METHODOLOGY AND SYSTEM FOR WAFER-LEVEL TESTING OF MEMS PRESSURE SENSORS

• US 20160107887A1
• Filed: 10/15/2014
• Published: 04/21/2016
• Est. Priority Date: 10/15/2014
• Status: Active Grant

• Current Assignee: NXP USA, Inc. (NXP Semiconductors NV)
• Original Assignee: Freescale Semiconductor, Inc. (NXP Semiconductors NV)
• Inventors: JONES, PETER T., MCWHORTER, WILLIAM D., DEBEURRE, BRUNO J., SESSEGO, RAIMONDO P.
• Granted Patent: US 9,527,731 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: B81C 99/004 during manufacturing
• CPC Class Codes: B81C 99/005 Test apparatus
• CPC Class Codes: B81C 99/007 Marking
• CPC Class Codes: G01L 27/005 Apparatus for calibrating pressure sensors

Abstract

A method for testing a plurality of pressure sensors on a device wafer includes placing a diaphragm of one of the pressure sensors on the device wafer in proximity to a nozzle of a test system. A pneumatic pressure stimulus is applied to the diaphragm via an outlet of the nozzle and a cavity pressure is measured within a cavity associated with the pressure sensor in response to application of the pneumatic pressure stimulus. The pneumatic pressure stimulus within the cavity corresponds to the pressure applied to the diaphragm. Methodology is executed to test the strength and/or stiffness of the diaphragm. Additionally, the methodology and test system can be utilized to determine an individual calibration factor for each pressure sensor on the device wafer.

Claims

1. A method for testing a plurality of pressure sensors on a device wafer comprising:

placing a diaphragm of one of said pressure sensors on said device wafer in proximity to a nozzle of a test system;

applying a pneumatic pressure stimulus to said diaphragm via an outlet of said nozzle; and

measuring a cavity pressure within a cavity associated with said one of said pressure sensors in response to said applying said pneumatic pressure stimulus.

2. The method of claim 1 wherein said placing comprises:

retaining said device wafer in said test system such that said device wafer is substantially parallel to an X-Y plane of said test system; and

moving at least one of said nozzle and said device wafer along a Z-axis substantially perpendicular to said X-Y plane to place said diaphragm of one of said pressure sensors in proximity to said nozzle.

3. The method of claim 1 wherein said pressure sensors are located on a first side of a substrate portion of said device wafer, a port extends through said substrate to said cavity, and said method further comprises:

positioning a seal element surrounding said outlet of said nozzle in contact with a second side of said substrate portion surrounding said port; and

applying mechanical force to said seal element to form a pressure seal between said second side of said substrate portion and said seal element such that said pneumatic pressure stimulus is imposed on said diaphragm via said port and said cavity.

4. The method of claim 1 wherein said pressure sensors are formed in a structural layer on a first side of a substrate portion of said device wafer, and said method further comprises:

positioning a seal element surrounding said outlet of said nozzle in contact with an exterior surface of said structural layer surrounding one of said pressure sensors; and

applying a mechanical force to said seal element to form a pressure seal between said exterior surface of said structural layer and said seal element, wherein said cavity associated with said one of said pressure sensors is formed between said diaphragm and said seal element with said outlet of said nozzle extending in said cavity, and said pneumatic pressure stimulus is imposed on said diaphragm via said nozzle extending in said cavity.

5. The method of claim 1 further comprising:

retaining said device wafer in a wafer chuck of said test system such that said device wafer is substantially parallel to an X-Y plane of said test system, wherein said wafer chuck is coupled to a movable X-Y stage of said test system;

indexing said X-Y stage to place successive diaphragms of successive ones of said plurality of pressure sensors in proximity to said nozzle; and

performing said applying and measuring operations for each of said successive ones of said plurality of pressure sensors.

6. The method of claim 1 further comprising:

sealing said cavity prior to said applying said pneumatic pressure stimulus; and

performing said measuring operation while a port into said cavity remains sealed.

7. The method of claim 1 wherein each of said plurality of pressure sensors has a maximum pressure rating, and said applying operation applies said pneumatic pressure stimulus having a magnitude that is at least equivalent to said maximum pressure rating.

8. The method of claim 1 wherein following said measuring operation, said method further comprises identifying said pressure sensor as a defective sensor when said cavity pressure is outside of a passing range defined by at least one of a low pressure threshold and a high pressure threshold.

9. The method of claim 8 further comprising:

performing said placing, applying, and measuring operations for each of said plurality of pressure sensors on said device wafer;

identifying a first subset of said pressure sensors on said device wafer as being defective sensors when said cavity pressure for each of said pressure sensors in said first subset is outside of said passing range;

identifying a second subset of said pressure sensors on said device wafer as being functional sensors when said cavity pressure of each of said pressure sensors in said second subset is within said passing range;

dicing said device wafer to produce a plurality of singulated pressure sensors; and

discarding said first subset of said pressure sensors following said dicing.

10. The method of claim 1 further comprising:

performing said placing, applying, and measuring operations for each of said plurality of pressure sensors on said device wafer, wherein;

for said each of said plurality of pressure sensors, said applying comprises applying successively greater magnitudes of said pneumatic pressure stimulus; and

for said each of said plurality of pressure sensors, said measuring comprises identifying a failure pressure, said failure pressure being one of said successively greater magnitudes of said pneumatic pressure stimulus at which said cavity pressure is outside of a passing range defined by at least one of a low pressure threshold and a high pressure threshold.

