Document:

<PAGE>
                                                                   EXHIBIT 10.29

                       FIRST AMENDMENT TO CREDIT AGREEMENT

         This FIRST AMENDMENT TO CREDIT AGREEMENT (this "First Amendment"),
dated as of February 5, 2002, is among CABOT MICROELECTRONICS CORPORATION, a
Delaware corporation (the "Company"), the financial institutions parties to the
Credit Agreement described below, as Banks thereunder, LASALLE BANK NATIONAL
ASSOCIATION, in its capacity as Administrative Agent and Issuing Bank under such
Credit Agreement, and NATIONAL CITY BANK OF MICHIGAN/ILLINOIS, in its capacity
as Syndication Agent under such Credit Agreement.

                                    RECITALS

         A. The Company, the Banks, the Administrative Agent, the Issuing Bank
and the Syndication Agent entered into a Credit Agreement dated as of July 10,
2001 (the "Credit Agreement"), pursuant and subject to the terms and conditions
of which, among other things, the Banks and the Issuing Bank agreed to make
loans and other financial accommodations to the Company.

         B. The Company has requested certain other amendments to the Credit
Agreement.

         C. Subject to the terms and conditions of this First Amendment, the
Banks, the Administrative Agent, the Issuing Bank and the Syndication Agent are
willing to agree to the requests of the Company.

         NOW, THEREFORE, in consideration of the mutual agreements contained
herein, and subject to the terms and conditions hereof, the parties hereto
hereby agree as follows:

         1. INCORPORATION OF RECITALS. The Recitals set forth above are
incorporated herein, are acknowledged by the Company to be true and correct and
are made a part hereof.

         2. DEFINITIONS. All capitalized terms used but not elsewhere defined
herein shall have the respective meanings ascribed to such terms in the Credit
Agreement, as amended by this First Amendment.

         3. AMENDMENTS TO CREDIT AGREEMENT. The Credit Agreement is amended by
deleting Section 7.4 in its entirety and substituting the following therefor:

                  "7.4 WAIVER OF SETOFF RIGHTS. The Administrative Agent, the
         Issuing Bank, the Syndication Agent, each Bank and the Company each
         hereby affirmatively waive all rights of set-off provided by applicable
         law with regard to any claim arising under or with respect to this
         Credit Agreement and their respective obligations hereunder. Without
         limiting the generality of the foregoing, the Administrative Agent and
         each Bank acknowledge and agree that none of them will apply to the
         payment of any obligations of the Company hereunder, whether or not due
         and whether or not any Event of Default exists, any balances, credits,
         deposits, accounts or moneys of the Company now or hereafter maintained
         with the Administrative Agent or such Bank or, in the absence of any
         order, decree, garnishment, injunction or other decision in a legal
         process or proceeding to the contrary, prohibit or freeze access to
         such balances, credits, deposits, accounts or moneys."

<PAGE>

         4. CONDITIONS TO EFFECTIVENESS. The effectiveness of this First
Amendment shall be subject to the satisfaction of all of the following
conditions in a manner, form and substance satisfactory to the Administrative
Agent.

         (A) DELIVERY OF DOCUMENT. This First Amendment shall have been executed
by the Company, Syndication Agent and each Bank and shall have been delivered to
the Administrative Agent.

         (B) PERFORMANCE; NO DEFAULT. The Company shall have performed and
complied with all agreements and conditions contained in the Loan Documents to
be performed by or complied with by it, and no Event of Default or Unmatured
Event of Default shall exist.

         (C) MATERIAL ADVERSE EFFECT. No event shall have occurred since
September 30, 2001 which has had or is reasonably expected to have a Material
Adverse Effect.

         The date on which all of the conditions set forth in this Paragraph 4
have been satisfied is referred to herein as the "Effective Date."

         5. REFERENCES. From and after the Effective Date, all terms used in the
Loan Documents which are defined in the Credit Agreement shall be deemed to
refer to such terms as amended by this First Amendment.

