Nikon Stepper Alignment Process

Nikon Stepper Alignment Process

PE:甯兵

光刻机的一般组成

照明系(光源+产生均匀光的光路) STAGE(包括RETICLE STAGE和WAFER STAGE), 镜头(这个是光刻机的核心), 搬送系(wafer handler+ reticle handler), alignment (WGA, LSA, FIA)

purpose确保shot以正确的位置和形状曝在wafer上面

1:按设计曝下shot(first layer). 2:使shot正确的套刻在前层shot上一个产品不可能只曝一层就可以了，这就需要每一层 之间的overlay要非常小。 问：保证overlay精度的重要因素有哪些？

Alignment System Machine Self Overlay

Reticle & Wafer StageProject Lens Stage Grid Matching

Total Overlay

Matching Error

Reticle Stage Matching

Distortion MatchingResist coating

Alignment Mark Error

Film deposition CMP

Process Error

Reticle Mark Error Non-linear wafer modifiedWafer expend RTP

Alignment Coordination system5 coordination system: 1. Reticle 2. Lens 3. Alignment sensor 4. Fiducial mark 5. Wafer Final purpose: Reticle, lens, wafer unified in one coordination system.

Alignment procedural Reticle align with lens ----- Reticle search Reticle and Lens align with Fiducial mark ---- Reticle search EGA sensor align with Reticle and Lens through Fiducial mark ----- baseline check EGA sensor align with wafer --- Search and EGA

Reticle and Lens align with Wafer

First Exposure第一层按设计规格曝光， 要求掩模板处于正确位 置：对掩模板的 measurement和 correction叫做掩模板 对准。

Second Exposure第二层与之后层需根据前层 情况正确曝光 要求能够对准前层留下的对准 标记。 需调整步进以满足前层shot 位置，需调整掩模板方位来 满足前层shot的方向。 于是，需测量出圆片上的shot 阵列的情况，

Wafer stage setWafer stage system: 原点在投影透镜 正中心的直角坐 标系

Two process: Wafer stage origin setting And correction

在水平方向，有能够自由运动的驱动部件 I14,使用线性马达驱动，stage使用的是气浮台，阻 力比丝杆小很多，提升速度。 垂直方向调节(保证wafer在lens焦面上 工作) Leaveling与rotation的补偿 由驱动马达完成。不同型号机器驱动马达有所差别， 但原理差不多。移动位置由测量系统给出。测量系统 是激光干涉仪。

Reticle stage coordinate system:位于投影透镜中心上方的 直角坐标系 作用就是找到reticle的mark,把它对准到lens上的reference 上，这样就相当于reticle的中心在lens中心了

Reticle alignment包括：reticle search, reticle alignment check 使得掩模板上的图像能够按照设计规范正确的投影到 圆片上 在第一层第二层以及之后各层均会执行该操作

Reticle AlignmentStartReticle search ToleranceValue or less

Re-set reticleExceeds value

RA-Auto focus

Mark shape

Mark types and positions

Reticle

fine alignmentReticle interfer.calib. Baseline check End

tolerances are as follows: Reticle rotation amount 5000urad Reticle position (X) =175um Reticle position (Y) =175um

=

Reticle interferometer calibration:– to obtain the relationship of the reticle stage coordinates and the reticle interferometer– for initial sequence only

Reticle search用VRA sensor找到reticle Mark 的位置.确保接下来的RA Check准确无误。 VRA sensor captures a static Image at each location to Detect the reticle alignment marks

Sensors中心即lens中心，sensor 对准mark即可认为reticle对准了 lens

Reticle alignment checkDetermine the attitude of a Reticle in the wafer coordinate system Reticle stage is moved to where The reticle alignment mark is Positioned directed under the VRA sensor using measurement Results of the reticle alignment

The VRA sensor derives the shifts of reticle alignment mark centers with Respect to the fiducial mark center 为了知道sensor的误差，用stage上的fiducial mark来check这个误差 从而得到reticle的rotation。

Baseline check

Lens与各个sensor之间的 相对距离，得到了baseline 才能够将sensor的测量结果 转移到透镜下方去，将wafer 正确曝光。

Wafer AlignmentStart Prealignment 1 Prealignment 2 1st layer Alignment Method Search alignment (FIA, LSA) Wafer rotation Fine alignment (FIA, LSA) Wafer exposure End500urad or more

Prealignment 1: –To find the notch of wafer Prealignment 2: –To measure the wafer attitude (center and rotation) before loaded on wafer stage using 3 CCD camera –Prealignment arm is used for wafer rotation correction

Less then 500urad

为什么要进行预对准？

Prealignment 2

由安装在wafer stage上的sensors测出wafer 边缘单元并 分析，得出wafer位置

Wafer search alignment The search alignment is conducted on a wafer On which the second or subsequent layer is exposed(a second exposure wafer)right after prealignment 2 finishes.