先進的半導體製造需要更精準的製程監控技術，以改善產品良率和可靠度。近來，以臨場(In-Situ)電漿感測器輔助監控的先進製程控制(Advanced Process Control, APC)，獲得極大的重視並被應用在蝕刻與鍍膜製程上。以電漿蝕刻製程為例，蝕刻製程特性如蝕刻速率、蝕刻選擇性、蝕刻側壁輪廓，與到達晶圓表面的離子通量、離子能量與蝕刻物通量有關。因此精確控制製程中的電漿參數就成為一個重要的課題。
本研究的目的為研製高密度電漿蝕刻之關鍵電漿參數即時回授控制系統，並探討其對於電漿蝕刻製程的影響。其中最重要的關鍵電漿參數是離子密度與離子能量，為了達成這個目的，吾人研製了一套離子密度與離子能量即時回授控制平台，並與開迴路的蝕刻結果作一比較。開迴路蝕刻機台的控制變數為射頻功率、氣體流量、腔體壓力等系統操作參數，並未直接控制影響蝕刻表面的關鍵電漿參數。因此，製程穩定性將受限於製程腔體狀態、機台保養時間、機台零件壽命等因素的影響。本研究研製之電漿蝕刻製程即時回授控制系統直接控制關鍵電漿參數，藉以提昇製程穩定性，將適合應用於更精準的製程要求。

研究中首先針對需求研製與改良數種非侵入式(Invasive)離子通量與離子能量量測裝置，以利即時回授控制系統發展。與離子通量相關之量測包括：平均離子流密度射頻診斷系統、TRG-OES(Trace Rare Gases-Optical Emission Spectroscopy)Cl+離子密度量測系統、36 GHz外差式毫米波干涉儀。與離子能量相關之量測則為射頻峰值電壓之射頻診斷系統與射頻電壓/電流量測系統。研究中已初步驗證36 GHz外差式毫米波干涉儀應用於電子密度即時回授控制的可行性。

其次，探討氯氣電漿蝕刻多晶矽製程中，系統操作參數-關鍵電漿參數-蝕刻速率三者之間的關係，並建立類神經網路蝕刻製程模型。驗證了離子流密度與電漿功率成正比；射頻偏壓與偏壓功率成正比；腔體壓力增加會使得離子流密度減少、射頻偏壓增加、氯原子密度增加；氯氣流量只會些微影響電漿參數和蝕刻速率。由於腔體壓力已由壓力控制器加以控制，因此可知透過降低製程正離子密度和射頻偏壓的穩態誤差，即可提昇多晶矽蝕刻速率重現性。

本研究最後一部份則是完成氯氣電漿正離子密度與離子能量蝕刻製程即時回授控制系統。研究中的採用TRG-OES量測方式獲得Cl+離子密度與射頻電壓探針量測射頻偏壓作為感測器；電漿功率與偏壓功率為致動器；兩個數位PI控制器則是以量化回授理論(Quantitative Feedback Theory, QFT)設計。實驗結果顯示多晶矽蝕刻製程中，即時回授控制確實比開迴路控制擁有更好的製程穩定性，蝕刻速率的變動量能夠被降低2.5至7倍。同時即時回授控制也能夠克服頭片晶圓效應、射頻反射功率干擾等因素對製程的影響。

The advanced semiconductor fabrication requires a much tighter process monitoring and control to improve production yield and reliability. Among the several hundreds of processing steps of modern ultralarge scale integrated circuits (ULSI) fabrication, plasma based processes play a crucial role in achieving the desired device performance. Plasma processes are primarily based on chemical and physical reactions of reactive species and charged particles with wafer surface. They also contribute to a great part of the problem associated with the fabrication yield because of their complex characteristics. Therefore, it is important to develop real-time control of plasma properties, such as ion density, ion energy, reactive species, etc., for plasma processing tools.
In this thesis, several non-invasive diagnostic systems of ion density and ion energy for real-time control system have been either developed or improved from existing tools. RF diagnostics, trace rare gases-optical emission spectroscopy (TRG-OES), and 36 GHz heterodyne interferometer were employed to measure positive ion density. On the other hand, the averaged ion energy was estimated by measuring peak RF voltage on the biased wafer electrode using a RF voltage probe.

In the second phase of this study, neural-network models for machine parameters–critical plasma parameters–etch rate were developed for polysilicon etch in an inductively-coupled chlorine plasma. Experimental results show that ion current density is proportional to the source power. While the RF bias voltage varies linearly with bias power. Increasing pressure will cause ion current density to decrease. Both RF bias voltage and chlorine atomic density increases with gas pressure, but the opposite was found for the ion current density. It was also demonstrated that plasma properties and etch rate depend weakly on the Cl2 flow rate. Consequently, the reproducibility of etch rate can be improved if the steady-state errors of both ion current density and rf bias voltage are reduced and a pressure controller is need to eliminate pressure variation.

For the proof of principle experiment, a real-time closed-loop control system of both ion density and ion energy in an inductively-coupled chlorine plasma etcher has been developed. The TRG-OES method was used to measure the chlorine positive ion density. An RF voltage probe is adopted to measure the rot-mean-square (RMS) RF voltage on the electrostatic chuck which varies linearly with the sheath voltage. One actuator is a 13.56 MHz RF generator to drive the inductively coil seated on a ceramic window. The second actuator is also a 13.56 MHz RF generator powering the electrostatic chuck. The two digital PI controllers were used to separately control the positive ion density and the RMS RF voltage. The plasma coupling effect and model uncertainty have been considered using the quantitative feedback theory (QFT) design technology such that the robust stability and performance can be achieved. The experimental results showed that the closed-loop control had a better repeatability of plasma parameters as compared with the open-loop control. The closed-loop control can eliminate the process the process disturbance resulting from reflected power. In addition, a better reproducibility in etch rate also obtained by the closed-loop control. Under a closed-loop control etch, the standard variation of etch rate was reduced by a factor of 2.5 –7.

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