         6. REPRESENTATIONS AND WARRANTIES. The Company represents and warrants
to the Banks, the Administrative Agent, the Syndication Agent and the Issuing
Bank that (i) the Company has full power and authority to execute and deliver
this First Amendment and to perform its obligations hereunder, (ii) upon the
execution and delivery hereof, this First Amendment will be valid, binding and
enforceable upon the Company in accordance with its terms, (iii) the execution
and delivery of this First Amendment does not and will not contravene, conflict
with, violate or constitute a default under (A) its articles of incorporation or
by-laws or (B) any applicable law, rule, regulation, judgment, decree or order
of any agreement, indenture or instrument to which the Company is a party or is
bound or which is binding upon or applicable to all or any portion of the
Company's properties or assets and (iv) as of the date hereof no Unmatured Event
of Default or Event of Default exists.

         7. NO FURTHER AMENDMENTS; RATIFICATION OF LIABILITY. Except as amended
hereby, the Credit Agreement and each of the other Loan Documents shall remain
in full force and effect in accordance with its respective terms. The Company
hereby ratifies and confirms its liabilities, obligations and agreements under
the Credit Agreement and the other Loan Documents, all as amended by this First
Amendment, and acknowledges that (i) it has no defenses, claims or set-offs to
the enforcement by the Banks, the Administrative Agent, the Syndication Agent or
the Issuing Bank of such liabilities, obligations and agreements, (ii) the
Banks, the Administrative Agent, the Syndication Agent and the Issuing Bank have
fully performed all obligations to the Company which they have had had or have
on and as of the date hereof and (iii) other than as specifically set forth
herein, the Banks, the Administrative Agent, the Syndication Agent and the
issuing Bank do not waive, diminish or limit any term or condition contained in
the Credit Agreement or the Loan Documents. The agreement of the Banks, the
Administrative Agent,

                                       2
<PAGE>

the Syndication Agent and the Issuing Bank to the terms of the First Amendment
or any other amendment of the Credit Agreement shall not be deemed to establish
or create a custom or course of dealing among the Banks, the Administrative
Agent, the Syndication Agent, the Issuing Bank and the Company. The Loan
Documents, as amended by this First Amendment, contain the entire agreement
among the Banks, the Administrative Agent, the Syndication Agent and the Issuing
Bank with respect to the transactions contemplated hereby.

         8. COUNTERPARTS. This First Amendment may be executed in one or more
counterparts, each of which shall be deemed an original, and all of which, when
taken together, shall constitute one and the same instrument.

         9. FURTHER ASSURANCES. The Company will at any time and from time to
time do, execute, acknowledge and deliver, or will cause to be done, executed,
acknowledged and delivered, all such further acts, documents and instruments as
reasonably may be required by the Banks, the Administrative Agent, the
Syndication Agent or the Issuing Bank in order to effectuate fully the intent of
this First Amendment.

         10. SEVERABILITY. If any term or provision of this First Amendment or
the application thereof to any part or circumstance shall be held to be invalid,
illegal or unenforceable in any respect by a court of competent jurisdiction,
the validity, legality and enforceability of the remaining terms and provisions
of this First Amendment shall not in any way be affected or impaired thereby,
and the affected term or provision shall be modified to the minimum extent
permitted by law so as most fully to achieve the intention of this First
Amendment.

         11. CAPTIONS. The captions in this First Amendment are inserted for
convenience of reference only and in no way define, describe or limit the scope
or intent of this First Amendment or any of the provisions hereof.

                (remainder of this page intentionally left blank)

                                       3
<PAGE>

         IN WITNESS WHEREOF, this First Amendment has been executed and
delivered by each of the parties hereto by a duly authorized officer of each
such part on the date first set forth above.

                  CABOT MICROELECTRONICS CORPORATION

                  By: /s/ Martin M. Ellen
                     --------------------------
                     Martin M. Ellen
                     Chief Financial Officer

                  LASALLE BANK NATIONAL ASSOCIATION,
                  as Administrative Agent, as Issuing Bank and as a Bank

                  By: /s/ Jeffrey A. Raider
                     --------------------------
                     Jeffrey A. Raider
                     Senior Vice President

                  NATIONAL CITY BANK OF MICHIGAN/ILLINOIS,
                  as Syndication Agent and as a Bank

                  By: /s/ James M. Wilber
                     --------------------------
                     James M. Wilber
                     Vice President

                  FIRSTAR BANK, N.A., as a Bank

                  By: /s/ Timothy A. Fossa
                     --------------------------
                     Timothy A. Fossa
                     Vice President

