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SEMI E136-1104 © SEMI 2004 2 connect various parts of the RF power delive r y system. 5.2.2 calorimeter — an RF power measurement instrument using differential tem perature and mass flow rate to determine true heating po…

SEMI E136-1104 © SEMI 2004 1

SEMI E136-1104

TEST METHOD FOR DETERMINING THE OUTPUT POWER OF RF

GENERATORS USED IN SEMICONDUCTOR PROCESSING

EQUIPMENT RF POWER DELIVERY SYSTEMS

This test method was technically approved by the Global Metrics Committee and is the direct responsibility

of the North American Metrics Committee. Current edition approved by the North American Regional

Standards Committee on July 11, 2004. Initially available at www.semi.org September 2004; to be published

November 2004.

1 Purpose

1.1 The purpose of this test method is to provide an

accurate method for measuring the output power of RF

generators used in RF power delivery systems for

semiconductor processing equipment to support SEMI

E113.

2 Scope

2.1 This test method specifies the testing procedures

and test equipment required for determining the true

output power (i.e., heating power) output of RF

generators. This test method uses a calorimetric power

meter, which was calibrated previously using precise

DC substitution techniques as a reference standard.

2.2 The primary focus for this test method is

semiconductor processing equipment including, but not

limited to, the following equipment types:

 Dry etch equipment, and

 Film deposition equipment (CVD and PVD).

NOTICE: This standard does not purport to address

safety issues, if any, associated with its use. It is the

responsibility of the users of this standard to establish

appropriate safety and health practices and determine

the applicability of regulatory or other limitations prior

to use.

3 Limitations

3.1 This test method is meant to provide a general

means of measuring the true output power of RF

generators operating over a wide range of frequency

and power. Limitations in the frequency and power

coverage of this method are determined by the

individual system components chosen.

3.2 This test method assumes that the transmission

system characteristic impedance is 50 .

3.3 International, national, and local codes, regulations

and laws should be consulted to ensure that the

equipment and procedures meet regulatory

requirements in each location.

3.4 Certain safety issues associated with the test

procedures themselves are mentioned as a reminder that

safety procedures are necessary for safe conduct of the

test.

3.5 This standard does not address any safety or

performance issues related to RF emissions or electrical

codes (e.g., Underwriter’s Laboratory, Inc. (UL), the

National Electrical Code (NEC



), Federal

Communications Commission (FCC)). It is the

responsibility of the users of this standard to conform to

the appropriate local codes and regulations as applied to

this type of equipment, some of which are covered by

referenced documents.

4 Referenced Standards

4.1 SEMI Standards

SEMI E113 — Specification for Semiconductor

Processing Equipment RF Power Delivery Systems

SEMI E114 — Test Method for RF Cable Assemblies

Used in Semiconductor Processing Equipment RF

Power Delivery Systems

NOTICE: Unless otherwise indicated, all documents

cited shall be the latest published versions.

5 Terminology

5.1 Abbreviations and Acronyms

5.1.1 AC — Alternating Current

5.1.2 CVD — Chemical Vapor Deposition

5.1.3 DC — Direct Current

5.1.4 NIST — National Institute for Standards and

Technology

5.1.5 PVD — Physical Vapor Deposition

5.1.6 RF — Radio Frequency

5.1.7 VSWR — Voltage Standing Wave Ratio

5.2 Definitions

5.2.1 cable assembly — the section of cable

(transmission line), including the connectors, used to

SEMI E136-1104 © SEMI 2004 2

connect various parts of the RF power delivery system.

5.2.2 calorimeter — an RF power measurement

instrument using differential temperature and mass flow

rate to determine true heating power.

5.2.3 harmonic frequency — the harmonic frequencies

are defined as integer multiples of the fundamental

frequency. For example, the second harmonic of 13.56

MHz is 27.12 MHz.

5.2.4 RF generator — a component in the RF power

delivery system used to develop RF energy.

5.2.5 RF termination — a device for terminating RF

transmission systems, and converting RF electrical

energy into heat. RF terminations normally have values

that are the same as the characteristic impedance of the

transmission system.

5.2.6 RF load — another term used to describe an RF

termination.

6 Test Apparatus

6.1 Calorimetric Power Meter — This instrument is

designed to be used in conjunction with a high

efficiency water-cooled RF termination, rated for the

maximum power output of the RF generator. Typical

calorimetric power meters use internal thermocouple-

or thermistor-type temperature sensors, a precision

coolant flow meter, and processing circuits for storage

of calibration constants and coolant physical

characteristics. Choose instruments capable of

providing a power measurement accuracy of ± 1% after

calibration at a specific power level.

6.2 Water-Cooled RF Termination — This device

provides a low VSWR (i.e., high return loss)

termination for the testing of the RF generator. Use an

RF termination sized appropriately for the RF generator

under test. Finally, use an RF termination capable of

dissipating DC energy, without damage due to the

effects of electrolysis. The return loss of the RF

termination, including the interconnecting cable

between the RF generator and the termination shall be

no less than 30 dB. This return loss ensures maximum

power transfer between the RF generator and the

calorimeter.

NOTE 1: See Section 7 for safety-related recommendations

related to RF terminations.

6.3 Voltage and Current Meters — These meters are

used to measure the voltage and current presented to the

calorimeter load during the DC calibration of the

calorimeter. These instruments shall have a certificate

indicating NIST traceability. Choose meters capable of

voltage and current measurement accuracy of less than

0.2%.

