Tungsten Film Analysis

To demonstrate the analytical precision of the 2830 ZT wafer analyzer, a 15-cycle repeated measurement was carried out. The wafer was loaded and unloaded between each cycle.

Production control of integrated circuits (ICs) frequently involves the analysis of tungsten layers on a Si substrate. Tungsten is used as conductor or metal film in the production of ICs, its role is to form the vertical interconnection wires between the transistors.

2830 ZT

Introduction

Production control of integrated circuits (ICs) frequently involves the analysis of tungsten layers on a Si substrate. Tungsten is used as conductor or metal film in the production of ICs, its role is to form the vertical interconnection wires between the transistors. The thickness of the W film is an important parameter. Due to its excellent selectivity and precision, wavelength dispersive X-ray fluorescence spectrometry is the ideal technique for monitoring the W film thickness in IC manufacturing.

Instrumentation

A Malvern Panalytical 2830 ZT XRF Wafer Analyzer equipped with a fixed channel for W is used for this report. Details of the measurement conditions are presented in Table 1.

Procedure

The W-Lα signal can be used to quantify the layer thickness of the film. A calibration line for W was set up. Fundamental parameter correction was implemented in the calibration to ensure validity over the whole calibration range in terms of layer thickness.

To demonstrate the analytical precision, a 15-cycle repeated measurement was carried out. The wafer was loaded and unloaded between each cycle.

Table 1. Measurement conditions
TubeTube settingChannelsMeasuring timeSpot sizeSoftware package
4 kW Rh anode, 
SST-mAX50

32 kV 
125 mÅ

Fixed channels:
W-Lα

100s40 mm diamaterSuperQ,
FP Multi

Results

A calibration line for the W layer thickness is presented in Figure1. The calibration unit for the layer thickness is Å.

Results for the repeated measurement of layer thickness are shown in Table 2. The low relative RMS values indicate excellent measurement repeability.

Figure 1. Calibration for W layer thickness 

figure1.PNG

Table 2. Repeatability results for W layer thickness
Seq.W Layer thickness (Å)
12000
22000
31999
42001
52000
62001
72000
82000
92000
102000
112000
122000
132001
142000
151999
Mean2000
RMS0.6
RMS rel. (%)0.03

Conclusion

The Malvern Panalytical 2830 ZT XRF Wafer Analyzer can accurately analyze the W layer thickness. The range can be adapted to customer requirements: extending up to 40 µm.

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