Gd靶激光等离子体6.7nm光源的实验研究

Experimental research on laser-produced Gd target plasma source for 6.7 nm lithography

本文对Gd靶激光等离子体极紫外光源进行了实验研究,在6.7 nm附近获得了较强的辐射,并研究了6.7nm附近光辐射随打靶激光功率密度变化的规律以及收集角度对极紫外辐射的影响.同时,对平面Gd靶激光等离子光源的离子碎屑角分布进行了测量,发现从靶面的法线到沿着靶面平行方向上Gd离子数量依次减少.进一步研究结果表明采用0.9 T外加磁场的条件下可取得较好的Gd离子碎屑阻挡效果.

Extreme ultraviolet（EUV） lithography at λ = 6.7 nm is a challenging subject for next generation semiconductor lithography beyond 13.5 nm.The availability of strong radiation at the operating wavelength and low-debris of the plasma source are the two most important aspects for the development of laser-produced Gd plasma source at 6.7 nm.In this paper,experimental research on the extreme ultraviolet source based on the laser-produced Gd plasma is performed.Strong radiation near 6.7 nm from the source has been obtained,which is attributed to the n = 4–n = 4 transitions in Gd ions that overlap to yield an intense unresolved transition array（UTA）.Dependence of spectral variation near the strong emission region of Gd plasma on the incident laser power density and detection angles is given.It is found that the intensity of EUV radiation around 6.7 nm is increased with increasing laser power density,and the emission peak around 7.1 nm increases faster than that of emission peak around 6.7 nm after the laser intensity reaching 6.4 × 1011W/cm2,which is ascribed to the unique spectroscopic behavior of Gd ions.In addition,the energy of the ion debris from laser-produced Gd plasma source as well as the angular distribution of the ion yield off the target normal are measured with Faraday cup.Results show that the ion energy corresponding to the peak position of Gd ion energy distribution is about 2.6 ke V at 10？off the target normal,and the yield of Gd ions decreases with the increase of the angle from the target normal.Furthermore,the stopping ability of an ambient magnetic field for ion debris from laser Gd plasma source is evaluated,and the result shows that the energetic Gd ion can be effectively mitigated by applying a 0.9 T magnetic field.