<PAGE>

                                                                   Exhibit 10.36
                                                                   -------------

Integrated Measurement Systems, Inc.
Attn: Fred Hall
9525 SW Gemini Drive
Beaverton, OR 97008



Credence Systems Corporation
Attn: Byron W. Milstead
5975 NW Pine Farm Place
Hilisboro, OR 97124



Gentlemen:

     This letter anticipates the closing of Integrated Measurement Systems,
Inc.'s (the "Company's") Merger Agreement (the "Merger") with Credence Systems
Corporation ("Credence"), and clarifies our common understanding of the effect
of that closing and events related to it upon rights under my employment
agreement.

     Section 4 of my employment agreement contains provisions that have the
effect of accelerating the vesting of my Company options upon a change in
control of the Company. Credence, the Company, and I understand those provisions
will work as follows:

     1.   My employment agreement will continue in force after the transaction
          closes in all respects except those identified in this letter. I
          confirm that "Exhibit A" to my employment agreement reads as attached
          effective as of the date of the Merger, and that except for changes
          solely related to the title and' reporting relationship changes
          associated with the Merger (to which I consent), this Exhibit A is
          unchanged from the benefits and salary in effect following raises
          determined in the course of IMS' ordinary course focal point review
          process earlier this spring.

     2.   My Company stock options will become Credence options as a result of
          the Merger. With respect to these transformed options, I will retain
          all rights in my employment agreement, including rights of
          acceleration to the extent granted in my employment agreement and on
          the conditions there described, and Company will owe me performance
          with respect to those rights and as a result of any such acceleration
          as outlined in my option agreement, employment agreement, and the
          Merger Agreement. Any new options I am granted to acquire Credence
          stock (that is, options that do not result from the transformation of
          my Company options as a result of the merger), and any Credence
          restricted stock I am issued under grants unrelated to my existing
          Company options, will be treated the same as Company options under the
          employment agreement, except that I agree that any new Credence
          options will not be subject to Section 4 of my employment agreement
          (dealing with acceleration upon change in control of the Company).

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          The foregoing provisions represent my understanding of the
implications of the Merger upon my Company and Credence options, and upon my
employment agreement.

Dated:   8/01/01
       -------------------------------------



                                Very truly yours,


                                /s/ Keith L. Barnes
                                Keith L. Barnes

ACKNOWLEDGED:

INTEGRATED MEASUREMENT SYSTEMS, INC.



By: /s/ Fred Hall
    ------------------------------------------------


Title: Chief Financial Officer
       ---------------------------------------------



CREDENCE SYSTEMS CORPORATION



By: /s/ Byron Milstead
    ------------------------------------------------


Title: Vice President
       ---------------------------------------------

<PAGE>

                        Exhibit A to Employment Agreement

                            Compensation Package for
                                 Keith L. Barnes
                                      as of
                                 August 1, 2001

1.   Position:          President of IMS and Executive Vice President of
                        Credence

2.   Annual Salary:     $280,000

3.   Bonus:             $200,000

4.   Severance Period:  24 months

5.   Other Benefits:    $6,000 per year car allowance; $4,000 per year club dues
allowance. If Company reassigns Executive, changes his title, or reduces
Executive's compensation without Executive's consent, or directs him to report
other than directly to the CEO or Board of Directors actually in charge of the
Company (that is, not the board of a wholly-owned or controlled subsidiary)
without Executive's consent, Executive may, at the Executive's option, decline
to accept the change in title or the new assignment or reduction in salary or
indirect reporting, and elect instead to treat the reassignment as effective
termination by Company, without cause.


Keith L. Barnes                             Integrated Measurement Systems, Inc.


Sign: /s/ Keith L. Barnes                   By: /s/ Fred Hall
      --------------------------------          --------------------------------

                                            Print: Fred Hall
                                                   -----------------------------

                                            Title: Chief Financial Officer
                                                   -----------------------------