Demystifying Semiconductor Chip Inspection: A Comprehensive Comparison of SSRM and SCM

在半导体工艺迈入14nm、甚至7nm/5nm节点的今天，诸如FinFET和GAA等先进结构的出现，对芯片内部掺杂区域的精确测量提出了前所未有的挑战。在二维载流子浓度分布（2D Carrier Profiling）检测中，扫描电容显微镜（SCM）和扫描扩展电阻显微镜（SSRM）是两种最主流的技术 。针对各类研发与失效分析需求，我们该如何选择？本文将从物理机制与实际落地难点为您深度拆解。[1], [2]

SSRM对比SCM的核心实战优势

SCM和SSRM虽然都能表征微观电学性质，但它们在空间分辨率和定量分析能力上有着显著差异 。[2]

空间分辨率机制的不同

SCM的分辨率主要受限于半导体的耗尽层宽度。随着工艺节点缩小到14nm以下，相邻掺杂区的耗尽层容易发生重叠，导致信号串扰，分辨率很难突破10-20nm的瓶颈 。相比之下，SSRM的分辨率仅取决于导电探针与样品的接触斑半径 。通过施加纳牛（nN）级别的高接触力，SSRM可以将接触面积压缩到10nm以内 。只要表面处理得当，它是目前7nm/5nm节点掺杂分布测绘中分辨率最高的原子力显微镜（AFM）类手段 。[1], [2], [3]

定量能力与动态范围的较量

SCM的测量信号（dC/dV）与载流子浓度之间存在严重的非线性关系 。在极高掺杂（大于 10^20 cm^-3）或极低掺杂区域信号非常微弱，这使得SCM很难直接反推绝对掺杂浓度，通常只能用于工艺间的定性对比 。而SSRM测量的是扩展电阻，其对数值与载流子浓度的对数值（Log(R)与Log(N)）在极大的范围内（ 10^15 至 10^21 cm^-3）呈现出高度的线性关系 。这种宽广且线性的动态范围可以直接输出定量的载流子浓度分布曲线，对于校准TCAD仿真模型具有极高的实战价值 。[3]

对表面状态的不同敏感度

SCM对表面的氧化物厚度和表面态密度极其敏感，极易由于表面污染直接导致电容信号发生漂移 。相反，SSRM的核心在于形成欧姆接触 。虽然它也受到表面态的影响，但通过超硬导电探针和高接触力，它可以直接穿透极薄的自然氧化层，有效避免肖特基势垒的形成，从而获取内部真实的电学信号 。[1], [3], [4]

挑战极限：SSRM样品制备的隐藏门槛

虽然SSRM在数据质量和分辨率上全面胜出，但它的样品制备是一个极其复杂的系统工程，容错率远低于相对宽容的SCM 。制备高质量的SSRM截面样品需要克服以下五大核心难点：

• 表面质量要求极高：样品必须达到原子级的平整度（表面粗糙度RMS小于0.5nm），因为任何表面起伏都会直接改变接触面积，进而严重影响接触电阻的测量 。[4]

• 表面损伤层控制极严：传统的机械抛光必然会引入非晶层和残余应力，而化学机械抛光（CMP）的参数窗口又极其狭窄 。此外，离子束加工也可能意外引入额外的掺杂或晶格损伤 。[4], [5]

• 表面态与氧化层干扰：暴露在空气中生长的自然氧化层极易形成肖特基势垒，阻碍欧姆接触的形成 。因此，样品的最终处理和测量往往需要在惰性气氛或高真空中快速完成，以避免载流子注入受到表面态密度的干扰 。[3], [4]

• 欧姆接触的精准构建：针对不同的掺杂类型和浓度，需要精细调整探针与样品的接触条件 。特别是在轻掺杂区域，维持一个稳定的欧姆接触极具挑战性 。[1]

• 截面样品的结构特殊性：芯片截面通常包含多种不同材质（如硅、氧化物、金属），它们的抛光速率各不相同，极易产生台阶效应 。同时，异质界面处容易发生脱落或污染，这对多材料表面的协同处理提出了极高要求 。

作为专业的半导体检测服务商，我们不仅具备深厚的SSRM样品制备工艺积累，能够稳定攻克先进器件截面在平整度、损伤层控制、表面氧化层处理及欧姆接触构建等方面的关键难题；同时，我们还在商用现有模块基础上进行了独家深度研发与优化，形成了自有特色的SSRM测试模组。

通过对系统噪音抑制、信号链优化、探针接触稳定性以及测量控制策略的持续改进，我们的模组在测试灵敏度、信噪比和空间分辨能力方面实现了显著提升，能够更有效地支撑先进制程节点下的高精度载流子分布测量。

依托“高质量制样 + 自研高性能模组”的一体化能力，我们能够为客户提供更稳定、更精细、更具定量价值的SSRM测试结果，在先进半导体工艺研发、器件分析和失效诊断场景中展现出专业水平。

Demystifying Semiconductor Chip Inspection: A Comprehensive Comparison of SSRM and SCM

As semiconductor manufacturing processes advance to 14nm and dive deeper into 7nm/5nm nodes with complex structures like FinFET and GAA, the precise measurement of internal doping regions has become an unprecedented challenge. For 2D carrier profiling, Scanning Capacitance Microscopy (SCM) and Scanning Spreading Resistance Microscopy (SSRM) stand as the two most prominent analytical techniques. To help our clients and engineers make informed decisions for R&D and failure analysis, this article breaks down their physical mechanisms and practical application hurdles. [1], [2]

