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SEMI MF1239-0305 © SEMI 2003, 2005 4 7.5 Facilities for cleaning and drying wafers by a standard pro cess as customarily used in the labo ratory performing the test. 7.6 Scribe or L a ser Marker — For m arking the wafers…

SEMI MF1239-0305 © SEMI 2003, 2005 3

6 Summary of Test Method

6.1 A representative sample is selected from each group of wafers to be tested.

6.2 The initial value of interstitial oxygen concentration is measured by the infrared absorption method at the

desired points on each wafer.

6.3 The wafers are passed through one of two simulation thermal cycles. Cycle A consists solely of a precipitation

step. Cycle B consists of a nucleation step followed by a precipitation step.

6.4 After the thermal cycle, the oxide film is stripped and the final value of oxygen concentration is measured at the

same points on each wafer using the same technique and instrumentation as was used to determine the initial value.

6.5 The oxygen reduction is determined for each wafer (or for each point on each wafer) tested as the difference

between the initial and final values.

6.6 If all samples have the same initial oxygen concentration (within a narrow range), the average oxygen reduction

for each test condition (such as, group or position on wafer) is computed, and the appropriate comparisons made.

6.7 If the samples have initial oxygen concentrations that cover a relatively wide range, a plot of oxygen reduction

against initial oxygen concentration is made for each group or position. Again appropriate comparisons can be

made.

7 Apparatus

7.1 Infrared Absorption Spectrophotometer, as specified in SEMI MF1188 or DIN 50438, Part 1.

7.2 Resistance Heated Tube Furnace, capable of providing temperatures in the range from 750°C to 1050°C to

±2°C over the length required to contain the load of wafers to be tested. The furnace shall be fitted with the

following:

7.2.1 Gas Manifold — That allows dry oxygen and nitrogen to be mixed at the required ratios and flows, (see Table

1);

Table 1 Thermal Cycle Tests for Oxygen Precipitation in Silicon

Parameter Value

Test A 1050°C for 16 h

Test B 750°C for 4 h followed by 1050°C for 16 h

Furnace Ambient Nitrogen plus 5% dry oxygen

Gas Flow Rate 4.2 ± 0.2 L/min

Push/Pull Temperature 750°C

Push/Pull Rate 25 cm/min

Ramp Up Rate 10°C/min

Ramp Down Rate 5°C/min

For 155 mm diameter tube; for other diameters flow rate should be proportional to the cross sectional area of the tube.

7.2.2 Quartz, Polysilicon, or Silicon Carbide Tube — Of diameter appropriate for the wafers to be tested to isolate

the wafers from external contamination;

7.2.3 Quartz Boats — To hold the wafers during processing;

7.2.4 Loader — To allow controlled insertion of the quartz boat into the hot zone, (see Table 1); and

7.2.5 Laminar Flow Load Station — To permit loading of the wafers without adding contamination to the surfaces.

7.3 Facilities for processing wafers through chem-mechanical polishing, or bright acid etching to provide smooth,

flat surfaces.

7.4 Facilities for dipping the wafers in hydrofluoric acid prior to the oxygen determination in order to remove the

surface oxide film grown during thermal cycling. Suitable protective clothing, acid disposal facilities, and

ventilation shall be provided.

SEMI MF1239-0305 © SEMI 2003, 2005 4

7.5 Facilities for cleaning and drying wafers by a standard process as customarily used in the laboratory performing

the test.

7.6 Scribe or Laser Marker — For marking the wafers with unique identification (unless premarked wafers are

available).

8 Reagents and Materials

8.1 Hydrofluoric Acid — In accordance with SEMI C28, Grade 1.

8.2 Oxygen — In accordance with grade 2.5 of SEMI C54.

8.3 Nitrogen — In accordance with grade 5.2 of SEMI C59.

8.4 Deionized Water — With purity equal to or greater than that specified for Type E-1 in ASTM Guide D 5127.

9 Hazards

9.1 The acids used in these test methods are hazardous. All precautions normally used with these chemicals should

be strictly observed. Obtain and read the material safety data sheet prior to use of any chemical.

10 Selection and Preparation of Test Specimens

10.1 Choose test wafers from each group being tested in such a way as to cover the entire range of oxygen

concentration found in the group. Choose at least two wafers with oxygen concentration in each 0.5 ppm (IOC-88)

interval in the range. For example, if the oxygen concentration range of a group is 3 ppma, at least 12 wafers from

that group should be tested.

10.2 Select or prepare test wafers with thickness, resistivity, and surface finish as required by the oxygen test

method being used.

10.3 Identify each test wafer individually with an alphanumeric laser marking or a hand scribed code unless pre–

marked wafers are used.

10.4 Prepare the wafers in accordance with SEMI MF1188, SEMI MF1619, DIN 50 438/1, or JEITA EM-3504, as

applicable.

11 Procedure

11.1 Determine the initial interstitial oxygen concentration of each wafer to be tested at the center in accordance

with SEMI MF1188, SEMI MF1619, DIN 50 438/1, or JEITA EM-3504. If desired, measure the interstitial oxygen

concentration at other locations on each wafer as specified by an appropriate pattern in SEMI MF951. Record the

oxygen value(s), the wafer identification, and measurement locations. Record the date of the test and the instrument

used in measuring the oxygen concentration. See Figure 1 for a suggested data sheet format.

11.2 Clean and dry the wafers in accordance with the usual wafer cleaning procedure employed by the laboratory

performing the test.

11.3 Process the samples as soon after cleaning as possible. If the samples must be stored between cleaning and

processing, store in clean covered cassettes.

11.4 Heat-treat in accordance with Cycle A or Cycle B, (see Table 1). Record the date of the heat treatment and the

cycle used.

11.5 Strip the surface oxide from the wafers with hydrofluoric acid (HF), and thoroughly clean and dry them with

the usual wafer cleaning procedure employed by the laboratory performing the test.

11.6 Measure the post-heat treatment interstitial oxygen concentration at each point measured before heat treatment.

Use the same instrument, test method, and set up for this measurement as was used for the initial measurement.

Record each final oxygen concentration on the same data sheet as was used to record initial oxygen concentration.

4 As defined in SEMI MF1188, SEMI MF1619, DIN 50 438/1, or JEITA EM-3504.

Apply only to interpretation by Method 2 (see ¶12.2.2).

Average and standard deviation of initial O

and O

reduction apply only to interpretation by Method 1 (see ¶12.2.1).

Figure 1

Suggested Data Sheet Format

12 Calculations and Interpretation of Results

12.1 Subtract each final oxygen concentration value from the corresponding initial oxygen concentration value to

determine the oxygen reduction. Record the oxygen reduction.

12.2 Interpret the results by Method 1 or Method 2 as follows:

12.2.1 Method 1

12.2.1.1 Use this method when the desired target oxygen concentration is already known, when each group tested

has the same target oxygen concentration, and when the range of oxygen concentration values measured in each

group has a range less than 4 ppma (IOC-88). This method cannot be used if the average initial oxygen

concentrations of the groups tested differ by more than 0.5 ppma (IOC-88).

12.2.1.2 Determine the averages and standard deviations of the initial oxygen concentration and oxygen reduction

for each group of wafers tested.