Module 6 — Graded Quiz (Summative)

20 questions

0 of 20 answered All questions must be answered to submit

Question 1 — Question 1

R1-A has been operating normally for several months. This morning, the pump-down from ~950 mbar to 1 mbar takes the usual ~90 seconds. Below 1 mbar, the pump-down slows dramatically and stalls at 0.30 mbar after 25 minutes. The pump was tested independently at its inlet and reaches 0.008 mbar — within specification. A rate-of-rise test shows a decreasing rate (0.08 to 0.02 mbar/min over 10 minutes). The operator also observes visible oil mist escaping from the R1-FLT-EXH exhaust outlet. What is the most likely cause of the performance degradation?

A. A leak in the chamber flange O-ring — the decreasing rate-of-rise is misleading because the leak is intermittent
B. The foreline (R1-L-FL) has developed an internal blockage
C. R1-FLT-EXH is saturated or blocked — the increased exhaust back-pressure reduces the pump's effective throughput, and oil mist bypassing the filter confirms the filter element has failed. The pump itself is fine (0.008 mbar independently), and the decreasing rate-of-rise rules out a leak.
D. The pump oil has completely evaporated, eliminating the internal seal

Question 2 — Question 2

A technician proposes replacing R1-P-RP (oil-sealed rotary vane pump) with a diaphragm pump to eliminate all oil contamination risk on R1-A. Using R1-A's normal operating parameters (base pressure 0.05 mbar, chamber volume pumped from ~950 mbar), interpret whether this proposal is viable.

A. Excellent idea — the diaphragm pump will match all current performance parameters while eliminating oil risk
B. Good idea — the slightly higher base pressure is an acceptable trade-off for cleanliness
C. Not suitable — diaphragm pumps have limited ultimate pressure (~1–10 mbar) and low pumping speed (~0.5–5 m³/h), which would prevent R1-A from reaching its current base pressure of 0.05 mbar and dramatically extend pump-down times. A scroll pump is the closest oil-free equivalent in terms of performance.
D. Not suitable — diaphragm pumps cannot pump air, only process gases

Question 3 — Question 3

On R1-A, the operator closes R1-V-ISO and performs a rate-of-rise test. The rate is constant at 0.04 mbar/min. The pump was independently verified at 0.009 mbar (within spec). All chamber O-rings were replaced last week and appear to be in good condition. A colleague suggests: "Just get a bigger pump — more pumping speed will fix it." Given that base pressure scales inversely with effective pumping speed for a given gas load, interpret why this suggestion does not address the underlying problem.

A. The suggestion is correct — increasing pumping speed would fully resolve the elevated base pressure
B. The suggestion is incorrect — pumping speed has no relationship to base pressure
C. A larger pump would lower the steady-state base pressure numerically, but the constant rate-of-rise proves a real leak exists. Increasing pump speed masks the leak without eliminating it — atmospheric contaminants (water, oxygen) continue entering the chamber. The leak is the root cause, and a larger pump only treats the symptom.
D. The suggestion is correct — a larger pump always solves all vacuum problems

Question 4 — Question 4

R1-A is in VENTED state (~950 mbar). A student describes the pump oil's function as "just lubrication — like motor oil in a car engine." Explain why this description is incomplete for a rotary vane vacuum pump.

A. The description is actually correct — pump oil serves only a lubrication function
B. The description is incomplete because the oil also acts as a coolant, but that is its only additional function
C. The description is incomplete because the oil serves three critical functions: (1) sealing the gaps between rotor, vanes, and stator to prevent gas from leaking past — this is the most important vacuum-specific function; (2) lubricating the sliding contacts; and (3) removing heat from the compression process. Without the sealing function, the pump could not achieve low pressure regardless of how well lubricated it was.
D. The description is incomplete because the oil also measures the pressure inside the pump

Question 5 — Question 5

Which of the following pump types operates by transferring momentum to individual gas molecules using high-speed rotating blades?

A. Rotary vane pump
B. Scroll pump
C. Turbomolecular pump
D. Diaphragm pump

Question 6 — Question 6

R1-A has been pumping at base pressure (0.05 mbar) for several hours with R1-V-ISO open and no gas flowing through the chamber. A thin-film coating specialist inspects the chamber and reports finding a faint oily film on the internal chamber walls. The system has no foreline trap. What is the most likely source of this contamination, and what is the mechanism?

