P型與N型金氧半電容元件於超薄氧化層之電特性比較及應用

Abstract

為了要對P型及N型金氧半電容元件有更進一步的了解，針對不同的製程條件，我們同時生長P型和N型的矽晶片之氧化層，並做成金氧半電容元件。在量測電壓與電流的關係時，發現兩種元件的電流對厚度有不同的相依性，且於薄氧化層時，N型金氧半電容元件中反轉區電流對溫度的響應遠小於P型元件。最主要的原因是因為N型元件在反轉區的電流受控於次氧化層中，界面陷阱處所發生的電子與電洞復合機制，而P型元件則是受控於電子電洞產生機制。我們並利用由此差異性，將兩種元件串聯，N型元件相當於固定電流源，設計出一種有趣的溫度感測器。 在量測電壓與電容的關係時，發現N型元件薄氧化層的品質比P型元件好得多，即兩元件的氧化層都很薄時，N型元件的界面陷阱密度比P型少。這也是因為次氧化層在兩種元件扮演不同角色的關係。我們將生長氧化層的時間增加，相當於將次氧化層的品質改善後，發現兩種元件的差異性明顯地減小。另外，當生長的氧化層較薄時，偏壓加在空乏區進入反轉區的附近時，N型元件會量測出現負值電容。這是因為當偏壓在此附近時，會造成電子電洞對的大量復合，氧化層界面附近之儲存電荷減少，故造成負值電容的現象。而氧化層厚度增加，或是生長氧化層時間增加，此效應會減少許多。再次驗證次氧化層在比較P型與N型元件時，所扮演的角色是相當重要的。

For deeper understanding of p- and n-type MOS capacitor devices, we grew oxide on p- and n-type silicon substrates simultaneously with different recipes. When measuring current-voltage (J-V) characteristics, it was found that the oxide thickness dependencies of the current magnitudes of these two devices were different. Furthermore, with thin oxide films, the response of inversion saturation current to temperature in n-type MOS capacitors was much lower than that in p-type devices. The origin of these differences was mainly that the inversion saturation current in n-type devices was controlled by the recombination mechanism in interface traps located in sub-oxide, while the inversion saturation current in p-type devices was controlled by the generation mechanism. Based on the different current response to temperature of n-substrate MOS devices, we designed an interesting temperature sensor by connecting two devices in series, where n-type device was regarded as a constant current source. When measuring capacitance-voltage (C-V) characteristics, it was found that the quality of the thin oxide film of n-type device was much better than that of p-type device. In other words, the interface trap density of n-type device is less than that of p-type device while both oxide films are very thin, which is strongly related to the sub-oxide. We improved the sub-oxide quality by increasing the growth time of oxidation, and then observed that the discrepancy between them became unapparent. Moreover, when the oxide film of n-type device was thinner, we found that negative capacitance occurred near the region when bias was changed from depletion to inversion. This is because when biasing in the neighborhood, lots of electron-hole pairs will start to recombine, which results in the stored charges near the interfacial layers decrease as the applied terminal voltage is increased. Again, when we increase the oxidation time, that is, thickening the oxide films, the negative-capacitance effect become unobvious. It is concluded that the sub-oxide plays an important role in the comparison of the characteristics of p- and n-type devices.