Enhanced resolution liquid crystal microthermography method and apparatus

• US 5,767,489 A
• Filed: 10/11/1996
• Issued: 06/16/1998
• Est. Priority Date: 12/14/1994
• Status: Expired due to Term

• Current Assignee: Avago Technologies General IP PTE Limited (Broadcom, Inc.)
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: Ferrier, Mark S.
• Primary Examiner(s): Paschall, Mark H.
• Application Number:
  US08/728,928
• Time in Patent Office: 613 Days
• Field of Search: 219/494, 219/497, 219/501, 219/505, 219/506, 219/508, 219/502, 219/209, 219/210, 219/492, 359/36, 359/44, 359/86
• US Class Current: 219/497
• CPC Class Codes: G01K 11/165 of organic liquid crystals

Abstract

Resolution of liquid crystal microthermographic measurements are improved by depositing a layer of organic pretreatment on the surface of a semiconductor device. A layer of thermographically sensitive liquid crystal material is then deposited on the organic pretreatment layer so that a controlled liquid crystal material layer thickness and an orientation of a majority of crystal molecules of the liquid crystal material parallel to the surface is achieved. The nominal temperature of the surface to be measured is controlled by sensing the nominal temperature near the surface, converting the sensed temperature to a current temperature sense signal, comparing the current temperature sense signal to a target temperature value, and activating a heater in thermal communication with the surface when the current temperature sense signal varies from the reference signal magnitude. A state of essential thermal equilibrium is maintained at and near the surface by thermally insulating the surface and a volume adjacent the surface.

Claims

1. A method of measuring temperature variations of a material surface comprising the steps of:

depositing a layer of organic pretreatment on the material surface;

depositing a layer of thermographically sensitive liquid crystal on said organic pretreatment layer whereby a controlled layer thickness is achieved and temperature variations detected;

controlling the nominal temperature of the material surface to he measured, including sensing the nominal temperature near the material surface with a temperature sensing element disposed in thermal communication with the material surface, converting said sensed temperature to a current temperature sense signal, comparing said current temperature sense signal to a target temperature value, and activating a heater in thermal communication with said material surface when said current temperature sense signal varies from said target temperature value; and

thermally insulating the material surface and a volume of gas adjacent the material surface.

2. A method in accordance with the method of claim 1 wherein said converting said sensed temperature further comprises the step of averaging said sensed temperature over time.

3. A method in accordance with the method of claim 2 wherein said step of comparing said current temperature sense signal to a target temperature value further comprises the steps of:

determining a period of time over which an adjustment of temperature of said heater will be calculated;

determining the trajectory of said current temperature sense signal during said determined period of time; and

categorizing said current temperature sense signal and said trajectory into one of at least three categories of heater responses.

5. A method in accordance with the method of claim 1 wherein said step of depositing a layer of organic pretreatment further comprises the step of depositing a layer of polyvinyl alcohol on the material surface.

4. A method of measuring temperature variations of a material surface comprising the steps of:

depositing a layer of organic pretreatment on the material surface;

depositing a layer of thernographically sensitive liquid crystal on said organic pretreatment layer whereby a controlled layer thickness is achieved and temperature variations detected;

controlling the nominal temperature of the material surface to be measured, including sensing the nominal temperature near the material surface, converting said sensed temperature to a current temperature sense signal, averaging said sensed temperature over time, comparing said current temperature sense signal to a target temperature value by

determining a period of time over which an adjustment of temperature of said heater will be calculated,

determining the trajectory of said current temperature sense signal during said determined period of time, and

categorizing said current temperature sense signal and said trajectory into one of at least three categories of heater responses;

activating a heater in thermal communication with said material surface when said current temperature sense signal varies from said target temperature value by

adjusting energy supplied said heater in an incremental step value over a period of time equal in duration to said predetermined period of time when said current temperature sense and trajectory are categorized into a first category of said at least three categories of heater responses,

adjusting energy supplied said heater with a pulsed change over a period of time less than the duration of said predetermined period of time when said current temperature sense and trajectory are categorized into a second category of said at least three categories of heater responses, and

adjusting energy supplied said heater with a bifurcated adjustment value equal in value to the sum of a current heater activation value and a value equal to the difference between said current heater activation value and a predetermined value; and

thermally insulating the material surface and a volume of gas adjacent the material surface.

6. A microthermographic measurement apparatus for a material surface comprising:

a layer of organic pretreatment deposited on the material surface;

a layer of thermographically sensitive liquid crystal material deposited on said organic pretreatment layer in a controlled layer thickness whereby temperature variations are detected;

a temperature sensing element disposed in thermal communication with the material surface for generating a temperature sense signal;

a comparator which compares said temperature sense signal to a target temperature value;

a heater disposed in thermal communication with the material surface and activated when said comparator indicates said temperature sense signal varies from said target temperature value, and

a thermal insulator encompassing the material surface and an adjacent volume of gas.

7. A microthermographic measurement apparatus in accordance with claim 6 wherein said layer of organic pretreatment further comprises polyvinyl alcohol.

8. A microthermographic measurement apparatus in accordance with claim 6 wherein said comparator further comprises a processor which determines a period of time over which an adjustment of temperature of heater will be calculated from the magnitude and trajectory of said temperature sense signal during said period of time.

9. A microthermographic measurement apparatus in accordance with claim 8 further comprising an electric power supply coupled to said heater and receiving heater control signal from said processor.

10. A microthermographic measurement apparatus for a material surface comprising:

a layer of organic pretreatment deposited on the material surface;

a layer of thermographically sensitive liquid crystal material deposited on said organic pretreatment layer in a controlled layer thickness whereby temperature variations are detected;

a temperature-sensing element disposed in thermal communication with the material surface for generating a temperature sense signal;

a comparator which compares said temperature sense signal to a target temperature value and includes a processor which determines a period of time over which an adjustment of temperature of a heater will be calculated from the magnitude and trajectory of said temperature sense signal during said period of time;

said heater disposed in thermal communication with the material surface and activated when said comparator indicates said temperature sense signal varies from said target temperature value;

an electric power supply coupled to said heater and receiving a heater control signal from said processor;

a first adjustment mode which supplies a change in voltage to said heater as an incremental step value over a period of time equal in duration to said predetermined period of time when said trajectory of said temperature sense signal will place the temperature sense signal greater than a predetermined magnitude apart from said target temperature value;

a second adjustment mode which supplies a change in voltage to said heater as a pulse over a period of time less than the duration of said predetermined period of time when said trajectory of said temperature sense signal will place the temperature sense signal less than said predetermined magnitude apart from said target temperature value but said trajectory is in a direction which will move said temperature sense signal away from said target temperature value;

third adjustment mode which supplies a bifurcated change in voltage to said heater equal in value to the sum of voltage currently supplied to the heater and the voltage equal to the difference between the voltage currently supplied to the heater and a predetermined voltage when said magnitude and trajectory of said temperature sense signal is greater than said predetermined magnitude apart from said target temperature value and will place the temperature sense signal greater than said predetermined magnitude apart from said target temperature value; and

a thermal insulator encompassing the material surface and an adjacent volume of gas.