A. Condensation of atmospheric water vapour on the cold chamber walls
B. Outgassing from the chamber's stainless steel surface
C. Backstreaming — at low pressure with minimal gas flow, pump oil vapour from R1-P-RP migrates backward through the foreline and R1-V-ISO into the chamber. Without a foreline trap to intercept it, the oil vapour deposits on the cooler chamber surfaces as a hydrocarbon film.
D. Residue from the vent filter R1-FLT-VENT

Question 7 — Question 7

An operator observes the following on R1-A: the pump (R1-P-RP) sounds normal, the oil sight glass shows clear amber oil at the correct level, R1-FLT-EXH exhaust is clean (no visible mist), and the pump body is warm but not unusually hot. However, the system is taking 15 minutes to reach 0.05 mbar instead of the usual 8 minutes. A rate-of-rise test shows a decreasing rate from 0.03 to 0.005 mbar/min. What does this evidence tell you about the likely cause?

A. The pump is failing — it needs immediate replacement
B. The pump appears healthy by all observable indicators (sound, oil, exhaust, temperature). The extended pump-down with a decreasing rate-of-rise points to an elevated but depletable gas load — most likely surface water desorption from the chamber, consistent with M02 gas load sources. This is a gas load problem, not a pump problem.
C. The foreline has developed a restriction that reduces conductance
D. R1-G-CH (the Pirani gauge) is malfunctioning and displaying incorrect readings

Question 8 — Question 8

R1-A has two filters — R1-FLT-VENT on the vent line and R1-FLT-EXH on the exhaust line. A colleague describes them both as "just filters" and questions why two are needed. Describe the distinct function of each filter and explain why each is necessary.

A. Both filters serve the same function — they are redundant for safety
B. R1-FLT-VENT filters pump oil; R1-FLT-EXH filters atmospheric dust
C. R1-FLT-VENT (sintered metal) filters incoming atmospheric air during venting — removing particles that would contaminate chamber surfaces. R1-FLT-EXH (oil mist/coalescing) captures oil aerosol from the rotary vane pump exhaust — preventing oil mist from entering the workspace. They protect different things from different contaminants in different parts of the system.
D. R1-FLT-VENT is for high-vacuum operation; R1-FLT-EXH is for rough-vacuum operation

Question 9 — Question 9

On a more complex system than R1-A, a turbomolecular pump is backed by a rotary vane pump. The turbo pump is operating normally, but the backing pump's oil has become contaminated and its ultimate pressure has degraded from 0.01 mbar to 0.5 mbar. What effect would this have on the system?

A. No effect — the turbo pump operates independently of the backing pump
B. The turbo pump's exhaust pressure would rise to 0.5 mbar. If this exceeds the turbo pump's maximum tolerable exhaust pressure, the turbo's compression ratio becomes insufficient and it can no longer maintain high vacuum at its inlet — the system's base pressure rises or the turbo pump stalls.
C. The turbo pump would automatically compensate by spinning faster
D. The system would switch to roughing-only mode

Question 10 — Question 10

R1-A has been shut down for maintenance. When the technician restarts R1-P-RP, the pump makes a loud knocking sound for approximately 30 seconds, then settles into its normal operating sound. The pump reaches base pressure normally. Is this a concern?

A. No — all pumps make noise on startup; this is completely normal
B. Yes — while some startup noise is common (oil redistributing, vanes seating), a loud knocking sound lasting 30 seconds is abnormal and should be documented and monitored. Even though the pump reached base pressure this time, the knocking suggests a developing mechanical issue (worn bearings, damaged vane, debris) that could worsen. Escalate with specific details: duration, character of the sound, and when it occurs.
C. No — the pump reached base pressure, which proves it is operating normally
D. Yes — the pump should be immediately disassembled for inspection

Question 11 — Question 11

R1-A's maintenance log shows the following entries over three months:

A. Month 1: Base pressure 0.05 mbar (normal), pump-down time 8 min (normal)
B. Month 2: Base pressure 0.07 mbar, pump-down time 10 min, note: "oil appears slightly darker than new"
C. Month 3: Base pressure 0.12 mbar, pump-down time 14 min, note: "oil visibly dark, slight exhaust odour"
D. 1st: Chamber leak (constant rates prove it); 2nd: Oil degradation; 3rd: Seal failure
E. All three months show different problems — each requires a separate diagnosis
F. 1st: Progressive pump oil degradation (darkening oil, increasing exhaust odour, and worsening pump performance all point to oil that is losing its sealing and lubricating effectiveness over time). 2nd: Developing seal leak (constant rate-of-rise supports this, but the oil symptoms are the dominant new evidence). Discriminator: replace the pump oil and retest — if base pressure returns to 0.05 mbar, oil degradation is confirmed. If performance does not improve, investigate the constant rate-of-rise as a seal leak.
G. 1st: Exhaust filter failure; 2nd: Foreline blockage; 3rd: Gauge drift