                                       4
<PAGE>

                                  SCHEDULE 2.1

                            BANKS AND PRO RATA SHARES

----------------------------------------------------------------------------
                                               PRO RATA SHARE
                                                OF REVOLVING        PRO RATA
                  BANK                        COMMITMENT AMOUNT      SHARE
----------------------------------------------------------------------------
LaSalle National Bank                             $30,000,000         40%
----------------------------------------------------------------------------
National City Bank of Michigan/Illinois           $22,500,000         30%
----------------------------------------------------------------------------
Firstar Bank, N.A.                                $22,500,000         30%
----------------------------------------------------------------------------
                          TOTALS                  $75,000,000        100%
----------------------------------------------------------------------------

                                       5<PAGE>
                                                                   EXHIBIT 10.33

                                   CPR SELECT

                        THE CORPORATEPLAN FOR RETIREMENT
                                   SELECT PLAN

                               ADOPTION AGREEMENT

                                 IMPORTANT NOTE

THIS DOCUMENT IS NOT AN IRS APPROVED PROTOTYPE PLAN. AN ADOPTING EMPLOYER MAY
NOT RELY SOLELY ON THIS PLAN TO ENSURE THAT THE PLAN IS "UNFUNDED AND MAINTAINED
PRIMARILY FOR THE PURPOSE OF PROVIDING DEFERRED COMPENSATION TO A SELECT GROUP
OF MANAGEMENT OR HIGHLY COMPENSATED EMPLOYEES" AND EXEMPT FROM PARTS 2 THROUGH 4
OF TITLE I OF THE EMPLOYEE RETIREMENT INCOME SECURITY ACT OF 1974 WITH RESPECT
TO THE EMPLOYER'S PARTICULAR SITUATION. FIDELITY MANAGEMENT TRUST COMPANY, ITS
AFFILIATES AND EMPLOYEES MAY NOT PROVIDE YOU WITH LEGAL ADVICE IN CONNECTION
WITH THE EXECUTION OF THIS DOCUMENT. THIS DOCUMENT SHOULD BE REVIEWED BY YOUR
ATTORNEY AND/OR ACCOUNT PRIOR TO EXECUTION.

<PAGE>

                               ADOPTION AGREEMENT
                                    ARTICLE 1

1.01     PLAN INFORMATION

         (a)   NAME OF PLAN:

               This is the Cabot Microelectronics Corporation Supplemental
               Employee Retirement Plan (the "Plan")

         (b)   NAME OF PLAN ADMINISTRATOR, IF NOT THE EMPLOYER:

               -----------------------------------------------------------------

               Address:
                        --------------------------------------------------------

               Phone Number:
                            ----------------------------------------------------

               The Plan Administrator is the agent for service of legal
               process for the Plan.

         (c)   THREE DIGIT PLAN NUMBER:  002

         (d)   PLAN YEAR END (month/day):12/31

         (e)   PLAN STATUS (check one):

               (1) [X]  Effective Date of New Plan:  5/1/00

               (2) [ ]  Amendment Effective Date:
                                                --------------------------------

                        The Original Effective Date of the Plan:
                                                                ----------------

                                       1
<PAGE>

1.02     EMPLOYER

         (a)  THE EMPLOYER IS:  Cabot Microelectronics Corporation
              Address:                  870 North Commons Drive
                                        Aurora, IL  60504
              Contact's Name:           Lynda Bessette
              Telephone Number:         630-375-5505

              (1) Employer's Tax Identification Number:  36-4324765

              (2) Business form of Employer (check one):

                  (A) [X] Corporation

                  (B) [ ] Sole proprietor or partnership

                  (C) [ ] Subchapter S Corporation

              (3) Employer's fiscal year end:  09/30

         (b)  THE TERM "EMPLOYER" INCLUDES THE FOLLOWING RELATED EMPLOYER(S)
              (as defined in Section 2.01(a)(21)):

              ------------------------------------------------------------------

              ------------------------------------------------------------------

              ------------------------------------------------------------------

              ------------------------------------------------------------------

                                       2
<PAGE>

1.03     COVERAGE

         (a)  ONLY THOSE EMPLOYEES LISTED IN ATTACHMENT A WILL BE ELIGIBLE TO
              PARTICIPATE IN THE PLAN

         (b)  THE ENTRY DATE(S) SHALL BE (check one)

              (1) [ ]  the first day of each Plan Year.

