technical explanation intended for educational purposes and does not refer to any specific company, product, or technology.
