Studying Nickel Contamination on Silicon Surfaces using XPS and Ultrahigh Vacuum Heating
Afzal, Hassan (2025-11-21)
Studying Nickel Contamination on Silicon Surfaces using XPS and Ultrahigh Vacuum Heating
(21.11.2025)
Julkaisu on tekijänoikeussäännösten alainen. Teosta voi lukea ja tulostaa henkilökohtaista käyttöä varten. Käyttö kaupallisiin tarkoituksiin on kielletty.
avoin
Julkaisun pysyvä osoite on:
https://urn.fi/URN:NBN:fi-fe20251124110897
https://urn.fi/URN:NBN:fi-fe20251124110897
Tiivistelmä
Nickel and Silicon systems hold a key value in modern semiconductor devices. Owing to their conductive properties, thermal stability, and ability to form nickel silicides, they are used in nanoscale contacts, Schottky junctions, and low-resistance interconnect technologies. Nickel silicides (Ni₂Si, NiSi, and NiSi₂) can be used to create thermally stable contact layers essential for MEMS, CMOS, and photovoltaic devices. Same material that delivers technologically valuable silicides can also produce challenges during improper Si wafer handling, leading to unintended Ni contamination.
Ni impurities can host deep-level traps, elevate leakage currents, and degrade carrier lifetime in Si wafers, which can lead to significant electrical defects, resulting in lower device performance and manufacturing yield. So it is important to understand Si surface chemistry and how Ni interacts with silicon based surfaces.
This thesis studies Si surface chemistry, Ni’s interaction with Si, cons and pros of Nickel Silicides, and behaviour of Ni contamination on different Si surfaces at high temperature treatments (range from 600°C to 1200°C) under ultra-high vacuum (10-8 and 10-9 mbar). Samples were analysed using high-resolution XPS to get more insights, including chemical states of Ni and other possible contaminations.
Ni contamination appeared at 1000°C when first sample was heated from 600°C (30mins), 800°C (30mins), 1000°C (5mins), 1200°C (5secs). Later on experiment was repeated for a new and the same Si surface but this time, temperature was increased to 900°C after 600°C. XPS spectrum showed appearance of Ni contamination at 900°C along with elimination of Si oxide state. Another sample, which already had Ni contamination and was cleaned by HF solution demonstrated elevation in Ni concentration at higher temperatures (same range above). The identified nickel exhibited Nickel oxide states towards higher binding energies along with Ni2O32p1/2 and Ni2p1/2 towards lower binding energy. However, appearance of Ni at higher temperatures is discussed in results and discussion chapter.
Through literature and experimental studies, this thesis facilitates a comprehensive understanding of Ni/Si contact behaviour, formation of nickel silicide, and the analytical methods most capable of detecting nanoscale impurities. The findings aim to support reliable device fabrication and contamination free processing within advanced semiconductor technologies, especially at higher temperatures and clean room facilities.
Ni impurities can host deep-level traps, elevate leakage currents, and degrade carrier lifetime in Si wafers, which can lead to significant electrical defects, resulting in lower device performance and manufacturing yield. So it is important to understand Si surface chemistry and how Ni interacts with silicon based surfaces.
This thesis studies Si surface chemistry, Ni’s interaction with Si, cons and pros of Nickel Silicides, and behaviour of Ni contamination on different Si surfaces at high temperature treatments (range from 600°C to 1200°C) under ultra-high vacuum (10-8 and 10-9 mbar). Samples were analysed using high-resolution XPS to get more insights, including chemical states of Ni and other possible contaminations.
Ni contamination appeared at 1000°C when first sample was heated from 600°C (30mins), 800°C (30mins), 1000°C (5mins), 1200°C (5secs). Later on experiment was repeated for a new and the same Si surface but this time, temperature was increased to 900°C after 600°C. XPS spectrum showed appearance of Ni contamination at 900°C along with elimination of Si oxide state. Another sample, which already had Ni contamination and was cleaned by HF solution demonstrated elevation in Ni concentration at higher temperatures (same range above). The identified nickel exhibited Nickel oxide states towards higher binding energies along with Ni2O32p1/2 and Ni2p1/2 towards lower binding energy. However, appearance of Ni at higher temperatures is discussed in results and discussion chapter.
Through literature and experimental studies, this thesis facilitates a comprehensive understanding of Ni/Si contact behaviour, formation of nickel silicide, and the analytical methods most capable of detecting nanoscale impurities. The findings aim to support reliable device fabrication and contamination free processing within advanced semiconductor technologies, especially at higher temperatures and clean room facilities.