              (2) [ ]  the first day of each Plan Year and the date six months
                       later.

              (3) [ ]  the first day of each plan year and the fourth, seventh,
                       and tenth months.

              (4) [X]  the first day of each month.

1.04     COMPENSATION

         FOR PURPOSES OF DETERMINING CONTRIBUTIONS UNDER THE PLAN, COMPENSATION
         SHALL BE AS DEFINED IN SECTION 2.01(A)(6), BUT EXCLUDING (check the
         appropriate box(es)):

         (a)  [X] Overtime Pay.

         (b)  [ ] Bonuses.

         (c)  [X] Commissions.

         (d)  [X] The value of a qualified or non-qualified stock option granted
                  to an Employee by the Employer to the extent such value is
                  includable in the Employee's taxable income.

         (e)  [ ] No exclusions.

1.05     CONTRIBUTIONS

         (a)  DEFERRAL CONTRIBUTIONS: THE EMPLOYER SHALL MAKE A DEFERRAL
              CONTRIBUTION IN ACCORDANCE WITH SECTION 4.01 ON BEHALF OF EACH
              PARTICIPANT WHO HAS AN EXECUTED SALARY REDUCTION AGREEMENT IN
              EFFECT WITH THE EMPLOYER FOR THE PLAN YEAR (OR PORTION OF THE PLAN
              YEAR) IN QUESTION, NOT TO EXCEED 4% OF COMPENSATION FOR THE PLAN
              YEAR.

                                       3
<PAGE>

         (b)  [ ]   MATCHING CONTRIBUTIONS

         (1)  The Employer shall make a Matching Contribution on behalf of each
              Participant in an amount equal to the following percentage of a
              Participant's Deferral contributions during the Plan Year (check
              one):

              (A) [ ]  50%

              (B) [ ] 100%

              (C) [ ] _____%

              (D) [ ] (Tiered Match) _____% of the first _____% of the
                      Participant's Compensation contributed to the Plan,

                      _____% of the next _____% of the Participant's
                      Compensation contributed to the Plan,

                      _____% of the next _____% of the Participant's
                      Compensation contributed to the Plan.

              (E) [ ] The percentage declared for the year, if any, by a Board
                      of Directors' resolution

              (F) [ ] Other:
                            ----------------------------------------------------

                            ----------------------------------------------------

                            ----------------------------------------------------

         (2)  [ ] Matching Contribution Limits (check the appropriate box(es)):

                  (A) [ ] Deferral Contributions in excess of _____% of the
                          Participant's Compensation for the period in question
                          shall not be considered for Matching Contributions.

                  Note:   If the Employer elects a percentage limit in (A)
                          above and requests the Trustee to account separately
                          for matched and unmatched Deferral Contributions, the
                          Matching Contributions allocated to each Participant
                          must be computed, and the percentage limit applied,
                          based upon each period.

                  (B) [ ] Matching Contributions for each Participant for each
                          Plan Year shall be limited to $__________.

                                       4
<PAGE>

         (3)  Eligibility Requirement(s) for Matching Contributions

              A Participant who makes Deferral Contributions during the Plan
              Year under Section 1.05(a) shall be entitled to Matching
              Contributions for that Plan Year if the Participant satisfies the
              following requirement(s) (Check the appropriate box(es). Options
              (B) and (C) may not be elected together.):

              (A) [ ] Is employed by the Employer on the last day of the Plan
                      Year.

              (B) [ ] Earns at least 500 Hours of Service during the Plan Year.

              (C) [ ] Earns at least 1,000 Hours of service during the Plan
                      Year.

              (D) [ ] No requirements

              Note:   If option (A), (B) or (C) above is selected then Matching
                      Contributions can only be MADE by the Employer AFTER the
                      Plan Year ends. Any Matching Contributions made before
                      Plan Year end shall not be subject to the eligibility
                      requirements of this Section 1.05(b)(3).