6.4 Calibration Power Supply — This power supply is

used as a source of clean DC energy for the purposes of

calibrating the calorimetric power meter. Use a power

supply sized for the calibration to be performed and that

provides a very stable output at all levels.

6.5 Cables and Connectors — Various interconnecting

cables are required to perform the tests outlined in this

test method. These include low-loss cables to connect

the DC power source to the measuring instrument and

to the RF load, in addition to low-loss RF cables and

connectors to connect the RF generator output to the

load.

6.5.1 In order to keep cable losses to a minimum,

minimize the lengths of interconnecting cables.

6.5.2 In addition, compensate for the losses associated

with interconnecting cables used.

NOTE 2: For example, if 6 m (20 feet) of #10 AWG copper

wire is used to connect the DC supply to the calorimeter, this

wire will add approximately 0.04  of resistance between the

DC source and the 50  termination. Using a DC supply

voltage of 500 V terminated by 50  (i.e., 5 kW), this will

result in a loss of about 4 W in the copper wire.

6.5.3 Adjust the reading obtained by the calorimeter

according to the cable loss value.

NOTE 3: For example, suppose that an RF generator,

operating at 13.56 MHz and developing 3 kW is connected to

the calorimeter through a 6 m (20-foot) length of RG-217/U

coaxial cable. RG-217/U coaxial cable has a loss

specification of 0.41 dB per 30 m (100 feet) of cable at 13.56

MHz. Therefore, for 6 m (20 feet) of cable, the loss would be

approximately 0.41/5, or 0.082 dB. If the RF generator is

developing 3 kW, this means that approximately 2.944 kW

would appear at the calorimeter due to the cable loss.

7 Safety Precautions

NOTE 4: The tests described in this test method involve

using low-output power test instrumentation (typically less

than 10 mW).

7.1 Work should be conducted in accordance with

local safety requirements and test device

manufacturer’s recommended safety procedures.

7.2 The area immediately surrounding the test setup

should be kept free and clear of unnecessary equipment

and materials.

7.3 Testing personnel should ensure they have

SEMI E136-1104 © SEMI 2004 3

adequate lifting devices for large weights such as long

RF cables and generators themselves.

7.4 Persons performing tests should determine which

method of water cooling of the resistor in the RF

termination is utilized by the test device manufacturer

and should take steps to ensure safe use of the device.

7.4.1 Cooling-water flow rates should be appropriate to

the test device manufacturer’s recommendations for

cooling of the power load level being tested. Consult

the RF generator operating manual load specifications

for this information.

7.4.2 An RF termination using internal resistor cooling

only is highly recommended because such resistors (of

the tubular ceramic, thin film type) are usually cooled

by routing the coolant to the inside of the ceramic tube

and away from the resistive film, thereby eliminating

the possibility of electrolysis affecting the resistive

film.

7.4.3 In an alternative method, the coolant is routed on

both the inside and the outside of the resistor. While

this method provides for more efficient cooling, the

proximity of the coolant to the resistive film can

potentially result in damage to the resistive film caused

by electrolysis generated by the DC energy passing

through the fluid in the termination.

7.4.3.1 For this reason, if an RF termination using both

internal and external cooling is used, it is important to

periodically check the resistor for damage due to

electrolysis. This can be done easily by measuring the

resistance of the load resistor using a simple digital

multimeter.

7.4.3.2 With the RF termination disconnected from the

RF cable, place one probe on the center conductor of

the termination, and the other probe on the

termination’s outer conductor.

7.4.3.3 Measure the DC resistance of this path. If the

DC resistance is more than 53 , replace the resistor in

the termination.

7.5 In order to prevent the possibility of ground loops

between the RF generator and the calorimeter system,

be sure to operate the calorimeter and the RF generator

on the same AC supply.

8 Test Setup for RF Generator Power Output

Test

8.1 The test setup for the RF generator output power

test consists of the RF generator connected to the

calorimeter power meter through a length of coaxial

cable.

8.2 Prior to making any measurements, calibrate the

calorimeter power meter using a source of stable DC

energy.

9 Test Procedure for Determining RF

Generator Output Power

9.1 Calorimetric power meters provide excellent

reference standards for the measurement of RF energy

in that they are capable of measuring the true heating

power of a waveform, including any harmonic- or

nonharmonic-related frequency components. The

technique employed for this test is to first calibrate the

calorimetric power meter with DC energy, which can

be very precisely determined. Then, use two digital

multimeters (e.g., Fluke™ 87 or equivalent) to

determine the actual DC power applied to the

calorimeter. Finally, once the DC calibration has been

performed at a particular power level, connect the

output of the RF generator under test to the calorimeter

and measure the output power of the RF generator. The

basic steps involved in the use of this system are

outlined below.

9.2 Calibrate the Calorimeter — Calibrate the

calorimeter with the stable DC power supply, using the

two digital multimeters to read the voltage and current

applied to the calorimeter’s RF load.

9.3 Connections — Connect the DC power supply, the

digital multimeters, and the RF load according to

Figures 1 and 2. Make the connections between the

multimeters, the DC power supply, and the RF load

using high-quality low-loss cable and high-quality

corrosion-free cable terminations.

Figure 1

Calorimeter Calibration Configuration