Question 12 — Question 12

A colleague argues: "On R1-A, the pump-down is slow below 1 mbar. Since R1-P-RP only has a pumping speed of 5 m³/h, we should upgrade to a 20 m³/h pump to speed things up." The foreline (R1-L-FL) is 15 mm bore, 1.2 m long, with two 90-degree bends. Using M03 conductance concepts, interpret whether the proposed pump upgrade would achieve the expected improvement.

A. Correct — a pump four times faster will make the pump-down four times faster at all pressures
B. Incorrect — a larger pump would actually slow things down
C. The improvement would be much less than expected. In the molecular flow regime below 1 mbar, the conductance of the restrictive foreline (narrow bore, long, with bends) limits the effective pumping speed at the chamber. When foreline conductance is low, increasing the pump speed gives diminishing returns because effective speed at the chamber cannot exceed the conductance of the path connecting them. The system is conductance-limited, not pump-limited.
D. The pump upgrade would work, but only during the viscous flow phase

Question 13 — Question 13

On R1-A, after a normal pump-down to 0.05 mbar, the operator isolates the chamber (R1-V-ISO closed) and turns off R1-P-RP. The pressure begins to rise. After 10 minutes, R1-G-CH reads 0.15 mbar. After 60 minutes, it reads 0.85 mbar. After 6 hours, it reads 12 mbar. After 24 hours, it reads 47 mbar. The rates decrease significantly over time. Is this behaviour normal for an isolated rough-vacuum system?

A. No — any pressure rise indicates a leak that must be repaired immediately
B. Yes — this is consistent with normal behaviour for an isolated rough-vacuum chamber. Outgassing from internal surfaces (primarily water desorption) causes an initial relatively rapid pressure rise that slows over time as the surface gas inventory depletes. The strongly decreasing rate over hours is the signature of outgassing, not a leak. A leak would produce a constant rate and the chamber would return to atmospheric pressure in a predictable time.
C. No — the pressure should remain at 0.05 mbar indefinitely once isolated
D. Yes — but only if the system reaches atmospheric pressure within 24 hours

Question 14 — Question 14

R1-A's pump oil is inspected and appears milky/cloudy instead of the normal clear amber. The system has been used in a workshop with very high humidity, and the chamber has been pumped down and vented repeatedly. What is the most likely explanation for the oil condition, and what is the consequence for pump performance?

A. The oil is fine — milky appearance is normal after several weeks of use
B. The oil has been contaminated with metal particles from vane wear
C. Water vapour pumped from the humid chamber has condensed in the pump oil, creating a milky emulsion. Water-contaminated oil has reduced sealing ability (the water disrupts the oil film between vanes and stator), increased vapour pressure (contributing to higher base pressure), and may cause corrosion of internal pump components.
D. The pump is overheating, which has bleached the oil colour

Question 15 — Question 15

A vacuum system uses a scroll pump instead of a rotary vane pump for a semiconductor application. The scroll pump has a slightly higher ultimate pressure (0.01 mbar vs 0.001 mbar). A project manager asks: "Why are we paying more for a pump that performs worse?" Explain why the scroll pump is used in this application despite its higher ultimate pressure.

A. The scroll pump is quieter, which justifies the higher cost for a cleaner working environment
B. The scroll pump is easier to maintain, which reduces long-term labour costs
C. In semiconductor processing, hydrocarbon contamination is catastrophic — even trace oil on wafer surfaces causes device failure. The rotary vane pump's lower ultimate pressure is achieved through oil sealing, but that same oil creates backstreaming risk that can contaminate the process chamber. The scroll pump's oil-free operation eliminates this contamination pathway entirely. The 0.01 mbar ultimate pressure is adequate for roughing/backing duty in a semiconductor system, and the absence of oil contamination risk is more significant than the difference in ultimate pressure. "Performs worse" is only true on one metric (ultimate pressure) while ignoring the critical metric (contamination risk).
D. The project manager is correct — the rotary vane pump is always the better choice for its superior vacuum performance

Question 16 — Question 16

A junior technician on a multi-pump system observes that the turbomolecular pump has been running for 10 minutes but the chamber pressure (reading on the high-vacuum gauge) has not dropped below 0.5 mbar. The roughing pump is running and its own inlet reads 0.8 mbar. What is the most likely problem, and which module's knowledge helps diagnose it?