1.06     DISTRIBUTION DATES

         A participant may elect to receive a distribution or commence
         distributions from his Account pursuant to Section 8.02 upon the
         following date(s) (check the appropriate box(es). If Option (c) is
         elected, then options (a) and (b) may not be elected):

         (a)  [ ] ATTAINMENT OF NORMAL RETIREMENT AGE. NORMAL RETIREMENT AGE
                  UNDER THE PLAN IS (check one).

                  (1) [ ] age 65.

                  (2) [ ] age _____ (specify from 55 through 64).

                  (3) [ ] later of the age _____ (cannot exceed 65) or the fifth
                          anniversary of the Participant's Commencement Date

         (b)  [ ] ATTAINMENT OF EARLY RETIREMENT AGE. EARLY RETIREMENT AGE IS
                  THE FIRST DAY OF THE MONTH AFTER THE PARTICIPANT ATTAINS AGE
                  _____ (SPECIFY 55 OR GREATER) AND COMPLETES _____ YEARS OF
                  SERVICE FOR VESTING.

         (c)  [ ] TERMINATION OF EMPLOYMENT WITH THE EMPLOYER.

                                       5
<PAGE>

1.07     VESTING SCHEDULE

         (a)  THE PARTICIPANT'S VESTED PERCENTAGE IN MATCHING CONTRIBUTIONS
              ELECTED IN SECTION 1.05(A) SHALL BE BASED UPON THE SCHEDULE(S)
              SELECTED BELOW:

              (1) [ ]  N/A - No Matching Contributions
              (2) [X]  100% Vesting immediately
              (3) [ ]  3 year cliff (see C below)
              (4) [ ]  5 year cliff (see D below)
              (5) [ ]  6 year graduated (see E below)
              (6) [ ]  7 year graduated (see F below)
              (7) [ ]  G below
              (8) [ ]  Other (Attachment "B")

YEARS OF SERVICE FOR
       VESTING                C           D           E          F         G
--------------------     --------      ------       ------    ------    ------
          0                   0%          0%          0%         0%       ___
          1                   0%          0%          0%         0%       ___
          2                   0%          0%         20%         0%       ___
          3                 100%          0%         40%        20%       ___
          4                 100%          0%         60%        40%       ___
          5                 100%        100%         80%        60%       ___
          6                 100%        100%        100%        80%       ___
          7                 100%        100%        100%       100%      100%

         (b)  [ ] YEARS OF SERVICE FOR VESTING SHALL EXCLUDE (check one):

                  (1) [ ] for new plans, service prior to the Effective date as
                          defined in Section 1.01(e)(1).

                  (2) [ ] for existing plans converting from another plan
                          document, service prior to the original Effective
                          Date as defined in section 1.01(e)(2).

         (c)  [ ] A PARTICIPANT WILL FORFEIT HIS MATCHING CONTRIBUTIONS UPON THE
                  OCCURRENCE OF THE FOLLOWING EVENT(S):
                                                       -------------------------

                                   ---------------------------------------------

                                   ---------------------------------------------

                                       6
<PAGE>

         (d)  A PARTICIPANT WILL BE 100% VESTED IN HIS MATCHING CONTRIBUTIONS
              UPON (check the appropriate box(es), if any):

              (1) [ ] Normal Retirement Age (as defined in Section 1.06(a)).

              (2) [ ] Early Retirement Age (as defined in Section 1.06(b)).

              (3) [ ] Death.

1.08     PREDECESSOR EMPLOYER SERVICE

         [X]  SERVICE FOR PURPOSES OF VESTING IN SECTION 1.07(a) SHALL INCLUDE
              SERVICE WITH THE FOLLOWING EMPLOYER(S):

         (a)  CABOT CORPORATION

         (b)  RIPPE CORPORATION

         (c)
             -------------------------------------------------------------------

         (d) -------------------------------------------------------------------

1.09     HARDSHIP WITHDRAWALS

         PARTICIPANT WITHDRAWALS FOR HARDSHIP PRIOR TO TERMINATION OF EMPLOYMENT
         (check one):

         (a)  [ ] WILL BE ALLOWED IN ACCORDANCE WITH SECTION 7.07, SUBJECT TO A
                  $________ MINIMUM AMOUNT. (MUST BE AT LEAST $1,000)

         (b)  [X] WILL NOT BE ALLOWED.

