臺灣博碩士論文加值系統

目前對於低伏數交換式電源供應器的電路應用來說，大家最關注的是如何去改善其傳統蕭特基整流器的特性。其整流特性希望是降低順向導通電壓以及能夠快速的順逆向切換。蕭特基整流器的順向導通電壓能夠藉由蕭特基能障的調降而降低，但是不幸地，較低的蕭特基能障會導致漏電流變大而使之在操作的時候影響其耐較高溫度的能力。更進一步的來說，蕭特基整流器如果在製造時使用小於 0.7eV 的能障製程有可能會導致其軟崩潰(Soft Breakdown)造成失效。因此，目前有幾種蕭特基結構的發明就是為了改善其傳統蕭特基整流器的缺點，例如：接面能障蕭特基整流器(JBS：Junction Barrier Schottky Rectifier)以及溝渠式金氧半蕭特基整流器(TMBS：Trench MOS Barrier Schottky)。
然而，JBS 結構的缺點是如果為了達到其順向導通電壓低於 250mV ，製作其 P+ 接面深度小於 0.3�慆 的時候，逆向特性會變差，其逆向崩潰耐壓會降低，而且 P+ 接面的橫向擴散會有死角較難控制，使之很難進行微縮。雖然傳統的 TMBS 使用溝渠式金氧半元件大幅改善了 JBS 橫向擴散死角的問題，但是其溝渠底角所產生的電場過於集中的效應還是會限制到其逆向崩潰耐壓的能力。
在這篇論文會介紹一個新式 TMBS 結構，在溝渠底部使用相反參雜的離子植入將溝渠底部包覆形成一個相反參雜的區域，使用此方式可在不影響順向特性的情況之下，明顯增加其結構逆向耐壓的能力。限制原本傳統 TMBS 逆向耐壓的溝渠底角最大電場，會因為相反參雜的電荷補償而得更加舒緩。其包覆溝渠底部的相反參雜區域會稍微伸入其電流導通的平台區，但是卻不會讓其順向導通電壓特性變差。並且在這次的研究當中發現，溝渠底部的植入參雜濃度若是太低，則無法提供足量的電荷做為補償效果，植入量若是太高，則會在溝渠底部產生更大的電場。依據此結果可得知，其離子植入劑量需適當才可以在不影響順向導通電壓特性的狀況之下，提供其結構得到更佳的耐逆向偏壓的能力。

Improved barrier controlled power Schottky rectifiers are of interest for application in low-voltage switching mode power supplies for integrated circuits. For these applications, it is desirable to have rectifiers with very low forward drop and high switching speed. The forward voltage drop of a Schottky rectifier can be reduced by decreasing the Schottky barrier height. Unfortunately, a low barrier height results in a severe increase in leakage current and reduction in maximum operating temperature. Further, Schottky power rectifiers fabricated with barrier heights of less than 0.7 eV have been found to exhibit extremely soft breakdown characteristics which make them prone to failure. So there’re several Schottky structures to improve the conventional Schottky disadvantages such as JBS (Junction Barrier Schottky) rectifier and TMBS (Trench MOS Barrier Schottky) rectifier.
However, JBS structure is difficult to scale down the device feature size to achieve forward drops below 250mV due to the dead-zone presented by P+ junction regions and the breakdown susceptibility of very shallow (<0.3�慆) junctions. Although TMBS structure has improved JBS dead-zone issue by using trench MOS technology, the conventional TMBS rectifier has MOS structure built into whole trench regions but there’s still trench bottom corner electric field crowding effect to restrict the reverse blocking capability.
In this paper, a novel trench MOS barrier Schottky (TMBS) rectifier has been proposed by carrying out trench-bottom counter-doping implantation. By additionally implementing a counter-doped region enclosing the trench bottom, the reverse blocking voltage of the conventional TMBS rectifier can be significantly enhanced without considerable degradation of on-state characteristics. The large peak electric field in the corner of trench bottom, which limits the blocking voltage of the conventional TMBS rectifier, can be largely alleviated due to charge compensation. Though the counter-doped region enclosing the trench bottom may partly encroach into the mesa region, no considerable deterioration of on-state characteristics is caused. In this study, a too low-dose trench-bottom implantation cannot provide sufficient charge compensation, and a too high-dose trench-bottom implantation would create a large peak electric field below the trench bottom. As a result, a proper trench-bottom implantation may be employed to significantly enhance the blocking voltage without considerable degradation of on-state characteristics.

Abstract (Chinese)………………………………………………………i
Abstract (English)……………………………………………………iv
Acknowledgement (Chinese)………………………………………vii
Contents………………………………………………………………viii
Figure Captions…………………………………………………………x
Chapter 1 Introduction…………………………………………………1
1-1 Background…………………………………………………1
1-2 Pinch Rectifier…………………………………………………2
1-2-1 Junction barrier Schottky rectifier………………………3
1-2-2 Trench MOS barrier Schottky rectifier……………………4
1-3 Motivation……………………………………………………7
1-4 Thesis organization………………………………………………7
Chapter 2 Device scheme……………………………………………15
Chapter 3 Results and discussion……………………………………19
3-1 Electrical characteristics of the conventional TMBS rectifier………16
3-1-1 Mesa width effect……………………………………19
3-1-2 Mesa Height Effect……………………………………20
3-2 Electrical characteristics of the trench bottom boron implantation TMBS rectifier………………………………………………26
3-2-1 Implantation dosage effect………………………27
3-2-2 Implantation energy effect…………………………29
3-2-3 Mesa width effect………………………………………29
3-2-4 Mesa height effect………………………………………30
3-2-5 Trench Width effect……………………………………31
3-2-6 Drive-in time effect……………………………………31
3-2-7 High implantation energy effect…………………………31
3-2-8 Summary………………………………………………32
Chapter 4 Conclusions…………………………………………………67
Reference………………………………………………………………69
Vita………………………………………………………………………71

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