CMOS compatible capacitive absolute pressure sensors

• US 10,556,791 B2
• Filed: 07/19/2017
• Issued: 02/11/2020
• Est. Priority Date: 07/19/2016
• Status: Active Grant

• Current Assignee: King Abdul AZIZ City For Science and Technology
• Original Assignee: King Abdul AZIZ City For Science and Technology
• Inventors: Alsaiary, Tariq Salim, Alhomoudi, Ibrahim Abdullah
• Primary Examiner(s): Smith, Bradley
• Assistant Examiner(s): Goodwin, David J
• Application Number:
  US15/653,898
• Publication Number:
  US 20180022600A1
• Time in Patent Office: 937 Days
• CPC Class Codes: B81B 2201/0264 Pressure sensors
• CPC Class Codes: B81B 7/02 containing distinct electrical or optical devices of particular relevance for their function, e.g. microelectro-mechanical systems [MEMS] B81B7/04 takes precedence
• CPC Class Codes: B81C 1/00246 Monolithic integration, i.e. micromechanical structure and electronic processing unit are integrated on the same substrate
• CPC Class Codes: B81C 1/00269 Bonding of solid lids or wafers to the substrate
• CPC Class Codes: B81C 2203/0742 Interleave, i.e. simultaneously forming the micromechanical structure and the CMOS circuit
• CPC Class Codes: G01L 19/0076 using buried connections
• CPC Class Codes: G01L 19/147 Details about the mounting of the sensor to support or covering means
• CPC Class Codes: G01L 9/0042 Constructional details associated with semiconductive diaphragm sensors, e.g. etching, or constructional details of non-semiconductive diaphragms details about the integration or bonding of piezoresistor in or on the diaphragm G01L9/0052 and G01L9/0057 respectively
• CPC Class Codes: G01L 9/0045 Diaphragm associated with a buried cavity
• CPC Class Codes: G01L 9/0054 integral with a semiconducting diaphragm
• CPC Class Codes: G01L 9/0072 using variations in capacitance

Abstract

Monolithic integration of microelectromechanical systems (MEMS) sensors with complementary oxide semiconductor (CMOS) electronics for pressure sensors is a very challenging task. This is primarily due to the requirement for a very high quality thin diaphragm to provide the pressure dependent MEMS deformation that can be sensed and, when seeking absolute rather than relative pressure sensors, a sealed reference cavity. Accordingly, a new manufacturing process is established based upon back-etching and bonding of a monolithic absolute silicon carbide (SiC) capacitive pressure sensor. Beneficially, the process embeds the critical features of the MEMS within a shallow trench formed within the silicon substrate and then processing the CMOS circuit. The process further benefits as it maintains that those elements of the MEMS element fabrication process that are CMOS compatible are implemented concurrently with those CMOS steps as well as the metallization steps. However, the CMOS incompatible processing is partitioned discretely.

Claims

1. A method comprising:

manufacturing a first portion of a microelectromechanical systems (MEMS) element for monolithic integration with a complementary oxide semiconductor (CMOS) integrated circuit (IC) using a high temperature MEMS process;

manufacturing the CMOS integrated circuit;

manufacturing a second portion of the MEMS element during and subsequent to the CMOS integrated circuit;

wherein

the second portion of the MEMS element is formed with a low temperature MEMS process;

the MEMS element is a self-contained monolithic differential capacitive pressure sensor measuring an external pressure with a capacitive pressure element relative to a reference pressure defined within a reference sealed monolithic capacitive pressure element;

the reference sealed monolithic capacitive pressure element is the first portion of the MEMS element fabricated with the high temperature MEMS process;

the capacitive pressure element is the second portion of the MEMS element fabricated with the low temperature MEMS process;

the first portion of the MEMS element is electrically connected to the CMOS integrated circuit using electrical connections formed during the low temperature MEMS process;

the first portion of the MEMS element is fabricated with the high temperature MEMS process comprising;

etching a trench within a first surface of a substrate;

depositing a first sacrificial material of predetermined geometry over a predetermined region of a bottom of the trench;

forming a diaphragm for the pressure sensor from a predetermined structural material upon a predetermined portion of the first sacrificial material;

etching a via from a second surface of the substrate distal to the first surface of the substrate to the bottom of the trench;

etching the first sacrificial material; and

sealing the via; and

the second portion of the MEMS element is fabricated with the low temperature MEMS process comprising;

forming a lower electrode comprising a first portion upon a surface of the diaphragm and a second portion interconnecting the first portion to a first electrical contact;

defining an isolation region using a second sacrificial material deposited upon a portion of the lower electrode;

forming an upper electrode comprising a first portion upon a surface of the second sacrificial material on the first side of the substrate and a second portion interconnecting the first portion to a second electrical contact; and

etching the isolation region.

2. The method according to claim 1, wherein

the first surface of the substrate is planarized post-formation of the first portion of the MEMS element such that a CMOS manufacturing process for manufacturing the CMOS integrated circuit utilizes contact photolithography.

3. The method according to claim 1, wherein

the predetermined structural material is selected from a group comprising silicon, silicon dioxide, silicon nitride;

silicon oxynitride, carbon, aluminum oxide, and silicon carbide.

4. The method according to claim 1, wherein

the low temperature MEMS processing limits a maximum temperature to which the substrate upon which the first portion of the MEMS element and the CMOS integrated circuit is subjected to 350°

C.

5. The method according to claim 1, wherein

the capacitive pressure element and reference sealed monolithic capacitive pressure element are vertically stacked upon the first surface of the substrate;

and

the CMOS integrated circuit is formed upon a second surface of the substrate.

6. A method comprising:

manufacturing a first portion of a microelectromechanical systems (MEMS) element for monolithic integration with a complementary oxide semiconductor (CMOS) integrated circuit (IC) using a high temperature MEMS process;

manufacturing the CMOS integrated circuit;

manufacturing a second portion of the MEMS element during and subsequent to the CMOS integrated circuit;

wherein

the second portion of the MEMS element is formed with a low temperature MEMS process;

the MEMS element is a self-contained monolithic differential capacitive pressure sensor measuring an external pressure with a capacitive pressure element relative to a reference pressure defined within a reference sealed monolithic capacitive pressure element;

the reference sealed monolithic capacitive pressure element is the first portion of the MEMS element fabricated with the high temperature MEMS process;

the capacitive pressure element is the second portion of the MEMS element fabricated with the low temperature MEMS process;

the first portion of the MEMS element is electrically connected to the CMOS integrated circuit using electrical connections formed during the low temperature MEMS process; and

the second portion of the MEMS element is fabricated with the low temperature MEMS process comprising;

forming a lower electrode comprising a first portion upon a surface of the diaphragm on a first surface of a substrate and a second portion interconnecting the first portion to a first electrical contact;

defining an isolation region using a second sacrificial material deposited upon a portion of the lower electrode;

forming an upper electrode comprising a first portion upon a surface of the second sacrificial material on the first surface of the substrate and a second portion interconnecting the first portion to a second electrical contact; and

etching the isolation region.