1.10     DISTRIBUTIONS

         SUBJECT TO ARTICLES 7 AND 8, DISTRIBUTIONS UNDER THE PLAN WILL BE PAID
         (check the appropriate box(es)):

         (a)  [X] AS A LUMP SUM.

         (b)  [ ] UNDER A SYSTEMATIC WITHDRAWAL PLAN (INSTALLMENTS) NOT TO
                  EXCEED 10 YEARS.

                                       7
<PAGE>

1.11     INVESTMENT DECISIONS

         (a)  [ ] INVESTMENT DIRECTIONS

                  INVESTMENTS IN WHICH THE ACCOUNTS OF PARTICIPANTS SHALL BE
                  TREATED AS INVESTED AND REINVESTED SHALL BE DIRECTED (check
                  one):

                  (1) [ ] by the Employer among the options listed in (b) below.

                  (2) [X] by each Participant among the options listed in (b)
                          below.

                  (3) [ ]  by each Participant with respect to deferral
                           Contributions and by the Employer with respect to
                           Employer Matching Contributions. The Employer must
                           direct the Employer Matching Contributions among the
                           same investment options made available for
                           Participant directed sources listed in (b) below.

         (b)      PLAN INVESTMENT OPTIONS

                  PARTICIPANT ACCOUNTS WILL BE TREATED AS INVESTED AMONG THE
                  FIDELITY FUNDS LISTED BELOW PURSUANT TO PARTICIPANT AND/OR
                  EMPLOYER DIRECTIONS.

<TABLE>
<CAPTION>
                                          FUND NAME                                     FUND NUMBER
                      ----------------------------------------------------------        -----------
<S>                                                                                     <C>
                  (1) Fidelity Diversified International Fund                               0325
                  (2) Fidelity Fund                                                         0003
                  (3) Fidelity Institutional Short-Intermediate Government Fund             0662
                  (4) Fidelity Low-Priced Stock Fund                                        0316
                  (5) Fidelity Retirement Money Market Portfolio                            0630
                  (6) Fidelity Freedom Funds                                              369-373
                  (7) Fidelity Equity Income II Fund                                        0319
                  (8) Fidelity Fifty Fund                                                   500
                  (9) Fidelity Aggressive Growth Fund                                       324
                  (10)Fidelity Balanced Fund                                               0304*

</TABLE>

                  Note: An additional annual recordkeeping fee will be charged
                        for each fund in excess of five funds.
                  Note: The method and frequency for change of investments will
                        be determined under the rules applicable to the selected
                        funds. Information will be provided regarding expenses,
                        if any, for changes in investment options.
                  *Effective Date: 1/15/2002

                                       8
<PAGE>

1.12     RELIANCE ON PLAN

         An adopting Employer may not rely solely on this Plan to ensure that
         the Plan is "unfunded and maintained primarily for the purpose of
         providing deferred compensation for a select group of management or
         highly compensated employees" and exempt from Parts 2 through 4 of
         Title I of the Employee Retirement Income Security Act of 1974 with
         respect to the Employer's particular situation. This Agreement must be
         reviewed by your attorney and/or accountant before it is executed.

         This Adoption Agreement may be used only in conjunction with the
         CORPORATEPLAN for Retirement Select Basic Plan Document.

                                       9
<PAGE>

                                 EXECUTION PAGE
                                (FIDELITY'S COPY)

IN WITNESS WHEREOF, the Employer has caused this Adoption Agreement to be
executed this 10th day of January, 2000.

                                    Employer   Cabot Microelectronics
                                               ---------------------------------
                                    By         /s/ William C. McCarthy
                                               ---------------------------------
                                    Title      Chief Financial Officer
                                               ---------------------------------

                                    Employer
                                               ---------------------------------
                                    By
                                               ---------------------------------
                                    Title
                                               ---------------------------------

                                       10
<PAGE>

                                 EXECUTION PAGE
                                (EMPLOYER'S COPY)

IN WITNESS WHEREOF, the Employer has caused this Adoption Agreement to be
executed this 10th day of January, 2000.

