Control of Ion Energy Distribution at Substrates during Plasma Processing

0078522 wendt等离子体材料加工广泛应用于半导体工业。在等离子蚀刻中，通过光刻定义的模板或掩模将硅片暴露于电离气体中，从而在硅片中定义图案。等离子体蚀刻相对于液体化学蚀刻的优点之一是定向蚀刻，它是由等离子体溅落的正离子轰击表面产生的。由于离子轰击是垂直于衬底表面的，因此可以避免掩膜下材料的切下或蚀刻。这使得制造越来越小的晶体管对集成电路性能的持续进步至关重要。在当今典型的等离子体制造工艺中，到达衬底表面的离子能量是通过改变施加在衬底电极上的射频正弦偏压的振幅来粗略控制的，但在衬底处产生的离子能量分布（IED）通常很宽。离子冲击时提供给衬底表面的能量可以通过几种机制增强化学反应，对蚀刻特征轮廓和蚀刻选择性具有重要意义。提议的活动采用了一种新开发的技术，可以显着减少衬底处IED的宽度，具有显着改善等离子体过程这些方面的潜力。此外，由于过去在实际工艺条件下难以控制基板上的离子能量，该方法为研究离子轰击能量在不同材料和工艺气体系统的蚀刻过程中的作用提供了可能性，同时对其他工艺参数的影响最小。这种离子能量控制技术取代了传统的正弦衬底偏置电压波形，在衬底表面产生由周期性电压尖峰打断的恒定电位波形。结果，大多数离子在基底和等离子体之间的“护套”上看到一个恒定的电压降，因此以相同的能量到达基底。潜在的测量已经证实了这种方法的可行性。此外，毯膜的初步蚀刻速率测量表明，氟碳等离子体中SiO2/Si蚀刻选择性显著提高。该方法将应用于几个蚀刻问题，以及离子能量在等离子体加工中的作用的基本理解。第一步将是直接测量衬底处的IED，以证实该方法产生窄离子能量分布的猜想，并验证通过外部电压测量可以有效地监测平均离子能量。此外，通过使用该方法对IED进行精确剪裁，将对图案硅片的蚀刻选择性和蚀刻特征轮廓控制进行研究。一个特别感兴趣的过程是蚀刻二氧化硅，它继续对等离子体处理构成挑战。最后，通过在测量蚀刻速率的同时扫描离子能量，有望提高对蚀刻过程中离子轰击影响表面侵蚀的机制的理解

0078522WendtPlasma processing of materials is used extensively in the semiconductor industry. In plasma etching, patterns are defined in silicon wafers by exposing them to an ionized gas through a lithographically defined stencil, or mask. One of the advantages of plasma etching over liquid chemical etching is the directional etching that results from bombardment of the surface by positive ions raining down from the plasma. Because the ion bombardment is normal to the substrate surface, undercutting, or etching of material under the mask, can be avoided. This enables the fabrication of ever-tinier transistors critical to the continuing advancement in integrated circuit performance.In typical manufacturing plasma processes today, the energy of ions reaching the substrate surface is coarsely controlled bv varying the amplitude of an RF sinusoidal bias voltage applied to the substrate electrode, but the resulting ion energy distribution (IED) at the substrate is generally broad. The energy provided to the substrate surface upon ion impact can enhance chemical reactions via several mechanisms, with significant implications for etched feature profiles and etch selectivity. The proposed activity employs a newly developed technique for significantly reducing the width of the IED at the substrate, with the potential for significantly improving these aspects of plasma processes. Furthermore, because of past difficulties in controlling ion energy at the substrate under realistic process conditions, this method opens up the possibility of examining the role of ion bombardment energy in etching processes for different materials and process gas systems with minimal impact on other process parameters.This technique for ion energy control replaces the conventional sinusoidal substrate bias voltage waveform with a waveform that produces, on the substrate surface, a constant potential punctuated by periodic voltage spikes. As a result, most ions see a constant voltage drop across the "sheath" that arises between the substrate and plasma, and therefore arrive at the substrate with the same energy. Potential measurements have confirmed the feasibility of this approach. In addition, preliminary etch rate measurements of blanket films show dramatic improvement in etch selectivity for SiO2/Si etching in a fluorocarbon plasma.This method will be applied to several etching problems, as well as to basic understanding of the role of ion energy in plasma processing. The first step will be to directly measure the IED at the substrate to both confirm the conjecture that this method produces a narrow ion energy distribution, and to verify that average ion energy can be effectively monitored through external voltage measurements. In addition, both etch selectivity and etch feature profile control on patterned silicon wafers by precise tailoring of the IED using this method will be examined. A particular process of interest is etching of silicon dioxide, which continues to pose challenges for plasma processing. Finally, by scanning the ion energy while measuring etch rates, improved understanding of the mechanisms by which ion bombardment affects surface erosion during etching processes is expected.***