A. The turbo pump has failed and needs replacement (M06)
B. The high-vacuum gauge is malfunctioning (M01)
C. The roughing/backing pump has not brought the foreline pressure low enough for the turbo pump to operate effectively. At 0.8 mbar on the roughing pump inlet, the turbo pump's exhaust is at too high a pressure — exceeding its compression capability. The roughing pump may have a problem (M06: pump performance), or the foreline may have a conductance restriction (M03) or a leak (M02). The turbo pump cannot function until its backing conditions are met.
D. The chamber has too many feedthroughs creating leaks (M05)

Question 17 — Question 17

On R1-A, R1-P-RP is observed vibrating noticeably more than usual. The pump body is also hotter than normal. The oil sight glass shows oil at the correct level, but the oil appears slightly foamy. The system is reaching 0.08 mbar instead of the normal 0.05 mbar. Which of the following best describes a structured R-I-C-E observation (Recognise, Interpret, Communicate, Escalate) for this scenario?

A. Recognise: pump is broken. Interpret: needs new pump. Communicate: "pump broken." Escalate: order replacement pump.
B. Recognise: all normal variation. Interpret: no action needed. Communicate: nothing to report. Escalate: not applicable.
C. Recognise: increased vibration, elevated body temperature, foamy oil, base pressure degraded from 0.05 to 0.08 mbar. Interpret: foamy oil suggests air ingress into the pump (possibly a failing shaft seal or gasket), which would explain both the vibration (air disrupting the compression cycle), the heat (pump working harder against internal leakage), and the elevated base pressure (reduced sealing effectiveness). Communicate: "R1-P-RP showing increased vibration, elevated body temperature, and foamy oil. Base pressure 0.08 mbar vs normal 0.05 mbar. Symptoms suggest possible air ingress into the pump mechanism." Escalate: request pump inspection by qualified maintenance personnel.
D. Recognise: vibration. Interpret: loose mounting bolt. Communicate: "tighten bolts." Escalate: not needed.

Question 18 — Question 18

The following evidence is observed on R1-A:

Question 19 — Question 19

The following evidence is collected from R1-A for a capstone analysis integrating all modules. R1-A shows the following: base pressure of 0.15 mbar (normal: 0.05 mbar), pump-down from 950 to 1 mbar takes 90 seconds (normal), pump-down from 1 to 0.15 mbar takes 25 minutes and stalls (normal: 6.5 minutes to 0.05 mbar). Rate-of-rise: 0.06 mbar/min at 1 min, decreasing to 0.04 mbar/min at 10 min. Pump independent test: 0.009 mbar. Oil: slightly dark. R1-FLT-EXH: clean exhaust. Foreline: original specification (25 mm bore, 0.6 m, straight). No chamber modifications. All seals replaced 2 months ago. Identify the TWO most likely contributing factors and explain what discriminating evidence would separate them.

A. Leak and pump failure — test by replacing the pump
B. Conductance restriction and gauge failure — test by replacing the gauge
C. Factor 1: Elevated outgassing from contamination inside the chamber (the decreasing rate-of-rise indicates a depletable gas source, the viscous phase is normal ruling out gross problems, and the system stalls in the molecular flow range where surface gas load dominates). Factor 2: Early-stage pump oil degradation (slightly dark oil suggests the oil is losing effectiveness, which contributes to a higher pump ultimate pressure and reduced sealing). Discriminating test: change the pump oil first (quick, reversible) — if base pressure improves but does not return to 0.05 mbar, some oil-related contribution is confirmed. Then perform multiple consecutive pump-down cycles — if each cycle is faster and reaches lower pressure, the gas source is depleting (contamination). If cycles are identical, the gas load is non-depletable (pointing back to a subtle leak despite the decreasing rate-of-rise pattern).
D. Foreline restriction and seal failure — test by replacing the foreline

Question 20 — Question 20

Which of the following correctly describes the function of R1-FLT-EXH on R1-A?

A. It filters particles from atmospheric air entering the chamber during venting
B. It prevents backstreaming of oil vapour toward the chamber
C. It captures oil mist aerosol from the rotary vane pump's exhaust gas before it is released into the workspace, and returns collected oil to the pump reservoir
D. It measures the exhaust gas composition to detect process gas contamination

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Graded Quiz