                                    Employer   Cabot Microelectronics
                                               ---------------------------------
                                    By         /s/ William C. McCarthy
                                               ---------------------------------
                                    Title      Chief Financial Officer
                                               ---------------------------------

                                    Employer
                                               ---------------------------------
                                    By
                                               ---------------------------------
                                    Title
                                               ---------------------------------

                                       11
<PAGE>

                                  ATTACHMENT A

Pursuant to Section 1.03(a), the following are the employees who are eligible to
participate in the Plan as of the Effective Date:

                                 McCarthy, William C.
                                 Neville, Matthew
                                 Pike, Daniel J.
                                 Yu, Chris C,
                                 Zwicker, Bruce M.

Additional employees may become eligible to participate in the Plan after the
effective Date, upon exceeding the compensation limits under the qualified Cabot
Microelectronics Corporation 401(k) Plan.

Fidelity Management Trust Company             Cabot Microelectronics Corporation

                                              /s/ William C. McCarthy
----------------------------------            ----------------------------------

By:                                           By: William C. McCarthy
   -------------------------------               -------------------------------
Its:                                          Its: Chief Financial Officer
    ------------------------------                ------------------------------
Dated:                                        Dated: April 17, 2000
      ----------------------------                  ----------------------------

<PAGE>

                                  ATTACHMENT B

Pursuant to Section 1.05, the following are the employees who will have an
Opening Balance in the Plan as a result of the transfer of balances from the
Cabot SERPs and/or the Cabot Deferred Compensation Plan:

              Vlasta Brusic
              Frank B. Kaufman
              William C. McCarthy
              Matthew Neville
              Daniel J. Pike
              Chris C. Yu
              Bruce M. Zwicker

Pursuant to Section 1.06, the following Employees' Opening Balance attributable
to the transfer of the Cabot Deferred Compensation Plan balances have elected
the following distribution election dates of their Opening Balance. All other
Opening Balances shall be paid in accordance with 1.07(c).

              Vlasta Brusic           January 1, 2002
              Frank B. Kaufman        January 2, 2005
              Matthew Neville         January 1, 2008

Fidelity Management Trust Company           Cabot Microelectronics Corporation

                                            /s/ William C. McCarthy
----------------------------                ------------------------------------
By:                                         By: William C. McCarthy
   -------------------------                   ---------------------------------
Its:                                        Its: Chief Financial Officer
    ------------------------                    --------------------------------
Dated:                                      Dated:   April 17, 2000
      ----------------------                      ------------------------------

<PAGE>

                                  ATTACHMENT C

ADOPTION AGREEMENT INSERT: WE ARE ADDING THE FOLLOWING SECTION 1.05 OF THE
ADOPTION AGREEMENT IMMEDIATELY AFTER SECTION (c):

"Anything contained in this adoption Agreement or the Plan to which it relates
to the contrary notwithstanding, with respect to any participant in this Plan
who was a participant in the Cabot Corporation Deferred Compensation Plan and
whose benefits under the Cabot Corporation Deferred Compensation Plan have been
transferred to this Plan, the value of such transferred benefits shall be paid
to such participant in a lump sun at the time specified by such Participant in
the applicable form completed by the Participant prior to the transfer of such
benefits to this plan."

BASIC PLAN DOCUMENT INSERTS: WE ARE ADDING THE FOLLOWING PROVISIONS:

1.       Added as the Final Sentence of Section 4.01:

2.       New Section 4.04:

         4.04.    Each Participant's Account shall be credited with a percentage
                  of such Participant's Compensation earned in each Plan Year,
                  such percentage to be determined by the Employer in its sole
                  discretion. In addition, upon a Participant's commencement of
                  participation in the Plan, the Employer may cause additional
                  amounts to be credited to the Account of such Participant as
                  it shall in its discretion determine (any such additional
                  amounts, an "Opening Account Balance").

3.       New Section 8.05:

         8.05     Notwithstanding any other provision of the Plan, different or
                  additional rules of distribution may apply to Opening Account
                  Balances.

Fidelity Management Trust Company           Cabot Microelectronics Corporation

                                            /s/ William C. McCarthy
------------------------                    ------------------------------------
By:                                         By: William C. McCarthy
   ---------------------                       ---------------------------------
Its:                                        Its: Chief Financial Officer
    --------------------                        --------------------------------
Dated:                                      Dated:  April 17, 2000
      ------------------                          ------------------------------

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