Core Practical Advantages of SSRM Over SCM

While both SCM and SSRM are capable of characterizing microscopic electrical properties, they exhibit significant differences in spatial resolution and quantitative analysis capabilities. [2]

Differences in Spatial Resolution Mechanisms

The spatial resolution of SCM is fundamentally limited by the depletion width of the semiconductor. As process nodes shrink below 14nm, the depletion layers of adjacent doped regions tend to overlap, causing signal crosstalk that makes it incredibly difficult to break the 10-20nm resolution barrier. In contrast, SSRM's resolution is solely dependent on the contact radius between the conductive tip and the sample. By applying a high contact force in the nano-Newton (nN) range, the contact area can be compressed to under 10nm. Provided the sample surface is properly prepared without damage, SSRM currently offers the highest spatial resolution among AFM-based techniques for mapping doping profiles at the 7nm and 5nm nodes. [1], [2], [3]

Quantitative Capability and Dynamic Range

SCM suffers from a severe non-linear relationship between its measurement signal (dC/dV) and carrier concentration. Its signal peaks at moderate doping levels but becomes extremely weak at both exceptionally high (greater than 10^20 cm^-3) and very low doping concentrations. This non-linearity makes absolute quantitative calibration highly difficult, restricting SCM primarily to qualitative comparisons between processes. SSRM, however, measures spreading resistance. The relationship between the logarithm of resistance and the logarithm of carrier concentration (Log(R) vs. Log(N)) exhibits strict linearity over a massive dynamic range spanning from spanning from 10^15 to 10^21 cm^-3. This allows SSRM to directly output quantitative carrier concentration curves, which are invaluable for calibrating TCAD simulation models. [3]

Varying Sensitivity to Surface Conditions

SCM is acutely sensitive to surface oxide thickness and surface state density; even minor surface contamination can lead directly to capacitance signal drift. Conversely, the core operational principle of SSRM is the formation of an Ohmic contact. While still affected by surface states, SSRM utilizes an ultra-hard conductive probe combined with high contact force to physically penetrate thin native oxide layers. This effectively prevents the formation of a Schottky barrier and ensures the extraction of genuine internal electrical signals. [1], [3], [4]

Pushing the Limits: The Hidden Challenges of SSRM Sample Preparation

Despite SSRM's comprehensive supremacy in data quality and resolution, preparing samples for it is a highly complex systems engineering task. The process is significantly more demanding and less forgiving than SCM preparation. Achieving high-quality cross-sectional samples for SSRM requires overcoming five primary hurdles:

• Exceptional Surface Quality: The sample must achieve atomic-level flatness with a root mean square (RMS) roughness of less than 0.5nm. Any topographic variation directly alters the contact area, thereby severely skewing the contact resistance measurement. [4]

• Strict Surface Damage Control: Standard mechanical polishing inevitably introduces amorphous layers and mechanical stress, while the parameter window for Chemical Mechanical Polishing (CMP) is extremely narrow. Furthermore, ion beam milling risks introducing unintended doping or crystal lattice damage.static. [4], [5]

• Native Oxide and Surface States: The natural oxide layer that forms upon exposure to air creates a Schottky barrier instead of the required Ohmic contact. Consequently, final surface treatments and subsequent measurements must often be executed rapidly in an inert atmosphere or high vacuum to prevent surface state density from interfering with carrier injection. [3], [4]

• Precise Ohmic Contact Formation: Maintaining a stable Ohmic contact requires meticulous adjustments to the tip-sample contact force based on different doping types and concentrations. This is particularly challenging to stabilize in lightly doped regions. [1]

• Complexities of Cross-Sectional Structures: Semiconductor cross-sections consist of multiple materials (e.g., silicon, oxides, metals) with varying polishing rates, which frequently results in undesired topographic steps. Additionally, heterogeneous interfaces are prone to peeling or contamination, demanding extraordinary precision when processing multi-material surfaces simultaneously.

As a professional semiconductor testing service provider, we offer not only strong expertise in SSRM sample preparation—covering critical challenges such as surface flatness, damage-layer control, native oxide management, and reliable Ohmic contact formation—but also a uniquely optimized SSRM module developed in-house on top of existing commercial platforms.

Through continuous improvements in noise suppression, signal-chain optimization, tip-sample contact stability, and measurement control strategies, our module delivers enhanced sensitivity, higher signal-to-noise ratio, and superior spatial resolution for high-precision carrier profiling in advanced technology nodes.

With this integrated capability combining high-quality sample preparation and a high-performance self-developed module, we provide customers with more stable, more refined, and more quantitative SSRM results, demonstrating internationally leading performance in advanced semiconductor process development, device characterization, and failure analysis.

Reference

[1] Park Systems. Scanning Spreading Resistance Microscopy (SSRM). 2024-03-02. Available at: https://www.parksystems.com/kr/products/research-afm/AFM-modes/Electrical-Modes/scanning-spreading-resistance-microscopy--ssrm-

[2] AZoNano. SSRM and SCM for Carrier Profiling. 2025-04-15. Available at: https://www.azonano.com/article.aspx?ArticleID=5636

[3] Microscopy Today / Oxford Academic. Dual Lens Electron Holography, Scanning Capacitance Microscopy ... 2021-04-30. Available at: https://academic.oup.com/mt/article/29/3/36/6813671?login=false

[4] NanoScientific. Primer: The Advancements and Applications of Scanning ... Available at: https://nanoscientific.org/articles/view/423

[5] ASM International. Aug_EDFA_Digital. Available at: https://static.asminternational.org/EDFA/202308/55/