High frequency switching mosfets with low output capacitance using a depletable p-shield

Abstract

Aspects of the present disclosure describe a high density trench-based power MOSFETs with self-aligned source contacts and methods for making such devices. The source contacts are self-aligned with spacers and the active devices may have a two-step gate oxide. A lower portion may have a thickness that is larger than the thickness of an upper portion of the gate oxide. The MOSFETS also may include a depletable shield in a lower portion of the substrate. The depletable shield may be configured such that during a high drain bias the shield substantially depletes. It is emphasized that this abstract is provided to comply with rules requiring an abstract that will allow a searcher or other reader to quickly ascertain the subject matter of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application is related to commonly-assigned, co-pending application Ser. No. ______, (Attorney Docket Number ANO-057 / US), filed the same day as the present application and entitled “HIGH DENSITY TRENCH-BASED POWER MOSFETS WITH SELF-ALIGNED ACTIVE CONTACTS AND METHOD OF MAKING SUCH DEVICES” to Lee, Chang, Kim, Lui, Yilmaz, Bobde, Calafut, and Chen, the entire disclosures of which are incorporated herein by reference.[0002]This application is related to commonly-assigned, co-pending application Ser. No. ______, (Attorney Docket Number ANO-058 / US), filed the same day as the present application and entitled “DEVICE STRUCTURE AND METHODS OF MAKING HIGH DENSITY MOSFETS FOR LOAD SWITCH AND DC-DC APPLICATIONS” to Yilmaz, Bobde, Chang, Lee, Calafut, Kim, Lui, and Chen, the entire disclosures of which are incorporated herein by reference.FIELD OF THE INVENTION[0003]This invention generally relates to metal oxide silicon field effect transistor...

AI Technical Summary

Benefits of technology

This patent is about improving the performance of high-density trench-based power MOSFETs used in load switching and DC-DC applications. The invention addresses the problem of reducing the on-resistance of the device while also optimizing its switching speed. The patent describes various designs and methods for achieving these improvements, including the use of a shielded gate MOSFET, a two-step gate oxide MOSFET, and a trench-based MOSFET with a thin layer of oxide near the top of the gate. These designs and methods offer various advantages and disadvantages, and the patent seeks to address these issues and provide a more optimized solution for high-density trench-based power MOSFETs.

Problems solved by technology

Finally, minimizing the ratio of Qgd / Qgs reduces the possibility of the device turning on due to a large dV / dt when the device is being switched off.

However, the basic trench based MOSFET does not have any charge balancing in the drift regions, and therefore causes an increase in the RdsA.

Also, the relatively thin gate oxide generates a high electric field under the trench, which leads to a lower breakdown voltage.

Further, as cell pitch continues to decrease, the trench based MOSFET may become a less desirable choice because of the difficulty in reducing the thickness of the gate oxide further.

Finally, complex processing is required in order to produce two electrically separated polysilicon electrodes within the same trench.

The complexity of the fabrication is further accentuated when the pitch of the device is scaled downwards to the deep sub-micron level.

However, the device shown in FIG. 1C is not easily downwards scalable because it is highly susceptible to body contact misalignment errors.

Also, if the contact mask is aligned too far away from the gate, then the turn on of the bipolar junction transistor (BJT) becomes an issue.

Images