11. The method of claim 10 wherein said device wafer is a first device wafer, and said method further comprises:

producing a substrate map of said first device wafer, said substrate map correlating those of said pressure sensors at locations on said first device wafer as having a same one of said failure pressure; and

categorizing a second plurality of pressure sensors on a second device wafer according to said failure pressure provided in said substrate map for said first device wafer.

12. The method of claim 1 further comprising:

measuring at least one output pressure signal from said pressure sensor in response to said pneumatic pressure stimulus; and

determining a calibration factor for said pressure sensor in response to said at least one output pressure signal.

13. A method for testing a plurality of pressure sensors located on a first side of a substrate portion of a device wafer, each of said pressure sensors including a diaphragm and a cavity, said diaphragm being formed in at least one wall surrounding said cavity, and said method comprises:

retaining said device wafer in a wafer chuck of a test system such that said device wafer is substantially parallel to an X-Y plane of said test system, wherein said device wafer chuck is coupled to a movable X-Y stage;

indexing said X-Y stage to place one of said plurality of pressure sensors in proximity to a nozzle of said test system;

moving at least one of said nozzle and said device wafer along a Z-axis substantially perpendicular to said X-Y plane to position said diaphragm of said one of said pressure sensors in proximity to said nozzle;

sealing a cavity associated with said one of said pressure sensors;

applying a pneumatic pressure stimulus from an outlet of said nozzle to said diaphragm via said cavity, said applying occurring following said sealing; and

measuring a cavity pressure within said cavity in response to said applying said pneumatic pressure stimulus, said measuring occurring while a port into said cavity remains sealed.

14. The method of claim 13 further comprising:

performing said indexing, moving, sealing, applying, and measuring operations for each of said plurality of pressure sensors on said device wafer;

identifying a first subset of said pressure sensors on said device wafer as being defective sensors when said cavity pressure for each of said pressure sensors in said first subset is outside of a passing range defined by at least one of a low pressure threshold and a high pressure threshold;

identifying a second subset of said pressure sensors on said device wafer as being functional sensors when said cavity pressure of each of said pressure sensors in said second subset is within said passing range;

dicing said device wafer to produce a plurality of singulated pressure sensors; and

discarding said first subset of said pressure sensors following said dicing.

15. The method of claim 13 further comprising:

performing said indexing, moving, sealing, applying, and measuring operations for each of said plurality of pressure sensors on said device wafer, wherein;

for said each of said plurality of pressure sensors, said applying comprises applying successively greater magnitudes of said pneumatic pressure stimulus; and

for said each of said plurality of pressure sensors, said measuring comprises identifying a failure pressure, said failure pressure being one of said successively greater magnitudes of said pneumatic pressure stimulus at which said cavity pressure is outside of a passing range defined by at least one of a low pressure threshold and a high pressure threshold; and

producing a substrate map of said device wafer, said substrate map correlating those of said pressure sensors at locations on said device wafer as having the same magnitude of said failure pressure.

16. The method of claim 13 further comprising:

performing said indexing, moving, sealing, applying, and measuring operations for each of said plurality of pressure sensors on said device wafer;

for said each of said pressure sensors, measuring at least one output pressure signal from said pressure sensor in response to said pneumatic pressure stimulus; and

for said each of said pressure sensors, determining a calibration factor for said pressure sensor in response to said at least one output pressure signal.

17. A test system for testing pressure sensors on a device wafer, each of said pressure sensors including a diaphragm, and said test system comprising:

a table for retaining said device wafer;

a nozzle;

an actuator for placing said nozzle and said diaphragm of one of said pressure sensors in proximity to one another;

a fluid supply line in communication with said nozzle for providing a pneumatic pressure stimulus, said pneumatic pressure stimulus being applied to said diaphragm via an outlet of said nozzle;

a pressure transducer for measuring a pressure within said fluid supply line in response to said pneumatic pressure stimulus, said pressure being indicative of a cavity pressure within a cavity associated with said one of said pressure sensors; and

a controller configured to receive said pressure and ascertain functionality of said one of said pressure sensors in response to said pressure.

18. The test system of claim 17 further comprising:

a movable X-Y stage;

a wafer chuck coupled to said movable X-Y stage, said wafer chuck being adapted to retain said device wafer, wherein said movable X-Y stage is indexed to place successive ones of said pressure sensors in proximity to said nozzle.

19. The test system of claim 17 wherein said pressure sensors are located at a first side of a substrate portion of said device wafer, a port extends through said substrate portion to said cavity, and said test system further comprises a seal element surrounding an outlet of said nozzle, wherein said seal element is adapted for mechanical contact with a second side of said substrate portion surrounding said port to form a pressure seal between said second side and said seal element.

20. The test system of claim 17 wherein said pressure sensors are formed in a structural layer on a first side of a substrate portion of said device wafer, and said test system further comprises a seal element surrounding said outlet of said nozzle, wherein said seal element is adapted for mechanical contact with an exterior surface of said structural layer surrounding one of said pressure sensors to form a pressure seal between said exterior surface of said structural layer and said seal element, and wherein said cavity associated with said one of said pressure sensors is formed between said diaphragm and said seal element with said outlet of said nozzle extending into said cavity.