L2上游
半导体材料
Silicon wafers, photoresist, specialty gases, and process chemicals — few suppliers per node.
需求为什么传导到这里
更多加速器意味着更多 HBM、更多先进封装，因而需要更多晶圆；而每片晶圆都要消耗硅衬底、光刻胶、特种气体和工艺化学品。这是整条链里最安静、也最集中的一段。
瓶颈在哪
不少材料品类在单一制程节点上只有屈指可数的合格供应商，且认证周期很长。这里的集中度是结构性的，不是周期性的。
这是关于供应商集中度与交期的结构性观察，不是对任何标的的看法。
本层级的公司
- ENTG受益
Advanced materials, filtration, and contamination control for wafer fabrication.
- LIN中性
Industrial gases broadly; electronics specialty gases are one segment, not the whole business.
- APD中性
Industrial gases broadly; electronics materials are one segment, not the whole business.
同一赛道
Descriptive positioning only. `stance` says whether a company's business is exposed to a layer, never whether to buy it. Layers with no exposure are not recommendations to add any.